Strain relaxed CsαFA1-αPbI3-βClβ perovskite by intercalation of cesium via antisolvent engineering for efficient photovoltaic devices over 22.9 %

Abstract

The phase stability of perovskite film is one of the key factors of commercialization of perovskite solar cells. To improve phase stability with high efficiency, numerous studies have explored various strategies, such as dopant engineering, interlayer engineering, and antisolvent engineering. Among them, modifying the perovskite composition through dopant engineering can significantly enhance phase stability as well as improving device performance by passivating cation and halide vacancies. However, when cesium ions and chloride ions are introduced in a perovskite precursor, they can lead to the precipitation of cesium chloride (CsCl), causing degradation of the perovskite film. In this study, we introduced an antisolvent method incorporating cesium(I) bis(trifluoromethanesulfonyl)imide (CsTFSI) as an additive, which effectively suppresses the formation of CsCl precipitates. Through various analytical techniques, we confirmed that Cs+ was successfully intercalated into the perovskite film. With this passivation, large perovskite grains with reduced lattice strain were achieved. Based on the improved crystallinity, the Cs+-incorporated device exhibited significantly suppressed charge recombination and enhanced stability, leading to markedly improved photoelectrochemical performance. As a result, Cs+ intercalated perovskite device achieved a power conversion efficiency of 22.9 %, along with enhanced stability, maintaining 98 % of the initial efficiency over 400 h.