DFT insights into physical characteristics of newly proposed halide-based double perovskites Na 2 GaBiZ 6 (Z = Cl/Br/I) for energy conversion applications

Halide double perovskites are also under consideration as a promising source of photovoltaic and thermoelectric applications. Density functional theory (WIEN2k) together with BoltzTraP was used in this study to examine the structural, electronic, optical and thermoelectric properties of Na 2 GaBiZ 6 (Z [Formula: see text] Cl, Br, I). Their structural stability (0.94, 0.92, 0.89) and negative formation energies ([Formula: see text]3.98, [Formula: see text]3.59, [Formula: see text]3.58[Formula: see text]eV) prove their high structural stability. Calculations with TB-mBJ functional predict direct band gaps of 2.22[Formula: see text]eV (Cl), 1.74[Formula: see text]eV (Br) and 1.47[Formula: see text]eV (I) with a tunable transition between UV light and visible light absorption with halogen substitution. High dielectric constants and high visible-light absorption, which are useful in optoelectronics, are obtained by optical measurements, such as dielectric function, refractive index and absorption spectrum. Thermoelectric transport properties depict the highest values of ZT of 0.76 (Cl), 0.85 (Br) and 0.89 (I). In general, Na 2 GaBiZ 6 is a stable and multifunctional compound to be used in efficient energy conversion technologies.