F. Baier et al., A combined photoelectron spectroscopy and capacity-voltage investigation of the aluminum oligothiophene interface, OPT MATER, 12(2-3), 1999, pp. 285-290
In order to better understand the electronic barriers at the metal contacts
of organic light emitting devices (OLEDs), we investigated interfaces of t
hin films of endcapped sexithiophene (EC6T) with metal contacts by Ultravio
let and X-ray Photoelectron Spectroscopy (UPS/XPS). We compare the interfac
e of an EC6T film deposited on an Ag(lll) surface and the interface obtaine
d by deposition of Al on an EC6T film. The two situations differ in so far
as a strong chemical reaction and diffusion of Al into the EC6T film occurs
in the latter. For the EC6T/Ag(111) interface we derive the existence of a
n interface dipole leading to a "band-offset" directly at the interface. Fo
r Al/EC6T, the data suggest a common vacuum level for the reacted molecules
and the Al. The band-offset is determined as 1.7 eV. These results are dis
cussed in context with capacity-voltage measurements performed on Al/EC6T/i
ndium-tin-oxide OLEDs. (C) 1999 Elsevier Science B.V. All rights reserved.