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Nature Energy (2026)Cite this article
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Two-step fabrication method of formamidinium–caesium metal halide perovskites (FA_1-xCs_xPbI₃) offers superior control over crystallization regulation and therefore is more suitable for solar cell manufacturing. However, forming the ideal α phase required for stable devices remains challenging due to limited Cs⁺ incorporation and unclear phase transition mechanism. Here we design caesium 4-(diphenylphosphino)benzoate to enable efficient Cs⁺ doping and to homogenize cation distribution, obtaining high-quality perovskite films with improved phase stability. As a result, the solar cells fabricated via the two-step process achieve an efficiency of 26.91% (certified 26.61%). The devices incorporating a thermally stable charge-transport layer retain 95% of their initial efficiency (23.76%) after continuous operation under 1-sun illumination at the maximum power point tracking and 85 °C (ISOS-L-2 protocol) for 1,500 hours. This study provides insights into the phase transition pathway and the corresponding transition-state structure of FA_0.9Cs_0.1PbI₃ as well as the mechanism of Cs⁺-driven lattice stabilization in perovskites.
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Y.C. thanks the National Natural Science Foundation of China (NSFC) (52527804). L.T. thanks the National Natural Science Foundation of China (NSFC) (52373186).
These authors contributed equally: Jiacheng He, Zhao Guo.
College of Chemistry and Chemical Engineering/Film Energy Chemistry for Jiangxi Provincial Key Laboratory/Institute of Polymers and Energy Chemistry, Nanchang University, Nanchang, China
Jiacheng He, Zhao Guo, Kaikai Liu, Wangping Sheng, Xiao Luo, Licheng Tan & Yiwang Chen
Department of Materials Science and Engineering, Institute of Innovative Materials, Shenzhen Key Laboratory of Full Spectral Solar Electricity Generation, Southern University of Science and Technology, Guangdong, China
Jiacheng He
Key Laboratory of Fluorine and Silicon for Energy Materials and Chemistry of Ministry of Education, Jiangxi Normal University, Nanchang, China
Yiwang Chen
College of Chemistry and Chemical Engineering, Gannan Normal University, Ganzhou, China
Yiwang Chen
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J.H. conceived of the idea and designed the project with L.T., and Y.C. directed and supervised the research. J.H. contributed to the fabrication and characterization of films and devices. Z.G. contributed to the device fabrication and characterization. K.L. and W.S. conducted the SEM measurements and GIWAXS measurements. J.H., Z.G. and X.L. fabricated and characterized the devices for the accelerated aging test. J.H., L.T. and Y.C. drafted, revised and finalized the paper. All authors contributed to data analysis and read and commented on the paper.
Correspondence to Licheng Tan or Yiwang Chen.
The authors declare no competing interests.
Nature Energy thanks Nam-Gyu Park and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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He, J., Guo, Z., Liu, K. et al. Controlled Cs⁺ incorporation through organocaesium salts in α-FA–Cs perovskite solar cells with a certified efficiency of 26.61%. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02016-7
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Received: 04 March 2025
Accepted: 25 February 2026
Published: 27 March 2026
Version of record: 27 March 2026
DOI: https://doi.org/10.1038/s41560-026-02016-7
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