High-Performance Platinum-Free Dye-Sensitized Solar Cells with Molybdenum Disulfide Films as Counter Electrodes

By using a radio-frequency sputtering method, we synthesized large-area, uniform, and transparent molybdenum disulfide film electrodes (1, 3, 5, and 7 min) on transparent and conducting fluorine-doped tin oxide (FTO), as ecofriendly, cost-effective counter electrodes (CE) for dye-sensitized solar cells (DSSCs). These CEs were used in place of the routinely used expensive platinum CEs for the catalytic reduction of a triiodide electrolyte. The structure and morphology of the MoS2 was analyzed by using Raman spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy measurements and the DSSC characteristics were investigated. An unbroken film of MoS2 was identified on the FTO crystallites from field-emission scanning electron microscopy. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve measurements reveal the promise of MoS2 as a CE with a low charge-transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide. Finally, an optimized transparent MoS2 CE, obtained after 5 min synthesis time, showed a high power-conversion efficiency of 6.0 %, which comparable to the performance obtained with a Pt CE (6.6 %) when used in TiO2 -based DSCCs, thus signifying the importance of sputtering time on DSSC performance.