1. Introduction
The provision of sustainable, renewable, human friendly and cheap energy sources is demand of utmost priority for future living on earth. The available possibilities to obtain such sources principally points the scientific attention towards utilization of solar energy to meet up the energy requirements [1]. There has been several strategies and devices to harvest the solar energy out of which photovoltaic cells have been of prime research and industrial interest. A survey of last 15 years indicates that the first and second generation solar cells, offering respective efficiencies of 20% and 30%, have dominated the market with 30% manufacturing annual growth rate [2-5]. However, considering the simplest synthesis, mechanism and the basic requirements mentioned above, dye-sensitized solar cell (DSSC) is taken as most auspicious device among all generations of solar cells [6].
The conversion of solar energy to electric energy by DSSC takes place in two steps; first is generation of charge by photoactive specie as a result of absorption of incident photon of visible region and the second is transportation of charge by semiconductor and electrolyte. Despite of the low production cost, the reported efficiency of DSSC till date is 12% which is very low when compared with first and second generation solar-cells [7]. The issue of low efficiency, if could not be addressed, may limit the utilization of DSSC in future technology. The efficiency of DSSC relies heavily on photoanode which is basically dye-semiconductor complex. DSSC comprises of three major parts; semiconductor coated with photosensitizer (Dye), electrolyte and counter-electrode. The working mechanism of DSSC is sketched in figure1.