OLED Display Technology

8/3/2019 OLED Display Technology

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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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OLED Display Technology

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