Enabling efficient heat-to-electricity generation at the mesoscale

We present a technology that efficiently harnesses the energy content of hydrocarbon fuels in a volume that is only a fraction of a cubic inch. A propane-fueled microcombustor heats a photonic crystal emitter to incandescence and the resulting spectrally-confined thermal radiation drives low-bandgap PV cells to generate electricity. We overcome the technical challenges that are currently limiting thermophotovoltaics in the following ways: we develop new fabrication processes; we adopt high-temperature alloys to improve the thermo-mechanical stability; we adopt commercial polycrystalline tantalum to fabricate large-area photonic crystals; and finally, we develop a passivation coating for improved thermo-chemical stability. We demonstrate unprecedented heat-to-electricity efficiencies exceeding 4%, greater than the 2-3% efficiencies that were previously thought to be the practical limit, and we predict that over 12% efficiency is achievable with only engineering optimization. For reference, a 1.5% efficiency corresponds to the energy density of lithium ion batteries. This work opens new opportunities to free portable electronics, robots, and small drones from the constraints of bulky power sources.