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OLED (Organic Light Emitting Diode)
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OLED (Organic Light Emitting Diode)
Power efficiency for OLED materials
Incandescent light bulbs : 10 – 20 lm/W
Florescent lamps : 80 – 100 lm/W
Yellow-Green Polymeric OLEDs : 20+ lm/W
Green Phosphorescent SM OLEDs : 90 lm/W
Other colors : 5 – 40 lm/W
White (not yet optimized) : ~ 5 lm/W
* Internal quantum efficiency : up to 100%
* all at low current operations
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OLED (Organic Light Emitting Diode)
3 important properties of light
- Polarization : LCD
- Color (wavelength)
- Intensity (brightness) : Cd/m2 (nit)
* Efficiency of light source is measured by lm/W
* Intensity of bright sunlight : 1,000 W/m2
2,000 Cd/m2 (nit)
* Best reading brightness : 150 – 200 nit
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Efficiency
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Efficiency
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OLED (Organic Light Emitting Diode)
HIL : Hole Injection Layer
EML : Emissive Layer
HTL : Hole Transport Layer
ETL : Electron Transport Layer
EIL : Electron Injection Layer
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OLED (Organic Light Emitting Diode)
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OLED (Organic Light Emitting Diode)
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OLED (Organic Light Emitting Diode)
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OLED (Organic Light Emitting Diode)
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OLED (Organic Light Emitting Diode)
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OLED configuration and Operation
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OLED configuration and Operation
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OLED configuration and Operation
Energy level Diagram of Two Layer OLED
LUMO
Low hole mobility in ETL
HOMO
Build-up hole density
HTL : Hole Transport Layer
ETL : Electron Transport Layer
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OLED configuration and Operation
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OLED (Organic Light Emitting Diode)
How to fabricate OLED ?
- RGB
Material
- charge transport
- efficiency
Device
- layer structure
- efficiency
- injection mechanism
- emission mechanism
- stability
Panel
- pixel design
- encapsulation
- driving scheme
- reliability
- production
METAL
EML
HTL
ITO
Glass
dot matrix
scan
line
data line
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Common OLED Device and Materials
Common electron and hole transport materials and a two layer OLED
ETL :
Alq3 (tris(8-hydroxyquinolinato)aluminum)
Electron mobility = 10-6 cm2/Vᆞs at 4×105 V/cm
Emission wavelength = 530 nm (green)
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Common OLED Device and Materials
HTL :
TPD (N,N’-diphenyl-N,N’-bis(3-methylphenyl)(1,1’-biphenyl)-4,4’-diamine)
NPB (N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine)
Hole mobility = 10-3 ~ 10-4 cm2/Vᆞs at 4×105 V/cm
Tg (glass transition temperature) < 100oC
Metal electrode : MgAg alloy (10:1) ( low work function (3.66 eV) metal )
ITO :
Transparent electrode ( high work function (4.5~5.0 eV) electrode )
UV-ozone or Oxygen plasma treatment enhances hole injection
Work function increase
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Hole Injection Materials
ITO surface treatments :
O2 plasma
CF4/O2 plasma
UV-ozone
Removal of organic contaminants
Work function increase up to near 5.0 eV
Work functions of common HTL materials ~ 5.5 eV
but still, about 0.5 eV lower than HOMO of HTL materials
Hole Injection Material in between ITO/HTL
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Hole Injection Materials
poly(3,4ethylenedioxythiophene)poly(styrene))
copper phthalocyanine
N,N’-diphenyl-N,N’-bis(3methylphenyl)(1,1’biphenyl)-4,4’-diamine
tris(4bromophenyl)aminium
hexachloroantimonate)
α-sexithophene
4,4’,4”-tris(N,Ndiphenylamino)triphenylamine)
tetra(fluoro)tetra(cyano)quinodimethane
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Hole Injection Materials
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Hole Transport Materials
NPB (N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine)
N
N
The most commonly used HTL material
Tg = 98oC
1. Biphenyl diamine derivatives
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Hole Transport Materials
2. Starburst amorphous molecules
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Hole Transport Materials
3. Spiro-linked molecules
HTM
NPB
Spiro-NPB
Spiro-TAD
Molecular weight
588.8
1185.5
985.3
Tg (oC)
98
147
133
Tm (oC)
290
294
276
Tsublim (oC at 4×10-5 mbar)
310
430
355
λmax (PL film)
440
450
405
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Hole Transport Materials
4. Miscellaneous examples
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Electron Transport and host emitting materials
Alq3 (tris(8-hydroxyquinolinato)aluminum)
N
O
N
O
The most commonly used ETL material
Al
O
N
1. Modified Alq3 molecules
tris(5-hydroxymethyl-8quinolinolato)aluminum
bis(5,7-dichloro-8quinolinolato)-(8quinolinolato)aluminum
(salicylidene-oaminophenolato)(8quinolinolato)aluminum
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Electron Transport Materials
2. Fluorescent metal chelates
(blue)
445nm (blue)
(green)
515nm (green)
(blue)
(blue)
ODZ : 2-(2-hydroxyphenyl)-5-phenyloxadiazole
BIZ : 1-phynyl-2-(2-hydroxyphenyl)benzimidazole
Bepp2 : bis(2-(2-hydroxyphenyl)pyridine)beryllium
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Electron Transport Materials
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Electron Transport Materials
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Electron Transport Materials
3. Novel electron transport materials
PBD : 2-biphenyl-4-yl-5-(4-t-butylphenyl)-1,3,4-oxadiazole
TPBI : 2,2’,2”-(benzene-1,3,5-triyl)-tris(1-phenyl-1H-benzimidazole)
COT : octaaryl-cyclooctatetraene
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Electron Transport Materials
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Fluorescent Materials (dopants)
1. Green
N,N’-diethylquinacridone
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Fluorescent Materials
2. Red
Target : 4 cd/A, color coordinates x=0.65, y=0.35, lifetime over 10,000hr at initial luminance of 300 cd/m2
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Fluorescent Materials
3. Blue
Target : 4~5 cd/A, color coordinates x=0.14~0.16, y=0.11~0.15, lifetime over 30,000 hr
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Fluorescent Materials
3. Blue
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Triplet emitting materials
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Triplet emitting materials
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Triplet emitting materials
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Charge injection and transport
Energy level alignment
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Charge injection and transport
Cathode
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Charge injection and transport
Cathode
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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Phosphorescence
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