Chemistry Reference
In-Depth Information
Figure 4.32. Band diagrams of PTCDA/
-NPD/Alq
3
and Alq
3
/PTCDA.
The experimental error, 0.2 eV, is indicated. Adapted from Rajagopal
et al.
, 1998.
α
-NPD,
α
(
E
III
−
V
(
E
III
−
V
E
Ge
exhibit the same band offset,
E
V
0
.
2eVand
|
−
VBM
)
−
−
VBM
VBM
E
S
VBM
)
−
(
E
S
VBM
−
E
Ge
|≤
.
2eV.
However, for organic/metal interfaces the commutativity rule is expected to
break down, since the preparation sequence is quite different due to differ-
entiated organic/metal and metal/organic diffusion profiles. F
16
CuPc/Au shows
E
F
−
VBM
)
0
2 eV. However, when gold atoms are evapo-
rated onto F
16
CuPc they diffuse into the organic film increasing the electron in-
jection barrier (Shen & Kahn, 2001). In general the interfacial properties of metal
contacts on organic materials are strongly determined by the preparation condi-
tions. Gold deposition at high rates and low substrate temperatures leads to well-
defined interfaces with limited amounts of interdiffusion. However, low deposition
rates combined with high substrate temperatures result in large interdiffusion (Durr
et al.
, 2002b).
Many published results on electronic transport properties of organic materials,
where metal contacts are usually made by evaporation of metals, do not describe
the quality of the organic/metal interface, and some exotic observed features may
perhaps be ascribed to extrinsic effects such asmetal diffusion. The relatively simple
contact lamination technique may become an alternative, since it provides a means
for establishing electrical contacts without the potential disruption of the organic
material associated with metal evaporation. The method consists in bringing the
organic layer into mechanical contact with an elastomeric element coated with a
thin metal film, which can also be patterned. The contacts are robust and reversible
E
HOMO
1
.
2eVand
0
.
