Dye-SensitizedSolar Cells

Carl C. WamserPortland State University

Nanomaterials Course - June 28, 2006

Energy & Global WarmingEnergy & Global Warming

•• M.I. Hoffert et al., M.I. Hoffert et al., NatureNature, 1998, , 1998, 395395, p 881, p 881““Energy Implications of Future Atmospheric Energy Implications of Future Atmospheric Stabilization of COStabilization of CO22 ContentContent””

•• M.I. Hoffert et al., M.I. Hoffert et al., ScienceScience, 2002, , 2002, 298298, p 981, p 981““Advanced Technology Paths to Global Climate Stability: Advanced Technology Paths to Global Climate Stability: Energy for a Greenhouse PlanetEnergy for a Greenhouse Planet””

The Kaya IdentityThe Kaya Identity

•• N N = population= population•• GDP/N GDP/N = gross domestic product per person= gross domestic product per person•• E/GDP E/GDP = energy intensity (per GDP unit)= energy intensity (per GDP unit)•• C/EC/E = carbon intensity (per energy unit)= carbon intensity (per energy unit)

Annual Energy = N*(GDP/N)*(E/GDP)Annual Energy = N*(GDP/N)*(E/GDP)

Annual COAnnual CO22 = N*(GDP/N)*(E/GDP)*(C/E)= N*(GDP/N)*(E/GDP)*(C/E)

Global Totals/Future TrendsGlobal Totals/Future Trends

Annual Energy = N*(GDP/N)*(E/GDP)Annual Energy = N*(GDP/N)*(E/GDP)

5.3 billion5.3 billion~9 billion ~9 billion by 2050by 2050

$4100$4100risingrising

1.6%/yr1.6%/yr

4.3 kWh/$4.3 kWh/$fallingfalling

1.0%/yr1.0%/yr

64 gC/kWh64 gC/kWhfallingfallingby ??by ??

Annual COAnnual CO22 = N*(GDP/N)*(E/GDP)*(C/E)= N*(GDP/N)*(E/GDP)*(C/E)

10 TW10 TW3030--40 TW40 TWby 2050by 2050

( 1990 data cited in ( 1990 data cited in HoffertHoffert’’ss Nature paper )Nature paper )

6 Gtons6 Gtons350 ppm350 ppm

rising to ??rising to ??

ConclusionsConclusions

Stabilization of atmospheric carbon Stabilization of atmospheric carbon will require immense amounts of will require immense amounts of carboncarbon--free energy in the near future free energy in the near future (2050):(2050):

•• 550 ppm 550 ppm -- about 15 TWabout 15 TW

•• 450 ppm 450 ppm -- about 25 TWabout 25 TW

•• 350 ppm 350 ppm -- over 30 TWover 30 TW

M.I. Hoffert et al., M.I. Hoffert et al., NatureNature, , 19981998, , 395395, p 881, p 881

05

101520253035404550

Oil

Coal GasFiss

ionBiom

assHyd

roelec

tric

Solar, w

ind, g

eothe

rmal

0.5%

Source: Internatinal Energy Agency

2002

Sources of Energy Supply - Worldwide

05

1015

202530

3540

4550

Oil

Coal

GasFiss

ionBiom

assHyd

roelec

tric

Solar, w

ind, g

eothe

rmal

2050

13 Terawatts 30-50 Terawatts

The ENERGY REVOLUTION(The Terawatt Challenge)

Partners in ScienceJanuary 18, 2003

R. E. SmalleyRice University

ConclusionsConclusions

““Researching, developing and Researching, developing and commercializing carboncommercializing carbon--free primary power free primary power technologies capable of 10technologies capable of 10--30 TW by the mid30 TW by the mid--21st century could require efforts, perhaps 21st century could require efforts, perhaps international, pursued with the urgency of the international, pursued with the urgency of the Manhattan Project or the Apollo space Manhattan Project or the Apollo space programme.programme.””

M.I. Hoffert et al., M.I. Hoffert et al., NatureNature, , 19981998, , 395395, p 881, p 881

Photovoltaic Land Area Requirements

20 TW

3 TW

Graphic fromNate LewisCaltech

3 TW= approx

total energycurrently

used in U.S.

20 TW= minimum carbon-freetotal energyneeded by

2050

6 Boxes at 3.3 TW Each

Photovoltaic Land Area Requirements

PhotosynthesisPhotosynthesis( 1961 Nobel Prize )( 1961 Nobel Prize )

Photosynthetic Reaction CenterPhotosynthetic Reaction Center

http://www.mpibp-frankfurt.mpg.de/~michael.hutter/rcenter.html

( 1988 Nobel Prize )( 1988 Nobel Prize )

Artificial PhotosynthesisArtificial Photosynthesis

Any solar energy conversion method that uses some aspects of nature’s strategy, compounds, or both

StrategyPhotoinduced Photoinduced

electron transfer electron transfer across a membraneacross a membrane

CompoundsChlorophyll dyes Chlorophyll dyes

and electronand electron--transfer mediatorstransfer mediators

Thermodynamic CriteriaThermodynamic Criteria

Optimize energy conversion (photopotential)

– Match the dye bandgap to the solar spectrumoptimum λbg ~ 1000 nm, efficiency ~ 30%

– Match the redox potentials (valence/conduction bands)

hν

e-

h+

ETM HTMdye

Kinetic CriteriaKinetic Criteria

Optimize quantum yield (photocurrent)

• Fast forward reactions:a) Light absorptionb) Charge separationc) Hole and electron mobilities

• Slow back reactions:d) Excited state deactivatione) Charge neutralization ETM HTMdye

DyeDye--Sensitized Solar CellSensitized Solar Cell

• Dyes– Ru(bipy)3 derivatives (N3)– Porphyrins

• Electron-transport media– n-type semiconductors– Nanoparticulate TiO2

• Hole-transport media– p-type semiconductors

– Redox electrolytes ( I- / I3- )

– Conductive polymers

The The GrGräätzel tzel

CellCell

B. O’Regan &M. Grätzel, Nature (1991) 353, 737-740.

TiO2 I-/I3-N3

~

-0.6-0.9

+0.8

+0.2

( V vs SCE )Optimized output

– Short-circuit currentIsc ~ 20 mA/cm2

– Open-circuit voltageVoc ~ 0.7 V

– Quantum yield ~ 1

– Efficiency ~ 11%

The GrThe Gräätzel Celltzel Cell

I-/I3-

Preparation of a Grätzel CellPreparation of a Grätzel Cell

ITO

or

FTO

ITO

or

FTO

TiO2 Porphyrin

hνISC ~ 20 mA/cm2

VOC ~ 0.7 Volts

Φ ~ 1

Efficiency ~ 11%

Operation of a Grätzel CellOperation of a Grätzel Cell

ITO TiO2 TCPP

-0.9

+1.1

+2.6

-0.6

Voc = 0.7 V ; Isc = 20 mA/cm2

I3 / I ITO

+0.2

- -

hv

Porphyrin LUMO

Porphyrin HOMOPP++

Photopolymerization Photopolymerization -- Proposed MechanismProposed Mechanism

HN

N

N

NH

NH2

COOHHOOC

HOOC

N

N

N

H

H H

N

5,10,15-tris(4-carboxyphenyl)-20-(4-aminophenyl)porphyrin (TC3APP)

H

e-hv

NH2 NH2

n

Stage II

e-

e-

Stage I10n H+

5n H2

e-TiO2

x10

DSSC Expt: ProceduresDSSC Expt: Procedures

1. Prepare Working ElectrodeTiO2 underlayer / nanoparticles / overlayer

Dye adsorption ( TCPP in EtOH )

2. Prepare Counter ElectrodeGraphite on FTO (F-doped tin oxide)

3. Assemble Cell

Redox electrolyte solution ( I-

/ I3-

)

4. Irradiate CellMonitor light intensity / photocurrent / photovoltage

DSSC Expt: ProceduresDSSC Expt: Procedures1. Prepare Working Electrode

TiO2 underlayer - dip in Ti(iOPr)4

Nanoparticle layer - dip in TiO2 slurry

Overlayer (skipped this time)

Bake at 450° for 30 minutes

( A pre-prepared electrode will be provided for testing while your electrode is baking )

DSSC Expt: ProceduresDSSC Expt: Procedures

2. Prepare Counter Electrode

Graphite on FTO (F-doped tin oxide)

(catalyst for iodide/triiodide reaction )

DSSC Expt: ProceduresDSSC Expt: Procedures

3. Dye Adsorption

Pre-prepared electrode will have TCPP, adsorbed from EtOH (takes overnight)

You will soak your electrode in blackberry juice

(natural anthocyanine dyes)

takes about 15 minutes

DSSC Expt: ProceduresDSSC Expt: Procedures

4. Assemble CellWorking electrode (with dye)

a) TCPP pre-prepared electrode

b) Blackberry electrode, rinsed and dried

Add redox electrolyte solution ( I- / I3- )

Assemble sandwich cell

Slide and back electrode in test fixture

DSSC Expt: ProceduresDSSC Expt: Procedures

5. Irradiate CellInstall cell in test fixture Install test fixture in Vertical Optical Bench

(VOB)Scan applied voltage from -700 to +100 mVMonitor light intensity Monitor photocurrent vs. applied voltage

(iV curve)Capture data on PC, export to ExcelSave to your personal USB drive

Slide being tested in the VOB

Light from the VOB Through 16mm hole

Light shining through test slide

Cell being tested on VOB

iV Curve for TCPP Cell

Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85)

-100100300500700900

110013001500

-800 -700 -600 -500 -400 -300 -200 -100 0 100mVolts

mic

roA

mps

Power Curve for TCPP Cell

Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85)

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.6000

-800 -700 -600 -500 -400 -300 -200 -100 0 100

mVolts

mW

atts

iV Curve for TCPP Cell

Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85)

-100100300500700900

110013001500

-800 -700 -600 -500 -400 -300 -200 -100 0 100mVolts

mic

roA

mps

Voc

IscPmax

Fill Factor

Test and Performance Parameters• Light source: Tungsten halide lamp

Intensity = 97 mW/cm2 = 0.97 Sun• Irradiated area = 0.71 cm2

• Pin = 69 mW• Voc = 652 mV• Isc = 1.3 mA• Pmax = 0.47 mW• Fill Factor = Pmax / ( Voc * Isc ) = 0.55• Efficiency = Pmax / Pin = 0.68 %

DSSC Expt: ReportDSSC Expt: Report

Check the class website for updated info

Title / AbstractIntroduction / BackgroundExperimental Procedure / ApparatusResults / DiscussionConclusions

Compare all performance data for both types of cells you tested

DSSC DSSC Expt: ReferencesExpt: References“Demonstrating Electron Transfer and Nanotechnology:

A Natural Dye-Sensitized Nanocrystalline EnergyConverter”, G. P. Smestad and M. Grätzel, J. Chem. Educ., 1998, 75(6), 752-756.

“Adsorption and Photoactivity of Tetra(4-carboxyphenyl)porphyrin on Nanoparticulate TiO2”, S. Cherian and C. C. Wamser, J. Phys. Chem. B, 2000, 104, 3624-3629.

“Basic Research Needs for Solar Energy Conversion”, U.S. Department of Energy, 2005.

Note - all of the above references can be found as .pdf files on Professor Wamser’s website:

http://chem.pdx.edu/~wamserc/Research/