Near‐Infrared Light‐Responsive Cu‐Doped Cs2AgBiBr6

Abstract Lead‐free halide double perovskites (A 2 B I B III X 6 ) with attractive optical and electronic features are considered to be a promising candidate to overcome the toxicity and stability issues of lead halide perovskites (APbX 3 ). However, their poor absorption profiles limit device performance. Here the absorption band edge of Cs 2 AgBiBr 6 double perovskite to the near‐infrared range is significantly broadened by developing doped double perovskites, Cs 2 (Ag:Cu)BiBr 6 . The partial replacement of Ag ions by Cu ions in the crystal lattice is confirmed by the X‐ray photoelectron spectroscopy (XPS) and solid‐state nuclear magnetic resonance (ssNMR) measurements. Cu doping barely affects the bandgap of Cs 2 AgBiBr 6 ; instead it introduces subbandgap states with strong absorption to the near‐infrared range. More interestingly, the near‐infrared absorption can generate band carriers upon excitation, as indicated by the photoconductivity measurement. This work sheds new light on the absorption modulation of halide double perovskites for future efficient optoelectronic devices.