Influence of Ag Layer Location on the Performance of Cu2ZnSnS4 Thin Film Solar Cells

In this work, the (Ag,Cu)2ZnSnS4 (ACZTS) thin films were fabricated via sputtering with a multi-target to form different layer stacks, i.e., (S1) ZnS/Sn/Cu/Ag/Mo,(S2) ZnS/Sn/Ag/Cu/Mo and (S3) ZnS/Ag/Sn/Cu/Mo. The stacked precursors were sulfurized through a soft annealing, followed by a two-step sulfurization in a chamber filled with N2 at standard atmospheric pressure. The x-ray photoelectron spectroscopy elemental profile showed a vertical non-uniform distribution of Ag in the film. Based on the results of scanning electron microscopy and electron probe microanalysis, Ag enrichment of the upper surface was beneficial for the grain size. Moreover, a dense, uniform surface could be obtained and the stability of the elemental composition could be maintained. After optimizing the order of the Ag layers, the efficiency of the solar cells increased from 1.30% to 3.65%, an improvement of 181%. The open circuit voltage is increased from 448 mV to 630 mV because of the reduced voids, increased grain size, and reduced CuZn antisite defects.