1. Department of Mechanical and Mechatronics Engineering and Waterloo Institute of Nanotechnology University of Waterloo Waterloo Ontario N2L 3G1 Canada
2. College of Materials Science and Technology Jiangsu Key Laboratory of Materials and Technology for Energy Conversion Nanjing University of Aeronautics and Astronautics Nanjing 210016 China
3. School of Physical Science and Technology Key Laboratory of Advanced Technology of Materials (Ministry of Education of China) Southwest Jiaotong University Chengdu Sichuan 610031 China
4. Department of Electrical and Computer Engineering University of Waterloo Waterloo Ontario N2L 3G1 Canada
5. School of Physics Henan Key Laboratory of Photovoltaic Materials Henan Normal University Henan 453007 China