progress & challenges in plasmon- enhanced photocatalysis ... · progress & challenges in...

Jen Dionne

Materials Science & Engineering | Stanford University

Progress & challenges in plasmon-enhanced photocatalysis and photovoltaics

Jon Scholl, Andrea Baldi, Ashwin Atre, Di Wu, Justin Briggs, Michael Wisser, Aitzol Garcia, Ai Leen Koh, Tim Burke,

Alberto Salleo, Mike McGehee

Oh the places plasmons go!

Jen Dionne

Materials Science & Engineering | Stanford University

Jon Scholl, Andrea Baldi, Ashwin Atre, Di Wu, Justin Briggs, Michael Wisser, Aitzol Garcia, Ai Leen Koh, Tim Burke,

Alberto Salleo, Mike McGehee

Oh, the plasmons go quantum When particles are small Their spectra shift blue Their peaks are less tall

But solar photons span Wavelengths red, green, and blue

For efficient PV We’ll use upconversion too!

And because they’re sensitive To their surroundings and charge

Catalytic sensing is easy On particles small and large.

Oh, the places plasmons go!

10 nm

Ag

TiO2

Wavelength (nm)

Inte

nsi

ty (

a.u

.)

50 e- added

uncharged Ag

We’ll coat titania over a metallic core:

UV light gets absorbed e-/h+ pairs separate more

Plasmon resonances of conducting nanoparticles

Electric field


r


r


εimag

εreal

50 nm 10 nm

Ag


8x10 nm 10 nm

Ag


H2O

Ag Ag

10 nm


5 nm

H2O

Ag


5 nm

H2O

Ag

+ 50 e– e–


5 nm

H2O

Ag

+ 100 e– e–


5 nm

H2O

Ag

+ 200 e– e–


Plasmon resonances and energy conversion

“Hot” electrons

e–

Au Si

EF

EC

EV

S

A

Near-field enhancement

Thomann, Brongersma, Nano Lett. (2011)

Reaction Sensors

Tang, Liu, Dionne, Alivisatos, JACS (2011)

100 nm

50 nm

Knight, Halas, Science (2011)

100 nm

50 nm

Au

Pd

830,000 e-

Novo et al., Nature Nanotech 3(10) 2008

Au

Scat

tere

d in

ten

sity

Wavelength

PdH

100 nm Peak

wav

elen

gth

Reaction time (min)

Pd

D- D+e-

Au

Au

Plasmon resonances and energy conversion C

atal

yst

acti

vity

(m

mol

CO

/gA

u)

Bulk Au: catalytically inactive

0 5 10 15 20 25 30

0.3

0

0.6

MgAl2O4

Al2O3

Fe2O3

SiO2

TiO2

Norskov, NanoToday, 2007

1. Can we detect plasmons from particles in the sub-10nm regime?

2. Can we use these plasmons to monitor photocatalytic reactions in-situ?

3. Can we improve below-bandgap absorption of solar photons for photocatalysis & (photovoltaics)

Diameter of Au particles (nm)

oxidation

5 μm

20 nm

• Probing the plasmonic properties of very small particles is challenging: weak optical scattering, particle heterogeneity in ensemble, organic ligands, etc.

Peng, Schatz PNAS (2010)

17.8 nm

2.2 nm (x420)

Ensemble Measurements:

Plasmon catalysis into the single-nm regime

oleylamine

Ag

20 nm

Diameter D=

D=

D=

Lindfors, Sandoghdar, PRL (2004) Peng, Schatz PNAS (2010)

17.8 nm

2.2 nm (x420)

Ensemble Measurements: Single Particle Measurements:

• Probing the plasmonic properties of very small particles is challenging: weak optical scattering, particle heterogeneity in ensemble, organic ligands, etc.

Plasmon catalysis into the single-nm regime

oleylamine

Ag

Scanning Transmission Electron Microscopy (STEM) EELS has an imaging spatial resolution of ~0.25nm

Monochromated STEM Electron Beam

Sample on Thin Carbon Film

EEL Spectrometer Prism

CCD

Annular Dark Field Detector

Jon Scholl, Ai Leen Koh

Probing very small plasmonic particles: EELS

Organic-ligand-free synthesis minimizes organic contamination and the influence of ligand surface damping

Individual, organic-ligand-free nanoparticles

EELS: Classically-sized Particles

Energy (eV) 2 3.5 5

Cou

nts

(a.

u.)

Surface resonance

Energy (eV) 2 3.5 5

Cou

nts

(a.

u.)


Surface resonance

Bulk resonance

Energy (eV) 2 3.5 5

Cou

nts

(a.

u.)


EELS: Size-dependent spectral response C

oun

ts (

a.u

.)

Energy (eV) 2.5 3.5 4.5

5 nm Scholl, Koh, Dionne, Nature 483 (2012)


oun

ts (

a.u

.)

Energy (eV) 2.5 3.5 4.5

5 nm

Par

ticl

e D

iam

eter

(n

m)

0

5

10

15

20

3 3.2 3.4 3.6 3.8 4 Peak Energy (eV)


oun

ts (

a.u

.)

Energy (eV) 2.5 3.5 4.5

5 nm

Par

ticl

e D

iam

eter

(n

m)

0

5

10

15

20

3 3.2 3.4 3.6 3.8 4 Peak Energy (eV)

Surface Bulk

3.7 3.9 4.1 Energy (eV)

Dia

met

er (

nm

)

5

20

• Classical treatment uses damping term:

• Accounts for peak broadening but predicts a red shift R

AvFBulk

Modeling the size-dependence of plasmons

• Classical treatment uses damping term:

• Accounts for peak broadening but predicts a red shift

• Instead, use a quantum approach:

R

AvFBulk

J. Garcia de Abajo, Nature 483 (2012)

Modeling the size-dependence of plasmons

Quantum Theory Matches Experiment

Incorporating these discrete electron transitions in the electric permittivity of Ag results in the blueshift seen experimentally

Par

ticl

e D

iam

eter

(n

m)

5

10

15

20

3 3.2 3.4 3.6 3.8 4

Energy (eV)

Norm

alized

absorp

tion efficien

cy

0

1

Quantum Theory Matches Experiment P

arti

cle

Dia

met

er (

nm

)

5

10

15

20

3 3.2 3.4 3.6 3.8 4

Energy (eV)

Norm

alized

absorp

tion efficien

cy

0

1


Scholl, Koh, Dionne, Nature 483 (2012)

DFT permittivity functions based on He & Zeng, JPCC. 2010

Quantum Theory Matches Experiment P

arti

cle

Dia

met

er (

nm

)

5

10

15

20

3 3.2 3.4 3.6 3.8 4

Energy (eV)

Par

ticl

e D

iam

eter

(n

m)

5

10

15

20

3 3.2 3.4 3.6 3.8 4

Energy (eV)

Norm

alized

absorp

tion efficien

cy

0

1 Analytic Ab-initio



atal

yst

acti

vity

(m

mol

CO

/gA

u)


0 5 10 15 20 25 30

0.3

0

0.6

MgAl2O4

Al2O3

Fe2O3

SiO2

TiO2




oxidation

5 μm

Yes. For particle diameters smaller than ~5nm, quantum-influenced electronic transitions will modify the plasmonic resonance


atal

yst

acti

vity

(m

mol

CO

/gA

u)


0 5 10 15 20 25 30

0.3

0

0.6

MgAl2O4

Al2O3

Fe2O3

SiO2

TiO2





oxidation

5 μm

Porous TiO2

IrO2nH2O

Youngblood et al., JACS (2009)

Case study: water-splitting photocatalysis

Porous TiO2

IrO2nH2O

H2O O2

Youngblood et al., JACS (2009)

Case study: water-splitting photocatalysis

1. Synthesis of well-dispersed Ag@TiO2 nanoparticles

2. Characterization of their photocatalytic activity in: Ensemble measurements Single particle measurements

Can small plasmonic particles help?

Ag TiO2

EtOH

EtOH

EF

V.B.

C.B.

Andrea Baldi

200 nm 20 nm

Synthesis of Ag@TiO2 nanoparticles

200 nm 20 nm


Ag

200 nm 20 nm


Ag Ag Ag Ag

TiO2

UV irradiation of de-aerated Ag@TiO2

Hg(Ne) lamp

Wavelength (nm)

254 313 365 436 405 19 nm

Ensemble Measurements

See also: Kamat et al., JACS (2005); ACS Nano (2011)

UV irradiation of de-aerated Ag@TiO2

19 nm

Ag TiO2

EtOH

EtOH



Discharge in O2

Ag TiO2

O2

O2–



A A A

Single Particle Optical Measurements

A

B

C


Charge 0 min UV


Charge 20 min UV


Charge 40 min UV


Charge 60 min UV


Discharge 0 min O2


Discharge 20 min O2


Discharge 40 min O2


Discharge 60 min O2


Discharge 80 min O2


Ensemble Particle A Particle B Particle C


Bars denote peak full-width at half maximum On-going: correlate single particle structure with catalytic activity


atal

yst

acti

vity

(m

mol

CO

/gA

u)


0 5 10 15 20 25 30

0.3

0

0.6

MgAl2O4

Al2O3

Fe2O3

SiO2

TiO2



oxidation

5 μm

Preliminary results are promising. It will be exciting to correlate catalyst size and shape with activity.




atal

yst

acti

vity

(m

mol

CO

/gA

u)


0 5 10 15 20 25 30

0.3

0

0.6

MgAl2O4

Al2O3

Fe2O3

SiO2

TiO2



oxidation

5 μm




5 % Ultraviolet 43 % Visible 52 % Infrared

Solar cell

30-50% of sun’s energy cannot be absorbed

Solar upconversion

5 % Ultraviolet 43 % Visible 52 % Infrared

Solar cell

30-50% of sun’s energy cannot be absorbed

Solar cell

Upconverter Insulator

Utilize low-energy transmitted photons

Solar upconversion

Modeling upconversion (UC) efficiencies

Trupke, et al. J. Appl. Phys. 92 (2002) Atre, Dionne. J. Appl. Phys. 115 2 (2011) &

1.0 2.0 2.5 1.5

Cell bandgap (eV) C

ell e

ffic

ien

cy (

%)

With upconverter

No upconverter

44

30

• Peak cell efficiency increases from 30% to 44% • Ideal cell bandgap blue-shifts from 1.1 eV to 1.8 eV • Challenges: UC absorption & emission efficiency, UC

absorption bandwidths , UC energy levels

Solar cell Upconverter

The need for efficient upconversion

• Effect of UC absorption bandwidth: higher

efficiencies with higher bandwidths

UC Bandwidth (eV)

Ce

ll B

an

dg

ap (

eV

) Ce

ll Effic

ien

cy (%

)

Thermodynamic limit (no UC)

cell Eg=1.7 eV

• Effect of UC absorption/recombination

efficiency: need high quantum efficiencies

Atre, Dionne. J. Appl. Phys. 115 2 (2011) Briggs, Dionne. In preparation (2012)

Two promising upconverting systems

Photos by Ashwin Atre; See also: Singh-Rachford, et al. JACS. 131 (2009)

Bimolecular systems Lanthanoid-doped nanoparticles

200 nm

Photos by Diane Wu; See also: Wang, Nature (2010)

Tunable and Enhanced Upconversion

UC Film

Plasmon composite UC film (as conductive as ITO)

4.3x

Wavelength (nm)

500 550 600 650 700

Inte

nsi

ty (

a.u

.)

Conductive upconverting composites

Diane Wu

4.1x

4.7x


UC Film

nanowire enhanced UC film

4.3x

4.1x

4.7x

Pressure (GPa)

Wavele

ngth

(nm

)

1.15 12.9 28.3 14.1 1.15

540

545

550

5552000

4000

6000

8000

10000

12000

14000

16000

Pressure (GPa)

1.15 12.9 28.3

Pressure (GPa)

Wavele

ngth

(nm

)

1.15 12.9 28.3 14.1 1.15

540

545

550

5552000

4000

6000

8000

10000

12000

14000

16000

Inten

sity (a.u.)

555

550

545

540

Wav

elen

gth

(n

m)

Wavelength (nm)

500 550 600 650 700

Inte

nsi

ty (

a.u

.)

Conductive upconverting composites Upconverters under pressure

Maverick Chea

Michael Wisser

Ashwin Atre 50 nm 50 nm

Solar cell Solar cell

Up

converted

pow

er tow

ards cell

No nanocrescent With nanocrescent


1 μm

Conclusions

10 nm

Ag

TiO2

Some see things as they are and ask why. Others dream things that never were and ask why not. – George Bernard Shaw.




Conclusions

Thanks to you and our funders!!: GCEP, TomKat, DOE

10 nm

Ag

TiO2




Bimolecular upconversion process

S = sensitizer; E = emitter

1S 1S*

hν1

ISC 3S*

1S

TET

3E*

1E

3E*

hν1 1S*

ISC 3S*

TET

1S

1E

1S* 1E

3S*

TTA

1E

1E*

hν2

3E*

3E*

1S 1S*

hν1

ISC 3S*

1S

TET

3E*

1E

3E*

hν1 1S*

ISC 3S*

TET

1S

1E

1S* 1E

3S*

TTA

1E

1E*

hν2

3E*

3E*

Energy Requirements:

Sensitizer

1S*

3S*

1S Emitter

1E*

3E*

1E

TTA

The need for efficient upconversion C

ell E

fficie

ncy (%

)

1 1.5 2 2.5 30

1

2

3

4

5

Cell Bandgap (eV)Id

ea

l P

ea

k P

ositio

n (

eV

)

All FWHM=0.1eV

Emitter

Absorber 1 Absorber 2

Bandgap

(slope=1)

Incre

ase

in J

sc (

mA

/cm

2)

0

6

UC absorption peak location (nm)

0 2000 4000

•UC absorption peak positions: usually in the near-infrared (811nm and 1200nm for a 1.7eV cell)

1000 3000

•Solar-spectrum matching: don’t want UC energy levels to overlap with

AM1.5 absorption lines Briggs, Dionne. In preparation (2012) Burke, McGehee. In preparation (2012)

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