1. School
of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
2. Chemical
Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
3. Key Laboratory of Flexible Electronics & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, 30 South Puzhu Road, Nanjing 211816, P. R. China