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In this study, we developed two novel conjugated polymers that can easily be doped with F4TCNQ organic dopants using a sequential doping method and then studied their organic thermoelectric (OTE) properties. In particular, to promote the intermolecular ordering of OTE polymers in the presence of the F4TCNQ dopant, alkylthiazole-based conjugated building blocks with highly planar backbone structures were synthesized and copolymerized. All polymers showed strong molecular ordering and edge-on orientation in the film state, even in the presence of the F4TCNQ organic dopant. Thus, the sequential doping process barely changed the molecular ordering of the polymer films while making efficient molecular doping. In addition, the doping efficiency was improved in the more π-extended polymer backbones with thienothiophene units due to the emptier space in the polymer lamellar structure to locate ionized F4TCNQ. Moreover, the study of organic thin-film transistors (OTFTs) revealed that higher hole mobility in OTFTs was the key to increasing the electrical conductivity of OTE devices fabricated using the sequential doping method. [ABSTRACT FROM AUTHOR]

Benzo[1,2-d:4,5-d′]bis(oxazole) (BBO) is a heterocyclic aromatic ring composed of one benzene ring and two oxazole rings, which has unique advantages on the facile synthesis without any column chromatography purification, high solubility on the common organic solvents and planar fused aromatic ring structure. However, BBO conjugated building block has rarely been used to develop conjugated polymers for organic thin film transistors (OTFTs). Three BBO-based monomers, BBO without π-spacer, BBO with non-alkylated thiophene π-spacer and BBO with alkylated thiophene π-spacer, were newly synthesized and they were copolymerized with a strong electron-donating cyclopentadithiophene conjugated building block to give three p-type BBO-based polymers. The polymer containing non-alkylated thiophene π-spacer showed the highest hole mobility of 2.2 × 10−2 cm2 V−1 s−1, which was 100 times higher than the other polymers. From the 2D grazing incidence X-ray diffraction data and simulated polymeric structures, we found that the intercalation of alkyl side chains on the polymer backbones was crucial to determine the intermolecular ordering in the film states, and the introduction of non-alkylated thiophene π-spacer to polymer backbone was the most effective to promote the intercalation of alkyl side chains in the film states and hole mobility in the devices. [ABSTRACT FROM AUTHOR]

Conjugated polymers based on cyclopentadithiophene (CPDT) moieties are widely used in optoelectronics applications but rarely in field‐effect transistors (FETs). This is due to the steric hindrance at the tetrahedral center of the CPDT core, which is a critical problem requiring resolution without diminishing the polymer crystallinity and solubility. A bulky CPDT‐based high‐mobility copolymers are synthesized here, which shows excellent π–π stacking in the film states with good solubility. The addition of bulky ethylhexyl side chains to CPDT does not interfere with the molecular ordering and promotes the intercalation of linear alkyl chains on the co‐monomeric units. The resulting polymer forms bimodal packing structures with strong lamellar ordering and π–π interactions. Furthermore, the free volume generated by the bulky ethylhexyl side chains allows for a small amount of fullerene additive to be contained in the film state without interfering with the molecular ordering, leading to enhanced on/off ratios and hole mobilities of the resulting FETs. As a result, promising hole mobilities of up to 1.08–1.64 cm2 V−1 s−1 are achieved with the optimized FETs, which are the highest mobilities reported for CPDT‐based conjugated polymers containing branched alkyl side chains. [ABSTRACT FROM AUTHOR]

Two thiophene backbone-based hole-transporting polymers, namely, poly[(2,2′-bithiophene-5,5′-diyl)-alt-(5,7-bis(2-butyloctyl)-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione-1,3-diyl)] (PT2-BDD) and poly[(3,3′-difluoro-[2,2′-bithiophene]-5,5′-diyl)-alt-(5,7-bis(2-butyloctyl)-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione-1,3-diyl)] (PF2-BDD), were prepared by using electron-withdrawing pendant groups such as ketone and fluorine moieties. They both exhibited a planar backbone with efficient π conjugation, which is suitable for hole transport in organic thin-film transistors (OTFTs). However, the fluorinated one (i.e., PF2-BDD), despite its perfect backbone planarity and strong intra- and intermolecular interactions, could not enhance the OTFT performance; due to its solvent resistance, electron negativity, and random orientation, PF2-BDD showed 10 times lower hole mobility than the non-fluorinated polymer (i.e., PT2-BDD). Nonetheless, the two-dimensional grazing incidence X-ray diffraction and temperature-dependent absorption spectra of the synthesized polymers provided crucial information to understand the relationship between their hole transport behavior and molecular structure. [ABSTRACT FROM AUTHOR]