Self-emissive organic light-emitting diodes (OLEDs) are a new promising technology with
high expected profitability on the display market, which is currently dominated by liquid
crystals. They show low driving voltages in combination with unrestricted viewing angles,
high color-brilliance, light weight, small film-thicknesses and low production costs. Because
of the plasticity of the materials they can be deposited on flexible substrates. Nowadays, there
are already OLED-display devices available such as PDAs, mp3 players, mobile phones,
navigation-systems etc. One can distinguish two material-classes used in OLED: OLEDs
based on small molecules, which are deposited by thermal evaporation and the low-cost
polymeric OLEDs, which are processed from solution. Initially, it was difficult to realise
polymeric multilayer OLEDs, since newly deposited layers dissolved the underlying layers,
but are now easily accessible by the use of direct lithography in combination with oxetanefunctionalised
polymers.
Despite intense research efforts during the last decade there are still improvements to be made
in OLED-lifetime and OLED-outcoupling. The light-outcoupling is limited by the refractive
indices of the OLED building layers. Simple ray-optics allows to estimate the external
quantum efficiency of a standard OLED to 20 % of the initially generated light. 80 %,
however, are lost to total internal reflection. To overcome this problem many approaches have
been introduced. They can be divided into modifications of the external OLED-architecture
(e.g. mesa structures, micro-lenses) and modifications of the internal layer structure. It was
demonstrated that diffraction elements, such as periodic structures, are highly suitable to
improve light-outcoupling. Doubling of the efficiency and luminescence enhancements up to
factors of five were reported with respect to the flat reference devices, but only in
combination with very poor overall efficiencies.
Subject of this thesis was to structure well-performing organic OLED-polymers by direct
lithography (DL) and investigate their applications in electro-optic devices as diffraction
elements. Additionally, photoembossing (PE) should be applied to access structured wellperforming
oxetane functionalised OLED-materials without any wet-development step. The
third method is a combination of direct lithography and photoembossing and is referred to as
“combined DL-PE structuring” in this thesis
2. Introduction
Uses organic light emitting diode(OLED).
Emerging Technology for displays in devices.
Main principle behind OLED technology is
electroluminescence.
Offers brighter, thinner, high contrast, flexible
displays.
3. What is an OLED?
OLEDs are solid state devices composed of thin films
of organic molecules that is100 to 500 nanometres
thick.
They emits light with the application of electricity.
They doesn’t require any backlight. i.e., they are self
emitting.
They are made from carbon and hydrogen.
4. History
The first OLED device was developed by Eastman
Kodak in 1987.
In 1996, pioneer produces the world’s first
commercial PMOLED.
In 2000, many companies like Motorola, LG etc
developed various displays.
In 2001, Sony developed world’s largest fullcolor
OLED.
5. History (contd.)
In 2002, approximately 3.5 million passive matrix
OLED sub-displays were sold, and over 10 million
were sold in 2003.
In 2010 and 2011, many companies announced
AMOLED displays.
Many developments had take place in the year 2012.
6. Features
Flexibility.
Emissive Technology.
Light weight and thin.
Low power consumption.
High contrast, brighter and perfect display from all
angles.
7. Structure of OLED
Substrate.
Anode.
Organic layer.
-Conductive layer (Hole Transport Layer).
made up of polyaniline or metal-phthalocyanine.
-Emissive layer( Electron Transport Layer).
made up of polyfluorene or metal chelates.
Cathode.
9. OLED Fabrication
Substrate preparation.
Device deposition
Deposit and pattern anode.
Pattern organic layers.
Vacuum deposit and pattern cathode.
Encapsulation.
Also involves making backplane.
10. Working Principle
A voltage is applied across the anode and cathode.
Current flows from cathode to anode through the organic
layers.
Electrons flow to emissive layer from the cathode.
Electrons are removed from conductive layer leaving holes.
Holes jump into emissive layer .
Electron and hole combine and light emitted.
13. Types of OLED
Six types of OLEDs
Passive matrix OLED(PMOLED).
Active matrix OLED(AMOLED).
Transparent OLED(TOLED).
Top emitting OLED.
Flexible OLED(FOLED).
White OLED(WOLED).
20. OLED Advantages
Thinner, lighter and more flexible.
Do not require backlighting like LCDs.
Can be made to larger sizes.
Large fields of view, about 170 degrees.
Faster response time.
Brighter.
High resolution, <5μm pixel size.
27. Conclusion
Organic Light Emitting Diodes are evolving as the
next generation displays.
As OLED display technology matures, it will be
better able to improve upon certain existing
limitations of LCD including
high power consumption
limited viewing angles
poor contrast ratios.