Dynamic stability of high-efficiency quantum dot light-emitting diodes

Dynamic stability of high-efficiency quantum dot light-emitting diodes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Dynamic stability of high-efficiency quantum dot light-emitting diodes Hongbo Li, Xiaonan Liu, Yan Gao, Bo Li, Yansong Yue, Jing Wei, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5370454/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Quantum dot light-emitting diodes (QD-LEDs) hold great potential for enabling ultra-clear and ultra-bright displays technologies. Although the operational lifetime of QD-LEDs under static conditions has reached commercial standard, their dynamic stability, i.e., performance consistency while being switched on and off, remains largely behind that of state-of-the-art III-V LEDs. In this work, we studied the degradation mechanism of red QD-LEDs with high external quantum efficiency (EQE) and long static operational lifetime and found that the accelerated EQE decline is mainly due to the fast-increasing electron leakage into the organic hole transport layer (HTL) under continuous voltage scans. To improve the dynamic stability of QD-LEDs, we refined the structure of CdZnSe/ZnSe QDs by introducing a ZnSeS/ZnS outer shell, where the ZnS shell improves the electron confinement and the ZnSeS mitigates the lattice mismatch between ZnSe and ZnS. Consequently, the electron leakage into the HTL is significantly inhibited, leading to QD-LEDs with minimal EQE drop of less than 4% after more than 5,000 voltage cycles within the range between 0 V and 4.5 V, while the devices still possess excellent static stability for maintaining 95% of its initial luminance (T 95 ) at 1,000 cd m -2 for over 61,000 h. Physical sciences/Nanoscience and technology/Nanoscale materials/Quantum dots Physical sciences/Materials science/Materials for optics/Lasers, LEDs and light sources/Inorganic LEDs Physical sciences/Materials science/Nanoscale materials/Quantum dots Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Colloidal quantum dots (QDs) are considered as a high-quality light emitting materials for display applications 1 – 4 due to their tunable emission color 5 – 7 , narrow spectral linewidths 8 – 11 , and high photoluminescent quantum yields (PLQYs) 12 – 14 . The static performance of quantum dot light-emitting diodes (QD-LEDs) has been significantly improved in recent years, e.g., the state-of-the-art QD-LEDs exhibit external quantum efficiencies (EQEs) exceeding 20% at a constant voltage 15 – 17 , and the operational lifetimes at a constant current density already meet the standards for display applications 17 – 21 . Despite significant advances in operational lifetime of OD-LEDs at constant voltage or current density, dynamic stability, which characterizes the stability of the device performance under varying driving voltage or current, is still considerably low in state-of-the-art QD-LEDs 21 , 22 . For example, QD-LEDs with high EQE ≈ 21.6% and long static operating lifetime (T 50 ≈ 1,600,000 h at 100 cd m − 2 ) still deteriorate fast under continuous voltage scans, where the EQE can drop by ~ 35% after only 6 voltage scans. 22 Importantly, in real scenario of display devices, the QD-LEDs must withstand frequent luminescence modulation by varying the driving voltage to create different color and brightness, which requires excellent dynamic stability. Therefore, studying the dynamic stability during voltage cycles and understanding the origin of device degradation is critical to push QD-LEDs towards commercial applications. Here, we identified that the degradation of EQE in typical QD-LEDs based on CdZnSe/ZnSe QDs primarily stems from electron leakage into the hole transport layer, which becomes more pronounced under continuous voltage scans. To address this issue, we propose a strategy to enhance the dynamic stability of QD-LEDs by introducing a ZnSeS/ZnS outer shell, where the ZnS layer improves electron confinement and the ZnSeS layer mitigates the lattice mismatch between ZnSe and ZnS. The modified QDs, with a structure of CdZnSe/ZnSe/ZnSeS/ZnS, have a high PLQY of 95%. The resulting QD-LEDs not only achieve a peak EQE exceeding 24%, but also show demonstrate excellent durability, with an EQE drop of less than 4% after 5,000 continuous voltage cycles from 0 to 4.5V. Furthermore, the devices also exhibit excellent static stability, maintaining 95% of its initial luminance (T 95 ) at 1,000 cd m − 2 for over 61,000 h. Results and Discussion Poor dynamic stability of QD-LEDs with high EQE A typical high performance QD-LED based on CdZnSe/ZnSe QDs, named ZnSe QD-LED in the following, is shown in Fig. 1 a. Owning to the high lattice match between the ZnSe shell and the CdSe core, the CdZnSe/ZnSe QDs exhibit a high PLQY of 88% with a photoluminescence (PL) peak at 639 nm and an average particle size of 15 nm. The detailed characterizations of QDs are shown in Supplementary Fig. 1. The ZnSe QD-LEDs are constructed by all-solution process with a structure of ITO/PEDOT:PSS/TFB/QDs/ZnMgO/Al. Since the ZnSe shell has a good match with the lowest unoccupied molecular orbital (LUMO) level of the HTL, it can significantly reduce the hole injection barrier and improve the EQE. As a result, the ZnSe QD-LED has a turn-on voltage of ~ 1.6 V, a peak EQE of 22.9%, and a luminance of more than 60,000 cd m − 2 at an operating voltage of 4.5 V. It also has a good static stability with T 95 exceeds 130 h at a constant current density of 50 mA cm − 2 (Fig. 1 b), corresponding to a luminance of greater than 8000 cd m − 2 . Based on the equation \(\:{L}_{0}^{n}{T}_{95}=constant\) 23 , the operating time of T 95 at lower luminance values are derived to be over 5,600 h at a luminance of 1,000 cd m −2 and 319,500 h at a luminance of 100 cd m − 2 . To explore the dynamic stability of ZnSe QD-LEDs, we monitored device characteristics including peak EQE, current density, and luminance for 35 continuous cycles under a voltage range of 0 − 4.5 V. The peak EQE rapidly dropped from 22.9–9.5% after 35 voltage sweeps (Fig. 1 c). As shown in the current density-voltage-luminance ( J-V-L ) curves (Fig. 1 d), the luminance decreased with increasing number of voltage scans, while the current density increased after 35 voltage scans, indicating growing proportion of non-radiative recombinations. Figure 1 e shows the evolution of EQE max , current density (@4.5 V) and luminance (@ 4.5 V) normalized to their initial values at the first voltage scan. After 35 scans, the current density increases by 15%, the luminance decreases by 41%, and the EQE max dropped by 58%. To eliminate the degradation due to heat accumulation 24 – 28 , we heated a fresh device at 50℃ for the same duration of 30 min as that for 35 voltage scans and found there was no obvious degradation after heating (Supplementary Fig. 2). Previous studies have shown that both QD charging and electron leakage into the HTL may cause rapid degradation of QD-LEDs 29 – 33 . The degradation caused by QD charging is reversible by extracting the extra charges, while the electron leakage into HTL results in degradation of the HTL and irreversible deterioration of device performance. After a two-hour recovery, the ZnSe QD-LED partially restored its EQE from 9.5–16.2% and luminance from 39,350 to 51,000 cd m − 2 (Supplementary Fig. 3), suggesting that both effects exist in ZnSe QD-LEDs, which agrees with the considerable increase of leakage current shown in Fig. 1 d. The origin of the degradation of ZnSe QD-LEDs under continuous voltage scans To gain insight into the degradation mechanisms, we conducted electrical and optical characterizations of the device before and after 35 voltage scans (Fig. 2 ). In typical QD-LEDs, the injection efficiency of holes is often lower than that of electrons due to the larger injection barrier and lower mobility of holes 34 – 38 , which results in excess electrons leakage into the HTL. Moreover, the electron confinement ability of QDs can also affect the extent of electron leakage into the HTL. The increased TFB emission after 35 voltage scans indicates that the electron leakage was intensified (Fig. 2 a, Supplementary Fig. 4). Meanwhile, the EL peak position at 4.5 V was red-shifted by 2 nm, which can be attributed to the bandgap narrowing caused by the increased temperature (Fig. 2 a inset). 39 , 40 We monitored the voltage-capacitance curves of ZnSe QD-LEDs to probe the carrier accumulation in the device, as shown in Fig. 2 b. In the fresh device, the two peaks near 1.6 V and 2.1 V correspond to the turn-on voltage and the peak EQE, respectively. Under negative bias, the HTL, QD layer, and ETL are depleted. The slowly increasing capacitance below 1.2 V can be attributed to the gradual filling of the QD layer and ETL. The rapidly increasing capacitance above 1.2 V is commonly attributed to the accumulation of holes at the HTL/QDs interface, and at 1.6 V, holes begin to inject into the QDs layer 41 . Under higher voltage, more holes are injected into the QDs layer and recombine with the electrons, and the capacitance decreases rapidly after reaching the peak EQE at 2.1 V. The peak packet near 1.6 V gradually evolves to a platform after multiple voltage scans, while the peak capacitance near 2.1 V continuously decreases. Meanwhile, Fig. 1 e shows that the current is increasing under continuous voltage scan, suggesting that more electrons are injected directly into the HLT rather than being involved in the radiative recombination in the QDs. Therefore, the peak packet near 1.6 V of ZnSe QD-LEDs is most likely due to the electron leakage and the degradation of HTL. Electrically-excited transient absorption (EETA) spectroscopy clearly reflects the charge injection dynamics, the balance of charge density and the strength of the electric field distribution in QD-LEDs 16 , 42 . Hence, the origin of device degradation can be revealed by comparing the EETA spectra of ZnSe QD-LEDs before and after 35 voltage scans (Fig. 2 c). Under reverse bias of -3 V (Fig. 2 c top panel), the Stark effect signal of the TFB HTL at 418 nm dropped by 8% after voltage scans, indicating significant degradation of the TFB layer. The absorption of QDs near 640 nm also dropped by 4%, which is accompanied by a prolonged average PL lifetime from 8.5 ns to 10.3 ns (Supplementary Fig. 5), indicating that the QDs are also degraded after continuous voltage scans. Under forward bias, the bleaching signal of the EETA spectrum is mainly contributed by the electrons, which is due to the much higher degeneracy of the valence band than that of the conduction band 43 . The significantly increased bleaching signals of the EETA spectra between 550 nm and 680 nm after voltage scans demonstrates increased electron density in the QD-LEDs (Fig. 2 c bottom panel), which deteriorates the electron-hole balance in the QDs layer and facilitates electron leakage into the HTL, causing parasitic luminescence and irreversible degradation (Fig. 2 d). The degraded HTL layer generates hole traps and reduces hole transport efficiency, which ultimately reduces the EQE. Therefore, there are primarily two strategies to improve the dynamic stability of QD-LEDs, i.e., using a more stable HTL material to block the electron leakage and enhance the hole injection, or tuning the structure of QDs to improve the electron confinement. Unfortunately, HTL materials that meet these requirements are not yet available. Hence, carefully designing the shell structure to adjust the band structures of QDs is an effective route. As shown in Fig. 2 d, if the excess electrons can be confined within the QDs, the device degradation caused by electron leakage to the HTL will be greatly alleviated. Improve the dynamic stability of QD-LEDs by modulating the bandgap structure of the QDs We synthesized CdZnSe/ZnSe/ZnSeS/ZnS QDs to improve the dynamic stability of QD-LEDs. Compared to ZnSe, ZnS has a wider bandgap and can increase the stability of QDs as the outermost shell 23 , 44 , 45 . To minimize the large lattice mismatch between ZnS and ZnSe, an alloyed gradient ZnSeS shell is inserted between the two, and the gradient-alloy core-shell QDs exhibited over 95% PLQY (Fig. 3 a and Supplementary Fig. 6). The elemental distribution of QDs, with a diameter of 16 nm, was measured using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It showed that Cd was primarily concentrated in the core of each QD, while Zn was predominantly located in the shell (Fig. 3 b and Supplementary Fig. 6). Additionally, elemental line scans of Cd, Zn, Se, and S revealed smoothly varying compositions, demonstrating the successful synthesis of the gradient-alloy shell (Fig. 3 c). Finally, the PL peak position of CdZnSe/ZnSe/ZnSeS/ZnS QDs (645 nm) was blue-shifted by 6 nm compared to the CdZnSe core (651 nm), which was less than the blue shift observed in CdZnSe/ZnSe QDs (12 nm at 639 nm). This indicates that the charge confinement in CdZnSe/ZnSe/ZnSeS/ZnS QDs is enhanced (Fig. 3 d and Supplementary Fig. 6c). Excellent dynamic stability of ZnS-based QD-LEDs QD-LEDs based on CdZnSe/ZnSe/ZnSeS/ZnS QDs, referred to as ZnS QD-LEDs hereafter, were fabricated using the same method as ZnSe QD-LEDs. A hybrid organic-inorganic structure was employed, and cross-sectional TEM images revealed the uniformity and homogeneity of each film layer (Fig. 4 a). TEM images of both devices (Supplementary Fig. 7) showed similar thickness for each functional layer. The devices have pure and bright luminescence (Fig. 4 b and Supplementary Fig. 8). The stable capacitance-voltage curves after 100 voltage scans indicated that no holes accumulated at the interface or been trapped by the defects (Fig. 4 c). To further investigate whether the HTL and QDs layers are damaged under continuous voltage scans, we measured the time-dependent EETA spectra of ZnS QD-LEDs under − 3 V and + 3 V voltages (Fig. 4 d). The Stark effect signal peaks of the HTL (TFB) and the bleaching signal peak of the emissive layer (ZnS QD) remained almost unchanged after 100 voltage scans. Specifically, the peak of TFB and the valley of ZnS QD both decreased by less than 1% after 30 min of voltage maintenance (equivalent to hundreds of voltage scans), which suggests that ZnS QDs with enhanced electron confinement can suppress the electron leakage and the degradation of the HTL layer. Finally, we characterized the dynamic stability of the ZnS QD-LEDs by monitoring the device performance between the 1st and the 5000th voltage scans. The EL spectra of the devices only shifted by < 1 nm after 5000 voltage scans while exhibiting a saturated deep red color with Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of (0.692, 0.293) (Supplementary Fig. 9). The leakage current below the turn-on voltage (~ 1.6 V) gradually decreased due to the better confinement of electrons within the QDs (Fig. 4 e). The EQE only decreased from 24.5–23.6% after 5000 voltage scans, demonstrating a substantial improvement in the dynamic stability of ZnS QD-LEDs (Fig. 4 f, g). Meanwhile, the CE max only dropped from 21 cd A − 1 to 20.2 cd A − 1 , and at a high voltage of 4.5 V, the EQE and current efficiency only slightly decreased by 0.4% (Supplementary Fig. 10). To understand the origin of the luminance decay, the current density and brightness at 4.5 V from each voltage scan were calculated (Supplementary Fig. 11). The C 95 (the cycle number after which the luminance decays to 95% of its initial value) was 200 cycles for the voltage range of 0 − 4.5 V. After 5000 voltage scans, the luminance and current densities decreased by 29% and 30%, respectively. The drop in luminance and current densities is significantly affected by the magnitude of the electric field, and lowering the voltage can greatly enhance the dynamic stability of QD-LEDs. Under a smaller voltage of 0 − 2.6 V, the maximum EQE only decreased by < 1% after 10,000 scan cycles (Fig. 4 g). Meanwhile, the luminance/current density declines are reduced to 24% and 23%, respectively (Supplementary Fig. 11), and the C 95 is more than 4,000 (the J-V-L curves and V-EQE are shown in the Supplementary Fig. 12). At the same time, the operational lifetime of the ZnS QD-LEDs matches that of the state-of-the-art red LEDs 20 . At an initial luminance of 10,039 cd m − 2 , the T 95 was measured as 1,056 h (Fig. 4 h), which is equivalent to a T 95 of 61,180 h at an initial luminance of 1,000 cd m − 2 . In summary, we investigated the origins of poor dynamic stability of high-efficiency red QD-LEDs by monitoring their performance under continuous voltage scans. Our findings reveal that charge confinement whthin the QD emissive layer plays a crucial role in the dynamic stability of QD-LEDs. Insufficient electron confinement leads to electron leakage, causing parasitic emission from the HTL, which degrades the HTL and generates hole traps. Moreover, poor electron confinement in the QDs increases non-radiative recombination rates due to QD charging. To address these issues, we enhance the dynamic stability of QD-LEDs by optimizing the shell structure to improve electron confinement. The CdZnSe/CdZnSe/ZnSe/ZnS QDs with a gradient-alloy shell demonstrate high PLQY and excellent electron confinement. As a result, the QD-LEDs based on these QDs show less than 5% drop in EQE after more than 5,000 voltage scan cycles in the voltage range of 0 − 4.5 V. In addition, the dynamic stability extends beyond 10,000 cycles when the voltage scan range is reduced to 0 − 2.6 V—setting a new benchmark for QD-LED dynamic stability. These findings represent a step toward the development of QD-LEDs with both high efficiency and long-term stability, advancing their potential for use in high-performance display applications. Methods Materials Cadmium oxide (CdO, 99.99%, powder), zinc oxide (ZnO, 99.9%, powder), sulfur (S, 99.998%, powder), 1-octanethiol (OT, 98%), oleic acid (OA, 90%), trioctylphosphine (TOP,97%), 1-octadecene (ODE, 90%), zinc acetate (Zn(OA) 2 , 99.99%), tetramethylammonium hydroxide (TMAH, 98%), dimethyl sulfoxide (DMSO, HLPC grade), chlorobenzene (99%), magnesium acetate tetrahydrate (Mg(OAc) 2 ·4H 2 O, 99.98%), zinc(II) acetate dihydrate (Zn(OAc) 2 ·2H 2 O, 99.99%), n-Octane (99%) and ethanol (99.8%) were purchased from Aldrich. Paraffin oil (analytical grade), hexanes (analytical grade), acetone (analytical grade), isopropanol (analytical grade), and methanol (analytical grade) were obtained from Beijing Chemical Reagent Co. Ltd, China. Poly (ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) was purchased from Heraeus Deutschland. Poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4’-(N-(p-butylphenyl)) diphenylamine)] (TFB, average molecular weight, ~ 67,000 g mol − 1 ) was purchased from American Dye Source, Inc. All materials were used as received. Preparation of precursors Zinc Precursor: ZnO (60 mmol), OA (60 mL) and ODE (90 ml) were filled into a 250 ml three-necked flask, which was heated and exhausted at 150°C for 15 minutes. Then, the solution was heated to 310°C under nitrogen with stirring to obtain a clear colorless solution. Selenium precursor: Selenium (20 mmol) and TOP (40 ml) were mixed in a 100 ml three-necked flask, which was heated and exhausted at 150°C to obtain a clear solution. Selenium-sulfur precursor: Selenium powder (2.5 mmol), sulfur powder (2.5 mmol) and TOP (10 ml) were mixed and stirred to form a clear solution. Synthesis of CdZnSe/ZnSe quantum-dots The synthesis of CdZnSe/ZnSe QDs was modified from previous reports 15 , 20 . Zn(OAc) 2 (1.5 mmol), CdO (1.5 mmol), ODE (20 ml) and OA (10 ml) were loaded into a three-necked flask and evacuated at 120°C for 10 min, followed by heating under N 2 flow to 310°C. Subsequently, 5 mL of selenium precursor was rapidly injected, and the temperature was maintained for 30 min to grow the CdZnSe cores. To grow the ZnSe shell, the temperature was decreased to 270°C, and 5 ml of zinc precursor was added dropwise for 10 min followed by adding 3 ml of selenium precursor for 20 min. Synthesis of CdZnSe/ZnSe/ZnSeS/ZnS quantum-dots First, CdZnSe/ZnSe QDs were synthesized using the same method as described above, except that the thickness of the ZnSe shell is reduced. The ZnSeS shell was grown by dropwise addition of 5 ml of zinc precursor for 10 min, followed by dropwise addition of 3 ml of selenium precursor for 20 min. To grow the ZnS shell, 5 ml of Zn(OA) 2 and octanethiol (2.8 mmol, equivalent to 1.4 mmol Zn(OA) 2 ) were added dropwise into the solution. Once the reaction was completed, the system was cooled down to room temperature. Synthesis and purification of ZnMgO nanoparticles ZnMgO nanoparticles were synthesized by slightly modifying the method reported previously 46 . For a typical synthesis, Zn(OAc) 2 ·2H 2 O (2.7 mmol) and Mg(OAc) 2 ·4H 2 O (0.3 mmol) were dissolved in DMSO (30 mL), TMAH (5 mmol) in ethanol (10 mL), and the two solutions were mixed and stirred for 1 h in air. Finally, the mixed solution was washed and the precipitated Zn 0.90 Mg 0.10 O nanoparticles were dispersed in ethanol at a concentration of 25 mg ml − 1 for spare use. Fabrication of quantum-dot light-emitting diodes All devices were fabricated on glass substrates with indium tin oxide (ITO) patterns. Substrates were ultrasonically cleaned with detergent, deionized water, acetone and isopropanol for 15 min, respectively, followed by treatment under UV ozone for 15 min. PEDOT:PSS (in water, Al 4083) was spin-coated onto ITO substrates at 5500 rpm. and baked at 140°C for 15 minutes in air. The substrates were transferred into a N 2 -filled glove box for the layer-by-layer deposition of TFB (in chlorobenzene, 8 mg mL − 1 ), QDs (in octane, 25 mg mL − 1 ) and ZnMgO (in ethanol, 30 mg mL − 1 ) by spin-coating at 3000 rpm, 3000 rpm and 2000 rpm, respectively, for 30 s. The substrates were baked at 150 ℃ and 60 ℃ for 30 min after deposition of the TFB and ZnMgO layers, respectively. Next, the silver anode was deposited via thermal evaporation at a rate of ≈ 0.1 nm s − 1 under a vacuum of 4 × 10 − 6 Torr. The device area defined by the overlapping of the ITO and silver electrodes is 4 mm 2 . Finally, the devices were encapsulated by bonding the glass cover sheet to the devices using a UV curable resin. Characterization and instrumentation UV-vis absorption and PL spectra were measured by an Ocean Optics spectrophotometer (model PC2000-ISA). Transmission electron microscopy (TEM) studies were performed using a JEOL JEM-2010 electron microscope operating at 200 kV. The energy-dispersive spectroscopy (EDS) mappings were carried out by four symmetrically designed EDS detectors on an FEI Talos F200X. The cross-section images of the QD-LEDs were collected with an FEI Talos F200X. The J-V characteristics of the QD-LEDs were analyzed using an Agilent 4155C semiconductor parameter analyzer with a calibrated Newport silicon diode under ambient conditions. The luminance was calibrated using a Photo Research spectroradiometer (PR735). The electroluminescence (EL) spectra were obtained with an Ocean Optics spectrometer (USB2000, relative irradiance mode) and a Keithley 2400 source meter. Capacitance-voltage measurements were carried out using an Agilent 4282A precision LCR meter with a modulating frequency of 10 KHz. The thermal images of the samples were acquired using a Fluke Ti401 PRO camera. Electrical excitation transient absorption measurement Electrical pulses (1 kHz, 10 us) were applied to the QD-LEDs by a Keysight 33512B waveform generator. The probe and reference beams were obtained from white laser pulses generated by a supercontinuum white laser (Leukos, Disco). An electrical pulse in device sent the probe beam to the excitation area, then was collected to the monochromator and charge-coupled device by an electronic time-delay module. The signal was collected by the difference between the probe intensity without and with the pump electrical pulse. Declarations Competing interests The authors declare no competing interests. Author contributions H. L. and H. S. conceived the idea and directed the project. X. L. fabricated and collected the performance data of the QD-LEDs. Y.G. synthesized QDs. B.L. performed EETA experiments. Y. Y. assisted the device characterizations. X. L., Y.G., B.L. and Z. W. conducted data analysis with help from J. W. and F. L. X. L. and H. 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Temperature effects on the spectral properties of colloidal CdSe nanodots, nanorods, and tetrapods. Appl. Phys. Lett. 90 , (2007). Chen S, et al. On the degradation mechanisms of quantum-dot light-emitting diodes. Nat. Commun. 10 , 765 (2019). Li B, et al. Origin of the Efficiency Roll-off in Quantum Dot Light-Emitting Diodes: An Electrically Excited Transient Absorption Spectroscopy Study. Nano Lett. 24 , 10650-10655 (2024). Efros AL, Rosen M, Kuno M, Nirmal M, Norris DJ, Bawendi MJPRB. Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: Dark and bright exciton states. 54 , 4843 (1996). Altintas Y, et al. Highly Stable, Near‐Unity Efficiency Atomically Flat Semiconductor Nanocrystals of CdSe/ZnS Hetero‐Nanoplatelets Enabled by ZnS‐Shell Hot‐Injection Growth. Small 15 , 1804854 (2019). Hines MA, Guyot-Sionnest P. Synthesis and characterization of strongly luminescing ZnS-capped CdSe nanocrystals. The Journal of Physical Chemistry 100 , 468-471 (1996). Qian L, Zheng Y, Xue J, Holloway PH. Stable and efficient quantum-dot light-emitting diodes based on solution-processed multilayer structures. Nat. Photon 5 , 543-548 (2011). Additional Declarations There is NO Competing Interest. Supplementary Files dynamicstabilitySIsubmit.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5370454","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":377172183,"identity":"32490e5a-3740-46af-be82-f42e1ecbc260","order_by":0,"name":"Hongbo Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYBACAyBmBmIZNvYehgNABmMDsVp42HjOMBw4QJIWBokcBgaitJiz9x5+XVDBwMMn+fbg4Q8MNrIbDjA/e4BPi2XPuTTrGWeADpPOSwA6LM14wwE2cwO8DruRY2bM2wbSkmMA1HI4ccMBHjYJ4rRIngFp+U+UFuPHYC0SPCAtB4jQcuaMGfOMMxLAQAb65YxBsvHMw2xm+LUc7zH+XFBhIyfffvbwh4oKO9m+483P8GoBApAzYGpg0UQAMH8grGYUjIJRMApGNAAAJvpGm8bQwaAAAAAASUVORK5CYII=","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":true,"prefix":"","firstName":"Hongbo","middleName":"","lastName":"Li","suffix":""},{"id":377172184,"identity":"1bd525f2-a2c9-4461-886c-8c5b36772f5f","order_by":1,"name":"Xiaonan Liu","email":"","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xiaonan","middleName":"","lastName":"Liu","suffix":""},{"id":377172185,"identity":"fc9c0af9-a462-4ce8-bb07-344a157bbe50","order_by":2,"name":"Yan Gao","email":"","orcid":"","institution":"Henan University","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Gao","suffix":""},{"id":377172186,"identity":"559444e5-a3ca-4dfb-9416-b12f677d494e","order_by":3,"name":"Bo Li","email":"","orcid":"","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Bo","middleName":"","lastName":"Li","suffix":""},{"id":377172187,"identity":"b300efce-e135-4a36-b000-692e265b95cd","order_by":4,"name":"Yansong Yue","email":"","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yansong","middleName":"","lastName":"Yue","suffix":""},{"id":377172188,"identity":"ae72a603-597c-4489-a003-d890e6fc71ad","order_by":5,"name":"Jing Wei","email":"","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Wei","suffix":""},{"id":377172189,"identity":"2b37e507-5187-4157-8a2d-1760234c5684","order_by":6,"name":"Zhenhui Wu","email":"","orcid":"","institution":"Henan University","correspondingAuthor":false,"prefix":"","firstName":"Zhenhui","middleName":"","lastName":"Wu","suffix":""},{"id":377172190,"identity":"1dae54ad-48d7-4507-9583-990eb64d1d94","order_by":7,"name":"Fangze Liu","email":"","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Fangze","middleName":"","lastName":"Liu","suffix":""},{"id":377172191,"identity":"e17a74b0-a763-4879-ac74-236a99050c71","order_by":8,"name":"Huaibin Shen","email":"","orcid":"https://orcid.org/0000-0002-6425-0514","institution":"Henan University","correspondingAuthor":false,"prefix":"","firstName":"Huaibin","middleName":"","lastName":"Shen","suffix":""}],"badges":[],"createdAt":"2024-11-01 04:15:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5370454/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5370454/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":68886402,"identity":"e9153563-ba98-4df4-844d-ef5558ca0e3e","added_by":"auto","created_at":"2024-11-13 06:40:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1366802,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRepresentative characteristics of high-EQE QD-LEDs with poor dynamic stability.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Schematic structure (left panel) and photographs (right panel) of a red QD-LED based on CdZnSe/ZnSe QDs with an active area of 2 mm × 2 mm under different operating voltages. \u003cstrong\u003eb\u003c/strong\u003e, At a constant current density of 50 mA cm\u003csup\u003e-2\u003c/sup\u003e and an initial luminance of 8,511 cd m\u003csup\u003e-2\u003c/sup\u003e, the T\u003csub\u003e95\u003c/sub\u003e operating lifetime of QD-LEDs was 134 h. \u003cstrong\u003ec–d\u003c/strong\u003e, The EQE and J-V-L characteristic curves of QD-LEDs during 35 voltage scans from 0 V to 4.5 V with a scanning speed of 0.15 V/s. \u003cstrong\u003ee\u003c/strong\u003e, The evolutions of peak EQE, current density (@ 4.5 V) and luminance (@ 4.5 V) normalized to their initial values during the 35 voltage scans. The three hollow points show the device performance after a two-hour recovery of the degraded devices.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/460939b834b7df9df3b16de7.png"},{"id":68886404,"identity":"2e239a58-171c-460a-824c-e7a03e413eb9","added_by":"auto","created_at":"2024-11-13 06:40:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":607364,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectron leakage and hole accumulation in devices during continuous voltage scans. a\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eElectroluminescence\u003cstrong\u003e (\u003c/strong\u003eEL) spectra of the ZnSe QD-LED at the first and 35th voltage scans at an operating voltage of 4.5 V. Inset: the surface temperatures after the first (top) and 35th (bottom) voltage scans measured by infrared thermography at a room temperature of 20℃. Scale bar is 1 cm. \u003cstrong\u003eb\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eThe voltage-capacitance characteristic curves of ZnSe QD-LED. \u003cstrong\u003ec\u003c/strong\u003e, EETA spectra of ZnSe QD-LEDs before and after 35th voltage scans at -3 V reverse bias (top) and 3 V forward bias (bottom), respectively. \u003cstrong\u003ed\u003c/strong\u003e, Schematics comparing the degradation mechanism of QD-LEDs based on CdZnSe/ZnSe QDs and the enhanced stability due to better electron confinement by QDs with a graded shell.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/cdfa301c7a14d4c85f775787.png"},{"id":68886406,"identity":"ff374b26-4738-49d7-b2ff-a30ea7434198","added_by":"auto","created_at":"2024-11-13 06:40:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":788810,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSuppression of electron leakage and TFB degradation by synthesizing CdZnSe/ZnSe/ZnSeS/ZnS QDs. a\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eSchematics showing the core-shell structure of CdSeZn/ZnSe/ZnSeS/ZnS QDs.\u003cstrong\u003e b\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eA high-angle annular dark field (HAADF) image and energy dispersive spectroscopy (EDS) elemental mapping of Zn and Cd elements from several CdZnSe/ZnSe/ZnSeS/ZnS QDs shown in HAADF image. The scale bar: 10 nm. \u003cstrong\u003ec\u003c/strong\u003e,Elemental line scan spectra of CdZnSe/ZnSe/ZnSeS/ZnS QDs with the scanning direction along the direction of the red dashed arrow in the inset. Scale bar of the inset image: 10 nm. \u003cstrong\u003ed\u003c/strong\u003e,Absorption and photoluminescence (PL) spectra of CdZnSe/ZnSe/ZnSeS/ZnS core/shell QDs. The inset is a photograph of the QD-octane dispersion under ultraviolet (UV) irradiation.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/397c2b8f28bc6ae467255fe6.png"},{"id":68886992,"identity":"9786223f-4907-4873-b36a-84401ddc70d9","added_by":"auto","created_at":"2024-11-13 06:48:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":749170,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDynamic stability of ZnS QD-LEDs. a, \u003c/strong\u003eSchematic device structure, cross-sectional scanning electron microscope (SEM) image of QD -LED. Scale bar: 200 nm.\u003cstrong\u003e b\u003c/strong\u003e, EL spectra of ZnS QD-LEDs under different driving voltages, and the inset shows the photograph of EL emission from the device operated at 3 V.\u003cstrong\u003e c\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eVoltage-capacitance characteristic curves of QD-LEDs based on CdZnSe/ZnSe/ZnSeS/ZnS QDs under continuous voltage scans. \u003cstrong\u003ed\u003c/strong\u003e, EETA spectra of ZnS QD-LEDs at reverse (-3 V) and forward (+3 V) bias voltages over time.\u003cstrong\u003e e\u003c/strong\u003e, \u003cem\u003eJ-V-L\u003c/em\u003e characteristic curve of ZnS QD-LED with 5000 voltage scans. The inset shows an enlarged view of the \u003cem\u003eJ-V\u003c/em\u003e curves before the device is turned on.\u003cstrong\u003e f\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003eV-EQE\u003c/em\u003e characteristic curves of ZnS QD-LED with 5000 voltage scans.\u003cstrong\u003e g\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eVariation of EQE\u003csub\u003emax\u003c/sub\u003e with increasing number of voltage scans.\u003cstrong\u003e h\u003c/strong\u003e, Operational lifetimes (actual luminance/ initial luminance (\u003cem\u003eL/L\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) versus time) of ZnS QD-LEDs. The inset shows the acceleration factor (n) used to estimate lifetimes by fitting the Log(\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e95\u003c/em\u003e\u003c/sub\u003e)-Log(\u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) data point. In the ZnS QD-LEDs, n is about 1.76.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/fa5954bb215b0f43cbe7f77f.png"},{"id":70021802,"identity":"2923274b-7caf-4b63-888f-5f978f308eb6","added_by":"auto","created_at":"2024-11-27 14:53:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4756586,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/f14d0982-669d-4628-bc53-18f531e40f13.pdf"},{"id":68886405,"identity":"a422870e-9e58-49af-8292-cfee88c91162","added_by":"auto","created_at":"2024-11-13 06:40:34","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1329707,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"dynamicstabilitySIsubmit.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5370454/v1/249a22448d710e3c9fc8c51a.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Dynamic stability of high-efficiency quantum dot light-emitting diodes","fulltext":[{"header":"Introduction","content":"\u003cp\u003eColloidal quantum dots (QDs) are considered as a high-quality light emitting materials for display applications\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e due to their tunable emission color\u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, narrow spectral linewidths\u003csup\u003e\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, and high photoluminescent quantum yields (PLQYs)\u003csup\u003e\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. The static performance of quantum dot light-emitting diodes (QD-LEDs) has been significantly improved in recent years, e.g., the state-of-the-art QD-LEDs exhibit external quantum efficiencies (EQEs) exceeding 20% at a constant voltage\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, and the operational lifetimes at a constant current density already meet the standards for display applications\u003csup\u003e\u003cspan additionalcitationids=\"CR18 CR19 CR20\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDespite significant advances in operational lifetime of OD-LEDs at constant voltage or current density, dynamic stability, which characterizes the stability of the device performance under varying driving voltage or current, is still considerably low in state-of-the-art QD-LEDs\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. For example, QD-LEDs with high EQE\u0026thinsp;\u0026asymp;\u0026thinsp;21.6% and long static operating lifetime (T\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;1,600,000 h at 100 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) still deteriorate fast under continuous voltage scans, where the EQE can drop by ~\u0026thinsp;35% after only 6 voltage scans.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Importantly, in real scenario of display devices, the QD-LEDs must withstand frequent luminescence modulation by varying the driving voltage to create different color and brightness, which requires excellent dynamic stability. Therefore, studying the dynamic stability during voltage cycles and understanding the origin of device degradation is critical to push QD-LEDs towards commercial applications.\u003c/p\u003e \u003cp\u003eHere, we identified that the degradation of EQE in typical QD-LEDs based on CdZnSe/ZnSe QDs primarily stems from electron leakage into the hole transport layer, which becomes more pronounced under continuous voltage scans. To address this issue, we propose a strategy to enhance the dynamic stability of QD-LEDs by introducing a ZnSeS/ZnS outer shell, where the ZnS layer improves electron confinement and the ZnSeS layer mitigates the lattice mismatch between ZnSe and ZnS. The modified QDs, with a structure of CdZnSe/ZnSe/ZnSeS/ZnS, have a high PLQY of 95%. The resulting QD-LEDs not only achieve a peak EQE exceeding 24%, but also show demonstrate excellent durability, with an EQE drop of less than 4% after 5,000 continuous voltage cycles from 0 to 4.5V. Furthermore, the devices also exhibit excellent static stability, maintaining 95% of its initial luminance (T\u003csub\u003e95\u003c/sub\u003e) at 1,000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for over 61,000 h.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePoor dynamic stability of QD-LEDs with high EQE\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA typical high performance QD-LED based on CdZnSe/ZnSe QDs, named ZnSe QD-LED in the following, is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. Owning to the high lattice match between the ZnSe shell and the CdSe core, the CdZnSe/ZnSe QDs exhibit a high PLQY of 88% with a photoluminescence (PL) peak at 639 nm and an average particle size of 15 nm. The detailed characterizations of QDs are shown in Supplementary Fig.\u0026nbsp;1. The ZnSe QD-LEDs are constructed by all-solution process with a structure of ITO/PEDOT:PSS/TFB/QDs/ZnMgO/Al. Since the ZnSe shell has a good match with the lowest unoccupied molecular orbital (LUMO) level of the HTL, it can significantly reduce the hole injection barrier and improve the EQE. As a result, the ZnSe QD-LED has a turn-on voltage of ~\u0026thinsp;1.6 V, a peak EQE of 22.9%, and a luminance of more than 60,000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at an operating voltage of 4.5 V. It also has a good static stability with T\u003csub\u003e95\u003c/sub\u003e exceeds 130 h at a constant current density of 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), corresponding to a luminance of greater than 8000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Based on the equation \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{L}_{0}^{n}{T}_{95}=constant\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e23\u003c/sup\u003e, the operating time of T\u003csub\u003e95\u003c/sub\u003e at lower luminance values are derived to be over 5,600 h at a luminance of 1,000 cd m\u003csup\u003e\u0026minus;2\u003c/sup\u003e and 319,500 h at a luminance of 100 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo explore the dynamic stability of ZnSe QD-LEDs, we monitored device characteristics including peak EQE, current density, and luminance for 35 continuous cycles under a voltage range of 0\u0026thinsp;\u0026minus;\u0026thinsp;4.5 V. The peak EQE rapidly dropped from 22.9\u0026ndash;9.5% after 35 voltage sweeps (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). As shown in the current density-voltage-luminance (\u003cem\u003eJ-V-L\u003c/em\u003e) curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed), the luminance decreased with increasing number of voltage scans, while the current density increased after 35 voltage scans, indicating growing proportion of non-radiative recombinations. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee shows the evolution of EQE\u003csub\u003emax\u003c/sub\u003e, current density (@4.5 V) and luminance (@ 4.5 V) normalized to their initial values at the first voltage scan. After 35 scans, the current density increases by 15%, the luminance decreases by 41%, and the EQE\u003csub\u003emax\u003c/sub\u003e dropped by 58%. To eliminate the degradation due to heat accumulation\u003csup\u003e\u003cspan additionalcitationids=\"CR25 CR26 CR27\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, we heated a fresh device at 50℃ for the same duration of 30 min as that for 35 voltage scans and found there was no obvious degradation after heating (Supplementary Fig.\u0026nbsp;2). Previous studies have shown that both QD charging and electron leakage into the HTL may cause rapid degradation of QD-LEDs\u003csup\u003e\u003cspan additionalcitationids=\"CR30 CR31 CR32\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The degradation caused by QD charging is reversible by extracting the extra charges, while the electron leakage into HTL results in degradation of the HTL and irreversible deterioration of device performance. After a two-hour recovery, the ZnSe QD-LED partially restored its EQE from 9.5\u0026ndash;16.2% and luminance from 39,350 to 51,000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;3), suggesting that both effects exist in ZnSe QD-LEDs, which agrees with the considerable increase of leakage current shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eThe origin of the degradation of ZnSe QD-LEDs under continuous voltage scans\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eTo gain insight into the degradation mechanisms, we conducted electrical and optical characterizations of the device before and after 35 voltage scans (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In typical QD-LEDs, the injection efficiency of holes is often lower than that of electrons due to the larger injection barrier and lower mobility of holes\u003csup\u003e\u003cspan additionalcitationids=\"CR35 CR36 CR37\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e, which results in excess electrons leakage into the HTL. Moreover, the electron confinement ability of QDs can also affect the extent of electron leakage into the HTL. The increased TFB emission after 35 voltage scans indicates that the electron leakage was intensified (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, Supplementary Fig.\u0026nbsp;4). Meanwhile, the EL peak position at 4.5 V was red-shifted by 2 nm, which can be attributed to the bandgap narrowing caused by the increased temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea inset).\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eWe monitored the voltage-capacitance curves of ZnSe QD-LEDs to probe the carrier accumulation in the device, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. In the fresh device, the two peaks near 1.6 V and 2.1 V correspond to the turn-on voltage and the peak EQE, respectively. Under negative bias, the HTL, QD layer, and ETL are depleted. The slowly increasing capacitance below 1.2 V can be attributed to the gradual filling of the QD layer and ETL. The rapidly increasing capacitance above 1.2 V is commonly attributed to the accumulation of holes at the HTL/QDs interface, and at 1.6 V, holes begin to inject into the QDs layer\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Under higher voltage, more holes are injected into the QDs layer and recombine with the electrons, and the capacitance decreases rapidly after reaching the peak EQE at 2.1 V. The peak packet near 1.6 V gradually evolves to a platform after multiple voltage scans, while the peak capacitance near 2.1 V continuously decreases. Meanwhile, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee shows that the current is increasing under continuous voltage scan, suggesting that more electrons are injected directly into the HLT rather than being involved in the radiative recombination in the QDs. Therefore, the peak packet near 1.6 V of ZnSe QD-LEDs is most likely due to the electron leakage and the degradation of HTL.\u003c/p\u003e \u003cp\u003eElectrically-excited transient absorption (EETA) spectroscopy clearly reflects the charge injection dynamics, the balance of charge density and the strength of the electric field distribution in QD-LEDs\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. Hence, the origin of device degradation can be revealed by comparing the EETA spectra of ZnSe QD-LEDs before and after 35 voltage scans (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Under reverse bias of -3 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec top panel), the Stark effect signal of the TFB HTL at 418 nm dropped by 8% after voltage scans, indicating significant degradation of the TFB layer. The absorption of QDs near 640 nm also dropped by 4%, which is accompanied by a prolonged average PL lifetime from 8.5 ns to 10.3 ns (Supplementary Fig.\u0026nbsp;5), indicating that the QDs are also degraded after continuous voltage scans. Under forward bias, the bleaching signal of the EETA spectrum is mainly contributed by the electrons, which is due to the much higher degeneracy of the valence band than that of the conduction band\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. The significantly increased bleaching signals of the EETA spectra between 550 nm and 680 nm after voltage scans demonstrates increased electron density in the QD-LEDs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec bottom panel), which deteriorates the electron-hole balance in the QDs layer and facilitates electron leakage into the HTL, causing parasitic luminescence and irreversible degradation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The degraded HTL layer generates hole traps and reduces hole transport efficiency, which ultimately reduces the EQE.\u003c/p\u003e \u003cp\u003eTherefore, there are primarily two strategies to improve the dynamic stability of QD-LEDs, i.e., using a more stable HTL material to block the electron leakage and enhance the hole injection, or tuning the structure of QDs to improve the electron confinement. Unfortunately, HTL materials that meet these requirements are not yet available. Hence, carefully designing the shell structure to adjust the band structures of QDs is an effective route. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, if the excess electrons can be confined within the QDs, the device degradation caused by electron leakage to the HTL will be greatly alleviated.\u003c/p\u003e\n\u003ch3\u003eImprove the dynamic stability of QD-LEDs by modulating the bandgap structure of the QDs\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eWe synthesized CdZnSe/ZnSe/ZnSeS/ZnS QDs to improve the dynamic stability of QD-LEDs. Compared to ZnSe, ZnS has a wider bandgap and can increase the stability of QDs as the outermost shell\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. To minimize the large lattice mismatch between ZnS and ZnSe, an alloyed gradient ZnSeS shell is inserted between the two, and the gradient-alloy core-shell QDs exhibited over 95% PLQY (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;6). The elemental distribution of QDs, with a diameter of 16 nm, was measured using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It showed that Cd was primarily concentrated in the core of each QD, while Zn was predominantly located in the shell (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;6). Additionally, elemental line scans of Cd, Zn, Se, and S revealed smoothly varying compositions, demonstrating the successful synthesis of the gradient-alloy shell (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Finally, the PL peak position of CdZnSe/ZnSe/ZnSeS/ZnS QDs (645 nm) was blue-shifted by 6 nm compared to the CdZnSe core (651 nm), which was less than the blue shift observed in CdZnSe/ZnSe QDs (12 nm at 639 nm). This indicates that the charge confinement in CdZnSe/ZnSe/ZnSeS/ZnS QDs is enhanced (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;6c).\u003c/p\u003e\n\u003ch3\u003eExcellent dynamic stability of ZnS-based QD-LEDs\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eQD-LEDs based on CdZnSe/ZnSe/ZnSeS/ZnS QDs, referred to as ZnS QD-LEDs hereafter, were fabricated using the same method as ZnSe QD-LEDs. A hybrid organic-inorganic structure was employed, and cross-sectional TEM images revealed the uniformity and homogeneity of each film layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). TEM images of both devices (Supplementary Fig.\u0026nbsp;7) showed similar thickness for each functional layer. The devices have pure and bright luminescence (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;8). The stable capacitance-voltage curves after 100 voltage scans indicated that no holes accumulated at the interface or been trapped by the defects (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). To further investigate whether the HTL and QDs layers are damaged under continuous voltage scans, we measured the time-dependent EETA spectra of ZnS QD-LEDs under \u0026minus;\u0026thinsp;3 V and +\u0026thinsp;3 V voltages (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). The Stark effect signal peaks of the HTL (TFB) and the bleaching signal peak of the emissive layer (ZnS QD) remained almost unchanged after 100 voltage scans. Specifically, the peak of TFB and the valley of ZnS QD both decreased by less than 1% after 30 min of voltage maintenance (equivalent to hundreds of voltage scans), which suggests that ZnS QDs with enhanced electron confinement can suppress the electron leakage and the degradation of the HTL layer.\u003c/p\u003e \u003cp\u003eFinally, we characterized the dynamic stability of the ZnS QD-LEDs by monitoring the device performance between the 1st and the 5000th voltage scans. The EL spectra of the devices only shifted by \u0026lt;\u0026thinsp;1 nm after 5000 voltage scans while exhibiting a saturated deep red color with Commission Internationale de l\u0026rsquo;Eclairage (CIE) chromaticity coordinates of (0.692, 0.293) (Supplementary Fig.\u0026nbsp;9). The leakage current below the turn-on voltage (~\u0026thinsp;1.6 V) gradually decreased due to the better confinement of electrons within the QDs (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The EQE only decreased from 24.5\u0026ndash;23.6% after 5000 voltage scans, demonstrating a substantial improvement in the dynamic stability of ZnS QD-LEDs (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef, g). Meanwhile, the CE\u003csub\u003emax\u003c/sub\u003e only dropped from 21 cd A\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 20.2 cd A\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and at a high voltage of 4.5 V, the EQE and current efficiency only slightly decreased by 0.4% (Supplementary Fig.\u0026nbsp;10).\u003c/p\u003e \u003cp\u003eTo understand the origin of the luminance decay, the current density and brightness at 4.5 V from each voltage scan were calculated (Supplementary Fig.\u0026nbsp;11). The C\u003csub\u003e95\u003c/sub\u003e (the cycle number after which the luminance decays to 95% of its initial value) was 200 cycles for the voltage range of 0\u0026thinsp;\u0026minus;\u0026thinsp;4.5 V. After 5000 voltage scans, the luminance and current densities decreased by 29% and 30%, respectively. The drop in luminance and current densities is significantly affected by the magnitude of the electric field, and lowering the voltage can greatly enhance the dynamic stability of QD-LEDs. Under a smaller voltage of 0\u0026thinsp;\u0026minus;\u0026thinsp;2.6 V, the maximum EQE only decreased by \u0026lt;\u0026thinsp;1% after 10,000 scan cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). Meanwhile, the luminance/current density declines are reduced to 24% and 23%, respectively (Supplementary Fig.\u0026nbsp;11), and the C\u003csub\u003e95\u003c/sub\u003e is more than 4,000 (the \u003cem\u003eJ-V-L\u003c/em\u003e curves and V-EQE are shown in the Supplementary Fig.\u0026nbsp;12). At the same time, the operational lifetime of the ZnS QD-LEDs matches that of the state-of-the-art red LEDs\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. At an initial luminance of 10,039 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the T\u003csub\u003e95\u003c/sub\u003e was measured as 1,056 h (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh), which is equivalent to a T\u003csub\u003e95\u003c/sub\u003e of 61,180 h at an initial luminance of 1,000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn summary, we investigated the origins of poor dynamic stability of high-efficiency red QD-LEDs by monitoring their performance under continuous voltage scans. Our findings reveal that charge confinement whthin the QD emissive layer plays a crucial role in the dynamic stability of QD-LEDs. Insufficient electron confinement leads to electron leakage, causing parasitic emission from the HTL, which degrades the HTL and generates hole traps. Moreover, poor electron confinement in the QDs increases non-radiative recombination rates due to QD charging. To address these issues, we enhance the dynamic stability of QD-LEDs by optimizing the shell structure to improve electron confinement. The CdZnSe/CdZnSe/ZnSe/ZnS QDs with a gradient-alloy shell demonstrate high PLQY and excellent electron confinement. As a result, the QD-LEDs based on these QDs show less than 5% drop in EQE after more than 5,000 voltage scan cycles in the voltage range of 0\u0026thinsp;\u0026minus;\u0026thinsp;4.5 V. In addition, the dynamic stability extends beyond 10,000 cycles when the voltage scan range is reduced to 0\u0026thinsp;\u0026minus;\u0026thinsp;2.6 V\u0026mdash;setting a new benchmark for QD-LED dynamic stability. These findings represent a step toward the development of QD-LEDs with both high efficiency and long-term stability, advancing their potential for use in high-performance display applications.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eCadmium oxide (CdO, 99.99%, powder), zinc oxide (ZnO, 99.9%, powder), sulfur (S, 99.998%, powder), 1-octanethiol (OT, 98%), oleic acid (OA, 90%), trioctylphosphine (TOP,97%), 1-octadecene (ODE, 90%), zinc acetate (Zn(OA)\u003csub\u003e2\u003c/sub\u003e, 99.99%), tetramethylammonium hydroxide (TMAH, 98%), dimethyl sulfoxide (DMSO, HLPC grade), chlorobenzene (99%), magnesium acetate tetrahydrate (Mg(OAc)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO, 99.98%), zinc(II) acetate dihydrate (Zn(OAc)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO, 99.99%), n-Octane (99%) and ethanol (99.8%) were purchased from Aldrich. Paraffin oil (analytical grade), hexanes (analytical grade), acetone (analytical grade), isopropanol (analytical grade), and methanol (analytical grade) were obtained from Beijing Chemical Reagent Co. Ltd, China. Poly (ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) was purchased from Heraeus Deutschland. Poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4\u0026rsquo;-(N-(p-butylphenyl)) diphenylamine)] (TFB, average molecular weight, ~\u0026thinsp;67,000 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was purchased from American Dye Source, Inc. All materials were used as received.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePreparation of precursors\u003c/h3\u003e\n\u003cp\u003eZinc Precursor: ZnO (60 mmol), OA (60 mL) and ODE (90 ml) were filled into a 250 ml three-necked flask, which was heated and exhausted at 150\u0026deg;C for 15 minutes. Then, the solution was heated to 310\u0026deg;C under nitrogen with stirring to obtain a clear colorless solution.\u003c/p\u003e \u003cp\u003eSelenium precursor: Selenium (20 mmol) and TOP (40 ml) were mixed in a 100 ml three-necked flask, which was heated and exhausted at 150\u0026deg;C to obtain a clear solution.\u003c/p\u003e \u003cp\u003eSelenium-sulfur precursor: Selenium powder (2.5 mmol), sulfur powder (2.5 mmol) and TOP (10 ml) were mixed and stirred to form a clear solution.\u003c/p\u003e\n\u003ch3\u003eSynthesis of CdZnSe/ZnSe quantum-dots\u003c/h3\u003e\n\u003cp\u003eThe synthesis of CdZnSe/ZnSe QDs was modified from previous reports\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Zn(OAc)\u003csub\u003e2\u003c/sub\u003e (1.5 mmol), CdO (1.5 mmol), ODE (20 ml) and OA (10 ml) were loaded into a three-necked flask and evacuated at 120\u0026deg;C for 10 min, followed by heating under N\u003csub\u003e2\u003c/sub\u003e flow to 310\u0026deg;C. Subsequently, 5 mL of selenium precursor was rapidly injected, and the temperature was maintained for 30 min to grow the CdZnSe cores. To grow the ZnSe shell, the temperature was decreased to 270\u0026deg;C, and 5 ml of zinc precursor was added dropwise for 10 min followed by adding 3 ml of selenium precursor for 20 min.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of CdZnSe/ZnSe/ZnSeS/ZnS quantum-dots\u003c/h2\u003e \u003cp\u003eFirst, CdZnSe/ZnSe QDs were synthesized using the same method as described above, except that the thickness of the ZnSe shell is reduced. The ZnSeS shell was grown by dropwise addition of 5 ml of zinc precursor for 10 min, followed by dropwise addition of 3 ml of selenium precursor for 20 min. To grow the ZnS shell, 5 ml of Zn(OA)\u003csub\u003e2\u003c/sub\u003e and octanethiol (2.8 mmol, equivalent to 1.4 mmol Zn(OA)\u003csub\u003e2\u003c/sub\u003e) were added dropwise into the solution. Once the reaction was completed, the system was cooled down to room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and purification of ZnMgO nanoparticles\u003c/h2\u003e \u003cp\u003eZnMgO nanoparticles were synthesized by slightly modifying the method reported previously\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. For a typical synthesis, Zn(OAc)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO (2.7 mmol) and Mg(OAc)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO (0.3 mmol) were dissolved in DMSO (30 mL), TMAH (5 mmol) in ethanol (10 mL), and the two solutions were mixed and stirred for 1 h in air. Finally, the mixed solution was washed and the precipitated Zn\u003csub\u003e0.90\u003c/sub\u003eMg\u003csub\u003e0.10\u003c/sub\u003eO nanoparticles were dispersed in ethanol at a concentration of 25 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for spare use.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of quantum-dot light-emitting diodes\u003c/h2\u003e \u003cp\u003eAll devices were fabricated on glass substrates with indium tin oxide (ITO) patterns. Substrates were ultrasonically cleaned with detergent, deionized water, acetone and isopropanol for 15 min, respectively, followed by treatment under UV ozone for 15 min. PEDOT:PSS (in water, Al 4083) was spin-coated onto ITO substrates at 5500 rpm. and baked at 140\u0026deg;C for 15 minutes in air. The substrates were transferred into a N\u003csub\u003e2\u003c/sub\u003e-filled glove box for the layer-by-layer deposition of TFB (in chlorobenzene, 8 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), QDs (in octane, 25 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and ZnMgO (in ethanol, 30 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) by spin-coating at 3000 rpm, 3000 rpm and 2000 rpm, respectively, for 30 s. The substrates were baked at 150 ℃ and 60 ℃ for 30 min after deposition of the TFB and ZnMgO layers, respectively. Next, the silver anode was deposited via thermal evaporation at a rate of \u0026asymp;\u0026thinsp;0.1 nm s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under a vacuum of 4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e Torr. The device area defined by the overlapping of the ITO and silver electrodes is 4 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Finally, the devices were encapsulated by bonding the glass cover sheet to the devices using a UV curable resin.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization and instrumentation\u003c/h2\u003e \u003cp\u003eUV-vis absorption and PL spectra were measured by an Ocean Optics spectrophotometer (model PC2000-ISA). Transmission electron microscopy (TEM) studies were performed using a JEOL JEM-2010 electron microscope operating at 200 kV. The energy-dispersive spectroscopy (EDS) mappings were carried out by four symmetrically designed EDS detectors on an FEI Talos F200X. The cross-section images of the QD-LEDs were collected with an FEI Talos F200X. The J-V characteristics of the QD-LEDs were analyzed using an Agilent 4155C semiconductor parameter analyzer with a calibrated Newport silicon diode under ambient conditions. The luminance was calibrated using a Photo Research spectroradiometer (PR735). The electroluminescence (EL) spectra were obtained with an Ocean Optics spectrometer (USB2000, relative irradiance mode) and a Keithley 2400 source meter. Capacitance-voltage measurements were carried out using an Agilent 4282A precision LCR meter with a modulating frequency of 10 KHz. The thermal images of the samples were acquired using a Fluke Ti401 PRO camera.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eElectrical excitation transient absorption measurement\u003c/h2\u003e \u003cp\u003eElectrical pulses (1 kHz, 10 us) were applied to the QD-LEDs by a Keysight 33512B waveform generator. The probe and reference beams were obtained from white laser pulses generated by a supercontinuum white laser (Leukos, Disco). An electrical pulse in device sent the probe beam to the excitation area, then was collected to the monochromator and charge-coupled device by an electronic time-delay module. The signal was collected by the difference between the probe intensity without and with the pump electrical pulse.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eH. L. and H. S. conceived the idea and directed the project. X. L. fabricated and collected the performance data of the QD-LEDs. Y.G. synthesized QDs. B.L. performed EETA experiments. Y. Y. assisted the device characterizations. X. L., Y.G., B.L. and Z. W. conducted data analysis with help from J. W. and F. L. X. L. and H. L. wrote the manuscript with inputs from all authors. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe gratefully acknowledge the financial support from the National Natural Science Foundation of China (grant numbers 61922028, 61874039, 22179009, U22A2072).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEkimov AI. Quantum size effect in three-dimensional microscopic semiconductor crystals. \u003cem\u003eJETP Lett.\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 345 (1981).\u003c/li\u003e\n\u003cli\u003eBrus LE. A simple model for the ionization potential, electron affinity, and aqueous redox potentials of small semiconductor crystallites. \u003cem\u003eThe Journal of chemical physics\u003c/em\u003e \u003cstrong\u003e79\u003c/strong\u003e, 5566-5571 (1983).\u003c/li\u003e\n\u003cli\u003eColvin VL, Schlamp MC, Alivisatos AP. 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Although the operational lifetime of QD-LEDs under static conditions has reached commercial standard, their dynamic stability, i.e., performance consistency while being switched on and off, remains largely behind that of state-of-the-art III-V LEDs. In this work, we studied the degradation mechanism of red QD-LEDs with high external quantum efficiency (EQE) and long static operational lifetime and found that the accelerated EQE decline is mainly due to the fast-increasing electron leakage into the organic hole transport layer (HTL) under continuous voltage scans. To improve the dynamic stability of QD-LEDs, we refined the structure of CdZnSe/ZnSe QDs by introducing a ZnSeS/ZnS outer shell, where the ZnS shell improves the electron confinement and the ZnSeS mitigates the lattice mismatch between ZnSe and ZnS. Consequently, the electron leakage into the HTL is significantly inhibited, leading to QD-LEDs with minimal EQE drop of less than 4% after more than 5,000 voltage cycles within the range between 0 V and 4.5 V, while the devices still possess excellent static stability for maintaining 95% of its initial luminance (T\u003csub\u003e95\u003c/sub\u003e) at 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e for over 61,000 h.\u003c/p\u003e","manuscriptTitle":"Dynamic stability of high-efficiency quantum dot light-emitting diodes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-13 06:40:29","doi":"10.21203/rs.3.rs-5370454/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":"53121297-d973-47ec-94c5-a8a4b85fb29a","owner":[],"postedDate":"November 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":40151476,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Quantum dots"},{"id":40151477,"name":"Physical sciences/Materials science/Materials for optics/Lasers, LEDs and light sources/Inorganic LEDs"},{"id":40151478,"name":"Physical sciences/Materials science/Nanoscale materials/Quantum dots"}],"tags":[],"updatedAt":"2024-11-27T14:45:28+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-13 06:40:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5370454","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5370454","identity":"rs-5370454","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}