Application of polyaniline (emeraldine base, EB) in polymer light-emitting devices

We report the fabrication of several multilayer light-emitting-diode (LED) devices based on a novel conjugated polymer, poly(2,5-dihexadecanoxy phenylene vinylene pyridyl vinylene) (PPV-PPy V), involving the use of polyaniline (emeraldine base, EB) as an insulating layer between the emissive polymer layer and the electrodes. In all the above devices with various configurations (‘3-layers’, ‘4-layers’-1’, ‘4-layers-2’ and ‘5-layers’), only the symmetrically configured a.c. light-emitting (SCALE) (‘5-layers’) device shows the capability of operating in both forward and reverse bias modes and in an a.c. mode. The SCALE devices have a typical turn-on voltage of about 4–6 V and work well under both forward and reverse bias modes. It is important to note that the total resistance (R= V/I+) of the four devices at any given applied potential decreases as the number of insulating polymer layers increases, suggesting that the nature of the electrode/polymer interface plays a critical role in determining the characteristics of the devices.