In this review, we describe and discuss recent advances in the performance of polymeric semiconductors in organic field effect transistors (OFETs). Design concepts such as short intermolecular contacts, low conformational disorder, side chain optimization, and noncovalent interactions have all been successfully employed to improve the charge carrier mobility of polymer thin films. The relationship between the molecular design, thin film microstructure, and electrical performance has been exemplified by a range of thiophene, bridged and fused ring, diketopyrrolopyrrole (DPP), and isoindigo containing polymers which are reviewed and discussed.

Advances in Charge Carrier Mobilities of Semiconducting Polymers Used in Organic Transistors

Recent progress in organic field-effect transistor (OFET) printing processes is reviewed, and a perspective on the future of the field is discussed. The principles underlying the OFET printing techniques are introduced according to two categories: direct write printing and transfer printing. A comprehensive overview of the use of printing techniques in OFET production processes is also provided. Considerations for improving OFET device performance using printing processes are explored. Prior to OFET commercialization, the OFET printing techniques must satisfy several requirements, as discussed here.

Recent Advances in Organic Transistor Printing Processes

Patterning of controllable surface wettability has attracted wide scientific attention due to its importance in both fundamental research and practical applications. In particular, it is crucial to form clear image areas and non-image areas in printing techniques based on wetting and dewetting. This review summarizes the recent research on and applications of patterning of controllable surface wettability for printing techniques, with a focus on the design and fabrication of the precise surface wettability patterning by enhancing the contrast of hydrophilicity and hydrophobicity, such as superhydrophilicity and superhydrophobicity. The selected topics mainly include patterned surface wettability for lithographic printing with different plate-making techniques, patterned surface wettability for microcontact printing with a patterned wetting stamp and special wettability mediated patterning microtransfer printing, patterned surface wettability for inkjet printing with controllable surface wettability of the substrate and printing head to ink, and patterned surface wettability by a combination of different printing techniques. A personal perspective on the future development and remaining challenges of this research is also briefly discussed.

Patterning of controllable surface wettability for printing techniques

There has been much interest in graphene-based electronic devices because graphene provides excellent electrical, optical, and mechanical properties. [ 1 ] In this sense, organic electronic devices using graphene electrodes have attracted considerable attention, and several reports have described the use of graphene source/drain electrodes in organic fi eld-effect transistors (OFETs). [ 2 ] One of the ultimate goals in the fabrication of OFETs using graphene electrodes lies in the fabrication of fl exible and transparent organic transistors, assembled on plastics substrates, that maintain their high performance under ambient conditions. However, no reports have described the fabrication of organic transistors assembled on plastic substrates because the synthesis of either graphene or reduced graphene oxide requires high-temperature fabrication processes. Another important goal in the context of fabricating organic electronic devices with graphene electrodes lies in the fabrication of highly transparent graphene electrodes that cover large areas. Graphene transmittance decreases linearly as the number of layers increases in n-layer graphene. [ 3 ] Thus, the use of monolayer graphene is necessary to achieve high transparency in graphene electrodes, provided that the conductivity of the graphene is suffi cient for device electrode applications. Another merit of monolayer graphene is its extremely low thickness (3–4 Å). Source/drain electrodes in staggered bottomcontact FET structures should be thin to ensure step coverage of the active layer during sequential transistor fabrication. [ 4 ] For this reason, one-atom-thick monolayer graphene provides ideal source/drain electrodes for effi cient charge injection. Recently, several groups succeeded in fabricating high-quality/largearea graphene with preferential monolayer thickness using a

Transparent flexible organic transistors based on monolayer graphene electrodes on plastic.

Ink-jet printed small-molecule organic single-crystal transistors are realized by using selective surface energy modification, precise control of volume density of ink droplets on spatially patterned areas, and a co-solvent system to control solvent evaporation properties. The single-crystal formation in bottom-contact-structured transistors via direct printing is expected to permit high-density array fabrication in large-area electronics.

Controlled Deposition of a High‐Performance Small‐Molecule Organic Single‐Crystal Transistor Array by Direct Ink‐Jet Printing

We demonstrate the influence of the surface wettability of a dielectric substrate on the crystalline microstructure and film morphology of an inkjet-printed organic semiconductor, namely 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS_PEN), using various self-assembled monolayers (SAMs). Self-aligned crystals with highly ordered crystalline structure are developed by printing on hydrophilic surfaces with high surface energy. It is found that the pinning of the contact line induces an outward convective flow as the evaporation proceeds, which results in the nucleation of crystals and the self-assembly of TIPS_PEN molecules from the periphery to the central region of the droplet. However, for hydrophobic surfaces with low surface energy, small agglomerates with random orientation of molecules are formed, which is induced by depinning of the contact line. The field-effect transistors fabricated with self-organized crystals printed on hydrophilic surfaces exhibit a high field-effect mobility of 0.15 cm2 V−...

Evaporation-Induced Self-Organization of Inkjet-Printed Organic Semiconductors on Surface-Modified Dielectrics for High-Performance Organic Transistors

WiHyoung Lee

Papers

Evaporation-Induced Self-Organization of Inkjet-Printed Organic Semiconductors on Surface-Modified Dielectrics for High-Performance Organic Transistors