DE19526733A1 - Patterned solar cell for building fascia or roof panel - Google Patents

Abstract

The solar cell has a flat semiconductor body (1) incorporating a diode structure, having current conducting contacts (2) on the rear side and an anti-reflection coating (3) on the front side. The anti-reflection coating is fully or partially removed in selected areas (6,7)to provide a required visual pattern. Pref. the pattern is formed by removing the anti-reflection coating to different depths, via an etching process, to provide optically readable, 2-dimensionable, alphanumeric characters.

Description

Usually solar cells become decentralized energy ver supply used. They can be network-independent Power supply or to support an already best serving central power grid. For a complete Power supply of residential or office buildings are, however, min at least a few square meters of solar cell area required. To set up the solar modules that the desired electri make available, must therefore be considerable Parts of roof and facade surfaces covered with solar modules will.

It has therefore already been proposed to use solar modules as a facade denelemente or building roof elements, the So lar cells or modules in addition to energy generation covering, covering, insulating, supporting or other of great functional importance. As well visible Facade element it also serves for the optical design of Facades.

An individual design of solar modules for at for example facade elements is because of the first Line desired technical function of electricity generation only limited possible. For example, the shape is possible or arrangement of the individual solar cells on a solar module to vary, to change the external shape of the solar module or the solar module with already designed facade elements to combine. However, one is always on the flat Solar modules and bound to the shape and color of the solar cells. A colored or patterned coating of solar modules ver offers itself because of the associated shading of So lar cells that produce reduced photovoltaic energy result.  

The object of the present invention is therefore a solar cell to indicate with which any pattern is represented with which, for example, building facades can be designed can be tet and which is not a significant disadvantage suffering from their photovoltaic energy generation. The Manufacturing process should come with existing manufacturing processes be patible and not significantly impair the perform actual solar cell functions.

This object is achieved by a solar cell Claim 1 solved. Advantageous embodiments of the Erfin a method of making the pattern and before preferred uses of the solar cell according to the invention are the further claims.

The basic idea of the invention is to create a desired predetermined pattern by structuring the anti-reflection to produce a layer. So the pattern is on the front the solar cell formed on the in certain areas Anti-reflective layer is partially or completely removed. It is surprising and advantageous that the efficiency of such a patterned solar cell only insignificantly is greater than that of a solar cell with complete and un anti-reflective coating. Otherwise all essential radio tional characteristics of the solar cell are unchanged the invention a fully functional solar cell available supply, which can also be influenced in design and with the front is a medium for recording or displaying a Provides patterns. This pattern can be a be a regular graphic pattern, any image represent or even information such as one Play lettering.

If you lay both contacts of the solar cell (p and n) on the Back of the solar cell (such as the "Interdigi  tated back contact solar cell ") so the front is complete free for the optical design.

In a further embodiment of the invention, generate a partial pattern on a single solar cell and then several solar cells with this or another partial pattern to a larger pattern in a solar module put together. This way, even large format Patterns, pictures or information can be displayed.

The optical recognizability of the pattern results from the different reflection of areas with intact Anti-reflective coating and the areas with at least partially removed anti-reflective layer. Usually one becomes two biges pattern obtained, the areas without antireflection layer the color of the semiconductor material used again give and for example a crystalline semiconductors can have metallic shine. The one with antireflection Areas covered with layers appear in the color that the Complementary color of the in the anti-reflective layer corresponds to the "extinguished" wavelength. An optimal antire flex layer prevents the reflection of light in a speculum tral range, the maximum sensitivity of the solar cell corresponds. Optimal solar cells made of crystalline silicon therefore appear in a dark blue because of their absorption maximum is in the red range (corresponds to 800 to 900 nm). For example, an anti-reflective layer that appears blue achieved with 70 nm titanium oxide or 90 nm silicon oxide. Also with Anti-reflective layers made of silicon nitride or magnesium fluoride, which have a thickness calculated according to the λ-quarter rule, a blue anti-reflective layer can be created.

However, about the layer thickness of the anti-reflective layer other colors can also be set. With increasing Therefore, an anti-reflective layer appears in the layer thickness Colors brown, purple, blue, yellow, green, pale blue and close silver again (over a reflective surface).  

In addition to two colored patterns, solar cells according to the invention However, len also have multi-colored patterns. This is with Reached solar cells, the front of which is in areas is divided, in which the anti-reflective layer at least two un assumes different layer thicknesses. This can be done by taking different abbots protrude from one area th anti-reflective layer can be achieved. However, it is possible also, the anti-reflective coating in different areas of the To produce solar cells in different thicknesses. This can a thin anti-reflective layer in certain areas to Er creation of a pattern by another thin anti-reflection layer to be reinforced. In addition, for multilayer AR layers different materials are applied, which are selectively etchable (e.g. TiOx and SiN). Not Layer areas to be reinforced can be covered with a Protective varnish to be covered.

The invention is independent of the semiconductor material from which the solar cell is manufactured. It is executable with all Chen solar cells / antireflection combinations, limited but beneficial to those solar cells for which already effective anti-reflective coatings are known. Particularly suitable are solar cells with an optically homogeneous smooth surface, especially monocrystalline solar cells. But also polycri stalline solar cells, for example made of polycrystalline Si Silicon are suitable for the invention. About the above too Flat crystal structure becomes an additional achieved pattern effect. Even solar cells with textured Surface, for example crystalline solar cells with kri stable-oriented etched [100] oriented surfaces suitable. In addition to the element semiconductors, there are also connections semiconductors with homo- or heterojunction are suitable.

The solar cell can have current dissipating con have clocks. These contacts can also be in the form of Mu star. The contacts can be in the  Semiconductor layer be buried, directly on the semiconductor body or applied over the anti-reflective layer. Of the last case requires additional contacting through the anti-reflective layer, which is usually made of a Dielek is trained. This via can be used for for example by baking a screen printing paste.

In solar cells according to the invention with front contacts it is advantageous to contact the shape and structure of the front to integrate into the pattern created in the anti-reflective layer freeze.

However, it is particularly advantageous to have solar cells without a front to use side contacts. Have such solar cells on the back both p⁺ and n⁺ doped areas, which makes electrical contact via separate metallizations are and thereby become functional.

In the following, the invention is illustrated by means of an embodiment game and the associated five figures explained in more detail.

Figs. 1 to 4 show cross-sections with reference to schematic views of a solar cell, various process steps in the production, while

Fig. 5, the front side of a solar cell according to the invention shows in a top view.

Embodiment

Fig. 1 is a solar cell made of crystalline silicon is made up of a p-type semiconductor body 1 . A phosphorus diffusion produces an n⁺-doped region in the front, which forms a pn junction with the rest of the semiconductor body 1 . On the back, a back contact 2 is applied, for example by printing on the entire surface and baking an electrically conductive paste.

Above the n⁺-doped region 8 of the front there is a thin anti-reflective layer 3 , which is produced, for example, by oxidation of the semiconductor body or by thin-layer deposition of silicon oxide, silicon nitride, titanium oxide or magnesium fluoride. The front side contacts not shown in the figure can be under the anti-reflective layer 3 , embedded in the anti-reflective layer or applied to the anti-reflective layer.

To define the pattern in the anti-reflective layer 3 , a photoresist layer 4 is applied over the entire surface.

Fig. 2: the photoresist layer in the area 5 is removed from the anti-reflective layer 3 by imagewise exposure of the photoresist layer 4 and then developing. The areas 5 form a pattern on the solar cell.

Fig. 3: the pattern comprising the photoresist structure is now used as an etch mask to remove the anti-reflection layer 3 in the regions 6 for which are not covered by the photoresist mask. The etching of the anti-reflective layer 3 is preferably carried out in a wet mix with an acidic solution. For etching the antireflection layer 3 consisting of silicon oxide in the exemplary embodiment, hydrofluoric acid buffered with ammonium fluoride is suitable. Antireflection layers made of the other materials mentioned can also be removed with this or other acidic solutions, nitric acid being particularly suitable for an antireflection layer made of magnesium fluoride.

The complete etching of the anti-reflective layer 3 in the areas 6 requires only a few seconds due to the small layer thickness of 90 nm here. The solar cell is then rinsed off with water and the photoresist mask is removed. The solar cell he shows shows the pattern provided by the photoresist mask in the form of the optically recognizable and silvery shimmering pattern 6 in the anti-reflective layer.

Fig. 4: In a further embodiment, the At tion of the anti-reflective layer is carried out with a weaker etchant, for a shorter period of time and / or at a lower temperature than in the first embodiment. In this way, it is possible to transfer the structure 5 specified with the photoresist mask into the form of regions 7 in the antireflection layer, in which the latter is only partially removed to a residual layer thickness. However, it is simpler to produce a multilayer antireflection layer from selectively etchable materials and to produce the pattern at least partially by selectively etching only a partial layer of the antireflection layer. In a further method step, as in the first exemplary embodiment, additional depressions 6 can be produced in accordance with a further pattern. The solar cell obtained has a three-color pattern in which the color of the depressions 6 differs from the color of the depressions 7 and the color of those areas with an undamaged anti-reflective layer.

In a further exemplary embodiment, areas of different thicknesses can be produced in the antireflection layer by means of a photoresist technique, a further antireflection layer, preferably made of the same material, being deposited over the first antireflection layer instead of the etching step. This technique can also be combined with the first exemplary embodiment, whereby depressions 6 with a completely removed anti-reflective layer and depressions 7 with a thinner anti-reflective layer are obtained (see FIG. 4).

Fig. 5 shows the front of a so treated Solarzel le, which has a pattern 6 in the form of an alphanumeric character (here the letter "S"). However, it is also possible to generate any other graphic, geometric, pictorial or information-bearing pattern.

In a further exemplary embodiment, the photoresist mask by printing an anti-corrosion varnish in the form of a NEN pattern replaced. Of course, this then no longer needs be structured. The remaining procedural steps remain unchanged.

The same method can also be carried out with other types of solar cells, the actual structuring of the antireflection layer 3 remaining the same for all types of solar cells.

A solar cell according to the invention, which has an image with a 30 percent pattern 6 in the antireflection layer, shows an output of at least 90 percent compared to an otherwise unchanged solar cell with a complete antireflection layer. A correspondingly finer pattern 6 , which takes up a smaller proportion of the surface of the solar cell front, shows a correspondingly higher output. Pattern 7 , in which the anti-reflective layer is only partially removed, also shows higher performances.

Claims (9)

1. solar cell with

• - A flat semiconductor body ( 1 ) with a diode structure
• - Current-conducting contacts ( 2 ) on at least the back of the semiconductor body
• - An anti-reflective layer ( 3 ) on the front of the semiconductor body and
• - Formed in the form of a pattern areas ( 6 , 7 ) on the front, in which the anti-reflective layer is completely or partially removed.

2. Solar cell according to claim 1, wherein the pattern ( 6 , 7 ) consists of different areas be, which differ by the layer thickness of the anti-reflective layer. 3. Use of a solar cell with structured anti-reflection layer for power generation and at the same time for display of images, patterns or information. 4. Use of a solar cell with structured anti-reflection layer in a solar module in which several solar cells at least partially an optically recognizable pattern in the An have a tireflex layer, arranged two-dimensionally in this way are that by the totality of the patterns a larger two tes pattern is formed. 5. Method for producing an optically recognizable pattern ( 6 , 7 ) on the surface of a solar cell,

• - in which the solar cell is provided on the front with an anti-reflective layer ( 3 ),
• - In which an etching mask ( 4 ) is produced in the form of a pattern on areas of the antireflection layer,
• - In which the anti-reflective layer ( 3 ) in the areas not covered by the etching mask ( 5 ) is completely or partially removed by etching and
• - in which the etching mask is finally removed.

6. The method according to claim 5, in which a photoresist layer ( 4 ) is applied to produce the etching mask, exposed according to the pattern and then developed. 7. The method according to claim 51 in which the etching mask by printing a protective varnish is fathered. 8. The method according to any one of claims 5 to 7, in which an antireflective layer ( 3 ) made of oxide is generated over a solar cell made of crystalline silicon and in which the etching is carried out by treatment with an acidic solution. 9. The method according to any one of claims 5 to 8, with a multilayer on the front of the solar cell anti-reflective coating made of different materials is witnessed and in which the pattern at least partially selective etching of a partial layer of the multilayer anti reflective layer is generated.