CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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Recently several methods like chemical vapor deposition (CVD) [6.6], decomposition of SiC
at higher temperature [6.7], and chemical methods like oxidation promoted exfoliation [6.8]
have been proposed as possible route to synthesis of graphene. Decomposition of SiC to form
hexagonal graphene lattice have shown promising behavior similar to the ones prepared by
micromechanical cleavage used by Geim et al [6.4]. However this method suffers from the
formation of multilayers along the surface, leading to inhomogeneity along the films of
graphene. Furthermore strong interaction with the SiC substrate lead to breakdown of A-B
sub-lattice symmetry leading to band gap opening at the K-point [6.9]. Klaus Mullen et al
have used bottom up approach to synthesize graphene sheets which are in principle defect
free however these methods are economically nonviable [6.10].On the other hand oxidation
induced exfoliation has captured the attention of several groups due to their ability to produce
these layer of GO in a large scale [6.11]. Furthermore, these samples can be processed by
chemical reduction to obtain monolayer graphene [6.8].
In the present study our focus is on charge separation behavior in graphene QD
nanocomposite. The graphene used is chemical reduced graphene oxide. Several previous
have demonstrated previously that for an efficient photovoltaics employing QD one needs to
separate charge carriers before trapping or recombination. This problem is particularly acute
in case of QD due to larger surface to volume ratio [6.12]. Studies by Alivisatos et al [6.13]
have demonstrated use to conducting polymers for charge separation which helps in
improving photovoltaic effcicincy.
Kamat and coworkers [6.14] employing carbon nanotubes for charge separation for TiO 2
based photovoltaics have demonstrated an increase in efficiency.