Improvement of the performance of Cu2ZnSn(S,Se)4 solar cells by synergistic effect of nonuniform Ag and In Co-doping

In this work, non-uniform Ag and In co-doped CZTSSe (NoU-Ag x In y , x = Ag/(Ag + Cu) = 0–15 %, y = In/(In + Zn + Sn) = 0–12 %) was prepared by doping Ag at the front surface of CZTSSe and doping In at the back surface of CZTSSe. CZTSSe solar cell with conventional structure but without anti-reflection layer was fabricated by using the NoU-Ag x In y as absorber (Cell-NoU-Ag x In y ). Through optimizing the Ag and In doping concentration, the highest PCE of 11.82 % was achieved in the cell-NoU-Ag x In y with x = 10 % and y = 8 %. It is higher than the highest PCE (9.05 %) of CZTSSe solar cells obtained in this work and the highest PCE (9.45 %) of uniform Ag and In co doped CZTSSe solar cells with similar doping concentrations of Ag and In. Compared to CZTSSe solar cell, the increased PCE of cell-NoU-AgIn is dominantly due to decreased J 0 , followed by increase in J L . The decrease in J 0 is mainly attributed to reduce in number of [2Cu Zn  + Sn Zn ] defect clusters and of ZnSe at front interface induced by Ag doping, as well as formation of passivation field at back interface induced by In doping. The increase in J L is mainly due to increase in depletion region width induced by the Ag doping and formation of the passivation field. This study demonstrates that non-uniform Ag and In doped CZTSSe is favorable to increasing PCE of CZTSSe solar cells.