Optimizing the bromide incorporation in mixed-halide Cs x FA1− x Pb(I1− y Br y )3 perovskites for improving solar cell performance

Halide compositional engineering has emerged as a powerful strategy to tailor the optoelectronic properties of hybrid perovskites for photovoltaic applications. In this work, the influence of bromide incorporation in mixed-cation perovskite absorbers with composition CsxFA1−xPb(I1−yBry)3 was systematically investigated. Thin films were deposited using a two-step solution process with controlled bromide precursor concentrations (0%–19%). The structural, optical, morphological, and compositional properties were analyzed by x-ray diffraction, UV–Vis spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Bromide incorporation produced a progressive lattice reduction and bandgap widening. Moderate bromide concentrations improved film morphology and reduced defect density. Perovskite solar cells with architecture fluorine tin oxide/TiO2/perovskite/copper(I) thiocyanate/Au were fabricated and characterized by J–V measurements. The optimal devices were obtained with 13.6% molar bromide in the precursor solution, achieving a power conversion efficiency of 10.2% with Voc = 0.935 V, Jsc = 20.04 mA cm−2, and fill factor = 0.55. Analysis of diode parameters revealed a reduction in saturation current density (J0) and an increase in shunt resistance (Rsh), indicating suppressed recombination pathways and improved junction quality. These results demonstrate that controlled bromide incorporation effectively optimizes the structural and electronic properties of hybrid perovskite absorbers, leading to improved photovoltaic performance.