1. School of Engineering, University of Warwick, Coventry, CV4 7AL, UK
2. Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg, Germany
3. Chair for Photovoltaic Energy Conversion, Institute for Sustainable Systems Engineering, University of Freiburg, Emmy-Noether-Straße 2, 79110 Freiburg, Germany
4. Department of Physics, University of Warwick, Coventry, CV4 7AL, UK