High-Pressure Band-Gap Engineering in Lead-Free Cs2 AgBiBr6 Double Perovskite.

Novel inorganic lead-free double perovskites with improved stability are regarded as alternatives to state-of-art hybrid lead halide perovskites in photovoltaic devices. The recently discovered Cs2 AgBiBr6 double perovskite exhibits attractive optical and electronic features, making it promising for various optoelectronic applications. However, its practical performance is hampered by the large band gap. In this work, remarkable band gap narrowing of Cs2 AgBiBr6 is, for the first time, achieved on inorganic photovoltaic double perovskites through high pressure treatments. Moreover, the narrowed band gap is partially retainable after releasing pressure, promoting its optoelectronic applications. This work not only provides novel insights into the structure-property relationship in lead-free double perovskites, but also offers new strategies for further development of advanced perovskite devices.