1. Department of Mechanical Engineering, University of California Berkeley, Berkeley, California
94720, United States
2. Environmental
Energy Technologies
Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department of Physics, University of Wisconsin Madison, Madison, Wisconsin
53706, United States
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California
94720, United States
5. Centro de Física de Materiales (CSIC-UPV/EHU), Material Physics Center,
20018, San Sebastian, Spain
6. International
Research Center for Renewable
Energy, Xian Jiaotong University, Xian
710049, PR China