Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 18: Organic semiconductors I
CPP 18.4: Vortrag
Mittwoch, 28. März 2012, 10:15–10:30, C 130
Charge Transfer in Polymer:PC60BM:PC70BM triple Blends: Which Fullerene gets the Electron? — •Andreas Sperlich1, Johannes Römer1, Hannes Kraus1, Carsten Deibel1, and Vladimir Dyakonov1,2 — 1Experimental Physics VI, Julius Maximilian University of Würzburg, D-97074 Würzburg, Germany — 2ZAE Bayern, D-97074 Würzburg, Germany
The highest efficiencies reported for organic solar cells are for devices incorporating blends of conjugated polymers and C70-derivatives, due to their higher optical absorption compared to C60. Yet the costly purification of higher fullerenes might hinder a widespread adoption of this promising material. However recent results showed that polymers blended with a PC60BM/PC70BM mixture without further purification yield solar cells with comparable performance. This is surprising, because from absorption and photoluminescence spectra, different energy levels for both fullerenes are expected. If there were a noticeable difference in electron affinity, one of the two fullerenes would act as an electron trap in a mixed phase, hence hindering transport and limiting device performance. This raises the question, on which fullerene derivate the electron is residing after light induced charge transfer from the polymer? Using Light-induced Electron Spin Resonance (LESR) we can distinguish between holes on the polymer and electrons on either C60 or C70, since their ESR spectra are slightly shifted against each other. Our results demonstrate that there is no strong preference for either fullerene. Thus from an economic point of view “unpurified” fullerenes might be a viable option for large scale production.