Investigation of electronic and optical properties in bismuth/antimony co-doped methylammonium lead bromide

Abstract

Lead halide perovskites, exemplified by methylammonium lead bromide (MAPbBr3), represent a cornerstone in the pursuit of next-generation photovoltaic materials owing to their tunable optoelectronic properties, defect tolerance, and cost-effective synthesis. However, their intrinsic bandgap limitations and carrier recombination pathways necessitate advanced doping strategies to enhance performance. Herein, density functional theory calculations were employed, utilizing the Perdew–Burke–Ernzerhof functional for structural optimization and the Heyd–Scuseria–Ernzerhof hybrid functional for precise electronic structure determination. Computations were conducted in a 2 × 2 × 2 cubic supercell, probing a spectrum of substitutional configurations at Pb2+ sites, including single-dopant systems (MAPb0.875Sb0.125Br3 and MAPb0.875Bi0.125Br3) and co-doped variants up to high concentrations, such as MAPb0.5Sb0.125Bi0.375Br3 and MAPb0.5Sb0.375Bi0.125Br3. Band structures, interpolated via maximally localized Wannier functions using the selected columns of the density matrix with k-point sampling method, reveal a pristine direct bandgap of 2.32 eV at the Γ point, which narrows non-rigidly upon doping due to the introduction of deep donor states from heterovalent Sb3+ and Bi3+ impurities. These states manifest as midgap impurity bands, shifting the conduction band minimum downward while preserving valence band integrity. Optical properties, derived from time-dependent density functional perturbation theory via the Lanczos recursion algorithm, exhibit a pronounced redshift in the absorption onset and an enhanced intensity in the imaginary dielectric function (ɛ2) across the visible spectrum, attributed to broadened interband transitions and synergistic dopant-induced polarizability. Formation energy calculations confirm the thermodynamic accessibility of these co-doped configurations.