Lead-free perovskite [H₃NC₆H₄NH₃]CuBr₄ with both a bandgap of 1.43 eV and excellent stability

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.