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Brief history of Lighting

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(1)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Changhee Lee

School of Electrical Engineering and Computer Science Seoul National Univ.

chlee7@snu.ac.kr

전자물리특강 2007. 2학기

Organic Semiconductor Lab

• 500,000 years ago – fire, 1st torch

• 70,000 years ago – 1st lamp (wick)

• 1,000 BC – 1st candle

• 1772 gas lighting

• 1879 T. A. Edison, incandescent filament lamp: Dawn of electric lighting.

• 1907 H. J. Round, 1st LED (SiC), Electrical World 49, 309 (1907)

• 1910 P. Claude, discharge lamps filled with inert gases

• 1938 GE and Westinghouse Electric Co. white fluorescent lamps.

• 1962 N. Holonyak Jr. and Bevaqua, GaAsP (visible light – red)

•1987 C. W. Tang, OLED (Alq3, Green)

• 1995 S. Nakamura et al, GaInN LED (blue & Green)

Brief history of Lighting

History of Lighting

(http://lighting.sandia.gov/)

pyroluminescence

More Efficient, Convenient

(2)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Incandescent Lamp

Edison’s US. Patent No.

444,530 (issued Jan 13, 1891)

Now, Lifetime ~ 2000 h Efficiency ~ 17 lm/W

300 500 1000 3000

Wavelength (nm)

Relative Intensity

black body (dot) and tungsten radiator (solid line) at 3000 K

전자물리특강 2007. 2학기

Organic Semiconductor Lab

레인콤 MP3 Player

‘CLIX’

SEC 40” WXGA a-Si AMOLED

Mass production of AMOLED Samsung SDI Updated the data in J. R. Sheats et al., Science 273, 884 (1996).

Evolution of OLED Performance

(3)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Performance of RGB OLED Devices

Color CIE (x,y) Efficiency

(cd/A) Half-Life (hr)

저 분 자

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

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 -

고 분 자

형 광

Red 0.68, 0.32 1.7 1790 @ 1000 cd/m2

Orange 0.58, 0.42 0.9 8138 @ 1000 nit

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

0.0 0.20 0.40 0.60 0.80 1.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

y

x 520 nm

550 nm

575 nm

600 nm

770 625 500 nm

475

1000 K 2000 K 3000 K 5000 K 10 000 K

20 000 K 5000 K

3000 K

NTSC OLED

Black body

OLED의 색좌표

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Efficiency Efficiency (lm/W) (lm/W)

Flickers

Cannot be dimmed Losses in ballast Noisy

0 20 40 60 80 100

Incandescent Halogen Fluorescent White LED (2000)

White LED (2010)

Solid State Lighting

Ref. A. Zukauskas, M. S. Shur, R. Caska, Introduction to Soild-State Lighting

Luminous Efficiency (lm/W) OLED 10 + LCD screen 1.5 CRT, PDP 1 Incandescent lamp 17 Fluorescent lamp 80

(4)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

White Organic Light-Emitting Devices

• Full-Color Display

• Backlight of TFT-LCD

• Lighting

– Light signs, decorative lighting, glowing wall paper, ceilling lights, etc.

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Advantages of using LEDs over

conventional light sources such as CCFL:

• long life

• ruggedness

• high frequency dynamical operation

• Hg-free light source

• Better color gamut

Wiep Folkerts (Lumileds Lighting), SID 04 Digest, p. 1226

LED backlighting

(5)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

• Improve efficiency of light generation

• Improve efficiency of light extraction

• Improve quality of light

• Reduce cost

Issues of Solid State Lighting

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Methods of Making White LEDs

Wavelength Conversion

1. Blue LED with phosphors 2. UV LED with several phosphors

• Color Mixing

3. Two or more emitting layers of different colors.

- white light with a high color rendering index (CRI).

- relatively easy to change the hue for different applications.

R+G+B=W

R+C = W;G +M = W;B+Y= W

OLED NET

(6)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

백색 LED 소자

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Energy transfer & Carrier trapping

electron -

hole + - Exciton +

host dopant

Energy transfer

hν

HOMO LUMO

Energy transfer

-

+

- Exciton +

host dopant

hν

HOMO

LUMO -

+

Direct trapping

electron

hole

Host Dopant

1.2 1.0 0.8 0.6 0.4 0.2 0.0

EL

800 700 600 500 400 300

Wavelength (nm) 1.2

1.0 0.8 0.6 0.4 0.2 0.0

800 700 600 500 400 300

Wavelength (nm)

PL

1.2 1.0 0.8 0.6 0.4 0.2 0.0

800 700 600 500 400 300

Wavelength (nm)

EL

N O

N O N O Al

Alq3

N O

NC CN

CH3

DCM2

(7)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab 13

Doping in OLEDs

• Doping

fluorescent dyes

C. W. Tang, S. A. VanSlyke, and C. H. Chen, J. Appl. Phys. 65, 3610 (1989)

• Doping

phosphorescent dyes

M. A. Baldo, et al, Nature 395, 151 (1998)

• Effects of doping:

1. Color tuning.

2. Increase the device quantum efficiency

3. In general, the doped layer is more thermally stable than the undoped layer (increase of entropy).

4. Proper dopants can increase the operational lifetime of the device.

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Exciton formation

M. Baldo and M. Segal, phys. stat. sol. (a) 201, 1205 (2004)

Caution for this simple method:

(1) It is necessary to correct for the differing photoluminescent efficiencies of the fluorescent and phosphorescent guest molecules.

(2) The efficiency of energy transfer to both guest materials must be determined to ensure that radiative emission accurately reflects the number of excitons formed within the device.

(3) The impact of quenching phenomena must be calculated for both singlet and triplet excitons.

(4) When applied to polymeric systems, it is especially important to ensure that excitons are formed on the polymeric host and not on the small molecularweight phosphorescent guest.

(8)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab 15

Fluorescent Dye doping

C. W. Tang and S. A. VanSlyke, C. H. Chen, J. Appl. Phys. 65, 3610 (1989)

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Excitonic interaction and excitation transfer

Donor (D) Acceptor (A) hν

D* A

Excitation

Excitation and energy transfer

D* A

electron transfer

D* A

hole transfer

excitation transfer 1

D* A

excitation transfer 2

D* A

D+A- D-A+

DA* DA*

Förster: overlap of spectra, dipole interaction Dexter: overlap of wavefunctions

(9)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Energy Transfer Processes

( ) ( )

ν

ν ν ν

ε ~

~

~

~ :

integral

Overlap 4F d

J=

A D

6 4

28

2 88 10 mol

nsfer energy tra Forster

r τ n . J k K

o A

D

= × exp ( 2 )

2

nsfer energy tra Dexter

2J - r/L

πP kETh

The Förster eq. is often written in the following form:

06

⎜ ⎞

= ⎛ R k R

WDA rD

( ) ( )

ν

ν ν ν ε

κ ~

~

~

~ 10

8 .

8 4 4

2 17 6

0 F d

R = n

A D

For photosynthetic systems R is typically 1 nm, R0is typically 8 nm,

1

107

5⋅

s

krDWDA≈1013s1

D* A

D A*

D* A

Dexter excitation transfer (electron exchange excitation

transfer) Förster excitation transfer

(Dipole-Dipole Excitation Transfer)

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Förster radius

Excitation dynamics of dye doped tris(8-hydroxy quinoline) aluminum films

K. Read, H. S. Karlsson, M. M. Murnane and H. C. Kapteyn, R. Haight, J. Appl. Phys. 90, 294 (2001)

κ=donor/acceptor orientation factor;

κ2= 2/3 for a randomly deposited film NAis Avogadro’s number

n=1.7 for Alq3

Ro = 31 Å

( ) ( ) ν

ν ν ν

ε

κ ~

~

~ 5291 ~

. 0

4 4

2 6

0 F d

N

R n A D

A

=

(10)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

T.A. Beierlein, B. Ruhstaller, D.J. Gundlach, H. Riel, S. Karg, C. Rost, W. Rieß, Synth. Met. 138, 213 (2003)

Location and extent of the recombination and emission zone

Schematic energy level diagram of delta- doped devices having a 25 Å Alq3/DCJTB (1%) sensing layer at various positions (d) in the Alq3 layer. The device structure is Ni/CuPc (150 Å)/NPB (500 Å)/Alq3 (500

Å)/Ca (200 Å).

J=20 mA/cm2

Exciton diffusion length ~ 120 Å

전자물리특강 2007. 2학기

Organic Semiconductor Lab

M. A. Baldo and S. R. Forrest, Phys. Rev. B 62, 10958–10966 (2000).

Triplet energy of R & G phosphors

(11)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab 21

Organic Electrophosphorescence devices

Princeton group

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Single emitting layer

Kido, APL (2005)

(12)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

1. The confinement of charge carriers in light-emitting quantum wells can enhance the forming probability of excitons and the light-emitting efficiencies of the devices.

2. Compared with multi-layer white OLEDs, the influence of band gap matching can be negligible, and the positions of different color light-emitting quantum wells can be exchangeable.

3. Easy turning of Commission International de I’Eclairange (CIE) chromaticity

Multi-Quantum Well Structure

N OBe

N O

BePP2

Rubrene

Z. Y. Xie (Jilin U), Appl. Phys. Lett., 74, 1999, 641 0.41 lm/W, (0.32, 0.38) at 9V

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Complementary Color Stack

ITO NPD

NPD:DCM2 BCP

Alq3

Hole-blocking layer

Interlayer sequential energy transfer (ISET):

NPD Æ Alq3 Æ DCM2

0.35 lm/W, (0.33, 0.33) , and 100 cd/ m2at 11..5 V R. S. Deshpande (Princeton U.), Appl. Phys. Lett., 75, 1999, 888

(13)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Complementary Color Stack

전자물리특강 2007. 2학기

Organic Semiconductor Lab

N N

N

Et p-EtTAZ

N O Et N

Et

O

Nile Red p-EtTAZ

ITO anode Glass substrate

G Alq3

Alq3:NileRed Alq3 Metal cathode

R B G

+ -

TPD

Multilayer RGB Stacks

J. Kido (Yamagata U), Science, 267, 1995, 1332. 0.5 Im/W, ~ 300cd/ m2, and (0.335, 0.415) at 12 V; 20h at 100cd/ m2

R. H. Jordan (AT&T), Appl. Phys. Lett., 68, 1996, 1192.

0.5 lm/ W, ηext=0.7 %, CIE (0.31, 0.41), and 105 cd/ m2 at 12 V

ITO/ TAD (600 Å)/ NAPOXA (150 Å)/Alq3(300 Å)/ Alq3 (200 Å)+ DCM1 (0.3 %)/ Alq3 (200 Å)/ Al (2000 Å)

(14)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

S. R. Forrest et al., Adv. Mater. 14, 1035 (2002)

RGB white OLEDs: Phosphorescence

전자물리특강 2007. 2학기

Organic Semiconductor Lab

38 cd/A, 18.4 lm/W and 16% EQE with CIE of (0.39, 0.39) at 1000 cd/m2

White Phosphorescent OLEDs

Yeh-Jiun Tung et al. (Universal Display Corporation), SID 04 Digest 48

(15)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Philips Lighting/Novaled 25 lm/W @ 1000 cd/m2

General Electric 15 lm/W (2 ft. x 2 ft.) @ 1200 lumen

UDC 20 lm/W @ 800 cd/m2

High efficiency white OLEDs

Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, S. R. Forrest, Nature 440, 908 (2006)

23.8 lm/W @ 500 cd/m2

전자물리특강 2007. 2학기

Organic Semiconductor Lab

High resolution but very difficult process (fabrication of electrodes)

Full-Color Method – Stacked OLED

(16)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab 31

High-efficiency tandem OLED

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

전자물리특강 2007. 2학기

Organic Semiconductor Lab

White OLEDs with multilayer stack structure

NPB

ITO

4.7 eV Al

3.1 eV 4.2 eV

5.7 eV Alq3 DPVBi 2.3 eV

5.4 eV PEDOT:

PSS

5.2 eV

2.8 eV

5.9 eV LiF

NPB

Al 3.1 eV

4.2 eV

5.7 eV Alq3 2.3 eV

5.4 eV

LiF 3.1 eV

5.7 eV Alq3 Alq3:D CM2

OLED with Blue-Red Stack

Blue Red

Al (3 nm)

ITO Al

4 ~ 200 mA/cm2 8

6

4

2

0

Light (arb. units)

800 700

600 500

400

Wavelength (nm)

(17)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

White OLED + CF

전자물리특강 2007. 2학기

Organic Semiconductor Lab

RGB vs RGBW

(18)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

RGB vs RGBW

전자물리특강 2007. 2학기

Organic Semiconductor Lab

• Chromaticity coordinates

• Color temperature

• Color rendering index (CRI)

CIE 1931 Color Matching Functions (2 deg. Observer)

CIE 1931 Color Matching Functions

1.5

1.0

0.5

0.0

Light (arb. unit)

700 600

500 400

Wavelength (nm)

x z

y

(19)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Chromaticity Coordinates & Color Temperature

λ λ dx S K

X =

380780 ( ) λ λ dy S K

Y=

380780 ( ) λ λ dy S K

Z =

380780 ( ) Z Y X x X

+

= +

Z Y X y Y

+

= +

K = 683 lm/W

=1 + +y z x

• A black body radiator (Planckian Source) glows with a color that is solely dependent on its temperature (in K).

• Standard source D65 (daylight, 6500 K)

(x,y) = (0.312, 0.329)

E = Equal Energy point: (0.333, 0.333)

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Correlated color temperature

Correlated colour temperature (CCT)

= Temperature of a Planckian radiator having the chromaticity nearest the chromaticity associated with the given spectral distribution on a CIE 1931 chromaticity diagram.

- Only applicable for sources close to the black body curve (white light).

- Standard source:

D65 (daylight, 6500 K) (x,y) = (0.312, 0.329) E = Equal Energy point: (0.333, 0.333)

McCamy΄s approximate formula TCCT=437n3+3601n2+6861n+5517

where n=(x-0.3320)/(0.1858-y), and x, y are the CIE 1931 chromaticity coordinates.

Ref. McCamy, Color Res. Appl. 18, 150 (1993).

(20)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Color Rendering Index (CRI)

• Color Rendering Index (CRI): a numerical system that rates the "color rendering"

ability of the light source in comparison with natural daylight (CRI=100, the highest possible CRI.).

• CRI is a relative measure of the colorimetric shift of an object when lit by a particular light source, compared with how the object would appear under a reference light source of similar color temperature.

전자물리특강 2007. 2학기

Organic Semiconductor Lab

1. Select a reference illuminant (Planck blackbody radiation below 6000K)

2. Measure the spectrum of the test source.

3. Determine the reflected spectra from each of the eight test samples

Calculation Method of CRI

) ( y x

S

r

( λ ) ⎯

x

⎯ →

,y

,z r

),

r

λ

) ( y x

S

k

( λ ) ⎯

x

⎯ →

,y

,z k

),

k

λ

) ( ) ( ) (

) ( ) ( ) (

ki ki i k

ri ri i r

, y x S

, y x S

λ ρ λ

λ ρ λ

λ λ dx S K

X =

380780 ( ) Y =K

380780S(λ d)y λ λ

λ dy S K

Z=

380780 ( )

Z Y X y Y Z Y X x X

+

= + +

= + ,

0.0 0.4 0.8

Light grayish red

0.0 0.4

0.8 Dark grayish yellow

0.0 0.4

0.8 Strong yellow-green

400 500 600 700

0.0 0.4 0.8 Moderate

yellowish green

Wavelength (nm)

Light bluish green

Light blue

Light violet

400 500 600 700

Light reddish purple

Reflectivity spectra of eight test samples (CIE 1964 )

(21)

Changhee Lee, SNU, Korea 전자물리특강

2007. 2학기

Organic Semiconductor Lab

Calculation Method of CRI

4. Transform the colorimetric data from the CIE 1931 values (X, Y, Z, x, y) to the (u, v) coordinates of the CIE 1960 uniform chromaticity scale (UCS) diagram by means of the following:

5. To account for the adaptive color shift due to the different state of chromatic adaptation under the lamp to be tested and under the reference illuminant use the following formula:

3 12 2

6 3

15 6

3 12 2

4 3

15 4

+ +

= − +

= +

+ +

= − +

= +

y x

y Z

Y X v Y

y x

x Z

Y X u X

u)/v .

- . v + .

d = ( v

v u

c

= ( 4 − − 10 ) / , 1 708 0 404 1 481

k ki r k ki r

k ki r k ki ki r

d d d c c c

d d d c c u c

/ /

481 . 1 518 . 16

/ 4 / 404 . 0 872 . 10

− +

= +

k ki r k ki r

ki cc c d d d

v

16 . 518 1 . 481 / / 520

. 5

= +

전자물리특강 2007. 2학기

Organic Semiconductor Lab

Calculation Method of CRI

17 24

1/3

= Y

W

5. Calculate lightness indices for all reflected spectra:

6. Calculate the special color rendering indices for each test-color sample.

7. Calculate the general color rendering index.

2 / 1 2 2

2 2

2

} )]

( ) ' ( [ 13

)]

( ) (

[ 13 ] {[

6 . 4 100

r ri ri r ki ki

r ri ri r ki ki ri

ki i

v v W v v W

u u W u u W W

W R

− +

′ − +

=

=

=

8

8

1

1 : value

i i

a R

R CRI

참조

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