1. Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail Stop 66, Berkeley, California 94720, USA
2. Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
3. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
4. Joint Center of Artificial Photosynthesis, Berkeley, California 94720, USA