DE102011107123A1 - Preparing surface coating with microstructure lattice on transparent carrier element, by applying precursor with transparent conductive oxide on carrier element by wet-chemical method, and drying the precursor with the conductive oxide - Google Patents

Abstract

The method comprises applying a precursor with a transparent conductive oxide (TCO) on a carrier element (2) by a wet-chemical method, drying the precursor with the TCO, irradiating the applied precursor with a laser along a pattern, where the precursor is sintered along the pattern, and removing a non-sintered precursor with the TCO from the carrier element using a solvent so that the sintered precursor remains on the carrier element and forms a microstructure lattice (10). The wet-chemical method is a sol gel method. The precursor contains a metal salt. The method comprises applying a precursor with a transparent conductive oxide (TCO) on a carrier element (2) by a wet-chemical method, drying the precursor with the TCO, irradiating the applied precursor with a laser along a pattern, where the precursor is sintered along the pattern, and removing a non-sintered precursor with the TCO from the carrier element using a solvent so that the sintered precursor remains on the carrier element and forms a microstructure lattice (10). The wet-chemical method is a sol gel method. The precursor contains a metal salt, and is dissolved in the solvent with an organic complexing agent. The precursor with the TCO and the laser is coordinated to each other so that the precursor with the TCO strongly absorbs an emitted wavelength (248 nm) of the laser. The laser is an excimer laser. An independent claim is included for a solar collector.

Description

The invention relates to a method for producing a surface coating with a microstructure grid of transparent conductive oxide on a transparent carrier element according to the preamble of patent claim 1, as well as a solar collector with such a surface coating according to the preamble of patent claim 11.

Microstructure gratings applied to a carrier element have webs of a material and interstices, either no material at all being present in the interspaces, or else the layer thickness of the material being substantially smaller than in the region of the webs.

Applied to a translucent support element such microstructure gratings are suitable for selectively allowing radiation of different wavelengths to pass or reflect. For this purpose, the microstructure grating ideally has layer thicknesses in the region of the ridges of 0.25-0.45 μm, ridge widths of 0.2-0.8 μm and ridge spacings of 1-3 μm. A microstructure grating of such size has a high transmissivity for light having wavelengths of 400-2,500 nm, but acts as a mirror for infrared heat radiation (wavelength about 10 μm).

These properties are suitable in many applications to achieve improvements compared to a surface coating consisting of a continuous thin layer of material. For example, such thin metal material layers are used in building technology as mirroring of window glass and also for heat-insulating glazings. Such windows are largely transmissive to visible light (wavelength 400-800 nm) and at the same time reduce heat exchange by infrared heat radiation from one side of the window to the other. However, they do not allow near-infrared radiation (800-2,500 nm wavelength) to pass, which accounts for approximately one third of the solar radiation energy.

For use as a cover plate of a solar collector, such full-surface coated disks are therefore much worse than a glass pane with microstructure-grid coating, which just lets the near-infrared radiation pass. In the case of a cover plate with a microstructure grid, sunlight can enter the solar collector almost unhindered, while at the same time radiation losses due to infrared heat radiation are very low. As a result, more solar radiation energy per area can be used.

US 2004/0036993 A1 describes several methods for producing such a microstructure grating on a translucent support element. Among others, coating materials of indium tin oxide and antimony tin oxide are used. These are among the so-called transparent conductive oxides [TCO].

In a first method, an alignment of material particles on a support member along a magnetic field is provided which is subsequently cured. Since magnetic field lines extend only in one direction, at least a two-stage production with different alignment of the field lines to the carrier element is necessary to produce a grid. In addition, the magnetic alignment limits the material selection and / or the possible lattice spacings. Large coating areas also require the use of very large and strong electromagnets to generate a homogeneous magnetic field.

Another method alternative described is an alignment of the material particles by ultrasound. However, this method is hardly suitable for large-scale production of larger surfaces at desired low production costs. Likewise, described ink jet printing methods are unsuitable. To use a proposed embossing process requires very expensive tools, eg. B. produced by photolithography, the fine structures are also quickly contaminated and lead to errors in the microstructure grid produced therewith.

Further describes US 2004/0036993 A1 an etching process by means of a mask, so that holes are etched into a material layer already applied to a light-transmissive element. However, this has the significant disadvantage that the etchant used penetrates at different speeds up to the carrier element and then also etches the carrier element, so that its light transmittance is reduced. Alternatively, a laser method is described in which, in turn, a closed material layer is first applied to the carrier element and cured before the interspaces between the bars are removed by means of a laser. This process is time consuming and is also not suitable for mass production with low production costs.

None of these processes could until today be transferred to mass production due to the existing problems.

The object of the invention is therefore to provide a method for producing a surface coating with a microstructure grid of transparent conductive oxide, which overcomes the disadvantages of the prior art and a cost-effective mass production allowed, wherein the microstructure grid is in particular also to be suitable to improve absorption of solar energy with a solar collector.

This is achieved with the characterizing part of claim 1 and the characterizing part of claim 11 according to the invention. Advantageous developments are given in the dependent claims 2 to 10 and 12.

• a) Aufbringen eines Precursors mit dem TCO durch ein nasschemisches Verfahren auf das Trägerelement,
• b) Bestrahlen des aufgebrachten Precursors mit einem Laser entlang eines Musters, wodurch der Precursor entlang des Musters gesintert wird,
• c) Entfernen des nicht gesinterten Precursors vom Trägerelement, sodass der gesinterte Precursor auf dem Trägerelement zurückbleibt und ein Mikrostruktur-Gitter bildet.

In a method for producing a surface coating with a microstructure grid of transparent conductive oxide [TCO] on a light-transmissive support element, the invention provides the following steps:

• a) applying a precursor to the TCO by a wet-chemical method onto the carrier element,
• b) irradiating the deposited precursor with a laser along a pattern, whereby the precursor is sintered along the pattern,
• c) removing the non-sintered precursor from the carrier element so that the sintered precursor remains on the carrier element and forms a microstructure grid.

In particular, indium-tin oxide, fluorine-tin oxide, aluminum-zinc oxide and antimony-tin oxide can be used as TCOs. Particularly suitable for the support element is low-iron glass with high solar transmission.

The method according to the invention allows a coating of large surfaces, since coating devices for wet-chemical processes are available in sufficient size and also a laser guidance over a large area can be designed. After the application of the precursor to the carrier element is not necessarily a separate drying of the precursor necessary before the laser is used.

During the irradiation, in the region of the laser beam, first of all, substantially the liquid present in the precursor evaporates, in particular the solvent. Immediately afterwards, the dried precursor hardens during laser irradiation through sintering processes. In this case, the remaining material of the precursor is also firmly connected to the carrier element. For this purpose, the irradiation intensity and wall should preferably be designed so that the precursor heats up to just below the melting temperature of the TCO in the irradiation area. The few and selected process steps of the surface coating are very fast, whereby the production costs are low.

Since the ridge widths of the microstructure grating are generally smaller than their spacing, the working time of the irradiation with the laser is also very low. In particular, it is significantly lower than a laser ablation in the area between the desired webs, as proposed in the prior art.

The contours of the support member may well be different and, for example, glass panels of different contour and thickness are coated on a production line. Accordingly, the tooling costs and the manufacturing costs are comparably low, since only a few special tools are required for different glass pane contours. In particular, different recordings may be necessary. The laser, on the other hand, can process different glass pane contours by means of different programs, as well as different patterns, so that different types of microstructure grids can be produced.

As a pattern, for example, a grid could be traversed, so that the microstructure grid thus produced forms a network structure. In such a the web widths and distances are relatively homogeneous and the spaces are rectangular or diamond-shaped. Preferably, the width of the webs between 0.2 and 0.8 microns, and the diameter of the interstices between 1 and 3 microns.

Depending on the application, however, other patterns can be traced with the laser. For example, by tracing a first serpentine line and a half-phased serpentine line, a microstructure grating could be created with gaps formed as round holes. If there are no further gaps, the webs in the area of the web connections / crossings are significantly wider than between two connection points. Alternatively, there is another space between at least three adjoining round holes.

Finally, the transmissivity can also be adjusted by not forming a closed path pattern, but activating and deactivating the laser on the path. Such a sintered precursor forms a microstructure grating, which consequently has no contiguous webs. If the pattern consists of dots, a microstructure grid can be formed as grain or granularity. However, the particular wavelength selectivity is largely lost because of the low surface conductivity.

According to a variant of the method, it is provided that the wet-chemical method is a sol-gel method. This method is suitable very good for a uniform application of the precursor to the support element. In the subsequent sintering by means of the laser thus creates a very uniform microstructure grid, in particular with regard to the web widths, web heights and web distances. As a result, the transmissivity of the microstructure grating is very easily adjustable. In the case of a non-uniform application, however, the energy of the laser would lead to different heat distributions in the precursor around the pattern worn off by the laser. The web widths would subsequently have a larger web width in zones with thin application than with thick application. At locations where the job is too thick, the land would not be fully formed and bonded to the support member so that it would be destroyed in the removal of the unsintered precursor. These problems can be effectively prevented with the sol-gel method.

An important variant of the method includes, as an intermediate step, drying of the precursor with the TCO after application to the carrier element and before irradiation with the laser. For drying, the precursor and / or the carrier element can be conditioned. In this case, a fully comprehensive conditioning of the entire surface coating or a partial conditioning can be considered. For full-scale conditioning, the support element with the applied precursor can be introduced, for example, into a climatic chamber, or it passes through a conditioning line. Among other things, the temperature, the ambient pressure and the humidity during drying can be changed. During drying, it is primarily the liquid constituents of the precursor, in particular the solvents, that evaporate. It creates a continuous surface coating, which is not very resistant.

Only then is the applied precursor irradiated with a laser along a pattern, whereby the precursor is sintered along the pattern. Consequently, the laser does not first have to evaporate the solvents before it comes to sintering. The laser can therefore have a higher travel speed, whereby the laser process takes only little time. This reduces the manufacturing costs of the surface coating, since the laser system has higher machine hour cost rates than a conditioning device. In addition, the quality of the microstructure grating is very high.

The precursor with the TCO may include at least one metal salt and be dissolved in a solvent with at least one organic complexing agent. Complexing agents are used to bind or remove metals and, above all, to dissolve them. By means of the complexing agent, the metal salts and other ingredients of the precursor can be converted by the complex formation in a readily soluble compound. Resulting solutions with the organometallic complexing agents are therefore stable, d. H. For example, none of the ingredients settle or flocculate. Thus, the precursor in its composition, d. H. Adjust the percentage of its ingredients in a wide range, which also allows a uniform and stable application of the precursor to the support element.

In a variant of the method, the precursor with the TCO and the laser are coordinated so that the precursor with the TCO strongly absorbs the emitted wavelength of the laser. The absorbency of a material is indicated by the proportion of unreflected light. A complete reflection is assigned the absorption degree zero and a complete absorption of the absorption degree 1. Highly absorbent material according to the invention has at least a value of 0.7. As a result, the energy of the laser is transferred very well to the precursor, since the laser radiation is strongly absorbed. Consequently, less energy is consumed in the irradiation and the irradiation time per area can be very short, whereby the production time is low. Thus, the manufacturing costs are low.

Preferably, the precursor with the TCO should contain at least indium and / or tin and / or zinc oxide and at least one doping element. The most important doping elements are the trivalent elements boron, aluminum and gallium for a p-type doping, and the pentavalent elements phosphorus, arsenic and antimony for an n-type doping. Microstructure gratings made with such a precursor are transparent not only in the area of the interspaces, but also in the region of the webs. For infrared heat radiation, however, such a microstructure grid acts as a mirror, since it is electrically conductive in this frequency range and the correspondingly fine structures of such large wavelengths can not be resolved.

An embodiment of the method provides that the laser emits a wavelength of approximately 248 nm. The wavelength can deviate by 10 nm from 248 nm. Such ultraviolet radiation is particularly well suited for lasering a very fine pattern to create the microstructure grating. Excellent results are achieved at such a wavelength, for example, with a precursor containing tin oxide (SnO). Most preferably, the laser is an excimer laser. Ideally, the excimer laser contains krypton fluoride [KrF]. Equipped with such a mixed gas, the excimer laser is capable of emitting a light wavelength of 248 nm.

To remove the non-sintered precursor with the TCO from the carrier element, provision may be made for it to be removed from the carrier element by means of a solvent. With the solvent, the precursor could be rinsed off or sprayed off. As a result, the non-sintered precursor is reliably removed from the interstices of the microstructure grid, without damaging the latter. Subsequently, a very high transmissivity for light of certain wavelengths r reaches, since no residues remain in the interstices. Alternatively or additionally, the non-sintered precursor can also be blown off with compressed air or nitrogen, or a brush can be used for brushing off.

If necessary, the entire process may also be repeated at least a second time. Thus, at least twice a precursor is applied to the carrier element, a pattern is traversed by means of the laser and then the non-sintered precursor is removed. In this way, higher web heights can be achieved.

• a) Aufbringen eines Precursors mit dem TCO durch ein nasschemisches Verfahren auf das Trägerelement,
• b) Bestrahlen des aufgebrachten Precursors mit einem Laser entlang eines Musters, wodurch der Precursor entlang des Musters gesintert wird,
• c) Entfernen des nicht gesinterten Precursors vom Trägerelement, sodass der gesinterte Precursor auf dem Trägerelement zurückbleibt und ein Mikrostruktur-Gitter bildet.

To protect the microstructure grid against external influences such as mechanical effects or chemical reactions, a protective shaft can be applied over the microstructure grid. Such then preferably consists of SiO _x N _y or SiO ₂ . The invention further relates to a solar collector with a light-transmitting carrier element arranged on the sun-facing side, on which a surface coating having a microstructure grid is arranged, in which the surface coating is produced by the following steps:

• a) applying a precursor to the TCO by a wet-chemical method onto the carrier element,
• b) irradiating the deposited precursor with a laser along a pattern, whereby the precursor is sintered along the pattern,
• c) removing the non-sintered precursor from the carrier element so that the sintered precursor remains on the carrier element and forms a microstructure grid.

The carrier element is then formed, for example, as a cover of the solar collector. Such a solar collector significantly improves the use of solar energy. Thus, more energy can be gained per roof area. This can be transferred from the solar collector, for example, to a refrigerant, which initially stores the energy and then transported to a destination. The cost of such a solar collector are only slightly higher than without the surface coating according to the invention and in relation to the significantly improved efficiency of solar energy makes sense.

The surface coating is preferably arranged on the side of the carrier element facing away from the sun. Here it is particularly protected against external influences such as flying objects and particles, whereby the life is high. In addition, the layer at this position, the heating of the support member by thermal radiation of the hot absorber down, thus improving the efficiency more efficient.

The drawings illustrate embodiments of the invention and show in FIG

1 an enlargement of a surface coating with a microstructure grid, wherein the structure forms a network structure;

2 an enlargement of a carrier element with applied precursor and sketched pattern along which a laser is to travel; and

3 a solar collector with a surface coating.

1 shows an enlargement of a surface coating 1 with a microstructure grid 10 made of transparent conductive oxide TCO on a translucent support element 2 ,

The microstructure grid 10 consists of bars 11 and spaces 12 , The bridges 11 have a minimal irregular web width. This is due to very small differences in the sintering speed, which may be due for example to machine vibrations and the smallest layer thickness differences of the precursor. Ideally, the web width is homogeneous. In the intervals 12 is no TCO available, so that the support element 2 is recognizable. According to the scale shown, it can be seen that the width of the webs 11 less than 0.5 μm and the spaces between them 12 are about 1 micron wide.

• a) Aufbringen eines Precursors mit dem TCO durch ein nasschemisches Verfahren auf das Trägerelement,
• b) Bestrahlen des aufgebrachten Precursors mit einem Laser entlang eines Musters M, welches in 1 gezeigt ist, wodurch der Precursor entlang des Musters M gesintert wird,
• c) Entfernen des nicht gesinterten Precursors vom Trägerelement, sodass der gesinterte Precursor auf dem Trägerelement zurückbleibt und ein Mikrostruktur-Gitter bildet.

Such a surface coating according to the invention 1 with microstructure grid 10 made of transparent conductive oxide TCO on a translucent support element 2 can be produced by a process in which the following steps are carried out:

• a) applying a precursor to the TCO by a wet-chemical method onto the carrier element,
• b) irradiating the deposited precursor with a laser along a pattern M, which in 1 is shown, whereby the precursor is sintered along the pattern M,
• c) removing the non-sintered precursor from the carrier element so that the sintered precursor remains on the carrier element and forms a microstructure grid.

According to 2 For example, a pattern M is described which moves a laser along one on a carrier element 2 irradiated deposited precursor with TCO along the pattern M. The pattern consists of staggered serpentine lines, each composed of semicircles juxtaposed, and connecting paths to move from one serpentine to the next. By displacing two serpentine lines by half a phase, a microstructure grating with circular gaps can be made. The harmonic movements of the laser shown with the pattern M lead to an exact irradiation time per area, whereby the web width of the sintered precursor is very homogeneous. In addition, such very fast travels of the laser can be realized, whereby the production time and the manufacturing costs of a surface coating produced in this way are low.

3 describes a solar collector 100 with a light-transmissive support element arranged on the sun-facing side SZ 2 on which a surface coating 1 with a microstructure grid 10 is arranged. In particular, the surface coating 1 on the side facing away from the sun SA of the support element 2 arranged.

LIST OF REFERENCE NUMBERS

1

surface coating

2

support element

10

Microstructure lattice

11

web

12

gap

100

solar collector

M

template

SA

sun-facing side

SZ

sun-facing side

TCO

transparent conductive oxide

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2004/0036993 A1 [0006, 0009]

Claims (12)

Process for producing a surface coating ( 1 ) with a microstructure grid ( 10 ) of transparent conductive oxide [TCO] on a light-transmitting carrier element ( 2 ), comprising the following steps: a) application of a precursor to the TCO by a wet-chemical process on the carrier element ( 2 b) irradiating the deposited precursor with a laser along a pattern (M), whereby the precursor is sintered along the pattern (M), c) removing the non-sintered precursor from the carrier element ( 2 ), so that the sintered precursor on the carrier element ( 2 ) and a microstructure grating ( 10 ). Process for producing a surface coating ( 1 ) according to claim 1, characterized in that the wet-chemical process is a sol-gel process. Process for producing a surface coating ( 1 ) according to one of claims 1 or 2, comprising as an intermediate step, the drying of the precursor with the TCO after application to the carrier element ( 2 ) and before irradiation with the laser. Process for producing a surface coating ( 1 ) according to any one of the preceding claims, characterized in that the precursor with the TCO contains at least one metal salt and is dissolved in a solvent with at least one organic complexing agent. Process for producing a surface coating ( 1 ) according to one of the preceding claims, characterized in that the precursor with the TCO and the laser are coordinated so that the precursor with the TCO strongly absorbs the emitted wavelength of the laser. Process for producing a surface coating ( 1 ) according to one of the preceding claims, characterized in that the precursor with the TCO contains at least indium and / or tin and / or zinc oxide and at least one doping element. Process for producing a surface coating ( 1 ) according to one of the preceding claims, characterized in that the laser emits a wavelength of approximately 248 nm. Process for producing a surface coating ( 1 ) according to one of the preceding claims, characterized in that the laser is an excimer laser. Process for producing a surface coating ( 1 ) according to claim 7, characterized in that the excimer laser contains krypton fluoride [KrF]. Process for producing a surface coating ( 1 ) according to one of the preceding claims, characterized in that the non-sintered precursor is removed with the TCO by means of a solvent from the carrier element. Solar collector ( 100 ) with a light-transmitting carrier element (FIG. 2) arranged on the side facing the sun (SZ) 2 ), on which a surface coating ( 1 ) with a microstructure grid ( 10 ), characterized in that the surface coating ( 1 ) is produced according to one of claims 1 to 10. Solar collector ( 100 ) according to claim 11, characterized in that the surface coating ( 1 ) on the side facing away from the sun (SA) of the support element ( 2 ) is arranged.

Images