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For energies where αCV is much larger than αFC, this essentially equals fBE (µCV) as for the simpler analysis of Sect. 3. Below the bandgap where αCV becomes rapidly smaller than αFC, the equilibrium photon occupancy decreases from this value towards the thermal value fBE (0). 39) is very similar to the simpler Beer’s law for photon absorption (Green 1982). Only a fraction αCV /(αCV + αFC) of absorbed photons, however, will result in electron-hole pair generation, with the remainder giving their energy to free carriers.

The middle term on the right corresponds to the situation in Fig. 3 where, as well as being radiated by the sun, the cell is radiated by black-body radiation from the rest of the hemisphere, assumed to be at the same temperature as the local ambient. This contribution has negligible effect upon most practical calculations but gives the satisfying result that, if the sun were replaced by a segment at the cell’s temperature and the cell short-circuited, no current would flow in the cell leads. 19) produces exactly the same results as Eq.

This is probably not too surprising since energy transfer, in this case, involves the exchange of photons, while heat transfer commonly involves phonons. Both are bosons, with similar fundamental properties. One difference is that radiative energy transfer often involves energy transfer directly between bodies at vastly different temperatures. This leads to entropy generation, unlike the case of transfer between nearly equal temperatures, and to a different approach to treating corresponding energy and entropy fluxes.