1. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology National Center for International Research on Green Optoelectronics Institute of Electronic Paper Displays South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 P. R. China
2. Department of Physics and Soft Materials Research Center University of Colorado Boulder CO 80309 USA
3. Materials Science and Engineering Program Department of Electrical, Computer and Energy Engineering University of Colorado Boulder CO 80309 USA
4. Renewable and Sustainable Energy Institute National Renewable Energy Laboratory and University of Colorado Boulder CO 80309 USA