Light Emitting Diode Seminar Report

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Light Emitting Diode
Devansh Gupta
M.Sc 1st
Year

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Contents
A. LED
Introduction
Working Principle
Advantages
Disadvantages
Applications
B. OLED
Introduction
Working Principle
Advantages
Disadvantages
Application
C. Comparison Between LED &OLED

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D. Reference
Light Emitting Diode (LED)
Introduction
A light emitting diode (LED) is essentially a PN
junction opto-semiconductorthat 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.
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 separatedby a junction.

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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.

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Working Principle Of LED
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.
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.

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Each time an electron recombines with a positive
charge, electric potential energy is converted into
electromagneticenergy.
For each recombination of a negative and a
positive charge, an electromagneticenergy is
emitted in the form of a photon of light. Efficiency
this light depends on the semi-conductor
materialwhich is usually a combination of the
chemical elements gallium, arsenic and
phosphorus.
Advantages

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Energy efficient(producemore 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
Disadvantages
Very expensive than other lighting technologies
Requires accurate voltage & constant current flow
Can shift colour due to age & temperature
Cannot be used in high temperature(Lead to device
failure)
Applications
Vehicle indicator lights and brake lights.

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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 signal has been successful & is also
growing rapidly.
Organic Light Emitting Diode
(OLED)
Introduction
OLED - OrganicLight Emitting Diode

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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.
History
The first OLED device was developed by Eastman
Kodak in 1987.
In 1996, pioneer produces the world’s first
commercialPMOLED.
In 2000, many companies like Motorola, LG etc.
developed various displays.
In 2001, Sony developed world’s largest full
colour OLED.
In 2002, approximately 3.5 million passive matrix
OLED sub-displays were sold, and over 10 million
were sold in 2003.

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In 2010 and 2011, many companies announced
AMOLED displays.
Many developments had take place in the year
2012.

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Structure Of An OLED

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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
 Itcontains two layers.
1. Conducting layer -
 This layer is made of organic plastic
molecules that transport holes from the
anode.
 One conducting polymer used in OLEDs
is Polyaniline.
2. 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.

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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.
Polyaniline (Emeraldine Salt)
Polyfluorene

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How OLED Works

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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.

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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.

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Applications
Display sources.
Mobile phones.
Keyboards.
Digital watches.
Light sources.

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OLED vs. LCD
Greater view angle.
High contrast.
Faster response time.
Do not require backlighting.
Temperature(~50°C – 80°C).
Limited view angle.
Low contrast.
Slow response time.
Require backlighting.
Temperature(~0°C-100°C).
OLED LCD
Reference
OrganicLight Emitting Devices By Joseph Shinar-springer-
Verlag, New York, 2004, Page No 150
OrganicElectronic 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
HartmutVersin,Wiley Publishers New York 2000, Page No 121
www.oled-info.com