Hiromi Minemawari

Bio: Hiromi Minemawari is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Organic semiconductor & Thin film. The author has an hindex of 13, co-authored 25 publications receiving 1935 citations. Previous affiliations of Hiromi Minemawari include Hokkaido University.

Inkjet printing of single-crystal films

Abstract: Printing electronic devices using semiconducting 'ink' is seen as a promising route to cheap, large-area and flexible electronics, but the performance of such devices suffers from the relatively poor crystallinity of the printed material. Hiromi Minemawari and colleagues have developed an inkjet-based printing technique involving controlled mixing on a surface of two solutions — the semiconductor (C8-BTBT) in its solvent and a liquid in which the semiconductor is insoluble. The products of this antisolvent crystallization technique are thin semiconductor films with exceptionally high and uniform crystallinity. The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science1. Whether based on inorganic2,3,4,5 or organic6,7,8 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 materials9,10,11. However, because of the strong self-organizing tendency of the deposited materials12,13, 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 crystallization14 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 (C8-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4 cm2 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.

Simple push coating of polymer thin-film transistors

Abstract: Organic semiconductors may be processed in solution under ambient conditions; however, liquid manipulation on hydrophobic surfaces is difficult, which may hinder development of devices. Here, a push-coating technique is used to produce large-area semiconducting polymer films over hydrophobic surfaces. 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.

Enhanced Layered-Herringbone Packing due to Long Alkyl Chain Substitution in Solution-Processable Organic Semiconductors

Abstract: Herein, we report the stabilization and modulation of layered-herringbone (LHB) packing, which is known to afford high-performance organic thin-film transistors, based on crystal structure analyses and calculations of intermolecular interaction energies for alkyl-substituted organic semiconductor (OSC) crystals. We systematically investigated the alkyl chain-length dependence of the crystal structures, solvent solubilities, and thermal characteristics for three series of symmetrically and asymmetrically alkyl-substituted benzothieno[3,2-b][1]benzothiophenes (BTBTs). All the series exhibit LHB packing when the BTBTs are substituted with relatively long alkyl chains (−CnH2n+1), i.e., n ≥ 4 for monoalkylated, n ≥ 6 for dialkylated, and n ≥ 5 for phenyl-alkylated BTBTs. LHB packing is also evident in the nonsubstituted and diethyl-substituted BTBTs, although those substituted with short alkyl chains generally did not feature LHB packing because of their lack of interchain ordering. The density functional theo...

Nanoparticle chemisorption printing technique for conductive silver patterning with submicron resolution

Abstract: 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.

25th anniversary article: organic field-effect transistors: the path beyond amorphous silicon.

Abstract: Over the past 25 years, organic field-effect transistors (OFETs) have witnessed impressive improvements in materials performance by 3–4 orders of magnitude, and many of the key materials discoveries have been published in Advanced Materials. This includes some of the most recent demonstrations of organic field-effect transistors with performance that clearly exceeds that of benchmark amorphous silicon-based devices. In this article, state-of-the-art in OFETs are reviewed in light of requirements for demanding future applications, in particular active-matrix addressing for flexible organic light-emitting diode (OLED) displays. An overview is provided over both small molecule and conjugated polymer materials for which field-effect mobilities exceeding > 1 cm2 V–1 s–1 have been reported. Current understanding is also reviewed of their charge transport physics that allows reaching such unexpectedly high mobilities in these weakly van der Waals bonded and structurally comparatively disordered materials with a view towards understanding the potential for further improvement in performance in the future.

Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%

Abstract: The past several years have witnessed the rapid emergence of a class of solar cells based on mixed organic–inorganic halide perovskites. Today’s state-of-the-art perovskite solar cells (PSCs) employ various methods to enhance nucleation and improve the smoothness of the perovskite films formed via solution processing. However, the lack of precise control over the crystallization process creates a risk of forming unwanted defects, for example, pinholes and grain boundaries. Here, we introduce an approach to prepare perovskite films of high electronic quality by using poly(methyl methacrylate) (PMMA) as a template to control nucleation and crystal growth. We obtain shiny smooth perovskite films of excellent electronic quality, as manifested by a remarkably long photoluminescence lifetime. We realize stable PSCs with excellent reproducibility showing a power conversion efficiency (PCE) of up to 21.6% and a certified PCE of 21.02% under standard AM 1.5G reporting conditions. Controlling the crystallization process of perovskite films is crucial to obtaining high efficiency in perovskite solar cells. Bi et al. propose the use of poly(methyl methacrylate) as a template for the controlled nucleation and growth of perovskite crystals achieving efficiency of 21.6%.

A vacuum flash-assisted solution process for high-efficiency large-area perovskite solar cells.

Abstract: Metal halide perovskite solar cells (PSCs) currently attract enormous research interest because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication costs, but their practical development is hampered by difficulties in achieving high performance with large-size devices. We devised a simple vacuum flash-assisted solution processing method to obtain shiny, smooth, crystalline perovskite films of high electronic quality over large areas. This enabled us to fabricate solar cells with an aperture area exceeding 1 square centimeter, a maximum efficiency of 20.5%, and a certified PCE of 19.6%. By contrast, the best certified PCE to date is 15.6% for PSCs of similar size. We demonstrate that the reproducibility of the method is excellent and that the cells show virtually no hysteresis. Our approach enables the realization of highly efficient large-area PSCs for practical deployment.

Molecular design and ordering effects in π-functional materials for transistor and solar cell applications.

Abstract: Organic electronics are broadly anticipated to impact the development of flexible thin-film device technologies. Among these, solution-processable π-conjugated polymers and small molecules are proving particularly promising in field-effect transistors and bulk heterojunction solar cells. This Perspective analyzes some of the most exciting strategies recently suggested in the design and structural organization of π-functional materials for transistor and solar cell applications. Emphasis is placed on the interplay between molecular structure, self-assembling properties, nanoscale and mesoscale ordering, and device efficiency parameters. A critical look at the various approaches used to optimize both materials and device performance is provided to assist in the identification of new directions and further advances.

Integrated materials design of organic semiconductors for field-effect transistors

Abstract: The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm2/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.