Stability Of Cesium Lead Halide Perovskite Quantum Dots And Electroluminescent Light-emitting Diodes

Cesium lead halide perovskite quantum dots(CsPbX₃,X=Cl,Br,I)have many advantages such as wider gamut,high photoluminescence quantum yield(PL QY),narrow fluorescence spectral linewidth,high carrier mobility and good mechanical properties,so they have good application prospects in rigid and flexible display and illumination fields.However,the poor water and oxygen stability prevents the commercialization of perovskite quantum dots,and the limited flexibility of perovskite layers limits their applications in flexible optoelectronic devices.At present,there are few reports on improving the optoelectronic performance and flexibility of perovskite optoelectronic devices by optimizing the perovskite materials.In this paper,the main objective is to enhance the luminescence performance and stability of CsPbI₃ quantum dot materials,as well as the optoelectronic performance and flexibility of the corresponding electroluminescent light-emitting diode(LED).The surface defects of perovskite quantum dots were passivated by adding ethyl cellulose(EC),a low-cost and environmentally friendly biomass material,into cesium lead halide perovskite quantum dots solution,and satisfactory results were obtained.(1)We synthesized CsPbI₃ perovskite quantum dots by thermal injection method,and added different concentrations of ethyl cellulose(EC)toluene solution into the quantum dot solution after centrifugation.By comparing the photoluminescence(PL)spectral intensity of the perovskite materials before and after adding EC,the optimal concentration of CsPbI₃ passivation by EC is determined.The PL QY of Cs Pb I₃increases from 63%to 87%at the optimal concentration.In order to investigate the effect of EC on the stability of perovskite,the PL spectra and X-ray diffraction patterns(XRD)of Cs Pb I₃ perovskite quantum dots with time were monitored before and after treatment.The CsPbI₃ perovskite quantum dot films treated by EC maintained phase stability for 35 days when placed in an environment with air humidity of 45%.The improvement of the luminescence performance and stability of perovskite quantum dots is attributed to the passivation of Pb²⁺defects on the surface of perovskite quantum dots by EC.(2)We prepared rigid and flexible LEDs using EC passivated CsPbI₃ perovskite quantum dots,explored the ethyl cellulose effect on the optoelectronic properties of rigid LEDs by using glass/ITO/ZnO/PEI/CsPbI₃/TCTA/MoO₃/Ag device structure,and explored the ethyl cellulose effect on the optoelectronic properties and flexibility of flexible LEDs by the NOA 63/Ag/Zn O/PEI/Cs Pb I₃/TCTA/Mo O₃/Au device structure.The results show that EC passivates the defects on the surface of perovskite quantum dots,thus reducing the non-radiative recombination of perovskite layers,and achieving efficient and balanced charge transfer and recombination of LEDs.In addition,the addition of EC improves the deformation resistance of the perovskite layer and realizes a highly flexible LED.The rigid LED achieved 9.6%External Quantum Efficiency(EQE)and a maximum brightness of 1049 cd/m²,while the flexible LED achieved 8.5%EQE and a maximum brightness of 821 cd/m².The brightness of this flexible LED remained 73%of the initial value after 1000 bends under a 3mm radius of curvature.