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Heat treatment in an oxygen-rich environment to suppress deep-level traps in Cu2ZnSnS4 solar cell with 11.51% certified efficiency

Nature Energy volume 10, pages 630–640 (2025)Cite this article

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Abstract

Sulfide kesterite Cu2ZnSnS4 (CZTS) is a competitive photovoltaic material, especially for multijunction solar cells. However, the device power conversion efficiency has remained stagnant for years. Deep-level defects, such as sulfur vacancies (VS), cause serious non-radiative recombination of charge carriers. Here we propose a passivation strategy for VS through the heat treatment of the CdS/CZTS heterojunction in an oxygen-rich environment. In this process, VS are occupied by oxygen atoms, suppressing VS defects. In addition, the diffusion of Cd ions to the CZTS absorber layer, and the formation of positive Na–O and Sn–O complexes can passivate related defects. These effects led to a reduced charge recombination and favourable band alignment. We demonstrate a certified efficiency of 11.51% for air-solution-processed CZTS solar cells (bandgap of 1.5 eV) without any extrinsic cation alloying. The study offers insights into defect passivation and performance improvement mechanism of kesterite solar cells.

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Fig. 1: Solar cell fabrication and photovoltaic performance.
Fig. 2: Characterization of oxygen distribution and element diffusion.
Fig. 3: Characterization of surface electrical properties and interface band alignment.
Fig. 4: Characterization of defect properties and carrier dynamics.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. The data that support the findings of this study are available within the Article and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (grant 52472225 to G.L.), Shenzhen University 2035 Program for Excellent Research (grant 2024B003 to G.L.), Guangdong Basic and Applied Basic Research Foundation (grant 2025A1515012041 to G.L.) and Science and Technology plan project of Shenzhen (grant 20220808165025003 to G.L.) China. We acknowledge the assistance on (TEM/STEM/FIB) received from the Electron Microscope Center of Shenzhen University. We acknowledge the assistance on TPC and TPV by Q. Meng of the Chinese Academy of Sciences. We acknowledge the assistance on DLTS by S. Wu of Henan University. We acknowledge the assistance on KPFM by Y. Zhang at Nankai University.

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Author notes

  1. These authors contributed equally: Tong Wu, Shuo Chen, Zhenghua Su, Zi Wang.

Authors and Affiliations

  1. Shenzhen Key Laboratory of Advanced Thin Films and Applications, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen, China

    Tong Wu, Shuo Chen, Zhenghua Su, Zi Wang, Ping Luo, Zhuanghao Zheng, Jingting Luo & Guangxing Liang

  2. CNRS, ISCR (Institut des Sciences Chimiques de Rennes), Université de Rennes, Rennes, France

    Tong Wu, Hongli Ma & Xianghua Zhang

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  1. Tong Wu
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Contributions

G.L. supervised the project and conceived the ideas. T.W. and Z.W. prepared the thin films, fabricated the solar cells, conducted data analysis and characterization. S.C., Z.S., P.L. and Z.Z. helped to design the experiments. H.M. and J.L. assisted with device optimization and data collection. T.W., S.C., Z.S. and Z.W. drafted the paper. G.L. T.W., S.C., Z.S. and X.Z. were involved in the paper writing and revisions. All the authors approved the final version of the paper.

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Correspondence to Guangxing Liang.

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Nature Energy thanks Alejandro Perez-Rodriguez and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Wu, T., Chen, S., Su, Z. et al. Heat treatment in an oxygen-rich environment to suppress deep-level traps in Cu2ZnSnS4 solar cell with 11.51% certified efficiency. Nat Energy 10, 630–640 (2025). https://doi.org/10.1038/s41560-025-01756-2

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