2,2 -BIPYRIDINE LIGAND, SENSITIZING DYE AND DYE SENSITIZED SOLAR CELL

Description

[0001] The present invention concerns an organic compound. The present invention further concerns a sensitizing dye incorporating said organic compound. Still further, the present invention concerns a dye-sensitized solar cell.

[0002] Dye-sensitized solar cells, or DSSCs, are regenerative photo-electrochemical cells comprising a photoanode, said photoanode comprising at least one semiconductive metal oxide layer on a conductive substrate, sensitized by at least one chromophoric substance, a counter-electrode, and an electrolyte positioned between these electrodes.

[0003] In cells of this type, at least one of these electrodes is sufficiently transparent or translucent for allowing light input. The afore-said semi-conductive metal oxide layer is conveniently made of oxides of transition metals or elements either of the third main group, or of the fourth, fifth and sixth sub-groups of periodic table of elements, the surface of the photoanode in contact with the electrolyte being porous, with a porosity factor of preferably at least 20. The "porosity factor" is defined as the ratio of the photo-electrochemically active surface of the photoanode to the surface area of the substrate covered by the layer(s) of semiconductive metal oxide. The use of nanocrystalline titanium dioxide was shown to be particularly advantageous. The term "nanocrystalline" means that the semiconductive metal oxide, in particular TiO₂, is in polycrystalline form with a granulometry of the order of several nanometers, for example 10 to 50 nanometers.

[0004] In this type of cell, a chromophoric substance, often called photosensitizer or photosensitizing dye, forms a substantially monomolecular layer attached to the semiconductive metal oxide layer, in particular the nanocrystalline TiO₂ layer. The chromophoric substance may be bound to the metal oxide layer by means of anchoring groups like carboxylate or phosphonate or cyano groups or chelating groups with π-conducting character like oxymes, dioxymes, hydroxyquinolines, salicylates and <-keto-enolates. Several transition metal complexes, in particular ruthenium complexes, but also osmium or iron complexes, with heterocyclic ligands like bidentate, tridentate or polydentate polypyridil compounds, have been shown to be efficient photosensitizing dyes. Sensitizing dyes and cells of this type are described inter alia in EP 0333641, EP 0525070, EP 0613466 and EP 0758337.

[0005] The mesoporous texture of the TiO₂ film in these cells significantly increases the cross section of light harvesting by surface-anchored charge transfer sensitizers while maintaining a good contact with electrolytes. In these photovoltaic devices, ultrafast electron-injection from a photoexcited dye into the conduction band of an oxide semiconductor, and subsequently dye regeneration and hole transportation to the counter electrode, are responsible for the efficient generation of electricity.

[0006] Among suitable electrolytes are those including a redox system consisting of a mixture of at least one electrochemically active salt and at least one molecule designed to form an oxidation-reduction system with either the anion or cation of the said salt. Electrolytes wherein said electrochemically active salt has a melting point below ambient temperature or forms with the afore-said molecule a phase with a melting point below ambient temperature have been described in EP 0737358. Additionally, gelified materials incorporating triiodide/iodide as a redox couple, as disclosed by EP 1087412, were introduced to substitute the liquid electrolytes by quasi-solid state materials.

[0007] A respectable 10.4 % light-to-electricity conversion efficiency at AM 1.5 solar irradiance has been obtained for photovoltaic devices with a panchromatic dye and a liquid electrolyte containing the triiodide/iodide couple, as reported in J. Am. Chem. Soc. 123, 1613-1624 (2001).

[0008] However the achievement of long-term stability at temperatures of 80∼85°C, which is an important requirement for outdoor application of the DSSC, still remains a major challenge:

The leakage of liquid electrolyte from such DSSC modules, possible desorption of loosely attached dyes and photodegradation in the desorbed state, as well as corrosion of the photoelectrode and/or counter electrode by the triiodide/iodide couple, may be considered as some critical factors limiting the long-term performance of the DSSC, especially at elevated temperature. A particular problem of stability at 80°C in DSSCs containing the iodide/triiodide redox couple, upon aging, is the drop in open circuit potential (V_oc), causing the poor stability. It is believed that the dark current of DSSCs increases and V_oc decreases, due to the interaction of triiodide with bare zones of the TiO₂ electrode, that is not completely covered with dye molecules.

[0009] Grätzel and co-workers demonstrated (Langmuir (2002) 18, 952) that heteroleptic amphiphilic complexes of formula RuLL'(NCS)₂, where L is the anchoring ligand 4,4'-dicarboxy-2,2'-bipyridine and L' is a 2,2'-bipyridine substituted by one or 2 long alkyl chains, are an interesting class of sensitizing dyes for DSSCs. The long alkyl chains in all likelihood interact laterally to form an aliphatic network, thereby impeding triiodide from reaching the TiO₂ surface, resulting in increased open circuit potential of the cell and enhanced stability versus time. They further found (Nature Materials (2003) 2, 402) that a cell using the sensitizer cis-(NCS)₂RuLL', where L' = 4,4'-dynonyl-2,2'-bipyridine, hereinafter referred to as Z907, in conjunction with a quasi solid state polymer gel electrolyte reaches an efficiency of > 6 % in full sunlight (air mass 1.5, 100 mW·cm^-2) with unprecedented stable performance under both thermal stress and soaking with light.

[0010] In EP 1091373A1, a dye-sensitized photoelectric conversion device is disclosed, in which a gel electrolyte is indicated to be useful for increasing conversion efficiency and durability. This reference discloses ruthenium dyes as mentioned above, but proposes that 2,2' bipyridine could be substituted, besides alkyl, with halogen, aralykyl and aryl. Furthermore, polymethine dyes are taught to be an alternative to the ruthenium dyes. Conversion efficiencies (η) obtained with the devices described in EP 1091373A1 are below 1%, which is too low.

[0011] A further remarkable increase in photovoltaic performance was achieved by co-grafting hexadecylmalonic acid (HDMA) with Z907 sensitizing dye onto nanocrystalline TiO₂ films (J.Phys. Chem. B (2003) 107, 14336). Like Z907, HDMA contains two carboxylate groups to anchor it on the TiO₂ surface. Co-grafting of the two amphiphiles results in the formation of a mixed monolayer which should be more tightly packed than when the sensitizing dye is adsorbed alone, providing a more effective insulating barrier for the back electron transfer from TiO₂ conduction band to triiodide in the electrode. Retarding this unwanted redox process by the hydrophobic spacer reduces the dark current and increases the open circuit voltage of the solar cell. The cell also showed good stability under light soaking at 55°C in simulated sunlight.

[0012] However, the molar extinction coefficient of known amphiphilic polypyridyl ruthenium sensitizers is lower than the one of N-719, the most efficient sensitizer for dye-sensitized solar cells. Additionally, the spectral response is blue-shifted compared with this most efficient sensitizing dye. Thus, the aim of the invention is to improve the light-harvesting capacity of amphiphilic sensitizing dyes by a rational design of the molecule while not decreasing their LUMO energy, allowing a high quantum efficiency of electron injection without lowering the conduction band of the mesoporous semiconductor and thus having a loss of device photovoltage.

[0013] These aims are achieved by using, as a ligand in sensitizing dyes of a dye sensisitzed solar cells, an organic compound L1 having a formula selected from the group of formulae (a), (a'), (b), (c), (d), (e), (f), (g), (h), (i) or (j)

wherein at least one of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', - R₂', - R₃', -R'' comprises an additional π system located in conjugated relationship with the primary π system of the bidentate or respectively tridentate structure of formulae (a) to (j) and,
wherein the other one(s) of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is (are) the same or a different substituent including a π system, or is (are) selected from H, OH, R2, (OR2)_n, N(R2)₂, where R2 is an alkyl of 1-20 carbon atoms or linear R cyclic polyether, 0 < n < 5.

[0014] Briefly speaking, use of compounds L1 permits to extend the conjugated π system of the donating ligand, increasing the light absorbance and keeing the LUMO energy level higher than that of the anchoring ligand.

[0015] In preferred compounds L1, the said substituent is of the type

wherein ⁅Π⁆ represents schematically the π system of the aforesaid substituent, Ral represents an aliphatic substituent with a saturated chain portion bound to the π system, and wherein q represents an integer, indicating that ⁅Π⁆ may bear more than one substituent Ral.

[0016] The π system ⁅Π⁆ may be an unsaturated chain of conjugated double or triple bonds of the type

wherein p is an integer from 1 to 8.
or an aromatic group Rar of from 6 to 22 carbon atoms, or a combination thereof.

[0017] The presence of an aromatic group is preferred, since it is less sensitive to oxydation than a long chain of conjugated double or triple bonds.

[0018] Among suitable aromatic groups, there are monocyclic aryls like benzene and annulenes, oligocyclic aryls like biphenyle, naphthalene, biphenylene, azulene, phenanthrene, anthracene, tetracene, pentacene, or perylene. The cyclic structure of Rar may incorporate heteroatoms.

[0019] Preferred ligands according to the invention are organic compounds L1 having a formula selected from the group of formulae (a) to (j)









wherein at least one of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is of formula (1), (2) or (3)





wherein p is an integer from 1 to 4, and for substituents (1) and (3) can also be 0
wherein q is an integer from 1 to 4,
wherein Rar is a monocyclic or oligocyclic aryl from C6 to C22,
wherein -Ral is H, -R1, (-O-R1)_n, -N(R1)₂, -NHR1,





wherein R1, R'1 is an alkyl from 1 to 10 carbon atoms, 20 ≥ X ≥ 0, and 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 or 2, and
wherein the other one(s) of substituent(s) -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is (are) the same or a different substituent of formula (1), (2) or (3), or is (are) selected from -H, -OH, -R₂, -OR₂ or -N(R₂)₂, wherein R₂ is an alkyl of 1 to 20 carbon atoms.

[0020] Compounds L1, in which p = 1 are preferred, because the molecular structure is more rigid, less sensitive to oxydation but is still an electron donator.

[0021] The invention faces more particularly compounds L1, wherein said compound is a 4,4'-disubstituted bipyridine of formula

wherein p = 1;
more particularly compounds L1, wherein R = R', p = 1, and wherein Rar is selected from the group consisting of benzene, naphthalene and anthracene.

[0022] Particularly preferred compounds L1 are:

4,4'-bis(4-hexyloxystyryl)-2,2' bipyridine,

4,4'-bis(4-hexyloxynaphtalene-1-vinyl)-2,2' bipyridine,

and 4,4'-bis[4-(1,4,7,10-Tetraoxyundecyl)styryl]-2,2'-bipyridine].

[0023] Figs 11 and 12 show further examples 1 to 10 of L1 compounds.

[0024] The resulting sensitizing dye is an organometallic complex of a metal Me selected from the group consisting of Ru, Os and Fe, comprising as a ligand a compound L1 as described herein before, said complex being of formula

        Me L1 L(Z)₂     (I)

if L1 is a compound of formula (a'), (b), (c), (d), (g), (h), (i) or (j)









and of formula

        Me L1 L Z     (II)

if L1 is a compound of formula (e) or (f)

wherein L is a ligand selected from the group of ligands of formula

wherein A and A' are anchoring groups selected from COOH, PO₃H₂, PO₄H₂, SO₃H₂, SO₄H₂, CONHOH, deprotonated forms thereof and chelating groups with Π conducting character,
wherein Z is selected from the group consisting of H₂O, Cl, Br, CN, NCO, NCS and NCSe and
wherein at least one of substituents R, R', R'' comprises a π system in conjugated relationship with the π system of the bidentate, respectively the tridentate structure of formulae (a') to (j),
and wherein the other one(s) of substituents R, R', R'' is (are) the same or a different substituent including a π system, or is (are) selected from H, OH, R2, (OR2)_n, N(R2)₂, where R2 is an alkyl of 1-20 carbon atoms and 0 < n < 5.

[0025] More particularly, the sensitizing dye according to the invention is a complex of formula

        Me L1 L(Z)₂     (I)

wherein Me designates Ru, Os or Fe,
wherein L is selected from ligands

wherein Z is selected from H₂O, -Cl, -Br, -I, -CN, -NCO, -NCS and -NCSe.
wherein L1 is a 4,4' disubstituted bipyridine of formula

wherein R is a substituent selected from the group of substituents (1), (2) and (3), and R' has the same meaning as above.





wherein p is an integer from 1 to 4, and for substituents (1) and (3), can also be 0
wherein q is an integer from 1 to 4
wherein Rar is a monocyclic or polycyclic aryl from C6 to C22
wherein each -Ral is, independently one from the others, -H, -R1, -(O-R1)_n, -NHR1, N(R1)₂,





wherein R1, R'1 is an alkyl from 1 to 10 carbon atoms, 20 ≥ X ≥ 0, and 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 or 2.

[0026] The use of heteroleptic ruthenium (II) sensitizing dyes may be preferred over the symmetrical ones. Heteroleptic sensitizing dyes can incorporate required properties in one molecule by selecting suitable ligands to enhance the photovoltaic performance.

[0027] A preferred family of sensitizers are Ru complexes of formula

        cis(NCS)₂RuLL1,

wherein L1 is of formula (a'), wherein R is of formula (1), (2) or (3), wherein p = 1, wherein Rar is selected from the group consisting of benzene, naphthalene, wherein q = 1 to 4, wherein Ral is OR1 and wherein R1 is an alkyl of 1 to 10 carbon atoms.

[0028] Particularly preferred sensitizers are:

cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxystyryl)-2,2' bipyridyl]-Ru(II), hereinafter referred to as K19,

cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxynaphtalene-1-vinyl)-2,2' bipyridyl]-Ru(II), hereinafter referred to as K24,

Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[ 4,4'-bis[4-(1,4,7,10-Tetraoxyundecyl)styryl]-2,2'-bipyridine]-Ru(II) hereinafter referred to as K60, and

cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(3-methoxystyryl)-2,2' bipyridyl]-Ru(II),hereinafter referred to as Z910.

[0029] These new sensitizing dyes have a very high light-harvesting capacity to UV photons. The UV photons can directly excite the wide band-gap metal oxide semiconductor to produce chemically active holes and thus decompose sensitizing dyes and organic electrolyte components or hole-transport materials. After absorbing of UV photons by these new sensitizers, excitons can move rapidly from the donating ligand to the metal center, leaving a hole there and giving an electron to the anchoring ligand, and the electron will be injected to the semiconductor film and realize interfacial charge separation. The strong UV photon absorbing ability makes this type of sensitizer like a "UV filter" while having the advantage of converting the normally unwanted UV photons for dye sensitized solar cells to useful electrons.

[0030] These new sensitizing dyes with enhanced light-harvesting capacity are particularly advantageous when used in combination with transparent mesoporous films (no scattering layer), and/or high-viscosity ionic liquid electrolytes, with which thinner mesoporous films are needed to reduce the mass transport problem, said thinner films having a relatively low surface area (larger metal oxide semiconductor particles) for inducing less back electron transfer. Additionally, with this excellent light harvesting property of these sensitizing dyes, less amount of materials are required for efficient devices.

[0031] According to a further aspect of the DSSC according to the present invention, an amphiphilic compacting compound is co-adsorbed with the dye on the surface of the semiconductive metal oxide layer forming a mixed monolayer. The molecular structure of said compacting compound comprises at least one anchoring group, a hydrophobic portion and a terminal group.

[0032] The anchoring group of the compacting compound, binding to the surface of the semiconductive metal oxide layer, may be the same as the anchoring group of the sensitizing dye or a different one. It may be selected from the group consisting of COOH, PO₃H₂, PO₄H₂, SO₃H₂, SO₄H₂, CONHOH or deprotonated forms thereof. The anchoring group of the compacting compound may also be a chelating group with π-conducting character, in particular an oxyme, dioxyme, hydroxyquinoline, salicylate or α-keto-enolate group.

[0033] The molar ratio of said sensitizing dye to said co-adsorbed compacting compound may be of between 10 and 1/2, and preferably of between 5 and 1. Depending upon the selection of the dye and the co-adsorbent, i.e. their relative affinity constant for the TiO₂ layer, the ratio of dye and co-adsorbent can be varied from 1:10 to 10:1 in their common solvent if they are adsorbed simultaneously, i.e. within the same preparative step. Alternatively, the compacting compound may be adsorbed in a preliminary adsorption step, before the adsorption of the dye, as a pre-treatment, or after the adsorption of the dye, as a post-treatment separate adsorption step.

[0034] Since optical density measurements of the mixed monolayer show a decrease in the optical density, if compared to the optical density of an adsorbed monolayer made of a neat dye, it appears that the compacting agent does go onto the surface along with dye molecules, rendering such a monolayer compact. It is thus believed that said sensitizing dye and said compacting compound form a self-assembled compact mixed monolayer on said semiconductive metal oxide layer.

[0035] Without being bound by theory, it is believed that the hydrophobic part of the amphiphilic sensitizing dye molecules and the hydrophobic portion of the compacting compound molecules co-adsorbed in the afore-said ratios constitute a closely packed hydrophobic monolayer forming a barrier shielding the surface of the semiconductor metal oxide layer, in particular versus triiodide. It is believed that the triiodide can no more reach the TiO₂ surface and that therefore the dark current decreases by decreasing the back electron transfer from the photo injected electrons of TiO₂ to triiodide. It is also believed that the hydrophobic portion of the mixed monolayer constitutes a barrier against H₂O, hindering water residues to reach the surface of the photoanode. It is further believed that the presence of the co-adsorbing compacting compound contributes in structuring the arrangement of the adsorbed dye molecules.

[0036] The terminal group of the compacting compound may be an uncharged group. The terminal group may consist of the free end of an alkyl, alkenyl, alkynyl, alkoxyl or poly-ether chain. The terminal group may consist of a neutral group taking up more space, like a branched alkyl, or a carbon atom substituted by several cycloalkyl or phenyl groups.

[0037] Without being bound by theory, it is believed that when the compacting molecules co-adsorbed with the sensitizing dye have a sufficient chain length and if the ends of these chains bear a terminal group (Y) constituted by a bulky neutral hydrophobic group like branched alkyls, these terminal groups have a capping function protecting the dye layer and the anode surface from electrolyte components, among them triiodide, and also from water, the presence of traces of the latter in a DSSC being hardly avoidable.

[0038] The terminal group of the compacting compound may be an anionic group. Such terminal group may be selected among the same group as the anchoring groups, that is to say SO₃^-, CO₂^-, PO^2-₃, PO₃H^-, CONHO^-. The terminal group of the compacting compound may be a cationic group. Such terminal group may be selected among ammonium, phosphonium, sulfonium, imidazolium, pyrrolidonium and pyridinium groups.

[0039] In turn, when the molecules co-adsorbed with the sensitizing dye have a sufficient chain length and if the ends of these chains bear a charged group (Y), these groups surmount the hydrophobic level of the mono-layer and are capable of repelling species present in the electrolyte, thereby preventing once again direct interaction of the species of the electrolyte with parts of the semiconductive metal oxide surface itself.

[0040] In view of an outdoor use, exposed to sun at elevated temperatures, the compacting compound is preferably selected so that said self-assembled monolayer is a dense packed monolayer having an order-disorder transition temperature above 80°C.

[0041] Preferred compacting compounds are selected among compounds of following formulae (1) to (27)

[0042] With the proviso that P = Q = H (hydrogen) or P = H and Q = F (fluoride)
or P = Q = F
that X and X' are, independently one from the other, one of the groups SO₃^-, CO₂^-, PO₃^2-, PO₃H^- and CONHO^-
that n, n' and n'' designate the same or different integers from 1 to 20
that Y and Y' are, independently one from the other, one of the groups SO₃^-, CO₂^-, PO₃^2-, PO₃H^- and CONHO^- or a group having one of formulae (101) to (106)





wherein R₁, R₂, R₃ designate independently one from the other H, a phenyl group or an alkyl group of 1 to 20 carbon atoms.

[0043] In particular, the compacting compound may be selected from the group consisting of alkyl carboxylic acids, alkyl dicarboxylic acids, alkyl carboxylates, alkyl phosphonic acids, alkyl phosphonates, alkyl diphosphonic acids, alkyl diphosphonates, alkyl sulphonic acids, alkyl sulphonates, alkyl hydroxamic acids, alkyl hydroxamates, wherein alkyl is linear or branched from C₁ to C₂₀, derivatives of said alkyl hydroxamic acids bearing a terminal group Y of one of formulae (101) to (106) or an anionic terminal group as aforesaid, cyclohexanecarboxylic acid, adamentane acetic acid, adamentane propionic acid and 4-pentylbicyclo (2,2,2)-octane-1-carboxylic acid.

[0044] None of the above-cited compacting compounds are electron donating species.

[0045] The chain length of the compacting compound, i.e. the length of the hydrophobic portion, is adapted to the dimension of the dye molecule, in particular to the length of substituent R, i.e. ⁅π⁆(̵Ral)_q.

[0046] According to another aspect of the DSSC, object of the present invention, the electrolyte of the DSSC may comprise a polar organic solvent having a high boiling point. Boiling points over 100°C at standard atmospheric pressure are preferred. A suitable compound to be used as organic solvent in the framework of the present invention may be found among nitriles. A preferred nitrile is 3-methoxypropionitrile (MPN). The solvent may be useful on one hand for solubilizing an electrochemically active salt present in the electrolyte, and/or the compound forming the redox couple with an ion of said salt.

[0047] In still another aspect of the DSSC according to the present invention, the electrolyte may comprise, instead of an electrochemically active salt which is solid at ambient temperature and shall be dissolved in a solvent, a so-called "room temperature molten salt", an electrochemically active salt having a melting point lower than ambient temperature, or a salt selected so that the mixture formed by this salt and another species of the redox system has a melting point lower than ambient temperature. Then, presence of a solvent may be avoided. The cation of the electrochemically active salt may comprise at least one quaternary nitrogen. The quaternary nitrogen may be comprised in a group selected from imidazolium and triazolium type groups, corresponding to the following general formulae (a) or (b):

where the groups R₁, R₂, R₃, R₄ and R₅ are identical or different and are selected from hydrogen and linear or branched alkyl groups, with 1 to 20 carbon atoms, linear or branched alkoxy groups with 1 to 20 atoms of carbon, fluoride substitution derivatives of alkyl groups, alkenyl groups, and combinations of these groups and the corresponding halogenides, or from the alkoxyalkyl and polyether groups.

[0048] The cation of the electrochemically active salt may also be an ammonium, a phosphonium or a sulfonium group corresponding to the following general formulae (c), (d) or (e) :

[0049] In which groups R₁, R₂, R₃, R₄ have the same meanings as above.

[0050] The anion of said ionic liquid salt may be selected from halide ions, or a polyhalide ion, or a complex anion containing at least one halide ion, CF₃SO₃^-, or CF₃COO^- or (CF₃SO₂)₃C^- or NO₃^- or PF₆^- or BF₄^- or N(CN)₂^- or NCS- SeCN^- or ClO₄^- or C(CN)₃^- or R₆SO₃^- or R₆SO₄^-, where R₆ is selected from hydrogen and linear or branched alkyl groups, with 1 to 20 carbon atoms, linear, or branched alkoxy groups with 1 to 20 atoms of carbon.

[0051] The redox system of the electrolyte may comprise two salts or more, each having a melting point below ambient temperature, the anions forming a couple of two different electrolytes, for example the iodide/bromide couple.

[0052] In a still further aspect of the DSSC, object of the present invention, the electrolyte incorporates a first compound co-operating with either the anion or the cation, of the electrochemically active salt, that is to say forming a redox couple with said ion. As a well-known example of such a couple, if the anion of the electrochemically salt is I^-, the neutral molecule, respectively element, is iodine.

[0053] In still a further aspect of the DSSC, object of the present invention, the electrolyte may incorporate a stabilizing additive in form of a neutral molecule comprising one or more nitrogen atom(s) with a lone electron pair.

[0054] Said neutral molecule may be selected from molecules having following formula:

wherein R'₁ and R'₂ can be H, alkyl, alkoxyl, alkenyl, alkynyl, alkoxy-alkyl, poly-ether, and/or phenyl, independently one from the other, the number of carbon atoms of each substituent ranging from 1 to 20, the substitute being linear or branched.

[0055] Preferred compounds are Benzimidazole, 1-methylbenzimidazole, 1-methyl-2-phenyl benzimidazole and 1,2 dimethyl benzimidazole.

[0056] The presence of the afore-said neutral additive compound in the electrolyte increases the stability of the DSSC.

[0057] Other particulars and advantages of the DSSC according to the invention, in particular improved performance and stability at high temperature, will appear to those skilled in the art from the description of the following examples in connection with the drawings, which show:

• Fig. 1: synthetic route of donating ligands L1;
• Fig. 2: synthetic route of RuLL1(NCS)₂;
• Fig. 3: absorption spectra of Z910, N-719, and Z-907 anchored on a 8 µm thickness transparent nanocrystalline TiO₂ film;
• Fig. 4: photocurrent action spectrum of device A sensitised with Z910 dye;
• Fig. 5: current density-voltage characteristics of devices A with Z910 dye under AM 1.5 sunlight (100 mW cm^-2) illumination and in the dark. Cell active area: 0.158 cm². Outside of the active area is completely masked with black plastic to avoid the diffusive light;
• Fig. 6: detailed photovoltaic parameters of devices B with Z910 dye during successive one sun visible-light soaking at 55 °C;
• Fig. 7: detailed photovoltaic parameters of devices C with K19 dye at 80 °C;
• Fig. 8: detailed photovoltaic parameters of devices C with K19 dye during successive one sun visible-light soaking at 55 °C;
• Fig. 9: detailed photovoltaic parameters of devices E with K19 dye and 1-decylphosphonic acid as coadsorbent at 80 °C;
• Fig. 10: detailed photovoltaic parameters of devices E with K19 dye and 1-decylphosphonic acid as coadsorbent during successive one sun visible-light soaking at 55 °C;
• Fig. 11 and 12: the molecular structures of examples of ligands L1;
• Fig. 13: the molecular structures of K 60 and Z910.

Example I: Synthesis of ligands L1

[0058] The synthesis steps are shown in Fig. 1.

1) 4-Hexyloxybenzaldehyde, intermediate compound 1

[0059] 4-formyl-phenol (5 g, 41 mmol), iodohexane (10.5 g, 49 mmol) and K₂CO₃ (8.5 g, 61 mmol) in acetonitrile (150 ml) were refluxed overnight under N₂. After being cooled to room temperature, water (10 ml) was added and acetonitrile was evaporated. Water (150 ml) and Et₂O (150 ml) were then added. The ethereal layer was extracted and washed with water (2 x 100 ml), brine (100 ml), dried over MgSO₄, filtered and evaporated to dryness to afford 8.3 g (98 %) of compound 1 as a slightly yellow oil after dring at 80 °C under vacum.
¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 0.94 (t, J = 6.5 Hz, 3H), 1.3-1.6 (m, 6H), 1.80 (m, 2H), 4.05 (t, J = 6.5 Hz, 2H), 7.00 (d, J = 8.7 Hz, 2H), 7.83 (d, J = 8.7 Hz, 2H), 9.89 (s, 1H). ¹³C-NMR (CDCl₃, 298K, 50 MHz, δ ppm) 14.0, 22.5, 25.6, 29.0, 31.5, 68.4, 114.7, 129.7, 131.9, 164.2, 190.7.

2) 1-Hexyloxynaphthalene, intermediate compound 2

[0060] 1-naphthol (5 g, 34.7 mmol), iodohexane (8.82 g, 41.6 mmol) and K₂CO₃ (7.2 g, 50 mmol) in acetonitrile (150 ml) were refluxed overnight under N₂. After being cooled to room temperature, water (10 ml) was added and acetonitrile was evaporated. Water (150 ml) and Et₂O (150 ml) were added. The ethereal layer was extracted and washed with water (2 x 100 ml), brine (100 ml), dried over MgSO₄, filtered and evaporated to dryness to afford 7.8 g (98 %) of compound 2 as an orange oil after dring at 80 °C under vacum.
¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 0.99 (t, J = 6.5 Hz, 3H), 1.3-1.7 (m, 6H), 1.96 (m, 2H), 4.18 (t, J = 6.5 Hz, 2H), 6.84 (dd, J = 1.7 and 6.8 Hz, 1H), 7.4-7.6 (m, 4H), 7.84 (m, 1H), 8.35 (m, 1H). ¹³C-NMR (CDCl₃, 298K, 50 MHz, δ ppm) 14.1, 22.7, 26.0, 29.3, 31.7, 68.1, 104.5, 119.9, 122.1, 125.0, 125.8, 125.9, 126.3, 127.4, 134.5, 154.9.

3) 1-Hexyloxy-4-formylnaphthalene, intermediate compound 3

[0061] POCl₃ (3.22 g, 21 mmol) was dropwise added to a solution of compound 2 (4 g, 17.5 mmol) in anh. DMF (5 ml) at room temperature and under N₂. The resulting dark red solution was heated to 100°C for 3 hours. Concentrated AcONa solution (5 ml) was then added and heating was continued for 2 hours more. After being cooled to room temperature, water (100 ml) was added. The mixture was extracted with Et₂O (2 × 150 ml), the ethereal combined fractions were washed with 10 % HCl solution (100 ml), water (100 ml), dried over MgSO₄, filtered and evaporated to dryness. Recrystallisation of the brown solid from EtOH afford 2.1 g (47 %) of compound 3 as brownish crystals.
¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 0.95 (t, J = 7 Hz, 3H), 1.3-1.7 (m, 6H), 1.98 (m, 2H), 4.24 (t, J = 6.4 Hz, 2H), 6.90 (d, J = 8 Hz, 1H), 7.58 (t, J = 8 Hz, 1H), 7.71 (t, J = 8 Hz, 1H), 7.90 (d, J = 8 Hz, 1H), 8.37 (d, J = 8 Hz, 1H), 9.32 (d, J = 8 Hz, 1H), 9.89 (s, 1H). ¹³C-NMR (CDCl₃, 298K, 50 MHz, δ ppm) 14.0, 22.6, 25.8, 29.0, 31.5, 68.8, 103.5, 122.4, 124.7, 124.8, 125.6, 126.3, 129.4, 131.9, 139.8, 160.4, 192.2.

4) 4,4'-bis[(trimethylsilyl)methyl]-2,2'-bipyridine, intermediate compound 4, was synthesized according to procedure published by A. P. Smith, J. J. S. Lamba, and C. L. Fraser (Organic Synthesis, 78, pp. 82-90).

5) 4,4'-bis(chloromethyl)-2,2'-bipyridine, intermediate compound 5

[0062] A solution composed of compound 4 (2 g, 6.1 mmol), hexachloroethane (5.8 g, 24.3 mmol) and KF (1.42 g, 24.3 mmol) in anhydrous DMF (30 ml) was stirred overnight at room temperature under N₂. EtOAc (150 ml) was added. The organic layer was washed with water (5 × 100 ml), dried over MgSO₄ and evaporated to dryness. The resulting solid was dissolved in the minimum volume of hexane and let stand in the freezer for few hours. The resulting white crystalline solid was filtered and washed with small cold portions of hexane to afford 1.4 g (91 %) of compound 5 as white crystalline solid.
¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 4.65 (s, 4H), 7.40 (d, J = 5 Hz, 2H), 8.45 (s, 2H), 8.70 (d, J = 5 Hz, 2H).

6) 4,4'-bis(diethyl methylphosphonate)-2,2'-bipyridine, intermediate compound 6.

[0063] Compound 5 (2.6 g, 10.3 mmol) was refluxed overnight under N₂ in triethylphosphite (50 ml). Excess P(OEt)₃ was evaporated and the resulting brown oil was column chromatographed (Al₂O₃, CH₂Cl₂/MeOH: 98/2). The yellow oil thus obtained was dissolved in a mixture of CH₂Cl₂/hexane (1/50 ml) and let stand in the freezer to afford after filtration 4 g (85 %) of compound 6 as a slightly yellow crystalline solid.
¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 1.27 (t, J = 7 Hz, 12H), 3.18 (s, 2H), 3.29 (s, 2H), 4.08 (m, 8H), 7.33 (d, J = 5 Hz, 2H), 8.34 (s, 2H), 8.60 (d, J = 5 Hz, 2H).

7) Procedure for the synthesis of 4,4'-bis(4-hexyloxystyryl)-2,2'-bipyridine, compound 7, and 4,4'-bis(4-hexyloxynaphthalene-1-vinyl)-2,2'-bipyridine, compound 8.

[0064] Solid ^tBuOK (740 mg, 6.6 mmol) was added to an anh. DMF (50 ml) solution of compound 6 (1 g, 2.2 mmol) and compound 1 or 3 (2.52 g, 5.5 mmol) and the resulting mixture was stirred overnight at room temperature under N₂. A copious precipitate appeared after few minutes. DMF was evaporated and the resulting slurry was stirred 30 minutes in MeOH (100 ml). The white precipitate was filtered, washed with small portions of MeOH and dried to afford compound 7 (85 %) as a slightly pink solid or compound 8 (78 %) as a white solid.
7 : ¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) 0.93 (t, J = 6.3 Hz, 6H), 1.2-1.5 (m, 12H), 1.85 (m, 4H), 4.00 (t, J = 6.4 Hz, 4H), 6.93 (d, J = 8.7 Hz, 4H), 7.00 (d, J = 17 Hz, 2H), 7.38 (d, J = 5 Hz, 2H), 7.43 (d, J = 17 Hz, 2H), 7.51 (d, J = 8.7 Hz, 4H), 8.53 (s, 2H), 8.66 (d, J = 5 Hz, 2H). ¹³C-NMR (CDCl₃, 298K, 50 MHz, δ ppm) 14.0, 22.6, 25.7, 29.2, 31.6, 68.1, 114.8, 118.0, 120.8, 123.8, 128.4, 128.8, 133.0, 146.1, 149.4, 156.5, 159.7.
8 : ¹H-NMR (CDCl₃, 298K, 200 MHz, δ ppm) ) 0.96 (t, J = 7 Hz, 6H), 1.3-1.7 (m, 12H), 1.98 (m, 4H), 4.21 (t, J = 6.4 Hz, 4H), 6.88 (d, J = 8 Hz, 2H), 7.13 (d, J = 16 Hz, 2H), 7.50-7.67 (m, 6H), 7.75 (d, J = 8 Hz, 2H), 8.20 (d, J = 16 Hz, 2H), 8.22-8.27 (m, 2H), 8.36-8.41 (m, 2H), 8.64 (s, 2H), 8.73 (d, J = 5 Hz, 2H). ¹³C-NMR (CDCl₃, 298K, 50 MHz, δ ppm) 14.4, 22.6, 25.9, 29.2, 31.6, 68.3, 104.6, 118.4, 120.9, 122.7, 123.3, 124.8, 125.2, 125.7, 126.1, 126.9, 127.0, 130.4, 132.3, 146.3, 149.5, 155.7, 156.6.

10) 4,4'-bis[4-(1,4,7,10-Tetraoxyundecyl)styryl]-2,2'-bipyridine.

[0065] 3,6,9-Trioxydecyl 4-toluenesulfonate and 4-(1,4,7,10-Tetraoxyundecyl)benzaldehyde were synthesized according to reference C. Lottner, K.-C. Bart, G. Bernhardt, H. Brunner J. Med. Chem. 2002, 45, 2079-2089).
Solid tBuOK (1.5 g, 13.4 mmol) was added to a solution of 4,4'-bis(diethylmethylphosphonate)-2,2'-bipyridine (1.5 g, 3.3 mmol) and 4-(1,4,7,10-Tetraoxyundecyl)benzaldehyde (2.1 g, 7.8 mmol) in anhydrous DMF (80 ml). The resulting mixture was stirred overnight at room temperature under nitrogen. After evaporation of DMF, water (100 ml) was added and extracted with CH₂Cl₂ (3x150 ml). The combined organic fractions were washed with water (100 ml), brine (100 ml), dried over MgSO₄, filtered and evaporated to dryness. The resulting residue was then dissolved in the minimum volume of CH₂Cl₂ and precipitated by addition of Et₂O with rapid stirring. The solid was filtered, washed with Et₂O and dried to afford 1.5 g (66%) of the titled compound as a slightly beige solid.
¹H NMR (200 MHz, 25°C, CDCl₃) δ 3.39 (s, 6H), 3.5-3.7 (m, 16H), 3.88 (t, J = 4.5 Hz, 4H), 4.18 (t, J = 4.5 Hz, 4H), 6.94 (d, J = 8 Hz, 4H), 7.00 (d, J = 16 Hz, 2H), 7.4-7.5 (m, 8H), 8.52 (s, 2H), 8.65 (d, J = 5 Hz, 2H). ¹³C NMR (50 MHz, 25°C, CDCl₃) δ 59.0, 67.5, 69.7, 70.6, 70.7, 70.8, 71.9, 114.9, 118.0, 120.8, 124.0, 128.4, 129.2, 132.8, 146.1, 149.4, 156.5, 159.3.

[0066] Those skilled in the art will observe that if the symetric starting compound of step 4, e.g. 4,4'-bis(methyl)-2,2'-bipyridine is replaced by an asymetric starting compound, e.g. 4-methyl-2,2'-bipyridine, an asymetric compound L1, e.g. 4-(4-hexyloxystyryl)-2,2' bipyridine will be synthetized.

Example II: Synthesis of Z910

[0067] The synthesis of Z910 was performed according to a one pot synthesis method reported in Nat. Mater(2003) 2, 402. [RuCl₂(p-cymene)]₂ (0.15 g, 0.245 mmol) was dissolved in DMF (50 ml) and to this solution dmsbpy (0.206 g, 0.49 mmol) was added. The reaction mixture was heated to 60°C under nitrogen for 4 h with constant stirring. To this reaction flask H₂dcbpy (0.12 g, 0.49 mmol) was added and refluxed for 4 h. Finally, excess of NH₄NCS (13 mmol) was added to the reaction mixture and continued the reflux for another 4 h. The reaction mixture was cooled down to room temperature and the solvent was removed by using rotary-evaporator under vacuum. Water was added to the flask and the insoluble solid was collected on a sintered glass crucible by suction filtration. The crude was dissolved in a basic methanol solution and purified by passing through a Sephadex LH-20 column with methanol as an eluent. After collecting main band and evaporating the solvent, the resultant solid was redissolved in water. Lowering the pH to 3.1 by titration with dilute nitric acid produced Z910 as a precipitate. The final product was washed thoroughly with water and dried under vacuum. ¹H NMR (δ_H/ppm in CD₃OD+ NaOD) 9.4 (d, 1H), 9.2 (d, 1H), 8. 9 (s, 1H), 8.8 (s, 1H), 8.3 (s, 1H), 8.15 (s, 1H), 7.9 (d, 1H), 7.80 (d, 1H), 7.7 to 6.9 (m, 16H), 4.1 (s, 3H), 4.0 (s, 3H). Anal. Calc. for RuC₄₂H₃₄N₆O₇S₂: C, 56.0; H, 3.78; N, 9.34 %. Found: C, 55.22; H, 3. 97; N, 9.39 %.

[0068] The molecular structure of Z910 is given in Fig. 13.

[0069] Fig. 3 compares the electronic absorption spectra of 8 m mesoporous TiO₂ films grafted respectively with Z907, N719 and Z910 dyes.

[0070] By extending the π-conjugated system of the ligand, the metal-to-ligand charge transfer (MLCT) transitions are red shifted with higher molar extinction coefficient. In addition to the increase in the optical density of MLCT transitions there is a huge increase in the optical density of ligand to ligand charge transitions in the UV regions. These UV transitions can serve as UV filters in DSSCs

Example III:

[0071] The synthesis steps of K19 or K24 or K60 are shown in Fig. 2.

Synthesis of Dye K19 Ru(LL1) (NCS)₂

[0072] Compound 7 (200 mg, 0.36 mmol) and dichloro(p-cymene)ruthenium(II) dimer (109 mg, 0.18 mmol) were refluxed in argon degased EtOH (50 ml) for 4 hours under argon. The orange-brown solution was evaporated to dryness to afford quantitatively the intermediate complex RuL(p-cymene)Cl₂ as a brown solid. This complex and 4,4'-dicarboxy-2,2'-bipyridine (88 mg, 0.36 mmol) were heated to 140°C in degased anh. DMF for 4 hours under argon and in the dark. To the resulting dark green solution was added solid NH₄NCS (411 mg, 5.4 mmol) and the mixture was allowed to heat 4 hours more at 140°C under argon and in the dark. DMF was evaporated and water (200 ml) was added. The formed purple solid was filtered off, washed with water, Et₂O, and purified on LH-20 sephadex to afford complex K₁₉. ¹H NMR (δ_H/ppm in CD₃OD+ NaOD) 9.4 (d, 1H), 9.2 (d, 1H), 8. 9 (s, 1H), 8.8 (s, 1H), 8.3 (s, 1H), 8.15 (s, 1H), 8.0 (d, 1H), 7.80 (d, 1H), 7.7 to 6.9 (m, 16H), 4.1 (s, 3H), 1.8 (t, 2H), 1.6 to 1.4 (m, 8H), 1.0 (t, 3H). The molecular structure of Ru(dcbpy)(dmsbpy)(NCS)₂ (where dcbpy is 4,4'-dicarboxylic acid-2,2'-bipyridine) referred to K19 is shown in Fig. 2.

Example IV:

Synthesis of Dye K24 Ru(LL1) (NCS)₂

[0073] Compound 8 (300 mg, 0.45 mmol) and dichloro(p-cymene)ruthenium(II) dimer (139 mg, 0.227 mmol) were refluxed in argon degased EtOH (50 ml) for 4 hours under argon. The orange-brown solution was evaporated to dryness to afford quantitatively the intermediate complex RuL(p-cymene)Cl₂ as a brown solid. This complex and 4,4'-dicarboxy-2,2'-bipyridine (111 mg, 0.45 mmol) were heated to 140°C in degased anh. DMF for 4 hours under argon and in the dark. To the resulting dark green solution was added solid NH₄NCS (520 mg, 6.8 mmol) and the mixture was allowed to heat 4 hours more at 140°C under argon and in the dark. DMF was evaporated and water (200 ml) was added. The formed purple solid was filtered off, washed with water, Et₂O, and purified on LH-20 sephadex to afford complexes K24.

Example V :

Synthesis of dye K 60 : Ru(LL')(NCS)₂

[0074] Compound 10 (850 mg, 1.24 mmol) and dichloro(p-cymene)ruthenium(II) dimer (380 mg, 6.2 mmol) were refluxed in argon degased EtOH (50 ml) for 4 hours under argon. The orange-brown solution was evaporated to dryness to afford quantitatively the intermediate complex RuL(p-cymene)Cl₂ as a brown solid. This complex and 4,4'-dicarboxy-2,2'-bipyridine (303mg, 1.24mmol) were heated to 140°C in degased anh. DMF for 4 hours under argon and in the dark. To the resulting dark green solution was added exces solid NH₄NCS (1.5 g) and the mixture was allowed to heat 4 hours more at 140°C under argon and in the dark. DMF was evaporated and water (200 ml) was added. The formed purple solid was filtered off, washed with water, Et₂O, and purified on LH-20 sephadex to afford complexe K 60 as purple solid. The molecular structure of Ru (dcbpy) (4,4'-bis[4-(1,4,7,10-Tetraoxyundecyl)styryl]-2,2'-bipyridine ) (NCS)2 (where dcbpy is 4,4'-dicarboxylic acid-2,2'-bipyridine) referred to K 60 is shown in Fig 13.

Example VI: Fabrication and photovoltaic performance of Z910 sensitized solar cells

[0075] A screen-printed double layer of TiO₂ particles was used as photoanode. A 10 µm thick film of 20 nm sized TiO₂ particles was first printed on the fluorine-doped SnO₂ conducting glass electrode and further coated by 4 µm thick second layer of 400 nm sized light scattering anatase particles. Fabrication procedure for the nanocrystalline TiO₂ photoanodes and the assembly as well as photoelectrochemical characterization of complete, hot-melt sealed cells has been described by P. Wang et al. (J. Phys. Chem. B, 2003, 107, 14336-14341). The electrolyte used for device A contained 0.6 M 1-propyl-3-methylimidazolium iodide (PMII), 30 mM M I₂, 0.13 M guanidinium thiocyanate, and 0.5 M 4-tert-butylpyridine in the 1:1 volume mixture of acetonitrile and valeronitrile. The TiO₂ electrodes were immersed at room temperature for 12 h into a solution containing 300 µM Z910 and 300 µM chenodeoxycholic acid in acetonitrile and tert-butanol (volume ratio: 1:1). For stability tests, the electrolyte was composed of 0.6 M PMII, 0.1 M I₂, and 0.5 M N-methylbenzimidazole in 3-methoxypropionitrile and the corresponding device with the Z910 dye alone is denoted as device B.

[0076] The photocurrent action spectrum of device A with Z910 as sensitizer is shown in Fig. 4. The incident photon to current conversion efficiency (IPCE) exceeds 80% in a spectral range from 470 to 620 nm, reaching its maximum of 87% at 520 nm. Considering the light absorption and scattering loss by the conducting glass, the maximum efficiency for absorbed photon to current conversion efficiency is practically unity over this spectral range. From the overlap integral of this curve with the standard global AM 1.5 solar emission spectrum, a short-circuit photocurrent density (J_sc) of 17.2 mA cm^□2 is calculated, which is in excellent agreement with the measured photocurrent. As shown in Fig. 5, its short-circuit photocurrent density (J_sc), open-circuit photovoltage (V_oc), and fill factor (ff) of device A with Z910 dye under AM 1.5 full sunlight are 17.2 mA cm^□2, 777 mV, and 0.764, respectively, yielding an overall conversion efficiency (|) of 10.2 %. At various lower incident light intensities, overall power conversion efficiencies are also over 10.2 %. With the double layer film (total thickness of 14 µm) and electrolyte used here, the power conversion efficiencies of N-719 and Z-907 dyes are 7 % less efficient than Z910.

[0077] The above-mentioned 3-methoxypropionitrile based electrolyte was used for the stability test of sensitizer Z910 under moderate thermal stress and visible light soaking. The advantage of using 3-methoxypropionitrile lies in its high boiling point, low volatility, non-toxicity and good photochemical stability, making it viable for practical application. Photovoltaic parameters (Jsc, Voc, ff, and |) of device B are 14.8 mA cm^□2, 696 mV, 0.695, and 7.2 %, respectively. The cells covered with a 50 µm thick of polyester film (Preservation Equipment Ltd, UK) as a UV cutoff filter (up to 400 nm) were irradiated at open circuit under a Suntest CPS plus lamp (ATLAS GmbH, 100 mW cm^-2, 55°C). As shown in Fig. 6, all parameters of the device are rather stable during 1000 h accelerating tests. It should be noted that under this condition the sensitizer showed similar stability but higher efficiency compared with Z-907 dye.

Example VII: Fabrication and photovoltaic performance of K19 sensitized solar cells with a organic solvent based electrolyte

[0078] A screen-printed double layer of TiO₂ particles was used as photoanode. A 10 µm thick film of 20 nm sized TiO₂ particles was first printed on the fluorine-doped SnO₂ conducting glass electrode and further coated by 4 µm thick second layer of 400 nm sized light scattering anatase particles. Fabrication procedure for the nanocrystalline TiO₂ photoanodes and the assembly as well as photoelectrochemical characterization of complete, hot-melt sealed cells C has been described above. The electrolyte used for device C contained 0.6 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 0.1 mM M I₂, and 0.5 M N-methylbenzimidazole in 3-methoxypropionitrile. The TiO₂ electrodes were immersed at room temperature for 12 h into a solution containing 300 µM K19 in the mixture of acetonitrile and tert-butanol (volume ratio: 1:1).

[0079] Figure 7 shows the evolution of photovoltaic parameters of device C at 80 °C in the dark. Figure 8 shows the evolution of photovoltaic parameters of device C covered with a UV filter at 55-60 °C under AM 1.5 sunlight (100 mW/cm²).

Example VIII: Fabrication and photovoltaic performance of K19 sensitized solar cells with a organic solvent based electrolyte

[0080] A screen-printed double layer of TiO₂ particles was used as photoanode. A 10 µm thick film of 20 nm sized TiO₂ particles was first printed on the fluorine-doped SnO₂ conducting glass electrode and further coated by 4 µm thick second layer of 400 nm sized light scattering anatase particles. Fabrication procedure for the nanocrystalline TiO₂ photoanodes and the assembly as well as photoelectrochemical characterization of complete, hot-melt sealed cells has been described as above. The electrolyte used for device D contained 0.2 M I₂, and 0.5 M N-methylbenzimidazole in the 65/35 volume mixture of 1-propyl-3-methylimidazolium iodide (PMII)and 1-ethyl-2-methylimidazolium tricyanomethide [EMIC(CN)₃). The TiO₂ electrodes were immersed at room temperature for 12 h into a solution containing 300 µM K₁₉ in the mixture of acetonitrile and tert-butanol (volume ratio: 1:1). Table 1 gives the detailed photovoltaic paprameters of device D under illumination of different light intensities.

Table 1 Detailed photovoltaic parameters of device D.

Pin/mW cm-2	Jsc/mA cm-2	Voc/mV	Pmax/mW cm-2	ff	η / %
9.45	1.42	634	0.7	0.78	7.4
51.7	7.31	682	3.75	0.77	7.2
99.9	13.0	700	6.7	0.74	6.7

[0081] The spectral distribution of the lamp simulates air mass 1.5 solar light. Incident power intensity: Pin; Short-circuit photocurrent density: J_sc; Open-circuit photovoltage: V_oc; Maximum electricity output power density: P_max; Fill factor: ff=P_max/P_in; Total power conversion efficiency: η. Cell active area: 0.158 cm².

Example IX: Fabrication and photovoltaic performance of cells with a TiO₂ film cografted with K19 dye and 1-decylphosphonic acid coadsorbent

[0082] A screen-printed double layer of TiO₂ particles was used as photoanode. A 10 µm thick film of 20 nm sized TiO₂ particles was first printed on the fluorine-doped SnO₂ conducting glass electrode and further coated by 4 µm thick second layer of 400 nm sized light scattering anatase particles. Fabrication procedure for the nanocrystalline TiO₂ photoanodes and the assembly as well as photoelectrochemical characterization of complete, hot-melt sealed cells has been described above. The electrolyte used for device E contained 0.6 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 0.1 mM M I₂, and 0.5 M N-methylbenzimidazole in 3-methoxypropionitrile. The TiO₂ electrodes were immersed at room temperature for 12 h into a solution containing 300 µM K₁₉ dye and 75 µM 1-decylphosphonic acid coadsorbent in the mixture of acetonitrile and tert-butanol (volume ratio: 1:1).

[0083] Figure 9 shows the evolution of photovoltaic parameters of device E at 80 °C in the dark. It is clear that the presence of 1-decylphosphonics has enhanced the stability of photovoltage under the thermal stress at 80 °C. Figure 10 shows the evolution of photovoltaic parameters of device E covered with a UV filter at 55-60 °C under AM 1.5 sunlight (100 mW/cm²)_.

[0084] In conclusion, new heteroleptic polypyridyl ruthenium complexes with high molar extinction coefficients have been synthesized and demonstrated as highly efficient, stable sensitizers for nanocrystalline solar cells. Enhancing the molar extinction coefficient of sensitizers has been demonstrated to be an elegant strategy to improve the photovoltaic performance of dye sensitized solar cells.

Claims

1. An organometallic complex of a metal Me selected from the group consisting of Ru, Os and Fe, comprising as a ligand a compound L1, said complex being of formula

        Me L1 L(Z)₂     (I)

if L1 is a compound of formula (a), (a'), (b), (c), (d), (g), (h), (i) or (j)









and of formula

        Me L1 L Z     (II)

if L1 is a compound of formula (e) or (f)

wherein L is a ligand selected from the group of ligands of formula

wherein A and A' are anchoring groups selected from COOH, PO₃H₂, PO₄H₂, SO₃H₂, SO₄H₂, CONHOH, deprotonated forms thereof and chelating groups with π conducting character,
wherein Z is selected from the group consisting of H₂O, Cl, Br, CN, NCO, NCS and NCSe and
wherein at least one of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' comprises a π system in conjugated relationship with the π system of the bidentate, respectively the tridentate structure of formulae (a) to (j),
and wherein the other one(s) of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is (are) the same or a different substituent including a π system, or is (are) selected from H, OH, R2, (OR2)_n, N(R2)₂, where R2 is an alkyl of 1-20 carbon atoms or linear R cyclic polyether, 0 < n < 5.

2. The organometallic complex as claimed in claim 1, wherein L1 is a compound of formula (a), wherein one substituent selected from -R, -R₁, -R₂, -R₃, and one selected from -R', -R₁', -R₂', -R₃', comprises a π system in conjugated relationship with the π system of the bidentate structure of formulae (a).

3. An organometallic complex as claimed in claim 1, said complex being of formula

        Me L1 L(Z)₂     (I)

wherein Me designates Ru, Os or Fe,
wherein L is selected from ligands

wherein Z is selected from H₂O, -Cl, -Br, -I, -CN, -NCO, -NCS and -NCSe.
wherein L1 is a substituted bipyridine of formula (a) or a 4,4'-disubstituted bipyridine of formula (a')

wherein at least one of the substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', is a substituent selected from the group of substituents (1), (2) and (3)





wherein p is an integer from 1 to 4, and for substituents (1) and (3) can also be 0
wherein q is an integer from 1 to 4
wherein Rar is a monocyclic or polycyclic aryl from C6 to C22
wherein each -Ral is, independently one from the others, -H, -R1, -(O-R1)_n, -NHR1 or -N(R1)₂,

or

or

wherein R1, R'1 is an alkyl from 1 to 10 carbon atoms, 20 ≥ X ≥ 0, and 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 or 2.

4. An organometallic complex as claimed in claim 3, of formula cis(NCS)₂ RuLL1, wherein L1 is of formula (a'),
wherein R is of formula (1), (2) or (3), wherein p = 1,
wherein Rar is selected from the group consisting of benzene and naphthalene, wherein q = 1 to 4, wherein Ral is OR1 and
wherein R1 is an alkyl of 1 to 10 carbon atoms or linear or cyclic polyethers.

5. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxystyryl)-2,2' bipyridyl]-Ru(II).

6. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxynaphtalene-1-vinyl)-2,2' bipyridyl]-Ru(II).

7. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(3-methoxystyryl)-2,2' bipyridyl]-Ru(II).

8. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[ 4,4'-bis[4-(1,4,7,10-Tetraoxyundecyl)styryl]-2,2'-bipyridine]-Ru(II).

9. 4,4'-bis(4-hexyloxystyryl)-2,2' bipyridine.

10. 4,4'-bis(4-hexyloxynaphtylene-1-vinyl)-2,2' bipyridine.

11. A regenerative photoelectrochemical cell comprising a photoanode, said photoanode comprising at least one semi-conductive metal oxide layer on a conductive substrate, sensitized by a photosensitizing dye, a counter electrode and an electrolyte arranged between said semi-conductive metal oxide layer and said counter electrode, characterized in that said photosensitizing dye is an organometallic complex as claimed in anyone of claims 1 to 8.

12. A cell as claimed in claim 11, characterized in that an amphiphilic compacting compound whose molecular structure comprises at least one anchoring group, a hydrophobic portion and a terminal group is co-adsorbed with said photosensitizing dye on said semi-conductive metal oxide layer in a mixed monolayer.

13. A cell as claimed in claim 12, characterized in that said compacting compound is selected from the group consisting of alkyl carboxylic acids, alkyl dicarboxylic acids, alkyl carboxylates, alkyl phosphonic acids, alkyl phosphonates, alkyl diphosphonic acids, alkyl diphosphonates, alkyl sulphonic acids, alkyl sulphonates, alkyl hydroxamic acids and alkyl hydroxamates, wherein said alkyl is linear or branched from C1 to C20.

14. A cell as claimed in claim 12 or 13, characterized in that the molar ratio of said photosensitizing dye to said co-adsorbed compacting compound is of between 10 and 1/2, and in that said self-assembled monolayer is a dense packed monolayer having an order-disorder transition temperature above 80°C.

15. A cell as claimed in anyone of claims 12 to 14, characterized in that the length of said hydrophobic chain portion of the compacting compound allows said terminal group to protrude above the sensitizing dye in said monolayer.

16. A cell as claimed in anyone of claims 11 to 15, characterized in that said electrolyte comprises a redox system, that said redox system comprises an electrochemically active salt and a first compound forming a redox couple with either the anion or the cation of said electrochemically active salt, wherein said salt is a room temperature molten salt, said molten salt being liquid at least between standard room temperature and 80°C above said room temperature.

17. A cell as claimed in anyone of claims 11 to 16, characterized in that said electrolyte further comprises a polar organic solvent having a boiling point of 100°C or greater than 100°C at normal atmospheric pressure.

18. A cell as claimed in claim 17, characterized in that said solvent is a nitrile selected from 3-methoxypropionitrile 3-ethoxypropionitrile, 3-butoxupropionitrile, and butyronitrile.

19. A cell as claimed in anyone of claims 11 to 18, characterized in that said electrolyte further comprises, as an additive, a compound formed by a neutral molecule comprising one or more nitrogen atom(s) with a lone electron pair.

20. A cell as claimed in claim 19, characterized in that said neutral molecule has following formula:

wherein R'₁ and R'₂ can be H, alkyl, alkenyl, alkynyl, alkoxyl, poly-ether, and/or phenyl, independently one from the other, the number of carbon atoms of each substituent ranging from 1 to 20, the substituent being linear or branched.

21. Use of a compound L1 as a ligand in sensitizing dyes of a dye sensitized solar cell, wherein the compound L1 has a formula selected from the group of formulae (a), (a'), (b), (c), (d), (e), (f), (g), (h), (i), (j) as defined in Claim 1, wherein at least one of -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' comprises an additional π system located in conjugated relationship with the primary π system of the bidentate or respectively tridentate structure of formulae (a) to (j), and,
wherein the other one(s) of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is (are) the same or a different substituent including a π system, or is (are) selected from H, OH, R2, (OR2)_n, N(R2)₂, where R2 is an alkyl of 1-20 carbon atoms or linear R cyclic polyether, 0 < n < 5.

22. The use of claim 21, wherein said at least one of substituents -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' is a substituent selected from the group of substituents (1), (2) and (3)





wherein p is an integer from 1 to 4, and for substituents (1) and (3) can also be 0
wherein q is an integer from 1 to 4
wherein Rar is a monocyclic or polycyclic aryl from C6 to C22
wherein each -Ral is, independently one from the others, -H, -R1, -(O-R1)_n, -NHR1 or -N(R1)₂,

or

or

wherein R1, R'1 is an alkyl from 1 to 10 carbon atoms, 20 ≥ X ≥ 0, and 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 or 2.

Ansprüche

1. Organometallkomplex eines Metalls Me aus der Gruppe Ru, Os und Fe mit einer Verbindung L1 als Ligand, welcher Komplex die Formel

        Me L1 L(Z)₂     (I)

hat, falls L1 eine Verbindung der Formel (a), (a'), (b), (c), (d), (g), (h), (i) oder (j) ist,









und die Formel

        Me L1 L Z     (II)

hat, falls L1 eine Verbindung der Formel (e) oder (f) ist,

wobei L ein aus der Ligandengruppe der Formel

gewählter Ligand ist,
in der A und A' Verankerungsgruppen aus der Gruppe COOH, PO₃H₂, PO₄H₂, SO₃H₂, SO₄H₂, CONHOH, deren deprotonierte Formen sowie Chelat bildende Gruppen mit π leitendem Charakter sind,
wobei Z aus der Gruppe H₂O, Cl, Br, CN, NCO, NCS und NCSe gewählt ist,
mindestens einer der Substituenten -R, -R₁, -R₂, -R₃, - R', -R₁', -R₂', -R₃', -R" ein π-System in konjugierter Zuordnung zum π-System der Bi- bzw. Tridentatstruktur der Formeln (a) bis (j) aufweist,
und wobei der bzw. die anderen der Substituenten -R, - R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R" der gleiche oder ein anderer Substituent bzw. die gleichen oder andere Substituenten mit einem π-System ist oder aus der Gruppe H, OH, R2, (OR2)_n, N(R2)₂ gewählt ist bzw. sind, in der R2 ein Alkyl mit 1 bis 20 C-Atomen oder ein linearer oder zyklischer Polyäther ist und 0 < n < 5 gilt.

2. Organometallkomplex nach Anspruch 1, in dem L1 eine Verbindung der Formel (a) ist und einen Substituent aus der Gruppe -R, -R₁, -R₂, -R₃ sowie einen Substituent aus der Gruppe -R', -R₁', -R₂', -R₃' ein π-System in konjugierter Zuordnung zum π-System der Bidentatstruktur der Formel (a) aufweist.

3. Organometallkomplex nach Anspruch 1 mit der Formel

        Me L1 L(Z)₂     (I)

in der Me gleich Ru, Os oder Fe ist und L aus den Liganden

gewählt ist, wobei Z aus der Gruppe H₂O, -Cl, -Br, -I, -CN, -NCO, -NCS und -NCSe gewählt ist,
wobei L1 ein substituiertes Bipyridin der Formel (a) oder ein 4,4'-disubstituiertes Bipyridin der Formel (a') ist:



wobei mindestens einer der Substituenten -R, -R₁, -R₂, - R₃, -R', -R₁', -R₂', -R₃' aus der Gruppe der Substituenten (1), (2) und (3) ist:





in denen p eine ganze Zahl von 1 bis 4 ist und für die Substituenten (1) und (3) auch gleich null sein kann, in denen q eine ganze Zahl von 1 bis 4 ist und in denen Rar ein mono- oder polyzyklisches Aryl von C6 bis C22 und jedes -Ral jeweils unabhängig von allen anderen -H, -R1, -(O-R1)_n, - NHR1 oder N(R1)₂,

oder

oder

ist, wobei R1, R'1 ein Alkyl mit 1 bis 10 C-Atomen ist und 20 ≥ X ≥ 0; 5 ≥ n ≥ 0; 8 ≥ Y ≥ 1; sowie Z = 1 oder 2 gelten.

4. Organometallkomplex nach Anspruch 3 der Formel cis(NCS)₂RuLL1, in dem L1 die Formel (a'), R der Formel (1), (2) oder (3) entspricht und p = 1 gilt, wobei weiterhin Rar aus der Gruppe Benzol und Naphthalen gewählt ist, wobei q = 1 bis 4 gilt, und wobei Ra1 gleich OR1 und R1 ein Alkyl mit 1 bis 10 C-Atomen oder linearen oder zyklischen Polyethern ist.

5. Cis-dithioxyanato-(2,2'-bipyridyl-4,4'-dicarboxylat)-[4,4'-bis(4-hexyloxystyryl)-2,2'-bipyridsyl]-Ru(II).

6. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylat)-[4,4'-bis(4-hexyloxynaphthalen-1-vinyl)-2,2'-bipyridyl]-Ru(II).

7. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylat)-[4,4'-bis(3-methoxystyryl-2,2'-bipyridyl]-Ru(II).

8. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylat)-[4,4'-bis[4-(1,4,7,10-tetraoxyundecyl)styryl]-2,2'-bipyridin]-Ru(II).

9. 4,4'-bis(4-hexyloxystyryl)-2,2'-bipyridyl.

10. 4,4'-bis(4-hexyloxynaphthylen-1-vinyl)-2,2'-bipyridin.

11. Regenerative photoelektrochemische Zelle mit einer Photoanode, die mindestens eine halbleitende Metalloxidschicht auf einem leitfähigen Substrat aufweist, die mit einem photosensibilisierenden Farbstoff sensibilisiert ist, mit einer Gegenelektrode sowie einem Elektrolyt zwischen der halbleitenden Metalloxidschicht und der Gegenelektrode, dadurch gekennzeichnet, dass der photosensibilisierende Farbstoff ein Organometallkomplex nach einem der Ansprüche 1 bis 8 ist.

12. Zelle nach Anspruch 11, dadurch gekennzeichnet, dass eine amphiphile Verdichtungsverbindung, deren Molekülstruktur mindestens eine Ankergruppe, einen hydrophoben Teil und eine Abschlussgruppe aufweist, gemeinsam mit dem photosensibilisierenden Farbstoff auf der halbleitenden Metalloxidschicht in einer gemischten Monoschicht absorbiert ist.

13. Zelle nach Anspruch 12, dadurch gekennzeichnet, dass die Verdichtungsverbindung aus der Gruppe gewählt ist, die aus den Alkylcarbonsäuren, Alkyldicarbonsäuren, Alkylcarboxylaten, Alkylphosphonsäuren, Alkylpholsphonaten, Alkyldiphosphonsäuren, Alkyldiphosphonaten, Alkylsulphonsäuren, Alkylsulphonaten, Alkylhydroxamsäuren und Alkylhydroxamaten besteht, wobei das Alkyl linear oder verzweigt mit C1 bis C20 ist.

14. Zelle nach Anspruch 12 oder 13, dadurch gekennzeichnet, dass das Molverhältnis des photosensibilisierenden Farbstoffs zur mit absorbierten Verdichtungsverbindung zwischen 10 und 1/2 liegt und die selbst anordnende Monoschicht eine dicht gepackte Monoschicht mit einer Übergangstemperatur Ordnung/Unordnung über 80 °C ist.

15. Zelle nach einem der Ansprüche 12 bis 14, dadurch gekennzeichnet, dass die Länge des hydrophoben Kettenteils der Verdichtungsverbindung der Abschlussgruppe erlaubt, über den sensibilisierenden Farbstoff in der Monoschicht hinaus vorzustehen.

16. Zelle nach einem der Ansprüche 11 bis 15, dadurch gekennzeichnet, dass der Elektrolyt ein Redoxsystem aufweist und das Redoxsystem ein elektrochemisch aktives Salz und eine erste Verbindung aufweist, die mit entweder dem Anion oder dem Kation des elektrochemisch aktiven Salzes zusammen ein Redox-Paar bildet, wobei das Salz ein bei Raumtemperatur geschmolzenes Salz und letzteres mindestens zwischen der Standard-Raumtemperatur und 80 °C über dieser flüssig ist.

17. Zelle nach einem der Ansprüche 11 bis 16, dadurch gekennzeichnet, dass der Elektrolyt weiterhin ein polares organisches Lösungsmittel mit einem Siedepunkt von 100 °C oder mehr bei normalem atmosphärischem Druck aufweist.

18. Zelle nach Anspruch 17, dadurch gekennzeichnet, dass das Lösungsmittel ein Nitril aus der Gruppe 3-Methoxyproprionitril, 3-Ethoxypropionnitril, 3-Butoxypropionitrile und Butyronitril gewählt ist.

19. Zelle nach einem der Ansprüche 11 bis 18, dadurch gekennzeichnet, dass der Elektrolyt weiterhin als Zusatz eine Verbindung aufweist, die von einem neutralen Molekül mit einem oder mehreren Stickstoffatomen mit einem ungebundenen Elektronenpaar ("lone electron pair") zusammen gebildet wird.

20. Zelle nach Anspruch 19, dadurch gekennzeichnet, dass

das neutrale Molekühl die folgende Formel hat:

bei der R'₁ und R'₂ gleich H, Alkyl, Alkenyl, Alkynyl, Alkoxy, Polyäther und/oder Phenyl unabhängig voneinander sein kann, die Anzahl der C-Atome jedes Substituenten im Bereich von 1 bis 22 liegt und der Substituent linear oder verzweigt ist.

21. Verwendung einer Verbindung L1 als Ligand in sensibilisierenden Farbstoffen einer farbstoffsensibilisierten Solarzelle, wobei die Verbindung L1 eine Formel aus der Gruppe (a), (a'), (b), (c), (d), (e), (f), (g), (h), (i) und (j) hat, wie sie im Anspruch 1 definiert sind, mindestens eines von -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R" ein π-System in konjugierter Zuordnung zum primären π-System der Bi- bzw. Tridentatstruktur der Formeln (a) bis (j) aufweist und mindestens der andere bzw. die anderen Substituenten der Gruppe -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R" der gleiche bzw. die gleichen Substituenten einschl. eines π-System ist/sind oder aus H, OH, R2, (OR2)_n, N(R2)₂ gewählt ist/sind, wobei R2 Alkyl mit 1 bis 20 C-Atomen oder ein linearer oder zyklischer Polyäther mit 0 < n < 5 ist.

22. Verwendung nach Anspruch 21, bei der der mindestens eine Substituent aus der Gruppe -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R" aus der Gruppe der Substituenten (1), (2) und (3)





gewählt ist, in der p eine ganze Zahl von 1 bis 4 ist und für die Substituenten (1) und (3) auch gleich 0 sein kann, q eine ganze Zahl von 1 bis 4 und Rar ein mono- oder polyzyklisches Aryl von C6 bis C 22 ist, wobei jedes -Ra1 unabhängig von allen anderen -H, -R1, -(O-R1)_n, -NHR1 oder - N(R1)₂ ist:

oder

oder

wobei R1, R'1 ein Alkyl mit 1 bis 10 C-Atomen, ist und 20 ≥ X ≥ 0; 5 ≥ n ≥ 0; 8 ≥ Y ≥ 1; und Z = 1 oder 2 gelten.

Revendications

1. Complexe organo-métallique d'un métal Me choisi dans le groupe consistant en Ru, Os et Fe, comprenant en tant qu'un ligand un composé L1, ledit complexe étant de formule

        Me L1 L(Z)₂     (I)

si L1 est un composé de formule (a), (a'), (b), (c), (d), (g), (h), (i) ou (j)









et de formule

        Me L1 L Z     (II)

si L1 est un composé de formule (e) ou (f)

dans lesquelles L est un ligand choisi dans le groupe de ligands de formule

dans laquelle A et A' sont des groupes d'ancrage choisis parmi COOH, PO₃H₂, PO₄H₂, SO₃H₂, SO₄H₂, CONHOH, leurs formes déprotonées et des groupes chélatants de caractère conducteur π,
dans lesquelles Z est choisi dans le groupe consistant en H₂O, Cl, Br, CN, NCO, NCS et NCSe et
dans lesquelles au moins un des substituants -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' comprend un système π en relation de conjugaison avec le système π de la structure bidentée ou tridentée, respectivement, des composés de formules (a) à (j),
et dans lesquelles le ou les autre(s) substituant(s) - R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' est ou sont un ou des substituant(s) identique(s) ou différent (s) comprenant un système π, ou est (sont) choisi(s) parmi H, OH, R2, (OR2)_n, N(R2)₂, R2 étant un groupe alkyle de 1 à 20 atomes de carbone ou un polyéther cyclique R linéaire, 0 < n < 5.

2. Complexe organo-métallique selon la revendication 1, dans lequel L1 est un composé de formule (a) dans laquelle un substituant choisi parmi -R, -R₁, -R₂, -R₃, et un substituant choisi parmi -R', -R₁', -R₂', -R₃', comprend un système π en relation de conjugaison avec le système π de la structure bidentée du composé de formule (a).

3. Complexe organo-métallique selon la revendication 1, ledit complexe étant de formule

        Me L1 L(Z)₂     (I)

dans laquelle Me désigne Ru, Os ou Fe,
dans laquelle L est choisi parmi les ligands

dans laquelle Z est choisi parmi H₂O, -Cl, -Br, -I, -CN, - NCO, -NCS et -NCSe,
dans laquelle L1 est une bipyridine substituée de formule (a) ou une bipyridine 4,4'-disubstituée de formule (a')

dans laquelle au moins un des substituants -R, -R₁, -R₂, - R₃, -R', -R₁', -R₂', -R₃' est un substituant choisi dans le groupe de substituants (1), (2) et (3)





dans lesquels p est un entier de 1 à 4, et pour les substituants (1) et (3) peut également être 0
dans lesquels q est un entier de 1 à 4
dans lesquels Rar est un groupe aryle monocyclique ou polycyclique en C6 à C22
dans lesquels chaque -Ral est, indépendamment des autres, -H, -R1, -(O-R1)_n, -NHR1 ou -N(R1)₂,

or

or

dans lesquels R1, R'1 est un groupe alkyle de 1 à 10 atomes de carbone,
20 ≥ X ≥ 0, et 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 ou 2.

4. Complexe organo-métallique selon la revendication 3, de formule cis(NCS)₂ RuLL1, dans laquelle L1 est de formule (a'), dans laquelle R est de formule (1), (2) ou (3), dans laquelle p = 1, dans laquelle Rar est choisi dans le groupe consistant en benzène et naphtalène, dans laquelle q = 1 à 4, dans laquelle Ral est OR1 et dans laquelle R1 est un groupe alkyle de 1 à 10 atomes de carbone ou un polyéther cyclique ou linéaire.

5. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxystyryl)-2,2'-bipyridyl]-Ru(II).

6. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(4-hexyloxynaphtalène-1-vinyl)-2,2'-bipyridyl]-Ru(II).

7. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis(3-méthoxystyryl)-2,2'-bipyridyl]-Ru(II).

8. Cis-dithiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylate)-[4,4'-bis[4-(1,4,7,10-tétraoxyundécyl)styryl]-2,2'-bipyridine]-Ru(II).

9. 4,4'-bis(4-hexyloxystyryl)-2,2'-bipyridine.

10. 4,4'-bis(4-hexyloxynaphtylène-1-vinyl)-2,2'-bipyridine.

11. Pile photoélectrochimique à régénération comprenant une photoanode, ladite photoanode comprenant au moins une couche d'oxyde métallique semi-conducteur sur un substrat conducteur, sensibilisé par un colorant photosensibilisateur, une contre-électrode et un électrolyte disposé entre ladite couche d'oxyde métallique semi-conducteur et ladite contre-électrode, caractérisée en ce que ledit colorant photosensibilisateur est un complexe organo-métallique selon l'une quelconque des revendications 1 à 8.

12. Pile selon la revendication 11, caractérisée en ce qu'un composé compactant amphiphile dont la structure moléculaire comprend au moins un groupe d'ancrage, une partie hydrophobe et un groupe terminal, est co-adsorbé avec ledit colorant photosensibilisateur sur ladite couche d'oxyde métallique semi-conducteur dans une monocouche mixte.

13. Pile selon la revendication 12, caractérisée en ce que ledit composé compactant est choisi dans le groupe consistant en acides alkyle carboxyliques, acides alkyle dicarboxyliques, carboxylates d'alkyle, acides alkyle phosphoniques, phosphonates d'alkyle, acides alkyle diphosphoniques, diphosphonates d'alkyle, acides alkyle sulfoniques, sulfonates d'alkyle, acides alkyle hydroxamiques et hydroxamates d'alkyle, ledit alkyle étant un alkyle linéaire ou ramifié en C1 à C20.

14. Pile selon la revendication 12 ou 13, caractérisée en ce que le rapport molaire dudit colorant photosensibilisateur sur ledit composé compactant co-adsorbé est compris entre 10 et ½, et en ce que ladite monocouche auto-assemblée est une monocouche dense compactée dont la température de transition entre les états ordonné et désordonné est supérieure à 80° C.

15. Pile selon l'une quelconque des revendications 12 à 14, caractérisée en ce que la longueur de ladite partie formant chaîne hydrophobe du composé compactant permet audit groupe terminal de faire saillie au-dessus du colorant sensibilisateur dans ladite monocouche.

16. Pile selon l'une quelconque des revendications 11 à 15, caractérisée en ce que ledit électrolyte comprend un système redox, en ce que ledit système redox comprend un sel électrochimiquement actif et un premier composé formant un couple redox avec l'anion ou le cation dudit sel électrochimiquement actif, ledit sel étant un sel en fusion à température ambiante, ledit sel en fusion étant liquide au moins entre la température ambiante standard et 80° C au-dessus de ladite température ambiante.

17. Pile selon l'une quelconque des revendications 11 à 16, caractérisée en ce que ledit électrolyte comprend en outre un solvant organique polaire dont le point d'ébullition est de 100° C ou supérieur à 100° C à pression atmosphérique normale.

18. Pile selon la revendication 17, caractérisée en ce que ledit solvant est un nitrile choisi parmi le 3-méthoxypropionitrile, le 3-éthoxypropionitrile, le 3-butoxypropionitrile et le butyronitrile.

19. Pile selon l'une quelconque des revendications 11 à 18, caractérisée en ce que ledit électrolyte comprend en outre, en tant qu'un additif, un composé formé par une molécule neutre comprenant un ou plusieurs atomes d'azote ayant un doublet non liant.

20. Pile selon la revendication 19, caractérisée en ce que ladite molécule neutre répond à la formule suivante :

dans laquelle R'₁ et R'₂ peuvent être H, alkyle, alcényle, alcynyle, alcoxyle, poly-éther et/ou phényle, indépendamment l'un de l'autre, le nombre d'atomes de carbone de chaque substituant allant de 1 à 20, le substituant étant linéaire ou ramifié.

21. Utilisation d'un composé L1 en tant qu'un ligand dans des colorants sensibilisateurs d'une pile photovoltaïque sensibilisée par un colorant, le composé L1 répondant à une formule choisie dans le groupe de formules (a), (a'), (b), (c), (d), (e), (f), (g), (h), (i), (j) tel que défini dans la revendication 1, dans lesquelles au moins un des radicaux -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' comprend un système π supplémentaire situé en relation de conjugaison avec le système π primaire de la structure bidentée ou tridentée, respectivement, des composés de formules (a) à (j), et,
et dans lesquelles le ou les autre(s) substituant(s) -R, - R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' est ou sont un ou des substituant(s) identique(s) ou différent(s) comprenant un système π, ou est (sont) choisi(s) parmi H, OH, R2, (OR2)_n, N(R2)₂, R2 étant un groupe alkyle de 1 à 20 atomes de carbone ou un polyéther cyclique R linéaire,
0 < n < 5.

22. Utilisation selon la revendication 21, dans laquelle au moins un des substituants -R, -R₁, -R₂, -R₃, -R', -R₁', -R₂', -R₃', -R'' est un substituant choisi dans le groupe de substituants (1), (2) et (3)





dans lesquels p est un entier de 1 à 4, et pour les substituants (1) et (3), peut également être 0
dans lesquels q est un entier de 1 à 4
dans lesquels Rar est un groupe aryle monocyclique ou polycyclique en C6 à C22
dans lesquels chaque -Ral est, indépendamment des autres, -H, -R1, -(O-R1)_n, -NHR1 ou -N(R1)₂,

or

or

dans lesquels R1, R'1 est un groupe alkyle de 1 à 10 atomes de carbone,
20 ≥ X ≥ 0, et 5 ≥ n ≥ 0, 8 ≥ Y ≥ 1, Z = 1 ou 2.

Drawing