phosphorescent oleds shortchemlabs.princeton.edu/macmillan/wp-content/uploads/sites/6/jml... ·...

Phosphorescent OLEDs

Jeffrey LipshultzMacMillan Lab Group Meeting

November 1, 2017

What is an Organic LED?

Three basic components:

1. Anode: inject holes (i.e. positive charges)2. Organic seminconductor Emission Layer (EML)3. Cathode: inject electrons

How does it work?

Zysman-Colman, E. Iridium(III) in Optoelectronic and Photonics Applications; John Wiley & Sons Ltd: Hoboken, NJ, 2017.Hartmut, Y. Highly Efficient OLEDs with Phosphorescent Materials; Wiley-VCH: Weinheim, 2008.

Early OLEDs

Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.Burroughes, J. H. et. al. Nature 1990, 347, 539.

1987: First “practical” (> 1% EQE) OLED using Alq3 (Eastman Kodak)

Alq3

N

OAl

3

“diamine”

N Np-tol

p-tol

p-tol

p-tol

External Quantum Efficiency (EQE) Internal Quantum Efficiency (IQE)

electrons injectedphotons emitted

excitons producedphotons emitted

!ex = !i =

Early OLEDs

Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.Burroughes, J. H. et. al. Nature 1990, 347, 539.


1990: First polymer-based OLED (~ 8% EQE) using PPV (Burroughes, Cambridge)

PPV

Alq3

N

OAl

3

n

“diamine”

N Np-tol

p-tol

p-tol

p-tol

Fluorescent OLEDs: Limitations

Baldo, M. A.; O’Brien, D. F.; Thompson, M. E.; Forrest, S. R. Phys. Rev. B. 1999, 60, 14422.


Alq3

N

OAl

3

Why only 1% EQE?

poor SOC means no emission from T1

BUT

spin statistics dictate that excitons formedin 1:3 singlet:triplet ratio,

somewhat verified experimentally

~25% IQEtheoretical limit

!s = (20±1)%

1990: First polymer-based OLED (~ 8% EQE) using PPV (Burroughes, Cambridge)

PPV

n

!s = (20±4)%

Segal, M.; Baldo, M. A.; Holmes, R. J.; Forrest, S. R.; Soos, Z. G. Phys. Rev. B. 2003, 68, 075211.

If


The basics of PhOLEDs

Fluorescence vs. Phosphorescence

Basic design concept

PhOLED architectures and materials

Multi-layered devices

Phosphorescent emitters

Small-molecule and polymer hosts

Current state-of-the-art

Blue emitters!

WOLEDs via mixed fluorescence/phosphorescence

Thermally-activated delayed phosphorescence (TADF)

Exciton formation/transfer

What makes a good dopant and host?

Specific considerations


Jablonski diagram upon photoexcitation

S0

S1T1

abs

fluor

esce

nce

inte

rnal

con

vers

ion

ISC

phos

phor

esce

nce

alt-I

SC

Jablonski diagram upon electroexcitation

S0

S1T1

excit

on fo

rmat

ion

fluor

esce

nce

inte

rnal

con

vers

ion

ISC

phos

phor

esce

nce

alt-I

SC

excit

on fo

rmat

ion

1. Efficient exciton-harvesting requires (?) triplet-harvesting

Key points for OLED development:

2. EL from T1 requires appreciable SOC3. T1 lifetime much longer than S1

4. E(T1) < E(S1)

Basic Design of PhOLEDs

Minaev, B.; Baryshnikov, G.; Agren, H. Phys. Chem. Chem. Phys. 2014, 16, 179.

Host/guest or host/dopant EML

1998: First phosphor-doped OLED (Forrest, Princeton)

Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoudtikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151.

N

N N

N

Et

Et

Et

Et Et

Et

Et

Et

Pt

PtOEP

anod

e

cath

ode

host

dopant

S1 T1

Alq3

N

OAl

3

peak efficiencies:!ex = 4%!i = 23%

EL lifetime 10-50 "s

Basic Principles of PhOLEDs

Hartmut, Y. Highly Efficient OLEDs with Phosphorescent Materials; Wiley-VCH: Weinheim, 2008.

Hole/electron recombination, aka exciton formation

Segal, M.; Singh, M.; Rivoire, K.; Difley, S.; Van Coorhis, T.; Baldo, M. A. Nature Mater. 2007, 6, 374.

anod

e

cath

ode

host

dopant

S1 T1

As hole and electron get closer, Coloumbic attractions come into play

ΔE(e-h) =e2

4!ℇ0ℇRC= kBT RC(300 K) ≈ 180 Å

These associated h+ and e- are called a charge transfer (CT) state.

They don’t necessarily need to be on a single molecule or polymer chain.



Hole/electron recombination, aka exciton formation

Reineke, S.; Baldo, M. A. Phys. Status Solidi A 2012, 209, 2341.

anod

e

cath

ode

host

dopant

S1 T1

Four main scenarios for exciton formation:

Sn formation in host

Tn formation in host

Sn formation in dopant

Tn formation in dopant

exciton in host exciton in dopant

Förster ET

Dexter ET

ISCISC



Host exciton energy transfer to dopant exciton, ISC/relaxation, phosphorescence

Yersin, H. Top. Curr. Chem. 2004, 241, 1.



Exciton formation on the dopant: hole trapping first

Yersin, H. Top. Curr. Chem. 2004, 241, 1.


Tao, Y.; Yang, C.; Qin, J. Chem. Soc. Rev. 2011, 40, 2943.

characteristics of good PhOLED host

Kappaun, S.; Slugove, C.; List, E. J. W. Int. J. Mol. Sci. 2008, 9, 1527.

1. Large HOMO-LUMO gap (high energy LUMO)

2. Long T1 lifetime = non-phosphorescent = poor SOC

3. Higher energy S1, T1 than dopant

4. Can efficiently transfer h+ or e-, or both (ambipolar)

5. Spectral overlap (for FRET) and energy overlap (for DET)

1. Lower LUMO than host

2. Shorter T1 lifetime = phosphorescent = good SOC

3. Lower energy S1, T1 than host

4. Can efficiently trap h+ or e-, or both

5. Spectral overlap (for FRET) and energy overlap (for DET)

characteristics of good PhOLED dopant/emitter










Blue emitters!






Mulitlayer OLED Device

Minaev, B.; Baryshnikov, G.; Agren, H. Phys. Chem. Chem. Phys. 2014, 16, 179.

representative multilayer PhOLED

Kappaun, S.; Slugove, C.; List, E. J. W. Int. J. Mol. Sci. 2008, 9, 1527.

glass substrateanode

hole-injection layer (HIL)

hole-transport layer (HTL)

host/guest

hole-blocker layer (HBL)

electron-transport layer (ETL)

electron-injection layer (EIL)

cathode

emission layer (EML)

examples

Al, Mg/Ag, metals

CsF, LiF

most common: Alq3

bathocuproine (BCP)

to be discussed in detail

bis(N,N’-diaryl)-biphenyls

PEDOT:PSS, [M]OnITO

characteristics/roles

… to be a cathode

high LUMO

high ETelectron-deficient (pyridines)

prevent “unused” h+from destroying ETL

transport h+/e– to form excitons

high ETelectron-rich (triarylamines)

low HOMOITO

Triplet-Emitting Dopants (Phosphors)

Nazeeruddin, M. K., et al. Top. Curr. Chem. 2017, 375, 39.

Heavy-metal organometallic complexes exhibit appropriate phosphorescence

N

N N

N

Et

Et

Et

Et Et

Et

Et

Et

Pt

PtOEP

T1 lifetime = 91 !sλmax = 650 nm

IrIII

N

N N

Ir(ppy)3

T1 lifetime = 2.1 !sλmax = 509 nm

Ir(ppy)2(acac)


IrIII

N

N

O

OMe

Me

IrIII

N

N

OO

N

F

F

FIrpic



Chou, P.-T.; Chi, Y. Chem. Eur. J. 2007, 13, 380.

really long lifetimehigh concentration of T1triplet-triplet annihilation

F

F

Triplet-Emitting Dopants (Phosphors)

Nazeeruddin, M. K., et al. Top. Curr. Chem. 2017, 375, 39.

Heavy-metal organometallic complexes exhibit appropriate phosphorescence

Ir(piq)3


IrIII

N

N N

Ir(ppy)3


Ir(ppy)2(acac)


IrIII

N

N

O

OMe

Me

FIrpic



Chou, P.-T.; Chi, Y. Chem. Eur. J. 2007, 13, 380.

IrIII

N

N N

IrIII

N

N

OO

N

F

F

F

F

Host Materials for PhOLEDs

Tao, Y.; Yang, C.; Qin, J. Chem. Soc. Rev. 2011, 40, 2943.Segal, M.; Singh, M.; Rivoire, K.; Difley, S.; Van Coorhis, T.; Baldo, M. A. Nature Mater. 2007, 6, 374.

Hole-transport-type hosts(electron-rich aromatic systems)

Electron-transport-type hosts(electron-deficient aromatic systems)

Ambipolar hosts(donor-acceptor systems)

anode

cathode

HIL

EIL

EML

*

anode

cathode

HIL

EIL

EML

*

anode

cathode

HIL

EIL

EML*

Type of host material determines exciton-generation zone

Host Materials for PhOLEDs

Tao, Y.; Yang, C.; Qin, J. Chem. Soc. Rev. 2011, 40, 2943.Segal, M.; Singh, M.; Rivoire, K.; Difley, S.; Van Coorhis, T.; Baldo, M. A. Nature Mater. 2007, 6, 374.

Hole-transport-type hosts(electron-rich aromatic systems)

Electron-transport-type hosts(electron-deficient aromatic systems)

Ambipolar hosts(donor-acceptor systems)

N

N 2

CBP

NnPVK

NN

N

TAZ

N

N

NPh

Ph

Ph

T2T

P

P 2

PO1

PhPh

OPh

O

Ph

TFTPA

N

O

N

R

Nalk

CzOXD

N N

Ph Ph

RN

m-CZBP

N

P(O)Ph2Ph2(O)P

PPO2NAr

Ar Ph

Dopant Concentration Effect

Reineke, S.; Baldo, M. A. Phys. Status Solidi A 2012, 209, 2341.Adachi, C. et al. Appl. Phys. Lett. 2005, 86, 071104.

high concentration of dopant leads to dimished efficiency“concentration quenching”

triplet-triplet annihilation

Förster-type

Staroske, W.; Pfeiffer, M.; Leo, K.; Hoffmann, M. Phys. Rev. Lett. 2007, 98, 197402.

case study: Ir(ppy)3 in CBP

RF = 2.9 nm

Dexter-type

Dopant Concentration Effect

Reineke, S.; Baldo, M. A. Phys. Status Solidi A 2012, 209, 2341.Adachi, C. et al. Appl. Phys. Lett. 2005, 86, 071104.

high concentration of dopant leads to dimished efficiency“concentration quenching”

triplet-triplet annihilation

Staroske, W.; Pfeiffer, M.; Leo, K.; Hoffmann, M. Phys. Rev. Lett. 2007, 98, 197402.

case study: Ir(ppy)3 in CBP

RF = 2.9 nm

0.1% Ir(ppy)3in TCTA

Increased IQE by Exciton Confinement

Adachi, C.; Baldo, M. A.; Forrest, S R.; Thompson, M. E. Appl. Phys. Lett. 2000, 77, 904.Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. J. Appl. Phys. 2001, 90, 5048.

N N

NPh Ph

host: TAZ dopant: Ir(ppy)2(acac)HTL: HMTPD ETL: Alq3

N

OAl

3

N

MeMe

Me

2

emission from HMTPD likely indicates exciton formation in HTL

poor hole injection to EML/poor recombination in EML

HOMO of host is below HOMO of HTL, unfavorable hole injection

IrIII

N

N

O

OMe

Me

12% Ir(ppy)2(acac)

!ext = (19±0.5)%

!i = (87±7)%










Blue emitters!






E(T1) FIrpic > E(T1) CBPbut

kR >> kh

uphill ET can occurto repopulate T1 of FIrpic

leading to delayed/prolongedphosphorescence!

“Endothermic Energy Transfer” for Phosphorescence

Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. Appl. Phys. Lett. 2001, 79, 2082.Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. J. Appl. Phys. 2001, 90, 5048.

host: CBP dopant: FIrpicHTL: NPD ETL: Alq3

N

OAl

3

N

2

N

2

IrIII

N

N

OO

N

F

F

F

F

up to 10 ms lifetimeof phosphorescence no CBP phosphorescence observed

FIrpic phosphorescence observedat both early and delayed times

!ext = (5.7±0.3)%

“Endothermic Energy Transfer” for Phosphorescence

Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. Appl. Phys. Lett. 2001, 79, 2082.Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. J. Appl. Phys. 2001, 90, 5048.


N

OAl

3

N

2

N

2

IrIII

N

N

OO

N

F

F

F

F

Improved Efficiency in Blue Phosphorescent LEDs

Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. Appl. Phys. Lett. 2001, 79, 2082.Tokito, S.; Ijima, T.; Suzuri, Y.; Kita, H.; Tsuzuki, T.; Sato, F. Appl. Phys. Lett. 2003, 83, 569.


N

OAl

3

N

2

N

2

host: CDBP dopant: FIrpicHTL: NPD ETL: Alq3

N

OAl

3

N

2

N

2

Me

!ext = (5.7±0.3)%

!ext = 10.4%

IrIII

N

N

OO

N

F

F

F

F

IrIII

N

N

OO

N

F

F

F

F

Improved Efficiency in Blue Phosphorescent LEDs

Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo, M. A.; Thompson, M. E.; Forrest, S R. Appl. Phys. Lett. 2001, 79, 2082.Tokito, S.; Ijima, T.; Suzuri, Y.; Kita, H.; Tsuzuki, T.; Sato, F. Appl. Phys. Lett. 2003, 83, 569.

host: CBP

N

2

host: CDBP

N

2

Me

!ext = (5.7±0.3)%

!ext = 10.4%

E(T1) = 2.6 eV

E(T1) = 3.0 eV

dopant: FIrpic

phosphorescence decays significantly faster

exothermic ET to phosphor is more efficient than endothermic

IrIII

N

N

OO

N

F

F

F

F

Improving Stability and Lifetime of Blue PhOLEDs

Seifert, R.; Rabelo de Moraes, I.; Scholz, S.; Gather, M. C.; Lussem, B.; Leo, K. Org. Electron. 2013, 14, 115.Endo, A.; Suzuki, K.; Yoshihara, T.; Tobita, S.; Yahiro, M.; Adachi, C. Chem. Phys. Lett. 2008, 460, 155.

FIrpic


IrIII

N

N

N

N

F

F


FIr6

as films in mCP

N N

N

NB

N

N

N

N

high triplet energy emittersrapid decay of pure films and OLED devicesstabilization with improved hosts, HBL, etc

IrIII

N

N

OO

N

F

F

F

F

F

F


Seifert, R.; Rabelo de Moraes, I.; Scholz, S.; Gather, M. C.; Lussem, B.; Leo, K. Org. Electron. 2013, 14, 115.Zhang, Y.; Lee, J.; Forrest, S. R. Nat. Commun. 2014, 5, 5008.

Ir(dmp)3λmax = 466 nm

IrIIINN

MeMe

3

NN

mCBP

E(HOMO) = 5.0 eV E(HOMO) = 6.0 eVhole transport in EML electron transport in EML

at high Ir(dmp)3 concentrations, exciton formation should occur

only in vicinty of/on Ir(dmp)3

anode




IrIIINN

MeMe

3

NN

mCBP




!ext= (8.5±0.1)%T50 = 510 h

!ext = (9.5±0.1)%T50 = 1500-1600 h

anode




IrIIINN

MeMe

3

NN

mCBP




!ext = (9.5±0.1)%T50 = 1500-1600 h

!ext = (18±0.2)%T50 = 3500-3700 h


Sarma, M.; Tsai, W.-L.; Lee, W.-K.; Chi, Y.; Wu, C.-C.; Liu, S.-H.; Chou, P.-T.; Wong, K.-T. Chem 2017, 3, 461.

FIrpic


MS2


IrIII

N

N

OO

N

F

F

F

F IrIII

N

N

N

N

OO

N

F

F

F

F

White OLEDs (WOLEDs)

Gather, M. C.; Köhnen, A.; Meerholz, K. Adv. Mater. 2011, 23, 233.

white light = blended blue, green, red

Red PhOLED ✓

Green PhOLED ✓

Blue PhOLED ?

Solution: combine blue fluorescence with red/green phosphorescence

Working principle:

trap singlets on blue flourescent emittertrap triplets on red/green phosphorescent emitter


Sun, Y.; Biebink, N. C.; Kanno, H.; Ma, B.; Thompson, M. E.; Forrest, S. R. Nature 2006, 440, 908.Chen, J.; Zhao, F.; Ma, D. Mater. Today 2014, 17, 175.


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

NEt

2

BCzVBi

O

OMe

Me

IrIII

N

N

IrIII

N

N N

Ir(ppy)3 PQIr

Working principle:

trap singlets on blue flourescent emittertrap triplets on red/green phosphorescent emitter


Schwartz, F.; Pfeiffer, M.; Reineke, S.; Walzer, K.; Leo, K. Adv. Mater. 2007, 19, 3672.Chen, J.; Zhao, F.; Ma, D. Mater. Today 2014, 17, 175.


Schwartz, F.; Pfeiffer, M.; Reineke, S.; Walzer, K.; Leo, K. Adv. Mater. 2007, 19, 3672.Chen, J.; Zhao, F.; Ma, D. Mater. Today 2014, 17, 175.

O

OMe

Me

IrIII

N

N

N

N Me

Me

IrIII

N

N N

Ir(ppy)3 Ir(MDQ)2(acac)4P-NPD

N

2

Thermally-Activated Delayed Fluorescence (TADF)

Yang, Z. et al. Chem. Soc. Rev. 2017, 46, 915.

Obviously not phosphorescence

S0

S1T1

excit

on fo

rmat

ion

fluor

esce

nce

inte

rnal

con

vers

ion

ISC

phos

phor

esce

nce

alt-I

SC

excit

on fo

rmat

ion

RISC

eosin Y, 1961(E-type delayed fluorescence)

O O

Br

BrO

Br

Br

CO2“the high-frequency band (which has a contour

identical with the fluorescence band) is the result of thermal activation to the upper singlet

level folowed by a radiative transition from there to the ground state, and we shall therefore call

this the delayed fluorescence band”

Parker, C. A.; Hatchard, C. G. Trans. Faraday Soc. 1961, 57, 1894.


Yang, Z. et al. Chem. Soc. Rev. 2017, 46, 915.Adachi, C. et al. Appl. Phys. Lett. 2011, 98, 083302.

N N

NN N

NPh PhN

PIC-TRZ

E(T1) = 2.55 eVE(S1) = 2.66 eV

ΔEST = 0.11 eV

!ext = 5.3%


Yang, Z. et al. Chem. Soc. Rev. 2017, 46, 915.Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Nature 2012, 492, 234

NC CNN

NN N

4-CzIPN

!ext = (19.3±1.5)%


Yang, Z. et al. Chem. Soc. Rev. 2017, 46, 915.Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Nature 2012, 492, 234

NC CNN

NN N

4-CzIPN

“Third-generation organic electroluminescence materials”

335 references in Review below, published Jan 2017

phosphorescent oleds shortchemlabs.princeton.edu/macmillan/wp-content/uploads/sites/6/jml... ·...

Documents