Anion (S) substitution as a pathway for tuning the physical properties of CsTaO3

Abstract

This endeavor examined the physical characteristics of sulfur-doped cesium tantalate perovskites (CsTaO_3−xS_x), focusing on their applicability in solar cells through bandgap narrowing. First-principles density functional theory (DFT) simulations were conducted to ascertain the influence of sulfur (S) doping on the structural, electronic, optical, and thermodynamic attributes of the systems under investigation. Our investigation has revealed a structural change where the cubic phase of CsTaO₃ reverts to a cubic phase in CsTaS₃, while the cubic phase of CsTaO₃ transforms into a tetragonal structure in CsTaO₂S and CsTaOS₂. A potential bandgap reduction in the visible region was noted when S was incorporated into the structures by replacing oxygen (O), which enhances the material's absorption capability in visible light. The Tran–Blaha modified Becke–Johnson (TB-mBJ) potential was employed to obtain accurate bandgap estimations (0.909 eV for CsTaO₂S, 0.376 eV for CsTaOS₂, and 0.143 eV for CsTaS₃). Phonon dispersion studies have confirmed that the sulfur-doped perovskites are dynamically stable. The optical characteristics, including the dielectric function, absorption coefficient, and optical reflectivity, were investigated in detail and possess impressive features suited for harnessing solar energy. Thermal properties, such as Debye temperature and lattice thermal conductivity, have also been studied, demonstrating the potential for using the compound CsTaO_3−xS_x as a foam semiconductor.