Thin semiconducting layers and nanostructures as active and passive emitters for thermophotonics and thermophotovoltaics

Thermophotovoltaics involves the photovoltaic conversion by a receiver cell of radiation from an emitter which could be heated by various sources including sunlight. A prime difference from normal solar photovoltaics is that emitted energy unable to be used by the receiver, in principle, can be recycled allowing high conversion efficiency. Thermophotonics is a recent development of this concept where the emitter is "active", namely a heated diode, increasing the rate of energy transfer for a given emitter temperature and concentrating emission in an energy range more suited for conversion by the receiver. Even as "passive selective emitters", thin semiconducting layers may provide an alternative offering increased design flexibility to standard rare-earth doped ceramics. The decreased emitter band gap at high temperature means that for spectral matching, the room temperature band gap of the emitter should be slightly higher than that of the absorber. Low-dimensional structures such as quantum wells, superlattices and nanocrystals offer scope for such band-gap control and for enhanced luminescence. (C) 2002 Elsevier Science B.V. All rights reserved.