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1.INTRODUCTION

An OLED(organic light-emitting diode) is a light-emitting diode (LED) in which

the emissive electroluminescent layer is a film oforganic compound which emits

light in response to an electric current. This layer of organic semiconductoris

situated between two electrodes. Generally, at least one of these electrodes is

transparent. OLEDs are used to create digital displays in devices such as

television screens, computer monitors, portable systems such as mobile

phones, handheld games consoles and PDAs.

An OLED display consists of very thin sandwiched layers of materials. When an

electric current is supplied, the negatively charged electrons in the cathode layermove through the organic substances towards the positively charged anode

layer. The reverse happens from the anode's side, as positively charged

electrons are drawn towards the cathode leaving holes in the conductive

material. These positively charged holes jump to the organic material to

recombine with electrons, which causes electroluminescent light. The chemical

composition of the organic material dictates which colors of light are produced

Contents.

FIG.1. Basic OLED diagram

Organic light emitting diodes (OLEDs) offer great promise in displays of all sizes

and shapes, and in both commercial and home lighting solutions. OLEDs, ororganic electro-luminescent (OEL) devices as some call them, are already in use

as mobile device displays and mobile phone displays. Prototype large screen

and HD OLED televisions always draw the eye away from any other model

regardless of its size. In addition OLED technology lends itself to innovative solid-

state lighting, as well as flexible lighting solutions and flexible displays, even

displays based on organic TFTs.
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OLED-A provides a forum for the interchange of technical and market

information. Our membership includes companies involved in small-molecule

OLED technology and polymer technology (PLED or light-emitting polymers).OLED-A serves its membership by fostering the more rapid development of

OLED technology and OLED products; serving as a resource on OLED markets

and products for media and investors; functioning as a catalyst in the

development of standards for OLEDs; and providing a forum to promote and

market OLED technology products.

OLEDs are used in television screens, computer monitors, small, portable

system screens such as mobile phones and PDAs, watches, advertising,

information, and indication. OLEDs are also used in light sources for space

illumination and in large-area light-emitting elements. Due to their early stage ofdevelopment, they typically emit less light per unit area than inorganic solid-state

based LED point-light sources.

There are two main families of OLEDs: those based on small molecules and

those employing polymers. Adding mobile ions to an OLED creates a light-

emitting electrochemical cell or LEC, which has a slightly different mode of

operation. OLED displays can use eitherpassive-matrix (PMOLED) oractive-

matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film

transistorbackplane to switch each individual pixel on or off, but allow for higher

resolution and larger display sizes.

An OLED display works without a backlight. Thus, it can display deep black

levels and can be thinner and lighter than a liquid crystal display (LCD). In low

ambient light conditions such as a dark room an OLED screen can achieve a

highercontrast ratio than an LCD, whether the LCD uses cold cathode

fluorescent lamps orLED backlight.
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2.HISTORY OF OLED DISPLAY

Fig.2.Sony XEL-1, the world's first OLED TV.

The first observations ofelectroluminescence in organic materials were in the

early 1950s by Andr Bernanose and co-workers at the Nancy-Universit,

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 ofanthracene and

on anthracene crystals doped with tetracene in 1963using a small area silver

electrode at 400 V. The proposed mechanism was field-accelerated electron

excitation of molecular fluorescence.

Pope's group reported in 1965that 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
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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(5001500 V) AC-driven (1003000 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.

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 1975and

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

ofpoly(p-phenylenevinylene).
http://en.wikipedia.org/wiki/Dow_Chemicalhttp://en.wikipedia.org/wiki/Tetracenehttp://en.wikipedia.org/wiki/Conductive_polymershttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/N-Vinylcarbazolehttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/Steven_Van_Slykehttp://en.wikipedia.org/wiki/Cavendish_Laboratoryhttp://en.wikipedia.org/wiki/Poly(p-phenylene_vinylene)http://en.wikipedia.org/wiki/Poly(p-phenylene_vinylene)http://en.wikipedia.org/wiki/Cavendish_Laboratoryhttp://en.wikipedia.org/wiki/Steven_Van_Slykehttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/N-Vinylcarbazolehttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/Conductive_polymershttp://en.wikipedia.org/wiki/Tetracenehttp://en.wikipedia.org/wiki/Dow_Chemical


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3.OLED Components

FIG.3. OLED structure

Like an LED, an OLED is a solid-state semiconductordevice 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.

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.

Organic layers - These layers are made of organic molecules or polymers.
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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.

Cathode (may or may not be transparent depending on the type of OLED) - The

cathode injects electrons when a current flows through the device.

The biggest part of manufacturing OLEDs is applying the organic layers to the

substrate. This can be done in three ways:

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 expensive and

inefficient.

Organic vapor phase deposition (OVPD) - 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.

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 largefilms for large displays like 80-inch TV screens or electronic billboards.
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4.How do OLEDs Emit Light?

FIG.4. OLED creating light

OLEDs emit light in a similar manner to LEDs, through a process

calledelectrophosphorescence.

The process is as follows:

The battery or power supply of the device containing the OLED applies a voltageacross the OLED.

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.)
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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's missing an electron). When thishappens, the electron gives up energy in the form of a photon of light (see How

Light Works).

The OLED emits light.

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.

The intensity or brightness of the light depends on the amount of electrical

current applied: the more current, the brighter the light.

5.WORKING OF OLED

FIG.5.Schematic of a bilayer OLED:

1. Cathode () 2. Emissive Layer.3. Emission of radiation.4. Conductive Layer 5.

Anode (+).

A typical OLED is composed of a layer of organic materials situated between two

electrodes, the anodeand cathode, all deposited on a substrate. The organic

molecules are electrically conductive as a result ofdelocalization ofpi

electrons caused by conjugation over all or part of the molecule. These materials
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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 semiconductorsare 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 synthesized by J. H. Burroughs et

al., which involved a single layer ofpoly(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. More recent

developments in OLED architecture improves quantum efficiency (up to 19%) by

using a graded heterojunction. In the graded heterojunction architecture, the

composition of hole and electron-transport materials varies continuously within

the emissive layer with a dopant emitter. The graded heterojunction architecture

combines the benefits of both conventional architectures by improving charge

injection while simultaneously balancing charge transport within the emissive

region.

During operation, a voltage is applied across the OLED such that the anode ispositive with respect to the cathode. A current ofelectrons 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 ofelectron 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 ofradiation 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 integerspin, 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
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for each singlet exciton. Decay from triplet states (phosphorescence) is spin

forbidden, increasing the timescale of the transition and limiting the internal

efficiency of fluorescent devices. Phosphorescent organic light-emittingdiodes make use ofspinorbit 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

ofPEDOT: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 areoften used for the cathode as they have low work functionswhich promote

injection of electrons into the LUMO of the organic layer. Such metals are

reactive, so they require a capping layer ofaluminium 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 energybarrier 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.

6.TYPES OF OLED

6.1.Classification according to Organic Material used
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Small molecules

FIG.6.structure ofAlq3

Efficient OLEDs using small molecules were first developed by Dr. Ching W.

Tang et al. at Eastman Kodak. The term OLED traditionally refers specifically tothis 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.[30]

Alq3 hasbeen 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
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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 beformed, 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

FIG.7. poly(p-phenylenevinylene

Polymer light-emitting diodes (PLED), also light-emitting polymers (LEP), involve

an electroluminescent conductive polymerthat emits light when connected to an

external voltage. They are used as a thin film forfull-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 coatingis 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
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thermal evaporation in vacuum. An alternative method to vacuum deposition is to

deposit a Langmuir-Blodgett film.

Typical polymers used in PLED displays include derivatives ofpoly(p-

phenylenevinylene) 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 unsubstitutedpoly(p-phenylenevinylene) (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

FIG.8. Ir(mppy)3, a phosphorescent dopant which emits green light.

Phosphorescent organic light emitting diodes use the principle of electro

phosphorescence 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 complexessuchas Ir(mppy)3are currently the focus of research, although complexes based on

other heavy metals such as platinumhave also been used.

The heavy metal atom at the centre of these complexes exhibits strong spin-orbit

coupling, facilitating intersystem crossing between singlet andtriplet 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
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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 oligomericsilsesquioxanes (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.

6.2.Classification according to Transparency

Transparent OLED

FIG.9. OLED transparent structure

Transparent OLEDs have only transparent components (substrate, cathode and

anode) and, when turned off, are up to 85 percent as transparent as their
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OLED DISPLAY


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.

Top-emitting OLED

FIG.10. OLED Top-Emitting Structure

Top-emitting OLEDs have a substrate that is either opaque or reflective. Theyare best suited to active-matrix design. Manufacturers may use top-emitting

OLED displays insmart cards

6.3.Foldable OLED
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FIG.11. Demonstration of a flexible OLED device

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

6.4.CLASSIFICATION ACCORDING TO PIXEL FORMATION USED

Passive-matrix OLED (PMOLED)
http://en.wikipedia.org/wiki/File:OLED_EarlyProduct.JPG


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FIG.12. Passive-matrix OLED

PMOLED means Passive Matrix Organic light emitting diode. Like the first LCDs

to be commercialized, the first OLEDs to reach the marketplace in the late 1990s

used a passivematrix drive configuration. Passive-matrix OLEDs are particularly

well suited for small-area display applications, such as cell phones and

automotive audio applications. Universal Display Corporations PHOLED

materials and technology are currently incorporated in a commercialpassive-

matrix OLED display product that is manufactured and sold by Pioneer Tohoku

Corporation for use in a cell phone product (shown above) and under evaluation

for a number of other products. Universal Display Corporation has designed and

fabricated several passive matrix OLED prototypes to demonstrate the

performance of its PHOLED technology and materials. The prototype shown here

is a 128 x 64 pixel display built on a glass substrate usingour green and redPHOLED materials system.

OLED displays are activated through a current driving method that relies on

either a passive-matrix (PM) or an active-matrix (AM) scheme. In a

PMOLEDdisplay, a matrix of electrically-conducting rows and columns forms a


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OLED DISPLAY


two-dimensional array of picture elements called pixels. Sandwiched between the

orthogonal column and row lines, thin films of organic material are activated to

emit light by applying electrical signals to designated row and column lines. Themore current that is applied, the brighter the pixel becomes. For a full image,

each row of the display must be charged for 1/N of the frame time needed to

scan the entire display, where N is the number of rows in the display. For

example, to achieve a 100-row display image with brightness of 100 nits, the

pixels must be driven to the equivalent of an instantaneous brightness of 10,000

nits for 1/100 of the entire frame time.

While PMOLEDs are fairly simple structures to design and fabricate, they

demand relatively expensive, current-sourced drive electronics to operate

effectively. In addition, their power consumption is significantly higher than that

required by a continuous charge mode in an active-matrix OLED. When

PMOLEDs are pulsed with very high drive currents over a short duty cycle, they

do not typically operate at their intrinsic peak efficiency. These inefficiencies

come from the characteristics of the diode itself, as well as power losses in the

row lines. Power analyses have shown that PMOLED displays are most practical

in sizes smaller than 2to 3 in diagonal, or having less than approximately 100row lines. PMOLEDs make great sense for many such display applications,

including cell phones, MP3 players and portable games.

Active-matrix OLED (AMOLED)


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FIG.13. Active-matrix OLED

Active-matrix OLED displays provide the same beautiful video-rate performance

as their passive-matrix OLED counterparts, but they consume significantly less

power. This advantage makes active-matrix OLEDs especially well suited for

portable electronics where battery power consumption is critical and for displays

that are larger than 2 to 3 in diagonal, as shown in this ultra -thin Sony prototype

above.

An active-matrix OLED (AMOLED) display consists of OLED pixels that have

been deposited or integrated onto a thin film transistor (TFT) array to form a

matrix of pixels that illuminate light upon electrical activation. In contrast to a

PMOLED display, where electricity is distributed row by row, the active-matrix

TFT backplane acts as an array of switches that control the amount of current

flowing through each OLED pixel. The TFT array continuously controlsthe current

that flows to the pixels, signaling to each pixel how brightly to shine. Typically,

this continuous current flow is controlled by at least two TFTs at each pixel, one

to start and stop the charging of a storage capacitor and the second to provide a

voltage source at the level needed to create a constant current to the pixel. As a


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result, the AMOLED operates at all times (i.e., for the entire frame scan),

avoiding the need for the very high currents required for passive matrix

operation.

Stacked OLEDs

Stacked OLEDs use a pixel architecture that stacks the red, green, and blue

subpixels on top of one another instead of next to one another, leading to

substantial increase ingamut and color depth, and greatly reducing pixel gap.

Currently, other display technologies have the RGB (and RGBW) pixels mapped

next to each other decreasing potential resolution.

Inverted OLED

In contrast to a conventional OLED, in which the anode is placed on the

substrate, an Inverted OLED uses a bottom cathode that can be connected to the

drain end of an n-channel TFT especially for the low cost amorphous silicon TFT

backplane useful in the manufacturing ofAMOLED displays..

6.5.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 ofincandescent 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.

7.ADVANTAGES
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IMPROVED BRIGHTNESS

It has a higher contrast ratio or improved brightness than TFT or LCD display

under all the environment conditions.

Condition OLED TFT-LCD

Dark

room> 10,000 : 1 300 : 1

Rainy 400 130

Cloudy 190 10

Sunlight 50 4

Light weight & flexible plastic substrates

OLED displays can be fabricated on flexible plastic substrates leading to the

possibility offlexible organic light-emitting diodes being fabricated or other new

applications such as roll-up displays embedded in fabrics or clothing. As the

substrate used can be flexible such as PET, the displays may be produced

inexpensively.
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OLED DISPLAY


Wider viewing angles & improved brightness

FIG.14. Comparision between viewing angle of OLED and LCD

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. OLED pixel colours appear correct and

unshifted, even as the viewing angle approaches 90 from normal.
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OLED DISPLAY


Better power efficiency

LCDs filter the light emitted from a backlight, allowing a small fraction of light

through so they cannot show true black, while an inactive OLED element does

not produce light or consume power.

Response time
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FIG.15. response graph of OLED and TFT display

OLEDs can also have a faster response time than standard LCD screens.

Whereas LCD displays are capable of between 2 and 16 ms response

time offering a refresh rate of 60 to 480 Hz, an OLED can theoretically have less

than 0.01 ms response time, enabling up to 100,000 Hz refresh rate.
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8.DISADVANTAGES

Current costs

OLED manufacture currently requires process steps that make it extremely

expensive. Specifically, it requires the use of Low-Temperature Polysilicon

backplanes; LTPS backplanes in turn require laser annealing from an amorphous

silicon start, so this part of the manufacturing process for AMOLEDs starts with

the process costs of standard LCD, and then adds an expensive, time-

consuming process that cannot currently be used on large-area glass substrates.

Lifespan

The biggest technical problem for OLEDs was the limited lifetime of the organic

materials. In particular, blue OLEDs historically have had a lifetime of around

14,000 hours to half original brightness (five years at 8 hours a day) when used

for flat-panel displays. This is lower than the typical lifetime of LCD, LED

orPDP technologyeach currently rated for about 25,00040,000 hours to half

brightness, depending on manufacturer and model. However, some

manufacturers' displays aim to increase the lifespan of OLED displays, pushing

their expected life past that of LCD displays by improving light outcoupling, thus

achieving the same brightness at a lower drive current. In 2007, experimental

OLEDs were created which can sustain 400 cd/m2 ofluminance for over 198,000

hours for green OLEDs and 62,000 hours for blue OLEDs.

Color balance issues

Additionally, as the OLED material used to produce blue light degrades

significantly more rapidly than the materials that produce other colors, blue light

output will decrease relative to the other colors of light. This variation in the

differential color output will change the color balance of the display and is much
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OLED DISPLAY


more noticeable than a decrease in overall luminance.This can be partially

avoided by adjusting colour balance but this may require advanced control

circuits and interaction with the user, which is unacceptable for some users.Morecommonly, though, manufacturers optimize the size of the R, G and B subpixels

to reduce the current density through the subpixel in order to equalize lifetime at

full luminance. For example, a blue subpixel may be 100% larger than the green

subpixel. The red subpixel may be 10% smaller than the green.

Efficiency of blue OLEDs

Improvements to the efficiency and lifetime of blue OLEDs is vital to the success

of OLEDs as replacements for LCD technology. Considerable research has been

invested in developing blue OLEDs with high external quantum efficiency as well

as a deeper blue color. External quantum efficiency values of 20% and 19% have

been reported for red (625 nm) and green (530 nm) diodes,

respectively. However, blue diodes (430 nm) have only been able to achieve

maximum external quantum efficiencies in the range of 4% to 6%.

Water damage

Water can damage the organic materials of the displays. Therefore, improved

sealing processes are important for practical manufacturing. Water damage mayespecially limit the longevity of more flexible displays.

Outdoor performance


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OLED DISPLAY


As an emissive display technology, OLEDs rely completely upon converting

electricity to light, unlike most LCDs which are to some extent reflective; e-

ink leads the way in efficiency with ~ 33% ambient light reflectivity, enabling the

display to be used without any internal light source. The metallic cathode in an

OLED acts as a mirror, with reflectance approaching 80%, leading to poor

readability in bright ambient light such as outdoors. However, with the proper

application of a circular polarizer and anti-reflective coatings, the diffuse

reflectance can be reduced to less than 0.1%. With 10,000fcincident illumination

(typical test condition for simulating outdoor illumination), that yields an

approximate photopic contrast of 5:1.

Power consumption

While an OLED will consume around 40% of the power of an LCD displaying an

image which is primarily black, for the majority of images it will consume 6080%

of the power of an LCD: however it can use over three times as much power to

display an image with a white background such as a document or website.This

can lead to reduced real-world battery life in mobile devices when whitebackgrounds are used

9.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 power It is lowered to about

mW though it is a

little higher than the

reflection type liquid

crystal panel

It is abundant when back

light is used
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OLED DISPLAY


Colour Indication form The flourscent

material of RGB is

arranged in orderand or a colour filter

is used.

A colour filter is used.

High brightness 100 cd/m 6 cd/m

The dimension of the panel Several-inches type

in the future to about

10-inch type.Goal

It is produced to 28-inch type

in the future to 30-inch

type.Goal

Contrast 100:14 6:1

The thickness of the panel It is thin with a little

over 1mm

When back light is used it is

thick with 5mm.

The mass of panel It becomes light

weight more than

1gm more than the

liquid crystal

With the one for the portable

telephone.10 gm weak

degree.

Answer time Several us Several ns

A wide use of temperature

range

86 *C ~ -40 *C ~ -10 *C

The corner of the view Horizontal 180 * Horizontal 120* ~ 170*

10.APPLICATIONS OF OLED DISPLAY

10.1.Manufacturers and commercial uses


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OLED DISPLAY


FIG.16. A 3.8 cm (1.5 in) OLED display from a CreativeZEN Vmedia player

OLED technology is used in commercial applications such as displays for mobile

phones and portable digital media players, car radios and digital camerasamong

others. Such portable applications favor the high light output of OLEDs for

readability in sunlight and their low power drain. Portable displays are also used

intermittently, so the lower lifespan of organic displays is less of an issue.

Prototypes have been made of flexible and rollable displays which use OLEDs'

unique characteristics. Applications in flexible signs and lighting are also beingdeveloped. Philips Lightinghave made OLED lighting samples under the brand

name 'Lumiblade' available online.

FIG.17.DELL MOBILES
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OLED DISPLAY


FIG.18.LAPTOP WITH OLED DISPLAY

OLEDs have been used in most Motorola and Samsung colour cell phones, as

well as some HTC, LG and Sony Ericsson models. Nokia has also recently

introduced some OLED products including the N85 and the N86 8MP, both ofwhich feature an AMOLED display. OLED technology can also be found in digital

media players such as the Creative ZEN V, the iriver clix, the Zune HD and the

Sony Walkman X Series.

The Google and HTC Nexus One Smartphone includes an AMOLED screen, as

does HTC's own Desire and Legend phones. However due to supply shortages

of the Samsung-produced displays, certain HTC models will use

Sony's SLCD displays in the future, while the Google and Samsung Nexus

S Smartphone will use "Super Clear LCD" instead in some countries.

Other manufacturers of OLED panels include Anwell Technologies Limited,Chi

Mei Corporation, LG, and others.

FIG.19.SAMSUNG OLED TV

DuPont stated in a press release in May 2010 that they can produce a 50-inch

OLED TV in two minutes with a new printing technology. If this can be scaled up

in terms of manufacturing, then the total cost of OLED TVs would be greatly
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reduced. Dupont also states that OLED TVs made with this less expensive

technology can last up to 15 years if left on for a normal eight hour day.

10.2.Military Application

FIG.20.THE NEAR EYE

MICRODISPLAY

Low-power Organic Light Emitting Diode (OLED) displays are used in a growing

numbers of applications supporting dismounted soldiers and commanders in

situational awareness, thermal imaging, simulation and training. Two types of

OLED applications are currently under various phases of maturation the near-

eye microdisplays, developed by eMagin and Flexible OLED developed by

Universal Display Corp. (UDC).

OLED technology promises to revolutionize everything known about information

display, from video walls, to dynamic pricing in supermarkets. For the military,

Top-emitting OLED (TOLED) applications could include wrist-mounted,

featherweight, rugged PDAs and wearable electronic displays such as "display

sleeves" Other applications could be conformed, high-contrast automotive

instrument panels, windshield displays and visor mounted displays to be used by

for pilots, drivers and divers, etc. More futuristic applications could be utilized in

camouflage systems, "smart" light emitting windows/shades etc.

Until 2005, OLEDs were used primarily for testing. Yet, in 2004 and mostly by

2005, this technology is being integrated in more military systems and on the

long run is expected to replace most small form-factor LCD displays. Among the

applications where OLED technology is already maturing are near-eye displays

of virtual images When projected on a head mounted, helmet mounted or visor

(see-through) display, such image appears like an image in a movie theater or on

a computer monitor, but is created using magnifying optics from a very small

display near to the eye. Such an image displayed with very high resolution, can
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OLED DISPLAY


appear solid and real, or made see-through depending on the type optics used.

Military and industrial customers are moving from the testing and evaluationphase into deployment. According to Kenneth Geyer, vice president of

development at Liteye Systems Inc, the company has ordered OLEDs in

production quantities, to supply orders received from military users in the USA,

Europe and Australia. Several systems have also been deployed to war fighters

in Iraq. "We anticipate additional programs moving into deployment phases in

2006 - 2007" said Geyer. Other users of OLED displays include SaabTech,

integrating eMagin's OLED into the prototype

Soldier.

10.3.Application of OLED Module in Intelligent Traffic Control System

OLED display module was used as a man-machine interface in the traffic signal

system. In this design, the OLED display realizes the 12864 pixels of picture

and character monochrome display with 16 gray-scales. The intelligent traffic

signal system with OLED display not only can provide good man-machine

interface, and adapt to the harsh outdoor environment, but also can achieve

multi-phase and multi-time control of traffic flow. The intelligent traffic signal

system with OLED display uses the ARM9 as processor, so a scientific algorithm

can be embedded in it to carry out effective control of traffic flow.

10.4.As a source of light


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OLED DISPLAY


FIG.21. Source of Lighting That Evenly Illuminates Wide Surface Areas

Until now, spaces have been illuminated by point or linear light sources, such as

incandescent light bulbs and fluorescent lamps. OLED lighting, in contrast, has

characteristics not found in conventional lighting, emitting a uniform light from thewhole surface, over a large area. Moreover, OLED lighting closely resembles

natural light. Not only that, it does not include ultraviolet rays, which reduces

negative impact on the eye.

10.5.PORTABLE DEVICES DISPLAY


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OLED DISPLAY


FIG.22.Lightweight, Thin, Flexible OLED Lighting Has Multiple Potential

Applications

With OLED lighting, the light source itself illuminates a wide area evenly. This

makes it possible to have an entire ceiling or wall serve as an illumination device.Moreover, if plastic film is used for the substrate base, then flexibly curved

lighting becomes a real possibility in the future. OLED lighting offers greater

potential for applications, including revolutionary design of indoor lighting and

new applications in interior spaces, illumination inside vehicles and aircraft, novel

monuments and artworks, and other exciting lighting options.

11. CONCLUSION

From above discussion we conclude that it is a field of rapid development in near

future. With the development in various technology this not only reduce the price

but also improve the quality of the display screen As it use organic chemical

which found in abundance , it reduce the problem of pollution . Organic molecule

and polymer have short life span, also they are bio degradable.


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Organic light emitting diode will also improve the efficiency of the electronic

screen. It has more efficient than the LCD, LED and CRT. It has more brightness

and contrast ratio as compare with other type of screen. In future we not onlyuse this in screen technology but also use as illumination, it will replace LED,

bulb, CFL completely because of the inexpensive device and greater efficiency.

It will also open the exciting field of flexible screen which find even more use in

the near future. The screen which can foldable will find great use in TV,

wallpaper display, advertizing board etc. Also military use of this technology

will find it attractive.

But from the current technology OLED find several hurdle in its path such as

high cost of production, short life span of the organic compound , fading effect ,

low brightness ratio and differential power consumption for different colures etc

.

With the development of the technology the problems in field of the organic light

emitting diode will be resolve and. OLED will find greater use in near future .

12. REFERENCE

http://impnerd.com/the-history-and-future-of-oled

http://www.oled-research.com/oleds/oleds-history.html

http://www.voidspace.org.uk/technology/top_ten_phone_techs.shtml#keep-your-

eye-on-flexible-displays-coming-soon

http://www.cepro.com/article/study_future_bright_for_oled_lighting_market/

http://www.technologyreview.com/energy/21116/page1/

http://optics.org/cws/article/industry/37032

http://jalopnik.com/5154953/samsung-transparent-oled-display-pitched-as-

automotive-hud

en.wikipedia.org


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