Enhancing Li tolerance via Ag doping in high-efficiency CZTSSe solar cells
image: High-concentration Li doping leads to the thickening of the fine grain layer and the formation of large voids at the back interface of the thin film. The introduction of Ag eliminates the fine grain layer and promotes the grain growth, significantly improving the overall quality of the thin film.
Credit: Nano research, Nankai University Press
Multi-element co-doping has become an effective approach to optimize thin-film quality and enhance device power conversion efficiency (PCE) in studies related to CZTSSe solar cells. However, most of co-doping studies have primarily concentrated on the isolated effects of individual doping elements on CZTSSe thin films, often neglecting the potential interactions between co-doping elements.
A team led by Yi Zhang from Nankai University in Tianjin, China recently discovered that the incorporation of Ag enhances the tolerance of the CZTSSe thin film to Li. In the case of Li single-doping, a concentration exceeding 4% leads to the deterioration of thin-film quality, consequently degrading the device's PCE. However, with the addition of Ag, the Li doping concentration can be increased up to 8%, which is more beneficial for improving the open-circuit voltage of the solar cells.
To elucidate the underlying mechanism, the team conducted a comprehensive investigation into the electrical properties of solar cells and the morphology of the absorber layer under different doping concentrations. They found that while both Li and Ag doping contribute to optimizing the overall electrical properties of the device, the key factor lies in the significant improvement in the quality of the absorber layer induced by Ag incorporation. Specifically, the fine grain layer and numerous voids at the back interface, which are typically caused by high-concentration Li doping, were notably mitigated with the addition of Ag. The further interruption experiment revealed that the incorporation of Ag facilitates the formation of a denser upper layer during the early stages of the reaction. This denser layer effectively regulates the rapid diffusion of Se into the interior, thereby slowing down the reaction rate at the back interface. As a result, the formation of the fine grain layer is controlled, contributing to the enhancement in thin film quality. This improvement effectively reduces the grain boundary density at the back interface, suppresses carrier recombination, and ultimately enhances the PCE of the CZTSSe solar cell.
“This study establishes a valuable framework for future research on co-doping strategies involving various elements. The systematic investigation of dopant interactions and optimization of doping concentrations may pave the way for achieving higher PCE of solar cells.” said Yi Zhang.
The team published their study in Nano Research on June 5, 2025
Other contributors include Yue Liu, Rutao Meng, Jiabin Dong, Han Xu, Xuejun Xu, Zixiu Cao, Jincheng Zhang, and Haoran Li from the Institute of Photoelectronic Thin Film Devices and Technology and Tianjin Key Laboratory of Photoelectronic Thin Film Devices and Technology, and Engineering Research Center of thin film optoelectronics technology, Ministry of Education, Nankai University, Tianjin 300350, China.
This work was supported by the National Key Research & Development Program of China (2024YFB4205300).
About the Authors
Dr. Yi Zhang is a full professor in the Institute of Photoelectronic Thin Film Devices and Technology, Nankai University, Tianjin 300350, China. His research interests focus on wide-bandgap compound semiconductor heterojunction optoelectronic devices, energy-oriented photoelectric conversion materials and devices, as well as novel photo-stimulated materials and optoelectronic devices. Until now, he has published more than 100 papers in Energy Environ. Sci., Adv. Mater and other journals, owns 6 invention patents. For more information, please pay attention to his research homepage. https://ceo.nankai.edu.cn/szll/gdzbmqjyjsyjs/zy.htm
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.