1. College of Materials and Metallurgy, Guizhou University, Guiyang 550025, P. R. China
2. The Molecular Foundry, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, United States
3. Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, United States
4. School of Polymer Science and Engineering, Center for Optoelectronic Materials and Devices The University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States
5. College of Physics, Guizhou University, Guiyang 550025, P. R. China