From: odcad@yahoo.com (ODCAD)
Newsgroups: sci.physics.plasma
Subject: [ODCAD] LECs: Bright and Efficient OLED
Date: 30 Apr 2004 17:47:09 -0700
Organization: http://groups.google.com


This is another buzz word. LECs means Light-emitting electrochemical
cells. This type of cell usually has a mixture of a conjugated
polymer, an ion conducting polymer, and a salt.

Its advantage over conventional OLED is that the cell has high
brightness and efficiency at very low operation voltages broadly
independent of the work functions of the electrode. The cell has
emitting in both forward and reverse bias. The onset voltage is almost
independent of the emitting layer thickness.

The following is the possible mechanism under external field.
Step 1. Salt dissociates into ions.
Step 2. Mobile ion drifts under field. Usually it has only one kind of
ion that is small and mobile in the polymer.
Step 3. Cation moves toward cathode, anion moves toward anode. If only
one ion moves, a balance charge moves another direction. Therefore, a
junction due to electrochemical cell is build up in the polymer. When
the junction is thin enough, the hole injected from the anode combines
with the electron from the cathode. This results in emitting light.

One example given here is by Rudmann lab of MIT. A cell with structure
ITO/t-butyl-Ru(II)+BF4+PMMA/Cathode. The t-butyl-R(II) is the charge
carrier conduction channel. Here Ru(II) allows charge carrier
transport by changing state from Ru(II) to Ru(I). Negative BF4 ion is
the mobile ion. They have done capacitance, and current measurements
that have solid prove to the model described above.

In addition to the advantage mentioned before, the electrode
independence does give wide choice of material as electrode. This is
particularly true for the cathode. However, there are a few
difficulties for LECs technology. For example, the operation voltage
schema, and its correspondence of the choice of mobile ion is tricky.

This is a modified copy posted on Organic Device
(http://groups.yahoo.com/group/OrganicDevice/).

ODCAD from OD Software Incorporated (ODSI)(http://www.odcad.com/)-the
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