Enhancement of power conversion efficiency of Ag-substituted Cu2ZnSn(S,Se)4 solar cells via tuning Cu2+/(Cu++Cu2+) percentage in precursor solution

Although trace silver (Ag) substitution for Cu in Cu 2 ZnSn(S, Se) 4 (CZTSSe) offers benefits in improving open-circuit voltage (V OC ) of CZTSSe solar cells, its further development is still hindered by the fairly low short-circuit current density (J SC ) owing to the increase of bandgap (E g ) of the absorber layer . Herein, a strategy is demonstrated to mitigate the poor J SC arising from the Ag substitution by tuning the Cu 2+ /(Cu + +Cu 2+ ) percentage in the (Cu, Ag) 2 ZnSnS 4 (CAZTS) precursor solution . Depth characterization indicates that the appropriate Cu 2+ /(Cu + +Cu 2+ ) percentage in the CAZTS precursor solution increases the photogenerated charges separation and carrier transport processes for Ag-substituted CZTSSe (CAZTSSe) solar cells. Benefiting from this strategy, the power conversion efficiency (PCE) of 9.57% is achieved when the Cu 2+ /(Cu + +Cu 2+ ) is 50 at.%. The main factor for the improvement of PCE is due to the increase in photogenerated current density (J L ) and decrease in shunt resistance (R sh ). It is demonstrated that the increase in J L results from a widening in the depletion layer width (W d ) of the p-n junction and an increase in carrier lifetime, induced by optimization of the Cu 2+ /(Cu + +Cu 2+ ) percentage. While the decrease in R sh comes from the change of reaction pathways due to the change in Cu 2+ /(Cu + +Cu 2+ ) percentage.