Dye-sensitized solar cells (DSCs) have achieved impressive conversion efficiencies for solar energy of over 11% with an electrolyte that contains triiodide/iodide as a redox couple. Although triiodide/iodide redox couples work efficiently in DSCs, they suffer from two major disadvantages: electrolytes that contain triiodide/iodide corrode electrical contacts made of silver (which reduces the options for the scale up of DSCs to module size) and triiodide partially absorbs visible light. Here, we present a new disulfide/thiolate redox couple that has negligible absorption in the visible spectral range, a very attractive feature for flexible DSCs that use transparent conductors as current collectors. Using this novel, iodide-free redox electrolyte in conjunction with a sensitized heterojunction, we achieved an unprecedented efficiency of 6.4% under standard illumination test conditions. This novel redox couple offers a viable pathway to develop efficient DSCs with attractive properties for scale up and practical applications.
In summary, we have demonstrated, for the first time, that CoS is very effective in catalyzing the reduction of triiodide to iodide in a DSC, superseding the performance of Pt as an electrocatalyst.
For the first time, CoS deposited ITO/PEN films were used as the counter electrodes in DSCs yielding 6.5% efficiency under full sunlight in conjunction with a Z907 sensitizer and an eutectic melt electrolyte. Remarkable cell stability under prolonged light soaking and thermal stress was demonstrated rendering CoS an extremely interesting candidate to replace Pt in photoelectrochemical cells employing the iodide/triiodide redox couple. This breakthrough will contribute to lowering the cost of the DSC, fostering large-scale lightweight outdoor applications of mesoscopic sensitized solar cells.