1. Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, California 91125, United States
2. Division of Solid State Physics, Lund University, Lund, SE-221 00, Sweden
3. Sol Voltaics AB, Lund, SE-223 63, Sweden
4. The Aerospace Corporation, El Segundo, California 90245-4609, United States
5. National Renewable Energy Laboratory, Golden, Colorado 80401, United States
6. The Kavli Nanoscience Institute, California Institute of Technology, Pasadena, California 91125, United States