1. College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060, People's Republic of China
2. Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060, People's Republic of China
3. Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583