1. The College of Electronic Information, Qingdao University, Qingdao 266071, China
2. Institute of New Energy Technology, College of Physics & Optoelectronic Engineering, Jinan University, Guangzhou 510632, China
3. Key Laboratory of New Semiconductors and Devices of Guangdong Higher Education Institutes, Jinan University, Guangzhou 510632, China
4. IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany