Investigating Light-Induced Metastabilities in Kesterite Solar Cells: Implications and Applications

Kesterite solar cells have recently achieved a significant efficiency milestone, now <b>at the edge of the 15% threshold</b>, thanks to the innovative solution-based approach developed by Gong et al [1]. While thin-film chalcogenides are renowned for their <b>stability </b>in comparison to organic or perovskite counterparts, the phenomenon of <b>light soaking has persisted as a recurring characteristic in solar cell devices</b>. Light soaking refers to the alteration of a solar cell's characteristics after being exposed to illumination for a specific duration. Importantly, this property, whether enhancing or diminishing efficiency, often exhibits reversibility, highlighting <b>a fundamental metastability</b> within the system. Typically, light soaking is conducted under AM1.5g illumination for several minutes, in order to reach a stable state before assessing the performance of the device.<br/>In this study, we aim at offering a comprehensive exploration of these instabilities by manipulating the<b> illumination power density and varying the wavelength</b> during the light soaking process, done both in short circuit and open circuit conditions. We systematically monitor the resultant dark current-voltage (JV) curve and observe noteworthy, reversible changes. These changes can be attributed to<b> interface defects</b>, which are investigated using wavelengths that are minimally absorbed by the absorber. Our approach is supported through optical modelling, utilizing a self-developed code to validate the optical characteristics.<br/>Leveraging numerical electrical modelling via SCAPS1D, we propose a physical interpretation based in the <b>bandgap position of interface defects and their charge states</b>. This comprehensive analysis combines theoretical insights with practical observations, to analyze the complex mechanisms at play during light soaking. Additionally, the results and hypotheses derived from our results are rigorously tested against materials characterizations, including Raman spectroscopy and Photothermal Deflection Spectroscopy.<br/>Beyond the implications for solar cells, these instabilities offer promising possibilities for applications extending <b>beyond the energy sector.</b> One such application is the potential for creating <b>optically controlled memristors</b>, a novel development with significant ramifications in the field of neuromorphic computing and beyond. This research offers a new perspective on light-induced metastabilities in Kesterite solar cells, shedding light on their potential for controlled applications in emerging technologies.