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Thin Films Exhibit Carrier Multiplication

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Pijpers Figure 3
A promising development for solar cell applications recently published in Nature Physics is the demonstration of carrier multiplication in single crystal films of lead sulfide and lead selenide.

In standard solar cells, incident photons typically generate a single electron-hole pair, with excess photon energy given off as heat. Carrier multiplication (CM) is the process where a single photon generates two or more electron-hole pairs. Therefore, the generation of multiple charge carriers per photon is especially relevant for increased efficiency of solar cell applications.

It is expected that CM would increase significantly in nanocrystalline materials, such as quantum dots, due to quantum confinement effects. Researchers from the Ilse Katz Institute for Nanoscale Science and Technology at the Ben Gurion University in Israel comparing the CM efficiency of quantum dots and bulk PbS and PbSe have determined to the contrary that quantum confinement effects do not enhance CM. Rather, for a given photon energy, the bulk materials generate more electron-hole pairs per photon.

Pipers JJH, et al. 2009. Assessment of carrier-multiplication efficience in bulk PbSe and PbS. Nature Physics. Published online 6 September. DOI: 10.1038/nphys1393.

See also: Nanowerk, Ben Gurion News Release.

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