1. Department of Chemical and Biological Engineering, University of Colorado 1 , Boulder, Colorado 80303, USA
2. Department of Material Science and Engineering, University of Colorado 2 , Boulder, Colorado 80303, USA
3. Swift Solar, Inc. 3 , 981 Bing St., San Carlos, California 94070, USA
4. Department of Chemical Engineering, University of Virginia 4 , Charlottesville, Virginia 22904, USA
5. National Renewable Energy Laboratory 5 , Golden, Colorado 80401, USA
6. Renewable and Sustainable Energy Institute (RASEI), University of Colorado 6 , Boulder, Colorado 80303, USA