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Nature Energy (2026)Cite this article
Flexible kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) photovoltaics are attractive for lightweight and portable applications, but their efficiency remains limited by uncontrolled alkali-metal incorporation. Here we elucidate and exploit the distinct and complementary roles of Na and Li in controlling CZTSSe crystallization on flexible substrates. Our results show that Na promotes crystal growth, but its induced Se enrichment simultaneously drives large-scale SnSe_x phase segregation. The incorporation of Li reshapes the free-energy landscape of Cu-related phases, promoting the formation of Cu_xSe that consumes Se and thereby suppressing SnSe_x phase growth while driving ordered phase evolution. This kinetic competition strategy yields high-quality CZTSSe films with reduced charge recombination loss and enables power conversion efficiencies of 14.5% (certified 14.2%) for flexible cells and 12.7% (certified 12.0%) for shingled modules. Our results provide mechanistic insights into alkali-metal regulation in chalcogenide solar cells and demonstrate a kinetic competition strategy that can be generalized to regulate crystallization in complex multinary materials.
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This work was supported by the National Key R&D Program of China (2024YFB4205000 to J.S.); the National Natural Science Foundation of China (52222212 to J.S., 52227803 to Q.M., 52172261 to Y. Luo, 52402243 to X.X. and 52502322 to Jinlin Wang); the Zhejiang Provincial Natural Science Foundation (LQN25E020011 to X.X.); and the China National Postdoctoral Program for Innovative Talents (BX20250177 to Jinlin Wang). J.S. also gratefully acknowledges support from the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2022006).
These authors contributed equally: Xiao Xu, Jinlin Wang.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, P. R. China
Xiao Xu, Jinlin Wang, Menghan Jiao, Bowen Zhang, Tan Guo, Yuan Li, Jingchen Wang, Shudan Chen, Yiming Li, Dongmei Li, Jiangjian Shi, Huijue Wu, Yanhong Luo & Qingbo Meng
Institute of Carbon Neutrality and New Energy, School of Electronics and Information, Hangzhou Dianzi University, Hangzhou, P. R. China
Xiao Xu & Wensheng Yan
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, P. R. China
Menghan Jiao, Bowen Zhang, Jingchen Wang, Shudan Chen, Dongmei Li & Yanhong Luo
College of Materials Sciences and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, P. R. China
Tan Guo
Songshan Lake Materials Laboratory, Dongguan, P. R. China
Dongmei Li, Yanhong Luo & Qingbo Meng
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, P. R. China
Qingbo Meng
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The manuscript was written through the contribution of all authors. All authors have given approval for the final version of the manuscript. Q.M., J.S. and W.Y. contributed to the supervision, discussion and writing (review and editing). X.X. and Jinlin Wang contributed to the experiments, simulation, characterization and writing (original draft). H.W. contributed to the discussion. M.J., B.Z., T.G., Yuan Li, Jinchen Wang and S.C. contributed to the data analysis and discussion. J.S. and Yiming Li contributed to the discussion and m-TPC/m-TPV analyses. D.L. and Y. Luo contributed to the data analysis.
Correspondence to Jiangjian Shi, Wensheng Yan or Qingbo Meng.
The authors declare no competing interests.
Nature Energy thanks Victor Izquierdo-Roca and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Notes 1–3, Figs. 1–29, Tables 1–3 and References.
Supplementary data for Figs. 12, 14–16 and 21.
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Xu, X., Wang, J., Jiao, M. et al. Alkali-metal-mediated control of phase segregation for flexible kesterite solar cells and modules with improved efficiency. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02018-5
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Received: 08 February 2025
Accepted: 27 February 2026
Published: 20 March 2026
Version of record: 20 March 2026
DOI: https://doi.org/10.1038/s41560-026-02018-5
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