1. Hebei Key Lab of Optic‐Electronic Information and Materials College of Physics Science and Technology Hebei University Baoding 071002 P. R. China
2. Institute of Nanotechnology Karlsruhe Institute of Technology 76344 Eggenstein‐Leopoldshafen Germany
3. State Key Laboratory of Photovoltaic Materials & Technology Yingli Green Energy Holding Co., Ltd. Baoding 071051 P. R. China