Abstract
The dynamic characteristics of multilayer organic light-emitting diodes
(OLEDs) determine the refresh rate in display applications, and are of great
importance for practical organic displays. They also serve as an important
tool in studying the transport mechanisms in organic conductors. Here, the
modulation characteristics of several conventional small-molecule OLED structures
[consisting of ITO/PEDOT:PSS(50 nm)/TPD(50 nm)/Alq<sub>3</sub>(various)/LiF(1 nm)/Al(90 nm)] are
measured and analyzed in terms of mobility in and thickness of the Alq<sub>3</sub> layer. Their
optical response was shown to be limited by electron transport across the Alq<sub>3</sub>. Extracted electron
mobilities were about 2-4×10<sup>-6</sup> cm<sup>2</sup>/V · s (consistent
with that reported in the literature) and near-identical values for mobility
were obtained from devices of different thicknesses, suggesting that this
method measures mobility independent of interface
trap charging. This novel technique is a complement to large signal
time of flight or delay time measurements (which can include interface and
trap charging during the measurement) and can serve as a flexible method to
study transport in actual devices.
© 2006 IEEE
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