Tom Vandervelde, assistant professor of electrical and computer engineering at Tufts University, has been given an early-career award from the National Science Foundation for promising research in thermophotovoltaics (TPVs). Vandervelde, the John A. and Dorothy Adams Faculty Development Professor, will use the $400,000, five-year prize to continue his studies on cells that convert thermal energy into electricity. His research has implications for a new class of green technologies. "Right now, heat sources have to be in excess of 1500 degrees Celsius in order for TPVs to work efficiently," said Vandervelde. His goal is to make TPVs more efficient at lower temperatures and, ultimately, to convert heat to electricity at a cool 37 degrees Celsius — the temperature of the human body. This technology has potential for medical devices, such as a pacemaker that is charged by the wearer's own body heat. When a photon strikes a TPV system, a charge carrier pair is created that generates an electron and, subsequently electricity; however, if the charge carriers recombine, a photon is re-emitted and is lost as light or heat. "Every time that recombination happens, that's less energy you get out, and in the end, that lowers your overall efficiency," he said. By using recent advances in infrared photodetectors, Vandervelde will investigate the use of a novel photodiode structure that contains a barrier preventing the recombination of the charge carriers, so the particles can flow out of the cell as unimpeded electrical current. "By putting the barriers in, we end up separating where those charge carriers are, so they end up not spending a lot of time near each other," said Vandervelde. "It makes recombination far less likely to occur, which means that you end up getting out a lot more current for the same amount of light coming in." For more information, visit: www.tufts.edu