Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 8: Charge Transfer Effects in Molecular Materials II (jointly with BP, CPP, HL)

DS 8.5: Talk

Monday, March 11, 2013, 16:30–16:45, H40

Triplet Exciton Generation and Electron Back Transfer in Organic Solar Cells — •Andreas Sperlich¹, Hannes Kraus¹, Stefan Väth¹, Alexander Förtig¹, Carsten Deibel¹, and Vladimir Dyakonov^1,2 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg — ²ZAE Bayern, 97074 Würzburg

To increase the power conversion efficiency of organic solar cells it would be extremely advantageous to improve the harvesting of singlet and charge transfer (CT) excitons. Dissociation of CT complexes into free charge carriers or, alternatively, their decay by electron back transfer (EBT) reactions depend on the energy levels of constituting donor and acceptor molecules, on microscopic structure of blends but also on the relative spin orientation of charges carriers within the e-h pair. We report on state-of-the-art organic semiconductors for polymer-fullerene bulk hetero-junction solar cells, such as blends based on the benzodithiophene donor PTB7 or the endohedral fullerene-derivative Lu₃N@C₈₀-PCBEH. We applied optical, current-voltage, morphology, and spin-sensitive techniques and found correlations between electrical performance of solar cells and formation of CT and triplet states. Combining results of these complementary experiments, we offer a physical picture on how pushing up the LUMO level of acceptors or tailoring the blends’ morphology may end up in unwanted loss mechanisms in bulk-heterojunction solar cells.