Origin of pressure-induced band gap tuning in tin halide perovskites†
Structural and optical high-pressure study of FASnBr3 (FA = formamidinium) revealed a cubic to orthorhombic phase transition near 1.4 GPa accompanied by a huge band gap red-shift from 2.4 to 1.6 eV, which is followed by a blue-shift of ∼0.2 eV upon further pressure increase. DFT calculations indicate that the variation in band gap is related to changes in Sn–Br bond length alternation, with an equalization of such difference predicted at high pressure. Extending the calculations to analogous lead-free systems provides a unifying mechanistic picture of pressure-induced band gap tuning in tin halide perovskites, which is correlated to the variation of specific structural parameters. These results represent a solid guide to predict and modulate the pressure-response of metal halide perovskites based on the knowledge of their structural properties at ambient pressure.