1. Key Laboratory of Advanced Display and System Applications of Ministry of Education Shanghai University Shanghai 200072 P. R. China
2. College of Materials Science and Engineering Jilin University Changchun 130012 P. R. China
3. College of Materials Science and Engineering Engineering Research Center of Alternative Energy Materials & Devices (MoE) Sichuan University Chengdu 610065 P. R. China
4. Department of Materials Science and Engineering and Centre for Functional Photonics (CFP) City University of Hong Kong Hong Kong SAR 999077 P. R. China