阅读说明：本技术 具有背侧接通的正侧的多结太阳能电池 (Multijunction solar cell with a front side that is connected on the rear side ) 是由 W·克斯特勒 于 2020-08-26 设计创作，主要内容包括：一种具有背侧接通的正侧的堆叠状的多结太阳能电池,该多结太阳能电池按顺序地彼此相继地具有构成多结太阳能电池的背侧的锗衬底、锗子电池以及至少两个III-V族子电池,并且具有从多结太阳能电池的正侧穿过子电池延伸至背侧的敷镀贯通开口和引导通过该敷镀贯通开口的金属的连接接通部,其中,敷镀贯通开口具有连贯的侧面和椭圆形横截面的外周,其中,从多结太阳能电池的正侧到背侧,敷镀贯通开口的直径台阶状地降低,其中,锗子电池的正侧构造有向敷镀贯通开口突出的具有第一出口深度的周向第一台阶,其中,从锗子电池的位于锗子电池的pn结下方的区域中构造有向敷镀贯通开口突出的具有第二出口深度的周向第二台阶。(A multi-junction solar cell in the form of a stack with a front side which is connected on the rear side, which multi-junction solar cell has, in succession one after the other, a germanium substrate which forms the rear side of the multi-junction solar cell, a germanium subcell and at least two III-V subcells, and having plated through openings extending from the front side of the multijunction solar cell through the subcell to the back side and connection vias leading through the metal of the plated through openings, wherein the plated through opening has a continuous lateral surface and an outer circumference with an elliptical cross section, wherein the diameter of the plated through opening decreases stepwise from the front side to the back side of the multijunction solar cell, wherein the front side of the germanium sub-cell is configured with a circumferential first step protruding towards the plated through opening and having a first outlet depth, wherein a circumferential second step with a second exit depth protruding towards the plated through opening is configured from a region of the germanium sub-cell located below the pn-junction of the germanium sub-cell.)

1. A multi-junction solar cell (10) in the form of a stack having a front side (10.1) which is connected on the rear side, having a germanium substrate (14), a germanium subcell (16) and at least two group III-V subcells (18, 20) in succession, wherein the germanium substrate forms the rear side (10.2) of the multi-junction solar cell (10), and the multi-junction solar cell has at least one plated through opening (12) which extends from the front side (10.1) of the multi-junction solar cell (10) through the subcells (16, 18, 20) to the rear side, and a metallic connection lead (22) which extends through the plated through opening (12);

-wherein the plated through opening (12) has a coherent side face (12.1) and a periphery with an elliptical cross section;

-wherein the diameter (D) of the plated through opening (12) decreases stepwise from the front side (10.1) of the multijunction solar cell (10) to the back side (10.2) of the multijunction solar cell (10);

-wherein in a projection in a direction from the front side (16.1) towards the germanium sub-cell (16)

-configured with a surrounding first step (24) protruding into the plated through opening (12) and having a first outlet depth (S1); and is

-configuring a surrounding second step (26) from a region of the germanium sub-cell (16) below a pn-junction (16.2) of the germanium sub-cell (16), the second step protruding into the plated through-opening (12) and having a second exit depth (S2).

2. The stacked multijunction solar cell (10) according to claim 1, characterised in that the side faces (12.1) of the plated through-openings (12) are coated with a dielectric isolating layer (28) and the metallic connection vias (22) are formed as metallic connection layers on the dielectric isolating layer (28) and on the regions of the upper side (10.1) of the multijunction solar cell adjoining the isolating layer (28): the metal contact layer extends from a front side (10.1) of the multijunction solar cell (10) to a rear side (10.2) of the multijunction solar cell (10).

3. The stacked multijunction solar cell (10) according to claim 1 or 2, characterised in that the group III-V subcells (18, 20) have a total layer thickness (H1) of 5-15 μ ι η or 6-8 μ ι η.

4. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the plated through-openings (12) have a diameter (D1) of at least 300 μ ι η or at least 400 μ ι η or at least 450 μ ι η at the front side (10.1) of the multijunction solar cell (10), wherein the diameter (D1) is not more than 1 mm.

5. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the lateral faces (12.1) of the plated through-openings (12) have an angle of at most 10 ° or at most 2 ° or at most 1 ° or at most 0.1 ° with respect to the longitudinal axis of the plated through-openings (12), respectively, between the steps (24, 26) and/or above the first step (24) and/or below the second step (26).

6. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the exit depth (S1) of the first step (24) is at least 100 μ ι η or at least 200 μ ι η.

7. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the exit depth (S2) of the second step (26) is at least 5 μ ι η or at least 10 μ ι η.

8. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the germanium subcell (16) together with the germanium substrate (12) has a layer thickness (H2) of 80-300 μ ι η or 140-160 μ ι η or 80-120 μ ι η.

9. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the rise height of the second step (26) relative to the first step (24) is 1-4 μ ι η or 1-3 μ ι η or 2 μ ι η.

10. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the multijunction solar cell (10) comprises a group III-V cladding layer (30) which constitutes the front side (10.1) and has a thickness of 150-500nm and a band gap of at least 1.86 eV.

Technical Field

The invention relates to a multi-junction solar cell in the form of a stack with a front side that is connected on the rear side.

Background

In order to reduce the shading of the front side of the solar cell, not only the front side can be externally connected to the through surface, but alsoThe negative outer through-plane is arranged on the backside. In so-called Metal Wrap Through (MWT) solar cells, for example, by plating through openings from the rear sideThe solar cell front side is turned on.

Different methods for producing holes or plated through openings through solar cells are known, which lead to correspondingly different plated through openings.

A production process for MWT single-junction solar cells made of polycrystalline silicon is known from Die Metal Wrap Through solar panel-end chararkterserung, phd article, 2009, month 2, in which plated Through openings are produced in a mc silicon substrate layer by means of a UV laser or an IR laser.

Only then is an emitter layer produced by means of phosphorus diffusion along the upper and side faces of the plated through opening and the lower side of the solar cell. The plated through openings are filled with a conductive through Paste (Via-Paste), such as silver Paste, by means of screen printing.

With the aid of the laser, a very smooth flank can be achieved in the region of the through-hole, and furthermore no undercuts occur with the laser ablation process. However, creating a hole through an existing pn junction by laser ablation may result in a short circuit.

An inverted growth-type GalnP/AlGaAs solar cell structure with plated through-openings is known from III-V multi-junction metal-wrap-through (mwt) solar cells, e.oliva et al, proceedings, 32 th european PV conference and exhibition, munich, 2016, 1367 pages 1371, wherein a solar cell structure with a pn junction is grown epitaxially before the plated through-openings are created by means of dry etching. Then, the side of the through opening is coated with an isolation layer, followed by filling the through opening with electroplated copper.

A solar cell stack is known from US 9680035B 1, which comprises a plurality of III-V subcells on a GaAs substrate with a front side that is back-side connected, wherein holes extending from the upper side of the solar cell through the subcells into the substrate layer that has not yet been thinned are produced by means of a wet chemical etching process.

The etching process is based on the fact that the etching rate does not differ significantly, at least for the different III-V materials used for the solar cell stack. The hole can only be opened downwards by thinning of the substrate layer. Passivation and metallization of the alignment side and the holes are performed before thinning of the substrate layer. The advantage of wet chemical etching compared to a corresponding dry etching process is that the sidewalls of the holes have a smoother surface and that the passivation layer can be deposited conformally and without defects.

Disclosure of Invention

Against this background, the object of the invention is to specify a device which expands the prior art.

This object is achieved by a multi-junction solar cell in the form of a stack having the features according to the invention. Advantageous embodiments of the invention are the subject matter of the dependent claims.

According to the subject matter of the invention, a multi-junction solar cell in the form of a stack with a back-side connected front side is provided.

The multijunction solar cell has, in succession (in der gen enthenfolge), a germanium substrate and at least two III-V subcells, the germanium substrate forming the back side of the multijunction solar cell and having germanium subcells.

Furthermore, the multijunction cell has at least one plated through-opening extending from the front side of the multijunction solar cell through the subcell to the back side, and a metallic connection via passing through the plated through-opening.

The plated through opening has continuityAnd an oval cross-sectional periphery.

The diameter of the plated through-opening decreases stepwise from the front side to the rear side of the multijunction solar cell, wherein, in a projection in the direction from the front side toward the germanium subcell, a circumferential first step is formed, which protrudes into the plated through-opening and has a first exit depth.

Furthermore, a circumferential second step is formed by the region below the pn junction of the germanium subcell, which second step protrudes into the plated through opening and has a second exit depth.

According to one embodiment, the multijunction solar cell has exactly two plated through openings.

It is to be understood that the individual subcells of a multijunction solar cell each have a pn junction and that the subcells are epitaxially grown on a layer following the substrate and/or connected to each other by means of wafer bonding.

Furthermore, it is to be understood that a Ge subcell has or consists of germanium, wherein the layer consisting of germanium may contain other substances, in particular dopants, but also impurities, in addition to germanium. Correspondingly, the same applies to group III-V subcells having or consisting of one or more materials of main group III and main group V, or a combination of these materials.

The larger diameter of the plated through-opening in the region of the upper side of the multijunction solar cell and the downward step-like tapering of the plated through-hole do not have an underetchingThis ensures that the coating (e.g. barrier layer) can be applied reliably and defect-free in a simple manner (e.g. by means of vapor deposition).

Furthermore, a stepped through-opening can be produced in a simple manner, for example by means of a two-stage etching process (removal of all pn junctions without under-etching) and a subsequent laser ablation process, and a rapid and simple severing (durchtrennenn) of the remaining Ge subcells from the Ge substrate can be achieved even if the Ge substrate has not been thinned or has not been particularly thinned.

The advantage of the multijunction solar cell according to the invention is particularly high reliability and efficiency at relatively low production costs.

According to a first embodiment, the side faces of the plated through opening are coated with a dielectric isolation layer.

Preferably, the metallic connection vias are formed as metallic connection layers on the dielectric separating layer, which extend from the front side to the rear side of the multijunction solar cell.

In another embodiment, the III-V subcells collectively have a layer thickness of 5-15 μm or 6-8 μm.

According to a further development, the plated through opening has a diameter of at least 300 μm or at least 400 μm or at least 450 μm at the front side of the multijunction solar cell, wherein the diameter is not greater than 1 mm.

According to a further development, the side faces of the plated through opening have an angle of at most 10 ° or at most 2 ° or at most 1 ° or at most 0.1 ° with respect to the longitudinal axis of the plated through opening between the steps and/or above the first step and/or below the second step, respectively.

In another embodiment, the first outlet depth of the first step is at least 100 μm or at least 200 μm.

In another embodiment, the second outlet depth of the second step is at least 5 μm or at least 10 μm.

In a further embodiment, the germanium subcell and the germanium substrate layer together have a layer thickness of 80-300 μm or 140-160 μm or 80-120 μm.

According to another embodiment, the rising height of the second step to the first step is 1-4 μm or 1-3 μm or 2 μm.

According to another embodiment, the multijunction solar cell comprises a group III-V capping layer, for example made of InGaP, constituting the front side and having a thickness of 150-.

Drawings

The invention is further elucidated below with reference to the drawing. Here, the same type of parts are labeled with the same name. The embodiments shown are very schematic, i.e. the distances and the lateral and vertical extensions are not to scale and have no derivable geometrical relation to each other, unless otherwise stated. The figures show:

fig. 1 shows a cross-sectional view of a first embodiment of a plated through-opening of a multi-junction solar cell in the form of a stack with a front side that is closed on the rear side according to the invention;

FIG. 2 illustrates a top view of a multijunction solar cell in accordance with one embodiment of the present invention;

fig. 3 shows a back side view of a multijunction solar cell according to an embodiment of the present invention;

fig. 4 shows a cross-sectional view of another embodiment according to the invention of plated through openings.

Detailed Description

The illustration of fig. 1 shows a partial view of a multi-junction solar cell 10 in cross section in the form of a stack with a front side that is switched on from the back side. The multijunction solar cell has an upper side 10.1 and a lower side 10.2 and a through opening 12 extending from the upper side 10.1 to the lower side 10.2.

The lower side 10.2 is formed by a germanium substrate 14. On the germanium substrate there follows in sequence a germanium subcell 16, a first III-V subcell 18 and a second III-V subcell 20 constituting the upper side 10.1.

The two III-V subcells 18 and 20 collectively have a first layer thickness H1. The germanium substrate 13 together with the germanium subcell has a second layer thickness H2.

The through-opening 12 has a side 12.1, wherein the side 12.1 is configured as a continuous piece like the cladding of a cylinder and has an oval (e.g., circular or elliptical) shape in cross section.

The through opening 12 also has two steps 24 and 26. The first step 24 is formed by the front side 16.1 of the germanium subcell 16, wherein the upper side 16.1 forms a circumferential outlet face with a constant outlet depth S1 in the radial direction.

The second step 26 is located in the region of the germanium subcell 16 below the pn junction 16.2 of the germanium subcell 16 and has a surrounding exit face with an exit depth S2.

The side surfaces 12.1 and the regions of the upper side 10.1 and the lower side 10.2 of the plated through opening 12 adjacent to the through opening 12 are covered by a dielectric isolation layer 28.

The metallic connection vias 22 are formed as metallic connection layers which extend from the upper side 10.1 of the multijunction solar cell 10 on the region of the dielectric isolating layer 28 adjoining the dielectric isolating layer 28 through the plated-through openings to the region of the lower side 10.2 of the multijunction solar cell covered by the dielectric isolating layer 28.

The metallic contact layer 22 is connected to the upper side 10.1 of the multijunction solar cell 10 and to the dielectric separating layer 28 in a material-locking manner.

In the illustration of fig. 2, a further embodiment of the multijunction solar cell is shown in a top view of the front side 10.1. Only the differences from the illustration of fig. 1 are explained below.

The multijunction solar cell 10 has exactly two plated through openings 12, wherein the two plated through openings 12 are each arranged at an end of a busbar (sammelschine) and the metallic contact layers 22 are each electrically conductively connected to a contact strip (kontake tschiene).

At regular intervals, the contact fingers (Kontaktfinger) extend perpendicular to the busbars on the upper side 10.1 of the multijunction solar cell, wherein each contact finger is electrically conductively connected to a busbar and/or one of the contact layers 22.

In the illustration of fig. 3, a further embodiment of the multijunction solar cell is shown in a top view of the rear side 10.2. Only the differences from the illustration of fig. 1 are explained below.

The multijunction solar cell 10 has exactly two plated through openings 12. The two plated through openings are surrounded by a coherent dielectric isolation layer 28.

In the illustration of fig. 4, a sectional view in the region of the through-opening of a further embodiment of the multijunction solar cell is shown, wherein only the differences from the illustration of fig. 1 are explained below.

The dielectric layer 28 and the metallic via layer 22 are not shown for clarity.

The multijunction solar cell has a group III-V cladding layer 30 (e.g. InGaP layer) on the second group III-V subcell 20, which constitutes the upper side 10.1 of the multijunction solar cell 10.

The through opening, which is produced, for example, by two etching processes and one laser ablation process, has three regions which are separated by one of the steps S1 or S2, respectively.

The first region extends from the upper side 10.1 of the multijunction solar cell 10 to the upper side 16.2 of the germanium subcell, wherein the first region has a constant or only slightly decreasing diameter D1 in the direction of the germanium subcell.

The second region extends from the upper side 16.1 of the germanium subcell 16 into the germanium subcell 16 and has a constant or decreasing diameter D2 in the direction of the germanium substrate 14.

The third region extends from the second step S2 to the lower side 10.2 of the multijunction solar cell and has a constant or slightly decreasing diameter D3 in the direction of the lower side 10.2.