[ODCAD] LECs: Bright and Efficient OLED

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 expert and toolkit provider of electronic material, device.
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