1. NSF Nanoscale Science and Engineering
Center (NSEC), University of California, Berkeley, 3112 Etcheverry Hall, UC Berkeley, California 94720, United States
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron
Road, Berkeley, California 94720, United States
3. Center for Advanced Photovoltaic
Devices and Systems, University of Waterloo, 200 University Ave W, Waterloo, Ontario N2L 3G1, Canada