Understanding proton radiation-induced degradation mechanisms in Cu2ZnSn(S,Se)4 kesterite thin-film solar cells

Inorganic kesterite Cu₂ZnSn(S,Se)₄ thin film solar cells are well suited for optoelectronic applications. However, severe deficits in open-circuit voltage (V_OC) and fill factor (FF), attributed to defect states at the interface and/or within the bulk material, pose significant obstacles to further efficiency improvements. Herein, we applied proton irradiation at varying energy to CZTSSe thin-film solar cells to deliberately alter the device structure and investigate the mechanisms behind performance degradation. Our results indicate that the open-circuit voltage is highly sensitive to both the quality of the CdS/CZTSSe interface and the distribution of sodium (Na) within the device. Changes in the interface characteristics can significantly degrade the V_OC and FF. Excessive diffusion of Na from the substrate can reduce device performance, emphasizing the necessity for an optimized Na distribution to achieve high efficiency. Notably, the CZTSSe absorption layer exhibits excellent resistance to proton irradiation. These findings are crucial for the continued development and potential commercialization of CZTSSe thin-film solar cells.