Two for one in solar power

A process that could revolutionise solar energy harvesting has been efficiently demonstrated in solution for the first time. We are only beginning to understand how this process works, and as we learn more we expect improvements in the technology to follow - Brian Walker Solar cells offer the opportunity to harvest abundant, renewable energy. Although the highest energy light occurs in the ultraviolet and visible spectrum, most solar energy is in the infrared. There is a trade-off in harvesting this light, so that solar cells are efficient in the infrared but waste much of the energy available from the more energetic photons in the visible part of the spectrum. When a photon is absorbed it creates a single electronic excitation that is then separated into an electron and a positively charged hole, irrespective of the light energy. One way to improve efficiency is to split energy available from visible photons into two, which leads to a doubling of the current in the solar cell. Researchers in Cambridge and Mons have investigated the process in which the initial electronic excitation can split into a pair of half-energy excitations.