Recently, the use of solution-processable conjugated polymer semiconductors in thin-film transistors (TFTs) has been extensively studied because of their suitability for fabricating large-area devices using established solution-deposition techniques (e.g., spin-coating, screen printing, or inkjet printing). [1][2][3][4][5][6][7][8] An attractive feature of the solution process is that different materials can be easily blended to optimize the electronic and optoelectronic properties for device applications. [9][10][11] Blends of semiconducting and dielectric polymers can combine the optical and electrical properties of semiconductors with the characteristics of dielectric polymers. However, the use of these blends as active layers in TFTs always causes a decrease in the device performance because the dielectric polymer ''dilutes'' the current density. [12,13] Controlling the phase separation in the direction perpendicular to the substrate to form bilayer structures should be an effective way to diminish this effect because it allows retention of the connectivity of the semiconducting layer in the channel region. To this end, organic-semiconductor/dielectric-polymer blends with vertical phase separation have been used to fabricate high-performance TFTs with low operating voltage [14] or with improved environmental stability [15] at high semiconductor concentration (!40%). In a recent publication, [16] Goffri et al. reported that the concentration of semiconductor in crystalline/crystalline bicomponent semiconductor/dielectricpolymer systems can be reduced to a value as low as 3 wt % without any degradation in device performance. However, all structures reported in previous studies are dielectric-top and semiconductor-bottom structures. It would be very interesting to investigate a semiconductor-top and dielectric-bottom bilayer structure, because this structure is identical to the configuration of the semiconductor and dielectric layers in the bottom-gate TFT device. For this reason formation of a semiconductor-top and dielectric-bottom bilayer in a one-step process may provide a simple route for the fabrication of TFT devices.In the present Communication, we report for the first time the fabrication of a semiconductor-top and dielectric-bottom bilayer structure by means of surface-induced vertical phase separation of poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate) (PMMA) blends. Because the ultrathin and defect-free PMMA dielectric layer can act as blind material, a modifier at the semiconductor/dielectric interface, or a dielectric layer, these bilayer blends have versatile uses in TFTs.Films composed of P3HT/PMMA blends were fabricated by spin-casting chlorobenzene solutions of the polymers onto bare silicon substrates (see Fig. 1a, inset). Since the hydrophilicities of P3HT and PMMA are very different, water contact-angle measurements were carried out to determine qualitatively the changes in composition taking place on the surface of the blended films. The variation of the water contact angle as a ...
We have demonstrated that organic thin-film transistors based on blends of poly(3-hexylthiophene) (P3HT) and polystyrene (PS) with high performance and low percolation threshold can be facilely fabricated by changing the solubility of solvent and the aging time of the precursor solution. The structural analysis reveals that these benefits arise from the improvements of both the crystallinity and connectivity of P3HT phase in the blend. In the case of crystallinity, we found that because of the solubility-aging-induced formation of ordered precursors, the molecular ordering of the poly(3-hexylthiophene) phase in the blend films increases, and thus the electronic properties of field-effect transistors (FETs) based on these films are significantly improved. For the connectivity, we found that either bilayered structure or highly connected P3HT nanofibrillar network could form in the blend by changing the solubility of the solvent. Both structures are extremely beneficial to keeping connectivity of active channels and thus keeping the charge-transport properties at low semiconductor content. By optimizing the conditions, the devices based on P3HT/PS blend films containing only 1 wt % P3HT can still show field-effect mobility as high as 1 × 10−2 cm2V−1 s−1, which is comparable with that obtained from the pristine P3HT film.
A novel semiconductor–rubber–semiconductor triblock copolymer has been designed and prepared according to the principle of thermoplastic elastomers (TPEs). It behaves as a TPE and exhibits good electrical properties.
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.
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