Polysiloxane Electrolytes for Mesoporous TiO2 based Solid State Dye Sensitized Solar Cell

Dye-sensitized solar cells (DSSC) have attracted a great attention due to their low production cost and high photo-conversion efficiencies since a new type of dye-sensitized solar cell has been reported by Grätzel [1, 2]. The electrolytes are one of the key components and their properties have much effect on the conversion efficiencies. An electrolyte containing a suitable redox couple plays a very important role in determining the photovoltaic characteristics and durability of DSSC. Although there is the inherent drawback of the cell due to the volatility and possible leakage problem of liquid electrolytes during the long-term out-door operation. Numerous efforts have been made to overcome this problem by replacing the liquid electrolytes with solid or quasi-solid state electrolytes composed of various polymers [3] and room temperature ionic liquids [4]. In this work, we report a new quasi-solid state polymer electrolyte based on polysiloxane consisting of imidazolium exhibiting higher ionic conductivity, good chemical, thermal and electrochemical stabilities. Three types of polymer electrolytes based on polysiloxane grafted with different ratio of imidazolium moieties and ionic liquids have been synthesized and characterized. Increasing the proportion of imidazolium moieties in polysiloxane increased the conductivity and viscosity of the polymer electrolyte respectively. The thermal stability of the polymer electrolytes is determined by thermogravimetric analysis. The porosity of the TiO2 photoanode plays a crucial role due to the requirement of excellent pore filling by the solid state electrolyte to ensure optimal interface. Therefore, TiO2 thin films with regular and large pores, designed for optimal electrolyte impregnation have been prepared using dual templating method. The techniques are derived from the classical Pluronic-templating synthesis of mesoporous TiO2 Anatase films [5]. The structural characterization of the TiO2 thin films have been done by techniques such as Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), XRD, etc.. The objective is to introduce a second population of pores to facilitate the accessibility of large species while keeping very high value of specific species. The performances of those combined components will be evaluated in assembled DSSC, with commercial dyes and transparent conductive glasses.

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[5] J. Zhao et al, Microporous and Mesoporous Materials 138, 2011, 200.