Lower subcell, tandem solar cell and method of producing a solar cell

Abstract

The invention relates to a lower subcell (11) for a tandem solar cell, having - a substrate (1) with a front side (12) and a reverse side (14), - a tunnel oxide layer (2) on the front side (12) of the substrate (1), - a compact poly-Si(n):O layer (7) on a side of the tunnel oxide layer (2) facing away from the substrate (1), and - a porous poly-Si(n):O layer (6) on a side of the compact poly-Si(n):O layer (7) facing away from the tunnel oxide layer (2). The invention further relates to a tandem solar cell having an upper subcell (10) and the lower subcell (11), and to a method of producing a solar cell.

Description

[0001] adares Q-420-WO IR-2023-00S1 porous WARP

[0002] - 1 -

[0003] Lower subcell, tandem solar cell and method for manufacturing a solar cell

[0004] Description:

[0005] The invention relates to a lower subcell for a tandem solar cell, a tandem solar cell, and a method for manufacturing a solar cell. In particular, the invention relates to a lower subcell comprising a substrate, a tunnel oxide layer, and a poly-Si layer, a tandem solar cell containing the lower subcell, and a method for manufacturing a solar cell. The substrate has a front and a back. During operation, the front is the side facing the light, while the back is the side facing away from the light, and edges extend between the front and back.

[0006] If the tunnel oxide layer is located on the back of the substrate, and the poly-Si layer is located on the side of the tunnel oxide layer facing away from the substrate, it is a so-called TOPCon (Tunnel Oxide Passivated Contact) solar cell. A TOPCon solar cell has a relatively high efficiency.

[0007] If the tunnel oxide layer is located on the front of the substrate, and the poly-Si layer is located on a side of the tunnel oxide layer facing away from the substrate, it is a “reversed” TOPCon solar cell.

[0008] The use of such an "inverted" TOPCon solar cell is described, for example, by Y. Wu et al. in "27.6% Perovskite / c-Si Tandem Solar Cells Using Industrial Fabricated TOPCon Device", Advanced Energy Materials, Vol. 12, Issue 27, July 21, 2022, 2200821. The "inverted" TOPCon solar cell is used here as a lower sub-cell or bottom cell of a tandem solar cell. Such a tandem solar cell exhibits a relatively high efficiency. adares Q-420-WO IR-2023-00S1 porous WARP

[0009] - 2 -

[0010] However, there is still a need to improve the reflection and absorption properties of solar cells.

[0011] It is an object of the present invention to provide a lower sub-cell for a tandem solar cell with improved reflection properties, a tandem solar cell with improved reflection properties, and a method for manufacturing a solar cell with improved reflection properties. At the same time, they should be cost-effective.

[0012] According to the invention, this problem is solved by a lower subcell with the features of claim 1, a tandem solar cell with the features of claim 7, and a method with the features of claim 8. Advantageous further developments and modifications are specified in the dependent claims.

[0013] A lower subcell with a porous, phosphorus- and oxygen-enriched polysilicon layer (poly-Si(n):O) exhibits advantageous reflection and absorption properties compared to a corresponding lower subcell without the porous poly-Si(n):O layer, particularly reduced reflection. This eliminates the need for an antireflection layer on the front side. Furthermore, the improved absorption results in a higher short-circuit current (Jsc). The porous poly-Si(n):O layer shows significantly reduced reflection across the entire wavelength range from 280 to 1000 nm, especially in the 280 to 600 nm range. This allows more light to be coupled into the lower subcell, resulting in a higher Jsc of +1 mA / cm². 2 reflects.

[0014] In the production of the compact poly-Si(n):O layer, it is not only deposited on the front side, but also by bending the substrate during the application of the layer using PECVD (plasma-enhanced chemical vapor deposition) or adares Q-420-WO IR-2023-00S1 porous WARP

[0015] - 3 -

[0016] CVD (Chemical Vapor Deposition) process also covers the edges and back side (so-called circumferential treatment). After the compact poly-Si(n):O layer is applied to the tunnel oxide layer, it must be removed from the back side and edges. For this purpose, the substrate, including the applied layers, is first immersed in a KOH bath and then in an HF bath. While the compact poly-Si(n):O layer is removed from the back side and edges, the porous poly-Si(n):O layer is simultaneously created on the front side. Therefore, no additional costs are incurred for the production of the porous poly-Si(n):O layer.

[0017] Without wishing to be bound to any theory, it is assumed that an enrichment of the compact poly-Si(n) layer with oxygen promotes the formation of a porous layer in the process according to the invention.

[0018] The invention relates to a lower sub-cell for a tandem solar cell with

[0019] - a substrate with a front and a back,

[0020] - a tunnel oxide layer located on the front side of the substrate,

[0021] - a compact poly-Si(n):O layer arranged on a side of the tunnel oxide layer facing away from the substrate, and

[0022] - a porous poly-Si(n):O layer located on a side of the compact poly-Si(n):O layer facing away from the tunnel oxide layer.

[0023] In a preferred embodiment, the overall porosity of the porous poly-Si(n):O layer is 30 to 90%. This means, in particular, that the porous poly-Si(n):O layer is composed of 30 to 90 vol% air and 70 to 10 vol% poly-Si(n):O. More preferably, the porous poly-Si(n):O layer contains 50 to 90 vol% air and 50 to 10 vol% poly-Si(n):O, i.e., the overall porosity of the porous poly-Si(n):O layer is 50 to 90%. Even more preferably, the porous poly-Si(n):O layer contains 70 to 90 vol% air and 30 to 10 vol% poly-Si(n):O, i.e., the total porosity of the porous poly-Si(n):O layer is Q-420-WO IR-2023-00S1 porous WARP

[0024] - 4 -

[0025] The layer thickness is 70 to 90%. The compact poly-Si(n):O layer is a poly-Si(n):O layer that contains no or essentially no air or up to 5 vol%.

[0026] The porosity can be indirectly determined using optical methods for characterizing thin films, e.g., ellipsometry or reflectance measurements. The lower the refractive index n of the porous layer compared to the refractive index of a compact poly-Si(n):O layer, which is preferably 2.9–3.1 at 632 nm, the higher the porosity. The total porosity includes open and / or closed porosity.

[0027] Preferably, the porous poly-Si(n):O layer has a thickness in the range of 20 to 40 nm. This thickness is advantageous for controlling the reflection within a satisfactory range.

[0028] Preferably, the compact poly-Si(n):O layer has a thickness in the range of 40 to 80 nm. Preferably, the tunnel oxide layer has a thickness of 1 to 2 nm. With these layer thicknesses, a lower subcell with a satisfactory efficiency is still provided.

[0029] In a preferred embodiment, the porous poly-Si(n):O layer has a refractive index of < 2.9 at a wavelength of 632 nm. Preferably, the compact poly-Si(n):O layer has a refractive index of 2.9 to 3.1 at a wavelength of 632 nm. This gradual difference in refractive indices results in further improved reflection properties.

[0030] In a preferred embodiment, the compact poly-Si(n):O layer is formed as a poly-Si(n) layer stack consisting of several poly-Si(n) layers, each enriched with phosphorus and oxygen. The poly-Si layers are sublayers of the compact poly-Si(n):O layer. Preferably, the poly-Si(n) layer stack has an oxygen concentration profile and a phosphorus concentration profile. Q-420-WO IR-2023-00S1 porous WARP

[0031] - 5 -

[0032] The concentration profile is such that the oxygen and phosphorus concentrations of the multiple poly-Si(n) layers differ from one another. Preferably, the poly-Si(n) layer stack comprises a first poly-Si(n) layer, arranged on a side of the tunnel oxide layer facing away from the substrate and representing a seed layer; a second poly-Si(n) layer, arranged on a side of the first poly-Si(n) layer facing away from the substrate and representing an intermediate layer; and a third poly-Si(n) layer, arranged on a side of the second poly-Si(n) layer facing away from the substrate and representing a main layer. In a preferred embodiment, the first and third poly-Si(n) layers are configured as oxygen-enriched layers. Preferably, the second poly-Si(n) layer is configured as an oxygen-depleted layer.In a comparison of the oxygen concentration of the poly-Si(n) layer stack between the three poly-Si(n) layers, the first and third poly-Si(n) layers preferentially exhibit a high oxygen concentration, while the second poly-Si(n) layer exhibits a relatively significantly lower oxygen concentration.

[0033] Preferably, the phosphorus concentration profile is designed such that the third poly-Si(n) layer has a concentration of an electrically active phosphorus of at least 5 x 10 +19 cnr 3 the second poly-Si(n) layer has a comparatively higher concentration of electrically active phosphorus, preferably at least 1 x 10 +20 cnr 3, and exhibits an interface at the first poly-Si layer, the tunnel oxide layer, and the substrate, a concentration gradient of electrically active phosphorus that displays a kink and a subsequent extension to a depth in the range of 200 to 500 nm of the substrate. The kink represents a rapid drop in the concentration of electrically active phosphorus at the tunnel oxide barrier. The concentration of electrically active phosphorus is preferably such that the second poly-Si(n) layer exhibits a concentration of electrically active phosphorus that is formed as a peak in the electrically active phosphorus doping profile. The second poly-Si(n) layer therefore exhibits the highest concentration of electrically active phosphorus compared to the concentrators.

[0034] - 6 - tions of the electrically active phosphorus of the first and third poly-Si(n) layer, while the interface has a decreasing concentration of electrically active phosphorus starting from the first poly-Si(n) layer to the substrate and the substrate has the lowest concentration of electrically active phosphorus.

[0035] For the purposes of the invention, electrically active phosphorus is phosphorus that contributes to the conductivity of the respective layer in which it is contained. In addition to electrically active phosphorus, the poly-Si(n) layers can contain electrically inactive phosphorus that does not contribute to the conductivity of the respective layer. Time-of-flight SiMS (ToF SiMS) combined with electrochemical capacitance-voltage (ECV) measurements, which detect only the electrically active phosphorus, allows the determination of the concentrations of electrically active and electrically inactive phosphorus.

[0036] In a preferred embodiment, the pores of the porous Si(n):O layer are at least partially or completely filled with TCO (transparent conductive oxides). The porous Si(n):O layer can contain 30 to 90 vol% TCO. TCO is preferably selected from the group consisting of ITO (indium tin oxide), AZO (aluminum-doped zinc oxide), or ZnO (zinc oxide). Preferably, when the pores are at least partially filled with TCO, a TCO layer is arranged on a side of the porous Si(n):O layer facing away from the tunnel oxide layer, which acts as a TCO interlayer to an upper subcell in a tandem solar cell. This interlayer preferably has a thickness of 5 to 30 nm and / or a refractive index of approximately 1.8 at a wavelength of 632 nm. The application of the TCO layer closes the open pores, or...Holes in the porous Si(n):O layer are at least partially filled with TCO, wherein TCO penetrates or fills the open pores of the porous Si(n):O layer during its deposition. adares Q-420-WO IR-2023-00S1 porous WARP.

[0037] - 7 -

[0038] The invention further relates to a tandem solar cell comprising an upper subcell and a lower subcell according to one or more of the embodiments described above. Preferably, the upper subcell is configured as an upper perovskite subcell. An intermediate layer, e.g., a TCO layer such as an ITO, AZO, or ZnO layer, is preferably arranged between the upper and lower subcells. This intermediate layer preferably has a thickness of 5 to 30 nm. It preferably has a refractive index of approximately 1.8 at a wavelength of 632 nm.

[0039] The invention further relates to a method for manufacturing a solar cell, comprising: a) providing a substrate with a front and a back, b) applying a tunnel oxide layer to the front of the substrate, c) applying an amorphous, phosphorus- and oxygen-enriched silicon layer (a-Si(n):O) layer to the tunnel oxide layer, d) annealing the substrate at a temperature > 800 °C, so that the applied a-Si(n):O layer is transformed into a compact poly-Si(n):O layer, e) immersing the substrate in a KOH bath, and then f) immersing the substrate in an RF bath.

[0040] The substrate itself, including the layers applied in steps b) and c), is subjected to steps d), e) and f).

[0041] During steps e) and f), an edge and backside wrap of the compact poly-Si(n):O layer is also removed. The compact poly-Si(n):O layer must be removed from the edge and backside after deposition, otherwise shunts to the emitter will exist. Steps e) and f) are preferably performed in a batch process. The batch process is less expensive than an in-line process. In an in-line process, several substrates are typically conveyed through a porous warp using transport rollers.

[0042] - 8 - the KOH bath and the HF bath were used, whereby in particular, if only the back side is immersed in the baths, the front side of the treated substrate is protected and therefore not treated due to a resulting ‘water cap’.

[0043] In a preferred embodiment, the KOH (potassium hydroxide) bath has a concentration of 3-4%. This concentration is sufficient to achieve the desired effects. Preferably, the KOH bath contains a polishing additive. In a preferred embodiment, step e) is carried out for a duration of 100 to 150 seconds. This duration is sufficient to achieve the desired effects.

[0044] Preferably, the HF (hydrofluoric acid) bath has a concentration of 1 to 25%, preferably 15 to 22%. This concentration is sufficient to achieve the desired effects. Preferably, step f) is carried out for a duration of up to 10 minutes, preferably 40 to 60 seconds. This duration is sufficient to achieve the desired effects. The duration depends on the HF concentration. The lower the HF concentration, the longer the duration.

[0045] In a preferred embodiment, step c) includes the application of an amorphous Si layer stack consisting of several amorphous Si sublayers onto the tunnel oxide layer, using oxygen and phosphorus as enrichment agents.

[0046] In a preferred embodiment, step b) is carried out by plasma oxidation. The tunnel oxide layer is therefore preferably SiO₂. x - Layer formed. Alternatively, a tunnel oxide layer of aluminum oxide (AlOx) can also be formed.

[0047] Steps b) and c) can be carried out using PECVD (plasma-enhanced chemical vapor deposition) or adares Q-420-WO IR-2023-00S1 porous WARP

[0048] - 9 -

[0049] LPCVD (low-pressure chemical vapor deposition) is performed. Preferably, steps b) and c) are carried out in one step using PECVD, preferably without vacuum interruption in a tube-PECVD system.

[0050] A manufacturing process, for example, further comprises the following steps: First, a substrate, such as a Si wafer (e.g., an n-type Si wafer), is provided and subjected to texturing. Then, emitter diffusion, such as boron diffusion with BB or BCU, is performed. Subsequently, borosilicate glass etching is carried out on the back side, followed by chemical edge isolation and polishing of the front side. A substrate produced in this manner is preferably provided in step a). Following step f), passivation of the back side, e.g., with AIO, is preferably performed. X (Aluminium oxide) and / or SiN x (Silicon nitride) was carried out.

[0051] Optionally, a laser contact opening (LCO) process can then be performed on the back side to create holes in the produced passivation layer. Preferably, after removing the edge banding or the LCO process, the back side is metallized completely or partially. An intermediate layer, e.g., a TCO or preferably an ITO layer, is then preferably applied to the front side. The upper subcell, preferably a perovskite subcell, is then preferably applied to the intermediate layer in one or more steps.

[0052] Further properties and advantages of the solar cell according to the invention are explained in more detail in the context of the preferred embodiments described below. The diagram shows a schematic representation, not to scale.

[0053] Fig. 1 shows a cross-sectional view of a tandem solar cell according to the invention with a lower sub-cell according to the invention; and

[0054] Fig. 2 shows a flowchart of a method according to the invention. adares Q-420-WO IR-2023-00S1 porous WARP

[0055] - 10 -

[0056] Fig. 1 shows a cross-sectional view of a tandem solar cell according to the invention, comprising a lower sub-cell according to the invention. The tandem solar cell has an upper sub-cell 10 and the lower sub-cell 11 according to the invention.

[0057] The lower subcell 11 comprises a substrate 1 with a front face 12 and a back face 14. The front face 12 is a light-incident face, which, during operation, is oriented towards light emitted by the sun 13, as indicated by arrows, while the back face 14 is a light-facing face. Edges (not shown) extend between the front face 12 and the back face 14. It further comprises a tunnel oxide layer 2, which is arranged on the front face 12 of the substrate 1, and a compact poly-Si(n):O layer 7 consisting of several poly-Si(n) sublayers 3, 4, 5. The compact poly-Si(n):O layer 7 is arranged on a side of the tunnel oxide layer 2 facing away from the substrate 1.

[0058] The compact poly-Si(n):O layer 7 has the following layer structure: a first poly-Si(n) layer 3, which is arranged on a side of the tunnel oxide layer 2 facing away from the substrate 1; a second poly-Si(n) layer 4, which is arranged on a side of the first poly-Si(n) layer 3 facing away from the substrate 1; and a third poly-Si(n) layer 5, which is arranged on a side of the second poly-Si(n) layer 4 facing away from the substrate 1. The compact poly-Si(n) layer 7 has an oxygen doping profile and a phosphorus doping profile 7, such that the oxygen and phosphorus content of the several poly-Si(n) layers 3, 4, 5 differ from one another.

[0059] The lower subcell 11 further features a porous poly-Si(n):O layer 6, which is arranged on a side of the compact poly-Si(n):O layer 7 facing away from the tunnel oxide layer 2. adares Q-420-WO IR-2023-00S1 porous WARP

[0060] - 11 -

[0061] A passivation layer 15, e.g. made of AIO, is arranged on the back side 14 of the substrate 1. X (Aluminium oxide) and SiN x (Silicon nitride).

[0062] An intermediate layer 9, e.g., a TCO layer or an ITO layer, is arranged between the upper sub-cell 10 and the lower sub-cell 11. A material of the intermediate layer 9, such as ITO, can penetrate the porous structure of the porous poly-Si(n):O layer 6. This means that open pores or holes in the porous structure, which are filled with air before the application of the intermediate layer 9, can also be at least partially filled with the material of the intermediate layer 9, such as ITO, in the finished tandem cell.

[0063] The upper subcell 10 can be configured as a perovskite solar cell. The upper subcell 10 and the lower subcell 11 also have local electrical contacts 8.

[0064] Fig. 2 shows a flowchart of a process according to the invention. The process for manufacturing a solar cell comprises the following steps. A first step involves providing 20 a substrate with a front and a back side. Following the provision 20, a tunnel oxide layer 21 is applied to the front side of the substrate. Following the application 21, an amorphous Si:O layer 22 is applied. The amorphous Si:O layer can be applied as a poly-Si(n) layer stack consisting of three amorphous Si layers with different oxygen and phosphorus concentrations. Following the application 22, the substrate with the applied tunnel oxide layer and the applied amorphous Si:O layer is annealed 23 at a temperature > 800 °C, so that the applied amorphous Si:O layer is transformed into a compact poly-Si(n):O layer.

[0065] The annealing 23 is followed by immersion 24 of the substrate with the applied tunnel oxide layer and the compact poly-Si(n):O layer in a KOH bath, preferably with a polishing additive, and immersion 25 in an HF-adare Q-420-WO IR-2023-00S1 porous WARP

[0066] - 12 -

[0067] A bath is applied. This creates a porous poly-Si(n):O layer, which is located on and formed from the side of the compact poly-Si(n):O layer facing away from the tunnel oxide layer. Furthermore, step 26 can follow step 25, in which an intermediate layer is applied to the side of the porous poly-Si(n):O layer facing away from the tunnel oxide layer, wherein a material of the intermediate layer, e.g., ITO, penetrates into and / or fills open pores or holes in the porous layer.

[0068] adares Q-420-WO IR-2023-00S1 porous WARP

[0069] - 13 -

[0070] Reference symbol list:

[0071] 1 substrate

[0072] 2 Tunnel oxide layer

[0073] 3, 4, 5 each poly-Si(n) layer

[0074] 6 porous poly-Si(n):O layer

[0075] 7 compact poly-Si(n):O layer

[0076] 8 Contact

[0077] 9 Intermediate shift

[0078] 10 upper subcell

[0079] 11 lower subcell

[0080] 12 Front

[0081] 13 suns

[0082] 14 Back

[0083] 15 Passivation layer

[0084] 20 Provide

[0085] 21 Applying

[0086] 22 Applying

[0087] 23 Tempering

[0088] 24 immersions

[0089] 25 Immersion

Claims

adares Q-420-WO IR-2023-00S1 porous WARP - 14 - Patent claims:

1. Lower subcell (11) for a tandem solar cell with - a substrate (1 ) with a front (12) and a back (14), - a tunnel oxide layer (2) arranged on the front side (12) of the substrate (1 ), - a compact poly-Si(n):O layer (7) arranged on a side of the tunnel oxide layer (2) facing away from the substrate (1), and - a porous poly-Si(n):O layer (6) arranged on a side of the compact poly-Si(n):O layer (7) facing away from the tunnel oxide layer (2).

2. Lower subcell (11) according to claim 1, characterized in that the total porosity of the porous Si(n):O layer (6) is 30 to 90%.

3. Lower subcell (11) according to claim 1 or 2, characterized in that the porous Si(n):O layer (6) has a layer thickness in the range of 20 to 40 nm, the compact poly-Si(n):O layer (7) has a layer thickness in the range of 40 to 80 nm and / or the tunnel oxide layer (2) has a layer thickness of 1 to 2 nm.

4. Lower subcell (11) according to one of the preceding claims, characterized in that the porous poly-Si(n):O layer (6) has a refractive index < 2.9 at a wavelength of 632 nm and / or the compact poly-Si(n):O layer (7) has a refractive index of 2.9 to 3.1 at a wavelength of 632 nm.

5. Lower subcell (11) according to one of the preceding claims, characterized in that the compact poly-Si(n):O layer (7) is formed as a poly-Si(n) layer stack consisting of several poly-Si(n) layers (3, 4, 5), each enriched with phosphorus and oxygen, wherein preferably the poly-Si(n) layer stack has an oxygen concentration profile and a phosphorus concentration profile, such that the oxygen concentration and the adares Q-420-WO IR-2023-00S1 porous WARP - 15 - The phosphorus concentration of the several poly-Si(n) layers (3, 4, 5) differs from each other.

6. Lower subcell (11) according to one of the preceding claims, characterized in that pores of the porous Si(n):O layer (6) are at least partially filled with TCO, wherein TCO is preferably selected from ITO, AZO or ZnO.

7. Tandem solar cell comprising an upper subcell (10), preferably designed as an upper perovskite subcell, and the lower subcell (11) according to any of the preceding claims.

8. Method for producing a solar cell, comprising a) providing (20) a substrate (1 ) with a front (12) and a back (14), b) applying (21 ) a tunnel oxide layer (2) to the front (12) of the substrate (1 ), c) applying (22) an amorphous Si(n):O layer to the tunnel oxide layer (2), d) annealing (23) the substrate (1 ) at a temperature > 800 °C, such that the applied amorphous Si(n):O layer is transformed into a compact poly-Si(n):O layer (7), e) immersing (24) the substrate (1 ) in a KOH bath, and then f) immersing (25) the substrate (1 ) in an HF bath.

9. Method according to claim 8, characterized in that the KOH bath has a concentration of 3-4% and / or the HF bath has a concentration of 1 to 25%, preferably 15 to 22%.

10. Method according to claim 8 or 9, characterized in that step e) is carried out for a duration of 100 to 150 seconds and / or step f) is carried out for a duration of up to 10 minutes, preferably 40 to 60 seconds. adares Q-420-WO IR-2023-00S1 porous WARP - 16 - 11. Method according to one of claims 8 to 10, characterized in that step c) comprises the application of an amorphous Si layer stack consisting of several amorphous Si layers (3, 4, 5) onto the tunnel oxide layer (2) as the amorphous Si(n):O layer, wherein oxygen and phosphorus are used as enrichment agents.

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