Je Hyeondoo, Cho Seunguk, Kwon Na Yeon, Lee Dong Won, Cho Min Ju, Choi Dong Hoon
Department of Chemistry, Research Institute for Natural Sciences, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Korea.
ACS Appl Mater Interfaces. 2022 Aug 10;14(31):35969-35977. doi: 10.1021/acsami.2c07659. Epub 2022 Jul 27.
Recently, various hosts and emitters for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) have been developed. However, a few studies have been conducted on hole transport materials (HTMs) with differentiated solubility characteristics for manufacturing multilayer OLEDs using a solution process. Here, three new hole transport (HT) styrene polymers, PICz, PPBCz, and PTPCz, were synthesized by radical polymerization. Each of the polymers exhibited increases in their highest occupied molecular orbital (HOMO) levels and better hole-transporting abilities than poly(9-vinylcarbazole) (PVK) as a reference HT polymer. Furthermore, the three HT polymers exhibited different solubilities in toluene. Therefore, it was not possible to use a toluene solution to prepare the emitting layer (EML). To overcome this problem, ethyl acetate (EA), in which the three HT polymers are insoluble, was used as an orthogonal solvent to prepare an EML solution. In EA-solution-processed green-emitting TADF-OLEDs, the three HT-polymer-based devices displayed somewhat low turn-on voltages of 2.8 V and high external quantum efficiencies (EQEs) of >23%. These values are superior to those of a device with a PVK-HT layer. In addition, the devices manufactured with the EA solution showed high-performance reproducibility owing to the stable formation of each layer. In this study, we removed the HTM solubility constraint by dramatically changing the solvent for preparing the EML solution and provided an efficient strategy for the fabrication of OLED devices via solution processes in the future.
最近，已开发出用于溶液可加工热激活延迟荧光有机发光二极管（TADF-OLED）的各种主体和发光体。然而，关于具有不同溶解性特征的空穴传输材料（HTM），用于通过溶液工艺制造多层OLED的研究却很少。在此，通过自由基聚合合成了三种新型空穴传输（HT）苯乙烯聚合物PICz、PPBCz和PTPCz。与作为参考HT聚合物的聚（9-乙烯基咔唑）（PVK）相比，每种聚合物的最高占据分子轨道（HOMO）能级均有所提高，且空穴传输能力更强。此外，这三种HT聚合物在甲苯中的溶解度不同。因此，无法使用甲苯溶液来制备发光层（EML）。为克服这一问题，使用了这三种HT聚合物不溶于其中的乙酸乙酯（EA）作为正交溶剂来制备EML溶液。在采用EA溶液工艺的绿色发光TADF-OLED中，三种基于HT聚合物的器件显示出略低的2.8 V开启电压和大于23%的高外量子效率（EQE）。这些值优于具有PVK-HT层的器件。此外，由于各层形成稳定，用EA溶液制造的器件表现出高性能的可重复性。在本研究中，我们通过大幅改变制备EML溶液的溶剂消除了HTM的溶解性限制，并为未来通过溶液工艺制造OLED器件提供了一种有效策略。
