Anion Vacancy Defect Elimination in CZTSe Solar Cells via Hydrogen-Assisted Selenization—In Operando X-Ray Nanoprobe Analysis

The conventional sulfur/selenization method in CZTSSe solar cell production frequently leads to the formation of localized anion vacancies, which act as carrier traps and reduce the efficiency of the solar cells. Despite their detrimental impact, direct evidence of their influence has been limited. In this study, we propose a hydrogen-assisted selenization (HAS) process, specifically designed to mitigate localized anion vacancies in CZTSe solar cells. Our findings, based on current–voltage (IV) and admittance spectroscopy (AS) measurements, demonstrate significant improvements in carrier collection efficiency and a reduction in defect states. The activation energy of the devices also decreased from 184 meV to 145 meV, indicating enhanced performance. Using synchrotron-based X-ray nanoprobes, we further investigated the relationship between local compositional distribution and photocurrent generation, employing nanoscale X-ray fluorescence and hard X-ray beam-induced current measurements. The results strongly indicate that minimizing anion vacancies in the CZTSe layer enhances the power conversion efficiency of CZTSe solar cells. This work highlights the critical role of anion vacancies in device performance and showcases the effectiveness of the HAS process in improving overall solar cell efficiency.