University develops thin films for solar uses

New Materials Asia, Nov, 2009

Researchers at Ben-Gurion University (BGU) of the Negev in Israel have developed thin films that exhibit carrier multiplication (CM). This development is of great interest for the future of solar cells.

The films were synthesized at BGU by Professor Yuval Golan and PhD student Anna Osherov of the Department of Materials Engineering and the Ilse Katz Institute for Nanoscale Science and Technology. The results was published in Nature Physics.

According to the researchers, an important factor limiting solar cell efficiency is that incident photons generate only one electron-hole pair, irrespective of the photon energy, with any excess energy lost as heat.

CM involves the generation of multiple electron hole pairs from the absorption of a single photon. CM may considerably increase the power conversion efficiency of nanocrystal-based solar cells.

CM has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions.

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.

Golan explains: "The new physics behind this work is that while CM has been mostly demonstrated in nanocrystalline materials (quantum dots), we now show that CM can be obtained also in single crystal (bulk) films of lead sulphide and lead selenide."

Notably, the films were prepared using chemical solution deposition, an attractive, inexpensive deposition technique for which the Golan group at BGU has received considerable recognition. The research was carried out as part of an international collaboration with counterparts in France and the Netherlands.

For further information, contact: Professor Yuval Golan, Department of Materials Engineering, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva 84105, Israel; tel: 97-2-8646-1474; fax: 97-2-8647-2944; e-mail: ygolan@bgumail.bgu.ac.il; http://bgu.ac.il