Multidentate-ligand assisted homogenized 1.77 eV wide-bandgap perovskite toward highly-efficient and photostable solar cells

Wide-bandgap (WBG) perovskites hold promising applicability in constructing high-efficiency tandem solar cells. However, WBG perovskites face serious light-induced phase segregation due to the presence of mixed halides, and the segregation tendency becomes notably exacerbated with increasing bromine content. In addition, the mixed halide anions bring discrepant crystallization rates and thereby induce an inhomogeneous halide distribution within the WBG perovskite film. Here, we strategically propose a multidentate-ligand additive, N, N’-methylene-bis(2-amino-5-sulfhydryl-1,3,4-thiadiazole) (BL), into 1.77 eV WBG perovskites to assist homogenized crystallization. The electron-donating groups in the BL molecule strongly coordinate with lead halides via Lewis acid-base complexation, while N–H groups anchor formamidinium (FA+) cations via hydrogen bonding, which delays crystallization and reduces the internal residual stress within the WBG perovskite films. Eventually, the optimized 1.77 eV WBG perovskite solar cells (PSCs) achieve a champion power conversion efficiency (PCE) of 19.24%. Most importantly, these WBG PSCs exhibit robust photostability, which maintain 88% of the initial PCE after 300 h of the maximum power point (MPP) tracking under one solar light illumination. This study demonstrates an effective route to solve the long-term stability of WBG perovskite and is of significance for the practical application of tandem solar cells in the future photovoltaic market.