CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...
CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...
CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...
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electricity. This forms the basis for a solar cell or photovoltaic cell and material that acts as a<br />
mediator is a semiconductor. The semiconductor on exposure of light creates electrons and<br />
holes in the CB and VB which has to be separated before recombination to build and efficient<br />
solar cell. The separation of electrons and holes created in photovoltaic cells can be achieved<br />
by forming and inbuilt field. Solar cells are usually divided into three generations. The first<br />
generation solar cells consisted of mainly silicon. Cell is achieved by creation of a pn<br />
junction from Si. Such cells are known to be efficient with efficiency ~24%. However cells<br />
are to be of electronic grade which means their purity should be extremely high. Therefore it<br />
is very expensive. The second generation solar cells consists of thin film based cells mainly<br />
consisting of poly-silicon, amorphous silicon, Copper Indium Selenide and Cadmium<br />
Telluride. These cells are comparatively cheaper but have a lower efficiency ~19%. The third<br />
generation solar cells are based on polymers, nanocrystals and dye sensitized solar cells. Dye<br />
sensitized solar cells use wide band gap semiconductor like TiO 2 and ZnO. The<br />
semiconductors do not absorb visible light. The light is absorbed by a dye which transfers<br />
charges to semiconductor and HOMO of cell is replenished by a redox electrolyte (see figure<br />
1.8.). One of the first studies on influence of mechanistic aspects electron transfer reactions<br />
in a cell was carried out by Gerischer and Memming [29-30]. These studies clearly showed<br />
potentials of a dye sensitized solar cell. In 1990s, Michael Graetzel in Ru(dcbpy) 2 (NCS) 2<br />
[dcbpy=(4,4’-dicarboxy-2,2’-bipyridine] or (Ru-N3) dye sensitized mesoporous TiO 2<br />
nanoparticles reported conversion efficiency of ~11% in a iodine/iodide based redox<br />
electrolyte [32]. The schematic shown in figure 1.8 describes different processes occurring in<br />
a DSSC. The efficiency of a DSSC depends on factors like electron injection time, efficiency<br />
of electron injection, free energy for back electron transfer (BET) etc. Though significant