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Influence of Dopant Concentration and Steric Bulk on Interlayer Diffusion in OLEDs
Advanced Materials Interfaces ( IF 4.3 ) Pub Date : 2017-10-25 , DOI: 10.1002/admi.201700872 Jake A. McEwan 1 , Andrew J. Clulow 1 , Andrew Nelson 2 , Renjie Wang 1 , Paul L. Burn 1 , Ian R. Gentle 1
Advanced Materials Interfaces ( IF 4.3 ) Pub Date : 2017-10-25 , DOI: 10.1002/admi.201700872 Jake A. McEwan 1 , Andrew J. Clulow 1 , Andrew Nelson 2 , Renjie Wang 1 , Paul L. Burn 1 , Ian R. Gentle 1
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The performance of organic light‐emitting diodes (OLEDs) can change when they are subjected to thermal stress after manufacture. The effect of heat on OLED film stacks is studied, in which the emissive layer (EML) comprises either a phosphorescent iridium(III) dopant blended in a host at different concentrations or materials with alkyl substituents to increase the steric bulk of the host and/or dopant. Neutron reflectometry with in situ photoluminescence measurements shows that interdiffusion between the emissive and hole transport layers within the films occurs on thermal annealing. Interdiffusion occurs independent of dopant concentration or steric bulk of the EML components. Importantly, when held at relatively low temperatures, the EML materials are found to only partially diffuse into an adjacent charge transport layer. The movement of materials is found to correlate with the change in luminescence from the hole transport material and an initial enhancement of the emission from the iridium(III) dopant. The results provide an explanation for the burn‐in often observed for OLEDs as well as the need to change the driving characteristics over time to ensure that pixels can be held at the requisite brightness.
中文翻译：
掺杂剂浓度和固溶体体积对OLED中层间扩散的影响
制造后受到有机应力的有机发光二极管（OLED）的性能可能会发生变化。研究了热量对OLED薄膜堆叠的影响，其中发射层（EML）包含以不同浓度掺入主体的磷光铱（III）掺杂剂或具有烷基取代基的材料，以增加主体的空间体积和/或掺杂剂。用原位光致发光测量的中子反射法表明，膜内的发射层和空穴传输层之间的相互扩散发生在热退火中。相互扩散的发生与EML组分的掺杂剂浓度或空间体积无关。重要的是，当在相对较低的温度下保持时，发现EML材料仅部分扩散到相邻的电荷传输层中。发现材料的运动与空穴传输材料的发光变化和铱（III）掺杂物的发射的初始增强相关。结果提供了对OLED经常观察到的老化的解释，以及需要随着时间改变驱动特性以确保像素可以保持在所需的亮度的原因。
更新日期：2017-10-25
中文翻译：
掺杂剂浓度和固溶体体积对OLED中层间扩散的影响
制造后受到有机应力的有机发光二极管（OLED）的性能可能会发生变化。研究了热量对OLED薄膜堆叠的影响，其中发射层（EML）包含以不同浓度掺入主体的磷光铱（III）掺杂剂或具有烷基取代基的材料，以增加主体的空间体积和/或掺杂剂。用原位光致发光测量的中子反射法表明，膜内的发射层和空穴传输层之间的相互扩散发生在热退火中。相互扩散的发生与EML组分的掺杂剂浓度或空间体积无关。重要的是，当在相对较低的温度下保持时，发现EML材料仅部分扩散到相邻的电荷传输层中。发现材料的运动与空穴传输材料的发光变化和铱（III）掺杂物的发射的初始增强相关。结果提供了对OLED经常观察到的老化的解释，以及需要随着时间改变驱动特性以确保像素可以保持在所需的亮度的原因。
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