4. Conclusion and outlook

Thermophotovoltaic devices are dedicated to the conversion of thermal radiation from radiating surfaces ranging from 500°C to several thousand degrees. At the lowest temperatures, cell materials are close to those used in infrared photodetectors, and differ greatly from those used in solar cells. Conversely, they come very close when the emitter temperature is very high. In contrast to solar photovoltaic converters, device optimization requires a detailed analysis of the operating point in the thermodynamic power output-pair efficiency diagram. Photonic engineering of the emitter-cell pair is one of the ingredients of this optimization, the other being the choice of materials and their arrangement in the cell. Pair efficiencies in excess of 40% have been achieved for single-junction and tandem cells, and electrical powers in excess of W · cm ^–2 ...