Conjugated polymer/paraffin blends for organic field-effect transistors with high environmental stability.

Improving the environmental stability of conjugated polymers remains a fundamental challenge that limits their widespread adoption and commercial application in electronic and photonic devices. Although paraffin can have excellent barrier properties against moisture in ambient air, the use of conjugated polymer/paraffin blends to fabricate organic field-effect transistors (OFETs) with high environmental stability has not been attempted. Here, we demonstrate that conjugated polymer/paraffin blends can greatly enhance the environmental stability of OFETs. Compared to conventional systems such as poly(3-hexylthiophene) (P3HT)/polystyrene and P3HT/polydimethylsiloxane blends, P3HT/paraffin blends exhibit superior environmental stability after 30 days of exposure to the ambient atmosphere. Furthermore, the conjugated polymer/paraffin blends provide stable electronic properties under severe mechanical deformation [a strain (ε) of ∼150%], overcoming a critical challenge arising from the use of fragile crystalline conjugated polymer films for flexible and stretchable electronic devices. In comparison with a conventional spin-coating method, a shear-coating technique provides enhanced molecular ordering and alignment, resulting in improved charge carrier mobility in the blend film OFETs. In particular, shearing in the evaporation regime improves the molecular ordering and alignment of the blend films more than shearing in the Landau-Levich regime. Interestingly, the environmental stability of the sheared blend films varies depending on the shear speed. Specifically, OFETs based on blend films sheared at 0.5 and 6.0-10.0 mm s-1 exhibit excellent environmental stability, maintaining 80% of their initial mobility after 30 days of exposure to air. In contrast, the environmental stability of the OFETs decreases considerably when the blend films are sheared at 1.0-4.0 mm s-1; the mobility decreases to as low as ∼20% of the initial value.

Large-Scale Alignment of Polymer Semiconductor Nanowires for Efficient Charge Transport via Controlled Evaporation of Confined Fluids.

Long-range alignment of conjugated polymers is as critical as polymer chain packing for achieving efficient charge transport in polymer thin films used in electronic and optoelectronic devices. Here, the present study reports a facile, scalable strategy that enables the deposition of macroscopically aligned polymer semiconductor nanowire (NW)-array films with highly enhanced charge carrier mobility, using a modified controlled evaporative self-assembly (MCESA) technique. Organic field-effect transistors (OFETs) based on highly oriented poly(3-hexylthiophene) (P3HT)-NW films exhibit more than 10-fold enhancement of carrier mobility, with the highest mobility of 0.13 cm2 V-1 s-1, compared to the OFETs based on pristine P3HT films. Significantly, large-area aligned P3HT NW-films, which are deposited over 12 arrays of transistors on a 4 in. wafer by an MCESA coating, result in lower device performance variation (i.e., standard deviation ≈ ±0.0172 (16%) cm2 V-1 s-1) as well as an excellent average device performance (i.e., average charge mobility ≈ 0.11 cm2 V-1 s-1), compared to those obtained using the conventional CESA coating, overcoming a critical challenge in the field of OFETs.

Solvent Additive-Assisted Anisotropic Assembly and Enhanced Charge Transport of π-Conjugated Polymer Thin Films.

Charge transport in π-conjugated polymer films involves π-π interactions within or between polymer chains. Here, we demonstrate a facile solution processing strategy that provides enhanced intra- and interchain π-π interactions of the resultant polymer films using a good solvent additive with low volatility. These increased interactions result in enhanced charge transport properties. The effect of the good solvent additive on the intra- and intermolecular interactions, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) films is systematically investigated. We found that the good solvent additive facilitates the self-assembly of P3HT chains into crystalline fibrillar nanostructures by extending the solvent drying time during thin-film formation. As compared to the prior approach using a nonsolvent additive with low volatility, the solvent blend system containing a good solvent additive results in enhanced charge transport in P3HT organic field-effect transistor (OFET) devices [from ca. 1.7 × 10-2 to ca. 8.2 × 10-2 cm2 V-1 s-1 for dichlorobenzene (DCB) versus 4.4 × 10-2 cm2 V-1 s-1 for acetonitrile]. The mobility appears to be maximized over a broad spectrum of additive concentrations (1-7 vol %), indicative of a wide processing window. Detailed analysis results regarding the charge injection and transport characteristics of the OFET devices reveal that a high-boiling-point solvent additive decreases both the contact resistance ( Rc) and channel resistance ( Rch), contributing to the mobility enhancement of the devices. Finally, the platform presented here is proven to be applicable to alternative good solvent additives with low volatility, such as chlorobenzene (CB) and trichlorobenzene (TCB). Specifically, the mobility enhancement of the resultant P3HT films increases in the order CB (bp 131 °C) < DCB (bp 180 °C) < TCB (bp 214 °C), suggesting that solvent additives with higher boiling points provide resultant films with preferable molecular ordering and morphologies for efficient charge transport.

Anti-inflammatory and heme oxygenase-1 inducing activities of lanostane triterpenes isolated from mushroom Ganoderma lucidum in RAW264.7 cells.

Ganoderma lucidum is a popular medicinal mushroom used in traditional medicine for preventing or treating a variety of diseases. In the present study, we investigated the anti-inflammatory and heme oxygenase (HO)-1 inducing effects of 12 lanostane triterpenes from G. lucidum in RAW264.7 cells. Of these, seven triterpenes, butyl lucidenateE2, butyl lucidenateD2 (GT-2), butyl lucidenate P, butyl lucidenateQ, Ganoderiol F, methyl ganodenate J and butyl lucidenate N induced HO-1 expression and suppressed lipopolysaccharide (LPS)-induced nitric oxide (NO) production. Inhibiting HO-1 activity abrogated the inhibitory effects of these triterpenes on the production of NO in LPS-stimulated RAW264.7 cells, suggesting the involvement of HO-1 in the anti-inflammatory effects of these triterpenes. We further studied the anti-inflammatory and HO-1 inducing effects of GT-2. Mitogen-activated protein kinase inhibitors or N-acetylcysteine, an antioxidant, did not suppress GT-2-mediated HO-1 induction; however, LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor, blocked GT-2-induced HO-1 mRNA and protein expression. GT-2 increased nuclear translocation of nuclear factor-E2-related factor 2 (Nrf2) and knockdown of Nrf2 by small interfering RNA blocked GT-2-mediated HO-1 induction, suggesting that GT-2 induced HO-1 expression via the PI3K/AKT-Nrf2 pathway. Consistent with the notion that HO-1 has anti-inflammatory properties, GT-2 inhibited the production of tumor necrosis factor-α and interleukin-6, as well as inducible nitric oxide synthase and cyclooxygenase-2 expression. These findings suggest that HO-1 inducing activities of these lanostane triterpenes may be important in the understanding of a novel mechanism for the anti-inflammatory activity of G. lucidum.