1. School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Ave, Singapore 637819, Singapore
2. Key laboratory for Organic Electronic & Information Displays, Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, 9 Wenyuan Road, Nanjing 210046, PR China
3. Department of Mechanical Engineering & Materials Science, Rice University, 6100 Main Street, Houston, Texas 77005, United States
4. Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P.O. Box 1129, Hefei 230031, People’s Republic of China
5. School of Physical and Mathematical Science, Nanyang Technological University, Singapore 637371, Singapore