Toward Stable and Efficient Mixed-Cation Mixed-Halide Perovskite Solar CellsCROSSMARK Color horizontal

Mixed-cation, mixed-halide lead halide perovskites have rapidly progressed from laboratory curiosities to contenders for next-generation photovoltaics. By judiciously alloying A-site cations (Cs⁺, FA⁺, MA⁺) and halide anions (I⁻/Br⁻), these materials marry outstanding optoelectronic quality and bandgap tunability, enabling single-junction devices exceeding 26% and hybrid perovskite–silicon tandems to approach ~35% certified efficiency. Despite these gains, light-induced halide segregation, ion migration, interfacial recombination, and environmental/thermal instability remain central challenges for scale-up and lifetime. This review synthesises the historical context and recent progress on triple-cation, mixed-halide absorbers; surveys at least twenty key studies spanning passivation such as FABr treatments, defect/strain management, and tandem integration; and outlines practical, research-grade synthesis/processing steps for Cs–FA– MA Pb (I, Br) ₃. We discuss characterization workflows via XRD, GIWAXS, PL/TPV/TRPL, UPS/Kelvin probe, JV under MPP tracking, EQE-EL reciprocity, and ISOS durability protocols, outline consensus findings, and map future directions, including wide-bandgap perovskites for stable tandems, ion-migrationaware design of devices, and AI-guided compositional/process discovery. Certified record data from NREL anchors the current efficiency landscape.