Application of x-ray nanoimaging to explore the reduction of anion vacancies in CZTSe solar cells via hydrogen-assisted selenization

Localized anion vacancies in Cu₂ZnSnSe₄ (CZTSe) solar cells act as carrier traps, significantlylimiting device efficiency. Conventional sulfur/selenization processes often exacerbate these defects, yet direct evidence of their impact remains scarce. This study introduces a hydrogenassisted selenization (HAS) technique to effectively mitigate anion vacancies in CZTSe absorbers. Electrical characterization, including current–voltage (IV) and admittance spectroscopy (AS) analyses, reveals enhanced carrier collection and a reduction in defect states. <br/> Notably, the activation energy of the devices decreases from 184 meV to 145 meV, correlating with improved performance. To gain deeper insights, synchrotron-based X-ray nanoprobe techniques were employed, integrating nanoscale X-ray fluorescence (nano-XRF) and hard X-ray beam-induced current (nano-XBIC) mapping. These high-resolution studies provide direct evidence that reducing anion vacancies significantly enhances local charge carrier dynamics and overall power conversion efficiency. Our results highlight the fundamental role of anion vacancies in CZTSe solar cell performance and demonstrate the effectiveness of the HAS approach as a viable strategy for improving next-generation kesterite-based photovoltaics.