Stability Of CsPbI₃ Quantum Dots Light-Emitting Diodes

Today’s world is in the information age of rapid development,and the development of information technology is changing with each passing day.Display technology as an important carrier of information is inseparable with the development of science and technology and human.At the same time,because of the proposition of the REC.2020 display standard,higher requirements have been put forward for the development of display technology.Perovskite quantum dots have a lot of excellent photoelectronic properties,such as ultra-high photoluminescence quantum yield（PLQY）,narrow half-peak width,tunable emission wavelength,high carrier mobility,high color purity,and simple solution synthesis method,showing broad application prospects,Therefore,the perovskite quantum dots are considered to be excellent candidate materials for the next generation light-emitting diodes（LED）.CsPbI₃ quantum dots with red emission are an important part of perovskite quantum dots.Although good progress has been made in PLQY and external quantum efficiency（EQE）,the stabilities of red light-emitting perovskite quantum dot and corresponding LEDs still need to be improved.Because CsPbI₃ quantum dots are easy to phase change from cubic structure to orthogonal structure,and the bond energy between the inorganic surface and the covered long-chain ligands is weak.The ligands are easy to dissociation in the process of purification and separation,thus resulting in the aggregation and growth of quantum dots into large particles,which reduces the stability of the material and PLQYs,and further affects the photoelectronic performance and operational stability of the device.In order to solve the above problems,relevant experimental studies were carried out to improve the stability of CsPbI₃ quantum dot and corresponding LED,and certain research results were obtained.（1）1H-Benzimidazole-2-sulfonic Acid（BS）was added into the synthesis process of CsPbI₃ quantum dots to study the optical properties,crystal structure,morphological characteristics and stability of CsPbI₃ quantum dots before and after BS passivation,and the mechanism of BS passivation was analyzed.Since the SO₃^-functional group in BS can interact with uncoordinated Pb²⁺ions on the surface of quantum dots to form coordination bond,and passivate the surface defects of CsPbI₃ quantum dots.Therefore,the fluorescence lifetime of CsPbI₃ quantum dots was extended,and the PLQY of the material was increased from 63%to 89%.In addition,the benzimidazole group in BS has certain hydrophobicity,which can improve the surface hydrophobicity of the quantum dots.Furthermore,the phase stability of CsPbI₃ quantum dot film was increased from 14 days to 45 days when the air humidity is 45%.（2）The CsPbI₃ quantum dots before and after BS passivation were used as the emission layer to prepare the LED with the device structure of glass/ITO/Zn O/PEI/CsPbI₃/TCTA/Mo O₃/Ag,and the influences of BS passivation on the photoelectronic performance and stability of LED devices were explored.Compared with the original CsPbI₃ quantum dot LED,the device performance of BS-passivated CsPbI₃ quantum dot LED was significantly improved.The maximum luminance and EQE of the device were increased from 1186 cd m^-2and 6.6%to 2063cd m^-2and 12.7%,respectively,and the T₅₀was increased from 29 minutes to 6 hours.In addition,the BS passivated CsPbI₃ quantum dot LED still retained 63%of its initial luminance after 40 times of repeated lighting,and the EL intensity of the device did not change significantly after 25 days of storage in the glove box.