The effects of crystal structure on the photovoltaic performance of perovskite solar cells under ambient indoor illumination

Organic-inorganic hybrid lead halide perovskite materials with the general formula MAPbI_3-nBr_n (n = 0, 1, 2, and 3) exhibiting a range of crystal structures and a wide range of optical bandgaps are explored for their potential to harvest energy from ambient light sources. The replacement of I⁻ with Br⁻ is found to transform the perovskite crystal structure from the tetragonal for MAPbI₃ to the pseudo cubic for MAPbI₂Br and MAPbIBr₂ and cubic for MAPbBr₃ while increasing the optical bandgap from 1.59 eV to 2.31 eV. Photovoltaic cells (PVCs) are constructed using these perovskites and are found to exhibit power conversion efficiencies (PCEs) of 29.83 (MAPbI₃), 23.75 (MAPbI₂Br), 21.47 (MAPbIBr₂), and 19.94% (MAPbBr₃) under LED light illumination (1000 lux; ~0.371 mW cm⁻²), with a record high open-circuit voltage (V_OC) of 1.15 V being observed for the MAPbBr₃. The effect of crystal structure variation on the charge carrier mobility, trap states, recombination losses, photovoltaic properties, and operational stabilities has been investigated systematically under indoor illumination. Overall, this work provides a clear vision on the influence of perovskite crystal structures upon the photovoltaic properties and shows a pathway to achieve high V_OC in perovskite PVCs under low-intensity ambient light sources.