Quantum Chemical Modeling of CH3NH3MX3 (MAM*X3: M* = Sn, Si, Ge; X = Cl, Br, I) Lead-Free Perovskites in Comparison with Lead-Based Perovskite Materials

Herein, the theoretical approach with the aid of solid-state density functional theory (DFT) and time-dependent density functional theory (TD-DFT) based codes has been utilized to investigate the structural, electronic, and optoelectronic properties of methyl ammonium MAM*X-3 (M* = Sn, Si, Ge; X = Cl, Br, I) lead-free engineered systems. Results elucidated from the structural lattice parameters when Ge, Sn, and Si were doped influences the halides to exhibit unique trend of I > Br > Cl which also reflects the stability of the engineered perovskite. Both Pb-contained and Pb-free organic-inorganic hybrid perovskites (PSCs) exhibit a direct bandgap in the direction of the <SIC> CYRILLIC CAPITAL LETTER GHE point symmetry for valence band maxima and conduction band minima. The calculated bandgaps for both MAPbX(3) and MAM*X-3 (M* = Sn, Si, and Ge) are 1.85 eV and 1.42, 1.40, and 1.52 eV, for M* = Sn, 1.24, 1.32, and 1.38 eV for M* = Si, 1.39, 1.22, and 1.43 for M* = Ge respectively, in accordance to halide contribution of the constituent Cl-3, I-3, and Br-3, correlatively. The UV-Vis results obtained from the turbo-lanczos TD-DFT computations explicates that three prominent peaks were evidently observed at different wavelengths of absorption. As such, at 300-350 and 350-380 nm, Sil(3) and SiBr3 (CH3NH3SiI3 and CH3NH3SiBr3) modelled perovskite solar cells (PSCs) gave the highest absorbance of 14.0% atomic unit (a.u), depicting a high level of electron excitation upon absorption of ultraviolet rays.