Effects of the Annealing Conditions on the Properties of Cu₂ZnGeSe₄ Thin Film Solar Cells

Cu₂ZnGeSe₄ (CZGSe) thin-film, as materials with a wide bandgap close to the ideal bandgap for solar cells, have attracted attention. However, the efficiency of the CZGSe devices is far below the theoretical efficiency mainly due to the presence of defects and defect clusters. This study aims to determine the optimal selenization temperature and time of Cu–Zn–Ge–S precursor prepared by spin coating deposition to improve CZGSe absorption layer quality and the corresponding device performance. Specifically, the CZGSe absorber layers were selenized using a three-step method, precisely annealing controlling the conditions of the first and second selenization stages, and adjusting the temperature and time of the last stage. The study emphasizes the effects of varying annealing temperatures and duration on CZGSe absorber layer grain growth and device performance. In-depth analysis was conducted through structural and electrical characterization. The results show that the CZGSe absorber layer exhibits a denser and smoother surface under the selenization temperature and time of 560 °C and 12 min respectively, resulting in the best device efficiency (PCE) of 5.12%, with a short-circuit current density (J_SC), a fill factor (FF) and an open-circuit voltage (V_OC) of 21.89 mA/cm², 39.00% and 599.92 mV respectively.