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Photoinduced charge and energy transfer in dye-doped conjugated polymers

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Author: Veldman, D. · Bastiaansen, J.J.A.M. · Langeveld-Voss, B.M.W. · Sweelssen, J. · Koetse, M.M. · Meskers, S.C.J. · Janssen, R.A.J.
Type:article
Date:2006
Publisher: Elsevier
Place: Amsterdam
Institution: TNO Industrie en Techniek
Source:Thin Solid Films, 511-512, 581-586
Identifier: 239387
Keywords: Charge transfer · Conjugated polymers · Energy transfer · Light-emitting diodes · Polymer solar cells · Absorption spectroscopy · Charge transfer · Dyes · Energy transfer · Fluorescence · Light emitting diodes · Open-circuit voltage · Optical excitation · Polymer solar cells · Reduction potentials · Organic polymers

Abstract

Conjugated polymer-molecular dye blends of MDMO-PPV (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene]) and PF1CVTP (poly[9,9-dioctylfluorene-2,7-diyl-alt-2,5-bis(2-thienyl-1-cyanovinyl)-1-(3′,7′-dimethyloctyloxy)-4-methoxybenzene-5″,5″-diyl]) with three dipyrrometheneboron difluoride (bodipy) dyes were studied by (time-resolved) fluorescence and photoinduced absorption spectroscopy to determine quantitatively the relation between the electronic HOMO and LUMO levels and the occurrence of energy or charge transfer after optical excitation. We find that for MDMO-PPV photoinduced charge transfer to the dyes occurs, while photoexcitation of PF1CVTP exclusively results in energy transfer. The differences can be rationalized by assuming that the energy of the charge separated state is 0.33-0.45 eV higher than the energy determined from oxidation and reduction potentials of donor and acceptor, respectively. This provides an important design rule to identify appropriate materials for polymer solar cells that can have a high open-circuit voltage.