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Hot-Electron Transfer from Semiconductor Nanocrystals

Science  18 Jun 2010:
Vol. 328, Issue 5985, pp. 1543-1547
DOI: 10.1126/science.1185509

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Abstract

In typical semiconductor solar cells, photons with energies above the semiconductor bandgap generate hot charge carriers that quickly cool before all of their energy can be captured, a process that limits device efficiency. Although fabricating the semiconductor in a nanocrystalline morphology can slow this cooling, the transfer of hot carriers to electron and hole acceptors has not yet been thoroughly demonstrated. We used time-resolved optical second harmonic generation to observe hot-electron transfer from colloidal lead selenide (PbSe) nanocrystals to a titanium dioxide (TiO2) electron acceptor. With appropriate chemical treatment of the nanocrystal surface, this transfer occurred much faster than expected. Moreover, the electric field resulting from sub–50-femtosecond charge separation across the PbSe-TiO2 interface excited coherent vibrations of the TiO2 surface atoms, whose motions could be followed in real time.

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