Carrier transport behavior in organic light emitting diode (OLED) is visualized by Modulus spectroscopy using typical layered devices ITO/α-NPD/Alq₃/LiF/Al. Two techniques of Modulus analysis, Dynamic Modulus Plot (DMP) and Distributed Circuit Element (DCE) analysis are presented. The hole distribution in NPD layer is visualized by DCE model. The DMP and the DCE model show that the hole and electron transport in NPD/Alq₃ devices up to 10 mA/cm² obey not to a space charge limited current but an Ohmic conduction. It is well known that holes accumulate in NPD even below the turn-on voltage of DC current. This hole accumulation depends on both of NPD and Alq₃ layer thicknesses. The voltage dependence is scaled by the Alq₃ thickness, whereas the carrier density dependence by the NPD thickness. We propose a model that the accumulated holes are supplied by the thermal activation of the finite number of shallow trap sites localizing at ITO/NPD interface.

使用典型的分层器件ITO /α-NPD/ Alq ₃ / LiF / Al，通过模量光谱法可以看到有机发光二极管（OLED）中的载流子传输行为。提出了两种模量分析技术，即动态模量图（DMP）和分布式电路元件（DCE）分析。DCE模型可以显示NPD层中的孔分布。DMP和DCE模型表明，高达10 mA / cm ^2的NPD / Alq ₃器件中的空穴和电子传输不服从空间电荷限制电流，而是服从欧姆传导。众所周知，即使在直流电流的开启电压以下，空穴也会在NPD中累积。该空穴积累取决于NPD和Alq ₃层的厚度。电压依赖性由Alq ₃缩放厚度，而载流子密度取决于NPD厚度。我们提出了一个模型，该模型通过有限数量的位于ITO / NPD界面的浅陷阱阱的热激活来提供积聚的空穴。