1.
NAST-625: NANOELECTRONICS AND BIOELECTRONICS
TOPIC: ORGANIC LED’S
COURSE INSTRUCTOR, PRESENTED BY,
DR .D.VANIDHA MUGILAN N
Centre for Nanoscience and Technology (16305012)
M.TECH 1ST YEAR NAST

2.
What is an LED?
Organic Light-emitting diode
OLED can use either use active or passive matrix.
1. Active matrix require thin flim transdistor backplane to
Switch individual pixels.but allow for higher resolution and
Larger display sizes.
2. Passive matrices uses a simple control scheme in which
You control each row in a display.
OLED is thinner and lighter than LCD.
OLED achieves a higher contrast ratio than LCD.
A major area of research is development of white OLED
Devices for solid state lighting applications.

3.
LED basic
When the electron falls down from
conduction band and fills in a hole in valence
band, there is an obvious loss of energy.
In order to achieve a reasonable efficiency for
photon emission, the semiconductor must
have a direct band gap.
Thus, for a direct band gap material, the excess
energy of the electron-hole recombination can
either be taken away as heat, or more likely, as
a photon of light.
• OLED displays without any backlight .
This gives rise to for us) a new type of device;
the light emitting diode (LED).

4.
Diode nothing but a pn Junction
Electron diffusion across a pn junction
creates a barrier potential (electric field)
in the depletion region.

5.
Diode in Reverse-biased
A reverse bias widens the depletion region, but allows minority carriers to move
freely with the applied field.

6.
Diode in Forward-biased
Lowering the barrier potential with a forward bias allows majority carriers to diffuse across the junction.

7.
Organic Semiconductors
These are not crystals! Not periodic structures
Band structure is somewhat different
◦ “Orbitals” determined by shape of organic molecule
◦ Quantum chemistry of pi bonds, not simple junior QM.
◦ Polymers are common.
Conduction is different
◦ Electrons or holes may wander along a polymer chain
◦ As with inorganic conductors.
◦ Some materials allow electrons to move.
◦ Some materials allow holes to move – typical for organics!!
Doping is more difficult
◦ Doping typically not used.
◦ Instead electrons/holes are provided by attached metals.

8.
OLED
An OLED (organic light-emitting diode) is a type of LED (light-
emitting diode), where the emissive electroluminescent layer is a
film of organic compound which emits light in response to an
electric current.
Demonstration of a flexible OLED
device

9.
Why OLEDs
Lighting efficiency
◦ Incandescent bulbs are inefficient
◦ Fluorescent bulbs give off ugly light
◦ LEDs (ordinary light emitting diodes) are bright points; not versatile
◦ OLEDs may be better on all counts
Displays: Significant advantages over liquid crystals
◦ Faster
◦ Brighter
◦ Lower power
Cost and design
◦ LEDs are crystals; LCDs are highly structured; OLEDs are not –
◦ Malleable; can be bent, rolled up, etc.
◦ Easier to fabricate
In general, OLED research proceeds on many fronts

10.
How OLEDs Operate - Components
• Substrate- support structure,
sometimes flexible
• Anode
• Organic Material
o Emissive
o Conductive
• Cathode

11.
The basic OLED

12.
The basic OLED
• The holes move more efficiently in organics

13.
The basic OLED
• The holes move more efficiently in organics
• Excitons begin to form in emissive layer

14.
Advantages
• Lighter
• Flexible
• Thinner
• Brightness
• Power Consumption and Efficiency
• Easier to Produce in Large Sizes
• 170 Degree Viewing Area
• Theoretically Cheaper to Make in the Future
• Faster Response Time

15.
Disadvantages
• Vulnerability to Fluids
• Lifetime of Blue Organic Film
• Cost of Manufacturing
• Power Consumption (White Backgrounds)

16.
Commercial Uses
• Portable Digital Media Players
• Mobile Phones
• Car Radios
• Digital Cameras
• High Definition TVs

17.
Points to remember
1. Four main components are the anode, cathode, emission, and conductive layers.
2. Unlike normal LED's, OLEDs use organic material layers in the process.
3. Photons are released when an electron and a hole are paired, giving off light.
4. The thickness of layers of an OLED are in the Angstrom range.
5. There are two general types of OLEDs. Those based on small molecules and those
made using polymers

18.
Jablonski diagram - OLED
Exciton
◦ Spin 0 (singlet)
◦ Spin 1 (triplet)
◦ Can transfer its energy but not its spin
to molecule
◦ Thus spin-1 can’t excite fluorescents
◦ Lose ¾ of excitons
But
◦ Use phosphors
◦ Bind to polymer so that exciton can
transfer spin
Then 4 times as many excitons cause
light emission

19.
THANKYOU