The role of pressure in engineering the band-gap of materials

Figure captions: Band gap evolution of the Cs<sub>2</sub>AgBiBr<sub>6</sub> crystal at high pressure, and the representative optical micrographs showing piezochromic transitions.
Figure captions: Band gap evolution of the Cs2AgBiBr6 crystal at high pressure, and the representative optical micrographs showing piezochromic transitions.

The lead hybrid perovskite (e.g. MAPbI3, MA=CH3NH3+) solar cell has been under fast development, with the highest certified power conversion efficiency now exceeding 22 %. The type of perovskite has become the first solution-processable photovoltaic material to surpass the efficiency of dominant crystalline silicon panels. The recently discovered Cs2AgBiBr6 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. A research team, using HPCAT facility, used high-pressure to regulate band gap in Cs2AgBiBr6 is, and observed a remarkable narrowing band gap 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. More in Q. Li et al, Angew. Chem., (2017)