【作者】 张东东； 段炼； 邱勇；

【Author】 Zhang Dongdong;Lian Duan;Yong Qiu;Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education,Department of Chemistry,Tsinghua University;

【机构】 有机光电子与分子工程教育部重点实验室,清华大学化学系；

【摘要】 具有小的单线态和三线态分裂能(ΔEST)的材料可以用来产生热活化延迟荧光(TADF),从而使得荧光器件也可以达到100%内量子效率。但是,根据费米黄金规则,小的ΔEST往往会导致较低的光致发光效率。为了解决小的ΔEST和高的发光效率这一矛盾,我们首次提出了利用具有小ΔEST的材料作为传统荧光的主体。主体材料在这里只需要将三线态激子上转换为单线态,然后通过Forster能量传递方式传给客体发光。根据我们的计算表明,敏化体系的效率只决定于敏化主体的三线态激子上转换效率和客体的发光效率,这样就解决了这一矛盾。在敏化体系中,客体直接的电荷捕获会降低整个器件的效率,因此要通过材料能级以及器件结构设计来避免。我们选用了基于三嗪和吲哚咔唑的PIC-TRZ(0.11 eV)和DIC-TRZ(0.06 eV)两种主体,同时选用发光效率为0.85的黄色荧光染料DDAF为客体,构筑的荧光器件达到了12.2%的外量子效率,最大功率效率也达到了45 lm/W。器件的电瞬态发光表明,高达59%的效率来自于上转换的三线态激子。更多还原

【Abstract】 Materials with a small singlet-triplet exchange energy(ΔEST) have been used as dopants to generate thermally activated delayed fluorescence, showing the potential to achieve 100% internal quantum efficiency in fluorescent organic light-emitting diodes(FOLEDs). However, a small ΔEST always leads to a low photoluminescence efficiency(ΦPL). Here, we demonstrate that this trade-off can be broken by using materials with a small ΔEST as sensitizing hosts for conventional fluorescent dopants. The host and the dopant are responsible for the thermally activated up-conversion of triplet excitons and the radiative decay of singlet excitons, respectively. A highly efficient orange FOLED was prepared using DIC-TRZ with a ΔEST of 0.06 eV as the sensitizing host and DDAF with a ΦPL of 0.85 as the dopant, showing a maximum external quantum efficiency of 14.2% and a maximum power efficiency of 45 lm W-1. The direct charge trapping on the guest will break this process, which will reduce the efficiency and should be prevented. The electroluminescence transient decay curves of the devices show that as high as 59% efficiency is due to the up-converted triplets of the host.更多还原