1. Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
2. Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water
Bay, Kowloon, Hong Kong, China (SAR)
3. Materials Department and Materials Research Laboratory University of California, Santa Barbara, California 93106, United States
4. Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States