1. Department of Chemistry, National University of Singapore, Singapore 117543, Singapore
2. Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, P. R. China
3. Joint Key Laboratory of the Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Avenida da Universidade, Taipa, Macau 999078, P. R. China
4. Strait Institute of Flexible Electronics (SIFE, Future Technologies), Fujian Normal University and Strait Laboratory of Flexible Electronics (SLoFE), Fuzhou 350117, P. R. China
5. Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 138634, Singapore