The present invention relates to a dye sensitized solar cell (DSC) which comprises in the electrolyte layer a verdazyl radical or a corresponding onium salt or the combination thereof. Moreover, the present invention pertains to the use of a verdazyl radical and a corresponding onium salt as a redox pair in the electrolyte of a dye sensitized solar cell and to onium salts.

US4927721 , US5084365, US5350644 and US5525440 describe dye sensitized solar cells which comprise in the electrolyte a redox pair such as iodine/iodide solutions, bromine/bromide solutions, hydroquinone solutions or solutions of transition metal complexes transferring a nonbonding electron. Mainly, iodine/iodide (IYI ₃ ^" ) solutions are used due to the high photovoltaic performance.

The 17I ₃ ^" redox pair has several unfavorable property for the practical uses. Firstly, I ₃ ^" has significant absorption in the visible wavelength range thus competing with the dye absorption so that the light absorption of the dye is reduced. Secondly, iodine has corrosive property against metal electrode. Thirdly, iodine easily evaporates through sealing due to the high vapor pressure.

Nitroxide radical / oxoammonium salt as the redox pair was proposed in Adv. Funct. Mater. 2008, 18, 341-346.

The above mentioned problems are solved by the dye sensitized solar cells of the instant invention by using verdazyl redox pair (e.g. corresponding to components (e-1a) and (e-1b) as defined below) as the redox mediator, thus providing a high DSC cell performance.

The underlying mechanism is the reversible oxidation / reduction of the verdazyl radical according to Scheme 1 : Scheme 1

verdazyl corresponding onium radical (e-1a) cation (e-1 b) An object of the present invention is a dye sensitized solar cell, comprising

(a) a transparent conductive electrode substrate layer,

(b) a working electrode layer containing a porous film made of oxide semiconductor fine particles,

(c) a photo-sensitizing dye layer on the surface of the working electrode b,

(d) a counter electrode layer, and

(e) an electrolyte layer (e.g. filled between the working electrode layer b and the counter electrode layer d) containing

(e-1)

either (e-1 a) a compound of formula (I) or (II) with G being j

or (e-1 b) a compound of formula (I) or (II) with G being , or the combination of (e-1 a) and (e-1 b), preferably the combination,

wherein

n is 2-5;

X and X' together are =0, =S or =NR ₄ ; or

X and X' are independently H; or Ci-C ₂ oalkyl, C ₂ -Ci ₆ alkenyl, C ₆ -C ₁₈ aryl, C ₇ -C ₁₈ aralkyl, C ₈ - C ₁₈ aralkenyl, each of which is unsubstituted or substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ -C(O)-R ₅ , OC(O)NR ₄ R ₅ or combinations thereof, the aryl can additionally be substituted by d-Ci ₆ alkyl, C ₂ -Ci ₆ alkenyl, perfluorinated CrC ₁₆ alkyl or combinations thereof, and the alkyl and alkenyl can additionally be interrupted by O, S, NR ₄ or combinations thereof;

Y is a direct bond; or C ₁₆ alkylene or C ₆ -Ci ₈ arylene, each of which is unsubstituted or substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ -C(O)-R ₅ , OC(O)NR ₄ R ₅ or combinations thereof, the arylene can additionally be substituted by C ₁ - C ₁₆ alkyl, C ₂ -C ₁₆ alkenyl, perfluorinated Ci-Ci ₆ alkyl or combinations thereof, and the alkylene and alkenylene can additionally be interrupted by O, S ₁ NR ₄ , C(O), C(O)O, O-C(O), C(O)NR ₄ , NR ₄ -C(O), NR ₄ -C(O)-O, OC(O)NR ₄ or combinations thereof; Y is independently linked to X, X', R ₁ , R ₂ Or R ₃ ;

A ^" is an anion of an organic or inorganic acid, preferably the anion of HPF ₆ , HCIO ₄ , HBF ₄ , HO ₃ SCF ₃ , HN(C ₂ F ₅ SO ₂ ), , HC(CF ₃ SO ₂ ) ₃ , HC(C ₂ F ₅ SO ₂ ) ₃ , HB(C ₂ O ₄ ) ₂ , HB(C ₆ H ₅ ),, HB(C ₆ F ₅ ) ₄ , HSbF ₆ , HAsF ₆ , HBr, HBF ₃ C ₂ F ₅ , HPF ₃ (CF ₂ CF ₃ ) ₃ , HCI, HI, CF ₃ COOH, CH ₃ COOH or combinations thereof;

R ₁ , R ₂ and R ₃ are independently hydrogen, halogen; or C-i-C ₂₀ alkyl, C ₂ -C ₂₀ alkenyl, C ₃ - C ₂₀ cycloalkyl, C ₄ -C ₂₀ cycloalkenyl, C ₆ -C ₂₆ aryl, C ₇ -C ₃₀ aralkyl, C ₈ -C ₃₀ aralkenyl, C ₃ -

C ₂₀ heteroaryl, C ₃ -C ₂₀ heteroaryl-CrC ₂₀ alkyl, C ₃ -C ₂₀ heteroaryl-C ₂ -C ₂₀ alkenyl or ferrocenyl, each of which is unsubstituted or substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ -C(O)-OR ₅ , OC(O)NR ₄ R ₅ or combinations thereof, the aryl and heteroaryl can additionally be substituted by d-C^alkyl, C ₂ -C ₁₆ alkenyl, perfluorinated C-ι-C ₁₆ alkyl or combinations thereof, and the alkyl, alkenyl, cycloalkyl and cycloalkenyl can additionally be interrupted by O, S, NR ₄ or combinations thereof; and

R ₄ and R ₅ are independently hydrogen; or C _r C ₂ oalkyl, C ₂ -C ₂₀ alkenyl, C ₃ -C ₂₀ cycloalkyl, C ₄ - C ₂₀ cycloalkenyl, C ₆ -C ₁₈ aryl, C ₆ -C ₃₀ aralkyl, C ₈ -C ₃₀ aralkenyl, C ₃ -C ₂₀ heteroaryl, C ₃ -

C ₂₀ heteroaryl-CrC ₂₀ alkyl, C ₃ -C ₂₀ heteroaryl-C ₂ -C ₂₀ alkenyl; or NR ₄ R ₅ form together an unsubstituted or substituted 5-, 6- or 7-membered heterocyclic ring. - A -

For example, the component e-1 is a compound of formula (I); for instance, X and X' together are =0, =S or =NR ₄ , especially =0; for instance, A ^" is HBF ₄ ; for example, Ri and R ₂ are independently C ₁ -C _2O aIhCyI, in particular d-C^alkyl, especially C _r C ₈ alkyl, e.g. C ₃ alkyl, such as iso-propyl (preferably R ₁ and R ₂ are identical). Preferably, X and X' together are =0, R ₁ and R ₂ are independently CrC _2O alkyl, for instance, A ^" is HBF ₄ . For example, substituted aryl is substituted by 1 , 2 or 3 groups.

For instance, n is 2-3;

X and X' together are =0, =S or =NR ₄ ;

Y is a direct bond; or CrC ₁₆ alkylene, C^C^alkenylene, CrC ₁₆ alkylene-C ₆ -C ₁₈ arylene-Cr C ₁₆ alkylene or C ₆ -C ₁₈ arylene, whereby the alkylene and alkenylene are uninterrupted or interrupted by O, S, NR ₄ or combinations thereof; Y is independently linked to R ₁ , R ₂ , R ₃ or =NR ₄ ;

A ^" is an anion of an organic or inorganic acid, preferably the anion of HPF ₆ , HCIO ₄ , HBF ₄ , HO ₃ SCF ₃ , HN(C ₂ F ₅ SO ₂ ), , HC(CF ₃ SO ₂ ) ₃ , HC(C ₂ F ₅ SO ₂ ) ₃ , HB(C ₂ O ₄ ) ₂ , HB(C ₆ Hg) ₄ , HB(C ₆ F ₅ ) ₄ , HSbF ₆ , HAsF ₆ , HBr, HBF ₃ C ₂ F ₅ , HPF ₃ (CF ₂ CF ₃ ) ₃ , HCI, HI, CF ₃ COOH, CH ₃ COOH or combinations thereof;

R ₁ and R ₂ are independently hydrogen; or CrC ₂₀ alkyl, C ₂ -C ₂₀ alkenyl, C ₃ -C ₂₀ cycloalkyl, C ₄ - C ₂₀ cycloalkenyl, C ₇ -C ₃₀ aralkyl or C ₈ -C _3O aralkenyl;

R ₃ is hydrogen, halogen; or C _r C ₂₀ alkyl, C ₂ -C ₂₀ alkenyl, C ₃ -C ₂₀ cycloalkyl, C ₄ -C ₂₀ cycloalkenyl, C ₆ -C _2e aryl, C ₇ -C ₃₀ aralkyl, C ₈ -C ₃₀ aralkenyI, C ₃ -C ₂₀ heteroaryl, C ₃ -C ₂ oheteroaryl-C ₁ -C ₂₀ alkyl, C ₃ - C ₂₀ heteroaryl-C ₂ -C ₂₀ alkenyl or ferrocenyl, each of which is unsubstituted or substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ - C(O)-OR ₅ , OC(O)NR ₄ R ₅ or combinations thereof, the aryl and heteroaryl can additionally be substituted by CrC ₁₆ alkyl, C ₂ -C ₁₆ alkenyl, perfluorinated C _r C ₁₆ alkyl or combinations thereof, and the alkyl, alkenyl, cycloalkyl and cycloalkenyl can additionally be interrupted by O, S, NR ₄ or combinations thereof; and R ₄ and R ₅ are independently hydrogen; or C ₁ -C _2O aIKyI, C ₂ -C ₂ oalkenyl, C ₃ -C ₂₀ cycloalkyl, C ₄ - C ₂₀ cycloalkenyl, C ₆ -C ₁₈ aryl, C ₆ -C ₃ oaralkyl or C ₈ -C ₃₀ aralkenyl.

Preferably, the component e-1 is a compound of formula (I) and X and X' together are =0, =S or =NR ₄ ;

A ^" is an anion of HPF ₆ , HCIO ₄ , HBF ₄ , HO ₃ SCF ₃ , HN(C ₂ F ₅ SO ₂ ); _? , HC(CF ₃ SO ₂ ) ₃ , HC(C ₂ F ₅ SO ₂ ) ₃ , HB(C ₂ O ₄ ),, HB(C ₆ H ₅ ),, HB(C ₆ F ₅ ),, HSbF ₆ , HAsF ₆ , HBr, HBF ₃ C ₂ F ₅ , HPF ₃ (CF ₂ CFs) ₃ , HCI, HI, CF ₃ COOH, CH ₃ COOH or combinations thereof;

R ₁ and R ₂ are independently CrC ₂₀ alkyl, C ₃ -C ₂₀ cycloalkyl or C ₇ -C ₃₀ aralkyl;

R ₃ is hydrogen; or CrC ₂₀ alkyl, C ₃ -C ₂ ocycloalkyl, C ₆ -C ₂₆ aryl, C ₃ -C ₂ oheteroaryl or ferrocenyl, each of which is unsubstituted or substituted by halogen, OR ₄ , NR ₄ R ₅ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ or combinations thereof, the aryl and heteroaryl can additionally be substituted by CrCi ₆ alkyl, perfluorinated CrC ₁₆ alkyl or combinations thereof; and

R ₄ and R ₅ are independently hydrogen; or CrC ₂₀ alkyl, C ₃ -C ₂₀ cycloalkyl or C ₆ -C ₃ oaralkyl.

For instance, X and X' together are =0;

A ^" is an anion Of HPF ₆ , HCIO ₄ , HBF ₄ , HO ₃ SCF ₃ , HN(C ₂ F ₅ SOz) ₂ , HC(CF ₃ SO ₂ ) ₃ , HC(C ₂ F ₅ SO ₂ ) ₃ , HB(C ₂ O ₄ ),, HB(C ₆ H ₅ ),, HB(C ₆ F ₅ ) ₄ , HSbF ₆ , HAsF ₆ , HBr, HBF ₃ C ₂ F ₅ , HPF ₃ (CF ₂ CF ₃ )S, HCI, HI, CF ₃ COOH, CH ₃ COOH or combinations thereof;

R ₁ and R ₂ are independently CrC ₁₀ alkyl; and

R ₃ is hydrogen; or CrC-ioalkyl, C ₄ -C ₅ heteroaryl or ferrocenyl; or C ₆ -C ₁₂ aryl which is unsubstituted or substituted by halogen, O-CrC^lkyl, Ci-C ₄ alkyl or perfluorinated CrC ₄ alkyl.

Particularly preferred as component (compound) e-1 a is a compound F1-F18 (e.g. F1-F15, especially F1 , F2 or F7). Particularly preferred as component (compound) e-1 b is the corresponding onium salt of the compounds F1-F18 (e.g. F1-F15), especially is the compounds G1 , G2 or G7. When a denotation (e.g. R ₄ , R ₅ ) occurs more than once (e.g. twice) in a compound, this denotation may be different groups or the same group unless otherwise stated.

It is to be understood that interrupted alkyl and alkylene comprises at least 2 carbon atoms and interrupted alkenyl and alkenylene comprises at least 3 carbon atoms.

In the definitions the term alkyl comprises within the given limits of carbon atoms, for example methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-ethylbutyl, n- pentyl, isopentyl, 1-methylpentyl, 1 ,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, 2- methylheptyl, 1 ,1 ,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, 2-ethylhexyl, 1 ,1 ,3-trimethylhexyl, 1 ,1 ,3,3-tetramethylpentyl, nonyl, decyl, undecyl, 1-methylundecyl or dodecyl.

Examples of alkenyl are within the given limits of carbon atoms vinyl, allyl, 1-methylethenyl, and the branched and unbranched isomers of butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl and dodecenyl. The term alkenyl also comprises residues with more than one double bond that may be conjugated or non-conjugated, for example may comprise one double bond.

Aryl is for example phenyl, biphenyl, naphthyl, anthracyl, phenanthryl or pyrenyl, in particular phenyl or naphthyl, especially phenyl.

Aryl can be (further) substituted by .... is to be understood to include the aryl of aralkyl and aralkenyl.

Heteroaryl may comprise one or more (e.g. 1-4, in particular 1-3, especially 1-2, such as 1) heteroatom preferably selected from the group consisting of O, S and N, especially O and N. Examples of heteroaryl are thiophenyl, bithiophenyl, terthiophenyl, tetrathiophenyl, furanyl, bifuranyl, terfuranyl, pyrrolyl, carbazolyl, indolyl, pyridinyl, 9H-purinyl, pteridinyl, chinolinyl, isochinyl, acridinyl and phenazinyl, preferred examples are furanyl and pyridinyl.

Aralkyl is for instance benzyl or α,α-dimethylbenzyl, especially benzyl. Aralkenyl includes, for instance, Λ /Λ

Some examples of cycloalkyl are cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl and dimethylcyclohexyl, for instance cyclohexyl.

Some examples of cycloalkenyl are cyclopentenyl, cyclohexenyl, methylcyclopentenyl, dimethylcyclopentenyl and methylcyclohexenyl. Cycloalkenyl may comprise more than one double bond that may be conjugated or non-conjugated, for example may comprise one double bond.

The term halogen may comprise fluorine, chlorine, bromine and iodine; for example halogen is fluorine or chlorine.

In the definitions the term alkylene comprises within the given limits of carbon atoms, for example methylene, ethylene, propylene, isopropylene, n-butylene, sec-butylene, isobutylene, tert-butylene, 2-ethyIbutylene, n-pentylene, isopentylene, 1-methylpentylene, 1 ,3-dimethylbutylene, n-hexylene, 1-methylhexylene, n-heptylene, 2-methylheptylene, 1 ,1 ,3,3-tetramethylbutylene, 1-methylheptylene, 3-methylheptylene, n-octylene, 2-ethylhexylene, 1 ,1 ,3-trimethylhexylene, 1 ,1 ,3,3-tetramethylpentylene, nonylene, decylene, undecylene, 1-methylundecylene or dodecylene.

Examples of alkenylene are within the given limits of carbon atoms vinylene, allylene, 1- methylethenylene, and the branched and unbranched isomers of butenylene, pentenylene, hexenylene, heptenylene, octenylene, nonenylene, decenylene, undecenylene and dodecenylene. The term alkenylene also comprises residues with more than one double bond that may be conjugated or non-conjugated, for example may comprise one double bond.

Arylene is for example phenylene, biphenylene, naphthalinylene, anthracenylene, phenanthrenylene or pyrenylene, in particular phenylene.

For instance, perfiuorinated alkyl is -CF ₃ , -CF ₂ CF ₃ , -CF ₂ CF ₂ CF ₃ , -CF(CF ₃ ) ₂ , -(CF ₂ ) ₃ CF ₃ or - C(CF ₃ ) ₃ , in particular -CF ₃ . The compounds e-1 a (i.e. verdazyl radicals) and their precursors are essentially known in the art. They can be prepared by known processes. Their preparation is disclosed, for example, in: Organic letters. 2007, 9, 23 4837-4840, J. Org. Chem. 2006,71,4889-4895, J. Org. Chem. 2007,72,8062-8069, J. Org. Chem. 2008,72,8062-8069, Org. Biomol, Chem., 2005,3,4258- 4261.

The oxidation of the compounds e-1a to the corresponding compounds e-1b (i.e. onium salts) can be carried out analogously to the oxidation of nitroxides to the corresponding oxoammonium salt. The oxidation of nitroxides to the corresponding oxoammonium salt is for instance described in WO 2004/031 150 or in J. M. Bobbit, M. C. L. Flores, Heterocycles (1988), 27(2), 509-533.

An exhaustive description of the verdazyl chemistry can be found, for example, in Bryyan D. Koivisto, Robin G. Hicks: "The magnetochmistry of verdazyl radical-based materials", Coordination Chemistry Reviews 249 (2005) 2612-2630.

Preferred is a dye sensitized solar cell, wherein the electrolyte layer e additionally comprises (e-2) a solvent or an ionic liquid or a combination thereof.

Preferably, the concentration of the component e-1a is 0 to 3.0M, especially 0.05 to 1.0M. Preferably, the concentration of the component e-1 b is 0 to 1.0M, in particular 0.01 M to 0.5M. For instance, it is also possible to use the component e-1 without solvent and ionic liquid (component e-2).

For instance, the solvent e-2 is acetonitrile, methoxy acetonitrile, methoxy propionitrile, propionitrile, ethylene carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, water or combinations thereof and the ionic liquid is a quaternary imidazolium salt, a quaternary pyridinium salt, a quartemary ammonium salt or combinations thereof, preferably the anion of the salt is BF ₄ ^" , PF ₆ ^" , F(HF) _n ^" , bis(trifluoromethanesulfonyl)imide [(CF ₃ SOa) ₂ N ^" ], N(CN) ₂ ^" , C(CN) ₃ ^" , B(CN) ₄ ^" , SCN ^" , SeCN ^" , I ^" , IQ ₃ ^" or combinations thereof. For example, the dye sensitized solar cell comprises a solvent (e.g. without an ionic liquid). For instance, the dye sensitized solar cell comprises an ionic liquid (e.g. without a solvent).

Preferably, the electrolyte layer e comprises a further additive e-3.

Examples of further additives e-3 are lithium salts (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e-2 is absent); for instance 0.05 to 2.0M, preferably 0.1 to 0.7M in case component e-2 is present) (e.g. LiCIO ₄ , LiSO ₃ CF ₃ or Li(CF ₃ SO ₂ )N); guanidinium thiocyanate (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e- 2 is absent); for instance 0.005 to 2.0M, preferably 0.02 to 0.7M in case component e-2 is present); pyridines (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e-2 is absent); for instance 0.005 to 2.0M, preferably 0.02 to 0.7M in case component e-2 is present) (e.g. pyridine, tert-butylpyridine or polyvinylpyridine); imidazoles (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e-2 is absent); for instance 0.005 to 2.0M, preferably 0.02 to 0.7M in case component e-2 is present) (e.g. imidazole, methylimidazole, ethylimidazole or propylimidazole); benzimidazoles (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e-2 is absent); for instance 0.005 to 2.0M, preferably 0.02 to 0.7M in case component e-2 is present) (e.g. benzimidazole, metylbenzimidazole, ethylbenzimidazole or propylbenzimidazole); quinolines (especially molar ratio of 0.005 to 2, preferably 0.01 to 1 based on component e-1 (for instance, in case component e-2 is absent); for instance 0.005 to 2.0M, preferably 0.02 to 0.7M in case component e-2 is present); or combinations thereof.

For instance, the transparent conductive electrode substrate layer a contains (e.g. consists of)

(a-1) a transparent insulating layer and

(a-2) a transparent conductive layer.

For example, the counter electrode layer d contains (e.g. consists of) (d-1 ) a conductive layer and (d-2) an insulating layer. Preferably, the transparent conductive electrode substrate layer a contains (e.g. consists of) (a-1) a transparent insulating layer and (a-2) a transparent conductive layer and the counter electrode layer d contains (e.g. consists of) (d-1) a conductive layer and (d-2) an insulating layer.

For instance, the transparent conductive layer a-2 can be between the transparent insulating layer a-1 and the electrolyte layer e and/or between the transparent insulating layer a-1 and the working electrode b.

Examples of the transparent insulating layer a-1 include glass substrates of soda glass, fused quartz glass, crystalline quartz glass, synthetic quartz glass; heat resistant resin sheets such as a flexible film; metal sheets, transparent plastic sheets made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyether sulfone (PES); a polished plate of a ceramic, such as titanium oxide or alumina.

Examples of transparent conductive layer a-2 are conductive metal oxides such as ITO (indium-tin compounded oxide), IZO (indium-zinc compounded oxide), FTO (fluorine-doped tinoxide), zinc oxide doped with boron, gallium or aluminum, and niobium-doped titanium oxide. The thickness of the transparent conductive layer a-2 is usually 0.1 to 5 μm. The surface resistance is usually below 40 ohms/sq, preferably below 20 ohms/sq. To improve the conductivity of the transparent conductive layer a-2, it is possible to form a metal wiring layer on it, made of for instance silver, platinum, aluminum, nickel or titanium. The area ratio of the metal wiring layer is generally within the range that does not significantly reduce the light transmittance of the transparent conductive electrode a. When such a metal wiring layer is used, the metal wiring layer may be provided as a grid-like, stripe-like, or comb-like pattern.

The conductive layer d-1 is usually between the insulating layer d-2 and the electrolyte layer e.

For instance, the conductive layer d-1 contains a conductive carbon (e.g. graphite, single walled carbon nanotubes, multiwalled carbon nanotubes, carbon nanofibers, carbon fibers, grapheme or carbon black), a conductive metal (e.g. gold or platinum), a metal oxide (e.g. ITO (indium-tin compounded oxide), IZO (indium-zinc compounded oxide), FTO (fluorine- doped tinoxide), zinc oxide doped with boron, gallium or aluminum, and niobium-doped titanium oxide).

Furthermore, the conductive layer d-1 may be one obtained by forming a layer of platinum, carbon or the like (generally with a thickness of from 0.5 to 2,000nm), on a thin film of a conductive oxide semiconductor, such as ITO, FTO, or the like (generally with a thickness of from 0.1 to 5 μm). The layer of platinum, carbon or the like is usually between the electrolyte layer e and the thin film of a conductive oxide semiconductor.

Examples of the insulating layer d-2 includes glass substrates of soda glass, fused quartz glass, crystalline quartz glass, synthetic quartz glass; heat resistant resin sheets such as a flexible film; metal sheets, transparent plastic sheets made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyether sulfone (PES); a polished plate of a ceramic, such as titanium oxide or alumina.

Preferably, the porous film made of oxide semiconductor fine particles of the working electrode b is made of TiO ₂ , SnO ₂ , WO ₃ , ZnO, Nb ₂ O ₅ , Fe ₂ O ₃ , ZrO ₂ , MgO, WO ₃ , ZnO, CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, CdTe or combinations thereof, preferably made of TiO ₂ .

Preferred is a dye sensitized solar cell, wherein the working electrode layer b is formed on an (especially outer) surface of the transparent conductive electrode substrate layer a. For instance, the working electrode layer b is formed on an (especially outer) surface of the transparent conductive layer a-2 of the transparent conductive electrode substrate layer a.

For example, the working electrode layer b can be between the transparent conductive electrode substrate layer a and the electrolyte layer e. For instance, the working electrode layer b can be between the transparent conductive layer a-2 (of the transparent conductive electrode substrate layer a) and the electrolyte layer e. For example, the working electrode layer b can be between the transparent conductive electrode substrate layer a and the photo- sensitzing dye layer c. For instance, the working electrode layer b can be between the transparent conductive layer a-2 (of the transparent conductive electrode substrate layer a) and the photo-sensitzing dye layer c. For example, there is no working electrode layer b between the transparent insulating layer a-1 and the transparent conductive layer a-2.

The oxide semiconductor fine particles can be prepared by a hydrothermal process, a sol/gel process or high temperature hydrolysis in gas phase. The fine particles usually have an average particle diameter of from 1 nm to 1000 nm. Particles with different size can be blended and can be used as either single or multi-layered porous film. The porous film of the working electrode b has usually a thickness of from 0.5 to 50 μm.

Preferred is a dye sensitized solar cell, wherein a blocking layer x is formed on the surface of the transparent conductive electrode substrate layer a or on the surface of the working electrode layer b or on both. For instance, the blocking layer x formed on the surface of the transparent conductive electrode substrate layer a is formed on the transparent conductive layer a-2 (of the transparent conductive electrode layer a).

For instance, the blocking layer x can be between the transparent conductive electrode layer a and the electrolyte layer e. For example, the blocking layer x can be between the working electrode layer b and the electrolyte layer e. For example, the blocking layer x can be between the working electrode b and the photo-sensitizing dye layer c. For instance, the blocking layer x can be between the transparent conductive layer a-2 and the electrolyte layer e. For example, there is no blocking layer x between the transparent insulating layer a- 1 and the transparent conductive layer a-2.

For instance, the blocking layer x is made of a metal oxide (e.g. TiO ₂ , SiO ₂ , AI ₂ O ₃ , ZrO ₂ , MgO, SnO2, ZnO, Eu ₂ O ₃ , Nb ₂ O ₅ or combinations thereof) or a polymer (e.g. poly(phenylene oxide-co-2-allylphenylene oxide) or poly(methylsiloxane)). Details of the preparation of such blocking layers x are described in, for example, Electrochimica Acta, 1995, 40, 643; J. Phys. Chem. B, 2003, 107, 14394; J. Am. Chem. Soc, 2003, 125, 475; Chem. Lett, 2006, 35, 252; J. Phys. Chem. B, 2006, 110, 19191 ; J. Phys. Chem. B, 2001 , 105, 1422.

Preferably, the photo-sensitizing dye layer c contains a dye selected from the group consisting porphyrin (e.g. zinc tetra (4-carboxyphenyl) porphyrin), a cyanide (e.g. iron- hexacyanide complexes), a phthalocyanine, a naphthalocyanine, a metal complex dye (e.g. the metal is Ru, Pt, Ir, Rh, Re, Os, Fe, W, Cr, Mo, Ni, Co, Mn, Zn or Cu, preferably Ru, Os or Fe, in particular Ru), and an organic dye selected from the group consisting of indoline, courmarin, cyanine, merocyanine, hemicyanine, methin, azo, quinone, quinonimine, diketo- pyrrolo-pyrrole, quinacridone, squaraine, triphenylmethane, perylene, indigo, xanthene, eosin and rhodamine.

The typical examples of the organic dye are:

lndoline-1

Coumarine-1 or methin dyes as described in PCT/EP2009/052243.

The ligands of the ruthenium, osmium or iron complex are usually bidentate, tridentate or polydentate polypyridyl compounds, which may be unsubstituted or substituted by for instance a cyano group. For example, the complex has at least one ligand comprising a mononuclear, cyano-containing pyridyl compound. Suitable as photo-sensitizing dye are chormophores as outlined in US5350644 from column 5, line 9 to column 6, line 25.

Typical examples of the ruthenium complex are:

The dye can be selected according to the application and the material used for the porous film made of oxide semiconductor fine particles. The dye may be chemi-sorbed, adsorbed or otherwise be permanently added to the surface of the working electrode b.

The instant dye sensitized solar cells and their components other than the compounds of formula I can be prepared as outlined in US4927721 , US5084365, US5350644 and US5525440. The electrolyte layer e with the compounds e-1 are generally analogously prepared to electrolyte layers containing IVI ₃ ^" as redox pair which is known in the art. Another embodiment of the instant invention is the use of a compound e-1 a and a compound e-1 b as defined herein as a redox pair in the electrolyte of a dye sensitized solar cell as defined herein.

Another object of this invention is a compound (e-1b) as defined herein.

For instance, a compound of formula (I) or (II) with G being as defined above,

wherein

Y is independently linked to X, X', R ₁ or R ₂ ;

with the proviso that X is not H, and that the following compounds are excluded

For example, R ₃ is hydrogen, halogen; or CrC ₂ oalkyl, C ₂ -C ₂₀ alkenyl, C ₃ -C ₂₀ cycloalkyl, C ₄ - C ₂₀ cycloalkenyl, C ₇ -C ₂₆ SrVl, C ₇ -C ₃₀ aralkyl, C ₈ -C ₃₀ aralkenyl, C ₃ -C ₂₀ heteroaryl, C ₃ -

C ₂₀ heteroaryl-CrC ₂₀ alkyl, C ₃ -C ₂₀ heteroaryl-C ₂ -C ₂₀ alkenyl or ferrocenyl, each of which is unsubstituted or substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ -C(O)-OR ₅ , OC(O)NR ₄ R ₅ or combinations thereof, the aryl and heteroaryl can additionally be substituted by Ci-C ₁₆ alkyl, C ₂ -C ₁₆ alkenyl, perfluorinated C ₁ - Ci ₆ alkyl or combinations thereof, and the alkyl, alkenyl, cycloalkyl and cycloalkenyl can additionally be interrupted by O, S, NR ₄ or combinations thereof, whereby the heteroaryl is selected from the group consisting of thiophenyl, bithiophenyl, terthiophenyl, tetrathiophenyl, furanyl, bifuranyl, terfuranyl, pyrrolyl, carbazolyl, indolyl, 9H- purinyl, pteridinyl, chinolinyl, isochinyl, acridinyl and phenazinyl, or R ₃ is phenyl substituted by halogen, OR ₄ , SR ₄ , NR ₄ R ₅ , C(O)R ₄ , C(O)OR ₄ , 0-C(O)-R ₄ , C(O)NR ₄ R ₅ , NR ₄ -C(O)-R ₅ , NR ₄ -C(O)-OR ₅ , OC(O)NR ₄ R ₅ , C _r C ₁₆ alkyl, C ₂ -C ₁₆ alkenyl, perfluorinated CrC^alkyl or combinations thereof.

For instance, X and X' together are =0;

A ^" is an anion Of HPF ₆ , HCIO ₄ , HBF ₄ , HO ₃ SCF ₃ , HN(C ₂ F ₅ SO ₂ ) ₂ , HC(CF ₃ SO ₂ ) ₃ , HC(C ₂ F ₅ SO ₂ ) ₃ , HB(C ₂ O ₄ ) ₂ , HB(C ₆ H ₅ ),, HB(C ₆ F ₅ ),, HSbF ₆ , HAsF ₆ , HBr, HBF ₃ C ₂ F ₅ , HPF ₃ (CF ₂ CFs) ₃ , HCI, HI, CF ₃ COOH, CH ₃ COOH or combinations thereof, preferably A ^" is an anion of HPF ₆ , HCIO ₄ , HBF ₄ , HN(C ₂ F ₅ SG ₂ ); _? , HSbF ₆ , HAsF ₆ , HBr, HCI, HI, CF ₃ COOH or combinations thereof, most preferably A ^" is an anion of HBF ₄ ;

R ₁ and R ₂ are independently CrC ₁₀ alkyl; and

R ₃ is d-C- _t oalkyl, phenyl; or phenyl substituted by 0-CrC^lkyl; preferably, R ₃ is CrC^alkyl; or phenyl substituted by O-Ci-C ₄ alkyl;

with the proviso that the following compounds are excluded

The preferences outlined herein apply to all aspects of the invention.

% are weight-% and ratio are weight ratio unless otherwise stated.

Preparation examples Example F1

Intermediate A:

In a 1000 ml flask 132.2 g (1 mol) of t-butylcarbazate is dissolved in Et ₂ O (400 ml), and then acetone (220 ml; 3 mol) is added at room temperature. The resulting solution is stirred at room temperature overnight, then solvent is removed at the rotavap and the residue dried under vacuum to afford 176.5 g (102%) of A as a light yellow solid.

Intermediate B: In a 2000 ml steel autoclave, to a solution of 172 g (1 mol) of A in THF (800 ml) is added 3.50 g of Pd/C (10% w/w). The mixture is hydrogenated under 10 bar of H ₂ for 24 h at 110 ⁰ C. The reaction mixture is then filtered over celite, the filter-cake is washed with THF, the solvent removed under reduced pressure and the residue dried under vacuum to afford 153.8 g (88%) of B as a white solid.

Intermediate C:

In a 250 ml flask with reflux condenser under N ₂ , 30.0 g (172 mmol) of B is dissolved in toluene (90 ml), and then triethylamine (17.4 g; 172 mmol) is added at room temperature. A solution of triphosgen (8.43 g; 28.4 mmol) in toluene (30 ml) is slowly added over a period of 20 minutes resulting in an increase of the internal temperature to 38 ⁰ C. After complete addition, the resulting white suspension is stirred at room temperature overnight. The reaction mixture is then heated to 80 ⁰ C to be filtered at this temperature; the filter-cake is washed with warm toluene (2 x 100 ml), and then dried under HV to afford 31.3 g (97%) of C as a white solid.

Intermediate D:

In a 500 ml flask with reflux condenser under N ₂ , 31.3 g (83.7 mmol) of C is dissolved in a 4M solution of HCI in dioxane (250 ml) at room temperature. The solution is heated to 100 ⁰ C for 4.5 h. The solvent is then removed under reduced pressure using a rotary evaporator to yield a sticky solid which is triturated with EtOAc (3 x 500 ml). The resulting white solid is dried under HV to afford 13.2 g (64%) of D. lntermediate E:

In a 250 ml flask with reflux condenser under N ₂ , 5.0 g (20.2 mmol) of D and 1.74 g (20.2 mmol) of trimethylacetaldehyde are dissolved in pyridine (75 ml) at room temperature. To the clear brown solution 3.32 g (40.4 mmol) of NaOAc (waterfree) is added and the resulting suspension stirred at room temperature for 24 h, then poured into 500 ml H ₂ O under vigorous stirring. The suspension is filtered, the filter-cake washed with 4L of deionized water, and dried under HV to afford 2.98 g (61%) of E as a yellow solid which is further utilized in the next step without purification.

Example F1:

In a 250 ml flask with reflux condenser under N ₂ , 2.98 g (12.3 mmol) of E is dissolved in toluene (75 ml) at room temperature. To the clear yellow solution 1.99 g (18.4 mmol) of benzoquinone is added, the resulting dark orange solution is then heated to reflux for 3 h. The resulting dark green-yellow mixture is cooled to room temperature and filtered over a plug of 50 g of silica gel. The plug is flushed with toluene/EtOAc 249:1 , then the combined filtrate is evaporated to dryness with a rotavap and the resulting residue purified by column chromatography (60 g SiO ₂ , hexane) to afford 2.07 g (70%) of F1 as a yellow solid. Melting point: 68.1-69.7 ⁰ C. The half-wave potential, E _1/2 , of F1 is measured by cyclic voltammetry. F1 (0.1 M) is dissolved in an organic solvent (acetonitrile containing 0.1 M of tetrabutylammonium perchlorate) and a scan is conducted at 100 mV/second rate by using platinum stationary electrode as working electrode. The value E _1/2 = + 0.08 V vs. Fc/Fc ⁺ is obtained, where voltage is reference to E _1/2 of Ferrocene measured under the same condition.

Example G1 :

In a 50 ml flask with reflux condenser under N ₂ , 0.75 g (3.1 mmol) of F1 is dissolved in CH ₂ CI ₂ (8 ml) at room temperature. To the clear orange solution 0,37 g (3.1 mmol) of nitrosyl tetrafluoroborate is added leading to gas formation and dark color. After 2.5 h the red solution is cooled in an ice-bath, and then 50 ml of hexane is added. After a few minutes of stirring, the resulting suspension is filtered and the filter-cake washed with 50 ml hexane, then dried under HV to yield 0.82 g (80%) of G1 as a yellow solid. Melting point: 200.2-200.8

⁰ C.

The half-wave potential, E _1/2 , of G1 is measured by cyclic voltammetry. G1 (0.1 M) is dissolved in an organic solvent (acetonitrile containing 0.1 M of tetrabutylammonium perchlorate) and a scan is conducted at 100 mV/second rate by using platinum stationary electrode as working electrode. The value E _1/2 = + 0.08 V vs. Fc/Fc ⁺ is obtained, where voltage is reference to E _1/2 of Ferrocene measured under the same condition.

Examples F2 to F19 Example F2 to F19 are prepared in analogy to the above-mentioned procedures. The half- wave potential, E _1/2 , is measured in analogy to the above-mentioned method.

iPr is iso-propyl

Examples G2 and G7 and G19

Examples G2, G7 and G19 are prepared in analogy to the above-mentioned procedures. The half-wave potential, E _1/2 , is measured in analogy to the above-mentioned method.

Aplication examples Examples DSC-1

As a transparent conductive electrode substrate, a glass base having an FTO (fluorine- doped tinoxide) film formed thereon is provided (< 12 ohms/sq, A11DU80 from AGC Fabritech Co., Ltd.). TiO ₂ blocking layer is formed on the FTO surface by spray pyrolysis method following the procedure described in Electrochimica Acta, 1995, 40, 643. Then TiO ₂ paste (PST-18NR, supplied by Catalysts&Chemicals Ind. Co., Ltd.) is applied on an area of 8x8 mm by the screen printing method. After being dried for 5 min. at 120°C, a working electrode layer having a thickness of 4-6μm is obtained by applying heating treatment at 500 ⁰ C for one hour Thus prepared transparent working electrode is immersed overnight in an acetonitπle + t-butyl alcohol (1 1) solution of dye (0 42mM lndolιne-1*) so as to adsorb dye As a counter electrode, an ITO (indium-tin compounded oxide) glass electrode substrate is prepared having an electrode layer made of platinum (8nm thickness) formed thereon by sputtering An electrolyte solution is prepared by dissolving 0 1 M of F1 and 0 05M of G1 in 3- methoxypropionitπle

DSC cell is fabricated by making the above working electrode and counter electrode opposed to each other and holding the above electrolyte solution between them with the Teflon spacer with 50μm thickness The prepared DSC cell is evaluated by KEITHLEY 2400 source meter using PEC-L11 solar simulator (Peccell Technologies, lnc ) under illumination of 100 mW/cm ² (1 5AM) The IPCE (incident photon-to-current efficiency) spectra are obtained by SM-10AC (Peccell Technologies, lnc ) *Purchased from Mitsubishi Paper Mills Limited, the commercial name is D149

Examples DSC-2

DSC cell is fabricated and evaluated in a same manner as DSC-1 except that electrolyte solution is prepared by dissolving 0 1 M of F2 and 0 05M of G2 in 3-methoxypropιonιtπle

Examples DSC-3

DSC cell is fabricated and evaluated in a same manner as DSC-1 except that electrolyte solution is prepared by dissolving 0 1 M of F19 and 0 05M of G19 in 3-methoxypropιonitπle

Example DSC-C1 (comparative example) DSC cell is fabricated and evaluated in a same manner as DSC-1 except that electrolyte solution is prepared by dissolving 0 1M of FC1 and 0 05M of GC1 in 3-methoxypropιonιtrιle

Table 1 DSC properties

FC1 GC1

Corrosiveness evaluation

Ag is vacuum-deposited onto glass substrate at 10nm thickness. Onto the Ag layer electrolyte solution is dropped, and the corrosiveness is evaluated from the appearance change of Ag. The electrolyte solution of 0.1 M F1 , 0.05M G1 in propylene carbonate do not give the damage of Ag, whereas electrolyte solution of 0.15M LiI, 0.05M I ₂ in propylene carbonate damages the Ag layer soon after dropping.