| Organic single crtstals exhibt much better device performance than their corresponding amophous or polycrystalline thin film,because they possess few grain boundaries,lower desity of defects and highly ordered molecular packing.Thus,they are widely applied in high-perpormance electronic devices.Recently,various techniques have been developed for controllable fabrication and orderly assembling organic single crystals.However,the crystal growth orientation is random and the growth site cannot be accurately positioned.Also,it is difficult to prepare highly aligned single crystal arrays by a one-step method on a flexible substrate,which largely limits its applications in high performance,wearable flexible electronics.Based on the above problems,my research focoused on the following two aspects:1.we reported a patterned microchannel dip-coating(PMDC)method to precisely pattern OSSC arrays at designed locations.Combining lithography technology with hydrophilic-hydrophobic modification,we designed the microchannel template.During dip-coating process,the solution adheres only to the wettable photoresist(PR)microchannel region,resulting in 2,8-difluoro-5,11-bis(triethylsilylethynyl)fluorene Dithiophene molecules selectively crystallize in this region.According to the computational fluid dynamics simulations of the shape and evaporation flux J of the solution in the PR microchannels,we observed the solution steadily pinned at the edges of PR stripes.and highly aligned growing along both sides of PR microchannel.Under an appropriate coating speed,i.e.the speed ranging from 94 to 115 ?m s-1,single crystal arrays with an average width of 1 ?m and a thickness of 200 nm were obtained on both sides of the photoresist.Notably,the optimal mobility of 50 discrete devices on the same substrate reaches to 2.44 cm2 V-1 s-1,the average mobility was 1.43 cm2 V-1 s-1,and the on/off ratio exceeded 105.At the same time,this method can be applied to other materials,such as 6,13-bis(triisopropyl-silylethynyl)pentacene.and precisely control the position of the OSSC.s arrays onto transistor source-drain electrodes.2.Organic semiconductor single crystal(OSSC)arrays with uniform morphology and unitary crystallographic orientation were prepared on the polymer insulating layer by shallow channel blade-coating,and applied in high performance flexible field-effect transistors.A patterned template with alternating polarity were formed on the PVP surface in combination with photolithography and oxygen plasma treatment.we further carried out X-ray photoelectron spectroscopy(XPS)measurements.It shows that,after oxygen-plasma treatment,the C-O peak increases remarkably,along with the appearance of an exotic C=O peak.Blade-coating of C8-BTBT solution was performed on the patterned PVP surface.With the solvent evaporation,molecules would selectively nucleate and crystallize on the patterned PVP surface,generating C8-BTBT crystal array with well-defined crystal facet and uniform height at treated PVP areas.We conducted cross-polarized optical microscope,transmission electron microscope and two-dimensional grazing incidence X-ray diffraction,the results show the single-crystalline nature of Cs-BTBT crystal array,indicating the well-organized molecular packing and high crystal quality inside the crystal.Besides,in-situ optical microscope observation,DFT calculation,and microscopic theory of nueleation were used to systematically investigate the growth mechnism.When the interval of the PVP shallow channel template is 2 ?m and the coating speed controlled between 94-115 ?m s-1,the flexible OFETs made from the C8-BTBT single crystal arrays exhibit a maximum mobility up to?2.25 cm2 V-1 s-1,with an on/off current ratio of?106 and a subthreshold swing of 730 mV dec-1.Moreover,the flexible device has excellent bending stability,and The OFETs can be bent a small bending radius down to 5 mm with small performance degradation of 26%... |
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