LAUSR

Wide-bandgap (∼1.8 eV) perovskite is an crucial component to pair with narrow-bandgap perovskite in low-cost monolithic all-perovskite tandem solar cells. However, the stability and efficiency of wide-bandgap perovskite solar cells are constrained by the light-induced halide segregation and by the large photovoltage deficit. Here we report a steric engineering to obtain high-quality and photostable wide-bandgap perovskites (∼1.8 eV) suitable for all-perovskite tandems. By alloying dimethylammonium and chloride into the mixed-cation mixed-halide perovskites, wide bandgaps are obtained with much lower bromide contents while the lattice strain and trap densities are simultaneously minimized. The wide-bandgap perovskite solar cells exhibit considerably improved performance and photostability, retaining >90% of their initial efficiencies after 1000 hours of operation at maximum power point. With the triple-cation/triple-halide wide-bandgap perovskites enabled by steric engineering, we further obtain a stabilized PCE of 26.0% in all-perovskite tandem solar cells. Our strategy provides an avenue to fabricate efficient and stable wide-bandgap subcells for multi-junction photovoltaic devices. This article is protected by copyright. All rights reserved.