Regensburg 2019 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 50: Organic Electronics and Photovoltaics III - Organic Photovoltaics
CPP 50.8: Vortrag
Donnerstag, 4. April 2019, 11:30–11:45, H18
How to Interpret Absorption and Fluorescence Spectra of Charge Transfer States in an Organic Solar Cell — •Frank-Julian Kahle1, Alexander Rudnick1, Heinz Bässler2, and Anna Köhler1,2 — 1Soft Matter Optoelectronics, Department of Physics, University of Bayreuth, Germany — 2Bayreuth Institute of Macromolecular Science (BIMF), University of Bayreuth, Germany
The aim of the present work is to identify the appropriate framework for analyzing photoluminescence and photocurrent (EQE) spectra of charge transfer (CT) states in donor-acceptor blends used as active materials for organic solar cells. We applied gated photoluminescence (PL) spectroscopy within a temperature range from 5 to 295 K combined with EQE as well as electroluminescence (EL) experiments on 1:1 Me-LPPP:PCBM blends by weight. We find that the PL spectra are virtually temperature independent and the temporal decay of the emission features a power law with an exponent close to -3/2 as Hong and Noolandi predicted for distributed geminately bound electron-holes pairs. The results are inconsistent with both Marcus* electron transfer theory and the original Marcus-Levich-Jortner (MLJ) theory, and they prove that disorder effects are crucial. Both PL and EQE spectra can be rationalized in terms of the classic Franck-Condon picture of electronic transitions that couple to intra-molecular vibrations as well as low frequency modes of the donor-acceptor pair that forms the CT state.