Stacked III-V multi-junction solar cell

Abstract

Stackable III-V multi-junction solar cell with a top and a bottom, comprising a metallic top contact area formed on the top of the multi-junction solar cell comprising a first metal layer, a metallic bottom contact area formed flat on the bottom of the multi-junction solar cell, an opening extending continuously from the top to the bottom, the opening having an upper edge area formed on the top and a lower edge area formed on the bottom, wherein the upper edge area adjoins the top contact area and the side wall and the two edge areas are covered with a dielectric layer, wherein the dielectric layer has a top and a bottom.wherein a first metallic cover layer is formed on a surface of the first metal layer and a second metallic cover layer is formed on the top side of the dielectric layer and on a part of the first metal layer adjacent to the upper edge region.

Description

[0001] US Patent 9,680,035 B1 discloses a solar cell contact arrangement comprising a solar cell stack with multiple III-V subcells on a GaAs substrate with a back-contacted front surface. In this arrangement, a hole extending from the top surface of the solar cell through the subcells and into an unthinned substrate layer is created using a wet chemical etching process. Passivation and metallization of the front surface and the hole are performed before the substrate layer is thinned.

[0002] Further solar cell contact arrangements with a formation of through-holes are known from DE 10 2021 004 707 A1 and EP 1 953 828 A1.

[0003] Against this background, the object of the invention is to provide a device that further develops the state of the art.

[0004] The problem is solved by a stacked III-V multi-junction solar cell with the features of claim 1. Advantageous embodiments of the invention are the subject of dependent claims.

[0005] According to the subject matter, a stacked III-V multi-junction solar cell is provided, wherein the III-V multi-junction solar cell has a top and a bottom.

[0006] A substrate layer is formed on the underside. Above the substrate layer, a first solar cell with a first band gap is arranged.

[0007] Above the first solar cell, a second solar cell with a second band gap is arranged, the second band gap being larger than the first band gap.

[0008] A tunnel diode is formed between the first solar cell and the second solar cell.

[0009] The multi-junction solar cell includes a metallic top-side contact area with a first metal layer.

[0010] To electrically connect the substrate, a flat metallic underside contact area is provided on the underside of the multi-junction solar cell, whereby the multi-junction solar cell is electrically connected by means of the top contact area and the bottom contact area.

[0011] A continuous oval opening extends from the top to the bottom.

[0012] The oval opening has a circumferential side wall and an upper edge area formed on the top and a lower edge area formed on the bottom, with the upper edge area bordering the top contact area.

[0013] It should be noted that the oval opening has a diameter in a range between 10 µm and 300 µm or in a range between 50 µm and 150 µm.

[0014] In a further training course, the oval opening is also designed to be exactly circular, i.e., it has a constant radius.

[0015] The side wall and the two edge areas are completely covered with a dielectric layer, the dielectric layer having a top and a bottom.

[0016] In one embodiment, the dielectric layer comprises a silicon oxide, in particular silicon dioxide, and / or a silicon nitride. Alternatively, the dielectric layer consists of silicon oxide, in particular silicon dioxide, and / or silicon nitride. In a further development, the thickness of the dielectric layer is in a range between 5 nm and 500 nm or in a range between 50 nm and 200 nm.

[0017] It is understood that the dielectric layer is applied using a deposition process, in particular a CVD or ALD process.

[0018] Furthermore, the dielectric layer forms a metallurgical bond with a semiconductor material in the area of ​​the side wall and in the upper and lower edge regions.

[0019] A first metallic cover layer is formed on a surface of the first metal layer, wherein the first metallic cover layer has a thickness in a range between 5 nm and 300 nm, or a thickness in a range between 10 nm and 200 nm, or a thickness in a range between 20 nm and 100 nm.

[0020] A second metallic covering layer is formed on the top surface of the dielectric layer and on a part of the first metal layer adjacent to the upper edge region, wherein the second metallic covering layer has a thickness in a range between 10 nm and 100 nm, or a thickness in a range between 20 nm and 50 nm.

[0021] On the second metallic top layer, a second metal layer is arranged in the part adjacent to the upper edge area and in the upper edge area and in the area of ​​the side wall adjacent to the upper edge area.

[0022] The second metal layer forms a metallurgical bond with the second metallic cover layer. In this case, the metallic cover layer comprises titanium or a titanium compound and / or nickel or a nickel compound. In a further development, the metallic cover layer consists of titanium or a titanium compound and / or nickel or a nickel compound.

[0023] Furthermore, it should be noted that the respective metal layers are designed as conductor tracks, with the metal layers in a further development exhibiting both a finger-shaped and a planar form.

[0024] III-V solar cells are preferably used in extraterrestrial applications. Reliable electrical contact is particularly important in extraterrestrial applications.

[0025] One advantage is that the metallic coatings allow for effective passivation of the metal layers on the surfaces. These coatings contain no gold or silver, nor any gold and / or silver compounds. By using titanium or nickel, or titanium and / or nickel compounds, the metallic coatings enable the reliable and durable bonding of different metal layers. It is understood that the second metal layer cannot form immediately after the first.

[0026] In a further training, the III-V multi-junction solar cell has a thickness in a range between 50 µm and 600 µm or in a range between 100 µm and 250 µm.

[0027] In one embodiment, a layered compound of titanium and oxygen and / or nitrogen is formed between the second metallic cover layer and the dielectric layer. This layered compound is hereinafter also referred to as the adhesive layer. An advantage is that the adhesive layer increases the reliability of the connection and reduces the risk of chipping or cracking of the second metallic cover layer.

[0028] In a further training, the thickness of the metallic covering layer is in a range between 2 nm and 30 nm, or in a range between 3 nm and 10 nm, or in a range between 4 nm and 7 nm.

[0029] In a further training process, a third metallic top layer is formed on a surface of the second metal layer.

[0030] In a further development, a fourth metallic cover layer is formed on the lower edge region, on the area of ​​the side wall adjacent to the lower edge region, and on a portion of the second metal layer formed on the side wall. Besides passivating and protecting the second metal layer, the fourth metallic cover layer particularly improves adhesion when a third metal layer is applied to the second metal layer. In other words, the arrangement of the fourth cover layer allows for the formation of a reliable and low-resistance bond between the two metal layers when applying the third metal layer.

[0031] In a further development, a third metal layer is formed on the fourth metallic cover layer, with the third metal layer extending continuously from the lower edge region and the part of the side wall adjacent to the lower edge region to the part of the second metal layer covered by the fourth metallic cover layer. In this case, the third metal layer forms a metallurgical bond with the respective substrate.

[0032] In one embodiment, the lower edge region is spaced apart from the underside contact area.

[0033] In another embodiment, a contact surface is formed in the lower edge region with the third metal layer. In other words, the third metal layer is at least partially designed as a contact layer for the electrical connection of the III-V multi-cell.

[0034] In a further development, the underside contact area has a fourth metal layer. In one embodiment, the third and fourth metal layers are formed in a common process step or in different process steps.

[0035] In another advanced development, a further metallic cover layer is formed on the surface of the fourth metal layer. One advantage is that the reliability of the contact is increased by means of this additional metallic cover layer.

[0036] In another embodiment, the top contact area is electrically connected to the contact surface on the underside by means of the second and third metal layers. In other words, the front of the III-V multi-junction solar cell can be contacted from the back, i.e., electrically connected. This simplifies the electrical contacting of the III-V multi-junction solar cell.

[0037] In a further training course, the side wall is completely covered all around with the second and third metal layers. It should be noted that both metal layers are necessary to achieve complete coverage of the side wall.

[0038] In another advanced training, the opening has a clear width after the application of the metal layers.

[0039] The invention is explained in more detail below with reference to the drawings. Similar parts are labelled with identical designations. The illustrated embodiments are highly schematic; that is, the distances and the lateral and vertical extents are not to scale and, unless otherwise indicated, do not exhibit any derivable geometric relationships to one another. The drawings show that Fig. 1 A view of a stacked III-V multi-junction solar cell with a through-hole, Fig. 2. A view on further training in the Fig. 1 depicted embodiment, Fig. 3. A view on further training in the Fig. 2 depicted embodiment.

[0040] The illustration of Fig. Figure 1 shows a view of an embodiment comprising a stacked III-V multi-junction solar cell MJ with a top OS and a bottom US.

[0041] The stacked III-V multi-solar cell MJ comprises a substrate layer SUB formed on the underside US with a first solar cell S1 arranged above the substrate layer SUB with a first band gap and a second solar cell S2 arranged above the first solar cell S1 with a second band gap, wherein the second band gap is larger than the first band gap.

[0042] A tunnel diode T1 is formed between the first solar cell S1 and the second solar cell S2.

[0043] A metallic top contact area OSKB is formed on the top surface of the multi-junction solar cell MJ, wherein the top contact area OSKB comprises a first metal layer M1.

[0044] To electrically connect the substrate SUB, a flat metallic underside contact area USKB is arranged on the underside US of the multi-junction solar cell MJ.

[0045] The multi-junction solar cell MJ is electrically connected via the top contact area OSKB and the bottom contact area USKB.

[0046] From the top (OS) to the bottom (US) extends a continuous oval opening (DU).

[0047] The opening DU has a circumferential side wall DS and an upper edge area OR formed on the top OS and a lower edge area UR formed on the bottom US.

[0048] Here, the upper edge region OR borders the upper surface contact region OSKB.

[0049] Furthermore, the side wall DS and the two edge regions OR, UR are completely covered with a dielectric layer DI, the dielectric layer DI having a top and a bottom.

[0050] Furthermore, the dielectric layer DI on the underside forms a metallurgical bond with a semiconductor material in the area of ​​the side wall DI.

[0051] A first metallic cover layer TN1 is formed on a surface of the first metal layer M1, wherein the first metallic cover layer TN1 has a thickness in a range between 5 nm and 300 nm.

[0052] In the illustration of the Fig. 2 is a further development of the embodiment of Fig. Figure 1 is shown. Only the differences are explained below.

[0053] A second metallic cover layer TN2 is formed on the top side of the dielectric layer DI and on a part of the first metal layer M1 adjacent to the upper edge region OR.

[0054] The second metallic cover layer TN2 preferably has a thickness in a range between 10 nm and 100 nm.

[0055] On the second metallic cover layer TN2, a second metal layer M2 is arranged on the part adjacent to the upper edge area OR and in the area of ​​the side wall DS adjacent to the upper edge area OR.

[0056] The second metal layer M2 forms a materially bonded connection with the second metallic cover layer TN2.

[0057] A compound of titanium and oxygen is formed between the second metallic cover layer TN2 and the dielectric layer DI. It is understood that this compound is layered.

[0058] In the illustration of the Fig. Figure 3 shows another embodiment. The differences to the embodiment of [the previous embodiment] are described below. Fig. 2 explained.

[0059] A third metallic top layer TN3 is formed on the surface of the second metal layer M2.

[0060] Furthermore, a fourth metallic cover layer TN4 is formed on the lower edge area UR and on the area of ​​the side wall DS adjacent to the lower edge area UR and on a part of the second metal layer M2 formed on the side wall DS.

[0061] A third metal layer M3 is formed on the fourth metallic cover layer TN4, and the third metal layer M3 extends continuously from the lower edge region UR and the part of the side wall DS adjacent to the lower edge region UR to the part of the second metal layer M2 covered by the fourth metallic cover layer TN4.

[0062] Furthermore, the third metal layer M3 forms a metallurgical bond with the substrate.

[0063] The lower edge area UR is spaced away from the bottom contact area USKB.

[0064] In the lower edge area UR, a contact surface is formed with the third metal layer M3.

[0065] The underside contact area USKB has a fourth metal layer M4 and a further metallic cover layer TNR is formed on a surface of the fourth metal layer M4.

[0066] Furthermore, the upper surface contact area OSKB is electrically connected to the contact surface on the underside US by means of the second metal layer M2 and the third metal layer M3.

[0067] Furthermore, the side wall DS is completely covered all around with the second metal layer M2 and the third metal layer M3.

[0068] Furthermore, the opening DU has a clear width after the application of the metal layers M1-M4.

Claims

[1] Stacked III-V multi-junction solar cell (MJ) with a top side (OS) and a bottom side (US), comprising - a substrate layer (SUB) formed on the underside (US), - a first solar cell (S1) arranged above the substrate layer (SUB) with a first band gap, - a second solar cell (S2) arranged above the first solar cell (S1) with a second band gap, wherein the second band gap is larger than the first band gap, - a tunnel diode (T1) formed between the first solar cell (S1) and the second solar cell (S2), - a metallic top contact region (OSKB) formed on the top side of the multi-junction solar cell (MJ), wherein the top contact region (OSKB) comprises a first metal layer (M1), - a metallic bottom contact area (USKB) formed on the underside (US) of the multi-junction solar cell (MJ) in order to electrically connect the substrate (SUB), whereby the multi-junction solar cell (MJ) is electrically connected by means of the top contact area (OSKB) and the bottom contact area (USKB), -an oval opening (DU) extending continuously from the top (OS) to the bottom (US), - the opening (DU) has a circumferential side wall (DS) and an upper edge region (OR) formed on the upper side (OS) and a lower edge region (UR) formed on the lower side (US), wherein the upper edge region (OR) adjoins the upper side contact region (OSKB), - the side wall (DS) and the two edge regions (OR, UR) are completely covered with a dielectric layer (DI), wherein the dielectric layer (DI) has a top side and a bottom side and the dielectric layer (DI) forms a material connection with a semiconductor material on the bottom side (US) in the region of the side wall (DI), - a first metallic cover layer (TN1) is formed on a surface of the first metal layer (M1), and the first metallic cover layer (TN1) has a thickness in a range between 5 nm and 300 nm, - a second metallic cover layer (TN2) is formed on the top side of the dielectric layer (DI) and on a part of the first metal layer (M1) adjacent to the upper edge region (OR), the second metallic cover layer (TN2) having a thickness in a range between 10 nm and 100 nm, - a second metal layer (M2) is arranged on the second metallic cover layer (TN2) in the part adjacent to the upper edge region (OR) and the upper edge region (OR) and in the region of the side wall (DS) adjacent to the upper edge region (OR), and the second metal layer (M2) forms a material-to-material connection with the second metallic cover layer (TN2). [2] Stacked III-V multi-junction solar cell (MJ) according to claim 1, wherein a layered compound of titanium and oxygen and / or nitrogen is formed between the second metallic cover layer (TN2) and the dielectric layer (Di). [3] A stacked III-V multi-junction solar cell (MJ) according to claim 1 or claim 2, wherein a third metallic covering layer (TN3) is formed on a surface of the second metallic layer (M2). [4] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein a fourth metallic cover layer (TN4) is formed on the lower edge region (UR) and on the region of the side wall (DS) adjacent to the lower edge region (UR) and a part of the second metal layer (M2) formed on the side wall (DS). [5] Stacked III-V multi-junction solar cell (MJ) according to claim 4, wherein a third metal layer (M3) is formed on the fourth metallic cover layer (TN4) and the third metal layer (M3) extends continuously from the lower edge region (UR) and the part of the side wall (DS) adjacent to the lower edge region (UR) to the part of the second metal layer (M2) covered with the fourth metallic cover layer (TN4) and the third metal layer (M3) forms a material connection with the respective base. [6] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein the lower edge region (UR) is spaced from the bottom contact region (USKB). [7] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein a contacting surface is formed in the lower edge region (UR) with the third metal layer (M3). [8] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein the bottom contact region (USKB) has a fourth metal layer (M4) and a further metallic cover layer (TNR) is formed on a surface of the fourth metal layer (M4). [9] Stacked III-V multi-junction solar cell (MJ) according to any one of claims 5-7, wherein the top contact region (OSKB) is electrically connected to the contacting area on the bottom side (US) by means of the second metal layer (M2) and the third metal layer (M3). [10] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein the side wall (DS) is completely covered all around with the second metal layer (M2) and the third metal layer (M3). [11] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein the opening (DU) has a clear width after the application of the metal layers (M1-M4). [12] Stacked III-V multi-junction solar cell (MJ) according to one of the preceding claims, wherein the metallic cover layers (TN1-TN4, TNR) are formed as a titanium layer or as a nickel layer or at least comprise titanium and / or nickel.

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