Wednesday, June 16, 2004

[ODCAD]PEDOT-Various Electronic Structure

PEDOT is commercial name (trade name) for mixture of organic semiconductor PEDT with dopant PSS. Polystyrene Sulfonic acid (PSS) functions as dopant that oxidizes Polyethylenedioxy-thiophene (PEDT) resulting in PEDT+ as p-type doped semiconductor.

Hewlett-Packard (HP) and Princeton university are working together to develop WORM memory with PEDOT material. They found[1] that doped material PEDT+ has energy levels with LUMO=4.4eV, and HOMO=5.0eV. These structure allows hole to be injected easily from ITO (work function=4.8eV) or other high work function material such as Au (work function=5.0eV). Therefore, device ITO/PEDOT/AU is conductive because PEDT+ has high hole concentration, and the hole injection energy barrier is trivial. The resistivity of the device is about 20 ohm/sq.

This doping reaction between PSS and PEDT can be reversed when the external field is applied.
Electrical energy + PEDT(+) + PSS(-) > PEDT + PSS
The neutral PEDT in this resulting mixture PEDT+PSS has different energy levels with LUMO=3.9 and HOMO=5.4V. This results in much higher energy barrier for hole injection from anode. Also, the reduced PEDT has much few hole charge carrier. Therefore, the device ITO/PEDOT/Au has much low conductivity because theses two effects.

1. S. Moller, S. R. Forrest, C. Perlov, W. Jackson, C. Taussig; J. Appl. Phys.; 94, 7811(2003)

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