Modification Of Hole Transport Layer Materialand Its Application In Perovskite Light-emitting Diodes

Metal halide perovskite materials show excellent application prospects in the field of perovskite light-emitting diode（Pe LED）due to their advantages of good conductivity,high color purity,adjustable band gap,low cost and solution machinability.Commonly used hole transport layer material poly（3,4-ethylene dioxythiophene）:poly（styrene sulfonic acid）（PEDOT:PSS）contains benzene sulfonic acid,which is acidic and sensitive to humidity,and after the application of voltage,benzene sulfonic acid protons will diffuse to the perovskite layer,destroy perovskite luminescent materials.In this paper,the optical properties,film morphology and effects of modified PEDOT:PSS on the efficiency and stability of light-emitting diode（LED）devices were investigated.This thesis aims to prepare high performance quasi-two-dimensional green Pe LED.Firstly,the composition ratio of perovskite precursor and the film forming conditions were optimized.Long chain molecules were introduced into the precursor to reduce the grain size of perovskite and reduce the dimension of perovskite.Passivating agent was added into the antisolvent to effectively passivate the defects in the film,and a series of film forming conditions such as annealing temperature and annealing time were optimized.Secondly,a simple solvent post-treatment method is used to modify the PEDOT:PSS film and optimize the interface between PEDOT:PSS film and perovskite layer,so that the efficiency and stability of perovskite light-emitting diode devices can be improved synchronously.Finally,PEDOT:PSS was taken as the research object,and the influence of alkyl amine chain length on the performance of PEDOT:PSS and its perovskite LED was studied by doping different alkyl amine chain lengths to modify PEDOT:PSS.The main research contents of this paper are as follows:（1）In this chapter,the composition ratio of perovskite precursor and film forming conditions were optimized.By optimizing the component ratio of perovskite precursor,the type of long chain organic cations,the type of antisolvent,the type of passivating agent,the drop time of antisolvent,PEDOT:PSS,and the annealing temperature and annealing time of perovskite films.The device optimization results showed that the molar ratio of each component of perovskite precursor was Pb Br:Cs Br:FABr:PEABr=10:8:2:4,the antisolvent was chloroform,in which the concentration of passivating agent triphenylphosphine oxide（TPPO）was 0.0359M,the antisolvent drip time was38s,and the rotational speed of perovskite film was 5000 rpm.the annealing time and temperature of PEDOT:PSS and perovskite films were optimized to 150℃+5min and80℃+5min,respectively.（2）In this chapter,based on the optimization of perovskite precursor components and film forming conditions,a simple solvent post-treatment method was used to optimize the interface between PEDOT:PSS film and perovskite layer.The electroluminescence peak（EL）of the prepared LED device was about 517 nm when different chain lengths of alkyl amines were directly coated on the surface of PEDOT:PSS film.Under the initial brightness of 100 cd m^-2,the half-lifetime of the device after heptamine treatment increased from 1.9h of the original to 6.95h.Further attempts were made to use other solvents to improve the device performance.The EQE was increased from 4.4%to 5.2%after PEDOT:PSS was treated with deionized water,and the half-lifetime was increased to 6.58h at the initial brightness of 100 cd m^-2.Deionized water was used to post-process PEDOT:PSS,which increased the half-lifetime of the device while improving the device EQE.More importantly,the device treated with deionized water has excellent color stability,and the corresponding shape and position of the EL spectrum do not change.（3）In this chapter,we modified PEDOT:PSS by doping alkyl amines with different chain lengths,studied the influence of alkyl amine chain length on the physicochemical properties of PEDOT:PSS,and used the modified alkyl amine PEDOT:PSS as the hole transport layer.The effect of modified PEDOT:PSS on the photoelectric performance and stability of Pe LED was investigated.The maximum external quantum efficiency（EQE）of 11%and the current efficiency of 36.2 cd A^-1of the pentylamine modified devices are obtained,which is 1.35 times higher than that of the control devices.Then,the brightness and working stability of Pe LED increased as the alkyl amine chain length increased.The Pe LED of heptamine modified with a high brightness of 65062 cd m^-2was prepared.Under the condition of initial brightness of100 cd m^-2,the life of the heptamine modified device was as high as 36.4h,while that of the control device was only 5.1h.