Morphology Driven by Molecular Structure of Thiazole-Based Polymers for Use in Field-Effect Transistors and Solar Cells.

The effects of the molecular structure of thiazole-based polymers on the active layer morphologies and performances of electronic and photovoltaic devices were studied. Thus, thiazole-based conjugated polymers with a novel thiazole-vinylene-thiazole (TzVTz) structure were designed and synthesized. The TzVTz structure was introduced to extend the π conjugation and coplanarity of the polymer chains. By combining alkylthienyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT) or dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DTBDT) electron-donating units and a TzVTz electron-accepting unit, enhanced intermolecular interactions and charge transport were obtained in the novel polymers BDT-TzVTz and DTBDT-TzVTz. With a view to using the polymers in transistor and photovoltaic applications, the molecular self-assembly in and their nanoscale morphologies of the active layers were controlled by thermal annealing to enhance the molecular packing and by introducing a diphenyl ether solvent additive to improve the miscibility between polymer donors and [6,6]phenyl-C71-butyric acid methyl ester (PC71 BM) acceptors, respectively. The morphological characterization of the photoactive layers showed that a higher degree of π-electron delocalization and more favorable molecular packing in DTBDT-TzVTz compared with in BDT-TzVTz leads to distinctly higher performances in transistor and photovoltaic devices. The superior performance of a photovoltaic device incorporating DTBDT-TzVTz was achieved through the superior miscibility of DTBDT-TzVTz with PC71 BM and the improved crystallinity of DTBDT-TzVTz in the nanofibrillar structure.

Directionally Aligned Amorphous Polymer Chains via Electrohydrodynamic-Jet Printing: Analysis of Morphology and Polymer Field-Effect Transistor Characteristics.

Electrohydrodynamic-jet (EHD-jet) printing provides an opportunity to directly assembled amorphous polymer chains in the printed pattern. Herein, an EHD-jet printed amorphous polymer was employed as the active layer for fabrication of organic field-effect transistors (OFETs). Under optimized conditions, the field-effect mobility (µFET) of the EHD-jet printed OFETs was 5 times higher than the highest µFET observed in the spin-coated OFETs, and this improvement was achieved without the use of complex surface templating or additional pre- or post-deposition processing. As the chain alignment can be affected by the surface energy of the dielectric layer in EHD-jet printed OFETs, dielectric layers with varying wettability were examined. Near-edge X-ray absorption fine structure measurements were performed to compare the amorphous chain alignment in OFET active layers prepared by EHD-jet printing and spin coating.

High-Field-Effect Mobility of Low-Crystallinity Conjugated Polymers with Localized Aggregates.

Charge carriers typically move faster in crystalline regions than in amorphous regions in conjugated polymers because polymer chains adopt a regular arrangement resulting in a high degree of π-π stacking in crystalline regions. In contrast, the random polymer chain orientation in amorphous regions hinders connectivity between conjugated backbones; thus, it hinders charge carrier delocalization. Various studies have attempted to enhance charge carrier transport by increasing crystallinity. However, these approaches are inevitably limited by the semicrystalline nature of conjugated polymers. Moreover, high-crystallinity conjugated polymers have proven inadequate for soft electronics applications because of their poor mechanical resilience. Increasing the polymer chain connectivity by forming localized aggregates via π-orbital overlap among several conjugated backbones in amorphous regions provides a more effective approach to efficient charge carrier transport. A simple strategy relying on the density of random copolymer alkyl side chains was developed to generate these localized aggregates. In this strategy, steric hindrance caused by these side chains was modulated to change their density. Interestingly, a random polymer exhibiting low alkyl side chain density and crystallinity displayed greatly enhanced field-effect mobility (1.37 cm(2)/(V·s)) compared with highly crystalline poly(3-hexylthiophene).

Nanowires: A Lattice-Strained Organic Single-Crystal Nanowire Array Fabricated via Solution-Phase Nanograting-Assisted Pattern Transfer for Use in High-Mobility Organic Field-Effect Transistors (Adv. Mater. 16/2016).

S. H. Kim, S. G. Hahm, C. E. Park, and co-workers fabricate a 50 nm-wide organic single-crystalline nanowire array on a centimeter-sized substrate via a facile roll-to-plate process, as described on page 3209. Nanowire growth in a nano-confined space adopts a lattice-strained and single-crystalline packing motif, which can be harnessed for strong intermolecular electronic coupling. Thus, nanowire-based field-effect transistors show extremely high field-effect mobilities up to 9.71 cm(2) V(-1) s(-1) .

Photo-Patternable ZnO Thin Films Based on Cross-Linked Zinc Acrylate for Organic/Inorganic Hybrid Complementary Inverters.

Complementary inverters consisting of p-type organic and n-type metal oxide semiconductors have received considerable attention as key elements for realizing low-cost and large-area future electronics. Solution-processed ZnO thin-film transistors (TFTs) have great potential for use in hybrid complementary inverters as n-type load transistors because of the low cost of their fabrication process and natural abundance of active materials. The integration of a single ZnO TFT into an inverter requires the development of a simple patterning method as an alternative to conventional time-consuming and complicated photolithography techniques. In this study, we used a photocurable polymer precursor, zinc acrylate (or zinc diacrylate, ZDA), to conveniently fabricate photopatternable ZnO thin films for use as the active layers of n-type ZnO TFTs. UV-irradiated ZDA thin films became insoluble in developing solvent as the acrylate moiety photo-cross-linked; therefore, we were able to successfully photopattern solution-processed ZDA thin films using UV light. We studied the effects of addition of a tiny amount of indium dopant on the transistor characteristics of the photopatterned ZnO thin films and demonstrated low-voltage operation of the ZnO TFTs within ±3 V by utilizing Al2O3/TiO2 laminate thin films or ion-gels as gate dielectrics. By combining the ZnO TFTs with p-type pentacene TFTs, we successfully fabricated organic/inorganic hybrid complementary inverters using solution-processed and photopatterned ZnO TFTs.

A Lattice-Strained Organic Single-Crystal Nanowire Array Fabricated via Solution-Phase Nanograting-Assisted Pattern Transfer for Use in High-Mobility Organic Field-Effect Transistors.

A 50 nm-wide 6,13-bis(triisopropylsilylethynyl) pentacene nanowire (NW) array is fabricated on a centimeter-sized substrate via a facile nanograting-assisted pattern-transfer method. NW growth under a nanoconfined space adopts a lattice-strained packing motif of the NWs for strong intermolecular electronic coupling, and thus a NW-based organic field-effect transistor shows high field-effect mobility up to 9.71 cm(2) V(-1) s(-1) .

Alkyl chain length dependence of the field-effect mobility in novel anthracene derivatives.

We report six asymmetric alkylated anthracene-based molecules with different alkyl side chain lengths for use in organic field-effect transistors (OFETs). Alkyl side chains can potentially improve the solubility and processability of anthracene derivatives. The crystallinity and charge mobility of the anthracene derivatives may be improved by optimizing the side chain length. The highest field-effect mobility of the devices prepared here was 0.55 cm(2)/(V s), for 2-(p-pentylphenylethynyl)anthracene (PPEA). The moderate side chain length appeared to be optimal for promoting self-organization among asymmetric anthracene derivatives in OFETs, and was certainly better than the short or long alkyl side chain lengths, as confirmed by X-ray diffraction measurements.