1. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, United States
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Research School of Engineering, The Australian National University (ANU), Canberra, Australian Capital Territory 0200, Australia
4. Photovoltaics and Thin Film Electronic Laboratory (PVLab), École Polytechnique Fédérale de Lausanne (EPFL), Institute of Micro Engineering (IMT), Maladière 71b, CH-200 Neuchatel, Switzerland