Semiconductor quantum dots may be used in so - called third - generation solar cellsthat have the potential to greatly increase the photon conversion efficiency via twoeffects: (1) the production of mul tiple excitons from a single photon of sufficient energyand (2) the formation of intermediate bands in the bandgap that use sub - bandgapphotons to form separable electron-hole pairs. This is possible because quantization ofenergy levels in quantum dots produces the following effects: enhanced Auger proc -esses and Coulomb coupling between charge carriers; elimination of the requirement toconserve crystal momentum; slowed hot electron-hole pair (exciton) cooling; multipleexciton generation; and forma tion of minibands (delocalized electronic states) in quantumdot arrays. For exciton multi plication, very high quantum yields of 300-700% for excitonformation in PbSe, PbS, PbTe, and CdSe quantum dots have been reported at photonenergies about 4-8 times the HOMO-LUMO transition energy (quantum dot bandgap),respectively, indi cating the formation of 3-7 excitons/photon, depending upon the photonenergy. For intermediate - band solar cells, quantum dots are used to create the intermediatebands from the con fined electron states in the conduction band. By means of theintermediate band, it is possible to absorb below - bandgap energy photons. This ispredicted to produce solar cells with enhanced photocurrent without voltage degradation.

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