Assembly of organic semiconductors with ordered crystal structure has been actively pursued for electronics applications such as organic field-effect transistors (OFETs). Among various film deposition methods, solution-based film growth from small molecule semiconductors is preferable because of its low material and energy consumption, low cost, and scalability. Here, we show scalable and controllable directed assembly of highly crystalline 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) films via a dip-coating process. Self-aligned stripe patterns with tunable thickness and morphology over a centimeter scale are obtained by adjusting two governing parameters: the pulling speed of a substrate and the solution concentration. OFETs are fabricated using the C8-BTBT films assembled at various conditions. A field-effect hole mobility up to 3.99 cm V s is obtained. Owing to the highly scalable crystalline film formation, the dip-coating directed assembly process could be a great candidate for manufacturing next-generation electronics. Meanwhile, the film formation mechanism discussed in this paper could provide a general guideline to prepare other organic semiconducting films from small molecule solutions.

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Carbon nanotubes (CNTs) are promising building blocks for emerging wearable electronics and sensors due to their outstanding electrical and mechanical properties. However, the practical applications of the CNTs face challenges of efficiently and precisely placing them at the desired location with controlled orientation and density. Here, we introduce an electro-fluidic assembly process to assemble highly aligned and densely packed CNTs selectively on a substrate with patterned wetted areas at a high rate. An electric field is applied during the electro-fluidic assembly process, which drives the CNTs close to the patterned regions and shortens the assembly time. Meanwhile, the electric field orientates the CNTs perpendicular to the substrate and anchors one end of the CNTs onto the substrate. When pulling the substrate out of the CNT suspension, the capillary force at the air–water–substrate interface stretches the free end of the CNTs and aligns the CNTs along the pulling direction. By adjusting two governing parameters, the direct current voltage and the pulling speed, we have demonstrated well aligned CNTs assembled in patterns with widths from 1 to 100 μm and lengths from 20 to 120 μm at a rate 20 times higher than a fluidic assembly process. The aligned CNTs show improved electrical conductivity compared with the random networks and prove possibility for strain detection. Precise and reproducible control of the orientation and the placement of the CNTs opens up their practical application in the next-generation electronics and sensors.

COMMUNICATION 1900898 (1 of 7)

Printing processes are increasingly used in the fabrication of organic field effect transistors (OFETs) owing to their merits of low cost, low processing temperature, vacuum-free nature, and compatibility with various substrates. Among various printing processes, transfer printing is preferable because of its high resolution and pattern fidelity. Here, we fabricate OFETs using directed assembled and transfer printed carbon nanotube (CNT) source/drain electrodes. The CNT electrodes are selectively assembled on a Damascene template using an electrophoretic directed assembly based inking process and then transferred onto a polyurethane film on a silicon substrate with a high pattern fidelity. Selective inking and direct transfer without sacrificial layers or intermediate transfer steps enable a high material efficiency and a low cost of our fabrication process. The fabricated OFETs with a spin-coated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene semiconducting film show typical p-type behavior with an on/off ratio of approximately 105, implying great potential to use our method for practical OFET fabrication.