High-Pressure Band-Gap Engineering and Metallization in the Perovskite Derivative Cs3 Sb2 I9.

Among photovoltaic materials, the antimony-based, perovskite-like structure Cs3 Sb2 I9 stands out owing to its low toxicity and air stability. Here, changes in the optoelectronic properties and crystal structure of the lead-free perovskite derivative Cs3 Sb2 I9 are reported, caused by pressure-induced lattice compression. At 20.0 GPa, Cs3 Sb2 I9 with a wide band gap (2.34 eV) successfully broke through the Shockley-Queisser limit (1.34 eV), accompanied by clear piezochromism from orange-yellow to opaque black. Additionally, Cs3 Sb2 I9 experienced completely reversible amorphization at 20.0 GPa. These optical changes could be attributed to atomic-orbital overlap enhancement caused by contraction of the Sb-I bond length and diminution of the Sb-I bond angle. In addition, Cs3 Sb2 I9 underwent a transition from semiconductor to conductor upon compression and obtained metallic properties at 44.3 GPa, indicating new electronic properties. The obtained results may further broaden the research prospects of halide perovskite materials in the field of photovoltaics.