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Electronic Properties of Polymer-Fullerene Solar Cells StudiedWith Light-Induced Electron Spin Resonance and Admittance Spectroscopy

Published online by Cambridge University Press:  01 February 2011

V. Dyakonov
Affiliation:
Dept. of Energy and Semiconductor Research, University of Oldenburg, D-26111 Oldenburg, Germany
I. Riedel
Affiliation:
Dept. of Energy and Semiconductor Research, University of Oldenburg, D-26111 Oldenburg, Germany
Z. Chiguvare
Affiliation:
Dept. of Energy and Semiconductor Research, University of Oldenburg, D-26111 Oldenburg, Germany
C. Deibel
Affiliation:
Dept. of Energy and Semiconductor Research, University of Oldenburg, D-26111 Oldenburg, Germany
J. Parisi
Affiliation:
Dept. of Energy and Semiconductor Research, University of Oldenburg, D-26111 Oldenburg, Germany
C.J. Brabec
Affiliation:
Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes-Kepler-University of Linz, A-4040 Linz, Austria
N.S. Sariciftci
Affiliation:
Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes-Kepler-University of Linz, A-4040 Linz, Austria
J.C. Hummelen
Affiliation:
Stratingh Institute and Materials Research Centre (MSC), University of Groningen, NL-9747 AG Groningen, The Netherlands
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Abstract

Within recent years, the development of polymer-fullerene plastic solar cells has made significant progress. In such devices, an efficient charge generation takes place via photoinduced charge transfer between the photoexcited conjugated polymer and acceptor-type fullerene molecules. Due to the paramagnetic nature of the radical species, the photoinduced charge transfer can be studied by means of light induced electron spin resonance (LESR) techniques. We carried out W-band (95 GHz) LESR at high magnetic field strengths. Two well separated line groups with a strong anisotropic structure were detected for the composite MDMOPPV: PCBM. From the line shape analysis, we obtained an environmental axial symmetry for the positive polaron P+ and a lower, rhomboedric symmetry for the fullerene anion. The signals were found to be independent of each other with different spin-lattice relaxation times; hence, the radical species can be investigated separately. In order to study the bulk transport properties, we carried out admittance spectroscopy on the ITO/PEDOT:PSS/MDMO-PPV:PCBM/Al device. Two frequency-dependent contributions to the device capacitance with the activation energies 9 meV and 177 meV were found. For the very shallow trap state, we assume a bulk impurity, whereas the latter one is assigned to an interfacial defect state, located at the composite- aluminium interface.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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