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INTERNATIONAL SCHOOL OF

PHOTONICS

SONU KUMAR SINGH

b-13 isp,cusat

ORGANIC

LIGHT

EMITTING

DIODE

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CONTENTS

Abstract

Introduction

Organic electronics

History

Application

OLED

Why so much excitement about OLED?

Inorganic vs organic semiconductor

What is OLED & it’s working?

Types of OLED

Difference between LEDs Incandescent Bulb & CFLs

Energy Efficiency & Energy Costs

Environmental

Impact

Important Facts

Light Output

COMPARISION BETWEEN LED AND OLED

What is an LED?

Black Level

Brightness

Color space

Response time

Viewing angles

Size

Lifespan

Size, weight, power consumption

Price

DIFFERENCE BETWEEN OLED &LCD

Operating principle

Performance matrix

Color saturation

Response time

Lifetime

Energy savings

Resolution

Ambient contrast ratio

Viewing angle

Potential game – changers

Challenges

Conclusion

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Abstract

Organic Light Emitting Diodes (OLED) are a different type of solid-state lighting source. An OLED device is

typically formed in a sheet with emissive organic layer(s) located between a cathode and anode and deposited on

a substrate. The substrate can be rigid such as glass or metal or flexible using a polymer plastic. The number of

emissive layers depends on the desired light output of the device. OLED technology has great potential for new

uses such flexible paper-thin OLED panels, transparent OLED panels and white OLED. White OLED was

developed as device with extremely high power efficiency and long lifetime. The performance achieved was

64lm/W, and 10.000 hours of lifetime at initial luminance of 1000cd/m2 with light out-coupling technique. New

technologies, such as sophisticated organic layer structure, were applied to the device. The device also exhibited

good durability such as storage stability, which is important performance in practical use. We hope that this paper

will show possibilities to practical use of OLED in different types of displays, lighting sources for illumination

use, back light and others. From a recent environmental problem and energy supply circumstances, light sources

of low energy consumption and eco-friendly are demanded. An enormous amount of research effort goes into the

field. Organic light-emitting diode (OLED) is regarded as a powerful candidate because it is an area light source,

can be driven at low voltage, and does not include a material which is harmful to the human body and environment

like mercury. As a light source for illumination or backlight, a white light is usually required. To realize a white

OLED device, plural light emissive materials such as blue, green, red are used generally.

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Introduction

OLED (Organic Light Emitting Diodes) is a flat light emitting technology, made by placing a series of organic

thin films between two conductors. When electrical current is applied, a bright light is emitted. OLEDs can be

used to make displays and lighting. Because OLEDs emit light they do not require a backlight and so are thinner

and more efficient than LCD displays (which do require a white backlight). An OLED 'light bulb' is a thin film

of material that emits light. OLED is the only technology that can create large "area" lighting panels (as opposed

to point or line lighting enabled by LEDs and Fluorescent bulbs). OLEDs can be used to make flexible and

transparent panels, and can also be color-tunable. OLEDs emit beautiful soft diffused light - in fact OLEDs

lighting is the closest light source to natural light (with the exception of the old incandescent lamps).

There are several types of OLED materials. The most basic division is between small-molecule OLEDs and large

molecule ones (called Polymer OLEDs, or P-OLEDs). All commercial OLEDs today are SM-OLED based. These

evaporable materials perform better than P-OLED materials (in terms of efficiency, lifetime, etc.). P-OLEDs had

great promise as they are naturally solution process able (and so can be used in Inkjet printing and spin-coating

fabrication methods). Intensive research is being performed to develop efficient solution-process able SM-

OLEDs.

OLED emitter materials are classified as either fluorescent or phosphorescent. Fluorescent materials last longer

but are much less efficient than phosphorescent materials. Currently most OLED displays use phosphorescent

emitter materials - except for the blue color which is still fluorescent as the lifetime is still not good enough.

Universal Display Corporation is pioneering PHOLED research, holding the basic patents in this area. An OLED

TV screen uses a new display technology called OLED (Organic Light Emitting Diodes). OLED televisions are

brighter, more efficient, and thinner feature better refresh rates and contrast than either LCD or Plasma. OLED

TVs deliver the best picture quality ever.

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Organic electronics

Organic electronics is a field of materials science concerning the design, synthesis, characterization, and

application of organic small molecules or polymers that show desirable electronic properties such as conductivity.

Unlike conventional inorganic conductors and semiconductors, organic electronic materials are constructed from

organic (carbon-based) small molecules or polymers using synthetic strategies developed in the context of organic

and polymer chemistry. One of the benefits of organic electronics is their low cost compared to traditional

inorganic electronics.

History

Conductive materials are substances that can transmit electrical charges. Traditionally, most known conductive

materials have been inorganic. Metals such as copper and aluminum are the most familiar conductive materials,

and have high electrical conductivity due to their abundance of delocalized electrons that move freely throughout

the inter-atomic spaces. Some metallic conductors are alloys of two or more metal elements, common examples

of such alloys include steel, brass, bronze, and pewter.

In the eighteenth and early nineteenth centuries, people began to study the electrical conduction in metals. In his

experiments with lightning, Benjamin Franklin proved that an electrical charge travels along a metallic rod. Later,

Georg Simon Ohm discovered that the current passing through a substance is directly proportional to the potential

difference, known as Ohm's law. This relationship between potential difference and current became a widely used

measure of the ability of various materials to conduct electricity. Since the discovery of conductivity, studies have

focused primarily on inorganic conductive materials with only a few exceptions.

Henry Letheby discovered the earliest known organic conductive material in 1862. Using anodic oxidation of

aniline in sulfuric acid, he produced a partly conductive material that was later identified as polyaniline. In the

1950s, the phenomenon that polycyclic aromatic compounds formed semi-conducting charge-transfer complex

salts with halogens was discovered, showing that some organic compounds could be conductive as well.

More recent work has expanded the range of known organic conductive materials. A high conductivity of 1 S/cm

(S = Siemens) was reported in 1963 for a derivative of tetraiodopyrrole. In 1972, researchers found metallic

conductivity (conductivity comparable to a metal) in the charge-transfer complex TTF-TCNQ.

In 1977, it was discovered that polyacetylene can be oxidized with halogens to produce conducting materials from

either insulating or semiconducting materials. In recent decades, research on conductive polymers has prospered,

and the 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, and Hideki

Shirakawa jointly for their work on conductive polymers.

Conductive plastics have recently undergone development for applications in industry. In 1987, the first organic

diode device of was produced at Eastman Kodak by Ching W. Tang and Steven Van Slyke. Spawning the field

of organic light-emitting diodes (OLED) research and device production. For his work, Ching W. Tang is widely

considered as the father of organic electronics.

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Technology for plastic electronics constructed on thin and flexible plastic substrates was developed in the 1990s.

In 2000, the company Plastic Logic was founded as a spin-off of Cavendish Laboratory to develop a broad range

of products using the plastic electronics technology

Attractive properties of polymer conductors include a wide range of electrical conductivity that can be tuned by

varying the concentrations of chemical dopants, mechanical flexibility, and high thermal stability. Organic

conductive materials can be grouped into two main classes: conductive polymers and conductive small molecules.

Conductive materials

Conductive small molecules are usually used in the construction of organic semiconductors, which exhibit degrees

of electrical conductivity between those of insulators and metals. Semiconducting small molecules include

polycyclic aromatic compounds such as pentacene, anthracene and rubrene.

Conductive polymers are typically intrinsically conductive. Their conductivity can be comparable to metals or

semiconductors. Most conductive polymers are not thermoformable, during production. However they can

provide very high electrical conductivity without showing similar mechanical properties to other commercially

available polymers. Both organic synthesis and advanced dispersion techniques can be used to tune the electrical

properties of conductive polymers, unlike typical inorganic conductors. The well-studied class of conductive

polymers is the so-called linear-backbone “polymer blacks” including polyacetylene, polypyrrole, polyaniline,

and their copolymers. Poly (p-phenylene vinylene) and its derivatives are used for electroluminescent

semiconducting polymers. Poly (3-alkythiophenes) are also a typical material for use in solar cells and transistors.

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Application of organic electronics

There are four major application areas: displays; lighting; photovoltaics and integrated smart systems. While

OLAE technology is currently used in many manufacturing processes, new applications are entering the

marketplace rapidly.

While organic light- emitting diodes (OLEDs) are already used commercially in displays of mobile devices and

significant progress has been made in applying organic photovoltaic cells to light-weight flexible fabrics to

generate low-cost solar energy, a brand new range of applications is possible such as biomedical implants and

disposable biodegradable RFID packaging tags.

In addition, low cost organic solar cells have the potential to drive down the cost of photovoltaics to levels, which

are not achievable with mono or poly-crystalline solar cells. Similarly, organic light emitting diodes will

revolutionize current lighting applications, significantly reducing CO2 impact. Also, smart devices incorporating

organic and printed circuits, sensors and energy sources will enable new approaches in logistics and consumer

packaging, and new flexible displays with exceptionally low energy consumption will be used anywhere and

anytime.

What are the possibilities?

The possibilities are limitless as the technology is evolving at such a rapid pace. Industrial designers across all

sectors and markets should be aware of the technology and looking at ways of harnessing its power and benefits

into new product design.

Possible applications could include:

Memory or logic devices

Detectors, lasers and light emitters

Information displays – advertising billboards and other media

Micro lenses

Batteries

Power or light sources

Subsystem packaging

Image patterning

Electrical or optical fibers

Transistors

Photoconductors

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Organic LED

Why so much excitement about Organic LED?

Easy to process

Processing is low cost

Less temperature required to fabricate

They can possess to low –cost substrates (i.e., plastic, paper even cloth)

Directly integrated to packages as it is light weight.

Solution processing is possible basically means that if we want to make them thin film for silicon we

have to use high cost evaporation technique but organic semiconductor just we can take a solution Spink

coated put on substrate new way of manufacturing technique is low cost.

Inorganic semiconductor Organic semiconductor

Crystalline in nature

Covalent bond, coordinate bond

More energy to make them

Electron is delocalized in whole

semiconductor

In case of inorganic electronics charge carriers

are e- and h+

Mobility (µn, µp) 100-104cm2/v-s

Amorphous in nature generally

Molecule in nature Vander walls bonds

Less energy to make them

Electron is localized in organic semiconductor

In case of organic electron interacts with lattice

carriers for charges called polarons.

Mobility (µn, µp) 10-6-1 cm2/v-s

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Working OLEDs

A typical OLED is composed of an emissive layer, a conductive layer, a substrate, and anode and cathode

terminals. The layers are made of organic molecules that conduct electricity. The layers have conductivity levels

ranging from insulators to conductors, so OLEDs are considered organic semiconductors.

The first, most basic OLEDs consisted of a single organic layer, for example the first light-emitting polymer

device synthesized by Burroughs et al. involved a single layer of poly (p-phenylene vinylene). Multilayer OLEDs

can have more than two layers to improve device efficiency. As well as conductive properties, layers 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.

fig-2

Fig-1

Schematic of a 2-layer OLED: 1. Cathode (−), 2. Emissive Layer, 3. Emission of radiation, 4. Conductive Layer,

5. Anode (+)

A voltage is applied across the OLED such that the anode is positive with respect to the cathode. This causes a

current of electrons to flow through the device from cathode to anode. Thus, the cathode gives electrons to the

emissive layer and the anode withdraws electrons from the conductive layer; in other words, the anode gives

electron holes to the conductive layer.

Soon, the emissive layer becomes negatively charged, while the conductive layer becomes rich in positively

charged holes. Electrostatic forces bring the electrons and the holes towards each other and they recombine. This

happens closer to the emissive layer, because in organic semiconductors holes are more mobile than electrons.

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The recombination causes a drop in the energy levels of electrons, accompanied by an emission of radiation whose

frequency is in the visible region. That is why this layer is called emissive.

The device does not work when the anode is put at a negative potential with respect to the cathode. In this

condition, holes move to the anode and electrons to the cathode, so they are moving away from each other and do

not recombine.

Indium tin oxide 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 polymer layer. Metals such as aluminum and calcium are

often used for the cathode as they have low work functions which promote injection of electrons into the polymer

layer.

There are different types of OLED based on the construction.

1. Transparent OLED – They have all transparent components like anode, cathode and substrate. OLED

technology enables thin, efficient and bright displays and lighting panels. OLEDs are currently used in many

mobile devices, some TVs and even in some lighting fixtures. OLED displays offer a better image quality

compared to LCD or Plasma displays - and can also be made flexible and transparent.

2. Top emitting OLED – Substrate layer is reflective or opaque. Top-emitting organic light-emitting diodes

(OLEDs), which are beneficial for lighting and display applications, where nontransparent substrates are used.

3. White OLED – Emit white light. These can be made into large sheets to make Fluorescent lamps. White organic

light emitting diodes (white OLEDs) show promise for a major role in ambient lighting in the future. Low material

costs, a wide choice of materials with customized properties, and easy production methods are features of the

OLED technology which have favored its fast development and industrial application in recent time. The

energetically broad emission spectra and almost Lambertian emission of OLEDs are especially favorable for

lighting applications, since they lead to homogeneous illumination and high quality color rendering. The

possibility to produce large area OLED panels will also open new ways for lighting design apart from common

incandescent bulbs or fluorescent tubes.

4. Foldable OLED – A flexible organic light emitting diode (FOLED) is a type of organic light-emitting diode

(OLED) incorporating a flexible plastic substrate on which the electroluminescent organic semiconductor is

deposited. This enables the device to be bent or rolled while still operating. Currently the focus of research in

industrial and academic groups, flexible OLEDs form one method of fabricating a roll able display.

5. Active matrix OLED-AMOLEDs will be similar to passive but will have full layers of cathode, organic

molecules, and anode; the anode layer will have a thin film transistor (TFT) back plate that forms a matrix. The

TFT controls the brightness and which pixel gets turned on to form an image. In AMOLED there will be two

TFT arrays per pixel, one starts and stops the charge and the other keeps a constant electrical current to the pixel.

.

6. Passive OLED – Presumably this will be the first to hit the market since it was the passive LCD screens that

came out first and more than likely OLEDs will follow in those footprints. PMOLEDs will be more expensive

and will need more power than other OLEDs, though they will still use less power than LCDs out today.

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White OLEDs

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ADVANTAGES

Difference between LEDs Incandescent Bulb & CFLs

Energy Efficiency

& Energy Costs Light Emitting Diodes

(LEDs)

Incandescent Light Bulbs

Fluorescents (CFLs)

Life Span (average) 50,000 hours 1,200 hours 8,000 hours

Watts of electricity

used (equivalent to 60 watt

bulb).

LEDs use less power

(watts) per unit of light

generated

(lumens). LEDs help

reduce greenhouse gas

emissions from power

plants and lower

electric bills

6 - 8 watts 60 watts 13-15 watts

Kilo-watts of

Electricity used

(30 Incandescent

Bulbs per year

equivalent)

329 KWh/yr. 3285 KWh/yr. 767 KWh/yr.

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Environmental Impact

Light Emitting

Diodes (LEDs) Incandescent Light Bulbs

Compact Fluorescents (CFLs)

Contains the

TOXIC Mercury No No

Yes - Mercury is very toxic to

your health and the environment

RoHS Compliant Yes Yes

No - contains 1mg-5mg of

Mercury and is a major risk to

the environment

Carbon Dioxide

Emissions

(30 bulbs per year)

Lower energy

consumption

decreases: CO2

emissions, sulfur

oxide, and high-

level nuclear waste.

451 pounds/year 4500 pounds/year 1051 pounds/year

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Important Facts

Light Emitting Diodes (LEDs)

Incandescent

Light Bulbs

Compact Fluorescents

(CFLs)

Sensitivity to low temperatures

None Some Yes - may not work under negative 10 degrees

Fahrenheit or over 120 degrees Fahrenheit

Sensitive to humidity

No Some Yes

On/off Cycling Switching a CFL on/off quickly, in

a closet for instance, may decrease the

lifespan of the bulb.

No Effect Some Yes - can reduce lifespan drastically

Turns on instantly

Yes Yes No - takes time to warm up

Durability Very Durable - LEDs can handle

jarring and bumping

Not Very Durable - glass or filament can break

easily

Not Very Durable - glass can break easily

Heat Emitted 3.4 btu's/hour 85 btu's/hour 30 btu's/hour

Failure Modes Not typical Some Yes - may catch on fire, smoke, or omit an odor

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Light Output

Light Emitting Diodes (LEDs)

Incandescent

Light Bulbs

Compact Fluorescents (CFLs)

Lumens Watts Watts Watts

450 4-5 40 9-13

800 6-8 60 13-15

1,100 9-13 75 18-25

1,600 16-20 100 23-30

2,600 25-28 150 30-55

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COMPARISION BETWEEN LED AND OLED

OLED technology isn’t exactly new to the consumer electronics space anymore. Mobile phones have been using

OLED screens in some form or another since 2001. But now that OLED televisions from Samsung and LG are

beginning to hit showrooms in the US, people’s interest in OLED is beginning to tick up, and they have questions.

What makes an OLED TV better than an LED or LCD TV? How is OLED superior? Are there any disadvantages

to OLDs?

What is an LED?

LED stands for light-emitting diode. These are little solid-state devices that make light because of the movement

of electrons through a semi-conductor. LEDs are relatively small compared to compact fluorescent and

incandescent light bulbs, but they can get extremely bright. However, LEDs aren’t small enough to be used as the

pixels of a television – they’re way too big for that. That’s why LEDs are only used as the backlight for LCD

televisions. For more info on that, visit our LED vs. LCD page.

Black Level – Winner: OLED

A display’s ability to produce deep, dark blacks is arguably the most important factor in achieving excellent

picture quality. Deeper blacks allow for higher contrast and richer colors (among other things) and, thus, a more

realistic and dazzling image. When it comes to black levels, OLED reigns as the undisputed champion.

LED TVs rely on LED backlights shining behind an LCD panel. Even with advanced dimming technology that

dims LEDs that don’t need to be on at full blast, LED TVs struggle to produce dark blacks. They also suffer from

light bleeding out from the edges.

OLED TVs suffer from none of those problems. If an OLED pixel isn’t getting electricity, it doesn’t produce any

light and is, therefore, totally black.

Brightness – Winner (by a smidge): LED/LCD

When it comes to brightness, LED TVs have a slight advantage. LEDs are just really good at getting extremely

bright. OLED TVs can get bright, too, but cranking OLED pixels to maximum brightness for extended periods

not only reduces that pixel’s lifespan, but the pixel also takes a little while to return to total black.

Color space – Winner: OLED

Both of the recently introduced OLED TVs are capable of covering a wider gamut of color space than LED/LCD

televisions. Very basically explained, this means they can reproduce finer shades of more colors within the visible

color spectrum.

Response time – Winner: OLED

While LED/LCD TVs have improved considerably over the past few years, OLED simply blows them out of the

water in terms of response time. In fact, OLED currently offers the fastest response time of any TV technology

in use today, making it a clear winner in this regard. With faster response time comes less motion blur and less

artifacts (source material notwithstanding).

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Viewing angles – Winner: OLED

This is a tricky topic right now, because both of the OLED TV’s currently available for purchase in the US are

curved. So, while OLED TV’s should offer perfect viewing angles due to the fact that OLEDs produce light rather

than attempt to block it as LED/LCD TVs do, the curve introduces a couple of complications. Foremost, the side

that is curved away from an off-axis viewer will be less visible than the side curved toward that viewer. Second,

because of the curve, anti-glare coatings can tend to tint the image when viewed from extreme angles. With that

said, OLED technology is still superior in this regard and a clear winner overall.

Size – Winner (for now): LED/LCD

One day, in the hopefully-not-too-distant future, we’ll all be dreaming of owning 80-inch OLED TV’s, but for

now, that dream is limited to 55-inches. Meanwhile, Sharp produces a mammoth 90-inch LED/LCD TV that you

can buy right now, albeit at roughly the same price as an OLED TV.

Lifespan – Winner (for now) LED/LCD

OLED is unproven when it comes to lifespan, and there is some cause for concern here because the compound

used to create the color blue in OLED televisions is known to have a shorter life span. As one color degrades, the

rest will go out of whack. Samsung appears to be battling this issue by using a blue pixel that is twice the size of

other colors and reducing the amount of voltage applied to it. LG uses white sub-pixels and lays a color filter over

them to create the desired red, green and blue colors. These bandages may very well work, but only time and use

in the public arena can tell how OLED will hold up on the long term. For that reason, we have to call LED/LCD

the winner, as its lifespan has proven itself to be adequate.

Screen Burn-in – Winner: LED/LCD

We include the section begrudgingly, both because burn-in is a misnomer (that’s just an aggravation) and, for

most folks, the effect will not be an issue.

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The effect we’ve come to know as burn-in stems from the days of the boxy CRT TV, when prolonged display of

a static image would cause that image to appear to “burn” into the screen. But what was actually happening was

the phosphors that coated the back of the TV screen would glow for extended periods of time without any rest,

causing the phosphors to wear out and resulting in the appearance of a burned-in image. We think this should be

called “burn out.” But … whatever.

The same issue is at play with plasma and OLED TVs because the compounds that light up can degrade over

time. If you burn a pixel long and hard enough, you will cause it to dim prematurely and ahead of the rest of the

pixels, creating a dark impression. However, in reality, this is not very likely to cause a problem for anyone.

You’d have to abuse the TV intentionally in order to get it to happen. Even the “bug” (or, logo graphic) that

certain channels use disappears often enough or is made clear so as to avoid causing burn-in. You’d have to watch

ESPN all day every day (for many days) at the brightest possible setting to cause a problem, and even then it still

isn’t very likely.

Size, weight, power consumption – Winner: OLED

OLED panels are extremely thin and they require no backlight. As such, OLED TV’s tend to be lighter than

LED/LCD TVs and considerably thinner. They also require less power, making them more efficient.

Price – Winner: LED/LCD

Currently, an OLED TV is going to cost you either $9,000 (Samsung) or $15,000 (LG). We would be shocked –

shocked! – If LG’s price didn’t come down in the coming months. Either way, $9,000 is a lot to pay for a

television. And even though you can spend a little more on a much larger TV, the vast majority of televisions in

the 55 – 65-inch price point are half OLED TV’s asking price or less. If affordability is a major consideration,

LED/LCD is your best bet, and it probably will be for a few years.

Challenges

They are still many challenges facing the OLED industry. Here's a list of some of the major ones:

Material lifetime (especially of the blue material)

Soluble OLED performance

Soluble-based production processes

Flexible OLED encapsulation

Better backplane materials for flexible OLED

Scaling of evaporation processes beyond Gen-6

OLED lighting capacity expansion

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Difference between OLED &LCD

The global display market has exceeded US$120 billion, making it one of the largest optics and photonics

industries. With so much to gain, there is strong competition for market share between Organic light-emitting

diode (OLED) display and liquid-crystal display (LCD) manufactures. the consequences of that competition are

showing up in people's hands: Apple's recently released iPhone 6, for example, uses a state-of-the-art LCD

screen, while Samsung’s flagship Galaxy S5 gave the nod to OlED.so which display will display will take largest

piece of the pie? Even though the answer depends on more than just performance (marketing strategy and

capital investment also influence success), it is interesting to take a look at each display's market potential from

a technical point of view.

Operating principle

Before examining the pros and cons of OLED display's and LCDs, it's important to understand the difference

between their operating principles "OLED displays are emissive - they produce their own light; - they produce

their own light; LCDs are non-emissive - they are illuminated with a backlight.

An OLED display is composed of multilayer film- stack and a circular polarizer that mitigates ambient - light

reflection. Each pixel can be turned on individually and requires multiple thin-film transistor (TFTs) to ensure

stable current flow.

LCD have a modular structure and require a backlight that illuminates the liquid -crystal module to create images

on the screen. The liquid - crystal cell can be optimized for specific applications, like high contrast television or

touch- panel Mobile devices. But unlike OLED displays that are driven by current, LCDs are voltage devices. So,

each pixel only require one TFT as voltage switch.

Performance metrics

To determine which display is technically superior, we conducted a quantitative comparison for eight

performance categories:

Color saturation

Most LCDs use a led backlight and color filters to display images. The color gamut is usually limited to 75 percent

Adobe RGB (a defined color space for displays).OLED displays, however can over 100 percent Adobe RGB and

deliver better image quality.

Response time

OLED displays can be turned on in microsecond by applying electric current. This translates to visually

undetectable frame changes - i.e., no motion blur. LCDs suffer from slow response time and motion blur because

the liquid crystals are unable to change their orientation fast enough from one frame to the next.

Thinness/ flexibility

OLED displays are thinner and more flexible than LCDs because they have fewer components; they do not need

a backlight and they have a solid rather than modular structure.

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Lifetime

In contrast to LCDs sensitivity to air and moisture greatly reduce an OLED display's long term stability. However,

short life time may not impede OLED technology's potential to capture the mobile display market, because

device lifetime isn't a main concern - smartphone lifespan is typically only two to three years.

Energy savings

OLEDs displays require multiple thin-film transistor (TFTs) per pixel to ensure stable current control. The

grouped TFTs cause high resistive and capacitive loss and require a circular polarizer to mitigate ambient light

reflection from metallic anodes and cathodes, which cuts screen brightness in half. LCDS consume less power

than OLED displays for the same size, brightness and resolution.

Resolution

In LCDs and OLED displays, each pixel is addressed by one or multiple TFTs respectively. When you increase

resolution, aperture ratio decreases and TFT charging time increases. Therefore, higher-electron-mobility TFT

charging time increases. Therefore, higher- electron- mobility TFT materials (e.g., low temperature poly-silicon

and oxide semiconductors) should reduce TFTS size, which in turn increases light output, especially for OLED

displays, which require multiple TFTs per pixel.

Ambient contrast ratio

Readability in bright light is a problems for both displays-

Especially for mobile devices. OLED displays have superior contrast ratio in dark light, because individual pixels

in the display can be switched off when not in use. However, even viewed under direct sunlight, the ambient

light reflected off a smartphone screen degrades the color and image contrast ratio, because a portion of the

reflected light is overserved as noise. LCDs do not have a strong reflection component, but their 75 percent

color gamut in low ambient light drops to less than 50 percent in bright light resulting in washed-out images.

Viewing angle

OLED pixels feature a Lambertian- like radiation pattern that creates pleasing wide - View matte images. State-

of-the art LCDs use compensation film and multidomain structure to expand the viewing angle. Both displays

offer picture accuracy at viewing angle -+ 30 degrees from the center of the screen.

Potential game - changers

OLED's superior response time and color saturation are being challenged by recent LCD advances. Conventional

LCDs rely on molecular reorientation to control light transmittance.

Making response time relatively slow (more than five milliseconds, compared with microseconds for OLEDs).But

emerging blue-phase liquid crystals based on kerr- effect induced isotropic-to- anisotropic transition can achieve

a sub-millisecond gray-to-gray response time. With blue- phase liquid crystals based on Kerr-effect induced

isotropic-to-anisotropic transition can achieve a sub - millisecond gray- to- gary response time would only be

governed by the TFT frame rate, so an LCD with a 240 Hz frame rate will have sharper image than an OLED

display with120 Hz frame rate.

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Emerging fast-response liquid crystals could enable field sequential color (FSC) displays. In a FSC display, the

backlight sequentially emits RGB lights. The LCD panel is synchronized to the backlight to display gray levels of

each color. This method of color generation does not require spatial color filters or subpixels to reproduce color

filter or subpixels to reproduce colors. As a result, it could offer significantly higher optical efficiency and

resolution density than OLED displays.

New quantum dot (QD) technology would also give LCDs an edge over OLED displays in color saturation, or at

least level the playing field. LCD color reproduction has been limited by white LEDs and color filters. But with

today’s blue LEDs, down – converted QD s added to an LCD can create emission spectra optimized to match the

transmission spectra of color filter, thereby simultaneously boosting LCD optical efficiency and color gamut to

be equal to be equal to or better than OLED. (This QD technique is used in amazon’s kindle fire HDX 7 and Sony’s

triluminos televisions.)

There are also new method for increasing OLED display readability in brighter light, like better green

phosphorene emitters and light extraction techniques. For LCDs sunlight readability could improve with a

“smart“ backlight that concentrates illumination toward the viewer’s eye or with a QD – enhanced backlight to

precompensate the color gamut reduction.

OLED manufacturing can be expensive and complicated because of the required special vacuum and hermetic

packaging – especially for larger displays. For example, a 55- inch OLED screen can cost US$5000- 5 times more

expensive than the equivalent LCD. However as manufacturing technology continues to evolve, the price gap

should gradually narrow.

Disadvantages

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.

Sunlight Effect:

Another disadvantage of OLED display is that they are hard to see in direct sunlight. So if you have open lobbies

where sunlight reaches directly, you will not get benefit of viewing these screens.

Color purity

Problems of color purity still remains: it is difficult to display fresh and rich colors

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OLED technology today

The leading AMOLED producer today is Samsung, who's making over 200 million displays a year, and is still

expanding production capacity. Samsung is focused on small displays (5 - 10 inch) mostly for mobile phones and

tablets. LG Display is also producing OLEDs, but only large size (55-77 inch) panels for OLED TV applications.

Both Samsung and LG also produce flexible OLED panels, used in mobile phones and wearable devices.

Production volume is still rather low, but both companies are expected to expand production capacity and

introduce new products and form factors to the market.

In the OLED lighting market, several companies (including as Philips, LG Chem, OSRAM and Konica Minolta)

are already shipping OLED panels, but production capacity is still low and prices are very high. OLED lighting

today is mostly used in premium lighting fixtures and installations.

Conclusion

And the winner is?

Our assessment suggests that there’s no clear winner in the match between OLED, LCD and LED. Each

technology has own unique characteristics to distinguish itself for different applications, and each camp has

invested tremendous resources to perfect the device performances.

Thankfully, no matter which technology dominates, the true winner will be consumers and the optics and

photonics industry as a whole. Consumers will enjoy cheaper, lighter, smarter and brighter displays, while the

companies that make them will benefits from component sales and manufacturing. LCD, LED and OLED displays

are like twin stars; their healthy competition will light up our sky.

REFERENCE:-

# Optics and photonics news feb-2015 (OSA magazine)

# Solid state physics M A Wahb

# http://www.globalmarket.com/sourcingtips/lighting/oled-advantages-vs-disadvantages-4549.html

# http://www.ledesl.com/01-12-2009/oled-working-principle.html

# http://www.digitaltrends.com/home-theater/oled-vs-led-which-is-the-better-tv-technology/

# http://www.explainthatstuff.com/how-oleds-and-leps-work.html

# http://www.oled-info.com/oled-technology

# https://en.wikipedia.org/wiki/OLED