Résumé
To date, the champion thermophotovoltaic (TPV) cells have an efficiency in the range 24-29% [1-2]. They are all made of InGaAs with an energy bandgap of 0.6 or 0.74 eV and convert thermal radiation from emitters at temperatures larger than 1000 °C. For medium-grade heat sources (<700 °C), cells with a lower energy bandgap (e.g. 0.36 eV with InAs) are required in order to efficiently collect the infrared photons. Since it is currently challenging to build large temperature differences between bodies separated by sub-micrometric distances, the requirement of a low-energy bandgap cell is stringent for near-field thermophotovoltaic converters.This communication reports on the specific design [3], fabrication and characterization [4] of micron-sized indium antimonide TPV cells (energy bandgap of 0.23 eV at 77 K) for proving that photovoltaic conversion of near-field thermal photons can be efficient [5]. The fabricated cells exhibit excellent performances in the dark, under far-field and near-field illuminations, with record efficiency (~15-20%) and electrical power densities (0.75 W cm-2). In the near field, the key parameters of the cell are its illuminated area, the doping of the p-layer and the thickness of the substrate. Experimental results suggest that 2D simulations of radiation transfer and electrical transport would probably help improving further the performances of the thermophotovoltaic cells for harnessing near-field thermal photons.