Crystallization Regulation,Defect Passivation And Photovoltaic Performance Of Highly Stable Perovskite Thin Films

In recent years,perovskite solar cells（PSCs）have experienced rapidly development,and their power conversion efficiencies（PCEs）have increased from 3%in 2009 to 25%in 2020,demonstrating its status as the hottest photoelectric material at present.Although many achievements in PCE have been achieved,the instability against light,heat and humidity severely limits its future commercialization.The main reasons for its instability are as follows:first,the perovskite material itself is unstable due to the presence of volatile and decomposable organic cations in the perovskite material;second,the charge transport layer is unstable;third,defects in the interfaces and bulk.To address these issues,we carried out the following research works and achieved a series of progresses:Firstly,a facile but effective strategy has been developed to finely tailor the crystallization of thermally stable cesium/formamidinium（Cs/FA）based perovskite via partially replacing Pb I₂ with Pb Cl₂ in the precursor solution.The incorporation of chlorine into the perovskite crystal lattice derived from Pb Cl₂ changes the crystallization process and improves the crystal quality,which further results in the formation of larger crystal grains compared to the control sample.The larger crystal grains with high crystallinity lead to reduced grain boundaries,suppressed non-radiative recombination,and enhanced photoluminescence lifetimes.Under the optimized conditions,the methylammonium free PSCs delivers a champion PCE of 21.30%with an open-circuit voltage as high as 1.18 V,which is one of the highest efficiencies for Cs/FA based PSCs to date.Importantly,the unencapsulated PSC devices retain more than 95%and 81%of their original PCEs even after（over one year）storage under ambient conditions or 2000 h’s thermal aging at 85 ^oC in a nitrogen atmosphere,respectively,indicating The Cs/FA-based perovskite system is a very promising light absorber material.Secondly,we show that D-penicillamine（PA）,an edible antidote for treating heavy metal ions,not only effectively passivates the iodine vacancies(Pb²⁺defects)through coordination with the–SH and–COOH groups in PA,but also finely tunes the crystallinity of Cs/FA-based perovskite film.Benefiting from these merits,a reduction of non-radiative recombination and an increase in photoluminescence lifetime have been achieved.As a result,the champion MA-free device exhibits a champion PCE of 22.4%,an open-circuit voltage of 1.163 V,a notable fill factor of82%,and excellent long-term operational stability.Moreover,the defect passivation strategy can be further extended to a mini module（substrate:4×4 cm²,active area:7.2 cm²）as well as a wide-bandgap（～1.73 e V）Cs/FA perovskite system by delivering PCEs of 16.3%and 20.2%,respectively,demonstrating its universality in defect passivation for efficient PSCs.Our research may pave a novel way for the development of stable and high-efficiency PSCs.