1. Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States
2. Department of Materials Science & Engineering, Stanford University, Stanford, California 94305, United States
3. Department of Physics, University of Patras, Patras 26504, Greece
4. Foundation for Research and Technology Hellas, Institute of Chemical Engineering Sciences (FORTH - ICE/HT), Patras 26504, Greece
5. School of Physics, Department of Solid State Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
6. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94305, United States
7. Precourt Institute for Energy, Stanford University, Stanford, California 94305, United States