Highly Efficient Full-Color Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes: Extremely Low Efficiency Roll-Off Utilizing a Host with Small Singlet-Triplet Splitting
Highly Efficient Full-Color Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes: Extremely Low Efficiency Roll-Off Utilizing a Host with Small Singlet-Triplet Splitting
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DOI：
10.1021/acsami.6b15272
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发表时间：
2017-02-08
影响因子：
9.5
通讯作者：
Duan, Lian
中科院分区：
文献类型：
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作者：
Zhang, Dongdong;Zhao, Chongguang;Duan, Lian
人们已经付出了许多努力来提高热激活延迟荧光(TADF)器件的效率；然而，抑制器件效率滚落的策略仍然迫切需要。本文提出了一种抑制TADF器件效率滚降的通用有效方法，即利用TADF材料作为TADF发射体的主体。TADF材料带有施主和受主单元的小单态-三态分裂(Delta E-ST)，作为主体的TADF材料具有与相邻传输层匹配的前沿能级，有利于平衡电荷注入和有利于平衡电荷传输的双极电荷输运迁移率。此外，可以预见增强的Forster能量从主体到掺杂剂的传递，这有助于降低激子浓度。在此基础上，合成了一种新型的基于吲哚并[2，1-b]咔唑/1，3，5-三氮杂衍生物的TADF材料，并将其作为全色TADF器件的通用基质。获得了显著的低效率衰减，即使在亮度为2000cd/m(2)的情况下，也保持了90%以上的最大外量子效率(S)，橙色、绿色和天蓝色TADF器件的EQE(Max)S分别为23.2%、21.0%和19.2%。通过计算模拟，我们发现了与采用传统主机的器件相比，激子湮没速率受到了抑制。这些TADF器件的最新低效率衰减体现了这种主机设计策略的巨大潜力，为其实际应用奠定了有效的策略。
Numerous efforts have been devoted to boost the efficiency of thermally activated delayed fluorescence (TADF) devices; however, strategies to suppress the device efficiency roll-off are still in urgent need. Here, a general and effective approach to suppress the efficiency roll-off of TADF devices is proposed, that is, utilizing TADF materials as the hosts for TADF emitters. Bearing small singlet-triplet splitting (Delta E-ST) with donor and acceptor units, TADF materials as the hosts possess the potential to achieve matched frontier energy levels with the adjacent transporting layers, facilitating balanced charge injection as well as bipolar charge transport mobilities beneficial to the balanced charges transportation. Furthermore, an enhanced Forster energy transfer from the host to the dopant can be anticipated, helpful to reduce the exciton concentration. Based on the principles, a new TADF material based on indeno[2,1-b]carbazole/1,3,5-triazin derivation is synthesized and used as the universal host for the full-color TADF devices. Remarkable low efficiency roll-off was achieved with above 90% of the maximum external quantum efficiencies (EQE(max)'s) maintained even at a brightness of 2000 cd/m(2), along with EQE(max)'s of 23.2, 21.0, and 19.2% for orange, green, and sky-blue TADF devices, respectively. Through computational simulation, we identified the suppressed exciton annihilation rates compared with devices adopting conventional hosts. The state-of-the-art low efficiency roll-off of those TADF devices manifests the great potential of such host design strategy, paving an efficient strategy toward their practical application.