1. Display Research Centre, School of Electronic Science and Engineering; Southeast University; Nanjing 210096 P. R. China
2. Department of Engineering; Electrical Engineering Division University of Cambridge; 9 JJ Thomson Avenue CB3 0FA UK
3. Nanjing Camray Technology Ltd, Nanjing Economic & Technological Development Zone; Nanjing 210000 P. R. China
4. Department of Materials; University of Oxford; Parks Road Oxford OX1 3PH UK
5. Department of Information Display; Kyung Hee University; Seoul 130701 Republic of Korea