1. Key Laboratory of Materials Physics Anhui Key Laboratory of Nanomaterials and Nanotechnology Institute of Solid State Physics Chinese Academy of Sciences University of Science and Technology of China Hefei 230031 P. R. China
2. Institutes of Physical Science and Information Technology Anhui University Hefei 230601 P. R. China
3. Photoelectric Conversion Energy Materials and Devices Key Laboratory of Anhui Province Anhui University Hefei 230601 P. R. China