EP1815521A1 - Arrangement comprising a solar cell and an integrated bypass diode - Google Patents

Abstract

The current invention concerns an arrangement comprising at least one solar cell, which is formed by a first sequence (1, 2, 11, 12) of differently doped layers on a substrate (6, 16), and at least one bypass diode, which is connected to the solar cell, in particular in a monolithic, series-connected solar module. The arrangement is characterised in that the bypass diode is formed by a second layer sequence (4, 5, 13, 14), which is arranged between the substrate and the first layer sequence (1, 2, 11, 12). With the current arrangement it is possible to form monolithic, series-connected solar modules in which the solar cells are protected by bypass diodes, with only a very slight loss of active receiving surface.

Description

 Arrangement with solar cell and integrated bypass diode

Technical application

The present invention relates to an arrangement with at least one solar cell, which is formed by a first layer sequence over a substrate, and at least one bypass diode, which is connected to the solar cell, in particular in a monolithic series-connected solar module.

State of the art

Solar cells are often used in solar modules in which they are arranged in rows and columns. By series connection of the solar cells in the solar module, a sufficiently high electrical voltage is generated for the consumer. In a Teilabschattung a solar module, however, there is the danger of destruction of the shadowed cells, which operate in this case as electrical loads due to the series connection. The individual solar cells in the solar module should therefore be protected against overvoltages in the reverse direction by bypass diodes.

However, the interconnection of the individual solar cells with bypass diodes is not possible without limitations in monolithically series-connected modules (MIM: Monolithically Interconnected Modules). Monolithic series-connected solar modules have a larger number of solar cells, which on a common, semi-insulating substrate are applied as Schicht¬ sequence. The individual solar cells are separated from each other by trenches in the layer sequence and interconnected via integrated metallic contacts. An example of a MIM solar module and a method for its production can be found, for example, in the publication by S. van Riesen et al. , "GaAs-Monolithically Interconnected Modules (MIMS) with an Efficiency above 20%," 19th European Photovoltaic Solar Energy Conference, 7-11 June 2004, Paris., The individual photovoltaically active surfaces of the solar cells of such a solar module usually exhibit 1 mm in width, in order to limit the current intensity in intense light incidence, and are therefore very well suited for use in concentrator systems, for example in parabolic and shape concentrators, in monolithic series in the interconnection of the individual cells - interconnected solar modules with bypass diodes, however, has so far been a significant loss active

Receiving area are accepted to integrate the bypass diodes between the solar cells in the solar module. Furthermore, the performance of the diodes is limited in such an arrangement.

Also in the generic US 6600100 B2 or in US 2004/0163698 Al only arrangements are described in which the bypass diodes are either on or next to the photovoltaically active layers.

The object of the present invention is to provide an arrangement of a solar cell with a Specify bypass diode, which allows a higher Leistungs¬ ability of the bypass diode and leads to a lower loss of active receiving surface during integration in a solar module.

Presentation of the invention

The object is achieved with the arrangement of solar cell and bypass diode according to claim 1. Advantageous embodiments of the arrangement are the subject matter of the subclaims or can be taken from the following description and the exemplary embodiments.

The present arrangement with a solar cell, which is formed in a known manner by a first layer sequence differently doped layers over a substrate, and a bypass diode, which connects to the solar cell, is characterized in that the bypass diode by a second layer sequence is formed, which is arranged between the substrate and the first layer sequence. In this case, the first layer sequence represents the photovoltaically active layer sequence of the solar cell.

In the present interconnection of the solar cell with the bypass diode, the bypass diode is thus integrated into the structure of the solar cell comprising the substrate and the first layer sequence. The bypass diode consists of a layer sequence of an n-conducting and a p-conducting layer, which are formed voll¬ surface between the photovoltaically active layer sequence of the solar cell and the substrate. Thus, for the bypass diode itself no additional Liehe surface next to the photovoltaically active surface, ie the active receiving surface of the solar cell needed. Only the area necessary for contacting the bypass diode causes a small additional loss of active reception area of less than 5%. Nevertheless, all solar cells in such a solar module, preferably a MIM solar module, are protected by the bypass diodes. The full-surface design of the bypass diode also leads to a higher performance of this device.

In an advantageous development of the present invention, a thin, highly doped layer sequence forms a tunnel diode between the photovoltaically active layer sequence of the solar cell and the layer sequence forming the bypass diode. Through this tunnel diode, a simplified structure of the arrangement can be realized.

The first layer sequence preferably comprises at least one p-type and one n-type layer which form the photovoltaically active area and lie on a highly doped lateral conduction layer (LCL). Furthermore, additional reflection and / or passivation layers can be provided. Such a layer sequence for the formation of a solar cell is known from the prior art, for example the publication by S. van Riesen mentioned in the introduction to the description.

In a preferred embodiment, the present arrangement is part of a monolithic series-connected solar module (MIM), in which several Solar cells with integrated bypass diode are arranged side by side and interconnected in series. In this case, the individual layers are preferably first applied over the whole area using an epitaxial process, preferably MOVPE (Metal Organic Vapor Phase Epitaxy), to a common substrate. The second layer sequence for forming the bypass diodes thereby comes to rest between the first layer sequence for forming the solar cells and the substrate. Subsequent to the application of the layer sequences, deeper semiconductor layers for electrical contacting are exposed by etching trenches and the individual solar cells of the solar module are insulated from one another by these trenches, which extend into the substrate. Where necessary or advantageous, the flanks of the etched trenches are covered by an insulator. Subsequently, the series connection of the adjacent solar cells takes place by applying a structured metal layer which electrically connects different semiconductor layers in the trenches and outside the trenches. With this electrical contacting, the bypass diodes are integrated into the interconnection.

In an advantageous embodiment of the present arrangement, a layer structure is selected in which a highly doped n-conducting transverse conductive layer, a thin layer sequence forming a tunnel diode, a p-doped layer, and on the semi-insulating substrate in the following order a highly doped n-type cross-conduction layer for forming the bypass diode, a thin layer sequence forming another tunnel diode, and a p-doped layer and an n-type layer. doped layer are applied to form the photovoltaically active layer sequence. Furthermore, additional reflection and / or passivation layers can also be provided here at a suitable location in the layer structure. In this structure, only n-doped layers must be metallically contacted for the series connection of adjacent solar cells, including the bypass diodes, so that this is possible with a uniform structured metal layer. This reduces the production effort compared to one

Embodiment in which both n-doped and p-doped semiconductor layers must be contacted, for which different metal layers are required.

Brief description of the drawings

The present arrangement is described below by means of embodiments in conjunction with the drawings without limitation by the

Patent claims predefined scope again explained. Hereby show:

1 shows a cross-sectional illustration of a first example of a structure of the present arrangement in a solar module;

Fig. 2 is an equivalent circuit diagram for the illustration of Figure 1;

Fig. 3 is a modified equivalent circuit diagram for the illustration of Figure 1; Fig. 4 in cross-sectional view a second

Example of a construction of the present arrangement in a solar module;

Fig. 5 is an equivalent circuit diagram for the illustration of Figure 4; and

6 is a modified equivalent circuit diagram for the illustration of FIG. 4.

Ways to carry out the invention

FIG. 1 shows an example of a construction of the present arrangement in a monolithically series-connected solar module (MIM). In the figure, a section of the solar module can be seen in which 3 series-connected solar cells with bypass diodes are at least partially shown. The figure shows a cross section through a layer structure and the interconnection of the adjacent solar cells. In the present exemplary embodiment, the layer structure consists of the following semiconductor layers:

A layer sequence 4, 5 of semiconductor layers of opposite doping, which form the bypass diode, is applied to the semi-insulating substrate 6, a GaAs wafer. The layer 4 of GaAs with a p-doping of about 2 * 10 ¹⁸ cm ^"3 and a thickness of about 50 nm represents the emitter of the bypass diode. The n-doped layer 5, also made of GaAs, is composed a 50 nm thick sub-layer with a doping of about 2 * 10 ¹⁸ cm ^"3 as the basis of the bypass diode and a 500 nm thick sub-layer with a doping of about 5 * 10 ¹⁸ cm ^"3 together, which forms a cross-conducting layer of the bypass diode.

On this layer sequence 4, 5, a further thin semiconductor layer 3 of GaAs is applied to form a tunnel diode. This layer is composed of a lower p-doped partial layer (20 nm; p = 10 ¹⁹ cm ^"3) doped n-type as a base and a top layer (20 nm; n = 10 ^{19 cm" 3)} as an emitter of the tunnel diode together.

Finally, a layer sequence 1, 2 of two semiconductor layers of opposite doping follows the layer 3 forming the tunnel diode. The upper layer 1 consists of a 1000 nm thick p-doped GaAs layer with a doping of approximately 2 × 10 ¹⁸ cm ^-3 as an emitter of the solar cell, on which a 20 nm thick passivation layer of AlGaAs is applied as the window layer. The n-doped layer 2 consists of three partial layers, of which the uppermost 2000 nm thick partial layer of GaAs with a doping of approximately 5 × 10 ¹⁷ cm ^{-3 forms} the base of the solar cell. Below this is a passivation layer made of AlGaAs with a thickness of 50 nm and a doping of approximately 5 × 10 ¹⁸ cm ^-3 . The lowermost partial layer of GaAs forms approximately 5 × 10 ¹⁸ cm ^-3 and its high thickness of 2000 nm due to its high doping a highly conductive crossover layer with low layer resistance.

For the separation of the individual solar cells within the solar module as well as for the electrical serial connection, trenches are embedded in the epitaxially grown layer introduced structure, which extend partly into the substrate. On the one hand, the isolation between the individual solar cells of the solar module is achieved by these trenches. On the other hand, these trenches serve the electrical contacting of the semiconductor layers located at different depths. The Seiten¬ flanks of the trenches are in this case first with an insulating layer 7, for example. Of polyimide, covered. The application of this insulator takes place in a known manner by means of suitable photolithographic and / or etching steps in structured form. The same applies to the metal layer 8, which serves an electrical connection for series connection of adjacent solar cells on the one hand and for parallel connection of the respective bypass diode with the solar cell on the other. It consists of common, thin metal contacts for the production of ohmic metal-semiconductor junctions and an overlying, highly conductive 2 μm thick silver layer. The metallization extends as Kontaktgrid 9 of fine contact fingers over the photovoltaically active surface of the respective solar cell.

FIG. 2 shows an equivalent circuit diagram for the interconnection of the individual solar cells and bypass diodes shown in FIG. The solar cells are repräsen¬ in this equivalent circuit in a known manner by a current source and a parallel diode, wherein parallel to the solar cell, the bypass diode and the tunnel diode are connected. From this equivalent circuit diagram can be seen that at a

Shading of a single solar cell in the reverse direction across the solar cell voltage applied across the bypass diode is reduced. Finally, FIG. 3 shows a modified equivalent circuit diagram in which the layer structure of the solar cell and the bypass diode are additionally taken into account.

The layer structure of the arrangement according to FIG. 1 in a solar module differs from known solar modules without integrated bypass diode due to the additional layer sequence of the semiconductor layer 4, 5 forming the bypass diode and the layer 3 forming the tunnel diode and the additional metallic contacting of the semiconductor layer 5, which is part of the bypass diode. In the layer structure shown in FIG. 1, there is a need for semiconductor layers of different doping, ie. H. both n-doped and p-doped semiconductors, kontak¬ animals. For this purpose, different metal layers are necessary, so that the production cost increases. This additional production effort can be achieved through the

Installation of another tunnel diode can be avoided, as shown with reference to the following figures.

FIG. 4 shows an example of a modified construction of the arrangement of solar cell and

Bypass diode within a MIM solar module. In this example, the epitaxially grown Schicht¬ structure consists of the following semiconductor layers:

Above the semi-insulating substrate 16 is initially a highly n-doped transverse conductive layer 15 (LCL). On this layer, a thin layer sequence 20 is applied to form a tunnel diode. Above the the Tunnel diode forming layer sequence 20 is a layer sequence of a p-doped layer 14 and a highly doped n-type cross-conducting layer 13, through whose pn junction the bypass diode is formed. This is followed by a further thin layer sequence 21 forming a tunnel diode, on which a p-doped semiconductor layer 12 is situated as the base of the solar cell. Finally, the n-doped semiconductor layer 11 forming the emitter of the solar cell follows. The formation of the trenches, the isolation of the sidewalls of the trenches with an insulating layer 17 and the electrical connection of the individual solar cells and bypass diodes of this structure with the metal layer 18, over the Photovoltaically active surface merges into a contact finger structure 19, carried out in the same manner as in the embodiment of Figures 1-3.

By the layer structure of Figure 4 is achieved that only semiconductor layers of the same

Doping (here: n-doping) with the metal layer 18 must be contacted. This reduces the production effort, but requires the installation of an additional tunnel diode.

Figure 5 shows an equivalent circuit diagram of this layer structure, in which the solar cell, the two tunnel diodes and the bypass diode can be seen. In the same way as FIG. 3, FIG. 6 shows a modified equivalent circuit diagram of this layer structure with additional consideration of the layer structure. It can also be seen from these equivalent circuit diagrams that the bypass diode protects the individual solar cells in the event of overvoltage in the reverse direction.

Furthermore, it is immediately apparent from FIGS. 1 and 4 that the presently selected integration of the bypass diode into the layer structure of the individual solar cells brings with it only a small loss of active receiving surface. Thus, when using the present arrangement in a monolithically series-connected solar module, large-area receivers can be provided in which each individual solar cell is protected by the bypass diodes.

LIST OF REFERENCE NUMBERS

1 p-doped semiconductor layer as the emitter of the solar cell 2 n-doped semiconductor layer as the basis of the solar cell

3 tunnel diode forming layer sequence

4 p-doped semiconductor layer as the emitter of the bypass diode 5 n-doped semiconductor layer as the basis of the bypass diode

6 semi-insulating substrate

7 insulation layer

8 metal layer 9 contact grid

11 n-doped semiconductor layer as the emitter of the solar cell

12 p-doped semiconductor layer as the basis of the solar cell 13 n-doped semiconductor layer

14 p-doped semiconductor layer

15 n-doped transverse conductive layer

16 semi-insulating substrate

17 Insulation layer 18 Metal layer

19 contact grid

20 tunnel diode forming layer sequence 21 tunnel diode forming layer sequence

Claims

claims 1. Arrangement with at least one solar cell, in particular in a monolithically series-connected solar module, which is formed by a first layer sequence (1, 2, 11, 12) of differently doped layers over a substrate (6, 16), and at least one bypass Diode, which is connected to the solar cell and formed by a second Schicht¬ sequence (4, 5, 13, 14), characterized in that the bypass diode between the substrate (6, 16) and the first layer sequence (1 , 2, 11, 12) is arranged. 2. Arrangement according to claim 1, characterized in that between the first (1, 2, 11, 12) and the second layer sequence (4, 5, 13, 14) at least a third layer sequence (3, 20, 21), which forms a tunnel diode. 3. Arrangement according to claim 1 or 2, characterized in that the first layer sequence (1, 2, 11, 12) at least one p-type and one n-type Layer, which form a photovoltaically active region, and lie on a highly doped transverse conductive layer. 4. Arrangement according to one of claims 1 to 3, characterized in that the second layer sequence (4, 5, 13, 14) comprises at least one p-type and one n-type layer. 5. Arrangement according to claim 1, characterized in that on the substrate (16) at least the following layers or layer sequences are applied in the stated order: - A highly doped n-conducting Querleitschicht (15); a thin layer sequence (21) forming a tunnel diode; - A p-doped layer (14) and a highly doped n-conducting Querleitschicht (13) as a second layer sequence; a thin layer sequence (20) forming another tunnel diode; and - A p-doped layer (12) and an n-doped layer (11) as a first layer sequence. 6. Arrangement according to one of claims 1 to 5, characterized in that the layer sequences are formed by epitaxially grown layers. 7. Arrangement according to one of claims 1 to 6, characterized in that underlying layers of the layer sequences via trenches in the layer sequences electrically are contacted. Solar module of a plurality of juxtaposed and interconnected in series with each other solar cells, which are connected in an arrangement according to one of claims 1 to 7 with bypass diodes.