1. Department of Materials Science and Engineering City University of Hong Kong Kowloon 999077 Hong Kong
2. Hong Kong Institute for Clean Energy City University of Hong Kong Kowloon 999077 Hong Kong
3. Department of Physics and Organic and Carbon Electronics Laboratories (ORaCEL) North Carolina State University Raleigh NC 27695 USA
4. Department of Chemistry City University of Hong Kong Kowloon 999077 Hong Kong
5. Frontier Institute of Science and Technology Xi'an Jiaotong University Xi'an 710054 P. R. China
6. Department of Chemistry College of Science Korea University Seoul 136‐713 Republic of Korea
7. Department of Materials Science and Engineering University of Washington Seattle WA 98195‐2120 USA