有机半导体图案化成膜中的马兰戈尼与咖啡环效应协同作用

有机场效应晶体管在柔性传感和显示驱动应用中展示出极大的潜力,但在大面积制备高性能有机薄膜及有机场效应晶体管方面仍面临大的挑战。本文介绍了一种利用等离子处理和马兰戈尼-咖啡环效应协同作用来图案化生长有机半导体薄膜的方法。经过对等离子体处理时间、混合溶剂的比例及溶液浓度等生长条件优化,在5 cm×5 cm的基片上得到了覆盖性较为完整的2,7-二辛基1]苯并噻吩并3,2-b]苯并噻吩(C8-BTBT)薄膜阵列。基于此薄膜构筑了底栅顶接触晶体管阵列,器件的平均迁移率达到7.9 cm~2·V~(-1)·s~(-1),阈值电压均小于-2 V,开关电流比大于10~4。本工作对未来大面积制备高性能有机半导体薄膜及晶体管具有一定的借鉴意义。

Fabrication of Patterned Organic Semiconductor Thin Films by the Synergy of Marangoni and Coffee-Ring Effects

Organic field effect transistors (OFETs) have great potential in flexible sensor and display driver applications. However, there are immense challenges in the development of large-area and high-quality thin-film fabrications. In this article, we introduce a method to fabricate patterned organic semiconductor films by oxygen plasma treatment and the synergy of Marangoni and coffee-ring effects. The procedure is as follows: First, we spin-coated the cyclic transparent amorphous fluoropolymers (CYTOP) on the substrate in the form of a hydrophobic layer. Then, parts of the substrate surface were treated with plasma and modified to make them hydrophilic. By comparing the water contact angle on the plasma treated surface with that on the untreated surface, we optimized the treating time to get a relatively uniform water contact angle on a different region of the substrate surface. The plasma treated substrate was dipped into 2, 7-dioctyl1]benzothieno3, 2-b]1]benzothiophene (C8-BTBT) solution with methylbenzene and carbon tetrachloride as a mixed solvent, and then lifted from it. So the mixed solution flowed down rapidly on the hydrophobic portion of the surface, leaving droplet on the hydrophilic portion. Subsequently, the droplet started evaporating under the synergy of Marangoni and coffee-ring effects. Based on the difference between the hydrophilic and hydrophobic portions on the substrate surface, we successfully obtained the patterned C8-BTBT thin films on the substrate. Furthermore, the solvent ratio was optimized while growing the C8-BTBT film to adjust the boiling point of the solution, which was due to a fully covered surface was obtained. From the grazing-incidence X-ray diffraction (GIXRD) measurement of the films with three different concentrations, we observed that increasing in the concentration of the solution yielded different molecular orientations. Based on the three films, OFETs with bottom gate and top contact structure were fabricated. Moreover, the mobility and the on/off current ratio became more uniform with the progressive increase in the concentration of the solution. This may be attributed to the increase in the number of different molecular orientations and charge transfer channels. Although the increase in the number of different molecular orientations might lead to the decrease in mobility, it could improve the alignment of the electric field and also increase π–π stacking direction of the molecules, which promote highly uniform device performance distribution. Since uniform distribution of device performance is significant for practical applications, we believe the transistors that are fabricated at the highest concentration are better than those generated at lower concentrations. Thus, on the 5 cm × 5 cm substrate, it is observed that the average mobility of the transistors is 7.9 cm²·V^-1·s^-1, and all the devices have threshold voltages less than -2 V with the on/off current ratio of 10⁴. This work is significant for the fabrication of large-area and high-performance thin films and transistors.