Influence of trapped and interfacial charges in organic multilayer light-emitting devices
- 1 February 2001
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 89 (3), 1704-1712
- https://doi.org/10.1063/1.1332088
Abstract
The influence of trapped and interfacial charges on the device characteristics of organic multilayer light-emitting devices is investigated. We have studied devices consisting of 20 nm copper phthalocyanine as buffer and hole-injection layer, 50 nm N,N′-di(naphthalene-1-yl)-N,N′ diphenyl-benzidine (NPB) as hole-transport layer, and 65 nm tris(8-hydroxyquinolinato)aluminum as electron transport and emitting layer sandwiched between a high-work-function metal and a semitransparent Ca electrode. Current–voltage measurements show that the device characteristics in negative bias direction and at low positive bias are influenced by charges trapped within the organic layers. This is manifested by a strong dependence of the current on the direction and speed of the voltage sweep in this range. Low-frequency capacitance–voltage and static charge measurements reveal a voltage-independent capacitance in negative bias direction and a significant increase between 0 and 2 V, indicating the presence of negative interfacial charges at the interface. Transient experiments show that the delay time of electroluminescence under forward bias conditions is controlled by the buildup of internal space charges rather than by charge-carrier transport through the organic layers.
Keywords
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