Development Of The Dye-sensitized Solar Cells Based On Iodine-free Redox Couples And Solid-state Electrolyte

The best and still most widely used electrolytes in DSSCs are based on theiodide/triiodide (I/I3) redox mediator. However, I/I3redox couple is not the mostdesirable mediator due to the following drawbacks:1) The corrosion of metal-basedcurrent collectors (such as Ag and Cu);2) The low redox potential of I/I3;3) The highconcentration of I3(formed by the reaction of I2with I) absorbs considerable part ofvisible light and thus reduces the efficiency of DSSCs. To overcome the disadvantages ofI/I3redox couple, elemental iodine-free redox couples have been investigated.To solve these problems, our work in this thesis can be summarized as follows:(1) A pyridinyl-functionalized ionic liquid was synthesized and applied as an additive fordye-sensitized solar cells (DSSCs). Compared with the volatile organic additive,[BuPyIm]Br can be used at a lower concentration for high overall power conversionefficiency DSSCs and a superior long-term stability. The Cell with pyridinyl-functionalized ionic liquid retained almost95%of its initial conversion efficiency after60days test, indicating a good stability of [BuPyIm]Br-based DSSCs. These results indicatethat the cells based on the pyridinyl-functionalized ionic liquid additive could overcomethe drawbacks of the volatile organic additive, and offer a feasible method to fabricateDSSCs in future practical applications.(2) An imidazolium functionalized cobalt tris(bipyridyl) complex redox mediator with highredox potential and good solubility in ionic liquid electrolyte has been synthesized andapplied in ionic liquid electrolyte DSSCs. The effect of the redox mediator on thephotovoltaic performance was investigated in pure ionic liquid as well as in binary ionicliquid. Efficiencies of7.37%is achieved in binary ionic liquid electrolyte under1.5solarspectrum illuminations at100mW cm2, which is higher than those of pure I/I3redoxmediator. (3) In solid-state dye sensitized solar cells (SSDSSCs) charge recombination at the TiO2photoelectrode/electrolyte interface plays a critical role in the cell efficiency because ofbad contact between the solid state electrolyte and the nano-particulate TiO2photoanode.For the first time we report on the influence of surfactant on the photovoltaic performanceof plastic crystal-based solid-state dye-sensitized solar cells. J-V curves, UV visspectroscopy, contact angle measurements show that the existence of surfactant AOT onTiO2interfaces is capable of facilitating the wetting of plastic crystal electrolytes into themesoporous TiO2resulting in the suppress of electron recombination at the TiO2photoelectrode/electrolyte interface, thus leads to a significant improvement of the solid-state dye-sensitized solar cells.