Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Organic semiconductors I

CPP 18.6: Talk

Wednesday, March 28, 2012, 10:45–11:00, C 130

Origin of Sub-Bandgap Absorption in P3HT:PCBM Solar Cells — Martin Presselt, •Felix Herrmann, Marco Seeland, Maik Bärenklau, Roland Rösch, Wichard J. D. Beenken, Erich Runge, Sviatoslav Shokhovets, Harald Hoppe, and Gerhard Gobsch — TU Ilmenau, Ilmenau, Germany

To explain the origin of sub-bandgap (SBG) absorption contributing to the photocurrent in bulk-heterojunctions (BHJ) made of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenylC61-butyric acid methyl ester (PCBM) at least four different models are discussed in the literature. In an earlier work we have shown that an exponential in addition to a Gaussian function is needed to reproduce SBG external quantum efficiency (EQE) spectra. There, the exponential function was assigned to a disorder related absorption tail, while the SBG EQE Gaussian was not assigned unambiguously. In the present work, the SBG EQE Gaussian is assigned to a hole-polaron transition at P3HT rather than to a direct charge transfer transition from the P3HT HOMO to the PCBM LUMO or absorption of molecularly dispersed PCBM as concluded from temperature dependent EQE measurements.