1. Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU United Kingdom, Applied Functional Polymers and Lab for Solar Energy Research, University of Bayreuth, 95440 Bayreuth, Germany, Cavendish Labortatory, University of Cambridge, J.J. Thomson Avenue, Cambridge,CB3 0HE United Kingdom, and Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland