Characterization and Electronic Modelling of Multilayer OLEDs for Microdisplays

Organic Light-Emitting Diodes (OLEDs) are of great interest for many applications including microdisplays for electronic viewfinders and head-mounted display systems. In the particular case of microdisplays the performance of OLED is already competitive in terms of key performance parameters such as power consumption, response time and contrast ratio. Future OLED microdisplays will require improved OLED devices and electronic drive-circuits. These topics are addressed within the new POLIS project funded by the EU through the ENIAC joint undertaking.
A key task is the development of an accurate electronic model of the OLED device for use in the design and optimization drive-circuits. To that end, this report describes our initial characterization and electronic modelling of a conventional multilayer OLED device structure developed for microdisplay applications. Some important electrical characteristics of the OLEDs, including built-in potential and variation of charge-carrier mobility have been investigated. Through experimentation, an OLED DC steady-state model has been developed that reliably describes the variation of current density as a function of applied-voltage and temperature. Next we plan to extent the characterisation to include the a.c. response then the transient response.
Tandem-structure OLEDs have been shown to exhibit higher efficiency compared to conventional structure OLEDs characterised here and will be developed within POLIS. In the longer term we plan to characterise and model the new tandem OLED devices.