The current standard of efficiency in solar cells is about 31%. Much of the energy from sunlight is lost as heat because photons with energies above the semiconductor bandgap generate hot charge carriers that cool before they can be utilized.

Two methods of capturing this energy need to be employed for improved efficiency:

• the rate of cooling of hot carriers needs to be slowed down, and
• hot carriers need to be captured before all their energy is lost.

Work by Xiaoyang Zhu, University of Texas at Austin, USA, and co-workers at the University of Minnesota, USA, brings researchers one step closer to solving the second problem.

They discovered that hot-electron transfer from colloidal PbSe nanocrystals to a TiO₂ electron acceptor was possible and proceeded rapidly when the surfaces were chemically treated.

Says Zhu: “Our next goal is to adjust the chemistry at the interface to the conducting wire so that we can minimize this additional energy loss.”

• Hot-Electron Transfer from Semiconductor Nanocrystals
  W. A. Tisdale, K. J. Williams, B. A. Timp, D. J. Norris, E. S. Aydil, X.-Y. Zhu
  Science 2010, 328 (5985), 1543 – 1547.
  DOI: 10.1126/science.1185509