Online proceedings - EDA Publishing Association

7-9 October 2009, Leuven, Belgium
Electro-thermal modeling of different LEP-thickness
white OLEDs
Ernő Kollár, Gusztáv Hantos @eet.bme.hu
Department of Electron Devices, Budapest University of Technology and Economics
H-1111 Budapest, Goldmann tér 3., Hungary
Abstract-In our project the final purpose is to develop a costeffective
roll-to-roll technology of fabricating large-surface,
high-output OLED (Organic Light Emitting Diode) devices for
intelligent lighting applications.
The electrical and optical characteristics of multi-layered
OLEDs depend on the thickness of the layers. To reach the
highest efficiency in an application is needed to optimize the
each layers. In this paper we have measured the I-V
characteristics of the different LEP (Light Emitting Polimer)
thickness white OLEDs. We have examined in 50C wide
temperature range. We have created an electro-thermal model,
which describe the temperature and LEP thickness dependence
of the forward bias.
The results work as the feedback for the fabrication process
and the OLED planning to our project partner.
I. INTRODUCTION
In our research project called Fast2Light [1] the overall
objective is to develop a novel, cost-effective, high-output,
roll-to-roll, large-surface deposition process for fabricating
light-emitting polymer-OLED [2] foils for intelligent
lighting applications. The tested OLED device was realized
on thin glass substrate, which was provided by a project
partner.
On the DUTs there are more different size OLEDs and
OLED groups. This design allows of the examination of the
pixel size devices and more cm 2 size ones in same
technology. The groups allows of gaining certain
information about fabrication process. In this paper we deal
with the about 10 mm 2 lighting surface OLEDs as is shown
by arrows on Fig.1.
Fig. 2. The layer structure of the OLED device under test
The project partner has provided 60, 80 and 100 nm LEP
thickness white OLED samples. Our purpose is to create a
model which helps to choose the optimal LEP thickness
adapted to the needs. Such a need can be, for example, the
principle of operation at a standard power supply.
The layer structure of an OLED device is shown in Fig. 2.
[3]
II.
MEASUREMENT ARRANGEMENT
We have studied the forward bias above 4 V. The end
points of I-V characteristics depend strongly on the
temperature and the LEP thickness, that’s why this point is
between 5 V and 9 V. For comparison we have used the
22 mA/cm 2 value as suggested limit by provider.
The measurement was carried out on GPIB and RS232
controlled conventional laboratory equipment. The OLEDs
were attached to a cold-plate of variable constant
temperature. We have applied an analogue measuring point
changer for the full automatic measuring. The I-V
characteristics were measured between 5 °C and 50 °C. The
power supply step was 0.01 V in every second. We
measured all of three OLEDs on every sample.
Fig. 1. The 10 mm 2 lighting surface OLEDs on the device under test
III.
FORWARD BIAS
Drawing the forward I-V values in log-log scale results
straight lines in two ranges. We have considered the forward
current of the device as the sum of two power functions [4].
The parameters of the power functions are: m for the
exponent and b for the factor. The LOW and HIGH
subscripts show in which forward bias range the power
function is effective (1).
©EDA Publishing/THERMINIC 2009 121
ISBN: 978-2-35500-010-2