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@PHDTHESIS{Pfeiffer:766175,
author = {Pfeiffer, Pascal},
othercontributors = {Vescan, Andrei and Wuttig, Matthias},
title = {{I}nnovative {OLED}-{T}echnologien für neue
{A}nwendungsgebiete},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2019-07896},
pages = {1 Online-Ressource (vii, 160 Seiten) : Illustrationen,
Diagramme},
year = {2019},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2019},
abstract = {OLED (Organic Light-Emitting Diode) displays have set new
standards in the field of small mobile devices. Organic
displays offer almost infinite contrast values, low
switching times and a very large color space with high
saturation values. In addition, OLEDs also enable new
applications that cannot be realized with conventional
technologies. For example, transparent OLEDs (TrOLEDs) are
key components for displays, which can be used in head-up
displays (HUD) or augmented reality (AR). When switched off,
such displays should be as transparent as possible. Windows
or room dividers made of TrOLEDs could be used as a light
source at night or at dusk. In order to conquer further
market shares, the relatively young technology must catch up
the remaining arrears (efficiency, lifetime) to the LC
displays. In addition, unique selling points of OLEDs
(homogeneous large-area light sources, high transparency)
must be further developed. In the present work, innovative
OLED technologies are investigated, which should ultimately
pave the way for such novel component concepts and
applications. As a basis for the following experiments, in
the first part of the dissertation a simplified, yet
efficient organic layer stack consisting of only three
organic semiconductor materials was developed. By precisely
setting a balanced charge carrier balance and having an
extended recombination zone, a high luminous efficacy of up
to 31 lm/W (at 3000 cd/m²) was achieved. The simple layer
stack also made it possible to identify and quantify
physical processes in the device volume and at interfaces
(e.g. exciton formation, diffusion and annihilation).As a
result, TrOLEDs were optimized in terms of lifetime and
transmission. Instead of the commonly used Ag or ITO
cathodes, a thin semi-transparent Au layer was implemented
as a (top) cathode. Thus, TrOLEDs with Au cathodes showed a
6-fold increased lifetime compared to those with Ag
cathodes. Ag diffusion was identified as the dominant
degradation process in the reference TrOLEDs and suppressed
by the Au cathodes. The average transparency of these
TrOLEDs in the visible spectrum is over $30\%.$ This
transparency was then maximized by the integration of an
optical coating layer of 2,2 ', 2 "- (1,3,5-benzene triyl)
tris (1-phenyl-1-H-benzimidazole) (TPBi) designed and
realized with the initially developed efficient organic
layer stack and optimized transparency of $65\%$ (at 555
nm).In the area of illumination, large-area OLEDs must be
produced with so-called gridlines for the current
distribution and homogenization of the local potential
difference between anode and cathode in order to achieve a
homogeneous luminance. However, the gridlines interrupt and
reduce the active luminous area and their cross-sections
scale superlinear with the total size of the OLEDs. In the
final chapter, a novel backside contact for potential
stabilization in large OLEDs was investigated. Simulations
have shown that the area required to achieve the same
homogeneity of the luminance can be reduced by more than
$90\%$ with backside contacts compared to gridlines. To
verify the simulations, back-contacted OLEDs were
successfully demonstrated on a laboratory scale. The
critical dry etching processes for exposing the ITO surface
for the auxiliary contacts are in the focus of this chapter.
The simulation results and the successful demonstrators
underline the potential of back-contacted OLEDs, and the
manufacturing process could be transferred industrially to
much larger areas. In addition, it was possible by a
skillful etching process to make the auxiliary contacts
almost invisible in OLED operation. This was achieved by
coupling out lateral guided optical ITO modes by a roughened
ITO/auxiliary contact metal interface. A similar process
could be developed in the future for better light extraction
from gridlines.With a consistent further development of the
technologies presented here, OLEDs can revolutionize both,
the lighting market (entire ceilings or walls with large
illuminants for uniform illumination) and the display market
(e.g. transparent displays for HUD and AR) in just a few
years.},
cin = {612020},
ddc = {621.3},
cid = {$I:(DE-82)612020_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2019-07896},
url = {https://publications.rwth-aachen.de/record/766175},
}
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