To investigate the effects of the phase state (ordered or disordered) of self-assembled monolayers (SAMs) on the growth mode of pentacene films and the performance of organic thin-film transistors (OTFTs), we deposited pentacene molecules on SAMs of octadecyltrichlorosilane (ODTS) with different alkyl-chain orientations at various substrate temperatures (30, 60, and 90 degrees C). We found that the SAM phase state played an important role in both cases. Pentacene films grown on relatively highly ordered SAMs were found to have a higher crystallinity and a better interconnectivity between the pentacene domains, which directly serves to enhance the field-effect mobility, than those grown on disordered SAMs. Furthermore, the differences in crystallinity and field-effect mobility between pentacene films grown on ordered and disordered substrates increased with increasing substrate temperature. These results can be possibly explained by (1) a quasi-epitaxy growth of the pentacene film on the ordered ODTS monolayer and (2) the temperature-dependent alkyl chain mobility of the ODTS monolayers.

With the aim of enhancing the field‐effect mobility of self‐assembled regioregular poly(3‐hexylthiophene), P3HT, by promoting two‐dimensional molecular ordering, the organization of the P3HT in precursor solutions is transformed from random‐coil conformation to ordered aggregates by adding small amounts of the non‐solvent acetonitrile to the solutions prior to film formation. The ordering of the precursor in the solutions significantly increases the crystallinity of the P3HT thin films. It is found that with the appropriate acetonitrile concentration in the precursor solution, the resulting P3HT nanocrystals adopt a highly ordered molecular structure with a field‐effect mobility dramatically improved by a factor of approximately 20 depending on the P3HT concentration. This improvement is due to the change in the P3HT organization in the precursor solution from random‐coil conformation to an ordered aggregate structure as a result of the addition of acetonitrile. In the good solvent chloroform, the P3HT molecules are molecularly dissolved and adopt a random‐coil conformation, whereas upon the addition of acetonitrile, which is a non‐solvent for aromatic backbones and alkyl side chains, 1D or 2D aggregation of the P3HT molecules occurs depending on the P3HT concentration. This state minimizes the unfavorable interactions between the poorly soluble P3HT and the acetonitrile solvent, and maximizes the favorable π–π stacking interactions in the precursor solution, which improves the molecular ordering of the resulting P3HT thin film and enhances the field‐effect mobility without post‐treatment.

We have demonstrated the influence of evaporation‐induced flow in a single droplet on the crystalline microstructure and film morphology of an ink‐jet‐printed organic semiconductor, 6,13‐bis((triisopropylsilylethynyl) pentacene (TIPS_PEN), by varying the composition of the solvent mixture. The ringlike deposits induced by outward convective flow in the droplets have a randomly oriented crystalline structure. The addition of dichlorobenzene as an evaporation control agent results in a homogeneous film morphology due to slow evaporation, but the molecular orientation of the film is undesirable in that it is similar to that of the ring‐deposited films. However, self‐aligned TIPS_PEN crystals with highly ordered crystalline structures were successfully produced when dodecane was added. Dodecane has a high boiling point and a low surface tension, and its addition to the solvent results in a recirculation flow in the droplets that is induced by a Marangoni flow (surface‐tension‐driven flow), which arises during the drying processes in the direction opposite to the convective flow. The field‐effect transistors fabricated with these self‐aligned crystals via ink‐jet printing exhibit significantly improved performance with an average effective field‐effect mobility of 0.12 cm2 V–1 s–1. These results demonstrate that with the choice of appropriate solvent ink‐jet printing is an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct‐write fabrication of high‐performance organic electronics.

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Solution‐processable functionalized acenes have received special attention as promising organic semiconductors in recent years because of their superior intermolecular interactions and solution‐processability, and provide useful benchmarks for organic field‐effect transistors (OFETs). Charge‐carrier transport in organic semiconductor thin films is governed by their morphologies and molecular orientation, so self‐assembly of these functionalized acenes during solution processing is an important challenge. This article discusses the charge‐carrier transport characteristics of solution‐processed functionalized acene transistors and, in particular, focuses on the fine control of the films' morphologies and structural evolution during film‐deposition processes such as inkjet printing and post‐deposition annealing. We discuss strategies for controlling morphologies and crystalline microstructure of soluble acenes with a view to fabricating high‐performance OFETs.

To enhance the electrical performance of pentacene‐based field‐effect transistors (FETs) by tuning the surface‐induced ordering of pentacene crystals, we controlled the physical interactions at the semiconductor/gate dielectric (SiO2) interface by inserting a hydrophobic self‐assembled monolayer (SAM, CH3‐terminal) of organoalkyl‐silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano‐layers in contact with the SAM could adopt two competing crystalline phases—a “thin‐film phase” and “bulk phase” – which affected the π‐conjugated nanostructures in the ultrathin and subsequently thick films. The field‐effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm2 V−1 s−1 for the disordered SAM‐treated SiO2 gate‐dielectric. This remarkable change in device performance can be explained by the production of well π‐conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.

Fabrication of organic fi eld-effect transistors (OFETs) using a high-throughput printing process has garnered tremendous interest for realizing low-cost and large-area fl exible electronic devices. Printing of organic semiconductors for active layer of transistor is one of the most critical steps for achieving this goal. The charge carrier transport behavior in this layer, dictated by the crystalline microstructure and molecular orientations of the organic semiconductor, determines the transistor performance. Here, it is demonstrated that an inkjet-printed single-droplet of a semiconducting/insulating polymer blend holds substantial promise as a means for implementing direct-write fabrication of organic transistors. Control of the solubility of the semiconducting component in a blend solution can yield an inkjet-printed single-droplet blend fi lm characterized by a semiconductor nanowire network embedded in an insulating polymer matrix. The inkjet-printed blend fi lms having this unique structure provide effective pathways for charge carrier transport through semiconductor nanowires, as well as signifi cantly improve the on-off current ratio and the environmental stability of the printed transistors.

Recent studies have revealed that following injuries, ligament tissues such as anterior cruciate ligaments (ACL), release large amounts of matrix metalloproteinases (MMPs). These enzymes have a devastating effect on the healing process of the injured ligaments. Although these enzymes are produced following ligament injuries, because of different healing capacities seen between the medial collateral ligament (MCL) and ACL, we were curious to find if the MMP activity was expressed and modulated differently in these tissues. For this purpose ACL and MCL fibroblasts were seeded on equi-biaxial stretch chambers and were stretched in different levels. The stretched cells were assayed using Zymography, Western Blot and global MMP activity assays. The results showed that within 72 h after injurious stretch, production of 72 kD pro-MMP-2 increased in both ACL and MCL. However, the ACL fibroblasts generated significantly more pro-MMP-2 than the MCL fibroblasts. Furthermore we found in ACL pro-MMP-2 was converted more into active form. With 4-aminophenyl mercuric acetate (APMA) treatment, large amounts of pro-MMP-2 were converted into active form in both. This indicates that there is no significant difference between ACL and MCL fibroblasts in post-translational modification of MMP-2. The fluorescent MMP activity assays revealed that the MMP family activities were higher in the injured ACL fibroblasts than the MCL. Since the MMPs are critically involved in extracellular matrix (ECM) turnover, these findings may explain one of the reasons why the injured ACL hardly repairs. The higher levels of active MMP-2 seen in the ACL injuries may disrupt the delicate balance of ECM remodeling process. These results suggest that the generation and modulation of MMP-2 may be directly involved in the different responses seen in ACL and MCL injuries.