DE102021123652A1 - tandem solar cell - Google Patents

Abstract

The present invention relates to a tandem solar cell composed of at least two partial solar cells monolithically stacked one on top of the other. In order to provide a tandem solar cell with increased mechanical stability, which also enables an advantageous application of solar cell structures containing perovskite, the invention proposes designing the tandem solar cell in such a way that at least one of the partial solar cells has a support structure which has at least one through a layered structure of this partial solar cell and filled with a supporting trench and has a supporting layer formed from the supporting material, materially bonded to the supporting material located in the at least one supporting trench and extending flatly over this layered structure of the partial solar cell and the at least one supporting trench.

Description

The present invention relates to a tandem solar cell composed of at least two partial solar cells monolithically stacked one on top of the other.

A tandem solar cell consists of two or more partial solar cells stacked on top of each other. The uppermost partial solar cell facing the light, the so-called top cell, of the tandem solar cell absorbs short-wave, high-energy light and lets long-wave, low-energy light through to the at least one partial solar cell located below. The respective sub-solar cell arranged underneath absorbs part of the light spectrum up to a limit wavelength determined by the band gap of the semiconductor material of this sub-solar cell. In the tandem solar cell, sub-solar cells made of different semiconductor materials or combinations or crystallinity are combined, which have optimal band gaps for individual spectral ranges. With such an arrangement, it is possible to increase the efficiency compared to conventional single solar cells, not only by expanding the absorption range, but also by increasing the efficiency of converting sunlight into electricity.

The best-known tandem solar cell consists of three stacked partial solar cells made of GaInP, GalnAs and Ge. New concepts of tandem solar cells are based on a combination of a silicon base partial solar cell with partial solar cells arranged on top made of A(III)-B(V) compound semiconductors or perovskites, which means that overall efficiencies of tandem solar cells of over 30% can be achieved in the future.

Perovskites are made from components such as metal salts that are readily available and inexpensive. They can also be significantly thinner than silicon layers in solar cells and still have high absorption, so that the light, thin solar cells made from them are particularly suitable for use on curved surfaces or can be folded. However, a disadvantage of perovskite is its low stability. The components it contains are sensitive to environmental influences. The solar cells in question are therefore laminated with suitable plastic films and/or glasses to form solar modules using pressure and temperature. On the one hand, the laminate forms a barrier against environmental influences and at the same time ensures the mechanical stability of the solar modules. Due to the mechanical instability of perovskite, however, the solar cells can fail during lamination due to the pressure used or subsequently due to thermal stresses during operation of the solar module.

There are similar problems with the electrical contacting of tandem solar cells having perovskite. To solve this, the pamphlet proposes WO 2020/109129 A1 proposed to design the tandem solar cells to be connected in such a way that the upper part of the tandem solar cell, which has perovskite, extends over a smaller area than the part of the solar cell below, so that a step is created that is not covered by the upper part of the solar cell structure, with the step initially is provided with an insulator layer and then with an electrically conductive layer and subsequently the electrically conductive layer is electrically connected to an electrical contact of a next tandem solar cell. However, the problems that arise as a result of delamination of the perovskite tandem solar cells when exposed to sunlight or as a result of other mechanical pressure effects are not solved by this publication.

It is therefore the object of the present invention to provide a tandem solar cell with increased mechanical stability, which also enables an advantageous use of solar cell structures containing perovskite.

This object is achieved by a tandem solar cell made of at least two monolithic partial solar cells stacked one on top of the other, in which at least one of the partial solar cells has a supporting structure which has at least one supporting trench which passes through a layered structure of this partial solar cell and is filled with a supporting material.

In the tandem solar cell according to the invention, the at least one supporting trench runs through the entire layer sequence of the partial solar cell, ie also through those layers of the partial solar cell that have low mechanical stability. The at least one support trench is filled with the support material, so it is itself mechanically stable. As a result, it acts like a sleeve or a frame or frame grid around and/or between the electronically active area(s) of the partial solar cell.

In the present invention, that partial solar cell which has the support structure is preferably the top cell of the tandem solar cell that is arranged at the top. However, if the tandem solar cell consists of more than two partial solar cells, the support structure can also be provided for several upper partial solar cells or only for one or more middle partial solar cells. In principle, it is also possible for the lowermost partial solar cell or several lower partial solar cells of the tandem solar cell to be provided with the supporting structure.

However, it makes sense if the tandem solar cell has at least one mechanically stable substrate or at least one other mechanically stable structure, such as a basic partial solar cell made of silicon or another stable semiconductor material, on which the support structure can be supported.

The at least one support trench can be created, for example, by masking during the deposition of the layers of the layer stack of the solar cell part to be supported with the support structure and/or by evaporating areas of the layers of the layer stack of the solar cell part to be supported with the support structure by means of a laser or electron beam after their deposition and/or by mechanically removing areas of the layers of the layer stack of the partial solar cell to be supported by the support structure by means of scratching, rubbing, scraping or by contact with adhesive elements.

The at least one supporting trench can be designed in the form of a hole, a strip, an angle, a ring or a frame, in each case in a plan view of a light incidence side of the tandem solar cell. The at least one supporting trench can be designed, for example, in a sectional top view of the tandem solar cell, round or as a slot with the same or alternating orientation. In principle, however, the at least one supporting trench can have any geometric shape.

The tandem solar cell particularly preferably has a plurality of supporting trenches arranged in a regular arrangement.

For example, these supporting trenches can each be arranged at crossing points of an imaginary planar cubic, tetragonal or hexagonal lattice.

The period length of such a grating is preferably less than 10 mm.

In a preferred embodiment of the present invention, the support structure also has at least one support layer which is materially bonded to the support material located in the at least one support trench and is flat above and/or below the layer structure of the partial solar cell through which the at least one support trench passes. extends.

In this embodiment of the invention, all trench structures of the at least one support trench are connected to one another by the continuous support layer, so that the respective trench structures do not slip relative to one another even if at least one layer of the layer structure of the partial solar cell has low mechanical stability.

The at least one support layer can be located both above and below the stack of layers to be supported. The support layer thereby connects all trench structures of the at least one support trench to form a single support structure in a materially bonded manner by connecting all the trench structures of the at least one support trench to one another like a bridge.

In an advantageous variant of this embodiment of the invention, the supporting layer is formed from the same supporting material with which the at least one supporting trench is also filled. As a result, both the at least one supporting trench can be filled and the support layer, which can also serve as a protective and anti-reflection layer, can be produced with one and the same deposition process.

The support material is preferably a mechanically stable, diffusion-tight or at least strongly diffusion-inhibiting material. The support material is preferably a dielectric material, particularly preferably an electrically insulating material.

The support material should have optical properties matched to the stack of layers it supports, ie if possible have an optical transparency in the order of an average value of the optical transparency of this stack of layers, so that it does not shadow this stack of layers too much.

The support material can be, for example, a nitride such as aluminum nitride or silicon nitride, an oxide such as aluminum oxide or silicon oxide, an oxynitride such as aluminum oxynitride or silicon oxynitride, and/or a polymer.

The supporting layer is particularly preferably a protective and/or antireflection layer of the at least one partial solar cell having the supporting structure.

In the present invention, the protective and/or antireflection layer is that layer or layer sequence which is on top of the respective partial solar cell, i. H. also lies on the contacting layer or the contacting layer with the contacts of the respective partial solar cell and is produced by means of layer deposition.

In this preferred embodiment of the invention, the support material is to be selected in such a way that it not only has the required mechanical stability, but also moisture diffusion sion barrier is and / or has anti-reflective properties.

The geometric shape of the at least one support trench and the respective spacing between individual trench structures of the at least one support trench are preferably selected as a function of the micromechanical properties of the support layer used. If, for example, the individual trench structures of the at least one supporting trench are hole structures, they should preferably be provided in a regular hole pattern. A regular arrangement is also advantageous with other geometric configurations of the at least one supporting trench.

In a preferred embodiment of the tandem solar cell according to the invention, at least one layer of the layer structure of the at least one partial solar cell having the support structure is made of perovskite, which is why this partial solar cell is referred to below as a perovskite partial solar cell.

As mentioned at the outset, perovskite in particular is mechanically unstable. However, the tandem solar cell according to the invention makes it possible to mechanically stabilize the partial solar cell(s) that has/have at least one perovskite layer in such a way that the corresponding tandem solar cell can be laminated in without any problems, without the risk of delamination and without the electronic properties of the respective tandem solar cell being noticeably impaired.

In this embodiment of the invention, the at least one perovskite partial solar cell is advantageously formed on a basic partial solar cell that does not have any perovskite.

In addition to its advantageous electronic properties, such as the absorption of a different light spectrum than that absorbed by the perovskite partial solar cell, the basic partial solar cell, which has no perovskite or no perovskite layer, creates a stable mechanical basis for placing the perovskite partial solar cell, which is mechanically stabilized by the support structure , which typically forms the upper part of the solar cell and absorbs the short-wave light radiation.

Particularly preferably, the at least one supporting trench of the perovskite solar cell part ends on a contacting layer of the solar cell part, such as on an indium tin oxide layer of the solar cell part.

In a preferred embodiment of the present invention, the basic partial solar cell has a heterojunction. The combination of a heterojunction partial solar cell and a mechanically stabilized perovskite partial solar cell allows long-lasting tandem solar cells to be formed with a very high level of efficiency.

• 1 schematisch eine Ausführungsform einer erfindungsgemäßen Tandem-Solarzelle im Querschnitt zeigt.

An embodiment of the present invention, its structure, function and advantages is described below with reference to 1 explained in more detail, where

• 1 schematically shows an embodiment of a tandem solar cell according to the invention in cross section.

1 shows a possible embodiment of a tandem solar cell 1 according to the invention in a schematic cross section. In the exemplary embodiment shown, the tandem solar cell 1 has two partial solar cells 2, 3 arranged one above the other. In other embodiments of the tandem solar cell 1 according to the invention that are not shown, it can also have more than two partial solar cells stacked one on top of the other.

In the embodiment shown, the partial solar cell 2 arranged below acts as a base partial solar cell, which forms a mechanically stable basis for the construction of the upper partial solar cell 3 stacked above it.

In the embodiment shown, the basic partial solar cell 2 has a heterojunction.

The basic partial solar cell 2 has an absorber 21 . In the embodiment shown, the absorber 21 consists of monocrystalline silicon, but in other embodiments of the invention it can also consist of a different semiconductor material and/or have a different solid-state structure. The absorber 21 can be textured on one or both sides. The absorber 21 is of a first conductivity type. In the embodiment shown, the absorber 21 is n-doped, but can also be p-doped in other embodiments of the invention.

A lower front-side doping layer 22 is located on a front side of the absorber 21. In the example shown, the lower front-side doping layer 22 is a doped amorphous semiconductor layer, particularly preferably an amorphous silicon layer saturated with hydrogen. In the exemplary embodiment shown, the lower front side doping layer 22 is of the same first conductivity type as the absorber 21, ie n-doped, but has a higher doping than the absorber 21. In the embodiment shown, it forms an emitter of the basic partial solar cell 2 . In other, not shown, embodiments of the present invention lower front-side doping layer 22 also have a conductivity type opposite to the conductivity type of the absorber 21, ie be p-doped in the example shown.

In other embodiments of the invention that are not shown, a lower front-side intrinsic layer, i. H. an intrinsic amorphous semiconductor layer, preferably made of amorphous silicon, can be provided.

A lower front-side wiring layer 24 lies on the lower front-side doping layer 22. The lower front-side wiring layer 24 is formed of electrically conductive, transparent material, such as indium tin oxide.

A lower protective and/or antireflection layer 26 is formed on the lower front-side conduction layer 24 of the base partial solar cell 2 .

A lower rear side doping layer 23 is located on a rear side of the absorber 21. In the example shown, the lower rear side doping layer 23 is a doped amorphous semiconductor layer, particularly preferably an amorphous silicon layer saturated with hydrogen. In the exemplary embodiment shown, the lower rear side doping layer 23 is of a conductivity type which is opposite to the first conductivity type of the absorber 21, ie p-doped. In the embodiment shown, it forms a collector of the base partial solar cell 2 . In other specific embodiments of the present invention that are not shown, the lower rear-side doping layer 23 can also be of the same conductivity type as the absorber 21 , ie n-doped in the example shown, but have a higher doping than the absorber 21 .

In other non-illustrated embodiments of the invention, a lower backside intrinsic layer, i. H. an intrinsic amorphous semiconductor layer, preferably made of amorphous silicon, may be provided.

A lower backside wiring layer 25 lies on the lower backside doping layer 22. The lower backside wiring layer 25 is formed of electrically conductive, transparent material, such as indium tin oxide.

On the lower rear side line layer 25 there are rear side contacts 27 of the basic partial solar cell 2, which are printed silver contacts in the exemplary embodiment shown.

The layer structure of the upper partial solar cell 3 of the tandem solar cell 1 is built up on the lower protective and/or anti-reflection layer 26 of the base partial solar cell 2 .

A support structure 4 of the upper partial solar cell 3 extends in the form of at least one supporting trench 40, 40' filled with a supporting material 41 through the layer structure of the upper partial solar cell 3 described below and also through the lower protective and/or anti-reflection layer 26 of the base partial solar cell 2 and over the entire upper partial solar cell 3 in the form of a support layer 42 consisting of the support material 41 .

The upper partial solar cell 3 has an absorber having perovskite, referred to below as perovskite layer 31 . In addition to perovskite, the absorber of the upper partial solar cell 3 can also have at least one further material layer, such as a salt layer.

An upper front-side doping layer 32 lies on a front side of the perovskite layer 31. In the example shown, the upper front-side doping layer 32 is a doped amorphous semiconductor layer. In the exemplary embodiment shown, the upper front side doping layer 32 is n-doped. In the embodiment shown, it forms an emitter of the upper partial solar cell 3 . In other non-illustrated embodiments of the present invention, the upper front side doping layer 32 can also be p-doped.

In other, non-illustrated embodiments of the invention, an upper front side intrinsic layer, i. H. an intrinsic amorphous semiconductor layer.

In the exemplary embodiment shown, an upper front-side conductive layer 34 lies on the upper front-side doping layer 32. The upper front-side conductive layer 24 is formed of electrically conductive, transparent material, such as indium tin oxide.

In other specific embodiments of the invention that are not shown, at least one further electrically conductive, transparent layer can be provided between the upper front-side doping layer 32 and the upper front-side conduction layer 34 .

On the upper front line layer 34 are front side contacts 37 of the tandem solar cell 1, which are printed silver contacts in the exemplary embodiment shown.

An upper protective and/or anti-reflection layer is formed on the upper front-side line layer 34 and the front-side contacts 37 , which also acts as a support layer 42 in the present case.

In the exemplary embodiment shown, the supporting layer 42 consists of the supporting material 41, which also forms the filling of the at least one supporting trench 40, 40' and which is made of a dielectric material in the exemplary embodiment shown, but can also be made of a polymer. In other embodiments of the present invention, the support layer 42 can also consist of a different material than the support material 41 used to fill the at least one support trench 40, 40'. In further embodiments of the present invention, the support layer 42 can also be omitted or replaced by another layer or layer sequence or structure.

On a rear side of the perovskite layer 31 is an upper rear side doping layer 33. In the example shown, the upper rear side doping layer 33 is a doped amorphous semiconductor layer. In the exemplary embodiment shown, the upper rear-side doping layer 33 is p-doped. In the embodiment shown, it forms a collector of the partial solar cell 3 . In other non-illustrated embodiments of the present invention, the upper rear side doping layer 33 can also be n-doped.

In other, non-illustrated embodiments of the invention, an upper backside intrinsic layer, i. H. an intrinsic amorphous semiconductor layer.

In the embodiment shown, the upper rear-side doping layer 33 lies directly on the lower protective and/or anti-reflection layer 26 of the base partial solar cell 2 . The upper rear-side conduction layer of the upper partial solar cell 3 is formed here by the lower front-side conduction layer 24 of the base partial solar cell 2 .

In the exemplary embodiment shown, the at least one supporting trench 40, 40' is formed by a plurality of holes running through the layer sequence of the upper partial solar cell 3. The holes are filled with the support material 41, which in the exemplary embodiment shown also forms the material of the protective and/or anti-reflection layer of the upper partial solar cell 3 and thus merges directly into this layer here. The protective and/or anti-reflection layer of the upper partial solar cell 3 acting as a support layer 42 forms a bridge which materially connects all support trench structures or holes filled with the support material 42 to one another.

The at least one supporting trench 40 , 40 ′ is located in an edge area of the upper partial solar cell 3 , so that although the supporting structure 4 gives it good mechanical stability, its efficiency is hardly or not at all impaired by the supporting structure 4 .

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2020109129 A1 [0005]

Claims (15)

Tandem solar cell (1) made up of at least two partial solar cells (2, 3) stacked monolithically one on top of the other, characterized in that at least one of the partial solar cells (3) has a support structure (4), which at least one goes through a layered structure of this partial solar cell (3). and having support trenches (40, 40`) filled with a support material (41). tandem solar cell claim 1 , characterized in that the at least one supporting trench (40, 40`) is designed round or as a slot in the same or alternating orientation in a sectional plan view of the tandem solar cell (1). tandem solar cell claim 1 or 2 , characterized in that the tandem solar cell (1) has a plurality of supporting trenches (40, 40`) arranged in a regular arrangement. tandem solar cell claim 3 , characterized in that the support trenches (40, 40`) are each arranged at crossing points of a planar cubic, tetragonal or hexagonal lattice. tandem solar cell claim 4 , characterized in that a period length of the grating is less than 10 mm. Tandem solar cell according to one of the preceding claims, characterized in that the support structure (4) also has at least one support layer (42) which is cohesively connected to the support material (41) located in the at least one support trench (40, 40`) and extends over an area above and/or below the layer structure of the partial solar cell (3), through which the at least one supporting trench (40, 40`) passes. Tandem solar cell according to one of the preceding claims, characterized in that the supporting layer (42) is formed from the same supporting material (41) with which the at least one supporting trench (40, 40`) is also filled. Tandem solar cell according to one of the preceding claims, characterized in that the supporting material (41) is a dielectric material. tandem solar cell claim 4 , characterized in that the supporting material (41) is a nitride, an oxide, an oxynitride and/or a polymer. tandem solar cell claim 6 or 7 , characterized in that the supporting layer (42) is a protective and/or antireflection layer of the at least one partial solar cell (3) having the supporting structure (4). Tandem solar cell according to one of the preceding claims, characterized in that the at least one supporting trench (40, 40`) in a top view of a light incidence side (10) of the tandem solar cell (1) has a hole, strip, angle, tire or is designed in the form of a frame. Tandem solar cell according to one of the preceding claims, characterized in that at least one layer of the layer structure of the at least one partial solar cell (3) having the support structure (4) is made of perovskite, so that this partial solar cell (3) is a perovskite partial solar cell. tandem solar cell claim 12 , characterized in that the at least one perovskite partial solar cell is formed on a perovskite-having base partial solar cell (2). tandem solar cell Claim 13 , characterized in that the at least one supporting trench (40, 40`) of the perovskite partial solar cell ends on a contacting layer (24) of the base partial solar cell (2). tandem solar cell Claim 13 or 14 , characterized in that the base partial solar cell has a heterojunction.

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