July 1, 2011
A research team at the University of Toronto has created the first two-layer solar cell made up of light-absorbing nanoparticles called quantum dots. Quantum dots, which can be tuned to absorb different parts of the solar spectrum by varying their size, have been seen as a promising route to low-cost solar cells because the particles can be sprayed onto surfaces much like paint. But cells based on this technology have been too inefficient to be practical. By discovering a way to combine two different types of quantum dots in a solar cell, the researchers could open the way to making such cells much more efficient.
Conventional solar cells are tuned to convert light of only one wavelength into electricity; the rest of the solar spectrum either passes through or is converted inefficiently. To harness a greater percentage of the energy in sunlight, manufacturers sometimes stack materials designed to capture different parts of the spectrum. A two-layer cell, called a tandem-junction cell, can theoretically achieve 42 percent efficiency, compared with a maximum theoretical efficiency of 31 percent for cells with a single layer.
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