Optimizing BaHf(S1−xTex)3 Chalcogenide Perovskites Through Anionic Substitution for Enhanced Photovoltaic Performance

This study investigates the systematic anionic alloying of BaHfS 3 with tellurium to optimize the bandgap for photovoltaic applications. Density functional theory calculations demonstrate that pristine BaHfS 3 exhibits a direct bandgap of 1.97 eV, exceeding the Shockley–Queisser optimal range. Strategic substitution of sulfur with tellurium in BaHf(S 1− x Te x ) 3 enables precise bandgap tuning from 1.7 eV to 0.9 eV across substitution levels of 10–40%. Notably, the composition BaHf(S 0.85 Te 0.15 ) 3 achieves the theoretically optimal bandgap of 1.35 eV, maximizing potential photovoltaic efficiency according to the Shockley–Queisser limit. Tellurium incorporation significantly enhances the optical properties, including absorption coefficient (>10 5 cm −1 ), dielectric constant, and refractive index, while maintaining the favorable direct bandgap nature. The systematic bandgap tunability coupled with enhanced visible and near-infrared absorption positions these chalcogenide perovskite alloys as viable candidates for next-generation photovoltaic devices and optoelectronic applications.