1. School of Electrical and Electronic EngineeringNanyang Technological University Singapore 639798 Singapore
2. Division of Physics and Applied PhysicsSchool of Physical and Mathematical SciencesNanyang Technological University Singapore 637371 Singapore
3. School of Materials Science and EngineeringNanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
4. Institute of Flexible ElectronicsNorthwestern Polytechnical University Xi’an 710072 China
5. Temasek Laboratories@NTUNanyang Technological University Singapore 637553 Singapore