Preparation And Electroluminescent Device Performance Study Of Formamidinium Lead Bromine Perovskite Nanocrystals

In the past three years,formamidinium leadbromine（FAPbBr₃）perovskite nanocrystals（NCs）materials has attracted considerable attention,due to the advantages of adjustable photoluminescence spectra,high color purity,high photoluminescence quantum yield（PLQY）,low cost and can be used in the field of light-emitting diodes（LEDs）.They have been widely studied by researchers and become one of the strong competitors in the field of high-efficiency perovskite luminescence materials in the future.With the efforts of researchers,the synthesis of FAPbBr₃ NCs and the preparation of its LEDs have made certain progress.However,compared with other perovskite materials and LED devices,there are fewer studies on FAPbBr₃ NCs and its devices are inefficient.Therefore,FAPbBr₃NCs is the focus of this thesis,the synthesis method of preparing FAPbBr₃ NCs and the PLQY were improved.Futhermore,the the luminous efficiency of LED devices based on FAPbBr₃ NCs was improved through optimizing device strcture.The details are as follows:（1）Monodisperse FAPbBr₃ NCs with high PLQY were synthesized by hot-injection method.The NCs are used as the emitting layer to fabricate LEDs.By optimizing the thickness of the perovskite layer,the recombination region of excitons in the LED device is regulated,resulting the parasitic emission in the device is disappeard and the luminescent efficiency is improved.Finally,high-purity green LED with external quantum efficiency,current efficiency,and maximum power efficiency of 3.8%,16.08 cd/A,and 12.95 lm/W,respectively,and the CIE coordinate of（0.183,0.763）was obtained.（2）The FAPbBr₃ NCs were synthesized by using simple ligand-assisted precipitate method at room temperature,in which octylamine,an amine ligand with shorter carbon chain length,was selected to replace oleamine.By regulating the molar ratio of FABr and PbBr₂ in the precursor solution,the bromine-rich environment on the surface of NCs was constructed to realize the self-passivation of defects,resulting high quality FAPbBr₃ NCs was synthesized.Through a series of test characterization,we found that excessive FABr can make the defects on the surface of NCs be adequately passivated,and improving the PLQY of NCs.（3）The influence of defect passivation on device performance was studied,and it was found that the FAPbBr₃ NCs and its devices effect of excessive FABr is twofold.On the one hand,the surface ligand density of self-passivation NCs was decreased which resulte carrier injection and transport capacity was promoted.On the other hand,the change of FABr addition has certain regulatory effect on the energy level of FAPbBr₃ NCs.The synergistic effect between them can improve the injection and transport capacity of carriers in the LED devices,thus greatly improving the efficiency of the devices.Consequently,the devices prepared with the optimal ratio（FABr:PbBr₂=2.2:1）of FAPbBr₃ NCs solution achieve the external quantum efficiency,current efficiency,and power efficiency of 17.1%,76.8 cd/A,and 55.4 lm/W,respectively.