Tuning band gap and enhancing optoelectronic performance of Fr-based perovskite FrBF3 (B = Ge, Sn) under pressure

Abstract

The commercial suitability of lead halide perovskites is deprived by stability and toxicity concerns despite their extraordinary physiochemical features and improved power conversion efficiency. There is an increasing preference towards reliable and ecologically sustainable alternatives with comparable optical and electronic characteristics. For this purpose, our study is concerned with identifying physical characteristics like structural, electronic, mechanical, and optical characteristics of FrBF₃ (B = Ge, Sn) under varying pressures up to 40 GPa. Both FrGeF₃ and FrSnF₃ have cubic crystal structures and their atomic bond length reduces with increasing pressure as lattice constant, and volume reduces with the application of hydrostatic pressure. They are structurally and mechanically stable in all the variations of pressure. Initially, both compounds have direct bandgap where FrGeF₃ has 2.14 eV bandgap and FrSnF₃ has 1.83 eV bandgap. The impact of pressure on band structure is notable as both compounds go through a linear transition from semiconductor to metal by concentrating electronic states at the Fermi level. The absorption, extinction coefficient, and optical conductivity also shift towards lower photon energy (redshift), which makes them viable options for solar cell development and optoelectronic devices under pressure as they can absorb photon energy of infrared and visible range. Besides, their mechanical features including elastic moduli, ductility, and anisotropy improve linearly with pressure. The findings of our study suggest that the perovskite FrBF₃ (B = Ge, Sn) exhibits an excellent improvement of mechanical, electronic, and optical characteristics when introduced to hydrostatic pressure, making them suitable for many real-life applications such as photodetector, sensor, energy storage devices, solar panels and other optoelectronic devices.