Ionic Liquid Based Gel Electrolyte Compositions for Dye Sensitized Solar Cells
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IONIC LIQUID BASED GEL ELECTROLYTE COMPOSITIONS FOR DYE SENSITIZED SOLAR CELLS K. G. Chittibabu, S. Hadjikyriacou and L. Li Konarka Technologies, 100 Foot of John Street, Lowell, MA 01852, USA. ABSTRACT: Konarka Technologies has developed efficient electrolyte compositions based on nonvolatile ionic liquids. The electrolyte compositions were subsequently gelled using a metal ion complexation technique, without compromising the photovoltaic performance of the dye sensitized solar cells (DSSCs). The photovoltaic performance of the gel electrolyte incorporated DSSCs is quite stable for extended period of time even in the absence of sealing. Detailed results on performance and stability of the gel electrolyte incorporated DSSCs are presented. INTRODUCTION: Thin film dye sensitized solar cells (DSSCs) composed of partially sintered titanium dioxide nanoparticle networks have been demonstrated to convert solar light to electricity with over 10 % efficiency using a liquid redox electrolyte.1 DSSCs offer the advantage of a significant reduction in the cost of solar electricity, due to the inexpensive raw materials used and simple fabrication process involved in the production of DSSC based solar modules. However, the sintering temperature of forming a robust titanium dioxide nanoporous thin film is over 450 °C, which limits the substrate to transparent conducting glass. Konarka Technologies, is developing a roll-to-roll manufacturing process by fabricating the DSSCs on flexible, transparent plastic substrates based on low temperature interconnection processes developed at the University of Massachusetts Lowell2 and Konarka Technologies.3 The use of liquid electrolytes in the flexible DSSCs, however, pose problems of leakage and long-term stability issue of sealant materials used in the modules. A solid or a quasi-solid electrolyte will avoid the leakage problems in addition to allowing easy application of electrolyte gels using a costeffective reel-to-reel manufacturing process. Attempts were made to solidify the liquid electrolytes by using polymeric matrices,4 organic gelators5 or through chemical crosslinking of poly(vinyl pyridine) using multifunctional alkyl halide compounds.6 Many efforts to raise the viscosity of the electrolyte were directed towards the incorporation of vinyl pyridine polymers in the ionic liquid based electrolytes that were crosslinked by quarternization reactions using multifunctional alkyl halides or ionomers that were crosslinked by zinc ions.6 In these approaches, cross-linked polymer networks were formed in situ by applying the electrolyte mixtures in the DSSC and subsequently heat treating electrolyte applied photoelectrodes to induce crosslinking.6 A typical crosslinking time of 15-30 minutes at elevated temperatures is not scalable to large scale manufacturing. A novel technique was developed at Konarka Technologies to prepare ionic liquid based gel electrolytes by crosslinking polymeric materials such as poly(4-vinylpyridine) employing metal ion, specifically lithium ion, induced c
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