[1] Univ Washington, Dept Mat Sci & Engn, Seattle, WA 98195 USA
[2] Univ Elect Sci & Technol China, Sch Optoelect Informat, State Key Lab Elect Thin Films & Integrated Devic, Chengdu 610054, Peoples R China
[3] N Carolina State Univ, Dept Phys & Organ, Raleigh, NC 27695 USA
[4] N Carolina State Univ, Carbon Elect Lab, Raleigh, NC 27695 USA
[5] Zhejiang Univ, Dept Polymer Sci & Engn, Hangzhou 310027, Zhejiang, Peoples R China