阅读说明：本技术 具有包括多层系统的金属化层的堆叠状的多结太阳能电池 (Multi-junction solar cell in the form of a stack with metallization layers comprising a multilayer system ) 是由 W·克斯特勒 B·哈格多恩 于 2020-08-25 设计创作，主要内容包括：一种具有包括多层系统的金属化层的堆叠状的多结太阳能电池,其中,多结太阳能电池具有构成该多结太阳能电池的下侧的锗衬底、锗子电池和至少两个III-V族子电池,金属化层的多层系统按顺序地具有第一层、第二层、第三层和至少一个金属的第四层：包括金和锗的第一层具有至少2nm和至多50nm的层厚度D1；包括钛的第二层具有至少10nm和至多300nm的厚度D2；包括钯或镍或铂的第三层具有至少5nm和至多300nm的层厚度D3；至少一个金属的第四层具有至少2μm的厚度,金属化层的多层系统覆盖至少一个第一表面区段和第二表面区段,并且与第一表面区段和第二表面区段材料锁合地连接,其中,第一表面区段由电介质的隔离层构成,第二表面区段由锗衬底或III-V族层构成。(A multijunction solar cell in the form of a stack with metallization layers comprising a multilayer system, wherein the multijunction solar cell has a germanium substrate constituting the underside of the multijunction solar cell, a germanium subcell and at least two group III-V subcells, the multilayer system of metallization layers having in order a first layer, a second layer, a third layer and a fourth layer of at least one metal: the first layer comprising gold and germanium has a layer thickness D1 of at least 2nm and at most 50 nm; the second layer comprising titanium has a thickness D2 of at least 10nm and at most 300 nm; the third layer comprising palladium or nickel or platinum has a layer thickness D3 of at least 5nm and at most 300 nm; the at least one fourth layer of metal has a thickness of at least 2 μm, and the multilayer system of metallization layers covers and is connected in a material-locking manner to the at least one first and second surface sections, wherein the first surface section is formed by a dielectric isolation layer and the second surface section is formed by a germanium substrate or a group III-V layer.)

1. A stacked multijunction solar cell (10) having a metallization layer comprising a multilayer system (12), wherein,

-the multijunction solar cell (10) has, in succession to one another, a germanium substrate (14) which constitutes the underside (10.2) of the multijunction solar cell (10), a germanium subcell (16) and at least two group III-V subcells (18, 20);

-the multilayer system of metallization layers (12) has, in sequence, a first layer (M1) comprising gold and germanium and having a layer thickness D1 of at least 2nm and at most 50nm, a second layer (M2) comprising titanium and having a layer thickness D2 of at least 10nm and at most 300nm, a third layer (M3) comprising palladium or nickel or platinum and having a layer thickness D3 of at least 5nm and at most 300nm, and a fourth layer of at least one metal (M4) having a layer thickness D4 of at least 2 μ ι η;

-the multilayer system of metallization layers (12) covers at least one first surface section and a second surface section and is connected in a material-locking manner both to the first surface section and to the second surface section; wherein the content of the first and second substances,

-the first surface section is constituted by an isolation layer (24) of a dielectric and the second surface section is constituted by the germanium substrate (14) or a group III-V layer.

2. The stacked multijunction solar cell (10) according to claim 1, characterised in that it has a front side which is back-side connected, wherein,

-the semiconductor wafer has at least one plated through hole (22) as follows: the at least one plated-through hole extends from an upper side (10.1) of the multijunction solar cell (10) through the subcell (16, 18, 20) to the lower side (10.2) and has a continuous side wall (22.1) and an outer circumference of elliptical cross-section;

-the side walls (22.1) of the plated through holes (22) are covered by an isolation layer (24) of dielectric.

3. The stacked multijunction solar cell (10) according to claim 1 or 2, characterised in that the fourth layer (M4) comprises silver and has a layer thickness D4 of at least 2.5 μ ι η and at most 6 μ ι η.

4. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the multilayer system (12) has a fifth layer (M5) comprising gold, which has a layer thickness D5 of at least 50nm and at most 1 μ ι η.

5. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the dielectric layer (24) comprises SiO_xAnd/or SiN_xOr from SiO_xAnd/or SiN_xAnd (4) forming.

6. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the dielectric layer (24) comprises an amorphous silicon layer.

7. 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.

8. The stacked multijunction solar cell (10) according to one of the preceding claims, characterised in that the multilayer system of metallization layers (12) extends from the upper side (10.1) of the multijunction solar cell (10) along the side walls (22.1) through the plated-through holes (22) to the lower side (10.2) of the multijunction solar cell (10).

Technical Field

The invention relates to a stacked multijunction solar cell (Mehrfachsolarelle) having a metallization layer (Metalliery) comprising a multilayer system.

Background

Different methods have been used for the metallization of semiconductor wafers. The desired metal structure is produced, for example, by means of a coating mask (Lackmask) made of a positive coating (Positivilak) or a negative coating (Negativilak), wherein the metal is applied in a planar manner, for example, by means of physical vapor deposition. Alternatively, printing methods are used which apply only the desired metal structure directly, for example screen printing (Siebdruck) or dispensing heads

In order to reduce the shading of the front side of the solar cell, through-openings can be applied by means of platingThe front side is switched on from the back side. Such a solar cell is also called a Metal Wrap Through (MWT) solar cell.

In addition to different methods for producing plated through openings, different metallization methods are also known, in particular in order to achieve reliable metallization in the region of the plated through openings.

A production process for MWT single-junction solar cells made of polycrystalline silicon is known from the word Wrap Through solar panel-end charaktersierring, phd paper, 2009, 2, by f.clement, 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.

An inverted through-plated opening is known from the III-V Multi-junction metal-wrap-through (MWT) controller solar cells of E.Oliva et al, proceedings, the 32 nd European PV conference and exhibition, Munich, 2016, 1367-A growing GalnP/AlGaAs solar cell structure, wherein a solar cell structure with a pn junction is epitaxially grown and subsequently plated through openings are produced by means of dry etching. Then, the isolation layer is used to form a through openingIs coated and then the through opening is filled 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 having a front side which is connected on the rear side, wherein a hole extending from the upper side of the solar cell through the subcell into the substrate layer which has not yet been thinned is produced by means of a wet chemical etching process and is open only by thinning of the substrate layer. Before thinning, a metallic contact surface is arranged on the upper side of the solar cell stack, the connecting upper and lateral sides of the hole are coated with a barrier layer, and then a metal layer is applied to the metallized contact surface and the barrier layer.

For good adhesion of the metal layer to the dielectric (e.g. silicon dioxide or silicon nitride), titanium is usually used. However, due to poor adhesion, Ti is used for the turn-on of Ge and III-V semiconductors. For example, silver, palladium or gold may enable reliable and durable adhesion on semiconductor layers made of germanium or group III-V semiconductors. However, noble metals such as silver, palladium or gold show insufficient adhesion to the dielectric.

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 multijunction solar cell having the features according to the invention. Advantageous configurations of the invention are preferred embodiments.

According to the subject matter of the invention, a multijunction solar cell is provided in the form of a stack with metallization layers comprising a multilayer system, wherein the multijunction solar cell has, in succession one after the other (in der gen and Reihenfolge), a germanium substrate, a germanium subcell and at least two III-V subcells, which form the underside of the multijunction solar cell.

The multilayer system of metallization layers has, in order, a first layer, a second layer, a third layer and at least one fourth layer of metal: the first layer comprising gold and germanium has a layer thickness D1 of at least 2nm and at most 50 nm; the second layer comprising titanium has a thickness D2 of at least 10nm and at most 300 nm; the third layer comprising palladium or nickel or platinum has a layer thickness D3 of at least 5nm and at most 300 nm; the fourth layer of at least one metal has a thickness of at least 2 μm.

The multilayer system of metallization layers covers at least one first surface portion and one second surface portion and is connected to the first surface portion and the second surface portion in a material-locking manner, wherein the first surface portion is formed by a dielectric barrier layer and the second surface portion is formed by a germanium substrate or a group III-V layer.

It should be understood that annealing (i.e., heat treatment) is performed on the multilayer system, such as is typical for metallization layers.

In one embodiment, the temperature in the heat treatment of the multilayer metal system is preferably in the range between 350 ° and 420 °.

Preferably, the heat treatment is performed by means of lamp heating, i.e. by means of a so-called Rapid Thermal Annealing (RTA) process.

The temperature of the heat treatment is in particular at least 350 ℃.

The eutectic temperature of the gold germanium layer is thereby reached, whereby the connection between the titanium layer and the dielectric layer can only be achieved.

It should furthermore be understood that according to an alternative embodiment the layers are respectively composed of the mentioned materials, wherein the term "composed of … …" includes the following: other substances such as impurities may also be included or contained.

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 as well as main group V.

Surprisingly, it has been shown that the proposed layer system adheres very reliably and durably not only on dielectrics, but also on semiconductors. A low layer thickness of the gold germanium layer leads to an inhomogeneous, but locally localized permeability of the Ti layer, which may enable a local connection between the titanium layer and the isolating layer of dielectric.

On the other hand, a low layer thickness of the gold-germanium layer is sufficient to achieve a reliable material-locking of the gold-germanium layer with the Ge layer or the III-V sub-cell.

The multilayer system of metallization layers therefore opens up a number of possibilities for optimizing the production process and also with regard to the configuration of the metallization (in particular with regard to the plating-through). In particular, process steps, additional or different metal structures can be saved.

The multijunction solar cell according to the invention therefore represents a particularly cost-effective and efficient solution.

According to a first embodiment, the multijunction solar cell has a front side which is closed on the rear side, wherein the semiconductor wafer has at least one through-hole via (Durchgangskontaktloch) which extends from the upper side of the multijunction solar cell through the subcell to the lower side and has a continuous thicknessAnd the outer perimeter of the elliptical cross-section, and the sidewalls of the plated through holes are covered by a dielectric spacer.

In another embodiment, the fourth layer comprises silver and has a layer thickness of at least 2.5 μm and at most 6 μm.

According to a further embodiment, the multilayer system has a fifth layer comprising gold, which has a layer thickness D5 of at least 50nm and at most 1 μm.

In a further embodiment, the dielectric layer comprises SiO₂And/or Si₃N₄Or from SiO₂And/or Si₃N₄And (4) forming.

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

In a further embodiment, the multilayer system of metallization layers extends from the upper side of the multijunction solar cell along the side walls through the plated-through holes up to the lower side of the multijunction solar cell.

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. Shown here are:

fig. 1 shows a cross-sectional view of a first embodiment of a stacked multijunction solar cell according to the invention, with a front side which is connected on the back side and a multilayer system as a metallization layer;

fig. 2 shows a back side view of a multijunction solar cell according to an embodiment of the present invention;

fig. 3 shows a cross-sectional view of a multilayer system of metallization layers according to a first embodiment of the invention.

Detailed Description

The illustration of fig. 1 shows a stack-like multijunction solar cell 10 with metallization layers comprising a multilayer system 12 and a front side with a back side connected, in a sectional illustration.

The multijunction solar cell 10 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 multijunction solar cell 10 comprises in sequence a germanium substrate 14 constituting the lower side 10.1, a germanium subcell 16 following the germanium substrate, a first III-V subcell 18 and a second III-V subcell 20 constituting the upper side 10.2 in the embodiment shown.

The through-opening 22 has a side face 22.1, wherein the side face 22.1 is configured as a continuous piece like a cladding face of a cylinder and has, in cross section, an oval (oval) shape, for example, circular or elliptical.

The side 22.1 of the through-opening 22 and the region of the upper side 10.1 and of the lower side 10.2 adjoining the through-opening 22 are covered by a dielectric isolation layer 24.

A multilayer system 12 of metallization layers is formed on the dielectric isolation layer 24, wherein the multilayer system 12 extends from a region of the upper side 10.1 of the semiconductor wafer 10 adjoining the dielectric isolation layer 24 along the side 22.1 of the through-opening 22 to a region of the dielectric isolation layer 24 formed on the lower side 10.2 adjoining the through-opening.

The multilayer system 12 therefore extends beyond the dielectric barrier layer 24 on the upper side 10.1 of the semiconductor wafer 10 and is connected in a material-locking manner both to the dielectric barrier layer 24 and to the upper side 10.1 of the semiconductor wafer 10 (here the second group III-V subcell 20).

The part of the lower side 10.2 not covered by the dielectric isolation layer 24 is also covered by the multi-layer system of metallization layers 12.

A backside view of a multijunction solar cell according to a first embodiment is shown in the illustration of fig. 2. Only the differences from the illustration of fig. 1 are explained below.

The multijunction solar cell 10 has exactly two through openings 22. Plate-like multilayer system 12 with metallization layers in the region of multilayer system 12 formed around through-opening 22Are connected and surrounded by an isolating layer 24 of dielectric.

The remaining surface of the lower side 10.2 of the semiconductor wafer is covered in a planar manner by a multilayer system 12.

The multilayer system according to the first embodiment is shown in more detail in the illustration of fig. 3. Only the differences from the illustration of fig. 1 are explained below.

The multilayer system 12 includes five layers. The first layer M1 comprising gold and germanium, which constitutes the lowermost layer adjoining the dielectric layer 24 and the semiconductor wafer 10, has a layer thickness of at most 50 nm.

A second layer M2 comprising titanium, having a layer thickness of at least 10nm, follows on the first layer M1. The third layer M3 comprises palladium, nickel or platinum and has a layer thickness of at least 5 nm.

The fourth metal layer, for example comprising silver, has a layer thickness of at least 2 μm. In the embodiment shown, the multilayer system 12 comprises a fifth metal layer (for example comprising gold) as the uppermost layer, which has a layer thickness of at least 50 nm.