Solid State Lighting: A Bright Opportunity for
Nanotechnology to Impact Energy Efficiency
Paul E. Burrows
Pacific Northwest National Laboratory
Richland, WA 99352
National Science Foundation
Joint U.S. Korea NanoForum
April 26th 2007
Items for Discussion
Solid state lighting as a high payoff research
area in energy efficiency
The Department of Energy’s Basic Research
Needs Report in Solid State Lighting
The role of nanoscience in optimizing next
generation solid state lighting
2
Artificial lighting was among the first
inventions of mankind…
The First
Invention
WARMTH
COOKING
LIGHT
3
Each subsequent improvement in lighting led to
major lifestyle improvements
and improvements in the energy efficiency of the light
Candle: 0.05 lumens per watt
Gaslamp: 0.5 lumens per watt
“Incandescent” Lightbulb
15 lumens per watt
(5% efficient)
4
Why does lighting impact
energy conservation?
Lighting consumes 22% of
the electricity generated in
the U.S.A.
That’s 8% of the total
energy consumption
Costs $50 billion per year
Releases 150 million tons
of CO2 into the
atmosphere each year
Much of it is 19th century
technology with poor
efficiency
5
We should be able to do better
Lighting is a highly attractive
target for reducing energy
consumption!
Energy Consumption (Quads)
1000
Efficiencies of energy
technologies in buildings:
Heating:
Elect. motors:
Fluorescent:
Incandescent:
70 - 80%
85 - 95%
20%
5%
94 Quads
100
Energy
34 Quads
Electricity
10
Lighting
6.9 Quads
1998
1
1970 1980
Projected U.S.
1990
2000
Year
2010 2020
6
Basic Research Needs for Solid State Lighting
May 22-24, 2006
Workshop Chairs: Julia Phillips (Sandia National Labs)
Paul Burrows (Pacific Northwest National Lab)
LED:
OLED:
Cross-Cutting:
Science Panel Chairs:
Jerry Simmons (SNL)
Bob Davis (Carnegie Mellon U)
Franky So (U of Florida)
George Malliaras (Cornell)
Jim Misewich (BNL)
Arto Nurmikko (Brown U)
Darryl Smith (LANL)
Total 79 participants
Charge: identify transformational science
Output: www.sc.doe.gov/bes/reports/list.html
33%
DOE Nat’l
Labs
20%
Federal
33%
Universities
14%
Industry & others
7
Workshop Output

12 Priority Research Directions (PRDs), each
specific to an individual panel

2 Grand Challenges (GCs) which overarch all
panels
LED Science
OLED Science
Cross-cutting
Science
www.sc.doe.gov/bes/reports/list.html
8
GRAND CHALLENGE 1:
Rational design of solid-state lighting structures
Today, light-emitting solid state materials are discovered
rather than designed.
The CHALLENGE:
Can we design
optimized device
components that
assemble into a high
efficiency charge-tolight conversion
system?
9
GRAND CHALLENGE 2: Control of radiative and
nonradiative processes in light-emitting materials
Light-emitting efficiency is determined by competition between
radiative and non-radiative processes.
The CHALLENGE:
Can we understand and
control the physics of
photon generation and
emission?
10
Inorganic solid state lighting
Composition and nanostructure determine color
Postively
charged carriers
Negatively
charged carriers
_
+
- With applied voltage positive and
negative charge carriers recombine
- Energy may be released as light or
heat
- Theoretically they can be 100%
efficient with unlimited life!
(compared to incandescent which is
5% efficient, 2000 hour life)
- Commercial LEDs can be expected to
reach 50% efficiency and possibly
more
Semiconductor
Bandgap
Determines Color
Colored LEDs:
Red, Yellow - AlInGaP
Blue, Green – InGaN
White LEDs:
Red + Green + Blue, or
Blue + phosphor
Buckingham Palace, London, England
Lit by Lumileds LEDs
Courtesy George Craford, Philips Lumileds
11
Molecular Light Emitting Materials:
Molecular Structure Determines Color
Phosphorescent
Blue
Green
Fluorescent
Polymeric
Weakly interacting molecules mean the
photophysics of a film is controlled by the
molecular structure of the fundamental
building block
Red
Research-Scale Organic Lightbulbs
General Electric: 2 ft OLED panel
Universal Display Corporation
Note the lack of a
luminaire,- these
are large area, low
intensity emitters)
Efficiency performance of OLED
Showa Denko K.K.:single layer
phosphorescent polymer OLEDs external
quantum efficiency of 17% (green) and 16%
(blue) with durability of 350,000 hours at 100
cd/m2. They will build a trial volumeproduction line by the middle of this year.
Novaled
Novaled claims "groundbreaking" results with
its p-i-n OLED technology.. White top emission
devices achieved a lifetime of 18,000 hours at
3 V and 1,000 cd/m2. Green top-emission
OLEDs achieve 1,000 cd/m2 at 2.5 V and 95
cd/A (about 110 lm/W) These green devices
are based on Ir(ppy)3.
Osram
UDC
Konica-Minolta
Universal Display Corporation achieved 30
lm/W at 1000 cd/m2 (warm white).
Osram: 25 lm/W white polymer devices
Konica Minolta 60 lm/W, details unclear
14
The problem of efficient white
electrophosphorescence
ENERGY
Exciton levels
must be even
higher than blue
S1
T1 > 2.9 eV
What is this
molecule?
Triplet
Excitons
phosphorescence
Ground
state
CHARGE TRANSPORTING
HOST MOLECULES
PHOSPHORESCENT
DOPANTS
The problem of efficient white
electrophosphorescence
Exciton levels
must be even
higher than blue
S1
Triplet
Excitons
ENERGY
T1
phosphorescence
Ground
state
CHARGE TRANSPORTING
MOLECULES
PHOSPHORESCENT
DOPANT
Aromatic and Heteroaromatic Chromophores with
Interesting Triplet Exciton Energies
All too volatile and do not form stable films!
2.55 eV
3.08 eV
TOO
LOW
2.64 eV
2.81 eV
2.84 eV
3.12 eV
3.04 eV
2.92 eV
Can we use these as building blocks?
Phosphine Oxide (PO) Compounds
Linda Sapochak, Paul Burrows, Asanga Padmaperuma and Paul Vecchi
O
d+
P
Active
Bridge
d+
P
inductive
effect of P=O
renders aryl
groups
electron
deficient
O
Outer groups
enhance
thermal
properties
High triplet
energy small
molecule
fragment
Phosphine
oxide point of
saturation to
isolate
photophysics
on bridge
18
(77K in DCM)
PO1
4,4'-dibromobiphenyl
1.2
1.2
0.8
Triplet Energy
2.72 eV
0.4
0.0
350
PO1
400
450
500
550
600
Normalized Emission
PO2
1-bromonaphthalene
0.8
0.4
0.0
400
450
500
550
Wavelength (nm)
600
PO10
3,6-dibromocarbazole
0.8
0.4
0.0
Wavelength (nm)
1.2
Normalized Emission
Normalized Emission
Phosphorescence of phosphine oxides
compared to brominated bridges
350 400 450 500 550 600 650
Wavelength (nm)
Ultraviolet Emission from PO1 OLEDs
?? ! eV
PO1
ITO ~4.7eV
CuPc 5.3 eV
UV Light
LiF/Al
338 nm
?? ! eV
Device
Geometry
CuPc/PO1
PO1
thickness (Å)
Normalized EL intensity
3.6 eV
1.2
PO1(250A)
PO1(400A)
PO1(600A)
PO1(800A)
0.8
0.4
0.0
300
400
500
600
(nm)
Operating
Voltage (V)
at 13 mA/cm2
External
QE (%)
270
3.1
0.008
430
4.3
0.032
540
5.3
0.044
810
7.6
0.016
LiF/Al
PO1
NPD
ITO
LiF/Al
Alq3
PO1
ITO
NPD emission
No light
Summary
New lighting technology is “low-hanging fruit”
in the drive for energy efficiency
• Increase efficiency by 10X
Extrapolations of current technologies will not
meet this goal
• Old technologies; fundamental limits
Solid-state lighting can transform the way we
light the world
Success requires:
•Fundamental understanding to optimize
current SSL approaches
•Discovery research to reveal the basis
for breakthrough efficiencies
www.sc.doe.gov/bes/reports/list.html
SSL research will also drive discoveries in
photon-matter interactions, new
materials/structures, and new tools/methods
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