Yves Geerts

Thieno[3,2-b]thiophene-Diketopyrrolopyrrole-Containing Polymers for High-Performance Organic Field-Effect Transistors and Organic Photovoltaic Devices

We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrole-based monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm(2) V(-1) s(-1), which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC(71)BM gave a power conversion efficiency of 5.4%.

Semi-metallic polymers

Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications. We measure the thermoelectric properties of various poly(3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.

Molecular Packing of High-Mobility Diketo Pyrrolo-Pyrrole Polymer Semiconductors with Branched Alkyl Side Chains

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm(2) V(-1) s(-1), with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.

Efficient white light-emitting diodes realized with new processable blends of conjugated polymers

An alternative method for producing efficient white light-emitting polymer diodes based on a blend of two polymers is reported. The white light emission is composed of a broad blue emission of laddertype (polyparaphenylene) (m-LPPP) and a red-orange emission of a new polymer, poly(perylene-co-diethynylbenzene) (PPDB). The red-orange electroluminescence emission is promoted by an excitation energy and charge transfer from m-LPPP to the PPDB. A concentration of 0.05% PPDB in the polymer blend is required in order to obtain white light emission. By inserting an insulating material in the blend, so that a maximum external quantum efficiency of 1.2% is obtained.

Rapid Charge Transport Along Self-Assembling Graphitic Nanowires

36 O WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0935-9648/98/0101-0036

Quaterrylenebis(dicarboximide)s: near infrared absorbing and emitting dyes

17.50+.50/0 Adv. Mater. 1998, 10, No. 1 [47] R. Schaffler, D. Hariskos, M. Kaiser, M. Ruckh, U. Ruhle, H. W. Schock, Cryst. Res. Technol. 1996, 31, 543. Note that while Cu vacancies create acceptors and hence promote p-type behavior, a decrease of the Cu contents promotes n-type behavior. For sizable deviations from stoichiometry, the point defect model is no longer applicable and detailed phase-diagram data should be used instead. [48] When using Na coming from the SLG without augmentation by Na precursor in the growth of laterally non-uniform samples, Ruckh et al. [34] found that the oxygen (and sodium) content is not maximal for Cu-poor compositions. This suggests that in this case, at least, it may be controlled by other factors. Homogenization (or lack thereof) of electrical performance in this case was not examined by Ruckh et al.

Highly Regular Organization of Conjugated Polymer Chains via Block Copolymer Self-Assembly

New ladder-type chromophores, the quaterrylenebis(dicarboxdiimide)s 2, 18 and 23, have been synthesised which, despite their extended π-system, exhibit good solubility in organic solvents and film forming properties when adequately substituted. These unprecedented dyes, which absorb and even emit light in the NIR window, are also characterized by oustanding chemical, thermal and photochemical stability with regard to their absorption range. The potential formation of J-aggregates in strongly acidic media has been investigated and has been ruled out by combined 1 H NMR and UV-VIS-NIR spectroscopy experiments. In addition, their photophysical and electrochemical characteristics have been explored and are discussed.

Doping of organic semiconductors : Impact of dopant strength and electronic coupling

The microscopic organization in thin films of block copolymers containing either polyparaphenylene, or polyphenyleneethynylene rigid segments covalently bound to a flexible polydimethylsiloxane or polystyrene sequence was investigated. Atomic force microscopy and theoretical modeling based on molecular mechanics/molecular dynamics calculations were combined. The typical morphology obtained revealed the presence of bright elongated structures.

Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matrices

Molecular doping: The standard model for molecular p-doping of organic semiconductors (OSCs) assumes integer charge transfer between OSC and dopant. This is in contrast to an alternative model based on intermolecular complex formation instead. By systematically varying the acceptor strength it was possible to discriminate the two models. The latter is clearly favored, suggesting strategies for the chemical design of more efficient molecular dopants.

Bulky End‐Capped [1]Benzothieno[3,2‐b]benzothiophenes: Reaching High‐Mobility Organic Semiconductors by Fine Tuning of the Crystalline Solid‐State Order

The fabrication of multifunctional high-performance organic thin-film transistors as key elements in future logic circuits is a major research challenge. Here we demonstrate that a photoresponsive bi-functional field-effect transistor with carrier mobilities exceeding 0.2 cm(2) V(-1) s(-1) can be developed by incorporating photochromic molecules into an organic semiconductor matrix via a single-step solution processing deposition of a two components blend. Tuning the interactions between the photochromic diarylethene system and the organic semiconductor is achieved via ad-hoc side functionalization of the diarylethene. Thereby, a large-scale phase-segregation can be avoided and superior miscibility is provided, while retaining optimal π-π stacking to warrant efficient charge transport and to attenuate the effect of photoinduced switching on the extent of current modulation. This leads to enhanced electrical performance of transistors incorporating small conjugated molecules as compared with polymeric semiconductors. These findings are of interest for the development of high-performing optically gated electronic devices.