Unveiling the Potential of X2RbAsI6 (X= K, Cs) Halide Double Perovskites for Advanced Applications Through First-Principles Modeling

Abstract

Herein, we have examined the novel geometrical, elastic, electrical, thermoelectric (TE), and photonic attributes of halide double perovskites (HDPs) X2RbAsI6 (X = K, Cs), which have been less explored in previous studies, particularly for their thermoelectric and optoelectronic potential. Using first-principles methods, we have investigated their fundamental properties to assess their suitability for next-generation energy conversion and optoelectronic applications. The calculated energy band structure exhibit an indirect bandgap of 2.12 eV for Cs2RbAsI6 and 2.14 eV for K2RbAsI6, obtained using the modified Becke–Johnson (mBJ) potential to enhance accuracy. Both compounds exhibit semiconductor behavior, as confirmed by the density of states (DOS), and have a cubic structure with space group Fm3m, ensuring their structural stability. Furthermore, we computed numerous optical properties that demonstrates strong absorption in the visible region, regarding these HDPs ideal contenders for optoelectronic and photovoltaic applications. The analysis of elastic properties, confirms their mechanical stability, further supporting their practical utility. A key highlight of this study is the high thermoelectric performance of these HDPs, with a figure of merit (ZT > 0.7), which surpasses that of single halide perovskites. This makes them competitive candidates for thermoelectric energy conversion. Given their semiconductor behavior, tunable optoelectronic features, and mechanical robustness, these compounds hold promise for multifunctional applications, including photodetectors, spintronic devices, and next-generation solar cell technologies. This study presents a base for further theoretical and experimental exploration of HDPs for energy and optoelectronic usage.

Keywords:Elastic properties; First principles; Halide double perovskites; Optoelectronics; Semiconductors; Thermoelectric