Jianyao Huang

Dibenzoannelated tetrathienoacene: synthesis, characterization, and applications in organic field-effect transistors.

Two structural isomers of six-fused-ring sulfur-containing molecules were synthesized as active materials for p-type organic field-effect transistors, and their optical and electrochemical properties were characterized. Field-effect transistors based on these compounds were fabricated to investigate the relationships between structures and semiconductor properties.

Novel Butterfly-Shaped Fused Heteroacenes: Synthesis, Properties, and Device Performance of Solution-Processed Field-Effect Transistors

Two tetrabrominated intermediates obtained by bromination of naphthodithiophene in different solvents were used to construct novel highly π-extended butterfly-shaped heteroarenes 1-6, containing either an 8- or 10-fused ring. The solution-processed organic field-effect transistors based on compound 1 exhibited promising device performance with a hole mobility of 0.072 cm(2) V(-1) s(-1) and a current on/off ratio of 10(6) under ambient atmosphere.

Tribological properties of silicon carbide under water-lubricated sliding

Abstract The friction and wear performances of three kinds of self-mated silicon carbide (SiC), reaction sintered SiC, pressureless sintered SiC and toughened SiC, were investigated with a block-on-ring arrangement under water-lubricated sliding. Furthermore, the morphologies, phases and element valences of the worn surface were observed, examined and analysed employing scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometer and Fourier transform infrared spectroscopy respectively. In addition, the effects of microstructure and mechanical properties of the ceramics on their tribological properties were also discussed. It was found that the three kinds of SiC obviously showed different tribological properties. Higher friction coefficient and wear coefficient occurred for reaction sintered SiC and pressureless sintered SiC. The wear mechanisms of them were explained in term of pull-outs of grains and grain fracture. However, excellent tribological property, friction coefficient of 0.01, which suggested the characterization of hydrodynamic lubrication and wear coefficient of 4.2 × 10 −7 mm 3 N −1 m −1 , was obtained for toughened SiC. This resulted from that tribochemical oxidation took place and a ultraflat surface was formed on the worn track as a result that the toughened SiC possessed higher fracture toughness.

Bis-Diketopyrrolopyrrole Moiety as a Promising Building Block to Enable Balanced Ambipolar Polymers for Flexible Transistors

A bis-diketopyrrolopyrrole (DPP dimer, 2DPP) core is synthesized with much stronger electron deficiency than DPP by homocoupling of DPP. 2DPP-based polymers, P2DPP-BT, P2DPP-TT, P2DPP-TVT, and P2DPP-BDT, are obtained. Top-gated organic field-effect transistors on plastic substrate are fabricated. Compared with their mono-DPP-based polymers, remarkable improvement of electron mobilities of P2DPPs is achieved. Meanwhile, their p-channel performance becomes higher.

Phenanthro[1,10,9,8-cdefg]carbazole-containing copolymer for high performance thin-film transistors and polymer solar cells

A highly π-extended copolymer, PPTT, was developed based on 6H-phenanthro[1,10,9,8-cdefg]carbazole (PCZ) and thiazolo[5,4-d]thiazole derivative units, being the first PCZ-containing polymer, as well as its first applications in OTFTs and OPVs. This polymer exhibited an excellent solubility in several common organic solvents, a good film-forming ability, a reasonably high thermal stability, and a deep-lying HOMO energy level, meeting well the requirements of OTFTs and OPVs. The investigation of the field-effect and photovoltaic performances demonstrated that PPTT had a high hole mobility of 0.13 cm2 V−1 s−1 and good power conversion efficiency (PCE) of 3.20%, which were among the highest mobilities and PCEs for a single polymer material with dual transistor and OPV functions simultaneously.

Approaching high charge carrier mobility by alkylating both donor and acceptor units at the optimized position in conjugated polymers

Flexible side chains have been the central issue in the design of solution-processable polymer semiconducting materials. On identical conjugated backbones, great differences can be made with different side chain densities and substitution positions. Generally, for donor–acceptor (D–A) copolymers, increasing the side chain density could readily improve the solubility of the polymers. However, it also results in backbone distortion and weaker interchain interactions, thus hindering charge transport, which limits the application of highly soluble D–A polymers. Herein, we synthesized two polymers of PD-n-DTTE-7 with both the moieties alkylated. Substituting side chains to DTTE units improved the solubility of the corresponding polymers. Induced by the promoted solubility, high purity of the high molecular weight component was obtained and uniform films were formed with these high molecular weight polymers. In addition, by carefully selecting the conjugation system and substitution positions, ordered packing and backbone coplanarity were also achieved, which facilitate interchain and intrachain charge transport. Through a simple spin coating technique, the polymers, PD-n-DTTE-7s, present the highest hole mobility of 9.54 cm2 V−1 s−1 with high average mobilities of over 5 cm2 V−1 s−1, which are among the highest values for polymer-based field-effect transistors.

High-performance polymer field-effect transistors fabricated with low-bandgap DPP-based semiconducting materials

A series of new π-conjugated D–A copolymers PDMOTT-n (n = 118, 122, 320, and 420) containing a diketopyrrolopyrrole unit and a 3,6-dimethoxythieno[3,2-b]thiophene moiety was designed and synthesized, and their field-effect properties were characterized. The polymers PDMOTT-n have a low bandgap of 1.27 eV and exhibit a broad absorption. Solution-processed field-effect transistors based on these polymers were fabricated with a bottom-gate/bottom-contact configuration and demonstrated typical p-type charge transporting properties. Of these, PDMOTT-420 with the longest alkyl side chains and having the longest distance between the branching point of the alkyl side chain and π-conjugated backbone of the polymer, exhibited the best carrier transporting performance with a hole mobility of 2.01 cm2 V−1 s−1 and with an on/off current ratio of 104–105. The characterization results of grazing incidence X-ray diffraction and tapping-mode atomic force microscopy showed that the thin film of the polymer PDMOTT-420 forms larger grains and more useful nanofibrillar intercalated structures and owns shorter π–π stacking distance and better crystallization than those of another three polymers. These results could help us to better understand the structure–property relationship of polymer semiconductors and to design novel π-conjugated polymers for high-performance field-effect transistors.

Vinylidenedithiophenmethyleneoxindole: a centrosymmetric building block for donor–acceptor copolymers

Further development of new building blocks is crucial for realizing next-generation, high-performance organic semiconducting materials. In the paper, the design and synthesis of a novel π-extended analogue of isoindigo, vinylidenedithiophenmethyleneoxindole (VDTOI), and two VDTOI-based copolymers is reported. The centrosymmetric VDTOI unit possesses a special acceptor–donor–acceptor structure and contains a highly planar conjugated backbone because of the presence of S⋯O conformational locks. Of special importance is the fact that the VDTOI unit has the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital and energy levels of −5.35 eV/−3.42 eV, which are similar properties to those of the thiophene-flanked diketopyrrolopyrrole building block. The previously mentioned structural features indicate that VDTOI might be a potential building block for constructing polymeric semiconductors. As a trial, two VDTOI-based copolymers were synthesized, namely P1 and P2. The two copolymers show good thermal stability and broad absorption spectra ranging from 330 to 740 nm. Their HOMO energy levels of around −5.40 eV match well with the work function (5.13 eV) of a gold (Au) electrode, which is indicative of effective hole injections from the Au electrodes to polymer semiconductor films. Both the P1- and P2-based field-effect transistors exhibited typical p-type transport characteristics. The highest mobility of 0.35 cm2 V−1 s−1 was achieved in P1-based devices.

Highly planar cross-conjugated alternating polymers with multiple conformational locks: synthesis, characterization and their field-effect properties

It is meaningful to explore new design principles for organic semiconductors. Herein, we have developed two cross-conjugated alternating polymers based on 1,2-di(thiophen-2-yl)ethane-1,2-dione (DTO), namely PDTO-C1 and PDTO-C3, and investigated their charge transport properties by fabricating field-effect transistors devices. Single crystal X-ray crystallography shows that non-covalent S⋯O and C–H⋯O interactions exist inside the DTO units. These non-covalent interactions in combination with the C–H⋯O interactions of the thiophene-flanked dithienothiophene units, acting as conformational locks, are beneficial for acquiring the planar backbone conformation. PDTO-C1 and PDTO-C3 possess broad absorption spectra and HOMO and LUMO energy levels of ca. −5.50 and −3.6 eV, respectively. The highest mobility of 0.54 cm2 V−1 s−1 was achieved in the PDTO-C3-based transistor devices, whereas PDTO-C1 affords a mobility of 0.22 cm2 V−1 s−1. Further thin film microstructure investigations indicate that both polymers can form highly-ordered lamellar packing with small π–π stacking distances down to 3.50 A. These results demonstrate that the incorporation of cross-conjugation may be used as an additional design tactic for organic semiconductors to alter their optoelectronic properties.

Synthesis, characterization, and field-effect transistor properties of tetrathienoanthracene-based copolymers using a two-dimensional π-conjugation extension strategy: a potential building block for high-mobility polymer semiconductors

In most instances, modulation of the π-conjugation length in polymer molecules is obtained through a linear (1D) extension of the polymer backbone. To date, very limited studies have been reported about the effect of the two-dimensional (2D) π-conjugation extension on the charge-transporting properties of polymer semiconductors. In this study, a 2D π-extended heteroacene, alkyl-substituted tetrathienoanthracene (TTB) moiety, is used to design and synthesize a class of novel polymer semiconductors for solution-processable organic field-effect transistor (OFET) applications for the first time. Three novel TTB-based alternating copolymers (PTTB-2T, PTTB-TT, and PTTB-BZ) are synthesized via Pd(0)-catalyzed Stille or Suzuki cross-coupling reactions, affording high weight-average molecular weights of 61.1–78.5 kDa. The thermal stabilities, optical properties, and energy levels, and charge transport properties of the three TTB-based alternating copolymers have been successfully tuned by copolymerization with bithiophene (2T), thienothiophene (TT), and benzothiadiazole (BZ) derivatives. The results indicate that, even with their highly extended π-framework, all the TTB-containing polymers show good solubility in most common solvents and fairly good environmental stability of their highest occupied molecular orbitals (HOMOs) ranging from −5.15 to −5.28 eV. Among the three TTB-based alternating copolymers, the PTTB-BZ thin film exhibits the best OFET performance with the highest hole mobility of 0.15 cm2 V−1 s−1 in ambient air. It can be attributed to the combinations of highly coplanar polymer backbones and strong D–A interactions between TTB donor units and BZ acceptor units, therefore leading to a compact solid-state packing, uniform fiber-like morphology, and a large polycrystalline grain associated with high hole mobility. These results demonstrate that our molecular design strategy for high-performance polymer semiconductors is highly promising.