1. IONIC LIQUIDS INIONIC LIQUIDS IN
DYE SENSITIZEDDYE SENSITIZED
SOLAR CELLSSOLAR CELLS
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-- ByMukundGhavreByMukundGhavre
2. IntroductionIntroduction
AA solar cell is a device that converts the solar energyis a device that converts the solar energy
directly into electricity by the photovoltaic effect.directly into electricity by the photovoltaic effect.
The first solar cell was built byThe first solar cell was built by
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The first solar cell was built byThe first solar cell was built by
Aleksandr Stoletov in 1891.
3. About hundred years later in 1991 Michael GrätzelAbout hundred years later in 1991 Michael Grätzel
andand Brian O'Regan invented dyeBrian O'Regan invented dye--sensitized solar cellssensitized solar cells
atat SFIT.
DyeDye--sensitized solar cells (DSSC, DSC, DYSC) aresensitized solar cells (DSSC, DSC, DYSC) are
basedbased on the semiconductor formed between a photoon the semiconductor formed between a photo--
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sensitized anode and an electrolyte. These are alsosensitized anode and an electrolyte. These are also
called as Grätzel cells.called as Grätzel cells.
4. Why solar cells ?Why solar cells ?
The world uses about 15 TW of power per year.
(TW = 1012W).
We probably need to generate ~ 30 TW of power in
2050.
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Current supply of petroleum and natural gas will
eventually run out.
If we do not dramatically reduce our emissions of
carbon dioxide, the average temperature of the planet
will probably rise by several degrees.
5. The power would be generated in 2050 by other
renewable sources is as follows,
The Biomass: 7-10 TW
Wind: 2.1 TW
Nuclear: 8 TW
Hydroelectric: 1.5 TW.
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The sun gives us 174,000 TW per year, out of which
89,000 TW reaches the earth surface.
Solar cells can be easily incorporated into
distributive systems.
8. Types of solar cellsTypes of solar cells
Single crystal SC.Single crystal SC.
Polycrystalline SC.Polycrystalline SC.
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Amorphous SC.Amorphous SC.
(Thin FilmSC)(Thin FilmSC)
9. DSSC: StructureDSSC: Structure
Granular TiOGranular TiO22 forming a nanoporous structure.forming a nanoporous structure.
A dye, which is a light sensitive substance spreadA dye, which is a light sensitive substance spread
on the TiOon the TiO22 surface.surface.
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A redox couple (IA redox couple (I--/I/I33
--), located in the space between), located in the space between
the dye and the cathode.the dye and the cathode.
A solvent for the redox couple, e.g. Acetonitrile,A solvent for the redox couple, e.g. Acetonitrile,
Ionic Liquid.Ionic Liquid.
11. DSSC: OperationDSSC: Operation
Dye electrons are excited by solar energy absorption.Dye electrons are excited by solar energy absorption.
TheyThey are injected into the conduction band of TiOare injected into the conduction band of TiO22..
Get to counterGet to counter--electrode (cathode) through the externalelectrode (cathode) through the external
circuit.circuit.
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: Redox regeneration at the counter: Redox regeneration at the counter--
electrode (oxidation).electrode (oxidation).
: Dye regeneration reaction (reduction).: Dye regeneration reaction (reduction).
The efficiency of the SC is calculated byThe efficiency of the SC is calculated by ηη == PPmm/(E.A/(E.Acc))
I-
3 + 2 e-
3 I-
3 I- I-
3 + 2 e-
19. New electrolytesNew electrolytes
Essentiallynon-volatile (negligible vapour
pressure).
Non-explosive & -flammable.
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Thermo- & electrochemicallystable.
Goodsolvent for both inorganics andorganics.
… not toxic until better studied.
20. Few ILs used in DSSCFew ILs used in DSSC
N N
N N N N
I -
NCS -
-
01/03/2010 20M. NazeeruddinM. Nazeeruddin et al J.Am.Chem.Soc., 1993et al J.Am.Chem.Soc., 1993, 115(14), 6382, 115(14), 6382--9090
N N
N N
N N
N(CN)-
2
NCS -
B(CN)4
-
NTf2
-
C(CN)3
-
22. Ionic Liquids with high viscosity give low photocurrents.Ionic Liquids with high viscosity give low photocurrents.
Ionic Liquids Viscosity
(mPa s)
Jsc
(mA cm2
)
Voc
(mV)
FF η(%)
EMImTFSI 39 9.4 550 0.45 2.4
EMImBF4 43 9.9 602 0.55 3.3
BMImPF6 352 4.3 576 0.62 1.6
BPTFSI 72 6.3 577 0.56 2.0
EMImDCA 21 7.8 703 0.66 3.8
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Ionic Liquids with high viscosity give low photocurrents.Ionic Liquids with high viscosity give low photocurrents.
However, diffusion of IHowever, diffusion of I33
-- (needed for the regeneration of the(needed for the regeneration of the
dye at the counterdye at the counter--electrode) is very slow in ILs of highelectrode) is very slow in ILs of high
viscosity.viscosity.
Charge hopping mechanism for the ICharge hopping mechanism for the I33
-- reduction.reduction.
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Dye regeneration is facilitated by the highDye regeneration is facilitated by the high
concentration of Iconcentration of I--
in the IL.in the IL.
Viscosity, cation size influence the charge transportViscosity, cation size influence the charge transport
in the electrolyte and the dye regenerationin the electrolyte and the dye regeneration
G. Wolfbauer, Solar Energy Materials & Solar Cells, 70, 2001, 85-101.
26. Charge transport in the electrolyteCharge transport in the electrolyte
How does the electrolyte influence the DSC properties?How does the electrolyte influence the DSC properties?
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30. Dicyanoamide (CN)2N- anion in an IL
IntensityIntensity
(W/m(W/m22))
IIscsc
(mA/cm(mA/cm22))
VVococ
(V)(V)
FillfactorFillfactor
EfficiencyEfficiency
(%)(%)
250250 3.03.0 0.700.70 0.690.69 6.06.0
250250 2.52.5 0.740.74 0.660.66 4.94.9
10001000 11.111.1 0.750.75 0.600.60 5.05.0
10001000 8.68.6 0.770.77 0.560.56 3.73.7
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10001000 8.68.6 0.770.77 0.560.56 3.73.7
Composition of electrolyte
0.2 M I2
0.1 M GuanSCN
0.5 M NMBI
2 M n-BuMeIm+ I-
BuMeIm+ N(CN)2
-
31. AdvantagesAdvantages
Ease of buildingintegration.Ease of buildingintegration.
Lowproduction cost.Lowproduction cost.
Bifacial cells capture light fromall angles.Bifacial cells capture light fromall angles.
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Bifacial cells capture light fromall angles.Bifacial cells capture light fromall angles.
Outperforms all other types for indoorOutperforms all other types for indoor
applications.applications.
Multicolour options available.Multicolour options available.
32. Ionic liquids in DSSC:
Future Challenges
Photovoltage optimization (redox couple)Photovoltage optimization (redox couple)
Study of diffusion properties of IStudy of diffusion properties of I00, I, I22 and Iand I33
-- in modelin model
ionic liquids.ionic liquids.
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Study the importance of cation size in the process ofStudy the importance of cation size in the process of
charge transport.charge transport.
UpUp--scalingscaling
