Suppressing the Photoinduced Halide Segregation in Wide‐Bandgap Perovskite Solar Cells by Strain Relaxation

Abstract Efficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light‐induced phase segregation of WBG perovskite result in large open‐circuit voltage (V_OC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis‐base trans‐Ferulic acid (t‐FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light‐induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of V_OC. Moreover, replacing a mixture of MeO‐2PACZ and Me‐4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and V_OC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin‐coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite‐based tandem devices.