A comprehensive analysis of structural, electronic, optical, mechanical, thermodynamic, and thermoelectric properties of direct band gap Sr3BF3 (B = As, Sb) photovoltaic compounds: DFT-GGA and mBJ approach

This study evaluates the physical properties of lead-free Sr₃BF₃ (B = As, Sb) photovoltaic compounds including structural, electronic, mechanical, optical, thermodynamic, and thermoelectric behavior using calculations based on DFT approach. Born stability criteria and formation enthalpy estimates show that the compounds under study are mechanically and thermodynamically stable. The initial lattice constants for Sr₃AsF₃ and Sr₃SbF₃ were determined to be 5.71 Å and 5.97 Å, respectively. While simulating the compounds under pressure, lattice constants, cell volumes, and bond lengths decrease. The band structure investigation shows that these compounds are semiconducting with an adjustable direct bandgap. The electronic band gap contracts by pressure, shifting the material from ultraviolet to the visible spectrum. This modification enhances electron transition from valence band maxima to conduction band minima, enhancing optical efficiency. The shift and rise in ductility and machinability index under pressure ensures good lubrication, low friction, and significant plastic deformation suitable for many industrial applications. Simultaneously, the static dielectric constant increases, increasing absorption and conductivity and red-shifting the optical spectrum, and reducing reflectivity in the visible spectrum. The thermodynamic behavior of the compounds was affected by both pressure and temperature variation. The thermoelectric figure of merit becomes closer to unity with a shorter band gap, indicating increased efficiency. Our findings suggest that Sr₃BF₃ (B = As, Sb) photovoltaic compounds could be used for the invention of next-generation solar cells and thermoelectric devices.