Optimization of nano-heterojunction heat treatment and interface composition control in solution-processed CZTSSe solar cells

This review examines how heterojunction annealing boosts efficiency of CZTSSe solar cells. Optimized annealing approaches improve element mixing, band alignment, and reduces interface recombination, thus mitigating open-circuit voltage deficit. Strategies such as low-temperature annealing, interlayer insertion, and cation substitution are highlighted. The study also outlines future directions for interface optimization to enhance photovoltaic performance of CZTSSe.

The research team published their review in Nano Research on September 28, 2025.

CZTSSe exhibits significant advantages including abundant elemental constituents, structural stability, tunable bandgap, and high light absorption coefficient. With a certified record efficiency of 15.8% to date, it has emerged as a highly promising novel thin-film photovoltaic material for commercial applications.

"Heterojunction heat treatment (JHT) is a process involving thermal annealing of pre-formed CZTSSe/CdS structures under controlled temperatures (typically 200–300 °C) and specific atmospheres," stated Zhi Zheng. "This technique enhances elemental interdiffusion—such as Cd diffusion into CZTSSe and Zn/Sn interdiffusion into CdS—while also passivating interface defects and optimizing band alignment."

Composition modulation at the heterojunction interface encompasses several strategies: ion engineering in the absorber layer, compositional design of the buffer layer, cadmium-free buffer layer alternatives, and the integration of intermediate interlayers. These approaches collectively contribute to passivating interface defects and optimizing the band structure.

CZTSSe solar technology is approaching industrial viability through advanced annealing methods, interface engineering, and scalable manufacturing techniques that enhance efficiency and production stability.

Other contributing authors include Mengyun Zhang, Lijie Zhao, Lin Sun, Xiangru Wang, Guizhen Liu, Siyu Liu, Junjie Fu, and Chaoliang Zhao from the School of Chemical and Materials Engineering at Xuchang University, as well as Professor Sixin Wu from the School of Materials Science and Engineering at Henan University.

This work was supported by the National Natural Science Foundation of China (Nos. 52472255 and 52072327), Higher Education and Teaching Reformation Project (No. 2014SJGLX064)，Natural Science Foundation of Henan Province (No.232300420099).

About the Authors

Zhi Zheng is a professor and a doctoral supervisor at the College of Chemical and Materials Engineering of Xuchang University, director of Key Laboratory of Micro-Nano Materials for Energy Storage and Conversion of Henan Province, a Zhongyuan Scholar, and a recipient of the New Century Excellent Talents award from the Ministry of Education of China. His research primarily focuses on materials for solar cells. To date, he has published over 280 SCI-indexed papers, including in journals such as J. Am. Chem. Soc., Adv. Mater., and Energy Environ. Sci. He was named a Highly Cited Researcher by Clarivate. He has led 6 projects funded by the National Natural Science Foundation of China and has been granted more than 60 national invention patents.

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.