DFT Insights on the Optoelectronic and Thermoelectric Characteristics of Lead-Free Na2InGaX6(X = Cl, I) Double Perovskites for Environmentally Friendly Energy Applications

This study addresses the scientific question of how lead-free double perovskites Na2InGaCl6 and Na2InGaI6 can serve as sustainable materials for next-generation thermoelectric and optoelectronic applications by evaluating their structural, optoelectronic, mechanical, and thermoelectric properties. Using first-principles calculations with GGA and mBJ-GGA methods within the Wien2K computational framework, we examine whether these materials properties make them viable alternatives to conventional lead-based perovskites. The electronic band gaps (1.98 eV for Na2InGaCl6 and 0.30 eV for Na2InGaI6) calculated by using the Tb-mBJ potential suggest their suitability for optoelectronic applications. We found that when the halogen anions change from Cl to I, the electronic band gap mitigates. The compound's structural stability is verified by the Goldsmith tolerance factor (tG) and negative formation energy validates their thermodynamic and structural stability. The elastic properties represent that both examined compounds are ductile and mechanically stable. The optical absorption results reveal that Na2InGaI6 absorbs a 128-471 nm wide range of UV-Visible electromagnetic radiations, which makes it a potential candidate for optoelectronic and solar cell applications. Furthermore, the transport parameters were computed by employing Boltztrap code. These compounds are appropriate for thermoelectric applications because of their large Seebeck coefficient (S) and ultralow lattice thermal conductivity, which further improve ZT. It demonstrates that Na2InGaX6 (X = Cl, I) has potential for use in solar cells and thermoelectric generators as sustainable and eco-friendly energy sources by confirming their stability, appropriate bandgaps, and remarkable thermoelectric qualities.