EP2755927A1

EP2755927A1 - Photocatalytic material and glazing or photovoltaic cell comprising said material

Info

Publication number: EP2755927A1
Application number: EP12773023.2A
Authority: EP
Inventors: Rosiana Aguiar
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2011-09-13
Filing date: 2012-09-12
Publication date: 2014-07-23
Also published as: FR2979910A1; JP2014534143A; CN103781738A; KR20140063682A; WO2013038104A1; US20140338749A1; FR2979910B1

Abstract

The subject matter of the invention is a material comprising a glass or vitroceramic sheet, of which at least part of one of the faces is furnished with a photocatalytic coating with titanium oxide base deposited on a silica-based substrate that is deposited by combustion chemical vapour deposition, having roughness Ra of between 4 and 30 nm including the limits thereof.

Description

PHOTOCATALYTIC MATERIAL AND GLAZING OR CELL

PHOTOVOLTAIC COMPRISING THIS MATERIAL

The invention relates to the field of materials comprising a glass substrate provided with a photocatalytic coating.

Photocatalytic coatings, in particular those based on titanium dioxide, are known to impart self-cleaning and anti-fouling properties to the substrates which are provided with them. Two properties are at the origin of these advantageous characteristics. Titanium oxide is first of all photocatalytic, that is to say that it is capable under suitable radiation, generally ultraviolet radiation, of catalyzing the degradation reactions of organic compounds. This photocatalytic activity is initiated within the layer by the creation of an electron-hole pair. In addition, the titanium dioxide has an extremely pronounced hydrophilicity when it is irradiated by this same type of radiation. This strong hydrophilicity, sometimes called "super-hydrophilic", allows the evacuation of mineral soils under water runoff, for example rainwater. Such materials, in particular glazing, are described for example in application EP-A-0 850 204.

Titanium dioxide has a high refractive index, which results in important light reflection factors for substrates with photocatalytic coatings. This is a disadvantage in the field of glazing for the building, and even more so in the field of photovoltaic cells, for which it is necessary to maximize the transmission to the photovoltaic material, and thus minimize any absorption and reflection of solar radiation. However, there is a need to provide photovoltaic cells with a photocatalytic coating, because the deposition of dirt is able to reduce the efficiency of photovoltaic cells by about 6% per month. This figure is obviously dependent on the geographical location of the cells.

To reduce the light reflection factor, it is possible to reduce the thickness of the photocatalytic coatings, but this is done to the detriment of their photocatalytic activity.

The aim of the invention is to propose photocatalytic materials based on titanium oxide, combining both high photocatalytic activity and low light reflection factors.

For this purpose, the subject of the invention is a material comprising a glass or glass-ceramic sheet provided on at least a part of one of its faces with a photocatalytic coating based on titanium oxide deposited on an undercoat layer. based on silica deposited by chemical vapor deposition by combustion, the roughness Ra of which is between 4 and 30 nm, including terminals.

The invention also relates to a process for obtaining a material according to the invention. This preferred method comprises the following steps: a silica-based underlayer is deposited on a sheet of glass or glass-ceramic using a chemical vapor deposition process by combustion, and then depositing on said silica-based underlayer a photocatalytic coating based on titanium oxide, said sublayer being subjected to a temperature of at least 300 ° C prior to deposition of said photocatalytic coating and / or during deposition of said photocatalytic coating. It has been found that the use of particularly rough silica-based undercoats obtained by chemical vapor deposition by combustion is able to significantly decrease the luminous reflectance of the material. The roughness Ra corresponds to the arithmetic average deviation of the roughness profile. This value is measured by atomic force microscopy on a 1000 nm square, in non-contact mode and using a silicon tip with a radius of curvature of 15 nm. The substrate is a sheet of glass or glass ceramic. The sheet may be flat or curved, and have any type of dimensions, especially greater than 1 meter. The glass is preferably of the silico-soda-lime type, but other types of glasses, such as borosilicate glasses or aluminosilicates can also be used. The glass may be clear or extra-clear, or tinted, for example blue, green, amber, bronze or gray. The thickness of the glass sheet is typically between 0.5 and 19 mm, especially between 2 and 12 mm, or even between 4 and 8 mm. In the field of photovoltaic cells, the glass is preferably extra-clear; it preferably comprises a total weight content of iron oxide of at most 150 ppm, or even 100 ppm and even 90 ppm, or even a redox of at most 0.2, especially 0.1 and even a zero redox. The term "redox" refers to the weight ratio of ferrous iron oxide (expressed as FeO) to the total weight content of iron oxide (expressed as Fe ₂ O ₃ ). The photocatalytic coating based on titanium oxide is preferably made of titanium oxide, in particular crystallized in anatase form, which is the most active form. A mixture of anatase and rutile phases is also conceivable. The titanium oxide may be pure or doped, for example by transition metals (especially W, Mo, V, Nb), lanthanide ions or noble metals (such as, for example, platinum or palladium), or by nitrogen, carbon or fluorine atoms. These different forms of doping make it possible either to increase the photocatalytic activity of the material, or to shift the gap of the titanium oxide towards wavelengths close to the visible range or included in this range.

The photocatalytic coating is normally the last layer of the stack deposited on the substrate, that is to say the layer of the stack farthest from the substrate. It is important that the photocatalytic coating is in contact with the atmosphere and its pollutants. It is however possible to deposit on the photocatalytic layer a very thin layer, generally discontinuous or porous. For example, it may be a layer based on noble metals intended to increase the photocatalytic activity of the material

The thickness of the photocatalytic coating is preferably between 1 and 20 nanometers, especially between 2 and 15 nm, or even between 3 and 10 nm, inclusive. A high thickness increases the photocatalytic activity of the layer but at the expense of light reflection. Throughout this text, the thicknesses are physical thicknesses.

The silica-based underlayer is preferably silica, i.e., silica. It is understood that the silica may be pure or doped, or not be stoichiometric. The silica may, for example, be doped with boron or phosphorus atoms, or with carbon or nitrogen atoms.

The silica-based underlayer is preferably deposited in contact with the substrate.

The roughness Ra of the silica-based underlayer is advantageously between 5 and 25 nm, including terminals, in particular between 8 and 20 nm or between 10 and 15 nm.

The thickness of the silica-based underlayer is preferably between 10 and 100 nm, including limits, especially between 10 and 80 nm, or even between 15 and 50 nm, and even between 20 and 30 nm. A sufficient thickness allows the underlayer to act as a barrier layer to the migration of alkali ions from the substrate when the latter contains (for example if it is a soda-lime-calcium glass substrate) ).

The silica-based underlayer is preferably non-porous, especially in the sense that no pores are observed by microscopic techniques, such as transmission electron microscopy (TEM). Subjecting the undercoat at a temperature of at least 300 ° C. used in the preferred process according to the invention, prior to the deposition and / or during the deposition of the photocatalytic coating, has the effect of densifying the underlayer. The material according to the invention preferably has a light transmittance (within the meaning of ISO 9050: 2003) of at least 85%, even 88% and even 90% or 91% and / or a light reflection factor (within the meaning of ISO 9050: 2003) of not more than 10%, in particular 9% or 8%. The silica-based underlayer is deposited by chemical vapor deposition by combustion. This technique, also known by its acronym CCVD (For "CVD Combustion"), consists in reacting or decomposing at least one precursor of the layer to be deposited (generally an organometallic compound, a metal salt or a halide) in a flame placed near the substrate. The process is normally carried out at atmospheric pressure. The precursor, pure or dissolved in a solvent, decomposes under the effect of heat and is deposited on the substrate. In a continuous process, the flame is typically derived from a fixed linear burner extending over the entire width of the substrate, the latter coming past the burner. The flame results from the reaction between a fuel (typically propane or butane, and in this case the solvent is preferably non-combustible, or the solvent when it is combustible) and an oxidizer (typically air, air enriched with oxygen or oxygen). The silica precursor is typically an organometallic silicon compound or an organic salt, such as a silane or siloxane. Hexamethyldisiloxane (HDMSO) and tetraethylorthosilicate (TEOS) are particularly suitable. The silica precursor may also be a halogenated compound, such as for example SiCl ₄ . The solvent may be combustible, such as an organic solvent, or preferably non-combustible, typically water. The substrate may be heated prior to deposition and / or during deposition, for example at a temperature of between 300 and 600 ° C., in particular between 400 and 550 ° C.

It has been found that such a process makes it possible, under certain conditions which are set out below, to obtain particularly rough silica layers, especially in comparison with other techniques, such as CVD. Without wishing to be bound by any scientific theory, it would seem that under certain conditions which are specified in the rest of the text the decomposition of the precursor within the flame forms silica nanoparticles which are then deposited on the layer forming clusters, thereby conferring a significant roughness. The subsequent heating of the underlayer makes it possible to densify it and to fix it to the substrate, but surprisingly without significantly reducing its roughness. High roughness of the silica-based layer can be achieved by increasing the size of the nanoparticles. To do this, it is possible to carry out at least one of the following adjustments: increase the residence time of the particles in the flame, decrease the flow of fuel and oxidizer, increase the distance between the burner and the substrate, increasing the precursor concentration in the solvent, increasing the precursor flow rate. The precise values to be given to these parameters are of course highly dependent on the depositing device used, so that they can not be specified here in absolute terms. The examples of realization detailed in the following of the text specify certain values.

The silica-based underlayer is preferably subjected to a temperature of at least 400 ° C, or even 500 ° C prior to deposition of said photocatalytic coating and / or during deposition of said photocatalytic coating.

The deposition of the photocatalytic coating is preferably carried out by chemical vapor deposition. It can also be achieved by other deposition techniques, such as chemical vapor deposition by combustion.

Chemical vapor deposition, generally referred to as CVD, is a pyrolysis process using gaseous precursors decompose under the effect of the heat of the substrate. In the case of titanium oxide, the precursors may be, for example, titanium tetrachloride, titanium tetraisopropoxide or titanium tetraorthobutoxide.

Preferably, the deposition of the underlayer and the deposition of the photocatalytic coating are carried out successively, on the glass production line by the float process (also called "float" process). In this continuous process, a glass ribbon is obtained by casting the glass at about 1100 ° C on a bath of molten tin in a chamber called floating chamber. At the outlet of this chamber, the temperature of the glass is of the order of 500 to 600 ° C, and the glass ribbon then passes into a chamber called lehr, where the glass is cooled in a controlled manner to eliminate any constraints mechanical residuals within it. Preferably, the deposition of the underlayer and the deposition of the photocatalytic coating are implemented successively, between the output of the floating vessel and the entrance of the lehr. The burner used for chemical vapor deposition by combustion and the chemical vapor deposition nozzle are therefore preferably installed between the exit of the floating vessel and the inlet of the lehr. Typically, the temperature of the glass during the implementation of the deposition of the silica-based underlayer is between 480 and 600 ° C., in particular between 500 and 550 ° C., and the temperature of the glass during the setting-up The photocatalytic coating deposited is between 430 and 550 ° C., in particular between 450 and 500 ° C. In this way, the silica-based underlayer is naturally subjected to a temperature of at least 300 ° C. prior to deposition and during deposition of the coating. photocatalytic, and therefore densified and attached to the substrate, without having to bring additional energy, for example by placing the substrate in an oven.

The invention also relates to a glazing unit or a photovoltaic cell comprising at least one material according to the invention.

The glazing may be single or multiple (in particular double or triple), in the sense that it may comprise several glass sheets leaving a space filled with gas. The glazing can also be laminated and / or tempered and / or hardened and / or curved.

The other face of the material according to the invention, or possibly a face of another substrate of the multiple glazing, may be coated with another functional layer or a stack of functional layers. It may especially be another photocatalytic layer. It may also be layers or stacks with thermal function, in particular antisolar or low-emissive, for example stacks comprising a silver layer protected by dielectric layers. It may still be a mirror layer, in particular based on silver. It can finally be a lacquer or an enamel intended to opacify the glazing to make a facade facing panel called lighter. The lighter is arranged on the facade alongside the non - opaque glazings and allows to obtain facades entirely glazed and homogeneous from the aesthetic point of view.

In the photovoltaic cell according to the invention, the material according to the invention is preferably the front face substrate of the cell, that is to say the one which is the first crossed by solar radiation. The photocatalytic coating is then positioned outwards, so that the self-cleaning effect can be useful.

For applications as photovoltaic cells, and in order to maximize the energy efficiency of the cell, several improvements can be made cumulatively or alternatively:

The glass sheet may advantageously be coated, on the face opposite to the face provided with the coating according to the invention, with at least one transparent and electroconductive thin layer, for example based on Sn0 ₂ : F, Sn0 ₂ : Sb, ZnO: Al, ZnO: Ga. These layers may be deposited on the substrate by various deposition methods, such as chemical vapor deposition (CVD) or sputtering deposition, in particular assisted by magnetic field (magnetron process). In the CVD process, halide or organometallic precursors are vaporized and transported by a carrier gas to the surface of the hot glass, where they decompose under the effect of heat to form the thin layer. The advantage of the CVD process is that it is possible to implement it in the process of forming the glass sheet, especially when it is a floating process. It is thus possible to deposit the layer when the glass sheet is on the tin bath, at the exit of the tin bath, or in the lehr, that is to say when the glass sheet is annealed to eliminate mechanical stress.

The glass sheet coated with a transparent and electroconductive layer may in turn be coated with a semiconductor based on amorphous or polycrystalline silicon, chalcopyrites (especially CIS - CuInSe2 or CIGS - CuInGaSe2) or CdTe to form a photovoltaic cell. In this case, another advantage of the CVD process lies in obtaining a higher roughness, which generates a phenomenon of trapping light, which increases the amount of photons absorbed by the semiconductor. The presence according to the invention of a rough silica underlayer also helps to amplify this phenomenon of trapping of light. the surface of the glass sheet may be textured, for example have patterns (especially pyramid), as described in WO 03/046617, WO 2006/134300, WO 2006/134301 or WO 2007/015017. These textures are generally obtained using a glass forming by rolling.

The invention will be better understood in the light of the nonlimiting examples which follow, illustrated by FIGS. 1 and 2.

FIRST SERIES OF EXAMPLES

Example 1

On a glass substrate is deposited a 30 nm thick silica underlayer by chemical vapor deposition by combustion (CCVD). To do this, a flame obtained by combustion of propane (flow rate of 6 L / min) with air (flow rate of 150 L / min) is disposed at 15 mm from the surface to be coated. The substrate travels at a speed of 2 m / min under the flame, while a precursor HDMSO (hexamethyldisiloxane) is introduced into the flame with a flow rate of 0.5 L / min.

After deposition of the underlayer, a photocatalytic coating of titanium oxide approximately 10 nm thick is deposited on the underlayer by a CVD technique. To do this, the substrate provided with the underlayer is heated to about 530 ° C, and a titanium oxide precursor, titanium tetraisopropoxide, dissolved in a carrier gas (nitrogen) is brought into contact with the surface of the substrate. substrate.

Example 2

This example is carried out in the same manner as Example 1, the only difference being that the silica underlayer is thicker (60 nm), thanks to a second pass. In the second pass, the propane flow rate is 10 L / min, the air flow rate is 250 L / min, and the precursor flow rate is 1 L / min. The distance between the flame and the substrate is 30 mm.

Comparative examples

In Comparative Example 1, the photocatalytic coating is obtained in the same manner as in the case of Example 1 according to the invention. On the other hand, the underlayer is a layer of silicon oxycarbide deposited by CVD (and not by CCVD), therefore much less rough. In Comparative Example 2, the underlayer is a layer of silica deposited by cathodic sputtering magnetron, also much less rough. The photocatalytic coating is the same as in the case of Comparative Example 1.

Figure 1 is a snapshot obtained by atomic force microscopy (AFM) of the surface of Example 1, to observe the high roughness imparted by the silica underlayer.

Figure 2 groups the transmission spectra of the four examples. Table 1 below summarizes the results of the tests. It indicates for each example the following quantities: the roughness Ra, expressed in nm, the photocatalytic activity Kb, expressed in μg .1 ^_1 . min ^-1 , the light reflection factor RL, the light transmittance TL and the energy transmission factor TE, in the meaning of ISO 9050: 2003, the transmittance "TSQE", corresponding to the convolution product of the spectrum of material transmission and the quantum efficiency curve of amorphous silicon. This factor makes it possible to evaluate the transmission of the material in the relevant wavelengths for the photovoltaic cells using amorphous silicon. The roughness Ra is measured using an atomic force microscope (AFM) Nanoscope Illa on a square of 1000 nm of side, in non-contact mode and using a silicon tip whose radius of curvature is 15 nm.

The photocatalytic activity is evaluated by measuring the rate of degradation of methylene blue in the presence of ultraviolet radiation. An aqueous solution methylene blue is placed in contact in a sealed cell with the coated substrate (the latter forming the bottom of the cell). After exposure to ultraviolet radiation for 30 minutes, the concentration of methylene blue is evaluated by a light transmission measurement. The value of photocatalytic activity (denoted Kb and expressed in μg.l ^-1 .min ^-1 ) corresponds to the decrease in methylene blue concentration per unit of exposure time.

Table 1

SECOND SERIES OF EXAMPLES

Example 3

A silica underlayer 20 nm thick by CCVD is deposited on a 2 mm thick clear glass sheet. To do this, 6 passes under an air-propane flame, using a solution of a precursor HDMSO in ethanol. Propane flows and of air are respectively 8 and 160 L / min. The concentration of precursor in ethanol is 0.1 mol / l, and the rate of introduction of the precursor solution into the flame of 2 μl / min. The distance between the burner and the substrate is 7 mm, and the speed of travel of the substrate 6 m / h. The substrate is heated to a temperature of 520 ° C prior to deposition.

The photocatalytic coating is similar to that of the previous examples.

Comparative Example 3

The deposition conditions of the silica underlayer differ from those of Example 3 in that the distance between the substrate and the burner is 5 mm, and the rate of introduction of the precursor solution is 1 μL. / min.

Table 2

The deposition conditions of Comparative Example 3 induce a very low roughness, compared with those of Example 3 according to the invention. These results demonstrate that the use of a rough undercoat obtained by CCVD makes it possible to significantly reduce the reflection of the material, until it reaches reflections of the order of that of bare glass, or even lower. This results in much higher light and energy transmissions of 3 to 4 points, without degrading the photocatalytic activity.

Raman spectrometry analysis shows the presence of anatase for all samples.

Observation of the materials by transmission electron microscopy performed on the wafer shows that the silica layer is dense, free of any porosity.

Claims

1. Material comprising a glass or glass-ceramic sheet provided on at least a part of one of its faces with a titanium oxide-based photocatalytic coating deposited on a silica-based underlayer deposited by chemical deposition in combustion vapor phase whose roughness Ra is between 4 and 30 nm, including terminals.

2. Material according to one of the preceding claims, such that the photocatalytic coating is titanium oxide, in particular crystallized in the anatase form.

3. Material according to one of the preceding claims, such that the silica-based underlayer is silica.

4. Material according to one of the preceding claims, such that the underlayer is deposited in contact with the substrate.

5. Material according to one of the preceding claims, such that the roughness Ra of the underlayer is between 5 and 25 nm, including terminals.

6. Material according to one of the preceding claims, such that the thickness of the silica-based underlayer is between 10 and 100 nm, especially between 10 and 80 nm, including terminals.

7. Material according to one of the preceding claims, such that the photocatalytic coating is the last layer of the stack deposited on the glass or glass-ceramic sheet.

8. Material according to one of the preceding claims, such that the thickness of the photocatalytic coating is between 1 and 20 nm, including terminals.

9. Material according to one of the preceding claims, having a light transmission factor according to ISO 9050: 2003 of at least 80%, in particular 90% and a light reflection factor according to ISO 9050: 2003 of not more than 10%, in particular 9%.

10. Glazing or photovoltaic cell comprising at least one material according to one of the preceding claims.

11. Process for obtaining a material according to one of claims 1 to 9, comprising the following steps: a silica-based underlayer is deposited on a glass or glass-ceramic sheet using a chemical vapor deposition process by combustion, then deposited on said silica-based underlayer a photocatalytic coating based on titanium oxide, said underlayer being subjected to a temperature of at least at least 300 ° C. prior to deposition of said photocatalytic coating and / or during deposition of said photocatalytic coating.

12. Method according to the preceding claim, such that the deposition of the photocatalytic coating is carried out by chemical vapor deposition.

13. Method according to one of claims 11 or 12, such that the photocatalytic coating is the last layer of the stack deposited on the glass sheet or glass-ceramic.

14. Method according to one of claims 11 to 13, such that the deposition of the underlayer and the deposition of the photocatalytic coating are carried out successively on a glass production line by the float process.

15. Method according to the preceding claim, such that the deposition of the underlayer and the deposition of the photocatalytic coating are implemented successively, between the output of the floating vessel and the inlet of 1 lehr.