1. Key Laboratory of Photovoltaic Materials, Henan University, Kaifeng 475004, P. R. China
2. Institute of New Energy Technology, College of Information Science and Technology, Jinan University, Guangzhou 510632, 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