16-10-2012, 04:40 PM
Organic Light Emitting Diodes
Organic Light Emitting Diodes.ppt (Size: 490.5 KB / Downloads: 49)
Plan of talk
Light-Emitting Diode
Bands and Conduction
Semiconductor
Standard Diode
Light Emission
Organic Light-Emitting Diode
Organic Semiconductors
Organic Diode
Light Emission
Electrons in a Lattice
Atom has bound states
Discrete energy levels
Partially filled by electrons
Periodic array of atoms (cf. QM textbook)
Effectively continuous bands of energy levels
Also partially filled
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
OLEDs
Similar physics to LEDs but
Non-crystalline
No doping; use cathode/anode to provide needed charges
Fluorescence/phosphorescence enhance excitonlight probability
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