Abstract
Platinum-free counter electrodes (CE) were developed for use in efficient and cost-effective energy conversion devices, such as dye-sensitized solar cells (DSSCs). Electrochemical deposition of CoS2 on fluorine-doped tin oxide (FTO) formed a hierarchical sheet-like structured CoS2 thin film. This film was engaged as a cost-effective platinum-free and high-efficiency CE for DSSCs. High stability was achieved using a phthaloychitosan-based gel-polymer electrolyte as the redox electrolyte. The electrocatalytic performance of the sheet-like CoS2 film was analyzed by electrochemical impedance spectroscopy and cyclic voltammetry. The film displayed improved electrocatalytic behavior that can be credited to a low charge-transfer resistance at the CE/electrolyte boundary and improved exchange between triiodide and iodide ions. The fabricated DSSCs with a phthaloychitosan-based gel-polymer electrolyte and sheet-like CoS2 CE had a power conversion efficiency (PCE, eta) of 7.29% with a fill factor (FF) of 0.64, J(sc) of 17.51 mA/cm(2), and a V-oc of 0.65 V, which was analogous to that of Pt CE (eta = 7.82%). The high PCE of the sheet-like CoS2 CE arises from the enhanced FF and J(sc), which can be attributed to the abundant active electrocatalytic sites and enhanced interfacial charge-transfer by the well-organized surface structure.