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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 23: Organic Photovoltaics I
CPP 23.5: Vortrag
Dienstag, 13. März 2018, 10:45–11:00, C 243
Charge photogeneration in organic solar cells composed of over 90% C60 — •Elisa Collado-Fregoso1, Johannes Benduhn2, Koen Vandewal2, and Dieter Neher1 — 1Institut für Physik und Astronomie, Potsdam University, Karl-Liebknecht-Straße 24-25, 14476 Potsdam-Golm, Germany — 2Dresden Integrated Center for Applied Physics and Photonic Materials, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany
The involvement of charge-transfer (CT) states in the processes of charge generation and recombination has been an important focus of study within the organic photovoltaic community. However, it has proved challenging to systematically address specific molecular properties without modifying the microstructure of the blend. In this work, we study the mechanism of charge generation in a series of solar cell devices with active layers composed mainly of vacuum deposited C60 and small amounts (~ 5% mol) of organic molecular donors. This ensures a constant morphology dictated by the fullerene acceptor. Using time-delayed collection field measurements, we demonstrate that the short circuit current and fill factor in these devices are largely determined by the charge generation efficiency and its bias dependence, which is more pronounced with decreasing CT state energy. This finding challenges current views that the existence of fullerene aggregates is sufficient to ensure efficient CT dissociation, and questions the picture of a necessary driving energy for charge generation. We discuss the implications of these findings within the framework of the Onsager-Brown model and propose guidelines to improve charge generation.