Stacked multi-junction solar cell with a dielectric insulation layer system

Abstract

Stacked multi-junction solar cell (10) with a dielectric insulating layer system (24), wherein - the multi-junction solar cell (10) comprises a germanium substrate (14) forming a bottom surface (10.2) of the multi-junction solar cell (10), a germanium subcell (16) and at least two III-V subcells (18, 20) in the aforementioned order, - a top surface of the multi-junction solar cell (10) is formed by one of the III-V sub-cells or a III-V cap layer, - the insulation layer system (24) comprises a layer sequence of at least one lowest insulation layer (M1) connected to a first surface section of the multi-junction solar cell (10) and an uppermost insulation layer (M2) forming a top surface of the insulation layer system (24) and - a metallization (12) of the multi-junction solar cell (10) is materially and electrically connected to a second surface section of the multi-junction solar cell (10) adjacent to the first surface section of the multi-junction solar cell (10) and is materially connected to a section of the top of the insulation layer system (24), wherein - the uppermost insulating layer (M2) comprises or consists of amorphous silicon, and - the first surface section and the second surface section are formed on the top of the multi-junction solar cell (10), and on the top of the multi-junction solar cell (10) the metallization (12) completely covers the insulation layer system (24).

Description

[0001] The invention relates to a stacked multi-junction solar cell with a dielectric insulation layer system.

[0002] Various processes are known for the passivation and metallization of semiconductor wafers. The desired metal structure is created, for example, using a resist mask made of positive or negative resist on an insulating layer, with the metal being applied over the entire surface, e.g., by physical vapor deposition.

[0003] Alternatively, printing processes are used, e.g. screen printing or dispensing heads, which directly apply only the desired metal structure.

[0004] To reduce shading of the front side of a solar cell, it is possible to connect the front side to the back side using a through-hole contact. Such solar cells are also called metal wrap-through (MWT) solar cells.

[0005] In addition to different manufacturing processes for the through-contact opening, different metallization processes are also known, in particular to achieve reliable insulation and metallization in the area of ​​the through-contact opening.

[0006] A silicon-based MWT solar cell is known from US 2013 / 0 220 396 A1. A silicon-based solar cell structure with an improved passivation layer sequence is also known from US 2014 / 0 174 518 A1.

[0007] From “III-V multi-junction metal-wrap-through (MWT) concentrator solar cells,” E. Oliva et al., Proceedings, 32 ndEuropean PV Solar Energy Conference and Exhibition, Munich, 2016, pp. 1367-1371, an inverted-growth GaInP / AlGaAs solar cell structure with vias is known. The solar cell structure with the pn junctions is grown epitaxially, and only then is the via created by dry etching. The side surface of the via is then coated with an insulating layer, and the via is subsequently filled with copper by electroplating.

[0008] From US 9 680 035 B1, a solar cell stack comprising several III-V sub-cells on a GaAs substrate with a back-contacted front side is known, wherein a hole extending from the top side of the solar cell through the sub-cells into a substrate layer that has not yet been thinned is created by means of a wet-chemical etching process and is only opened downwards by thinning the substrate layer.

[0009] Before thinning, metallic contact surfaces are arranged on the top side of the solar cell stack, the adjacent top side and the side surface of the hole are coated with an insulating layer, and then a metal layer is applied to the metallic contact surfaces and the insulating layer.

[0010] Titanium is typically used to ensure good adhesion of a metal layer to a dielectric, such as silicon dioxide or silicon nitride. Reliable and long-lasting adhesion to semiconductor layers made of germanium or III-V semiconductors, however, is achieved with materials such as silver, palladium, or gold-germanium.

[0011] Against this background, the object of the invention is to provide a device that further develops the state of the art.

[0012] The object is achieved by a stacked multi-junction solar cell having the features of patent claim 1. Advantageous embodiments of the invention are the subject of subclaims.

[0013] In the subject matter of the invention, a stacked multi-junction solar cell with a dielectric insulation layer system is provided, wherein the multi-junction solar cell has a germanium substrate forming a bottom side of the multi-junction solar cell, a germanium sub-cell and at least two III-V sub-cells in succession in the stated order.

[0014] The insulation layer system has a layer sequence of at least one lowest insulation layer that is integrally connected to a first surface section of the multi-junction solar cell and an uppermost insulation layer that forms an upper side of the insulation layer system.

[0015] A metallization of the multi-junction solar cell is materially and electrically conductively connected to a second surface section adjacent to the first surface section of the multi-junction solar cell.

[0016] In addition, the metallization is integrally bonded to a section of the upper side of the insulation layer system.

[0017] The top insulation layer comprises or consists of amorphous silicon.

[0018] It is understood that the first surface portion and the second surface portion are formed on the top side of the multi-junction solar cell or on the bottom side of the multi-junction solar cell.

[0019] It should be noted that the first surface portion is predominantly or completely covered with a dielectric layer, preferably comprising at least one silicon dioxide layer. The second surface portion is predominantly or completely covered with a III-V material.

[0020] Accordingly, the surface sections are formed either from the Ge substrate or from a layer forming the top side of the semiconductor wafer, e.g. a III-V subcell or a III-V cap layer, ie a covering layer.

[0021] Furthermore, it is understood that a Ge subcell comprises germanium or consists of germanium, whereby a layer consisting of germanium may also contain, in addition to the germanium, further substances, in particular dopants, but also impurities.

[0022] The same applies to the III-V subcells, which contain one or more materials from the III and V main groups or consist of such materials.

[0023] The a-silicon layer ensures reliable and long-lasting adhesion with a wide variety of metallizations. This makes it possible, in particular, to achieve a material bond between a typical metallization for semiconductor surfaces, such as germanium in particular, but also III-V semiconductor materials, and the dielectric layer.

[0024] The entire insulation layer system can be easily produced in a single deposition process, e.g. plasma-enhanced chemical vapor deposition or APCVD or atomic layer deposition.

[0025] One advantage is that the insulation layer system does not require any further process steps and, on the other hand, opens up many possibilities for optimizing the manufacturing process as well as the design of the metallization, preferably with regard to through-hole contacts.

[0026] In particular, process steps and additional or different metal structures can be eliminated. This makes the multi-junction solar cell a particularly cost-effective and efficient solution.

[0027] In a first embodiment, the lowermost insulation layer comprises SiO2 and / or Si3N4 or consists of SiO2 and / or Si3N4.

[0028] In another embodiment, the insulation layer system comprises at least one further middle insulation layer, wherein the at least one middle insulation layer comprises SiO2 and / or Si3N4 or consists of SiO2 and / or Si3N4. It is understood that the bottom insulation layer comprises a different material than the middle insulation layer.

[0029] In a further embodiment, the multi-junction solar cell has a back-contacted front side, wherein the semiconductor wafer has at least one through-contact hole extending from a top side of the multi-junction solar cell through the sub-cells to the bottom side, with a continuous side wall and a circumference that is oval in cross section parallel to the surface, and a side wall of the through-contact hole is covered by the dielectric insulation layer system.

[0030] In a further development, the metallization on the insulation layer system extends from the top side of the multi-junction solar cell along the side wall through the through-hole to the bottom side of the multi-junction solar cell.

[0031] In another embodiment, the metallization comprises a multilayer system. In one further development, the multilayer system comprises an AuGe / Ti / Pd / Ag / Au layer sequence or a Pd / Au / Ge / Ti / Pd / Ag / Au layer sequence. In particular, the AuGe / Ti / Pd / Ag / Au layer sequence is a widely used and proven layer sequence for achieving metallization on germanium layers.

[0032] The Pd / Au / Ge / Ti / Pd / Ag / Au layer sequence has proven particularly successful for concentrator solar cells (CPV). Since Pd has higher reflectivity and conductivity in the 1 µm to 3 µm wavelength range than Ti, the so-called "backside reflector" provides a further advantage for the solar cells.

[0033] In an alternative development, the multi-layer system has a nickel-comprising layer or a layer comprising aluminum as the bottom layer.

[0034] The invention is explained in more detail below with reference to the drawings. Similar parts are labeled with identical designations. The illustrated embodiments are highly schematic, meaning the distances and the lateral and vertical dimensions are not to scale and, unless otherwise stated, do not have any deducible geometric relationships to one another. In the drawings: Fig. 1 shows a section of a first embodiment of a multi-junction solar cell with a dielectric insulation layer system, Fig. 2 shows another embodiment of a multi-junction solar cell with a dielectric insulation system, Fig. 3 shows another embodiment of a multi-junction solar cell with a dielectric insulation system, Fig. 4 a rear view of the multi-junction solar cell in another embodiment.

[0035] The illustration of the Fig. Figure 1 shows a section of a surface of a stacked multi-junction solar cell 10. The surface is formed by a semiconductor layer, e.g., a layer comprising germanium or a III-V semiconductor. On a first surface section A1 of the top side 10.1, there is a dielectric insulation layer system 24 comprising a bottom insulation layer M1 and a top insulation layer M2.

[0036] The lowermost insulation layer M1 is firmly bonded to the upper side 10.1 of the multi-junction solar cell 10. An upper side of the insulation layer system 24 is formed by the uppermost insulation layer M2, wherein the uppermost insulation layer M2 consists of α-silicon.

[0037] A metallization 12 is formed on a second surface section A2 adjoining the first surface section A1 and on the upper side of the insulation layer system 24. The metallization is integrally and electrically conductively connected to the upper side 10.1 of the multi-junction solar cell 10. Furthermore, the metallization 12 is integrally connected to the upper side of the insulation layer system 24, i.e., to the α-silicon layer M2.

[0038] In the illustration of the Fig. 2 shows another embodiment. In the following, only the differences to the illustration of the Fig. 1 explained.

Claims

[1] Stacked multi-junction solar cell (10) with a dielectric insulation layer system (24), wherein - the multi-junction solar cell (10) comprises a germanium substrate (14) forming a bottom side (10.2) of the multi-junction solar cell (10), a germanium sub-cell (16) and at least two III-V sub-cells (18, 20) following one another in the order mentioned, - an upper side of the multi-junction solar cell (10) is formed by one of the III-V sub-cells or a III-V cap layer, - the insulation layer system (24) comprises a layer sequence of at least one bottom insulation layer (M1) bonded to a first surface section of the multi-junction solar cell (10) and an uppermost insulation layer (M2) forming an upper side of the insulation layer system (24), and - a metallization (12) of the multi-junction solar cell (10) is materially and electrically conductively connected to a second surface section of the multi-junction solar cell (10) adjacent to the first surface section of the multi-junction solar cell (10) and is materially connected to a section of the upper side of the insulation layer system (24), wherein - the top insulation layer (M2) comprises or consists of amorphous silicon, and - the first surface section and the second surface section are formed on the upper side of the multi-junction solar cell (10), and on the upper side of the multi-junction solar cell (10) the metallization (12) completely covers the insulation layer system (24). [2] Stacked multi-junction solar cell (10) according to claim 1, characterized by that the lowermost insulation layer (24) comprises SiO2 and / or Si3N4 or consists of SiO2 and / or Si3N4. [3] Stacked multi-junction solar cell (10) according to claim 1 or 2, characterized by that the insulation layer system (24) has at least one further middle insulation layer (M3, M4), wherein the at least one middle insulation layer (M3, M4) comprises SiO2 and / or Si3N4 or consists of SiO2 and / or Si3N4. [4] Stacked multi-junction solar cell (10) according to one of the preceding claims, characterized by that the multi-junction solar cell (10) has a back-contacted front side, wherein - the semiconductor wafer has at least one through-hole (22) extending from a top side (10.1) of the multi-junction solar cell (10) through the sub-cells (16, 18, 20) to the bottom side (10.2) with a continuous side wall (22.1) and an oval circumference in cross-section parallel to the surface, and - a side wall (22.1) of the through contact hole (22) is covered by the dielectric insulation layer system (24). [5] Stacked multi-junction solar cell (10) according to claim 4, characterized by that the metallization (12) on the insulation layer system (24) extends from the top side (10.1) of the multi-junction solar cell (10) along the side wall (22.1) through the through contact hole (22) to the bottom side (10.2) of the multi-junction solar cell (10). [6] Stacked multi-junction solar cell (10) according to one of the preceding claims, characterized by that the metallization comprises a multi-layer system (12). [7] Stacked multi-junction solar cell (10) according to claim 6, characterized by that the multilayer system comprises an AuGe / Ti / Pd / Ag / Au layer sequence or a Pd / Au / Ge / Ti / Pd / Ag / Au layer sequence. [8] Stacked multi-junction solar cell (10) according to claim 6, characterized by that the multi-layer system has a nickel-containing layer or an aluminum-containing layer as the bottom layer.

Images