Lv Dong, Liu Xuelei, Li Junhang, Hou Saiyin, Li Yinghan, Wang Zehao, Zhang Qiang, Wang Shumeng, Yu Xinhong, Han Yanchun
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China.
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei 230026, PR China.
ACS Appl Mater Interfaces. 2024 Dec 4;16(48):66301-66315. doi: 10.1021/acsami.4c15774. Epub 2024 Nov 21.
Stretchable organic light-emitting diodes (OLEDs) are a key component of stretchable electronics. Inkjet printing is a potential processing method for stretchable and flexible OLEDs. However, improving the uniformity and stretchability of the emission layer (EML) prepared by inkjet printing is challenging. Here, we propose a strategy to simultaneously improve the uniformity and stretchability of inkjet-printed films by tuning the Marangoni flow and increasing the free volume. To verify our idea, Triton X (TX) with a lipophilic alkyl end and a hydrophilic hydroxyl end was added to the Super Yellow (SY)/polystyrene--polybutadiene--polystyrene (SBS) blend film. TX played two roles. (1) To inhibit the coffee ring effect. The surface tension of the solution decreased because the hydrophilic ends of TX repelled with the nonpolar solvent toluene to decrease the cohesion of toluene molecules on the surface. Thus, the surface tension at the edges was lower than in the middle due to the high evaporation rate at the edges during solvent evaporation. This resulted in the generation of the inward Marangoni flow to drive the solute toward the middle. Therefore, the coffee ring effect was inhibited, and a uniform film was formed. (2) To improve the stretchability. With TX, the glass transition temperature decreased because TX acted as a plasticizer to insert between the polymer chains due to the attraction between the lipophilic ends of TX and the alkyl side chains of SY. This provided more free volume for the polymer chains to move and orientate under strain, which is beneficial for the stretchability. Finally, we fabricated OLEDs with the inkjet-printed stretchable EML. At 100% strain, the luminance kept 70% of the initial luminance, much higher than that without the surfactant (33%).
可拉伸有机发光二极管（OLED）是可拉伸电子器件的关键组件。喷墨印刷是制备可拉伸及柔性OLED的一种潜在加工方法。然而，提高通过喷墨印刷制备的发光层（EML） 的均匀性和可拉伸性具有挑战性。在此，我们提出一种策略，通过调节马兰戈尼流并增加自由体积来同时提高喷墨印刷薄膜的均匀性和可拉伸性。为验证我们的想法，将具有亲脂性烷基端和亲水性羟基端的 Triton X（TX）添加到超黄（SY）/聚苯乙烯-聚丁二烯-聚苯乙烯（SBS）共混薄膜中。TX起到两个作用。（1）抑制咖啡环效应。由于TX的亲水端与非极性溶剂甲苯相互排斥，降低了甲苯分子在表面的内聚力，溶液的表面张力降低。因此，在溶剂蒸发过程中，由于边缘处的高蒸发速率，边缘处的表面张力低于中间处。这导致向内的马兰戈尼流产生，将溶质驱向中间。因此，咖啡环效应受到抑制，形成了均匀的薄膜。（2）提高可拉伸性。有了TX，玻璃化转变温度降低，因为TX作为增塑剂，由于TX的亲脂端与SY的烷基侧链之间的吸引力而插入聚合物链之间。这为聚合物链在应变下移动和取向提供了更多的自由体积，这有利于可拉伸性。最后，我们用喷墨印刷的可拉伸EML制造了OLED。在100%应变下，亮度保持为初始亮度的70%，远高于没有表面活性剂时的亮度（33%）。
