French researchers have built very-low-bandgap thermophotovoltaic (TPV) cells using a barrier structure that suppresses dark current, allowing the devices to run at higher temperatures, according to pv magazine.
The cell has a bandgap of 0.23 eV at 200 K and relies on an indium arsenide/indium arsenide antimonide (InAs/InAsSb) type-II superlattice absorber, pv magazine reported. The publication described the work as the first fabrication and characterization of a TPV cell at that bandgap.
After processing, cells exposed to an 800 C emitter performed more than tenfold better than standard PIN devices at temperatures above 150 K, per pv magazine. That threshold matters because conventional low-bandgap detectors and converters lose output as thermal generation swamps the photocurrent, which is the failure mode the barrier design targets.
A passivated barrier micro cell kept showing a photovoltaic effect at 273 K, around 0 C, with an open-circuit voltage of about 75 mV, according to pv magazine. Cryogenic cooling is the usual requirement for absorbers in this bandgap range, so operation at the freezing point of water is the specific result the group is putting forward.
Researchers from the French National Centre for Scientific Research (CNRS), the University of Montpellier, the University of Orleans, and the University of Toulouse contributed to the study, which appeared in Solar Energy Materials and Solar Cells, pv magazine said.
Thermophotovoltaic conversion turns radiant heat from a hot emitter into electricity through a semiconductor junction, and the absorber bandgap sets which part of the emitted spectrum can be harvested. Pushing the bandgap down to 0.23 eV extends collection deeper into the infrared, capturing photons from cooler emitters that wider-bandgap cells pass through. The trade is thermal noise: the narrower the gap, the more dark current the junction generates at a given operating temperature. The barrier architecture reported by the French group attacks that trade directly rather than accepting cooling as the price.
The measured 75 mV open-circuit voltage is modest, and the tenfold comparison is against PIN reference cells rather than against a commercial converter. The result establishes device feasibility at the bandgap and the temperature, not a deployment case.