Charge Separation and Efficient Light Energy Conversion in Sensitized Mesoscopic Solar Cells Based on Binary Ionic Liquids

Wang, Peng; Wenger, Bernard; Humphry‐Baker, Robin; Moser, Jacques-E.; Teuscher, Joël; Kantlehner, Willi; Mezger, Jochen; Stoyanov, Edmont V.; Zakeeruddin, Shaik M.; Grätzel, Michaël

doi:10.1021/ja042232u

Cited by 392 publications

(358 citation statements)

References 85 publications

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“…Previously, with a similar thick, double-layer TiO 2 film, we obtained an efficiency of over 9.5% using an optimized volatile I 3 2 /I 2 electrolyte 21,22 . As indicated in Fig.…”

Section: Resultsmentioning

confidence: 88%

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

et al. 2010

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Dye-sensitized solar cells (DSCs) have achieved impressive conversion efficiencies for solar energy of over 11% with an electrolyte that contains triiodide/iodide as a redox couple. Although triiodide/iodide redox couples work efficiently in DSCs, they suffer from two major disadvantages: electrolytes that contain triiodide/iodide corrode electrical contacts made of silver (which reduces the options for the scale up of DSCs to module size) and triiodide partially absorbs visible light. Here, we present a new disulfide/thiolate redox couple that has negligible absorption in the visible spectral range, a very attractive feature for flexible DSCs that use transparent conductors as current collectors. Using this novel, iodide-free redox electrolyte in conjunction with a sensitized heterojunction, we achieved an unprecedented efficiency of 6.4% under standard illumination test conditions. This novel redox couple offers a viable pathway to develop efficient DSCs with attractive properties for scale up and practical applications. Since the beginning of the 1990s much attention has been paid to alternative energy sources, in particular to photovoltaic solar energy 1,2 . DSCs (or Grätzel cells) currently attract considerable interest because of their high light-to-electricity conversion efficiencies, relatively easy fabrication procedures and low production cost 3 . The most common electrolyte in high-performance DSCs uses the triiodide/iodide (I 3 2 /I 2 ) redox couple 4-6 . Even though this redox couple works efficiently, it has disadvantages, such as the corrosion of silver-based current collectors and the partial absorption of visible light around 430 nm by the triiodide species 7 . Therefore, it is important to study alternative redox couples [8][9][10][11] , including p-type semiconductors 12 and solid-state, hole-transporting materials 13 . Electrolytes composed of a high molecular weight poly(ethylene oxide)-based copolymer in complex with an alkali metal polysulfide (M 2 S n ; redox couple S n 22 /S nþ1 22) or a caesium thiolate salt (redox couple disulfide/thiolate) are used successfully in all solid-state, electrochemical photovoltaic cells (n-CdSe|polymer redox electrolyte|ITO, where ITO represents the indium-tin-oxide conductive layer on the glass electrode) 14,15 . These studies encouraged us to introduce disulfide/thiolate (T 2 /T 2 ) molecules (instead of I 3 2 /I 2 ones) as redox mediators in DSC electrolytes. Results and discussionCharacterization of the DSC redox couple. The redox couple T 2 /T 2 , where T 2 represents the 5-mercapto-1-methyltetrazole ion and T 2 stands for its dimer (Fig. 1), was characterized electrochemically (Supplementary Fig. S1) and studied as an electrolyte for DSCs. The redox potential for T 2 /T 2 was found to be 0.485 V against a normal hydrogen electrode (NHE, Supplementary Fig. S1), which is close to that of the I 3 2 /I 2 redox couple (reported values range from 0.4 V to 0.53 V against NHE in organic solvents 16,17 ) used in a DSC. Delocalization of the negative charge fo...

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“…Previously, with a similar thick, double-layer TiO 2 film, we obtained an efficiency of over 9.5% using an optimized volatile I 3 2 /I 2 electrolyte 21,22 . As indicated in Fig.…”

Section: Resultsmentioning

confidence: 88%

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

et al. 2010

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“…We note that we have previously shown that the kinetics of charge recombination, and indeed overall device performance, are dependent upon the peptisation step employed. 42 At present the origin of the different dependence of electron injection and recombination upon film peptisation is unclear, although we note that the recombination dynamics have been suggested to be particularly sensitive to intraband recombination sites on the film surface which in turn may be sensitive to the peptisation procedure.…”

Section: Other Materials Factors Influencing Electron Injection Kineticsmentioning

confidence: 80%

Parameters Influencing the Efficiency of Electron Injection in Dye-Sensitized Solar Cells

et al. 2009

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In this paper we focus upon the electron injection dynamics in complete dye sensitized nanocrystalline titanium dioxide solar cells (DSSCs) employing the ruthenium bipyridyl sensitizer dye N719. Electron injection dynamics and quantum yields are studied by time resolved single photon counting and the results are correlated with device performance. In typical DSSC devices, electron injection kinetics were found to proceed from the N719 triplet state with an half time of 200 ± 60 ps and quantum yield of 84 ± 5 %. We find that these injection dynamics are independent of presence of iodide / triiodide redox couple and of the pH of the peptisation step used in the synthesis of the TiO 2 nanoparticles. They are furthermore found to be only weakly dependent upon the application of electrical bias to the device. In contrast, we find these dynamics to be strongly dependent upon the concentration of t-butyl pyridine (tBP) and lithium cations in the electrolyte. This dependence is correlated with shifts of the TiO 2 conduction band energetics as a function of tBP and Li + concentration, from which we conclude that a 100 meV shift in band edge results in approximately a two fold retardation of injection dynamics.We find that electron injection quantum yield determined from these transient emission data as a function of tBP and Li + concentration shows a linear correlation with device short circuit density J sc . We thus conclude that the relative energetics of the dye excited state versus the titanium dioxide acceptor states is a key determinant of the dynamics of electron injection in DSSC, and that variations in these energetics, and therefore in the kinetics and efficiency of electron injection, impact directly upon device photovoltaic efficiency. Finally we discuss these results in terms of singlet versus triplet electron injection pathways and the concept of minimisation of kinetic redundancy.

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“…Melting temperatures of room temperature ILs can therefore be much lower compared to those of salts based on atomic ions, such as NaCl, which has a melting temperature of 1074 K. In addition to having low melting temperatures, ILs have a number of unique properties, including excellent solvation ability, extraordinarily low volatility, and high thermal stability. [1][2][3][4][5][6][7][8][9] Since the physical and chemical properties of ILs can be varied by the choices of the cation and anion pair, 1 they can be used for many applications such as fuel cells, [3][4][5] batteries 6,7 and solar cells. 8,9 Furthermore, ILs are also used in ionic propulsion, 10,11 for hypergolic fuels 12 and various chemical extraction applications.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9] Since the physical and chemical properties of ILs can be varied by the choices of the cation and anion pair, 1 they can be used for many applications such as fuel cells, [3][4][5] batteries 6,7 and solar cells. 8,9 Furthermore, ILs are also used in ionic propulsion, 10,11 for hypergolic fuels 12 and various chemical extraction applications. 13 The vast number of possible anion-cation combinations 14 makes it valuable to rationally predict IL properties based on their constituents, 15 and considerable experimental and theoretical work has been performed to predict and measure ionic liquid properties.…”

Section: Introductionmentioning

confidence: 99%

Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors

et al. 2009

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Charge Separation and Efficient Light Energy Conversion in Sensitized Mesoscopic Solar Cells Based on Binary Ionic Liquids

Cited by 392 publications

References 85 publications

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

Parameters Influencing the Efficiency of Electron Injection in Dye-Sensitized Solar Cells

Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors

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