Defects in kesterite materials towards high-efficiency solar cells: origin, impact, characterization, and engineering

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most promising materials for photovoltaics. CZTSSe solar cells have achieved an efficiency of 15.1%, yet further improvements have been challenging. Defects in light-absorbing layers have indelible effects on the performance of kesterite solar cells. In the development of CZTSSe solar cells, a good understanding and effective engineering of the defects in CZTSSe absorbers have been demonstrated to be crucial factors for the fabrication of high-efficiency CZTSSe solar cells. Some effective defect passivation strategies have successfully been applied to reduce defects in CZTSSe absorbers to improve film quality and device properties. Defect characterization techniques also play an important role in clarifying the mechanism of defect passivation in CZTSSe solar cells, allowing the development of more prospective passivation strategies. This review summarizes the types of defects in CZTSSe absorbers and the mechanisms for their formation, as well as their impact on the device performance. Furthermore, commonly used defect passivation strategies and advanced measurements of defects were precisely reviewed, aiming to provide powerful guidelines for further commercialization and applications of CZTSSe solar cells. The origins and effects of defects in kesterite absorbers as well as commonly used defect characterization and passivation techniques are summarized, and critical insights toward high-efficiency CZTSSe solar cells are presented.