3. Light Emitting Diode(LED) Introduction
A light emitting diode (LED) is essentially a PN junction opto-
semiconductor that emits a monochromatic (single color)
light when operated in a forward biased direction.
LEDs convert electrical energy into light energy. They are
frequently used as "pilot" lights in electronic appliances to
indicate whether the circuit is closed or not.
4. The most important part of a light emitting diode (LED) is the
semi-conductor chip located in the center of the bulb as
shown at the right image.
The chip has two regions separated by a junction.
1.P region
2.N region
The p region is dominated by positive electric charges, and
the n region is dominated by negative electric charges.
The junction acts as a barrier to the flow of electrons between
the p and the n regions.
When sufficient voltage is applied to the chip, the electrons
which is in n region cross the junction and transfer into the p
region. This results in current flow.
5.
6. Working Principle Of LED
When sufficient voltage is applied
to the chip across the leads of the
LED, electrons can move easily in
only one direction across the
junction between the p and n
regions.
When a voltage is applied and the
current starts to flow, electrons in
the n region have sufficient energy
to move across the junction into
the p region.
7. Each time an electron recombines with a positive charge,
electric potential energy is converted into electromagnetic
energy.
For each recombination of a negative and a positive charge, a
electromagnetic energy is emitted in the form of a photon of
light. Efficiency this light depends on the semi-conductor
material which is usually a combination of the chemical
elements gallium, arsenic and phosphorus
8. Forward Bias (Current Flow)
+ -
P region(Hole) N region(Electron)
ElectronPath
Current (HOLE) Path
Depletion Layer
Resistors are used to maintain voltage.
9. Advantages
Energy efficient(produce more light per watt)
Long lifetime(60,000 Hours or more)
Rugged(made-up of solid material, no breakage like filament)
No warm-up period(achieve full bright light in nanoseconds)
Not effected by cold temperature(used in sub zero weather)
Directional(direct the light where you want)
Environment Friendly(contains no mercury)
Controllable(brightness and colour can be controlled)
Can sustain over frequent on-off cycle
10. Disadvantages
Very expensive than other lighting technologies
Requires accurate voltage & constant current flow
Can shift colour due to age & temperature
Can not be used in high temperature(Lead to device failure)
11. Applications
Vehicle indicator lights and brake lights.
Currently Audi & BMW integrate high power LEDs.
Mobile phone flash lights.(Surface Mount Diode)
LED screens for advertising & information.
Due to low power consumption, small size & long life
LEDs are used in many electrical equipments.(indicator)
Now a days airports, hotels, subways, shopping centers
and some homes feature LEDs.
LED based traffic signals has been successful & is also
growing rapidly.
12. Organic Light Emitting Diode (OLED)
Introduction
OLED - Organic Light Emitting Diode
An OLED is any light emitting diode (LED) which
emissive electroluminescent layer is composed of a
film of organic compounds.
In OLED a electroluminescent layer is an organic
semiconductor material which is sandwiched
between two electrodes. One of these electrodes is
transparent.
13.
14. History
The first OLED device was developed by Eastman Kodak in
1987.
In 1996, pioneer produces the world’s first commercial
PMOLED.
In 2000, many companies like Motorola, LG etc. developed
various displays.
In 2001, Sony developed world’s largest full colour OLED.
15. In 2002, approximately 3.5 million passive matrix OLED sub-
displays were sold, and over 10 million were sold in 2003.
In 2010 and 2011, many companies announced AMOLED
displays.
Many developments had take place in the year 2012.
17. 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 layer: It contains two layers.
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.
20. Advantages
Faster response time than LCDs.
Consume significantly less energy.
Can be transparent when off.
Flexible and conformal displays.
Thinner display.
Safer for the environment.
Wider viewing angles; up to 170 degrees.
OLEDs refresh almost 1,000 times faster then LCDs.
Low cost materials and fabrication method.
Less expensive than LCD due to lesser components.
Can be made using plastic screens; LCDs require glass
backing.
21.
22. Disadvantages
OLED seems to be the perfect technology for all
types of displays, but it also has some problems.
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).
Currently, manufacturing is more expensive than LCDs.
Water can easily damage OLEDs.
OLED screens are even worse than LCD in direct sunlight.
Overall luminance degradation.
Limited market availability.
24. Each key can be
programmed to perform a
series of functions
Keys can be linked to
applications such as display
notes, numerals, special
symbols, etc...
27. Reference
Organic Light Emitting Devices By Joseph Shinar-
springer- Verlag, New York, 2004, Page No 150
Organic Electronic Materials By Riccardo
Farchichi,g.Grosso,2000, Page No 135
Physics Of Semiconductors By Wolf Gang Brutling ,VBH
Publishers, New York,1999, Page No 451
Highly Efficient OLED,S With Phosphorescent Materials By
Hartmut Versin, Wiley Publishers New York 2000, Page
No 121
www.oled-info.com