| Autor: |
Fish GC; Photochemical Dynamics Group, Institute of Chemical Sciences and Engineering, École polytechnique fédérale de Lausanne, Station 6, 1015 Lausanne, Switzerland. je.moser@epfl.ch., Moreno-Naranjo JM; Photochemical Dynamics Group, Institute of Chemical Sciences and Engineering, École polytechnique fédérale de Lausanne, Station 6, 1015 Lausanne, Switzerland. je.moser@epfl.ch., Billion A; Institut für Anorganische und Analytische Chemie, and Freiburger Materialforschungszentrum, Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany., Kratzert D; Institut für Anorganische und Analytische Chemie, and Freiburger Materialforschungszentrum, Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany., Hack E; Laboratory for Transport at Nanoscale Interfaces, Swiss Federal Laboratories for Materials Science and Technology, Empa, Überlandstrasse 129, 8600 Dübendorf, Switzerland., Krossing I; Institut für Anorganische und Analytische Chemie, and Freiburger Materialforschungszentrum, Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany., Nüesch F; Laboratory for Functional Polymers, Swiss Federal Laboratories for Materials Science and Technology, Empa, Überlandstrasse 129, 8600 Dübendorf, Switzerland.; Institute of Materials, School of Engineering, École polytechnique fédérale de Lausanne, Station 12, 1015 Lausanne, Switzerland., Moser JE; Photochemical Dynamics Group, Institute of Chemical Sciences and Engineering, École polytechnique fédérale de Lausanne, Station 6, 1015 Lausanne, Switzerland. je.moser@epfl.ch. |
| Abstrakt: |
The mechanism of photoinduced symmetry-breaking charge separation in solid cyanine salts at the base of organic photovoltaic and optoelectronic devices is still debated. Here, we employ femtosecond transient absorption spectroscopy (TAS) to monitor the charge transfer processes occurring in thin films of pristine pentamethine cyanine (Cy5). Oxidized dye species are observed in Cy5-hexafluorophosphate salts upon photoexcitation, resulting from electron transfer from monomer excited states to H-aggregates. The charge separation proceeds with a quantum yield of 86%, providing the first direct proof of high efficiency intrinsic charge generation in organic salt semiconductors. The impact of the size of weakly coordinating anions on charge separation and transport is studied using TAS alongside electroabsorption spectroscopy and time-of-flight techniques. The degree of H-aggregation decreases with increasing anion size, resulting in reduced charge transfer. However, there is little change in carrier mobility, as despite the interchromophore distance increasing, the decrease in energetic disorder helps to alleviate the trapping of charges by H-aggregates. |
