1. Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, 79110 Freiburg, Germany
2. Solaronix SA, Rue de l'Ouriette 129, Aubonne 1170, Switzerland
3. Freiburg Materials Research Center FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg, Germany
4. Solar Energy Conversion Group, Department of Physics, Philipps-University Marburg, Renthof 7, 35037 Marburg, Germany