In this work, we develop mechanically robust and high-performance organic thin-film transistors (OTFTs) based on poly(3-hexylthiophene) (P3HT) regioblock copolymers (block-P3HTs). These block-P3HTs consist of regioregular (rre) and regiorandom (rra) P3HTs, where the highly crystalline rre block allows efficient charge transport while the amorphous rra block provides mechanical robustness and interdomain connection. To examine the effects of the molecular architecture on the OTFT performance and stretchability, we prepare a series of block-P3HTs having different number-average molecular weight (M n) values of rra blocks (from 0 to 32 kg mol–1) and a fixed M n of rre blocks (11 kg mol–1). Thin films of all of the block-P3HTs exhibit a high charge-carrier mobility due to the formation of well-developed edge-on crystallites from the rre blocks confined within the rra domains, leading to a hole mobility of 1.5 × 10–1 cm2 V–1 s–1, which is superior to that of the rre P3HT homopolymer. In addition, the mechanical toughness of block-P3HT thin films is remarkably enhanced by the rra block. While the rre P3HT homopolymer thin film shows a brittle behavior with an elongation at break of only 0.3%, the elongation at break of the block-P3HT thin films increases by a factor of 100, yielding 30.2% with increasing M n of the rra block, without sacrificing the electrical properties. In particular, a noticeable enhancement of both elongation at break and toughness is observed between M n values of the rra block of 8 and 20 kg mol–1, indicating that the critical molecular weight of rra P3HT plays an important role in determining the mechanical response of the block-P3HT thin films. This study provides guidelines and strategies to improve the mechanical properties of organic electroactive materials without the disruption of optoelectrical properties, which is critical to fabricate high-performance soft electronics.
In the last decade, extensive academic and industrial efforts have been devoted to developing efficient conjugated polymers (CPs) for organic electronics. Specifically, the relationship between the molecular structures, properties, and...
Discrete oligomers (i.e., highly monodisperse) can provide a deep understanding of chain-length-dependent properties of polymers and their self-assembly behaviors. Herein, discrete oligo(3-hexylthiophene)s (D-o3HTs) with a dispersity (Đ) of 1.0 and degree of polymerization (DP) between 6 and 18 were obtained through a simple synthetic procedure of 3-hexlythiophene trimer-based polymerizations and automated column chromatography purification. As the DP of D-o3HTs increases, longer conjugation lengths cause red shifts in their optical properties and yield tunable crystalline properties. Interestingly, D-o3HTs with DP ≤ 9 have a dominant face-on Form II structure in thin films, while a fiber morphology is also not observed in thin films. In contrast, D-o3HTs with DP ≥ 12 assemble into a dominant edge-on Form I structure in thin films and show highly ordered fiber morphologies. In addition, Bragg rod patterns are observed in thin films by transmission electron microscopy and grazing incidence X-ray scattering with these patterns being distinctive when compared to those for conventional regioregular poly(3-hexylthiophene) with Đ = 1.1. Finally, the formation of 2-dimensional flowerlike nanostructures with overall micrometer dimensions is obtained from D-o3HTs via solvent-mediated self-assembly. These results offer an understanding of self-assembly behaviors of discrete conjugated polymers, leading to exquisite control over their crystallinity and nanoscale morphology.
Microphase-separation behavior of conjugated–amorphous block copolymers (BCPs) is driven by a complex interplay between Flory–Huggins interaction (χ), liquid crystalline (LC) interaction, and crystallization. Herein, in order to elucidate the influence of LC interaction on the morphology of the BCPs, we report the effects of regioregularity (RR) on the microphase separation and molecular packing structures of poly(3-dodecylthiophene)-block-poly(2-vinylpyridine) (P3DDT-b-P2VP). To decouple the effect of LC interactions from crystallization kinetics, we investigate the morphological behavior of the P3DDT-b-P2VP at above the melting temperature of P3DDT (∼160 °C). Both electron microscopy and X-ray scattering show an abrupt reduction in the domain spacing of both lamellar and cylindrical phases as the RR of P3DDT block increases. Specifically, lower RR (i.e., 85, 79, and 70%) BCPs have larger domain spacings than high RR (94%) by 50% (lamellar) or 80% (cylindrical), even though the overall molecular weights and P2VP volume fractions were similar for each RR. We propose that the RR-driven transition in domain spacing is caused by a change in P3DDT conformations and interchain interactions. When RR is low, the system assembles into a typical bilayer structure like other semiflexible and flexible block copolymer systems. When RR is high, the less flexible P3DDT chains are extended, driving their assembly into an LC monolayer. Significantly, this study demonstrates that tunable RR provides a simple route to manipulate melt state self-assembly of conjugated–amorphous materials.
Degradable organic semiconductors have significant potential for transient and biomedical organic electronics, but there have been only a few studies on fully degradable conjugated polymers (CPs) that achieve high electrical performance. In addition, these examples are limited to p‐type CPs. In this study, a series of fully degradable n‐type CPs, naphthalene diimide (NDI)‐based terpolymer (PNDIT2/IM‐f) are developed. The incorporation of an imine linker (IM) into the CP backbone affords the capability of facile hydrolysis degradation while maintaining efficient π‐conjugations and excellent electrical properties. An additional benefit of this molecular design is the systematic tunability of the degradation characteristics and electrical performance depending on the IM content (fIM). At the optimal point (fIM = 0.45) that enables complete degradation of the polymer under acidic conditions, the resulting PNDIT2/IM‐0.45 film exhibits high electron mobility (μe) of 0.04 cm2 V−1 s−1 in organic field‐effect transistors (OFETs), demonstrating excellent potential as transient OFETs. The high μe value is mainly attributed to the enlarged edge‐on orientations and tighter stacking of PNDIT2/IM‐f crystallites as increasing fIM. Thus, this study provides useful guidelines for the design of fully degradable n‐type CPs and establishes an important correlation between the molecular structure−electronic performance−transient properties.
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