Organic Optoelectronic Devices:
Organic Light-Emitting Diodes
(OLED)
Minlu Zhang
Outline
– Small molecular OLEDs (OLED)
– Polymer OLEDs (PLED)
– Applications
– Challenges
Small molecular OLEDs — Structure
Single layer device
Cathode
Organic Layer
Anode
Substrate
P-n junction device
Cathode
Electron transport layer
Hole transport layer
Anode
Substrate
Multiple layers device
Cathode
Electron Injection layer
Electron transport layer
Emissive layer
Hole transport layer
Hole Injection layer
Anode
Substrate
Small molecular OLEDs — Device operation principle
Cathode
Electron Injection layer
Electron transport layer
Emissive layer
Hole transport layer
Hole Injection layer
Anode
 Electrons injected from cathode
 Holes injected from anode
 Transport and radiative recombination of
electron hole pairs at emissive layer
Substrate
LUMO — Ec
Light
eTransparent
substrate
e-
e-
ITO HIL HTL EML ETL EIL Cathode
h+
h+
h+
HOMO — Ev
Small molecular OLEDs — Materials
EIL, ETL: n-type materials
Alq3, PBD
PBD
Alq3
HIL, HTL: p-type materials
NPB, TPD
EML:
NPB
TPB
Fluorescent dye
DCM2
Phosphorescent dye
PtOEP, Ir(ppy)3
DCM2
Small molecular OLEDs — Electrodes
Anode:
Indium-tin-oxide (ITO): 4.5-5.1 eV
Au: 5.1 eV
Pt: 5.7 eV
Cathode:
Ca: 2.9 eV
Mg: 3.7 eV
Al: 4.3 eV
Ag: 4.3 eV
Mg : Al alloys
Ca : Al Alloys
Small molecular OLEDs — Device preparation
Thermal vacuum evaporation
Cathode
Substrate
Vacuum
Electron transport layer
Hole transport layer
Anode
Substrate
Small
molecules
Growth:
~10-5-10-7 Torr
Room temperature
Heater
~20 Å- 2000 Å
Polymer OLEDs — Structure and Operation
Cathode
Cathode
Emissive polymer
Anode
Emissive polymer
Conducting polymer
Substrate
Anode
Substrate
http://www.ewh.ieee.org/soc/cpmt/presentations/cpmt0401a.pdf
Polymer OLEDs — Materials
Conducting polymers:
PANI:PSS
PANI
PDOT:PSS
PDOT
Emissive polymers:
R-PPV
PFO
PSS
Polymer OLEDs — Fabrication
Spin coating
Ink jet printing
Screen printing
Spin coating
Polymer film
Web coating
Substrate
Ink jet printing
Substrate
Why Organic LED?
 Vibrant colors
 High contrast
 Wide viewing angles from all directions
 Low power consumption
 Low operating voltages
 Wide operating temperature range
 A thin and lightweight form factor
 Cost-effective manufacturability , etc
Applications — Full color OLED display
A full color, 13-inch diagonal small-molecular-weight OLED display with
2mm thickness.
Flexible internet display screen
S. R. Forrest in Nature428, 911 (2004)
Applications — Full color OLED display
Samsung large OLED displays
KODAK OLED displays
http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=1473/1481/1491&pq-locale=en_US
Applications — Solid state white lighting
White OLEDs
From Universal Display Corporation
http://www.universaldisplay.com/white.htm
Challenges
 Lifetime
Red
Green
Blue
>10,000 hrs
>10,000 hrs
~1,000hrs ?
 High efficiency ?
 Pure color?