An investigation of multifunctional properties of Ba2XBiO6 (X = Ga, In) double perovskites for green energy applications via first-principles calculations

Lead-free double perovskites have gained significant attention as promising materials for optoelectronic and high-temperature thermoelectric green energy applications. In this study, we investigate the structural, electronic, optical, and thermoelectric properties of thermodynamically, dynamically, and structurally stable lead-free double perovskites, Ba₂XBiO₆ (X = Ga, In), through first-principles calculations. Both compounds exhibit narrow direct band gaps of approximately 0.43 eV (Ba₂GaBiO₆) and 0.42 eV (Ba₂InBiO₆). The calculated effective masses for electrons and holes are notably low, facilitating efficient charge transport. The combination of these low effective masses and direct band gap characteristics enhances their suitability for photovoltaic and optoelectronic devices, as evidenced by calculated high absorption coefficients and low reflectivity. Thermoelectric assessments within the temperature range of 200–1000 K reveal high figures of merit of 0.674 (Ba₂GaBiO₆) and 0.731 (Ba₂InBiO₆) at 1000 K, confirming their potential as high-temperature thermoelectric materials.