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*X₃ (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 Г point symmetry for valence band maxima and conduction band minima. The calculated bandgaps for both MAPbX₃ and MAM^*X₃ (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 Cl₃, I₃, and Br₃, 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, Sil₃ 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.