Solution mediated halide exchange engineering for the fabrication of a thick CsPbCl3 film and its application in photovoltaics with outstanding performance

Abstract

It is a big challenge to prepare thick CsPbCl₃ films using traditional solution processed approaches owing to the low solubility of precursors of PbCl₂ and CsCl in common solvents. Here, we propose an indirect solution process to prepare thick CsPbCl₃ films. In this new approach, a mother film of CsPbBr₃ is first prepared through a solution process, and then it is dipped into a diluted HCl/methanol solution. During the dipping process, it triggers a halide exchange reaction between Br⁻ and Cl⁻, and it eventually produces a thick CsPbCl₃ film (∼400 nm) with high quality and purity. Afterwards, a carbon based hole transportation layer (HTL) free solar cell with a configuration of FTO/TiO₂/CsPbCl₃/carbon is constructed, and it delivers an average PCE of 1.23% and an outstanding PCE of 1.39% in a batch of PSCs. Meanwhile, the solar cell maintains its 82% initial PCE after storage in open air for 31 days. This work overcomes the obstacle of the traditional solution approach for the preparation of CsPbCl₃ films, which makes it promising for preparing various CsPbCl₃ film-based devices via a solution process.