1. CAS Key Laboratory of Nanophotonic Materials and Devices CAS Key Laboratory of Standardization and Measurement for Nanotechnology CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing 100190 P. R. China
2. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Department of Electronic and Electrical Engineering University of Bath Bath BA2 7AY UK
4. School of Electronic Science and Engineering University of Electronic Science and Technology of China Chengdu 611731 P. R. China
5. State Key Laboratory of Optoelectronic Materials and Technologies Guangdong Province Key Laboratory of Display Material and Technology School of Electronics and Information Technology Sun Yat‐sen University Guangzhou 510275 P. R. China
6. Institut für Physik Center of Interface Science Carl von Ossietzky Universität 26129 Oldenburg Germany