But solar cells made of a single material have a maximum efficiency of about 31 percent, a limitation of the fixed energy level they can absorb.
Quantum dot solar cells do not share this limitation and can in theory be far more efficient. The energy levels of electrons in quantum dot semiconductors depends on their size the smaller the quantum dot, the larger the energy needed to excite electrons to the next level.
So quantum dots can be tuned to absorb a certain wavelength of light just by changing their size. And they can be used to build more complex solar cells that have more than one size of quantum dot, allowing them to absorb multiple wavelengths of light.
Because of these advantages, Bent and her students have been investigating ways to improve the efficiency of quantum dot solar cells, along with associate Professor Michael McGehee of the department of Materials Science and Engineering.
The researchers coated a titanium dioxide semiconductor in their quantum dot solar cell with a very thin single layer of organic molecules. These molecules were self-assembling, meaning that their interactions caused them to pack together in an ordered way. The quantum dots were present at the interface of this organic layer and the semiconductor. Bent's students tried several different organic molecules in an attempt to learn which ones would most increase the efficiency of the solar cells.
But she found that the exact molecule didn't matter just having a single organic layer less than a nanometer thick was enough to triple the efficiency of the solar cells. "We were surprised, we thought it would be very sensitive to what we put
|Contact: Louis Bergeron|