Effect Of Acetate Additive On Photovoltaic Performance Of CsPbI₂Br Films

All-inorganic perovskite has attracted intense research attention due to its excellent thermal stability as compared with organic-inorganic hybrid perovskite materials.Among them,CsPbI₂Br stands out for both suitable band gap（～1.91 e V）and good environmental stability,which has achieved high photoelectric conversion efficiency in rencent several years.However,present high-efficiency CsPbI₂Br solar cells are commonly composed of expensive and unstable organic hole transport materials（HTM）and noble metal（Au,Ag）electrodes,resulting in higher device costs and reduced environmental stability.In addition,the still high defect density in current CsPbI₂Br thin films greatly limits the open circuit voltage of this kind of solar cells.In an attempt to stress above problems,hole transport layer free perovskite solar cell was constructed based on carbon electrode.Firstly,the effect of the anti-solvent process on the quality of CsPbI₂Br film and device performance was systematically studied via the one-step spin coating process.Then influences of acetate additives on the morphology and crystallinity of the CsPbI₂Br film was investigated,and the related mechanism impacting the CsPbI₂Br device performance was also deeply explored upon the device parameter analysis.The research results obtained in this thesis were as follows:（1）The effect of anti-solvent dropping moment and the type of anti-solvent on the quality of CsPbI₂Br film and device performance was studied.The results showed that the moment of applying the anti-solvent during spin coating process can significantly affect the quality of the CsPbI₂Br film.Any deviations from a crucial moment（either too early or too late）would lead to the generation of holes.At the optimal dripping moment,four kinds of common anti-solvents were compared.It was found that perovskite films deposited with aid of the four anti-solvents all show good compactness,while the film obtained by using isopropanol（IPA）as the anti-solvent showed the best light trapping ability and longer carrier lifetime.Its corresponding carbon-based device exhibits a highest photoelectric conversion efficiency of 9.09%.（2）Based on the optimized preparation process of CsPbI₂Br perovskite film,cesium acetate（CsAc）was used as a basic additive to investigate the influence of acetate concentration on the film quantlity and device performance of CsPbI₂Br.It was revealed that CsAc can effectively improve the crystallinity,light trapping ability and carrier lifetime of the CsPbI₂Br film at an optimal addition amount of CsAc/CsPbI₂Br=0.8%.The binding energy shift in Pb²⁺and Br^-XPS spectrum upon the introduction of CsAc confirmed the interactions of Ac^-with Pb²⁺and Br^-in the perovskite film,thereby slowing down the crystallization process and passivating surface defects.Benefiting from above effects,the CsAc-doped CsPbI₂Br carbon-based device achieved a conversion efficiency of 10.71%.（3）On the basis of the optimized the acetate concentration,significant performance improvement in CsPbI₂Br device was further achieved by utilizing magnesium acetate（Mg（Ac）₂）as an additive.Mg（Ac）₂ was found not to be incorporated into the lattice,but enriched on the surface of the perovskite film.Despite the fact that the addition of Mg（Ac）₂ would reduce the grain size of the film,the crystallinity of CsPbI₂Br was indeed improved.The CsPbI₂Br film treated with Mg（Ac）₂ thus exhibits a denser film surface and high light-trapping capabilities.At an optimal Mg（Ac）₂ addition content of 0.4%,the CsPbI₂Br film demonstrates longer carrier lifetime,indicating the effective passivation of Mg（Ac）₂on surface defects of the perovskite film.Finally,a quite high conversion efficiency of 13.08%was realized on a carbon-based HTM-free solar cell device based on CsPbI₂Br absorbers with 0.4%Mg（Ac）₂ additive.The encapsulated device also shows good long-term environmental stability.