1. IONIC LIQUIDS INIONIC LIQUIDS IN DYE SENSITIZEDDYE SENSITIZED SOLAR CELLSSOLAR CELLS 01/03/2010 1 -- 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 01/03/2010 2 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 GrtzelAbout hundred years later in 1991 Michael Grtzel 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-- 01/03/2010 3 sensitized anode and an electrolyte. These are alsosensitized anode and an electrolyte. These are also called as Grtzel cells.called as Grtzel 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. 01/03/2010 4 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. 01/03/2010 5 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. 6. 01/03/2010 6 7. 01/03/2010 7 8. Types of solar cellsTypes of solar cells Single crystal SC.Single crystal SC. Polycrystalline SC.Polycrystalline SC. 01/03/2010 8 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. 01/03/2010 9 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. 10. Structure of DSSC 01/03/2010 10 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. 01/03/2010 11 : 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 == PPmm/(E.A/(E.Acc)) I- 3 + 2 e- 3 I- 3 I- I- 3 + 2 e- 12. 01/03/2010 12 13. Nanocrystalline TiONanocrystalline TiO22 01/03/2010 13 TiO2 particles, d 25 nm 1 cm2 contains 1013 particles 300 nm 14. ZnO rods TiO2 rods In2S3 rods TiO2 hollow spheres 01/03/2010 14 TiO2 nanotubes TiO2 DW nanotubes TiO2 foam 15. Various dyes usedVarious dyes used 01/03/2010 15 N 719 N 3 16. ElectrolyteElectrolyte Organic nitriles (originally acetonitrile) Redox couple (commonly I-/I3 -) Additives. 01/03/2010 16 Performance: Maximum over-all efficiencies up to 12 % Everyday efficiencies of 7-8% 17. LimitationsLimitations Volatility(solvent evaporation) Chemical stability(sensitive to air andmoisture) Electrochemical stability(narrowwindow) 01/03/2010 17 Electrochemical stability(narrowwindow) Limitedtemperature range Toxicity 18. Solution...... ? Ionic Liquids ! 01/03/2010 18 Green ? 19. New electrolytesNew electrolytes Essentiallynon-volatile (negligible vapour pressure). Non-explosive & -flammable. 01/03/2010 19 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 - 21. Some experimental factsSome experimental facts 01/03/2010 21 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 (%) 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 01/03/2010 22 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. 23. 01/03/2010 23 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. 24. 01/03/2010 24 25. 01/03/2010 25 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? 01/03/2010 26 27. 01/03/2010 27 N N I - N N NTf2 - N N NTf2 - PMII + EMI-TFSI EMI-TFSI 28. 01/03/2010 28 29. Choice of Anions SCN- , NTf2 -, (CN)2N-, PF6 -, TfO-, I-, IBr2 -, I2Br-, Br3 -, I3 -, 01/03/2010 29 Structure of [Me2BuIm]IBr2 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 01/03/2010 30 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. 01/03/2010 31 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. 01/03/2010 32 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 33. 01/03/2010 33 34. 01/03/2010 34 35. 01/03/2010 35 36. 01/03/2010 36 37. THANK YOU 01/03/2010 37