Exploring phase stability and functional properties of lead-free Rb₂CuMoX₆ (X = Cl, Br) double perovskites for next generation energy solutions

This study examines the structural, dynamic, electronic, optical, and thermoelectric properties of Rb₂CuMoX₆ (X = Cl, Br) double perovskites in detail to determine whether they are suitable for future sustainable energy applications. We used the Generalized Gradient Approximation and the modified Becke–Johnson potential to perform density functional theory calculations that provided a very good description of the electronic structure. Both compounds are mechanically and thermodynamically stable semiconductors with spin-polarized electronic states. The mBJ functional makes band-gap estimates much more accurate, yielding values that work well for optoelectronic and energy-conversion applications. The study of the optical response shows that the material absorbs substantial light in the visible and near-ultraviolet regions and exhibits good dielectric properties. This means that it could be useful in photovoltaic and photodetector technologies. Calculations of thermoelectric transport indicate that these compounds are good thermoelectric materials, as evident from the Seebeck coefficient and power factor plots.