Dresden 2011 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 40: Organic Electronics and Photovoltaics HL-II (jointly with CPP, HL, and O)
DS 40.1: Vortrag
Mittwoch, 16. März 2011, 10:15–10:30, FOE Anorg
Charge transport and electron trapping in a donor/acceptor-type copolymer — •Marcel Schubert1, Eduard Preis2, Ullrich Scherf2, and Dieter Neher1 — 1Universität Potsdam, Institut für Physik und Astronomie, 14476 Potsdam — 2Bergische Universität Wuppertal, Makromolekulare Chemie, 42119 Wuppertal
Low bandgap polymers are the driving force of the ongoing increase in efficiency of organic solar cells (OSC). Most of them are so called donor/acceptor-type copolymers. The polymer PFTBTT was one of the first of this material class, specially design for use in OSC [1]. It has been successfully incorporated as donor material in combination with soluble fullerenes or as acceptor in all-polymer solar cells.
Here, we present a detailed study of the electron transport properties of PFTBTT. By making use of an ultra thin charge generation layer, we were able to (1) selectively address the charge transport of electrons, (2) perform time-of-flight measurements on samples with less than 200 nm thickness and (3) to combine the time-of-flight and Photo-CELIV technique to investigate charge carrier dynamics. Our measurements proof that PFTBTT is an ambipolar material with a high electron bulk mobility. Furthermore, detailed investigations of the charge carrier dynamics with time-delayed extraction fields revealed a power law-type relaxation of the free electron mobility over two orders in time. These results help to quantify relaxation phenomena reported recently for PFTBTT containing all-polymer solar cells [2].
[1] M. Svensson et al., Adv. Mater. 15, 988 (2003).
[2] C. R. McNeill et al., J. Appl. Phys. 106, 024507 (2009).