1. INTRODUCTION- Organic light emitting
diodes (OLEDs) are optoelectronic
devices based on small molecules or polymers that emit light when an
electric current flows through them. Simple OLED consists of a
fluorescent organic layer sandwiched between two metal electrodes. Under
application of an electric field, electrons and holes are injected from
the two electrodes into the organic layer, where they meet and
recombine to produce light. They have been developed for applications
in flat panel displays that provide visual imagery that is easy to
read, vibrant in colors and less consuming of power.
OLEDs are light weight, durable, power efficient and ideal for
portable applications
devices based on small molecules or polymers that emit light when an
electric current flows through them. Simple OLED consists of a
fluorescent organic layer sandwiched between two metal electrodes. Under
application of an electric field, electrons and holes are injected from
the two electrodes into the organic layer, where they meet and
recombine to produce light. They have been developed for applications
in flat panel displays that provide visual imagery that is easy to
read, vibrant in colors and less consuming of power.
OLEDs are light weight, durable, power efficient and ideal for
portable applications
An OLED is a solid-state semiconductor device
that is 100 to 500 nanometers thick or about 200 times smaller than a human
hair.
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 either passive-matrix (PMOLED) or active addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane 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 higher contrast
ratio than
an LCD, whether the LCD uses cold
cathode fluorescent lamps or LED backlight.
OLEDs can replace the current technology in many applications
due to following performance advantages over LCDs.
·
Greater
brightness
·
Faster
response time for full motion video
·
Fuller
viewing angles
·
Lighter
weight
·
Greater
environmental durability
·
More power efficiency
·
Broader
operating temperature ranges
·
Greater cost-effectiveness
2. MAKING OF OLEDs
An OLED is made by placing a series of organic thin
films between two conductors. When electrical current is applied, a bright
light is emitted.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.
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.
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 large films for
large displays like 80-inch TV screens or electronic billboards
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Organic light emitting diode(OLED) is a thin film multilayer device composed of carbon molecules or polymers including metal foil, organic light emitting diode oled
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