Effect of the duration of a wet KCN etching step and post deposition annealing on the efficiency of Cu2ZnSnSe4 solar cells

The influence of the duration of the KCN etching step on the efficiency of Cu₂ZnSnSe₄(CZTSe) solar cells and Post deposition annealing (PDA) has been explored. CZTSe thin film absorbers prepared by selenization at 450 °C were etched by 5 wt% KCN/KOH from 30s up to 360 s before solar cell processing. KCN etching times above 120 s resulted in poor efficiencies. The fill factor (FF) and short circuit current density (Jsc) of these devices were affected severely. After annealing the solar cells at 200 °C in N₂atmosphere the best devices degraded and poor devices improved. Combined physical and optoelectronic characterization of the solar cells showed that PDA modifies the bulk defect density and also surface composition which reflects in the solar cell performance.