MIT researchers have reported a breakthrough in "wavelength tuning" that promises to boost the efficiency of thermophotovoltaic (TPV) systems and in turn could lead to lighter, longer-lasting portable power sources.
Rather than relying on sunlight to produce electricity, thermophotovoltaic systems use heat to supply radiation to a PV cell by using a thermal emitter. These systems have been in development for half a century, but they are inefficient because they emit more infrared wavelengths than sunlight. Filters are one way of optimizing these wavelengths and the relatively recent advent of "low band-gap" PV materials that can make use of more infrared radiation have also improved these systems, but there's plenty of room for further efficiency gains.
The MIT solution involves designing a thermal emitter with a surface that's been "etched" on the nanoscale so that it resonates wavelengths that match those that the photovoltaic cells are best at converting into electricity, while at the same time suppressing wavelengths that aren't useful.
The prototype device is a button-sized TPV generator that uses butane fuel to provide the heat source. According to the researchers it runs three times longer than a lithium-ion battery of the same weight, while recharging is as easy as replacing the fuel cartridge.
Research engineer Ivan Celanovic believes the team can triple the current energy density. "At that point, our TPV generator could power your smartphone for a whole week without being recharged," he says.