Engineering light-harvesting in oxyselenides with perovskite-like motifs: a first-principles exploration of cation substitution effects in X2Mo3SeO12 (X = Cu, Ag, Li) for high-efficiency solar energy conversion

In this study, we explored the structural, electronic, optical, and photovoltaic properties of oxyselenide compounds X2Mo3SeO12 (X = Cu, Ag, Li) that exhibit perovskite-like motifs, using ab initio calculations based on density functional theory (DFT). The GGA-PBE approximation was used for structural optimisation, while the advanced Meta-GGA RSCAN functional allowed for a more accurate description of the electronic, optical and photovoltaic properties. The crystal structures are stable with a direct band gap in each case. Analysis of the energy bands and density of states (TDOS and PDOS) reveals a good separation between the valence and conduction bands. Optical properties such as dielectric function, absorption coefficient, refractive index, reflectivity, energy loss function, and optical conductivity were calculated to evaluate light absorption potential. Photovoltaic performance was estimated by simulating the external quantum efficiency (EQE), open-circuit voltage (Voc), short-circuit current density (Jsc), and current–voltage (I–V) characteristics, considering the AM1.5G solar spectrum and a thickness of 600 nm. The results show that Cu2Mo3SeO12 is the best-performing compound, with Jsc = 31.34 mA/cm2, Voc = 0.97 V, and power P = 30.4 mW/cm2, demonstrating its strong potential for next-generation lead-free solar cells.