April 19, 2007
Solar power Progress
Semiconductor for splitting CO2 powered by sunlight
Kubiak and Sathrum initially used a silicon semiconductor to test the merits of their device because silicon is well-studied. However, silicon absorbs in the infrared range and the researchers say it is "too wimpy" to supply enough energy. The conversion of sunlight by silicon supplied about half of the energy needed to split carbon dioxide, and the reaction worked if the researchers supplied the other half of the energy needed.
They are now building the device using a gallium-phosphide semiconductor. It has twice the band gap of silicon and absorbs more energetic visible light. Therefore, they predict that it will absorb the optimal amount of energy from the sun to drive the catalytic splitting of carbon dioxide.
Graphic depicting steps in solar splitting of CO2. Credit: Aaron Sathrum, UCSD
Plastic solar cells from Wake Forest are now 6% efficient. They were less than 5% efficient last year and were 3% the year before In order to be considered a viable technology for commercial use, solar cells must be able to convert about 8 percent of the energy in sunlight to electricity. Wake Forest researchers hope to reach 10 percent in the next year, said Carroll, who is also associate professor of physics at Wake Forest.
Because they are flexible and easy to work with, plastic solar cells could be used as a replacement for roof tiling or home siding products or incorporated into traditional building facades. These energy harvesting devices could also be placed on automobiles. Since plastic solar cells are much lighter than the silicon solar panels structures do not have to be reinforced to support additional weight.
Hopefully plastic can scale up through 2009-2015 after the initial technical challenges have been overcome. These are two promising developments that hopefully can help prevent environmental damage from energy and repair some of the damage.