1. Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439,
United States
2. Institute
of Materials, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
3. Division of Physical Sciences
and Engineering, Solar and Photvoltaics Engineering Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia