EP3049504A1 - Luminescent composite comprising a polymer and a luminophore and use of this composite in a photovoltaic cell - Google Patents

Abstract

The composite of the invention comprises (a) a polymer selected from ethylene-vinyl acetate, polyethylene terephthalate, ethylene tetrafluoroethylene, ethylene trifluorochloroethylene, fluorinated ethylene propylene, polyvinyl butyral, polyurethane and silicones; (b) an inorganic luminophore based on at least one element chosen from the rare earths, zinc and manganese, which has an external quantum yield greater than or equal to 40% for at least one excitation wavelength between 350 nm and 440 nm; an absorption less than or equal to 10% for a wavelength greater than 440 nm; an average particle size less than 1 μm; this luminophore also having an emission peak in the wavelength region between 440 nm and 900 nm.

Description

LUMINESCENT COMPOSITE COMPRISING A POLYMER AND A LUMINOPHORE AND THE USE OF THIS COMPOSITE IN A PHOTOVOLTAIC CELL The present application claims the priority of the earlier French application FR 13 02230 ^' filed on September 25, 2013, the contents of which are incorporated by reference in this document. request. In case of inconsistency between the present application and the previous French application affecting the clarity of a term, reference is made exclusively to the present application,

The present invention relates to a luminescent composite film comprising a polymer and at least one inorganic phosphor and the use of this composite film in a photovoltaic cell.

The technical problem

 Currently your photovoltaic technologies are mainly based on silicon technologies. Although the growth of the photovoltaic market is very high, one of the main obstacles to the development of photovoltaic energy however is the limited conversion efficiency of cells (from 15% to 17% for crystalline silicon commercial modules), This is explained by the fact that only part of the solar spectrum can be absorbed by silicon and converted into electricity. Indeed, more than 50% of the solar spectrum is in a range too much or not enough energy to be sufficiently absorbed.

It has been proposed to ^incorporate into the cells of the phosphor which can absorb photons in the wavelength range of 320 nm to 450 nm, which is too energy range to be effectively absorbed by a photovoltaic cell, and which can emit in the range of 450 nm to 900 nm, such that these new visible or near infrared photons are absorbed by the semiconductor, thus increasing the number of photons available for conversion into electricity. However, the incorporation of these luminophores in the constituent elements of the cells, for example ymers arranged on glass layers protecting the silicon elements, can reduce the transmission of the light toward these silicon elements and actually compromise the desired performance enhancement.

The object of the invention is to provide a luminescent composite film for truly improving the conversion efficiency of the cells.

The composite according to the invention thus makes it possible to increase the absolute efficiency of conversion of the light energy into electrical energy (r) of a photovoltaic cell. The composite also serves to protect the cell against UV radiation.

Another characteristic of the composite in the form of a film is that the film must have sufficient mechanical strength to be rolled up and / or delivered to customers.

The invention

 For this purpose, the luminescent composite, characterized in that it comprises:

- a polymer selected from ethylene vinyl acetate (EVA), polyethylene terephthalate, the trétrafluoroéthylène ethylene, ^the ethylene trifluorochloroethylene, perfluorinated ethylene propylene, polyvinyl butyral and polyurethane;

 at least one inorganic phosphor based on at least one element which is chosen from rare earths, zinc and manganese and which has the following characteristics:

 An external quantum yield greater than or equal to 40% for at least one excitation wavelength between 350 nm and

440 nm;

^■ an absorption less than or equal to 10% for a wavelength greater than 440 nm;

^■ a mean particle size d50 of less than 1 pm;

 An average particle size d50 of at least 30 nm;

^■ a maximum ^emission in a range of wavelengths between 440 nm and 900 nm.

Other features, details and advantages of the invention will appear even more fully on reading the description which follows, as well as various concrete but non-limiting examples intended to illustrate it. Eiflyiâ

 Fig. 1 represents the measured volume particle size distribution for the aionate powder of Example 4.

 US 2013/0075892 describes light emitting layers based on quantum dots-type particles or quantum dots or nanocrystals dispersed in a polymer that can be EVA, PET, PE, PP, PC, PS, PVDF, etc. Quantum boxes are particles whose size is critical for light to be emitted. The particle size ranges from 2 to 10 nm in general (in [0006] from US 2013/0075692: 2-50 nm). The phosphor particles of the invention have a size that is greater than 20 nm, or even greater than 30 nm, or greater than 50 nm. The composite film according to the invention does not include particles of the quantum dot or quantum dots type.

WO 2009/115435 discloses submicron particles of barium aluminate and magnesium which can be used in luminescent devices or as markers in semitransparent inks. The particles can be incorporated into a polymer matrix such as PC, PM A or silicone. This application does not therefore describe the same polymers as those of the present application. The mass fraction of particles may be between 20 and 99%, ^that is to say a proportion greater than that contemplated in the present invention. The thickness of the layer comprising the particles dispersed in the polymer is between 30 nm and 10 μm. There is also no mention of the photovoltaic application.

FR 2792460 discloses a photovoltaic generator comprising a photovoltaic cell and a transparent matrix which may be PMMA.

WO 2012/032880 describes a composition useful for the manufacture of a photovoltaic module made of a transparent resin and a phosphor of formula (Bai. _{X. A} M _{'x) (y} Mgi. _B M') (A " _z ^Μ ΙΜ ζ) _{Ι 0} Oi _{7:... b} Eu _a Mn The resulting resin preferably polyaddition This is preferably an acrylic resin particles may have a size varying from 0 00Q1 (0 1 nm) at 100 μ ·>>>> · τ>-> 1 μm The reduced sizes of the particles are obtained using coarse grinding techniques (mill ball mill, jet mill. ) But these techniques do not allow to ^obtain aluminates having a d50 as in claim 1,

FR 2993409 discloses a transparent matrix containing a plurality of optically active components absorbing light energy in a first absorption wavelength and re-emitting energy in a second wavelength greater than the first wavelength. The transparent matrix may be PMMA, PVC, silicone, EVA, PVDF.

Definitions

 Rare earth means the elements of the group consisting of tetrium and the elements of the Periodic Table with an atomic number included between 57 and 71.

The external quantum efficiency (QE) under an excitation wavelength _{λ exc} is evaluated by the ratio, expressed in percentage, between the integration of the photon emission of the phosphor of the composite of the invention, in the range emission 400 nm - 900 nm, and the number of emitted photons pa a reference phosphor, in the same range of emission ^wavelength, when excited at the wavelength k _mc, measurement can be carried out after acquisition of the emission spectrum of the dried suspension on a Jobin-Yvon type spectrofluorometer. The reference phosphor (QE = 100%) is a luminophore of the aluminate type of barium and magnesium. This is the product for which the precursor is obtained according to the method described in ^Example 1 of WO 2004/106263. The raw materials used are boehmite sol (specific surface of 265 m ² / g) at 0.157mol Al per 100g of gel, a 99.5% barium nitrate, a 99% magnesium nitrate and a nitrate solution of europium at 2.102 mol / l in Eu (d = 1, 5621 g / ml). 200 ml of boehmite sol (ie 0.3 mol of Al) are produced. In addition, the salt solution (150 ml) contains 7.0585 g of Ba (NO ₃ ) ₂ , 7.9260 g of Mg (NO ₃ ). ₂ and 2.2294 g of the solution of Eu (NO ₃ ) ₃ The final volume is completed at 405 ml (ie 2% in Al) with water (complete dissolution of the salts). The final pH after mixing the soil and the salt solution is 3.5. The mixture obtained is atomized in an APV ^® type atomizer with a temperature of 145X at the outlet. The dried powder is calcined at 90 ° C. for 2 hours in air. The powder thus obtained is white precursor responds to the chemical composition Bao.sEuo.iMgAIioOu. This precursor product is then mixed with MgF ₂ as a flux in a mass proportion of 1% MgF ₂ (1 part of MgF ₂ for 93 parts of precursor). This mixture is then calcined under Ar-H ₂ (5% vol) at 1550 ° C. for 4 h. The calcined product is washed at 60 ° C. in dilute nitric acid for 2 hours with stirring, then it is filtered and dried in an oven at 100 ° C. for 12 hours. The luminophore thus obtained constitutes the reference phosphor. The particle size characteristics and in particular the particle sizes given in the present application are measured using a laser diffractometer which is a Malvern Mastersizer 2000 device or a Malvern Zeta sizer Nano ZS device. The Mastersizer is used for a d50> 200 nm and Zetasizer Nano ZS for a d50 <200 nm. Distributions are in volume. The average size is the average size (d50) by volume, measured on a suspension diluted in the water of the phosphor, without ultrasound and without dispersion additive. An example of an illustrative granulometric curve is given in FIG. 1 for the aluminate of example 4. The term "dispersion index" refers to the ratio;

σ / m = (d _S4 -d ₁₆ ) / 2d ₅₀

in which :

d ₈₄ is the particle diameter for which 84% of the particles have a diameter of less than ₈₄ ;

- di ₆ is the particle diameter for which 16% of the particles have a diameter less than d ";

d ₅₀ is the average diameter of the particles.

Absorption means the percentage of light absorbed in the wavelength range between 400 nm and 780 nm, measured by diffuse reflection on a Visible UV spectrometer of Perkin Elmer Lambda 900 type.

Detailed description of the invention

As regards the polymer of the luminescent composite, this (also denoted P1) can be chosen from ethylene vinyl acetate (EVA), polyethylene terephthalate (PET), a fluorinated polymer, polyvinyl butyrai and polyurethane. EVA designates a copolymer of ^ethylene and vinyl acetate. The EVA may consist solely of these two monomers or be composed of these two monomers and at least one other comonomer chosen from vinyl esters such as, for example, vinyl propionate or vinyl benzoate, the (meth) ) C1-C6 alkyl acrylates such as, for example, methyl acrylate or butyl acrylate, or (meth) acrylic acids or their salts, such as, for example, methacrylic acid. The EVA may be formed from 55 to 95% weight of ethylene, 5 to 40% by weight ^of vinyl acetate, 0 to 5% by weight of another comonomer. The proportion of vinyl acetate may be between 30 and 35%.

The polymer is capable of being extruded into a film form. The choice of the polymer is important also because it must make it possible to prepare a film that is able to be rolled up and delivered to the user customers. The polymer is also important to obtain a good compromise of mechanical and optical properties necessary for the use of the composite in the intended application.

This polymer may be especially PET or EVA. The polymer of the composite may be crosslinkable or not.

Regarding the phosphor that is dispersed in the composite, it must have a number of characteristics as to its absorption and emission properties. It must therefore have a higher external quantum efficiency than or equal to 40% for at least a length ^of excitation wavelength between 350 nm and 440 nm. This external quantum efficiency may be more particularly greater than 50% for at least one excitation wavelength between 350 nm and 440 nm.

The phosphor absorbs well in ^the UV and little or not in the visible (440-700 nm). Thus, it has an absorption less than or equal to 10% for a wavelength greater than 440 nm, preferably less than 5% and more particularly less than 3%.

It must also be able to present an emission maximum in a domain ^of wavelengths between 440 nm and 900 nm. preferably between 500 nm and 900 nm. The phosphors of the composite of the invention also have a specific particle size distribution. In fact, they consist of particles of which at least 50% have a diameter less than 1pm, this average size d50 may be at most 0.7 μιτι, especially at most 0.5 pm and more particularly ^of at plus 0.3 μm. This average size d50 is at least 30 nm, more particularly at least 50 nm.

The phosphor may have a d50 of between 80 and 400 nm, preferably between 80 and 300 nm.

Moreover, these particles may have a narrow particle size dispersion; more precisely their dispersion index may be at most 1, preferably at most 0.7 and even more preferably at most 0.5. The luminophore of the composite of the invention is chosen from luminophores which contain at least one element chosen from rare earths, zinc and manganese. According to one embodiment, they contain at least one element chosen from rare earths, in particular the rare earths M ¹ described below. aluminate doped with a rare earth and or manganese

The phosphor may be chosen from rare earth doped aluminates and / or manganese. These aluminates can be of the formulas AMgAl ₁₀ Oi ₇ : Eu ⁺ or AMgAI ₁₀ Oi ₇ : Eu ²⁺ , n ²⁺ , where A represents the elements Ba, Sr, Ca alone or in combination. Examples of these aluminates are given below.

BaMgAI ₁₀ O ₁₇ : Eu ²⁺

Ba GHA ₁₀ O ₁₇ : Eu ²⁺ , Mn ²⁺

Other examples of aluminates that may be mentioned are those of formula a (Mi.DEdO) .b (gi MneO) .c (Al ₂ O 3) in which:

M denotes Ba, Sr and Ca or combinations thereof; and a, b, c, d, and e verify relationships:

 0.25 <a <2; 0 <b. <2; 3≤c <9; 0≤ ≤ 0.4 and 0 <e <0.6.

(halo) phosphates .. aSem

The phosphors may also be chosen from europium doped phosphates. These phosphates can be of formula ABF in which A represents the elements U, Na, K alone or in combination and B the elements Ba, Sr, Ca alone or in combination. Examples of this type of products are given below,

LiCaP0 ₄ : Eu ²⁺

UBaP0 ₄ : Eu ²⁺ The europium doped halophosphates may also be suitable in the context of the invention. These products may correspond to the formula A5 (PO ₄ ) 3: Eu ²⁺ in which A represents the elements Ba, Sr, Ca alone or in combination, X being OH, F and Cl. Examples of these are given below. halophosphate. rare earth oxysulfides

The rare earth oxysulfides doped with europium can also be used as luminophores. These products have a formulation of Lna0 ₂ S: Eu ^{3+ type} with Ln representing the elements La, Gd, Y, Lu, alone. An example of such an oxysulfide is given below.

La ₂ O ₂ S: Eu ³⁺ vanadates rare earth doped ^europium

Vanadates of rare earth doped ^europium are also phosphors. They generally have a formula of the type LnV0 ₄ : Eu ³⁺ , Bi ³ with Ln representing the elements La, Gd, Y, Lu, alone or in combination. An example is given below.

YV0 ₄ iEu ³⁺ _f Bi ³⁺ other phosphors

Phosphors of formula LnPVO ₄ may also be mentioned. Ln designating a rare earth.

The compounds of zinc doped with manganese, zinc, ^silver and / or copper may also be suitable as phosphors. Examples of these compounds are given below.

ZnS n ²

 ZnS: Ag, Cu

ZnO.Zn Rare earth borates

Rare earth borates doped with cerium can also be used as phosphors. These borates are generally in a formula of the type LnB0 ₃ : Ce ³⁺ or LnB0 ₃ iCe ³⁺ , Tfa ³⁺ in which Ln represents the elements La, Gd, Y, Lu alone or in combination.

The phosphors mentioned above can advantageously be prepared by a process of the type described below. This method comprises a first step in which a medium is formed comprising a colloidal suspension and / or salts of the constituent elements (other than oxygen) of the phosphor that is to be prepared. A precipitation is then carried out by adding a basic compound to the medium previously formed. The precipitate is then separated from the liquid medium, it is dried and then calcined in air at a temperature generally between 200 ° C and 900 ° C, preferably between 60CTC and 900 ° C. A second calcination is then carried out under air or under a reducing atmosphere, which makes it possible to obtain a luminophore. The phosphor is then wet milled to obtain the particle size necessary for the implementation of the present invention.

According to a particular embodiment, the phosphor used as a component of the composite of the invention in the preparation thereof is derived from the separation of the solid product from the liquid phase from ^a specific suspension. More specifically, it is a liquid phase suspension of particles of a rare earth borate, these particles being substantially monocrystalline and having an average size of between 100 and 400 nm.

For a description of this luminophore, reference may be made to patent application WO 2007/042653. Some of the characteristics of this phosphor are recalled below. The particles of the suspension may more particularly have a mean size of between 100 and 300 nm and a dispersion index of at most 0.7. The constitutive rare earth borate belongs to the group including fyttrium, gadolinium. lanthanum lutetium and scandium L- wate may comprise '.- OI ¹ "dopant, at least one element selected from muth antimoii and rare earths other than that of the constitutive borate, the rare earth dopant being more particularly cerium, terbium, europium, thalium, erbium and praseodymium,

The slurry is obtained by a process in which a rare earth borocarbonate or hydrogenoxy carbonate is calcined at a temperature sufficient to form a borate and to obtain a product having a specific surface area of at least 3 m ² / g; the product resulting from the calcination is then wet-milled. For this process, a rare earth borocarbonate or hydroxyborocarbonate is used which was obtained by reaction of a rare earth carbonate or hydroxycarbonate with boric acid, the starting reaction medium being in the form of an aqueous solution. It is also possible to use a rare earth borocarbonate or hydroxyborocarbonate which has been obtained by a process in which boric acid and a rare earth salt are mixed; the mixture thus obtained is reacted with a carbonate or a bicarbonate; finally, the precipitate thus obtained is recovered. In order to obtain a luminophore powder, a separation of the solid product from the liquid phase is carried out from the suspension as obtained after the wet grinding.

According to another embodiment, the phosphor used as a component of the composite of the ^invention in the preparation thereof is derived from the separation of the solid product from the liquid phase from a specific suspension. More specifically, it is a liquid phase suspension ^of a barium aluminate and magnesium consisting of substantially single-crystal particles of average size between 80 nm and 400 nm.

For a description of this luminophore, reference may be made to patent application WO 2009/115435. Below are some of the features of this product.

A characteristic of the constitutive particles of alumina according to this embodiment of the invention is their monocrystallinity. Indeed, essentially, that is to say for at least about ^90% ss st and preferably for all of them, these particles consist of a single crystal. This monocrystalline aspect of the particles can be demonstrated by the transmission electron microscopy (TEM) analysis technique. For its suspensions, the particles of which are in a size range d50 of at most about 200 nm, the monocrystalline appearance Particle size can also be demonstrated by comparing the average particle size measured by the laser diffraction technique mentioned above with the value of the crystal size or coherent domain measurement obtained from the diffraction analysis of the particles. X-ray (XRD). The Scherrer model, as described in the book Theory and Technique of Radiocrystallography, A.Guinier, Dunod, Paris, 1956, is used for this measurement. It is specified here that the value measured in XRD corresponds to the size of the domain. coherent calculated from the diffraction line corresponding to the crystallographic plane of the main diffraction peak (eg crystallographic plane [102]). Both values: average laser diffraction size and DRX in fact have the same order of magnitude, ^that is to say they are in a ratio (measurement value of ₅₀ measurement value XRD) less than 2, more particularly of at most 1, 5. Example 1 illustrates this. As a consequence of their monocrystalline character, the particles of the aluminate of the invention are in a well separated and individualized form. There are no or few particle agglomerates. This good individualization of the particles can be demonstrated by comparing the so measured by the laser diffraction technique and that measured from an image obtained by transmission electron microscopy ( TEM). It is possible to use a transmission electron microscope giving access to magnifications up to 800 000. The principle of the method consists in examining under microscope different regions (approximately 0) and in measuring the dimensions of 250 particles deposited on a support ( for example after deposition on the support of a suspension of the particles and allowing the solvent to evaporate), considering these particles as spherical particles. A particle is considered identifiable when at least half of its perimeter can be defined. The MET value corresponds to the diameter of the circle correctly reproducing the circumference of the particle. The identification of exploitable particles can be done using ImageJ software, Adobe Photoshop or Analysis. After measuring the particle sizes by the above method, we deduce a granulometric distribution cumi · s particles that are grouped into several size classes ranging from 0 at 500 nm, the width of each class being 10 nm. The number of particles in each class is the basic datum to represent the particle size distribution, The MET value is the median diameter such that 50% of the particles (in number) counted on MET plates have a diameter smaller than this value . Here again, the values obtained by these two techniques present a ratio (measured value "½ measured value MET) in the same order of magnitude and therefore in the proportions given in the preceding paragraph. ^The barium aluminate of this embodiment can have the formula (I) below:

in which :

M ¹ denotes a rare earth which may be more particularly gadolinium, terbium, iyftriutn, ytterbium, europium, neodymium and dysprosium;

M ² denotes zinc, manganese or cobalt;

a, b, c, d and e check relationships:

 0,25≤a≤2; 0 <b≤2; 3≤c <9; 0≤d≤0.4 and 0≤e <0.6.

M ¹ can be even more particularly the europium.

M ² may be more particularly manganese.

More particularly, the aluminate of the invention may have the formula (I) above in which a = 1 and b = c = 5. In another particular embodiment, the aluminate of the ^invention can meet formula (I) above wherein a = b = 1 and c = 7. According to another embodiment, e = 0. According to another embodiment, d = 0.1. According to another embodiment, 0.09 <d <0.11. The aluminate may be that of Example 1.

^The aluminate can be obtained by a multistage process.

Step ^1: forming a liquid mixture comprising water of aluminum compounds and other components used in the composition of the aluminate. The mixture is a solution, a suspension or a gel. The starting compounds may be inorganic salts or hydroxides or carbonates. As salts, mention may preferably be made of nitrates, such as for barium, aluminum, europium and magnesium. One can also use ^aluminum sulfate or chloride _or Itates. For aluminum, it is also possible to use a soil or a colloidal dispersion of aluminum whose particle size can be between 1 and 300 nm. Aluminum may be present in the form of boehmite.

2 step i dry the mixture obtained in the 1 ^st step. The drying can preferably be done by atomization which has the advantage of controlling the size of the particles resulting from drying. Spray drying involves spraying the mixture of the ^1st step by means of a spray nozzle. The person skilled in the art knows how to adapt the parameters of the spray drying (temperature of the mixture before spraying, flow of the mixture, characteristics of the spray nozzle, pressure in the spray chamber in which the mixture is sprayed, etc.). to obtain dry particles. The atomization can be carried out using an apple-watering-type nozzle or other. It is also possible to use so-called turbine atomizers. We can refer to M Asters' book "spray-drying" ^2nd ed., 1976, George Godwin editions). It is possible to use an atomizer of APV type. The atomization-drying operation may also be implemented by means of a "flash" reactor, for example of the type described in French Patent Application Nos. 2,257,326, 2,419,754 or 2,431,321. atomizer can be used to prepare particles whose d50 is low. In this case, the hot gases are driven by a helical movement and flow into a vortex well. The mixture to be dried is injected along a path coincident with ^the axis of symmetry of the helical trajectories desdrts gas. which makes it possible to perfectly transfer the momentum of the gases to the mixture to be treated. The gases thus perform a dual function: on the one hand, the spraying, that is to say the transformation into fine droplets, of the initial mixture, and on the other hand, the drying of the droplets obtained. Moreover, the extremely low residence time (for example less than 1/10 of a second or so) of the particles in the reactor has the advantage, among other things, of limiting any risk of overheating as a result of too long contact with the reactor. the hot agz.

Reference may be made to Figure 1 of French Patent Application No. 2431321 This reactor consists ^of a combustion chamber and a contact chamber composed ^of a double cone or ^a truncated cone with the part superior diverges. The combustion chamber opens into the contact chamber through a reduced passage. The upper part of the combustion chamber is provided with an opening allowing the introduction of the fuel phase. On the other hand, the combustion chamber comprises a coaxial inner cylinder, thus defining inside it a central zone and an annular peripheral zone, with perforations situated for the most part towards the upper part of the apparatus. The chamber comprises at least six perforations distributed over at least one circle, but preferably on several circles spaced axially. The total area of the perforations located in the lower part of the chamber may be very small, of the order of 1/10 to 1/100 of the total surface area of the perforations of said coaxial inner cylinder.

The perforations are usually circular and have a very small thickness. Preferably, the ratio of the diameter thereof to the thickness of the wall is at least 5, the minimum thickness of the wall being limited only by the mechanical requirements.

Finally, an angled pipe opens into the reduced passage, the end of which opens in the axis of the central zone. The gas phase animated by a helical movement (hereinafter called helicoidal phase) is composed of a gas, generally air, introduced into an orifice made in the annular zone, preferably this orifice is situated in the lower part of said zone. In order to obtain a helicoidal phase at the reduced passage, the gaseous phase is preferably introduced at low pressure into the aforementioned orifice, that is to say at a pressure of less than 1 bar and more particularly at a pressure comprised between between 0.2 and 0.5 bar above the pressure in the contact chamber. The speed of this helicoidal phase is generally between 10 and 100 m / s and preferably between 30 and 60 m / s.

Furthermore, a fuel phase, which may in particular be methane, is injected axially through the above-mentioned opening in the central zone at a speed of approximately 100 to 150 m / s.

fuel is ignited by any known means, in the region where the fuel and the helical phase are in contact By (a more _"the imposed passage of gas into the narrow passage is made according to a number of paths coincident with families of generatrices of a hyperboloid. These generators are based on a family of circles of small rings located near and below the reduced passage, before diverging in all your directions.

The mixture to be treated in the form of liquid is then introduced through the aforementioned pipe. The liquid is then fractionated into a multitude of drops, each of which is transported by a volume of gas and subjected to a movement creating a centrifugal effect. Usually, the flow rate of the liquid is between 0.03 and 10 m / s.

The ratio of the intrinsic momentum of the helical phase to that of the liquid mixture must be high. In particular, it is at least 100 and preferably between 1000 and 10000. The amounts of movement at the reduced passage are calculated as a function of the inlet flow rates of the gas and of the mixture to be treated, as well as the section of the passage. An increase in flow leads to a growth in the size of the drops. Under these conditions, the proper movement of the gases is imposed in its direction and its intensity to the drops of the mixture to be treated, separated from each other in the convergence zone of the two currents. The speed of the liquid mixture is further reduced to the minimum necessary to obtain a continuous flow.

The atomization is generally carried out with a solid exit temperature of between 100 ° C. and 300 ° C.

₃ èm ^@ _step . _cons i _S e to calcine the product from the 2 ^nd step. The calcination is at a temperature which is sufficiently high to obtain a crystalline phase. This temperature is at least 1100 ° C., more particularly at least 1200 ° C. It can be at most 1500 ^S C. It can be between 1200 and 1400X. The calcination is carried out under air and / or under a reducing atmosphere, for example under hydrogen mixed in nitrogen or argon. The duration of this calcination is for example between 30 minutes and 10 hours. It is possible to perform calcination in air ^followed by calcination in a reducing atmosphere. In some _{cases, "it} may be useful to carry out a preliminary calcination at the calcination described above, that is to say between ia ^2nd and ^3rd stage. This preliminary calcination is carried out at a temperature slightly lower than that given above, for example below 1000X, in particular between 900 and 1000 ° C.

4 ^ema step i consists in carrying out a wet grinding of the product resulting from the 3 ^rd step. The wet grinding can be carried out in water or in a water / solvent mixture which is miscible with water. The solvent may be an alcohol (eg methanol, ethanol) or a glycol (eg ethylene glycol) or a ketone (eg acetone).

A dispersant whose function is to contribute to the stability of the suspension can be used for grinding. Wet grinding is known to those skilled in the art.

5 ^th step: from The suspension obtained in ^Step 4 ia, aluminate is recovered in powder form by a liquid / solid separation, such as filtration, optionally followed by drying. In order to obtain the luminophore in the form of a powder, the suspension is started as obtained after wet grinding and the solid product is separated from the liquid phase using any known separation technique, for example by filtration. We can refer to Example 1 for more details on the process used. In particular, the process for preparing the aluminate does not include a step of calcining a precursor of the phosphor with a flux such as MgF ₂ as for the reference product described above. Indeed, in the presence of such a step, it is difficult to grind the aluminate so as to obtain the particles of the phosphor according to claim 1.

As regards the composite, this is obtained by mixing the polymer and the phosphor for example by extrusion of such a mixture. It is possible to directly extrude the mixture of the polymer and the phosphor powder or to use a masterbatch.

In addition to the invention, the compound may also include additives customary in the field of solar cell films. The composite may comprise one or more additives selected from antistatic additives, antioxidants, réticulanis ,,,, The crosslinker can be for example one of those disclosed in US 2013/0328149, These additives are introduced during ^the extrusion.

In the case of a masterbatch, the polymer of the composite film which has been described above (P1) is extruded and a masterbatch comprising the phosphor predispersed in a polymer (P2). The polymer of the masterbatch P2 may be of the same type as the polymer (P1) of the composite film or different. The two polymers P1 and P2 are preferably compatible with each other so as to form a homogeneous mixture. Thus, for example, in the case where P1 is an EVA, it is possible to use a masterbatch based on a polymer P2 which is the same grade of EVA or another EVA or else a polymer compatible with P1, for example a polyethylene. The masterbatch is itself prepared by extrusion in an extruder or using a kneader.

In US 2013/0328149, it is taught that the phosphor particles are dispersed in spherical or substantially spherical polymer particles, which themselves are dispersed in the polymer of the composite. These particles are prepared by emulsion or suspension polymerization. The polymeric particles are PMMA-based example as in Example 1 of US 2013/00328149 The proposed dispersion in US 2013/0328149 requires ^to adjust the nature of the polymeric particles to the polymer composite. It also requires an additional step of preparing the polymeric particles. In the context of the present invention, this technique thus described in US 2013/00328149 is preferably not used, so that the composite does not comprise such polymeric particles.

The invention also relates to a process for preparing a composite according to the invention in which one extrudes a polymer P1 and the phosphor or the polymer P1 and a masterbatch comprising the phosphor predispersed in a polymer P2.

^Generally, the amount of phosphor in the polymer can vary between 0, 1% and 5%, especially between 0 0 and 2% and more particularly 0.5% to 1% by mas .--->the; together iuminophore-polymè ', Γ>. When ^a masterbatch is used, the amount of phosphor is related to the phosphor-polymer assembly of the polymer composite film P1 of the masterbatch P2.

This composite may be in the form of a film whose average thickness may be between 25 μm and 800 μm and more particularly from 100 μm to 500 μm. The thickness of the film is adjusted by adjusting the thickness of the lips. The average thickness is measured at 25X on the film using a micrometer from 20 measurements taken at random over the entire surface of the film.

This film can be obtained by extrusion. An extruder such as that described in the examples can be used.

The composition according to the invention is also characterized by the fact that in the form of a film, the latter can have a total transmission (TT) of at least 85%, measured for a film thickness of 250 μm. The film may also have a determined haze of at most 10%, measured for a film thickness of 250 μm. The total transmission and the haze are determined with a Perkin Elmer Lambda 900 UV-Vis device under the conditions recalled later at a wavelength of 550 nm.

Regarding the photovoltaic cell. this comprises a luminescent composite as described above. The invention may relate more specifically to conventional solar cells, crystalline silicon. It can also be applied to second-generation solar cells, called "thin films", which are, for example, cells based on amorphous silicon, cadmium telluride (CdTe) or indium, copper and gallium (CIGS) seienide. and their counterparts. Finally, it can be applied to third generation cells such as organic photovoltaic systems (OPV) and dye solar cells (DSSC).

The composite, generally in the form of a film, may be placed on the front face of the active elements of the cell, for example directly as an encapsulant of these elements or in place of the cell glass or in a layer deposited on top of the cell. . An active element of the cell is an element that converts light energy into electricity. The composite film makes it possible to increase the absolute conversion efficiency of the light energy into electrical energy (r) of the active elements of the cell, once affixed to the photovoltaic cell. It makes it possible to convert the UV into visible radiation absorbed by the active elements, which increases the number of usable solar photons. More specifically, the film of the invention is such that the absolute efficiency of a cell to which is applied the composite film of the invention is greater than the absolute cell efficiency ^when applied is a composite film of the same thickness and consisting of the same polymer and of the same additives but not loaded with luminophore: efficiency r of the cell in the presence of a composite film affixed> efficiency of the cell in the presence of a composite film of the same thickness and consisting of the same polymer and the same additives but not charged with phosphor (r _ref ). The improvement (r - r _ref) / r _ref x 100 may be at least 5%, or even at least 7%.

The invention is therefore also related to the use of a composite film for increasing the conversion efficiency of light energy into electrical energy of a photovoltaic cell. The invention also relates to a process for converting light energy into electrical energy using a photovoltaic cell of increasing ^using the composite according to ^the invention the number of solar photons usable by the elements assets for the conversion of light energy into electricity.

Examples

 Example 1

 i «j¾ Mop hore

In this example, a phosphor is used as described in Example 1 of the application WO 2009/1 1 435 and of formula Bao.gEuo.iMgAlioO, ₇ . The product used here is the powder obtained after drying, in an oven and at 60 ° C., the suspension which was obtained at the end of the wet milling step described in this example 1. In the preparation of this luminophore, no flow like gF. has not been used.

The average product size measured by laser diffraction is 140 μη dispersion o: 0.6. The size of the coherent domain calculated from the diffraction line corresponding to the plane [102] is 101 nm. Hence a measured value d507 DRX measurement value equal to 140/101 = 1, 386. We note that the value of the d50 (laser) and that of the size of the coherent domain (DRX) have the same order of magnitude, which confirms the monocrystalline nature of the particles.

The phosphor has an absorption of at most 8% in the wavelength range between 500 nm and 750 nm. Its external quantum yield is 51% under an excitation wavelength λ _ex of 380 nm. Its maximum emission is 450 nm.

Preparation of a luminescent composite

 A composite film is prepared from a mixture of 696.5 g of Eastar 6763 PET copolyester resin and 3.5 g of phosphor previously described, which corresponds to a proportion by weight of 0.5%.

The formulation is premixed in a rotary mixer and then extruded in a Leistritz LSM 30/34 co-rotating twin-screw extruder with a diameter of 34 mm and a length / diameter ratio of 35. The extrusion temperature is 250X.

The films are directly implemented at the extruder outlet. A flat die is fitted on the convergent. This makes it possible to put the extruded material in the form of a ply 300 mm wide and 250 μm thick.

The filmmaker is composed of:

 - two rollers regulated at a temperature of 70 ° C.

 - six "support" rollers that guide the film to a winding roller on which the finished product is stored.

Optical characterizations in the visible

The films obtained are characterized in total (TT) and diffuse (TD) transmissions using a Perkin Elmer Lambda 900 UV-Vis spectrometer equipped with an integrating sphere. The total and diffuse transmissions are measured over a range of 450 to 8 '^"''- · · <t normalized between 0 and; 100%,>"> s is determined by the formula: haze {%) = TD TT x 100, Comparative film of PET without phosphor has a total transmission of 90% over the entire wavelength range, while the composite film

PET - phosphor has a total transmission of 88.6% in the same wavelength range. The transmission values given above show that the presence of the phosphor does not lead to a significant change in transparency.

Organic solar cell based on conjugated polymers

The films mentioned above were then tested in OPV devices (organic photovoltaic). The solar cell used for this test is of direct structure with anode on the front face. On a glass coated with a transparent conductive layer of ITO (indium and tin oxide), a polymer film PEDOT-PSS (Poly (3,4-ethylenedioxythiophene-polystyrene sulfonate) was deposited by spin-coating . The film is composed of photoactive PCDTBT (poly [N-9'-heptadécanyI-2,7-carbazol ^ a] t-5 _I 5 ^ 4 _i ^{7-di-2-thienyl-2,} _I ^1,, 3 ' benzothiadiazole), mixed with PC70BM (methyl [6,6] -phenyl-Cro-butanoate) in a solvent mixture chloroform: orthodichlorobenzene No heat treatment was carried out

Finally the cathode contacts are evaporated thermally under high vacuum through a mask which defines on each substrate 6 pixels of 0.045 cm ² of active surface. Each pixel corresponds to a small OPV cell. Electrical tests

 The J / V tests are carried out outside the glove box in a chamber in an inert atmosphere comprising a quartz window. The PET - phosphor films are applied to this quartz window. The PET-phosphor film measurements are made by comparison with the measurements made by applying the comparative PET film (uncharged phosphor).

The electrical tests are carried out under an illumination equivalent to 1 sun, through a standardized filter AM 1.5. The intensity of the solar simulator is calibrated thanks to a silicon photovoltaic cell. A voltage is applied to the cell (between -1 to 5V 1 5V) and the current produced is measured using ^a Keithley jrant generator which applies an electric field across a system and the Surer resulting electric current. First, the comparative PET film is applied to the photovoltaic device and the absolute yield of the cell is recorded. Three measurements are made per sample, then the average value is used. The same measurements are then made with PET-phosphor film.

The absolute yield of the comparative PET film cell is r = 2.54%.

The absolute yield of the PET-phosphor film cell is r = 2.74%, which represents a 7.9% relative increase in cell efficiency.

Comparative examples

Several attempts have been made to show that the barium aluminate according to the invention has a compromise of properties. The polymer used is the same as for example 1 and the film prepared has the same thickness of 250 .mu.m. Example 2: Use of barium aluminate (0.5%) having the following characteristics: EQ = 100% (under k _mc 380 nm); d50 = 6.5 pm. This aluminate was obtained using a flow of MgF ₂ conversely aluminate of Example 1. This aluminate is the product of said reference to the extent of QE such that ^it has been described in example page 3 : is used 1% of the reference aluminate ^of example 2 instead of 0.5% example 4 1 using ^a barium aluminate (0.5%) identical to the reference aluminate ia only difference that it was not treated by calcination in the presence of MgF ₂ : QE = 75% (under X _exc 380 nm); d50 = 3.3 pm. Table 1

 d50: nm (laser diffractometer)

QE: external quantum yield in% (under excitation wavelength _β χο 380 nm)

TT: transmission rate (%) - substantially constant over the entire wavelength range of the measurement

 haze (%)

r: absolute yield of the cell determined under the same conditions as in example 1 improvement = (absolute yield of the cell - r _ref ) / r _re , x 100

 the absolute yield of the cell with the reference film (2.54%), that is to say with the composite film of the same thickness and consisting of the same polymer and the same additives but not loaded with phosphor.

It is found that there is a compromise between the size of the particles and the efficiency QE, In order not to lose efficiency in the visible range, it is necessary that the haze of the film is low. However, we realize that if we reduce the average particle size, the QE yield tends to decline.

Example 1 illustrates the invention and shows that the property compromise allows an improvement of 7.9% for a proportion of 0.5% even though, surprisingly, the QE yield is lower for the aluminate of this type. example for the aluminates of Example 2 or Example 4.

In the case of Example 3, it can be seen that increasing the proportion to 1% does not make it possible to increase the improvement significantly.

Examples 5-6

 Examples 5 and 6 were made with EVA. Dupont's Elvax 150 grade (32% vinyl acetate, mw = 43 g / 10 min 190 ° C. 2.16 kg) was used.

The composite film was obtained by extruding ^the EVA and the type of phosphor aluminate 0.5% The film thickness is 250 pm. eicgn i uses the barium aluminate of Example 1 (0.5%) Example 6: Use of a barium aluminate (0.5%) of the same composition as the reference aluminate but not finished with the treatment with MgFa: QE = 75% (under λ _βχε 380 nm) ; dSO = 3.3 nm. Table it

It is also noted that the total transmission is not affected much by the presence of the particles. Example 7

 It was sought to reduce the d50 of the aluminate of Example 2 using several conventional grinding techniques including ball milling or wet milling but without reaching the d50 <1 .mu.m.

Claims

1- luminescent composite, characterized in that it comprises:

 a polymer chosen from ethylene vinyl acetate (EVA), polyethylene terephthalate, ethylene tetrafluoroethylene, ethylene trifluorochloroethylene, perfluoroethylene propylene, polyvinyl butyral and polyurethane;

 at least one inorganic phosphor based on at least one element which is chosen from rare earths, zinc and manganese and which has the following characteristics:

 An external quantum yield greater than or equal to 40% for at least one excitation wavelength between 350 nm and 440 nm;

^■ an absorption less than or equal to 10% for a wavelength greater than 440 nm;

 An average particle size d50 of less than 1 μm;

^■ a mean particle size d50 of at least 30 nm;

 A maximum emission in a wavelength range between 440 nm and 900 nm. 2. Composite according to claim 1 characterized in that the phosphor has an average particle size of at most 0.4 .mu.m. more particularly at most 0.3 μm.

3. Composite according to claim 1 or 2 characterized in that the particles of the phosphor have a d50 between 80 and 400 nm, preferably between

80 and 300 nm.

4. Composite according to claim 1 to 3, characterized in that the luminophore is chosen from aluminates doped with a rare earth and / or manganese, borophosphates doped with europium; europium doped halophosphates, rare earth borates doped with cerium, rare earth oxysulfides doped with europium. rare earth vanadates doped with europium. zinc compounds doped with manganese. 5. Composite according ^to one of claims 1 to 4 characterized in ^that it comprises no particu> pe quantum dots

8. Composite according to one of the preceding claims, characterized in that the luminophore is derived from the separation of the solid product from the liquid phase from a suspension of a barium aluminate and magnesium consisting of substantially monocrystalline particles of average size between 80 nm and 400 nm.

7. Composite according to claim 8, characterized in that the barium and magnesium aSuminate consists of particles of average size between 100 nm and 200 nm.

8. Composite according to one of the preceding claims, characterized in that the phosphor is an aluminate corresponding to formula (I);

a (Bai, _d M ¹ _d O) b (Mgi _.e iv1 ² _e O) .c (AI ₂ 0 ₃ )

in which :

M ¹ is a rare earth which can be especially gadolinium, terbium, yttrium, ytterbium, ^europium, neodymium and dysprosium;

M ² denotes zinc, manganese or cobalt;

a, b, c, d and e check relationships:

0.25 <a <2; 0 <b <2; 3 <c <9; 0 <d <0.4 and 0 <e <0.6.

9- Composite according to claim 8, characterized in that the aluminate has the formula (!) Above wherein a = b = 1 and c = 5; where a = b = 1 and c = 7 or a = 1; b = 2 and c = 8. 10. Composite according to claim 6 to 9 characterized in that the aluminate particles are in a well separated and individualized form.

11. Composite according to claim 6 to 10 characterized in that the particles of the aluminate have a ratio d50 / average size determined by DRX less than 2.

12 A composite according to claim 6 to 11, characterized in that the particles of ^the aluminate have a ratio DSQ / median diameter as measured by TEM of less than 2

Γ. V-mposite according to one of the claims - in that the luminophore is derived from the separation of the solid product from the liquid phase from a suspension of particles of a rare earth borate, these particles being substantially monocrystalline and having an average size of between 100 and 400 nm.

14. Composite according to claim 8 to 12 characterized in that the luminophore is an aluminate obtained by a process comprising the following steps:

 A liquid mixture comprising, in the desired proportions, in the water, the compounds of aluminum and the other elements forming part of the aluminate composition in the form of inorganic salts, hydroxides or carbonates, the mixture being in the form of a solution, suspension or gel;

 The mixture of the preceding step is spray-dried;

 The product dried in the preceding step is calcined at a sufficiently high temperature to obtain a crystalline phase;

 The calcined product obtained in the preceding step is subjected to wet grinding so as to lead to the aluminate in suspension;

 The aluminate is recovered in the form of a powder from the suspension obtained in the preceding step by a liquid / solid separation.

15. Composite according to claim 11 characterized in that the method does not use a calcination in the presence of a flow.

16. Composite according to one of the preceding claims being in the form of a film with a thickness of between 25 and 800 pm. Photovoltaic cell comprising a luminescent composite according to one of the preceding claims.

18. Use of a composite film according to claim 16 for increasing the conversion efficiency of light energy into electrical energy of a photovoltaic cell.

19. A method of converting ^the light energy into electrical energy using ^a photovoltaic cell of increasing with the composite according to claim 1 to 16 the number of solar photons used by the active elements for the conversion light energy into electricity