1. Hefei National Research Center for Physical Sciences at Microscale CAS Key Laboratory of Materials for Energy Conversion School of Chemistry and Materials Science University of Science and Technology of China Hefei Anhui 230026 P. R. China
2. Institute of Energy Hefei Comprehensive National Science Center Hefei 230041 P. R. China
3. Australian Centre for Advanced Photovoltaics School of Photovoltaic and Renewable Energy Engineering University of New South Wales Sydney NSW 2052 Australia