A modified deposition of CdS buffer layer and its application in Cu2ZnSn(S,Se)4 solar cells

In this paper, we prepared CdS buffer layers using a modified chemical bath deposition process and applied the buffer layers in Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. For the deposition of the buffer layers, we added zinc acetate and ammonia acetate into the typical deposition solution of CdS. We found the adding of ammonia acetate could improve the uniformity and prevent the formation of pin-pores in the deposited buffer layers. Then different buffer layers were prepared by changing the ratio between the concentrations of Cd and Zn ions (Cd/Zn ratio) in the deposition solution. Composition measurement prove that Zn exist at the surface of the buffer layers but the concentration of Zn in the whole layer is limited. The electrical properties of the buffer layers can be changed by changing the Cd/Zn ratio in the solution. Moreover, the open-circuit voltage of the CZTSSe solar cells using the CdS buffer layers can be increased by decreasing the Cd/Zn ratio in the deposition solution, implying the junction properties of the CZTSSe solar cells can be changed by modifying the deposition of buffer layer.