1. Chongqing Key Laboratory of Optoelectronic Information Sensing and Transmission Technology, School of Optoelectronic Engineering, Chongqing University of Posts and Telecommunications, Chongqing 400065, P. R. China
2. State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
3. School of Energy and Environment, Southeast University, Nanjing 210096, P. R. China