First-Principle Insights of Electronic and Optical Properties of Cubic Organic-Inorganic MAGexPb(1-x)I3 Perovskites for Photovoltaic Applications

Owing to power conversion efficiencies of as high as 22.1%, hybrid organic-inorganic lead halide perovskites have become the fastest growing solar technology, competing with the conventional thin-film technology. Though unique and exceptional, long-term stability issue and toxic behavior caused by the lead content in the perovskites hamper large-scale commercial production. With this motivation toward achieving a stable and reduced toxic perovskite, we have investigated the structural, electronic, and optical properties of mixed MAGe(x)Pb((1-x))I(3) perovskites with the generalized gradient approximation-Perdew, Burke, Ernzerhof exchange-correlation functional within the framework of density functional theory. Under structural properties, we have calculated the lattice constants, bond lengths, tolerance factors, enthalpies of formation, bulk moduli, and their derivatives for x = 0.0, 0.125, 0.375, 0.625, and 0.875. We found that mixed MAGe(x)Pb((1-x))I(3) perovskites are stable except at x = 0. The electronic properties such as band gaps, energy band level, and effective masses have been predicted for all combinations of x. We have also analyzed the projected and total density of states in detail. Optical properties like imaginary and real parts of dielectric function, refractive index, and extinction coefficient have been discussed. Further, to understand the light trapping capacity, we have examined the absorption coefficients for x = 0.0, 0.125, 0.375, 0.625, and 0.875, and interband transitions are well estimated. The calculated values of all parameters were compared with the available experimental and theoretical values. A fairly good agreement has been obtained between them.