Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, P. R. China.
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Adv Mater. 2018 Feb;30(7). doi: 10.1002/adma.201705406. Epub 2018 Jan 8.
Maintaining high efficiency at high brightness levels is an exigent challenge for real-world applications of thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Here, versatile indolocarbazole-isomer derivatives are developed as highly emissive emitters and ideal hosts for TADF-OLEDs to alleviate efficiency roll-off. It is observed that photophysical and electronic properties of these compounds can be well modulated by varying the indolocarbazole isomers. A photoluminescence quantum yield (η ) approaching unity and a maximum external quantum efficiency (EQE ) of 25.1% are obtained for the emitter with indolo[3,2-a]carbazolyl subunit. Remarkably, record-high EQE/power efficiency of 26.2%/69.7 lm W at the brightness level of 5000 cd m with a voltage of only 3.74 V are also obtained using the same isomer as the host in a green TADF-OLED. It is evident that TADF hosts with high η values, fast reverse intersystem crossing processes, and balanced charge transport properties may open the path toward roll-off-free TADF-OLEDs.
在实际应用中，热致延迟荧光有机发光二极管（TADF-OLED）需要在高亮度水平下保持高效率，这是一项艰巨的挑战。在这里，我们开发了多功能吲哚咔唑异构体衍生物作为高效发光体和 TADF-OLED 的理想主体，以缓解效率滚降。可以观察到，通过改变吲哚咔唑异构体，可以很好地调节这些化合物的光物理和电子性质。对于具有吲哚并[3,2-a]咔唑基部分的发射器，获得了接近 1 的光致发光量子产率（η）和 25.1%的最大外量子效率（EQE）。值得注意的是，在绿色 TADF-OLED 中，使用相同的异构体作为主体，在亮度为 5000 cd m 时，仅使用 3.74 V 的电压，也获得了创纪录的 26.2%/69.7 lm W 的 EQE/功率效率。显然，具有高 η 值、快速反向系间窜越过程和平衡电荷输运性质的 TADF 主体可能为无滚降 TADF-OLED 开辟了道路。
