1. Materials Department, University of California, Santa Barbara, California 93106
2. Department of Chemical Engineering, University of California, Santa Barbara, California 93106
3. National Renewable Energy Laboratory, Golden, Colorado 80401
4. Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106
5. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China