One-step hydrothermal synthesis of ZnS-CoS microcomposite as low cost counter electrode for dye-sensitized solar cells

Herein, we report a one-step hydrothermal procedure to prepare ZnS-CoS microcomposite which was employed as counter electrode (CE) for dye-sensitized solar cells (DSSCs). The microcomposite exhibits a morphology with ZnS microspheres decorated with CoS nanoparticles, and the decoration effect on electrocatalytic activity of prinstine ZnS toward I−/I3− redox couple was investigated with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements. Experimental results show that ZnS-CoS microcomposite exhibits remarkably enhanced electrocatalytic activity compared with that of pristine ZnS in catalyzing the reduction of I3−, and the electrocatalytic activity enhancement closely depends on Co/Zn molar ratio. As a result, the optimized DSSC using ZnS-CoS with a Co/Zn molar ratio of 3: 7 as CE exhibits a highest power conversion efficiency of 6.11%, in comparison with the reference device using Pt CE which shows an efficiency of 7.27%. The enhanced performance compared with DSSC using pristine ZnS CE which has an efficiency of 0.59% can be attributed to the introduction of more electrocatalytic active sites in ZnS-CoS microcomposite. Our study thus provides an effective approach to improve electrocatalytic activity of ZnS and proves its potential suitability as CE for the fabrication of DSSCs.