Triplet-exciton quenching in organic phosphorescent light-emitting diodes with Ir-based emitters
Triplet-exciton quenching in organic phosphorescent light-emitting diodes with Ir-based emitters
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DOI：
10.1103/physrevb.75.125328
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发表时间：
2007-03-01
影响因子：
3.7
通讯作者：
Leo, Karl
中科院分区：
文献类型：
--
作者：
Reineke, Sebastian;Walzer, Karsten;Leo, Karl
我们研究了导致磷光有机发光二极管（OLED）在高亮度下量子效率下降的猝灭过程：三重态-三重态湮灭，能量转移到带电分子（极化子），以及激子解离成自由电荷载流子。所研究的OLED在现有技术的OLED结构内包括作为发射层的主体-客体系统-即，一种五层器件，包括掺杂的传输层和薄的电荷载流子层以及激子阻挡层。在红色磷光器件中，使用N，N-′-二（萘-2-基）- N，N-′-二苯基联苯胺作为基质，三（1-苯基异喹啉）铱[Ir（piq）（3）]作为发光分子。将该结构与具有主体-客体体系的绿色磷光OLED进行比较，所述主体-客体体系包含基质4，4（'），4（'）-三（N-咔唑基）-三苯胺和公知的三重态发射体面-三（2-苯基吡啶）铱[Ir（ppy）（3）]。三重态-三重态湮灭的特征在于由时间分辨光致发光实验确定的速率常数k（TT）。为了研究三重态极化子猝灭，制备了单极器件。一定的激子密度，由连续波照明，分析作为一个函数的电流密度流过的设备。这提供了相应的速率常数k（P）。在典型的OLED操作条件下没有观察到场致猝灭。实验数据实施的分析模型，同时考虑三重态-三重态湮灭和三重态-极化子淬灭。这表明，这两种工艺强烈影响OLED性能。与红色Ir（piq）（3）OLED相比，绿色Ir（ppy）（3）器件显示出更强的效率滚降，这主要是由于更长的磷光寿命τ和更薄的激子形成区w。
We investigate quenching processes which contribute to the roll-off in quantum efficiency of phosphorescent organic light-emitting diodes (OLED's) at high brightness: triplet-triplet annihilation, energy transfer to charged molecules (polarons), and dissociation of excitons into free charge carriers. The investigated OLED's comprise a host-guest system as emission layer within a state-of-the-art OLED structure-i.e., a five-layer device including doped transport and thin charge carrier and exciton blocking layers. In a red phosphorescent device, N,N-'-di(naphthalen-2-yl)- N,N-'-diphenyl-benzidine is used as matrix and tris(1-phenylisoquinoline) iridium [Ir(piq)(3)] as emitter molecule. This structure is compared to a green phosphorescent OLED with a host-guest system comprising the matrix 4,4('),4(')-tris (N-carbazolyl)-triphenylamine and the well-known triplet emitter fac-tris(2-phenylpyridine) iridium [Ir(ppy)(3)]. The triplet-triplet annihilation is characterized by the rate constant k(TT) which is determined by time-resolved photoluminescence experiments. To investigate triplet-polaron quenching, unipolar devices were prepared. A certain exciton density, created by continuous-wave illumination, is analyzed as a function of current density flowing through the device. This delivers the corresponding rate constant k(P). Field-induced quenching is not observed under typical OLED operation conditions. The experimental data are implemented in an analytical model taking in account both triplet-triplet annihilation and triplet-polaron quenching. It shows that both processes strongly influence the OLED performance. Compared to the red Ir(piq)(3) OLED, the green Ir(ppy)(3) device shows a stronger efficiency roll-off which is mainly due to a longer phosphorescent lifetime tau and a thinner exciton formation zone w.