1. Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China
2. Department of Physics, School of Sciences, Nantong University, Nantong 226019, China
3. National Institute of Clean-and-Low-Carbon Energy, and Beijing Engineering Research Center of Nano-structured Thin Film Solar Cells, Beijing 102211, China
4. Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China
5. School of Materials Science and Engineering, Nankai University, Tianjin 300350, China