Study On Light-emitting Diodes Based On MAPbBr₃ Nanocrystalline Film

Organic-inorganic hybrid perovskite has become the potential candidate for high performance light-emitting diodes(LED)due to its high carrier mobility,high photoluminescence quantum yield(PLQY),adjustable band gap and narrow emission width.However,the rough surface morphology of perovskite films greatly increases the defect density,and the low exciton binding energy increases the probability of exciton dissociation,resulting in a serious decline in luminescent efficiency.In order to obtain high performance perovskite light-emitting diodes(Pe LED),it is necessary to improve the morphology of perovskite films and enhance the exciton binding energy.In this thesis,the effects of excess MA ion and Cs ion doping on the morphology MAPb Br₃films and device photoelectric properties of the LED based on MAPb Br₃ were studied.By adding long-chain ligands,perovskite nanocrystalline thin films were prepared in situ,which significantly enhanced PLQY of MAPb Br₃ films and current efficiency of Pe LED based on MAPb Br₃.Our research work are focused on following three aspects:(1)By changing the molar ratio of MABr to Pb Br₂ in the precursor solution,the effect of nonstoichiometry in the precursor solution on the photoelectric properties of perovskite films was studied.Excessive MABr can effectively reduce the grain size and weaken nonradiative recombination in the films,thus enhancing the PL lifetime.Compared with the basic device,Pe LED based on MABr:Pb Br₂(2:1)shows more excellent performance,whose current efficiency is increased by more than 30 times,and turn-on voltage is reduced to 3.3 V from 4.6 V.(2)Cs Br was introduced in the precursor solution of MAPb Br₃ with excess MABr to form double cation perovskite.The PL lifetime increased to 10.79 ns from 4.65 ns,when the Cs Br/MABr ratio rise from 0:2 to 0.8:2,which indicates that the defects in the films can be further reduced by adding appropriate amount of Cs.The maximum brightness and current efficiency of the device based on double cation perovskite are25701 cd m^-2 and 6.4 cd A^-1,respectively.(3)Phenylpropylammonium bromide(PPABr)was added to the precursor solution to prepare MAPb Br₃ nanocrystalline films by one-step spin coating method.The morphology and optical properties of perovskite films can be improved by adding optimum amount of PPABr.The surface of optimized MAPb Br₃ nanocrystalline films is smooth and pinhole-free.The results of PL lifetime,light-intensity-dependent PLQY and temperature-dependent PL spectra measurements show that the defects of the film are effectively passivated and the exciton recombination is fully utilized,resulting in 61%PLQY.The maximum brightness and current efficiency of the device based on MAPb Br₃nanocrystalline film are 31821 cd m^-2 and 48.4 cd A^-1,respectively.