Tang Pengyu, Xie Liming, Xiong Xueying, Wei Changting, Zhao Wenchao, Chen Ming, Zhuang Jinyong, Su Wenming, Cui Zheng
Printable Electronics Research Center, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou Industrial Park, Suzhou, Jiangsu 215123, People's Republic of China.
School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
ACS Appl Mater Interfaces. 2020 Mar 18;12(11):13087-13095. doi: 10.1021/acsami.0c01001. Epub 2020 Mar 5.
Poly[(9,9-dioctylfluorenyl-2,7-diyl)-(4,4'-(-(4-butylphenyl)))] (TFB) has been widely used as a hole transport layer (HTL) material in cadmium-based quantum dot light-emitting diodes (QLEDs) because of its high hole mobility. However, as the highest occupied molecular orbital (HOMO) energy level of TFB is -5.4 eV, the hole injection from TFB to the quantum dot (QD) layer is higher than 1.5 eV. Such a high oxidation potential at the QD/HTL interface may seriously degrade the device lifetime. In addition, TFB is not resistant to most solvents, which limits its application in inkjet-printed QLED display. In this study, the blended HTL consisting of TFB and cross-linkable small molecular 4,4'-bis(3-vinyl-9-carbazol-9-yl)1,1'-biphenyl (CBP-V) was introduced into red QLEDs because of the deep HOMO energy level of CBP-V (-6.2 eV). Compared with the TFB-only devices, the external quantum efficiency (EQE) of devices with the blended HTL improved from 15.9 to 22.3% without the increase of turn-on voltage for spin-coating-fabricated devices. Furthermore, the blended HTL prolonged the T90 and T70 lifetime from 5.4 and 31.1 to 39.4 and 148.9 h, respectively. These enhancements in lifetime are attributed to the low hole-injection barrier at the HTL/QD interface and high thermal stability of the blended HTL after cross-linking. Moreover, the cross-linked blended HTL showed excellent solvent resistance after cross-linking, and the EQE of the inkjet-printed red QLEDs reached 16.9%.
聚[(9,9 - 二辛基芴 - 2,7 - 二亚基)-(4,4'-(-(4 - 丁基苯基)))]（TFB）因其高空穴迁移率而被广泛用作基于镉的量子点发光二极管（QLED）中的空穴传输层（HTL）材料。然而，由于TFB的最高占据分子轨道（HOMO）能级为 -5.4 eV，从TFB到量子点（QD）层的空穴注入高于1.5 eV。在QD/HTL界面处如此高的氧化电位可能会严重降低器件寿命。此外，TFB对大多数溶剂不耐受，这限制了其在喷墨打印QLED显示器中的应用。在本研究中，由于可交联小分子4,4'-双(3 - 乙烯基 - 9 - 咔唑 - 9 - 基)1,1'-联苯（CBP - V）的HOMO能级较深（-6.2 eV），由TFB和CBP - V组成的混合HTL被引入到红色QLED中。与仅使用TFB的器件相比，对于旋涂制备的器件，具有混合HTL的器件的外量子效率（EQE）从15.9%提高到了22.3%，且开启电压没有增加。此外，混合HTL将T90和T70寿命分别从5.4小时和31.1小时延长至39.4小时和148.9小时。寿命的这些提高归因于HTL/QD界面处较低的空穴注入势垒以及交联后混合HTL的高热稳定性。此外，交联后的混合HTL在交联后表现出优异的耐溶剂性，喷墨打印的红色QLED的EQE达到了16.9%。
