1. State Key Laboratory of Optoelectronic Materials and Technologies Guangzhou Key Laboratory of Flexible Electronic Materials and Wearable Devices Nanotechnology Research Center School of Materials Science and Engineering Sun Yat‐sen University Guangzhou 510275 P. R. China
2. School of Electrical and Electronic Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
3. School of Physics School of Optoelectronic Science and Engineering University of Electronic Science and Technology of China Chengdu 610054 P. R. China
4. School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
5. State Key Laboratory of Precision Measuring Technology and Instruments Tianjin University Tianjin 300072 P. R. China
6. School of Physics and Electronics Central South University Changsha 410083 P. R. China