Reducing carrier recombination loss by suppressing Sn loss and defect formation via Ag doping in Cu2ZnSn(S,Se)4 solar cells†

In this study, we analyzed the effect of the position of Ag in the stacked precursor structure of CZTSSe solar cells. Five precursor structures were designed by adding a 5-nm-thick Ag layer to soda-lime glass (SLG)/Mo/Zn/Cu/Sn at various positions, and CZTSSe devices were fabricated through a sulfo-selenization process. The SLG/Mo/Ag/Zn/Cu/Sn precursor structure device (C2) showed the best efficiency. This improvement is attributed to Ag promoting grain growth by forming a Cu–Sn alloy at a low temperature and suppressing the formation of defects and defect clusters. Conversely, the SLG/Mo/Zn/Ag/Cu/Sn precursor structure device (C3) hindered Cu–Zn interdiffusion, degrading the performance. C2 exhibited a small difference between the bandgap energy (E_g) and the photoluminescence, a high activation energy (E_A)/E_g, and a long carrier lifetime, indicating reduced defect and carrier recombination loss. This study suggests that the location of Ag plays an important role in optimizing the CZTSSe efficiency. Additionally, a precursor containing Ag has been shown to suppress Sn loss during the sulfo-selenization process and improve device performance through liquid-assisted grain growth. This study shows that the location of Ag plays an important role in suppressing the carrier recombination loss of CZTSSe devices.