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OLED DISPLAY SYSTEMS

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TABLE OF CONTENTS
ABSTRACT
HISTORY
INTRODUCTION
WHAT IS OLED
WORKING PRINCIPLE
MATERIAL TECHNOLOGIES
LIMITATIONS OF LCD-EVOLUTION OF OLED
ORGANIC LED AND LIQUID CRYSTAL DISPLAY COMPARISON
OLED COMPONENTS
MAKING OLED
OPERATION
TYPES OF OLEDs
ADVANTAGES
DISADVANTAGES
CURRENT AND FETURES OF OLED APPLICATIONS
EFFICIENCY OF OLED
THE ORGANIC FUTURE
CONCLUSION
REFERENCE

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ABSTRACT :-
Over the time there are many changes came into the field of output/display devices. In
this field first came the small led displays which can show only the numeric contains. Then came
the heavy jumbo CRTs (Cathode Ray Tubes) which are used till now. But the main problem with
CRT is they are very heavy & we couldn’t carry them from one place to another the result of this
CRT is very nice & clear but they are very heavy & bulky & also required quiet large area then
anything else.
Then came the very compact LCDs (Liquefied Crystal Displays). They are very lighter in
weight as well as easy to carry from one place to the other. But the main problem with the LCDs
is we can get the perfect result in the some particular direction. If we see from any other
direction it will not display the perfect display.
To over come this problems of CRTs & LCDs the scientist of Universal Laboratories,
Florida, United States & Eastman Kodak Company both started their research work in that
direction & the overcome of their efforts is the new generation of display technologies named
OLED (Organic Light Emitting Diode) Technology.
In the flat panel display zone unlike traditional Liquid-Crystal Displays OLEDs are self
luminous & do not required any kind of backlighting. This eliminates the need for bulky &
environmentally undesirable mercury lamps and yields a more thinner ,more compact display.
Unlike other flat panel displays OLED has a wide viewing angle (upto 160 degrees),even
in bright light.Their low power consumption(only 2 to 10 volts) provides for maximum
efficiency and helps minimize heat and electric interference in electronic devices.
Because of this combination of this features, OLED displays communicate more information in
a more engaging way while adding less weight and taking up less space. Their application in
numerous devices is not only a future possibility but a current reality.

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HISTORY :-
The first observations of electroluminescence in organic materials were in the early 1950s by A.
Bernanose and co-workers at the Nancy-Université, France. They applied high-voltage
alternating current (AC) fields in air to materials such as acridine orange, either deposited on or
dissolved in cellulose or cellophane thin films. The proposed mechanism was either direct
excitation of the dye molecules or excitation of electrons.
In 1960, Martin Pope and co-workers at New York University developed ohmic dark-injecting
electrode contacts to organic crystals. They further described the necessary energetic
requirements (work functions) for hole and electron injecting electrode contacts. These contacts
are the basis of charge injection in all modern OLED devices. Pope's group also first observed
direct current (DC) electroluminescence under vacuum on a pure single crystal of anthracene and
on anthracene crystals doped with tetracene in 1963 using a small area silver electrode at 400V.
The proposed mechanism was field-accelerated electron excitation of molecular fluorescence.
Pope's group reported in 1965 that in the absence of an external electric field, the
electroluminescence in anthracene crystals is caused by the recombination of a thermalized
electron and hole, and that the conducting level of anthracene is higher in energy than the exciton
energy level. Also in 1965, W. Helfrich and W. G. Schneider of the National Research Council
in Canada produced double injection recombination electroluminescence for the first time in an
anthracene single crystal using hole and electron injecting electrodes,the forerunner of modern
double injection devices. In the same year, Dow Chemical researchers patented a method of
preparing electroluminescent cells using high voltage (500–1500 V) AC-driven (100–3000 Hz)
electrically-insulated one millimetre thin layers of a melted phosphor consisting of ground
anthracene powder, tetracene, and graphite powder. Their proposed mechanism involved
electronic excitation at the contacts between the graphite particles and the anthracene molecules.
Device performance was limited by the poor electrical conductivity of contemporary organic
materials. This was overcome by the discovery and development of highly conductive polymers.
For more on the history of such materials, see conductive polymers.

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Electroluminescence from polymer films was first observed by Roger Partridge at the National
Physical Laboratory in the United Kingdom. The device consisted of a film of poly(n-
vinylcarbazole) up to 2.2 micrometres thick located between two charge injecting electrodes. The
results of the project were patented in 1975 and published in 1983.
The first diode device was reported at Eastman Kodak by Ching W. Tang and Steven Van Slyke
in 1987. This device used a novel two-layer structure with separate hole transporting and
electron transporting layers such that recombination and light emission occurred in the middle of
the organic layer. This resulted in a reduction in operating voltage and improvements in
efficiency and led to the current era of OLED research and device production.
Research into polymer electroluminescence culminated in 1990 with J. H. Burroughes et al. at
the Cavendish Laboratory in Cambridge reporting a high efficiency green light-emitting polymer
based device using 100 nm thick films of poly(p-phenylene vinylene).
INTRODUCTION :-
Organic light emitting diodes (OLEDs) are optoelectronic devices based on small molecules or
polymers that emit light when an electric current flows through them. simple OLED consists
of a fluorescent organic layer sandwiched between two metal electrodes.Under application of
an electric field, electrons and holes are injected from the two electrodes into the organic layer,
where they meet and recombine to produce light. They have been developed for applications
in flat panel displays that provide visual imagery that is easy to read, vibrant in colors and less
consuming of power.
OLEDs are light weight, durable, power efficient and ideal for portable applications.
OLEDs have fewer process steps and also use both fewer and low-cost materials than LCD
displays. OLEDs can replace the current technology in many applications due to following
performance advantages over LCDs.
 Greater brightness
 Faster response time for full motion video
 Fuller viewing angles
 Lighter weight
 Greater environmental durability

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 More power efficiency
 Broader operating temperature ranges
 Greater cost-effectivenes
WHAT IS OLED :-
An OLED is a solid state device or electronic device that typically consists of organic
thin films sandwiched between two thin film conductive electrodes. When electrical current is
applied, a bright light is emitted. OLED use a carbon-based designer molecule that emits light
when an electric current passes through it. This is called electrophosphorescence. Even with the
layered system, these systems are thin . usually less than 500 nm or about 200 times smaller than
a human hair. When used to produce displays. OLED technology produces self-luminous
displays that do not require backlighting and hence more energy efficient. These properties result
in thin, very compact displays. The displays require very little power, ie, only 2-10 volts.
OLED technology uses substances that emit red, green, blue or white light. Without any other
source of illumination, OLED materials present bright, clear video and images that are easy to
see at almost any angle. Enhancing organic material helps to control the brightness and colour of
light.
WORKING PRINCIPLE :-
Schematic of a bilayer OLED: 1. Cathode (−), 2. Emissive Layer, 3. Emission of radiation, 4.
Conductive Layer, 5. Anode (+)

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A typical OLED is composed of a layer of organic materials situated between two electrodes, the
anode and cathode, all deposited on a substrate. The organic molecules are electrically
conductive as a result of delocalization of pi electrons caused by conjugation over all or part of
the molecule. These materials have conductivity levels ranging from insulators to conductors,
and therefore are considered organic semiconductors. The highest occupied and lowest
unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to
the valence and conduction bands of inorganic semiconductors.
Originally, the most basic polymer OLEDs consisted of a single organic layer. One example was
the first light-emitting device synthesised by J. H. Burroughes et al., which involved a single
layer of poly(p-phenylene vinylene). However multilayer OLEDs can be fabricated with two or
more layers in order to improve device efficiency. As well as conductive properties, different
materials may be chosen to aid charge injection at electrodes by providing a more gradual
electronic profile, or block a charge from reaching the opposite electrode and being wasted.Many
modern OLEDs incorporate a simple bilayer structure, consisting of a conductive layer and an
emissive layer.
During operation, a voltage is applied across the OLED such that the anode is positive with
respect to the cathode. A current of electrons flows through the device from cathode to anode, as
electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the
HOMO at the anode. This latter process may also be described as the injection of electron holes
into the HOMO. Electrostatic forces bring the electrons and the holes towards each other and
they recombine forming an exciton, a bound state of the electron and hole. This happens closer to
the emissive layer, because in organic semiconductors holes are generally more mobile than
electrons. The decay of this excited state results in a relaxation of the energy levels of the
electron, accompanied by emission of radiation whose frequency is in the visible region. The
frequency of this radiation depends on the band gap of the material, in this case the difference in
energy between the HOMO and LUMO.
As electrons and holes are fermions with half integer spin, an exciton may either be in a singlet
state or a triplet state depending on how the spins of the electron and hole have been combined.
Statistically three triplet excitons will be formed for each singlet exciton. Decay from triplet

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states (phosphorescence) is spin forbidden, increasing the timescale of the transition and limiting
the internal efficiency of fluorescent devices. Phosphorescent organic light-emitting diodes make
use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states,
thus obtaining emission from both singlet and triplet states and improving the internal efficiency.
Indium tin oxide (ITO) is commonly used as the anode material. It is transparent to visible light
and has a high work function which promotes injection of holes into the HOMO level of the
organic layer. A typical conductive layer may consist of PEDOT:PSSas the HOMO level of this
material generally lies between the workfunction of ITO and the HOMO of other commonly
used polymers, reducing the energy barriers for hole injection. Metals such as barium and
calcium are often used for the cathode as they have low work functions which promote injection
of electrons into the LUMO of the organic layer.Such metals are reactive, so require a capping
layer of aluminium to avoid degradation.
Single carrier devices are typically used to study the kinetics and charge transport mechanisms of
an organic material and can be useful when trying to study energy transfer processes. As current
through the device is composed of only one type of charge carrier, either electrons or holes,
recombination does not occur and no light is emitted. For example, electron only devices can be
obtained by replacing ITO with a lower work function metal which increases the energy barrier
of hole injection. Similarly, hole only devices can be made by using a cathode comprised solely
of aluminium, resulting in an energy barrier too large for efficient electron injection.
MATERIAL TECHNOLOGIES :-
Small molecules

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Alq3, commonly used in small molecule OLEDs.
Efficient OLEDs using small molecules were first developed by Dr. Ching W. Tang et al. at
Eastman Kodak. The term OLED traditionally refers specifically to this type of device, though
the term SM-OLED is also in use.
Molecules commonly used in OLEDs include organometallic chelates (for example Alq3, used
in the organic light-emitting device reported by Tang et al.), fluorescent and phosphorescent
dyes and conjugated dendrimers. A number of materials are used for their charge transport
properties, for example triphenylamine and derivatives are commonly used as materials for hole
transport layers. Fluorescent dyes can be chosen to obtain light emission at different
wavelengths, and compounds such as perylene, rubrene and quinacridone derivatives are often
used. Alq3 has been used as a green emitter, electron transport material and as a host for yellow
and red emitting dyes.
The production of small molecule devices and displays usually involves thermal evaporation in a
vacuum. This makes the production process more expensive and of limited use for large-area
devices than other processing techniques. However, contrary to polymer-based devices, the
vacuum deposition process enables the formation of well controlled, homogeneous films, and the
construction of very complex multi-layer structures. This high flexibility in layer design,
enabling distinct charge transport and charge blocking layers to be formed, is the main reason for
the high efficiencies of the small molecule OLEDs.
Coherent emission from a laser dye-doped tandem SM-OLED device, excited in the pulsed
regime, has been demonstrated. The emission is nearly diffraction limited with a spectral width
similar to that of broadband dye lasers.
Polymer light-emitting diodes
poly(p-phenylene vinylene), used in the first PLED.

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Polymer light-emitting diodes (PLED), also light-emitting polymers (LEP), involve an
electroluminescent conductive polymer that emits light when connected to an external voltage.
They are used as a thin film for full-spectrum colour displays. Polymer OLEDs are quite efficient
and require a relatively small amount of power for the amount of light produced.
Vacuum deposition is not a suitable method for forming thin films of polymers. However,
polymers can be processed in solution, and spin coating is a common method of depositing thin
polymer films. This method is more suited to forming large-area films than thermal evaporation.
No vacuum is required, and the emissive materials can also be applied on the substrate by a
technique derived from commercial inkjet printing. However, as the application of subsequent
layers tends to dissolve those already present, formation of multilayer structures is difficult with
these methods. The metal cathode may still need to be deposited by thermal evaporation in
vacuum.
Typical polymers used in PLED displays include derivatives of poly(p-phenylene vinylene) and
polyfluorene. Substitution of side chains onto the polymer backbone may determine the colour of
emitted light or the stability and solubility of the polymer for performance and ease of
processing.
While unsubstituted poly(p-phenylene vinylene) (PPV) is typically insoluble, a number of PPVs
and related poly(naphthalene vinylene)s (PNVs) that are soluble in organic solvents or water
have been prepared via ring opening metathesis polymerization.
Phosphorescent materials
Ir(mppy)3, a phosphorescent dopant which emits green light.

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Phosphorescent organic light emitting diodes use the principle of electrophosphorescence to
convert electrical energy in an OLED into light in a highly efficient manner, with the internal
quantum efficiencies of such devices approaching 100%.
Typically, a polymer such as poly(n-vinylcarbazole) is used as a host material to which an
organometallic complex is added as a dopant. Iridium complexes[41] such as Ir(mppy) are
currently the focus of research, although complexes based on other heavy metals such as
platinum have also been used.
The heavy metal atom at the centre of these complexes exhibits strong spin-orbit coupling,
facilitating intersystem crossing between singlet and triplet states. By using these phosphorescent
materials, both singlet and triplet excitons will be able to decay radiatively, hence improving the
internal quantum efficiency of the device compared to a standard PLED where only the singlet
states will contribute to emission of light.
Applications of OLEDs in solid state lighting require the achievement of high brightness with
good CIE coordinates (for white emission). The use of macromolecular species like polyhedral
oligomeric silsesquioxanes (POSS) in conjunction with the use of phosphorescent species such
as Ir for printed OLEDs have exhibited brightnesses as high as 10,000 cd/m2.
LIMITATIONS OF LCD-EVOLUTION OF OLED :-
Most of the limitations of LCD technology come from the fact that LCD is a non- emissive
Display device. This means that they do not emit light on their own. Thus, an LCD Operates
on the basis of either passing or blocking light that is produced by an external light Source
(usually from a backside lighting system or reflecting ambient light). Applying an electric
field across an LCD cell controls its transparency or reflectivity. A cell blocking (absorbing)
light will thus be seen as black and a cell passing (reflecting) light will be seen as white. For a
color displays, there are color filters added in front of each of the cells and a single pixel is
represented by three cells, each responsible for the basic colors: red, green and blue.
The basic physical structure of a LCD cell is shown in Figure.The liquid crystal
(LC) material is sandwiched between two polarizers and two glass plates (or between one

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glass plate and one Thin Film Transistor (TFT) layers). The polarizers are integral to the
working of the cell. Note that the LC material is inherently a transparent material, but it has a
property where its optical axis can be rotated by applying an electric field across the material.
When the LC material optical axis is made to align with the two polarizers’ axis, light will
pass through the second polarizer. On the other hand, if the optical axis is rotated 90 degrees,
light will be polarized by the first polarizer, rotated by the LC material and blocked by the
second polarizer.
Note that the polarizers and the LC material absorb light. On a typical monochrome
LCD display the polarizers alone absorb 50% of the incident light. On an active matrix display
TFT layer, the light throughput may be as low as 5% of the incident light. Such low light
output efficiency requires with a LC based displays to have a powerful backside or ambient
light illumination to achieve sufficient brightness. This causes LCD’s to be bulky and power
hungry.The LC cells are in fact relatively thin and their operation relatively power efficient. It
is the backside light that takes up most space as well as power. In fact with the advent of low
power microprocessors, the LCD module is the primary cause of short battery life in notebook
computers.
Moreover, the optical properties of the LC material and the polarizer also causes
what is known as the viewing angle effect. The effect is such that when a user is not directly in
front of the display, the image can disappear or sometime seem to invert (dark images become
light and light images become dark).
With these disadvantages of a LC based display in mind, there has been a lot of
research to find an alternative. In recent years, a large effort has been concentrated on Organic
Light Emitting Device (OLED) based displays. OLED-based displays have the potential of
being lighter, thinner, brighter and much more power-efficient than LC based displays.
Moreover, OLED-based displays do not suffer from the viewing angle effect. Organic
Optoelectronics has been an active field of research for nearly two decades. In this time device
structures and materials have been optimized, yielding a robust technology. In fact, OLEDs
have already been incorporated into several consumer electronic products. However, there are
basic properties of organic molecules, especially their instability in air, that hamper the
commercialization of the technology for high quality displays.

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ORGANIC LED AND LIQUID CRYSTAL DISPLAY COMPARISON :-
An organic LED panel Liquid crystal Panel
A luminous form Self emission of light Back light or outside
light is necessary
Consumption of Electric It is lowered to about It is abundant when back
power mW though it is a little light is used
higher than the
reflection type liquid
crystal panel
Colour Indication form The flourscent material A colour filter is used.
of RGB is arranged in
order and or a colour
filter is used.
High brightness 100 cd/m2 6 cd/m2
The dimension of the Several-inches type in It is produced to 28-inch
panel the future to about 10- type in the future to 30-
inch type.Goal inch type.Goal
Contrast 100:14 6:1
The thickness of the It is thin with a little When back light is used
panel over 1mm it is thick with 5mm.

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The mass of panel It becomes light weight With the one for the
more than 1gm more portable telephone.10 gm
than the liquid crystal weak degree.
panel in the case of one
for portable telephone
Answer time Several us Several ns
A wide use of 86 *C ~ -40 *C ~ -10 *C
temperature range
The corner of the view Horizontal 180 * Horizontal 120* ~ 170*
OLED COMPONENTS :-
Like an LED, an OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick
or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers
of organic material; in the latter design, the third layer helps transport electrons from the cathode
to the emissive layer. In this article, we'll be focusing on the two-layer design.

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An OLED consists of the following parts:
 Substrate (clear plastic, glass, foil) - The substrate supports the OLED.
 Anode (transparent) - The anode removes electrons (adds electron "holes") when a
current flows through the device.
 Cathode (may or may not be transparent depending on the type of OLED) - The cathode
injects electrons when a current flows through the device.
 Organic layers - These layers are made of organic molecules or polymers.
 Conducting layer - This layer is made of organic plastic molecules that transport
"holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
 Emissive layer - This layer is made of organic plastic molecules (different ones
from the conducting layer) that transport electrons from the cathode; this is where
light is made. One polymer used in the emissive layer is polyfluorene.
MAKING OLED :-
The biggest part of manufacturing OLEDs is applying the organic layers to the substrate.
This can be done in three ways:
1.Vacuum deposition or vacuum thermal evaporation(VTE):
In a vacuum chamber, the organic molecules are gently heated(evaporated) and allowed to
condense as thin films onto cooled substrates. This process is very expensive and inefficient.
2.Organic vapour phase deposition
In a low pressure, hot-walled reactor chamber, a carrier gas transports evaporated organic
molecules onto cooled substrates, where they condense into thin films. Using a carrier gas
increases the efficiency and reduces the cost of making OLEDs.

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The OVPD process employs an inert carrier gas to a precisely transfer films of organic
material onto a cooled substrate in a hot-walled, low pressure chamber. The organic materials are
stored in external, separate, thermally-controlled cells .Once evaporated from these heated cells,
the materials are entrained and transported by an inert carrier gas such as nitrogen, using gas
flow rate, pressure and temperature as process control variables. The materials deposit down
onto the cooled substrate from a manifold located only several centimeters above the substrate.
Usually we go for this method.
However, 100% of the excitons can be converted into light using a process known
as electrophosphorescence.Thus. the efficiency of an OLED is up to four times
higher than that of a conventional OLED
Higher deposition rates :- Deposition rates with OVPD can be several times higher than
the rate for conventional VTE processes because the OVPD deposition rate is primarily
controlled by the How of the carrier gas.

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Higher materials utilization :- Because the organic materials do not deposit on the heated
surfaces of the chamber, materials' utilization is much better than with VTE where the materials
deposit everywhere. This feature should translate into lower raw material cost, less downtime
and higher production throughput
Better device performance :- The OVPD process can provide better film thickness control
and uniformly over larger areas than VTE. With three variable process control, OVPD offers
more precise deposition rates and doping control at very low levels. As a result, sharper or
graded layer interfaces can be more easily achieved. In addition, multiple materials can be co-
deposited in one chamber without the cross-contamination problems commonly experienced in
VTE systems.
Shadow mask patterning :- OVPD offers better shadow mask-to-substrate distance control
than is possible with VTE up-deposition. Because the mask is above, instead of below the
substrate, its thickness can be dictated by the desired pattern shape rather than the need for
rigidity. Thus precise, reproducible pixel profiles can be obtained.
Larger substrate sizes :- Because the Aixtron AG-proprietary showerhead can be designed
to maintain a constant source-to-substrate distance, OVPD may be more readily scaled to larger
substrate sizes. This also may render OVPD more adaptable to in-line and roll-to-roll processing
for flexible displays.

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3. Inkjet printing
With inkjet technology, OLEDs are sprayed onto substrates just like inks are sprayed onto paper
during printing. Inkjet technology greatly reduces the cost of OLED manufacturing and allows
OLEDs to be printed onto very large dims for large displays like 80 inch TV screens or
electronic billboards
OPERATION :-
How do OLEDs emit light?
OLEDs emit light in a similar manner to LEDs. through a process called
electrophosphorescence
The process is as follows:
1. The battery or power supply of the device containing the OLED applies a voltage across
the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers(an
electrical current is a flow of electrons)
• The cathode gives electrons to the emissive layer of organic molecules.
• The anode removes electrons from the conductive layer of organic molecules.(This is the
equivalent to giving electron holes to the conductive layer)
3. At the boundary between the emissive and the conductive
layers, electrons find electron holes.
• When an electron finds an electron hole, the electron fills the hole (it falls into an energy
level of the atom that is missing an electron).
• When this happens, the electron gives up energy in the form of a photon of light.

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4. The OLED emits light.
5.The color of the light depends on the type of organic molecule in the emissive layer.
Manufacturers place several types of organic films on the same OLED to make color displays.
6. The intensit y or brightness of the light depends on the amount of electrical
current applied. The more the current, the brighter the light

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When electricit y is applied to OLED, charge carriers (holes and electrons) are
injected from the electrodes into the organic thin films.They migrate through the
device under the influence of an electrical field. The charge carriers then
recombine, forming excitons. In conventional LED onl y about 25% of these
excitons could generate light, with the remaining 75% lost as heat. This was
known as fluorescent emission.
Types of OLEDs :-
There are several types of OLEDs:
 Passive-matrix OLED
 Active-matrix OLED
 Transparent OLED
 Top-emitting OLED
 Foldable OLED
 White OLED
Each type has different uses. In the following sections, we'll discuss each type of OLED. Let's
start with passive-matrix and active-matrix OLEDs.
Passive-matrix OLED (PMOLED) :-
PMOLEDs have strips of cathode, organic layers and strips of anode. The anode strips are
arranged perpendicular to the cathode strips. The intersections of the cathode and anode make up
the pixels where light is emitted. External circuitry applies current to selected strips of anode and
cathode, determining which pixels get turned on and which pixels remain off. Again, the
brightness of each pixel is proportional to the amount of applied current.
PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly
due to the power needed for the external circuitry. PMOLEDs are most efficient for text and

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icons and are best suited for small screens (2- to 3-inch diagonal) such as those you find in CELL
PHONES,PDA’s and MP3 Players. Even with the external circuitry, passive-matrix OLEDs
consume less battery power than the LCDs that currently power these devices.
Active-matrix OLED (AMOLED) :-
AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer
overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the
circuitry that determines which pixels get turned on to form an image.

22.
AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than
external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh
rates suitable for video. The best uses for AMOLEDs are computer monitors, large-screen TVs
and electronic signs or billboards.
Transparent OLED :-
Transparent OLEDs have only transparent components (substrate, cathode and anode) and, when
turned off, are up to 85 percent as transparent as their substrate. When a transparent OLED
display is turned on, it allows light to pass in both directions. A transparent OLED display can be
either active- or passive-matrix. This technology can be used for heads-up displays.

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Top-emitting OLED :-
Top-emitting OLEDs have a substrate that is either opaque or reflective. They are best suited to
active-matrix design. Manufacturers may use top-emitting OLED displays in SMART CARDS.

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Foldable OLED :-
Foldable OLEDs have substrates made of very flexible metallic foils or plastics. Foldable
OLEDs are very lightweight and durable. Their use in devices such as cell phones and PDAs can
reduce breakage, a major cause for return or repair. Potentially, foldable OLED displays can be
attached to fabrics to create "smart" clothing, such as outdoor survival clothing with an
integrated computer chip, cell phone, GPS receiver and OLED display sewn into it.

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White OLED :-
White OLEDs emit white light that is brighter, more uniform and more energy efficient than that
emitted by fluorescent lights. White OLEDs also have the true-color qualities of incandescent
lighting. Because OLEDs can be made in large sheets, they can replace fluorescent lights that are
currently used in homes and buildings. Their use could potentially reduce energy costs for
lighting.In the next section, we'll discuss the pros and cons of OLED technology and how it
compares to regular LED and LCD technology.
ADVANTAGES :-
The different manufacturing process of OLEDs lends itself to several advantages over flat-panel
displays made with LCD technology.
 Lower cost in the future: OLEDs can be printed onto any suitable substrate by an inkjet
printer or even by screen printing, theoretically making them cheaper to produce than
LCD or plasma display. However, fabrication of the OLED substrate is more costly than
that of a TFT LCD, until mass production methods lower cost through scalability.
 Light weight & flexible plastic substrates: OLED displays can be fabricated on flexible
plastic substrates leading to the possibility of flexible organic light-emitting diodes being
fabricated or other new applications such as roll-up displays embedded in fabrics or
clothing.
 Wider viewing angles & improved brightness: OLEDs can enable a greater artificial
contrast ratio (both dynamic range and static, measured in purely dark conditions) and
viewing angle compared to LCDs because OLED pixels directly emit light.
 Better power efficiency: LCDs filter the light emitted from a back light

 Response time: OLEDs can also have a faster response time than standard LCD screens.

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DISADVANTAGES :-
 Outdoor performance: As an emissive display technology, OLEDs rely completely
upon converting electricity to light, unlike most LCDs which are to some extent reflective
 Power consumption: While an OLED will consume around 40% of the power of an
LCD displaying an image
 Screen burn-in: Unlike displays with a common light source, the brightness of each
OLED pixel fades depending on the content displayed. The varied lifespan of the organic
dyes can cause a discrepancy between red, green, and blue intensity. This leads to image
persistence, also known as burn in
 UV sensitivity: OLED displays can be damaged by prolonged exposure to UV light. The
most pronounced example of this can be seen with a near UV laser (such as a Bluray
pointer) and can damage the display almost instantly with more than 20mW leading to
dim or dead spots where the beam is focused.
 Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000
hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours
 Manufacturing - Manufacturing processes are expensive right now.
 Water - Water can easily damage OLEDs.
Current and Future OLED Applications :-
Currently, OLEDs are used in small-screen devices such as
cell phones
OLED display for Sony Clie
Kodak was the first to release a digital camera with an OLED display in March 2003, the
EasyShare LS633

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Kodak LS633 EasyShare with OLED display
Several companies have already built prototype computer monitors and large-screen TVs that use
OLED technology. In May 2005, Samsung Electronics announced that it had developed a
prototype 40-inch, OLED-based, ultra-slim TV, the first of its size .And in October 2007, Sony
announced that it would be the first to market with an OLED television. The XEL-1 will be
available in December 2007 for customers in Japan. It lists for 200,000 Yen -- or about $1,700
U.S.
Photo Courtesy Sony
The Sony 11-inch XEL-1 OLED TV.
Research and development in the field of OLEDs is proceeding rapidly and may lead to future
applications in heads-up displays, automotive dashboards, billboard-type displays, home and
office lighting and flexible displays. Because OLEDs refresh faster than LCDs -- almost 1,000
times faster -- a device with an OLED display could change information almost in real time.

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Video images could be much more realistic and constantly updated. The newspaper of the future
might be an OLED display that refreshes with breaking news and like a regular newspaper, you
could fold it up when you're done reading it and stick it in your backpack or briefcase.
EFFICIENCY OF OLED :-
Recent advantages in boosting the efficiency of OLED light emission have led to the
possibility that OLEDs will find early uses in many battery-powered electronic appliances
such as cell phones, game boys and personal digital assistants. Typical external quantum
efficiencies of OLEDs made using a single fluorescent material that both conducts electrons
and radiates photons are greater than 1 percent. But by using guest-host organic material
systems where the radiative guest fluorescent or phosphorescent dye molecule is doped at low
concentration into a conducting molecular host thin film, the efficiency can be substantially
increased to 10 percent or higher for phosphorescence or up to approximately 3 percent for
fluorescence. Currently, efficiencies of the best doped OLEDs exceed that of incandescent
light bulbs. Efficiencies of 20 lumens per watt have been reported for yellow-green-emitting
polymer devices and 40 lm/W for a typical incandescent light bulb. It is reasonable to that of
fluorescent room lighting will be achieved by using phosphorescent OLEDs.
The green device which shows highest efficiency is based on factris(2-
phenylpyridine) iridium[Ir(PPY)3],a green electro phosphorescent material. Thus
phosphorescent emission originates from a long-lived triplet state.
THE ORGANIC FUTURE :-
The first products using organic displays are already being introduced into the
market place. And while it is always difficult to predict when and what future products will be
introduced, many manufacturers are now working to introduce cell phones and personal digital
assistants with OLED displays within the next one or two years. The ultimate goal of using
high-efficiency, phosphorescenct, flexible OLED displays in lap top computers and even for
home video applications may be no more than a few years into future.
However, there remains much to be done if organics are to establish a foothold in
the display market. Achieving higher efficiencies, lower operating voltages, and lower device

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life times are all challenges still to be met. But, given the aggressive world wide efforts in this
area, emissive organic thin films have an excellent chance of becoming the technology of
choice for the next generation of high-resolution, high-efficiency flat panel displays.
In addition to displays, there are many other opportunities for application of organic
thin-film semiconductors, but to date these have remained largely untapped. Recent results in
organic electronic technology that may soon find commercial outlets in display black planes
and other low-cost electronics.
CONCLUSION :-
Performance of organic LEDs depend upon many parameters such as electron and
hole mobility, magnitude of applied field, nature of hole and electron transport layers and
excited life-times. Organic materials are poised as never before to transform the world IF
circuit and display technology. Major electronics firms are betting that the future holds
tremendous opportunity for the low cost and sometimes surprisingly high performance
offered by organic electronic and optoelectronic devices.
Organic Light Emitting Diodes are evolving as the next generation of light sources.
Presently researchers have been gong on to develop a 1.5 emitting device. This wavelength is
of special interest for telecommunications as it is the low-loss wavelength for optical fibre
communications. Organic full-colour displays may eventually replace liquid crystal displays
for use with lap top and even desktop computers. Researches are going on this subject and it is
sure that OLED will emerge as future solid state light source.