Enhancing the Photocurrent Density and Stability in CZTSSe Photocathode for PEC System Through Defect Control Inside Grain Boundary of Active Layer

Cu₂ZnSn(S,Se)₄(CZTSSe) has been shown to overcome CIGS disadvantage as a favorable material applied to thin film solar cells and photocathodes because of its eco-friendly, earth-abundant, and high absorption. However, the device performance like the power conversion efficiency and solar to hydrogen was still low, therefore further study is essential to decrease the resistance and control defects in the active layer. CZTSSe was known to be very difficult to control its phase and had many defects such as voids, vacancies, and mismatch band energy levels. In this work, we have synthesized the CZTSSe thin films by doping the Cd atom using the CBD method to control defects inside its grain boundary which caused recombination. When a proper Cd amount is doped, the deep level and shallow defects in grain interior and boundary are reduced, significantly preventing recombination. As a result, the Cd-doped CZTSSe thin film solar cells demonstrated the highest average current density and performance of ~9.26% and ~34.76 mA/cm², respectively. Furthermore, the Cd-doped CZTSSe photocathode had a promising photocurrent density of ~19.05 mA/cm² in neutral electrolyte. Therefore, affected by the Cd doping, the CZTSSe photodevices showed remarkable performance among photocathodes synthesized using a DC-sputtering system.