Photonic Crystals: Shaping the Flow of Thermal Radiation Ivan Čelanović Massachusetts Institute of Technology Cambridge, MA 02139
Photonic Crystals:Shaping the Flow of Thermal Radiation
Ivan ČelanovićMassachusetts Institute of Technology
Cambridge, MA 02139
Overview:
• Thermophotovoltaic (TPV) power generation
• Photonic crystals, design through periodicity
• Tailoring electronic- and photonic bandgap properties: a path towards record efficiencies
• Photovoltaic module: design and characterization
• TPV system design challenges
• Quasi-coherent thermal radiation via photonic crystals
Thermophotovoltaic power generation: basic ideas and concepts
Thermo-photo-voltaic conversion
TPV power conversion describes the direct conversion of thermal radiation into electricity.
Photons
Brief History
1956 - Dr. H. Kolm / Dr. P. Aigrain independently propose TPV power conversion concept
1970’s - Loss of interest in TPV due to low efficiencies
1990’s - Advancements in microfabrication technology allow for production of low-bandgap diodes, opening the
door for more efficient TPV
1994 - First NREL Conference on TPV Generation of Electricity
2000’s -Photonic crystals for thermal radiation control
Basic TPV energy conversion diagram
Pout + –
Em
itte
r
P N
Heat Waste Heat Blackbody Radiation
Cell Surface
Reflection
GaS
b
PV vs. TPV
Properties:
PV (Solar Cells) TPV
Sensitivity Range Visible and NIR NIR and IR
Source Sun Thermal emitter
Source
Temperature Over 5000K (sun’s surface) 1000-1500K
Distance from
Source Over 90 million miles µm to cm
Energy reflected
from cell surface Lost to atmosphere Recycled to the emitter
Courtesy of DOE/NREL, Credit - Beck Energy.
TPV Technologies and applicationsTPV Technologies and applications
su
n r
adia
tio
n
TPhC
absorber/photonic crystal
Solar cell
concentrator
Solar TPV
Radioisotope TPV power system for
deep space and Mars missions
18 W/kg, (PuO2 fuel)
for 30 years
24% efficient
1 We
15% efficiency
micro-TPV power generator (propane/butane operated) AA radioisotope TPV battery:
~10 mWe
30 years life time
24% efficiency
Plutonium pellet
Photo courtesy of LLNL.
Images courtesy of NASA. Photo courtesy of Sandia National Labs.
Courtesy of Klavs Jensen. Used with permission.
Heat
Input
Waste
Heat
thermal emitter filter PV diode Heat sink
Thermophotovoltaics: converting thermal radiation into electricity, with no moving parts
GaSb (0.72 eV) InGaAs (0.6 eV) InGaAsSb (0.53 eV) Si (1.23 eV)
bad photons
good photons
Photonic Crystals: shaping thermal radiation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Norm
aliz
ed
radia
ted
pow
er
1 2 3 4 5 6 7 8
wavelength [µm]
System design
TPV Technology roadmap: the time is nowTPV Technology roadmap: the time is now
Si and Ge
PV III-V’s (GaSb, InGaAs, GaInAsSb)diode
rare earth oxides
Spectral Dielectric stack
control filters Photonic
Crystals
JX
Thermo Power…
1950’s 1960’s 1970’s 1980’s 1990’s 2000’s
Photonic crystals, design through periodicity
Photonic crystals are periodical structures with 1D, 2D or 3D periodicity
),,(),,( zyxzyx x λεε +=
1-D Periodicity 2-D Periodicity 3-D Periodicity
),,(),,( zyxzyx yx λλεε ++= ),,(),,( zyx zyxzyx λλλεε +++=
Metamaterial:
optical properties determined from its nano-structure
(rather than its composition)
Hig h ind e x
o f re fra c tio n
Lo w ind e x
o f re fra c tio n
Allowed
Allowed
Forbidden
Freq
uenc
y
3D photonic crystal: a “semiconductor for photons”
High index of refraction
Low index of refraction
freq
uenc
ywavevector Refs: E.Yablonovitch, Phys. Rev. Lett. 58, 2059, (1987).
S.John, Phys. Rev. Lett. 58, 2486, (1987).
Controlling density of photonic states
⇓⇓⇓⇓controlling thermal emission spectrum
hω
( , T ) = N ω ∗u ω ( )
freq
uenc
y
hω
e kBT − 1
energy
density
density of
photonic
modes
energy in each
photonic mode
wavevector
Photonic crystals are analogous to semiconductors
Face center cubic lattice
states electronic
E E
Conduction band
forbidden bandgap states E
allowed g
states valence kk band
allowed
Naturally occurring photonic crystals:
Butterfly wings Opal
P. Vukusic, I. Hooper, “Directionally controlled fluorescence emission in butterflies,” Science, vol. 310, pp. 1151
Photo by Megan McCarty at Wikimedia Commons.Images removed due to copyright restrictions.Please see: http://www.tils-ttr.org/photos/Mitoura-gryMDneo.jpghttp://www.tils-ttr.org/photos/Mitoura-gryMVneo.jpg
Fig. 11 in Ghiradella, Helen. "Light and Color on the Wing: Structural Colors in Butterflies and Moths."Applied Optics 30 (1991): 3492-3500. Fig. S1a, S2, and S4a in Vukusic, Pete, and Ian Hooper. "Directionally Controlled Fluorescence Emission in Butterflies."Science 310 (November 18, 2005): 1151.Fig. 3 in Pendry, J. B. "Photonic Gap Materials." Current Science 76 (May 25, 1999): 1311-1316.
Tailoring electronic- and photonic bandgap properties:
a path towards record efficiencies
Photonic crystal as omnidirectional mirror
Selective emitter Front-side filter
Waste
Heat
Heat
A B C
1D Si/SiO2 photonic crystals exhibit omni-directional bandgap
εo ε1 ε2 ε3 εn εPV
0 1 2 n PV
y z
θ1
TPV
Heat
thermal emitter
Heat
thermal emitter filter
Waste
Heat
PV diode Heat sink
0
Ang
ula
r fre
quenc
y ω
(2π
c/a
)A
ng
ula
rfre
quenc
yω
(2π
c/a
)
0.0 7.7
0.0 6.6
0.0 5.5
0.0 4.4
0.0 3.3
0.0 2.2
0.0 1.1
00
Projected photonic band diagram
0 0.6 10.80.2 0.4
TE modesTM modes
vacuu
mlig
htlin
e
SiClig
htlin
e
gNωΔ
0.6 10.8
TE modesTM modes
vacuu
mlig
htlin
e
SiClig
htlin
e
0 0.2 0.4
gNωΔ
10.80 0.2 0.4 0.6
Reflectance
1 0.81 0.8 0.6 0.40.6 0.4 0.0 2.2
Parallel wave vector ky (2π/a)Parallel wave vector ky (2π/a)
Spectral characterization of 1D photonic crystal
500 nm
TEM cross section of LPCVD* grown quarter-wave stack filter with half-layer at the top
Si = lighter layers (170nm) SiO2 = darker layers (390nm)
1 1.5 2 2.5 3 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
Tra
nsm
itta
nce
measured simulated mmeasured simulated m easuredsimulated
easuredsimulated
Image removed due to copyright restrictions.Please see Fig. S2 in Vukusic, Pete, and Ian Hooper."Directionally Controlled Fluorescence Emission in Butterflies."Science 310 (November 18, 2005): 1151.
Front side PhC designs, 0.72 eV, 0.6 eV, 0.52 eV
Tra
nsm
itta
nce
T
ran
sm
itta
nce
11
1D & plasma 0.52 eV
1D w/plasma 0.6 eV 1D & plasma 0.52 eV
0.9 1D w/plasma 0.6 eV
1DSi/SiO2 0.72 eV 0.9
1DSi/SiO 0.72 eV 2
0.8 0.8
0.7 0.7
0.6 0.6
0.5 0.5
0.4 0.4
0.3 0.3
0.2 0.2
0.1 0.1
001 1.5 2 2.5 3 3.5 4 4.5 51 1.5 2 2.5 3 3.5 4 4.5 5
wavelength [µm] wavelength [µm]
0 1 2 n PV BB 0 1 2 n PV BB
θBB θBB
εε2 ε3ε o ε1 n εPV εplasma εε2 ε3εBB ε o ε1 n εPV εBB
y L oy L o z
z
1D Si/SiO2 photonic crystals: quarter-wave based stack and genetic algorithm optimized stack as a spectral control tool
Quarter-wave photonic crystal
1 2 10 PV TPV
1
0.8
0.6 (a)
0.4
0 1 2 3 4 5 6 7 8
ε1 ε2 ε1 ε2 ε1 ε2 εPV
0.2
0 half layer
Wavelength [µm]
Tra
nsm
itta
nce
T
ransm
itta
nce
1
0.8
0.6 (b)
0.4
0.2
0 0 1 2 3 4 5 6 7 8
Genetic algorithm optimized stack
1 2 10 PV TPV
Wavelength [µm]
ε2 ε1ε1 ε2 ε1 ε2 εPV
Spectral characterization of fabricated 1D photonic crystal
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
Refle
cta
nce
a)
b)
TE 20° TE 30° TE 40° TE 50°
TM 20° TM 30° TM 40° TM 50°
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6
Wavelength (µm)
Improving the spectral efficiency via selective thermal emission
Selective emitter Front-side filter
Waste
Heat
Heat
A B C
But remember thermal emitter is really hot! (up to 1500K)
Refractory metals have high melting temperature, especially tungsten, and that is why
it has been used for incandescent light bulbs ever since
William D. Coolidge, invented the process for producing the
ductile tungsten in 1909 that revolutionized light bulbs
and X-ray tubes. His first light bulb was named “Mazda”
http://www.harvardsquarelibrary.org/unitarians/coolidge.html
Images removed due to copyright restrictions.Please see:http://www.harvardsquarelibrary.org/unitarians/images/coolidge4.jpghttp://www.harvardsquarelibrary.org/unitarians/images/coolidge10.jpghttp://www.harvardsquarelibrary.org/unitarians/images/coolidge11.jpghttp://www.harvardsquarelibrary.org/unitarians/images/coolidge12.jpg
Adding an array of resonant cavities in tungsten can help us tailor the emittance
Lorentz-Drude model for tungsten
ω1ω2
meas. 2D W PhC (r=450nm d=560nm)
sim. 2D W PhC (r=450nm d=560nm)
meas. 2D W PhC (r=440nm d=315nm)
sim. 2D W PhC (r=440nm d=315nm)
meas. 2D W PhC (r=390nm d=600nm)
sim. 2D W PhC (r=390nm d=600nm)
meas. flat tungsten
sim. flat tungsten
2D W PhC as selective thermal emitter:
1 1.5 2 2.5 3 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
wavelength [µm]
Em
itta
nce
1 1.5 2 2.5 3 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
wavelength [µm]
Em
itta
nce
meas. 2D W PhC (r=450nm d=560nm)
sim. 2D W PhC (r=450nm d=560nm)
meas. 2D W PhC (r=440nm d=315nm)
sim. 2D W PhC (r=440nm d=315nm)
meas. 2D W PhC (r=390nm d=600nm)
sim. 2D W PhC (r=390nm d=600nm)
meas. flat tungsten
sim. flat tungsten
2D W PhC exhibits tunable cut-off and resonant enhancement
Fabrication process improvements
• Old • New
Fabrication Process
Laser Interference
Lithography Development Soft-mask etch Hard-mask etch
ARC = Anti-Reflective Coating
Soft-mask removal Tungsten etch Hard-mask removal
Tailoring electronic- and photonic bandgap properties:
a path towards record efficiencies
GaSb and GaInAsSb diode comparison
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
V
]V[
co
GaSb
GaInAsSbV oc
(V
)
1
Qu
an
tum
eff
icie
nc
y
Exte
rnal Q
uantu
m E
ffic
iency
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
GaInAsSb
GaSb EQE
EQE
GaSb
GaInAsSb 0.1
0 -4 -3 -2 -1 0 1 1 1.5 2 2.5 3
10 10 10 10 10 10
J [A/cm2]sc
Isc (A/cm2) wavelength [µm]
Wavelength (µµµµm)
Tuning the PhC and PV diode bandgaps: GaSb (0.72 eV) and GaInAsSb (0.52 eV)
GaSb GaInAsSb
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
wavelength [µm]
EQ
E, T
ran
sm
itta
nce
PhC Transmittance
GaSb QE
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
wavelength [µm]
EQ
E, T
ran
sm
itta
nce
PhC Transmittance
GaSb QE
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
EQ
E, T
ran
sm
itta
nce
PhC Transmittance
InGaAsSb QE
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
EQ
E, T
ran
sm
itta
nce
PhC Transmittance
InGaAsSb QE
ηspectral = 80 %
T>Eg = 79 %
ηspectral = 80 %
T>Eg = 79 %ηspectral = 41 %
T>Eg = 70 %
ηspectral = 41 %
T>Eg = 70 %
Qu
an
tum
eff
icie
nc
y,
Tra
nsm
itta
nce
Qu
an
tum
eff
icie
nc
y,
Tra
nsm
itta
nce
Photonic crystals tailoring photonicPhotonic crystals tailoring photonic-- ana dnd
electronic bandgapselectronic bandgaps
Tuning the PhC and PV diode bandgaps: GaSb (0.72 eV)
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
Ga
Sb E
QE
, 1
D P
hC
Tra
nsm
itta
nce
, 2
D P
hC
Em
itta
nce
2D PhC Emittance
1D PhC Transmittance
GaSb EQE
1 1.5 2 2.5 3 3.5 4 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
Ga
Sb E
QE
, 1
D P
hC
Tra
nsm
itta
nce
, 2
D P
hC
Em
itta
nce
2D PhC Emittance
1D PhC Transmittance
GaSb EQE
Heat Waste
Heat
Selective emitter
Front-side filter
Electricity out
A B C
PV diode
Spectral efficiency Above bandgap
transmittance
1D PhC and 2D W
PhC 93 % 70 %
Photovoltaic module:
design and characterization
Simple TPV diode model
GaInAsSb diode characterization cont’d
Packaged Cells External Quantum Efficiency 0.4 100
99-017-08
00-202-18 90
01-471-15
01-471-16
0.35 80
70
60
50
40
0.3
0.25
30
20 0.2
10
0 0.15 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6
-2 -1 0 10 10 10 Wavelength (µm)
J (A/cm2)sc
99-017-08
00-202-18
01-471-15
01-471-16
EQ
E (
Perc
ent)
V
(V)
oc
GaInAsSb diode characterization
V
(V)
V
(V)
oc
oc
99-017-08 00-202-18 0.35 0.35
0.2
Unpackaged
Packaged
AR Coated
0.2
0.15 0.15
Unpackaged
Packaged
AR Coated
-2 -1 0 -2 -1 0 10 10 10 10 10 10
J (A/cm2) J (A/cm2)sc sc
01-471-15 01-471-16
V
(V)
oc
0.3 0.3
0.25 0.25
0.35
0.3
0.25
0.2
0.15 0.15
0.2
0.25
0.3
0.35
V o
c (V
)
-2 -1 0 -2 -1 0 10 10 10 10 10 10
J sc
(A/cm2) J sc
(A/cm2)
MITMIT µµµµµµµµ--TPV GeneratoT r Pr ror jej ctcPV Generato P o e t
Key innovations in: photonic crystals,Key innovations in: photonic crystals,
MEMs reactors, power electronics, PVMEMs reactors, power electronics, PV
1D photonic crystal 2D tungsten photonic crystal
Power electronicsLow-bandgap PV cells
Si micro-fabricated reactor
Photonic crystals tailoring photonicPhotonic crystals tailoring photonic-- ana dnd
electronic bandgapselectronic bandgaps
Robust, integrated catalyticRobust, integrated catalytic
micromicro--reactorr ded sis gngeactor e i n
Integrated power electronics controllerIntegrated power electronics controller
single chip
integrated MPPT
Quasi-coherent thermal emission via photonic crystals •Vertical-cavity resonant thermal emitter •2D PhC slab resonant thermal emission
θθθθ
z
y
L0
εM
εcavity
εH
εL
εH
εL
εH
εH
ε0
Narrow-band spectral control
1 1.5 2 2.5 3 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (µm)
Re
flec
tance
measured
simulated
Broad-band spectral control
1 1.5 2 2.5 3 3.5 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 flat W 2D W PhC (r=440 nm,d=315 nm) 2D W PhC (r=390 nm,d=560 nm) 2D W PhC (r=440 nm, d=560 nm)
Generation 1
Generation 2
Emitt
ance
Ref
lect
ance
Vertical cavity resonant thermal emitter is highly-directional, quasi-coherent radiation source
θθθθ
z
y
L0
εM
εcavity
εH
εL
εH
εL
εH
εH
ε0
Vertical cavity resonant thermal emitter:
narrow-band, highly directional and
Tun
gste
n
ca
vity
mirro
r
Quasi-coherent thermal emission via photonic crystals •Vertical-cavity resonant thermal emitter •2D PhC slab resonant thermal emission
Black/Gray-
Body Physics
Th
erm
al
Th
erm
al
Th
erm
al
Th
erm
al
Ref: Max Planck, Annalen der Physik, 4, 553, (1901).
Modes of a 2D PhC slab
odd guided resonance
|Hz|
even guided resonance mode
|Hz|
x
yz
Fano resonances of a 2D PhC slab
z y
x
Ref: S. Fan and J. D. Joannopoulos, Phys. Rev. B 65, 235112 (2002).
x
yz
Thermal emittance of a 2D PhC slab T
herm
al E
mit
tan
ce
Im(ε)≈0.005
Ref: D.Chan, I.Celanovic, J.D.Joannopoulos, and M.Soljačić, submitted for publication.
x
z y
θ
θ increases
θ increases
e
cn
attim
El
amr
eh
Te
c
natti
mE
l a
mre
hT
Dependence on angle of observation
Analytical understanding of Fano resonances
⇒
2
2 QABS QRADa = PhC 2 2 ω 1 1
4 − 1 + + ωFANO QRAD QABS
ε R=QABS σε I
Q = Q ⇒ aPhC MAX = 50%ABS RAD
Rules for designing thermal emission
x
yz
ωωωωEMIT(θθθθ): • slab thickness
• Re(ε) • lattice constant
ΓΓΓΓEMIT ⇔⇔⇔⇔ QRAD: • “size” of holes
Peak emission ⇔⇔⇔⇔ QABS: • Im(ε)
Th
erm
al E
mit
tan
ce
2
2 QABS QRAD a = PhC ω
4 − 2
1 1 1
+ +ωFANO Q QRAD ABS
2
An example of thermal design
QRAD=370
QRAD=2000
Th
erm
al
z y
x
Quasi-coherent thermal radiation: summary and
opportunities
•PhC’s offer unprecedented opportunities for tailoring
thermal emission spectra
• Highly anomalous thermal spectra can be obtained
• Even dynamical tuning of spectra is possible
•Research in the combined near-field and quasi-coherent PhC
radiation is opening up new frontiers
• Possible applications include: masking thermal targets,
coherent thermal sources, high-efficiency TPV generation, chemical sensing, etc.
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