High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts

Top Cited Papers
Publisher Website
Google Scholar
Abstract
The presence of organic solvents in solar cells has hindered the application of devices, especially in flexible cells. Now, by mixing three solid salts, a solvent-free liquid electrolyte for dye-sensitized solar cells has been discovered that shows both excellent efficiency and stability. Low-cost excitonic solar cells based on organic optoelectronic materials are receiving an ever-increasing amount of attention as potential alternatives to traditional inorganic photovoltaic devices. In this rapidly developing field, the dye-sensitized solar cell1 (DSC) has achieved so far the highest validated efficiency of 11.1% (ref. 2) and remarkable stability3. However, the cells with the best performance use volatile solvents in their electrolytes, which may be prohibitive for outdoor solar panels in view of the need for robust encapsulation. Solvent-free room-temperature ionic liquids4,5,6,7,8,9,10,11 have been pursued as an attractive solution to this dilemma, and device efficiencies of over 7% were achieved by using some low-viscosity formulations containing 1-ethyl-3-methylimidazolium thiocyanate8, selenocyanate9, tricyanomethide10 or tetracyanoborate11. Unfortunately, apart from tetracyanoborate, all of these low-viscosity melts proved to be unstable under prolonged thermal stress and light soaking. Here, we introduce the concept of using eutectic melts to produce solvent-free liquid redox electrolytes. Using a ternary melt in conjunction with a nanocrystalline titania film and the amphiphilic heteroleptic ruthenium complex Z907Na (ref. 10) as a sensitizer, we reach excellent stability and an unprecedented efficiency of 8.2% under air-mass 1.5 global illumination. Our results are of importance to realize large-scale outdoor applications of mesoscopic DSCs.