Comprehensive insights into thermodynamic stability, optoelectronic properties, thermoelectric properties, and photocatalytic hydrogen evolution potential of halide double perovskites Rb2TlAlX6 (X = Cl, Br, I): first-principles and AIMD approach

Abstract

Rubidium (Rb)-based halide double perovskites (HDPs) possessing tunable optoelectronic features have emerged as promising substances for optoelectronic, thermoelectric, and photocatalytic hydrogen production technologies. In the present work, Rb2TlAlX6 (X = Cl, Br, and I) HDPs are reported using a first-principles approach. The optimized lattice parameters, tolerance factors, and formation energy validate the cubic phase and thermal integrity of the studied HDPs at 300 K. Ab initio molecular dynamics (AIMD) simulation confirms thermal stability at 300 K, and phonon spectra validate dynamic stability at 0 K for Rb2TlAlX6 (X = Cl, Br, and I). The Born–Huang criteria, along with Pugh's and Poisson's ratios, confirm the mechanical robustness and ductility of these HDPs. The electronic features of the explored HDPs reveal indirect bandgaps of 0.85, 0.63, and 0.35 eV by PBE-GGA, 1.57, 1.29, and 0.89 eV by TB-mBJ, and 1.55, 1.26, and 0.85 eV by the mBJ+SOC functional for Rb2TlAlCl6, Rb2TlAlBr6, and Rb2TlAlI6, respectively. The effective mass calculated using band profiles demonstrates a low value for electrons and a high value for holes. The current investigation also analyzes polarization, refraction, reflection, optical loss, and light absorption, which suggest that the studied HDPs demonstrate exceptional visible to near-ultraviolet absorption, evidencing suitability for optoelectronic and photovoltaic technologies. Thermoelectric analysis as a function of temperature and chemical potential demonstrates the contribution of holes and electrons to conductivity and high figure of merit values (0.757–0.731), suggesting the importance of these halides for designing thermoelectric technologies. Lastly, photocatalytic characteristics suggest the effective photocatalytic activity of Rb2TlAlX6 under solar energy to produce hydrogen. Collectively, these results theoretically justify the potential of these HDPs for optoelectronic, thermoelectric, and photocatalytic hydrogen evolution, which needs experimental confirmation.