Abstract: In order to obtain high-quality Zn（O,S）cadmium-free buffer layers in Cu（In,Ga）Se2thin film solar cells,the deposition mechanism of Zn（O,S）films prepared by trisodium citrate as a complexing agent was expounded,and the effects of reaction parameters on the chemical bath deposition were systematically investigated. The results show that the concentration of trisodium citrate significantly affects the type of reaction,and heterogeneous reaction is more conducive to the deposition of high-quality films. Besides that,the ratio of trisodium citrate to metal ion concentration directly affects the deposition quality and the deposition rate. A suitable pH solution environment helps to improve the quality of Zn（O,S）thin film. Furthermore,the device efficiency of Zn（O,S）/CIGS solar cells is close to that of traditional CdS/CIGS solar cells through the optimization of process parameters.