1. King Abdullah
University of Science and Technology (KAUST), Physical Sciences and
Engineering Division, Solar and Photovoltaics Engineering Research Center (SPERC), Thuwal 23955-6900, Saudi Arabia
2. Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
3. Department of Physics and Astronomy, University of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States
4. Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
5. Center
for Nanoscale Materials, Argonne National Laboratory, 9700 South
Cass Avenue, Argonne, Illinois 60439, United States
6. Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States