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Title:
QUANTUM DOT DYE-SENSITIZED SOLAR CELL
Document Type and Number:
WIPO Patent Application WO/2015/015377
Kind Code:
A1
Abstract:
Quantum dot dye-sensitized solar cell (QDDSSC) comprising an anode, a cathode, an electrolyte between the anode and the cathode, wherein the anode comprises: -a semiconductor electrode layer absorbed with at least one organic dye, said organic dye comprising at least one triaryl-amine group and at least one benzo-heterodiazole group; -at least one quantum dot (QD) distributed within the semiconductor electrode layer, said quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm.

Inventors:
BIAGINI PAOLO (IT)
BAWENDI MOUNGI G (US)
LELII CAMILLA (IT)
Application Number:
PCT/IB2014/063382
Publication Date:
February 05, 2015
Filing Date:
July 24, 2014
Export Citation:
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Assignee:
ENI SPA (IT)
MASSACHUSETTS INST TECHNOLOGY (US)
International Classes:
H01G9/20; C09B57/00
Domestic Patent References:
WO2011089611A12011-07-28
WO2010062015A12010-06-03
Foreign References:
US20110120540A12011-05-26
Other References:
WEIHONG ZHU ET AL: "Organic D-A- -A Solar Cell Sensitizers with Improved Stability and Spectral Response", ADVANCED FUNCTIONAL MATERIALS, WILEY - V C H VERLAG GMBH & CO. KGAA, DE, vol. 21, no. 4, 22 February 2011 (2011-02-22), pages 756 - 763, XP001560462, ISSN: 1616-301X, [retrieved on 20101210], DOI: 10.1002/ADFM.201001801
BARNHAM K. W. J. ET AL., NATURE MATERIALS, vol. 5, 2006, pages 161 - 164
BREDAS J. L. ET AL., ACCOUNTS OF CHEMICAL RESEARCH, vol. 42, no. 11, 2009, pages 1689 - 1690
NAZEERUDDIN ET AL., COORDINATION CHEMISTRY REVIEWS, vol. 249, no. 13-14, 2005, pages 1460 - 1467
ROBERTSON N., ANGEWANDTE CHEMIE INTERNATIONAL EDITION, vol. 45, 2006, pages 2338 - 2345
HAGFELDT A. ET AL., CHEMICAL REVIEWS, vol. 110, 2010, pages 6595 - 6663
VOGEL R. ET AL., JOURNAL OF PHYSICAL CHEMISTRY, vol. 98, 1994, pages 3183 - 3188
YU P. ET AL., JOURNAL OFPHYSICAL CHEMISTRY B, vol. 110, 2006, pages 25451 - 25454
MORA-SERO 1. ET AL., JOURNAL OFPHYSICAL CHEMISTRY C, vol. 114, 2010, pages 6755 - 6761
MORA-SERO 1 ET AL., JOURNAL OF PHYSICAL CHEMISTRY C, vol. 114, 2010, pages 6755 - 6761
ITZHACOV S. ET AL., ADVANCED ENERGY MATERIALS, vol. 1, 2011, pages 626 - 633
ETGAR L. ET AL., RSC ADVANCES, vol. 2, 2012, pages 2748 - 2752
FAN S. Q. ET AL., OPTOELECTRONICS AND ADVANCED MATERIALS - RAPID COMMUNICATIONS, vol. 3, no. 10, 2009, pages 1027 - 1033
MARTIN R. ET AL., ACCOUNT OF CHEMICAL RESEARCH, vol. 41, no. 11, 2008, pages 1461 - 1473
ROQUET S ET AL., JOURNAL OF AMERICAN CHEMICAL SOCIETY, vol. 128, no. 10, 2006, pages 3459 - 3466
MIKROYANNIDIS J. A. ET AL., JOURNAL OF POWER SOURCES, vol. 195, no. 9, 2010, pages 3002 - 3010
CARBONE ET AL., NANO LETTERS, vol. 7, 2007, pages 2942 - 2950
GRATZEL M. ET AL., THIN SOLID FILM, vol. 516, 2008, pages 4613 - 4619
FUKE N. ET AL., ACS NANO, vol. 11, 2010, pages 6377 - 6386
GOMEZ R. ET AL., JOURNAL OF PHYSICAL CHEMISTRY C, vol. 113, 2009, pages 4208 - 4214
PENG X. ET AL., CHEMISTRY OF MATERIALS, vol. 15, 2003, pages 2854 - 2860
Attorney, Agent or Firm:
BOTTERO, Carlo (Via Borgonuovo 10, Milano, IT)
Download PDF:
Claims:
CLAIMS

Quantum dot dye-sensitized solar cell (QDDSSC) comprising an anode, a cathode, an electrolyte between the anode and the cathode, wherein the anode comprises:

a semiconductor electrode layer absorbed with at least one organic dye, said organic dye comprising at least one triaryl-amine group and at least one benzo-heterodiazole group;

at least one quantum dot (QD) distributed within the semiconductor electrode layer, said quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm.

Quantum dot dye-sensitized solar cell (QDDSSC) according to Claim 1, wherein said quantum dot (QD) have an average diameter ranging from 1.6 nm to 3.2 nm.

Quantum dot dye-sensitized solar cell (QDDSSC) according to Claim 1 or 2, wherein said organic dye is selected from organic dyes having general formula (I):

wherein:

D represents a triaryl-amine group having the following general formulae (II), (III), (IV),(V), (VI), (VII), (VIII):

(II) (HI) (IV)

(VIII) wherein Ri and R2, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, C1-C20 alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, polyethylenoxide groups having general formula: R'-0-[-CH2-CH2- 0]r- wherein R' represents a hydrogen atom or is selected from C1-C20 saturated alkyl groups, linear or branched, r is an integer ranging from 1 to 20;

A represents a benzo-heterodiazole group having general formula (IX):

wherein:

R-3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6- C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups;

or R3 and R4 can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl-phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

Z represents a heteroatom such as oxygen, sulphur, selenium, tellurium; or is selected from groups having general formula X(Rs) wherein X represents a heteroatom such as nitrogen, phosphorous, arsenic, boron, and R5 represents a hydrogen atom, or is selected from C1-C20, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, or from groups having general formula Y(R6R7) wherein Y represents an atom such as carbon, silicon, germanium, and R6 and R7, equal to or different from each other, are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted;

n is an integer ranging from 1 to 5;

P represents a π-conjugated unit having general formulae (X), (XI), (XII):

(ΧΠ) wherein:

R8 and R9, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6- C24 aryl groups optionally substituted, C4-Cn heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as fluorine, chlorine, bromine, iodine;

Rio and Rn, equal to or different from each other, are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups, optionally substituted;

or R8 and R9 in general formula (X), and/or R10 and Rn, can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4- C11 heterocyclic groups optionally substituted, trialkyl- or triaryl- silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl- phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

W represents an heteroatom such as oxygen, sulphur, selenium, tellurium; V represents an atom such as carbon, silicon, germanium;

m is an integer ranging from 1 to 7;

p is an integer ranging from 1 to 3;

G is an anchoring group selected among the following groups: a - COOH group, a phosphonic group having formula -PO(OH)2 or general formula -PO(OH)(Ri2) wherein Ri2 represents a Ci-C2o alkyl group, linear or branched, saturated or unsaturated, a carboxycyanovinylene group having general formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein Ri3, Ri and Ri5, equal to or different from each other, represent a hydrogen atom; or a halogen atoms such as fluorine, chlorine, bromine, iodine; or are selected from Ci-C20 alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C2 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Ci2 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, cyano groups, nitro groups. Quantum dot dye-sensitized solar cell (QDDSSC) according to Claim 3, wherein said organic dye is selected from organic dyes having general formula (I):

wherein:

D represents a triaryl-amine group having general formula (II):

(Π) wherein Ri and R2, equal to or different from each other, represent an hydrogen atom; or are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

A represents a benzo-heterodiazole group having general formula (IX):

wherein:

R3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

Z is sulphur;

n is 1;

P represents a π-conjugated unit having general formula (X):

wherein:

R8 and R9, equal to or different from each other, represent an hydrogen atom; or are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

W is sulphur;

m is 1;

p is 1;

G is an anchoring group selected from a carboxycyanovinylene group having formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein Ri3, Ri4 and Ri5, equal to or different from each other, represent a hydrogen atom; or are selected from Ci-C2o alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom.

Quantum dot dye-sensitized solar cell (QDDSSC) according to anyone of the preceeding claims, wherein said said quantum dot (QD) is selected from: lead sulphide (PbS), zinc sulphide (ZnS), cadmium sulphide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), silver (Ag), gold (Au), aluminium (Al), or mixture thereof.

Quantum dot dye-sensitized solar cell (QDDSSC) according to Claim 5, wherein said said quantum dot (QD) is cadmium selenide (CdSe), or cadmium sulphide (CdS).

Quantum dot dye-sensitized photoelectric transformation element comprising at least one organic dye having general formula (I) according to Claim 3 or 4 and at least one quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm according to Claim 5 or 6, said quantum dot dye- sensitized photoelectric transformation element being supported on oxide semiconductor particles.

8. Organic dyes having general formula (I):

wherein:

D represents a triaryl-amine group having the following general formulae (II), (III), (IV),(V), (VI), (VII), (VIII):

(VIII) wherein Ri and R2, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, polyethylenoxide groups having general formula: R'-0-[-CH2-CH2-0]r- wherein R' represents a hydrogen atom or is selected from C1-C20 saturated alkyl groups, linear or branched, r is an integer ranging from 1 to 20;

A represents a benzo-heterodiazole group having general formula (IX):

R3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6- C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups;

or R3 and R4 can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl-phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

Z represents a heteroatom such as oxygen, sulphur, selenium, tellurium; or is selected from groups having general formula X(Rs) wherein X represents a heteroatom such as nitrogen, phosphorous, arsenic, boron, and R5 represents a hydrogen atom, or is selected from C1-C20, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted,

C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, or from groups having general formula Y(ReR7) wherein Y represents an atom such as carbon, silicon, germanium, and R6 and R7, equal to or different from each other, are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted;

n is an integer ranging from 1 to 5; P represents a π-conjugated unit having general formulae (X), (XI), (XII):

(ΧΠ) wherein:

R8 and R9, equal to or different from each other, represent an hydrogen atom; or are selected from: C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6- C24 aryl groups optionally substituted, C4-Cn heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as fluorine, chlorine, bromine, iodine;

Rio and Rn, equal to or different from each other, are selected from C1-C20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12 cycloalkyl groups optionally substituted, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted;

or Rg and R9 in general formula (X), and/or R10 and Rn, can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with Ci-C2o alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Ci2 cycloalkyl groups optionally substituted, heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl- phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as fluorine, chlorine, bromine, iodine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

W represents an heteroatom such as oxygen, sulphur, selenium, tellurium;

V represents an atom such as carbon, silicon, germanium;

m is an integer ranging from 1 to 7;

p is an integer ranging from 1 to 3;

G is an anchoring group selected among the following groups: a - COOH group, a phosphonic group having formula -PO(OH)2 or general formula -PO(OH)(Ri2) wherein Ri2 represents a Ci-C20 alkyl group, linear or branched, saturated or unsaturated, a carboxycyanovinylene group having general formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein Ri3, Ri4 and Ri5, equal to or different from each other, represent a hydrogen atom; or a halogen atoms such as fluorine, chlorine, bromine, iodine; or are selected from Ci-C2o alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, C6-C24 aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-Ci2 cycloalkyl groups optionally substituted, C4-Cn heterocyclic groups optionally substituted, cyano groups, nitro groups; with the proviso that, when in general formula (I) D represent a triaryl-amine group having general formula (II) or (V), Z in general formula (IX) represent sulphur, n and p are 1, and at least one of Ri, R2, R3 and R4, is different from hydrogen.

Description:
QUANTUM DOT DYE-SENSITIZED SOLAR CELL

The present invention relates to a quantum dot dye- sensitized solar cell (QDDSSC).

More in particular, the present invention relates to a quantum dot dye- sensitized solar cell (QDDSSC) comprising an anode, a cathode, an electrolyte between the anode and the cathode, wherein the anode comprises: a semiconductor electrode layer absorbed with at least one organic dye, said organic dye comprising at least one triaryl-amine group and at least one benzo-heterodiazole group; at least one quantum dot (QD) distributed within the semiconductor electrode layer, said quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm.

Moreover, the present invention also relates to a quantum dot dye- sensitized photoelectric transformation element comprising at least one organic dye, said organic dye comprising at least one triaryl-amine group and at least one benzo- heterodiazole group, and at least one quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm, said quantum dot dye-sensitized photoelectric transformation element being supported on oxide semiconductor particles.

The worlwide increasing in energy demand together with the concern about the global warming induces scientists to find alternative and ecologically friendly energy resources. Concerning this, the sun represents the ideal source of energy because it is clean and freely available as reported, for example, by Barnham K. W. J. et al. in "Nature Materials" (2006), Vol. 5, pg. 161-164; Bredas J. L. et al. in "Accounts of Chemical Research" (2009), Vol. 42, No. 11, pg. 1689-1690.

Among the photovoltaic technologies, dye- sensitized solar cells (DSSCs), which have been developed by Gratzel et al. on 1991, have attracted considerable attention in recent years due to their high efficiency and remarkably low manufacture costs compared to the existing silicon solar cells.

The dye-sensitized solar cells (DSSCs) are photoelectrochemical solar cells generally comprising four main components: an electrode optically transparent (anode); organic or organometallic dye molecules adsorbed on a semiconductor oxide, usually on a mesoporous titanium dioxide (Ti0 2 ); a liquid inorganic electrolyte or a hole-transport solid organic material; and a counter-electrode (cathode). The dye molecules are photochemically excited when absorbing the sun light and their electrons are promoted, in this way, from the fundamental state to a more high energy orbital (LUMO), from which they can be transferred to the conductive band of the semiconductor oxide [i.e. titanium dioxide (Ti0 2 )], leaving the dye molecules in their oxidized form. Subsequently, the electrons are collected on a transparent conductive layer, generally constituted of a fluorine-doped tin oxide (FTO) and, through an external circuit, reach the counter electrode (cathode), generally constituted of platinum. The oxidized dye molecules are regenerated as follows: through a transfer catalyzed by the platinum of the cathode, the electrons trigger a series of redox reactions mediated by a redox couple which acts as electrolyte (usually the couple I2/I3 " ), at the end of said reactions the redox couple in its reduced form transfer an electron to the oxidized dye molecule making it available for a new cycle.

A lot of organic dyes for dye-sensitized solar cells (DSSCs) have been already disclosed in the prior art such as, for example, by Nazeeruddin et al. in "Coordination Chemistry Reviews" (2005), Vol. 249, Issues 13-14, pg. 1460-1467; Robertson N. in "Angewandte Chemie International Edition" (2006), Vol. 45, pg. 2338-2345; Hagfeldt A. et al. in "Chemical Reviews" (2010), Vol. 110, pg. 6595- 6663.

Recently, new approaches emerged to further improve the efficiencies of the dye-sensitized solar cells (DSSCs). For example, replacing organic dyes with small band gap semiconductor nanocrystals quantum dots (QDs) is one of these new approaches.

Said quantum dots (QDs) are very interesting because they are able to preserve bulk properties important for efficient light-energy conversion devices such as, for example, high molar extinction coefficients and large intrinsic dipole moment.

In addition, they show properties arising from the quantum confinement such as, for example, tunable band gap due to the capability of controlling their size and shape providing a fertile ground for the design of light-absorbing materials with tailored optical properties. Further details about said quantum dots (QDs) are reported, for example, by: Vogel R. et al. in "Journal of Physical Chemistry" (1994), Vol. 98, pg. 3183-3188; Yu P. et al. "Journal of Physical Chemistry B" (2006), Vol. 110, pg. 25451-25454; Mora-Sero I. et al. in "Journal of Physical Chemistry C (2010), Vol. 114, pg. 6755-6761.

However, the utilization of quantum dots (QDs) as sensitizers in dye- sensitized solar cells (DSSCs) implies efficient charge transfer to the wide band gap semiconductor photoelectrode such as, for example, titanium dioxide (Ti0 2 ) photoelectrode, that renders internal radiative recombination and the concomitant photoluminescent emission, detrimental for said dye- sensitized solar cells (DSSCs). For example, anchoring of cadmium selenide (CdSe) quantum dots (QDs) onto titanium dioxide (Ti0 2 ) photoelectrode leads to significant quenching of their emission, due to the injection of photogenerated electrons into titanium dioxide (Ti0 2 ) photoelectrode conduction band. In that case, steady as well as transient photoluminescence measurements can be fruitfully applied to quantify charge transfer kinetics from quantum dots (QDs) of different sizes to titanium dioxide (Ti0 2 ) photoelectrode as well as to trace the influence of the absorption method. Furthermore, photoluminescence measurements can be used to elucidate the interactions of quantum dots (QDs) with other materials used for cosensitizing or coating purposes such as molecular dyes and zinc sulfide (ZnS). In fact, it has been shown that zinc sulfide coating of cadmium selenide (CdSe) quantum dots (QDs) leads to almost double photocurrent in dye-sensitized solar cells (DSSCs).

On the other end, combination of quantum dots (QDs) and molecular dyes provides a particularly powerful route to create novel composite heterostructures with enhanced light harvesting ability. In this sense, quantum dots (QDs), in particular colloidal quantum dots (QDs), may serve as an excellent component for the development of more sophisticated heterostructures such as supracollector nanocomposites, exploiting the charge transfer between semiconductor quantum dots (QDs) and molecular dyes. The main purpose is to augment the spectral absorption range in dye-sensitized solar cells (DSSCs) and to reduce the internal recombination of quantum dots (QDs). In that case, fast scavenging of photogenerated holes in quantum dots (QDs) sensitizers by a molecular dye can outbalance the competition between electron transfer from quantum dots (QDs) to titanium dioxide (Ti0 2 ) photoelectrode and the internal relaxation of the quantum dots (QDs) excited state, leading to higher electron injection yields. Simultaneously, light absorption can be drastically enhanced over a broad spectral range better matching the solar irradiance, provided that a suitable combination of quantum dots (QDs) and dye complexes with appropriate charge transfer energetics is used.

For example, Mora-Sero I. et al. in "Journal of Physical Chemistry C (2010), Vol. 114, pg. 6755-6761, above cited, disclose the interaction between colloidal CdSe/ZnS-coated quantum dots (QDs) and the polypyridyl ruthenium molecular dye N719: the results obtained are said to have important applications for the development of the use of quantum dots in dye- sensitized solar cells (DSSCs) exploiting the synergistic function of composite heterostructures consisting of quantum dots (QDs) and molecular dyes.

It is known that the traditional organic dyes used in dye-sensitized solar cells (DSSCs) suffer from narrow absorption spectra or low molar extinction coefficients. The utilization of Forster resonance energy transfer (FRET) from a donor to a sensitizing dye introduces a new degree of freedom in the design of dye- sensitized solar cells (DSSCs).

As a matter of fact, combining properly quantum dots (QDs) and dye, the interaction between them can led to Forster resonance energy transfer (FRET) as reported, for example, by Itzhacov S. et al. in "Advanced Energy Materials" (2011), Vol. 1, pg. 626-633. In particular, they disclose a dye- sensitized solar cell (DSSC) wherein the quantum dot (QD) "antennas" that serve as donor are incorporated into the solid titania electrode, providing isolation from electrolyte quenching, and potentially increasing photostability. The energy transferred to the dye acceptor from the quantum dot (QD) donor, in addition to the direct light absorption by the dye, finally induce dye excitation and electron injection to the metal oxide semiconductor electrode. The effects of the interaction between quantum dots (QDs) and dyes have been reported also in other studies.

For example, Etgar L. et al. in "RSC Advances" (2012), Vol. 2, pg. 2748- 2752, disclose the enhancement of the efficiency of a dye- sensitized solar cell (DSSC) due to the energy transfer between cadmium selenide (CdSe) quantum dots (QDs) and a designed squaraine dye. In particular, they disclose that the photoelectric transformation efficiency (η) of a dye- sensitized solar cell (DSSC) with tailored squaraine dye is enhanced by 47% due to Forster resonance energy transfer from cadmium selenide (CdSe) quantum dots (QDs) to the squaraine dye. The incident photons to collection efficiency of electrons indicate pancrhomatic response from the visible to the near-infrared spectrum. However, it has to be outlined that, notwistanding the enhancement of the photoelectric transformation efficiency (η) up to 47%, the overall photoelectric transformation efficiency (η) of a dye-sensitized solar cell (DSSC) herein reported, is still rather low, i.e. is equal to 1.48%.

Fan S. Q. et al. in "Optoelectronics and Advanced Materials - Rapid Communications" (2009), Vol. 3, No. 10, pg. 1027-1033, disclose the use of CdSe quantum dots (QDs) as co-sensitizers of organic dyes in solar cells with a polysulfide electrolyte in order to obtain red-shifted light-harvesting. However, also in this case, it has to be outlined that, notwithstanding the enhancement of the photoelectric transformation efficiency (η) up to 150%), the overall photoelectric transformation efficiency (η) of a dye-sensitized solar cell (DSSC) herein reported, is still rather low, i.e. is equal to 1.03%.

American Patent Application US 2011/0120540 relates to a quantum dots- sensitized solar cell (QDDSSC), comprising an anode, a cathode, and an electrolyte between the anode and the cathode, wherein the anode comprises:

a semiconductor electrode layer absorbed with a dye (for example, a commercial N719 dye);

a plurality of quantum dots (QDs) distributed within the semiconductor electrode layer [for example, copper indium gallium selenide (CIGS) quantum dots (QDs)];

a plurality of metal nanoparticles distributed within the semiconductor electrode layer [for example, gold (Au) nanoparticles].

The abovementioned quantum dots-sensitized solar cell (QDDSSC) is said to have an improved conversion efficiency and an improved light utilization efficiency. It has to be noted that, also in this case, the overall photoelectric transformation efficiency (η) of a quantum dot dye-sensitized solar cell (QDDSSC) is still rather low, i.e. is equal to 3.23%.

Therefore, there have been continuous attempts to develop novel combination of organic dyes, in particular between metal-free organic dyes, with quantum dots (QDs), able to give quantum dot dye-sensitized solar cells (QDDSSCs) having improved photoelectric transformation efficiency (η) with respect to the prior art.

The Applicant has faced the problem of finding a quantum dot dye- sensitized solar cells (QDDSSCs) having improved photoelectric transformation efficiency (η), i.e. a photoelectric transformation efficiency (η) higher than or equal to 4.5%.

The Applicant has found that the combination of at least one organic dye comprising at least one triaryl-amine group and at least one benzo-heterodiazole group with at least one quantum dot (QD) having a specific average diameter (i.e. an average diameter not higher than or equal to 3.6 nm), is able to give a quantum dot dye-sensitized solar cell (QDDSSC) having improved photoelectric transformation efficiency (η), i.e. a photoelectric transformation efficiency (η) higher than or equal to 4.5%. Moreover, said quantum dot dye- sensitized solar cell (QDDSSC) also has good or even improved Voc (open circuit photovoltage), FF (fill factor) and Jsc (short-circuit photocurrent density). Moreover, said quantum dot dye-sensitized solar cell (QDDSSC) shows an increase of the photoelectric transformation efficiency (η) higher than or equal to 10% with respect to the dye- sensitized solar cell comprising only an organic dye or only a quantum dots.

An object of the present invention therefore relates to a quantum dot dye- sensitized solar cell (QDDSSC) comprising an anode, a cathode, an electrolyte between the anode and the cathode, wherein the anode comprises:

a semiconductor electrode layer absorbed with at least one organic dye, said organic dye comprising at least one triaryl-amine group and at least one benzo-heterodiazole group;

at least one quantum dot (QD) distributed within the semiconductor electrode layer, said quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm.

For the aim of the present invention and of the following claims, the definitions of the numerical ranges always comprise the extremes unless otherwise specified.

For the aim of the present invention and of the following claims, the term "comprising" also includes the terms "consisting essentially of or "consisting of.

In accordance with a preferred embodiment of the present invention, said organic dye may be selected from organic dyes having general formula (I): wherein:

D represents a triaryl-amine group having the following general formulae (II), (III), (IV),(V), (VI), (VII), (VIII):

(II) (HI) (IV)

(V) (VI) (VII)

(VIII) wherein Ri and R 2 , equal to or different from each other, represent an hydrogen atom; or are selected from: C 1 -C 2 o, preferably C 1 -C 12 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 24 , preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, C1-C20, preferably C1-C12, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, polyethylenoxide groups having general formula: R'-0-[-CH 2 -CH 2 -0] r - wherein R' represents a hydrogen atom or is selected from Ci-C 20 , preferably Ci-Ci 2 , saturated alkyl groups, linear or branched, r is an integer ranging from 1 to 20, preferably ranging from 2 to 10;

A represents a benzo-heterodiazole group having general formula (IX):

R 3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from: Ci-C 20 , preferably Ci-Ci 2 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12, preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 2 4, preferably C 6 -Ci 4 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C 5 -C 7 , heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups;

or R 3 and R4 can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with C1-C2 0 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -

Ci4, aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12, preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl-phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as, for example, oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

Z represents a heteroatom such as, for example, oxygen, sulphur, selenium, tellurium, preferably sulphur; or is selected from groups having general formula X(Rs) wherein X represents a heteroatom such as, for example, nitrogen, phosphorous, arsenic, boron, preferably nitrogen, and R 5 represents a hydrogen atom, or is selected from C1-C2 0 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -Ci 4 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12, preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C 5 -C 7 , heterocyclic groups optionally substituted, or from groups having general formula Y(R 6 R 7 ) wherein Y represents an atom such as, for example, carbon, silicon, germanium, preferably carbon or silicon, and R 6 and R 7 , equal to or different from each other, are selected from C 1 -C 20 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 24 , preferably C 6 -Ci , aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C 12 , preferably C -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted;

n is an integer ranging from 1 to 5, preferably is 1 or 2;

P represents a π-conjugated unit having general formulae (X), (XI), (XII):

(X) (XI)

(ΧΠ) wherein:

Rg and R 9 , equal to or different from each other, represent an hydrogen atom; or are selected from: C 1 -C 20 , preferably C 1 -C 12 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 24 , preferably C 6 -Ci , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C 5 -C 7 , heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine;

Rio and Rn, equal to or different from each other, are selected from Ci- C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C4-C12, preferably C 4 - Cg, cycloalkyl groups, optionally substituted, C 6 -C 2 4, preferably C 6 -Ci 4 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups, optionally substituted;

or R 8 and R 9 in general formula (X), and/or R i0 and Rn, can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with Ci- C 2 o alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -Ci 4 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12, preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl- phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as, for example, oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

W represents an heteroatom such as, for example, oxygen, sulphur, selenium, tellurium, preferably sulphur; V represents an atom such as, for example, carbon, silicon, germanium, preferably carbon or silicon;

m is an integer ranging from 1 to 7, preferably ranging from 1 to 3; p is an integer ranging from 1 to 3, preferably is 1;

G is an anchoring group selected among the following groups: a -COOH group, a phosphonic group having formula -PO(OH) 2 or general formula - PO(OH)(Ri 2 ) wherein R i2 represents a C 1 -C 2 o, preferably C1-C12, alkyl group, linear or branched, saturated or unsaturated, a carboxycyanovinylene group having general formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein R i3 , R i and Ri 5 , equal to or different from each other, represent a hydrogen atom; or a halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, bromine; or are selected from Ci-C 2 o, preferably Ci-Ci 2 , alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 , preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -C 12 , preferably C -C 8 , cycloalkyl groups optionally substituted, C -Cn, preferably C5-C7, heterocyclic groups optionally substituted, cyano groups, nitro groups. In accordance with a further preferred embodiment of the present invention, said organic dye is selected from organic dyes having general formula (I): wherein: D represents a triaryl-amine group having general formula (II):

(II)

wherein Ri and R 2 , equal to or different from each other, represent an hydrogen atom; or are selected from C 1 -C 2 o, preferably C 1 -C 12 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

A represents a benzo-heterodiazole group having general formula (IX):

wherein:

R 3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from C 1 -C 20 , preferably C 1 -C 12 , alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

Z is sulphur;

n is 1;

P represents a π-conjugated unit having general formula (X):

(X)

wherein: R 8 and R 9 , equal to or different from each other, represent an hydrogen atom; or are selected from C 1 -C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom;

W is sulphur;

m is 1;

p is 1;

G is an anchoring group selected from a carboxycyanovinylene group having general formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein R i3 , R i4 and R15, equal to or different from each other, represent a hydrogen atom; or are selected from C1-C2 0 , preferably C1-C12, alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, preferably an hydrogen atom.

It has to be pointed out that some of the organic dyes having general formula (I) are new.

Therefore, it is a further object of the present invention an organic dye having general formula (I):

D represents a triaryl-amine group having the following general formulae (II), (III), (IV),(V), (VI), (VII), (VIII):

(VIII) wherein Ri and R 2 , equal to or different from each other, represent an hydrogen atom; or are selected from: C 1 -C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 24 , preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, polyethylenoxide groups having general formula: R'-0-[-CH 2 -CH 2 -0] r - wherein R' represents a hydrogen atom or is selected from Ci-C 20 , preferably Ci-Ci 2 , saturated alkyl groups, linear or branched, r is an integer ranging from 1 to 20, preferably from 2 to 10; A represents a benzo-heterodiazole group having general formula (IX):

wherein:

R-3 and R4, equal to or different from each other, represent an hydrogen atom; or are selected from: C 1 -C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 2 4, preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups;

or R 3 and R4 can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with C1-C2 0 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 - Ci4, aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl-phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as, for example, oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

Z represents a heteroatom such as, for example, oxygen, sulphur, selenium, tellurium, preferably sulphur; or is selected from groups having general formula X(Rs) wherein X represents a heteroatom such as, for example, nitrogen, phosphorous, arsenic, boron, preferably nitrogen, and R 5 represents a hydrogen atom, or is selected from C 1 -C 2 o, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C 5 -C 7 , heterocyclic groups optionally substituted, or from groups having general formula Y(ReR 7 ) wherein Y represents an atom such as, for example, carbon, silicon, germanium, preferably carbon or silicon, and R6 and R 7 , equal to or different from each other, are selected from C1-C2 0 alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted;

n is an integer ranging from 1 to 5, preferably is 1 or 2;

P represents a π-conjugated unit having general formulae (X), (XI), (XII):

(X) (XI)

(ΧΠ) wherein:

R 8 and R 9 , equal to or different from each other, represent an hydrogen atom; or are selected from: C 1 -C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 4 -C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 6 -C 2 4, preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, trialkyl- or triaryl-silyl groups, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine;

Rio and Rn, equal to or different from each other, are selected from Ci- C 2 o, preferably C1-C12, alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 4 -C 12 , preferably C 4 - Cg, cycloalkyl groups optionally substituted, C 6 -C 2 4, preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted;

or Rg and R 9 in general formula (X), and/or R 10 and Rn, can be optionally bound to each other to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic, cycle containing from 1 to 12 carbon atoms, optionally substituted with Ci-

C 2 o alkyl groups, linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 24 , preferably C 6 -C 14 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C 12 , preferably C 4 -Cg, cycloalkyl groups optionally substituted, eterocyclic groups optionally substituted, trialkyl- or triaryl-silyl groups, dialkyl- or diaryl-amino groups, dialkyl- or diaryl-phosphine groups, alkoxyl or aryloxyl groups optionally substituted, thioalkoxyl or thioaryloxyl groups optionally substituted, halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, cyano groups, nitro groups; said cycle optionally containing other heteroatoms such as, for example, oxygen, sulphur, nitrogen, silicon, phosphorous, selenium, boron;

W represents an heteroatom such as, for example, oxygen, sulphur, selenium, tellurium, preferably sulphur;

V represents an atom such as, for example, carbon, silicon, germanium, preferably carbon or silicon;

m is an integer ranging from 1 to 7, preferably ranging from 1 to 3; p is an integer ranging from 1 to 3, preferably is 1;

G is an anchoring group selected among the following groups: a -COOH group, a phosphonic group having formula -PO(OH) 2 or general formula - PO(OH)(Ri 2 ) wherein R i2 represents a C 1 -C 2 o, preferably Ci-Ci 2 , alkyl group, linear or branched, saturated or unsaturated, a carboxycyanovinylene group having general formula (XIII) or (XIV):

(ΧΠΙ) (XIV) wherein R i3 , R i and Ri 5 , equal to or different from each other, represent a hydrogen atom; or a halogen atoms such as, for example, fluorine, chlorine, bromine, iodine, preferably fluorine, bromine; or are selected from Ci-C 20 , preferably C1-C12, alkyl groups linear or branched, saturated or unsaturated, optionally containing heteroatoms, C 6 -C 2 4, preferably C 6 -Ci 4 , aryl groups optionally substituted, heteroaryl groups optionally substituted, C4-C12, preferably C 4 -Cg, cycloalkyl groups optionally substituted, C 4 -Cn, preferably C5-C7, heterocyclic groups optionally substituted, cyano groups, nitro groups; with the proviso that, when in general formula (I) D represent a triaryl-amine group having general formula (II) or (V), Z in general formula (IX) represent sulphur, n and p are 1, and at least one of Ri, R 2 , R3 and R4, is different from hydrogen.

The term "C1-C2 0 alkyl groups" refers to alkyl groups having from 1 to 20 carbon atoms, linear or branched, satured or unsaturated. Specific examples of Ci- C 2 o alkyl groups are: methyl, ethyl, ^-propyl, zso-propyl, «-butyl, zso-butyl, t-butyl, pentyl, hexyl, eptyl, octyl, 2-ethyleptyl, 2-ethylhexyl, 2-butenyl, 2-pentenyl, 2-ethyl- 3-hexenyl, 3-octenyl, l-methyl-4-hexenyl, 2-butyl-3-hexenyl.

The term "C1-C2 0 alkyl groups optionally containing heteroatoms" refers to alkyl groups having from 1 to 20 carbon atoms, linear or branched, saturated or unsaturated, wherein at least one of the hydrogen atoms is substituted with a hetroatom selected from: halogen such as, for example, chlorine, bromine, preferably fluorine; nitrogen; sulfur; oxygen. Specific examples of C1-C2 0 alkyl groups optionally containing heteroatoms are: fluoromethyl, difluoromethyl, trifluoromethyl, trichloromethyl, 2,2,2-trifluoroethyl, 2,2,2-trichlororoethyl, 2,2,3,3- tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, perfluoropentyl, perfluoroctyl, perfluorodecyl, oxymethyl, thiomethyl, thioethyl, dimethylamino, propylamino, dioctylamino.

The term "C4-C12 cycloalkyl groups" refers to cycloalkyl groups having from 4 to 12 carbon atoms. Said cycloalkyl groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C1-C12 alkyl groups; C1-C12 alkoxyl groups; C1-C12 thioalkoxyl groups; trialkyl- or triaryl-silyl groups; polyethyleneoxyde groups; cyano groups; amino groups; C1-C12 mono- o di-alkylamino groups; nitro groups. Specific examples of

C4-C12 cycloalkyl groups are: cyclopropyl, 2,2-difluorocyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, metoxycyclohexyl, fluorocyclohexyl, phenylcyclohexyl, decalin, abietyl.

The term "C 6 -C 24 aryl groups" refers to carbocyclic aromatic groups containing from 6 to 24 carbon atoms. Said aryl groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C1-C12 alkyl groups; C1-C12 alkoxyl groups; C1-C12 thioalkoxyl groups; trialkyl- or triaryl-silyl groups; polyethyleneoxyde groups; cyano groups; amino groups; Ci-Ci 2 mono- o di-alkylamino groups; nitro groups. Specific examples of C 6 -C 24 aryl groups are: phenyl, methylphenyl, trimethylphenyl, metoxyphenyl, hydroxyphenyl, phenyloxyphenyl, fluorophenyl, pentafluorophenyl, chlorophenyl, bromophenyl, nitrophenyl, dimethylaminophenyl, naphthyl, phenylnaphthyl, phenanthrene, anthracene.

The term "heteroaryl groups" refers to heterocyclic aromatics groups, penta- o hexa-atomics, also benzocondensed or heterobicyclic, containing from 6 to 24 carbon atoms and from 1 to 4 heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus. Said heteroaryl groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; Ci-Ci 2 alkyl groups; Ci-Ci 2 alkoxyl groups; Ci-Ci 2 thioalkoxyl groups; trialkyl- or triaryl-silyl groups; polyethyleneoxyde groups; cyano groups; amino groups; Ci-Ci 2 mono- o di-alkylamino groups; nitro groups. Specific examples of heteroaryl groups are: pyridine, methylpyridine, methoxypyridine, phenylpyridine, fluoropyridine, pyrimidine, pyridazine, pyrazine, triazine, tetrazine, quinoline, quinoxaline, quinazoline, furan, thiophene, hexylthiophene, bromothiophene, dibromothiophene, pyrrole, oxazole, thiazole, isooxazole, isothiazole, oxadiazole, thiadiazole, pyrazole, imidazole, triazole, tetrazole, indole, benzofuran, benzothiophene, benzooxazole, benzothiazole, benzooxadiazole, benzothiadiazole, benzopyrazole, benzimidazole, benzotriazole, triazolepyridine, triazolepyrimidine, coumarin.

The term "C 4 -Cn heterocyclic groups" means rings having from 3 to 12 atoms, saturated or unsaturated, containing at least one heteroatom selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus, optionally condensed with other aromatic or non-aromatic rings. Said heterocyclic groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C1-C12 alkyl groups; C1-C12 alkoxyl groups; C1-C12 thioalkoxyl groups; trialkyl- or triaryl-silyl groups; polyethyleneoxyde groups; cyano groups; amino groups; C1-C12 mono- o di-alkylamino groups; nitro groups. Specific examples of heterocyclic groups are: pyrrolidine, methoxy pyrrolidine, piperidine, fluoropiperidine, methylpiperidine, dihydropyridine, piperazine, morpholine, thiazine, induline, phenylindoline, 2-ketoazetidine, diketopiperazine, tetrahydrofuran, tetrahydrothiophene.

The term "alkoxyl or aryloxyl groups" means groups having an oxygen atom attached to a C1-C12 alkyl group or to a C 6 -Ci 2 aryl group. Said alkoxyl or aryloxyl groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C1-C12 alkyl groups; C1-C12 alkoxyl groups; C1-C12 thioalkoxyl groups; trialkyl- or triaryl-silyl groups; polyethyleneoxyde groups; cyano groups; amino groups; C1-C12 mono- o di- alkylamino groups; nitro groups. Specific examples of alkoxyl or aryloxyl groups are: methoxyl, ethoxyl, propoxyl, butoxyl, isobutoxyl, 2-ethylhexyloxyl, phenoxyl,?ara-methylphenoxyl, /?ara-fluorophenoxyl, orto-butylphenoxyl, naphthyloxyl, anthracenoxyl.

The term "thioalkoxyl or thioaryloxyl groups" means groups having an oxygen atom and a sulfur atom attached to a C1-C24 alkyl group or to a C 6 -Ci 4 aryl group. Specific examples of thioalkoxyl or thioaryloxyl groups are: thiomethoxyl, thioethoxyl, thiopropoxyl, thio-«-butoxyl, thio-zso-butoxyl, 2-ethylthiohexyloxyl, thiophenoxyl, thiobenzyloxyl.

The term "trialkyl- or triaryl-silyl groups" means groups comprising a silicon atom to which are bound three C1-C12 alkyl groups, or three C 6 -C 2 4 aryl groups, or a combination thereof. Specific examples of trialkyl- or triaryl-silyl groups are: trimethylsilane, triethylsilane, trihexylsilane, tridodecylsilane, dimethyldodecylsilane, triphenylsilane, methyldiphenylsilane, dimethyl-naphthylsilane.

The term "dialkyl- or diaryl-amino groups" means groups comprising a nitrogen atom to which are bound two C1-C12 alkyl groups, or two C 6 -C 2 4 aryl groups, or a combination thereof. Specific examples of dialkyl- or diaryl-amino groups are: dimethylamine, diethylamine, di-«-butylamine, di-zso-butylamine, diphenylamine, methylphenylamine, dibenzylamine, ditolylamine, dinaphthylamine.

The term "dialkyl- or diaryl-phosphine groups" refers to groups comprising a phosphorous atom to which are bound two C1-C12 alkyl groups, or two C 6 -C 2 4 aryl groups, or a combination thereof. Specific examples of dialkyl- or diaryl-phosphino groups are: dimethylphosphine, diethylphosphine, dibutylphosphine, diphenylphosphine, methylphenylphosphine, dinaphthylphosphine.

The term "cycle" means a system contanining a ring having from 1 to 12 carbon atoms, optionally containing heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorous. Specific examples of cycle are: toluene, benzonitrile, cicloheptatriene, ciclooctadiene, pyridine, piperidine, tetrahydrofuran, thiadiazole, pirrole, thiophene, selenophene, t-butylpyridine.

The organic dye having general formula (I) may be prepared by processes known in the art. For example, said organic dye having general formula (I) may be prepared by the palladium-catalyzed aryl-aryl cross-coupling reactions (e.g., Suzuki reaction) such as described, for example, by Martin R. et al. in "Account of Chemical Research" (2008), Vol. 41(1 1), pg. 1461-1473; or by the Vilsmaier-Heck formilation of thiophene groups such as described, for example, by Roquet S. et al. in "Journal of American Chemical Society" (2006), Vol. 128, No. 10, pg. 3459- 3466; or by the reaction of formil derivatives with cyanoacetic acid such as described, for example, by Mikroyannidis J. A. et al. in "Journal of Power Sources" (2010), Vol. 195, Issue 9, pg. 3002-3010. Further details about the synthesis of said organic dye having general formula (I) may be found in the examples which follows.

Quantum dots (QDs) may be composed of different elements which may be selected from elements belonging to the groups 12-16, 13-15, 14-16 or 13, of the Periodic Table of the Elements. It has to be noted that for the aim of the present invention and of the claims which follows, the term "Periodic Table of the Elements" refers to "IUPAC Periodic Table of the Elements", version dated 22 June 2007, reported to the following Internet site: wwwiupac.org/fileadmin/user_upload/news/ITJPAC_Periodic_Tabl e- Uunl2.pdf.

In accordance with a preferred embodiment of the present invention, said quantum dot (QD) may be selected, for example, from: lead sulphide (PbS), zinc sulphide (ZnS), cadmium sulphide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), silver (Ag), gold (Au), aluminium (Al), or mixture thereof. Preferably, said quantum dot (QD) is cadmium selenide (CdSe), or cadmium sulphide (CdS).

The quantum dot (QD) may be prepared by processes known in the art, such as described, for example, by Carbone et al. in "Nano Letters" (2007), Vol. 7, pg. 2942-2950. Further details about the synthesis of said quantum dot (QD) may be found in the examples which follows.

According to a further aspect, the present invention relates to a quantum dot dye-sensitized photoelectric transformation element comprising at least one organic dye having general formula (I) and at least one quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm, said quantum dot dye-sensitized photoelectric transformation element being supported on oxide semiconductor particles.

The photoelectric transformation element according to the present invention may be prepared by a process for preparing a quantum dot dye- sensitized photoelectric transformation element for dye- sensitized solar cells (DSSCs) of the prior art, except of using a combination among an organic dye having general formula (I) and a quantum dot (QD) having an average diameter ranging from 1.5 nm to 3.6 nm, preferably ranging from 1.6 nm to 3.2 nm.

The present invention will now be illustrated in further details by means of an illustrative embodiment with reference to the attached Figure 1 which is a sectional view of a quantum dot dye-sensitized solar cell (QDDSSC) according to the present invention. With reference to Figure 1, a quantum dot dye- sensitized solar cell (QDDSSC) (100) comprises an anode (40), a cathode (60), and an electrolyte (50) between the anode (40) and the cathode (60). The anode (40) comprises a semiconductor electrode layer (70) absorbed with an organic dye (80) and quantum dots (QDs) (90) distributed within the semiconductor electrode layer (70). The anode (40) is formed on a transparent conductive substrate (30) and a light beam enters from a transparent conductive substrate (30) at the anode (40). The transparent conductive substrate (30) comprises a transparent substrate (10) and a conductive layer (20), wherein the conductive layer (20) may be made of indium-tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), gadolinium-doped zinc oxide (ZnO-Ga 2 0 3 ), antimony-doped tin oxide (Sn0 2 - Sb 2 0 3 ), graphene, or a mixtures thereof, fluorine-doped tin oxide (FTO) is preferred.

The transparent substrate (10) is not limited as long as it is transparent, and may be exemplified by a transparent inorganic substrate, such as quartz or glass, or a transparent plastic substrate such as, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate, polystyrene, polypropylene, polyimides, polyetherimides, or mixtures thereof. The semiconductor electrode layer (70) may be made of one or more metal oxides selected from the group consisting of titanium dioxide (Ti0 2 ), tin dioxide (Sn0 2 ), zinc oxide (ZnO), tungsten trioxide (W0 3 ), niobium pentaoxide (Nb 2 0 5 ), or titanium- strontium trioxide (TiSr0 3 ), or mixtures thereof and, more preferably, anatase-type titanium dioide (Ti0 2 ), absorbed with an organic dye (80) and quantum dots (QDs) (90) distributed within the same.

Any conductive material may be used to produce the cathode (60): however, it is preferable to use an electrochemically stable material as an electrode. In general, it is preferable to use platinum, gold, silver, aluminium, rhodium, ruthenium, carbon, carbon nanotubes (CNT), or mixtures thereof.

The electrolyte (50) may be liquid, a coagulated form (gel and gel phase), solid. The liquid may be selected, for example, from those obtained by dissolving redox electrolyte, dissolved salt, hole-transport material, or p-type semiconductor in a solvent, and a room temperature dissolved salt. The coagulated form (gel and gel phase) may be selected, for example, from those obtained by including redox electrolyte, a dissolved salt, hole-transport material, or p-type semiconductor in a polymer matrix, or low molecular gellant. The solid may be selected, for example, from redox electrolyte, a dissolved salt, hole-transport material, or p-type semiconductor.

The hole-transport material may be selected, for example, from: amine derivatives; conductive polymers such as, for example, polyacetylene, polyaniline, polythiophene; or discotic liquids crystal phase such as, for example, triphenylene. The p-type semiconductor may be selected, for example, from copper iodide (Cul), copper thiocyanate (CuSCN). As the counter electrode, those having conductivity and catalytic function on reduction of redox electrolyte may be preferably used, and, for example, those obtained by depositing platinum, gold, silver, aluminium, carbon, rhodium, ruthenium, on a glass or a polymer film, or applying conductive particles thereon may be used.

The redox electrolyte used in the quantum dot dye- sensitized solar cell (QDDSSC) according to the present invention may include halogen redox electrolyte comprising halogen compounds comprising halogen ion as a counter ion and a halogen molecule; metal redox electrolytes such as ferrocyanide-ferrocyanide or ferrocene-ferricynium ion; metal complexes such as cobalt complexes; organic redox electrolytes such as, for example, alkylthio-alkyldisulfide, viologen dye, hydroquinone-quinone; halogen redox electrolytes, or cobalt complexes, may be preferable. As the halogen molecule comprised in the halogen redox electrolyte, an iodine molecule may be preferable. As the halogen compounds comprising halogen ion as counter ion, a halogenated metal salt such as, for example, lithium iodide (Lil), sodium iodide (Nal), potassium iodide (KI), calcium diiodide (Cal 2 ), magnesium diiodide (Mgl 2 ), copper iodide (Cul), or an organic ammonium salt of halogen such as, for example, tetraalkylammonium iodide, imidazolium iodide, pyridium iodide, or iodine (I 2 ), may be used.

In case the redox electrolyte is in the form of a solution comprising the same, an electrochemically inert solvent may be used. For example, acetonitrile, propyl enecarbonate, etylenecarbonate, 3-methoxypropionitrile, methoxy- acetonitrile, valeronitrile, ethyleneglycol, propyleneglycol, diethyleneglycol, triethyleneglycol, butyrolactone, dimethoxy ethane, dimethylcarbonate, 1,3- dioxolane, methylformate, 2-methyltetrahydrofurane, 3-methoxy-oxazolidin-2-one, sulforane, tetrahydrofurane, water, may be used. Acetonitrile, valeronitrile, propyl enecarbonate, ethylenecarbonate, 3-methoxypropionitrile, ethyleneglycol, 3- methoxy-oxazolidin-2-on, or butyrolactone, may be preferable. Said solvents may be used alone or in combination.

As a gel phase positive electrolyte, those obtained by including electrolyte or electrolyte solution in oligomer or polymer matrix, or including electrolyte or electrolyte solution in a starch gellant, may be used.

The concentration of the redox electrolyte may preferably ranges from 0.01% by weight to 99% by weight, and more preferably from 0.1 % by weight to 30% by weight, with respect to the total weight of the solution.

The anode (40) may be prepared by processes known in the art such as described, for example, by Gratzel M. et al. in "Thin Solid Film" (2008), Vol. 516, pg. 4613-4619; Fuke N. et al. in "ACS Nano" (2010), Vol. 11, pg. 6377-6386; Gomez R. et al. in "Journal of Physical Chemistry C" (2009) Vol. 113, pg. 4208- 4214. Further details about the synthesis of said anode (40) may be found in the examples which follows.

Preferably, the anode (40) is prepared by forming the semiconductor electrode layer (70) on a transparent substrate (30), dipping the obtained semiconductor electrode layer (70) supported on a transparent substrate (30), in a quantum dots (QDs) solution and subsequently dipping the obtained semiconductor electrode layer (70) with quantum dots (QDs) dispersed therein (90), supported on a transparent substrate (30), in a solution of the organic dye (80).

The semiconductor electrode layer (70) may be prepared by means of different know techniques such as, for example: by spraying particles of the metal oxide in order to form a thin film thereof directly on a transparent substrate (30); by electrically depositing particles of said metal oxide to form a thin film using a transparent substrate (30) as an electrode; by applying slurry or paste containing particles of said metal oxide obtained by hydrolysis of suitable precursors such as a metal halogenide or a metal alkoxide, on a transparent substrate (30) ("doctor- blade" technique), and drying, curing or sintering. Preferably, the paste may be applied on a transparent substrate (30), and in this case, slurry may be obtained by dispersing particles of said metal oxides in a dispersion medium by a method known in the art.

As the dispersion medium, those capable of dispersing particles of said metal oxides may be used without limitation. Preferably, said dispersion medium may be selected, for example, from: water; alcohols such as, for example, ethanol; ketones such as, for example, acetone, acetylacetone; hydrocarbons such as, for example, hexane; or mixtures thereof. Water may be preferable because it minimizes change in viscosity of slurry. Optionally, a dispersion stabilizer may be used in order to stabilize the dispersion of the said metal oxides. Preferably, said dispersion stabilizer may be selected, for example, from: acids such as, for example, acetic acid, hydrochloric acid, nitric acid, acrylic acid; ketones such as, for example, acetylacetone; glycols such as, for example, polyethyleneglycol; alcohols such as, for example, terpineol, polyvinylalcohol; or mixtures thereof.

The substrate on which slurry is applied may be sintered, and the sintering temperature may be higher than or equal to 100°C, preferably higher than or equal to 200°C. In any case, the upper limit of the sintering temperature may be the melting point or the softening point of the substrate, commonly 900°C, preferably 600°C. The sintering time may not be specifically limited, but preferably within 4 hours.

The thickness of the semiconductor electrode layer (70) on the transparent conductive substrate (30) may range from 1 μπι to 200 μπι, preferably may range from 1 μπι to 50 μπι, more preferably may range from 2 μπι to 20 μπι. The semiconductor electrode layer (70) may be subjected to a secondary treatment. For example, the semiconductor electrode layer (70) may be immersed in a solution of alkoxide, chloride, nitride, or sulfide, of the metal oxide identical to the metal oxide used to make the semicoductor electrode layer (70), and dried or re-sintered, thereby improving the property of the semiconductor electrode layer (70) obtained.

The metal alkoxide may be selected, for example, from: titanium ethoxide, titanium isopropoxide, titanium t-butoxide, di-«-butyl-diacetyl tin, or mixtures thereof.

Preferably, an alcohol solution of said metal alkoxide may be used. The metal chloride may be selected, for example, from: titanium tetrachloride, tin tetrachloride, zinc chloride, or mixtures thereof. Preferably, an aqueous solution of said metal chloride may be used.

The method for dispersing quantum dots (QDs) (90) and of absorbing the organic dye (80) on the semiconductor electrode layer (70) in the form of a thin film may not be specifically limited, and for example, as reported above, a transparent conductive substrate (30) having the semiconductor electrode layer (70) formed thereon may be immersed in a solution obtained by dissolving the quantum dots

(QDs) (90) in a solvent capable of dissolving the same, or in a dispersion obtained by dispersing said quantum dots (QDs) (90). The concentration of the solution or of the dispersion, may be appropriately determined. Immersion temperature may range from -60°C to 100°C, preferably from 0°C to 50°C, more preferably is room temperature (25°C), and immersion time may range from about 1 minute to 48 hours, preferably from 1 hour to 26 hours. The solvent used for dissolving the quantum dots (QDs) (90) may be selected, for example, from: methanol, ethanol, acetonitrile, dichloromethane, dimethylsulfoxide, dimethylformamide, acetone, t- butanol, or mixtures thereof. Usually, the concentration of the solution may range from lxlO "6 M to 1 M, preferably from lxlO "5 M to lxlO "1 M. Thus, a semiconductor electrode layer (70) having a plurality of quantum dots (QDs) (90) dispersed therein, may be obtained. Subsequently, the obtained semiconductor electrode layer (70) having a plurality of quantum dots (QDs) (90) dispersed therein, may be immersed in a solution obtained by dissolving the organic dye (80) in a solvent capable of dissolving the same, or in a dispersion obtained by dispersing said organic dye (80). The concentration of the solution or of the dispersion, may be appropriately determined. Immersion temperature may range from -60°C to 100°C, preferably from 0°C to 50°C, more preferably is room temperature (25°C), and immersion time may range from about 1 minute to 48 hours, preferably from 1 hour to 26 hours. The solvent used for dissolving the organic dye (80) may be selected, for example, from: methanol, ethanol, acetonitrile, dichloromethane, chloroform, chlorobenzene, dichlorobenzene, dimethylsulfoxide, dimethylformamide, acetone, t- butanol, tetrahydrofuran, diethyl ether, or mixtures thereof. Usually, the concentration of the solution may range from lxlO "6 M to 1 M, preferably from lxlO "5 M to lxl 0 "1 M. Thus, a semiconductor electrode layer (70) having a plurality of quantum dots (QDs) (90) dispersed therein and an organic dye (80) absorbed therein, may be obtained.

In order to prevent aggregation of the organic dye on the semiconductor electrode layer (70), optionally, the organic dye (80), may be mixed with an inclusion compound: the obtained mixture may be adsorbed on a semiconductor thin layer. The inclusion compound may be selected, for example, from: cholic acids such as deoxycholic acid, dehydrodeoxycholic acid, kenodeoxycholic acid, cholic acid methyl ester; cholic acid sodium salts; polyethyleneoxides; crown ethers; cyclodextrins; calyxarenes; or mixtures thereof.

Optionally, after a semiconductor electrode layer (70) having a plurality of quantum dots (QDs) (90) dispersed and an organic dye (80) absorbed therein is obtained, its surface may be treated with a compound which can be selected from: amine compounds such as, for example, 4-t-butyl pyridine; alcohols such as, for example, methanol, ethanol, butanol, or mixtures thereof; organic acids such as, for example, acetic acid, propionic acid, or mixtures thereof; or mixtures thereof. For example, a semiconductor electrode layer (70) having a plurality of quantum dots (QDs) (90) dispersed and an organic dye (80) absorbed therein may be immersed in an ethanol solution of 4-t-butyl pyridine.

The present invention will be further illustrated below by means of the following examples which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLES

Reagents and materials

The reagents and materials used in the following examples, as well as their manufacturers, have been reported below: 4,7-dibromobenzo[l,2,5]thiadiazole (Aldrich): used as received;

toluene (Carlo Erba): used as received;

potassium carbonate (K 2 C0 3 ) (Aldrich): used as received;

N,N-diphenyl-4-aminophenylboronic acid (Aldrich): used as received;

1- propanol (Aldrich): used as received;

tetrakis(triphenylphosphine)palladium(0) [Pd(PPh 3 ) 4 ] (Aldrich): used received;

dichloromethane (CH 2 C1 2 ) (Aldrich): used as received;

heptane (Aldrich): used as received;

anhydrous magnesium sulfate (MgS0 4 ) (Aldrich): used as received;

palladium (Il)acetate (PdOAc) (Aldrich): used as received;

tricyclohexylphosphine tetrafluoroborate (PCy3*HBF ) (Aldrich): used received;

pivalic acid (Aldrich): used as received;

2- thiophenecarboxaldehyde (Aldrich): used as received;

cyanoacetic acid (CNCH 2 COOH) (Aldrich): used as received;

piperidine (Aldrich): used as received;

acetonitrile (Carlo Erba): used as received;

hydrochloric acid (HCl) (Carlo Erba): used as received,

diethyl ether (Carlo Erba): used as received;

methanol (MeOH) (Carlo Erba): used as received;

ethyl acetate (EtOAc) (Carlo Erba): used as received;

trioctylphosphine oxide (TOPO) (Aldrich): used as received;

octadecylphosphonic acid (ODPA) (Aldrich): used as received;

cadmium oxide (CdO) (Aldrich): used as received;

trioctylphosphine (TOP) (Aldrich): used as received;

selenium powder (Se powder) (Aldrich): used as received;

butanol (Carlo Erba): used as received;

titanium tetrachloride (TiCl 4 ) (Aldrich): used as received;

l-butyl-3-methylimidazolium iodide (Aldrich): used as received;

iodine (Carlo Erba): used as received; lithium iodide (Aldrich): used as received;

guanidinium-thiocyanate (Aldrich): used as received;

t-butylpyridine (Aldrich): used as received;

valeronitrile (Aldrich): used as received.

In the examples, the following characterization methods have been used.

NMR spectra

The NMR spectra of compounds have been carried out with a spectrometer NMR Bruker Avance 400. To this aim, about 10 mg of the sample have been dissolved in about 0.8 ml of a suitable deuterated solvent directly on the glass pipe used for the measurement. The chemical shifts scale has been calibrated with respect to the tetramethylsilane signal set at 0 ppm.

EXAMPLE 1

Synthesis of 2-cyano-3-{5-[7-(4-diphenylamino-phenynbenzo[1.2.5]thiadiazo l-4- yl]-thiophen-2-yl}acrylic acid having general formula (la)

In a 500 ml three neck flask containing 4,7-dibromobenzo[l,2,5]thiadiazole having formula (2) (6.63 g, 22.5 mmol) in toluene (80 ml), an aqueous solution (80 ml) of potassium carbonate (K 2 C0 3 ) (20.73 g, 150 mmol) was added and the obtained reaction mixture was degassed. Subsequently, a degassed solution of N,N- diphenyl-4-aminophenylboronic acid having formula (1) (4.34 g, 15 mmol) in 1- propanol (50 ml) was added, under nitrogen flux. Finally, tetrakis(triphenylphosphine)palladium(0) [Pd(PPh 3 ) 4 ] (360 g, 0.3 mmol) was added and the obtained mixture was refluxed overnight. Subsequently, water was added to quench the reaction and the obtained product was extracted with dichloromethane (CH 2 C1 2 ) (3 x 25 ml) obtaining an organic phase and an aqueous phase which were separated. The organic phases obtained were collected, joined together, dried over anhydrous magnesium sulfate (MgS0 4 ), at room temperature (25°C), and filtered. The solvent was subsequently evaporated under vacuum and the obtained solid residue was purified by chromatography on silica gel column using heptane/dichloromethane (CH 2 C1 2 ) (70:30) as eluent, obtaining 3.2 g (about 47% yield) of 4-(7-bromo-benzo[l,2,5]thiadiazol-4-yl)-phenyl]diphenylamine having formula (3) as a dark yellow solid, which was characterized by 1H- MR (400 MHz, CD 2 C1 2 ): ppm = 7.89 (d, 1H), 7.81 (d, 2H), 7.55 (d, 1H), 7.31-7.27 (t, 4H), 7.14 (d, 6H), 7.09-7.05 (t, 2H).

4-(7-bromo-benzo[ 1 ,2,5]thiadiazol-4-yl)-phenyl]diphenylamine having formula (3) (0.950 g, 2.07 mmol) obtained as disclosed above, potassium carbonate (K 2 C0 3 ) (0.430 g, 3.1 mmol), palladium(II)acetate (PdOAc) (0.009 g, 0.04 mmol), tricyclohexylphosphine tetrafluorob orate (PCy3*HBF 4 ) (0.044 g, 0.12 mmol) and pivalic acid (0.031, 0.3 mmol), were placed in a screw-capped 50 ml vial equipped with a magnetic stirrer and purged with nitrogen. Subsequently, toluene (20 ml) and 2-thiophenecarboxaldehyde having formula (4) (0.5 ml, 4.15 mmol) were added to the reaction mixture. The reaction mixture was vigorously stirred, at 110°C, for 16 hours. Subsequently, the reaction mixture was cooled at room temperature (25°C), diluted with dichloromethane (CH 2 C1 2 ) and water obtaining an aqueous phase and an organic phase which were separated. The acqueous phase was extracted with dichloromethane (CH 2 C1 2 ) (3 x 30 ml) and dried over anhydrous magnesium sulfate (MgS0 4 ). The solvent was subsequently evaporated under vacuum and the obtained solid residue was purified by chromatography on silica gel column using heptane/ethyl acetate (EtOAc) (90: 10, v/v) as eluent, obtaining 0.523 g (about 42% yield) of 5-[7-(diphenylamino-phenyl)-benzo[l,2,5]thiadiazol-4-yl]-thi ophene-2- carbaldehyde having formula (5) as a dark red powder, which was characterized by 1H- MR (400 MHz, CD 2 C1 2 ): ppm = 9.95 (s, 1H), 8.20 (d, 1H), 8.08 (d, 1H), 7.94 (d, 2H), 7.85 (d, 1H), 7.76 (d, 1H), 7.32-7.28 (t, 4H), 7.16 (d, 6H), 7.10-7.06 (t, 2H). To a 100 ml flask containing 5-[7-(diphenylamino-phenyl)- benzo[l,2,5]thiadiazol-4-yl]-thiophene-2-carbaldehyde having formula (5) obtained as disclosed above (0.471 g, 0.83 mmol), cyanoacetic acid (CNCH 2 COOH) (0.141 g, 1.66 mmol), piperidine (0.4 ml, 3.75 mmol), and acetonitrile (50 ml), were added. The reaction mixture was heated at 70°C and refluxed, under nitrogen atmosphere, overnight. Subsequently, the reaction mixture was cooled at room temperature (25°C) and hydrochloric acid (HQ) 1 M (15 ml) was added obtaining a dark powder which was filtered in order to eliminate the solvent, washed with water, diethyl ether and methanol (MeOH), and finally dried under vacuum obtaining 0.420 g (about 90% yield) of 2-cyano-3-{5-[7-(4-diphenylamino-phenyl)benzo[l,2,5]thiadiaz ol-4- yl]-thiophen-2-yl} -acrylic acid having formula (la) which was characterized by 1H- MR (400 MHz, CD 2 C1 2 ): ppm = 8.63 (s, 1H), 8.44 (d, 1H), 8.38 (d, 1H), 8.19 (d, 1H), 8.08 (d, 2H), 8.03 (d, 1H), 7.45-7.41 (t, 4H), 7.20-7.16 (m, 8H).

EXAMPLE 2

Synthesis of CdSe486 quantum dots (QDs).

Trioctylphosphine oxide (TOPO) (3.0 g), octadecylphosphonic acid (ODPA) (0.280 g) and cadmium oxide (CdO) (0.060 g), are mixed in a 50 ml flask, heated to 150°C and exposed to vacuum for 1 hour. Subsequently, the solution obtained was heated, under nitrogen, at 300°C in order to dissolve the cadmium oxide (CdO), until it turns optically clear and colorless. At this point, 1.5 g of trioctylphosphine (TOP) was injected in the flask, the temperature was increased up to 380°C and, subsequently, 0.5 ml of a solution of selenium powder (Se powder) in trioctylphosphine (TOP), obtained by dissolving 0.058 g selenium powder (Se powder) in 0.360 g of trioctylphosphine (TOP), was injected: the heating mantle was removed immediately after the injection and the mixture was allowed to cooling to room temperature (25°C). The obtained nanocrystals were precipitated with methanol/butanol (90: 10, v/v) mixture, washed by re-dissolution in hexane and re- precipitation with methanol/butanol (90: 10, v/v) mixture for at least four times, and finally dissolved in hexane, obtaining 20 ml (lxlO "6 M) of a solution of green fluorescent quantum dots (QDs) CdSe486. The diameter of the obtained quantum dots (QDs) CdSe486 were determined by measuring the value of the first absorption peak of the solution at 350 nm, as disclosed by Peng X. et al. in "Chemistry of Materials" (2003), Vol. 15, pg. 2854-2860. In this case, a first absorption peak was measured at 486 nm, corresponding to an average diameter of 2.7 nm.

EXAMPLE 3 (invention)

Preparation of qauntum dot dye-sensitized solar cell (QDDSSC) with dye having formula la and CdSe486 quantum dots (QDs)

The titanium dioxide (Ti0 2 ) paste was purchased from Solaronix (T/SP, 20 nm). FTO glass (TEC 15; thickness, 2.2 mm; 15 Ω/square; Pilkington, USA) was first cleaned in a detergent solution using an ultrasonic bath for 15 minutes, then rinsed with water and ethanol. The FTO glass plates were immersed in a 40 mM aqueous titanium tetrachloride (TiCl 4 ) solution at 80°C, for 30 minutes, and washed with water and ethanol. A layer of titanium dioxide (Ti0 2 ) paste was deposited on the FTO glass by "doctor blade" technique and then dried for 5 minutes, at 120°C. This procedure was repeated to achieve an appropriate thickness of 10 μιη. At the end of said operations, the obtained titanium dioxide (Ti0 2 ) film-coated FTO glass was sintered at 500°C, for 30 minutes. After cooling at 80°C, the titanium dioxide (Ti0 2 ) film is 10 μιη thick (measured by means of a VEECO Dektak 150 profilometer) and is ready to be sensitized. The titanium dioxide (Ti0 2 ) film-coated FTO glass was immersed in a lxl 0 "6 M solution of green fluorescent CdSe486 quantum dots (QDs) obtained as disclosed in Example 2 in hexane, at room temperature (25°C), for 24 hours, rinsed with ethanol and dipped again into a 5x10 "4 M solution of the organic dye having formula (la) obtained as disclosed in Example 1 in dichloromethane (CH 2 C1 2 ), at room temperature (25°C), for further 24 hours, obtaining a photoanode.

The counter-electrode was 100-nm-thick platinum sputtered on a FTO glass (Delta Technologies). The electrolyte was a solution of l-butyl-3- methylimidazolium iodide (0.6 M), iodide (I 2 ) (0.03 M), guanidinium thiocyanate (0.10 M) and t-butylpyridine (0.5 M) in a 85: 15 (v/v) mixture of acetonitrile and valeronitrile. The photoanode obtained as disclosed above, having dimensions of about 0.16 cm 2 (4 mm x 4 mm) and the platinum counter-electrodes, were assembled into a sandwich-type cell and sealed with a hot-melt Surlyn spacer with a thickness of 25 mm (Solaronix) and area of 0.36 cm 2 (6 mm x 6 mm). Subsequently, a copper tape was adhered on the external edge of the cell: the position of the copper tape was 1 mm away from the edge of the Surlyn spacer and 4 mm away from the edge of the titanium dioxide (Ti0 2 ) film.

Photovoltaic measurements were performed using an AM 1.5 solar simulator (Photo Emission Tech.). The power of the simulated light was calibrated to 100 mW/cm 2 by using a reference silicon photodiode with a power meter (1835-C, Newport) and a reference silicon solar cell to reduce the mismatch between the simulated light and AM 1.5. I-V curves were obtained by applying an external bias to the cell and measuring the generated photocurrent with a Keithley model 2400 digital source meter. The voltage step and delay time of photocurrent were 10 mV and 40 ms, respectively.

The following results were obtained:

Voc (open circuit photovoltage) = 672 mV;

FF (fill factor) = 77%;

Jsc (short-circuit photocurrent density) = 9.59 mA/cm 2 ;

η (photoelectric transformation efficiency) = 4.94 %.

EXAMPLE 4 (comparative)

Preparation of dye- sensitized solar cell (DSSC)

The example was carried under the same operative conditions reported in Example 3, the only difference being that, in this example, the titanium dioxide (Ti0 2 ) film-coated FTO glass was dipped only in a 5x10 "4 M solution of the organic dye having formula (la) obtained as disclosed in Example 1 in dichloromethane (CH 2 C1 2 ) (green fluorescent CdSe486 quantum dots (QDs) were not used).

The following results were obtained:

Voc (open circuit photovoltage) = 629 mV;

FF (fill factor) = 76%;

Jsc (short-circuit photocurrent density) = 8.37 mA/cm 2 ;

η (photoelectric transformation efficiency) = 4.0%.

It is clear, from the above reported results that the use of green fluorescent CdSe486 quantum dots (QDs) and of the organic dye having formula (la) according to the present invention, allows to obtain an increase of the photoelectric transformation efficiency (η) (4.94%) equal to 23.5% with respect to that one obtained using only the organic dye having formula (la) (4.0%).

EXAMPLE 5 (comparative)

Synthesis of CdSe538 quantum dots (QDs)

The example was carried out under the same operative conditions reported in Example 2, the only difference being that, in this example, after the injection of a solution of selenium powder (Se powder) in trioctylphosphine (TOP) at 380°C, the heating mantle was removed after 3 minutes and the mixture was allowed to cool to room temperature (25°C) following the procedure reported in Example 2 so obtaining 20 ml of solution of orange fluorescent CdSe538 quantum dots (QDs) in hexane having an average diameter, measured as disclosed in Example 2, of 3.7 nm. EXAMPLE 6 (comparative)

Preparation of quantum dot dye-sensitized solar cell (QDDSSC) with dye having formula la and CdSe538 quantum dots (QDs)

The example was carried out under the same operative conditions reported in Example 3, the only difference being that, in this example, a lxlO "6 M solution of orange fluorescent CdSe538 quantum dots (QDs) in hexane, obtained as described in the Example 5, was used.

The following results were obtained:

Voc (open circuit photovoltage) = 639 mV;

FF (fill factor) = 74%;

Jsc (short-circuit photocurrent density) = 8.28 mA/cm 2 ;

η (photoelectric transformation efficiency) = 3.9%.

It is clear, from the above reported results that the use of orange fluorescent CdSe538 quantum dots (QDs) and of the organic dye having formula (la), does not allow to obtain an increase of the photoelectric transformation efficiency (η) (3,9%) with respect to that one obtained using only the organic dye having formula (la) (4,0%). EXAMPLE 7 (comparative)

Preparation of quantum dot dye-sensitized solar cell (QDSSC) with CdSe486 quantum dots (QDs)

The example was carried out under the same operative conditions reported in Example 3, the only difference being that, in this example, the titanium dioxide (Ti0 2 ) film-coated FTO glass was dipped only in a lxlO "6 M solution of CdSe486 quantum dots (QDs) in hexane, obtained as disclosed in Example 2 (organic dye having formula (la) was not used).

The following results were obtained:

Voc (open circuit photovoltage) = 615 mV;

FF (fill factor) = 61%;

Jsc (short-circuit photocurrent density) = 0.34 mA/cm 2 ;

η (photoelectric transformation efficiency) = 0.13%.

It is clear, from the above reported results that the use of green fluorescent CdSe486 quantum dots (QDs) alone allows to obtain a very low photoelectric transformation efficiency (η) (0.13%) with respect to that one obtained using only the organic dye having formula (la) (4,0%).