Y. He et al., CHARACTERIZATION AND STABILITY OF LIGHT-EMITTING-DIODES BASED ON POLY(BITHIAZOLE)S, I.E.E.E. transactions on electron devices, 44(8), 1997, pp. 1282-1288
We report, for the first time, electroluminescence (EL) from a new cla
ss of conjugated polymers: poly(bithiazole)'s, based light-emitting di
odes. The emission spectra of these polymers range throughout the visi
ble, from blue-green to red. These polymers also show high thermal and
oxidative stabilities. LED's based on poly(N-methyl-4,4'-dinonyl-2,2'
-bithiazole triflate) (MPNBT), one member of this polymer class, have
been electrically characterized under ambient conditions, a dc voltage
of about 5.0 V is needed to induce the light emission, and a stable e
mission is observed when current density is greater than or equal to 9
5 mA/cm(2), However, after the light emission has occurred, a rapid de
gradation of diode current level at a fixed voltage has been observed.
At the same time, the current-voltage characteristic of the diode str
ucture changes from a typical diode-like behavior to a nearly linear o
hmic-like behavior, indicating a transformation at/or near the Al/poly
mer contact. Further, some bubbles appear at the surface of the top el
ectrode after light emission has occurred, showing the loss of adhesio
n between the top Al contact layer and the polymer layer. We believe t
hat the LED characteristic change and bubble formation originate front
the same mechanism-the adhesion loss at the top contact/polymer inter
face. The roughness of back contact and uniformity of polymer active l
ayer are found to be critical far LED electrical stability.