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Plasmonic nanostructures for enhanced light concentration devoted to photovoltaic applications
Valeria Marrocco, Marco Grande, Roberto Marani, Giovanna Calò, Vincenzo Petruzzelli, and Antonella D’OrazioDipartimento di Elettrotecnica ed Elettronica, Politecnico di Bari,
Via Re David 200, 70125 Bari, Italy
Tiziana Stomeo, Massimo De Vittorio and Adriana PassaseoNational Nanotechnology Laboratory, CNR-NANOSCIENZE,
Via Arnesano 73100 Lecce, Italy
E-mail: [email protected]
ICTON 2010 – June 27- July 1st, 2010, Munich (Germany)
OUTLINESOUTLINESPlasmonicPlasmonic forfor improvedimproved light light absorptionabsorption and and trapping: maintrapping: main strategiesstrategiesEffectsEffects of of MNPsMNPs sizesize, , shapeshape and and substratessubstrates on on light light trappingtrappingMetallicMetallic strip strip asas resonatorresonator antennasantennasFDTD forFDTD for the evaluationn of forwardthe evaluationn of forward and and backbackscattering scattering forfor MNPsMNPs on Si on Si thinthin filmsfilmsRoleRole of the finite of the finite thicknessthickness of the of the substratesubstrateNanostructuresNanostructures FabricationFabricationOutlook and work in progressOutlook and work in progress
StrategyStrategy forfor the the optimizationoptimization of of solarsolar cellcell performanceperformance
Increasing the scattering
Light-trapping AR coating
Nanotecnology
Photonic Crystals
Metal nanoparticles
Metal nanostructures
Nanoantennas
Single layer: wideband havinghigher R (0.5%)
Multilayers: smaller bands and different frequency
ranges; lower R (0.15%)
Plasmonic NPs for light absorption improvement
Carrier diffusion from the region where photocarriersare generated to the p–n junction. Charge carriersgenerated far away (more than the diffusion lengthLd) from the p–n junction are not effectively collected, owing to bulk recombination
AM1.5 solar spectrum, together with a graph that indicatesthe solar energy absorbed in a 2-µm-thick crystalline Si film (assuming single-pass absorption and no reflection)
Scattering Excitation of localized SPs Excitation of localized SPPs
Plasmonic for improved photovoltaic devices, H.A. Atwater and A. Pollman, Natural Materials, Vol. 9, 205-213, (2010)
Scattering and Scattering and absorptionabsorption byby metal metal nanoparticlesnanoparticles
Depend on the size of the particles
Metal particles smaller than the wavelength of light tend to absorb more, hence extinction is dominated by absorption in the metal particles
Increasing size of the particles, extinction is dominated by scattering (suitable for light trapping)
Scattering Cross Section for metal NPs
Scattering and absorption by metal Scattering and absorption by metal nanoparticlesnanoparticles: effects induced by the : effects induced by the
substrate and surrounding environmentsubstrate and surrounding environmentRed-shift in plasmon resonance:
larger size particles deposited on a substrate tend to lose their spherical property and hence look more like ellipsoids (shape changes)
the dielectric function of the surrounding medium increases
Overcoating of the metal particles on a substrate
Red-shift of resonance leads to an increase in scattering cross section at longer wavelengths: possibility to increase the absorption of solar cells because of the indirect band gap of silicon
Plasmonic for improved photovoltaic devices, H.A. Atwater and A. Pollman, Natural Materials, Vol. 9, 205-213, (2010)
Metal Metal NPsNPs and and corrugationcorrugation enhancingenhancing light light absorptionabsorption
Enhanced absorption: reduced thickness requirement of absorber material used in making a cell per generated Watt of electricity.For silicon, enhanced absorption and light trapping makes it possible to design crystalline silicon thin film cells with acceptably good spectral quantum efficiency, even for absorber layers a few micronsin thickness.
Metal nanoparticle array scatterssunlight into guided modes in thinfilm absorbers
Corrugated metallic back contact couples sunlight into surfaceplasmon polariton and photonicmodes at metal absorber interface
Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells, V.E. Ferry, L.A. Sweatlock, D. Pacifici, and H.A. Atwater Nano Letters, 8, 4391-4397 (2008)
Finite Finite metallicmetallic stripsstrips: : resonatorresonatorantennasantennas
Thin metallic film supports two distinct types of SPP modes: long range SPP (LR-SPP) and short range SPP (SR-SPP), resulting from the coupling of the SPPssupported by the two individual surfaces.
SR-SPPs LR-SPPs
• poorly confined• low mode indices• provide little field enhancementideally suitanle for the realizationof low loss plasmonic components
• increased mode indices• increased field-confinement forfilms much thinner than the wavelength of light • strong reflections off metal film terminations large local fieldenhancements in wavelengthscalestructures due to constructiveinterference effects
FabryFabry--PerotPerot resonancesresonances in in metallicmetallicstrip strip havinghaving finite finite widthwidth
Fabry-Perot Resonance in metallic strip in
homogeneous environment
E. S. Barnard, J. S. White, A. Chandran and M. L. Brongersma,“Spectral properties of plasmonic resonatorantennas”, Optics Express, October2008, Vol. 16, No. 21, 16529
Sketch of the analyzed structures and FDTD Scheme
Si Si
period period
Back scattering surface
Incident Field
Forward scattering surface
Physical Phenomena
periodRise of SPP modes
Si
Finite substrate inducesappereance of Fabry-Perot resonant modes
Si
Rise of LSP modes
periodSiO2
SiO2
FabryFabry--PerotPerot modesmodes in finite Si in finite Si substratessubstratesof of differentdifferent thicknessthickness
Wavelength (µm)0.3 0.4 0.5 0.6 0.7
0.0
0.2
0.4
0.6
0.8
1.0
Transmittance
Reflectance
Wavelength (µm)0.3 0.4 0.5 0.6 0.7
0.0
0.2
0.4
0.6
0.8
1.0
Transmittance)
Reflectance
t = 100 nm, N = 2 FP modes t = 300 nm, N = 4 FP modes
Wavelength (µm)0.3 0.4 0.5 0.6 0.7
0.0
0.2
0.4
0.6
0.8
1.0
Transmittance
Reflectance
Wavelength (µm)0.3 0.4 0.5 0.6 0.7
0.0
0.2
0.4
0.6
0.8
1.0
Transmittance
Reflectance
t = 500 nm, N = 7 FP modes t = 1000 nm, N = 14 FP modes
1D case: Transmission Matrix Method
Ag
Si
SiO2
tSi = 100 nmt Ag = 40 nm
SiO2
Si tSi = 100 nm
Structure with the metal layer Structure without the metal layer
( ) ( )
( ) ( )( ) ( )
2
1
1 11 12 1 21 22
2
11 12 1 21 22
11 12 1 21 22
2t
t t
t t
t t
p pTp m m p p m m p
m m p p m m pR
m m p p m m p
⎧⎪ =
+ + −⎪⎪⎨⎪ + − −
=⎪ + + −⎪⎩
1 11
p cosµ θ=εt t
t
p cosµ θ=ε
0 0
0 0
( ) ( )
( ) ( )
i i i i i iii
i i i i i i i
jcos k d cos sin k d cospM
jp sin k d cos cos k d cos
µ θ µ θ
µ θ µ θ
⎡ ⎤−⎢ ⎥= ⎢ ⎥⎢ ⎥−⎣ ⎦
ε ε
ε ε
Characteristic matrix of each layer
11arcsin sini
i ii
εθ θ
ε−
−
⎛ ⎞= ⎜ ⎟⎜ ⎟
⎝ ⎠
11 12
121 22
layersN
ii
m mM M
m m =
⎡ ⎤= =⎢ ⎥⎣ ⎦
∏
Transmission and reflection definitions
Transmission and reflection diagrams
Shift of the substrate Fabry‐Pèrotresonant wavelength
ForwardForward and Back Scattering and Back Scattering consideringconsidering FF--P P modesmodes in the finite in the finite substratesubstrate
Forward and backward scattering (field enhancement)
met
nomet
TFST
= met
nomet
RBSR
=
FS and BS parametric analysis changing the substrate thickness
Silver Silver fitfitThe permittivity of silver has been fitted by means of three Drude-Lorentz oscillators:
1 2 3
01 1 02 2 03 3
2 2 2
2 2 2 2 2 2( ) 1 p p p
j j jω ω ω
ε ωω ω ωγ ω ω ωγ ω ω ωγ
− −− − −
= −+ + +
1
2
3
1
2
3
01
02
03
7.0338
3.7
7.9
0.05362.21.05
04.75.6922
p
p
p
γγγ
ωωω
ωωω
=
=
=
===
=
==
Metal nanoparticle with variable diameter D on semi-infinte Si substrate
D
Metal nanoparticle with variable diameter D on 100 nm thick Si/SiO2 substrate
D
Metal nanobrick (s = 40 nm and l =40->140 nm) on semi-infinite substrate
l
s
Metal nanobrick (s = 40 nm and l=40->140 nm) on 100 nm thick Si/SiO2
l
s
Normalized Poynting Vector @440 nmL = 140 nm
L = 100 nm
L = 80 nm
L = 40 nm
Array of metal nanoparticle with period =100 nm semi-infinite Si substrate
Nanobricks withdifferent sides
Nanospheres withdifferent diameters
Array of metal nanoparticle with period =100 nm on 100 nm thick Si on SiO2
Nanobricks withdifferent sides
Nanospheres withdifferent diameters
Normalized Poynting Vector
Si=100 nm, D= 100 nmλ = 410 nm
Si=100 nm, D= 100 nmλ = 679 nm
Plasmon resonance on
Resonant mode off
Plasmon resonance off
Resonant mode on
Array of metal nanoparticle on a semi-infinite Si substrate
Variation of the period
(a) (b)
p= 80 nm p= 100 nm p= 150 nm
(a) (b)
p=80nm p=100 nm p=150 nm
Array of metal nanoparticle on 100 nm thick Si substrateVariation of the period
(a) (b)
(a) (b)
Array of nanobricks withs=40 nm
Array of nanospheres withD=40 nm
(a) (b)
(a) (b)
ForwardForward and back scattering and back scattering forfor metal metal nanoparticlesnanoparticleson on differentdifferent Si Si substratesubstrate thicknessthickness whenwhen p =150 p =150 nmnm
Array of nanobricks withs=40 nm
Array of nanospheres withD=40 nm
PoyntingPoynting VectorVector (10(1055*W/m*W/m22))Si = 1000 nm Si = 500 nm
Si = 100 nmSi = 300 nm
FabricationFabrication of of coupledcoupled nanoantennasnanoantennas
Deposition of bi-layer resist by spin-coating
PMMAPMMA-MA
FabricationFabrication of of coupledcoupled nanoantennasnanoantennas
Electron Beam Exposure
PMMA-MAPMMA
FabricationFabrication of of coupledcoupled nanoantennasnanoantennas
The resist is developed in MIBK:IPA giving an undercut
PMMA-MAPMMA
FabricationFabrication of of coupledcoupled nanoantennasnanoantennasMetal deposition and lift-off
gap
PlasmonicPlasmonic NanostructuresNanostructuresSEM SEM ImagesImages
Ag
AuAu
Au
Sisubstrate
GaNsubstrate
Outlook and future work Outlook and future work
The The MNPsMNPs and and SPPsSPPs modify the scattering (forth and back) in modify the scattering (forth and back) in dependence of their size, shape, environment and finite dependence of their size, shape, environment and finite substrate resonant modessubstrate resonant modesWhen metal NPs are When metal NPs are nanobricksnanobricks ((SPPsSPPs), the FP modes in the ), the FP modes in the finite substrates are shifted and the phase is switched of finite substrates are shifted and the phase is switched of ππ..AR AR coatingcoating can can bebe optimizedoptimized toto furtherfurther reduce the back reduce the back scatteringscatteringNSOM NSOM MeasurementsMeasurements (scattering, (scattering, nearnear--fieldfield and and absorptionabsorption) ) are on the way are on the way ……notnot yetyet readyready forfor the the currentcurrent date date
ForFor FabricationFabrication questionsquestions pleaseplease contact: contact: [email protected]@deemail.poliba.it
[email protected]@unisalento.it
NormalizedNormalized PoyintingPoyinting VectorVector forfor nanobricksnanobricks and and nanospheresnanospheres on semion semi--infinite and finite infinite and finite substratessubstrates
p=100 nm
p=100 nm
p=150 nm
p=150 nm
(a) (b)
(c) (d)
p =100 nm
p =100 nm
p =150 nm
p =150 nm
(a) (b)
(c) (d)
AR AR coatingcoating toto decreasedecrease back back scatteringscattering
AR
Thickness
AR thickness = 100 nm
