Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes,Advanced Materials

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Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes
Advanced Materials ( IF 27.4 ) Pub Date : 2017-09-11 , DOI: 10.1002/adma.201701987
Markus Einzinger ₁ , Tianyu Zhu ₂ , Piotr de Silva ₂ , Christian Belger ₂ , Timothy M. Swager ₂ , Troy Van Voorhis ₂ , Marc A. Baldo ₁

Affiliation

Multiexcited‐state phenomena are believed to be the root cause of two exigent challenges in organic light‐emitting diodes; namely, efficiency roll‐off and degradation. The development of novel strategies to reduce exciton densities under heavy load is therefore highly desirable. Here, it is shown that triplet exciton lifetimes of thermally activated delayed‐fluorescence‐emitter molecules can be manipulated in the solid state by exploiting intermolecular interactions. The external heavy‐atom effect of brominated host molecules leads to increased spin–orbit coupling, which in turn enhances intersystem crossing rates in the guest molecule. Wave function overlap between the host and the guest is confirmed by combined molecular dynamics and density functional theory calculations. Shorter triplet exciton lifetimes are observed, while high photoluminescence quantum yields and essentially unaltered emission spectra are maintained. A change in the intersystem crossing rate ratio due to increased dielectric constants leads to almost 50% lower triplet exciton densities in the emissive layer in the steady state and results in an improved onset of the photoluminescence quantum yield roll‐off at high excitation densities. Efficient organic light‐emitting diodes with better roll‐off behavior based on these novel hosts are fabricated, demonstrating the suitability of this concept for real‐world applications.

中文翻译：

通过外部重原子效应缩短激子寿命：减轻有机发光二极管中双分子过程的影响

人们认为，多激发态现象是有机发光二极管面临两个紧迫挑战的根本原因。即效率下降和降级。因此，迫切需要开发减少重载下激子密度的新策略。在这里，表明通过激活分子间的相互作用，可以在固态下控制热激活的延迟荧光发射体分子的三重态激子寿命。溴化宿主分子的外部重原子效应导致自旋-轨道偶联增加，进而提高了客体分子的系统间交叉速率。结合的分子动力学和密度泛函理论计算证实了主体和客体之间的波函数重叠。观察到更短的三重态激子寿命，同时保持高的光致发光量子产率和基本不变的发射光谱。由于介电常数增加而引起的系统间交叉速率比的变化导致稳态时发射层的三重态激子密度降低了近50％，并导致了高激发密度下光致发光量子产率下降的开始。基于这些新颖的主体，制造了具有更好滚降性能的高效有机发光二极管，证明了该概念在现实应用中的适用性。由于介电常数增加而引起的系统间交叉速率比的变化导致稳态时发射层的三重态激子密度降低了近50％，并导致了高激发密度下光致发光量子产率下降的开始。基于这些新颖的主体，制造了具有更好滚降性能的高效有机发光二极管，证明了该概念在现实应用中的适用性。由于介电常数增加而引起的系统间交叉速率比的变化导致稳态时发射层的三重态激子密度降低了近50％，并导致了高激发密度下光致发光量子产率下降的开始。基于这些新颖的主体，制造了具有更好滚降性能的高效有机发光二极管，证明了该概念在现实应用中的适用性。

更新日期：2017-09-11

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