1. Department
of Physics and Astronomy and Wright Center for Photovoltaics Innovation
and Commercialization, The University of Toledo, Toledo, Ohio 43606, United States
2. Ordered
Matter Science Research Center, Southeast University, Nanjing 211189, China
3. Key
Laboratory of Artificial Micro/Nano Structures of Ministry of Education,
School of Physics and Technology, Wuhan University, Wuhan 430072, China
4. Chemistry
and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States