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Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

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Figure 23 Change of the PL intensity in a film of 28- and 40-Å InP QDs as a functionof separation between the QDs. (From Ref. 134.)VI.APPLICATIONS: QUANTUM-DOT SOLAR CELLSA. BackgroundThe maximum thermodynamic efficiency for the photovoltaic conversion ofunconcentrated solar irradiance into electrical free energy in the radiativelimit assuming detailed balance and a single threshold absorber was calculated<strong>by</strong> Shockley and Queissar in 1961 [149] to be about 31%; this analysis isalso valid for the conversion to chemical free energy [150,151]. Becauseconversion efficiency is one of the most important parameters to optimizefor implementing photovoltaic and photoelectrochemical cells on a truly largescale [152], several schemes for exceeding the Shockley–Queissar (S-Q) limithave been proposed and are under active investigation. These approachesinclude tandem cells [153], hot carrier solar cells [37,81,154], solar cellsproducing multiple electron-hole pairs per photon through impact ionization[155–157], multiband and impurity solar cells [152,158], and thermophotovoltaic/thermophotoniccells [152]. Here, we will only discuss hot carrier andimpact ionization solar cells and the effects of size quantization on the carrierdynamics that control the probability of these processes.<strong>Copyright</strong> <strong>2004</strong> <strong>by</strong> <strong>Marcel</strong> <strong>Dekker</strong>, <strong>Inc</strong>. <strong>All</strong> <strong>Rights</strong> <strong>Reserved</strong>.

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