1. Innovative Centre for Flexible Devices (iFLEX), School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
2. Max Planck − NTU Joint Lab for Artificial Senses, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
3. Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Innovis, Singapore 138634