Boron–halide interactions for crystallization regulation of a 1.68 eV wide-bandgap perovskite prepared via a two-step method

Abstract

An all-solution two-step method for preparing wide-bandgap perovskites has the advantages of low cost, good repeatability and scalability. However, achieving high-quality wide-bandgap perovskite films via an all-solution two-step method remains challenging due to uneven distribution of halogens and incomplete reactions between organic salts and inorganic salts. Herein, we introduced tris(pentafluorophenyl)borane (BCF) into an inorganic layer resulting in boron–halide bonding, which stabilized uniform halide distribution and regulated the porous structure of the lead halide films, facilitating the diffusion of organic salts. Additionally, the fluorine substituents formed hydrogen bonds with organic cations, making BCF a bifunctional additive that delayed the reaction between the organic ammonium salt and the inorganic precursor, which was conducive to the growth of large-grained perovskite crystals. During the perovskite crystallization process, BCF molecules migrated to grain boundaries and the film surface, achieving a highly positive regulation influence on the nanoscale morphology and structure of the perovskite absorber films, thus leading to a pinhole-free, stress-free and less defect perovskite films. Ultimately, the approach enabled single-junction 1.68 eV wide-bandgap perovskite solar cells with a champion efficiency of 23.49% (certified 22.73%) and a V_OC of 1.291 V. Furthermore, the optimized perovskite films were pioneeringly and successfully integrated into monolithic perovskite/silicon tandem solar cells on textured silicon and achieved an efficiency of 31.12%, which is the highest value among tandem solar cells prepared by an all-solution two-step method, retaining >90% of initial performance after 500 hours of continuous operation.