Dye-Sensitized
Dye
Sensitized Solar Cells with
Nanotechnologies
Li
Liyuan
H
Han
Advanced Photovoltaics Center
National Institute for Materials Science （NIMS)
Japan Nano 2009
Expectations to PV market
World markket scale ((MW)
W
12,000
10,000
10,000
8,000
6,150
6 000
6,000
3,950
4,000
2,446
1,870
2,000
1,064
170
256
400
605
2000
2001
2002
2003
1,382
0
2004
2005
2006
2007
2008
2009
2010
Source： IEA PVPS 2007
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Scenario for improving the economic efficiency of
PV p
power ggeneration
PV2030
V 030
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Types of solar cells
Single crystalline
Bulk
Multi crystalline
Silicon
Thin film
Si uc-Si
Si）
（a-Si,
GaAs
Solar cells
Compound
CdS CdT C l G S 2
CdS,CdTe,CulnGaSe
Dye-sensitized
New materials
Thin film (Polymer SC)
Quantum Dot
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Advanced Photovoltaics Center
Dye sensitized
OPV
QD
Compound
Si thin film
Interband
Light
Light
TCO
TiO2
Dye
Electrolyte
CE
I 3-
I-
ee-
TCO
PCBM
e
-
e-
Polymer
h+
e
-
h+
h+
Multi exiton
CE
p
i
n
p
i
Glass
SnO２
a‐Si
uc‐Si
n
ZnO Ag
Materials Fundamental Simulation
Materials, Fundamental, Simulation
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Dye Sensitized solar cell
TCO
TiO2
Electrolyte
Dye
(I-/I3-）
CE
Light
II 3-
External circuit
electron
Merit
1) Low manufacture cost
・No
N vacuum process
・Cheap materials
2)) Colorful
3) Flexibility
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Features of dye-sensitized solar cells - 1
Device Concept: “Artificial Photosynthesis”
TCO
-4.0
TiO2
導電帯e-
Electrolyte
Dye
S*
LHS
Fermi Level
Vmax
e-
-4.5
-5.0
-5.5
55
CE
e-
S
Red
Ox
e-
RC
LHS
The principles of DSCs are different from those that conventional solar cells,
are more similar to plant photosynthesis, as light absorption (dye) and carrier
transportations
p
in both TiO2 and electrolyte
y in DSCs occur separately.
p
y
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Equivalent Circuits of DSC
1F
ＤＳＣ
C3
R3
Isc
Z2
2 F
C1
R1
I
Rh
Rsh
Main origin
Element
Ｒｈ
Resistance of TCO
Series
Resistance
Ｒｓ
Ｒ１
Electrolyte/CE
Ｒ３
Diffusion in the
El t l t
Electrolyte
Diode
Ｒ２
TiO2/Dye/Electrolyte
The experience & knowledge of Si solar cells are useful to DSCs
In the DC condition
Ｓｉ Ｓｏｌａｒ Ｃｅｌｌｓ
Isc
Rs = Rh + R1 + R3
Rs I
Rsh
V
Equivalent circuit of DSC is similar to
th t off Si solar
that
l cells
ll when
h working
ki in
i DC
condition.
L Han et el,
L.
el Appl.
Appl Phys.
Phys Lett.
Lett 84,
84 2433(2004)
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Improvement
p
of efficiency
y of
dye-sensitized solar cells
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Approaches for improving efficiency
  Jsc  Voc  FF
Curre
ent Densitty (mA/cm
m2)
20
J
Jsc
15
1) Jsc
FF
2) Voc
10
Voc : 0.693 V
Jsc : 18.9 mA/cm2
FF : 0.686
 : 9.0 %
5
3) FF
Voc
0
0
0.2
0.4
0.6
0.8
Voltage (V)
Typical I-V curve of the cell
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Improvement of Jsc
Enhancement of the light harvesting efficiency
J SC   qF ( )(1  r ( )) IPCE ( )d
70
1.2
60
1
50
0.8
40
0.6
30
0.4
20
0.2
10
0
0
300
500
700
900
Wavelength (nm)
1100
(1) Improvement of IR-response by
development of new dyes
h
Cou
unter Elecctrode
1.4
Electrolytte
E
80
Trransparen
nt
Cond
ductive G
Glass
energy[mW/(sscm*10nm)]
1.6
Nanocrrystalline TiO2 film
m
90
energy[mW/(scm*10nm)]
IPCE (%)
IPCE
E (%)
1.8
h
(2) Increase of effective light path length
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(1) Improvement of IR-response
Photocurrentby
action
spectra of Ru
Ru-based
sensitizers
development
of based
new dyes
80
Jsc: 21mA/cm2
HO
70
OC
N
HOOC
NCS
NC
S
COO-TBA+
HOOC
40
N
N
HOOC
30
N
NCS
Black dye
Ru
N
NCS
COO-TBA+
N719
20
0
400
Ru
N
50
10
N
NCS
HO
OC
IPCE (%)
60
Jsc: 17mA/cm2
500
600
700
800
900
Wavelength / nm
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Photovoltaic Properties of Fph-tfac sensitizer
IPCE = 82%
80
IPC
CE / %
F
60
40
O
TBAO
20
0
F F
F
O O
OTBA
N
Ru
O
N
N N
C
S
OH
O
Jsc = 22.0 mA cm-2
Voc = 0.59
0 59 V
F h tf
Fph-tfac
400
500 600 700 800
Wavelength / nm
900
13
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STM images of dye/TiO2 surface
Low Jsc
High Jsc
Absorption of dye
y without DCA
Absorption of dye
y with DCA
[001]
40 × 40 nm2
40 × 40 nm2
Aggregation
Isolated
LANGMUIR, 24, 8056 (2008)
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(2) Increase of effective light path length in TiO2
External quantum efficiency (QE) spectrum
1
L
Optical path length = L
Scattered TiO2 film
Externa
al%)QE
IPCE (%
Transparent TiO2 film
0.8
TCO
Scattered
CEfilm
TiO2 Electrolyte
0.6
0.4
Transparent film
02
0.2
0
400
600
800
Wavelength (nm)
J SC   qF ( )(1  r ( )) IPCE ( ) d
Effective path length >> L
Light scattering effect
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1000
How to estimate the light scattering effect ?
T0
TCO
TCO
Ti
H
Ti
Tｊ
Haze of TCO substrates has
been used as a useful index
of light trapping effects in aa
Si solar cells.
A. Loffl et al., EUPVSEC-14, (1998) 2089.
Incident light
T
i
T0
i
 (T  T )
i
j
TiO2
i j
i,
Tｊ
Ti
Tj
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Effect of haze on IPCE and Jsc
100
90
80
70
60
50
40
30
20
10
0
Curre
ent densityy (mA/cm2
External
QE
IPCEQ
(%)(%)
22
Haze 76% @ 800nm
Haze 60%
Haze 53%
H
Haze 36%
400
600
800
Wavelength (nm)
1000
21
20
19
18
17
20
40
60
Haze factor @ 800nm (%)
Y. Chiba et al. Jpn. J. Appl. Phys. 45 L638 (2006)
Haze of TiO2 is a useful index for improvement of Jsc.
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80
2) Improvement of Voc
Suppression of recombination
TCO
TiO2 Electrolyte CE
I-
I3-
e- Injection
Regeneration
e-
I-
I3-
ee-
IElectrolyte
Recombination
TiO2
  q(V  IRS )   V  IRS
I  I ph  I 0 exp
  1 
RSh
 
  nkT
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Improvement of Voc
Effect of TBP
25
COOH
with TBP
SCN
SCN Ru
Jsc (mA/cm
J
m2)
20
Ru
COO-
SCN
e-
15
without TBP
10
5
COO-
CH3
H 3C C
CH3
N
TiO2
0
0
0.2
0.4
0.6
Voltage (V)
TBP
Voc was improved by absorption of TBP
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0.8
3) Improvement
Improvement
p
of of
FF FF
L．Han et el, Appl. Phys. Lett. 84, 2433 (2004)
RCE RELE RTCO I
TCO
TiO2
Electrolyte CE
I3-
Isc
Rsh
I-
S i Resistance:
Series
R i t
Rs
Rs = RCE + RELE + RTCO
Reductions of RCE , RELE and RTCO were investigated
investigated.
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Elevating of Voc without decrease of Jsc
20
18
Currennt Densityy (mA/cm
m2)
16
14
12
10
8
No additive
Adding of THF
6
4
2
0
0
02
0.2
04
0.4
06
0.6
08
0.8
Voltage (V)
A. Fukui, L. Han et al., Sol. Energy Mater. Sol. Cells , 90, 649 (2006).
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Reduction of RCE
RCE (cm2)
4
3 TCO
Roughness factor
RF = Stotal / Sproj
y
CE
TiO2 Electrolyte
Stotal
2
I3-
1
I-
0
0.85
0.9
0.95
1/RF
RF: increase
1
1.05
Sproj
→ measured by AFM
RCE : decrease
RCE decreased by using high roughness factor of CE.
L.Han et al. Appl. Phys. Lett. 86 213501-3 (2005)
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Reduction of RELE
Thickness
TCO
6
TiO2
Electrolyte CE
2
RELE (cm
m)
8
4
I3-
2
I-
0.7 cm2
0
0
20
40
60
80
Thickness of electrolyte layer (m)
Thickness: decrease
RELE : decrease
RELE ≧ 0.7 cm2
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1
0.5
0
optimize
sheet
resistance
and
transmittance
of TCO
Rh
RTCO
Increase
surface
roughness
of CE
R1
R
CE
Decrease
thickness
of
electrolyte
layer
R3
RELE
Afte
er optimizzation
3
2.5
2
1.5
Befo
ore optim
mization
n
Resisttance (cm
R
m2)
Optimization of series resistance of DSC
Total
FF : 0.69 → 0.72
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Results
Jsc : 18.9 mA/cm2
Jsc : 20.9 mA/cm2
Voc : 0.693 V
Voc : 0.73 V
FF : 0.686
F.F. : 0.72
The I-V curve of the DSC was independently measured
by the public test center (AIST, JAPAN).
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The Highest Efficiency for single cell
Effi : 11.1%
Jsc : 20.9 mA/cm2
Voc : 0.736 V
FF : 0.722
0 722
(AIST: National Institute of Advanced Industrial Science and Technology)
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How to further improve the efficiency ?
Efficiency of DSC > 11% in small cell
Cell Effi.(%)
Practical module
Effi (%)
Effi.
Single crystal Si
24.7
16-18
Polyy crystal
y
Si
17.2
12-16
Thin film Si
14
12
1) Improvement of cell structure
2) Understanding of mechanism
3) Development of new materials
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1) Improvement of cell structure
100
Absorbance of TCO
90
80
Back Contact Dye-sensitized Solar Cells
(BCDSCs)
70
Back contact electrode（BCE)
counter electrode (CE)
60
C
Counter
t electrode(CE)
l t d (CE)
Electrolyte Electrolyte
40
TiO2
30
Dye
TCO
T%
50
20
h
10
0
200
400
TiO2
Glass
Merit
・Low Cost
800
1000
・High Transmittance
600
Wavelength(nm)
hν
=7.1%
1200
 : 8.9%
Chem. Mater., Chemistry of Materials, 20, 4974 (2008)
J. Appl. Phys., 104, 064307 (2008)
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Thank you for your kind attention
Acknowledgements
A part of this work was carried out in SHARP Corp. I acknowledge
the colleagues.
g
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