Impact Of CH₃ On The Formation Of Organic-inorganic Perovskite Thin Films

Organic-inorganic perovskite material CH3NH3PbX3(X=I,Br,Cl)has become one of the popular candidate materials for photovoltaic devices such as solar cells and lightemitting diodes due to its superior performance.Although organic-inorganic perovskite materials show excellent performance in various photoelectric parameters,the chemical stability of organic-inorganic perovskite is poor under environmental conditions,such as humidity,heat,oxygen,light and interface defects,which seriously affects the development of photoelectric devices.In order to improve the stability of organicinorganic perovskite materials,cationic engineering,ligand engineering and ion migration inhibition methods have been proposed.Therefore,only by mastering the essential reasons of poor stability of organic-inorganic perovskite devices,can researchers prepare more superior performance of organic-inorganic hybrid perovskite photoelectric devices,laying a theoretical foundation for practical application.At present,the corresponding research work only focuses on the improvement of stability,but neglects the exploration of its essential cause.This paper conducted a comparative experiment on two organic-inorganic perovskite films based on different halogens with different(CH3)3PbX doping concentrations to study the stability of CH3NH3+site during the formation of organic-inorganic perovskite lattice by CH3+,and analyzed its chemical environment and preferred binding site during the formation of crystal structure.(CH3)3PbX was introduced into organic-inorganic perovskite to observe whether the small molecule CH3 replaces larger CH3NH3.This experiment is to compare the C1s core levels as measured by X-ray photoelectron spectroscopy(XPS)of(CH3)3PbX with that of CH3NH3PbX3 and CH3NH3X,and observe the arrangement of C species.In such a way,the binding locations of CH3 species in the perovskite lattice can be determined:binding to halides(X=Br or Cl),or binding to Pb.This thesis explores the changes of crystallinity,morphology,optical properties and CH3 key position of bromo-based and chlorine-based perovskite films by doping with(CH3)3PbBr and(CH3)3PbCl,respectively.In the second chapter,organic-inorganic perovskite films with different halogens show completely different effects by(CH3)3PbX doping.X-ray diffraction(XRD)is used to analyze the influence of CH3+on crystallinity of these two kinds of perovskite and their doped compound films.In terms of morphology,the grain growth was observed by scanning electron microscopy(SEM).Its optical properties were studied by photoluminescence(PL)spectrometer and UV-vis absorption measurements.In chapter 3,surface modification of CH3NH3PbBr3 was carried out in nitrogen environment with different doping concentrations of(CH3)3PbX.XPS aims to narrow the preferred binding sites of CH3 in CH3NH3PbBr3 film and study how the Pb environment is affected by the presence of CH3+.The results show that CH3+exists in the original perovskite with or without doping,and the concentration cannot be ignored.The goal of chapter 4 is to reduce the preferred binding sites of methyl impurities in CH3NH3PbCl3 films.The influence of CH3+on the formation of CH3NH3PbCl3 crystal lattice was studied by comparing the CH3+doping concentration of chlorine-based organic-inorganic perovskite films.The two types of C 1s species(CH3NH3+and CH3+)on the surface of the perovskite film are worth studying.In addition,the possible binding positions of CH3+species were also obtained by analyzing the XPS map.