1. State Key Laboratory of Solidification Processing Center for Nano Energy Materials Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU) Xi'an 710072 P. R. China
2. Department of Chemistry National University of Singapore 3 Science Drive 3 Singapore 117543 Singapore
3. Department of Chemical and Biomolecular Engineering National University of Singapore 4 Engineering Drive 4 Singapore 117585 Singapore
4. Frontiers Science Center for Flexible Electronics (FSCFE) Northwestern Polytechnical University (NPU) 127 West Youyi Road Xi'an 710072 P. R. China