Performance Optimization Of CsPbBr₃ Perovskite Light-emitting Diodes And Regulation Of Electron Transport Layer

Perovskite materials have excellent characteristics,so it has a very good application prospect in the field of photoelectric devices.Especially in perovskite light-emitting diodes,the external quantum efficiency has been rapidly improved from below 0.1%at the beginning to more than 20%at present in just a few years.However,the instability of perovskite materials hinders its commercial applications.In this thesis,all inorganic perovskite CsPbBr₃ is used as the research object,and the perovskite thin film is prepared by one-step method.The preparation process of the perovskite film is optimized,and the performance of the device is improved by optimizing the conditions such as the hole transport layer,additives and electron transport layer.The main research work of the thesis is as follows:(1)First of all,by PSS-Na doping in PEDOT:PSS improves the work function of the hole transport layer PEDOT:PSS effectively,reduces the energy barrier between the emission layer,and helps the holes injection into the emission layer to playing a role in balancing carrier.The maximum luminance of the device is increased from 1915 cd m^-2to 13603 cd m^-2,and the maximum current efficiency is increased from 0.11 cd A^-1 to 1.01cd A^-1.Secondly,the controlled variable method is optimized in the preparation process of perovskite film.When the concentration of CsPbBr₃ precursor solution is 70 mg mL^-1,and the spin-coating speed is 1500 rpm,the luminance and efficiency of perovskite light-emitting diodes are the best.Finally,by preparing perovskite light-emitting diodes with different additives,it was found that the coverage of the perovskite film with 3 wt%mPEG is increased to 67.32%,the perovskite grains size is decreased,the diffraction peaks are obviously enhanced,and the film crystallinity is better.As a consequence,the luminance and current efficiency of the device are improved.The coverage of the perovskite film with 2 wt%MACl is increased to 77.20%,and the leakage current of the device is reduced,so that the luminance and current efficiency of the device are improved.However,the coverage of the perovskite film with excessive MACl is reduced to 72.42%and the performance of the device is reduced.By adding mPEG and MACl as the synergistic additives to the device,the coverage of the perovskite film is increased to69.48%,the perovskite grain becomes smaller,the diffraction peaks are significantly enhanced,and the film crystallinity is the best.Therefore,the luminance and current density of the device are optimized.(2)The devices with different electron transport layers of Bphen,TPBi and TmPyPB are prepared by solution method and vacuum evaporation method,respectively.And the reasons for the differences in performance among the devices were analyzed.Among the perovskite light-emitting diodes with the solution-processed electron transport layer,the device with Bphen as the electron transport layer has the best performance.The turn-on voltage of the device is 2.6 V,the maximum luminance is 9641cd m^-2,and the maximum current efficiency is 1.32 cd A^-1.Because Bphen has a relatively high electron mobility that matches PEDOT:PSS,and no electron injection barrier.While the electron mobility of TPBi is low,and the electron injection needs to overcome the energy barrier,so the luminance and current efficiency of TPBi device are relatively low.The electron mobility of TmPyPB does not match the hole mobility of PEDOT:PSS,and the electron injection needs to overcome the energy barrier,so the luminance and current efficiency of TmPyPB device are very small.Vacuum evaporation and solution method have similar performance relationships among devices with different electron transport layers.Combining the turn-on voltage,luminance and current efficiency,the solution-processed Bphen electron transport layer is more suitable for our devices.Therefore,we have further optimized the concentration and the spin-coating speed of Bphen.The experimental results show the best concentration of Bphen is 10 mg mL^-1,and the best spin-coating speed is 2000 rpm.