Two-for-One in Solar Cells-Mr. Bruno Ehrler

Conventional solar cells are limited to a maximum achievable power conversion efficiency of about 34%. They are made from a single semiconductor material that determines the amount of light that is absorbed in the solar cell. The more light a solar cell absorbs, the less energy can be extracted per photon. This trade-off is called the Shockley-Queisser limit. We are working on a new type of hybrid organic/inorganic solar cell, pairing two materials with different absorption properties. The organic material has the property of converting one high-energy photon into two low-energy excited states, a process called singlet-exciton fission. Using this process it is possible to design solar cells in such a way that they are not limited by the Shockley-Queisser limit. We have made the first solar cell of that kind and have already reached efficiencies that are comparable with the best hybrid organic/inorganic solar cell efficiencies.