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Impact of defects on exciton diffusion in organic light-emitting diodes
Organic Electronics ( IF 3.2 ) Pub Date : 2017-07-11 , DOI: 10.1016/j.orgel.2017.07.017
Grayson L. Ingram , Zheng-Hong Lu

The impact of defect concentration and current density on the effective singlet exciton diffusion length in 4’-bis(carbazol-9-yl)biphenyl (CBP) is quantified by analyzing the electroluminescent characteristics of several sets of OLEDs. The defect concentration and effective diffusion length are determined through fitting of the defect and CBP emission bands in the electroluminescence spectra under constant current operation using an analytical model derived based on the competition between exciton diffusion and energy transfer to defects. Defect concentrations of 3 ± 1 × 1018 cm−3, 2 ± 1 × 1018 cm−3 and 0.3 ± 0.7 × 1018 cm−3 are calculated in three sets of OLEDs, in which the effective diffusion length decreases as the defect concentration increases. Modelling the dependence of the effective diffusion length on defect concentration a “defect free” diffusion length of 4.5 ± 0.3 nm is obtained for CBP singlet excitons in these devices operated under low current density. We also show that the driving voltage scales linearly with the defect concentration.



中文翻译:

缺陷对有机发光二极管中激子扩散的影响

通过分析几套OLED的电致发光特性,定量了缺陷浓度和电流密度对4'-双(咔唑-9-基)联苯(CBP)中有效单线态激子扩散长度的影响。缺陷浓度和有效扩散长度是通过在恒定电流操作下使用基于激子扩散和向缺陷的能量转移之间的竞争而得出的分析模型拟合电致发光光谱中的缺陷和CBP发射带来确定的。缺陷浓度为3±1×10 18  cm -3,2 ±1×10 18  cm -3和0.3±0.7×10 18  cm -3在三组OLED中计算出的有效掺杂量,其中有效扩散长度随缺陷浓度的增加而减小。通过对有效扩散长度对缺陷浓度的依赖性进行建模,可以在这些器件中以低电流密度工作的CBP单重态激子获得4.5±0.3 nm的“无缺陷”扩散长度。我们还表明,驱动电压与缺陷浓度成线性比例关系。

更新日期:2017-07-11
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