In situ epitaxial growth of blocking structure in mixed-halide wide-band-gap perovskites for efficient photovoltaics

Mixed-halide perovskite solar cells (PSCs) with wide band gap (WBG) have attracted increasingly intensive attention because they are ideally suited for tandem photovoltaics. However, the de-vice performance and stability are still undesirable due to the exis-tence of photoinduced phase segregation. Here, we precisely assembled a highly crystalline blocking structure onto the WBG perovskite plane via in situ epitaxial growth to address this issue. It was found that the blocking structure contributes to the release of lattice strain, the enhancement of the halide-ion migration bar-rier, and effective defect passivation of WBG perovskites. Conse-quently, an impressive open-circuit voltage of 1.25 V (maximum 1.26 V) with a champion efficiency of 21.80% (certified 21.52%) was obtained in a 1.65 eV mixed-halide PSC with outstanding photo -stability. The semitransparent device with a certified efficiency of 19.15% was overlaid on a silicon subcell to make a four-terminal tan-dem configuration, demonstrating a high efficiency of 28.83%.