DFT and TD-DFT studies of perovskite materials LiAX3 (A=Ge, Sn; X= F, Cl, Br, I) in reference to their solar cell applications

Halide perovskite materials have attracted a huge interest of researchers due to their fascinating optoelectronic properties. In this report, structural, electronic, optical, and thermoelectric properties of Li-based perovskite materials LiAX3 (A = Ge, Sn; X = F, Cl, Br, I) are analyzed using Density Functional Theory (DFT). FunctionalsB3LYP/LanL2DZ, B3LYP/def2-TZVP and B3LYP/LanL08 within the DFT framework are applied for geometry optimization of these perovskites. The results show a marked variation in magnitude of HOMO-LUMO energy gap of LiGeX3 and LiSnX3 with respect to different functionals viz. B3LYP/LanL2DZ, B3LYP/def2-TZVP and B3LYP/ LanL08. LiGeF3 and LiSnF3 show the maximum values of HOMO-LUMO energy gap. The computed energy gap lies in the range required for perovskite materials to exhibit solar cell applications. A number of CDFT-based descriptors and Optical properties of LiAX3 are also studied and reported accordingly. Our computed results show that lattice constants, volume, formation energy, polarizability, refractive index, dielectric constant, entropy, heat capacity and wavelength of LiAX3 increases from F to I, whereas, HOMO-LUMO energy gap, electronegativity, electrophilicity index, optical electronegativity, vibrational frequencies, peak IR intensity, vibrational energy, total energy, zero-point vibrational energy, Gibbs free energy and photon energy decreases in the reverse direction.