solar module

Abstract

The invention relates to a solar module with a front side as the main light incidence side and a rear side, comprising - a plurality of interconnected heterojunction or tandem solar cells (2), and - an embedding material (1) which encapsulates the plurality of interconnected heterojunction or tandem solar cells (2) in a weather-resistant manner, wherein the embedding material (1), which is arranged on the front side, has a first layer (11) which is designed to convert UV radiation into visible light, and a second layer (12) which is designed to absorb UV radiation, wherein the second layer (12) is arranged on a side of the first layer (11) which faces the plurality of heterojunction or tandem solar cells (2).

Description

The invention relates to a solar module. The present invention preferably relates to a solar module having a front side as main light incidence side and a rear side, wherein the solar module has a multiplicity of heterojunction or tandem solar cells connected to one another and an embedding material.A tandem solar cell has two or more solar cells, also called sub-cells, made of different materials, which are layered one above the other when viewed in the direction of incidence of light. There are tandem solar cells with sub-cells stacked structurally separately from one another, in which the sub-cells have a hybrid structure separately from one another. However, monolithically constructed tandem solar cells are more frequently used, in which all the sub-cells are constructed on the same substrate. The sub-cells are configured to absorb and transmit light of different wavelength ranges. With this structure and configuration, the conversion efficiency of sunlight into electric power is increased compared to single solar cells because a broader spectrum of sunlight is used more efficiently for conversion into electric power.A heterojunction solar cell is a solar cell based on a so-called heterojunction between semiconductors having different band gaps. A heterojunction solar cell generally comprises an n-doped crystalline silicon wafer which is surrounded on both sides by thin amorphous crystalline layers generally silicon layers. A heterojunction solar cell has a comparatively high efficiency.However, it is a problem that UV (ultraviolet) radiation components of sunlight can lead to undesired degradation of the heterojunction or tandem solar cells during the lifetime of such solar cells.From a prior art not mentioned in the publication, it is known to use UV filter materials as embedding material for protection against UV radiation or UV solar radiation, preferably as rear side embedding material for protection of a rear side encapsulation element lying in front of it, in order to bring about a reduction of photochemical degradation of the rear side encapsulation element. In addition to the interconnected heterojunction or tandem solar cells and the embedding material, the solar module generally also has a front side encapsulation element and a rear side encapsulation element which are generally formed from glass or a plastic film and which sandwich the interconnected heterojunction or tandem solar cells embedded in the embedding material.It is therefore an object of the present invention to provide a solar module having a multiplicity of heterojunction or tandem solar cells connected to one another, in which degradation of the heterojunction or tandem solar cells by UV radiation is prevented or at least significantly reduced.This object is achieved by a solar module having the features of claim 1. Preferred embodiments are evident from the dependent claims explained below.The invention relates to a solar module having a front side as main light incidence side and a rear sidea plurality of interconnected heterojunction or tandem solar cells, andan embedding material that weather-resistantly encapsulates the plurality of interconnected heterojunction or tandem solar cells, wherein the embedding material disposed on the front side comprises a first layer configured to convert UV radiation into visible light and a second layer configured to absorb UV radiation, wherein the second layer is disposed on a side of the first layer facing the plurality of heterojunction or tandem solar cells.As a result of this construction of the solar module and the embedding material, the heterojunction or tandem solar cells and in particular UV-sensitive heterojunction or tandem solar cells are protected from UV radiation or at least exposed to reduced UV radiation by the embedding material having the first layer which is formed as a UV radiation conversion layer and by the second layer which is formed as a UV filter layer. By means of the first layer, at least a portion of the entering UV radiation is first converted into visible light at least on the main light incidence side. Because this will not be completely possible, the second layer arranged below the first layer for the main light incidence absorbs the remaining unconverted UV radiation.By combining the property of the first layer to convert UV radiation into visible light, i.e. light usable for power generation in the heterojunction or tandem cell, and the property of the second layer to absorb UV radiation, the embedding material having both properties is obtained. The main light incidence side is the side of the solar module which faces the sun during operation and, in the sense of this application, the front side of the solar module.By combining the first layer and the second layer, UV-sensitive heterojunction or tandem solar cells can be effectively protected against UV degradation, preferably in the UV range <350 nm, without radiation losses which usually occur up to 95% owing to pure absorption lowering the solar module performance. Instead, the harmful UV radiation is partially converted into visible light with the aid of the first layer, which visible light can thereby be used by the heterojunction or tandem solar cells for generating energy.The method of operation of the two-layer embedding material is thus as follows: the sunlight incident on the solar module with a corresponding UV fraction impinges mainly on the front side of the solar module.Wavelengths from the light spectrum below 400 nm are first absorbed by the first layer, but not completely, and converted to higher wavelengths in the visible wavelength range by so-called wavelength conversion to longer, visible wavelengths, which do not damage the UV-sensitive heterojunction or tandem solar cells and at the same time lie within the spectral sensitivity of the heterojunction or tandem solar cell. Thus, a power gain is accordingly realized within the scope of the cell EQE (External Quantum Efficiency) for a wavelength range >400 nm. The UV radiation <400 nm not yet absorbed by the first layer is then preferably absorbed almost completely, more preferably up to 95%, by the second layer. Thus, the heterojunction or tandem solar cells only reach (solar) light of a wavelength >400 nm, which does not have a damaging effect. The wavelengths of visible light are between 380 nm and 780 nm, while UV radiation has wavelengths in the range from 100 to 380 nm.In a preferred embodiment, the second layer is configured to absorb incident sunlight having wavelengths in a range from 200 to 400 nm by at least 70%, preferably by 80%, and particularly preferably by 90%. The inventors have found that UV radiation up to about 350 nm can lead to degradation of the heterojunction or tandem solar cells. The second layer therefore preferably has the property of absorbing wavelengths of 100 to 400 nm or 200 to 400 nm. Thus, it offers UV protection for the heterojunction or tandem solar cells located behind it, as seen from the main light incidence side.The first layer preferably contains a pigment and / or an additive which is designed to convert at least a portion of 20%, more preferably of 30%, and particularly preferably of 40%, of incident sunlight having wavelengths below 400 nm into light having comparatively longer wavelengths. This converted light with comparatively longer wavelengths can be used by the heterojunction or tandem solar cells for generating energy, whereby its efficiency is increased.In a preferred embodiment, the pigment and / or the additive is selected from the group consisting of dimethyl trans stilbenes. The pigment and / or the additive is or are preferably capable of converting wavelengths below 400 nm into light having comparatively longer wavelengths.The first layer is preferably designed to convert at least 20%, preferably at least 30%, and particularly preferably at least 40%, of incident UV solar radiation into visible light. The converted visible light can be used by the heterojunction or tandem solar cells for generating energy Therefore, a conversion percentage which is as high as possible is advantageous, but which is limited by the material properties of the first layer. The material of the first layer can be filled with the pigment and / or the additive only to a certain extent. The material of the first layer is preferably polyethylene, e.g. LLDPE (linear low density polyethylene, i.e. linear low density polyethylene), e.g. with a melt index of less than 17 g / 10 min. The first layer preferably has a degree of filling of pigments and / or additives in the range up to 1000 ppm. The use of the first layer is not sufficient for protecting the UV-sensitive heterojunction or tandem solar cells, since the degree of filling of the pigment and / or of the additive in the first layer is low and only a part of the critical UV radiation is absorbed and converted by wavelength conversion to the visible spectral range. Thus, a significant portion of the critical UV radiation would transmit to the UV sensitive heterojunction or tandem solar cell, which is prevented by the second layer acting as a UV filter.In a preferred embodiment, the first layer and the second layer are coextruded as a film. In this case, the embedding material is manufactured and processed as a co-extruded two-layer film and arranged in the solar module. The weather-resistant encapsulation of the interconnected heterojunction or tandem solar cells is usually carried out by means of a lamination process. The lamination process is carried out by means of a laminator in which the interconnected heterojunction or tandem solar cells are arranged, wherein one or more layers of the embedding material are arranged in each case on their front sides and their rear sides and the front side encapsulation element and the rear side encapsulation element sandwich this structure. In this case, in this variant, the co-extruded film which comprises or consists of the first and the second layer is used as the embedding material at least on the front sides of the plurality of heterojunction or tandem solar cells which are interconnected to one another during the lamination process. The back sides of the heterojunction or tandem solar cells can be provided during the lamination process with the co-extruded film as embedding material or alternatively combined with a further embedding material.Alternatively or additionally preferably, the first layer and the second layer are laminated one above the other as separate films. In this variant, the first layer and the second layer are combined as two separate films or sheets in the lamination process. That is to say that in this variant, the first layer and the second layer are placed as separate films on at least the front sides of the interconnected heterojunction or tandem solar cells and are laminated one above the other during the lamination process, while the first layer and the second layer are likewise placed as separate films on the rear sides of the interconnected heterojunction or tandem solar cells or can alternatively be used in combination with a further embedding material.In a preferred embodiment, the second layer comprises POE (polyolefin elastomer), TPO (thermoplastic polyolefin) and / or EVA (ethylene polyolefin), preferably POE or TPO. Alternatively preferably, the second layer consists of POE, TPO and / or EVA, preferably of POE or TPO. By using these materials, UV radiation in the range of 100 to 400 nm can be absorbed efficiently. Preferably, the second layer comprises polyethylene, e.g. LLDPE, as the base material, which is co-polymerized with octane co-monomer and / or butene. The polyethylene preferably has a melt index of less than 17 g / 10 min. During the processing of the layers or films in module production, the polyethylene can be crosslinked up to 90% by means of peroxides, for example Luperox 101 (Arkema S. A., France, Colombes) and crosslinking co-agents, i.e. co-crosslinking agents, for example TAIC (Avokal GmbH Heinrich Heller GmbH, Germany, Wuppertal), in order to improve the mechanical properties. Depending on the degree of crosslinking, elastomers are first formed by crosslinking polymers and thermosetting plastics are also formed with increasing crosslinking. Highly crosslinked polymers have a very high density of crosslinking points, leading to high stiffness, while lightly crosslinked polymers are less stiff.Preferably, the plurality of interconnected heterojunction or tandem solar cells each have an upper subcell and a lower subcell. The heterojunction or tandem solar cell preferably consists of the upper subcell and the lower subcell. Sunlight entering the solar module on the main light incident side first enters the upper subcell and then the lower subcell. The upper subcell is preferably a perovskite subcell. The lower subcell is preferably an Si subcell. Such a perovskite silicon heterojunction or tandem solar cell has low production costs, low resource consumption and comparatively high efficiency.In a preferred embodiment, the embedding material is furthermore arranged on the rear side of the heterojunction or tandem solar cells. As a result, the plurality of heterojunction or tandem solar cells connected to one another can be further protected on their rear side from damage by UV radiation.Further properties and advantages of the assembled solar module according to the invention are explained in more detail within the scope of the preferred embodiments described below.They are schematic and not to scale: FIG. 1 shows a cross-sectional view of a solar module according to a first embodiment; and FIG. 2 shows a cross-sectional view of a solar module according to a second embodiment.FIG. 1 shows a cross-sectional view of a solar module according to a first embodiment. The solar module is formed with a front side as a main light incidence side and a rear side. It has a plurality of interconnected heterojunction or tandem solar cells 2 and an embedding material 1 which encapsulates the plurality of interconnected heterojunction or tandem solar cells 2 in a weather-resistant manner. The embedding material 1 comprises a first layer 11 configured to convert UV radiation into visible light and a second layer 12 configured to absorb UV radiation. The second layer 12 is disposed on a side of the first layer 11 that is oriented toward the plurality of heterojunction or tandem solar cells 2. The embedding material 1 is arranged on the front side and the rear side of the solar module, so that it encapsulates the plurality of solar cells connected to one another in a weather-resistant manner.In operation, incident sunlight L substantially falls on the front side as the main light incident side, as indicated by an arrow. The sunlight L therefore strikes the solar module on the front with a corresponding UV component. Wavelengths from the light spectrum below 400 nm are first absorbed by the first layer 1, but not completely, and converted and / or emitted towards higher wavelengths by shifting. The UV radiation not yet absorbed by the first layer 1 is subsequently absorbed almost completely, for example up to 95%, by the second layer 2. Thus, the heterojunction or tandem solar cells 2 substantially only reach light with a wavelength >400 nm, which does not have a damaging effect on the microstructure of the heterojunction or tandem solar cell 2.FIG. 2 shows a cross-sectional view of a solar module according to a second embodiment. The solar module shown in FIG. 2 corresponds to the solar module shown in FIG. 1, with the difference that it has a further embedding material 3 on the rear side instead of the embedding material. That is, the solar module has the embedding material 1 only on the front side.List of reference numbers:L sunlight 1 embedding material 11 first layer 12 second layer 2 heterojunction or tandem solar cell 21 upper subcell 22 lower subcell 3 further embedding material

Claims

Solar module having a front side as main light incidence side and a rear side, having - a plurality of interconnected heterojunction or tandem solar cells (2), and - an embedding material (1) which encapsulates the plurality of interconnected heterojunction or tandem solar cells (2) in a weather-resistant manner, wherein the embedding material (1) arranged on the front side has a first layer (11) which is configured to convert UV radiation into visible light and a second layer (12) which is configured to absorb UV radiation, wherein the second layer (12) is arranged on a side of the first layer (11) which faces the plurality of heterojunction or tandem solar cells (2).Solar module according to claim 1, characterised in that the second layer (12) is configured to absorb incident sunlight with wavelengths in a range from 200 to 400 nm in order to absorb at least 70%, preferably by 80% and particularly preferably by 90%.Solar module according to claim 1 or 2, characterised in that the first layer (11) contains a pigment and / or an additive which is designed to convert at least a portion of 20%, more preferably of 30%, and particularly preferably of 40%, of incident sunlight having wavelengths below 400 nm into light having comparatively longer wavelengths.Solar module according to claim 3, characterised in that the pigment and / or the additive is selected from the group consisting of dimethyl trans stilbenes.Solar module according to claim 3 or 4, characterised in that the first layer (11) is designed to convert at least 20%, preferably at least 30% and particularly preferably at least 40%, of incident UV solar radiation into visible light and / or that the first layer has a degree of filling of pigments and / or additives in the range < 1000 ppm.Solar module according to one of the preceding claims, characterized in that the first layer (11) and the second layer (12) are coextruded as a film or the first layer (1) and the second layer (12) are laminated on top of one another as separate films.Solar module according to one of the preceding claims, characterized in that the second layer (12) comprises POE, TPO and / or EVA or consists of POE, TPO and / or EVA, wherein preferably the second layer (12) comprises polyethylene as base material, which is co-polymerized with co-monomer octene and / or butene.Solar module according to one of the preceding claims, characterized in that the plurality of interconnected heterojunction or tandem solar cells (2) each have an upper subcell (21) and a lower subcell (22), wherein the upper subcell (21) is preferably a perovskite subcell and the lower subcell (22) is preferably an Si subcell.Solar module according to one of the preceding claims, characterized in that the embedding material (1) is furthermore arranged on the rear side of the heterojunction or tandem solar cells (2).

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