High‐Performance Planar‐Heterojunction Solar Cells Based on Ternary Halide Large‐Band‐Gap Perovskites

High-performance planar-heterojunction (PHJ) solar cells based on large band-gap (1.70–1.83 eV) perovskites are demonstrated. By incorporating Cl− into the MAPb(I1-YBrY)3, the crystallinity and homogeneity of the solution-processed perovskite thin films are much improved, which results in an increased charge carrier diffusion length from ≈160 nm to ≈700–800 nm. This enhancement leads to a high power conversion efficiency (PCE) of 10% in the low-temperature solution-processed PHJ devices.