10 September 2009

New thin films show solar promise

Thin films that exhibit carrier multiplication could give a boost to solar cells.

One of the important factors limiting solar-cell efficiency is incident photons generate only one electron-hole pair, regardless of the photon energy. Any excess photon energy is lost as heat.

Carrier multiplication gains significant enhancement in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions.

The synthesized thin film development occurred at Ben-Gurion University (BGU) of the Negev by Professor Yuval Golan and Ph.D. student Anna Osherov of the Department of Materials Engineering and the Ilse Katz Institute for Nanoscale Science and Technology.

The BGU team demonstrated that contrary to this expectation, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe films than in nanocrystalline films of the same materials.

“Films developed at BGU show [carrier multiplication], in which each incoming photon (tiny quantity of sunlight) creates more than one electron-hole pair,” Golan said. “This can potentially be used for making more efficient solar cells. The new physics behind this work are that while [carrier multiplication] has been mostly demonstrated in nanocrystalline materials (“quantum dots”), we now show that [carrier multiplication] can be obtained also in single crystal (‘bulk’) films of lead sulfide and lead selenide.”

Notably, the films came together using chemical solution deposition, an attractive, inexpensive deposition technique.

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