Abstract
The effect of alkali metal (Li
+
,Na
+,K
+
,Rb
+
, and Cs
+) acetates and fluorides at an aluminum/tris(8-hydroxyquinoline)
aluminum (Alq3
) interface on performance of organic electroluminescent (EL) devices is described. We also studied the effect of
acetates with different metals, such as Mg
2+
and Al
3+
, on the performance of the EL devices. EL characteristics of the devices
with Al/alkali metal acetates were compared with those of devices with Al/alkali metal fluorides or an Al cathode itself. We found
that the bilayer cathodes with alkali metal acetates exhibited better device performance than the bilayer cathodes with alkali metal
fluorides. The improvement can be attributed to lowering of the work function of the Al cathode and doping of Alq3
with alkali
metals that were formed by the higher reactivity of alkali metal acetates than alkali metal fluorides with hot Al atoms impinging
on these salts during the vapor deposition. The enhanced electron injection resulted in more balanced charge-carrier injection and
thus higher EL efficiencies. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Organic electroluminescent devices; Al cathode; Enhanced electron injection; Alkali metal acetates; Alkali metal fluorides