Preparation And Properties Of ASnI₃?A=Cs,MA And FA? Perovskite Films

AbstractIn recent years,lead-based perovskite solar cells?PSCs?have been greatly developed,but the toxicity of Pb has become a stumbling block for the commercialization of batteries.Therefore,actively exploring and developing non-Pb-based PSCs that are non-toxic or low-toxic has become a research hotspot and task.The research of new perovskite materials mainly focuses on halides such as Sn²⁺,Ge²⁺,Bi³⁺and Sb³⁺,but only Sn-based batteries can obtain considerable conversion efficiency.This is mainly because Sn²⁺and Pb²⁺belong to the same main group and have similar s² valence electron configurations and similar ionic radii.However,the performance of the battery is far less than that of the Pb-based device.The main reasons are:1)the formation energy of the Sn vacancy(V_Sn)is low,so that the film has a high intrinsic hole density;2)after exposure to air,Sn²⁺is rapidly oxidized into Sn⁴⁺makes the film semi-metallized;3)The reaction between SnI₂ and AI?A=Cs,MA or FA?is more rapid,and the film's morphology,defects,and crystallization characteristics etc are more difficult to control.In addition,when SnI₂ is used as the precursor,the purity of the material,and the oxidation of Sn²⁺in the precursor solution or in the spin coating and annealing process all affect the quality of the film.Therefore,in this paper,SnCl₂ was used as the source of Sn to regulate the growth process of the film.The ASnI₃ film was prepared by one-step solution method.The effects of annealing temperature,HI acid and NH₄I additives on the properties of the film were studied.and we conducted a theoretical analysis of the battery working mechanism.The paper mainly includes the following contents:1)Simulation of FASnI₃-based PSCs and preparation of thin films:First,the performance of FTO/PEDOT:PSS/perovskite/PCBM/Au inversion planar structure PSC was simulated by one-dimensional SCAPS software.The results show that:?1?The defect density of the PEDOT:PSS/perovskite interface is more directly related to the performance of the device than the perovskite/PCBM interface.?2?The intrinsic carrier concentration in the absorption layer,rather than its type and distribution characteristics,determines the performance of the device.In order to obtain a highly efficient battery,it is necessary to reduce the hole density of the film to be lower than1×10¹⁶cm^-3.In addition,the optimal electron affinity of 3.9 eV was obtained by regulation of the energy band.These results show that improving the interface contact characteristics,improving the stability of Sn²⁺,reducing the defect density of the absorber layer,and optimizing the device structure are the key to preparing high-performance Sn-based PSCs in the future.The experimentally prepared film did not find the FASnCl₃ component,and the film's stability was not high,the film will decompose after standing in the air for a few minutes.After adding hydroiodic acid to the precursor solution,the hydration and oxidation problems of the film are serious;when a certain amount of NH₄I is doped,the stability of the film can be improved.2)Preparation of MASnI₃ perovskite film.The film is a mixed film of MASnI₃and MASnCl₃,and the composition of MASnCl₃ increases as the annealing temperature increases;when the annealing temperature is too high,the film decomposes.The addition of HI acid to the precursor fluid reduces the amount of MASnCl₃ in the film.However,the excessive addition of HI acid increases the water content of the precursor liquid and the film will be oxidized.When MAI is added simultaneously to the precursor solution,the MASnCl₃ component in the film rises first and then falls,and the band gap of the film decreases.When the molar ratio of the precursor is 1:0.9?SnCl₂:MAI=1:0.9?,the film has a dense morphology and high stability.3)Preparation of CsSnI₃ perovskite film.The study found that the CsSnI₃ film obtained at an annealing temperature of 100?is relatively flat and dense,When the annealing temperature is 80?,the film is a yellow phase.When the annealing temperature is higher than 200?,the film decomposes and generates CsI.And when the annealing temperature is high,diffraction peaks of SnI₄ and Cs₂SnI₆ appear,which indicates that the film oxidizes when the annealing temperature is high.Next,the anti-solvent chlorobenzene was used in the preparation of the CsSnI₃ perovskite film.It was found that the chlorobenzene was added best at the 12th s high speed,and the morphology of the prepared film was greatly improved.Finally,adding a certain amount of hypophosphorous acid to the precursor liquid will greatly improve the stability of the film,but the amount of hypophosphorous acid added is not too much,because the water in the hypophosphorous acid will have a relatively large effect on the film and make Its stability is greatly reduced.It was finally determined that the optimum addition amount of hypophosphorous acid was 20?l/ml,and the crystallinity and stability of the film prepared under these conditions were greatly improved.