Predicting Optoelectronic, Transport and 3D-Elastic Properties of RbKTiX₆ (X = Cl, Br, I) Perovskites for Energy Applications

Organic–inorganic hybrid perovskite compounds attract tremendous research attention due to their remarkable and interesting optoelectronic properties and high power conversion efficiency (PCE). This work aims to predict various properties of some new halide perovskites RbKTiX₆ (X = Cl, Br, I) to investigate their feasibility as active materials for energy storage and photovoltaic application. The Density Functional Theory (DFT) implemented in the Quantum Espresso code was applied to calculate the materials’ properties, including the optoelectronic and transport properties. The evaluation of their calculated structural parameters reveals that the perovskites are highly stable, both chemically and mechanically and that there is a decline in the lattice constant and the Ti-X bond length when the I anion is substituted with its isoelectronic i.e. Br and Cl. From their electronic band structure, the materials are projected to be direct-gap semiconducting materials with energy gap ranging from 0.77 eV to 2.3 eV. Strong light absorption (up to 10⁵ cm⁻¹) in ultraviolet–visible regions is predicted for all studied perovskites, which is crucial for solar cell applications. This is also supported by their low reflectivity (below 23%). To investigate the power conversion efficiency (PCE) of these materials, we suggest n-i-p solar cells diagram, using RbKTiX₆ (X = Cl, Br, I) as the light absorber. The calculated PCE values of RbKTiCl₆, RbKTiBr₆ and RbKTiI₆ are ƞ \(=\) $=$ 10.03%, ƞ \(=\) $=$ 7.21% and ƞ \(=\) $=$ 4.18%, respectively. Finally, it is found that the perovskites exhibit high thermo-power convergence efficiency, as indicated by their thermoelectric figure of merit which is near unity.