***Opsys Breaks New Ground As High Efficiency Light Emitting
Dendrimer OLEDs Are Produced
(March 20)

High efficiency organic light emitting diodes (OLEDs) using
dendrimer materials have been developed by scientists sponsored
by display technology developer Opsys. The results have broad
implications for the commercialization of OLED technology in the
flat panel display industry.

The Opsys sponsored teams, led by Dr Paul Burn at the University
of Oxford and by Professor Ifor Samuel at the University of St
Andrews, have shown that dendrimers can be used to produce
efficient solution processed OLED devices with just a single
layer of organic material between the electrodes. In contrast,
existing phosphorescent materials require multiple layers of
deposition by more expensive evaporation techniques.

The only OLED materials other than dendrimers that can be
deposited by solution processing methods are light emitting
polymers (LEPs). However, LEPs are not as versatile, as the same
chemical components of an LEP are responsible for both its light
emitting features and its processing features. In dendrimers,
the surface groups may be tuned independently of the emitting
core, providing flexibility in the processing properties.

The results will be announced by Professor Ifor Samuel at the
American Physical Society conference on 22 March 2002. They will
also be published in Applied Physics Letters on 15 April 2002,
under the title 'High efficiency green phosphorescence from spin-
coated single layer dendrimer LED structures '.

Dendrimer Technology
Light emitting dendrimers constitute a materials technology in
the field of OLEDs. They comprise an organic or organometallic
light-emitting core, which is connected to surface groups by
branched organic dendrons. The dendritic structure controls
core-core interactions and hence the photoluminescence and device
properties of the materials. A key advantage of dendrimers is
that the luminescent cores are kept well apart by the bulky
dendrons, which minimizes luminescence quenching.

The newly published research findings showed that a first
generation iridium cored dendrimer doped into a wide bandgap
biphenyl host displayed a peak power efficiency of 6.9 lm/W,
measured at ~1500 cd/m2 brightness and a current density of 5
mA/cm2.

www.opsys.co.uk



Wave Issue 0210 3/25/02 Article 3-01