Discovery of High-performance Blue OLED Materials and ... · MS 2 MS 17 MS 19 Wavelength (nm) e / 10 4 L M-1 cm-1 0.0 0.4 0.6 0.8 1.0 Abs. RT PL Norm. intensity /a.u. 0 2 4 6 8 10-3

Discovery of High-performance Blue OLED Materials and

Experience of Publishing in CHEM Journal

Ken-Tsung Wong (汪根欉)Department of Chemistry

National Taiwan University

Frontier Sciences online workshop –Chemistry & Materials Science

Taipei, May 29, 2020

1

Smart 3C for Daily Life

Brilliant and Colorful for Entertainment

Nature Mimic Lighting

Organic Light-Emitting Device (OLED)

ETL: Electron Transporting LayerEL: Emitting LayerHTL: Hole Transporting Layer

Anode

CathodeHTL

ETL

LUMO

HOMO

EL

hext = hinthph = rhchrhPL

hPL : intrinsic quantum efficiency (PLQY)hr : ratio of exciton formation (singlet vs. triplet)hc : light out-coupling efficiency (optical engineering)r : electron-hole recombination ratio (r £ 1) (mobility)

OLED Basic Working Principle

3

S1

S0

T1

Phosphorescence (X)Fluorescence (O)

h e

Electricalexcitation25%

75%

• OLED Evolution: G1

ηext = ηint ηc = γ ηr ηPL ηc

100% 20~30%

- OLED (Pope 1963, Tang 1987 )

ηr = 25% => ηext = 5~7.5%

Selection rule limitation !!

4

Molecular Design for Blue Emitters

Y.-Y. Chien, R.T. Chen, C.-F. Wang J. Am. Chem. Soc. 2002, 11576.5

Double Confinement Devices ITO/PEDT:PSS/TCTA(40 nm)/T3 or B3 (30 nm)/TPBI(30 nm)/LiF/Al

ITO / PEDT:PSS / T3 (50 nm) / TPBI (37 nm) / LiF / Al

300 350 400 450 500 550 600 650 700 7500.0

0.2

0.4

0.6

0.8

1.0 PL EL

Inte

nsity

(a.u

.)

Wavelength (nm)

EQE: 3.0%

0 20 40 60 80 100 120 140

0.0

1.0

2.0

3.0

4.0

5.0

6.0 T3 B3

Qua

ntum

Effi

cien

cy (%

)

Current Density (mA/cm2)

EQE: T3 5.3%B3 4.1%

R.-T. Chen, Y.-Y. Chien, C. C. Wu, Adv. Mater. 2004, 61.

Highly Efficient Blue OLED

6

200 400 600 800 100010-4

10-3

10-2

.Electron

T3

Hole

T3

B3 µ (c

m2 / V

s)

Hole

Electron

B3

E1/2 (V/cm)1/2

T3

B3

Ambipolar Charge Mobility and Record High Electron Mobility for Amorphous Molecular Solids

J. Am. Chem. Soc. 2003, 125, 3710.

Nondispersive Ambipolar Carrier Transport

0 1 2 3 4 5 6 70

30

60

90

120

150

Phot

ocur

rent

(µA)

Time (µsec)0 2 4 6 8 10 12 14

0

25

50

75

100

125

Phot

ocur

rent

(µA)

Time (µsec)

10-7 10-6 10-5

100

101

102 tT

Phot

ocur

rent

(µA)

Time (sec)10-7 10-6 10-5

100

101

102tT

Phot

ocur

rent

(µA)

Time (sec)

Electron Hole

7

M. Baldo Ph.D. Thesis, 2001

• OLED Evolution: G2Phosphorescent Emitters

Spin-orbit Coupling Effect !!

8

S1�

S0�

T1�

Phosphorescence.(O)�

Fluorescence.(O)�

25%�

75%�

• �Evolu;on:.G1�

ηext.=.ηint.ηc.=.γ.ηr.ηPL.ηc.�

100%� 20~30%�

- OLED (Pope.1963,.Tang.1987.). ηr = 25% => ηext = 5~7.5%�

Selec;on.rule.limita;on.!!.

- PhOLED..(Forrest,.1999).....ηr.=.100%.=>..ηext.=.20~30%�

Triplet emitters are normally used as emittingguests in a host material due to long excited-state lifetimes and triplet-triplet annihilationquenching process.

Reverse Energy Transfer !!

Mark E. Thomson et al.J. Am. Chem. Soc. 2003, 125, 7796.

Host-Guest Working Principles

9

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

-0.08

-0.04

0.00

0.04

0.08

0.12

Cur

rent

(mA

)

Potential (V vs.Ag/AgCl)

CzSi

NN

Cur

rent

(mA

)


mCP

N

Si Si

N

BrBr

Ph3SiCl / THF

n-BuLi / -78 oC

CzSiCzSi is bulky with Tg = 131 oC, and electrochemically stable as compared to that of mCP.

Carbazole-based Blue Host Material

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

-0.08

-0.04

0.00

0.04

0.08

0.12

Cur

rent

(mA

)


CzSi

NN

Cur

rent

(mA

)


mCP

0 1 2 3 4 5 6 7 8 9 10 11 12

10-4

10-3

10-2

10-1

100

101

102

103

104

10-4

10-3

10-2

10-1

100

101

102

103

104

10-3 10-2 10-1 100 101 1020

2

4

6

8

10

12

14

16

0

4

8

12

16

20

24

28

32

Brightness (cd/m

2)

C

urre

nt D

ensi

ty (m

A/c

m2 )

Voltage (V)

Qua

ntum

Effi

cien

cy (%

)

Current Density (mA/cm2)

100 cd/m2

Power Efficiency (lm

/W)

High external EL quantum efficiency of 15.7% photon/electron (30.6 cd/A, maximum) Maximum brightness ~59,000 cd/m2 (at 14.5 V)

Maximal power efficiency: 26.7 lm/W.

At 100 cd/m2

EQE = 12 %, 24 cd/A power efficiency = 16 lm/W

Adv. Mater. 2006, 18, 1216.

NIr

2

FIrpic

F

N

O O

FN

Si Si

N

BrBr

Ph3SiCl / THF

n-BuLi / -78 oC

CzSi

Device Characteristics

PhOLEDs with Hole-Transporting Host Materials

Charges Recombination Occurs at Interfacial Layer between EL and ETL

Narrow Emission ZoneRisk for Triplet Excitons Quench

Host with BalanceElectron/Hole Mobility

12

Combine the structural features of HTL and ETL into a bifunctional host materials

Bipolar Host Materials☆ Balanced charge recombination: high efficiency☆ Simple device configuration: cost-effective

Bipolar Hosts

Prevent strong electronic interactions between donor and acceptor for giving a reasonably high triplet energy

Sub$project,leader:,Prof.,Ken$Tsung,Wong,(Department,of,Chemistry,,NTU),

!

I.#High#Energy#TADF#Bipolar#Hosts#for#High#Efficiency#and#Low#Roll?off#OLEDs###

C.,Adachi,,Thermally,AcFvated,Delay,Fluorescence,(TADF),

π" π" π" π"

FuncFonal,,Blocks,

Spacer,

Bipolar,Host,Materials,

25%,S1,+,75%,T1�h�

e�TADF,Host�

Prompt,+,Delayed,Fluorescence�

Energy,Transfer,

EmiTer,

Molecular,Designs:,Molecular Design Strategies:• Twisted Conformation• Saturated Spacer

Adv. Mater. 2011, 23, 3876. 13

– High triplet energy, good thermal and morphological stability– Relatively simple device structures– High R, G, B efficiencies– Stable white (RB, RGB) emission

Twisted conformation Saturated spacer

!Red!(20%)�Blue!(15.1%)�

Green!(17.9%)!!

White!(17.3%)!CRI=89�

Yellow(18%)�

!YellowishBgreen!!!!!!!!!!!!!(17.4%)!!

Universal Host


!



π" π" π" π"

FuncFonal,,Blocks,

Spacer,


25%,S1,+,75%,T1�h�

e�TADF,Host�


Energy,Transfer,

EmiTer,

Molecular,Designs:,–  High&triplet&energy,&good&thermal&and&morphological&stability&–  Rela7vely&simple&device&structures&–  High&RGB&efficiencies&–  Stable&white&(RB,&RGB)&emission&&

Red (33.8 cd/A, 27 lm/W)�

Blue (29 cd/A, 30.5 lm/W)�

Green (66.8 cd/A, 59.4 lm/W)�

White (35 cd/A, 36.6 lm/W)�

N

NNNN

Summary

Twisted conformation Saturated spacer

!Red!(20%)�Blue!(15.1%)�

Green!(17.9%)!!

White!(17.3%)!CRI=89�

Yellow(18%)�

!YellowishBgreen!!!!!!!!!!!!!(17.4%)!!

Universal Host


!



π" π" π" π"

FuncFonal,,Blocks,

Spacer,


25%,S1,+,75%,T1�h�

e�TADF,Host�


Energy,Transfer,

EmiTer,

Molecular,Designs:,

14

Universal Bipolar Host Materials

15

NIr

2

FIrpic

F

N

O O

F

New Blue Phosphorescent Dopants

Chem 2017, 3, 461–476.

250 300 350 400 450 500 5500

1

2

3

4

5 FIrpic MS 2 MS 17 MS 19

Wavelength (nm)

e / 1

04 L M

-1 c

m-1

0.0

0.2

0.4

0.6

0.8

1.0 Norm

. intensity /a.u.

RT PLAbs.

0 2 4 6 810-3

10-2

10-1

100

FIrpic MS2 MS17 MS19

Cou

nts

/a.u

.

Time /µs

PLQYsolution film

FIrpic 85 93MS 2 88 95

MS 17 88 98MS 19 86 97

Physical Properties

• Tunable blue emissions• High PLQYs• Short excited state lifetime

17

400 450 500 550 600 650 7000.0

0.2

0.4

0.6

0.8

1.0

1.2EL

Inte

nsity

/a.u

.

Wavelength (nm)

FIrpic MS 2 MS 17 MS 19

0.0 0.1 0.2 0.3 0.4 0.50.0

0.1

0.2

0.3

0.4

0.5

(0.33 0.33)

yx

100 101 102 103 1040

5

10

15

20

25

30

35


Brightness /cd/m2

EQE

/%

0

20

40

60

80

100

120

Power Efficiency /lm

/W

0 1 2 3 4 5 6 7 8 9 1010-5

10-4

10-3

10-2

10-1

100

101

102


Voltage /V/

Cur

rent

Den

sity

/mA

/cm

2

10-1

100

101

102

103

104

105

106B

rightness /cd/m2

0 500 1000 1500 2000 250040

50

60

70

80

90

100

L/L0

/%

Time /hr

FIrpic MS-2 MS-17 MS-19

0 2 4 6 8 10405060708090

100

L/L0

/%

Time /hr

Device Properties

• High device efficiency• High device lifetime T50 > 2, 200 hr

17

0

10

20

30

40

50

60

70

S0S0S0S0

3MC dd

3MC dd3

MC dd3MC dd

3MLCT/pp

*3MLCT/pp

*

3MLCT/pp

*3MLCT/pp

*

MS 19MS 17MS 2

rela

tive

ener

gy (k

cal/m

ol)

FIrpic18

0 500 1000 1500 2000 25002030405060708090

100

I/I0 /

%

Time /hr

C"

N"

X"

X"

Long"life-me"Ir1based"sky"blue"emi9er"!!"

S1

S0

T1

Phosphorescence (X)

E-type DF

h e


75%

20~30%

ηext = ηint ηc = γ ηr ηPL ηc

100%

PromptFluorescence

Delayed Fluorescence (DF)- E-type DF (TADF)ηr = 100% =>

RISC

Limitation:• ∆EST < 100 meV, while

environmental thermal energy only gives ca. 25 meV

• Evolution: G3

19

TADF (Thermally Activated Delayed Fluorescence)

q Intramolecular charge transfer: weak-coupled D and A


!



π" π" π" π"

FuncFonal,,Blocks,

Spacer,


25%,S1,+,75%,T1�h�

e�TADF,Host�


Energy,Transfer,

EmiTer,

Molecular,Designs:,

NN

NN

DMAC-TRZ

PLQY 90% (83%)Doped 26.5% EQE

Chem. Commun. 2015, 51, 13662. (CC Wu)

Non-doped 20% EQE !!




!



π" π" π" π"

FuncFonal,,Blocks,

Spacer,


25%,S1,+,75%,T1�h�

e�TADF,Host�


Energy,Transfer,

EmiTer,

Molecular,Designs:,

Chem. Comm. 2012, 48, 9580

Spirobiflurorene

DEST = 57 meVηPL = 27%; ηext = 4.4%

Carbazole/Triazine

DEST = 90 meVηPL = 39.7%, ηext = 6%

Phys. Chem. Chem. Phys. 2013, 15, 15850.

NN

CNNC

Spiro-CN

N

N N

NN

CzT

NN

NN

Ph

PhDMAC-TRZ

NN

NN

Ph

Ph

Ph

Ph

DPAC-TRZ

NN

NN

Ph

PhSpiroAC-TRZ

PLQY (%) 90 10075

Highly Efficient TADF Emitters

22With CC Wu, Adv. Mater. 2016, 6976.

100 101 102 103 1040

10

20

30

40

50

60

70

EQE

(%)

w/o lens

Brightness (cd/m2)

w/ lens

400 450 500 550 600 650 700 750 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1530

45

60

75

90

Lambertian

1

Nor

mal

ized

Inte

nsity

(a.u

.)

Wavelength (nm)

TC98 TC68 DMAC-TRZ

High OLED Efficiency

0 10 20 30 40 50 60 70 80 900.00.20.40.60.81.01.21.41.6

Simulation Q//=67% Q//=83% Q//=100%

Experiment TC98

Nor

mal

ized

inte

nsity

(a.u

.)

Angle (degree)0 10 20 30 40 50 60 70 80 90

0.00.20.40.60.81.01.21.41.6

Simulation Q//=67% Q//=72% Q//=100%

Experiment DMAC-TRZ

Nor

mal

ized

inte

nsity

(a.u

.)

Angle (degree)

High Horizontal Emission Dipole


x

y

100 101 102 103 1040

10

20

30

40

50

60

70

EQE

(%)

w/o lens

Brightness (cd/m2)

w/ lens

400 450 500 550 600 650 700 750 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1530

45

60

75

90

Lambertian

1

Nor

mal

ized

Inte

nsity

(a.u

.)

Wavelength (nm)

TC98 TC68 DMAC-TRZ

High OLED EfficiencyTADF (Thermally Activated Delayed Fluorescence)

q Intermolecular charge transfercombined D and A à exciplex

• Suitable energy levels for charge injections • High charge mobility for both donor and acceptor • Large energy level offsets to accumulate charges at interface• High triplet energy for confining the exciplex emission

TADFIntramolecular vs. Intermolecular Charge Transfer



!



π" π" π" π"

FuncFonal,,Blocks,

Spacer,


25%,S1,+,75%,T1�h�

e�TADF,Host�


Energy,Transfer,

EmiTer,

Molecular,Designs:,

25

New ET material for blue exciplex

-2.83 eV

-6.83 eV

300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Emission (a. u.)

Abs

. (a.

u.)

Wavelength (nm)

mCP PO-T2T mCP:PO-T2T (1:1)

PLQY 52%

mCPET ~ 3.0 eV -6.1 eV

-2.1 eV

26Sci. Report 2014, 4, 5161.

10-1 100 101 102 103 1040

2

4

6

8

10

0

10

20

30

Qua

ntum

Effi

cien

cy (

%)

Brightness (cd/m2)

(b)


/W)

Device OptimizationsITO/mCP:ReO3(60 nm)/mCP(15 nm)/mCP:PO-T2T(1:1)(20 nm)/X (50 nm)/Liq/Al

ETL Von[V]

Lmax[cd/m2]

Imax[mA/cm2]

hextmax[%,cd/A]

hp max[lm/W]

At 1000 nit [%, V]

PO-T2T 2.6 38822 (14.8 V) 1234 10.28%,

19.71 20.83 7.93%, 6.7

CN-T2T 2.6 21272 (13.0 V) 1715 6.15%,

11.28 13.08 4.39%, 6.3

PO-T2T/CN-T2T 2.4 20439

(12.6 V) 1330 10.47%, 19.57 23.23 8.66%, 5.4

0 3 6 9 12 1510-2

100

102

104

0

500

1000

1500

2000 ETL PO-T2T CN-T2T PO-T2T(10)/CN-T2T(40)

Brig

htne

ss (c

d/m

2 )

Voltage(V)

(a) Current D

ensity (mA/cm

2)

400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0 ETL CIE PO-T2T (0.16,0.30) CN-T2T (0.16,0.28) PO-T2T(10)/CN-T2T(40) (0.16,0.29)

EL. (

a.u.

)

Wavelength (nm)

(c)

EQE over 10% and relatively low roll-off !!27

200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Emission (a. u.)

Abs

. (a.

u.)

Wavelength (nm)

D:A 1:1 (Film) FL-2CBP:POT2T Cbz2-F:POT2T

Remote Steric Effect for Improving Blue/Green Exciplex OLED Efficiency

200 300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Emission (a. u.)

Abs

. (a.

u.)

Wavelength (nm)

D:A 1:1(Film) DSDTAF:3NT2T DTAF:3NT2T

9.4% 11.3% EQE

11.6% 13.0% EQE

N

N

N

N

N

N3N-T2T

N

N

N

POPh2

POPh2

Ph2OP

PO-T2T

ACS Appl. Mater. Interfaces 2017, 9, 7355.

20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

21

Figure 4. a) Schematic diagram of the device structure with the energy levels of the organic layers, b) Current density�voltage�luminance (J�V�L) characteristics, and c) Calibrated external quantum efficiency (EQE) and power efficiencies of the optimized blue PhOLED as a function of luminance.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

J. J. Kim, Adv. Funct. Mater. 2015, 25, 361.

mCP2.94 eV

T1

S1

Exciplex2.64 eV

Po-T2T2.99 eV

FIrpic2.63 eVNN

mCP

29

N

N

N

POPh2

POPh2

Ph2OP

PO-T2T

Searching for High Efficiency Exciplex

N

N

Cz2-Ph

N

NNC

CN-Cz2

ITO

Liq/Al4%ReO3: HTL HTL

PO-T2T

CN-T2TDonor

60 (nm) 15 20 10 40

HIL HTL EML HBL ETL

100 101 102 103 1040

3

6

9

12

15

0

20

40

60

Qua

ntum

Effi

cien

cy (

%)

Brightness (cd/m2)


/W)

Nat. Commun. 2018, 9, 3111.

30

P-type DF

S1

S0

T1

Phosphorescence

E-type DF

h e


75%

Triplet FusionPromptFluorescence

RISC

Prospects for OLED Materials

G1:• Blue fluorescence dyes with strong

T-T annihilation character.

G2:• Bipolar host materials and blue Ir-emitter

with long device lifetime.

G3:• Highly efficient TADF materials Including

exciplex as host materials for G2 or G3.• TADF RGB emitters with high PLQYs for

high device lifetime.

31

Documents

Discovery of High-performance Blue OLED Materials and ... · MS 2 MS 17 MS 19 Wavelength (nm) e / 10 4 L M-1 cm-1 0.0 0.4 0.6 0.8 1.0 Abs. RT PL Norm. intensity /a.u. 0 2 4 6 8 10-3