Organic Light Emitting Diodes (OLED)
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21-09-2008, 11:03 AM


Definition
Scientific research in the area of semiconducting organic materials as the active substance in light emitting diodes (LEDs) has increased immensely during the last four decades. Organic semiconductors was first reported in the 60Confused and then the materials where only considered to be merely a scientific curiosity. (They are named organic because they consist primarily of carbon, hydrogen and oxygen.). However when it was recognized in the eighties that many of them are photoconductive under visible light, industrial interests were attracted. Many major electronic companies, such as Philips and Pioneer, are today investing a considerable amount of money in the science of organic electronic and optoelectronic devices. The major reason for the big attention to these devices is that they possibly could be much more efficient than todays components when it comes to power consumption and produced light. Common light emitters today, Light Emitting Diodes (LEDs) and ordinary light bulbs consume more power than organic diodes do. And the strive to decrease power consumption is always something of matter. Other reasons for the industrial attention are i.e. that eventually organic full color displays will replace todays liquid crystal displays (LCDs) used in laptop computers and may even one day replace our ordinary CRT-screens.

Organic light-emitting devices (OLEDs) operate on the principle of converting electrical energy into light, a phenomenon known as electroluminescence. They exploit the properties of certain organic materials which emit light when an electric current passes through them. In its simplest form, an OLED consists of a layer of this luminescent material sandwiched between two electrodes. When an electric current is passed between the electrodes, through the organic layer, light is emitted with a color that depends on the particular material used. In order to observe the light emitted by an OLED, at least one of the electrodes must be transparent.

When OLEDs are used as pixels in flat panel displays they have some advantages over backlit active-matrix LCD displays - greater viewing angle, lighter weight, and quicker response. Since only the part of the display that is actually lit up consumes power, the most efficient OLEDs available today use less power.
Based on these advantages, OLEDs have been proposed for a wide range of display applications including magnified microdisplays, wearable, head-mounted computers, digital cameras, personal digital assistants, smart pagers, virtual reality games, and mobile phones as well as medical, automotive, and other industrial applications.



OLED Versus LED
Electronically, OLED is similar to old-fashioned LEDs -- put a low voltage across them and they glow. But that's as far as the similarity goes: instead of being made out of semiconducting metals, OLEDs are made from polymers, plastics or other carbon-containing compounds. These can be made very cheaply and turned into devices without all the expensive palaver that goes with semiconductor fabrication.

Light-emitting diodes, based upon semiconductors such as Gallium Arsenide, Gallium Phosphide, and, most recently, Gallium Nitride, have been around since the late '50s. They are mostly used as indicator lamps, although they were used in calculators before liquid crystals, and are used in large advertising signs, where they are valued for very long life and high brightness. Such crystalline LEDs are not inexpensive, and it is very difficult to integrate them into small high-resolution displays.
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17-07-2009, 07:42 PM

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29-08-2009, 12:34 AM

An organic light emitting diode (OLED), also light emitting polymer (LEP) and organic electro luminescence (OEL), is a light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors.

Such systems can be used in television screens, computer displays, small, portable system screens such as cell phones and PDAs, advertising, information and indication. OLEDs can also be used in light sources for general space illumination, and large-area light-emitting elements. OLEDs typically emit less light per area than inorganic solid-state based LEDs which are usually designed for use as point-light sources.

A significant benefit of OLED displays over traditional liquid crystal displays (LCDs) is that OLEDs do not require a backlight to function. Thus they draw far less power and, when powered from a battery, can operate longer on the same charge. Because there is no need for a backlight, an OLED display can be much thinner than an LCD panel.



en.wikipediawiki/Organic_light-emitting_diode
lighting.sandia.gov/lightingdocs/OIDA_SSL_OLED_Roadmap_Full.pdf
sa.rochester.edu/jur/issues/fall2002/tonzetich.pdf
ee.jlu.edu.cn/uploads/189b3515c85ab435f7c312ec0ddd2adf.pdf
nanolab.usc.edu/PDF%5CNanoLett8-997.pdf
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15-03-2012, 10:06 AM

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04-04-2012, 11:59 AM

Organic Light Emitting Diodes (OLED)



.ppt   OLED MEHDI.ppt (Size: 1.67 MB / Downloads: 21)

OLED

An OLED is an LED in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current

OLED structure


Substrate
Anode
Organic Layers
-Emissive Layer
-Conductive Layer
Substrate


he basic OLED


The holes move more efficiently in organics

Excitons begin to form in emissive layer


Why OLEDs


Lighting efficiency
Incandescent bulbs are inefficient
Fluorescent bulbs give off ugly light
LEDs (ordinary light emitting diodes) are bright points; not versatile
OLEDs may be better on all counts

Displays: Significant advantages over liquid crystals
Faster
Brighter
Lower power

Cost and design
LEDs are crystals; LCDs are highly structured; OLEDs are not –
Malleable; can be bent, rolled up, etc.
Easier to fabricate





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#7
07-02-2013, 09:02 AM

Organic Light Emitting Diodes (OLEDs)


.ppt   1Organic Light.ppt (Size: 490.5 KB / Downloads: 29)

Why OLEDs

Lighting efficiency
Incandescent bulbs are inefficient
Fluorescent bulbs give off ugly light
LEDs (ordinary light emitting diodes) are bright points; not versatile
OLEDs may be better on all counts
Displays: Significant advantages over liquid crystals
Faster
Brighter
Lower power
Cost and design
LEDs are crystals; LCDs are highly structured; OLEDs are not –
Malleable; can be bent, rolled up, etc.
Easier to fabricate
In general, OLED research proceeds on many fronts

Electrons in a Lattice

Atom has bound states
Discrete energy levels
Partially filled by electrons
Periodic array of atoms (cf. QM textbook)
Effectively continuous bands of energy levels
Also partially filled

Excitons

Electron in higher band meets a hole in lower band
The two form a hydrogen-like bound state! Exciton!
Like “positronium”
Can have any orbital angular momentum
Can have spin 0 or spin 1
Annihilation
Rate is slow
Electron falls into hole
Energy emitted
Energy released as electron falls into hole
May turn into vibrations of lattice (“phonons”) – heat
May turn into photons (only in some materials)
Infrared light (if gap ~ 1 eV) – remote control
Visible light (if gap ~ 2-3 eV) – LED
May excite other molecules in the material (if any; see below)

Organic Semiconductors

These are not Crystals! Not periodic structures
Band structure is somewhat different
“Orbitals” determined by shape of organic molecule
Quantum chemistry of pi bonds, not simple junior QM
Polymers are common
Conduction is different
Electrons or holes may wander along a polymer chain
As with inorganic conductors
Some materials allow electrons to move
Some materials allow holes to move – typical for organics!!
Doping is more difficult
Doping typically not used
Instead electrons/holes are provided by attached metals
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