oled technology report file
TRANSCRIPT
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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
http://www.howstuffworks.com/oledhttp://www.howstuffworks.com/oledhttp://www.howstuffworks.com/oledhttp://www.oled-info.com/introductionhttp://www.oled-info.com/introductionhttp://www.oled-info.com/introductionhttp://www.oled-info.com/introductionhttp://www.oled-info.com/http://www.oled-info.com/https://en.wikipedia.org/wiki/OLEDhttps://en.wikipedia.org/wiki/OLEDhttps://en.wikipedia.org/wiki/OLEDhttps://en.wikipedia.org/wiki/OLEDhttps://en.wikipedia.org/wiki/OLEDhttp://www.oled-info.com/http://www.oled-info.com/introductionhttp://www.oled-info.com/introductionhttp://www.oled-info.com/introductionhttp://www.howstuffworks.com/oledhttp://www.howstuffworks.com/oled