1. Research Centre of Excellence for Organic Electronics; Hong Kong Baptist University; Hong Kong SAR P. R. China
2. Department of Physics; Hong Kong Baptist University; Hong Kong SAR P. R. China
3. Department of Chemistry and Institute of Creativity; Hong Kong Baptist University; Hong Kong SAR P. R. China
4. Institute of Materials Research and Engineering (IMRE); Agency for Science; Technology and Research, Singapore; 3 Research Link Singapore 117602 Singapore
5. College of Materials Science and Engineering; Fujian Normal University; Fuzhou 350007 P. R. China