1. Wood Materials Science, ETH Zürich, 8046 Zürich, Switzerland
2. Applied Wood Materials, Empa — Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
3. Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, People's Republic of China
4. Laboratory for Thin Films and Photovoltaics, Empa — Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland