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Jay Dhamsaniya
Rakesh Adroja
Department of E & C Engineering
Institute of Technology
Nirma University
Ahemedabad
OCT - 2011
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Definition :
An organic light emitting diode (OLED) is a light-emitting diode (LED)
in which the emissive electroluminescent layer is a film of organic
compounds that emits light when an electric current passes through it.
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2 layer structure Active & In-active condition
Material used in layer
o Anode (+) p Indium tin oxide (ITO)
o Cathode (-) p Metals such as aluminium (Al) and calcium (Ca)
o Emissive layer p Alq3 which emits radiation in the range of
green lighto Conductive layer p Diamine
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For efficient emission p recombination zone should be in themiddle of the organic emissive layer
In organic semiconductors, holes are more mobile than electrons
Recombination happens closer to the emissive layer
Problem solution : Multi layer structured OLED
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Electron-hole recombination zone is shifted in the middle of the emissive
layer
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OLED
OLED
Organicmaterial used
Organicmaterial used
Small MoleculeOLED
Small MoleculeOLED
Polymer OLED
Polymer OLED
PhosphorescentOLED
PhosphorescentOLED
Transparency
Transparency
Bottom or Topemitting OLED
Bottom or Topemitting OLED
TransparentOLED
TransparentOLED
Foldable OLED
Foldable OLEDPixel
Formation used
PixelFormation used
Active MatrixOLED
Active MatrixOLED
Passive MatrixOLED
Passive MatrixOLED
Stacked OLED
Stacked OLED
Inverted OLED
Inverted OLED
White OLED
White OLED
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[A] Classification according to Organic Material used
1. SMALLMOLECULEOLEDs:
First developed at Eastman Kodak by Dr. Ching W. Tang
Example: Alq3
2. POLYMERMOLECULEOLEDs:
Example: poly(p-phenylene vinylene)
3
. PHOSPHORESCENTMATERIALSOLEDs: Example: Ir(mppy)3,
It is a phosphorescent dopant which emits green light
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[B]Classification according to Transparency
1. Bottom or top emissive OLEDs:
One of the electrode is kept transparent
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[B]Classification according to Transparency
2. Transparent OLEDs:
Both electrodes are kept transparent
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[C] FOLDABLE OLED
Flexible substrate is used
It is prepared by roll-to-roll patterning method
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[C] FOLDABLE OLED
FOLEDs offer Revolutionary Features for Display:
1. Flexibility
2. Ultra-lightweight, thin form
3. Durability
4. Cost-effective processing
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[D] CLASSIFICATION ACCORDING TO PIXELFORMATION USED
1. Active Matrix OLEDs (AM-OLEDs):
Display is a set of pixel
Pixel is a single oled
Individual Cathode and Anode
Biasing current provided to pixel, is
controlled by TFT according to information
A/D: Reduces power consumption
D/A: Patterning/Fabrication cost is high
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[D] CLASSIFICATION ACCORDING TO PIXELFORMATION USED
2. Passive Matrix OLEDs (PM-OLEDs):
Cathode and Anode are kept common for
each rows/columns
Pixel formed at the intersection
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Advantages:
1. Very thin panel of approximately 1mm
2. Low power consumption
3. High brightness
4. High contrast ratio of 10,000 : 1
5. Wide viewing angle of 170r
6. No environmental drawbacks
7. Foldable display panel
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Advantages ofOLED Display over TFT-LCD Display:
1. Contrast Ratio
Higher contrast ratio than TFT-LCD display
Better impression for higher brightness
Contrast
Ratio
(Sunlight
Readable)
Condition OLED TFT-LCD
Dark room > 10,000 : 1 300 : 1
Rainy 400 130
Cloudy 190 10
Sunlight 50 4
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2. Viewing Angle
Higher viewing angle
up to 170r
for constant contrast ratio
Graph:
contrast V/S viewing angle
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3. Response Time
Fast time response
in order of
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4. Backlight Function
No backlight required in OLED display
During black background OLED is turned OFF
In LCD backlight is still required
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4. Power Efficiency
OLED display is more power efficient
than TFT-LCD display
For the same power OLED display is
more brighter
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1. Limited life time
2. Color balancing issues
3. Water damage
4. Power consumption
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Light weight
Thin
Unbreakable
Low cost processing
potential for Roll-to-Roll
patterning
New product possibility
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There are many other opportunities for application of organic thin-
film semiconductors and challenges are remain for development that is
shown following table.
Challenges Opportunities
Matireals blue & white EL, low-cost ITO alternatives
Process cost high
OLED Industry still in the early stage of development
Driving Tech for AMOLED is still under development
White OLED high performance WOLED is needed
Solution Printing tech is viable for large size and low cost
FOLED will be very attractive for application inconformal,
fordable or even flexible lighting and displays
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