1. Key Laboratory of Photovoltaic Materials, Henan University, Kaifeng 475004, P. R. China
2. Engineering Research Center of Environment-Friendly Functional Materials, Ministry of Education, Institute of Materials Physics and Chemistry, Huaqiao University, Xiamen 361021, P. R. China
3. MOE Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, CQU-NUS Renewable Energy Materials & Devices Joint Laboratory, School of Energy & Power Engineering, Chongqing University, Chongqing 400044, P. R. China