department of applied physics chalmers vägar mot en hållbar värld 2009 [email protected]...

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



• Några inledande tankar kring solenergi, solceller och nanoteknik

• Nanopartikelplasmoner – vad är det för något ?

• Nanopartikelplasmoner i solceller

Innehåll



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.



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



Si Solar Cell(1st Generation PV)



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



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



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



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 ?



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



Early Nanotechnology

The Lycurgus CupThe British Museum

4th century AD

Window of the Seasons, (Jan. and Feb.) Chartres Cathedral (France)

13th century (?)



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

+++

---+++

---



Solar Spectrum and Plasmons

500 1000600 700 800 900Wavelength [nm]

Ab

so

rban

ce

[a.u

.]



p-Si

n-Si

Al-electrode

Al-electrode

200µm

2000

µm

Polarized light

I

Model Si Solar Cell

Au nanoparticles

X

Y

Z



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”.



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



TiO2

Glass support

Au/Ti-electrode

± V

10µm

2000

µm

Elongated Ag or Au nanoparticle

Polarized light

X

Y

Z

Model DSSC

Dye



Optical properties

• Polarization-dependent microextinction measurement

• Two clearly separated peaks corresponding to particle short and long axis

PP



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)



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


[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 !

department of applied physics chalmers vägar mot en hållbar värld 2009 [email protected]...

Documents