Water-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions

Water-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Water-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions Martyn McLachlan, Zhaoyi Du, Ding Ding, Martina Rimmele, Jiewen Wei, and 12 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6443068/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Metal halide perovskites (MHPs) have revolutionised photovoltaics and emerging optoelectronic technologies, offering performance that rivals or exceeds that of conventional materials. Their rapid rise has been driven by their exceptional properties, including tuneable band gaps, high absorption coefficients, long carrier diffusion lengths and high mobilities, all combined with relatively simple synthesis. However, current MHP production relies heavily on the use of toxic solvents, which pose significant environmental and health risks. In addition, these methods often require complex multicomponent solvent systems and thermal processing to achieve the desired material phases, further hindering scalability and sustainability. Overcoming these challenges is critical to the future development of MHP-based technologies. Here, we present a novel water-based solvent system and synthetic approach for the controlled preparation of MHP nanocrystals. Our method enables the synthesis, in ambient air and at room temperature, of size-controlled CsPbBr₃ perovskite nanocrystals (PNCs) with a photoluminescence quantum yield (PLQY) exceeding 60%. To demonstrate the light to current conversion ability of our PNCs a series of photoconductors were prepared, with the best performing devices achieving a specific detectivity (D*) of 1.2 x 10 11 Jones. Thus, this green, scalable, and low-cost approach offers a sustainable pathway for precise size and compositional control of MHP nanocrystals, opening new possibilities for environmentally friendly optoelectronic applications. Physical sciences/Materials science/Nanoscale materials/Synthesis and processing Physical sciences/Chemistry/Environmental chemistry Physical sciences/Nanoscience and technology/Nanoscale materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Perovskite nanocrystals (PNCs) are promising candidates for next-generation light-emitting diodes (LEDs), photovoltaics (PVs), photodetectors (PDs), and other optoelectronic applications. Their exceptional properties—including high-purity, bright emission, tuneable absorption, ambipolar charge transport, long charge carrier diffusion lengths, and intrinsic defect tolerance—make them highly attractive for advanced device technologies 1 – 3 . The relative ease by which compositional control can be afforded through well-established synthesis methods permits facile doping, thus a broad range of bandgaps can be prepared whereby absorption and/or emission wavelength can be tuned to suit the application. Recent PNC developments have demonstrated tuneable emission across the visible spectrum and beyond e.g. CsSnI 3 with near-infrared emission 4 to CsPbCl 3 with blue-to-violet emission 5 , and quantum yields (QYs) approaching 100%. Synthesis of PNCs broadly follows two well-reported synthetic methods, namely ligand-assisted reprecipitation (LARP) 6 and hot-injection (HI) 7 . LARP is generally considered to be more facile than HI, and more efficient, and as elevated temperatures are not required there is a greater potential for scale-up 8 , 9 . The main limitations of the LARP method stem from the significant environmental and health risks posed by the solvents used, particularly the combination of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), which present challenges for scalingup and mass production 1 0 . As PNCs continue to garner interest, there is a requirement to identify synthesis methods that retain the positive attributes of LARP and, in parallel, address the environmental and human health risks associated with the solvents employed. Despite this growing need there remain few reports focusing on PNC synthesis using green solvents or processes. Some notable examples include the work of Lu et al ., who developed natural deep eutectic solvents (NADES) to substitute DMF and ligands used in LARP, demonstrating the successful synthesis of CsPbBr 3 PNCs 11 . In 2019, Ambroz et al. demonstrated a room-temperature injection method for FAPbBr 3 and CsPbBr 3 PNCs using a phosphine-based ligand combination that enabled the dissolution of all precursors without the need for polar aprotic solvents such as DMF or DMSO 12 . Hoang et al. utilized an environmentally friendly ionic liquid, based on a series of methylammonium carboxylates, to prepare MAPbBr 3 PNCs 13 and Chatterjee et al. used menthol-based deep eutectic solvents (DESs) to prepare CsPbX 3 (X = I, Br, Cl) PNCs and nanoplates 14 . Water, the greenest of solvents, has not yet been utilised as the primary solvent in the synthesis of PNCs 15 – 18 . This is largely attributed to the remarkably low solubility of lead halide compounds in water, coupled with the widely held perception of the detrimental effects of H 2 O on metal-halide perovskites 19 , 20 . Consequently, there are no reported instances of successful utilisation of aqueous precursors for the synthesis of PNCs. Here, we report the development of a novel, waterbased solvent capable of dissolving lead halide compounds at room temperature and the subsequent development of a facile, rapid, efficient, and non-toxic synthetic route for the preparation of sizecontrolled CsPbBr 3 PNCs. Our solvent consists solely of water, βalanine (βA, 3-aminopropanoic acid) and malic acid (MA, 2-hydroxybutanedioic acid) - all naturally occurring. The dissolution of PbBr 2 is facilitated by the formation of an adduct with the carboxylate end group of aqueous MA. Although PbBr 2 is insoluble in pure water we demonstrate the room temperature preparation of aqueous solutions with concentrations exceeding 0.2 mol dm − 3 . Hydrobromic acid (HBr) is then used to initiate and aid the precipitation of our PNCs. We rigorously investigate the role of MA, βA, PbBr 2 and HBr and their relative concentrations on PNC synthesis, resulting in the successful formation of size-controlled PNCs with sizes ranging from 60 %. Our novel, environmentally benign solvent provides a clean, scalable, and cost-effective strategy for precise control over the size of PNCs. Results Developing an aqueous solvent system βA and MA are naturally occurring molecules, the former is naturally synthesised in the human liver and is often taken as a sports supplement whilst MA is the primary acid of many common fruits, the molecular structures of both are shown in Fig. 1 a. We first consider the molecular states that each molecule, and mixtures of the two, can adopt in aqueous solution, Figure S1 . βA contains an amine and a carboxylic acid group that, in aqueous environments, can undergo proton transfer leading to the zwitterionic form containing ammonium and carboxylate charged end groups (pK a values of around 3.55 and 10.2 respectively) 21 . MA contains two carboxyl groups (pK a1 of 3.4 and pK a2 of 5.1) 22 which can be partially or fully deprotonated in water, forming carboxylate groups. To determine the molecular states present in each solution we used attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) initially on solid samples of βA and MA, Figure S2 . In βA the absorption cented at 1631 cm − 1 and the shoulder at 1650 cm − 1 can be assigned to νas COO − with and δ as NH 3 + respectively ( δ as NH 3 + also at 1540 cm − 1 and δ s NH 3 + also at 1504 cm − 1 ) indicating βA is in a zwitterionic form 23 . For MA, the absorption at 1680 cm − 1 and the ajacent absorptions at 1714 and 1737 cm − 1 collectively correspond to ν (C = O) of dimeric COOH formed between MA molecules 24 . Aqueous solutions of βA and MA were prepared each with mole fractions ( Χ βA / Χ MA ) of 0.091, resulting in solutions with pH values of 7.48 and 1.32 respectively, Table S1 . In solution, significant changes in the FTIR spectra of both molecules are seen Figure S2 . Considering the FTIR spectra of the solution for βA we anticipate, owing to the zwiterionic nature, that the molecule will be heavily solvated by water. The discrete absorptions observed around 1504–1650 cm − 1 are replaced by a broad absorption band centred at 1560 cm − 1 that indicates a strong interaction of water with these charged end groups. In solution, MA shows a similar broad band centred around 1714 cm − 1 that shows the dimers formed in the solid are disrupted and the carboxlate groups are solvated. Solutions of both molecules were then prepared where the concentration of each was systematically varied, Table S1 , resulting in changes in the FTIR spectra, Figure S3 , that can be attributed to solution composition and the relative concentrations of each molecule. As conductivity is derived from the concentration of dissolved ions in solution i.e. the non-neutral molecular states, we measured the pH of our solutions, Fig. 1 b, to further interrogate the molecular states of βMA. For βA the zwitterionic nature means in solution the molecule will be electrically neutral i.e. a form that will not contribute to conductivity 25 and this is supported by our results (0.1 mS cm − 1 ). We then mix solutions of the two molecules, initially increasing the quantity of MA added to a fixed quantity of βA, Table S1 . The addition of MA ( Χ MA = 0.015) results in a sharp increase in conductivity (15.5 mS cm − 1 ) driven by the formation of carboxylate groups caused by the interaction of MA with βA. Systematically raising the amount of MA to Χ MA = 0.043 results in increased conductivity, (18.2 mS cm − 1 ), however further increases in the quantity of MA, that is until equivalent mole fractions of MA and βA are reached results in a subtle fall in conductivity, Table S1 .In contrast, pure solutions of MA have a measured conductivity of 5.7 ± 1.2 mS cm − 1 and conductivity steadily increases as βA is added. We note that when the relative quantities of MA βA and whilst the solution only containing MA has the lowest pH the conductivity is not derived alone from pH, rather the molecular forms of βA and MA in solution. Assessing the solubility of perovskite precursors in our aqueous solvents : We now consider the solubility of CsBr and PbBr 2 in our solvent mixtures noting that PbBr 2 is insoluble in water. We observe that solubility is only achieved in three of the compositions studied, shown in Figure S5 and detailed in Table 1 . At room temperature, solutions containing equimolar quantities of CsBr and PbBr 2 up to a concentration of 0.3 mol dm - 3 can be solubilised, however all results herein reported contain equimolar quantities at a concentration of 0.2 mol dm - 3 i.e. away from the solubility limit. Unless otherwise stated all data reported herein were obtained from the aqueous Solvent 1 shown in Table 1 . We propose that the insoluble nature of PbBr 2 is overcome through adduct formation between the carboxylate groups of MA and PbBr 2 , whereby these negatively charged groups function as a Lewis base enabling dissolution , Fig. 1 c. Table 1 Aqueous solvent systems enabling the solubilisation of CsBr and PbBr₂. Summary of the aqueous solvent formulations in which both CsBr and PbBr₂ are solubilised. Comprehensive details of all solvent compositions investigated are provided in Table S1 . Solvent MA mole fraction (Χ MA ) βA mole fraction (Χ βA ) H 2 O mole fraction (Χ H2O ) pH Conductivity (mS cm − 1 ) 1 0.015 0.090 0.895 4.46 ± 0.1 15.5 ± 0.56 2 0.029 0.088 0.883 4.18 ± 0.1 18.2 ± 1.05 3 0.043 0.087 0.870 3.91 ± 0.1 18.2 ± 1.15 We investigate this by drying a mixture of CsBr, PbBr 2 and our solvent and conducting FTIR, Fig. 1 d. The 1650–1000 cm − 1 region of the dried solid closely resembles that of pure βA, the bands at 1633 cm − 1 and 1573 cm − 1 ( ν s COO − with and δ as NH 3 + respectively) are unchanged, indicating minimal interaction between βA and the precursors whilst ν (C = O) of MA shifts considerably, indicating there is an interaction between this group and the precursors. To confirm that adduct formation is between the deprotonated carboxyl group of MA and PbBr 2 we attempted to dissolve PbBr 2 in aqueous solutions of pure MA and pure βA, however neither solution was capable of dissolving PbBr 2 ( Figure S4 ). The addition of small quantities of base (NaOH or NH 4 OH) to these solutions did result in dissolution in the case of MA but not βA, Figure S5 . 1 H NMR offers further evidence of an interaction of MA with PbBr 2 (Figure S6) . Compared to MA alone, mixing with βA resulted in an upfield shift of the proton on the carbon bearing the hydroxyl group, indicative of carboxylate deprotonation. The addition of PbBr 2 resulted in a downfield shift, suggesting interaction of carboxylate with Pb. This dissolution mechanism is also applicable in acids with similar structure as MA e.g. succinic acid (SA) Figure S7 . Having developed an understanding of this unusual solubility we turn to consider the nature of the species formed in solution. Using dynamic light scattering (DLS) we probed our neat solvent system and our solvent with the addition of CsBr and PbBr 2 . Although MA and βA exhibit high solubility in H 2 O we predicted that in our solvent systems, owing to the interaction of the molecules at relatively high concentration and their individual interactions with water, that they may possess some colloidal properties. DLS analysis shows the dynamic size of our neat solvent to be around 1 nm. Following the addition of CsBr and PbBr 2 a portion of the solvent remains, presumably not involved in adduct formation, however there is a large population of species with a mean size around 600 nm that we attribute to the adduct formed with PbBr 2 , Fig. 1 e. Understanding Growth and Nucleation Processes To synthesize PNCs, it is necessary to precipitate the perovskite from the precursor solution by disrupting the interactions between MA and PbBr 2 . Based on our model of precursor dissolution we propose a mechanism that utilises protons (HBr) to disrupt the adduct formed between MA and PbBr 2 , driven by the conversion of carboxylate groups into carboxylic acid groups, Figure S8 , followed by precipitation of the desired perovskite. Owing to the high solubility of CsBr in water the addition of a proton source to the mixture will likely only precipitate PbBr 2 and not the desired perovskite. Therefore, it is necessary to introduce a co-solvent with the proton source that has good miscibility with water but poor solubility with our precursors. We identified and investigated three such solvents, methanol, isopropanol (IPA), and acetone—however acetone was the only solvent that successfully facilitated the formation of PNCs ( Figure S9 ). The synthesis proceeds by mixing known quantities of concentrated HBr with 3mL of acetone and injecting 100 µL of our aqueous precursor mixture to this solution. Our precursor contains deprotonated MA and βA both insoluble in acetone, their mixing results in the formation of gel-like aggregates and phase separation, Figure S10 . However, protonated MA and βA are soluble in acetone, hence mixing with HBr breaks the adduct formed between MA and PbBr 2 , thereby releasing PbBr 2 to react with Cs + and Br − ions forming insoluble PNCs. The proposed reaction pathway is outlined in Fig. 2 a. The synthesised PNCs are unstable in polar solvents, acetone and water in this case, therefore surface passivation is required to achieve stability. Passivation is achieved by adding the synthesised PNC solution to a mixture of oleylamine (OAm) in toluene, followed by centrifugation. The supernatant is removed, and the precipitate redispersed in a mixture of OAm, oleic acid (OA) and toluene creating a stable dispersion. Ligand addition is critical, without which aggregation occurs, leading to challenges in dispersion and the loss of quantum confinement effects ( Figure S11 ). To better understand PNC growth, we studied the role HBr plays in the synthesis. A series of HBracetone solutions were prepared in which the HBr concentration was systematically varied from 1.5 to 4. % v/v, Table 2 . Distinct differences in reaction rate were observed as HBr concentration was changed as indicated by the formation of orangecoloured solution. At the lowest HBr concentration the reaction proceeds over 2–3 seconds and gets faster until 37 % v/v is used, at which point the colour change is instantaneous upon mixing. Further increasing the concentration results in the precipitation of bulk CsPbBr 3 ( Figure S12 ). Transmission electron microscopy (TEM) was carried out on the PNCs prepared over the HBr concentration range, Figs. 2 b. Analysis of the images reveals a small increase in size with increased HBr concentration accompanied by a slight reduction in dispersity Table 1 . We propose that size increase is driven by the rate of the reaction of MA with HBr, resulting in PbBr 2 dissociating from the adduct and forming PNC precipitates. At higher HBr concentrations, PbBr 2 is released to the reaction quickly, thus the nucleation concentration (C cr ) is achieved and exceeded rapidly (t H1 < t L1 ). Nucleation and subsequent nanocrystal growth then consumes the released PbBr 2 and thus the PbBr 2 concentration quickly falls back to below C cr (t H2 < t L2 ). In this regime there is no further nucleation, allowing more time for crystal growth resulting in larger PNCs, (Fig. 2 c). The changes in size and dispersity were also reflected in the photoluminescence spectra (PL), Figure S13 . As the PNC size increases, a redshift in the spectra occurs with an accompanying narrowing of the emission, Table 2 . In some samples there is some signal observed around 450 nm that is likely arising from broad band defect states owing to halide vacancies 26 . The photoluminescence quantum yields (PLQYs) fall by almost an order of magnitude as PNC size/HBr concentration increased, Fig. 2 d, with PLQY falling from 25.3% (1.5% v/v) to 3.3% (3.7% v/v). Table 2 Size, dispersity, and optical properties of PNCs as a function of HBr content and solvent ageing. Transmission electron microscopy was used to determine the average size and size dispersity of perovskite nanocrystals synthesised from fresh and 1-hour aged HBr–acetone solutions with systematically varied HBr concentrations. PL emission maxima (λ max ) and fullwidth at halfmaximum values are also shown. HBr% v/v Fresh HBr-acetone 1-hour aged HBr-acetone Size (nm) Dispersity (nm) λ max (nm) FWHM (nm) Size (nm) Dispersity (nm) λ max (nm) FWHM (nm) 1.5 30.9 ± 30.1 516.1 21.5 6.3 ± 1.2 498 31.0 2.3 34.0 ± 15.9 518.9 20.8 9.9 ± 4.1 513 24.0 3.0 39.4 ± 26.9 517.0 21.2 10.1 ± 4.9 512 24.0 3.7 38.1 ± 25.7 518.9 20.4 45.2 ± 22.0 515 23.5 4.4 N/A N/A N/A N/A N/A N/A N/A N/A To explore the recombination processes affecting PLQY, we carried out timecorrelated single photon counting (TCSPC) experiments. The measured data were fitted to biexponential decays Fig. 2 e (see Table S3 for fitting parameters) where the first term reflects a fast decay phase, assigned to trapping into nonradiative deep traps, and a second decay phase assigned to bimolecular recombination of longlived free carriers, Equation S1 . The short-lived lifetime (τ 1 ) is related to the recombination of excitons initially generated upon photon absorption whilst the long-lived carrier lifetime (τ 2 ) is related to exciton recombination at surface states 27 . PNCs prepared from 1. %v/v HBr showed the highest PLQY, where the short- (τ 1 ) and long-lived carrier lifetimes (τ 2 ) were 5.4 ns and 37.3 ns respectively. PNCs prepared by precipitating using 2.3 and 3.0% 5v/v HBr had similar PLQY values to PNCs prepared with 1.5% v/v HBr, and comparable τ 1 lifetimes, however their τ 2 values were considerably greater. From these data we have calculated the radiative (k r ) and non-radiative (k nr )recombination rate constants, Table S3 . Generally, carrier lifetime depends not only on the intrinsic properties of the perovskite but additionally on the defect density, composition and surface chemistry 28 ,29 . The observed reduction in k nr and k r seen as HBr concentration increases is attributed to the accompanying increase in PNC size, where larger PNCs become affected by surface defects 30 ,31 . Additionally, we have investigated the influence of reducing the volume of HBr-acetone added to the synthesis, Table S2 and Figures S14-15 . Microstructural and compositional characterisation : The X-ray diffraction (XRD) patterns of PNCs prepared with varying HBr concentrations are shown in Fig. 3 a. At 1.5% v/v HBr the (110), (112), (004), and (220) peaks were observed, consistent with the stabilisation of orthorhombic CsPbBr 3 (ICDD 01-090-0544). Additionally, peaks from the (113), (300), (024) and (214) planes were observed, which can be attributed to hexagonal Cs 4 PbBr 6 (ICDD 04-014-8071). As the concentration of HBr is increased, the quantity of the hexagonal phase decreases until the formation of phase pure CsPbBr 3 at 3.7% v/v HBr is observed , Fig. 3 b. To study the surfaces of our PNCs, FTIR and X-ray photoelectron spectroscopy (XPS) were used in combination. The FTIR spectra of OA, OAm, βA, MA, and prepared PNCs are shown in Fig. 3 c. In the spectra of OA and OAm, two bands from 2800 to 2990 cm – 1 represent -CH 2 stretching 32 . These bands were also present in the spectrum of PNCs, indicating the presence of OA and OAm on the surface. Additionally, the presence of a broad band from 2800 to 3300 cm − 1 is characteristic of Hbonding, absent in OAm and OA but present in MA and βA. The band at 1567 cm –1 in the βA spectrum is attributed to NH 3 + stretching, while the band at 1097 cm –1 corresponds to C-O stretching mode in MA 2 4 . These bands were also observed in the spectrum of PNCs, although they are less prominent, suggesting residual amounts of MA and βA still exist on the surface of the PNCs. High-resolution XPS spectra obtained from PNCs prepared using 1.5% v/v HBr are shown in Fig. 3 d. The N 1s core level was fitted with two components at 399.9 eV and 401.6 eV, representing − NH 2 and − NH 3 + respectively 33 . In traditional LARP methods, where OA and OAm have been used as surface ligands, both -NH 2 and -NH 3 + are reported in XPS results, originating from OAm. In our case the reported intensity of the peak at 399.9 eV was higher than 401.8 eV, which was attributed to a greater concentration of surface -NH 2 32 . In our data the intensity of -NH 3 + is greater than -NH 2 , indicating -NH 3 + from βA also exists on the surface, consistent with FTIR results. In the O 1s spectrum, Fig. 3 d, the broad peak from 534.5 eV to 529 eV is fitted with four components. A small peak at 529.7 eV is likely originating from PbO, is consistent with the Pb 4f spectrum ( Figure S16 ), although the quantity present is small. The peaks at 531 eV and 533 eV are attributed C = O and -OH respectively, which is present in both OA and MA. The peak at 532 eV arises from the hydroxyl group of MA i.e. indicating the presence of residual MA in the PNC, again consistent with the ATR data, Fig. 3 c. The Pb 4f doublet is shown in Figure S16 , which also indicate the presence of small quantities of metallic Pb, indicated by the additional peak at 136.0 eV. The main, broad peak centred at 137.7 eV can be fitted to Pb 2+ (from the perovskite) 34 . Ageing effects of precipitating solution mixture We observed that if the HBr-acetone solution was not used immediately after its preparation that it developed a brown colour, ascribed to the acidcatalysed enolisation of acetone, if this was then used to prepare PNCs their properties changed considerably. To elucidate the origins of this we prepared solutions of HBr and deuterated acetone (acetone-d 6 ) and recorded 1 H-NMR spectra over time. The 1 H NMR spectra (1.5% v/v HBr) of the fresh 0-, 1-, 5- and 96-hour aged mixtures are shown in Fig. 4 a. The quintet peak at 2.05 ppm originates from the presence of small amounts of residual protonated species in the acetone-d 6 and is used as a reference. Since there was also trace water in the mixture, the proton exchange between HBr, H 3 O + Br − , and water molecules was fast, resulting in a composite singlet peak located at 8.27 ppm at 0-h aging 3 5 . The chemical shift of this singlet peak is given by Eq. 1 , where \(\:\varvec{f}\) and \(\:\varvec{\delta\:}\) are the fraction and chemical shift of the corresponding component, respectively $$\:\begin{array}{c}{\delta\:}_{av}\left(H\right)={f}_{{H}_{2}O}{\delta\:}_{{H}_{2}O}+{f}_{{H}_{3}{O}^{+}}{\delta\:}_{{H}_{3}{O}^{+}}+{f}_{HBr}{\delta\:}_{HBr}\:\#Equation\:1\end{array}$$ The chemical shift of this peak is therefore related to the acidity of the precipitating solution. 1 H NMR was also carried out on 1.5 and 2.3% v/v HBr solutions immediately after mixing (0-hour), Figure S17 . The composite peak of 2.3% v/v HBr showed a larger chemical shift than that of 1.5% HBr v/v equivalent i.e. at higher H 3 O + concentration the composite peak shifted downfield. Figure 4 a shows that with increasing time the composite peak shifts upfield, from 8.27 ppm (0hours) to 6.7 ppm (48hours). The UV-vis absorption spectra of the 0-hour and aged HBr-acetone mixtures are displayed in Fig. 4 c. For the 0-hour samples the absorption onset was located at 260 nm, consistent with pure acetone in water. However, with increased time the absorption onset was shifted to 250 nm which was attributed to the formation of 1-propen-2-ol (CH 2 C(OH)CH 3 ) following the enolisation of acetone, consistent with 1 H NMR observations. The TEM images of PNCs prepared using HBr aged for 1-hour are presented in Fig. 4 b. For PNCs made from 1-hour aged 1.5% v/v HBr, a regular cubic morphology was observed, and the average size was calculated to be 7.2 nm, which is smaller compared to when a fresh acetone-HBr solution was used, and like the case when unaged HBr-acetone was used, there is a systematic increase in PNC size with increasing HBr concentration, Table 2 , However, aging the precipitating solution results in a reduction in the absolute dimensions when compared with unaged equivalents. The PL data, Fig. 4 d, reflect the observations made by TEM. For the smallest PNCs the PL emission maximum was located at 498 nm and the narrow size distribution resulted in relatively narrow FWHM (23.3 nm). A progressive redshift in emission was observed as the size increased, with maxima up to 515 nm occurring for the largest PNCs, Table 2 . According to the 1 H NMR data (Fig. 4 a) the composite peak of H 3 O + , H 2 O and HBr shifted upfield with increased ageing time, indicating that the fraction of H 3 O + decreased with time. This could be caused by Br − being consumed by oxidation to Br 2 , which would be accompanied by the presence of a brown colour as observed (see Figure S18 ). Another possibility could be that the concentration of molecular HBr was increased and correspondingly the fraction of H 3 O + /Br + reduced. In both cases the reduction in concentration of H 3 O + results in a reduction of the rate of PbBr 2 released into the solution i.e. nucleation is slowed, thus PNC size is reduced when the aged HBr solutions are used. Having obtained an understanding of the role of the precipitating solution we consider the impact of changing the quantities of βA and MA in our aqueous solvent, noting that the solubility of PbBr 2 and CsBr could be achieved in three of our solvent compositions (Table 1 ) The results presented thus far have been obtained only using Solvent 1. We turn to the use of Solvents 2 and 3 in our synthesis Using precipitating solutions containing 1.5–3.7% v/v HBr aged for 1-hour, the representative TEM images are shown in Figs. 5ab . It is apparent that the samples follow the same trend seen previously, increasing in size with increasing HBr concentration (Figs. 5 a-d). There are little appreciable differences in the size of PNCs prepared in each precipitating solution however the HBr concentration is having a significant impact. In each solvent the mean diameter is around 7–8 nm when 1. % v/v HBr is used for precipitation increasing to 27–28 nm with 3. % v/v HBr, although notably the dispersity of the PNCs prepared using Solvent 3 is greater in every case. The anticipated red-shift in PL emission is seen in both systems as PNC size increases, Fig. 5 e, comparable with previous results, Fig. 2 a. All data shown were obtained using 1-hour aged HBr–acetone solutions containing 1.5–3.7% v/v HBr, unless otherwise noted. ab) Transmission electron microscopy images of PNCs synthesised using Solvent 2 and Solvent 3, respectively (scale = 50 nm). cd) Size distribution histograms corresponding to PNCs in panels a and b, derived from particle analysis of TEM images. e) Photoluminescence spectra of PNCs synthesised using Solvent 2 and Solvent 3. f) X-ray diffraction patterns of PNCs prepared using Solvents 1–3, compared to reference patterns from ICDD: CsPbBr₃ (01-090-2544, blue), Cs₄PbBr₆ (04-014-8071, grey), and CsBr (01-090-0382, red). g) Photoluminescence quantum yield values for PNCs from different solvent systems. h) Timecorrelated single photon counting measurements, revealing photoluminescence lifetimes and recombination dynamics. The PLQY data for PNCs prepared using Solvent 1 and precipitated from solutions containing 1.5 3. % v/v HBr aged for 1-hour are shown in Fig. 6 g. A reduction in PLQY was observed as the HBr concentration increased, consistent with previous observations however the PLQY values for all samples prepared using 1-hour aged HBr solutions exceed those prepared using fresh equivalents. Additionally, the maximum PLQY values showed a significant enhancement for the 1-hour mixture compared with the fresh solution, with averages of 56% and 16% respectively. To gain insight into the PLQY enhancement TCSPC was again employed where the PLQY data were fitted to biexponential decays Fig. 6 h (see Table S4 for fitting parameters). When compared to data obtained from PNC prepared using fresh HBr-acetone solutions there is a small reduction in the τ 1 component, from 5 ns to 4 ns, and a significant reduction in the slow component (τ 2 ), falling from 40 ns to 20 ns. This indicates that the carriers show higher tendency to recombination in PNCs prepared from the aged HBracetone solutions. This is consistent with the values of the recombination rates calculated from Equations S2-3. Both radiative and non-radiative recombination rates increased for PNCs prepared with aged HBr-acetone solvents, possibly associated with a stronger quantum confinement effect induced by the smaller size of the PNCs (~ 7 nm), forcing excitons generated after photoexcitation to radiatively recombine at a faster rate 36, 37 , explaining the higher PLQY. Photoconductor device measurements Photoconductors were prepared to probe the light-to-current conversion capability of the PNCs. The device structure is illustrated in the inset in Fig. 6 a. The PNCs used in this study were synthesised from 1-hour aged 1.5% v/v HBr (Solvent 1), and measurements were conducted in air and at room temperature. The devices were tested under illumination from a 530 nm LED, with the power intensity ( P in ) varied from 0.37 to 21.4 mW cm − 2 . The current densities of the devices were measured with voltage range between − 20 and + 20 V and revealed a clear, monotonic increase in measured current density with increasing illumination intensity, Fig. 6 a. The responsivity was found to increase with increasing bias, Fig. 6 b. The maximum responsivity of 0.019 A W − 1 was achieved at -20 V under 21.4 mW cm − 2 illumination. The specific detectivity (D*) of the photoconductors was evaluated by measuring the noise level with an applied bias between − 1 and − 20 V. The noise spectral density as a function of frequency is shown in Fig. 6 c. The calculation of D* was performed by utilising the noise spectral density at 10 Hz, which resulted in a D* value of 1.2 x 10 11 Jones (at -20 V and 21 mW cm − 2 illumination), Fig. 6 d. The results obtained for our aqueousprocessed PNCs are consistent with existing literature reports using common, yet toxic solvents 38 – 4 0 , further emphasising the potential of preparing optoelectronic devices these benign solvents. Discussion We report the development of a novel aqueous, environmentally benign solvent system and synthetic protocol for the preparation of size- and composition-controlled metal halide PNCs. The solvent comprises only water, MA, and βA all naturally occurring and non-toxic species that pose no risks to human health or the environment. Central to the process is the formation of a soluble adduct between MA and PbBr 2 , enabling dissolution of an otherwise water-insoluble precursor. Subsequent mixing with HBr in acetone disrupts the adduct, driving the rapid precipitation of PNCs. Detailed spectroscopic analysis using FTIR and ¹H NMR reveals specific interactions between solvent components and precursor species, allowing us to propose a mechanistic framework for crystal growth and identify the parameters governing PNC size and dispersity. We also uncover a solvent ageing effect within the HBracetone phase that significantly influences nanocrystal shape, size, and uniformity. The resulting PNCs exhibit strong photoluminescence, with quantum yields exceeding 60% in selected samples. Imaging by TEM confirms size tunability under different synthetic conditions, with size dispersity reflected in the breadth of the PL spectra. To demonstrate optoelectronic functionality, we fabricated proof-of-concept photodetectors, which display pronounced responses to both light intensity and applied bias, achieving a maximum specific detectivity of 1.2 × 10¹¹ Jones. Notably, the entire synthesis is performed in ambient air, in water, and without the need for any thermal treatment. This establishes a simple and sustainable route for the preparation of PNCs, with clear potential for scalable and sustainable manufacturing. Methods Preparation of solvent system Aqueous solutions of malic acid (DL-MA, 98%, Aldrich), β-alanine (βA, 99%, Aldrich) were prepared at room temperature over the concentration range detailed in Table S1 . CsPbBr 3 precursor solutions were prepared by dissolving equimolar quantities of caesium bromide (CsBr, 99.9%, Aldrich) and lead bromide (PbBr 2 , 99.999%, Aldrich) into solutions of mixture of MA, βA and water and stirred at room temperature for 30 minutes to ensure complete dissolution Synthesis and purification of CsPbBr nanocrystals The entire synthesis process was carried out under ambient conditions and at room temperature. Acetone (3 mL, Aldrich) was transferred to a small vial and to it added different volumes of hydrobromic acid (HBr, 48% v/v). Either 100 µL or 75µL of aqueous solvent (Solvents 1–3) containing MA and βA was added into the HBr-acetone mixture followed by shaking to precipitate the PNCs. The entire synthesis process was carried out under ambient conditions and at room temperature. Acetone (3 mL, Aldrich) was transferred to a small vial and to it added different volumes of hydrobromic acid (HBr, 48% v/v). Either 100 µL or 75µL of aqueous solvent (Solvents 1–3) containing MA and βA was added into the HBr-acetone mixture followed by shaking to precipitate the PNCs. The resultant solutions were mixed with toluene (2mL, Aldrich) containing 50 µL oleylamine (OAm, TCI) and centrifuged 5000 rpm for 3 minutes. The supernatant was discarded, and a further 2 mL toluene containing 50 µL OAm and 100 µL oleic acid (OA, 99%, TCI) were added to the precipitate, resulting in a stable dispersion. A series of further toluene washing-centrifuge cycles were carried out (3000-5000rpm, 3–5 min) to reduce PNC dispersity resulting in a stable dispersion of PNCs in toluene. Modifying precipitating solvent volume As HBr concentration was having a direct influence on PNC properties we investigated the impact of reducing the volume precursor solution from 100 µL to 75 µL whilst varying HBr concentration ( Table S2 ), with representative TEM images are shown in Figure S14 . At HBr concentrations of 1.5–2.3% v/v the resulting PNC size is significantly smaller than the equivalent samples made using 100 µL of precursor in solvent, at around 9 nm. Notably the shape of the PNCs is also different, with a cuboidal morphology observed (for reporting size we quote the length of the shortest edge). PNC prepared using solvent 3.0% v/v HBr retain an average size 50 nm observed, at 3.7% v/v HBr the PNC average size increases significantly to around 32 nm. The size variation observed in the TEM images, Figure S14 , is accompanied by changes in the PL spectra, Figure S15 . The data reveal the impact of size and dispersity variation in the PNCs, with a progressive red-shift observed as average size increases accompanied by an increase of peak FWHM as sample dispersity increases. Overall, PNC size is reduced as precursor quantity reduces, however we did not observe any appreciable differences in the growth rate and suggest that the reduced quantity of HBr results in the formation of smaller PNCs. Photoconductor fabrication: Photoconductors were prepared under ambient conditions. Glass substrates were sequentially cleaned by sonicating sequentially in acetone and isopropanol, nitrogen blowdried and treated by UV-ozone prior to PNC deposition. Following the synthesis and purification procedure PNCs stabilised by OAm in toluene were centrifuged, the supernatant removed, and 1.6 mL of toluene and 0.4 mL of methyl acetate (MeOAc) were added. Repeated centrifugation (3x5000 rpm, 5 min) resulted in a precipitate that was dispersed in 200 µL chloroform, creating a concentrated dispersion of PNCs that could be deposited as a continuous thinfilm. Then, 100 µL of this solution was deposited onto a 2 × 2 cm 2 glass substrate and spin-coated at 1500 rpm for 20 seconds, the process repeated 4 times. Following film deposition 50 nm Au was thermally evaporated through a shadow mask (channel length of 40 µm and a width of 1000 µm). Materials Characterisation Conductivity and Dynamic light scattering (DLS) were measured by using Malvern Zetasizer Nano. Fourier Transform Infrared Spectroscopy (FTIR) was conducted on Agilent Cary 630 FTIR spectrometer with ATR sampling module. Proton nuclear magnetic resonance ( 1 H NMR) was conducted on Bruker AV-400 spectrometer using either D 2 O or Acetone-d 6 as the solvent. Transmission electron microscopy (TEM) images were collected using a JOEL 2100 PLUS at an accelerating voltage of 200 kV, samples were dispersed onto a holey carbon film on a Cu support. UV-vis absorption spectra were collected using an Agilent Cary 60 in absorption mode. Photoluminescence (PL) spectra were acquired by Agilent Cary Eclipse Fluorescence Spectrophotometer. X-ray diffraction (XRD) patterns were acquired by MPD XRD PANalytical diffractometer operated at 40kV and 40mA. X-ray photoelectron spectroscopy (XPS) was performed by Thermo Fisher K-Alpha + equipped with a monochromated Al Ka Micro-focused X-ray source. Photoluminescence quantum yield (PLQY) and Time-resolved PL (TRPL) were acquired using an Edinburgh Instruments FLS1000 spectrometer. TRPL decays were taken with an Edinburgh Instruments EPL 375 nm picosecond pulsed diode laser. The repetition rate was controlled by an external trigger input and set to 1 MHz. The emission signal frequency was set to 3% that of the start rate to maintain single photon counting statistics. A visible PMT-980 detector was used for TRPL measurements. The photoluminescence quantum yield (PLQY) measurements were measured on the FLS 1000 fluorescence spectrophotometer with the assistance of an integrating sphere accessory (diameter = 150 nm). Photoconductor Characterisation: The optoelectronic characterisations were conducted in ambient environment with a Keithley 4200 equipped with a current amplifier and the light illumination was provided by a 530 nm Thorlab LED (M530L4). Noise measurements were conducted with probes consisting of a platinum wire counter electrode integrated with Zurich MFLI Lock-in Amplifier. The signal has been recorded after amplification with a Stanford Research System SR570 low-noise current preamplifier. Responsivity (R) is defined as the ratio of photogenerated current over the incident optical power output ( P opt ), by considering the optical power density E opt and the device area (A): $$\:{R}_{c}=\frac{{I}_{ph}}{{P}_{opt}}=\frac{{I}_{illumination}-\:{I}_{dark}}{{E}_{opt}\:A}$$ The specific detectivity (D*) is defined by R and the electronic noise spectral density ( i n Δf − 1/2 ) of the device, normalising by the area of the photodetector (A, in this case, 0.0004 cm 2 ) to enable comparability between different photodetectors: $$\:{D}^{*}=\frac{\sqrt{A\varDelta\:f}{R}_{C}}{{i}_{n}}$$ i n Δf − 1/2 can be extracted experimentally from the dark current recorded with a lock-in amplifier, followed by a fast Fourier transform (Fig. 6 c). Declarations Acknowledgments M.A.M. and W.R.K. gratefully acknowledge the EPSRC and SFI Centre for Doctoral Training in Advanced Characterisation of Materials ( EP/S023259/1) for financial support. M.H. and M.R. thank the EPSRC (EP/T028513/1)for financial support and M.H. KAUST for baseline funding. T.J.M. thanks the Royal Commission for the Exhibition of 1851 for their financial support through a Research Fellowship and acknowledges funding from a Royal Society University Research Fellowship (URF/R1/221834). References Mi Z et al (2024) Real-time single-proton counting with transmissive perovskite nanocrystal scintillators. Nature Materials 2024 23:6 23, 803–809 Yang W et al (2023) Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells. Adv Mater 35 Dey A et al (2021) State of the Art and Prospects for Halide Perovskite Nanocrystals. ACS Nano 15:10775–10981 Xing G et al (2016) Solution-Processed Tin‐Based Perovskite for Near‐Infrared Lasing. Adv Mater 28:8191–8196 Mondal N, De A, Samanta A (2019) Achieving Near-Unity Photoluminescence Efficiency for Blue-Violet-Emitting Perovskite Nanocrystals. 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Adv Mater 28:8718–8725 Lin W-C et al (2021) In situ XPS investigation of the X-ray-triggered decomposition of perovskites in ultrahigh vacuum condition. Npj Mater Degrad 5:13 Lerum HV, Andersen NH, Eriksen DØ, Hansen EW, Omtvedt J (2020) P. NMR study of the influence and interplay of water, HCl and LiCl with the extraction agent Aliquat 336 dissolved in toluene. J Mol Liq 317:114160 Polavarapu L, Nickel B, Feldmann J, Urban AS (2017) Advances in Quantum-Confined Perovskite Nanocrystals for Optoelectronics. Adv Energy Mater 7 Al-Maskari S et al (2023) Dye-induced photoluminescence quenching of quantum dots: role of excited state lifetime and confinement of charge carriers. Phys Chem Chem Phys 25:14126–14137 Maduwanthi C, Jong C-A, Mohammed WS, Hsu S-H (2024) Stability and photocurrent enhancement of photodetectors by using core/shell structured CsPbBr 3 /TiO 2 quantum dots and 2D materials. Nanoscale Adv 6:2328–2336 Wang S et al (2025) A high-performance photodetector based on a ZnO/CsPbBr 3 quantum-dot-level-contact hybrid sandwich structure. J Mater Chem C Mater 13:902–909 Dong Y et al (2016) Improving All-Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect. Small 12:5622–5632 Additional Declarations There is NO Competing Interest. Supplementary Files DuetalWaterbasedsynthesisofperovskitenanocrystalsSI.docx Water-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions Supplementary Information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6443068","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":444125728,"identity":"0194363c-0713-4628-9186-da97954dce72","order_by":0,"name":"Martyn 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PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e solubilization and measured properties of the aqueous solvent system\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e) Molecular structures and pK\u003csub\u003ea\u003c/sub\u003e values of malic acid (MA) and β-alanine (βA). \u003cstrong\u003eb\u003c/strong\u003e) Conductivity and pH measurements of aqueous solutions containing MA, βA, and their mixtures (see Table S1). \u003cstrong\u003ec\u003c/strong\u003e)Schematic illustration of the proposed dissolution mechanism for CsBr and PbBr₂ in the MA/βA solvent system. \u003cstrong\u003ed)\u003c/strong\u003e\u0026nbsp;Fourier transform infrared spectra of βA, MA, and the dried product obtained after mixing the solvent with CsBr and PbBr₂, indicating coordination interactions. \u003cstrong\u003ee\u003c/strong\u003e) Dynamic light scattering data showing changes in particle size distribution before and after precursor dissolution.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/bdb092363cfc60489ed5a926.png"},{"id":80870175,"identity":"16cccc8d-3c6c-4feb-96e7-6ace5d7f93e6","added_by":"auto","created_at":"2025-04-18 04:55:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":812797,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProposed reaction mechanism, physical and optical properties of perovskite nanocrystals (PNCs) synthesised from aqueous solution.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e) Schematic of the proposed reaction pathway: solubilisation of PbBr₂ via adduct formation in water, followed by precipitation and ligand-mediated surface passivation. All subsequent data correspond to PNCs precipitated using 1.5%, 2.3%, 3.0%, and 3.7% v/v HBr in acetone. \u003cstrong\u003eb\u003c/strong\u003e) Transmission electron microscopy images of PNCs (scale = 50 nm) and corresponding statistical size analysis. \u003cstrong\u003ec\u003c/strong\u003e) LaMer diagram illustrating the effect of HBr concentration on nucleation and growth dynamics. \u003cstrong\u003ed\u003c/strong\u003e) Photoluminescence quantum yield of PNCs as a function of HBr content. \u003cstrong\u003ee\u003c/strong\u003e) time‑correlated single photon counting measurements showing exciton lifetime dynamics under varying synthesis conditions.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/a0d3aed1e19ecf7b5b39fa04.png"},{"id":80870174,"identity":"d6321502-ac9e-46d8-a43d-bc90da2b12d1","added_by":"auto","created_at":"2025-04-18 04:55:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":244954,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural and surface chemical analysis of CsPbBr₃perovskite nanocrystals (PNCs) prepared with varying HBr concentrations.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e X-ray diffraction patterns of PNCs as a function of HBr concentration, alongside reference patterns for CsPbBr₃(ICDD 01-090-0544, dark blue) and Cs₄PbBr₆ (ICDD 04-014-8071, grey). \u003cstrong\u003eb)\u003c/strong\u003e Estimated phase composition of PNCs, determined from quantitative analysis of the XRD data. \u003cstrong\u003ec)\u003c/strong\u003e Fourier transform infrared spectra of oleylamine, oleic acid, β-alanine (βA), methylammonium (MA), and CsPbBr₃PNCs. and fitted high‑resolution X-ray photoelectron spectroscopy spectra for \u003cstrong\u003ed)\u003c/strong\u003eN 1\u003cem\u003es\u003c/em\u003e and \u003cstrong\u003ee)\u003c/strong\u003e O 1\u003cem\u003es\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/1cb15fc07f6991926b5f10bf.png"},{"id":80870902,"identity":"6392f12b-0e24-4f3d-98d2-dd642a11ac12","added_by":"auto","created_at":"2025-04-18 05:03:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":287286,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eImpact of HBr–acetone ageing on precursor chemistry, nanocrystal morphology, and optical properties.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e) Time-resolved ¹H NMR spectra of precipitating solutions containing 1.5% v/v HBr, showing chemical evolution upon ageing. \u003cstrong\u003eb\u003c/strong\u003e) TEM images of perovskite nanocrystals (PNCs) synthesised from solutions aged for 1‑hour with varying HBr content (1.5 ‑ 3.7% v/v), scale bar=50 nm. \u003cstrong\u003ec\u003c/strong\u003e) UV–vis absorption spectra of 1.5% v/v HBr precipitating solutions aged over a 5-hour period. \u003cstrong\u003ed\u003c/strong\u003e) Photoluminescence spectra of PNCs prepared from 1-hour aged solutions containing 1.5 ‑ 3.7% v/v HBr. \u003cstrong\u003ee)\u003c/strong\u003e Size dispersity measurements of PNCs derived from the same ageing conditions, highlighting the sensitivity of nanocrystal uniformity to precursor solution composition.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/27381cf787165bdf995807ab.png"},{"id":80870180,"identity":"73f3f4e4-47a7-4588-8e74-e328c3c21d9a","added_by":"auto","created_at":"2025-04-18 04:55:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":222684,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural and optical characterisation of perovskite nanocrystals (PNCs) synthesised using alternative aqueous solvent compositions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data shown were obtained using 1-hour aged HBr–acetone solutions containing 1.5–3.7% v/v HBr, unless otherwise noted. \u003cstrong\u003ea‑b)\u003c/strong\u003e Transmission electron microscopy images of PNCs synthesised using Solvent 2 and Solvent 3, respectively (scale = 50 nm). \u003cstrong\u003ec‑d)\u003c/strong\u003e Size distribution histograms corresponding to PNCs in panels a and b, derived from particle analysis of TEM images. \u003cstrong\u003ee)\u003c/strong\u003e Photoluminescence spectra of PNCs synthesised using Solvent 2 and Solvent 3. \u003cstrong\u003ef)\u003c/strong\u003e X-ray diffraction patterns of PNCs prepared using Solvents 1–3, compared to reference patterns from ICDD: CsPbBr₃(01-090-2544, blue), Cs₄PbBr₆ (04-014-8071, grey), and CsBr (01-090-0382, red). \u003cstrong\u003eg)\u003c/strong\u003e Photoluminescence quantum yield values for PNCs from different solvent systems. \u003cstrong\u003eh)\u003c/strong\u003e Time‑correlated single photon counting measurements, revealing photoluminescence lifetimes and recombination dynamics.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/2e81103160a9ccf1df3c58de.png"},{"id":80870183,"identity":"e60af8d3-e20f-4f01-97f8-56725b358861","added_by":"auto","created_at":"2025-04-18 04:55:08","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":213046,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotodetector performance of PNC-based devices under varying illumination and bias conditions.\u003c/strong\u003e\u003cbr\u003e\n \u003cstrong\u003ea\u003c/strong\u003e) Current density as a function of incident light intensity, measured under different applied biases. Inset shows schematic illustration of the device architecture. \u003cstrong\u003eb\u003c/strong\u003e) Calculated responsivity of the devices as a function of light intensity and applied bias. \u003cstrong\u003ec\u003c/strong\u003e) Noise spectral density as a function of applied bias. \u003cstrong\u003ed\u003c/strong\u003e) Specific detectivity (D*) calculated from responsivity and noise data, as a function of light intensity and bias.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/52ed6b30219e61dbb60ce64d.png"},{"id":92064601,"identity":"a8373523-f1cb-438b-b1cc-e1474925222e","added_by":"auto","created_at":"2025-09-24 08:40:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3639739,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/25f31ce6-3792-4756-81cd-92340bf55b85.pdf"},{"id":80870901,"identity":"585b4ef9-2567-4a6f-9301-e4e3a147d5c9","added_by":"auto","created_at":"2025-04-18 05:03:08","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5619722,"visible":true,"origin":"","legend":"Water-Based Synthesis of CsPbBr\u0026#x2083; Perovskite Nanocrystals Under Ambient Conditions Supplementary Information","description":"","filename":"DuetalWaterbasedsynthesisofperovskitenanocrystalsSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-6443068/v1/f628b8bc96949e70b2b7c946.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eWater-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePerovskite nanocrystals (PNCs) are promising candidates for next-generation light-emitting diodes (LEDs), photovoltaics (PVs), photodetectors (PDs), and other optoelectronic applications. Their exceptional properties\u0026mdash;including high-purity, bright emission, tuneable absorption, ambipolar charge transport, long charge carrier diffusion lengths, and intrinsic defect tolerance\u0026mdash;make them highly attractive for advanced device technologies\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The relative ease by which compositional control can be afforded through well-established synthesis methods permits facile doping, thus a broad range of bandgaps can be prepared whereby absorption and/or emission wavelength can be tuned to suit the application. Recent PNC developments have demonstrated tuneable emission across the visible spectrum and beyond \u003cem\u003ee.g.\u003c/em\u003e CsSnI\u003csub\u003e3\u003c/sub\u003e with near-infrared emission\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e to CsPbCl\u003csub\u003e3\u003c/sub\u003e with blue-to-violet emission\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, and quantum yields (QYs) approaching 100%. Synthesis of PNCs broadly follows two well-reported synthetic methods, namely ligand-assisted reprecipitation (LARP)\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e and hot-injection (HI)\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. LARP is generally considered to be more facile than HI, and more efficient, and as elevated temperatures are not required there is a greater potential for scale-up\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. The main limitations of the LARP method stem from the significant environmental and health risks posed by the solvents used, particularly the combination of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), which present challenges for scalingup and mass production\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e0\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAs PNCs continue to garner interest, there is a requirement to identify synthesis methods that retain the positive attributes of LARP and, in parallel, address the environmental and human health risks associated with the solvents employed. Despite this growing need there remain few reports focusing on PNC synthesis using green solvents or processes. Some notable examples include the work of Lu \u003cem\u003eet al\u003c/em\u003e., who developed natural deep eutectic solvents (NADES) to substitute DMF and ligands used in LARP, demonstrating the successful synthesis of CsPbBr\u003csub\u003e3\u003c/sub\u003e PNCs\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. In 2019, Ambroz \u003cem\u003eet al.\u003c/em\u003e demonstrated a room-temperature injection method for FAPbBr\u003csub\u003e3\u003c/sub\u003e and CsPbBr\u003csub\u003e3\u003c/sub\u003e PNCs using a phosphine-based ligand combination that enabled the dissolution of all precursors without the need for polar aprotic solvents such as DMF or DMSO\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Hoang \u003cem\u003eet al.\u003c/em\u003e utilized an environmentally friendly ionic liquid, based on a series of methylammonium carboxylates, to prepare MAPbBr\u003csub\u003e3\u003c/sub\u003e PNCs\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e and Chatterjee \u003cem\u003eet al.\u003c/em\u003e used menthol-based deep eutectic solvents (DESs) to prepare CsPbX\u003csub\u003e3\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;I, Br, Cl) PNCs and nanoplates\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Water, the greenest of solvents, has not yet been utilised as the primary solvent in the synthesis of PNCs\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. This is largely attributed to the remarkably low solubility of lead halide compounds in water, coupled with the widely held perception of the detrimental effects of H\u003csub\u003e2\u003c/sub\u003eO on metal-halide perovskites\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Consequently, there are no reported instances of successful utilisation of aqueous precursors for the synthesis of PNCs.\u003c/p\u003e \u003cp\u003eHere, we report the development of a novel, waterbased solvent capable of dissolving lead halide compounds at room temperature and the subsequent development of a facile, rapid, efficient, and non-toxic synthetic route for the preparation of sizecontrolled CsPbBr\u003csub\u003e3\u003c/sub\u003e PNCs. Our solvent consists solely of water, βalanine (βA, 3-aminopropanoic acid) and malic acid (MA, 2-hydroxybutanedioic acid) - all naturally occurring. The dissolution of PbBr\u003csub\u003e2\u003c/sub\u003e is facilitated by the formation of an adduct with the carboxylate end group of aqueous MA. Although PbBr\u003csub\u003e2\u003c/sub\u003e is insoluble in pure water we demonstrate the room temperature preparation of aqueous solutions with concentrations exceeding 0.2 mol dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. Hydrobromic acid (HBr) is then used to initiate and aid the precipitation of our PNCs. We rigorously investigate the role of MA, βA, PbBr\u003csub\u003e2\u003c/sub\u003e and HBr and their relative concentrations on PNC synthesis, resulting in the successful formation of size-controlled PNCs with sizes ranging from \u0026lt;\u0026thinsp;5 nm to 100 nm and photoluminescence quantum yields (PLQY)\u0026thinsp;\u0026gt;\u0026thinsp;60 %. Our novel, environmentally benign solvent provides a clean, scalable, and cost-effective strategy for precise control over the size of PNCs.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cstrong\u003eDeveloping an aqueous solvent system\u003c/strong\u003e \u003cp\u003eβA and MA are naturally occurring molecules, the former is naturally synthesised in the human liver and is often taken as a sports supplement whilst MA is the primary acid of many common fruits, the molecular structures of both are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. We first consider the molecular states that each molecule, and mixtures of the two, can adopt in aqueous solution, Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e. βA contains an amine and a carboxylic acid group that, in aqueous environments, can undergo proton transfer leading to the zwitterionic form containing ammonium and carboxylate charged end groups (pK\u003csub\u003ea\u003c/sub\u003e values of around 3.55 and 10.2 respectively)\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. MA contains two carboxyl groups (pK\u003csub\u003ea1\u003c/sub\u003e of 3.4 and pK\u003csub\u003ea2\u003c/sub\u003e of 5.1)\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e which can be partially or fully deprotonated in water, forming carboxylate groups.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eTo determine the molecular states present in each solution we used attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) initially on solid samples of βA and MA, \u003cb\u003eFigure S2\u003c/b\u003e. In βA the absorption cented at 1631 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the shoulder at 1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e can be assigned to \u003csub\u003eνas\u003c/sub\u003eCOO\u003csup\u003e\u0026minus;\u003c/sup\u003e with and \u003csub\u003eδ\u003cem\u003eas\u003c/em\u003e\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e respectively (\u003csub\u003eδ\u003cem\u003eas\u003c/em\u003e\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e also at 1540 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and \u003csub\u003eδ\u003cem\u003es\u003c/em\u003e\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e also at 1504 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) indicating βA is in a zwitterionic form\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. For MA, the absorption at 1680 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the ajacent absorptions at 1714 and 1737 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e collectively correspond to \u003csub\u003eν\u003c/sub\u003e(C\u0026thinsp;=\u0026thinsp;O) of dimeric COOH formed between MA molecules\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Aqueous solutions of βA and MA were prepared each with mole fractions (\u003cem\u003eΧ\u003c/em\u003e\u003csub\u003eβA\u003c/sub\u003e /\u003cem\u003eΧ\u003c/em\u003e\u003csub\u003eMA\u003c/sub\u003e) of 0.091, resulting in solutions with pH values of 7.48 and 1.32 respectively, \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. In solution, significant changes in the FTIR spectra of both molecules are seen \u003cb\u003eFigure S2\u003c/b\u003e. Considering the FTIR spectra of the solution for βA we anticipate, owing to the zwiterionic nature, that the molecule will be heavily solvated by water. The discrete absorptions observed around 1504\u0026ndash;1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are replaced by a broad absorption band centred at 1560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e that indicates a strong interaction of water with these charged end groups. In solution, MA shows a similar broad band centred around 1714 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e that shows the dimers formed in the solid are disrupted and the carboxlate groups are solvated. Solutions of both molecules were then prepared where the concentration of each was systematically varied, \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e, resulting in changes in the FTIR spectra, \u003cb\u003eFigure S3\u003c/b\u003e, that can be attributed to solution composition and the relative concentrations of each molecule.\u003c/p\u003e \u003cp\u003eAs conductivity is derived from the concentration of dissolved ions in solution \u003cem\u003ei.e.\u003c/em\u003e the non-neutral molecular states, we measured the pH of our solutions, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, to further interrogate the molecular states of βMA. For βA the zwitterionic nature means in solution the molecule will be electrically neutral \u003cem\u003ei.e.\u003c/em\u003e a form that will not contribute to conductivity\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e and this is supported by our results (0.1 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). We then mix solutions of the two molecules, initially increasing the quantity of MA added to a fixed quantity of βA, \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. The addition of MA (\u003cem\u003eΧ\u003c/em\u003e\u003csub\u003eMA\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.015) results in a sharp increase in conductivity (15.5 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) driven by the formation of carboxylate groups caused by the interaction of MA with βA. Systematically raising the amount of MA to \u003cem\u003eΧ\u003c/em\u003e\u003csub\u003eMA\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.043 results in increased conductivity, (18.2 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), however further increases in the quantity of MA, that is until equivalent mole fractions of MA and βA are reached results in a subtle fall in conductivity, \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e.In contrast, pure solutions of MA have a measured conductivity of 5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and conductivity steadily increases as βA is added. We note that when the relative quantities of MA\u0026thinsp;\u0026lt;\u0026thinsp;βA the solution conductivity is greater than when MA\u0026thinsp;\u0026gt;\u0026thinsp;βA and whilst the solution only containing MA has the lowest pH the conductivity is not derived alone from pH, rather the molecular forms of βA and MA in solution.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eAssessing the solubility of perovskite precursors in our aqueous solvents\u003c/span\u003e: \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eWe now consider the solubility of CsBr and PbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ein our solvent mixtures noting that PbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eis insoluble in water. We observe that solubility is only achieved in three of the compositions studied, shown in\u003c/span\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eFigure S5\u003c/span\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eand detailed in\u003c/span\u003e Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eAt room temperature, solutions containing equimolar quantities of CsBr and PbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eup to a concentration of 0.3 mol dm\u003c/span\u003e\u003csup\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e-\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ecan be solubilised, however all results herein reported contain equimolar quantities at a concentration of 0.2 mol dm\u003c/span\u003e\u003csup\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e-\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"ItalicUnderline\" class=\"ItalicUnderline\" name=\"Emphasis\"\u003ei.e.\u003c/span\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eaway from the solubility limit. Unless otherwise stated all data reported herein were obtained from the aqueous Solvent 1 shown in\u003c/span\u003e Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eWe propose that the insoluble nature of PbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eis overcome through adduct formation between the carboxylate groups of MA and PbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e, \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ewhereby these negatively charged groups function as a Lewis base enabling dissolution\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e \u003cb\u003eAqueous solvent systems enabling the solubilisation of CsBr and PbBr₂.\u003c/b\u003e Summary of the aqueous solvent formulations in which both CsBr and PbBr₂ are solubilised. Comprehensive details of all solvent compositions investigated are provided in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSolvent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMA mole fraction (Χ\u003csub\u003eMA\u003c/sub\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eβA mole fraction (Χ\u003csub\u003eβA\u003c/sub\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO mole fraction (Χ\u003csub\u003eH2O\u003c/sub\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eConductivity\u003c/p\u003e \u003cp\u003e(mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.090\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.895\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e15.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.088\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.883\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e18.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.043\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.087\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.870\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e3.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e18.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWe investigate this by drying a mixture of CsBr, PbBr\u003csub\u003e2\u003c/sub\u003e and our solvent and conducting FTIR, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. The 1650\u0026ndash;1000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region of the dried solid closely resembles that of pure βA, the bands at 1633 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1573 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003csub\u003eν\u003cem\u003es\u003c/em\u003e\u003c/sub\u003eCOO\u003csup\u003e\u0026minus;\u003c/sup\u003e with and \u003csub\u003eδ\u003cem\u003eas\u003c/em\u003e\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e respectively) are unchanged, indicating minimal interaction between βA and the precursors whilst \u003csub\u003eν\u003c/sub\u003e(C\u0026thinsp;=\u0026thinsp;O) of MA shifts considerably, indicating there is an interaction between this group and the precursors. To confirm that adduct formation is between the deprotonated carboxyl group of MA and PbBr\u003csub\u003e2\u003c/sub\u003e we attempted to dissolve PbBr\u003csub\u003e2\u003c/sub\u003e in aqueous solutions of pure MA and pure βA, however neither solution was capable of dissolving PbBr\u003csub\u003e2\u003c/sub\u003e (\u003cb\u003eFigure S4\u003c/b\u003e). The addition of small quantities of base (NaOH or NH\u003csub\u003e4\u003c/sub\u003eOH) to these solutions did result in dissolution in the case of MA but not βA, \u003cb\u003eFigure S5\u003c/b\u003e. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR offers further evidence of an interaction of MA with PbBr\u003csub\u003e2\u003c/sub\u003e \u003cb\u003e(Figure S6)\u003c/b\u003e. Compared to MA alone, mixing with βA resulted in an upfield shift of the proton on the carbon bearing the hydroxyl group, indicative of carboxylate deprotonation. The addition of PbBr\u003csub\u003e2\u003c/sub\u003e resulted in a downfield shift, suggesting interaction of carboxylate with Pb. This dissolution mechanism is also applicable in acids with similar structure as MA \u003cem\u003ee.g.\u003c/em\u003e succinic acid (SA) \u003cb\u003eFigure S7\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eHaving developed an understanding of this unusual solubility we turn to consider the nature of the species formed in solution. Using dynamic light scattering (DLS) we probed our neat solvent system and our solvent with the addition of CsBr and PbBr\u003csub\u003e2\u003c/sub\u003e. Although MA and βA exhibit high solubility in H\u003csub\u003e2\u003c/sub\u003eO we predicted that in our solvent systems, owing to the interaction of the molecules at relatively high concentration and their individual interactions with water, that they may possess some colloidal properties. DLS analysis shows the dynamic size of our neat solvent to be around 1 nm. Following the addition of CsBr and PbBr\u003csub\u003e2\u003c/sub\u003e a portion of the solvent remains, presumably not involved in adduct formation, however there is a large population of species with a mean size around 600 nm that we attribute to the adduct formed with PbBr\u003csub\u003e2\u003c/sub\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee.\u003c/p\u003e\u003cp\u003e \u003cstrong\u003eUnderstanding Growth and Nucleation Processes\u003c/strong\u003e \u003cp\u003eTo synthesize PNCs, it is necessary to precipitate the perovskite from the precursor solution by disrupting the interactions between MA and PbBr\u003csub\u003e2\u003c/sub\u003e. Based on our model of precursor dissolution we propose a mechanism that utilises protons (HBr) to disrupt the adduct formed between MA and PbBr\u003csub\u003e2\u003c/sub\u003e, driven by the conversion of carboxylate groups into carboxylic acid groups, \u003cb\u003eFigure S8\u003c/b\u003e, followed by precipitation of the desired perovskite. Owing to the high solubility of CsBr in water the addition of a proton source to the mixture will likely only precipitate PbBr\u003csub\u003e2\u003c/sub\u003e and not the desired perovskite. Therefore, it is necessary to introduce a co-solvent with the proton source that has good miscibility with water but poor solubility with our precursors. We identified and investigated three such solvents, methanol, isopropanol (IPA), and acetone\u0026mdash;however acetone was the only solvent that successfully facilitated the formation of PNCs (\u003cb\u003eFigure S9\u003c/b\u003e).\u003c/p\u003e \u003c/p\u003e \u003cp\u003eThe synthesis proceeds by mixing known quantities of concentrated HBr with 3mL of acetone and injecting 100 \u0026micro;L of our aqueous precursor mixture to this solution. Our precursor contains deprotonated MA and βA both insoluble in acetone, their mixing results in the formation of gel-like aggregates and phase separation, \u003cb\u003eFigure S10\u003c/b\u003e. However, protonated MA and βA are soluble in acetone, hence mixing with HBr breaks the adduct formed between MA and PbBr\u003csub\u003e2\u003c/sub\u003e, thereby releasing PbBr\u003csub\u003e2\u003c/sub\u003e to react with Cs\u003csup\u003e+\u003c/sup\u003e and Br\u003csup\u003e\u0026minus;\u003c/sup\u003e ions forming insoluble PNCs. The proposed reaction pathway is outlined in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. The synthesised PNCs are unstable in polar solvents, acetone and water in this case, therefore surface passivation is required to achieve stability. Passivation is achieved by adding the synthesised PNC solution to a mixture of oleylamine (OAm) in toluene, followed by centrifugation. The supernatant is removed, and the precipitate redispersed in a mixture of OAm, oleic acid (OA) and toluene creating a stable dispersion. Ligand addition is critical, without which aggregation occurs, leading to challenges in dispersion and the loss of quantum confinement effects (\u003cb\u003eFigure S11\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eTo better understand PNC growth, we studied the role HBr plays in the synthesis. A series of HBracetone solutions were prepared in which the HBr concentration was systematically varied from 1.5 to 4. % v/v, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Distinct differences in reaction rate were observed as HBr concentration was changed as indicated by the formation of orangecoloured solution. At the lowest HBr concentration the reaction proceeds over 2\u0026ndash;3 seconds and gets faster until 37 % v/v is used, at which point the colour change is instantaneous upon mixing. Further increasing the concentration results in the precipitation of bulk CsPbBr\u003csub\u003e3\u003c/sub\u003e (\u003cb\u003eFigure S12\u003c/b\u003e). Transmission electron microscopy (TEM) was carried out on the PNCs prepared over the HBr concentration range, Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. Analysis of the images reveals a small increase in size with increased HBr concentration accompanied by a slight reduction in dispersity Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. We propose that size increase is driven by the rate of the reaction of MA with HBr, resulting in PbBr\u003csub\u003e2\u003c/sub\u003e dissociating from the adduct and forming PNC precipitates. At higher HBr concentrations, PbBr\u003csub\u003e2\u003c/sub\u003e is released to the reaction quickly, thus the nucleation concentration (C\u003csub\u003ecr\u003c/sub\u003e) is achieved and exceeded rapidly (t\u003csub\u003eH1\u003c/sub\u003e \u0026lt; t\u003csub\u003eL1\u003c/sub\u003e). Nucleation and subsequent nanocrystal growth then consumes the released PbBr\u003csub\u003e2\u003c/sub\u003e and thus the PbBr\u003csub\u003e2\u003c/sub\u003e concentration quickly falls back to below C\u003csub\u003ecr\u003c/sub\u003e (t\u003csub\u003eH2\u003c/sub\u003e \u0026lt; t\u003csub\u003eL2\u003c/sub\u003e). In this regime there is no further nucleation, allowing more time for crystal growth resulting in larger PNCs, (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). The changes in size and dispersity were also reflected in the photoluminescence spectra (PL), \u003cb\u003eFigure S13\u003c/b\u003e. As the PNC size increases, a redshift in the spectra occurs with an accompanying narrowing of the emission, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In some samples there is some signal observed around 450 nm that is likely arising from broad band defect states owing to halide vacancies\u003csup\u003e26\u003c/sup\u003e. The photoluminescence quantum yields (PLQYs) fall by almost an order of magnitude as PNC size/HBr concentration increased, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, with PLQY falling from 25.3% (1.5% v/v) to 3.3% (3.7% v/v).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u003cb\u003eSize, dispersity, and optical properties of PNCs as a function of HBr content and solvent ageing.\u003c/b\u003e Transmission electron microscopy was used to determine the average size and size dispersity of perovskite nanocrystals synthesised from fresh and 1-hour aged HBr\u0026ndash;acetone solutions with systematically varied HBr concentrations. PL emission maxima (λ\u003csub\u003emax\u003c/sub\u003e) and fullwidth at halfmaximum values are also shown.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eHBr% v/v\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003e\u003cem\u003eFresh HBr-acetone\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e \u003cp\u003e\u003cem\u003e1-hour aged HBr-acetone\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eSize (nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eDispersity\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eλ\u003c/b\u003e\u003csub\u003e\u003cb\u003emax\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eFWHM\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003eSize (nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003eDispersity\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003eλ\u003c/b\u003e\u003csub\u003e\u003cb\u003emax\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003eFWHM\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nm)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;30.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e516.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e498\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e31.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e518.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e513\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e24.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;26.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e517.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e512\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e24.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;25.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e518.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e45.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;22.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e515\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e23.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo explore the recombination processes affecting PLQY, we carried out timecorrelated single photon counting (TCSPC) experiments. The measured data were fitted to biexponential decays Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee (see \u003cb\u003eTable S3\u003c/b\u003e for fitting parameters) where the first term reflects a fast decay phase, assigned to trapping into nonradiative deep traps, and a second decay phase assigned to bimolecular recombination of longlived free carriers, \u003cb\u003eEquation S1\u003c/b\u003e. The short-lived lifetime (τ\u003csub\u003e1\u003c/sub\u003e) is related to the recombination of excitons initially generated upon photon absorption whilst the long-lived carrier lifetime (τ\u003csub\u003e2\u003c/sub\u003e) is related to exciton recombination at surface states\u003csup\u003e27\u003c/sup\u003e. PNCs prepared from 1. %v/v HBr showed the highest PLQY, where the short- (τ\u003csub\u003e1\u003c/sub\u003e) and long-lived carrier lifetimes (τ\u003csub\u003e2\u003c/sub\u003e) were 5.4 ns and 37.3 ns respectively. PNCs prepared by precipitating using 2.3 and 3.0% 5v/v HBr had similar PLQY values to PNCs prepared with 1.5% v/v HBr, and comparable τ\u003csub\u003e1\u003c/sub\u003e lifetimes, however their τ\u003csub\u003e2\u003c/sub\u003e values were considerably greater. From these data we have calculated the radiative (k\u003csub\u003er\u003c/sub\u003e) and non-radiative (k\u003csub\u003enr\u003c/sub\u003e)recombination rate constants, \u003cb\u003eTable S3\u003c/b\u003e. Generally, carrier lifetime depends not only on the intrinsic properties of the perovskite but additionally on the defect density, composition and surface chemistry\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,29\u003c/sup\u003e. The observed reduction in k\u003csub\u003enr\u003c/sub\u003e and k\u003csub\u003er\u003c/sub\u003e seen as HBr concentration increases is attributed to the accompanying increase in PNC size, where larger PNCs become affected by surface defects\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,31\u003c/sup\u003e. Additionally, we have investigated the influence of reducing the volume of HBr-acetone added to the synthesis, \u003cb\u003eTable S2\u003c/b\u003e and \u003cb\u003eFigures S14-15\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eMicrostructural and compositional characterisation\u003c/span\u003e: \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eThe X-ray diffraction (XRD) patterns of PNCs prepared with varying HBr concentrations are shown in\u003c/span\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eAt 1.5% v/v HBr the (110), (112), (004), and (220) peaks were observed, consistent with the stabilisation of orthorhombic CsPbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e3\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(ICDD 01-090-0544). Additionally, peaks from the (113), (300), (024) and (214) planes were observed, which can be attributed to hexagonal Cs\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e4\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ePbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e6\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(ICDD 04-014-8071). As the concentration of HBr is increased, the quantity of the hexagonal phase decreases until the formation of phase pure CsPbBr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e3\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eat 3.7% v/v HBr is observed\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003eTo study the surfaces of our PNCs, FTIR and X-ray photoelectron spectroscopy (XPS) were used in combination. The FTIR spectra of OA, OAm, βA, MA, and prepared PNCs are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. In the spectra of OA and OAm, two bands from 2800 to 2990 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e represent -CH\u003csub\u003e2\u003c/sub\u003e stretching\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. These bands were also present in the spectrum of PNCs, indicating the presence of OA and OAm on the surface. Additionally, the presence of a broad band from 2800 to 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is characteristic of Hbonding, absent in OAm and OA but present in MA and βA. The band at 1567 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e in the βA spectrum is attributed to NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e stretching, while the band at 1097 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e corresponds to C-O stretching mode in MA \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e4\u003c/sup\u003e. These bands were also observed in the spectrum of PNCs, although they are less prominent, suggesting residual amounts of MA and βA still exist on the surface of the PNCs.\u003c/p\u003e \u003cp\u003eHigh-resolution XPS spectra obtained from PNCs prepared using 1.5% v/v HBr are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed. The N 1s core level was fitted with two components at 399.9 eV and 401.6 eV, representing\u0026thinsp;\u0026minus;\u0026thinsp;NH\u003csub\u003e2\u003c/sub\u003e and \u0026minus;\u0026thinsp;NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e respectively\u003csup\u003e33\u003c/sup\u003e. In traditional LARP methods, where OA and OAm have been used as surface ligands, both -NH\u003csub\u003e2\u003c/sub\u003e and -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e are reported in XPS results, originating from OAm. In our case the reported intensity of the peak at 399.9 eV was higher than 401.8 eV, which was attributed to a greater concentration of surface -NH\u003csub\u003e2\u003c/sub\u003e \u003csup\u003e32\u003c/sup\u003e. In our data the intensity of -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is greater than -NH\u003csub\u003e2\u003c/sub\u003e, indicating -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from βA also exists on the surface, consistent with FTIR results. In the O 1s spectrum, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, the broad peak from 534.5 eV to 529 eV is fitted with four components. A small peak at 529.7 eV is likely originating from PbO, is consistent with the Pb 4f spectrum (\u003cb\u003eFigure S16\u003c/b\u003e), although the quantity present is small. The peaks at 531 eV and 533 eV are attributed C\u0026thinsp;=\u0026thinsp;O and -OH respectively, which is present in both OA and MA. The peak at 532 eV arises from the hydroxyl group of MA \u003cem\u003ei.e.\u003c/em\u003e indicating the presence of residual MA in the PNC, again consistent with the ATR data, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. The Pb 4f doublet is shown in \u003cb\u003eFigure S16\u003c/b\u003e, which also indicate the presence of small quantities of metallic Pb, indicated by the additional peak at 136.0 eV. The main, broad peak centred at 137.7 eV can be fitted to Pb\u003csup\u003e2+\u003c/sup\u003e (from the perovskite)\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eAgeing effects of precipitating solution mixture\u003c/strong\u003e \u003cp\u003eWe observed that if the HBr-acetone solution was not used immediately after its preparation that it developed a brown colour, ascribed to the acidcatalysed enolisation of acetone, if this was then used to prepare PNCs their properties changed considerably. To elucidate the origins of this we prepared solutions of HBr and deuterated acetone (acetone-d\u003csub\u003e6\u003c/sub\u003e) and recorded \u003csup\u003e1\u003c/sup\u003eH-NMR spectra over time. The \u003csup\u003e1\u003c/sup\u003eH NMR spectra (1.5% v/v HBr) of the fresh 0-, 1-, 5- and 96-hour aged mixtures are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The quintet peak at 2.05 ppm originates from the presence of small amounts of residual protonated species in the acetone-d\u003csub\u003e6\u003c/sub\u003e and is used as a reference. Since there was also trace water in the mixture, the proton exchange between HBr, H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e Br\u003csup\u003e\u0026minus;\u003c/sup\u003e, and water molecules was fast, resulting in a composite singlet peak located at 8.27 ppm at 0-h aging\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e5\u003c/sup\u003e. The chemical shift of this singlet peak is given by \u003cb\u003eEq.\u0026nbsp;1\u003c/b\u003e, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{f}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{\\delta\\:}\\)\u003c/span\u003e\u003c/span\u003e are the fraction and chemical shift of the corresponding component, respectively\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equa\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\delta\\:}_{av}\\left(H\\right)={f}_{{H}_{2}O}{\\delta\\:}_{{H}_{2}O}+{f}_{{H}_{3}{O}^{+}}{\\delta\\:}_{{H}_{3}{O}^{+}}+{f}_{HBr}{\\delta\\:}_{HBr}\\:\\#Equation\\:1\\end{array}$$\u003c/div\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe chemical shift of this peak is therefore related to the acidity of the precipitating solution.\u003c/p\u003e \u003cp\u003e \u003csup\u003e \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e \u003c/sup\u003eH NMR was also carried out on 1.5 and 2.3% v/v HBr solutions immediately after mixing (0-hour), \u003cb\u003eFigure S17\u003c/b\u003e. The composite peak of 2.3% v/v HBr showed a larger chemical shift than that of 1.5% HBr v/v equivalent \u003cem\u003ei.e.\u003c/em\u003e at higher H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e concentration the composite peak shifted downfield. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea shows that with increasing time the composite peak shifts upfield, from 8.27 ppm (0hours) to 6.7 ppm (48hours).\u003c/p\u003e \u003cp\u003eThe UV-vis absorption spectra of the 0-hour and aged HBr-acetone mixtures are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. For the 0-hour samples the absorption onset was located at 260 nm, consistent with pure acetone in water. However, with increased time the absorption onset was shifted to 250 nm which was attributed to the formation of 1-propen-2-ol (CH\u003csub\u003e2\u003c/sub\u003eC(OH)CH\u003csub\u003e3\u003c/sub\u003e) following the enolisation of acetone, consistent with \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR observations. The TEM images of PNCs prepared using HBr aged for 1-hour are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. For PNCs made from 1-hour aged 1.5% v/v HBr, a regular cubic morphology was observed, and the average size was calculated to be 7.2 nm, which is smaller compared to when a fresh acetone-HBr solution was used, and like the case when unaged HBr-acetone was used, there is a systematic increase in PNC size with increasing HBr concentration, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, However, aging the precipitating solution results in a reduction in the absolute dimensions when compared with unaged equivalents. The PL data, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, reflect the observations made by TEM. For the smallest PNCs the PL emission maximum was located at 498 nm and the narrow size distribution resulted in relatively narrow FWHM (23.3 nm). A progressive redshift in emission was observed as the size increased, with maxima up to 515 nm occurring for the largest PNCs, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. According to the \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR data (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) the composite peak of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003eO and HBr shifted upfield with increased ageing time, indicating that the fraction of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e decreased with time. This could be caused by Br\u003csup\u003e\u0026minus;\u003c/sup\u003e being consumed by oxidation to Br\u003csub\u003e2\u003c/sub\u003e, which would be accompanied by the presence of a brown colour as observed (see \u003cb\u003eFigure S18\u003c/b\u003e). Another possibility could be that the concentration of molecular HBr was increased and correspondingly the fraction of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e/Br\u003csup\u003e+\u003c/sup\u003e reduced. In both cases the reduction in concentration of H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e results in a reduction of the rate of PbBr\u003csub\u003e2\u003c/sub\u003e released into the solution \u003cem\u003ei.e.\u003c/em\u003e nucleation is slowed, thus PNC size is reduced when the aged HBr solutions are used.\u003c/p\u003e\u003cp\u003eHaving obtained an understanding of the role of the precipitating solution we consider the impact of changing the quantities of βA and MA in our aqueous solvent, noting that the solubility of PbBr\u003csub\u003e2\u003c/sub\u003e and CsBr could be achieved in three of our solvent compositions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) The results presented thus far have been obtained only using Solvent 1. We turn to the use of Solvents 2 and 3 in our synthesis Using precipitating solutions containing 1.5\u0026ndash;3.7% v/v HBr aged for 1-hour, the representative TEM images are shown in \u003cb\u003eFigs.\u0026nbsp;5ab\u003c/b\u003e. It is apparent that the samples follow the same trend seen previously, increasing in size with increasing HBr concentration (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d). There are little appreciable differences in the size of PNCs prepared in each precipitating solution however the HBr concentration is having a significant impact. In each solvent the mean diameter is around 7\u0026ndash;8 nm when 1. % v/v HBr is used for precipitation increasing to 27\u0026ndash;28 nm with 3. % v/v HBr, although notably the dispersity of the PNCs prepared using Solvent 3 is greater in every case. The anticipated red-shift in PL emission is seen in both systems as PNC size increases, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, comparable with previous results, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAll data shown were obtained using 1-hour aged HBr\u0026ndash;acetone solutions containing 1.5\u0026ndash;3.7% v/v HBr, unless otherwise noted. \u003cb\u003eab)\u003c/b\u003e Transmission electron microscopy images of PNCs synthesised using Solvent 2 and Solvent 3, respectively (scale\u0026thinsp;=\u0026thinsp;50 nm). \u003cb\u003ecd)\u003c/b\u003e Size distribution histograms corresponding to PNCs in panels a and b, derived from particle analysis of TEM images. \u003cb\u003ee)\u003c/b\u003e Photoluminescence spectra of PNCs synthesised using Solvent 2 and Solvent 3. \u003cb\u003ef)\u003c/b\u003e X-ray diffraction patterns of PNCs prepared using Solvents 1\u0026ndash;3, compared to reference patterns from ICDD: CsPbBr₃ (01-090-2544, blue), Cs₄PbBr₆ (04-014-8071, grey), and CsBr (01-090-0382, red). \u003cb\u003eg)\u003c/b\u003e Photoluminescence quantum yield values for PNCs from different solvent systems. \u003cb\u003eh)\u003c/b\u003e Timecorrelated single photon counting measurements, revealing photoluminescence lifetimes and recombination dynamics.\u003c/p\u003e \u003cp\u003eThe PLQY data for PNCs prepared using Solvent 1 and precipitated from solutions containing 1.5 3. % v/v HBr aged for 1-hour are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg. A reduction in PLQY was observed as the HBr concentration increased, consistent with previous observations however the PLQY values for all samples prepared using 1-hour aged HBr solutions exceed those prepared using fresh equivalents. Additionally, the maximum PLQY values showed a significant enhancement for the 1-hour mixture compared with the fresh solution, with averages of 56% and 16% respectively. To gain insight into the PLQY enhancement TCSPC was again employed where the PLQY data were fitted to biexponential decays Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eh (see \u003cb\u003eTable S4\u003c/b\u003e for fitting parameters). When compared to data obtained from PNC prepared using fresh HBr-acetone solutions there is a small reduction in the τ\u003csub\u003e1\u003c/sub\u003e component, from 5 ns to 4 ns, and a significant reduction in the slow component (τ\u003csub\u003e2\u003c/sub\u003e), falling from 40 ns to 20 ns. This indicates that the carriers show higher tendency to recombination in PNCs prepared from the aged HBracetone solutions. This is consistent with the values of the recombination rates calculated from \u003cb\u003eEquations S2-3.\u003c/b\u003e Both radiative and non-radiative recombination rates increased for PNCs prepared with aged HBr-acetone solvents, possibly associated with a stronger quantum confinement effect induced by the smaller size of the PNCs (~\u0026thinsp;7 nm), forcing excitons generated after photoexcitation to radiatively recombine at a faster rate\u003csup\u003e36, 37\u003c/sup\u003e, explaining the higher PLQY.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003ePhotoconductor device measurements\u003c/strong\u003e \u003cp\u003ePhotoconductors were prepared to probe the light-to-current conversion capability of the PNCs. The device structure is illustrated in the inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. The PNCs used in this study were synthesised from 1-hour aged 1.5% v/v HBr (Solvent 1), and measurements were conducted in air and at room temperature. The devices were tested under illumination from a 530 nm LED, with the power intensity (\u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ein\u003c/em\u003e\u003c/sub\u003e) varied from 0.37 to 21.4 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The current densities of the devices were measured with voltage range between \u0026minus;\u0026thinsp;20 and +\u0026thinsp;20 V and revealed a clear, monotonic increase in measured current density with increasing illumination intensity, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. The responsivity was found to increase with increasing bias, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. The maximum responsivity of 0.019 A W\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was achieved at -20 V under 21.4 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e illumination. The specific detectivity (D*) of the photoconductors was evaluated by measuring the noise level with an applied bias between \u0026minus;\u0026thinsp;1 and \u0026minus;\u0026thinsp;20 V. The noise spectral density as a function of frequency is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec. The calculation of D* was performed by utilising the noise spectral density at 10 Hz, which resulted in a D* value of 1.2 x 10\u003csup\u003e11\u003c/sup\u003e Jones (at -20 V and 21 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e illumination), Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed. The results obtained for our aqueousprocessed PNCs are consistent with existing literature reports using common, yet toxic solvents\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e0\u003c/sup\u003e, further emphasising the potential of preparing optoelectronic devices these benign solvents.\u003c/p\u003e "},{"header":"Discussion","content":"\u003cp\u003eWe report the development of a novel aqueous, environmentally benign solvent system and synthetic protocol for the preparation of size- and composition-controlled metal halide PNCs. The solvent comprises only water, MA, and βA all naturally occurring and non-toxic species that pose no risks to human health or the environment. Central to the process is the formation of a soluble adduct between MA and PbBr\u003csub\u003e2\u003c/sub\u003e, enabling dissolution of an otherwise water-insoluble precursor. Subsequent mixing with HBr in acetone disrupts the adduct, driving the rapid precipitation of PNCs. Detailed spectroscopic analysis using FTIR and \u0026sup1;H NMR reveals specific interactions between solvent components and precursor species, allowing us to propose a mechanistic framework for crystal growth and identify the parameters governing PNC size and dispersity. We also uncover a solvent ageing effect within the HBracetone phase that significantly influences nanocrystal shape, size, and uniformity. The resulting PNCs exhibit strong photoluminescence, with quantum yields exceeding 60% in selected samples. Imaging by TEM confirms size tunability under different synthetic conditions, with size dispersity reflected in the breadth of the PL spectra. To demonstrate optoelectronic functionality, we fabricated proof-of-concept photodetectors, which display pronounced responses to both light intensity and applied bias, achieving a maximum specific detectivity of 1.2 \u0026times; 10\u0026sup1;\u0026sup1; Jones. Notably, the entire synthesis is performed in ambient air, in water, and without the need for any thermal treatment. This establishes a simple and sustainable route for the preparation of PNCs, with clear potential for scalable and sustainable manufacturing.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of solvent system\u003c/h2\u003e \u003cp\u003eAqueous solutions of malic acid (DL-MA, 98%, Aldrich), β-alanine (βA, 99%, Aldrich) were prepared at room temperature over the concentration range detailed in \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. CsPbBr\u003csub\u003e3\u003c/sub\u003e precursor solutions were prepared by dissolving equimolar quantities of caesium bromide (CsBr, 99.9%, Aldrich) and lead bromide (PbBr\u003csub\u003e2\u003c/sub\u003e, 99.999%, Aldrich) into solutions of mixture of MA, βA and water and stirred at room temperature for 30 minutes to ensure complete dissolution\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSynthesis and purification of CsPbBr nanocrystals\u003c/h3\u003e\n\u003cp\u003eThe entire synthesis process was carried out under ambient conditions and at room temperature. Acetone (3 mL, Aldrich) was transferred to a small vial and to it added different volumes of hydrobromic acid (HBr, 48% v/v). Either 100 \u0026micro;L or 75\u0026micro;L of aqueous solvent (Solvents 1\u0026ndash;3) containing MA and βA was added into the HBr-acetone mixture followed by shaking to precipitate the PNCs. The entire synthesis process was carried out under ambient conditions and at room temperature. Acetone (3 mL, Aldrich) was transferred to a small vial and to it added different volumes of hydrobromic acid (HBr, 48% v/v). Either 100 \u0026micro;L or 75\u0026micro;L of aqueous solvent (Solvents 1\u0026ndash;3) containing MA and βA was added into the HBr-acetone mixture followed by shaking to precipitate the PNCs. The resultant solutions were mixed with toluene (2mL, Aldrich) containing 50 \u0026micro;L oleylamine (OAm, TCI) and centrifuged 5000 rpm for 3 minutes. The supernatant was discarded, and a further 2 mL toluene containing 50 \u0026micro;L OAm and 100 \u0026micro;L oleic acid (OA, 99%, TCI) were added to the precipitate, resulting in a stable dispersion. A series of further toluene washing-centrifuge cycles were carried out (3000-5000rpm, 3\u0026ndash;5 min) to reduce PNC dispersity resulting in a stable dispersion of PNCs in toluene.\u003c/p\u003e\n\u003ch3\u003eModifying precipitating solvent volume\u003c/h3\u003e\n\u003cp\u003eAs HBr concentration was having a direct influence on PNC properties we investigated the impact of reducing the volume precursor solution from 100 \u0026micro;L to 75 \u0026micro;L whilst varying HBr concentration (\u003cb\u003eTable S2\u003c/b\u003e), with representative TEM images are shown in \u003cb\u003eFigure S14\u003c/b\u003e. At HBr concentrations of 1.5\u0026ndash;2.3% v/v the resulting PNC size is significantly smaller than the equivalent samples made using 100 \u0026micro;L of precursor in solvent, at around 9 nm. Notably the shape of the PNCs is also different, with a cuboidal morphology observed (for reporting size we quote the length of the shortest edge). PNC prepared using solvent 3.0% v/v HBr retain an average size\u0026thinsp;\u0026lt;\u0026thinsp;10 nm however there are occasionally particles\u0026thinsp;\u0026gt;\u0026thinsp;50 nm observed, at 3.7% v/v HBr the PNC average size increases significantly to around 32 nm. The size variation observed in the TEM images, \u003cb\u003eFigure S14\u003c/b\u003e, is accompanied by changes in the PL spectra, \u003cb\u003eFigure S15\u003c/b\u003e. The data reveal the impact of size and dispersity variation in the PNCs, with a progressive red-shift observed as average size increases accompanied by an increase of peak FWHM as sample dispersity increases. Overall, PNC size is reduced as precursor quantity reduces, however we did not observe any appreciable differences in the growth rate and suggest that the reduced quantity of HBr results in the formation of smaller PNCs.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePhotoconductor fabrication:\u003c/h2\u003e \u003cp\u003ePhotoconductors were prepared under ambient conditions. Glass substrates were sequentially cleaned by sonicating sequentially in acetone and isopropanol, nitrogen blowdried and treated by UV-ozone prior to PNC deposition. Following the synthesis and purification procedure PNCs stabilised by OAm in toluene were centrifuged, the supernatant removed, and 1.6 mL of toluene and 0.4 mL of methyl acetate (MeOAc) were added. Repeated centrifugation (3x5000 rpm, 5 min) resulted in a precipitate that was dispersed in 200 \u0026micro;L chloroform, creating a concentrated dispersion of PNCs that could be deposited as a continuous thinfilm. Then, 100 \u0026micro;L of this solution was deposited onto a 2 \u0026times; 2 cm\u003csup\u003e2\u003c/sup\u003e glass substrate and spin-coated at 1500 rpm for 20 seconds, the process repeated 4 times. Following film deposition 50 nm Au was thermally evaporated through a shadow mask (channel length of 40 \u0026micro;m and a width of 1000 \u0026micro;m).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMaterials Characterisation\u003c/h3\u003e\n\u003cp\u003e \u003cb\u003eConductivity and Dynamic light scattering (DLS)\u003c/b\u003e were measured by using Malvern Zetasizer Nano.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFourier Transform Infrared Spectroscopy (FTIR)\u003c/b\u003e was conducted on Agilent Cary 630 FTIR spectrometer with ATR sampling module.\u003c/p\u003e \u003cp\u003e \u003cb\u003eProton nuclear magnetic resonance (\u003c/b\u003e \u003csup\u003e \u003cb\u003e \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e \u003c/b\u003e \u003c/sup\u003e \u003cb\u003eH NMR)\u003c/b\u003e was conducted on Bruker AV-400 spectrometer using either D\u003csub\u003e2\u003c/sub\u003eO or Acetone-d\u003csub\u003e6\u003c/sub\u003e as the solvent.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTransmission electron microscopy (TEM)\u003c/b\u003e images were collected using a JOEL 2100 PLUS at an accelerating voltage of 200 kV, samples were dispersed onto a holey carbon film on a Cu support.\u003c/p\u003e \u003cp\u003e \u003cb\u003eUV-vis\u003c/b\u003e absorption spectra were collected using an Agilent Cary 60 in absorption mode.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePhotoluminescence (PL)\u003c/b\u003e spectra were acquired by Agilent Cary Eclipse Fluorescence Spectrophotometer.\u003c/p\u003e \u003cp\u003e \u003cb\u003eX-ray diffraction (XRD)\u003c/b\u003e patterns were acquired by MPD XRD PANalytical diffractometer operated at 40kV and 40mA.\u003c/p\u003e \u003cp\u003e \u003cb\u003eX-ray photoelectron spectroscopy (XPS)\u003c/b\u003e was performed by Thermo Fisher K-Alpha\u0026thinsp;+\u0026thinsp;equipped with a monochromated Al Ka Micro-focused X-ray source.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePhotoluminescence quantum yield (PLQY) and Time-resolved PL (TRPL)\u003c/b\u003e were acquired using an Edinburgh Instruments FLS1000 spectrometer. TRPL decays were taken with an Edinburgh Instruments EPL 375 nm picosecond pulsed diode laser. The repetition rate was controlled by an external trigger input and set to 1 MHz. The emission signal frequency was set to 3% that of the start rate to maintain single photon counting statistics. A visible PMT-980 detector was used for TRPL measurements. The photoluminescence quantum yield (PLQY) measurements were measured on the FLS 1000 fluorescence spectrophotometer with the assistance of an integrating sphere accessory (diameter\u0026thinsp;=\u0026thinsp;150 nm).\u003c/p\u003e\n\u003ch3\u003ePhotoconductor Characterisation:\u003c/h3\u003e\n\u003cp\u003eThe optoelectronic characterisations were conducted in ambient environment with a Keithley 4200 equipped with a current amplifier and the light illumination was provided by a 530 nm Thorlab LED (M530L4). Noise measurements were conducted with probes consisting of a platinum wire counter electrode integrated with Zurich MFLI Lock-in Amplifier. The signal has been recorded after amplification with a Stanford Research System SR570 low-noise current preamplifier.\u003c/p\u003e \u003cp\u003eResponsivity (R) is defined as the ratio of photogenerated current over the incident optical power output (\u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003eopt\u003c/em\u003e\u003c/sub\u003e), by considering the optical power density \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eopt\u003c/em\u003e\u003c/sub\u003e and the device area (A):\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{R}_{c}=\\frac{{I}_{ph}}{{P}_{opt}}=\\frac{{I}_{illumination}-\\:{I}_{dark}}{{E}_{opt}\\:A}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe specific detectivity (D*) is defined by R and the electronic noise spectral density (\u003cem\u003ei\u003c/em\u003e\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eΔf\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1/2\u003c/em\u003e\u003c/sup\u003e) of the device, normalising by the area of the photodetector (A, in this case, 0.0004 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) to enable comparability between different photodetectors:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{D}^{*}=\\frac{\\sqrt{A\\varDelta\\:f}{R}_{C}}{{i}_{n}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cem\u003ei\u003c/em\u003e \u003csub\u003e \u003cem\u003en\u003c/em\u003e \u003c/sub\u003e \u003cem\u003eΔf\u003c/em\u003e \u003csup\u003e \u003cem\u003e\u0026minus;\u0026thinsp;1/2\u003c/em\u003e \u003c/sup\u003e can be extracted experimentally from the dark current recorded with a lock-in amplifier, followed by a fast Fourier transform (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec).\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eM.A.M. and W.R.K. gratefully acknowledge the EPSRC and SFI Centre for Doctoral Training in Advanced Characterisation of Materials ( EP/S023259/1) for financial support. M.H. and M.R. thank the EPSRC (EP/T028513/1)for financial support and M.H. KAUST for baseline funding. T.J.M. thanks the Royal Commission for the Exhibition of 1851 for their financial support through a Research Fellowship and acknowledges funding from a Royal Society University Research Fellowship (URF/R1/221834).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMi Z et al (2024) Real-time single-proton counting with transmissive perovskite nanocrystal scintillators. \u003cem\u003eNature Materials 2024 23:6\u003c/em\u003e 23, 803\u0026ndash;809\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang W et al (2023) Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells. Adv Mater 35\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDey A et al (2021) State of the Art and Prospects for Halide Perovskite Nanocrystals. 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Small 12:5622\u0026ndash;5632\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6443068/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6443068/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMetal halide perovskites (MHPs) have revolutionised photovoltaics and emerging optoelectronic technologies, offering performance that rivals or exceeds that of conventional materials. Their rapid rise has been driven by their exceptional properties, including tuneable band gaps, high absorption coefficients, long carrier diffusion lengths and high mobilities, all combined with relatively simple synthesis. However, current MHP production relies heavily on the use of toxic solvents, which pose significant environmental and health risks. In addition, these methods often require complex multicomponent solvent systems and thermal processing to achieve the desired material phases, further hindering scalability and sustainability. Overcoming these challenges is critical to the future development of MHP-based technologies. Here, we present a novel water-based solvent system and synthetic approach for the controlled preparation of MHP nanocrystals. Our method enables the synthesis, in ambient air and at room temperature, of size-controlled CsPbBr₃ perovskite nanocrystals (PNCs) with a photoluminescence quantum yield (PLQY) exceeding 60%. To demonstrate the light to current conversion ability of our PNCs a series of photoconductors were prepared, with the best performing devices achieving a specific detectivity (D*) of 1.2 x 10\u003csup\u003e11\u003c/sup\u003e Jones. Thus, this green, scalable, and low-cost approach offers a sustainable pathway for precise size and compositional control of MHP nanocrystals, opening new possibilities for environmentally friendly optoelectronic applications.\u003c/p\u003e","manuscriptTitle":"Water-Based Synthesis of CsPbBr₃ Perovskite Nanocrystals Under Ambient Conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-18 04:55:03","doi":"10.21203/rs.3.rs-6443068/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e3470edd-1e9f-445d-9367-4eb61e756df8","owner":[],"postedDate":"April 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":47343558,"name":"Physical sciences/Materials science/Nanoscale materials/Synthesis and processing"},{"id":47343559,"name":"Physical sciences/Chemistry/Environmental chemistry"},{"id":47343560,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials"}],"tags":[],"updatedAt":"2025-09-24T08:39:34+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-18 04:55:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6443068","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6443068","identity":"rs-6443068","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}