The partial substitution of Cu+ with Ag+ into the host lattice of Cu2ZnSn(S,Se)4 thin films can reduce the open-circuit voltage deficit (Voc,deficit) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH2) and 1,2-ethylenediamine (en) and used for the formation of (Cu1–xAgx)2ZnSn(S,Se)4 (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the Voc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.
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.
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