1. Beijing Key Laboratory of Novel Thin-Film Solar CellsBeijing Key Laboratory of Energy Safety and Clean UtilizationNorth China Electric Power University Beijing 102206 P. R. China
2. School of Economics and ManagementNorth China Electric Power University Beijing 102206 P. R. China
3. Key Laboratory of Photovoltaic and Energy Conservation MaterialsInstitute of Applied TechnologyHefei Institutes of Physical ScienceChinese Academy of Sciences Hefei 230031 P. R. China
4. Fujian Provincial Key Laboratory of Photoelectric Functional MaterialsInstitute of Materials Physical ChemistryHuaqiao University Xiamen 361021 P. R. China