How LED & OLED Works? Advantages & Disadvantages Of LED & OLED Their Applications Comparision Between LED & OLED

1. Light
Emitting
Diode
Presented by
Devansh Gupta
M.Sc Polymer Science
Semester 1

2. Contents
A. LED
Introduction
Working Principle
Advantages
Disadvantages
Applications
B. OLED
Introduction
Working Principle
Advantages
Disadvantages
Application
C. Comparison BetweenLED & OLED
D. Reference

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.

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.

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.

16. Structure OfAn OLED

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.

18. Polyaniline(EmeraldineSalt)
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.

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.

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.

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

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...

26. 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

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