Nonalloyed α-phase formamidinium lead triiodide solar cells through iodine intercalation.

Zhang, Yu; Chen, Yanrun; Liu, Guilin; Wu, Yuetong; Guo, Zhenyu; Fan, Rundong; Li, Kailin; Liu, Huifen et al. · Science · 2025

basic_science · Level V

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Abstract

Formamidinium lead triiodide (FAPbI<sub>3</sub>) is considered the most promising composition for high-performing single-junction solar cells. However, nonalloyed α-FAPbI<sub>3</sub> is metastable with respect to the photoinactive δ-phase. We have developed a kinetic modulation strategy to fabricate high-quality and stable nonalloyed α-FAPbI<sub>3</sub> films, assisted by cogenetic volatile iodine intercalation and decalation. The intercalation of iodine facilitated the formation of corner-sharing Pb-I framework building blocks and reduced the kinetic barrier for α-FAPbI<sub>3</sub> formation, whereas the iodine decalation improved the final perovskite film quality in terms of composition purity and overall homogeneity. Solar cells based on this nonalloyed α-FAPbI<sub>3</sub> (free of other extrinsic composition ions) achieved a power conversion efficiency of >24%. The devices also exhibited excellent durability, retaining 99% of their original power conversion efficiency after operating for more than 1100 hours at 85° ± 5°C under illumination.