1. Laboratory of Condensed Matter Spectroscopy and Opto-Electronic Physics; and Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education); Department of Physics and Astronomy, and Institute of Solar Energy; Shanghai Jiao Tong University; Shanghai 200240 P. R. China
2. School of Science; Huaihai Institute of Technology; Lianyungang 222005 P. R. China
3. Nice Sun PV Co., Ltd; Jiangsu Province Wuxi 214233 P. R. China
4. Collaborative Innovation Center of Advanced Microstructures; Nanjing 210093 P. R. China