1. School of Electronic and Optical Engineering, Nanjing University of Science and Technology, 200 Xiaolingwei Street, Nanjing 210094, China
2. Department of Physics, Research Centre of Excellence for Organic Electronics, and Institute of Advanced Material, Hong Kong Baptist University, Hong Kong, China
3. School of Physical Science and Technology, Chongqing Key Lab of Micro&Nano Structure Optoelectronics, Southwest University, Chongqing 400715, China