Facile synthesis of mixed-phase cobalt sulfide counter electrodes for efficient dye sensitized solar cells

We report a facile and simple approach for growing low-cost and mixed-phase cobalt sulfide counter-electrodes (CEs) for efficient dye sensitized solar cells (DSSCs). The whole process involves growth of cobalt sulfide powders using a solution containing cobalt acetate and sodium sulfide by a chemical precipitation method at room temperature, preparation of cobalt sulfide pastes with ethyl cellulose, formation of cobalt sulfide films by screen-printing method, and treatment of the formed cobalt sulfide layers at 400 °C. Mixed-phase cobalt sulfide was formed on the FTO substrate after annealing. The electronic and ionic processes in platinum and cobalt sulfide based DSSCs are examined, analyzed and compared. Highly efficient DSSCs with mixed-phase cobalt sulfide CEs have been fabricated. The DSSC featuring a mixed-phase cobalt sulfide electrode achieved an energy efficiency as high as 7.2 %. The proposed cobalt sulfide CE manufacturing method is cheap and scalable. It can make large-scale electro-catalytic film fabrication cost competitive for both energy harvesting and storage applications.