1. Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, United States
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Materials Science and Engineering, University of California, Berkeley, California 94720, United States
4. KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia