high efficiency and stable white oled using a single … · high efficiency and stable white oled...

Jian Li, [email protected] Arizona State University

High efficiency and stable white OLED using a single emitter

2014 Building Technologies Office Peer Review

2

Project Summary Timeline:

Start date: 10/1/2011

Planned end date: 9/30/2014

Key Milestones

1. demonstrating a single-doped white device (CRI> 80) with a PE of 40 lm/W @ 1000 cd/m2 and an operational lifetime over 100 hrs @ 1000 cd/m2; 9/30/13

2. blue device using halogen-free Pt-based emitters with an EQE of over 15%; 9/30/14

3. demonstrating a single-doped white device (CRI> 80) with a PE of 50 lm/W @ 1000 cd/m2 and an operational lifetime over 10000 hrs @ 1000 cd/m2; 9/30/14

Budget:

Total DOE $ to date: $664,785

Total future DOE $: $0

Key Partners:

Project Goal: This project is to demonstrate an efficient and stable white OLED using a single emitter on a planar glass substrate. The successful outcome of this project will provide a solution to lower the fabrication cost of white OLEDs significantly by decreasing the complexity of device fabrication, increasing the robustness of materials and providing more cost-effective alternates to the state-of-the-art Iridium-based phosphorescent emitters.

ASU

Target Market/Audience:

OLED based solid state lighting industry/ R&D and manufacturing people

3

Purpose and Objectives

Problem Statement: The state-of-the art WOLED technology requires the use of multiple emissive materials, which will generate color instability and color aging issues, affecting the performance and operational lifetime of WOLEDs. Moreover, the manufacturing process of white OLED becomes more complicated with the incorporation of multiple emissive layers or a single emissive layer with multiple dopants. In order to prevent the color aging and enhance the color stability, the device structures will become inevitably more complexed. The goal of this project is to demonstrate an efficient and stable white OLED using a single emitter, which will provide a solution to lower the fabrication cost of white OLEDs significantly by decreasing the complexity of device fabrication.

(a) (b) (c) (d)

Schemes for 4 possible WOLED architectures: (a) triple-

doped emissive layer; (b) multiple emissive layers; (c)

emissive layer with monomer and excimer; (d) emissive

layer with a single broadband emitter.

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Target Market and Audience: Lighting consumes ~765 trillion Whr of electricity every year in the United States, i.e. 22% of all electricity generated nation-wide. It costs close to $58 billion a year to light the residential, business and manufacture buildings. However, two current widely used lighting devices have their drawbacks and limitations. Incandescent lamp, a one-hundred-year-old technology, has a low power efficiency (average 12-17 lm/W), which still accounts for 42% consumption of electricity. On the other hand, a fluorescent lamp with high power efficiency (> 80 lm/W) could be potentially environmental hazardous due to its use of mercury. In addition to inorganic white LEDs, the white organic light emitting diodes (WOLEDs) with high power efficiency (>100 lm/W) , are also considered as strong candidates for next generation illumination devices. Especially, WOLEDs use environmentally benign organic materials and their fabrication cost can be significantly reduced with potential roll-to-roll processing technology. Our project focus on developing an efficient and stable WOLED in a simpler device structure, in order to reduce the manufacture cost of WOLEDs.

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Impact of Project: The ultimate objective of this project is to demonstrate an efficient and stable white OLED using a single emitter on a planar glass substrate without outcoupling enhancement and a luminous efficiency of at least 50 lm/W and an operational lifetime over 10000 hrs @ 1000 cd/m2. In a more advanced device structure with enhanced outcoupling effect (2-3x improvement), a stable single-doped white OLED with an efficacy of 100-150 lm/W can be demonstrated using the outcome of this project. The successful outcome of this project will provide a solution to lower the fabrication cost of white OLEDs significantly by decreasing the complexity of device fabrication, increasing the robustness of materials and providing more cost-effective alternates to the state-of-the-art Iridium-based phosphorescent emitters. Moreover, a single-doped white OLED will also provide a greater control of emission color by eliminating color aging. This could help to meet the targeted cost of organic solid state lighting set in the DOE MYPP.

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Approach

N

P t

O

OF

F

[FPt-FPt]*

orange like emission

N

P t

O

O

F

F

FPt

blue-green like

emission

Adamovich et. al., New J. Chem. (2002).

N

P t

O

O

F

F

Benefits

(a) No problem of energy transfer from

blue to red emitters

(b) No problem of Differential Aging

(c) Spectrum is voltage independent

(d) Simple structure

(e) Easy to manufacture

Plus, Pt complexes will be more cost-

effective.

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Approach

Approach: To deliver this research goal, the project will be focused on two main areas including 1) the development of efficient and stable square planar phosphorescent emitters and ambipolar host materials; and 2) the device optimization using stable injection materials to balance charge in the recombination zone.

Key Issues: 1) controlling emission color of emitters and their excimers, 2) improving optical and electrical stability of emissive dopants, 3) incorporating the state-of-the-art of transporting and blocking materials to maximize the power efficiency and operational lifetime of WOLEDs at the same time.

8

Approach

Distinctive Characteristics: Compared with the stat-of-the-art white OLEDs using Ir complexes with different emission colors, the proposed research has several advantages. First of all, because an excimer does not have a bound ground state, the cascade of energy from the host or the “blue” (higher energy) emitter to the excimer can be prevented, leading to a stable emission color independent of the driving voltage. Secondly, the problem of “color aging” can be resolved due to the use of a single emitter. Thirdly, the Pt-based emitters will be more preferable over Ir-analogue for displays and lighting with equal performance, which can be justified by potentially large cost difference between Ir (natural abundance: 3x10-6 ppm) and Pt complexes (natural abundance: >1x10-3 ppm). On the other hand, single-doped white OLED has not demonstrated to be efficient and stable enough compared with the current best white OLEDs due to insufficient research effort from the community.

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Progress and Accomplishments

Fleetham et al. Adv. Mater. (2013)

300 400 500 600 700 800

NN

Pt

Cl

N N

N

F

F

Pt

O

OCIE (.44, .45)

CRI - 75

CIE(.33, .35)

CRI - 53

Wavelength (nm)

CIE(.33, .33)

CRI - 80

NN Pt

Cl

F F

Pt-4

Pt-16

FPt

For Pt-16 WOLED, power efficiency exceeds 50 lm/W

(no n/p-doping and enhanced outcoupling), CIE (0.33,

0.32), CRI >=80, showing promise for lighting

applications.

Power efficiency is 29 lm/W at 1000 cd/m2

1E-4 1E-3 0.01 0.1 1 100

5

10

15

20

25

EQ

E (

%)

J (mA/cm2)

PO15 (40 nm)

PO15(10nm)/BmPyPB(30nm)

device structure:ITO/PEDOT:PSS/NPD(30nm)/TAPC(10nm)/

10%Pt-16:TAPC:PO15(25nm)/ ETL/LiF/Al.

10


device structure:ITO/PEDOT:PSS/NPD(30nm)/ TAPC(10nm)/x%dopant:26mCPy25nm)/ PO15(40nm)/LiF/Al.

It is very interesting to find out that the behavior of excimers could be so different with similar

monomer structures.

400 500 600 700 800 1E-3 0.01 0.1 1 10 1000

5

10

15

20

400 500 600 700 8000

1

400 500 600 700 800 1E-3 0.01 0.1 1 10 1000

5

10

15

400 500 600 700 8000

1

(d)

(c)(b)

Wavelength (nm)

[Pt-16]

2%

10%

14%

18%

Wavelength (nm)

(a)

Js (mA/cm

2)

EQ

E (

%)

EQ

E (

%)

Js (mA/cm

2)

[Pt-16]

2%

10%

14%

18%

[Pt-16]

2%

: (42±5)%

18%

: (71±5)%

(f)(e)[Pt-17]

2%

10%

14%

18% [Pt-17]

2%

10%

14%

18%

EL

In

ten

sit

y (

a.u

.)E

L In

ten

sit

y (

a.u

.)

PL

In

ten

sit

y (

a.u

.)

Wavelength (nm)

PL

In

ten

sit

y (

a.u

.)Wavelength (nm)

[Pt-17]

2%

: (68±5)%

18%

: (48±5)%

NN

P t

C l

N N

NN

P t

C l

N N

Pt-16

Pt-17

Fleetham et al. Adv. Mater. (2013)

11


Complex λmax (nm) Φ(%) τ

(μs)

kr

(x104 s-1)

knr

(x104 s-1)

PtON7 452 89 4.1 21 2.6

PtOO7 442 58 2.5 23 17

Pt-16[9b] 450 32 5.1 6.3 13.3

Pt(Mepmic)[9a] 419 20 25 0.8 3.2

Ir(cnpmic)3[7b] 425(sh), 450 78 19.5 4 1.1

Ir(dbfmi)[7a] 445 70a 19.6 3.6 1.5

PtON1 449 85 4.5 19 3.3

Hang et al. Angew Chem. Int. Ed. (2013)

O

O

N

Pt

PtOO7 PtON7

N

N

N

O

N

PtN

N

O

O

PtN

N

N N

N NPt

Cl

Pt-16

Pt(Mepmi)

Pt[pmi-O-POPy] Pt[pmi-O-CbPy]

IrN

N

Ir(dpfmi)

O

33

N

N

CN

Ir

Ir(cnpmic)

• With such molecular design principle, PtON7

shows a better photophysical properties than

its Pt analogs and Ir analogs;

• A deep blue OLED with a maximum EQE of

22% and CIE coordinates of (0.14, 0.15) was

fabricated using PtON7.

400 500 600 700 8000

1

Ele

ctr

olu

min

escence (a

.u.)

Wavelength (nm)

Device 1

(Pt-16)

CIE: (0.16,0.15)

400 500 600 700 8000

1

E

lectr

olu

min

escence (

a.u

.)

Wavelength (nm)

Device 2

(PtOO7)

CIE: (0.15,0.10)

400 500 600 700 8000

1

Ele

ctr

olu

min

escence (a

.u.)

Wavelength (nm)

PtON7

Device 3

CIE: (0.14,0.19)

Device 4

CIE: (0.14,0.15)

1E-3 0.01 0.1 1 10 1000

10

20

Exte

rnal Q

uantu

m E

ffic

iency (

%)

Current Density (mA/cm2)

Device 1

Device 2

Device 3

Device 4

ITO/PEDOT:PSS/NPD(30 nm)/TAPC(10 nm)/2% emitter:26mCPy(25

nm)/PO15(40 nm)/LiF/Al.

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400 450 500 550 600 650 700

0.0

0.5

1.0 Pt-16

PtON7

Pt7O7

PL

in

ten

sity (

a.u

.)

Wavelength (nm)

400 500 600 700 800

0.0

0.5

1.0

EL

In

ten

sity (

a.u

.)

Wavelength (nm)

2% Pt7O7

CIE: (0.12, 0.24)

14% Pt7O7

CIE: (0.37, 0.43)

CRI: 69

18% Pt7O7

CIE: (0.41, 0.45)

CRI: 69

0.1 1 10 100 1000 10000

0

5

10

15

20

25

30

2% Pt7O7

14% Pt7O7

18% Pt7O7

EQ

E (

% P

ho

ton

/ele

ctr

on

)

Brightness (cd/m2)

ITO/HATCN(10 nm)/NPD(30 nm)/TAPC(10 nm)/x% Pt7O7:

mCBP (25 nm)/DPPS(10 nm)/BmPyPB(30 nm)/LiF/Al

Following the materials design principle from tetradentate

Pt complexes, Pt7O7 was synthesized and fabricated in

the device settings. We were very thrilled to report that the

monomer and excimer can both be efficient at the same

time with peak EQE close to 25% and peak power

efficiency close to 60 lm/W. 0.01 0.1 1 10 100 10000

10

20

30

40

50

60

70

Po

we

r E

ffic

ien

cy (

Lm

/W)

Brightness (cd/m2)

Li et al. Adv. Mater. In Press.

13


400 500 600 700 800

0.0

0.5

1.0

14% Pt7O7

0.1 1 10 100 1000

0

2

4

6

8

10

Ext

ern

al Q

ua

ntu

m E

ffic

ien

cy (

%)

Brightness (cd/m2)

14% Pt707

CIE: (0.37,0.41)

CRI: 72

EL

In

ten

sity (

a.u

.)

Wavelength (nm)

0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Re

lativ

e L

um

ina

nce

(@

20

mA

/cm

2)

Time (hours)

14% Pt7O7

ITO/HATCN(10 nm)/NPD(30 nm)/ 14% Pt7O7:mCBP (25 nm)/BAlq(10 nm)/Alq3(30 nm)/LiF/Al.

14% doped Pt7O7 device have demonstrated a reasonable device operational

lifetime with Lt50 over 35 hrs at constant current of 20 mA/cm2 with initial

luminance of around 3000 cd/m2, which can be translated to a LT50 over 300 hrs

at initial luminance of 1000 cd/m2 citing the formula: Lt50 = Lt50‘(L0’/L0)

1.8. The use

of state-of-the-art of transporting and blocking materials will further improve the

power efficiency, which is also expected to significantly improve the operational

lifetime of Pt7O7 device @1000 cd/m2.

Li et al. Adv. Mater. In Press.

14


0 20 40 60

0.80

0.85

0.90

0.95

1.00

Lu

min

en

ce

@ 2

0 m

A/c

m2 (

a.u

.)

time (hr)

10% PtON9Me:co-host

20% PtON9Me:co-host

20% PtON9Me:CBP

20% PQIr:CBP

NIrO

O

PQIr

NPt

O

NN

PtON11Me

2

ITO/HATCN(10 nm)/NPD(40 nm)/EML(25 nm)/

BAlq(10 nm)/Alq3(30 nm)LiF/Al.

0 2 4 6 8

1E-5

1E-4

1E-3

0.01

0.1

1

10

100

Js

V

10% PtON11Me

20% PtON11Me

10% PQIr

20% PQIr

400 600 800

0.0

0.2

0.4

0.6

0.8

1.0

inte

nsity

lambda

10% PtON11Me

20% PtON11Me

10% PQIr

20% PQIr

Li et al. in preparation

PtON11-Me, a analog to PtON1 and PtON7, have

demonstrated a remarkable operational stability in OLEDs.

The LT97 is more than 70 hrs at a very high current density

of 20 mA/cm2, indicating the potential of such class of

emitters as emitters for the stable and efficient blue and

white phosphorescent OLEDs.

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Lessons Learned: Excimer-based WOLEDs can be as efficient as the state-of-the-art WOLEDs employing multiple emissive materials. Accomplishments: 1) demonstrating the most efficient excimer-based WOLEDs; 2) demonstrating the most efficient Pt-based deep blue phosphorescent OLEDs; 3) demonstrating great operational stability of Pt-based OLEDs, which is comparable to the state-of-the-art Ir-based OLEDs. Market Impact: we are still on track to achieve the ultimate goal of project. The research progress has been reported in multiple high-profile publications and also presented in various research conferences. Awards/Recognition: N/A

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Project Integration: PI and one postdoc, two graduate students and one hourly undergraduate student are working on this project. Partners, Subcontractors, and Collaborators: N/A Communications: The research progress has been presented in various research conferences, including DOE solid state lighting R&D workshop, ACS and MRS national meetings, and international research conferences or workshops.

Project Integration and Collaboration

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Next Steps and Future Plans: we will optimize the efficacy and performance of the excimer-based WOLEDs by employing the state-of-the-art transporting and blocking materials through collaboration with industrial partners.

Next Steps and Future Plans

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REFERENCE

1) T.B. Fleetham, J. Ecton, Z. Wang, N. Bakkan, and J. Li*, “Single-Doped White Organic Light-Emitting Device with an External Quantum Efficiency Over 20%”, Adv. Mater., 25, 2573-2576 (2013).

2) X.C. Hang, T.B. Fleetham, E. Turner, J. Brooks and J. Li*, “Highly Efficient Blue-Emitting Cyclometalated Platinum(II) Complexes by Judicious Molecular Design”, Angew. Chem. Inter. Ed., 52, 6753-6756 (2013).

3) G. Li, T.B. Fleetham and J. Li*, “Stable and Efficient White OLEDs Employing a Single Emitter”, Adv. Mater., In Press.

4) E. Turner, N. Bakkan and J. Li*, “Cyclometalated Platinum Complexes with Luminescent Quantum Yields Approaching 100%,” Inorg. Chem., 52, 7344-7351 (2013).

5) N. Bakkan, Z. Wang and J. Li*, “High efficiency excimer-based white organic light emitting device using platinum complex,” J. Photon. for Energy, 2, 021203 (2012).

19

Project Budget: DOE share - $664,785, ASU share - $170,547 Variances: N/A Cost to Date: over 95% budget has spent at the end of FY2013. Additional Funding: N/A

Budget History

FY2012– FY2013 (past)

FY2014 (current)

FY2015 – N/A (planned)

DOE Cost-share DOE Cost-share DOE Cost-share $443k $111k $221k $59k $0 $0

Project Budget

20

Project Plan and Schedule Project Schedule

Project Start: 10/1/11

Projected End: 9/30/14

Task

Q1

(Oct

-Dec

)

Q2

(Jan

-Mar

)

Q3

(Apr

-Jun

)

Q4

(Jul

-Sep

)

Q1

(Oct

-Dec

)

Q2

(Jan

-Mar

)

Q3

(Apr

-Jun

)

Q4

(Jul

-Sep

)

Q1

(Oct

-Dec

)

Q2

(Jan

-Mar

)

Q3

(Apr

-Jun

)

Q4

(Jul

-Sep

)

Past Work

Milestone A: blue device using Pt-based emitters with an EQE of

over 15%

Milestone B: reducing the driving voltage of FPt device to 4.5 V @

1000 cd/m2

Milestone C: demonstrating a single-doped white device (CRI>80)

with a PE of 25 lm/W @ 1000 cd/m2

Milestone D: blue device using Pt-based emitters with an EQE of

over 20%

Milestone E: blue device using halogen-free Pt-based emitters

with an EQE of over 10%

Milestone G: blue device using halogen-free Pt-based emitters

with an EQE of over 15%

Current/Future Work

Milestone F: demonstrating a single-doped white device (CRI>

80) with a PE of 40 lm/W @ 1000 cd/m2 and an operational

lifetime over 100 hrs @ 1000 cd/m2

Milestone H: demonstrating a single-doped white device (CRI>

80) with a PE of 50 lm/W @ 1000 cd/m2 and an operational

lifetime over 10000 hrs @ 1000 cd/m2

Completed Work

Active Task (in progress work)

Milestone/Deliverable (Originally Planned) use for missed

Milestone/Deliverable (Actual) use when met on time

FY2012 FY2013 FY2014

high efficiency and stable white oled using a single … · high efficiency and stable white oled...

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