Searching less toxic materials with both ideal bandgaps (1.0-1.5 eV for single-junction solar cells) and excellent stability remains a big challenge in perovskite optoelectronic materials field.Here,we report the optoelectronic properties and stability of the[H3NC6H4NH3]CuBr4 perovskite material.Intriguingly,the material features a bandgap of 1.43 eV which approaches that of GaAs (1.42 eV)—the state of the art semiconductor for single-junction solar cells.Furthermore,the[H3NC6H4NH3]CuBr4 film shows excellent stability,and can tolerate continuous moisture exposure for 1200 h in air (relative humidity: 40-50%) and ultraviolet light exposure for 1008 h in a glove box filled with nitrogen.Finally,we successfully realized a pinhole-free,smooth,and large-area (>20 cm2)[H3NC6H4NH3]CuBr4 film—the largest Cu-based perovskite film ever reported—via a hot-casting technique.Owing to its ideal bandgap and excellent stability,[H3NC6H4NH3]CuBr4 can be considered as a milestone in the development of low bandgap,highly stable,and lead-free perovskite materials for potential optoelectronic applications.