1. State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, People’s Republic of China
2. College of Chemistry and Material Science, Sichuan Normal University, Chengdu 610068, People’s Republic of China
3. School of Engineering, Brown University, Providence, Rhode Island 02912, USA