Kigook Song

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%.

Molecular origin of high field-effect mobility in an indacenodithiophene–benzothiadiazole copolymer

One of the most inspiring and puzzling developments in the organic electronics community in the last few years has been the emergence of solution-processable semiconducting polymers that lack significant long-range order but outperform the best, high-mobility, ordered semiconducting polymers to date. Here we provide new insights into the charge-transport mechanism in semiconducting polymers and offer new molecular design guidelines by examining a state-of-the-art indacenodithiophene-benzothiadiazole copolymer having field-effect mobility of up to 3.6 cm(2) V(-1) s(-1) with a combination of diffraction and polarizing spectroscopic techniques. Our results reveal that its conjugated planes exhibit a common, comprehensive orientation in both the non-crystalline regions and the ordered crystallites, which is likely to originate from its superior backbone rigidity. We argue that charge transport in high-mobility semiconducting polymers is quasi one-dimensional, that is, predominantly occurring along the backbone, and requires only occasional intermolecular hopping through short π-stacking bridges.

Random benzotrithiophene-based donor-acceptor copolymers for efficient organic photovoltaic devices

A series of benzotrithiophene-containing random terpolymers for polymer solar cells is reported. Through variations of the two other components in the terpolymers, the absorption profile and the frontier energy levels are optimized and maximum power conversion efficiencies are nearly doubled (5.14%) relative to the parent alternating copolymer.

Systematic Improvement in Charge Carrier Mobility of Air Stable Triarylamine Copolymers

The electrical performance of organic semiconducting polymers in field-effect transistor devices is now sufficient for initial low complexity circuit applications. To achieve high performance, either operation in an inert atmosphere or a hydrophobic surface treatment and annealing step is typically required. In this communication we report a strategy to prepare fully air stable, amorphous semiconducting polymers which can achieve charge carrier mobilities in the range of 0.04 cm(2)/(V s), remaining over a period of over 3 months in ambient conditions.

Liquid crystalline blue phase I observed for a bent-core molecule and its electro-optical performance

We investigated the liquid crystalline blue phase I (BP I) observed for a nematogenic achiral bent-core molecule doped with a small percentage of a chiral additive with a high twisting power. We also observed the electro-optical performance of BP I by incorporating in-plane electric field geometry.

Pyrroloindacenodithiophene containing polymers for organic field effect transistors and organic photovoltaics

The synthesis of the novel electron-rich pyrroloindacenodithiophene (NIDT) unit is reported. Stille copolymerization of the distannylated NIDT unit, with the electron-deficient dibrominated benzothiadiazole (BT), difluorobenzothiadiazole (ffBT), thienopyrrolodione (TPD) and 1,1′-bithienopyrrolodione (biTPD) units afforded a series of low band gap semiconducting polymers. Initial testing shows promise for the use of these materials as p-type semiconductors in organic field effect transistors (OFETs) with mobilities as high as 0.07 cm2V−1s−1 being measured. These materials have also been tested as the donor polymer in polymer/fullerene bulk heterojunction organic photovoltaics (OPVs) giving maximum efficiencies of 2.5%.

Synthesis of a Novel Fused Thiophene-thieno[3,2-b]thiophene-thiophene Donor Monomer and Co-polymer for Use in OPV and OFETs

The synthesis of a novel fused hexacyclic electron rich monomer incorporating thieno[3,2-b]thiophene is reported and characterized by single crystal X-ray diffraction. Suzuki co-polymerization with benzothiadiazole (BT) afforded a novel low band-gap polymer P4TBT with high molecular weights and good solution processability. Bulk heterojunction solar cell devices using the P4TBT and [70]PCBM gave power conversion efficiencies of 2.5%. Top-gate, bottom-contact field effect transistors (FETs) using P4TBT displayed high hole mobilities of 0.07 cm(2) · Vs(-1) demonstrating the suitability of the novel monomer and polymer for use in high performing organic electronic devices.

Pyrroloindacenodithiophene polymers: the effect of molecular structure on OFET performance

The synthesis, characterization and testing of four novel pyrroloindacenodithiophene (NIDT) copolymers, in organic field effect transistor (OFET) devices, is reported. Copolymerization of thiophene, thienothiophene, thienopyrrolodione and diketopyrrolopyrrole with NIDT, to form alternating copolymers, is described. Two-dimensional Grazing Incidence Wide Angle X-ray Diffraction (2D GIWAXD) is used to probe the thin film molecular structure and, together with DFT studies, help to explain why the diketopyrrolopyrrole containing polymer outperforms the others in terms of hole transport, exhibiting an average mobility of 0.01 cm2 V−1 s−1.

Improved Field-Effect Transistor Performance of a Benzotrithiophene Polymer through Ketal Cleavage in the Solid State

A benzotrithiophene polymer with a new thermally cleavable ketal substituent is reported. It is shown how this functional group can be used to facilitate solvent processing and, subsequently, how it can be removed by a thermal annealing process to generate a structurally ordered and crystalline thin film with significantly improved field-effect transistor properties.

Wide-Band Reflective Polarizers from Variable Pitch Cholesteric Liquid Crystal Films

Due to their periodic helical structure, cholesteric liquid crystals (CLC) have a unique ability to selectively reflect visible light. CLC films reflecting a broad wavelength band were made by inducing a pitch gradient in CLC through a diffusion of small molecules and through a thermal diffusion between two CLC oligomer films with different pitch gradients.