1. School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, Oregon 97331, United States
3. Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
4. Department of Material Science & Engineering, National University of Singapore, Singapore 117575, Singapore
5. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456, Singapore
6. The Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Science, Beijing 100190, China
7. University of Chinese Academy of Sciences, Beijing 100190, China