Abstract
An electrical model based on drift diffusion is described. We have explored systematically how the shape of the current density-voltage
(
J
-
V
)
curves is determined by the input parameters, information that isessential when deducing values of these parameters by fitting to experimental data for an ITO/PPV/Al organic light-emitting device (OLED), where ITO is shorthand for indium tin oxide and PPV is poly(phenylene vinylene). Our conclusion is that it is often possible to obtain a unique fit even with several parameters to fit. Our results allowing for a tunneling current show remarkable resemblance to experimental data before and after the contacts are conditioned. We have demonstrated our model on single-layer devices with ITO/PFO/Au and ITO/PEDOT/PFO/Au at room temperature and ITO/TPD/Al over temperatures from
130
to
290
K
. PFO is shorthand for poly(
9
,
9
′
-dialkyl-fluorene-2,7-dyl) and TPD is shorthand for
N
,
N
′
-diphenyl-
N
,
N
′
-bis(3-methylphenyl)1-
1
′
-biphenyl-
4
,
4
′
-diamine. Good fits to experimental data have been obtained, but in the case of the TPD device, only if a larger value for the relative permittivity
ϵ
s
than would be expected is used. We infer that a layer of dipoles at the ITO/TPD interface could be responsible for the observed
J
-
V
characteristics by locally causing changes in
ϵ
s
. The strong temperature dependence of the hole barrier height from fitting
J
-
V
characteristics to the experimental data may indicate that the temperature dependence of the thermionic emission model is incorrect.