urn:nbn:de:hbz:468-20130312-112320-7 - Bergische Universität ...

Abstract
There is a growing demand for “tailor-made“ new materials for special applications, in
particular when the reservoir of the presently used raw materials is limited. Conjugated
polymers, especially alternating copolymers meet these requirement and can be “tailor-made“
for particular application or processing issues. In this thesis, several conjugated, alternating
copolymers with fused ring systems for optoelectronical applications are presented. The
mostly used building blocks are benzothiadiazole, benzobis(thiadiazole),
cyclopentadithiophene, and indoloindole.
Alternating copolymers based on cyclopentadithiophene and benzothiadiazole- or
benzobis(thiadiazole)-moieties (with and without additional thiophene “spacers“) are
described in Chapter 2 and 3, respectively. Due to the smaller HOMO/LUMO energy gap of
benzobis(thiadiazole) compared to benzothiadiazole, the absorption maxima of the
corresponding copolymers are bathochromically shifted to wavelengths above 1 000 nm. The
benzothiadiazole-based copolymers were tested with different acceptor materials (fullerenes,
nanoparticles) in bulk-heterojunction-type organic solar cells. The best power conversion
efficiency of ca. 4.5 % was reached with poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-
b;3,4-b‘]-dithiophene)-alt-4,7-[2,1,3]-benzothiadiazole] and C 70 -PCBM as acceptor in the
active layer.
In Chapter 4, several indoloindole-based homo- and copolymers are presented. However, the
properties of the polymers (regarding molecular weight, solubility, absorption, emission,
HOMO/LUMO energy gap) vary considerably. Dual fluorescence, which is observed for the
benzothiadiazole containing copolymers, and the oxidation behaviour of the indoloindole
homopolymer are studied in detail.