1938-1
Workshop on Nanoscience for Solar Energy Conversion
27 - 29 October 2008
Power from the Sun: the Advent of Mesoscopic Solar Cells
Michael GRAETZEL
EPFL, IPI, Departement de Chimie
CH-1015 Lausanne
Switzerland
Power from the Sun
The Advent of Mesoscopic Solar Cells
JOINT ICPT-KFAS Workshop on Nanoscience for
Solar Energy Conversion
Trieste Italy October 27-29, 2008
Michael Graetzel,
ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE
Michael.Graetzel@epfl.ch
Acknowledgement Present LPI Members
PhD Students
Chen Peter
Moon Soo-Jin
Teuscher Joël
Wenger Sophie
Zhang Zhipan
Technical & Administrative Staff
Comte Pascal
Duriaux Arendse Francine
Gonthier Ursula
Gourdou Nelly
Academic Visitors
Barroso Monica
Bessho Takeru
Post-docs
Cevey-Ha Ngoc Le
Baranoff Etienne
El Roustom Bahaa Jang Song-Rim
Le Formal Florian
Evans Nicholas
Yoneda Eiji
Kay Andreas
Yum Jun Ho
Kuang Daibin
Zakeeruddin Shaik Mohammed
Lee Hyo Joong
Sivula Kevin
Thorsmolle Verner
Professor Jacques E. Moser
Wang Deyu
Wang Mingkui
Staff Scientists
Graetzel Carole
Humphry-Baker Robin
Kalyanasundaram
Kuppuswamy
Liska Paul
Moser Jacques-E. (titled prof.)
Nazeeruddin Md. Khaja
Péchy Péter
Rothenberger Guido
Rotzinger François
Thampi Ravindranathan
2
Renewable energy sources need to cover the supply gap
Solar
100’000 TW at Earth surface
Wind
14 TW
Tide/Ocean
Currents
0.7 TW
1.9 TW
from Nate Lewis
Biomass
5-7 TW
all cultivatable
land not used
for food
Hydroelectric
Geothermal
3
10,000 TW (technical value)
(1.5 hr sunlight globally = 13 TW-yr)
energy gap
~ 14 TW by 2050
~ 33 TW by 2100
1.2 TW technically feasible
0.6 TW installed capacity
Quantum Energy Conversion Strategies
THE SOLAR CHALLENGE
Fuel
!"With a projected global population of 12 billion by
2050 coupled with moderate economic growth, the total
global energy consumption is estimated to be ~28 TW.
Current global use is ~11 TW.
! To cap CO2 at 550 ppm (twice the pre-industrial level),
most of this additional energy needs to come from
carbon-free sources.
! Solar energy is the largest non-carbon-based energy
source (100,000 TW).
! However, it has to be converted at reasonably low
cost.
Light
Electricity
Fuels
Electricity
CO
H
O2
2
Sugar
sc
HO
2
sc
H 2O
2
Photosynthesis
Semiconductor/Liquid
Junctions
70
"=
2
2
70
)
Integrated photon flux (mA/cm
6000K BB integrated current
60
!(E) = AM1.5G Solar Spectrum
100 mW/cm2
50
50
6000K Blackbody Spectrum
100 mW/cm2
40
40
30
30
AM1.5G integrated current
20
20
10
10
0.5
1.0
1.5
2.0
2.5
Energy (eV)
3.0
3.5
Photovoltaics
Power conversion efficiency
80
80
60
M
O
Solar Spectrum and Available Photocurrent
Solar Photon Flux (mA/cm
.eV)
M
e
Correct device characterisation is essential
THE SOLAR RESOURCE
0
0.0
2
e
4.0
0
7
Pmax ISC # UOC # FF
=
Pin
Pin
!
Characterisation Standard:
• intensity of 1000 W/m2
• spectral power distribution
corresponding to AM1.5 ! 1Sun
• temperature 298 K
8
The yearly shipments of PV cells are growing exponentially
The market size in 2030 for the four main
PV segments is projected to be 200 bio !
Off-Grid Industrial
Consumer
70 GWp p.a.
20 GWp p.a.
Total 300 GWp
" 200 bio !
Modul Turnover
in 2030
Rural Electrification
On-Grid
60 GWp p.a.
150 GWp p.a.
9
Courtesy Dr. Winfried Hoffman, CEO, RWE, SCHOTT Solar GmbH
Disruptive PV technology approach required to
meet cost targets
PV Module Price (2003$/Wp)
Production Forecasts of Solar Modules Call for
Contributions from Different Technologies
100.0
1976
2007 ??
Evolutionary path
10.0
Revolutionary new
technology created
from basic science
2003
90%
1.0
75 GW
20??
80%
70%
0.1
0
1
10
100
1,000
10,000
100,000
Cumulative Production (MWp)
From T. Surek, JCG, 2005
1,000,000
(1 TW)
Dye sensitized nanocrystalline solar cells lead the new PV generation
A new paradigm :
Mesoscopic solar cells
based on interpenetrating
network (bulk) junctions
NATURE PHOTONICS WEB RELEASE OCTOBER 2008
15
16
The dye sensitized solar cell (DSC) is the only photovoltaic cell using amolecules that
generated charge carriers after photo-excitation without the need for excitonic transport
Dye sensitized solar cells separate light absorption from carrier transport
p-n junction photovoltaic cells
p-Si
h#
dye sensited solar cells DSC
TiO2
D*/D+
cb
h#
Electrolyte
e--R
EF
n-Si
Electron conductor
Charge separation by
electric field at the p-n
junction
D/D+
Dye
Hole conductor
Charge separation by
kinetic competition as in
photosynthesis
17
A dye sensitized nanocrystaline film generates over 1000 times more
photocurrent than a single crystal electrode
single crystal of anatase
Dye sensitized nanocrystals achieve quantitative
conversion of photons into electric current
The incident photon to electrical current conversion efficiency
(external quantum efficiency) can reach close to 100 %
! =!!abs*"inj* !coll
Nanocrystalline anatase film
A key question is how electrons are quantitively collected
from the disordered network of nanoparticles.
19
20
The collection of photo-generated electrons by the nanoparticle array is quantitative
Titania (anatase) nanoparticles show well facetted surfaces
with preferred (101) orientation
dye
40
TiO2
Number
30
100 nm
20
10
The electrons ad holes move in different phases and are separated by a phase boundary
21
retarding their recombination
The average particle size is ca 20 nm 0
0
10
20
30 22
40
Diameter of particles, nm
50
Ruthenium complexes are widely used as sensitizers due to
their extraordinary performance and excellent stability
N3 (N719)
Spontaneous uptake of N3 sensitizer by a
nanocrystalline TiO2 film supported on
conducting glass
COOH
HOOC
N
N
NCS
Ru
N
HOOC
NCS
N
COOH
23
Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Mueller, E.; Liska, P.;
Vlachopoulos, N.; Graetzel, M. J. American Chemical Society (1993), 115(14), 6382-90.
Anchoring of the carboxylate groups occurs by unidentate
and bridging bidentate coordination to surface titanium ions
The RuL2 (NCS)2 sensitizer is anchored to the (101) TiO2 anatase
surface through coordinative binding of two carboxyl groups to
surface titanium ions.
Side view
R
R
C
C
O
O
Ti
Unidentate !!!!!!
O
O
M
M
Bridging bidentate
25
26
Photo Induced Heterogeneous Electron
Transfer Cycle
O
4+
E
ID
N
C
N
Ru
O
-O
OX
C
-O
Time dependent DFT Modeling of TiO2 nanoparticles
produces correct band gap in water
Stoichiometric anatase Ti38O76 cluster of nanometric
dimensions exposing (101) surfaces
MLCT EXCITATION
forward reaction
–
–
Tis
Top view
–
Backward transfer
Energy
–
kf
–
LIGAND !*
ORBITAL
Ti 4+/3+
h ! (" 1.7 eV)
kb
–
Ru (II/III)
d xy, d xz, dyz
spatial contraction of d orbitals upon
oxidation from Ru(II) to Ru(III)
27
B3LYP/3-21g* : 3.20 eV, B3LYP/DZVP: 3.13 eV
Experimental gap in aqueous solutions: 3.20 – 3.30 eV
28
F. De Angelis, A. Tilocca, A. Selloni J. Am. Chem. Soc. 2004, 126, 15024
Photoinduced
interfacial electron
injection occurs
on a femtosecond time
scale
N719 + h!
N719*
N719+ + 1 e -
MD and DFT calculations provide important
insight into sensitizer interaction with surface
Two prototypical configurations of N719/TiO2 were examined:
(A The two protons are located on the dye or (B) on the TiO2
A
B
h!
1e-
29
30
F. De Angelis, S. Fantacci, A. Selloni, M. Grätzel J. Am. Chem. Soc. 2007
Electron injection from excited
N 719 sensitizer in the conduction
band of TiO2 is asssisted by
surface protonation
HOMO
De Angelis, . Fantacci, S.; Selloni, A.; Nazeeruddin, M. K.;
Graetzel, M JACS (2007), 129(46), 14156-14157
B
A
31
LUMO: 2 protons transferred from
LUMO: 2 protons remain on N719
N719 to TiO2 nanoparticle
32
Dynamic Competition
electron
injection
dye
regeneration
electron
interfacial
transport recombination
time [s]
electron transport
Competition "
loss mechanism:
interfacial
recombination
Electron diffusion length
Ln =
Dn
"
$n
$n: electron lifetime
Dn: electron diffusion coefficient
33
34
!
The electron diffusion length exceeds
largely the film thickness
Ln = D!
Typical values for high performance ( % >10% )
cells at Vmpp:
The solar to electric power conversion
efficiency of the DSC in full AM 1.5
sun light validated by accredited PV
calibration laboratories has presently
reached over 11 %.
D = 10-4 cm2/s, $ = 1 s, L = 100 µm
The film thickness is less than 30 micrometer
35
Chiba, Y., Islam, A.; Watanabe, Y; Komiya, R.; Koide, N.; Han, L..
Dye-sensitized solar cells with conversion efficiency of 11.1%.
Japanese Journal of Applied Physics, Part 2: Letters & Express Letters (2006), 45(24-28),
the work horse of the DSC is the N3 (or N719)
ruthenium dye,
Ongoing research
•
•
•
•
•
•
•
•
Advanced nanostructures
Light induced charge separation
new sensitizers
new redox mediators
Solid state heterojunctions
Quantum dot cells
redox active ionic liquids
tandem devices
Dr. Md. K. Nazeeruddin
Senior Scientist and
Adjoint scientifique
LPi/EPFL Lausanne
COOH anchoring groups
Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Mueller, E.; Liska, P.;
38
Vlachopoulos, N.; Graetzel, M. J. American Chemical Society (1993), 115(14), 6382-90.
37
Z991
C101
S
S
S
S
S
S
C
N
S
S
N
N
C
N
N
Ru
S
C
N
N
Ru
N
N
COOH
COO-Na+
S
C
N
N
N
N
COO-
COOH
39
40
Takeru. B
"!!
Jsc = 20.2 mA/cm2
9"!"
<**"
=("*
>?#
*!
)!
789:454;
(!
'!
&!
%!
./012#345
!
"#
$$%&
''(
)(%&
'*(
$+%,
'-(
$!
#!
"!
CYC-B1
!
$&!
%!!
%&!
&!!
&&! '!! '&! (!!
+,-./.012345406
(&!
)!!
)&!
Figure. Comparison of IPCE curve with Z960 electrolyte from C101(blue),
Z991(pink) and N719(orange) sensitizer, respectively. 8.4(DSL18)+4.8(CCIC400)
41
TiO2 film was used as semiconductor.
Takeru. B
In collaboration with Professor; Wu, Chun-Guey;
42
Department of Chemistry, National Central University, Jung-Li, Taiwan
The C101 sensitizer maintains outstanding stabiity at efficieny levels over 9
percent under light soaking at 60oC with a non-volatile electrolyte
43
Shimane Institute for Industrial Technology
High temperature stability reached on the module scale
The New Dye “J2” developed by SIIT
140
Continued Heat Stress for 1000 hours at 85 C
J2
Fig.2 Structure of J2 dye
N719
EFF Retention [%]
120
100
80
!"#$%!&'&()*)$"(+,*-./&0$#-&(+&.+*1
2)3,/.)4)(-$56.$#/7#60&.$8)00
60
40
20
0
0
200
400
600
800
1000
Time [h]
Adsorption spectra of J2 and N719
45
Courtesy Professor Katsumi Yoshino
Development of Large Size Dye-Sensitized Solar Cell
Modules with High Temperature Durability
46
Courtesy A. Yoshino, Shimane Institute of Technology
Organic dyes are catching up in conversion efficiency
Shuji NODA, Kazuhide NAGANO, Eiji INOUE,
Toshio EGI, Takeshi NAKASHIMA, Naoto IMAWAKA,
Masahiro KANAYAMA, Shiro IWATA, Kunihiro TOSHIMA, Keiko NAKADA
and Katsumi YOSHINO
Shimane Institute for Industrial Technology (JAPAN)
9:)$#:/4&()$"(*;-,-)$56.$"(+,*-./&0$9)<:(606=>$%#""91$/*$&($6.=&(/?&;6($@:6*)$',.'6*)$/*$-6$'.6A/+)$-)<:(/<&0$&**/*-&(<)$-6
<6.'6.&;6(*$/($#:/4&()$B.)5)<-,.)$-:&-$<&..>$6,-$'/6())./(=$.)*)&.<:$&(+$+)A)06'4)(-$56.$-:)$<.)&;6($65$$()@$/(+,*-./)*C
47
&(+$-6$@6.D$56.$-:)$/4'.6A)4)(-$$65$/(+,*-./&0$<64');;A)()**E
48
Source: Tetsuo Nozawa Nikkei Electronics Asia -- July 2008,
Organic push-pull sensitizers are catching up
49
50
D&'&A Dyes gaining red response
A: D-204 (n=1)
C: D-205 (n=2)
51
In collaboration with Peng Wang CAS Changchun
Red: D-204 , blue: D205
52
Ongoing research
TiO2 Dye OMeTAD
Glass
(or other hole
conductor)
e-
e-
Gold
h+
Light
Hole Conductor
Advanced nanostructures
Light induced charge separation
new sensitizers
new redox mediators
Solid state heterojunctions
Quantum dot cells
redox active ionic liquids
tandem devices
SnO2
•
•
•
•
•
•
•
•
Glass transition temperature: 121 °C
Melting Point: 246 °C
Work function: 4.9 eV
(CV in CH2Cl2. 110 mV vs. Fc/Fc+)
Absorption maximum neutral:
(max=372 nm ()=40100)
Radical cation:
(max=511 nm ()=37400)
Mobility ~ 1 x10-4 V/cm
53
Dynamic Competition
electron
injection
dye
regeneration
electron
interfacial
transport recombination
HOOC
CN
Electron diffusion length
Ln =
Dn
"
S
$n
$n: electron lifetime
Dn: electron diffusion coefficient
55
!
N
S
Competition "
loss mechanism:
interfacial
recombination
54
JK72
time [s]
electron transport
Spiro-OMeTAD
Solid State Dye Sensitized PV cell
56
Gain of red response in photocurrent by
formation of JK72
Influencedye
of TiO2aggregates
on IPCE
60
50
JK72(A)
JK72(D)
IPCE [%]
40
JK73(A)
JK73(D)
30
JK74(A)
JK74(D)
20
JK75(A)
JK75(D)
10
0
400
500
600
700
wavelength [nm]
800
57
Ongoing research
•
•
•
•
•
•
•
•
58
Quantum dot sensitizers for mesoscopic solar cells
Advanced nanostructures
Light induced charge separation
new sensitizers
new redox mediators
Solid state heterojunctions
Quantum dot cells
redox active ionic liquids
tandem devices
59
Quantum
dot
TiO2
100 nm
The electrons ad holes move in different phases and are separated by a phase boundary
60
Quantum dot sensitizers reach 60 percent IPCE
Ongoing research
80
PbS cell (cobalt electrolyte)
CdS cell (cobalt electrolyte)
60
PbS
IPCE (%)
IPCE (%)
60
CdS
40
40
20
20
0
400
0
400
450
500
550
600
Wavelength (nm)
Data : Dr. Hy-Yoong Lee
650
700
500
600
700
800
900
Wavelength (nm)
61
Ionic Liquids (Ils )have attractive features
•
•
•
•
•
Advanced nanostructures
Light induced charge separation
new sensitizers
new redox mediators
Solid state heterojunctions
Quantum dot cells
redox active ionic liquids
tandem devices
•
•
•
•
•
•
•
•
Thermal Stability;
Non Flammability;
High Ionic Conductivity;
Negligible Vapor Pressure;
Wide Electrochemical Window;
62
The light absorption-viscosity dilemma
Mesoporous photoanode
counterelectrode
I-
light
I3-
Solid polymer/IL gels are formed by the addition of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF–HFP)
Wang, P; Zakeeruddin, S. M.; Exnar, I.; Graetzel, M..
High efficiency dye-sensitized nanocrystalline solar cells
based on ionic liquid polymer gel electrolyte.
Chemical Communications (Cambridge, United Kingdom) 2002, 24, 2972-2973.
63
Due the high viscosity of the ionic liquids, diffusion limitation
of the photocurrent is expected under full sunlight.
64 M. Grätzel,
N. Papageorgiou, Y. Athanassov, M. Armand, P. Bonhôte, H. Pettersson, A. Azam,
J. Electrochem. Soc. 1996, 143, 3099&3108
N
N
N
+
I-
N
880 cP
NCS
N
N
[(CF3SO2)2N]
21 cP
N
N
28 cP
N
N(CN)2
18 cP
N
C(CN)3
N
N
17 cP
•
•
•
•
B(CN)4
20 cP
New mixed ionic liquid (three compounds) with high conductivity
Record conversion efficiency of 8.2%
Excellent stability (1000h light soaking test)
An interesting option for flexible cells
65
66
Ionic liquids
Tri-iodide transport
Fluidity (temp. dependent) vs. diffusion coefficient for I3-
PMII
EMII
1-propyl-3-methylimidazolium iodide
1-ethyl-3-methylimidazolium iodide
I
N
Stokes-Einstein relation
for hydrodynamic I3radius of 2.1Å
I
N
N
N
DMII
AMII
1,3-dimethylimidazolium iodide
1-allyl-3-methylimidazolium iodide
N
I
N
Melts with high iodide
concentration
! Grotthus transport?
I
N
Melt with low iodide
concentration
N
EMITCB
1-ethyl-3-methylimidazolium tetracyanoborate
67
I3
-
I
-
I
-
I3
-
Grotthus bond exchange:
enhanced diffusion coefficent
68
Dye sensitized solar cells outperform silicon at lower light levels
Dye sensitized solar cells deliver high overall performance
Effect of temperature on module conversion efficiency
69
The DSC can meet future customer demands and needs
70
Source: Tetsuo Nozawa, Nikkei Electronics Asia (July 2008), Data from Sony
House of the Future from Inside
Emerging and new applications call for:
•Ease of building integration
•transparency and multicolor option (for power window application) *
•flexibility
•light weight
•Low production cost
•feedstock availability to reach terrawatt scale
•Short energy pay back time (< 1 year)
•enhanced performance under real outdoor conditions
•Bifacial cells capture light from all angles
•Tandem cell configurations boost efficiency over 15 %
•Outperforms competitors for indoor applications
* Unique selling proposition
71
HOUSE
OF THE
FUTURE
73
74
Various colours in a series-connected dye solar cell module
75
Courtesy Dr. Andreas Hinsch, FHI, ISE Freiburg Germany
Courtesy Dr. Nam Gyu Park KIST
transparent, colorful, beautiful
Transparency: due to nano-sized (~20 nm) TiO2 particle film
Color: due to visible light absorption by dye
77
* DSC costs lower than Si solar cell; 1/4 -1/5 of Si solar cell
green solar cells mimic the green leave
80%
60
IPCE [%]
WMC 273
40
N
N
Zn
N
N
20
HO2 C
0
400
500
CO2 H
600
Wavelength [nm]
700
800m
In collaboration with Professor David Officer, Univ.Wollongon,Australia
Artificial Plant with Leaves exhibited at EXPO 2005
Butterflies flutter and
stop using!the
electricity generated by
this plant under the
intermittent lightings.
Leaf-shaped transparent DSC
with four colors
SC!DEVELOPMENT!GROUP,!ENERGY! DEVELOPMENT !DEPT.
AISIN SEIKI CO.,LTD.
#
th!
82
SEPTEMBER. 2006
Scale-up and production
A.Kay, M.Graetzel, Low cost PV modules
based on dye sensitized nanocrystalline
titanium dioxide and carbon powder.
Solar En. Mat. Solar Cells 1996), 44(1), 99- 17.
83
The first monolithic in series connected DSC modules showed a
validated standard AM 1.5 G conversion efficiency of 5.3 %
Real Outdoor Test of DSC Modules!
Module Unit
Series connected
64 DSC cells
Outdoor Test
Kariya City at lat. 35°10’N,
Asimuthal angle: 0°
Facing due south, Tilted at 30°
The Toyota Dream House
DSC
made by
AISIN -SEIKI
!"#$%&'()*+
"#$%&'%()*
G24I builds 120 MeW capacity plant for flexible DSC production in Wales
Founders of G24I: Ed Stevenson and Robert Hertzberg (64th speaker of
Californian State Assembly)
The G24I plant in Cardiff has started production on June 21 (solstice),2007
The first G24I product is a light weight flexible power supply for mobile
telephones
95
96
97
World first solar car,1912 Baker Electric Brougham
10 640 solar cells
99
Electric car: Tesla Roadster
AC induction motor, 200 kW, 35 kg,
6831 Li-cells 18650 (Ø 18 x 65 mm), 50 kWh, 450 kg
range 400 km per charge, acceleration to 100 km/h in 4 s
price $ 92.000
100
http://www.teslamotors.com
The First Solar Car Driven by DSSC
101
!"#$%&&#"'()*+,-.'*/0.1123"#00%45-6%745#*#234-)48019,&)
102