1. OLEDs Theory & Fabrication
Teddy Dowling 4/17/17
Organic Light Emitting Diodes are becoming the standard in modern displays. This presentation will go over the structure of OLEDs, the theory behind them, and various fabrication techniques. Different types as well as advantages and disadvantages will also be covered.

2. OUTLINE Organic Semiconductors OLED Structure – What they are made of
Electro-Phosphorescence – How they work
Fabrication – How they are made
Types of OLEDs
Advantages/Disadvantages

3. Organic Semiconductors
Made from carbon based polymers
Emit Light when electricity is applied through them
Development of the technology began in the early 2000’s
Most organic materials are intrinsically p- type
Higher hole mobility than electron mobility
Opposite of non-organic semiconductors

4. OLED Structure OLEDs are solid state semiconductors
nm thick
OLEDs produce holes and electrons using organic molecules Instead of using layers of n-type and p- type semiconductors
OLEDs have at least six layers
Modern OLEDs use many more layers for efficiency, with basic functionality remaining the same

5. OLED Structure Substrate (clear material) Anode Removes electrons
Conducting layer (P-type material)
Organic plastic molecules that transport "holes" from the anode
Emissive layer (N-type material)
Organic plastic molecules (different than the conducting layer) transport electrons from the cathode
This layer emits photons
Cathode 
Injects electrons

6. Electro-phosphorescence
Electron-hole recombination
Voltage is applied across OLED
Current flows from cathode to anode through at least two organic layers
Electrons flow from the cathode to the emissive layer
Anode generates holes in the conductive layer by removing electrons
Electron-Hole pairs are formed at the boundary between the emissive and the conductive layers
The electron emits energy in the form of a photon

7. Electro-phosphorescence
Recombination of charges leads to the emission of a photon
Different materials and dopants can be used to generate different colors
Frequency is given by the energy gap (E = hν)
Combinations can be used to create a white light source
Variable currents can increase or decrease light intensity

8. Fabrication Three Types:
Vacuum Deposition/Vacuum Thermal Evaporation(VTE)
Organic Vapor Phase Deposition
Inkjet Printing

9. Vacuum Thermal Evaporation
Done in a vacuum chamber with very low pressure
Organic molecules are heated until they evaporate
A cooled substrate condenses them into films
Disadvantages
Difficult to prevent contamination
Difficult to ensure uniformity and doping concentration over large substrates
Expensive

10. Organic Vapor Phase Deposition
Also done under low-pressure in a reactor chamber with heated walls
Materials are condensed into thin films on a cooled substrate.
Carrier gas transports evaporated organic molecules
Improves control over doping using temperature and carrier gas flow rate
Advantages
Increased efficiency for large-area substrates
Reduced cost

11. Inkjet Printing Advantages
Organic materials are diluted into a liquid and sprayed onto substrate
Similar to other modern ink printers
Prints Using vaporized organic materials instead of liquid
Advantages
Cheaper to manufacture using this method
Allows OLEDs to be printed onto very large films (TV’s, Billboards, etc.)

12. Types of OLEDs Transparent OLED Passive-matrix OLED (PMOLED)
Active-matrix OLED (AMOLED)
Foldable OLED
White OLED

13. Transparent OLED Transparent components (substrate, cathode and anode)
Up to 85 percent as transparent as their substrate when turned off
Allow light to pass in both directions when turned on
A transparent OLED display can be either active or passive matrix

14. Passive-matrix OLED (PMOLED)
Strips of cathode, organic layers, and strips of anode
Anode strips are arranged perpendicular to cathode strips
Intersections of cathode and anode make up the pixels where light is emitted
External circuitry applies current to selected strips of cathode and anode
Easy to make but consume more power than other types (still less than LCDs)

15. Active-matrix OLED (AMOLED)
Full layers of cathode, organic molecules, and anode
Anode layer overlays a thin film transistor (TFT) array that forms a matrix
Consume less power than PMOLEDs and are very efficient for large displays
Faster refresh rates

16. Foldable OLED
Substrates made of very flexible metallic foils or plastics
Very lightweight and durable
Potentially could be attached to fabrics to create "smart" clothing

17. White OLED Emit white light that is very bright
More energy efficient than fluorescent lights
Reduces energy costs for lighting

18. Advantages/Disadvantages
Flexible, foldable, and transparent
Brighter than other displays
Fast
Relatively easy to produce
Low power consumption
Disadvantages
Expensive to manufacture
Prone to water damage
Blue organics have shorter life (14,000 hours)

19. References
technology/

20. 5 Key Concepts OLEDs are made of organic semiconductors
Layers of OLEDs – Cathode, Emissive, Conductive, Anode
Electro-phosphorescence produces the emission of photons
Three Fabrication Techniques (Advantages/Disadvantages)
OLEDs reduce power consumption

21. Questions?