Conducting polythiophene (PTh) composites with the host filler multiwalled carbon nanotube (MWNT) have been used, for the first time, in the dye-sensitized solar cells (DSCs). A quasi solid-state DSCs with the hybrid MWNT-PTh composites, an ionic liquid of 1-methyl-3-propyl imidazolium iodide (PMII), was placed between the dye-sensitized porous TiO2 and the Pt counter electrode without adding iodine and higher cell efficiency (4.76%) was achieved, as compared to that containing bare PMII (0.29%). The MWNT-PTh nanoparticles are exploited as the extended electron transfer materials and serve simultaneously as catalyst for the electrochemical reduction of I ？ 3 . 1. Introduction Dye-sensitized solar cells (DSCs) have attracted significant attention as promising solar-to-electricity power conversion devices because of their higher energy conversion and potential for low-cost production [1–6]. In general, DSCs comprise an electrode consisting of nanocrystalline titanium dioxide (TiO2) films modified with a dye, a platinum counterelectrode, and an electrolyte solution in between the electrodes. Photoexcitation of the dye results in the injection of an electron into the conduction band of the oxide. The original state of the dye is subsequently restored by electron donation from a redox system, such as the iodide/triiodide (I？/I3？？) couple. At the present, DSCs are mainly constructed by using liquid electrolyte as a charge transport material. The charge transport in these liquid electrolytes is typically achieved by using I？/I3？？ redox reaction in electrolyte solution. Therefore, long-term durability of DSCs is limited by leakage and the volatilization of organic solvent-based electrolytes. Numerous investigations have been conferred to overcome this drawback, replacing the liquid electrolyte by organic and inorganic hole transport materials [7–9], polymer and gel electrolytes [10–14], and nanocomposite ionic liquid (IL) electrolytes [15–20] resulting in solid-state and quasi solid-state DSCs. Imperfect pour filling of the dye-coated nanocrystalline TiO2 film with organic and inorganic hole transport materials results in a poor device efficiency. Moreover, the ionic conductivity for the majority of the amorphous polymer electrolytes is too low (<10？5？S？cm？1), limiting the device efficiency. Although nanocomposite IL electrolyte can reduce leakages, it is not satisfactory, because of the high concentration of corrosive and volatile iodine present in the electrolyte. The introduction of I2 into the electrolytes could increase the conductivity of the electrolyte
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