Inkjet printing of single-crystal films.

The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. 'Printed electronics' is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials. However, because of the strong self-organizing tendency of the deposited materials, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C(8)-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4 cm(2) V(-1) s(-1). This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.

Competition of polar and antipolar states hidden behind a variety of polarization switching modes in hydrogen-bonded molecular chains.

Switchable π-electron systems are very powerful fragments to emphasize ferroelectric or antiferroelectric polarizations up to record-high levels among organic molecular crystals. According to the Cambridge Structural Database, many azole crystals such as imidazoles and tetrazoles contain polar and bistable hydrogen-bonded molecular sequences suitable for ferroelectricity or antiferroelectricity. Indeed, polarization hysteresis experiments on the 5-phenyl-1H-tetrazole (PHTZ) family combined with single crystal structural analysis have revealed one ferroelectric, two antiferroelectrics, and two hybrid-like dielectrics. Here, the rich variations for the interrelation between the hydrogen-bonding states and the polarization switching modes are interpreted by density functional theory (DFT) calculations with an excellent consistency. Large switchable polarizations are theoretically confirmed, and, as expected, the largest contribution is the switchable π-electron systems. By mapping the energy levels of polar/antipolar states, the disordered hydrogen bonds always appear when the ground state is accompanied by a nearly degenerate state. The straightforward case is the hybrid-like dielectric caused by the competition between the polar and antipolar states. However, contrastive behaviors are observed when the switchable dipoles are involved in competition between the different antipolar arrangement. For example, the PHTZ crystal exhibits typical antiferroelectric switching regardless of the hydrogen disorder, whereas polarization switching is silent in the imidazole derivatives. The latter is explained by the switching field increase with depth of the ground state relative to the energy level of the polar state.

Nanoparticle chemisorption printing technique for conductive silver patterning with submicron resolution.

Silver nanocolloid, a dense suspension of ligand-encapsulated silver nanoparticles, is an important material for printing-based device production technologies. However, printed conductive patterns of sufficiently high quality and resolution for industrial products have not yet been achieved, as the use of conventional printing techniques is severely limiting. Here we report a printing technique to manufacture ultrafine conductive patterns utilizing the exclusive chemisorption phenomenon of weakly encapsulated silver nanoparticles on a photoactivated surface. The process includes masked irradiation of vacuum ultraviolet light on an amorphous perfluorinated polymer layer to photoactivate the surface with pendant carboxylate groups, and subsequent coating of alkylamine-encapsulated silver nanocolloids, which causes amine-carboxylate conversion to trigger the spontaneous formation of a self-fused solid silver layer. The technique can produce silver patterns of submicron fineness adhered strongly to substrates, thus enabling manufacture of flexible transparent conductive sheets. This printing technique could replace conventional vacuum- and photolithography-based device processing.

Simple push coating of polymer thin-film transistors.

Solution processibility is a unique advantage of organic semiconductors, permitting the low-cost production of flexible electronics under ambient conditions. However, the solution affinity to substrate surfaces remains a serious dilemma; liquid manipulation is more difficult on highly hydrophobic surfaces, but the use of such surfaces is indispensable for improving device characteristics. Here we demonstrate a simple technique, which we call 'push coating', to produce uniform large-area semiconducting polymer films over a hydrophobic surface with eliminating material loss. We utilize a poly(dimethylsiloxane)-based trilayer stamp whose conformal contact with the substrate enables capillarity-induced wetting of the surface. Films are formed through solvent sorption and retention in the stamp, allowing the stamp to be peeled perfectly from the film. The planar film formation on hydrophobic surfaces also enables subsequent fine film patterning. The technique improves the crystallinity and field-effect mobility of stamped semiconductor films, constituting a major step towards flexible electronics production.