Optoelectronic and thermoelectric properties of new lead-free K₂NaSbZ₆ (Z = Br, I) halide double-perovskites for clean energy applications: a DFT study

In this study, the density functional theory (DFT) is employed to investigate the structural, elastic, optoelectronic, and thermoelectric (TE) properties of K₂NaSbZ₆ (Z = Br, I) halide double perovskites (HDPs). The evaluated second-order elastic constants and formation energy analysis confirm that the studied HDPs are cubic, stable, and ductile. The electronic band structure calculations disclose that both compounds are determined to be p-type semiconductors with indirect band gaps of 3.20 eV and 2.40 eV for K₂NaSbZ₆ (Z = Br, I), respectively. The optical features demonstrate the prominent role of the present HDPs in photovoltaic conversion and optoelectronic devices. In the visible region, both HDPs exhibit high optical absorption (> 10⁵ cm⁻¹) with excellent refractive index. Furthermore, the studied TE properties show that for both HDPs, n-type doping is more suitable for improving their TE performances. Therefore, the present study would be beneficial for emerging optoelectronic and TE technologies.