Quantum dot coupling is to restrict number of states and increase efficiency. Columb coupling is to avoid the blackbody limit.
This is a follow up of
The current quantum-mechanical resonant-coupling model confirms the predictions of both n2 and “beyond n2” enhancement, which removes a major limitation in thermophotovoltaics. Not only can the efficiency of TPV converters be increased, the emitter radiative efficiency can also be improved because energy that would otherwise be lost (in the form of long-wavelength light or heat) is recycled and selectively coupled into a resonant TPV converter. This selectivity further allows a reduction in the temperature of the emitter, while maintaining useful overall system efficiencies. A key feature to remember is that the new energy-transfer mechanism does not depend only on release of the blackbody radiation trapped within the emitter (as does the classical n2 effect). The additional energy source is the non-propagating photon modes that are normally dissipated in self-excitation of the emitter atoms and in resonance-coupling effects. This means that the blackbody law of power emission (which pertains only to the propagating modes) is not violated. We can not get more power out than we put in. However, we can extract energy more rapidly and more selectively at any emitter temperature. Therefore, with microgap coupling and a given thermal-energy input, the emitter can be kept at a lower temperature and still operate at a higher efficiency than previously possible. This is important in that it opens the possibility of selecting emitter materials and structures that would not survive higher temperatures.