1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
2. Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA
3. Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong
4. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA
5. Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
6. ICMUV, Instituto de Ciencia de Materiales, Universitat de València, P.O. Box 22085, 46071 Valencia, Spain
7. Department of Experimental Physics, Wrocław University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland
8. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA