J. Laubender et al., The influence of oxygen and air on the characteristics of organic light-emitting devices studied by in vacuo measurements, SYNTH METAL, 111, 2000, pp. 373-376
Organic light-emitting devices (OLEDs) based on end-capped sexithiophene or
aluminium-quinolate (Alq(3)) with aluminium and ITO contacts were prepared
by vapour deposition in high-vacuum (10(-6) mbar). Current-voltage (I-V),
capacitance-voltage (C-V) and impedance measurements were performed in situ
without breaking the vacuum. The OLEDs were then deliberately exposed to o
xygen or air. For both materials, the I-V curves of pristine OLEDs are non-
rectifying and show significant anomalies at about +/-5 V. The capacities a
re found to be voltage- and frequency-independent. Whereas doping with dry
oxygen has only small influence on the electrical properties, doping with a
ir yields a rectifying I-V behaviour without anomalies, but at significantl
y reduced currents. This is attributed to a decrease in carrier mobility. T
he capacitance of the Alq(3)-OLEDs remains voltage- and frequency-independe
nt, whereas for thiophene-based OLEDs, a "Schottky-like" capacitance with a
net carrier concentration of about N-eff approximate to 10(17) cm(3) is ob
served. (C) 2000 Elsevier Science S.A. All rights reserved.