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Dye-Sensitized Solar Cell
(DSSC)
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M. Grtzel, Nature (2001)
Solar Cell Changwoo
Photoelectrochemical Cells (Solar Cell and Water Cleavage)
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Electrode Potential (E0) vs. Vacuum Potential (eV)
Solar Cell/Semiconductor Chunjoong
M. Grtzel, Nature (2001)
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Dye-Sensitized Solar Cells (DSSCs)
Prof. Kyo Han Ahns group (POSTECH)
http://www.postech.ac.kr/chem/mras
Solar Cell Chunjoong
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Dye-Sensitized Solar Cell
1. Dye electrons are excited by solar energy absorption.
2. They are injected into the conduction band of TiO2.
3. Get to counter-electrode (cathode) through the external circuit.
4. : Redox regeneration at the counter-electrode (reduction).
5. : Dye regeneration reaction (oxidation).
6. Potential used for external work:
--
3 I32I e
e2II3 -3
-
redoxFext VEV
Michael Grtzel (Ecole Polytechnique)Inorg. Chem. 44, 6841 (2005)
Solar Cell Hongsik
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Exciton Binding Energy
P3HT: Poly(3-hexylthiophene)
Dye-Sensitized Solar Cells
Organic Solar Cell
Jinsang Kims group (University of Michigan)
Adv. Funct. Mater. (2012)
Carsten Deibels group (Julius-Maximilians-University of
Wrzburg)Phys. Rev. B 81 085202 (2010)
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Dye-Sensitized Solar Cell
< Introduction >
Dye-sensitized solar cells (DSSC) were invented by Michael Grtzel and Brian O'Regan
[Nature, 353, 737 (1991)] .
The DSSC is formed by a combination of organic and inorganic components that could be
produced at a low cost.
The DSSC offers the prospect of a cheap and versatile technology for large scale production of
solar cells.
The basic element of a DSSC is a nanostructured material, an assembly ofTiO2 nanoparticles
about 20 nm diameter, well connected to their neighbors.
TiO2 is the preferred material since its surface induces highly effective electron transfer.
However, TiO2 only absorbs a small fraction of the solar photons (those in the UV).
Molecular sensitizers (dye molecules) attached to the semiconductor surface, are used to harvest agreat portion of the solar light.
The main dye molecules consist on one Ru metal atom and a large organic structure that provides
the required properties (wide absorption range, fast electron injection, and stability).
Solar Cell Hongsik
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Dye-Sensitized Solar Cell
Homepage in Grtzels group
Solar Cell Jongmin
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Silicon Solar Cell Dye Sensitized Solar Cell
- Costly fabrication process
- Expensive raw materials
- Toxic gases
- Easy to be fabricated
- Low cost
- Friendly to the environment
Solar Cell Hongsik
The Benefits of DSSC
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M. Grtzels group, Nature (1991)
Solar Cell Changwoo
Dye-Sensitized Solar Cell (DSSC)
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M. Grtzels group,
J. Am. Ceram. Soc.
(1997)
hydrothermal method
~20 nm size, anatase phase
~10 m thickness for efficientphoton absorption
Solar Cell Changwoo
TiO2 Nanoparticles for DSSC
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TiO2 Phase Dependency for DSSC
Rutile phase DSSC , anatase phase . .
N.-G. Park et al.,J. Phys. Chem. B(2000)
Rutile phase nanoparticle 20 nm 80 nm rod , spherical anatase nanoparticle20 nm .
rutile nanoparticle anatase nanoparticle dye , photocurrent .
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proton detachment chemical bonding with TiO2
M. Grtzel, Inorganic Chemistry (2005)
Solar Cell Changwoo
Dyes for DSSC
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Chemical Structure of N719
dye
Solar Cell Changwoo
Dyes for DSSC (N719)
M. Grtzel, Inorganic Chemistry (2005)
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Chemical Structure of N719 dye
Ti
bonding . dye adsorption to TiO2
cf) Chemical Structure of N3 dye
Bu4N: tetrabutylammonium
Solar Cell Changwoo
Dyes for DSSC (N719)
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Optimizing Dyes for DSSC
Organometallic dye: charge separation
HOMOLUMO
N3
Anchoring
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anatase (001) anatase (101) the most stable plane
H. G. Yang et al.Nature 453, 638 (2008)
A. SelloniNat. Mater. 7, 613 (2008)
Anatase TiO2 chemical adsorption , Ti bonding .
Solar Cell Changwoo
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dye
anatase (101)
M. Graetzels groupJPCB (2003)
, dye-coated TiO2 film FT-IR , TiO2 Ti dye chemical bonding .
Ti Ti
N719 dye
Solar Cell Changwoo
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3-D Structure of Ru complex
Solar Cell Changwoo
Dyes for DSSC (N719)
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good photon absorption,good charge separation
IPCE(%)
IPCE: Incident Photon to Current Conversion Efficiency
M. Grtzel, Inorganic Chemistry (2005)
Solar Cell Changwoo
Operation of DSSC
_______
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Dye-Sensitized Photovoltaic Cells
M. Grtzel, Inorganic Chemistry (2005)
__________________________________________________
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10 electrons per TiO2particle under AM1.5. More than 90% of electrons in TiO2 are trapped and
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Open-Circuit Potential
The two main determinants ofVoc are the recombination rate constant and the TiO2 conduction band
edge offset relative to the I-/I3- redox potential.
Short-Circuit Current
This efficiency depends upon the diffusion constant (mobility) and recombination rate of the electrons
in TiO2
.
Brian C. ORegan,s group,Account of Chemical Research (2009).
Solar Cell Chohui
Kinetic and Energetic Paradigms
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Brian C. ORegan,s group,
Account of Chemical Research (2009).
Solar Cell Chohui
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Ti deposition by sputtering (500 nm)
Anodizing Ti film at constantpotential, 12 V. (HF condition)
Pore diameter: 46 nmWall thickness: 17 nmLength: 360 nm
C. A. Grimess group,
Nano Letters (2006)
Solar Cell Changwoo
TiO2 Nanotubes for DSSC
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= 2.9%
360 nm
Solar Cell Changwoo
TiO2 Nanotubes for DSSC
C. A. Grimess group,
Nano Letters (2006)
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Solutions
Core-shell Structure
wide bandgap materials
Surface Treatment
Ar or O2 plasma, TiCl4 treatment
Nanoscale Coating on the TCO
Solar Cell Changwoo
TiO2-Electrode / Electrolyte Interface Problem
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CaCO3: basic than TiO2 carboxyl group of
dye can adsorb more easily
CaCO3 is insulator (band gap: 6 eV)
thick shell of CaCO3 block electrontransfer from dye to TiO2
K. Hongs group,
Sol. Energy Mater. Sol. Cells (2006)
CaCO3-coated TiO2 nanoparticle (core-shell)
Solar Cell Changwoo
CaCO3-Coated TiO2 Nanoparticles
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CaCO3-Coated TiO2 Nanoparticles
M O C d TiO N i l
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MgO-coated TiO2 nanoparticle (nanoporous structure)
K. Hongs group,
Langmuir (2005)
Jsc enhancement: increase of the dyeadsorption
Voc enhancement: suppression of thecharge recombination
Solar Cell Changwoo
MgO-Coated TiO2 Nanoparticles
M O C t d TiO N ti l
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K. Hongs group,
Langmuir (2005)
Solar Cell Changwoo
MgO-Coated TiO2 Nanoparticles
M t l O id C ti TiO N ti l
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Effect of TiO2 Coating Layer
1. The insulating layers with wide band gap and high conduction band edge can retard the
back transfer of electrons from TiO2 to the electrolytes or dye molecules (decrease trap state).
2. The enhanced dye adsorption by the oxide layers can improve the cell performance
The coated surface favors the dye adsorption through the carboxylic acid group of the dye.
Coating Layer
Sujuan Wu et al. (Wuhan University)
Nanotechnology 19, 215704 (2008)
Solar Cell Hongsik
Metal-Oxide Coating on TiO2 Nanoparticles
MgO Coated TiO Nanoparticles
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34http://bp.snu.ac.krDye adsorption increase with sputtering time
Resistance at the TiO2/dye/electrolyte increase with
sputtering time
Excessively thick MgO layer beyond the tunneling distance plays a negative role in the photoelectron conversion process.
Sujuan Wu et al. (Wuhan University)
Nanotechnology 19, 215704 (2008)
Solar Cell Hongsik
MgO-Coated TiO2 Nanoparticles
MgO Coated TiO Nanoparticles
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MgO-Coated TiO2 Nanoparticles
FTO / Blocking La er / Poro s TiO
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Porous interfaces between FTO substrate and TiO2 layers can be electron recombination site,
i.e., electron leakage sites exist especially when solid or highly viscous redox species such as
ionic liquid iodides once infiltrate into the interfaces.
Blocking layer can suppress back electron transfer
from FTO to electrolytes.
Introduction
Shozo Yanagida Group (Osaka University)
J. Phys. Chem. C 111, 8092 (2007)
Solar Cell Hongsik
FTO / Blocking Layer / Porous TiO2
FTO / Nb O / Porous TiO
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Shozo Yanagida Group (Osaka University)
J. Phys. Chem. C 111, 8092 (2007)
Sputtering method has the merits of good
reproducibility, of homogeneous coverage and
suitability for the large scale production.
Excessively thick blocking layers beyond
tunneling distance would play a negative role in the
photoelectron conversion process.
Solar Cell Hongsik
FTO / Nb2O5 / Porous TiO2
FTO / Nb2O5 / Porous TiO2
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FTO / Nb2O5 / Porous TiO2
FTO / TiO2 Thin-Film Layer / TiO2 Nanoparticles
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FTO/TiO2 compact layer/TiO2 Efficiency (1 Sun)With compact layer : 1.6%Without compact layer : 1.0 %
Michael Grtzel et al. (Ecole Polytechnique)
Nano Lett. Vol. 8, No. 4, (2008)
Efficiency (1/10 Sun)
With compact layer : 1.6%Without compact layer : 0.6 %
Recombination rate decrease between FTO / Electrolyte
JSC , VOC increase
Solar Cell Hongsik
FTO / TiO2 Thin Film Layer / TiO2 Nanoparticles
FTO / TiO2 Thin-Film Layer / TiO2 Nanoparticles
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FTO / TiO2 Thin Film Layer / TiO2 Nanoparticles
New Methods for TiO2 Nanostructures
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New Methods for TiO2 Nanostructures
Inverse-Opal Ti Anodization
500 nm
100 nm
~ 3.5%
~ 4.2%
Hyunjung Lees Group
(KIST)
Adv. Funct. Mater(2009)
P. Schmukis Group
(Univ. Erlangen-Nuremberg, Germany)
Angew. Chem. Int. Ed. (2009)
New Methods for the TiO2 Nanostructures
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2
Hyunjung Lees Group
(KIST)
Adv. Funct. Mater(2009)
P. Schmukis Group
(Univ. Erlangen-Nuremberg, Germany)
Angew. Chem. Int. Ed. (2009)
Aggregates/Nanocrystallites Mixed TiO2 DSSCs
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Guozhong Caos group,Electrochimica Acta, (2011).
Aggregates/Nanocrystallites Mixed TiO2 DSSCs
Solar Cell Chohui
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Guozhong Caos group,Electrochimica Acta (2011).
Solar Cell Chohui
I- Free Electrolyte
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I Free Electrolyte
M. Graetzels Group
Nat. Chem. (2010)
Licheng Suns Group
(Dalian Univ. of Tech.)
Angew. Chem. Int. Ed. (2010)
conventional I-/I3-
electrolyte
new electrolyte
I- Free Electrolyte
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M. Grtzels Group
Science (2011)
Licheng Suns Group
(Dalian Univ. of Tech.)
Angew. Chem. Int. Ed.
(2010)
_____________________________
______
_________________________
- 2012-03-07
DSSC Exceeding 12% in Efficiency
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YD2-o-C8 dye
M. Grtzels GroupScience (2011)
DSSC Exceeding 12% in Efficiency
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M. Grtzels Group
Science (2011)
Characteristics of ZnO-Based DSSCs
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Advantages
Single-crystal ZnO has carrier mobility of 115 - 155 cm2/Vs, which is 2 orders of magnitude
higher than that of TiO2 (2 - 4 cm2/Vs).
Easy to fabricate various nanostructures.
C. M. L. Wus group,
J. Phys. Chem. C(2010).K.-C. Hos group,
Energy Environ. Sci. (2011).
S. Fujiharas group,
J. Electrochem. Soc. (2011).
Nanoflower Nanodisk Nanosheet
NanowireNanotube
J. S. Bendalls group,Energy Environ. Sci. (2011). W.-G. Diaus group,Energy Environ. Sci. (2011).
Solar Cell Chohui
Characteristics of ZnO-Based DSSCs
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High acidity of the ruthenium-based dye can lead to dissolution of ZnO.
Precipitation of dissolved Zn2+ ions and dye molecules is attached on the surface.
G. Caos group,J. Phys. Chem. C(2007).
G. Caos group,Adv. Mater. (2009).
Formation of Zn2+
/Dye Aggregates
Without Dye With Dye for 12 h
200 nm 200 nm
Disadvantages
G. Caos group,J. Phys. Chem. C(2007).
Solar Cell Chohui
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G. Caos group,J. Phys. Chem. C(2007).
Solar Cell Chohui
____________
ZnO Aggregates DSSCs
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Guozhong Caos group,Angew. Chem. Int. Ed. (2008).
Desired specific surface area for dye loading + light scattering
= High conversion efficiency in dye-sensitized solar cells
Solar Cell Chohui
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Guozhong Caos group,Angew. Chem. Int. Ed. (2008).
Solar Cell Chohui
Effect of an Ultrathin TiO2 Layer
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-
-
Guozhong Caos group,Adv. Mater. (2010).
Solar Cell Chohui
_______
_
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Guozhong Caos group,Adv. Mater. (2010).
Solar Cell Chohui
MgO- or ZrO2- Coated ZnO Nanowire DSSCs
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N. O. V. Plank,J. Phys. Chem. C(2009).
Solar Cell Chohui
_
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N. O. V. Plank,J. Phys. Chem. C(2009).
Solar Cell Chohui
Lithium Ions on ZnO DSSCs
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Guozhong Caos group, Chem. Mater. (2010).
Solar Cell Chohui
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Guozhong Caos group, Chem. Mater. (2010).
Solar Cell Chohui
____________________
Surface-Plasmon Resonance in Metal Nanoparticles
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Oscillation of Free Electrons in
Metal Nanoparticles
[L. M. Liz-Marzan,Langmuir(2006)]
Unique Optical Properties of Au
Surface-Plasmon Resonance in Metal Nanoparticles
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L. M. Liz-Marzn
(Univ. de Vigo, Spain)
Langmuir(2006)
Field Enhancement vs. Scattering
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I: Light Intensity
E: Amplitude ofE-Field
Both field-enhancement and scattering effects can contribute to the
improvement of photovoltaic properties.
[H. A. Atwateret al.,Nat. Mater. (2010)]
Field Enhancement Scattering
Metal Contact
Active
Material
h
h
Field Enhancement vs. Scattering
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H. Atwateret al.
(Caltech)
Nat. Mater. (2010)
Electric-Field Enhancement by Surface-Plasmon Resonance
H
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-4 -3 -2 -1 0 1 2 3 4-4
-3
-2
-1
0
1
2
3
4
Au
Relative Position (r/a)
R
elativePosition(
r/a)
0.10
0.20
0.50
1.0
1.5
2.0
3.0
5.0
10
20
50
Au
E0
H0
h
at hv = 550 nm
Field Enhancement Light Absorption Photocurrent
|E|2
Solar Cell Changwoo
E-Field Enhancement by One Metal Nanoparticle
K T b (U i f T k )
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inside the sphere outside the sphere
K. Tanabe (Univ. of Tokyo)
JPCC(2008)
Ag NP in air
(at = 0)
(at any r and )
(Boundary Condition)
in water, at r=a
E-Field Enhancement by Metal Nanoparticle
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K. Tanabe (Univ. of Tokyo)
JPCC(2008)
Metal Induced Dye-Sensitized Solar Cells (DSSCs)
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e-e-
Metal-Oxide Nanoparticles
TCO TCO
Pt
Electrolyte
Dye
Au-SiO2 Core-Shell Nanoparticle for DSSC
SiO2-Ag Core-Shell Nanoparticle for DSSC
[H. J. Snaiths group,Nano Letters (2011)]
[Jung-Kun Lees group,Adv. Energy Mater. (2011)]
SiO2
Au
Solar Cell Changwoo
Metal Induced Dye-Sensitized Solar Cells (DSSCs)
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Henry J. Snaiths group,
(Univ. of Oxford)
Nano Letters (2011)
Metal Induced Dye-Sensitized Solar Cells (DSSCs)
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Jung-Kun Lees group
(Univ. of Pittsburgh)
Adv. Energy Mater. (2011)
___
____________
DSSC + Surface Plasmon Resonance
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Ag NP deposition TiO2 ALD Dye adsorption
Absorption Difference Spectra (Ag + TiO2 + dye) (Ag + TiO2)
J. T. Hupps group,
(Northwestern Univ.)
JACS(2009)
dyes on theglass substrate
Ag evaporation onglass substrate dye solution drop
TiO2 thickness increasedye amount
increase
M. Iharas group, (Univ. of Tokyo)
JPCB (1997)
Ag enhance the absorption rate of dye.
DSSC + Surface Plasmon Resonance
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J. T. Hupps group,
(Northwestern Univ.)
JACS(2009)
DSSC + Surface Plasmon Resonance
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M. Iharas group, (Univ. of Tokyo)JPCB (1997)
Metal Nanosize Effect
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The size of metal nanoparticles used in theprevious researches on DSSCs was limited to 10 - 30 nm.
[Y. A. Akimovs group,Plasmonics (2009)]
Theory (with One Nanoparticle)
[G. Chumanovs group,J. Phys. Chem. B (2004)]
Experiments
(nm) (nm)
Total
Absorption
Scattering
Inte
nsity
Total
Scattering
Absorption
Absorption
Absorption
2r= 2r=
rAg = 50 nm
rAg = 30 nm
rAg = 10 nm
Scattering
Scattering
Absorption
Backward
Scattering
Solar Cell Changwoo
Metal Nanosize Effect
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Y. A. Akimovs group,
(Institute of High Performance Computing, Singapore)
Plasmonics (2009)
Metal Nanosize Effect
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G. Chumanovs group,
(Clemson Univ., U.S.A.)
JPCB (2004)
Absorptance + Reflectance + Transmittance = 1
Extinction = -log T
Scattering vs. Absorption by One Metal Nanoparticle
90 Absorption (or Scattering) Efficiency
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500 600 700 8000
10
20
30
4050
60
70
80
90
Ag (20 nm)
Ag (100 nm)
Au (20 nm)
Sc
atteringEfficiency(%)
Wavelength (nm)
Au (100 nm)
Absorption (or Scattering) Efficiency
Cabs + Csca
Cabs (or Csca)=
m: dielectric function of metal
d: dielectric function of dielectric material
V: volume of metal nanoparticle
Higher imaginary part of dielectric function of Au
Dominant absorption-nature of Au Nanoparticle
d = 2 + 0i (assumption)
Solar Cell Changwoo
Quenching by Surface Plasmon vs. DSSC Kinetics
Exciton Quenching by Metal Kinetic Parameters in DSSC
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Exciton
metal: over 100 picosecond e-h separation: sub-picosecond
metal >> e-h separation Quenching reaction by Au is negligible in DSSC.
M. Grtzels group,Inorg. Chem. (2005)
TiO2 Dye
A. O. Govorov et al.Nano Lett. (2007)
AuAu Diameter
:12 nmQuinone
MoleculeQuinone
Molecule
Solar Cell Changwoo
Exciton Quenching by Metal Nanoparticles
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dielectric function of metaldipole moment of semiconductor
A. O. Govorovs group (Ohio Univ.)Nano Lett. (2006)
Exciton Quenching by Metal Nanoparticles
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A. O. Govorovs group (Ohio Univ.)
Nano Lett. (2006)
Molecules near the Metal Nanoparticles
Field Enhancement Quantum Efficiency
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Y =
Quantum Yield forCharge Generation
time constant forrecombination
+
A. O. Govorovs group (Ohio Univ.)
Nano Lett. (2007)
Molecules near the Metal Nanoparticles
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A. O. Govorovs group (Ohio Univ.)
Nano Lett. (2007)
Schematic Figure
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Localized surface plasmons induce the electromagnetic-field amplifications.
Solar Cell Changwoo
B. Parks group (SNU)
APL (2011)
Au Nanoparticle-Embedded DSSC
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B. Parks group (SNU)
APL (2011)
p-type Sensitized Solar Cell
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Advantage
p-njunction solar cellCombine an n-type TiO2-based photoanode with ap-typeNiO-based photocathode
Improving open circuit voltage (Voc)
Schematic energy diagram forp-type sensitized solar cell
Errol Blarts Group (Universit de Nantes)Acc. Chem. Res. 48 1063 (2010)
(1) Electron transfer from the excited sensitizer to
the oxidized species in the electrolyte.
(2) Electron transfer from valence band ofp-type
NiO to the HOMO level of the sensitizer.
(1)
(2)
TiO2 (0.8 m ) NiO (3.3 m)
p-n Junction Solar Cell
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U. Bachs group (Monash University)
Nat. Mater. 9 31 (2009)
Scheme for the electron-transfer processesoccurring in the dye-sensitized tandem solar cell
Voc =EF(n-TiO2) EF(p-NiO)
In the case of TiO2 DSSCs, the maximum
Voc is limited to about 1 V.
Larger Voc (> 1 V) can be achieved
byp-njunction solar cell
Solar Cell Hongsik
p-n Junction Solar Cell
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1 L i i l ( 0 1 V)
Limitation forp-type Sensitized Solar Cell
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1. Low open-circuit voltage (~0.1 V)
Small difference in potential between the Femi level in the NiO photocathode
and the redox potential of electrolyte (iodide system)
Solution: 1. New electrolyte system (sulfur system)
2. Modify NiO electrode (tuningp-type characteristic)
2. Low hole diffusivity in NiO
Rapid recombination of photogenerated hole
Hole diffusion coefficient of NiO film (~10-8 - ~10-7 cm2/s)
Electron diffusion coefficient of TiO2 (~10-5 - ~10-4 cm2/s)
Solution: 1. Metal oxide (Al2O3) coating on NiO electrode (suppress recombination)
2. Graphene / NiO composite (Improve conductivity)
Solar Cell Hongsik
Modification ofp-type DSSC: Al2O3 coating
Suppression of the carrier recombination by
Al2
O3
coating layer
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Yiying Wus Group (Ohio State University)
Langmuir28 950 (2012)
Charge transfer resistance at the
NiO/dye/electrolyte increase by Al2O3coating layer
Carrier collection efficiency increased by
Al2O3 coating
2 3
Solar Cell Hongsik
Modification ofp-type DSSC: Al2O3 coating
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_________________
Modification ofp-type DSSC: Graphene / NiO Composites
Solid arrows: charge transport (desired)
Dashed arrow: recombination (undesired)
Synthesis Procedure for NiO/Graphene Composite Films
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Chang Ming Lis Group (Nanyang Technological
University) JPCC115 12209 (2011)
Solar Cell Hongsik
Dashed arrow: recombination (undesired)
Charge recombination is significantly suppressed
due to the enhanced hole transportby thepresence of graphene.
NiO/Graphene Composite
Higher conductivity than the bare NiO film
Jsc, Voc
Modification ofp-type DSSC: Graphene/ NiO composite
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