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Abstract
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Tin-based perovskite solar cells are promising lead-free alternatives, yet their performance is limited by chemical instability and inefficient charge transport. In this work, FAxMA1−xSnI3 devices were systematically studied across the full compositional range (x = 0–1) using electrical, optical, and impedance analyses. The results reveal that end-member MASnI3 suffers from Sn2+ oxidation and halide vacancy formation, while FA-rich cells exhibit lattice softness and ionic disorder, both leading to trap-assisted recombination and poor junction quality. In contrast, mixed FA/MA compositions (x = 0.5–0.7) stabilize the Sn–I framework, suppress defect formation, and optimize dielectric relaxation. These devices show sharp Napp responses, minimal Nyquist arcs, higher built-in potentials (Vbi = 0.68–0.72 V), fill factors above 83%, and peak efficiencies approaching 24.5%. The findings highlight the critical role of compositional balance in mitigating chemical instabilities and enhancing physical transport, establishing FA/MA mixing as a key strategy for high-performance tin-based perovskite photovoltaics.
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