1. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing210093, P. R. China
2. Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductors Materials and Applications, Future Display Institute in Xiamen, Xiamen University, Xiamen361005, P. R. China
3. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, Nanjing National Laboratory of Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing210093, P. R. China
4. College of Electronic and Optical Engineering, College of Flexible Electronics (Future Technology), Nanjing University of Posts and Telecommunications, Nanjing210023, P. R. China