high efficiency and stable white oled using a single...
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Jian Li, jian.li.1@asu.edu 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.
4
Purpose and Objectives
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.
5
Purpose and Objectives
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.
6
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.
7
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.
9
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
Progress and Accomplishments
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
Progress and Accomplishments
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.
12
Progress and Accomplishments
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
Progress and Accomplishments
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
Progress and Accomplishments
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.
15
Progress and Accomplishments
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
16
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
17
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
18
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
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