Efficient Non-corrosive Electron-Transfer Mediator Mixtures for Dye-Sensitized Solar Cells

Cazzanti, Silvia; Caramori, Stefano; Argazzi, Roberto; Elliott, C. Michael; Bignozzi, Carlo Alberto

doi:10.1021/ja062087f

Cited by 123 publications

(129 citation statements)

References 11 publications

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“…knowledge, this is the highest power-conversion efficiency under full sunlight conditions reported for a DSC that does not use I 3 2 /I 2 as a redox mediator 8,20 . 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 .…”

Section: Resultsmentioning

confidence: 79%

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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Section: Resultsmentioning

confidence: 79%

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

et al. 2010

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“…All reagents and solvents were used as received. 1,10-phenantroline (phen) and 3,4,7, were obtained from Aldrich.…”

Section: Methodsmentioning

confidence: 99%

“…n+ with L-L = 1,10-phenanthroline (phen), 5-amino-1,10'-phenanthroline (phen-NH 2 ), 3,4,7,, pyrazino [2,3- [3,2-a:2',3'-c]phenazine (dppz-NH 2 ), were synthesized and systematically studied, mainly from a spectroscopic and electrochemical point of view. Differentiating from previous literature reports in this area, where the Co(III) species are generated in situ, in this work the Co(III) species were isolated as a solid, to permit its characterization, and a better control of the Co(II)/Co(III) concentration relation.…”

Section: +/3+mentioning

confidence: 99%

“…6 The slower rate of interaction with electrons in the photoanode for the Co polypyridyl couples when compared to the ferrocene/ferrocinium couple arises mainly from the change in spin multiplicity involved in the former. 4 On the other hand, when compared to the iodine couple, that possesses a sole redox potential, the possibility to tune the redox potential by changes in the ligand electronic properties appears as an additional advantage of Cobalt polypiridine type complexes.…”

Section: Introductionmentioning

confidence: 99%

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SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF A SERIES OF SUBSTITUTED POLYPYRIDINE Co(II)/Co(III) COUPLES AND THEIR POTENTIALITY AS MEDIATORS FOR SOLAR CELLS

Gajardo

Loeb

2011

J. Chil. Chem. Soc.

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This paper reports the synthesis, characterization and spectroscopic and electrochemical study of a series of polypyridine Co(II) and Co(III) complexes. The effect on the redox potential of the presence of donor or acceptor substituents on the ligand, as well as the effect of an increased ligand aromaticity, was analyzed.n+ type were prepared, with n = 2,3, and L-L = 1,10-phenanthroline (phen), 5-amino-1,10'-phenanthroline (phen-NH 2 ), 3,4,7,8-tatramethyl phenantroline (phen-4Me), pyrazino[2,3-f][1,10]phenanthroline (ppl), 2-methylpyrazino[2,3-f][1,10]phenanthroline (ppl-Me), dipyrido [3,2-a:2',3'-c]phenazine (dppz), 7-methyldipyrido[3,2-a:2',3'-c]phenazine (dppz-Me) and 7-aminodipyrido[3,2-a:2',3'-c]phenazine (dppz-NH 2 ). The results of this study open the possibility to have a battery of potential mediators for photoelectrochemical solar cells. Ultimately, the election of a determined couple as mediator will depend mainly on the electronic properties of the specific dye in a given cell.

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“…Tandem redox systems have previously been used in DSCs, [ 17,18 ] and some of them have involved cobalt-complex redox systems in the electrolytes. [ 19,20 ] However, the presence of multiple redox species in the electrolyte makes it a complicated system to study and intertwined results to resolve. In 2006, Bignozzi et al studied the tandem Co(DTB) 3 2+ /Fc (ferrocene) system (DTB = 4,4′-dimethyl-2,2′-bipyridine).…”

mentioning

confidence: 99%

Two Redox Couples are Better Than One: Improved Current and Fill Factor from Cobalt‐Based Electrolytes in Dye‐Sensitized Solar Cells

Cong

Hao

Sun

et al. 2014

Advanced Energy Materials

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Since Grätzel and O'Regan signifi cantly improved the effi ciency of dye-sensitized solar cells (DSCs) in 1991, [ 1 ] large research efforts have been put towards realization of this promising technology. Although the recent improvement of the effi ciency of DSCs, for a long time, the most effi cient redox couple for DSCs has been the I¯/I 3 ¯ system. [2][3][4][5][6] In 2010, the Hagfeldt and Sun groups combined an electrolyte based on metal-organic cobalt complexes with bulky organic dyes. [ 7 ] The new strategy greatly improved the effi ciency of DSCs and has opened the possibilities to reach conversion effi ciencies well above 15%. The Grätzel group reported a record cell with an effi ciency of 12.3% using a cobalt-based electrolyte in 2011. [ 8 ] Since then, cobalt-complex redox systems have become the most promising type of redox system to replace the traditional I¯/I 3 ¯ system. However, there are still several problems that limit the efficiency of DSCs involving cobalt-based electrolytes.One of the most important challenges is mass-transport limitation. Because of the larger effective size of the cobalt complexes as compared to polyiodide species, the ion mobility of the cobalt complexes are considerably lower; in particular inside the mesoporous TiO 2 fi lm. [ 9,10 ] Recently, TiO 2 fi lms with a higher degree of porosity and larger pore size was proven to reduce the mass-transport problem. [ 11,12 ] However, for non-volatile solvent electrolytes, implicitly also of higher viscosity used in DSCs, mass transport is still a serious problem. Another signifi cant challenge for cobalt-complex redox systems is the ineffi cient charge transfer at the counter electrode. [ 10 ] Most recent studies have focused on fi nding new materials to replace the traditional catalytic Pt on the counter electrode. Graphene, [ 13,14 ] PEDOT [ 15 ] and other materials, such as TiC, [ 16 ] etc., have proven better performance than platinized fl uorine-doped tin oxide (FTO) as counter electrode materials.Here, a tandem electrolyte system is used in an attempt to resolve some of the intrinsic problems arising from the use of cobalt-based electrolyte systems. Tandem redox systems have previously been used in DSCs, [ 17,18 ] and some of them have involved cobalt-complex redox systems in the electrolytes. [ 19,20 ] However, the presence of multiple redox species in the electrolyte makes it a complicated system to study and intertwined results to resolve. In 2006, Bignozzi et al. studied the tandem Co(DTB) 3 2+ /Fc (ferrocene) system (DTB = 4,4′-dimethyl-2,2′-bipyridine). They claimed that the photo-oxidized dye would be reduced/regenerated by the co-mediator Fc. The oxidized form (Fc + ) could then be rapidly intercepted by the Co(II) in the Co(DTB) 3 2+ /Fc system. [ 19 ] 3+ mediator could be used to improve the electron-collection effi ciency in a DSC sensitized by a (thienylterpyridine)ruthenium complex (DMB = 4,4′-di-methyl-2,2′-bipyridine). The Fe-based redox system was assumed to mainly work on the TiO 2 working-electrode sid...

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Efficient Non-corrosive Electron-Transfer Mediator Mixtures for Dye-Sensitized Solar Cells

Cited by 123 publications

References 11 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

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF A SERIES OF SUBSTITUTED POLYPYRIDINE Co(II)/Co(III) COUPLES AND THEIR POTENTIALITY AS MEDIATORS FOR SOLAR CELLS

Two Redox Couples are Better Than One: Improved Current and Fill Factor from Cobalt‐Based Electrolytes in Dye‐Sensitized Solar Cells

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