WO2014128648A1

WO2014128648A1 - Luminescent solar concentrator comprising disubstituted naphthothiadiazole compounds

Info

Publication number: WO2014128648A1
Application number: PCT/IB2014/059135
Authority: WO
Inventors: Andrea Alessi; Samuele Santarelli
Original assignee: Eni SpA
Current assignee: Eni SpA
Priority date: 2013-02-21
Filing date: 2014-02-20
Publication date: 2014-08-28
Anticipated expiration: 2015-08-21
Also published as: ITMI20130247A1

Abstract

A luminescent solar concentrator (LSC) comprising at least one disubstituted naphthothiadiazole compound having general Formula (I) : wherein : - R₁, R₂, R₃, R₄, R₅, R₆ and R₇, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C₁ -C₂₀,preferably C₁ -C₁₀, alkyl groups, optionally containing heteroatoms, cycloalkyl groups optionally substituted, aryl groups optionally substituted, linear or branched C₁ -C₂₀, preferably C₁ -C₁₀, alkoxyl groups, optionally substituted; - or R₁ and R₂, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; - or R₂ and R₃, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; - or R₁ and R₄, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; - or R₅ and R₆, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; - or R₆ and R₇, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium.

Description

LUMINESCENT SOLAR CONCENTRATOR COMPRISING DISUBSTITUTED NAPHTHOTHIADIAZOLE COMPOUNDS

DESCRIPTION

The present invention relates to a luminescent solar concentrator (LSC) comprising at least one disubstituted naphthothiadiazole compound.

The present invention also relates to the use of at least one disubstituted naphthothiadiazole compound in the construction of luminescent solar concentrators (LSCs) .

The present invention also relates to a photovoltaic device (or solar device) selected, for example, from photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), on both rigid and flexible supports, comprising a luminescent solar concentrator (LSC) including at least one disubstituted naphthothiadiazole compound.

It is known that single-junction photovoltaic cells (or solar cells) are not capable of efficiently exploiting all solar radiation. Their efficiency, in fact, is maximum only within a certain spectrum range which comprises a part of visible radiation and a part of infrared radiation.

Spectrum converter materials which can capture solar radiation outside the optimal spectral range and convert it to effective radiation, can be used for enhancing the performance of photovoltaic cells (or solar cells) . Furthermore, luminescent solar concentrators (LSCs) can be produced with these materials, which allow a further increase in the production of current in photovoltaic cells (or solar cells ) .

Said luminescent solar concentrators (LSCs) generally consist of large sheets of material transparent to solar radiation, in which fluorescent substances are dispersed or chemically bound to said material, which act as spectrum converters. Due to the effect of the optical phenomenon of total reflection, the radiation emitted by the fluorescent molecules is "guided" towards the thin edges of the sheet wherein it is concentrated on photovoltaic cells (or solar cells) positioned therein. In this way, large surfaces of low- cost materials (photoluminescent sheets) can be used for concentrating the light on small surfaces of high- cost materials [photovoltaic cells (or solar cells) ] .

A fluorescent compound should have numerous characteristics for being advantageously used in the construction of luminescent solar concentrators (LSCs) and these are not always compatible with each other.

First of all, the frequency of the radiation emitted by fluorescence must correspond to an energy higher than the threshold value below which the semiconductor, representing the core of the photovoltaic cell, is no longer able to function.

Secondly, the absorption spectrum of the fluorescent compound should be as extensive as possible, so as to absorb most of the inciding solar radiation and then re-emit it at the desired frequency.

It is also desirable that the absorption of the solar radiation be extremely intense, so that the fluorescent compound can exert its function at the lowest possible concentrations, avoiding the use of large quantities. Furthermore, the absorption process of solar radiation and its subsequent re-emission at lower frequencies, must take place with the highest possible efficiency, minimizing the so-called non-radiative losses, often collectively indicated with the term "thermalization" : the efficiency of the process is measured by its quantic yield.

Finally, the absorption and the emission frequencies must be as different as possible, as otherwise the radiation emitted by a molecule of the fluorescent compound would be absorbed, and at least partially diffused, by the adjacent molecules. Said phenomenon, generally called self-absorption, inevitably leads to a significant loss in efficiency. The difference between the frequencies of the peak with the lower frequency of the absorption spectrum and of the peak of the radiation emitted, is normally indicated as Stokes shift and measured in nm (i.e. it is not the difference between the two frequencies that is measured, but the difference between the two wavelengths which correspond to them) . High Stokes shifts are absolutely necessary for obtaining high efficiencies of luminescent solar concentrators (LSCs), bearing in mind the necessity, already mentioned, that the frequency of the radiation emitted corresponds to an energy higher than the threshold value below which the photovoltaic cell (or solar cell) is not able to function .

It is known that some benzothiadiazole compounds, in particular 4 , 7-di- ( thien-2 ' -yl ) -2 , 1 , 3-benzothia- diazole (DTB) , are fluorescent compounds which can be used in the construction of luminescent solar concentrators (LSCs) . Compounds of this type are described in international patent application WO 2011/048458 in the name of the Applicant.

4, 7-di- (thien-2 '-yl) -2,1, 3-benzothiadiazole (DTB) is characterized by an emission centred around 579 nm, which corresponds to an energy well above the minimum threshold value for the functioning of photovoltaic cells (or solar cells), said threshold corresponding, for example, to a wavelength of about 1100 nm for the most widely-used photovoltaic cells (or solar cells), based on silicon. Furthermore, its absorption of light radiation is intense and extends over a relatively wide range of wavelengths, indicatively ranging from 550 nm (green radiation wavelength) to ultraviolet. Finally, 4 , 7-di- ( thien-2 ' -yl ) -2 , 1 , 3-benzothiadiazole (DTB) has a Stokes shift in dichloromethane solution, equal to 134 nm, well above that of most of the commercial products so far proposed for use in luminescent solar concentrators (LSCs).

For these reasons, the use of 4 , 7-di- ( thien-2 ' - yl ) -2 , 1 , 3-benzothiadiazole (DTB) has enabled the production of high-quality luminescent solar concentrators (LSCs).

Although 4, 7-di- (thien-2 '-yl) -2,1, 3-benzothiadi- azole (DTB) absorbs a significant part of the solar spectrum, however, it has a modest absorption in its higher wavelength regions, corresponding to yellow and red radiations which cannot therefore be converted into other radiations more effectively exploited by the photovoltaic cell (or solar cell) . For this reason, it is desirable to avail of fluorescent compounds having a wider absorption spectrum towards red. The Applicant has therefore considered the problem of finding compounds having a wider absorption spectrum towards red, capable of minimizing the self-absorption phenomenon .

The Applicant has now found that disubstituted naphthothiadiazole compounds having a specific general formula (i.e. having general formula (I) indicated hereunder) can be advantageously used in the construction of luminescent solar concentrators (LSCs) . Said luminescent solar concentrators (LSCs) can be advantageously used in the construction of photovoltaic devices (or solar devices) such as, for example, photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), on both rigid and flexible supports. Said disubstituted naphthothiadiazole compounds, in fact, have an absorption spectrum which extends much more towards red with respect to known benzothiadiazole compounds. Furthermore, said disubstituted naphthothiadiazole compounds have higher Stokes shifts than those of the known benzothiadiazole compounds .

An object of the present invention therefore relates to a luminescent solar concentrator (LSC) comprising at least one disubstituted naphthothiadiazole compound having general formula (I) :

Ri, R2, R3, R4, R5, R6 and R₇, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched Ci-C20_f preferably C1-C10, alkyl groups, optionally containing heteroatoms, cycloalkyl groups optionally substituted, aryl groups optionally substituted, linear or branched Ci-C20_f preferably C1-C10, alkoxyl groups, optionally substituted;

or Ri and R2, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or R₂ and R3, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or Ri and R₄, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

- or R₅ and ]¾, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

- or R6 and R_7f can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, preferably from 4 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium.

According to a preferred embodiment of the present invention, in said general formula (I) the substituents Ri, R₂, R3, R4, R5, R6 and R₇, represent a hydrogen atom.

A particularly preferred aspect of the present invention therefore relates to a luminescent solar concentrator (LSC) comprising 4 , 9-bis- ( thien-2 ' -yl ) - naphtho [ 2 , 3-c] [ 1 , 2 , 5 ] -thiadiazole (DTN) having formula (la)

As mentioned above, the naphthothiadiazole compound having general formula (I), has an absorption which, with respect to that of 4 , 7-di- ( thien-2 ' -yl ) -2 , 1 , 3- benzothiadiazole (DTB) , extends much more towards red: said absorption is intense and extensive over a relatively wide wavelengths range which, for example, for 4 , 9-bis- ( thien-2 ' -yl ) -naphtho [ 2 , 3-c ] [ 1 , 2 , 5 ] -thia- diazole (DTN) having formula (la) ranges, from 200 nm to 600 nm. Furthermore, said compound having general formula (I) has a particularly high Stokes shift. 4,9- bis- (thien-2 '-yl) -naphtho [2, 3-c] [1,2,5] -thiadiazole (DTN) having formula (la), for example, has a Stokes shift, in dichloromethane solution, equal to 202 nm : therefore a Stokes shift higher than that, already high, of 4 , 7-di- ( thien-2 ' -yl ) -2 , 1 , 3-benzothiadiazole (DTB) equal to 134 nm (measured under the same conditions ) .

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

For the aim of the present description and of the following claims, the term "comprising" also includes the terms "which essentially consists of" or "which consists of".

The term "C1-C2₀ alkyl groups" refers to linear or branched alkyl groups having from 1 to 20 carbon atoms. Specific examples of C1 -C2₀ alkyl groups are: methyl, ethyl, Ώ-propyl, iso-propyl, n-butyl, iso-butyl, t- butyl, pentyl, ethyl-hexyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl .

The term " C 1 -C2₀ alkyl groups optionally containing heteroatoms" refers to linear or branched alkyl groups having from 1 to 20 carbon atoms, saturated or unsaturated, wherein at least one of the hydrogen atoms is substituted with a heteroatom selected from: halogens such as, for example, fluorine, chlorine, preferably fluorine; nitrogen; sulfur; oxygen. Specific examples of C1 -C2₀ alkyl groups optionally containing heteroatoms are: fluoromethyl, difluoromethyl, trifluoromethyl , trichloromethyl , 2 , 2 , 2-trifluoroethyl , 2,2, 2-trichloroethyl, 2,2,3, 3-tetrafluoropropyl,

2,2,3,3, 3-pentafluoropropyl, perfluoropentyl, perfluoroctyl , perfluorodecyl, oxymethyl, thiomethyl, thioethyl, dimethylamine , propylamine, dioctylamine .

The term "cycloalkyl groups" refers to cycloalkyl groups having from 3 to 10 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, preferably fluorine; hydroxyl groups; C 1 -C2₀ alkyl groups; C 1 -C2₀ alkoxyl groups; cyano groups; amino groups; nitro groups; aryl groups. Specific examples of cycloalkyl groups are: cyclopropyl, 1,4-dioxine, 2, 2-difluorocyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl , methoxycyclohexyl , fluorocyclohexyl, phenylcyclohexyl .

The term "aryl groups" means aromatic carbocyclic groups. Said aryl groups can be optionally substituted by one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, preferably fluorine; hydroxyl groups; C 1 -C2₀ alkyl groups; C 1 -C2₀ alkoxyl groups, cyano groups; amino groups; nitro groups; aryl groups. Specific examples of aryl groups are: phenyl, methylphenyl , trimethylphenyl , methoxyphenyl , hydroxyphenyl , phenyloxyphenyl , fluorophenyl, pentafluorophenyl , chlorophenyl , nitrophenyl, dimethylaminophenyl , naphthyl, phenylnaphthyl , phenanthrene , anthracene.

The term " C 1 -C20 alkoxyl groups" refers to linear or branched alkoxyl groups having from 1 to 20 carbon atoms. Said alkoxyl 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, preferably fluorine; hydroxyl groups; C1 -C20 alkyl groups; C 1 -C20 alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of C1 -C20 alkoxyl groups are: methoxyl, ethoxyl, fluoroethoxyl, n-propoxyl, iso- propoxyl, n-butoxyl, n-fluoro-butoxyl , iso-butoxyl, t- butoxyl, pentoxyl, hexyloxyl, heptyloxyl, octyloxyl, nonyloxyl, decyloxyl, dodecyloxyl.

The term "cyclo or polycyclic system" relates to a system containing one or more rings containing from 3 to 14 carbon atoms, optionally containing heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorous. Specific examples of the cyclo or polycyclic system are: thieno [3, 2-b] thiophene, thiadiazole, benzothiophene, quinoxaline, pyridine. Said compound having general formula (I) can be obtained according to processes known in the art.

Said compound having general formula (I) can be obtained, for example, by means of a Stille reaction as indicated in the followin scheme:

wherein R_lf R₂, R3, R4, R5, R6 and R₇, have the same meanings indicated above, Rs is a linear or branched C₁-C₁₀ alkyl group, preferably n-butyl, X is a halogen atom such as, for example, chlorine, bromine, preferably bromine, Pd(PPh3)2Cl2 is bis-

( triphenylphosphine ) palladium (II) dichloride, DMSO is non-anhydrous dimethylsulfoxide .

The naphthothiadiazole compounds having general formula (II) can be obtained according to processes known in the art, for example, by halogenation of the corresponding naphthothiadiazole compounds. Further details relating to said processes can be found, for example, in "Journal of Heterocyclic Chemistry" (1968), Vol. 5, pages 295-297.

The tri-alkyl-stannane compounds having general formula (III) can be obtained according to processes known in the art, for example, by reaction with n-butyl lithium or lithium di-iso-propylamide (LDA) with a tri- alkyltin chloride. Further details relating to said processes can be found, for example, in: "Macromolecules" (2006), Vol. 39, pages 2831-2834. In particular, 2- [ tri ( n-butyl ) stannyl ] thiophene corresponding to a compound having general formula (III), wherein R₅ , ]¾ and R_{7 f} are hydrogen atoms, and Rs is n-butyl, can be prepared as described, for example, in "Journal of the Chemical Society, Perkin Transaction" (1988), pages 2415-2421.

2- [ tri ( n-butyl ) stannyl ] thiophene can also be easily found on the market.

A further object of the present invention also relates to the use of at least one disubstituted naphthothiadiazole compound having general formula (I) in the construction of luminescent solar concentrators (LSCs) .

The naphthothiadiazole compound having general formula (I) can be used in said luminescent solar concentrator (LSC) in the following forms: dispersed in the polymer or in the glass, chemically bound to the polymer or glass, in solution, in gel form.

The luminescent solar concentrator (LSC) can contain, for example, a transparent matrix, wherein the term "transparent matrix" refers to any transparent material used in the form of a carrier, ligand, or a material in which at least one disubstituted naphthothiadiazole compound having general formula (I) is dispersed or englobed. The material used for the matrix is transparent, as such, to the radiations of interest and, in particular, to radiations having a frequency within the effective spectrum of the photovoltaic device (or solar device) such as, for example, the photovoltaic cell (or solar cell) in which it is used. Materials suitable for the aim of the present invention can therefore be selected from materials transparent at least to radiations having a wavelength ranging from 250 nm to 1100 nm.

The transparent matrix that can be used for the aim of the present invention can be selected, for example, from polymeric or vitreous materials. Said matrix is characterized by a high transparency and by a high duration with respect to heat and light. Polymeric materials which can be advantageously used for the aim of the present invention are, for example, polymethylmethacrylate (PMMA) , epoxy resins, silicon resins, polyalkylene terephthalates , polycarbonates, polystyrene, polypropylene. Vitreous materials which can be advantageously used for the aim of the present invention are, for example, silicas.

If the matrix is of the polymeric type, said at least one disubstituted naphthothiadiazole compound having general formula (I) can be dispersed in the polymer of said matrix by means, for example, of melt dispersion, and subsequent formation of a sheet comprising said polymer and said at least one disubstituted naphthothiadiazole compound having general formula (I), operating, for example, according to the technique known as casting. Alternatively, said at least one disubstituted naphthothiadiazole compound having general formula (I) and the polymer of said matrix can be solubilized in at least one solvent obtaining a solution which is deposited on a sheet of said polymer, forming a film comprising said at least one disubstituted naphthothiadiazole compound having general formula (I) and said polymer, operating, for example, with the use of a Doctor Blade-type film applicator: said solvent is subsequently left to evaporate .

If the matrix is of the vitreous type, said at least one disubstituted naphthothiadiazole compound having general formula (I) can be solubilized in at least one solvent obtaining a solution which is deposited on a sheet of said matrix of the vitreous type, forming a film comprising said at least one disubstituted naphthothiadiazole compound having general formula (I), operating, for example, with the use of a Doctor Blade-type film applicator: said solvent is subsequently left to evaporate.

A further object of the present invention also relates to a photovoltaic device (or solar device) selected, for example, from photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), on both rigid and flexible supports, comprising a luminescent solar concentrator (LSC) including at least one disubstituted naphthothiadiazole compound having general formula (I) .

Said photovoltaic device (or solar device) can be obtained, for example, by assembling the above luminescent solar concentrator with a photovoltaic cell (or solar cell ) .

According to a preferred embodiment of the present invention, the above solar concentrator can be produced in the form of a transparent sheet obtained through the solubilization of said at least one disubstituted naphthothiadiazole compound having general formula (I) and of the polymer of the matrix of the polymeric type, in at least one solvent, obtaining a solution which is deposited on a sheet of said polymer forming a film comprising said at least one disubstituted naphthothiadiazole compound having general formula (I) and said polymer, operating, for example, with the use of a Doctor Blade-type film applicator: said solvent is subsequently left to evaporate. In said photovoltaic devices (or solar devices), said sheets can then be coupled with a photovoltaic cell (or solar cell) .

Some illustrative and non-limiting examples are provided hereunder for a better understanding of the present invention and for its embodiment.

4, 7-di- (thien-2 '-yl) -2,1, 3-benzothiadiazole (DTB) was obtained as described in patent application MI2010A001316 in the name of the Applicant, whose content is incorporated herein as reference.

EXAMPLE 1

Synthesis of 4 , 9-bis (thien-2 '-yl) -naphtho [2,3- c] [ 1 , 2 , 5 ] thiadiazole (DTN) (having formula (la)

4 , 9-bis (thien-2 '-yl) -naphtho [2,3-c] [1,2,5] thiadiazole (DTN) was obtained operating according to the following scheme:

(^IIa> '

1.0 g (2.9 mmoles) of 4,9-dibromo-

[2,1,3] [ 1 , 2 , 5 ] naphthothiadiazole having formula (Ha) (Santai Labs), 50.5 mg (0.072 mmol, 2,5%_moi/moi ) of bis ( triphenylphosphine ) palladium (II) dichloride [Pd (PPh₃) ₂C1₂] (Aldrich) , 2 ml (7.4 mmoles, 2.55 eq) of 2- [ tri ( Ώ-butyl ) stannyl ] thiophene having formula (Ilia) (Aldrich) and 45 ml of non-anhydrous dimethylsulfoxide (DMSO) (Acros Organics), were charged into a 100 ml 3- necked flask, equipped with magnetic stirring, thermometer and cooler: the reaction mixture obtained was heated to 70°C, for 5 hours, in the presence of a light stream of nitrogen (N₂) .

The advance degree of the reaction was controlled by means of gas-chromatographic analysis which, at the end of the same, indicated the formation of 4,9- bis (thien-2 '-yl) -naphtho [2, 3-c] [ 1 , 2 , 5 ] thiadiazole (DTN) (yield 100%) .

At the end of the reaction, the mixture obtained was immersed in a mixture of dichloromethane (CH₂CI₂) (Aldrich) /saturated solution of sodium chloride (NaClg_at.) (Aldrich) in a ratio of 1:10 (v/v) obtaining, after stirring, two phases: one prevalently organic and the other prevalently aqueous. The organic phase obtained was extracted three times with a saturated solution of sodium chloride (NaCl_sat.) (Aldrich) to remove the dimethylsulfoxide (DMSO) : the aqueous phases obtained were joined and extracted twice with dichloromethane (CH₂CI₂) (Aldrich) . The organic phases obtained in the various steps indicated above were joined, dried on calcium chloride (CaCl₂) (Aldrich) for 3 hours and subsequently subjected to filtration by means of a vacuum pump. The solvent was then removed in a rotating evaporator whereas the optional residual traces of dimethylsulfoxide (DMSO) were removed, maintaining the residue obtained after evaporation under a stream of nitrogen (N₂) .

The residue obtained was subsequently dissolved in the minimum volume of dichloromethane (CH₂CI₂) (Aldrich) and the resulting solution was deposited on a silica panel (S1O₂) (Carlo Erba) and filtered using a mixture of ethyl acetate (Aldrich) /n-heptane (Aldrich) in a ratio of 1:10 (v/v) . The filtrate obtained was brought to dryness obtaining a solid residue which was dissolved in the minimum volume of dichloromethane (CH₂CI₂) (Aldrich) and subsequently crystallized by means of a stream of nitrogen (N₂) saturated with n- pentane (Carlo Erba) . The crystals obtained were filtered at reduced pressure obtaining 1.02 g of red crystals of 4 , 9-bis ( thien-2 ' -yl ) -naphtho [ 2 , 3- c] [1, 2, 5] thiadiazole (DTN) (yield 100%).

EXAMPLE 2

6 g of polymethylmethacrylate Altuglas VSUVT 100 (PMMA) and 84.1 mg of 4 , 9-bis ( thien-2 ' -yl ) -naphtho [ 2 , 3- c] [ 1 , 2 , 5 ] thiadiazole (DTN) obtained as described in Example 1, were dissolved in 30 ml of 1,2- dichlorobenzene (Aldrich) . The solution obtained was then uniformly deposited on a sheet of polymethylmethacrylate Altuglas VSUVT 100 (PMMA) (dimensions 300 mm x 90 mm x 6 mm) ) using a Doctor Blade-type film applicator and the solvent was left to evaporate at room temperature (25°C), in a light stream of air, for 24 hours. A red-coloured transparent sheet was obtained (sheet 1), the colour being conferred by the film, whose thickness proved to range from 50 μπι to 100 μπι.

A photovoltaic cell IXYS-KXOB22-12 , having a surface of 1.2 cm was then applied to one of the edges of the polymeric sheet.

The main side of the polymeric sheet [that covered by the thin film containing 4 , 9-bis ( thien-2 ' -yl ) - naphtho [ 2 , 3-c] [ 1 , 2 , 5 ] thiadiazole (DTN)] was then illuminated with a light source having a power of 1 sun (1000 W/m²) and the electric power generated by the effect of the illumination was measured.

The power measurements (P) were carried out by illuminating a portion of sheet having dimensions of 100 mm x 90 mm, at an increasing distance (d) from the edge on which the photovoltaic cell was fixed. These measurements, at a variable distance from the photovoltaic cell, allow the contribution of optional waveguide, edge and self-absorption effects, to be quantified .

Figure 1 shows the curve relating to the value of the power (P) generated, expressed in mW (indicated in ordinate), in relation to the distance (d) from the edge on which the photovoltaic cell was fixed, expressed in cm (indicated in abscissa) .

It can be seen that, in the absence of edge effects, the average power generated is equal to 8.86 mW (Figure 1 ) .

EXAMPLE 3 (comparative)

6 g of polymethylmethacrylate Altuglas VSUVT 100 (PMMA) and 49.5 mg of 4 , 7-di- ( thien-2 ' -yl ) -2 , 1 , 3- benzothiadiazole (DTB) , were dissolved in 30 ml of 1,2- dichlorobenzene (Aldrich) . The solution obtained was then uniformly deposited on a sheet of polymethylmethacrylate Altuglas VSUVT 100 (PMMA) (dimensions 300 mm x 90 mm x 6 mm) ) using a Doctor Blade-type film applicator and the solvent was left to evaporate at room temperature (25°C), in a light stream of air, for 24 hours. A yellow-coloured transparent sheet was obtained (sheet 2), the colour being conferred by the film, whose thickness proved to range from 50 μπι to 100 μπι.

It can be seen that, in the absence of edge effects, the average power generated is equal to 5.01 mW (Figure 1), consequently lower than that generated using 4 , 9-bis ( thien-2 ' -yl ) -naphtho [ 2 , 3-c ] [1,2,5]- thiadiazole (DTN) (Example 2) according to the present invention .

Claims

A luminescent solar concentrator (LSC) comprising at least one disubstituted naphthothiadiazole compound having general formula (I) :

Ri, R-2, R3, 4, R5, R6 and R₇, the same or different, represent a hydrogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups, optionally containing heteroatoms, cycloalkyl groups optionally substituted, aryl groups optionally substituted, linear or branched C1-C20 alkoxyl groups, optionally substituted;

or Ri and R₂, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or R₂ and R₃, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

- or Ri and R₄, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

- or R₅ and R6, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

- or R6 and R_7f can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium.

2. The luminescent solar concentrator (LSC) according to claim 1, wherein in said general formula (I), the substituents Ri, R₂, R3, R₄, R5, R6 and R₇, represent a hydrogen atom.

The luminescent solar concentrator (LSC) according to claim 1 or 2, wherein said disubstituted naphthothiadiazole compound having general formula (I) is 4, 9-bis- (thien-2 '-yl) -naphtho [2, 3-c] [1, 2, 5] - thiadiazole (DTN) having formula (la) :

Use of at least one disubstituted naphthothiadiazole compound having general formula (I) :

wherein :

- Ri, R-2, R-3, R-4, R-5, R-6 and R₇, the same or different, represent a hydrogen atom; or they are selected from linear or branched C1-C2₀ alkyl groups, optionally containing heteroatoms, cycloalkyl groups optionally substituted, aryl groups optionally substituted, linear or branched C1-C2₀ alkoxyl groups, optionally substituted; or Ri and R₂, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or R₂ and R3, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or Ri and R₄, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium;

or R₅ and R6, can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; - or R6 and R_7f can be optionally bound to each other so as to form, together with the carbon atoms to which they are bound, a cycle or a polycyclic system containing from 3 to 14 carbon atoms, saturated, unsaturated, or aromatic, optionally containing one or more heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium,

in the construction of luminescent solar concentrators (LSCs).

Use according to claim 4, wherein in said general formula (I), the substituents Ri, R2, R3, R4, R5, R6 and R7, represent a hydrogen atom.

Use according to claim 4 or 5, wherein said disubstituted naphthothiadiazole compound having general formula (I) is 4 , 9-bis- ( thien-2 ' -yl ) - naphtho [ 2 , 3-c] [ 1 , 2 , 5 ] -thiadiazole (DTN) having formula ( la) :

A photovoltaic device (or solar device) selected from photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), on both a rigid and a flexible support, comprising a luminescent solar concentrator (LSC) including at least one disubstituted naphthothiadiazole compound having general formula (I), according to any of the claims from 1 to 3.