1. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays National Center for International Research on Green Optoelectronics South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 P. R. China
2. School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
3. College of Materials Science and Engineering Zhengzhou University Zhengzhou 450001 P. R. China