dye-sensitized solar cells - cimavcongreso.cimav.edu.mx/2010/wp-content/uploads/2010/... ·...

Centro de Investigación y de Estudios Avanzados del I.P.N. - Mérida, Yucatán - México

Departamento de Física Aplicada [email protected]

CIMAV – Chihuahua

Octubre 26, 2010

Gerko Oskam

Departamento de Física AplicadaCentro de Investigación y de Estudios Avanzados del I.P.N. (Cinvestav)

Mérida, Yucatán, MEXICO

Dye-Sensitized Solar Cells Basic Principles & Applications



Efficiency Record: 11.1%

O'Regan & Grätzel, Nature 1991, 353, 737.

• photoelectrochemical cell

• porous, high surface area metal oxide film

• light absorption by adsorbed sensitizer molecules

• electron transport in solid and ion transport in solution

Dye-sensitized TiO2 solar

cells

Chiba, Y.; Islam, A.; Watanabe, Y.; Komiya, R.; Koide, N.; Han, L.Y.,

Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%

Jap. J. Appl. Phys. Part 2 - Letters & Express Letters 2006, 45, L638.

Jsc = 20.9 mA cm-2

Voc = 0.736 V

FF = 0.722

(Rs = 1.6 Ω cm2)



OUTLINE

• Modules & large-scale applications

• Fundamentals & processes

• Current research topics

• Research at Cinvestav – Mérida



www.g24i.com 120 MW plant in Cardiff, Wales; June 2007

G24 Innovations, Ltd



TOYOTA-AISIN-SEIKI

Module:

64 cells of 10 x 10

cm2 connected in

series

10 µm film

15 nm TiO2 particles

N3 sensitizer

MPN electrolyte with

LiI, DMII, I2, TBP

Kariya City; N. 35010‟

facing South; 300 tilt

Outdoor performance of large

scale DSC modules

T. Toyoda et al, J. Photochem. Photobiol. A:

Chem.

164 (2004) 203-207

Division of Energy Engineering,

AISIN, SEIKI, Japan

TOYOTA Central R&D Lab.

Japan

monolithic series module design



Series interconnect design

2005

Dyesol, Australia

• materials & equipment

for

fabrication of DSC

• flexible panels for

military

• panels on flexible steel

with Corus; roofs, etc.

www.dyesol.com

„camouflage‟ panel

IPS 17, Sydney, 2008



M.A

. Gre

en e

t al, P

rog. P

hoto

volt: R

es. A

ppl.

2010; 1

8:3

46

–352



Advantages DSC:

• inexpensive materials• inexpensive production process• low energy content; payback in a few months instead of years

• performance increases with higher temperature• better performance under low light intensity conditions• efficiency is less sensitive to the angle of incidence

• flexible cells• bifacial configuration• transparency for power windows• colorful cells• near-infrared sensitizers: non-colored, transparent PV cells are possible

• outperforms amorphous silicon

Disadvantages

• sealing• questions on performance stability• low efficiency compared to silicon and thin films



Operational mechanisms

• absorption of light by the dye, D0, results in a molecule in the excited state, D*

• an electron is injected from D* into the TiO2 conduction band

• the electron is transported through the nanostructured film to the TCO back

contact

• the dye is regenerated by the electron donor in the solution

• the oxidized redox species is, in turn, reduced at the Pt/TCO counter

electrode.

e-

dye

donor

acceptor

CB

Eredox

E

TCO TiO2 electrolyte solution

h

TCO

D0/D+

D*/D+



e-

dye

donor

acceptor

CB

Eredox

E

TCO TiO2 electrolyte solution

h

D0/D+

D*/D+

recombination

Recombination processes

• electron transfer from the TiO2 to:

- the oxidized dye

- the electron acceptor in

solution

• electron transfer from the TCO to

the

electron acceptor in solution

3I-

3I-

I -

I -

I -

+

Transport processes

• electron transport in the nanostructured,

mesoporous film is complicated, and

accompanied by ion transport in the solution

• transport is dominated by (ambipolar) diffusion,

due to screening effects in the permeating

solution

• transport is described by a multiple trapping

mechanism, and is non-linear in electron density



New Architectures for Dye-Sensitized Solar Cells

Alex B. F. Martinson, Thomas W. Hamann, Michael J. Pellin,

and Joseph T. Hupp

Chem. Eur. J. 2008, 14, 4458 – 4467

Interface Kinetics Transport Kinetics

• transport is trap-limited

• transport kinetics become faster at higher EF• recombination kinetics become faster at higher E

CB

EF

ENtraps



The nanostructured, mesoporous TiO2 electrode

• large internal surface area: roughness factor 1000

• adequate surface chemistry for dye adsorption

• good internal connectivity for electron transport

C. J. Barbé, F. Arendse, P. Comte, M. Jirousek

F. Lenzmann, V. Shklover, and M. Graetzel

J. Am. Ceram. Soc., 80 [12] 3157–71 (1997)

Current research topics



A 4.2% efficient flexible

dye-sensitized TiO2 solar

cells using stainless steel

substrate, M G Kang et

al.,

Sol Energ Mater Sol C

2006, 90, 574.

8.6% efficiency:

J. Electrochem. Soc.

2008, 155(7), F145.

Collector electrode substrates

Plastic/ ITO: efficiencies 2 - 6 %

Optimization of dye-sensitized solar cells prepared by compression

method

G Boschloo, H Lindström, E Magnusson, A Holmberg, A Hagfeldt

Journal of Photochemistry and Photobiology A: Chemistry 2002, 148,

11.

Low-temperature fabrication of dye-sensitized solar cells by

transfer of composite porous layers,

M Dürr et al., Nature Materials 2005, 4, 607

Flexible dye-sensitised nanocrystalline semiconductor solar

cells

S A Haque, E Palomares, H M Upadhyaya, L Otley, R J

Potter,

A B Holmes and J R Durrant, Chem. Commun. 2003, 24,

3008.

High-efficiency (7.2%) flexible dye-sensitized solar cells

with

Ti -metal substrate for nanocrystalline-TiO2 photoanode

S Ito, et al., Chem. Commun. 2006, 38, 4004.

Eff = 2.5% at 1 sun



New materials, concepts

K. Shankar, G. K Mor, H. E Prakasam, S. Yoriya,

M. Paulose, O. K Varghese and C. A Grimes,

Nanotechnology 2007, 18, 065707 (11pp)

TiO2 nanotubes

20 µm long

efficiency: 6.9%

Lower temp. processing

Faster electron transport

C.-Y. Kuo and S.-Y. Lu,

Nanotechnology 2008, 19, 095705

inverse opal solid TiO2 structure

lined with TiO2 nanoparticles:

- thickness: 12 µm

- efficiency: 4%



N

M

M

Ru

MLCT

recombination

back transfer

C

C

O

O

N

O

O

injection

IPCE (%)

TiO2

400 500 600 700 800 900 1000

20

80

60

40

0

wavelength (nm)

A B C D

A: RuL3C: RuL2(SCN)2 (N3)

D: RuL‟(SCN)3

L = 4,4‟-dicarboxy-2,2‟-bipyridyl-

L‟ = 4,4‟,4”-tricarboxy-2,2‟:6‟,2”-terpyridyl-

“black dye” N719

Successful Dyes - Grätzel group

Engineering of Efficient Panchromatic Sensitizers for Nanocrystalline TiO2-Based Solar Cells

Md. K. Nazeeruddin, P. Péchy, T. Renouard, S. M. Zakeeruddin, R. Humphry-Baker, P. Comte,

P. Liska, L. Cevey, E. Costa, V. Shklover, L. Spiccia, G. B. Deacon, C. A. Bignozzi, and M. Grätzel

J. Am. Chem. Soc. 2001, 123, 1613-1624



New dyes & electrolyte solutions

Temperature stability: molecular engineering of ruthenium-based dyes

Z907

1000 hrs at 80 oC: 94% of initial

performance

in a quasi-solid state cell.

DSC with eutectic melt of

three ionic liquids:

8.2% efficiency

maintaining 93% of initial

performance after light

soaking at 1 sun at 60 oC.

Y. Bai et al., Nature Materials 2008, 2224.

Wang et al, Nature Materials 2003, 2, 402

1,3-dimethyl-imidazolium iodide

N N+DMII I

-

N N+

EMII I-N N+

I-AMII



Ruthenium-based dyes: (max) = 1.4 x 104 mol-1 L

cm-1

Novel organic dyes: (max) 3 to >10 times higher

allows thinner films!

More viscous electrolyte solutions, ionic liquids, or

even

solid-state hole conductors can become more

efficient

stability is still an issue

Organic dyesD205

D149: Ito et al., Adv. Mater. 2006, 18,

1202

D205: Kuang et al., Angew. Chem. Int.

Ed.

2008, 47, 1923

Indoline dyes

D149: (max) = 6.9 x 105 mol-1 L cm-1

D205: (max) = 6.9 x 105 mol-1 L cm-1

DSC with low viscosity solvent:

D149: 9.0% efficiency

DSC with ionic liquid electrolyte:

D205: 7.2% efficiency

N719

10.3%

JK-45

7.4%JK-46

8.6%

Choi et al, Angew. Chem. Int. Ed. 2008, 47, 327

low viscosity solvent



Nanoparticle synthesis

• introduction

• nucleation and growth of ZnO nanoparticles from solution

• synthesis of phase-pure TiO2 nanoparticles: anatase, brookite, and rutile

Dye-sensitized solar cells

• efficiency of cells based on TiO2 and ZnO; organic dyes

• numerical calculations of the electrical properties of dye-sensitized solar cells

Research at Cinvestav - Mérida



• control over nucleation and growth

processes

• control over aging process

Controlled Synthesis of Monodisperse Nanoparticles

Which experimental parameters affect the nucleation,

growth, and phase formation processes?

Solution-phase synthesis of ZnO nanoparticles:

ethanol

ZnCl2 + 2 NaOH water, RT ZnO + 2 NaCl +

H2O

Solution-phase synthesis of TiO2 nanoparticles:

Ti(IV) iso-propoxide + 2 H2O TiO2 + 4 iso-

propanol



nucleation

growth

coarsening

Synthesis kinetics: ZnO nanoparticles

1 mM ZnCl2 + 1.6 mM NaOH + 50 mM H2O

Absorbance is proportional to the total volume of ZnO (for r



1 mM ZnCl2 + 1.6 mM NaOH + x M H2O

no added

water

200 mM

water

50 mM

water

220

min

270

min

Effect of Water

• ZnO formation does not occur in the absence of water

• the ZnO formation rate increases with increasing water concentration

• at 200 mM water, nucleation is very fast, and only coarsening is observed



Reaction scheme:

reactants precursor ZnO nuclei growth &

coarsening

Precursor Formation:

ZnCl2 + NaOH + H2O ZnnClx(OH)y(H2O)z

The final structure of the precursor depends on the concentrations of all

reactants.How does the water concentration affect the nucleation kinetics?

• through the solubility of the solid materials:

at higher water content, the solubility and dissociation of the salts are

expected to increase, which would lead to a faster

formation of precursor molecules.

• through the precursor structure:

at higher water content, condensation can occur through olation,

which is expected to be faster than oxolation. In the case where n >

1, the precursor formation rate would increase with water

concentration. If n = 1, nucleation could be faster.



Autohydrolysis

(J. Phys. Chem. B 2005, 109, 11209)

Zn(OOC-CH3)2 + H2O ZnO + 2 HOOC-CH3

solvent: iso-propanol (ethanol, etc.)

Particle size distribution can be obtained from

the absorbance spectrum:



ZnO nanopowders

Preparation

• 0.1 M ZnCl2 + 0.2 M NaOH in ethanol

• T = 55 ˚C / 1 hour

• filtered & washed with water to remove

NaCl

• dried at 50 ˚C for 20 hours

• Yield: 4 g for a 500 mL synthesis;

practical yield ≈ 90%

Particle size control

• heat at elevated temperature to increase

particle size

• increasing water concentration results in

increased particle size

dried

450 ˚C

1 hour

450 ˚C

2 hours

500 ˚C

3 hours

0

0.5

1

rel. In

ten

sity

47 47.5 48 48.5

2theta (Þ)

r = 16 nm

0

0.5

1

rel. I

nte

nsity

r = 12 nm

0

0.5

1

rel.

Inte

nsi

ty

r = 10 nm

0

0.5

1

rel. I

nte

nsity

r = 6.4 nm



Crystalline TiO2 Nanoparticles from Amorphous TiO2

anatase

rutile

brookite

X-ray Diffraction

1.5 M acetic

acid; 200 oC4 M HCl

200 oC

3 M HCl

175 oC



anatase brookiterutile

anatase brookiterutile

Scherrer equation: relation between

the peak width and the grain or

particle size.

radius

rutile: 5 nm to >100 nm

brookite: 4 nm to 11 nm

anatase: 3 nm to 15 nm



Amorphous TiO2

AnataseTEM

Amorphous Titania:

short-range ordering suggests

presence of chains of

octahedral species with Ti - O

- Ti bridges

of 2 - 4 octahedra.

Anatase:

highly-crystallized, facetted

nanoparticles of uniform size



Rutile

After 5 hrs of hydrothermal treatment at 200 oC: presence of nanoparticles, as well as large,

compact, rod-shaped agglomerates of

nanoparticles which tend to be aligned

(oriented attachment of nanoparticles).

After 21 hours (after the change of

mechanism observed in the growth

kinetics): the nanoparticles recrystallize into

large rods.

Dynamic light scattering



Brookite

large particles:

hydrothermal treatment in

NaOH

What determines phase formation?

Total energy considerations:

• bulk energy: rutile < anatase < brookite

• surface energy: anatase < brookite < rutile

for nanoparticles: anatase has the lowest total energy

lower surface energy results in faster nucleation kinetics

Precursor chemistry:

composition and symmetry of precursor molecules determine the crystal structure

(kinetics approach)



Dye-Sensitized Solar Cells

Fabrication:• synthesis of TiO2 or ZnO nanoparticles from solution

• deposit thin, porous film on FTO-glass

• soak film in dye-solution for 24 hours

• put the platinum-coated TCO-glass on the top, a Surlyn spacer to seal

the cell

• add electrolyte solution through holes in the counter electrode

(0.6 M DMPII + 0.1 M LiI + 0.05 M I2 + 0.5 M TBP in MPN)

• seal the small holes with microscope cover glass and Surlyn.

Anatase-based cell

with N-719

ZnO-based cell

with N-719

Isc = 31 mA

Voc = 2.1 V

15 cm2

65 mW cm-2



Dye-sensitized solar cells

100 mW/cm2

(Nanomaterials prepared in our laboratory)

Cells: 0.5 cm2

anatase cells: 6.8%

brookite cells: 4.0%

rutile cells: 2%

ZnO cells

(forced hydrolysis): 3.0%

ZnO cells

(electrodeposition): 2.0%



ZnO dye-sensitized solar cells

ZnO cells from Degussa ZnO

2 sun

T = 50 oC

cell stability

Photovoltaic performance of nanostructured zinc oxide

sensitised with xanthene dyes

E Guillén, F Casanueva, J A Anta, A Vega-Poot, G Oskam,

R Alcántara, C Fernández-Lorenzo, J Martín-Calleja,

J. Photochem. Photobiol. A: Chem. 200, 364-370 (2008).



Absorbance

x

e-

e-e-

gla

ss

TCO

light

electron density

x

electron acceptors

ionsions

• Particles are too small for band bending

• Solution with ions provide shielding

• Electron transport is impeded by transfer

to electron acceptor in the solution

steady-state measurements (Lindquist et al.): photocurrent is dominated by diffusion

Electron Transport in Dye-sensitized TiO2 Films

Electron

density



Conduction Band

Valence Band

EF,n

k1 k-1Band diagram showing trap states in the band gap. The

rate constants k1 and k-1 denote trapping and de-trapping

of electrons, respectively. The Fermi-energy determines

which traps dominate the transport kinetics.

n

t

1

e

J

xR G

J en nx

eDn

x

Continuity equation

n is the electron density under illumination

J is the current density in the film

G and R are the generation and recombination ratesCurrent density

n is the electron mobility

is the electrical potential

D is the electron diffusion coefficient

n(x, t)

tD

2n(x, t)

x2

n(x, t) n0

0

exp( x) 0

Diffusion transport equation

electron injectionrecombinationflux

The diffusion coefficient and recombination term are dependent to the light intensity

transport equation is more complex: numerical methods to model electron transport



Electron Transport in Porous Nanocrystalline TiO2 Photoelectrochemical

Cells Fei Cao, Gerko Oskam, Gerald J. Meyer, and Peter C. Searson

J. Phys. Chem. 1996, 100, 17021-17027.

Rise time

IMPS

D is a power law function of the light intensity,i.e, the electron density

Experimental current transients under short circuit conditions



n(x,t)

t x(D(n)

n(x,t)

x) R G

max

min0 )(exp )( )( dxIxG CellCellinj

Dye absorption

coefficient

Injection quantum

yield

(0 < inj < 1) 350 400 450 500 550 600 650 700 750 8000.00.1

0.2

0.3

0.4

0.5

0.6

0.7

N3-Dye, CSol

= 0.16 mM

AS

ol

(nm)

GENERATION



D(n) Dref f (n) Drefn

nref

1

Electron density-dependent

- or Fermi level-dependent -

diffusion coefficient

DIFFUSION

= 0.2-0.5

n(x,t)

t x(D(n)

n(x,t)

x) R G

g(E)Nt

kTexp

E

kT



RECOMBINATIONnanostructured film

kR kRref f (n) kR

ref n

nref

1

g(E)Nt

kTexp

E

kT

n(x,t)

t x(D(n)

n(x,t)

x) R G

Recombination depends the same way

on the Fermi-level as diffusion

R kr[n(x,t) n0]



CHARGE TRANSFERFROM TCO SUBSTRATE

(Butler-Volmer equation) a 0.5

JTCO JTCO0 exp

(1 a)eV

kBTexp

aeV

kBT

RECOMBINATIONFrom TCO

Open circuit voltage decay



EXPERIMENTS & SIMULATION

0.0 1.0x10-2

2.0x10-2

3.0x10-2

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Experimental

Model = 0.22

Model = 0.26

J (

mA

cm

-2)

t (s)

TiO2 Cell

1E-4 1E-3 0.01 0.1 1 10

0.0

0.2

0.4

0.6

0.8

Experimental

Model

V (

V)

t (s)

TiO2 Cell



0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

J (

mA

cm

-2)

V(V)

Experimental

Model

Model R=0

TiO2 CellTiO2/N719/organic electrolyte

Numerical simulation: Solving the continuity equation using FTCS + Lax scheme



0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

J (

mA

cm

-2)

V(V)

Experimental

Model

Model R=0

ZnO Cell

ZnO/N719/solvent-free electrolyte



Parameter Z Cell (ZnO) T Cell (TiO2)

CCell (M) 0.14 0.25

kR0 (s-1) 9.0 10-7 3.1 10-9

0.18 0.20

b 0.50 0.55

J0 (A cm-2) 1.0 10-4 1.1 10-5

R ( ) 37.5 11.3

L ( m) 10.5 180

Numerical Simulation of the Current-Voltage Curve in Dye-Sensitized

Solar Cells Julio Villanueva, Juan A. Anta, Elena Guillén, and Gerko Oskam

J. Phys. Chem. C 2009, 113, 19722–19731.



“transport-limited

recombination”

“transfer-limited

recombination”

Alternative Recombination Mechanism

n(x,t)

t

1

e x(D(n)

n(x,t)

x) R G



“Influence of the recombination mechanism on the IV-curve of dye-

sensitized solar cells”, J Villanueva, G Oskam and J A Anta,

Solar Energy Materials & Solar Cells, 94 (2010) 45–50.



How do materials properties affect the transport & recombination characteristics?

• Through the trap distribution parameters Nt and

• Through the recombination characteristics

- interactions traps – solution

- electron transfer properties from the conduction band

- surface chemistry



Current projects & activities

Synthesis and characterization of metal oxide nanoparticles: TiO2, ZnO, core-shell

- mechanisms of nucleation, growth, and controlled aging

Optimization and application of nanomaterials in the dye-sensitized solar cell

- TiO2 and ZnO nanoparticles

- electrodeposition and electrophoretic deposition of nanostructures

New organic and natural dyes for application in the dye-sensitized solar cell

- extraction, separation, purification, synthesis (Dr. Gonzalo Mena Rejón)

- TD-DFT calculations optoelectronic structure (Dr. Andreas Köster)

Electron transport and recombination mechanisms

- numerical simulations (Dr. Juan A. Anta)

- experimental studies (Professor Laurie Peter; Dr. Petra Cameron)

Hydrogen generation using solar energy

- tandem cells using DSCs and new materials - Fe2O3 and WO3

Nanotoxicology

- interaction of TiO2 nanoparticles with cell membranes in Tilapia

(Dr. Omar Zapata, Dr. Romeo de Coss)

Conservation of national monuments – Mayan structures

- nanomaterials for prevention of biofilm formation (Dr. Juan José Alvarado

Gil; Dr. Patricia Quintana Owen)



Gerko Nikté Germán Julio Alberto

Manuel Iván

GroupDr. Gerko Oskam

M. Sc. Alberto Vega Poot (PhD student)M. Sc. Iván Lizama TzecM. Sc. Nikté Gómez OrtízM. Sc. Manuel Rodríguez PérezIng. Humberto Mandujano Ramírez

(Master’s student – not in photo)Ing. Jairo Góngora Lizama

(Master’s student – not in photo)

Funding:

Conacyt projects 33171-A (2002-2003); 43828-Y (2004-2007); 80002-Y (2008-2011)

British Council Amerlinks; FOMIX Yucatán; LENERSE; Red de Fuentes de Energía.

Current undergraduate students:

Nalleli Ruiz Tabasco, Israel Juárez Pérez, Renán Escalante Quijano, Esdras Canto

Aguilar

Graduates:

Dr. David Reyes Coronado (2008); Dr. César Cab Cauich (2010); Dr. Julio Villanueva Cab

(2010)Ex-postdocs:

Dr. Geonel Rodríguez Gattorno (2007-2008); Dr. Germán Pérez Hernández (2009 –

2010)

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