1938-15

Workshop on Nanoscience for Solar Energy Conversion

Md. Khaja NAZEERUDDIN

27 - 29 October 2008

ISIC, Lab. Photonique et InterfacesCH G1 526 (Bat.CH) Station 6, CH-1015

LausanneSwitzerland

Molecular Engineering of Sensitisers for Solar Cells Applications

11/12/2008 1

Molecular Engineering of Sensitizers for Solar Cell Applications

Dr. Md. K. NazeeruddinSwiss Federal Institute of Technology

CH 1015-Lausanne, Switzerland

Joint ICTP-KFAS Workshop on Nanoscience for Solar Energy Conversion

27-29 October 2008

Financial supportSwiss Federal Institute of Technology

Swiss Federal Office for Energy (OFEN)

Synthesis

Dr. S. M. ZakeeruddinDr. Eiji YonedaDr. Il JungDr. Cedric KleinDr. E. BaranoffDr. P. Péchy

Dr. Barolo (Italy)Prof. Viscardi (Italy)

Photovoltaic measurements

Dr. J-H YumDr. P. LiskaDr. Ines RaabeTakeru BesshoPascal Comte

AcknowledgmentProf. M. Graetzel

DFT Computational studyProf. Filippo De Angelis, Perugia, Italy

Prof. Ursula Roethlisberger,

EPFL

Prof. David L. OfficerUniversity of WollongongAustralia

Prof. Jaejung KoKorea University

Prof. Tomas TorresUniversidad Autonoma de Madrid

National Geography, June 2004

Module UnitModule Unit Outdoor TestOutdoor Test

Real Outdoor Test of DSC ModulesReal Outdoor Test of DSC Modules

Series connected 64 DSC cells

Kariya City at lat. 35°10’N, Asimuthal angle: 0°Facing due south, Tilted at 30°

A cross section of the dye sensitized solar cell

TiO2with monolayer of dye

Glass

Fluorine-doped SnO2

Redox electrolyte I- /I3 -Pt Catalyst

Glass

Working electrode

Counter electrode

Fluorine-doped SnO2

e-

e-

Requirements of the Sensitizers

+ The optimal sensitizer for the dye sensitized solar cell should be panchromatic, i.e. absorb visible light of all

colors.

+ It should possess suitable ground- and excited state redox properties (0.5 and -0.8 V vs.SCE)

+ It should exhibit thermal and photochemical stability

+ It must be firmly grafted to the semiconductor oxide surface and inject electrons into the conduction band with a quantum yield of unity.

Splitting pattern of d-orbital in an octahedral field for Fe2+, Ru2+ and Os2+

Operating Principles of the Dye-Sensitized Solar Cell

cb

e-e-e-

e-

TiO2

S+/S

S+/S*e-

e-

( R / R- )

e-

( e- )

Δv

-0.6

0

0.2

-0.2

0.6

1.0

-1.0

e- e-

e-

Load

Counter electrode

V vs SCE

Electrolyte

TCO TiO2N

NHOOC

COOH

N

N

HOOC

HOOC

RuNCS

NCS=

Electron injection from the excited dye into the TiO2 conduction band (CB) is a very fast process femtosecondscale τ1 < 20 fs.

The reduction of the oxidized dye by the redoxelectrolyte’s I- ions occurs in about 10-8 seconds.

Recombination of photoinjected CB electrons with oxidized dye molecules or with the oxidized form of the electrolyte redox couple (I3

- ions) occurs in microseconds.

η=iph Voc ff / Is

N

NHOOC

COOTBA

NN

HOOC

COOTBA

RuNCS

NCSN719

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Abs

orba

nce

800700600500400300Wavelength [nm]

Absorption Spectra of N719 Sensitizer

Abs. λmax : 535 nm

ε: 13600 M-1cm-1

Em. λmax : 780 nm

Photocurrent-voltage characteristics of nanocrystalline TiO2 cell sensitized with N3 (4 protons), N719 (2 protons), N3[TBA]3 (1 proton) and N712 (zero proton)

dyes measured under AM 1.5 sun.

15

10

-5

Cur

rent

[mA

]

0.8 0.6 0.4 0.0Potential [V]

5

20

0.2

N3

N719

N712

N3[TBA] 3

Sensitizer Number

of protons Solvent for dye adsorption

Current mA/cm2

Potential (mV)

Fill Factor Efficiency at 1.5 AM

N3 4 1:1 CH3CN+ tert-BuOH

19 ± 0.5 600 ± 30 0.65 ± 0.05 7.4

N719 2 1:1 CH3CN+ tert-BuOH

16 ± 0.5 730 ± 30 0.70 ± 0.05 8.2

N712 0 C2H5OH 13 ± 0.5 900 ± 30 0.7 ± 0.05 8.2 N3[TBA]3 1 5:95 CH3CN

+tert-BuOH 17±0.5 770 ±20 0.73±0.05 9.56

N3[TBA] 3 1:1 CH3CN+ tert-BuOH

17 ± 0.5 700 ± 20 0.65 ±0.05 7.7

cb

e-e-e-

e-

TiO2

S+/S

S+/S*e-

e-

( R / R- )

e-

( e- )

Δv

-0.6

0

0.2

-0.2

0.6

1.0

-1.0

e- e-

e-

Load

Counter electrode

V vs SCE

Electrolyte

TCO TiO2N

NHOOC

COOH

N

N

HOOC

HOOC

RuNCS

NCS=

TBA Cheno

Chenodeoxycholic acid3α,7α-dihydroxy-5β-cholani cacid

HOH

H3C

H H

H

CH3

O+N(C4H9)4-O

CH3

OH

20

15

10

5

0

Cur

rent

[mA

/cm

2]

8006004002000Potential [mV]

I sc = 17.73 mA/cm2

Voc = 846 mV

FF = 0.745

Efficiency = 11.18

80

60

40

20

0

IPC

E (%

)

800700600500400Wavelength [nm]

NN

ABTO O

HO

O

N

N

ABTO O

HO

O

Ru

NC

S

NC

S

Conversion efficiency of 11.2 % have been reached under AM 1.5 sunlight

Nazeeruddin, Mohammad K.; De Angelis, Filippo; Fantacci, Simona; Selloni, Annabella; Viscardi, Guido;Liska, Paul; Ito, Seigo; Takeru, Bessho; Graetzel, Michael. JACS, 127, 16835, 2005.

η=iph Voc ff / Is

Illustration of the interfacial charge transferprocesses in nanocrystalline dye sensitized solar cell.

-0.6

0

0.2

-0.2

0.6

1.0

-1.0S+/S*

S+/S

I3-/I-

TiO2E (V) vs SCE

e-

(1)(3)

(5)

(6)

(2)

(4)

(1) An excited state. (2) electron injection onto the conduction band of TiO2. (4) The oxidized sensitizer gets reduced by I- / I3

- redox couple. (5) The injected electrons into the conduction band may react either with the oxidized redox couple or with oxidized dye molecule (6).

Pictorial representation of blocking of the oxidized redox couple I3- reaching

onto the surface of TiO2 for conduction band electrons using hydrophobicsensitizers, which forms aliphatic net work.

TCOTiO2

RuN

N

-OOC

-OOC

NCSNCS

N

N

RuN

N

-OOC

-OOC

NCSNCS

N

N

I3-/I-

e-

X

S. M. Zakeeruddin, M. K. Nazeeruddin, R. Humphry-Baker, P. Pechy, P. Quagliotto, C. Barolo, G. Viscardi, M. Grätzel, Langmuir 2002, 18, 952P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin, T. Sekiguchi, M. Grätzel, Nat. Mater. 2003, 2, 402M. K. Nazeeruddin, S. M. Zakeeruddin, J-J. Lagref, P. Liska, P. Comte, C. Barolo, G. Viscardi, K. Schenk, M. Graetzel Coord. Chem. Rev. 248 (13-14): 1317-1328 (2004)

80

60

40

20

0800700600500400

Wavelength [nm]

Enhancing charge separation

N. Hirata, J.-J. Lagref, E. J. Palomares, J. R. Durrant, M. K. Nazeeruddin, M. Graetzel, D. Di Censo, Chem. Eur. J. 2004 10 595

triarylaminetriarylamine moietymoiety1000-fold retardation of the recombination dynamics in comparison with N-719!

4 Å increase in distance between the cationic center of charge and the TiO2surface respect to N-719

-0.6

0

0.2

-0.2

0.6

1.0

-1.0S+/S*

S+/S

I3-/I-

TiO2E (V) vs SCE

e-

(1)

(3)

(5)

(6)

(2)

(4)

New Sensitizers with π-extended donor ligands

N

NHOOC

COOTBA

NN

HOOC

COOTBA

RuNCS

NCSN719

Ko et al. Inorganic Chemistry, Vol. 47, No. 7, 2008, 2267

D

A

Sensitizers with π-extended donor ligands

K66

N

N

HOOC

HOOC

Ru

N

C

S

NC

S

N

N

O

O

O

O

N

N

HOOC

HOOC

Ru

N

C

S

NC

S

N

N O

O

O

O

N

N

N

NRu

NC

S

NC

S

OH

O

O

O

HO

O

K19

N945

N

N

N

NRu

NC

S

NC

S

OH

O

O

O

HO

OO

O

O

O

K69

K77

N

N

N

NRu

NC

S

NC

S

OH

O

O

O

HO

O

Inorg. Chem. 45, 787-797, 2006.

Comparison UV-Vis spectra of N719 (red), K19 (blue) and K77 (black)

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Abs

orba

nce

[OD

]

800700600500400Wavelength [nm]

K77

K19

N719

Molecular orbital energy diagram of N719, N945 and K19 compared to that of a TiO2 nanoparticle

model

N

N

-OOC

HOOC Ru

N

C

S

NC

S

N

NO

O

O

O

N

OABTO

N

O

HO

N

OABTO

N

O

HO

N

NC

C

S

S

Ru

0102030405060708090

100

340 420 500 580 660 740 820Wavelength (nm)

IPCE

(%)

02468

101214161820

0 0.2 0.4 0.6 0.8Potential (V)

Curre

nt(m

A/cm

2 ) 10.82%

11.41%

11.23%

99.2%SunVoc 783.20mVJsc 18.84mA/cm2

FF 0.728EF 10.82%

N

N

-OOC

HOOC

Ru

N

C

S

NC

S

N

N O

O

O

O

N+

C101

Note: 7+5 film, overnightDye solution: 300 ⎧M C101 and 300 ⎧M cheno in AN/t‐BuOHElectrolyte: Z960

Jsc=17.94 mA cm 2

Voc=778 mVff=0.785⎜=11.0%

Peng Wang et al. J. AM. CHEM. SOC. 2008, 130, 10720–10728

New Sensitizers with π-extended acceptor ligands

N

NHOOC

COOTBA

NN

HOOC

COOTBA

RuNCS

NCSN719

Ko et al. Inorganic Chemistry, Vol. 47, No. 7, 2008, 2267

D

A

NN

NN

HO

O

RuN C S

N CS

HO O

Z907

NN

NN

HO O

HO

O

RuN C S

N CS

K9

NN

NN

RuN C S

N CS

K23

HO

O

HO O

Sensitizers with π-extended acceptor ligands to enhance spectral response

Absorption spectra of Z907, K9 and K23

0

0.2

0.4

0.6

0.8

1

1.2

1.4

250 350 450 550 650 750

Wavelength [nm]

K23

K9

Z907

80

60

40

20

0800700600500400

Wavelength [nm]

NN

NN

HO

O

RuN C S

N CS

HO O

Z907

NN

NN

HO O

HO

O

RuN C S

N CS

K9

NN

NN

RuN C S

N CS

K23

HO

O

HO O

Sensitizers with π-extended acceptor ligands to enhance spectral response

New Sensitizers with extended π-system

N

N

HOO

N

N

Ru

NC

S

NC

S

3'

HO

O

HOO

OH

O

NN

HO O

HO

O

N

N

HO O

HO

O

Ru

NC

S

NC

S

NN

HO O

HO

O

N

N

HO O

HO

O

Ru

NC

S

NC

S

N3λmax 535 nmε= : 13800 M-1cm-1

Em. λmax : 780 nmEox = 0.85 (irrev)

K-8Abs. λmax : 555 nm

ε: 17600 M-1cm-1

Em. λmax : 840 nm

Eox = 0.77 (rev)

K-27Abs. λmax : 566 nm

NN

HO O

N

N

Ru

NC

S

NC

S

3'

HO

O

O

O

K-29Abs. λmax : 575 nm

UV/Vis Spectra of N719 and K8 Sensitizers

1.5

1.0

0.5

0.0

Abs

orba

nce

[AU

]

800700600500400Wavelength [nm]

N

NHOOC

COOTBA

NN

HOOC

COOTBA

Ru

NCS

NCSN719

N

N

COOH

HOOC

Ru

NCS

NCS

NN

COOH

HOOC

K 8

λmax : 555 nmε : 17600 M-1cm-1

λmax : 535 nmε : 13600 M-1cm-1

80

60

40

20

0

IPC

E [%

]

800700600500400 Wavelength [nm]

N

N

COOH

HOOC

Ru

NCS

NCS

NN

COOH

HOOC

Solar AM 1.5 (1000 W/cm2) is 18 - 19 mA/cm2

Incident Photon to Current Conversion Efficiency of K 8 Sensitizer

M. K. Nazeeruddin, C. Klein, P. Liska, M. Graetzel, Coord. Chem. Rev. 2005, 249, 1460C. Klein, M. K. Nazeeruddin, P. Liska,D. Di Censo, N. Hirata, E. Palomares, J. R. Durrant, M. Graetzel, Inorg. Chem. 2005, 44, 178

Spectral irradiance of the Sun at mean Earth-Sun separation

One factor that limiting further improvement of DSC is lack of energy capture by dyes in the IR region.

Half of the sun’s energy reaching earth’s lies above 700 nm and one third beyond 1000 nm

Absorption and Emission (ex = 700 nm) of Trithiocyanato (4,4’,4’’-tricarboxy-2,2’;6,2’’-terpyridine)Ruthenium(II)

complex in MeACN

2.0

1.5

1.0

0.5

0.0

Abs

orba

nce

1000800600400Wavelength [nm]

2.0

1.5

1.0

0.5

0.0

emissionabsorption

100ns80604020

Lifetime 72 nsN

N

NCS

RuSCN

N

NCS

CO2TBA

CO2TBATBAO2C

Separation of Linkage Isomers of Trithiocyanato (4,4’,4’’-tricarboxy-2,2’;6,2’’-terpyridine)Ruthenium(II)

NC

S

N

N Ru

NN

SC

O

O OTBA

OTBAO

N SC

OH

N

N Ru

N

O

O OTBA

OTBAO

OHN

N Ru

NN

SC

O

O OTBA

OTBAO

OH

{(C 4 H 9 )4 N} 2 [Ru(H 2 tcterpy)(NCS) 3 ] 2

pH = 5

pH = 4.5 pH = 3.8

N SC

Isomer 1

Isomer 2 Isomer 3

- -

-

NC

S

NS C

NS C

NS C

Isomers of the Black dye

0.8

0.6

0.4

0.2

0.0

Abs

orba

nce

[OD

]

900800700600500400300

Wavelength [nm]

Isomer #1 Isomer #2 Isomer #3

NC

S

N

N Ru

NN

SC

O

OH

O O TB A

OTB AO

N SC

_

NC

S

N

N Ru

NN

SC

O

OH

O O TB A

OTB AO

NS C

_

NC

S

N

N Ru

NN

SC

O

OH

O O TB A

OTB AO

NS C

_

Photocurrent action spectrum of different ruthenium complexes attached to

nanocrystalline TiO2 films

60

40

20

01000800600400

Wavelength [nm]

TiO 2

RuL 2(NCS) 2

RuL'(NCS) 3

L = 4,4'-COOH-2,2'-bipyridine L' = 4,4',4"-COOH-2,2':6',2"-terpyridine

8 0

JACS, 2001, 123, 1613

Photocurrent-voltage characteristics of a nanocrystallinephotoelectrochemical cell sensitized with the Black Dye

The results were obtained at the NREL calibration laboratory measured with an area of 0.1863 cm2 and irradiance of 1000 Wm-2. V

oc= 0.72 V, Jsc = 20.53 mAcm-2; fill factor = 70.41%;

the efficiency = 10.4.

Data from Prof. Arakawa’s lab:

Irradiance of 1000 Wm-2.

Voc

= 700 mV

Jsc = 21.49 mAcm-2

Fill factor = 69.9%

Eficiency = 10.5.

Data from Sharp:

Irradiance of 1000 Wm-2.

Voc

= 729 mV

Jsc = 21.0 mAcm-2

Fill factor = 70.4%

Eficiency = 10.8 (11.2)

Cis- and trans-Isomers of N8200.5

0.4

0.3

0.2

0.1

0.0

Abs

orba

nce

[OD

]

900800700600500400300

Wavelength [nm]

N

N

NN

HOOC

COOTBA

RuNCS

NCS

cis-820

N

N

HOOC

HOOC

trans-820

N

NRu

N

N

C

S

C

S

Md. K. Nazeeruddin et al. Coord. Chem. Rev. 208 213 (2000)

Comparison of UV/Vis Absorption Spectra of N719 and trans-[Ru(L)(NCS)2]

0.30

0.25

0.20

0.15

0.10

0.05

0.00

Abs

orba

nce

[OD

]

900800700600500400300Wavelngth [nm]

N N

NC N

C

CC

Ru

NCS

N

C

O

OH

OHO C

S

SN886

N

NHOOC

COOTBA

NN

HOOC

COOTBA

Ru

NCS

NCSN719

C. Barolo, Md. K. Nazeeruddin, Simona Fantacci, D. Di Censo, P. Comte, P. Liska, G. Viscardi, P. Quagliotto,Filippo De Angelis, S. Ito, and M. Graetzel Inorg. Chem. 2006, 45, 4642-4653

N719

Tuning the properties of Ru(II) sensitizersN3Effect of

deprotonationBypyridinefunctionalization

Ligand engineering

Z907

N866

C. Mater. Chem. 2006, 16, 4468.J. Photochem. Photobiol. A 2007, 185, 331.

Inorg. Chem. 2006,45,4642

749

N945

Heteroleptic Ru(II) TiO2 sensitizers

N719 Z907

9.550.7375917.251N945

6.020.7370011.801N886

Sensitizer Number of protons

Current mA/cm2

Potential (mV)

Fill Factor Efficiency at 1.5 AM

N719 2 16.66 846 0.73 10.28

N621 1 16.22 766 0.70 8.69

K19 1 16.40 768 0.73 9.19

N749 1 21.00 729 0.72 10.80

A considerable reduction of the open circuit potential (ca. 100 mV) is observed with heteroleptic and black sensitizers J. AM. CHEM. SOC., 129, 14156, 2007

Nano Lett. 3189, 7, 2007.

N945

N866

Homoleptic/Heteroleptic comparison

Two prototypical configurations of N719/TiO2

The two protons are located on the dye (left) or on the TiO2 (trans to NCS)

Homoleptic (N719 c) and heteroleptic (N621) sensitizers, adsorbed via a single bipyridineligand, exert strong dipolar fields at the TiO2surface, causing a down-shift of the TiO2 conduction band.

Sensitizers with new donor ligands

N

NHOOC

COOTBA

NN

HOOC

COOTBA

Ru

NCS

NCSN719

Organic Dyes

7.050.6974513.73D25L6

7.250.7273313.70D21L6

6.080.7064113.36D9L6

6.290.7468512.50D5L6

efficiencyFFV (mV)J (mA/cm2)Dye

NS

COOHNC

S

D5L6

NS

COOHNC

S

O

O D9L6

NS

COOHNC

S

O

O D21L6NS

COOHNC

S

O

O

D25L6

350 400 450 500 550 600 650 700 7500

102030405060708090

100

D5L6 D21L6

IPC

E (%

)

Wavelength ( nm)

Stability with IL z655 under light soaking + 60 degree

0 200 400 600 800 10000246

0 200 400 600 800 10000.40.60.8

0 200 400 600 800 1000200400600

0 200 400 600 800 100005

10

J sc

(mA

/cm

2 )

Time (hr)

Voc

(mV

)

Fill

Fact

or

Eff

icie

ncy

(%)

0 200 400 600 800 100002468

0 200 400 600 800 10000.40.60.8

0 200 400 600 800 1000200400600800

0 200 400 600 800 100005

1015

J sc

(mA

/cm

2 )Time (hr)

Voc

(mV

)

Fill

Fact

or

Eff

icie

ncy

(%)

88%

11.44 10.72

646 615

0.692 0.688

5.11 4.53

13.44 12.63

686 644

0.648 0.668

5.98 5.43

90%

D5L6 D21L6

Absorption spectrum

1.2x10 6

1.0

0.8

0.6

0.4

0.2

0.0

Emission Intensity [cps]

800700600500400300200Wavelength [nm]

0.8

0.6

0.4

0.2

0.0

Abs

orba

nce

[OD

]

800700600500400300200Wavelength [nm]

S

S

NC

COOH

N

N

S

NCCOOH

354 nm (ε = 34,000 dm3mol-1cm-1)436 nm (ε = 30,000 dm3mol-1cm-1)

364 nm (ε = 44,000 dm3mol-1cm-1) 452 nm (ε = 39,000 dm3mol-1cm-1)

IPCE and IV data of JK1 and JK2 dyes

91 % IPCEpower conversion 7.20% (JK-1)and 8.01% (JK-2)

400 500 600 700 8000

102030405060708090

100

IPC

E (%

)

Wavelength ( nm)

3 trans 6 trans 9 trans

5.400.7266711.49 +5

4.000.6616459.316 trans

4.280.65462110.509 trans

efficiencyFFV (mV)J (mA/cm2)Film (μm)

Thickness effect

N

OH

O

O

O

N

N+

NO

HO

O

O-

N

S

S

NC COOH

JK2

Zinc Phthalocyanine

400 500 600 700 8000

102030405060708090

100

IPC

E (%

)Wavelength ( nm)

TT1 W900

N NN

NN N

N NZnHOOC

COOH

COOH

COOH

N NN

NN N

N NZn

COOH

Isc = 7.3Voc = 595 mVFF = 0.74Efficiency = 3.25

400 500 600 700 8000

102030405060708090

100

IP

CE

(%)

Wavelength ( nm)

TT1 JK2 JK2+TT1

7.770.72676.8215.96after 1 day

7.330.7650.0216.11JK2+TT17.080.709690.0314.45JK22.940.746601.56.55TT1

efficiencyFFV (mV)J (mA/cm2)Dye

400 500 600 700 8000

102030405060708090

100

IPC

E (%

)

Wavelength ( nm)

JK2+TT1

400 500 600 7000

102030405060708090

100

IPC

E (%

)

Wavelength ( nm)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-2

0

2

4

6

8

10

12

14

dark

9.3 % sun

51.4 % sun

Cur

rent

(m

A/c

m2 )

Voltage (V)

99.9 % sun

51.4%

99.9%

Light Intensity

7.180.7667156.74

6.800.73672812.68

efficiencyFFV

(mV)

J (mA/cm2)

SS

o oo

N

5.790.720696.111.55toluene

5.180.696707.510.52DCB

0.880.72550792.39DMB

6.800.722728.612.68BiCH

6.310.714718.912.28CCl4

6.450.708725.012.57CB

4.850.723651.010.30DCM:AcN

1.770.740641.03.75EtOH

efficiencyFFV (mV)J (mA/cm2)Solvent

Effect of solvent on performance of BASF_ID94 at 1 sunTIO2: 6+4 μm; electrolyte A7117

IPCE of WMC 27380%

60

40

20

0

IPC

E [%

]

800m700600500400Wavelength [nm]

N

N

N

N

Zn

HO2CCO2H

WMC 273

-14mA

-12

-10

-8

-6

-4

-2

0

Cur

rent

den

sity

[mA

/cm

2]

0.6V0.40.20.0Potential [V]

N

N

N

N

Zn

HO2CCO2H

WMC 273Current = 13.85 mA/cm2Potential = 0.679 VFF = 0.72Efficiency = 6.76%