Recent technological innovations in organic light-emitting diodes (OLEDs) have enabled their applicability to be expanded to not only displays but also the lighting industry. In addition, the high scalability and flexibility of OLEDs render them promising candidates for next-generation displays. However, their insufficient lifetime and low uniformity/stability are challenging issues, mainly because of inadequate understanding regarding the fundamental degradation mechanism of OLEDs owing to their complex device structure. Herein, based on impedance spectroscopy (IS), we report the origin of the relaxation frequency (fR) shift in blue OLEDs as a function of electrical stress time for up to 1000 h with a constant current stress condition of 1 mA. These experimental conditions allow us to separately study the degradation mechanisms of the emission and transport layer (TPL) interfaces. On the basis of thorough understanding of the theoretical expression of fR, we mainly attribute the variation in fR at the charge-balancing voltage to the degradation of the TPL interface; this is further rationalized by the negligible difference between fR values obtained from IS and the equivalent circuit theory. This strong correlation consequently renders fR a powerful degradation indicator for the TPL interface. Our results provide a basis for the realization of highly reliable blue OLEDs with a sufficient lifetime.

中文翻译：

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蓝色有机发光二极管弛豫频移的起源

有机发光二极管 (OLED) 的最新技术创新使其适用性不仅扩展到显示器，还扩展到照明行业。此外，OLED 的高可扩展性和灵活性使其成为下一代显示器的有希望的候选者。然而，它们的寿命不足和均匀性/稳定性低是具有挑战性的问题，主要是因为由于其复杂的器件结构，对 OLED 的基本降解机制了解不足。在此，基于阻抗谱 (IS)，我们报告了蓝色 OLED 中弛豫频率 (fR) 偏移的起源，作为电应力时间的函数，在 1 mA 的恒定电流应力条件下长达 1000 小时。这些实验条件使我们能够分别研究发射和传输层 (TPL) 界面的退化机制。在充分理解fR的理论表达式的基础上，我们主要将电荷平衡电压下fR的变化归因于TPL界面的退化；通过从 IS 和等效电路理论获得的 fR 值之间的差异可以忽略不计，这进一步合理化。因此，这种强相关性使 fR 成为 TPL 接口的强大退化指标。我们的结果为实现具有足够寿命的高度可靠的蓝色 OLED 提供了基础。我们主要将电荷平衡电压下 fR 的变化归因于 TPL 界面的退化；通过从 IS 和等效电路理论获得的 fR 值之间的差异可以忽略不计，这进一步合理化。因此，这种强相关性使 fR 成为 TPL 接口的强大退化指标。我们的结果为实现具有足够寿命的高度可靠的蓝色 OLED 提供了基础。我们主要将电荷平衡电压下 fR 的变化归因于 TPL 界面的退化；通过从 IS 和等效电路理论获得的 fR 值之间的差异可以忽略不计，这进一步合理化。因此，这种强相关性使 fR 成为 TPL 接口的强大退化指标。我们的结果为实现具有足够寿命的高度可靠的蓝色 OLED 提供了基础。