Modern solar systems are based on modules assembled from arrays of semiconductor solar cells with a mix of rare earth metal components. This design approach is comparatively expensive and even if costs are going down consistently, there is widespread sentiment that it will take another technological approach to really improve affordability.The rise of dye sensitized cells as viable alternative is one of the solutions currently being fronted as having this capacity.
Dye sensitized solar cells combine low-cost organic dyes as well as titanium dioxide nanoparticles as the main component of the cells. Although up to now a technology that is largely considered experimental, there are applications that have been developed that have some robust capacity. With improvements announced constantly, it can only be hoped that this capacity will be improved considerably in the not too distant future.
It is the organic dye that is used to absorb the sunlight and convert it to electricity which is then transmitted into the porous layer of Titanium dioxide particles. The sun facing side of these solar cells is covered by a transparent electrode which carries the electric charge from the cells. Up to now, the standard material used for the transparent electrode is indium tin oxide (ITO)
Although at their best ITO electrodes are considered efficient, they have a couple of limitations that inhibits their application. To begin with , they are brittle and crack easily from continued exposure to the sun. They are also comparatively expensive, sometimes responsible for up to 60% of the cost of manufacturing dye sensitized solar cells.
A recent announcement by the A* STAR Institute of Materials Research and Engineering indicates that their research team led by Zhaohong Huang may have landed on a workable alternative. They have used thin film carbon nanotubes to provide a workable transparent electrode for dye sensitized solar cells. These nanotubes are transparent, flexible and more durable than ITO.
However, there is a fair amount of photo-generated charge carriers in the nanotubes which often combine with ions in the dye. This has been found to drive down the efficiency levels of such dye sensitized solar cells considerably. To try and overcome this, the A* team used a titanium dioxide thin film layer between the nanotubes and the porous layer. This strategy improved performance of the cells but had the effect of increasing electrical resistance and reduce optical transparency and therefore the cells have even lower conversion efficiencies.
The A* Star team is working on a number of approaches that promise to increase the conductivity and of these dye sensitized solar cells without affecting their optical transparency. Should these efforts bear fruit, the costs of these novel solutions should be driven down even further. Moreover, the researchers are on the way to finding a replacement of the bottom platinum electrode with a carbon thin film nanotube for even greater affordability.
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