Pressure-induced bandgap narrowing to Shockley–Queisser limit of quasi-two-dimensional perovskite (BA)2(FA)Sn2I7

Quasi-two-dimensional (2D) tin-based perovskites are promising photoelectric materials due to their non-toxicity and excellent photoelectric properties. However, the addition of organic ligands leads to an increase in bandgap, which is unfavorable for the application of perovskites in the field of photovoltaics. The bandgap of the two-dimensional tin-based perovskite (BA)2(FA)Sn2I7 is reduced to the Shockley–Queisser limit through the application of pressure. Also, the bandgap of (BA)2(FA)Sn2I7 decreases by 0.108 eV/GPa within a pressure range of 0.0–4.0 GPa, reaching a value of 1.34 eV at 4.0 GPa, which corresponds to the Shockley–Queisser limit. With further increases in pressure above 4.0 GPa, the bandgap starts to increase and then re-decreases above 15.0 GPa. When released to ambient pressure, the reduced bandgap is still partially preserved due to structural recrystallization. Further analysis indicated that the continuous narrowing of the bandgap within 0.0–4.0 GPa is mainly due to the layer-to-layer compression before the interlayer compression in the sample, which increases the deformation pressure of the [SnI6]4− octahedra. In addition, high-pressure in situ electrical tests show that (BA)2(FA)Sn2I7 exhibits optical response under laser irradiation at 405, 450, 980, and 1532 nm and extends the optical response range to the near-infrared region. In summary, the bandgap of 2D perovskite was reduced by applying pressure, which opened up a potential way to design materials with improved properties.