Tuning of the Photoinduced Charge Transfer Process in Donor- Acceptor “Double Cable” Copolymers S. Luzzati *a , A. Mozer d , P. Denk d , M.C Scharber b,d , M. Catellani a , N.O. Lupsac a , F.Giacalone c , J. L. Segura c , N. Martin c , H.Neugebauer b , N. S. Sariciftci b a Istituto per lo Studio delle Macromolecole, C.N.R, via Bassini 15, 20133 Milano, Italy; b Linz Institute for Organic Solar Cells, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria; c Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040- Madrid, Spain; d Konarka Austria, Forschungs- und Entwicklungs GmbH, Gruberstraße 40–42, A-4020 Linz, Austria ABSTRACT The covalent linking of acceptor molecules to electron donating conjugated polymer is an approach for the development of new photoactive materials for the fabrication of organic photoelectric conversion devices. With this strategy we have designed a polyalkylthiophene copolymer series containing in the side chain anthraquinone molecules as electron acceptor. The peculiar features of the copolymers are the good processability and the ease in tailoring the content of acceptor moieties. Their potential use as photoactive materials is investigated in terms of the photoinduced charge transfer properties, studied by FTIR photoinduced absorption and Light Induced Electron Spin Resonance spectroscopies. The results indicate the photoinduced electron transfer from the polythiophene backbone to the anthraquinone substituents and its tunability by changing the content of acceptor molecules. The photovoltaic response of these polymers is also discussed. Keywords: photoinduced charge transfer, polyalkylthiophene copolymers, anthraquinone, photovoltaic devices, spectroscopy 1. INTRODUCTION The preparation of polymeric photovoltaic cells processable as easily as plastics can provide a new hint both in the exploitation of solar energy and in the demands for more advanced photodetectors. For these reasons the possibility to use conjugated polymers to fabricate inexpensive and flexible large area solar cells and photodetectors is intensively investigated 1,2 . The photovoltaic effect in conjugated polymers consists in photogeneration of excitons on the chain and their dissociation in presence of electron-acceptor species like fullerene. The most promising active layer is the so called bulk-heterojunction where the electron donor polymer (D) and the acceptor molecules (A) are blended together 3,4 . The blend morphology is affecting both charge photogeneration and transport, having thus a crucial role for the device performance. The tendency to phase segregation of the two components has to be tailored having in mind that: i) an intimate mixing of the donor and acceptor is beneficial for charge photogeneration; ii) a bicontinuos network of the donor and acceptor phases favours a balanced transport of the photogenerated charges to the electrodes. A proposed approach to attain an intimate mixing of the D/A components is the covalent linking of electron accepting moieties to a hole transporting conjugated polymer backbone. This kind of material is called “double cable” because has, in principle, two different pathways (cables) for the transport of electrons and holes to the electrodes 5 . Different types of conjugated polymers, bearing as acceptor substituents fullerene 6-8 or tetracyanoantraquinodimethane 9 moieties have been synthesised, and their use for photovoltaics has been studied. One of the major issues in the design of “double cable” polymers is to improve the processability in order to obtain soluble materials with a high content of acceptor moieties. For example, soluble conjugated polymers containing fullerene exhibit a content of acceptors not exceeding 20 % by weight 5 . * Silvia.Luzzati@ismac.cnr.it ; phone +390223699372; fax +390270636400 Organic Photovoltaics IV, edited by Zakya H. Kafafi, Paul A. Lane, Proceedings of SPIE Vol. 5215 (SPIE, Bellingham, WA, 2004) · 0277-786X/04/$15 · doi: 10.1117/12.503913 41