A theoretical approach to study oxide-based perovskite materials XTiO₃ (X = Be, Mg, Ca, Sr and Ba) for photovoltaic applications

Abstract Oxide-based perovskite materials have a large application in fuel and hydrogen sensors, non-volatile random access memory devices, semiconductor fabrications, optoelectronic, thermoelectric and photovoltaic devices. In this report, equilibrium geometries, and optoelectronic properties of oxide-perovskite materials XTiO 3 (X = Be, Mg, Ca, Sr and Ba) are investigated through Conceptual Density Functional Theory (CDFT) technique. The HOMO–LUMO energy gap obtained from functional B3LYP/LANL2DZ and B3PW91/LANL2DZ are observed in the range of 1.201 eV–4.647 eV and 1.519 eV–4.903 eV respectively, which justifies their applications in solar cells and optoelectronic devices. HOMO–LUMO energy gap shows a downward trend when materials travel from Be to Mg to Ca to Sr to Ba, except for BaTiO 3 in B3PW91/LANL2DZ. BeTiO 3 displays the maximum value of HOMO–LUMO gap, hardness and electronegativity value. Hardness and softness of these substances are found between 0.600–2.452 eV and 0.204–0.788 eV respectively whereas refractive index and dielectric constant of XTiO 3 are observed in the range of 2.017–3.684 and 4.067–13.574 respectively. Across all relationships, XTiO 3 ’s dielectric constant and refractive index show a rising pattern from Be to Mg to Ca to Sr to Ba, except for BaTiO 3 computed using B3PW91/LANL2DZ. The lowest refractive index and dielectric constant are displayed by the BeTiO 3 . TD-DFT calculation is performed to understand the absorption spectra of these materials. Optical transition energy and wavelength of XTiO 3 are found between 0.339–3.535 eV and 350.68–3656.15 nm respectively. An interesting relationship is established between HOMO–LUMO energy gap, optical transition energy and wavelength of XTiO 3 materials. The investigated compounds exhibit a linear pattern between HOMO–LUMO energy gap and optical transition energy whereas wavelength shows an inverse trend. MEP of these compounds are also discussed.