First‐Principles and SCAPS‐1D Exploration of CsXO ₃ (X = Ta, Nb) as Promising Materials for Photocatalytic and Solar Cell Applications

This study offers a comprehensive first‐principles study on the electrical, thermodynamic, and optical characteristics of the cubic perovskite CsTaO 3 and CsNbO 3 with an emphasis on their potentials in energy conversion applications. We systematically analyze their electronic band structures using DFT with the GGA; improved by hybrid functional corrections (HSE06). The bandgaps predicted by HSE06 are 2.42 (0 GPa) and 1.67 eV (100 GPa) for CsTaO 3 , whereas GGA‐PBE yields 1.43 and 0.94 eV, respectively. In comparison to 1.36 and 1.01 eV with GGA‐PBE, the band gaps for CsNbO 3 are 1.59 (0 GPa) and 1.32 eV (100 GPa) with HSE06. Direct bandgap in the visible region, and optical calculations indicate that CsNbO 3 can be used for photovoltaic systems and photocatalysis. A solar cell model of CsXO 3 (X = Ta, Nb) exhibits the band alignment of charge transport layers and substantial optical absorption throughout the visible range, suggesting a high potential for solar‐to‐electric conversion. The results of this study indicate that the optimized device on CsNbO 3 could achieve an outstanding power conversion efficiency (PCE) of 28.79%, which is higher than PEC of CsTaO 3 (25.47%). These materials can be theoretically understood through this study, resulting in energy harvesting and conversion technologies, especially photocatalysis and photovoltaics.