DE102011089916A1 - Solar cell arrangement in tandem configuration - Google Patents

Abstract

The invention relates to a solar cell arrangement with a superstrate module (1) and a substrate module (2) in tandem configuration, wherein the superstrate module as a thin film module in the form of a-Si submodule (1a) of a-Si cells (3) and the substrate module in the form of a c-Si submodule (2a) is formed of contacted crystalline silicon elements (14) enclosed between transparent insulating layers.

Description

The invention relates to a solar cell arrangement according to claim 1 and a manufacturing method for such an arrangement according to claim 7.

State of the art

Solar cells are known in a tandem configuration. These consist of two sub-cells, a so-called top cell, which is oriented in the direction of the incident sunlight, and a so-called bottom cell located behind it. The tandem cells are then connected in series on the module. In such a structure, the different absorption and transmission properties of different materials are exploited so as to be able to use different wavelength ranges of the incident light for effective energy generation by a skillful vote between top and bottom cell.

The tandem cells are carried out according to the known state of the art as so-called 2-terminal components, which then have to provide both in lighting to avoid limitation both the same power. The o. G. However, the solution has a number of serious disadvantages. The known from the prior art standard tandem configurations with internal transition are limited mainly by the necessary power matching in their efficiency and applicability. As a result, in particular the structure based on thin silicon layers must be very different in its layer thicknesses in the case of the top cell from that of the bottom cell. The bottom cell must be made significantly thicker due to the lower absorption of the microcrystalline silicon material. In addition, electricity matching is subject to seasonal and regional fluctuations and is dependent on the given solar spectrum. In addition, the a-Si formed top cell is subject to light-induced degradation during the first 1000 hours of sunshine. Therefore, the layer thickness adjustments must also be adjusted to this degraded state. The efficiencies of such solar cells are partially below those expected for crystalline solar cell structures.

To avoid the mentioned disadvantages, a configuration is known from the prior art which consists of a decoupled a-Si top cell and a separate CIGS bottom cell. The decoupling is achieved by the design as a 4-terminal device. Both top and bottom cell are connected separately to their own modules by means of laser structuring in series. In this context, one then speaks of superstrate and substrate modules. A superstrate module is understood in this description to mean a first submodule of a solar cell arrangement in tandem configuration. Accordingly, a substrate module is understood to mean a second submodule of a solar cell arrangement in tandem configuration. The advantage of such a 4-terminal structure compared to the standard tandem technology is the avoidance of an internal transition and thus the elimination of a necessary matching of the generated photocurrent in top and bottom cell. Technical restrictions resulting from the condition of the current matching such. For example, strongly differing absorber thicknesses, mismatch due to spectral shifts etc. are canceled.

Disclosure of the invention

The object of the invention is therefore to specify a solar cell configuration which makes use of the above-mentioned advantages of a 4-terminal component, while making use of the advantages of the crystalline technology for the execution of the bottom cell.

This is achieved with a solar cell arrangement according to the features of claim 1 and a manufacturing method with the steps according to claim 7. The subclaims contain expedient and advantageous embodiments.

According to the invention, an arrangement is provided for a solar cell with a superstrate module and a substrate module, in which the superstrate module is a thin-film module of a-Si cells and the substrate module is in the form of contacted crystalline crystalline layers enclosed between transparent insulating layers Silicon elements is formed.

In contrast to the prior art, in which thin-film solar cells are assumed to produce the tandem configuration, according to the invention crystalline silicon is used as part of the substrate and thus a combination of a thin film and a thick-film module or a high-voltage module and a low-voltage module. It turns out that the combined properties of both modules in terms of efficiency, the performance of the entire solar module and manufacturing are extremely advantageous over the known configurations.

In a first embodiment, the a-Si cells of the superstrate have a reduced absorber thickness compared to known tandem configurations. This is accompanied by a lower material consumption, a better transmission and a significantly reduced light-induced degradation.

In a second embodiment, the a-Si submodule is formed as a light scattering antireflection unit for the c-Si submodule. This necessitates a complete omission of the otherwise customary antireflection coatings and surface structuring for the crystalline cell component, whereby the part of the solar cell structure used for solar energy generation likewise increases proportionately.

As an antireflective element of the antireflection layer, in an advantageous embodiment, a transparent conductive oxide layer of the a-Si submodule which is opacified by the action of light is used. This layer is already present in a-Si thin-film cells of their structure anyway.

Furthermore, the a-Si submodule acts as a blue filter for the c-Si submodule, thereby allowing the c-Si submodule to have increased doping of a p-emitter region compared to known configurations. This increased doping is otherwise problematic in crystalline cells, but can be used advantageously by the optical properties of a-Si.

Expediently, the c-Si submodule has a layer structure comprising an encapsulation film, contacted crystalline silicon elements, a further encapsulation film and a back glass or backsheet.

A method of manufacturing a solar cell comprising a superstrate module and a substrate module comprises the steps of providing a superstrate module with an amorphous silicon absorption layer, providing a substrate module of contacted crystalline silicon wafers enclosed in a sandwich arrangement, joining the superstrate and the substrate module. It can be used on existing production facilities. There is no additional manufacturing effort.

drawings

The arrangement according to the invention will be explained in more detail using an exemplary embodiment. To clarify serve the 1 and 2 , The same reference numbers are used for identical or equivalent parts.

Show it:

1 a known from the prior art configuration consisting of a decoupled a-Si and a CIGS submodule and

2 an exemplary configuration according to the invention.

Embodiments of the invention

1 first shows a tandem configuration according to the latest state of the art. The known configuration comprises a superstrate a-Si module and decouples a substrate CIGS module.

The contained semiconductor diodes are in the form of a layer structure of an absorber layer 4 including a p- and n-type contact layer. The semiconductor diodes are by trench structures 5a separated from each other and a existing example of TCO contacting 5 . 6 connected in series. The layers mentioned are on a front glass 7 or back glass 8th applied as a carrier material.

The substrate module, like the superstrate module, has a series connection of semiconductor diode cells. The layer structure essentially corresponds to the structure of the superstrate module. Instead of the a-Si layer, however, a CIGS layer is formed in the region of the substrate 8th used. This forms with a side oriented to the illuminated TCO layer 9 the photovoltaically activated boundary layers within the substrate module. As in the case of the superstrate module, in this area too there is a contact made, for example, of molybdenum 10 and one as a back-glass 11 designated rear carrier glass layer provided. Both the superstrate and the substrate module have electrode leads with contacts 12 on, via which the photovoltaic generated electrical voltages of the individual modules are tapped.

To bond the superstrate to the substrate is usually to a lamination 13 made of ethylene vinyl acetate (EVA) or polyvinyl butyral (PVB).

2 shows an arrangement according to the invention. This consists of an a-Si submodule arranged at the location of the superstrate 1a and a c-Si submodule located at the location of the substrate 2a , The a-Si submodule 1a essentially shows the structure of a conventional a-Si superstrate of the a-Si cells 3 with an a-Si layer 4 , a Rückseitungskontaktierung in the form of a TCO layer 5 , the front contacting 6 and the front glass 7 , The a-Si cells are also here through trenches 5a separated from each other. Furthermore, the contacts and electrode leads 12 arranged. On the reverse side, the a-Si submodule is through the lamination foil 13 completed.

The c-Si submodule consists of an array of crystalline silicon elements or c-Si elements 14 , These are between the lamination 13 and a backside lamination 15 and the back-glass or polymer backsheet behind it (Tedlar) 11 locked in. The c-Si elements 14 form together with out of the figure level leading contacting tracks 16 a series of crystalline silicon strips, also called c-Si strings 17 be designated. The lamination 13 forms a transparent front cover for the construction of the c-Si submodule, the backside lamination 15 a back covering of the c-Si strings.

The contact 16 runs in such a way that the c-Si strings are connected in series with each other. The voltage applied across the entire series connection photovoltaically generated voltage is via contacts 18 tapped.

The structure of the invention is compared to the known from the prior art example significantly more robust, especially against moisture. In the structure according to the invention, a low-voltage module is combined in the form of the c-Si submodule and a high-voltage module in the form of the a-Si submodule. This eliminates a series of manufacturing steps for the c-Si submodule, which shortens the process chain during their production. This can thus be cheaper to produce and use as known c-Si cells for the present hybrid application. In particular, the antireflection coatings and texture etching otherwise customary for such cells can be dispensed with because the a-Si submodule already carries out a sufficiently clear light scattering by the matting of its TCO layer for the c-Si submodule. Finally, the structure of the invention allows a higher p-type doping of the crystalline Si regions. There is no need to pay attention to a higher absorption in the UV range, because the a-Si submodule can already be regarded as a sufficient blue filter.

Because in the design of the a-Si submodule no longer has to be taken into account with the conventionally located behind it μc-Si bottom cell, in particular the absorber thickness of the a-Si cells can be significantly reduced. This requires a significantly reduced use of materials in their production, especially in view of the cleaning and coating gases used nitrogen trifluoride and silane. In addition, the reduced absorber thickness significantly reduces the photoinduced degradation within the a-Si submodule.

Thus, the advantages of crystalline and amorphous thin film technologies can be combined. These show up in particular in the form of high energy yields in the a-Si submodule due to a very good low-light behavior and a low temperature coefficient in conjunction with the very stable and robust c-Si cells in their properties. In particular, no current or voltage matching is necessary.

The manufacture of the structure according to the invention is uncomplicated and can be realized with a conventional manufacturing for conventional c-Si solar modules. This requires superstrates with the illustrated construction of amorphous silicon as well as longitudinal contacts and cross connectors. The processing of the crystalline c-Si strings is carried out in the known manner.

The invention has been explained with reference to an embodiment. In the context of expert action, further embodiments are possible, all of which remain within the scope of the basic concept according to the invention. Further embodiments emerge from the subclaims.

Claims (7)

Solar cell arrangement with a superstrate module ( 1 ) and a substrate module ( 2 ) in tandem configuration, wherein the superstrate module as a thin film module in the form of an a-Si submodule ( 1a ) from a-Si cells ( 3 ) and the substrate module in the form of a c-Si submodule ( 2a ) made of contacted with crystalline insulating layers of contacted crystalline silicon elements ( 14 ) is trained. Arrangement according to claim 1, characterized in that the a-Si cells ( 3 ) have a reduced absorber thickness. Arrangement according to claim 1 or 2, characterized in that the a-Si submodule ( 1a ) as a light scattering antireflection unit for the c-Si submodule ( 2a ) is trained. Arrangement according to claim 3, characterized in that as a antireflective element of the antireflection unit, a transparent conductive oxide layer opacified by the action of light ( 5 ) of the a-Si submodule ( 1a ) is provided. Arrangement according to one of the preceding claims, characterized in that the a-Si submodule ( 1a ) as a blue filter for the c-Si submodule ( 2a ) is formed, and the c-Si submodule is designed with an increased doping of a p-emitter region. Arrangement according to one of the preceding claims, characterized in that the c-Si submodule has a layer structure consisting of a transparent front cover ( 13 ), contacted crystalline Silicon elements ( 14 ), a back cover ( 15 ) and a back glass ( 11 ) having. Production method for a solar cell comprising a superstrate module and a substrate module with the steps: Providing a superstrate module with an amorphous silicon absorption layer, Providing a substrate module of sandwiched crystalline silicon wafers enclosed in a sandwich arrangement, - Connecting the superstrate and the substrate module.

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