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Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Photo-voltaics
H2 production & storageFuel cells
Photo-catalysis
Emission cleaningBatteries
Chalmers vägar mot en hållbar värld 2009
Ljus framtid för solenergi tack vare nanoteknik ?
Michael Zäch Chalmers tekniska högskola Institutionen för teknisk fysik
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
• Några inledande tankar kring solenergi, solceller och nanoteknik
• Nanopartikelplasmoner – vad är det för något ?
• Nanopartikelplasmoner i solceller
Innehåll
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Energikällor
•Solen täcker världens årliga energibehov på en timma!
Fotosy
ntes
Vind
Vatte
n
So
l
Kol
Uran
GasOlja
Vär
lden
sen
erg
ibeh
ov
(15
TW
)
cont.
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Hur mycket är en TW?• 1 TW = 1 Terawatt =
1’000 GW = 1’000 Gigawatt =1’000’000 MW = 1’000’000 Megawatt =1’000’000’000 kW = 1’000’000’000 kilowatt1’000’000’000’000 W
1 W 1 kW 1 MW 1 GW 1 TWback
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Si Solar Cell(1st Generation PV)
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Monocrystalline Si Solar Cells(1st Generation Photovoltaics)
E
n-Si
p-Si
holetransport
electrontransport
IR
• Essentially a p-n junction, with contacts to p- and n-sides
• Photons with E ≥ 1.12eV generate charge carriers (e-h pairs) in silicon
• Charges are separated by built-in electric field and driven through external load
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Issues with 1st Generation PV• Si has an indirect bandgap
low optical absorptionSi needs to be thick to
absorbmost of the light (>> 100m)
• e-h pairs must diffuse to the junction region
• Minority carrier diffusion length (recombination rate) depends on material purity and crystallinity
• Efficient devices can only be made with very pure (solar-grade) Si, which is expensive and energy-intensive in the production
Czochralski process to make single-crystal Si
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Dye-Sensitized Solar Cells(3rd Generation PV)
• Fundamental difference: light absorption occurs in a dye rather than in a semiconductor (i.e. it is separated from charge separation)
• Need rather thick layer of dye use 3-D scaffold of mesoporous titania
• (Rather) cheap raw materials, and “simple” production process cost advantages
• Efficiency is smaller than for Si cells (≈ 10%)
• Good price/performance ratio
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Overview of State-of-the-Art
• Lab Module(%) (%)
• Monocrystalline Si 24.7 14-16• Polycrystalline Si 20.3 12-15• Amorphous Si 12.1 6-8• CIGS 19.9 9-11• DSSC 11.1 3-8• Organic 5.4 ?
Chalmers vägar mot en hållbar värld 2009 [email protected]
Department of Applied Physics
How small is a nm?1 µm = one millionth of a meter
1 nm = one billionth of a meter≈ 1/50,000 thickness of a hair
If we shrunk all distances 110,000,000,000 times,the sun and earth would be separated by 1m.A football field would then be 1nm.
Human hair thickness ~ 50 µm
110,000,000 km
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Early Nanotechnology
The Lycurgus CupThe British Museum
4th century AD
Window of the Seasons, (Jan. and Feb.) Chartres Cathedral (France)
13th century (?)
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Nanoparticle Plasmons
• Observed when electronsin metallic nanostructuresoscillate collectivelyunder the influence ofan electric field (light)
• Resonance frequency of theoscillation (= color) can be tuned by varying particle size
• For particles in the size range ≈ 20-200nm, the resonance frequency falls into the visible regime Metallic nanoparticles are good at absorbing and scattering sunlight
E-field Metalsphere
e- cloud
+++
---+++
---
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Solar Spectrum and Plasmons
500 1000600 700 800 900Wavelength [nm]
Ab
so
rban
ce
[a.u
.]
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
p-Si
n-Si
Al-electrode
Al-electrode
200µm
2000
µm
Polarized light
I
Model Si Solar Cell
Au nanoparticles
X
Y
Z
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Enhancement = (Photocurrent with nanoparticles)
(Photocurrent without nanoparticles)
Hägglund, C., Zäch, M., Petersson, G., and Kasemo, B., Appl. Phys. Lett. 92 (2008) 053110
Optical properties
• Elliptical particles with two distinct NPPs (corresponding to long- and short axis)
• Light polarization can be used to “switch NPPs on and off”.
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Photocurrent
• Photocurrent clearly polarization dependent
• Clear correlation with plasmon resonance peaks
• Net decreaseof photocurrentat resonance (<1)
• Increase off resonance (>1)
Hägglund, C., Zäch, M., Petersson, G., and Kasemo, B., Appl. Phys. Lett. 92 (2008) 053110
(Ph
oto
curr
ent
wit
h n
ano
par
ticl
es)
(Ph
oto
curr
ent
wit
ho
ut
nan
op
arti
cles
)
Wavelength [nm]
s-polarized light
p-polarized light
// to minor axis // to major axis
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
TiO2
Glass support
Au/Ti-electrode
± V
10µm
2000
µm
Elongated Ag or Au nanoparticle
Polarized light
X
Y
Z
Model DSSC
Dye
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Optical properties
• Polarization-dependent microextinction measurement
• Two clearly separated peaks corresponding to particle short and long axis
PP
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Photoconductance with Au particles
• Clear polarization dependence
• Clear correlation with plasmon peak
• Net increase of photoconductance with Au particles
PP
G
G//
Hägglund et al, Applied Physics Letters 92 013113 (2008)
Department of Applied Physics
Chalmers vägar mot en hållbar värld 2009 [email protected]
Plasmonic charge carrier generation in photovoltaic solar cells
Far field effects Photoemission of charge carriers
Near field effects
Electromagnetic field influenceon the charge carrier generation
PV PV PV
Schematic taken from Carl Hägglund’s PhD thesis
Department of Applied Physics
[email protected] STÄNGDA DÖRRAR – 19 feb 2009
Acknowledgements
• EU, Mistra, SSF and Chalmers Foundation for financial support
• Collaborators in the Chemical Physics group
• Many of the students who attended the course TIF165 - “Nanotechnology for Sustainable Energy”
• And you for your attention !
Tack !