Zinc sulfide (ZnS) quantum dots were prepared by successive ion layer adsorption and reaction (SILAR) technique based on spin coating (spin-SILAR). The effect of the number of SILAR cycle () on optical and photovoltaic properties was studied. An optimized ZnS quantum dot sensitized solar cell demonstrated maximum power conversion efficiency of 3.58% with a short-circuit current of and an open-circuit voltage of 0.58 V under one sun illumination (AM1.5). The results showed that a ZnS QD layer with (thickness ) can be used as a highly efficient sensitizer for solar cells. The ZnS QD layer acts as a light absorber and a recombination blocking layer in the ITO/ZnO film/ZnS QD/P3HT/PCBM/Ag structure.