Thienoisoindigo-Based Semiconductor Nanowires Assembled with 2-Bromobenzaldehyde via Both Halogen and Chalcogen Bonding

We fabricated nanowires of a conjugated oligomer and applied them to organic field-effect transistors (OFETs). The supramolecular assemblies of a thienoisoindigo-based small molecular organic semiconductor (TIIG-Bz) were prepared by co-precipitation with 2-bromobenzaldehyde (2-BBA) via a combination of halogen bonding (XB) between the bromide in 2-BBA and electron-donor groups in TIIG-Bz, and chalcogen bonding (CB) between the aldehyde in 2-BBA and sulfur in TIIG-Bz. It was found that 2-BBA could be incorporated into the conjugated planes of TIIG-Bz via XB and CB pairs, thereby increasing the pi - pi stacking area between the conjugated planes. As a result, the driving force for one-dimensional growth of the supramolecular assemblies via pi - pi stacking was significantly enhanced. TIIG-Bz/2-BBA nanowires were used to fabricate OFETs, showing significantly enhanced charge transfer mobility compared to OFETs based on pure TIIG-Bz thin films and nanowires, which demonstrates the benefit of nanowire fabrication using 2-BB

Inducing Elasticity through Oligo-Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers

The promise of wearable and implantable devices has made stretchable organic semiconductors highly desirable. Though there are increasing attempts to design intrinsically stretchable conjugated polymers, their performance in terms of charge carrier mobility and maximum fracture strain is still lacking behind extrinsic approaches (i.e., buckling, Kirigami interconnects). Here, polymer crosslinking with flexible oligomers is applied as a strategy to reduce the tensile modulus and improve fracture strain, as well as fatigue resistance for a high mobility diketopyrrolopyrrole polymer. These polymers are crosslinked with siloxane oligomers to give stretchable films stable up to a strain ε = 150% and 500 strain‐and‐release cycles of 100% strain without the formation of nanocracks. Organic field‐effect transistors are prepared to assess the electrical properties of the crosslinked film under cyclic strain loading. An initial average mobility (μavg) of 0.66 cm2 V−1 s−1 is measured at 0% strain. A steady μavg above 0.40 cm2 V−1 s−1 is obtained in the direction perpendicular to the strain direction after 500 strain‐and‐release cycles of 20% strain. The μavg in the direction parallel to strain, however, is compromised due to the formation of wrinkles

High performance p-type chlorinated-benzothiadiazole-based polymer electrolyte gated organic field-effect transistors

We report the evaluation of charge transport parameters of four p-type dichlorinated-2,1,3-benzothiadiazole (2ClBT) based conjugated polymers end-capped with different electron-donor units (thiophene (T), thieno[3,2-b] thiophene (TT), 2,2'-bithiophene (DT), and (E)-2-(2-(thiophen-2-yl) vinyl) thiophene (TVT)) in electrolyte gated organic field-effect transistors operating at a driving voltage of -2V. Remarkable hole mobility improvement of 0.13-0.56 cm(2)V(-1)s(-1) were achieved in 2ClBTs based polymers, with P2ClBT-DT recording the highest mobility of 0.56 cm(2)V(-1)s(-1) and current on/off ratio similar to 10(7). Interestingly, a positive threshold voltage shift (Delta V-Th) was observed in the transfer characteristics from the linear to saturation regime of all the 2ClBTs based polymer electrolyte gated OFET devices of L = 10 mu m, contrary to devices with conventional poly(methyl methacrylate) gate dielectric, which showed a negative.V-Th shift. Among the 2ClBTs based polymers, P2ClBT-TVT devices showed the lowest mobility and.V-Th shift, which is attributed to severe ion diffusion in the polymer semiconducting layer owing to the vinyl group backbone susceptible to electrochemical doping. Our results emphasize essential selection consideration of the monomeric moieties, molecular ordering, pi-pi stacking and backbone planarity of conjugated polymers for electrolyte based organic devices

Effect of electron-donating unit on crystallinity and charge transport in organic field-effect transistors with thienoisoindigo-based small molecules

We report the effect of an electron-donating unit on solid-state crystal orientation and charge transport in organic field-effect transistors (OFETs) with thienoisoindigo (TIIG)-based small molecules. End-capping of different electron-donor moieties [benzene (Bz), naphthalene (Np), and benzofuran (Bf)] onto TIIG (giving TIIG-Bz, TIIG-Np, and TIIG-Bf) is resulted in different electronic energy levels, solid-state morphologies and performance in OFETs. The 80??C post-annealed TIIG-Np OFETs show the best device performance with a best hole mobility of 0.019 cm2 V-1 s-1 and threshold voltage of -8.6 ?? 0.9 V using top gate/bottom contact geometry and a CYTOP gate dielectric. We further investigated the morphological microstructure of the TIIG-based small molecules by using grazing incidence wide angle X-ray scattering, atomic force microscopy and a polarized optical microscope. The electronic transport levels of the TIIG-based small molecules in thin-film states were investigated using ultraviolet photoelectron spectroscopy to examine the charge injection properties of the gold electrode. © 2015 Elsevier B.V. All rights reservedclose0

Difluorobenzothiadiazole and Selenophene-Based Conjugated Polymer Demonstrating an Effective Hole Mobility Exceeding 5 cm2 V-1 s-1 with Solid-State Electrolyte Dielectric

We report synthesis of a new poly(4-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b???]dithiophene-2-yl)-7-(4,4-bis(2-ethylhexyl)-6-(selenophene-2-yl)-4H-silolo[3,2-b:4,5-b???]dithiophene-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (PDFDSe) polymer based on planar 4,7-bis(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b???]dithiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (DFD) moieties and selenophene linkages. The planar backboned PDFDSe polymer exhibits highest occupied molecular orbital and lowest unoccupied molecular orbital levels of −5.13 and −3.56 eV, respectively, and generates well-packed highly crystalline states in films with exclusive edge-on orientations. PDFDSe thin film was incorporated as a channel material in top-gate bottom-contact organic thin-film transistor with a solid-state electrolyte gate insulator (SEGI) composed of poly(vinylidene difluoride-trifluoroethylene)/poly(vinylidene fluoride-co-hexafluroropropylene)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, which exhibited a remarkably high hole mobility up to ?? = 20.3 cm2 V-1 s-1 corresponding to effective hole mobility exceeding 5 cm2 V-1 s-1 and a very low threshold voltage of −1 V. These device characteristics are associated with the high carrier density in the semiconducting channel region, induced by the high capacitance of the SEGI layer. The excellent carrier mobility from the PDFDSe/SEGI device demonstrates a great potential of semiconducting polymer thin-film transistors as electronic components in future electronic applications

Bar-coated high-performance organic thin-film transistors based on ultrathin PDFDT polymer with molecular weight independence

We report high-performance organic thin-film transistors (OTFTs) with an ultrathin active layer of difluorobenzothiadiazole-dithienosilole copolymer (PDFDT) form by using the wire bar-coating process. The top-gate/bottom contact (TG/BC) OTFTs based on bar-coated PDFDT polymer as channel material and poly(methyl methacrylate) (PMMA) as gate dielectric show a hole mobility of up to 2.2 cm(2) V-1 s(-1) with a current ON/OFF ratio (I-on/I-off) of 10(4)-10(5), with the mobility being two times larger than that of the spincoated PDFDT based OTFTs. The higher mobility of the bar-coated PDFDT polymer films can be attributed to the well-organized fibril structures of the polymer chains. Importantly, two different molecular weight polymers (M-n = 23 and 34 kDa) were employed to conduct these experiments and both batches showed about the same performance, which mitigates the typical batch-to-batch variation in OTFT performance. Furthermore, we explored the operational stability of the bar-coated OTFTs in ambient air and nitrogen environments. The bias-stress and cycling tests between the ON/OFF states of the bar-coated devices showed high stability in both nitrogen and air. Conclusively, here we demonstrate that (i) a simple barcoating process is a better method to control and obtain good polymer morphology in comparison to spin-coating, and (ii) the PDFDT polymer has great potential to provide good reproducibility and stability in large-area OTFT devices

A Timely Synthetic Tailoring of Biaxially Extended Thienylenevinylene Polymer Analogs for Systematic Investigation on Field-Effect Transistors

With the growing interest in the superior charge transport in the (E)-2-(2-(thiophen-2-yl)-vinyl)thiophene (TVT)-based polymer, an forward step is to provide a comprehensive understanding of the structure-property relationships of their polymer analogs. Here, a set of DPP-TVT-n polymers are reported, involving different thiophene content in the diketopyrrolopyrrole(DPP)-TVT repeating units, where n is the number of thiophene spacer units. Their OFET characteristics demonstrate ambipolar behavior; with no spacer, the charge transports are observed nearly balanced, but with the electron-donating spacer, the majority of the properties changed from ambipolar to p-type dominant with enhanced hole mobility. Although both the lamellar d-spacings and ??-stacking distances decreased with the number of spacers, DPP-TVT-1 shows the highest hole mobility due to the unique structural conformations derived from its smaller paracrystalline distortion parameter and narrower plane distribution