Chitosan is a natural polymer derived from chitin that can be found in shrimps, lobsters and crabs and can be used as the host in polymer electrolytes. By improving its solubility, researchers at the University of Malaysia developed a gel polymer electrolyte based on phthaloylchitosan for dye-sensitized solar cells.
These dye-sensitized solar cells (DSSC) have the potential as a low cost greener alternative to the available silicon cells. While single cyrstal solar cells have reached efficiencies of 30% in the lab and 15-16% in the field, they can be expensive. Polycrystalline and other thin film based solar cells are comparatively cheaper but lower in efficiency, and less expensive amorphous silicon solar cells have lower life time of around three to four years.
A DSSC on the other hand can reach efficiencies of aorund 8% and is signifcantly chaper to make. It consists of a cheaper wide band semiconductor such as titanium dioxide (TiO2) sensitized with a dye to absorb light, and an electrolyte. The TiO 2 is deposited on a conducting glass substrate (indium tin oxide, ITO or Fluorine doped tin oxide, FTO) and forms a nanoporous network of particles which increases the surface area for the dye coverage. The counter electrode is another conducting glass coated with a thin layer of platinum and the electrolyte is sandwiched between the working electrode containing the dye sensitized TiO 2 and the electrode.
In the DSSC cell, the photoanode consists of a transparent conducting glass (TCG) onto which is coated with the TiO 2 and soaked in a ruthenium dye. The gel phthaloylchitosan electrolyte that has been added with mediators is sandwiched between the photoanode and the counter electrode, usually platinum. The dye molecules absorb incident light and become energized. This leads to an electron being released from each dye molecule. The electrons enter and percolate the TiO2 semiconductor and leave the cell to the external circuit through the TCG and finally reach the counter electrode.