1. Light Emitting Diodes(LED) and Organic Light Emitting Diodes(OLED)

2. Plan of talk Light-Emitting Diode Organic Light-Emitting Diode
Bands and Conduction
Semiconductor
Standard Diode
Light Emission
Organic Light-Emitting Diode
Organic Semiconductors
Organic Diode

3. The Bands on Stage E E E E E No Gap Small Gap Gap Insulator Conductor
Semiconductor
Doped Semiconductors

4. Doping – Add Impurities
N-type
P-type

5. The Bands on Stage E E E E E N-type P-type No Gap Small Gap Gap
Insulator
Conductor
Semiconductor
Doped Semiconductors

6. Diode: p-type meets n-type

7. Diode: p-type meets n-type

8. Diode: p-type meets n-type

9. Diode: p-type meets n-type
Electric Field
Excess Negative Ions
Excess Positive Ions

10. Diode: p-type meets n-type
Try to make current flow to left?
Depletion Zone Grows
Electric Field

11. Diode: p-type meets n-type
Try to make current flow to right?
Current Flows!
Electrons in higher band meet Holes in lower band
Electric Field
Current

12. A light-emitting diode (LED) is a two-lead semiconductor light source
A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.

13. Organic Semiconductors
These are not crystals! Not periodic structures
Band structure is somewhat different
“Orbitals” determined by shape of organic molecule
Polymers are common
Conduction is different
Electrons or holes may wander along a polymer chain
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

14. The basic OLED
Anode
Cathode
Conductive Layer
Emissive Layer

15. The basic OLED The holes move more efficiently in organics Anode
Cathode
Conductive Layer
Emissive Layer

16. The basic OLED The holes move more efficiently in organics
Excitons begin to form in emissive layer
Anode
Cathode
Conductive Layer
Emissive Layer

18. OLEDs Similar physics to LEDs but Manufacturing advantages
Non-crystalline
No doping; use cathode/anode to provide needed charges
Manufacturing advantages
Soft materials – very malleable
Easily grown
Very thin layers sufficient
Many materials to choose from
Relatively easy to play tricks
To increase efficiency
To generate desired colors
To lower cost
Versatile materials for future technology

19. Some references How Stuff Works Hyperphysics Website
Craig Freudenrich, “How OLEDs work”
Tom Harris, “How LEDs Work”
Hyperphysics Website
http ://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html
“The P-N Junctions”, by R Nave
Connexions Website
“The Diode”, by Don Johnson
Webster Howard, “Better Displays with Organic Films”
Scientific American, pp 5-9, Feb 2004
M.A. Baldo et al, “Highly efficient phosphorescent emission from organic electroluminescent devices”
Nature 395, (10 September 1998)
Various Wikipedia articles, classes, etc.