Download Organic Light Emitting Diodes

Light Emitting Diodes(LED) and
Organic Light Emitting
Diodes(OLED)
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Plan of talk
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Light-Emitting Diode
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Bands and Conduction
Semiconductor
Standard Diode
Light Emission
Organic Light-Emitting Diode
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Organic Semiconductors
Organic Diode
Light Emission
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The Bands on Stage
E
Gap
Insulator
E
E
No
Gap
Small
Gap
Conductor
Semiconductor
E
E
Doped Semiconductors
3
Doping – Add Impurities
N-type
P-type
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The Bands on Stage
E
E
E
E
E
N-type
Gap
Insulator
No
Gap
Conductor
P-type
Small
Gap
Semiconductor
Doped Semiconductors
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Diode: p-type meets n-type
E
E
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Diode: p-type meets n-type
E
E
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Diode: p-type meets n-type
E
E
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Diode: p-type meets n-type
E
E
Electric Field
Excess
Negative
Ions
Excess
Positive
Ions
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Diode: p-type meets n-type
Try to make current flow to left?
Depletion Zone Grows
Electric Field
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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
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A light-emitting diode (LED) is a twolead 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.
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Organic Semiconductors
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These are not crystals! Not periodic structures
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Band structure is somewhat different
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“Orbitals” determined by shape of organic molecule
Polymers are common
Conduction is different
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Electrons or holes may wander along a polymer chain
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Some materials allow holes to move – typical for organics!
Doping is more difficult
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Doping typically not used
Instead electrons/holes are provided by attached metals
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The basic OLED
Anode
Conductive Layer
Cathode
Emissive Layer
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The basic OLED
• The holes move more efficiently in organics
Anode
Conductive Layer
Cathode
Emissive Layer
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The basic OLED
• The holes move more efficiently in organics
• Excitons begin to form in emissive layer
Anode
Conductive Layer
Cathode
Emissive Layer
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OLEDs
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Similar physics to LEDs but
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Manufacturing advantages
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Soft materials – very malleable
Easily grown
Very thin layers sufficient
Many materials to choose from
Relatively easy to play tricks
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Non-crystalline
No doping; use cathode/anode to provide needed charges
To increase efficiency
To generate desired colors
To lower cost
Versatile materials for future technology
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Some references
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How Stuff Works
http://electronics.howstuffworks.com
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Craig Freudenrich, “How OLEDs work”
Tom Harris, “How LEDs Work”
Hyperphysics Website
http ://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html
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“The P-N Junctions”, by R Nave
Connexions Website
http://cnx.org
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Webster Howard, “Better Displays with Organic Films”
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Scientific American, pp 5-9, Feb 2004
M.A. Baldo et al, “Highly efficient phosphorescent
emission from organic electroluminescent devices”
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“The Diode”, by Don Johnson
Nature 395, 151-154 (10 September 1998)
Various Wikipedia articles, classes, etc.
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