Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection

Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection | 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 Research Article Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection Huayushuo Zhang, Qian Ma, Pan Gao, Bolong Li, Xiaoxia Yang, Chao Li, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7601158/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Dec, 2025 Read the published version in Journal of Materials Science: Materials in Electronics → Version 1 posted You are reading this latest preprint version Abstract X-ray detection has extensive applications in medical imaging, scientific research, and security inspection. Despite the superior radiation detection properties of lead-based perovskites, including high carrier mobility and superior attenuation efficiency, their toxicity and instability arising from ion migration hinders further development. To address these challenges, a series of halogen-tuned lead-free 3-methylpiperidine bismuth halides, (C6H14N)3Bi2I9, (C6H14N)2BiBr5 and (C6H14N)2BiCl5 (C6H14N = 3-methylpiperidine) single crystals were grown and systematically characterized. 3-methylpiperidine was selected for their steric effect stabilizing the lattice, and the synergistic tuning through halogen variation enabled a structural transition along with modulation of their properties. Notably, lateral-structured (C6H14N)3Bi2I9 single crystal-based X-ray detectors achieved remarkable sensitivity of 388.05 μC Gy⁻¹ cm⁻², a low detection limit of 71.05 nGy s⁻¹ and a dark current drift of 2.16 × 10⁻8 nA cm⁻¹ s⁻¹ V⁻¹. Importantly, the material retained its original morphology after eight months of ambient storage. Furthermore, flexible X-ray devices fabricated via spin-coating (C6H14N)3Bi2I9 exhibited excellent X-ray response with a sensitivity of 121.48 μC Gy⁻¹ cm⁻² and outstanding mechanical stability. This work reveals that halogen tuning effectively optimizes the structure and performance of Bi-based perovskites, providing valuable insights for advancing them in X-ray detection applications. halogen tuning 3-methylpiperidine bismuth halides low detection limit stability flexible detector Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction X-ray detection plays a vital role across multiple domains, including medical diagnostics, advanced scientific research, and security screening systems [ 1 , 2 ].Current commercial detectors predominantly rely on conventional inorganic semiconductors, such as monocrystalline silicon and amorphous selenium (α-Se). However, these materials exhibit inherent limitations due to their low atomic numbers, which result in inefficient X-ray attenuation coefficients and inadequate sensitivity (typically < 0.1 µC Gy − 1 cm − 2 ), thereby constraining their detection performance [ 3 , 4 ]. This technological gap has driven intensive exploration of cost-effective materials with superior optoelectronic characteristics. In this context, metal halide perovskites (MHPs) have emerged as revolutionary candidates for radiation detection since 2016. Notably, lead-based perovskites demonstrate exceptional radiation response characteristics, achieving carrier mobility exceeding 10 cm 2 V − 1 s − 1 , remarkable X-ray attenuation coefficients, and ultra-low trap densities (< 10 10 cm − 3 ) [ 5 – 8 ]. Nevertheless, the neurotoxicity of lead poses significant constraints on clinical adoption. Chronic exposure to this heavy metal can cause irreversible neurological damage, manifesting as cognitive impairment in children (average IQ reduction: 2–5 points per 10 µg/dL blood Pb²⁺) and progressive memory dysfunction in adults [ 9 ]. This safety concern has spurred the development of eco-friendly alternatives. Recently, bismuth-based MPHs are gaining prominence as sustainable substitutes, leveraging the ionic similarity between Bi³ + and Pb² + to preserve optoelectronic performance while eliminating toxicity risks through their inherent environmental benignity [ 10 ]. According to previous studies, the synthesis of materials like Cs 3 Bi 2 Br 9 demands complex and stringent conditions, such as high-temperature and vacuum environments[ 11 ]. In contrast, replacing inorganic cations with organic molecules enables preparation via solution cooling method, significantly reducing the technical barriers in material synthesis. Consequently, the latter has become a dominant direction of current scientific exploration in the field. In addition, the dimensionality of the MHPs plays a pivotal role in tailoring the performance of X-ray detection [ 12 ]. Various dimensions spanning three-dimensional (3D), two-dimensional (3D), one-dimensional (1D) and zero-dimensional (0D) frameworks demonstrate distinct optoelectronic behaviors [ 13 ]. Among these, 3D MHPs exhibit high X-ray sensitivity, attributable to their superior mobility-lifetime product and strong X-ray absorption coefficient [ 14 ]. For example, 3D CH 3 NH 3 PbI 3 feature continuous charge transport pathways, enabling a notably high sensitivity of up to 2.2 × 10 8 µC Gy − 1 cm − 2 [ 15 ]. However, the internal ion migration induces severe baseline drift, resulting in detector instability [ 16 ]. As the dimensionality decreases, the activation energy (E a ) increases, effectively suppressing ion migration [ 17 ]. Liu et al. demonstrated that the 0D (CH 3 NH 3 ) 3 Bi 2 I 9 exhibits pronouncedly suppressed ion migration compared to 2D (PEA) 2 PbI 4 and 3D CH 3 NH 3 PbI 3 systems, with a remarkably low dark current drift of 5.0×10⁻ 10 nA cm − 1 s − 1 V − 1 [ 18 ]. These superior properties establish low-dimensional MHPs as robust candidates for high-stability direct X-ray detection applications. Although Bi-based low-dimensional MHPs have addressed toxicity and stability challenges through ionic substitution and dimensional engineering, the resulting bulk single crystals suffer from inherent brittleness that restricts their conformability to flexible or curved detection surfaces. In recent years, the integration of low-dimensional perovskite films with compliant substrates like polyethylene terephthalate (PET) or polydimethylsiloxane (PDMS), has enabled devices to withstand bending curvatures exceeding 5 mm − 1 while maintaining conformal contact with biological tissues. As demonstrated by Li et al., their flexible perovskite-based detector retains 90% of its initial X-ray sensitivity after 5000 bending cycles, showcasing exceptional mechanical robustness [ 19 ]. This advancement positions MHPs-based detectors as strong contenders in X-ray detection applications involving wearable radiation monitoring. Here, facile growth is reported for three novel halogen-tuned Bi-based MHPs via solution cooling method. The structural dimensionalities of these compounds exhibit a sequential transition from 0D ((C 6 H 14 N) 3 Bi 2 I 9 ) to 1D ((C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 ), coupled with a notable blue-shift in their bandgaps. To assess their X-ray detection performance, lateral-structure detectors were fabricated with symmetrical silver electrodes on high-quality single crystals of each compound. Notably, (C 6 H 14 N) 3 Bi 2 I 9 single crystal demonstrated outstanding X-ray detection capabilities and maintained great structural integrity for eight months ambient storage, outperforming most lead-based perovskites in environmental stability. Additionally, flexible detectors prepared by spin-coating (C 6 H 14 N) 3 Bi 2 I 9 onto a PET substrate exhibited excellent mechanical robustness and stable X-ray response. These superior characteristics highlight the potential of Bi-based halide perovskites not only for X-ray detection technologies but also for next-generation flexible sense technologies. 2. Experimental procedures 2.1 Materials 3-Methylpiperidine (97.00%), bismuth oxide (Bi 2 O 3 ) (99.99%), hydroiodic acid (HI, 55.0 − 58.0%, ≤ 1.5% H 3 PO 2 ), hydrobromic acid (HBr, ACS, 48%), hypophosphorous acid (H 3 PO 2 , AR, 50 wt%) and N, N-dimethylformamide (DMF, C 3 H 7 NO, 99.5%) were purchased from Aladdin (Shanghai, China). Hydrochloric acid (HCl, 35.0 − 38.0%, GR) was purchased from Yantai Far East Fine Chemical Co., Ltd. Unless otherwise indicated, all reagents and solvents do not require further purification. 2.2 Synthesis of (C 6 H 14 N) 3 Bi 2 I 9 Single Crystals A solvent composed of HI and H 3 PO 2 in a 5:1 volume ratio enables the dissolution of Bi 2 O 3 and 3-methylpiperidine according to the stoichiometric ratio in the chemical formula at a molar concentration of 0.18 M, followed by continuous stirring at 80°C until complete dissolution. The homogeneous solution was then transferred to a preheated temperature-controlled oven. A stepwise cooling protocol was applied. The temperature was initially lowered from 80°C to 60°C at a rate of 1°C/h, followed by further cooling to room temperature at a reduced rate of 0.5°C/h, which resulted in the formation of (C 6 H 14 N) 3 Bi 2 I 9 crystals. 2.3 Synthesis of (C 6 H 14 N) 2 BiBr 5 Single Crystals A solvent composed of HBr and H 3 PO 2 in a 5:1 volume ratio enables the dissolution of Bi 2 O 3 and 3-methylpiperidine following the stoichiometric ratio specified in the chemical formula at a molar concentration of 0.28 M. The mixture was stirred at 90°C until fully dissolved to form a clear precursor solution. The homogeneous solution was then transferred to a preheated temperature-controlled oven and subjected to a programmed cooling process, wherein the temperature was gradually lowered from 90°C to room temperature at a rate of 1°C/h to obtain (C 6 H 14 N) 2 BiBr 5 single crystals. 2.4 Synthesis of (C 6 H 14 N) 2 BiCl 5 Single Crystals The (C 6 H 14 N) 2 BiCl 5 crystals were synthesized via the solution cooling method by mixing 3-methylpiperidine and Bi 2 O 3 in HCl as the solvent (0.62 M) following the stoichiometric ratio specified in the chemical formula. The mixture was stirred at 80°C until complete dissolution to form a clear precursor solution. The solution was then transferred to a temperature-controlled oven and subjected to a programmed cooling process, in which the temperature was gradually reduced from 80°C to room temperature at a rate of 1°C/h 2.5 The fabrication of (C 6 H 14 N) 3 Bi 2 I 9 -based flexible devices The (C 6 H 14 N) 3 Bi 2 I 9 -based flexible device was fabricated via a spin-coating method. First, (C 6 H 14 N) 3 Bi 2 I 9 crystals were dissolved in DMF at a concentration of 0.55 M. The mixture was stirred continuously for 10 minutes until complete dissolution to obtain the precursor solution. For the spin-coating process, a layer of PEDOT (poly(3,4-ethylenedioxythiophene)) was initially deposited onto a indium tin oxide (ITO)/polyethylene terephthalate (PET) substrate and annealed at 60°C for 10 minutes. Subsequently, 40 µL of the precursor solution was evenly spread onto the PEDOT layer and spin-coated at 3000 revolutions per minute (rpm). After spin-coating, the film was annealed sequentially at 60°C for 5 minutes followed by a second annealing step at 100°C for another 5 minutes. The flexible X-ray detector was fabricated by directly coating silver onto the surface of the flexible film, forming a vertical structure with the underlying ITO layer. 2.6 Characterization All single-crystal X-ray diffraction (SCXRD) data were measured from a Bruker SMART APEX-II using a CCD detector (Mo Kα, λ = 0.71073 Å). Crystal structure optimization was performed using OLEX2 software. Powder X-ray diffraction (PXRD) data were measured from an XRD analyses (XRD, D8-ADVANCE of Bruker Corporation). The XRD test procedure was performed from 5 ° to 80 ° scanning in steps of 0.02 ° at a speed of 20 °/min. X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB Xi + X-ray photoelectron spectrometer (Thermo Fisher Scientific). All crystals were dried at 60°C for 3 h prior to the XPS test to minimize contamination of the instrument by I and Br elements. The UV-Vis absorption spectrum was measured on a UV-visible spectrophotometer (Hitachi U-4100). Thermogravimetric analysis (TG) was performed on HCT-2 equipment ranging from room temperature to 1173 K with a rate of 5°C/min, and high-purity nitrogen gas was used as the test atmosphere. Scanning electron microscopy (SEM) was obtained using field emission scanning electron microscopy (Gemini 300) measurements. The X-ray detector was fabricated by coating symmetric silver electrodes on the surface of high-quality single crystals of the sample to form a lateral structural configuration. X-ray detection tests were performed using a tungsten anode X-ray tube with a photon energy in the range of 40–150 keV as the radiation source, with signals recorded via a multifunction digital source meter (Keithley 2636B). The flexible device was tested using the Prtronic FT2000 instrument, specifically employing its tensile module. The device was securely fixed onto the tensile module and subjected to bending deformation at a rate of 1 mm/s. Following the bending process, the device was subsequently removed for X-ray detection performance evaluation. 3. Results and discussion The high-quality single crystals of (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 were successfully grown via a solution cooling method in a concentrated HX (X = I, Br, and Cl) acid solution containing a stoichiometric ratio of 3-methylpiperidine and Bi 2 O 3 specified in the chemical formula (Fig. 1 a-c). As depicted in Fig. 1 d-f, the structures of (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 were characterized by Single crystal X-ray diffraction (SCXRD) analysis, respectively. (C 6 H 14 N) 3 Bi 2 I 9 adopts a 0D structure comprising two BiI 6 octahedra linked by three I atoms between the Bi centers. Differently, (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 feature 1D structures comprising BiX 6 octahedra (X = Br or Cl) interconnected by bridging X atoms between adjacent Bi atoms. Additional single-crystal structure views from different orientations are provided in Fig S1 a-c . SCXRD results indicate that both (C 6 H 14 N) 3 Bi 2 I 9 and (C 6 H 14 N) 2 BiCl 5 crystallize in the orthorhombic system with the Pnma space group, while (C 6 H 14 N) 2 BiBr 5 exhibits the Pna2 1 space group within the same crystal system. Detailed structural parameters, including bond lengths and angles, are summarized in Tables S1-S4 . Specifically, Table S2-S4 reveal that the Bi-I bond lengths in (C 6 H 14 N) 3 Bi 2 I 9 range from 2.8949(12) to 3.3940(11) Å, the Bi-Br bond lengths in (C 6 H 14 N) 2 BiBr 5 span 2.7022(14) to 3.1387(12) Å, and the Bi-Cl bond lengths in (C 6 H 14 N) 2 BiCl 5 vary between 2.5320(6) and 3.0420(5) Å. The average bond lengths in (C 6 H 14 N) 3 Bi 2 I 9 are observed to be longer than those in (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 . This longer bond length weakens electron delocalization, consequently reducing the bandgap, which aligns with our experimental measurements. Figure 1 g-i presents the experimental and simulated powder X-ray diffraction (PXRD) patterns of (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 , respectively. Notably, the excellent agreement between the experimental and theoretical patterns confirms the high phase purity of all synthesized crystals, indicating negligible impurities or secondary phases. X-ray photoelectron spectroscopy (XPS) was further used to study the elemental composition and valence states of the (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 single crystals. The C 1s peak at 284.80 eV serves as an energy calibration reference in XPS measurements ( Fig S2 ). Figure 2 a displays the XPS survey spectra, featuring distinct characteristic peaks for C 1s, N 1s, Bi 4f, I 3d, Br 3d and Cl 2p. The N 1s peak appears at 402.00, 401.71, and 401.84 eV for the three compounds, respectively (Fig. 2 b ) . As shown in Fig. 2 c, the Bi 4f doublet peaks for the three compounds locate at 158.89/164.20 eV, 159.20/164.50 eV, and 159.48/164.81 eV, respectively. In these three samples, the Bi 4f 7/2 and Bi 4f 5/2 peaks are seen to be separated by 5.3 eV, which is a characteristic of Bi 3+ state[ 20 ]. Notably, the Bi 4f peaks of (C 6 H 14 N) 3 Bi 2 I 9 exhibit a low-binding-energy shift compared to those of the bromide and chloride analogues. This is due to differences in the halogens. From Cl to I, the electronegativity gradually decreases. A more electronegative halogen (Cl) attracts greater electron density from the Bi atom, reducing the electron cloud density around Bi and thereby increasing its effective nuclear charge. Consequently, the inner-shell electrons experience stronger nuclear attraction, leading to an increase in binding energy and a shift of the XPS peaks toward higher binding energies. In contrast, a less electronegative halogen (I) exerts weaker electron-withdrawing effects on the Bi electron cloud, resulting in lower binding energy and a corresponding shift of the XPS peaks toward lower energies. indicating stronger electron-withdrawing ability of Bi [ 21 , 22 ]. Figure 2 d confirms the presence of I- through characteristic I 3d peaks at 619.15 eV (I 3d 5/2 ) and 630.62 eV (I 3d 3/2 ). Similarly, Br 3d peaks at 68.15 eV (Br 3d 5/2 ) and 69.20 eV (Br 3d 3/2 ), and Cl 2p peaks at 198.14 eV (Cl 2p 3/2 ) and 199.73 eV (Cl 2p 1/2 ), are observed for (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 , respectively (Fig. 2 e-f), which is in agreement with literature reports [ 4 , 23 ]. From the scanning electron microscope (SEM) image in Fig S3 , the surface of (C 6 H 14 N) 3 Bi 2 I 9 is observed to be smooth with minimal defects, whereas the crystal surfaces of (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 exhibit rough morphologies with numerous voids. These surface imperfections are likely to deteriorate charge transport properties by enhancing carrier scattering and trapping. Energy dispersive spectroscopy (EDS) is employed to ascertain the elemental composition and map the elemental distribution of a material. According to Fig S4-S6 , the elements C, N, Bi and I (Br and Cl) are uniformly distributed in the (C 6 H 14 N) 3 Bi 2 I 9 ((C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 ), confirming the structural integrity and compositional homogeneity of the crystals. Thermogravimetric analysis (TGA) shows that (C 6 H 14 N) 3 Bi 2 I 9 and (C 6 H 14 N) 2 BiBr 5 exhibit excellent thermal stability, with decomposition onset temperatures of 268°C and 258°C. respectively. In contrast, (C 6 H 14 N) 2 BiCl 5 exhibits relatively lower thermal stability, with its decomposition starting at only 202°C (Fig. 3 a). Beyond thermal stability, the surface wettability of (C 6 H 14 N) 3 Bi 2 I 9 was also evaluated via contact angle measurements. Fig S7 shows the contact angle of 82.208 ° for (C 6 H 14 N) 3 Bi 2 I 9 , indicating a moderately hydrophobic behavior. This hydrophobicity, suggesting low hygroscopicity in air, contributes to excellent environmental stability and maintained structural integrity over extended periods under atmospheric conditions. The UV-vis absorption spectrum in Fig. 3 b shows a broad absorption range with absorption edges located at 658.09, 470.65 and 407.04 nm for (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 , respectively [ 24 ]. Using Tauc equation (αhν) 1/n =B(hν-Eg), the band gaps (Eg) were determined to be 1.92, 2.55, and 3.05 eV [ 25 ]. Within a reasonable range, a smaller band gap facilitates enhanced carrier concentration, thereby promoting carrier transport and carrier mobility [ 26 ]. Figure 3 c presents the capacitance (C) versus dielectric constant (ε) curve as a function of frequency, where ε was calculated using the formula ε = Cd/ε 0 A [ 27 ] (d: crystal thickness; A: surface area; ε 0 :vacuum dielectric constant). The calculated dielectric constants of (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 were 6.00, 5.60, and 5.37, respectively. A higher dielectric constant can mitigate internal electric field distortion and suppress the dark current generation. For example, Dong et al. fabricated MAPbI 3 crystals with a high dielectric constant (ε ≈ 30, which stabilized the dark current density within the range of 10 − 9 -10 − 10 A/cm 2 [ 28 ]. Figure 4 a illustrates a lateral X-ray detector structure of Ag/(C 6 H 14 N) 3 Bi 2 I 9 single crystal/Ag for evaluating detection performance. Using the photon cross-section database (XCOM database), the X-ray absorption coefficients were calculated for (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 , (C 6 H 14 N) 2 BiCl 5 , and commercial inorganic semiconductors (Si, α-Se, and CdTe) (Fig. 4 b). Owning to the heavy atoms Bi and I in (C 6 H 14 N) 3 Bi 2 I 9 , its absorption coefficient is much higher than that of Si and α-Se (in the 40–150 keV energy range), which is comparable to other classical inorganic materials. Fig S8 shows the attenuation efficiency at different thickness of these materials for 40 keV X-ray photons. (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 with 1 mm thickness can attenuate X-rays with efficiencies of 98.76%, 83.57%, and 62.52%, respectively. Notably, (C 6 H 14 N) 3 Bi 2 I 9 exhibits 9.8-fold higher attenuation efficiency than Si (10%). Figure 4 c illustrates the X-ray response of (C 6 H 14 N) 3 Bi 2 I 9 under bias voltages ranging from 2 to 200 V. Increasing the applied bias enhances carrier collection efficiency, consequently strengthening the X-ray response. The current density increases linearly with bias voltage. Similarly, as shown in Fig S9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 also exhibit a strong correlation between bias voltage and X-ray response performance. This demonstrates that all three materials maintain stable X-ray response, with no saturation observed in charge carriers generation or collection within their operational range. Figure 4 d presents the current-time (I-t) tests under 2 V and 200 V biases. Obviously, the photocurrent increases with rising dose rate, while the dark current remains stable. Additionally, Fig. 4 e displays the X-ray response of (C 6 H 14 N) 3 Bi 2 I 9 under a 200 V bias with a total dose rate of 69.264 mGy, where the total photocurrent variation reaches 24 pA under high-voltage and high-dose irradiation. This result confirms its exceptional stability during prolonged X-ray exposure, even under such high bias voltage conditions. As depicted in Fig S10 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 exhibit good photocurrent stability at a total irradiation dose of 44.404 mGy. However, the overall photocurrent variation had already surpassed that of (C 6 H 14 N) 3 Bi 2 I 9 at an irradiation duration of 350 seconds. Dark current drift is also a key indicator demonstrating the stability of the material. The dark current drift of (C 6 H 14 N) 3 Bi 2 I 9 in Fig. 4 f, calculated as 2.16×10⁻ 8 nA cm⁻¹ s⁻¹ V⁻¹, demonstrates its exceptional stability under measurement conditions and significantly lower than previously reported values as compared in Table S5 [ 3 , 16 , 29 ]. These comparisons highlight the superior dark current stability of (C 6 H 14 N) 3 Bi 2 I 9 in this work. The sensitivity of (C 6 H 14 N) 3 Bi 2 I 9 was calculated from Fig. 4 c. Under bias voltages of 2.5, 10, 20, 50, 100, and 200 V, the sensitivity values are 107.00, 122.00, 149.88, 163.61, 224.50, 276.60, and 388.05 µC Gy − 1 cm − 2 , respectively. This performance exceeds that of previously reported Bi-based MHPs, such as Rb 3 Bi 2 I 9 (159.7 µC Gy − 1 cm − 2 ) and (Gua) 3 Bi 2 I 9 (18.23 µC Gy − 1 cm − 2 ) listed in Table S6 [ 24 , 30 ]. Figure 4 g compares the sensitivity of three compounds, underscoring that (C 6 H 14 N) 3 Bi 2 I 9 exhibits a significantly higher value than (C 6 H 14 N) 2 BiBr 5 (178.85 µC Gy − 1 cm − 2 ) and (C 6 H 14 N) 2 BiCl 5 (120.58 µC Gy − 1 cm − 2 ) ( Fig S11 ). This disparity primarily arises from the lower X-ray absorption coefficients of bromide and chloride analogues compared to (C 6 H 14 N) 3 Bi 2 I 9 , which directly impairs their capacity to absorb X-ray photons and thus diminishes their sensitivity. Figure 4 h shows the current-time (I-t) curve of (C 6 H 14 N) 3 Bi 2 I 9 under low dose rate. It can be observed that even at this low dose rate, the photocurrent still exhibits regular variations. Figure 4 i shows the detection limit is determined as 79.18 nGy s − 1 using \(\:\text{SNR}\text{=}\frac{\text{（}{\stackrel{\text{-}}{\text{I}}}_{\text{p}\text{h}\text{oto}}\text{-}{\stackrel{\text{-}}{\text{I}}}_{\text{dark}}\text{)}}{\sqrt{\frac{\text{1}}{\text{N}}{\sum\:}_{\text{i}}^{\text{n}}{\text{(}{\text{I}}_{\text{i}}\text{-}{\stackrel{\text{-}}{\text{I}}}_{\text{p}\text{h}\text{oto}}\text{)}}^{\text{2}}}}\) . Comparative tests under identical conditions demonstrate higher detection limits for (C 6 H 14 N) 2 BiBr 5 (247.96 nGy s − 1 ) and (C 6 H 14 N) 2 BiCl 5 (2430 nGy s − 1 ), respectively ( Fig S12 ). To evaluate the device stability under repeated high-voltage and high-dose-rate switching cycles, the detector was subjected to approximately 400 on-off cycles at 200 V bias and a dose rate of 301.8 mGy s⁻¹. As shown in Fig. 4 j, the photoresponses of the first three and last three cycle, reveal no significant performance degradation between initial and final cycles. Remarkably, the overall switching characteristics, including rise time, fall time, and baseline current, remain consistent throughout the entire cycling process. These experimental results unequivocally demonstrate that (C 6 H 14 N) 3 Bi 2 I 9 exhibits outstanding operational stability under high electric field and intense X-ray irradiation, indicating strong resistance to cumulative radiation damage and electrical stress. Figure 5 a depicts the fabrication process of flexible films via spin-coating method. A layer of PEDOT (poly(3,4-ethylenedioxythiophene)) is first spin-coated onto the PET substrate to optimize charge transport and enhance device efficiency. The PEDOT layer exhibits excellent mechanical flexibility, high bend tolerance, and superior conformal adhesion. As shown in Fig S13 , the fabricated flexible film features a smooth surface morphology in its SEM image. Figure 5 b demonstrates that the photocurrent density of the flexible device maintains a strong linear dependence on dose rate under 1, 2, 5, 10, and 20 V bias, showcasing performance comparable to single-crystal devices. From these data, the sensitivity at 20 V bias is calculated as 121.48 µC Gy − 1 cm − 2 ( Fig S14 ). Figure 5 c presents the I-t response curve of the device, showing highly regular and reproducible behavior. Fig S16 shows the I-t curve of flexible film under low dose rate and SNR analysis determines the detection limit under 5 V to be 66.59 nGy s − 1 (Fig. 5 d), enabling effective low-dose X-ray detection for practical applications. Mechanical stability tests performed using a flexible electronics tester reveal the device preserves 84.38% of its original sensitivity after 500 bending cycles, confirming excellent durability ( Fig. 5 e). These results validate the potential of (C 6 H 14 N) 3 Bi 2 I 9 for flexible device applications, offering a promising pathway for flexible electronics development. 4. Conclusion In summary, three halogen-engineered 3-methylpiperidine bismuth halides (C 6 H 14 N) 3 Bi 2 I 9 , (C 6 H 14 N) 2 BiBr 5 and (C 6 H 14 N) 2 BiCl 5 single crystals have been successfully grown, aiming to explore their potential for X-ray detection applications. Among them, (C 6 H 14 N) 3 Bi 2 I 9 exhibited a low detection limit of 71.05 nGy s − 1 and dark current drift of 2.16×10⁻ 8 nA cm − 1 s − 1 V − 1 , maintaining stable performance under high-voltage and high-dose-rate conditions. More importantly, the fabricated (C 6 H 14 N) 3 Bi 2 I 9 -based flexible X-ray detectors retained 84.38% of its original sensitivity after 500 bending cycles, demonstrating excellent mechanical durability. This research advances the development of organic bismuth halides and flexible devices in X-ray detection applications. Declarations Acknowledgements The authors express thanks for the financial support from projects ZR2024ME223, ZR2022QF036 and ZR2025MS1001 supported by Shandong Provincial Natural Science Foundation, project 62305195 from the National Natural Science Foundation of China and Youth Innovation Team Development Program of Shandong Higher Education Institutions (2024KJN010). Author contributions Huayushuo Zhang: Investigation, software, writing-original draft, data curation, formal analysis. Qian Ma: Supervision, investigation, conceptualization, methodology, writing-review & editing, resources. Pan Gao: Investigation, formal analysis, visualization. Bolong Li: Investigation, data curation. Xiaoxia Yang: Visualization, data curation. Chao Li: Data curation. Mingming Song: Data curation. Zhiwei Hou: Data curation. Xiaomei Jiang: Supervision, investigation, conceptualization, methodology, writing-review & editing, resources. 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\u003c/strong\u003e(C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, (c)\u003cstrong\u003e \u003c/strong\u003e(C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e. Schematic illustration of the single-crystal structure of (d) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (e) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (f) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e. Experimental and simulated PXRD patterns of (g) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (h) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (i) (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/267110b3087b0a58265f0bfa.png"},{"id":93008059,"identity":"4dc411ec-9ed7-48e7-b956-120689880a05","added_by":"auto","created_at":"2025-10-08 07:04:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":449095,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e. (a) Survey, (b) N 1s, (c) Bi 4f, (d) I 3d, (e) Br 3d, and (f) Cl 2p.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/e5720636b66df5dbed402b76.png"},{"id":93008060,"identity":"4cfdead4-2d2c-4f7b-bb7f-a7bedd6050fb","added_by":"auto","created_at":"2025-10-08 07:04:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":138747,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TG curves. (b) UV−vis absorption spectra (Inset: Tauc curves). (c) Capacitance and dielectric constant curves of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/b9a63378984859440c61abea.png"},{"id":93008064,"identity":"81c9ddde-033d-4750-944c-98f81c282c7e","added_by":"auto","created_at":"2025-10-08 07:04:43","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":688455,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of the lateral X-ray detector structure. (b) X-ray absorption coefficient of Si, α-Se, CdTe, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e. (c) The photocurrent densities as a function of X-ray dose rates under various bias voltages. (d) The I-t response curves of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based detectors under bias voltages ranging from 2 V to 200 V. (e) Photocurrent stability and (f) Dark current drift measurement of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based detectors. (g) Sensitivity comparison of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e-based detectors. (g) I-t diagrams at low dose rates and (i) Signal-to-noise ratio at 20 V bias of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based detectors. (j) Response current stability of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based detectors under pulsed X-rays at 200V.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/8d798540f120799ce77ad484.png"},{"id":93008073,"identity":"d12b0c1b-cd58-4e0e-81f5-32a8ee253878","added_by":"auto","created_at":"2025-10-08 07:04:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":538392,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fabrication process of flexible detectors. (b) Dose-rate-dependent X-ray response current density and (c) I-t response curves under different bias voltages. (d) Signal-to-noise ratio at 20 V bias and (e) Sensitivity variation under various bending cycles of flexible film.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/02b52b6ca29541393ad7317c.png"},{"id":98813995,"identity":"99409b4c-6eae-4c9b-8303-0a2cecc18e3f","added_by":"auto","created_at":"2025-12-22 16:09:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3389513,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/c447606a-c7b8-41b9-8c9a-37c3c2db5c17.pdf"},{"id":93008085,"identity":"ff4920ae-2a97-414a-aaee-6f0cc6125fa1","added_by":"auto","created_at":"2025-10-08 07:04:44","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":36470605,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/102ca8b2698569ad3ef23d1f.docx"},{"id":93008063,"identity":"8f952488-a234-4a67-81d6-d1a951c6d2c6","added_by":"auto","created_at":"2025-10-08 07:04:42","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2069815,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-7601158/v1/e7d6344ff325e8f4bfe44007.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eX-ray detection plays a vital role across multiple domains, including medical diagnostics, advanced scientific research, and security screening systems [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].Current commercial detectors predominantly rely on conventional inorganic semiconductors, such as monocrystalline silicon and amorphous selenium (α-Se). However, these materials exhibit inherent limitations due to their low atomic numbers, which result in inefficient X-ray attenuation coefficients and inadequate sensitivity (typically\u0026thinsp;\u0026lt;\u0026thinsp;0.1 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), thereby constraining their detection performance [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This technological gap has driven intensive exploration of cost-effective materials with superior optoelectronic characteristics. In this context, metal halide perovskites (MHPs) have emerged as revolutionary candidates for radiation detection since 2016. Notably, lead-based perovskites demonstrate exceptional radiation response characteristics, achieving carrier mobility exceeding 10 cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, remarkable X-ray attenuation coefficients, and ultra-low trap densities (\u0026lt;\u0026thinsp;10\u003csup\u003e10\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) [\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Nevertheless, the neurotoxicity of lead poses significant constraints on clinical adoption. Chronic exposure to this heavy metal can cause irreversible neurological damage, manifesting as cognitive impairment in children (average IQ reduction: 2\u0026ndash;5 points per 10 \u0026micro;g/dL blood Pb\u0026sup2;⁺) and progressive memory dysfunction in adults [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This safety concern has spurred the development of eco-friendly alternatives. Recently, bismuth-based MPHs are gaining prominence as sustainable substitutes, leveraging the ionic similarity between Bi\u0026sup3;\u003csup\u003e+\u003c/sup\u003e and Pb\u0026sup2;\u003csup\u003e+\u003c/sup\u003e to preserve optoelectronic performance while eliminating toxicity risks through their inherent environmental benignity [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. According to previous studies, the synthesis of materials like Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e demands complex and stringent conditions, such as high-temperature and vacuum environments[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. In contrast, replacing inorganic cations with organic molecules enables preparation via solution cooling method, significantly reducing the technical barriers in material synthesis. Consequently, the latter has become a dominant direction of current scientific exploration in the field.\u003c/p\u003e\u003cp\u003eIn addition, the dimensionality of the MHPs plays a pivotal role in tailoring the performance of X-ray detection [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Various dimensions spanning three-dimensional (3D), two-dimensional (3D), one-dimensional (1D) and zero-dimensional (0D) frameworks demonstrate distinct optoelectronic behaviors [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Among these, 3D MHPs exhibit high X-ray sensitivity, attributable to their superior mobility-lifetime product and strong X-ray absorption coefficient [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. For example, 3D CH\u003csub\u003e3\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003ePbI\u003csub\u003e3\u003c/sub\u003e feature continuous charge transport pathways, enabling a notably high sensitivity of up to 2.2 \u0026times; 10\u003csup\u003e8\u003c/sup\u003e \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, the internal ion migration induces severe baseline drift, resulting in detector instability [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. As the dimensionality decreases, the activation energy (E\u003csub\u003ea\u003c/sub\u003e) increases, effectively suppressing ion migration [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Liu et al. demonstrated that the 0D (CH\u003csub\u003e3\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibits pronouncedly suppressed ion migration compared to 2D (PEA)\u003csub\u003e2\u003c/sub\u003ePbI\u003csub\u003e4\u003c/sub\u003e and 3D CH\u003csub\u003e3\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003ePbI\u003csub\u003e3\u003c/sub\u003e systems, with a remarkably low dark current drift of 5.0\u0026times;10⁻\u003csup\u003e10\u003c/sup\u003e nA cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. These superior properties establish low-dimensional MHPs as robust candidates for high-stability direct X-ray detection applications.\u003c/p\u003e\u003cp\u003eAlthough Bi-based low-dimensional MHPs have addressed toxicity and stability challenges through ionic substitution and dimensional engineering, the resulting bulk single crystals suffer from inherent brittleness that restricts their conformability to flexible or curved detection surfaces. In recent years, the integration of low-dimensional perovskite films with compliant substrates like polyethylene terephthalate (PET) or polydimethylsiloxane (PDMS), has enabled devices to withstand bending curvatures exceeding 5 mm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e while maintaining conformal contact with biological tissues. As demonstrated by Li et al., their flexible perovskite-based detector retains 90% of its initial X-ray sensitivity after 5000 bending cycles, showcasing exceptional mechanical robustness [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. This advancement positions MHPs-based detectors as strong contenders in X-ray detection applications involving wearable radiation monitoring.\u003c/p\u003e\u003cp\u003eHere, facile growth is reported for three novel halogen-tuned Bi-based MHPs via solution cooling method. The structural dimensionalities of these compounds exhibit a sequential transition from 0D ((C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e) to 1D ((C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e), coupled with a notable blue-shift in their bandgaps. To assess their X-ray detection performance, lateral-structure detectors were fabricated with symmetrical silver electrodes on high-quality single crystals of each compound. Notably, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e single crystal demonstrated outstanding X-ray detection capabilities and maintained great structural integrity for eight months ambient storage, outperforming most lead-based perovskites in environmental stability. Additionally, flexible detectors prepared by spin-coating (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e onto a PET substrate exhibited excellent mechanical robustness and stable X-ray response. These superior characteristics highlight the potential of Bi-based halide perovskites not only for X-ray detection technologies but also for next-generation flexible sense technologies.\u003c/p\u003e"},{"header":"2. Experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003e3-Methylpiperidine (97.00%), bismuth oxide (Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) (99.99%), hydroiodic acid (HI, 55.0\u0026thinsp;\u0026minus;\u0026thinsp;58.0%, \u0026le;\u0026thinsp;1.5% H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e), hydrobromic acid (HBr, ACS, 48%), hypophosphorous acid (H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e, AR, 50 wt%) and N, N-dimethylformamide (DMF, C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eNO, 99.5%) were purchased from Aladdin (Shanghai, China). Hydrochloric acid (HCl, 35.0\u0026thinsp;\u0026minus;\u0026thinsp;38.0%, GR) was purchased from Yantai Far East Fine Chemical Co., Ltd. Unless otherwise indicated, all reagents and solvents do not require further purification.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Synthesis of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e Single Crystals\u003c/h2\u003e\u003cp\u003eA solvent composed of HI and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e in a 5:1 volume ratio enables the dissolution of Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and 3-methylpiperidine according to the stoichiometric ratio in the chemical formula at a molar concentration of 0.18 M, followed by continuous stirring at 80\u0026deg;C until complete dissolution. The homogeneous solution was then transferred to a preheated temperature-controlled oven. A stepwise cooling protocol was applied. The temperature was initially lowered from 80\u0026deg;C to 60\u0026deg;C at a rate of 1\u0026deg;C/h, followed by further cooling to room temperature at a reduced rate of 0.5\u0026deg;C/h, which resulted in the formation of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e crystals.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Synthesis of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e Single Crystals\u003c/h2\u003e\u003cp\u003eA solvent composed of HBr and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e in a 5:1 volume ratio enables the dissolution of Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and 3-methylpiperidine following the stoichiometric ratio specified in the chemical formula at a molar concentration of 0.28 M. The mixture was stirred at 90\u0026deg;C until fully dissolved to form a clear precursor solution. The homogeneous solution was then transferred to a preheated temperature-controlled oven and subjected to a programmed cooling process, wherein the temperature was gradually lowered from 90\u0026deg;C to room temperature at a rate of 1\u0026deg;C/h to obtain (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e single crystals.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Synthesis of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e Single Crystals\u003c/h2\u003e\u003cp\u003eThe (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e crystals were synthesized via the solution cooling method by mixing 3-methylpiperidine and Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in HCl as the solvent (0.62 M) following the stoichiometric ratio specified in the chemical formula. The mixture was stirred at 80\u0026deg;C until complete dissolution to form a clear precursor solution. The solution was then transferred to a temperature-controlled oven and subjected to a programmed cooling process, in which the temperature was gradually reduced from 80\u0026deg;C to room temperature at a rate of 1\u0026deg;C/h\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 The fabrication of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based flexible devices\u003c/h2\u003e\u003cp\u003eThe (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based flexible device was fabricated via a spin-coating method. First, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e crystals were dissolved in DMF at a concentration of 0.55 M. The mixture was stirred continuously for 10 minutes until complete dissolution to obtain the precursor solution. For the spin-coating process, a layer of PEDOT (poly(3,4-ethylenedioxythiophene)) was initially deposited onto a indium tin oxide (ITO)/polyethylene terephthalate (PET) substrate and annealed at 60\u0026deg;C for 10 minutes. Subsequently, 40 \u0026micro;L of the precursor solution was evenly spread onto the PEDOT layer and spin-coated at 3000 revolutions per minute (rpm). After spin-coating, the film was annealed sequentially at 60\u0026deg;C for 5 minutes followed by a second annealing step at 100\u0026deg;C for another 5 minutes. The flexible X-ray detector was fabricated by directly coating silver onto the surface of the flexible film, forming a vertical structure with the underlying ITO layer.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6 Characterization\u003c/h2\u003e\u003cp\u003eAll single-crystal X-ray diffraction (SCXRD) data were measured from a Bruker SMART APEX-II using a CCD detector (Mo Kα, λ\u0026thinsp;=\u0026thinsp;0.71073 \u0026Aring;). Crystal structure optimization was performed using OLEX2 software. Powder X-ray diffraction (PXRD) data were measured from an XRD analyses (XRD, D8-ADVANCE of Bruker Corporation). The XRD test procedure was performed from 5 \u0026deg; to 80 \u0026deg; scanning in steps of 0.02 \u0026deg; at a speed of 20 \u0026deg;/min. X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB Xi\u0026thinsp;+\u0026thinsp;X-ray photoelectron spectrometer (Thermo Fisher Scientific). All crystals were dried at 60\u0026deg;C for 3 h prior to the XPS test to minimize contamination of the instrument by I and Br elements. The UV-Vis absorption spectrum was measured on a UV-visible spectrophotometer (Hitachi U-4100). Thermogravimetric analysis (TG) was performed on HCT-2 equipment ranging from room temperature to 1173 K with a rate of 5\u0026deg;C/min, and high-purity nitrogen gas was used as the test atmosphere. Scanning electron microscopy (SEM) was obtained using field emission scanning electron microscopy (Gemini 300) measurements. The X-ray detector was fabricated by coating symmetric silver electrodes on the surface of high-quality single crystals of the sample to form a lateral structural configuration. X-ray detection tests were performed using a tungsten anode X-ray tube with a photon energy in the range of 40\u0026ndash;150 keV as the radiation source, with signals recorded via a multifunction digital source meter (Keithley 2636B). The flexible device was tested using the Prtronic FT2000 instrument, specifically employing its tensile module. The device was securely fixed onto the tensile module and subjected to bending deformation at a rate of 1 mm/s. Following the bending process, the device was subsequently removed for X-ray detection performance evaluation.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003eThe high-quality single crystals of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e were successfully grown via a solution cooling method in a concentrated HX (X\u0026thinsp;=\u0026thinsp;I, Br, and Cl) acid solution containing a stoichiometric ratio of 3-methylpiperidine and Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e specified in the chemical formula (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-c). As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed-f, the structures of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e were characterized by Single crystal X-ray diffraction (SCXRD) analysis, respectively. (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e adopts a 0D structure comprising two BiI\u003csub\u003e6\u003c/sub\u003e octahedra linked by three I atoms between the Bi centers. Differently, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e feature 1D structures comprising BiX\u003csub\u003e6\u003c/sub\u003e octahedra (X\u0026thinsp;=\u0026thinsp;Br or Cl) interconnected by bridging X atoms between adjacent Bi atoms. Additional single-crystal structure views from different orientations are provided in \u003cb\u003eFig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea-c\u003c/b\u003e. SCXRD results indicate that both (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e crystallize in the orthorhombic system with the Pnma space group, while (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e exhibits the Pna2\u003csub\u003e1\u003c/sub\u003e space group within the same crystal system. Detailed structural parameters, including bond lengths and angles, are summarized in \u003cb\u003eTables S1-S4\u003c/b\u003e. Specifically, \u003cb\u003eTable S2-S4\u003c/b\u003e reveal that the Bi-I bond lengths in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e range from 2.8949(12) to 3.3940(11) \u0026Aring;, the Bi-Br bond lengths in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e span 2.7022(14) to 3.1387(12) \u0026Aring;, and the Bi-Cl bond lengths in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e vary between 2.5320(6) and 3.0420(5) \u0026Aring;. The average bond lengths in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e are observed to be longer than those in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e. This longer bond length weakens electron delocalization, consequently reducing the bandgap, which aligns with our experimental measurements.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg-i presents the experimental and simulated powder X-ray diffraction (PXRD) patterns of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e, respectively. Notably, the excellent agreement between the experimental and theoretical patterns confirms the high phase purity of all synthesized crystals, indicating negligible impurities or secondary phases. X-ray photoelectron spectroscopy (XPS) was further used to study the elemental composition and valence states of the (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e single crystals. The C 1s peak at 284.80 eV serves as an energy calibration reference in XPS measurements (\u003cb\u003eFig S2\u003c/b\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea displays the XPS survey spectra, featuring distinct characteristic peaks for C 1s, N 1s, Bi 4f, I 3d, Br 3d and Cl 2p. The N 1s peak appears at 402.00, 401.71, and 401.84 eV for the three compounds, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb\u003cb\u003e)\u003c/b\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, the Bi 4f doublet peaks for the three compounds locate at 158.89/164.20 eV, 159.20/164.50 eV, and 159.48/164.81 eV, respectively. In these three samples, the Bi 4f\u003csub\u003e7/2\u003c/sub\u003e and Bi 4f\u003csub\u003e5/2\u003c/sub\u003e peaks are seen to be separated by 5.3 eV, which is a characteristic of Bi\u003csup\u003e3+\u003c/sup\u003e state[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Notably, the Bi 4f peaks of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibit a low-binding-energy shift compared to those of the bromide and chloride analogues. This is due to differences in the halogens. From Cl to I, the electronegativity gradually decreases. A more electronegative halogen (Cl) attracts greater electron density from the Bi atom, reducing the electron cloud density around Bi and thereby increasing its effective nuclear charge. Consequently, the inner-shell electrons experience stronger nuclear attraction, leading to an increase in binding energy and a shift of the XPS peaks toward higher binding energies. In contrast, a less electronegative halogen (I) exerts weaker electron-withdrawing effects on the Bi electron cloud, resulting in lower binding energy and a corresponding shift of the XPS peaks toward lower energies. indicating stronger electron-withdrawing ability of Bi [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed confirms the presence of I- through characteristic I 3d peaks at 619.15 eV (I 3d\u003csub\u003e5/2\u003c/sub\u003e) and 630.62 eV (I 3d\u003csub\u003e3/2\u003c/sub\u003e). Similarly, Br 3d peaks at 68.15 eV (Br 3d\u003csub\u003e5/2\u003c/sub\u003e) and 69.20 eV (Br 3d\u003csub\u003e3/2\u003c/sub\u003e), and Cl 2p peaks at 198.14 eV (Cl 2p\u003csub\u003e3/2\u003c/sub\u003e) and 199.73 eV (Cl 2p\u003csub\u003e1/2\u003c/sub\u003e), are observed for (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-f), which is in agreement with literature reports [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFrom the scanning electron microscope (SEM) image in \u003cb\u003eFig S3\u003c/b\u003e, the surface of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e is observed to be smooth with minimal defects, whereas the crystal surfaces of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e exhibit rough morphologies with numerous voids. These surface imperfections are likely to deteriorate charge transport properties by enhancing carrier scattering and trapping. Energy dispersive spectroscopy (EDS) is employed to ascertain the elemental composition and map the elemental distribution of a material. According to \u003cb\u003eFig S4-S6\u003c/b\u003e, the elements C, N, Bi and I (Br and Cl) are uniformly distributed in the (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e ((C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e), confirming the structural integrity and compositional homogeneity of the crystals. Thermogravimetric analysis (TGA) shows that (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e exhibit excellent thermal stability, with decomposition onset temperatures of 268\u0026deg;C and 258\u0026deg;C. respectively. In contrast, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e exhibits relatively lower thermal stability, with its decomposition starting at only 202\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Beyond thermal stability, the surface wettability of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e was also evaluated via contact angle measurements. \u003cb\u003eFig S7\u003c/b\u003e shows the contact angle of 82.208 \u0026deg; for (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, indicating a moderately hydrophobic behavior. This hydrophobicity, suggesting low hygroscopicity in air, contributes to excellent environmental stability and maintained structural integrity over extended periods under atmospheric conditions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe UV-vis absorption spectrum in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb shows a broad absorption range with absorption edges located at 658.09, 470.65 and 407.04 nm for (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e, respectively [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Using Tauc equation (αhν)\u003csup\u003e1/n\u003c/sup\u003e=B(hν-Eg), the band gaps (Eg) were determined to be 1.92, 2.55, and 3.05 eV [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Within a reasonable range, a smaller band gap facilitates enhanced carrier concentration, thereby promoting carrier transport and carrier mobility [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec presents the capacitance (C) versus dielectric constant (ε) curve as a function of frequency, where ε was calculated using the formula ε\u0026thinsp;=\u0026thinsp;Cd/ε\u003csub\u003e0\u003c/sub\u003eA [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] (d: crystal thickness; A: surface area; ε\u003csub\u003e0\u003c/sub\u003e:vacuum dielectric constant). The calculated dielectric constants of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e were 6.00, 5.60, and 5.37, respectively. A higher dielectric constant can mitigate internal electric field distortion and suppress the dark current generation. For example, Dong et al. fabricated MAPbI\u003csub\u003e3\u003c/sub\u003e crystals with a high dielectric constant (ε\u0026thinsp;\u0026asymp;\u0026thinsp;30, which stabilized the dark current density within the range of 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e-10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e A/cm\u003csup\u003e2\u003c/sup\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea illustrates a lateral X-ray detector structure of Ag/(C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e single crystal/Ag for evaluating detection performance. Using the photon cross-section database (XCOM database), the X-ray absorption coefficients were calculated for (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e, and commercial inorganic semiconductors (Si, α-Se, and CdTe) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Owning to the heavy atoms Bi and I in (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, its absorption coefficient is much higher than that of Si and α-Se (in the 40\u0026ndash;150 keV energy range), which is comparable to other classical inorganic materials. \u003cb\u003eFig S8\u003c/b\u003e shows the attenuation efficiency at different thickness of these materials for 40 keV X-ray photons. (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e with 1 mm thickness can attenuate X-rays with efficiencies of 98.76%, 83.57%, and 62.52%, respectively. Notably, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibits 9.8-fold higher attenuation efficiency than Si (10%). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec illustrates the X-ray response of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e under bias voltages ranging from 2 to 200 V. Increasing the applied bias enhances carrier collection efficiency, consequently strengthening the X-ray response. The current density increases linearly with bias voltage. Similarly, as shown in \u003cb\u003eFig S9\u003c/b\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e also exhibit a strong correlation between bias voltage and X-ray response performance. This demonstrates that all three materials maintain stable X-ray response, with no saturation observed in charge carriers generation or collection within their operational range. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed presents the current-time (I-t) tests under 2 V and 200 V biases. Obviously, the photocurrent increases with rising dose rate, while the dark current remains stable. Additionally, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee displays the X-ray response of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e under a 200 V bias with a total dose rate of 69.264 mGy, where the total photocurrent variation reaches 24 pA under high-voltage and high-dose irradiation. This result confirms its exceptional stability during prolonged X-ray exposure, even under such high bias voltage conditions. As depicted in \u003cb\u003eFig S10\u003c/b\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e exhibit good photocurrent stability at a total irradiation dose of 44.404 mGy. However, the overall photocurrent variation had already surpassed that of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e at an irradiation duration of 350 seconds. Dark current drift is also a key indicator demonstrating the stability of the material. The dark current drift of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef, calculated as 2.16\u0026times;10⁻\u003csup\u003e8\u003c/sup\u003e nA cm⁻\u0026sup1; s⁻\u0026sup1; V⁻\u0026sup1;, demonstrates its exceptional stability under measurement conditions and significantly lower than previously reported values as compared in \u003cb\u003eTable S5\u003c/b\u003e [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. These comparisons highlight the superior dark current stability of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e in this work. The sensitivity of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e was calculated from Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. Under bias voltages of 2.5, 10, 20, 50, 100, and 200 V, the sensitivity values are 107.00, 122.00, 149.88, 163.61, 224.50, 276.60, and 388.05 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively. This performance exceeds that of previously reported Bi-based MHPs, such as Rb\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e (159.7 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) and (Gua)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e (18.23 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) listed in \u003cb\u003eTable S6\u003c/b\u003e [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg compares the sensitivity of three compounds, underscoring that (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibits a significantly higher value than (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e (178.85 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e (120.58 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) (\u003cb\u003eFig S11\u003c/b\u003e). This disparity primarily arises from the lower X-ray absorption coefficients of bromide and chloride analogues compared to (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, which directly impairs their capacity to absorb X-ray photons and thus diminishes their sensitivity. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh shows the current-time (I-t) curve of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e under low dose rate. It can be observed that even at this low dose rate, the photocurrent still exhibits regular variations. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei shows the detection limit is determined as 79.18 nGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{SNR}\\text{=}\\frac{\\text{（}{\\stackrel{\\text{-}}{\\text{I}}}_{\\text{p}\\text{h}\\text{oto}}\\text{-}{\\stackrel{\\text{-}}{\\text{I}}}_{\\text{dark}}\\text{)}}{\\sqrt{\\frac{\\text{1}}{\\text{N}}{\\sum\\:}_{\\text{i}}^{\\text{n}}{\\text{(}{\\text{I}}_{\\text{i}}\\text{-}{\\stackrel{\\text{-}}{\\text{I}}}_{\\text{p}\\text{h}\\text{oto}}\\text{)}}^{\\text{2}}}}\\)\u003c/span\u003e\u003c/span\u003e. Comparative tests under identical conditions demonstrate higher detection limits for (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e (247.96 nGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e (2430 nGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), respectively (\u003cb\u003eFig S12\u003c/b\u003e). To evaluate the device stability under repeated high-voltage and high-dose-rate switching cycles, the detector was subjected to approximately 400 on-off cycles at 200 V bias and a dose rate of 301.8 mGy s⁻\u0026sup1;. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ej, the photoresponses of the first three and last three cycle, reveal no significant performance degradation between initial and final cycles. Remarkably, the overall switching characteristics, including rise time, fall time, and baseline current, remain consistent throughout the entire cycling process. These experimental results unequivocally demonstrate that (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibits outstanding operational stability under high electric field and intense X-ray irradiation, indicating strong resistance to cumulative radiation damage and electrical stress.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea depicts the fabrication process of flexible films via spin-coating method. A layer of PEDOT (poly(3,4-ethylenedioxythiophene)) is first spin-coated onto the PET substrate to optimize charge transport and enhance device efficiency. The PEDOT layer exhibits excellent mechanical flexibility, high bend tolerance, and superior conformal adhesion. As shown in \u003cb\u003eFig S13\u003c/b\u003e, the fabricated flexible film features a smooth surface morphology in its SEM image. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb demonstrates that the photocurrent density of the flexible device maintains a strong linear dependence on dose rate under 1, 2, 5, 10, and 20 V bias, showcasing performance comparable to single-crystal devices. From these data, the sensitivity at 20 V bias is calculated as 121.48 \u0026micro;C Gy\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (\u003cb\u003eFig S14\u003c/b\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec presents the I-t response curve of the device, showing highly regular and reproducible behavior. \u003cb\u003eFig S16\u003c/b\u003e shows the I-t curve of flexible film under low dose rate and SNR analysis determines the detection limit under 5 V to be 66.59 nGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed), enabling effective low-dose X-ray detection for practical applications. Mechanical stability tests performed using a flexible electronics tester reveal the device preserves 84.38% of its original sensitivity after 500 bending cycles, confirming excellent durability \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). These results validate the potential of (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e for flexible device applications, offering a promising pathway for flexible electronics development.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, three halogen-engineered 3-methylpiperidine bismuth halides (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiBr\u003csub\u003e5\u003c/sub\u003e and (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eBiCl\u003csub\u003e5\u003c/sub\u003e single crystals have been successfully grown, aiming to explore their potential for X-ray detection applications. Among them, (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e exhibited a low detection limit of 71.05 nGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and dark current drift of 2.16\u0026times;10⁻\u003csup\u003e8\u003c/sup\u003e nA cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maintaining stable performance under high-voltage and high-dose-rate conditions. More importantly, the fabricated (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eN)\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eI\u003csub\u003e9\u003c/sub\u003e-based flexible X-ray detectors retained 84.38% of its original sensitivity after 500 bending cycles, demonstrating excellent mechanical durability. This research advances the development of organic bismuth halides and flexible devices in X-ray detection applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors express thanks for the financial support from projects ZR2024ME223, ZR2022QF036 and \u0026nbsp;ZR2025MS1001 supported by Shandong Provincial Natural Science Foundation, project 62305195 from the National Natural Science Foundation of China and Youth Innovation Team Development Program of Shandong Higher Education Institutions (2024KJN010).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHuayushuo Zhang: Investigation, software, writing-original draft, data curation, formal analysis. Qian Ma: Supervision, investigation, conceptualization, methodology, writing-review \u0026amp; editing, resources. Pan Gao: Investigation, formal analysis, visualization. Bolong Li: Investigation, data curation. Xiaoxia Yang: Visualization, data curation. Chao Li: Data curation. Mingming Song: Data curation. Zhiwei Hou: Data curation. Xiaomei Jiang: Supervision, investigation, conceptualization, methodology, writing-review \u0026amp; editing, resources.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available upon reasonable request from the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u0026nbsp;\u003c/strong\u003eThe online version contains supplementary material available at .\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eY. Wang, H. Lou, C.Y. Yue, X.W. 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Mater. \u003cb\u003e30\u003c/b\u003e, 1910648 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adfm.201910648\u003c/span\u003e\u003cspan address=\"10.1002/adfm.201910648\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"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":"halogen tuning, 3-methylpiperidine bismuth halides, low detection limit, stability, flexible detector","lastPublishedDoi":"10.21203/rs.3.rs-7601158/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7601158/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"X-ray detection has extensive applications in medical imaging, scientific research, and security inspection. Despite the superior radiation detection properties of lead-based perovskites, including high carrier mobility and superior attenuation efficiency, their toxicity and instability arising from ion migration hinders further development. To address these challenges, a series of halogen-tuned lead-free 3-methylpiperidine bismuth halides, (C6H14N)3Bi2I9, (C6H14N)2BiBr5 and (C6H14N)2BiCl5 (C6H14N = 3-methylpiperidine) single crystals were grown and systematically characterized. 3-methylpiperidine was selected for their steric effect stabilizing the lattice, and the synergistic tuning through halogen variation enabled a structural transition along with modulation of their properties. Notably, lateral-structured (C6H14N)3Bi2I9 single crystal-based X-ray detectors achieved remarkable sensitivity of 388.05 μC Gy⁻¹ cm⁻², a low detection limit of 71.05 nGy s⁻¹ and a dark current drift of 2.16 × 10⁻8 nA cm⁻¹ s⁻¹ V⁻¹. Importantly, the material retained its original morphology after eight months of ambient storage. Furthermore, flexible X-ray devices fabricated via spin-coating (C6H14N)3Bi2I9 exhibited excellent X-ray response with a sensitivity of 121.48 μC Gy⁻¹ cm⁻² and outstanding mechanical stability. This work reveals that halogen tuning effectively optimizes the structure and performance of Bi-based perovskites, providing valuable insights for advancing them in X-ray detection applications.","manuscriptTitle":"Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-08 07:04:38","doi":"10.21203/rs.3.rs-7601158/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":"280135ab-63ab-43e0-b722-b3baa0c622c3","owner":[],"postedDate":"October 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-22T16:02:22+00:00","versionOfRecord":{"articleIdentity":"rs-7601158","link":"https://doi.org/10.1007/s10854-025-16356-9","journal":{"identity":"journal-of-materials-science-materials-in-electronics","isVorOnly":false,"title":"Journal of Materials Science: Materials in Electronics"},"publishedOn":"2025-12-18 15:58:06","publishedOnDateReadable":"December 18th, 2025"},"versionCreatedAt":"2025-10-08 07:04:38","video":"","vorDoi":"10.1007/s10854-025-16356-9","vorDoiUrl":"https://doi.org/10.1007/s10854-025-16356-9","workflowStages":[]},"version":"v1","identity":"rs-7601158","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7601158","identity":"rs-7601158","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}