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.