1. Research School of Engineering; Australian National University; Canberra 0200 Australia
2. Department of Electrical Engineering and Computer Sciences; University of California; Berkeley CA 94720 USA
3. Materials Sciences Division; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA
4. Department of Physics; University of Basel; Klingelbergstrasse 82 Basel CH-4056 Switzerland
5. Institute of Micro Engineering; Photovoltaics and Thin-Film Electronic Laboratory; École Polytechnique Fédérale de Lausanne; Maladière 71b CH-200 Neuchatel Switzerland
6. KAUST Solar Center (KSC); King Abdullah University of Science and Technology (KAUST); Thuwal 23955-6900 Saudi Arabia