Advantages of OLEDs

(1)

Organic Semiconductor EE 4541.617A 2009. 1^stSemester

2009 5 28

Changhee Lee, SNU, Korea Changhee Lee

School of Electrical Engineering and Computer Science Seoul National Univ.

[email protected] 2009. 5.28.

Advantages of OLEDs

• Superior viewing performance:

emissive bright colors, wide viewing angle, fast response time, and high contrast

• Simple fabrication processes:

vacuum deposition, inkjet printing, spin coating, roll-to-roll (web) processing

Substrate Vacuum Deposition

Ink-jet cartridge Inkjet Printing

• Excellent operating characteristics:

low operating voltage, power efficient, and wide temperature range

• Good form factor:

Thin, light-weight, rugged, and flexible Æ Ultimate Portable Communication Devices

Fine Metal Shadow Mask

Source

Red ink Green ink Blue ink

http://www.universaldisplay.com/

OLED vs LCD (http://www.oled- display.net/oled-television)

http://amoled.samsungsdi.com/

(2)

Development of OLED technology

1998 19991999 2000 200

1

200

2 2003 2004 2005

Pioneer

S K d k Pioneer,

PM Sony SDI 15.1” Sanyo IDTech S

1982 1990 • • • 2006

Samsung SDI AMOLED 양산 2007

5.2” PM-OLED Sanyo-Kodak 5.5” AM-OLED 4 Area

Color OLED

Sony 13”

AMOLED AM-OLED

XGA

LG, 8”-Full color

LGE 1.8”PMOLED Motolora Area color

Toshiba 2.8”고분 자LED

TMD 17” AM-PLED

XGA Sanyo 14.7”AMOL EDWhite EL

5cd/A IDTech 20”a-Si AMOLED

Sanyo-Kodak 2.2” AMOLED

Samsung SDI 17” UXGA AMOLED

LGE-LPL 20.1” XGA AMOLED

SEC 40” WXGA

a-Si AMOLED

Samsung SDI 2.6” AMOLED

Sony 3.8”

PDA Top- 1^stOLED

ITO/Diamine/

Alq3/MgAg USP 4,356,429 Ching W. Tang Eastman Kodak

Samsung SDI 31” AMOLED TV 개발

Sony TMD (‘06) 25” LTPS AMOLED TV

Changhee Lee, SNU, Korea

ETRI 2” PM-OLED

UDC OLED

Pioneer OLED DNP OLED

Flexible OLED

Seiko-Epson 40” WXGA

AMOLED (tiled, Ink-jet) emission AMOLED

1^stPolymer LED ITO/PPV/Al USP 5,247,190 Sir Richard Friend, FRS

Cambridge University

Sony 11”

AMOLED TV(XEL-1) 판매 AMOLED TV

LGE (‘07) 3.5” AMOLED

Oxide TFT

Progress in the efficiency of white OLEDs

N. Ide (Matsushita Electric Works, Ltd.), et al., SPIE (2008)

(3)

Organic LEDs (polymers or small molecules)

Electron-transporting materials

N O N O N

O Al

Alq3

N N (H₃C)₃C O

PBD Emitting materials

NC CN

ETL Cathode

EML

－

Exciton

- LUMO_ETL

LUMO_HTL ^Electron

injection -

LUMO_EML ^N ^N

Hole-transporting materials

N N

CH H3C

TPD NPD

DPVBi

Alq3

N O

N O N OAl

N O NC CN

Ir(ppy)₃ N

3 Ir

DCJTB

Glass

ITO HIL HTL

+

Changhee Lee, SNU, Korea

+ +

+

- - Φe

light

Φ_metal HOMO_ETL HOMO_HTL

ΦITO

Hole injection

+

+ -

HOMO_EML

CH3TPD α-NPD Hole-injecting materials

PEDOT:PSS

n

S O3- S O3- S O3H S O3H S O3H S O3H

S S S S S S

O O

O

O O O

n

CuPC

Cu N N

N

N N

N

N N

CH3

H3C CH3

m-MTDATA

Kodak

B G Y R

R=H, t-Bu ADN Kodak Ar Ar

R

N O O N

O Si

Me

Fluorescent emitters

DPVBi

Idemitsu Kosan Alq3

Host

Almq3

TBP Kodak

R=H Coumarin-545

Al N N O O Al N

N O O

N S

O O

N R R R

Si Me

2PSP Chisso

rubrene rubrene

Dopant

Mitsubishi

R₁=R₂=R₃=R₄=H, R₅=Me DCM-2

R₁=R₂=R₃=R₄=Me, R₅=t-Bu DCJTB

Kodak Me-QA

Pioneer BCzBi

Idemitsu Kosan

R=H, Coumarin-545 Pioneer

R=CH₃, Coumarin-545T Kodak

N

DPAVBi Idemitsu Kosan

R R

(4)

Blue Green Red

Dopant

FI i

Ir(ppy)

₃

Ir(ppy)

2

acac

Btp

₂

Ir(acac)

N Ir

O

2 N O

F

F Ir

N O O

2 N

Ir N O O CF3 F3C

2 N N

N Ir

O

2 O S N

Ir

3 N H₃C

Host and Phosphorescent Dopant Materials

Host

CN-PPV CBP

mCP

UGH2 TAZ

PVK FIrpic

(CF

₃

ppy)

₂

Ir(pic) Ir(mpp)

₃

PtOEP

n O

CN

CHCH2n N

N N

N

N N

N N Pt 2

Si CH3 H3C

N Ir

2

Changhee Lee, SNU, Korea Hole/Exciton

Blocking Materials

BCP C

₆₀

F

₄₂

mCP V

N N H3C CH3

F F F F F

F F

FF F

F F

F

F F

FF F F F F F

FF

F F F F

FF F F

F F

Dr. H. N. Cho (InkTek)

N O N OAl

O

BAlq

Fluorescence Phosphorescence

Host Alq3, ... CBP, TCTA, mCP, …

Excited state Singlet Triplet

Comparison of fluorescent and phosphorescent OLEDs

Excited state Singlet Triplet

Exciton diffusion length 50 ~ 100 Å > 1000 Å

Exciton blocking layer - BCP, Balq, etc.

Dopant concentration 0.1 ~ 3 % 5 – 15 %

Maximum quantum efficiency 25 % 100 %

Luminous efficacy

Red: ~6 cd/A Green: ~20 cd/A Blue: ~6 cd/A

Red: 6~20 cd/A Green: 17~50 cd/A Blue: ~ 10 cd/A

Lifetime ~ 50,000 hour ~10,000 hour

(5)

Color CIE (x,y) Efficiency (cd/A) Half-Life (hr)

저 형 광

Red 0.65, 0.35 5.5 >80,000 @ 1000 cd/m²

Green 0.32, 0.62 19 40,000 @ 1000 cd/m²

Light blue 0.17, 0.30 12 21,000 @ 1000 cd/m²

Blue 0.15, 0.15 5.9 7,000 @ 1000 cd/m²

White 0 30 0 34 12 23 000 @ 1000 cd/m²

OLED Performance

저 분 자

White 0.30, 0.34 12 23,000 @ 1000 cd/m²

인 광

Red 0.65, 0.35 15 >22,000 @ 500 cd/m²

Orange 0.61, 0.38 22 15,000 @ 300 cd/m²

Green 0.31, 0.64 27 25,000 @ 600 cd/m²

Light blue 0.14, 0.23 8 -

White 0.39, 0.39 38 -

Red 0.68, 0.32 1.7 1790 @ 1000 cd/m²

Orange 0.58, 0.42 0.9 8138 @ 1000 nit

Changhee Lee, SNU, Korea

고 분 자

형 광

Yellow 0.50, 0.49 2.1 2420 @ 4000 cd/m²

Green 0.43, 0.55 7.7 2912 @ 2000 cd/m²

Blue 0.16, 0.22 6.9 >1147 @ 800 cd/m²

White 0.30, 0.33 3.8 235 @ 800 cd/m²

인 광

Red 0.67, 0.28 1.3 >8350 @ 100 cd/m²

Green 0.36, 0.59 22.8 2649 @ 400 cd/m²

• Electron-Hole Balance Æ improved efficiency & Lifetime η

_φ

= χγβφ L

Electron-Hole Balance

1 0

balanced recombine all

Charge balance factor

η

_φ

χγβφ L

χ:coupling-out factor γ:charge balance factor

β:probability of production of emissive species φL

:quantum efficiency of luminescence

To maximize the charge balance factor γ : γ=1.0

γ=0.5

- Equal amount of electrons and holes are injected.

- All the injected electrons and holes recombine.

Æ Ambipolar emitting layer

Æ Mixed emitting layer (co-doped host)

Æ p-type or n-type doping at the electrode interface J. C. Scott et al., SPIE Proc., 3476, 111 (1998)

γ=0

hole only electron only

balanced escape all

(6)

Al

Metal-doped organic layer (n-doping)

Control of:

• Dopant concentration (Extent of reaction)

Electron injection layer

Enhanced electron injection in OLEDs using an Al/LiF electrode

Al

p ( )

• Thickness of doped layer

• Realize ohmic contact

• Increase conductivity

J.Kido et al., Appl.Phys.Lett.(1998) L. S. Hung, C. W. Tang, and M. G. Mason, APL 70, 152, (1997)

ZnPC

Vacuum level

3.34 eV 5.28 eV

5.24 eV 8.34 eV

E

LUMO

e

−

Hole injection layer (p-doped organic layer)

F₄TCNQ

E

F

E

F

HOMO

LUMO

HOMO

e

p-type doping

(a) (b)

(a) undoped (b) p-type doped

M. Pfeiffer , K. Leo, X. Zhou, J.S. Huang, M. Hofmann, A. Werner, J. Blochwitz-Nimoth, Organic Electronics 4 (2003) 89–103 Weiying Gao and Antoine Kahn, Appl. Phys. Lett. 79, 4040 (2001) zinc phthalocyanine (ZnPc) doped with tetrafluorotetracyanoquinodimethane

(7)

Alq3(30 nm) BCP:Cs(21 nm, 1:1)

Al

N-type

Insulator

- -

--- - -

- +

+ + +

+ +

+

+ ^BCP

Cs+

Alq3

N O O AlN

p-i-n OLED

10¹ 10² 10³

cm2 ) 10⁴

10⁵

L

ITO

aNPD:F4TCNQ aNPD(30 nm)

p-i-n structure

Insulator

P-type

+ +

+ ++

+ + ++ + + - -

- - -

- -

- - -

α-NPD

F4TCNQ^- +-

Alq3 N

O N

N N

α-NPD

10^-4 10^-3 10^-2 10^-1 10⁰ 10

Current Density (mA/c

10⁰ 10¹ 10² 10³

Luminance (cd/m 2)

Current Density Luminance

10^-5

10 8 6 4 2 0

Voltage (V)

10^-1

M. Pfeiffer , K. Leo, X. Zhou, J.S. Huang, M. Hofmann, A. Werner, J. Blochwitz- Nimoth, Organic Electronics 4 (2003) 89–103

Organic Semiconductor EE 4541.617A 2009. 1^stSemester US 20080030131 (2008.02.07) Francisco J. Duarte, Kathleen M. Vaeth, Liang-Sheng

Liao, Eastman Kodak Company

A light-emitting device, comprising: a multi-layer stack of materials supported on an optically transparent support member, a first spatial filter, and a second spatial filter spaced from the first spatial filter. The multi-layer stack including at least one organic light- emitting layers, an anode layer, and a cathode layer. The first spatial filter is disposed intermediate the multi-layer stack of materials and the second spatial filter.

Tandem OLED

2 2

3

OLED 2 Unit P-N junction CBP:Ir(ppy)3 doped

OLED 3 OLED 3 Unit

cathode Mg:Ag

CBP:Ir(ppy)3 doped OLED 2 aNPD:FeCl3(48nm, 1 %) Alq3:Li(24nm, 1.2%)

1

Glass ITO

P-N junction

anode OLED 1 Unit aNPD:FeCl3(48nm, 1 %)

Alq3:Li(24nm, 1.2%) CBP:Ir(ppy)3 doped OLED 1

3배의 빛

L. S. Liao, K. P. Klubek, and C. W. Tang, Appl. Phys. Lett.84, 167 (2004)

(8)

I-V characteristics of organic semiconductors

Injection limited

Thermionic emission ] 1 )

[exp( −

= k T

J eV J

B

s ^* ²

exp( )

T k T e

A J

B bn s

φ

= −

Current

Bulk Limited

Ohmic (Doped semiconductor) E

ep J = μ Tunneling

)

2

exp(

E E b

J ≈ −

qh q b m

3 ) ( 2

8 π

^*

φ

³^/²

=

Changhee Lee, SNU, Korea SCLC (undoped semicond. or Insulator)

3 2

8 9

d J

_SCLC

= ε

_o

ε

_r

μ V

2.9 eV

Al 4.3 eV ITO

O

MEH PPV

Thermionic Emission into low mobility organic semiconductor

E

_F

4.8 eV

5.3 eV

MEH-PPV

P. S. Davids, I. H. Campbell, and D. L. Smith, J. Appl. Phys.82, 6319 (1997).

(9)

(a) (b)

Tunneling mechanism

(c) (d)

I. D. Parker, J. Appl. Phys. 75, 1656 (1994).

0<V<V_Ω +

Organic Semiconductor

electrode

electrode + + + + + +

d

Space-charge-limited (SCL) current

ITO Au

OC1C10-PPV

+

d

t

τ

τ >

(a) (Ohmic current)

V_Ω<V

electrode +

+ + +

Organic Semiconductor

9 V

2

0.3 μm d=0.13

μm

0.7 μm

electrode

++ + + + ++++

d

t

τ

τ <

(b) (SCL current)

+ +

t.

predominan is

conduction SCLC

, At

t.

predominan is

conduction ohmic

, At

d t

τ τ

<

>

8

3

9 d J

_SCLC

= ε

_o

ε

_r

μ V

P. W. M. Blom M. J. M. de Jong, and J. J. M. Vleggaar, Appl. Phys. Lett. 68, 3308 (1996).

(10)

Field-dependent mobility in SCL current

] ) 891 (

. exp[ 0 8

9

₁_/₂

3 2

d V T

k d

J V

_PF

B r

o

SCLC

= ε ε μ β

P. N. Murgatroyd, J. Phys. D: Appl. Phys.

3

, 151 (1970).

OC

1

C

10

-PPV

P. W. M. Blom, M. J. M. de Jong, and M. G. van Munster, Phys. Rev. B 55, R656 (1997).

ITO

+

Au

Space-charge-limited (SCL) current

ITO Au

OC1C10-PPV

+

Poly(dialkoxy-p-phenylene vinylene) (OC1C10-PPV)

P. W. M. Blom M. J. M. de Jong, and J. J. M. Vleggaar, Appl. Phys. Lett. 68, 3308 (1996).

(11)

. , SCLC limited - Trap

1 2

1

T m T d N V N

J

_m ^t

m m t

v

=

∝ μ

⁻ ⁺₊

3 18

eV 15 .

≈ 0 E

t

SCL current with an exponential trap distribution

3 -

18

cm

≈ 10 N

t

P. E. Burrows, Z. Shen, V. Bulovic, D. M. McCarty, S. R. Forrest, J. A. Cronin and M. E. Thompson, J. Appl. Phys. 79, 7991 (1996).

Interface-limited injection model

M. A. Baldo and S. R. Forrest, Phys. Rev. B 64, 085201 (2001)

(12)

Carrier Recombination

Recombination of electron hole pairs Singlet exciton S=0

↑↑

2 =

1χ χ

Triplet exciton S=1

Spin-allowed transition

fast efficient Spin-forbidden transition

) (

2 1

2

1χ = ↑↓−↓↑

χ ( )

2 1

2

1χ = ↑↓ +↓↑

χ

↓↓

2 =

1χ χ

M. Segel, M. A. Baldo, R. J. Holmes, S. R. Forrest, Z. G. Soos, Phys.

Rev. B 68, 075211 (2003)

Singlet exciton S=0 fast, efficient Fluorescence

Triplet exciton S=1 slow, inefficient Phosphorescence

Exciton Recombination Zone

- Electron -

e-h Recombination

Zone ~ 10 nm

+

Φ

meta l

Φ

ITO hole

EML ETL

+

C. Adachi, T. Tsutsui, and S. Saito,Optoelectron. Devices Technol. 6, 25 (1991).

(13)

TPD

(65 nm) Alq

3

(50 nm) 2.5 eV

3 eV

N N

CH3 H3C

TPD Alq3

N O O N N O Al

(a) (c)

Electron-hole and electric field distribution

5.4 eV 5.7 eV

(b) (d)

B. Ruhstaller, S. A. Carter, S. Barth, H. Riel, W. Riess, and J. C. Scott, J. Appl. Phys.89, 4575 (2001).

Quantum efficiency roll-off at high current

(2002) 1465 80, Lett.

Phys.

Appl.

Kafafi, H.

Z.

and Kalinowski J.

Stampor, W.

i, Szmytkowsk J.

- field

E 1

1

, T X , X

S

: excitons of on dissociati field

Electric

+

−

⎯

⎯ →

⎯

∗

(2002) 874 80, Lett.

Phys.

Appl.

Marchetti, P.

Alfred and Tang, W.

Ching Young, H.

Ralph

0 X or X 1

1

, T S

S

: quenching exciton

- Polaron

⎯

-

⎯

⎯ →

⎯

∗

+

(14)

Quantum Efficiency vs Current of phosphorescent OLEDs

Triplet – Triplet (T – T) Annihilation

⎥ ⎦

⎢ ⎤

⎣

⎡ − + +

⎥ =

⎦

⎢ ⎤

⎣

⎡ − + +

=

T T

T

J

J J

k

qd 8

1 4 1

1 8 2

²

1

0

τ

η η

Ref. M. A. Baldo, C. Adachi, and S. R. Forrest, Phys. Rev. B 62, 10967 (2000)

= 0 dt dn

_T

2 0

1

2

+ − =

gd J n n

k

_T _T ^T

τ

( 근의 공식 )

⎤

⎤ ⎡ + ⎡

+

−

^T

J qd Jk

Jk

8 1

2 1

) 2 ( 1 1

2 2

τ τ

τ k

²

T – T Annihilation: Steady-state solution

⎥ ⎦

⎢ ⎤

⎣

⎡ − + +

⎥ =

⎥ ⎦

⎤

⎢ ⎢

⎣

⎡ − + +

=

T T

T

J

J k

qd Jk k

k

n qd 8

1 1 1

1 2 1 1

τ τ

τ )

( 4

¹

2

=

_T−

T

J

qd k τ Q

τ

^T

L = n QE : η τ

J n J L =

_T

=

n

L

^T

1

η

0

: k

_T

= 0 인 경우 , 즉 , T-T annihilation 이 없는 경우이므로

gd J n

_T

=

τ Light emission intensity

qd J J

L 1

0

= = =

∴ η τ

⎥ ⎦

⎢ ⎤

⎣

⎡ − + +

⎥ =

⎦

⎢ ⎤

⎣

⎡ − + +

=

T T

T

J

J J

k

qd 8

1 4 1

1 8

2

1

0

τ

η η

M. A. Baldo, C. Adachi, and S. R. Forrest, Phys. Rev. B62,10967 (2000)

(15)

Triplet exciton – polaron quenching

S. Reineke, K. Walzer, and K. Leo, Phys. Rev. B75, 125328 (2007)

1 1 2 1

2

ρ ρ ρ P

τ τ

₂

ρ

₁

ρ

₂

P

₂

τ

₂

ρ

₁

P

₁

τ

₂

P

₂

P

₂

P

₁

고 반사

전극

투명 유기 박막 전극

Spontaneous emission from planar microcavity

L

-z 0 z’=L-z

ρ

1

ρ

₂

, τ

₂

2 c L

2 ) ( 2 )

( )

(

₂ ₂ ₁ ¹ ₂ ₁ ₂

2

c

t L c WP

t z WP t

WP t

E

_L

= τ + τ ρ − + τ ρ ρ −

2 ) ( 2

¹

2 1 1

2

c

L c

t z

WP − −

+ τ ρ ρ ρ

D. G. Deppe, C. Lei, C. C. Lin, and D. L. Huffaker, J. Modern Optics 41, 325 (1994)

(16)

∫

−^∞∞

∞

−

+ −

= i t dt

c t z WP dt

t i t WP

E

_L

2 ) exp( )

2 ( ) exp(

) 2 (

)

(

² ² ¹ ¹

2

ω

π ρ ω τ

π ω τ

dt t c i

t L

∫

−^∞∞

WP −

+ 2 ) exp( )

2 (

2 1

2

ω

π ρ ρ τ

(ω ) WP

....

) exp(

2 ) ( 2

2

1 2

1 1

2

− − +

+ ∫

−^∞∞

i t dt

c L c t z

WP ω

π ρ ρ ρ τ

...

1 )[

(

...

) ( )

(

) ( )

( )

(

2 2 1 2 1 2 1 2

4 2 1 2 1 2 2 2

1 2 1 2

2 2 1 2 2

1 2 2

2

1 1

+ +

+

=

+ +

+

+ +

=

+ +

c i L c i z c

i z

c i L c

i L c i z

c i L c

i z L

e e

WP

WP e WP

e

WP e WP

e WP

E

ω ω ω

ω ω

ω

ω ω

ρ ρ ρ ρ

ω τ

ω ρ

ρ ρ ρ τ ω ρ

ρ ρ τ

ω ρ

ρ τ ω ρ

τ ω τ ω

Changhee Lee, SNU, Korea ]

...

4 2 1 2 1 2 2 1

1 2 1 1

2

+ +

+ e

ⁱ ^c^L

e

ⁱ ^c^L

ω ω

ρ ρ ρ ρ ρ

ρ

}]

...

1 {

...}

1 { 1

)[

( ) (

2 2 1 2 2 1

2 1 2 2

1 2

2

1

+ +

+

+ +

+

=

c i L c

i L

c i L c

i z L

e e

WP E

ω ω

ρ ρ ρ

ρ

ρ ρ ρ

ω τ ω

c i L c

i L

e

_ω

ω

ρ ρ ρ

ρ

₂

1 2 2

1 2

1 ... 1 1

−

= + +

c i L

c i z

L

e WP e

E

_ω

ω

ρ ρ ω ρ τ

ω

₂

2 1

2 1 2

2

1 ) 1 ( )

(

1

−

= +

2

2 1 2

1

1 1

1 2 2

2

4

) ( 2 )

cos(

2 1

2 )]

cos(

2 1

)[

1 ( ) (

π ω ω ω ω

nz

WP c

R L R R

R

c R nz

R R

E

_L

− +

+ +

= −

Emission spectrum in the forward direction

Interference effect

Fabry-Perot Resonator

2

2 1 2

1

1 1

1 2

) ( 4 )

cos(

2 1

4 )]

cos(

2 1

)[

1 (

ω

λ π λ

π nL WP R

R R

R

R nz R

R

− +

+ +

= −

2 2

2 2 2 2 1 2

1

| , | | , | | 1

| ρ = R ρ = R τ = − R

D. G. Deppe, C. Lei, C. C. Lin, and D. L. Huffaker, J. Modern Optics 41, 325 (1994)

(17)

ρ

₂

θ θ

Semitranspar ent cathode Radiation mode in top-emitting OLED

L

z ρ

₁

o

Emitting layer

Reflective anode cos )

exp( 4 1

2 )

,

(_s_p

π nz θ

_o

i + r

32

C. Qiu, H. Peng, H. Chen, Z. Xie, M. Wong, and H. S. Kwok, IEEE Trans. on Electron Dev. 51, 1207 (2004).

) ( cos )

exp( 4 1

) exp(

1 ) ,

(

₂ ₂⁽ ^, ⁾ _int⁽ ^, ⁾

) , ( 2 ) , ( 1

) , ( 1 )

,

(

λ

λ θ π

λ λ

θ

^s^p ^s^p

p o s p s

p o p

s

ext

T I

i nL r

r

i r

I

− +

=

Resonant emission from microcavity

A. Dodabalapur, L. J. Rothberg, R. H. Jordan, T. M. Miller, R. E. Slusher, and J. M. Phillips, J. Appl. Phys. 80, 6954 (1996).

Blue Green Red

(18)

Radiation mode in top-emitting OLED

Conventional OLED

Top-emission OLED Conventional

Top-emission Lambertian Simulation (TE)

C ti l OLEDT i i OLED

Simulation (TE)

Conventional Top-emission

Changhee Lee, SNU, Korea

C. Qiu, H. Peng, H. Chen, Z. Xie, M. Wong, and H. S. Kwok, IEEE Trans. on Electron Dev. 51, 1207 (2004).

Conventional OLEDTop-emission OLED

% 51

~ : )

(

sin

⁻¹

= θ

c₂

≤ θ

organic substrate

n n

External quantum efficiency of OLED

% . n ~ n η

n

C org organic

air

c

17 5

2 : 1 ) (

sin

¹ ₂

1

= ≈

≤ θ

⁻

θ

organic

% 31.5

~

2

:

1 c

c

θ θ

θ ≤ ≤ θ

Metal/Alq₃(x)/PVK (40 nm)/ITO (150 nm) Metal/Alq₃(80 nm)/PVK (40 nm)/ITO (x)

G. Gu, DZ Garbuzov, PE Burrows, S. Venkatesh, SR Forrest, ME Thompson, Opt. Lett. 22, 396 (1997)

(b)

A. Chutinan, K. Ishihara, T. Asano, M. Fujita, S. Noda, Org. Electron. 6, 3 (2005).

(19)

Standard OLED structure OLED with aerogel interlayer OLED with integrated DFB grating

Methods of improving out-coupling efficiency

2

1

org

C

n

η ≈

OLED with scattering microspheres OLED with microlenses OLED built atop a mesa structure

K. Meerholz and D. C. Müller, Adv. Funct. Mater. 11, 251 (2001).

Doubling Coupling-Out Efficiency in Organic Light-Emitting Devices Using a Thin Silica Aerogel Layer T. Tsutsui, M. Yahiro, H. Yokogawa, K. Kawano, M. Yokoyama, Adv. Mater. 13, 1149-1152 (2001).

Index matching using a thin aerogel layer

(20)

Photonic crystal

Yong-Jae Lee, Se-Heon Kim, Joon Huh, Guk-Hyun Kim, and Yong-Hee Lee, Sang-Hwan Cho, Yoon-Chang Kim, and Young Rag Do, Appl. Phys. Lett. 82, 3779 (2003).

Degradation Processes

Cathode

Cathode

- Delamination of metal (Peel-off) - Corrosion & oxidation; O2, H2O

•Encapsulation

- Permeation of H2O and O2, etc.

•Ambient environment:

- Temperature, moisture, and UV light, etc.

•Joule heating, etc.

H2O, O2

ETL

HIL HTL EML

－ EIL

Exciton

- Diffusion of metals such as Ca, Al, etc.

Electrode Interfaces - Interfacial degradation

ÆChanges in injection efficiency - Formation of oxide layer: injection barrier - Electrochemical reaction with organic layers - Degradation of PEDOT:PSS

- Degradation of p-, n-doped layers, etc.

Organic layers

- Degradation of organic materials - Photo-oxidation

두께: 100~200 nm

39

Substrate (Glass, plastics, etc.)

ITO + HIL

Anode

- ITO inhomogeneity: injection barrier

- Oxygen or In diffusion ÆDegradation of organic layers - Dust, particles, etc.

- Morphological changes (Crystallization):

change of mobility, trap distribution Æchange in e-h balance, etc.

- Interdiffusion between org./org. interfaces - Trap formation at org./org. interfaces

(21)

Real-Time Observation of Temperature Rise and Thermal Breakdown Processes in Organic LEDs Using an IR Imaging and Analysis System

Joule heating

Xiang Zhou, Jun He, Liang S. Liao, Ming Lu, Xun M. Ding, Xiao Y. Hou, Xiao M. Zhang, Xiao Q. He, and Shuit T. Lee, Adv. Mater. 12, 265 (2000)

Impact of Joule heating on the brightness homogeneity of OLEDs

Brightness distribution of a device having an active area of 15 cm²at a current density of 33.3 mA/cm².

C. Gärditz, A. Winnacker, F. Schindler, R. Paetzold, Appl. Phys. Lett. 90, 103506 (2007)

(22)

Coulombic degradation scaling law

Y. Sato, Electroluminescence I, edited by G. Mueller (Acade mic Press, San Diego, 2000) pp. 209-254.

C. Féry, B. Racine, D. Vaufrey, H. Doyeux, and S. Cinà, Appl. Phys. Lett. 87, 213502 (2005)

constant

; =

∝ − τ τ J n L o n

1.7 n constant.

t

L

₀ⁿ

×

_1/2

= =

Degradation due to H 2 O permeation

M. Schaer, F. Nüesch, D. Berner, W. Leo, and L. Zuppiroli, Adv. Funct. Mater. 11, 116 (2001).

(d)

(23)

Encapsulation

P. E Burrows, G. L. Graff, M. E. Gross, P. M. Martin, M. Hall, E. Mast, C. Bonham, W. Bennett, L. Michalski, M. Weaver, J. J.

Brown, D. Fogarty, L. S. Sapochak, Proceedings of SPIE4105, 75 (2001).

•Inorganic:

•Aluminum oxide deposited by DC reactive sputtering

•Thickness 30-100 nm

•Organic:

•Monomer mixture deposited in vacuum

•Non-conformal deposition: Liquid-Vapor-Liquid- (UV curing)-Solid

•Thickness 0 25 several mm

Thin film encapsulation

Liquid precursor (monomer)

Inorganic barrier deposition Cure

Liquid precursor (monomer) Cure

•Thickness 0.25 – several mm

•4-5 polymer / inorganic pairs (dyads) for encapsulation

L. L. Moro, T. A. Krajewski, N. M. Rutherford, O. Philips, R. J. Visser, M. E. Gross, W. D. Bennett, and G. L. Graff, Proceedings of SPIE 5214, 83 (2004).

(24)

Methods of Full Color Display Fabrication

RGB method Color conversion method Color filter method

ETL

Cathode Cathode

ETL

Cathode ETL

Glass Anode

HTL

Blue emitting layer ETL

Anode

Color conversion filter

HTL

White emitting layer

Anode

Color filter

Changhee Lee, SNU, Korea Red Green Blue

Glass

Red Green Blue

Glass

Red Green Blue

Items Evaporation

(Precision Shadow Mask)

Ink-Jet Printing

Laser-Induced Thermal Imaging (LITI)

M i l

Molecular Materials Only Polymer (LEP) Polymer (LEP) Molecular Materials Hybrids (Blend)

Comparison of OLED color patterning methods

Materials

Printing

Accuracy ± 15㎛ ± 15㎛ ± 2.5㎛

Resolution ~180ppi ~150ppi ~300ppi

Aperture Ratio

40 50% 60% 70 80%

p

(Top Emission) 40~50% ~60% 70~80%

Materials Usage - Smallest -

Glass Size 730x460mm (~2005) 730x920mm 730x920mm (~2005)

Machine Price Very Expensive Cheapest Middle

Source: Samsung SDI, FPD int. 2004

(25)

PMOLED

Data Line(Anode : ITO)

Changhee Lee, SNU, Korea Scan Line (Cathode : Al)

AMOLED

IC

TFT

OLED pixel

TFT backplane

ITO HIL HTL ETL Cathode

EML

＋

－

COLUMN DRIVERS (DATA VOLTAGE)

DRIVERS LECT SIGNAL)

Metal Cathode Transparent Anode

Translucent Cathode

Transparent Plate Light Emissive

Layer

Buffer Layer

FPC

Driver IC

Light Emission Glass

ITO ROW (PIXEL SEL

Power Line V_DD Scan Line Data Line

V_DATA

Bottom Emission Top Emission

Al Wiring Light

Metal Anode Emissive

Layer Driving

TR C

Light Switching

TR OLED RGB

(26)

AM OLED Process Map

TFT Backplane Heat Treatment Washing Surface Treatment

Oxygen plasma…etc

Organic Layer Deposition

Hole injection, transport layers

RGB material Depoisition Color patterning Shadow Mask

Cleaning Shadow Mask Tension & Align Inspection

Module

Scribing

Changhee Lee, SNU, Korea Organic Layer

Deposition Cathode Deposition ETL…

Sealing Encap.

glass cleaning

g

Source: B. D. Chin (KIST), IMID 2006