OLED Technology Report File

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SHRI ATMANAND JAIN INSTT. OF MGT. & TECH.

AMBALA CITY

A

Seminar Report

On

OLED

(Organic Light Emiting Doides)

Submitted To : Submitted By:

Computer Department Shubham Kanojia

MCA(III-sem)

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Contents :

Introduction

History

Components of OLED

How Do OLEDs emit light

Types Of OLEDs

OLED Advantages

OLED Disadvantages

Applications of OLED

Conclusion

References

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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). OLEDs are not just thin and efficient - they can also be

made flexible (even rollable) and transparent.

OLEDs are organic because they are made from carbon and hydrogen. There's no connection to

organic food or farming - although OLEDs are very efficient and do not contain any bad metals -

so it's a real green technology.

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History :

Andr Bernanose and co-workers at the Nancy-Universit in France made the first observations

of electroluminescence in organic materials in the early 1950s. They applied high alternating

voltages 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 some of his 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 single pure crystal

of anthracene and on anthracene crystals doped withtetracene in 1963 using a small area silver

electrode at 400 volts. 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 (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.

Roger Partridge made the first observation of electroluminescence from polymer films 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.

Ching W. Tang and Steven Van Slyke at Eastman Kodak reported the first OLED device 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

that led to the current era of OLED research and device production.

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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).

Universal Display Corporation holds the majority of patents concerning the commercialization of

OLEDs.

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Components of OLED :

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.

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:

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Vacuum depositionor 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 large films for large

displays like 80-inch TV screens or electronic billboards.

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How do OLEDs Emit Light :

Thebattery or power supply of the device containing the OLED applies a voltage

across 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.)

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 theatom that's missing an electron). When this happens,

the electron gives up energy in the form of a photon of light .

The OLED emits light.

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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.

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Types of OLEDs :

Passive-matrix OLED (PMOLED) :

PMOLEDs have strips of cathode, organic layers and strips of anode. The anode stripsare 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 icons and are best suited for small screens (2- to 3-inch diagonal) such asthose you find in cell phones, PDAs and MP3 players. Even with the external circuitry,

passive-matrix OLEDs consume less battery power than the LCDs that currently power

these devices.

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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.

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.

White OLED

White OLEDs emit white light that is brighter, more uniform and more energy efficientthan 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.

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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.

Foldable OLED :

Foldable OLEDs have substrates made of very flexible metallic foils or plastics. FoldableOLEDs 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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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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OLED Advantages :

The LCD is currently the display of choice in small devices and is also popular in large-screen

TVs. Regular LEDs often form the digits on digital clocks and other electronic devices. OLEDs

offer many advantages over both LCDs and LEDs:

The plastic, organic layers of an OLED are thinner, lighter and more flexiblethan

the crystalline layers in an LED or LCD.

Because the light-emitting layers of an OLED are lighter, the substrate of an OLED

can be flexibleinstead of rigid. OLED substrates can be plastic rather than the glass

used for LEDs and LCDs.

OLEDs are brighter than LEDs. Because the organic layers of an OLED are much

thinner than the corresponding inorganic crystal layers of an LED, the conductive and

emissive layers of an OLED can be multi-layered. Also, LEDs and LCDs requireglass for support, and glass absorbs some light. OLEDs do not require glass.

OLEDs do not require backlighting like LCDs . LCDs work by selectively blocking

areas of the backlight to make the images that you see, while OLEDs generate light

themselves. Because OLEDs do not require backlighting, they consume much less

powerthan LCDs (most of the LCD power goes to the backlighting). This is

especially important for battery-operated devices such as cell phones.

OLEDs are easier to produce and can be made to larger sizes. Because OLEDs are

essentially plastics, they can be made into large, thin sheets. It is much more difficult

to grow and lay down so many liquid crystals.

OLEDs have large fields of view, about 170 degrees. Because LCDs work by

blocking light, they have an inherent viewing obstacle from certain angles. OLEDs

produce their own light, so they have a much wider viewing range.

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OLED Disadvantages :

OLED seems to be the perfect technology for all types of displays, but it also has some

problems:

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.

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Applications of OLED :

Televisions

SONY

LG transparent TV

Cell Phone screens

Wrist Watch

Computer Screens

Laptops

Desktops

Bendable Devices

Portable Device displays

Philips Go Gear MP3 Player

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Conclusion :

Easily Portable because it can be folded and keep it at anywhere.

Currently, there is a lot of research and development going on in the field of OLEDs

and experts feel that these might lead to novel applications such as automotive

dashboards, heads-up displays, home and office lighting and billboard-type displays

in the future.

OLED devices can keep refreshing information at real time and videos can look more

realistic in them. So we can also fancy thin and foldable OLED newspapers in the

future, which keep refreshing news even as you read them!

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References :

www.howstuffworks.com/oled

www.oled-info.com/introduction

www.oled-info.com

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