FR2670200A1 - Process for forming a semiconductive layer of aluminium-doped zinc oxide on glass, glazing thus obtained - Google Patents

Abstract

The process consists in forming, by liquid pyrolysis, on glass heated to elevated temperature, a layer of ZnO:Al from a solution including at least one zinc compound and an aluminium chelate and subjecting the layer obtained to a reducing treatment. Application to low-emission and heating glazing.

Description

PROCESS FOR FORMING A SEMICONDUCTOR LAYER
ZINC OXIDE DOPED WITH ALUMINUM ON GLASS,
GLASS THUS OBTAINED
The present invention relates to a method for forming on a glass support, a transparent, semiconductor layer of aluminum-doped zinc oxide; it also relates to glazing carrying this layer as well as its use, in particular, in glazing for the building or the automobile.

 Glazing intended for buildings is advantageously made of clear silica-soda-lime glass which has high light and energy transmission factors, for example of the order of 90% for a thickness of 4 mm.

 To improve user comfort, especially in winter, by reducing the energy loss due to a leakage of calories from the interior of the building to the outside, it is known to form glazing by covering one side with a sheet of glass. , a semiconductor layer of metal oxide, called low emissivity, which increases the reflection rate of the glazing in the infrared.

 To improve the performance of insulating glass, we started by acting mainly on heat exchange by conduction and by convection, but, with low emissivity glasses, we also act on radiation. Radiation exchanges are a function of the emissivity of the bodies present. The lower the emissivity, the less the exchange between these bodies or environments.

 Glass glazing coated with such a layer can be combined with another sheet of uncoated glass, trapping an air space between them, to form a double insulating glazing.

 The low emissivity of the semiconductor layer is linked to a low resistivity of the layer. Glass sheets having this type of layer can therefore also be used as heated glazing, particularly in the automotive field, to form windshields and rear windows and as substrates in particular products such as opto-electronic devices. such as photovoltaic cells and liquid crystal display devices.

 Glazing carrying transparent coatings and having low emissivity properties are known.

They can, for example, consist of a glass support and a thin layer of metal oxide, such as a layer of tin oxide doped, for example, with fluorine (SnO2: F).

 These layers can be obtained by various processes, vacuum processes (thermal evaporation, sputtering) or by pyrolysis of metal compounds in the form of a solution, powder or vapor, sprayed onto the heated substrate. In this case, the compounds, in contact with the glass heated to high temperature, decompose and oxidize to form a layer of metal oxide.

 When the semiconductor layers are to be formed on a moving glass ribbon, as is the case on a manufacturing line, the pyrolysis process is of interest compared to the other processes since it can be carried out at atmospheric pressure and directly after the glass has been produced.

 Thus, the layers of tin oxide doped with fluorine are advantageously obtained by pyrolysis of powders and, in this case, layers with a thickness of 180 nm have a light transmission of about 80%, an emissivity of 0.35 and a resistivity of approximately 10-3 Q.cm.

 Although these fluorine-doped tin oxide layers have advantageous properties suitable for certain applications, we are still looking for layers which have a low resistivity, and therefore a low emissivity, and which can be obtained by pyrolysis processes. adaptable to a glass production line in which the glass, in the form of a ribbon, can pass at a speed of between 3 and 25 m / min.

 It is known that layers of zinc oxide doped with aluminum can be obtained by vacuum deposition processes and that these layers have a resistivity of the order of 10-4R.cm, therefore lower than that of the layers d fluorine doped tin oxide. However, vacuum deposits do not have the same advantage as pyrolyzed deposits because of the manufacturing constraints already mentioned.

 The object of the invention is therefore to form, on a glass support, layers of zinc oxide doped with aluminum, transparent and having a low resistivity, by an easily usable process, that is to say essentially without the constraints of vacuum techniques. In this connection, it is interesting that this process can be used directly on a glass production line.

In particular, the fact that the method according to the invention can be implemented on a production line in which the glass is capable of running at high speed, in particular a float line, is considered to be an essential advantage.

 The method according to the invention for forming a transparent semiconductor layer of aluminum-doped zinc oxide on a glass support is characterized in that the support is heated to a temperature below its softening temperature and between 500 C and 6500C and in that it consists in projecting onto this support, using a carrier gas, a solution of at least one zinc compound and aluminum chelate thermally decomposable at temperature of the support, these compounds pyrolyzing on contact with the hot support to form said layer of zinc oxide doped with aluminum.

 The method is also characterized in that the glass support consists of a ribbon of glass moving at a speed of between 3 and 25 m / min.

 Advantageously, the aluminum chelate is non-hydrolyzable and then aluminum isovalerylacetonate is preferably used. The aluminum chelate chosen for carrying out the invention is advantageously non-hydrolyzable because a hydrolyzable chelate can transform into an alumina hydrate which precipitates and is no longer pyrolysable and therefore the parts of the chelate solution thus hydrolysed may cause defects in the layer. Also preferably, the solution used is non-aqueous. In addition, the layer thus obtained is subjected to a reducing reduction.

 The zinc compounds which can be used for carrying out the invention are organic compounds which preferably do not contain halogen. Indeed, the presence of chlorine, for example, can cause the formation of sodium chloride as a result of the reaction with the sodium ions of the glass support, which modifies the optical characteristics of the glass. Useful zinc compounds are, for example, zinc acetate and zinc nitrate.

 The process used to form the aluminum doped zinc layers according to the invention is a liquid phase pyrolysis process. Liquid pyrolysis processes and devices for their implementation are described for example in French patents 2 176 760, 2 211 411 and European patents 12 679, 25 738, 60 747 and 51 538.

 Generally, in its elaborate form, the process consists in passing a glass ribbon, formed for example in a "float" oven and maintained at high temperature, in a station for spraying a solution of thermally decomposable metallic compounds. at the temperature of the glass ribbon. The gas used to atomize the liquid is air or nitrogen. This station essentially comprises one or more spray guns for the solution, which can be moved back and forth over the glass ribbon.

The mechanism of liquid pyrolysis is roughly as follows
the aerosol is projected towards the substrate brought to high temperature; the reactions take place as follows: the solvent evaporates, the starting compounds melt and vaporize; their vapors diffuse towards the substrate in contact with which the decomposition and oxidation reaction take place.

 Pyrolysis requires an adjustment of the deposition conditions: liquid flow rate, gas flow rate and temperature of the support.

 The flow of liquid and the flow of carrier gas determine the size of the aerosol droplets and therefore its reactivity. The metal compounds and the solvents used are directly responsible for the feasibility of the reaction. The substrate temperature must be constant and as uniform as possible to avoid differences in yield.

 In addition, control of the flow rate of liquid and gas sent into the spray gun (s), the speed of movement of the glass and that of transverse movement of the gun (s) when that -this (these) is (are) mobile (s), makes it possible to adapt the thickness of the deposit according to the subsequent use envisaged.

 The semiconductor layers which it is desired to obtain, according to the invention, must be transparent and have a low resistivity. The parameters which influence the optical and electrical properties are the temperature of the glass, the atomic percentage of aluminum in the solution, the flow rates of the solution as well as the thickness of the layer.

 The glass ribbon is, as indicated, at a temperature below the softening temperature of the glass, a temperature which depends on the composition of the glass. It is generally that of the glass at its exit from the float furnace, that is to say between approximately 500 "C and 6500C. It has been noted that it is in this temperature range that the resistivity of the layers obtained otherwise under the same conditions, was the lowest.

 The solutions of the aluminum and zinc compounds, used during spraying on the glass support, are generally prepared by dissolving the compounds beforehand in one of their solvents.

 The aluminum compound, aluminum isovalerylacetonate, is a viscous liquid at room temperature. It is used in the form of a solution in ethyl acetate containing from 1 to 3 g of aluminum per 100 ml of solution.

 The zinc compound, especially zinc acetate, is dissolved in an alcohol, such as methanol or ethanol.

These solvents do not significantly influence the pyrolysis yields of the solutions.

 In general, the solutions of the aluminum and zinc compounds are adapted to have an appropriate viscosity to allow their use in the spraying devices usually used for liquid pyrolysis.

 On the other hand, the use of a large amount of solvent has the effect of cooling the glass ribbon so that the organometallic compounds may not be decomposed satisfactorily by heat, which leads to layers of properties. mediocre.

 The solutions of the zinc and aluminum compounds, which can be used to form the layers according to the invention, contain an atomic percentage of aluminum relative to the zinc, ie Al% solution = nA J n ,, / n ,, + nz =, between 0.05 and 0.3%, n being the number of moles of the compounds.

 The presence of the particular compounds, according to the invention, aluminum isovalerylacetonate and compound of non-halogenated zinc and comprising oxygen, in non-aqueous solution as indicated above, makes it possible to obtain, on the glass substrate, by liquid pyrolysis , a transparent layer which adheres well, which is homogeneous and has a very uniform thickness, a thickness which, for example, can be between 80 nm and 500 nm.

 As indicated above, a non-halogenated zinc compound is used to avoid the formation of sodium chloride, due to the presence of sodium ions in the glass which migrate when the glass is hot. This makes it possible to obtain a layer having better optical characteristics.

 To improve the optical characteristics of the layers according to the invention, use is preferably made of a non-aqueous solution of the metal compounds since it has been noted that the layers obtained from an aqueous solution could have a certain white diffusing haze.

 The use of an aluminum chelate such as aluminum isovalerylacetonate has advantages. In particular, it is easily dissolved in the solvents used for the zinc compound to obtain solutions of viscosity suitable for spraying. On the other hand, this chelate allows a high deposition rate, which is, for example, three times greater than that obtained with aluminum acetylacetonate; this is an important factor when the deposition takes place on a glass manufacturing line where the glass ribbon can pass, as indicated above, at a speed of between 3 and 25 m / min.

 The percentage of aluminum in the spray solution is an important factor for the production of layers according to the invention. Indeed, the amount of aluminum, present in the solution used for spraying, influences the pyrolysis yield and acts on the thickness of the layers formed.

 Thus, under identical deposition conditions, when the atomic percentage of aluminum in the solution increases, the maximum thickness of the layers that can be obtained decreases. This factor must therefore be taken into account since the resistivity of the layers decreases notably when the thickness of the layers increases.

 In addition, to obtain layers of low resistivity, the amount of aluminum used must be controlled. Too much aluminum would lead to the risk of formation of alumina, a poorly conductive compound, which would lead to an increase in resistivity.

 On the other hand, we know that the resistivity depends on the number of charge carriers and their mobility. The charge carriers are linked to the aluminum atoms substituted for the zinc atoms, because it is they which provide the conduction electrons. However, it has been observed that, in the layers obtained according to the invention, that is to say by liquid pyrolysis and reducing treatment, the number of charge carriers increases with the atomic percentage of aluminum in the layer, then decreases. As regards the mobility of these charge carriers, it decreases when the atomic percentage of aluminum in the layer is increased.

 Thus, the atomic percentage of aluminum in the solution used for spraying (and therefore that in the layer obtained) must be controlled in order to obtain layers having low resistivities. According to the invention, as indicated above, an atomic percentage of aluminum in the solution of between 0.05 and 0.3% has been chosen, leading to an atomic percentage of aluminum in the layer of between 1 and 2% approximately. .

 The carrier gas used for atomizing the solution is generally air or an inert gas such as nitrogen and argon so as to limit the quantity of oxygen at the time of pyrolysis and thus avoid or reduce the alumina formation.

 The flow rates of the solution and of the carrier gas, as mentioned above, must be carefully controlled since these are parameters involved in obtaining the desired thickness of the layer and its resistivity. Indeed, the flow rates of the solution and of the carrier gas determine the quantities of metallic compounds which reach the support and it has been noted that the resistivity of the layers, of the same thickness, increases with the flow rate of solution.

 For carrying out the invention, it was determined that the flow rate of the solution was preferably between 25 and 35 l / h and that of the carrier gas between 25 and 40 m3 / h.

 According to the invention, the zinc oxide layer doped with aluminum, obtained by liquid pyrolysis, is subjected to a reducing treatment. This treatment improves and stabilizes the electrical properties of the layer. This treatment, or reducing annealing, takes place in a reducing atmosphere consisting of nitrogen and from 0 to 10% by volume of hydrogen. It is carried out in several phases.

The first is a phase of slow rise in temperature to about 4500C, if the temperature following the pyrolysis is lower than this value or if the reducing annealing does not take place immediately after the pyrolysis. The slow rise in temperature makes it possible to avoid any thermal shock which could break the glass. The second phase consists in maintaining the glass carrying the layer at the temperature of the order of 450 "C for approximately 45 min to 60 min.

Too high a temperature, for example 500au and above, as well as a longer duration could lead to deterioration of the semiconductor layer. The third phase consists of gradual cooling, always under a reducing atmosphere, to room temperature.

 It seems that the annealing is all the more effective when it is carried out on thin layers.

 By the process of liquid pyrolysis and reducing annealing, according to the invention, carried out under specific conditions, it is possible to obtain glazings which are formed from a glass support and a layer of doped zinc oxide. with aluminum, containing an atomic percentage of aluminum between 1 and 2% and having a thickness of 80 to 500 nm.

 These layers have a resistivity less than or equal to 5 x 10-3 Q.cm and also have a light transmission of 80 to 85%, when they are formed on clear glass.

 The glass support can be formed from a soda-lime-silica glass conventionally used for automobile glazing and for buildings. It can be a clear glass, that is to say a non-colored glass, having a high light transmission, for example greater than 90% under a thickness of 4 mm. It may also be a glass colored in its mass capable of providing increased summer comfort for the passengers of the vehicle or of the premises equipped with such glasses, due to its reduced energy transmission. Generally, for automobile glazing for example, the glass constituting the substrate is chosen to comply with the regulations, that is to say a glass and layer assembly having a light transmission (T1) of at least minus 75% or 70% depending on the legislation.

 As colored glass, so-called "TSA" glass containing Fe2O3 can be used in weight proportions of the order of 0.55 to 0.62%, FeO for approximately 0.11 to 0.16%, which leads to a Fe2 + / Fe ratio of the order of 0.19 to 0.25, CoO for less than 12 ppm and even preferably for less than 10 ppm.

 This results in properties, for example, for a thickness of 3.85 mm, of high light transmission (T) close to 78%, (illuminant D65), a relatively low energy transmission factor (T) and close to 60, which leads to a ratio T, / T, of the order of 1.30.

 One can use as colored glass, in particular when the regulation imposes only a light transmission of 70%, a glass a little more colored than "TSA", but having on the other hand a slightly weaker light transmission, namely a "TSA2 +" glass.

 This "TSAZ" glass is colored with the same oxides as above but in slightly different proportions.

Thus, the proportions of metal oxides are as follows
Fe2O3: approximately between 0.75 and 0.90%
FeO: approximately between 0.15 and 0.22%
or FeZ + / Fe = about 0.20
CoO: less than 17 ppm and even preferably less
less than 10 ppm.

I1 results for this glass "TSA2 +", in 3.85 mm thickness the following properties Tr.: Of the order of 72%
TE: around 50%.

 This leads to a T / Tz ratio of the order of 1.40 or 1.50.

 The glass support preferably consists of a dealkalized glass at least on the surface. In fact, during the pyrolysis according to the invention, the glass is hot and the alkaline ions tend to migrate in the layer formed on the glass; this results in a decrease in the electrical and optical properties of the layer.

 To avoid the diffusion of alkaline ions in the semiconductor layer, it is also possible to form this layer on a sublayer, called barrier layer to the alkaline ions, previously formed on the glass support. This barrier layer is made, for example, of silica, silicon oxycarbide, silicon oxynitride, obtained for example by vapor phase pyrolysis.

 The following nonlimiting examples illustrate the invention.

EXAMPLE 1
A solution of zinc acetate in methanol is prepared in an amount of 50 g per liter of methanol. As regards the aluminum compound, a solution containing 30 g of aluminum isovaleryl acetonate per liter of ethyl acetate is used.

 The two solutions are mixed to have an atomic percentage of aluminum (Al% at = n ,, / n ,, + nz =) of 0.1%.

 This mixture is used in a spraying device, as described in French patent 2,176,760, to form a layer of zinc oxide doped with aluminum on float glass. The spraying device is arranged at the outlet of the float oven. The temperature of the clear glass substrate is approximately 550 ° C. and the running speed of the glass is 6 m / min.

 Nitrogen is used as the carrier gas at a rate of 34 m3 / h.

 The solution of metal compounds is sprayed onto the glass ribbon at a rate of 33 l / h from a spray gun which moves transversely to the direction of movement of the glass ribbon, at a speed of 2.5 m / s.

 An aluminum doped zinc oxide layer is obtained in which the atomic percentage of aluminum is 1.4%. This layer has a thickness of 490 nm.

 The layer is subjected to annealing, under a reducing atmosphere formed of a mixture of nitrogen and 10% hydrogen by volume.

 The temperature of the product is brought to 4500C and maintained at this value for 45 min; the product is then regularly cooled to room temperature. The resistivity of the layer, determined from the resistance per square, measured by the method as "four points", is 3 x 10-3 n.cm. The light transmission TL, determined for the illuminant D65, usually used for building, is 83%.

EXAMPLE 2
The procedure is as in Example 1.

 The support is clear glass.

 The solution used for spraying comprises an atomic percentage of aluminum of 0.2%.

 Pyrolysis carried out under the same conditions as in Example 1, makes it possible to obtain a layer of ZnO: Al with a thickness of 405 nm containing an atomic percentage of aluminum of 1.8%. After annealing, the layer has a resistivity of 4.6 x 10 -3 n.cm. It has a light transmission of 84.4%.

EXAMPLE 3
The procedure is as in Example 1, but the layer of ZnO: Al is formed on a glass support carrying a barrier layer to alkaline ions consisting of silicon oxycarbide with a thickness of 20 nm. The solution of metal compounds comprises an atomic percentage of aluminum of 0.2%.

Pyrolysis carried out under the same conditions as in Example 1, makes it possible to obtain a layer with a thickness of 340 min and containing an atomic percentage of aluminum of 1.8%.

 After annealing, the layer has a resistivity of 2.2 x 10-3 Q.cm and a light transmission of 84%.

The emissivity is 0.36. It may be noted that the presence of the silicon oxycarbide sublayer blocks the diffusion of the alkaline ions from the glass; this results in better resistivity for the ZnO: Al layer.

 The products according to the invention can also be useful as automobile glazing, for example heated glazing, in particular for forming windshields.

 In this case, these products can be combined with a plastic polymer sheet such as polyurethane placed in contact with the semiconductor layer to form a laminated glazing with a single glass support. The products according to the invention can also be combined with another glass plate by means of a plastic polymer sheet such as polybutyralvinyl, polyurethane or polyvinyl chloride, to form a laminated glazing with two glass plates .

 For the supply of electrical current to the semiconductor layer, these glazings comprise current leads, such as copper foils and / or silver screen-printed strips, arranged along the upper and lower edges of the glazings. The black enamel generally deposited on these glazings to hide, in particular, the current leads, is not denatured by the presence of the layer of ZnO: Al.

Claims (22)

 1. A method of forming a transparent semiconducting layer of zinc oxide doped with aluminum on a glass support, characterized in that it consists in spraying onto this support of glass heated to a temperature below its softening temperature and between 5000C and 6500C, using a carrier gas, a solution of at least one zinc compound and an aluminum chelate thermally decomposable at the temperature of the support.  2. Method according to claim 1, characterized in that the glass support is in relative movement relative to the projection with a speed between 3 and 25 m / min and consists in particular of a glass ribbon at the outlet d '' a float glass manufacturing line.  3. Method according to one of the preceding claims, characterized in that the solution is non-aqueous.  4. Method according to one of the preceding claims, characterized in that the aluminum chelate is non-hydrolyzable.  5. Method according to one of the preceding claims, characterized in that the layer is subjected to a reducing annealing.  6. Method according to one of the preceding claims, characterized in that the zinc compound is a non-halogenated compound.  7. Method according to claim 6, characterized in that the zinc compound is zinc acetate or zinc nitrate.  8. Method according to claim 4 and to one of claims 6 or 7, characterized in that the non-hydrolyzable aluminum chelate is aluminum isovalerylacetonate.  9. Method according to any one of claims 1 to 8, characterized in that the solvent of the spray solution is methanol or ethanol.  10. Process according to any one of claims 1 to 9, characterized in that the solution contains an atomic percentage of aluminum relative to the zinc of between 0.05% and 3%.  11. Method according to any one of claims 1 to 10, characterized in that the carrier gas is an inert gas such as nitrogen or argon.  12. Method according to one of the preceding claims, characterized in that the carrier gas flow is between 25 and 40 m3 / h.  13. Method according to one of the preceding claims, characterized in that the flow rate of the liquid solution is between 25 and 35 l / h.  14. Method according to any one of the preceding claims, characterized in that the annealing takes place in a reducing atmosphere consisting of nitrogen and from 0 to 10% by volume of hydrogen and comprises a phase of temperature rise up to 'at 450 "C if necessary, a temperature plateau at 4500C for 45 min to 60 min and a regular cooling phase to room temperature.  15. Glazing obtained by the method according to one of the preceding claims comprising a glass support and a layer of zinc oxide doped with aluminum containing an atomic percentage of aluminum of between 1 and 2%, having a thickness between 80 nm and 500 nm, a resistivity less than or equal to 5 x 10 -3 Q.cm.  16. Glazing according to claim 15, characterized in that it comprises a barrier sublayer to alkaline ions.  17. Glazing according to claim 16, characterized in that the sub-layer is formed of silica, silicon oxycarbide or silicon oxynitride.  18. Glazing according to one of claims 15 to 17, characterized in that the support is formed of a clear or colored silica-soda-lime glass.  19. Glazing according to any one of claims 15 to 18, characterized in that the support is clear glass and in that the glazing has a light transmission between 80 and 85%.  20. Glazing according to one of claims 15 to 19, characterized in that the support is formed from a dealkalized glass.  21. Use of the glazing according to one of claims 15 to 20 as heated laminated glazing which comprises, in contact with the semiconductor layer, a sheet of polymer of plastic polymer, in particular of polyurethane, and current leads arranged on along the upper and lower edges of the glazing.  22. Use of the glazing according to one of claims 15 to 21, as heated laminated glazing which comprises, in contact with the semiconductor layer, an interlayer sheet of plastic polymer of the PVB, PVC or PU type, associated with a plate glass, and current leads arranged along the upper and lower edges of the glazing.