Density Functional\nTheory Study of Alkaline Earth-Based\nTitanate Perovskite Oxides: Unraveling Their Significance for Solar\nCell Applications

Charge transport\nlayers (CTLs) and transparent conductive\nelectrodes\n(TCEs) are important constituents of polymer solar cells (PSCs) and\nperovskite solar cells (Per-SCs), affecting the efficiency and stability\nof these devices. We employed density functional theory to study the\nstructural, optoelectronic, thermal, and elastic properties of alkaline\nearth-based titanate perovskite oxides to determine the appropriate\ncompounds for PSCs and Per-SCs. Based on the calculations, CaTiO<sub>3</sub> exhibits a direct band gap of 3.535 eV, while BeTiO<sub>3</sub>, MgTiO<sub>3</sub>, SrTiO<sub>3</sub>, and BaTiO<sub>3</sub> displayed\nindirect band gap energies of 3.618, 4.852, 3.193, and 2.960 eV, respectively.\nConsidering the calculated valence and conduction band edges and energy\nband diagram alignment of the perovskite oxide structures with widely\nused photoactive layers, SrTiO<sub>3</sub>, BaTiO<sub>3</sub>, and\nCaTiO<sub>3</sub> emerge as promising materials to be applied as electron\ntransporting layer (ETL) in the structure of the PSCs and Per-SCs.\nThe findings also reveal that SrTiO<sub>3</sub> and CaTiO<sub>3</sub> exhibit the greatest electron mobility, making them more appropriate\ncandidates for ETL. The minimal exciton binding energy found in SrTiO<sub>3</sub> signifies its high separability and enhances its suitability\nfor efficient carrier generation as the most effective ETL. The results\nobtained from optical parameters confirmed that the investigated compounds\nare appropriate candidates for TCE and CTL as they demonstrate low\noptical conductivity and absorptivity, minimal refractive index, and\nreflectivity in the solar range of the light spectrum (1–4\neV). The calculated elastic parameters verified that SrTiO<sub>3</sub> and CaTiO<sub>3</sub> are mechanically and thermally stable, which\nfurther supports their potential function in solar cells.