1. School of Materials Science and Engineering Harbin Institute of Technology Shenzhen 518055 China
2. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute for Advanced Materials South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 P. R. China
3. National Center for International Research on Green Optoelectronics South China Normal University Guangzhou 510006 P. R. China
4. Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Wenhua Road 72 Shenyang 110016 China
5. Flexible Printed Electronics Technology Center Harbin Institute of Technology Shenzhen 518055 China
6. Department of Physics Southern University of Science and Technology Shenzhen 518055 China
7. Department of Materials Science and Engineering University of California Berkeley CA 94720 USA
8. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA