In preliminary studies, carbon nanotubes that were engineered into the architecture of semiconductor solar cells (composed of cadmium sulfide, zinc oxide and titanium dioxide) resulted in a doubling of the cells’ photoconversion efficiencies (converting light into energy). In some cases, the efficiency of solar cells jumped from 5 percent to 10 percent in the presence of carbon nanotubes, according to Prashant Kamat, Ph.D., a professor of chemistry at the University of Notre Dame in Indiana. Carbon nanotubes also could be added to other types of solar cells, such as dye-sensitized solar cells and organic solar cells based on conducting polymers, to create similar or even stronger efficiency boosts, he says.
The dye-sensitized solar cells are discussed at length in the MIT technology review. The dye-sensitized cells being made in China and should be just under $1 per watt. Researchers in Switzerland have developed dye-sensitized solar cells that have reached the highest efficiencies to date among a new generation of thin film photovoltaic devices that show promise as a low-cost energy source. The new cells, composed of an ultrathin film of nano-sized semiconductor crystals such as titanium dioxide, have been shown in laboratory studies to produce efficiencies of 11 percent, whereas most new solar cells have efficiencies between 4 percent and 5 percent, according to Michael Graetzel, Ph.D., a chemist at the Swiss Federal Institute of Technology, Lausanne. These cells, which can be engineered into inexpensive, flexible sheets, could be used as coatings on glass windows to supply electric power to homes and businesses or as coatings on tents to supply power for soldiers in the field. The cells could be used in consumer applications within two to three years, the researcher says.
UPDATE: Related articles: (as noted by Jonathan Pugh in the comments)
The quantum dots can theoretically get 65% efficiency and multiple excitons per photon. They have to work out the issue of collecting the power. One high efficiency solar energy device has not been created. The charges need to be taken from the quantum dots to the electrode efficiently. Then the process needs to be scaled up and the costs lowered to be competitive with other methods. See the links at the end of the first article in the link just below.
Quantum dots could get nearly 65% efficiency from solar cells
Part II of quantum dots and solar cells