Direct Band Gap Mixed-Valence Organic–inorganic Gold Perovskite as Visible Light Absorbers

Lead-free halide perovskite semiconductors are necessary due to the atmospheric instability and lead toxicity associated with the 3D lead halide perovskites. However, a stable lead-free perovskite with an ideal band gap (1.2–1.4 eV) for photovoltaics is still missing. In this work, we synthesized organic–inorganic gold halide double perovskites ((CH 3 NH 3 ) 2 Au 2 X 6, X = Br, I) through a solution-processed route that offers an ideal direct band gap for photovoltaic applications. Density functional theory calculations confirm the direct nature of the band gap with reasonable absorption coefficients in the visible range and excellent charge transport properties. In addition, the Au-halide perovskites show high chemical stability and photoresponse. These combined properties demonstrate that Au-based halide perovskites can be a promising group of compounds for optoelectronic applications.