Correlations of impedance–voltage characteristics and carrier mobility in organic light emitting diodes

The correlation of accumulation charges at the interfaces of organic layers and carrier mobility in organic light emitting devices (OLEDs) were investigated through the impedance versus voltage (Z–V) characteristics of devices. The properties of devices with various combinations of cathode structures, HTLs and ETLs were investigated to understand the impedance transition in Z–V characteristics of OLEDs. It was observed that there is an extra impedance transition before devices turn on when the hole mobility in the HTL is much greater than the electron mobility in the ETL in the devices, which makes the Z–V characteristics a potential tool to compare the electron mobility in ETL and hole mobility in HTL.

The (a) current density versus voltage (J–V), (b) impedance versus voltage (Z–V), and (c) phase versus voltage characteristics of OLEDs with various HTLs and ETLs combinations.The equivalent circuit of hole transport layer (HTL) and electron transport layer (ETL) in OLEDs.Figure optionsDownload as PowerPoint slideHighlights
► We correlate the Z–V characteristics and the carrier mobilities in OLEDs.
► Extra impedance transition associated with the unbalanced carrier mobility.
► Z–V can be used to roughly estimate the carrier mobility.