Multi-junction solar cell and method for producing a multi-junction solar cell

Abstract

The invention relates to a multi-junction solar cell having a front face that forms a light incidence face, a rear face facing away from the light incidence face, and edges (3) extending between the front face and the rear face, the multi-junction solar cell having: an upper thin-film sub-cell (2), which has an optically transparent electrically conductive front electrode layer (22) that forms the light incidence face of the upper thin-film sub-cell (2), and a lower sub-cell (1), which has a semiconductor wafer substrate (11) with p-n junction layers and with an insulation layer (12) that extends along the edges (3) in the region of the lower sub-cell (1) such that at least the semiconductor wafer substrate (11) is covered by the p-n junction layers (12) in the region of the edges (3). The invention further relates to a method for producing a multi-junction solar cell having a front face which forms a light incidence face, a rear face facing away from the light incidence face, and edges (3) extending between the front face and the rear face, the method having the following steps: providing a semiconductor wafer substrate (11) with p-n junction layers; applying an insulation layer (12) along the edges (3) of the semiconductor wafer substrate (11) with the p-n junction layers; and applying an upper thin-film sub-cell (2) having an optically transparent electrically conductive front electrode layer (22) onto the semiconductor wafer substrate (11) with the p-n junction layers of the lower sub-cell (1).

Description

[0001] Tandem solar cell and method for manufacturing a tandem solar cell

[0002] The invention relates to a tandem solar cell and a method for manufacturing a tandem solar cell. In particular, the invention relates to a tandem solar cell with an upper thin-film subcell, which has an optically transparent, electrically conductive front electrode layer that is designed as the light-incidence side of the upper thin-film subcell, and to a method for manufacturing such a tandem solar cell.

[0003] The tandem solar cell, also called a multi-junction solar cell, consists of two or more solar cells stacked on top of each other. This also includes triple or quadruple multi-junction cells. A distinction is made between solar cells stacked using hybrid technology, where the solar cells are manufactured separately and then combined, and monolithic multi-junction solar cells, where all solar cells are manufactured on the same substrate.

[0004] The tandem solar cell has a front side facing the light incidence and a back side facing away from the light incidence, with edges extending between the front and back sides. However, the deposition of the optically transparent, electrically conductive front electrode layer, for example by sputtering, is not strictly monofacial, i.e., only on the front side, but results in a conductive surround in the form of a thin-film deposition on the edges, so that the edges are also at least partially covered. This creates an undesirable electrical contact between the upper and lower cell sections. This surround cannot be avoided due to the process. Through this electrical contact path between the optically transparent, electrically conductive front electrode layer and the lower cell section, unwanted side currents flow, reducing the performance of the tandem solar cell and degrading its reliability characteristics.This electrical contact reduces, in particular, the short-circuit resistance, often referred to as shunt resistance or Rsh parameter, or the fill factor, which has a negative impact on cell performance and the reliability characteristic of reverse current resistance.

[0005] Tandem solar cells with perovskite thin-film cells are not yet a commercial product, and a mass-production-ready solution to the above problem is not known. In research, the edges of tandem solar cells are typically separated from the active cell area by stripping. This is usually achieved by masking during the deposition of different layers of the sub-cells, but can also be accomplished by laser cutting or a combination of laser cutting and fracturing. However, this approach is not economical for the mass production of tandem solar cells.

[0006] It is an expenditure to provide a tandem solar cell and a method for manufacturing such a tandem solar cell, so that the tandem solar cell has improved performance and improved reliability characteristics without significantly increasing the process costs.

[0007] The problem is solved by a tandem solar cell having the features of claim 1 and by a method having the features of claim 7. Advantageous further developments and modifications are specified in the dependent claims.

[0008] The invention relates to a tandem solar cell with a front side forming a light-incidence side and a back side facing away from the light incidence, and edges extending between the front and the back side, wherein the tandem solar cell comprises: an upper thin-film subcell, which has an optically transparent electrically conductive front electrode layer, which is formed as the light-incidence side of the upper thin-film subcell, and a lower subcell, which has a semiconductor wafer substrate with p-n junction layers and with an insulating layer, which extends along the edges in the region of the lower subcell, such that in the region of the edges at least the predominant part of the semiconductor wafer substrate with the p-n junction layers is covered by the insulating layer.

[0009] A predominant proportion of the semiconductor wafer substrate within the meaning of the invention is understood to be a coverage of more than 50%, preferably more than 70% and particularly preferably more than 90%.

[0010] The insulating layer along the edges of the lower subcell prevents electrically conductive contact between these edges and the optically transparent, electrically conductive front electrode layer. For effective short-circuit suppression, all electrically conductive layers of the lower subcell must be covered by the insulating layer in the edge region. The semiconductor wafer substrate of the lower subcell is preferably a single wafer, more preferably a silicon wafer. The semiconductor wafer substrate is electrically conductive because it comprises, for example, doped poly-Si with a conductivity typically <150 Ω / sq. The lower subcell also includes an electrically conductive emitter, which, for example, has a conductivity <150 Ω / sq.The influence of the layers of the upper subcell adjacent to the lower subcell is negligible for the formation of the electrical contact, since such layers can be produced with very high electrical resistances, e.g., >1 kΩ / sq. Even if the upper subcell has a recombination layer, this has a limited influence because it exhibits low lateral conductivity towards the edges and only allows current to tunnel vertically.

[0011] In a preferred embodiment, the insulating layer is designed as one or more passivation layers. These are ideally suited for electrical insulation and can be produced relatively inexpensively at the edges using mass-production-ready methods. Preferably, the one or more passivation layers are an AlOx layer or aluminum oxide layer and / or SiO₂. x N yA layer or silicon oxynitride layer is formed. Preferably, the AlOx layer has a thickness in the range of 1 to 30 nm. The SiO x N y The insulating layer preferably has a thickness in the range of 20 to 160 nm. Preferably, the insulating layer is formed as several passivation layers and is preferred over the AlOx layer and the SiO₂ layer. x N y -layer formed. The advantage of the AlOx layer, as explained below, is that it can be produced using ALD, which, when coating the back side of the lower subcell facing away from the light, involves a surrounding deposition at the edges. This saves process steps and costs for producing the insulating layer at the edges. Advantage of SiO x N y The advantage of the layer is that it is chemically robust.

[0012] In a preferred embodiment, the insulating layer extends further over the side of the lower subcell facing away from the light. This further increases the efficiency of the lower subcell. The lower subcell is preferably configured as a PERC (Passivated Emitter and Rear Cell) or TopCon (Tunnel oxide passivated Contact) type cell.

[0013] Preferably, the upper thin-film subcell is designed as a perovskite solar cell and borders an emitter of the lower subcell, which also acts as an electron transport layer for the upper thin-film subcell. A perovskite subcell exhibits a relatively high efficiency, its spectral properties can be well matched to those of silicon wafer solar cells, and it is simple and inexpensive to manufacture.

[0014] In a preferred embodiment, the optically transparent, electrically conductive front-side layer at least partially covers the edges of the upper thin-film subcell and the lower subcell, with the insulating layer electrically isolating the transparent, electrically conductive front-side layer from the semiconductor wafer substrate containing the pn junction layers of the lower subcell, at least along the lower subcell. This ensures that no short circuits occur during operation, even if, due to process or production constraints, it is unavoidable that the optically transparent, electrically conductive front-side layer extends along the edges.

[0015] Preferably, the tandem solar cell is designed as a monolithic tandem solar cell. Such a tandem solar cell is simple to manufacture and can be produced in a closed process flow.

[0016] The invention further relates to methods for manufacturing a tandem solar cell with a front side forming a light-incidence side and a back side facing away from the light incidence, and edges extending between the front and the back side, wherein the method comprises the following steps

[0017] Providing a semiconductor wafer substrate with pn junction layers,

[0018] Applying an insulating layer along the edges of the semiconductor wafer substrate with the pn junction layers, applying an upper thin-film subcell with an optically transparent electrically conductive front electrode layer to the semiconductor wafer substrate with the pn junction layers of the lower subcell.

[0019] The steps are performed in the specified sequence, such that the upper thin-film subcell is applied in a monolithic structure to the lower subcell after the insulating layer has been deposited along the edges of the semiconductor wafer substrate with the pn junction layers. This ensures that the optically transparent, electrically conductive front electrode layer is electrically insulated from the semiconductor wafer substrate with the pn junction layers of the lower subcell. Further developments, modifications, and advantages described for the tandem solar cell apply accordingly to this method, and vice versa. This method can also be used to process solid wafers. In a preferred embodiment, the insulating layer is applied using ALD (atomic layer deposition) or PECVD (plasma-enhanced chemical vapor deposition).These process steps can be easily integrated into a process flow for manufacturing the tandem solar cell.

[0020] Preferably, an AlOx layer is applied as an insulating layer along the edges using ALD, e.g., with a layer thickness in the range of 10 to 30 nm. The AlOx layer can also be applied using PECVD or another suitable method. SiO₂ can also be used. x N y The SiOxNy layer is ideally suited as an insulating layer, either as an alternative or in addition to other applications, and is preferably applied using PECVD, e.g., with a layer thickness in the range of 50 to 90 nm. The SiOxNy layer is chemically robust enough.

[0021] Preferably, the step of applying an insulating layer along the edges of the semiconductor wafer substrate with the pn junction layers involves applying the insulating layer to the side of the semiconductor wafer substrate facing away from the light exposure, such that the insulating layer wraps around the edges from the side facing away from the light exposure. An advantage of ALD is its strong coverage; therefore, applying the insulating layer using ALD is particularly suitable for coating the edges with essentially the same deposition rates as the side facing away from the light. Unwanted coating of the side facing away from the light exposure of the lower subcell can be prevented by ensuring the wafers are flush against each other during loading.However, PECVD or similar processes can also be used; here too, the insulating layer is deposited at the edges, but the deposition rates at the edges are usually lower.

[0022] If the light-incident side of the lower sub-cell is also covered with the insulating layer in the process, a surface cleaning of the light-incident side of the lower sub-cell is preferably carried out, e.g. by etching, in such a way that the insulating layer remains at the edges, i.e., is not removed at the edges, but at the light-incident side.

[0023] In a preferred embodiment, the insulating layer along the edges of the semiconductor wafer substrate with the pn junction layers is applied before the upper thin-film subcell, in the form of a perovskite solar cell with an optically transparent, electrically conductive front layer, is applied. This ensures that the semiconductor wafer substrate with the pn junction layers is electrically isolated from the optically transparent, electrically conductive front layer. Furthermore, a tandem solar cell manufactured in this way, with a perovskite solar cell as the upper subcell, exhibits a high overall efficiency.

[0024] In a preferred embodiment, after applying an insulating layer along the edges of the semiconductor wafer substrate with the pn junction layers and before applying an upper thin-film subcell with an optically transparent electrically conductive front electrode layer to the semiconductor wafer substrate with the pn junction layers of the lower subcell, a process step is carried out in which the lower subcell is provided with a metallization on the side of the lower subcell facing away from the incidence of light.

[0025] Further features and advantages of the invention are explained in more detail in the context of the preferred embodiments described below.

[0026] It shows a schematic representation, not to scale:

[0027] Fig. 1 shows a cross-sectional view of a tandem solar cell according to the prior art;

[0028] Fig. 2 shows a cross-sectional view of a tandem solar cell according to the invention;

[0029] Figs. 3 to 8 show a process of a method according to the invention, wherein a tandem solar cell or its lower subcell is shown in cross-section; and Fig. 9 shows a cross-sectional view of a lower subcell of a tandem solar cell according to the prior art.

[0030] Fig. 1 shows a cross-sectional view of a prior art tandem solar cell. The tandem solar cell has a front face, which forms a light-incident side, and a back face, which faces away from the light-incident side. Edges 3 extend between the front and back faces. The tandem solar cell has an upper thin-film subcell 2 and a lower subcell 1, which are stacked one above the other. The upper subcell 2 has a semiconductor with selective contacts 21 in the form of a perovskite layer and an optically transparent, electrically conductive front electrode layer 22, which forms the light-incident side of the upper thin-film subcell 2. The lower subcell 1 has a semiconductor wafer substrate 11 with pn junctions and a passivation layer 15, which extends over a side facing away from the light-incident side of the lower subcell 1.The edges 3 are partially covered by the optically transparent, electrically conductive front electrode layer 22 in such a way that it also extends along the semiconductor wafer substrate 11. This creates an electrical contact during operation, indicated by an arrow, which can lead to an unwanted short-circuit current, symbolically represented by a lightning bolt.

[0031] Fig. 2 shows a cross-sectional view of a tandem solar cell according to the invention. The tandem solar cell shown in Fig. 2 corresponds to the tandem solar cell shown in Fig. 1, with the difference that it has an insulating layer 12 which extends along the edges 3 in the region of the lower subcell 1, so that in the region of the edges 3 at least the semiconductor wafer substrate 11 with the pn junction layers is covered by the insulating layer 12. The insulating layer 12 is designed as a passivation layer 15, which also extends over the side of the lower subcell 1 facing away from the light incidence. Figs. 3 to 8 show a sequence of a process according to the invention, wherein the step-by-step fabrication of a tandem solar cell is shown in cross-section. In Fig. 3, the lower subcell 1 is provided with a semiconductor wafer substrate 1 with pn junction layers comprising an emitter 13.The semiconductor wafer substrate 1 has a front side designed as the light-incidence side and a back side facing away from the light-incidence side, between which edges 3 extend. An insulating layer 12 is applied to the back side of the provided semiconductor wafer substrate 11, as shown in Fig. 4, so that the insulating layer 12 also extends along the edges 3, although it is not always possible to avoid, due to process limitations, that the insulating layer 12 also partially covers the front side. The insulating layer 12 is designed as a passivation layer 15, which is made, for example, of AIO. X The insulation layer 12 can have more than one passivation layer, i.e., it can be multilayered. An optional process step involves applying another passivation layer 15, e.g., made of SiO₂. x N yThe insulating layer 12 is formed, as shown in Fig. 5, with the further passivation layer 15 extending by circumferentially along the edges 3 and partially onto the light-incident side of the lower subcell 1. Subsequently, a metallization 14 can be applied to the back side of the lower subcell 1 facing away from the light incidence, as shown in Fig. 6, which is in electrical contact with the semiconductor substrate 11. This process step can comprise several sub-steps, which are not shown here. If the two insulating layers 12—as shown here in Figs. 4 to 6—also extend partially onto the front side, they are removed from there, e.g., by etching, as shown in Fig. 7. A further process step involves applying an upper thin-film subcell 2 with an optically transparent, electrically conductive front electrode layer 22 to the semiconductor wafer substrate 11, in particular to its emitter 13.This process step can in turn be divided into a multitude of process steps. The application of the upper thin-film subcell 2 with an optically transparent, electrically conductive front electrode layer 22 comprises the application of a perovskite layer 21 to the lower subcell 1 and subsequently the application of the optically transparent, electrically conductive front electrode layer 22 to the perovskite layer 21. The optically transparent, electrically conductive front electrode layer 22 also extends along the edges 3 on the further insulating layer 12, which electrically insulates the semiconductor substrate 11 and the emitter 13 from the optically transparent, electrically conductive front electrode layer 22.

[0032] Fig. 9 shows a cross-sectional view of a lower sub-cell of a tandem solar cell according to the prior art. In a prior art method, starting from the lower sub-cell 1 shown in Fig. 6, edge insulation is carried out in which the two insulating layers 12 are removed from the edges 3, so that the lower sub-cell 1 shown in Fig. 9 corresponds to the sub-cell 1 shown in Fig. 7, with the difference that the two insulating layers 12 extend exclusively along the back side of the lower sub-cell 1, but not along the edges 3. The lower sub-cell 1 shown in Fig. 9 is produced from the lower sub-cell 1 shown in Fig. 6, for example, by laser cutting the two insulating layers 12 along the edges 3.

[0033] Reference symbol list:

[0034] 1 lower subcell

[0035] 11 Semiconductor wafer substrate

[0036] 12 Insulation layer

[0037] 13 emitters

[0038] 14 Metallization

[0039] 15 Passivation layer

[0040] 2 upper subcell

[0041] 21 Perovskite layer with selective contacts

[0042] 22 front sides - layer

Claims

Patent claims:

1. Tandem solar cell with a front side forming a light-incidence side and a back side facing away from the light-incidence side and edges (3) extending between the front and the back side, wherein the tandem solar cell comprises: an upper thin-film subcell (2) which has an optically transparent electrically conductive front electrode layer (22) which is formed as the light-incidence side of the upper thin-film subcell (2), and a lower subcell (1) which has a semiconductor wafer substrate (11) with pn junction layers and with an insulating layer (12) which extends along the edges (3) in the region of the lower subcell (1) such that in the region of the edges (3) at least the predominant part of the semiconductor wafer substrate (11) with the pn junction layers is covered by the insulating layer (12).

2. Tandem solar cell according to claim 1, characterized in that the insulating layer (12) is designed as one or more passivation layers (15).

3. Tandem solar cell according to claim 2, characterized in that one or more passivation layers (15) are composed of AlO x -layer and / or SiOxNy layer(s) is or are formed, wherein preferably the AlOx layer has a layer thickness in the range of 1 to 30 nm and / or SiO x N y -Layer has a layer thickness in the range of 20 to 160 nm.

4. Tandem solar cell according to one of the preceding claims, characterized in that the insulating layer (12) further extends over the side of the lower subcell (1) facing away from the incidence of light.

5. Tandem solar cell according to one of the preceding claims, characterized in that the upper thin-film subcell (2) is designed as a perovskite solar cell and borders an emitter (13) of the lower subcell (1) in the direction of the lower subcell (1), which also acts as an electron transport layer for the upper thin-film subcell (2).

6. Tandem solar cell according to one of the preceding claims, characterized in that the optically transparent electrically conductive front-side layer (22) at least partially covers the edges (3) of the upper thin-film subcell (2) and the lower subcell (1), wherein the insulating layer (12) at least along the lower subcell (1) electrically insulates the transparent electrically conductive front-side layer (22) from the semiconductor wafer substrate (11) with the pn junction layers of the lower subcell (1).

7. Method for manufacturing a tandem solar cell with a front side forming a light-incidence side and a back side facing away from the light-incidence side and edges extending between the front side and the back side (3), wherein the method comprises the following steps Providing a semiconductor wafer substrate (11 ) with pn junction layers, Applying an insulating layer (12) along the edges (3) of the semiconductor wafer substrate (11 ) with the pn junction layers, applying an upper thin-film subcell (2) with an optically transparent electrically conductive front electrode layer (22) to the semiconductor wafer substrate (11 ) with the pn junction layers of the lower subcell (1 ).

8. Method according to claim 7, characterized in that the insulating layer (12) is applied using ALD or PECVD.

9. Method according to claim 7 or 8, characterized in that the step of applying an insulating layer (12) along the edges (3) of the semiconductor wafer substrate (11 ) with the pn junction layers, the insulating layer (12) is applied to the side of the semiconductor wafer substrate (11 ) facing away from the light incidence, such that the insulating layer (12) extends from the side of the semiconductor wafer substrate (11 ) facing away from the edges (3).

10. Method according to one of claims 7 to 9, characterized in that the application of the insulating layer (12) along the edges (3) of the semiconductor wafer substrate (11 ) with the pn junction layers is carried out before the application of the upper thin-film subcell (2) in the form of a perovskite solar cell with an optically transparent electrically conductive front layer (22).

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