1. Materials Research Center, University of Freiburg, Stefan-Meier-Strasse 21, 79104 Freiburg, Germany, Department of Chemical Engineering, University of Pennsylvania, 220 South 33rd Street, Philadelphia, Pennsylvania 19104, and Fraunhofer Institute for Solar Energy Systems (FhG-ISE), Heidenhofstrasse 2, 79110 Freiburg, Germany