Pressure-driven perfection: Advancing lead-free halide perovskites RbAgBiX (X = Br, Cl) for optoelectronic applications.

This research employs first-principles simulations to systematically study the structural, elastic, electronic mechanical, and optical characteristics of lead free halide RbAgBiX (X = Br, Cl) perovskites under pressure. The computed structural parameters are in good agreement with previous experimental and theoretical results. The obtained elastic constants met the Born stability requirements, showing that our materials are mechanically stable at variable hydrostatic pressures, as supported by the computed negative formation energy values. The covalent bond exhibits metallic characteristics, and induced hydrostatic pressure leads to a decrease in bond lengths. Mechanical analysis demonstrates that the studied materials are ductile and mechanically stable, with enhanced ductility under pressure. The materials are small band gap (1.30 eV, 1.801 eV for RbAgBiX (X = Br, Cl, respectively) semiconductors at ambient pressure with superior optoelectronic performance. Under hydrostatic pressure, RbAgBiX (X = Br, Cl) experiences a reduction in its band gap (0.545 eV, 1.305 eV for RbAgBiX (X = Br, Cl, respectively), accompanied by improved physical characteristics. This suggests the potential for increased utilization of this material in optoelectronic devices and solar cells compared to ambient pressure conditions.