This document provides information on light emitting diodes (LEDs) and organic light emitting diodes (OLEDs). It defines LEDs and OLEDs, describes their basic structures and working principles. The key differences are that LEDs use inorganic semiconductors while OLEDs use organic thin films. The document lists advantages of each such as energy efficiency and flexibility for OLEDs. It also discusses applications in devices like phones, displays and lighting. In conclusion, it compares both technologies on factors like viewing angle, response time and temperature range.

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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