1. College of Materials Science & Engineering, Henan Key Laboratory of Photovoltaic Materials, Henan Normal University, Xinxiang 453007, China
2. College of Physics, Henan Key Laboratory of Photovoltaic Materials, Henan Normal University, Xinxiang 453007, China
3. Photovoltaics and Optoelectronics Laboratory, Center for Renewable and Low Carbon, School of Water, Energy and Environment, Cranfield University, Cranfield, Bedfordshire MK43 0AL, U.K.
4. London Centre for Energy Engineering, School of Engineering, London South Bank University, London SE1 0AA, U.K.