Vandervelde Wins NSF CAREER Award for Thermophotovoltaic Research

Assistant Professor of Electrical and Computer Engineering Tom Vandervelde has been awarded an early-career award from the National Science Foundation for promising research on the conversion of heat to electricity.

Vandervelde, the John A. and Dorothy M. Adams Faculty Development Professor in the Department of Electrical and Computer Engineering, received a NSF CAREER Award for his research on thermophotovoltaics (TPVs)—cells that convert thermal radiation, or heat, into electricity—with implications for a new class of green energy technologies.

"Right now, thermophotovolatics are used when the heat source is very hot," says Vandervelde, citing that generally heat sources have to be in excess of 1500°C for TPVs to work efficiently. His goal is to make TPVs more efficient at lower temperatures, and ultimately, convert heat to electricity at a cool 37°C—or the temperature of the human body. This could have implications for medical devices, such as a pacemaker that keeps a charge from the electricity generated by one's own body heat.

In a TPV system, when a photon—an energy packet of light or heat—strikes the TPV, a charge carrier pair is created that generates an electron and subsequently electricity. But 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," says Vandervelde.

By using recent advances in infrared photodetectors, Vandervelde will investigate the use of a novel photodiode structure to enhance the efficiency of current TPV devices. The new photodiode structure contains a barrier that prevents the recombination of the charge carriers, while allowing them to 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," says 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."

More efficient TPVs could also be used to recoup the heat lost to keep massive computer data server farms cool. "The realization of cooler-running, more energy-efficient, server farms— which occupy 20% of energy consumption off the energy grid in some locations—alone will change the very nature of our nation's energy needs in a positive way," he says.

At higher temperatures, like the heat thrown from a car's engine, more efficient thermophotovoltaics could capture the more than 60% of power lost to waste heat in the engine compartment or out the tailpipe. "In electric cars, lithium ion batteries put out a lot of heat. If you could harness even a little bit of that heat and put it toward recharging the batteries, you could extend the life of the battery and the drive time," Vandervelde says.

In Vandervelde's Renewable Energy and Applied Photonics (REAP) Labs, he and his graduate students have engineered a test chamber for this new class of TPV cell samples that can measure the samples' end energy efficiencies.

"The ability to harness the ubiquitous waste heat represents a significant jump forward to our becoming a truly green society," Vandervelde says.