1. Institute of Microelectronics, Peking University, Beijing 100871, P. R. China
2. Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Shenzhen 518055, P. R. China
3. Guangdong Poly Optoelectronics Co., Ltd., Jiangmen 529040, P. R. China
4. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China