Studies On The Defect Passivation Of Wide-bandgap Mixed Halide Perovskites And Their Related Perovskite Solar Cells

Wide-bandgap mixed halide perovskite solar cells are key components in perovskite-silicon tandem cells.Scientific issues such as open-circuit voltage loss,ion migration,and light-induced phase separation in mixed halogen wide-bandgap perovskite cells restrict the application of wide-bandgap cells.In this study,interfacial engineering and additive engineering strategies were used to improve the power conversion efficiency of wide-bandgap perovskite cells and phase stability of thin films phase under illumination.The research contents and related results are as follows:（1）Using a two-step continuous deposition method,combined with the control of the lead halide salt composition,a mixed-halogen wide-bandgap perovskite CH₃NH₃Pb(Br_0.27I_0.73)₃ active layer with a band gap of1.70 e V was obtained.The power conversion efficiency of the corresponding cells reaches 15.24%.Gas treatment of perovskite films with 3-（Aminomethyl）pyridine increased the power conversion efficiency from 15.12%to 16.36%and reducing the open-circuit voltage loss.（2）The effect of additive doping based on alkali metal halides on the performance of wide-bandgap cells and the phase stability of the films under illumination was investigated.It was found that the effect of potassium iodide was superior than cesium iodide.Potassium iodide significantly improved cell efficiency from 15.30%to 17.53%;reduced open-circuit voltage loss and increased carrier lifetime.The mechanism of efficiency improvement can be attributed to the passivation of iodine vacancies in the grain boundaries.（3）The effect of surface treatment of three halogen-containing orga-nic compounds（such as Iodopentafluorobenzene and Bromopentafluorob-enzene）on the efficiency of wide-bandgap perovskite cells was investigated.Three kinds of halogen-containing organic compounds were studied.Studies have shown that passivation of the perovskite surface with halogen-containing organic compounds can improve the power conversion efficiency of the cells,which is increased from 15.30%to 17.52%.The mechanism of the efficiency improvement can be attributed to the decreasing of iodine vacancy defects on the film surface by the passivator.（4）The phenomenon of phase separation in mixed halide perovskites is analyzed.Studies have shown that density of iodide ion vacancies can be reduced and ion movement can be alleviated by interfacial engineering and additive engineering strategies,but the light-induced phase separation phenomenon cannot be directly and effectively suppressed.Although the internal formation mechanism of the phase separation phenomenon is still inconclusive,the results of this study show that the phase separation phenomenon can be constituted by two different processes,and the influence of the bulk phase and surface iodine vacancies on the formation of the phase separation effect is preliminarily discussed.This study provides an effective strategy for the preparation of high-efficiency mixed halide wide-bandgap perovskite cells,deepens the understanding of phase separation behavior through experiments,and provides a reference for the development of efficient and stable wide-bandgap mixed halide perovskite active layers.