1. Key Laboratory of Optoelectronic Technology & Systems Education Ministry of China Chongqing University and College of Optoelectronic Engineering Chongqing University Chongqing 400044 China
2. State Key Laboratory of Power Transmission Equipment & System Security and New Technology and School of Electrical Engineering Chongqing University Chongqing 400044 China
3. College of Chemistry and Materials Science Hebei Normal University Shijiazhuang Hebei 050024 China
4. School of Materials Science and Engineering Georgia Institute of Technology Atlanta GA 30332 USA