document: PV cells are one of the most promising technologies for conversion of incident solar radiation into electric power. However, this technology is still far from being able to compete with fossil fuel-based energy conversion technologies because of its relatively low efficiency and energy density. Theoretically, there are three unavoidable losses that limit the solar conversion efficiency of a device with a single absorption threshold or band gap Eg: (1) incomplete absorption, where photons with energies below Eg are not absorbed; (2) thermalization or carrier cooling, where solar photons with sufficient energy generate electron-hole pairs and then immediately lose almost all energy in excess of Eg in the form of heat; and (3) radiative recombination, where a small fraction of the excited states radioactively recombine with the ground state at the maximum power output (Hanna & Nozik, 2006; Henry, 1980). Taking an air mass of 1.5 as an example, for different band gap Eg these three losses can be calculated and the results are indicated by areas S1, S2, and S3 in Fig. 1. Note that the area under the outer curve is the solar power per unit area, and that only S4 can be delivered to the load.
doc_bio_tags: B I O O O O O O O O B I I I I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B O O O O O O O B O B O O O O O O O O B O B I O O B O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O
extractive_keyphrases: absorption carrier cooling conversion of incident solar radiation into electric power photons pv cells radiative recombination solar conversion solar power thermalization
abstractive_keyphrases: electric power electron-hole pairs fossil fuel-based energy conversion incident solar radiation incomplete absorption solar photons