Tufts Engineering Professor Wins NSF Career Award for Thermophotovoltaic Research

Vandervelde, the John A. and Dorothy Adams Faculty Development Professor, will use the $400,000, five year award to continue his studies in thermophotovoltaics (TPVs)—cells that convert thermal energy, or heat, 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,” says Vandervelde. His goal is to make TPVs more efficient at lower temperatures, and ultimately, convert heat to electricity at a cool 37 degrees Celsius—or the temperature of the human body. This could have potential use in 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 that contains a barrier which prevents recombination of the charge carriers. This allows the particles 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.

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

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