Lamination method for producing a perovskite solar cell using a graphite substrate

Abstract

The invention relates to a method for producing a solar cell for converting incident electromagnetic radiation into electrical power, wherein a layer structure is formed, comprising at least one charge-selective front contact structure, at least one charge-selective rear contact structure, and an absorber structure comprising at least perovskite, wherein the rear contact structure is designed to comprise at least one rear graphite layer. According to the invention: a sub-cell comprising at least the front contact structure and the absorber structure is formed; the rear contact structure, which comprises at least the rear graphite layer and a charge-selective rear contact layer, is initially formed separately from the sub-cell; and, after the rear contact structure has been formed, the rear contact structure is arranged on the sub-cell such that the charge-selective rear contact layer is positioned between the rear graphite layer and the sub-cell.

Description

[0001] title

[0002] Method for manufacturing a solar cell for converting incident electromagnetic radiation into electrical power

[0003] Description

[0004] Perovskite solar cells offer high efficiency at lower manufacturing costs compared to solar cells based on other semiconductor materials such as silicon. Long-term stability remains a challenge for perovskite solar cells. Using graphite back electrodes in perovskite solar cells is advantageous for minimizing degradation.

[0005] Previously known perovskite solar cells with graphite back electrode are described in Wagner et al., "High Photovoltage of 1 V on a Steady-State Certified Hole Transport Layer-Free Perowskite Solar Cell by a Molten-Salt Approach", DOI: 10.1039 / D0EE02175J.

[0006] High efficiencies were demonstrated by laminating graphite paper-based back electrodes, as described in E. Baghestani et al., “A conductive adhesive ink for carbon-laminated perovskite solar cells with enhanced stability and high efficiency”, Solar Energy

[0007] Volume 266, December 2023, 112165, DOI: 10.1016 / j.solener.2023.112165 described.

[0008] The present invention is based on the objective of improving charge extraction and reducing surface recombination in graphite-based back electrodes.

[0009] This problem is solved by a method for manufacturing a solar cell for converting incident electromagnetic radiation into electrical power according to claim 1. Advantageous embodiments are found in the dependent claims.

[0010] The invention is based on the understanding that the main challenges when using graphite electrodes are:

[0011] 34511-P-WO Di / co 08.10.2025 The lower charge carrier selectivity of graphite leads to a high charge carrier recombination at the perovskite / graphite interface and thus to a reduction, in particular, of the open clamping stress.

[0012] Typically, an unfavorable coupling occurs between graphite and perovskite at the back electrode, resulting in reduced charge carrier extraction. This is due, among other things, to the formation of the graphite layer from graphite particles and / or porosity of the graphite layer.

[0013] Based on these findings, the present invention provides a method in which a backside graphite layer of a backside contact structure of the solar cell is formed separately and provided with a functional layer before the backside contact structure is arranged to the other layers of the solar cell:

[0014] In the inventive method for manufacturing a solar cell for converting incident electromagnetic radiation into electrical power, a layered structure is formed, comprising at least one charge-selective front contact structure, at least one charge-selective back contact structure, and a perovskite-containing absorber structure. The back contact structure is formed comprising at least one back graphite layer.

[0015] It is essential that a subcell is formed comprising at least the front contact structure and the absorber structure, and that the back contact structure, which has at least the back graphite layer and a charge-selective back contact layer, is initially formed separately from the subcell.

[0016] After forming the backside contact structure, the backside contact structure is arranged on the subcell, so that the charge-selective backside contact layer is positioned between the backside graphite layer and the subcell.

[0017] The method according to the invention thus has the advantage that the backside contact structure and the backside graphite layer are separate from the partial cell.

[0018] 34511-P-WO Di / co 08.10.2025 a charge-selective backside contact layer is formed. In an intermediate stage, two unconnected objects are present: the subcell and the backside contact structure. Subsequently, the backside contact structure is attached to the

[0019] Partial cells are arranged. This offers significant advantages, as previously, the formation of a back-side, charge-selective layer was subject to limitations regarding the applied methods and process parameters in order to avoid damaging the perovskite, or sufficient porosity had to be present in both the charge-selective layer and the back-side graphite layer to subsequently integrate perovskite into a porous structure.

[0020] to be able to supply the absorber structure in liquid form. These limitations are avoided by the method according to the invention.

[0021] In the inventive method, materials and solvents can therefore be used to form the backside contact structure which were not applicable in previously known methods because they would either destroy the perovskite layer or be damaged by the solvents contained in the graphite paste.

[0022] Furthermore, the inventive method increases the degrees of freedom for the application of multilayer charge extraction layers between the perovskite-containing absorber structure and the backside graphite layer: The method enables the application of layers on the one hand on the subcell and on the other hand on the separate backside contact structure before joining the backside contact structure and subcell, thus doubling the number of possible permutations compared to previously known methods.

[0023] Advantageously, before the backside contact structure is attached to the subcell, the backside contact structure, in particular the charge-selective backside contact layer, is processed. The processing preferably comprises at least one of the following process steps.

[0024] Heating to a temperature of at least 150°C, preferably at least 200°C, in particular at least 400°C;

[0025] 34511-P-WO Di / co 08.10.2025 Oxidizing, in particular at a temperature of 150°C, preferably at least 200°C, in particular at least 400°C; wet chemical processing, in particular the use of solvents incompatible with perovskite, in particular water or aqueous solutions, processing by means of electroplating processes or by means of the application of acids / alkalis.

[0026] These process steps offer the following advantages:

[0027] Heating to at least 200°C, ideally at least 400°C, removes binder materials from the back contact structure that could negatively affect its electrical properties. This also allows the use of a wider range of carbon-based pastes, including those that require high-temperature baking.

[0028] Furthermore, at these temperatures of at least 200°C, and in particular at least 400°C, charge-selective backside contact layers, designed as metal oxide charge extraction layers (i.e., layers containing at least one metal oxide), can be sintered onto the graphite layer to improve, for example, their conductivity and electronic matching to the perovskite or the backside graphite layer. In all the aforementioned cases, the high temperature is incompatible with perovskite layers and therefore cannot be used for the production of solar cells in which such layers are already applied to the perovskite prior to heat treatment.

[0029] The charge-selective backside contact layer is therefore preferably formed as a metal oxide charge extraction layer. Preferably, after forming the metal oxide charge extraction layer and before arranging the backside contact structure, the backside contact layer is sintered, particularly at a temperature of at least 200°C, and more specifically at least 400°C.

[0030] 34511-P-WO Di / co 08.10.2025 Similarly, charge-selective contact layers, especially metal oxides, can be deposited at elevated temperatures by spray pyrolysis, for example, the deposition of a TiO2 layer by spraying a solution of titanium diisopropoxide bis(acetylacetonate) in isoporopanol (1:15, v / v) at 450 °C. Therefore, the charge-selective backside contact layer is preferably formed by spray pyrolysis, and preferably the charge-selective backside contact layer is formed by spray pyrolysis as a metal oxide charge extraction layer.

[0031] Furthermore, the process enables the deposition of metal layers and subsequent oxidation at elevated temperatures and / or oxidation in oxygen-containing atmospheres, particularly ozone, or the use of acids to form the charge-selective backside contact layer. This is not possible with conventional methods because perovskites are unstable at both high temperatures and in the presence of oxygen. Oxidation can also be used, for example, to precisely adjust the stoichiometry of metal oxide charge extraction layers. In addition, oxidation allows the doping level of semiconductors used as charge extraction layers to be adjusted. This makes it possible, in particular, to control the charge selectivity for electrons or holes.

[0032] In both cases, the best possible electronic matching to the perovskite or the backside graphite layer must be ensured. In all cases mentioned, the oxidation step is not compatible with perovskite layers and therefore cannot be used for the production of solar cells in which such layers have already been applied to the perovskite prior to oxidation.

[0033] Advantageously, therefore, prior to arranging the backside contact structure on the subcell to form the charge-selective backside contact layer, a metal layer is applied and one or more of the process steps are carried out: oxidation of the metal layer at elevated temperatures, preferably at a temperature greater than 200 °C, in particular greater than 400 °C, or oxidation in an oxygen-containing atmosphere, in particular ozone.

[0034] 34511-P-WO Di / co 08.10.2025 an application of acids for the formation of the charge-selective backside contact layer.

[0035] Since graphite layers typically consist of carbon particles with sizes in the micrometer range, while perovskite layers with thicknesses around 400 nm exhibit a surface roughness in the range of < 100 nm, it is advantageous to first deposit a charge-selective layer onto the graphite layer to minimize the surface unevenness of the coated graphite layer and thus improve the electrical coupling to the perovskite layer. Filling unevenness in the graphite layer is not possible with conventional, sequential deposition methods.

[0036] Advantageously, the charge-selective back contact layer is applied by liquid phase deposition before the back contact structure is arranged on the subcell. This leveles any rough surface of the back graphite layer.

[0037] Additionally or alternatively, in an advantageous embodiment, before forming the charge-selective backside contact layer, at least the side of the backside graphite layer on which the backside contact layer is applied is smoothed, particularly by pressing. The application of pressure with a smooth, flat, planar object during pressing results in leveling and thus smoothing of the surface of the backside graphite layer. After smoothing, the charge-selective backside contact layer is preferably applied by vapor deposition, sputtering (cathode sputtering), or electroplating.

[0038] Deposition, atomic layer deposition (ALD) or wet chemical deposition.

[0039] Since perovskite is not water-stable, water-based solutions, such as water-based PEDOT:PSS or water-soluble SnO2 nanoparticles, cannot be applied to the perovskite. The method described here enables the use of such solutions for the deposition of charge-selective layers between

[0040] 34511-P-WO Di / co 08.10.2025 Perovskite and graphite layer.

[0041] Advantageously, therefore, before arranging the backside contact structure on the subcell, the charge-selective backside contact layer is formed using a water-based solution, in particular using water-based PEDOT:PSS or water-soluble SnOj nanoparticles.

[0042] The process described here also enables the electroplating of charge-selective layers in a water bath, for example nickel, which is then oxidized to nickel oxide.

[0043] Advantageously, before the backside contact structure is arranged on the subcell, the charge-selective backside contact layer is formed by electroplating, preferably in a water bath. Preferably, a metallic layer is deposited, which is then oxidized.

[0044] Preferably, a nickel-containing layer is formed by electroplating and subsequently the nickel-containing layer is oxidized to form the charge-selective backside contact layer.

[0045] As previously described, the inventive method for forming the charge-selective backside contact layer does not require consideration of any potential impairment of the perovskite, nor does it require the creation of a porosity for subsequent perovskite filling. Advantageously, the formation of the charge-selective backside contact layer therefore comprises at least one of the following process steps:

[0046] Use of a polar solvent, especially in water, for example PEDOT:PSS dissolved in water or SnO2 nanoparticles dissolved in water;

[0047] Electroplating, especially in water baths; spray pyrolytic deposition.

[0048] 34511-P-WO Di / co 08.10.2025 The formation of a charge-selective layer containing nickel enables advantageous charge selectivity. In an advantageous embodiment, the charge-selective layer is therefore formed comprising nickel oxide. Preferably, as described above, nickel is electroplated and subsequently oxidized to form the charge-selective layer. In an alternative advantageous embodiment, a nickel-containing layer is formed by vapor deposition and preferably subsequently oxidized to form the charge-selective backside contact layer.

[0049] As previously explained, the method according to the invention further has the advantage that layers can additionally be formed on a rear side of the subcell before the rear side contact structure is arranged on the subcell. The rear side of the subcell is the side to which the rear side contact structure is arranged.

[0050] Advantageously, before the backside contact structure is attached to the subcell, a charge-selective subcell layer is formed on the back side of the subcell. This formation is preferably carried out using wet chemical methods and / or physical deposition, in particular vapor deposition, sputtering, or atomic layer deposition (ALD).

[0051] This achieves the advantage that, after arranging the backside contact structure, a layered structure consisting of two charge-selective layers—the charge-selective sub-cell layer and the charge-selective backside contact layer—is present, thus enabling increased charge selectivity. In particular, the wet-chemical formation of the charge-selective sub-cell layer, and preferably also the wet-chemical formation of the charge-selective backside contact layer, enables high charge selectivity.

[0052] Preferably, when arranging the backside contact structure on the subcell, the charge-selective subcell layer is arranged directly adjacent to the charge-selective backside contact layer. This has the advantage that no further intermediate layers need to be formed.

[0053] In an alternative embodiment, at least one intermediate layer is arranged between the charge-selective sub-cell layer and the charge-selective backside contact layer.

[0054] 34511-P-WO Di / co 08.10.2025, in particular an adhesive intermediate layer. The intermediate layer is preferably applied to the back side of the subcell or to the back side contact structure, preferably to the charge-selective back side contact layer.

[0055] An exemplary, preferred embodiment is as follows: An electrically conductive adhesive is produced as the adhesion material by mixing water-based PEDOT:PSS with D-sorbitol (50 mg / ml). This mixture is applied to the graphite paper by spin coating at 3000 RPM and baked at 100°C for 5 minutes to create the adhesion layer. Before application to the subcell, the graphite paper coated with the adhesion layer is heated to 100°C for 10 minutes to melt the D-sorbitol and thus activate the adhesive. Alternatively, the adhesive mixture is preferably applied by dipping, by immersing the graphite paper in the adhesive. The thickness of the adhesion layer is preferably in the range of 50 nm to 200 nm, particularly 75 nm to 150 nm, and preferably 100 nm.

[0056] In an advantageous embodiment, the backside contact structure is designed to include a backside perovskite layer, with the charge-selective backside contact layer preferably being arranged between the backside perovskite layer and the graphite layer. This offers the advantage of improved electrical contact, since perovskite is directly layered on perovskite, ideally creating a lattice-gap-matched homojunction. Because perovskites are ionic crystals, at least partial recrystallization is preferably carried out in a post-treatment step.

[0057] In the advantageous embodiment described above, it is advantageous that no charge-selective layer is formed on the back side of the subcell before the back side structure is arranged on the subcell, so that the back side perovskite layer of the back side contact structure is arranged indirectly or directly, preferably directly, on the perovskite-containing absorber structure of the subcell.

[0058] It is within the scope of the invention that the backside graphite layer has sufficient stability to serve as a substrate for forming the backside contact structure.

[0059] 34511-P-WO Di / co 08.10.2025. It is also within the scope of the invention that the backside contact structure is designed to have an additional carrier substrate.

[0060] In an advantageous embodiment, the backside graphite layer is used as a support substrate for forming the backside contact structure. In particular, it is advantageous to use a backside graphite layer designed as graphite paper. Graphite paper has sufficient stability to allow the charge-selective backside contact layer to be applied to the backside of the backside graphite layer serving as the support substrate without the need for an additional support substrate.

[0061] Graphite paper is preferably a film made of carbon particles, in particular graphite particles, which is electrically conductive and preferably has a paper-like consistency.

[0062] An example of how to produce graphite paper is described in Huiyin Zhang et al., “Self-Adhesive Macroporous Carbon Electrodes for Efficient and Stable Perovskite Solar Cells”, Advanced Functional Materials, Volume 28, Issue 39, September 26, 2018, doi.org / 10.1002 / adfm.201802985.

[0063] Graphite papers can also include so-called "gas diffusion layers," as well as carbon cloth, carbon felt, or carbon foils. All these materials have in common that they consist primarily of carbon / graphite, are electrically conductive, and have a paper-like texture.

[0064] In an advantageous embodiment, a support substrate is used to form the backside contact structure, on which at least the backside graphite layer and the backside contact layer are arranged. Preferably, the backside graphite layer is arranged between the support substrate and the backside contact layer.

[0065] This results in the advantage that there are greater degrees of freedom with regard to the methods and process parameters for forming the backside graphite layer.

[0066] 34511-P-WO Di / co 08.10.2025 In an advantageous embodiment, the carrier substrate is removed after arranging the backside contact structure on the subcell.

[0067] It is particularly advantageous to use one of the following carrier substrates: glass, PET film, PTFE film, polished metal substrates, metal foils, especially aluminum foil, graphite paper.

[0068] In an alternative advantageous embodiment, the support substrate is not removed after the backside structure is attached to the subcell. In this embodiment, the support substrate thus remains permanently on the backside of the solar cell. It is particularly advantageous to use the following support substrates: glass, plastic films, especially PET or PTFE, coated barrier films, metal foils, especially aluminum foil, and graphite paper.

[0069] A charge-selective layer or structure is characterized by different conductivities for different charge carriers, especially holes and electrons, as described in U. Würfel et al. “Charge Carrier Separation in Solar Celis”, 10.1109 / JPHOTOV.2014.2363550. A layer or structure with n-charge selectivity exhibits higher conductivity for electrons, and a layer or structure with the opposite p-charge selectivity exhibits higher conductivity for holes.

[0070] Advantageously, the charge-selective backside contact layer is formed with a charge selectivity opposite to that of the charge-selective frontside contact structure.

[0071] The aforementioned perovskite material, of the perovskite-containing absorber structure and / or of another aforementioned perovskite-containing structure or layer, is preferably selected from or combinations of: Semiconducting perovskites of the general form KM-A3 (K: cation, M: metal, A: anion), as well as derived low-dimensional perovskites such as Ruddleston-Popper perovskites of the structure CjKn-iMnAan+i and Dion-Jacobson perovskites of the structure DK n -in the n A3n+i, where C represents a large, monovalent cation K, D

[0072] 34511-P-WO Di / co 08.10.2025 represents a large bivalent cation K. These large cations preferentially form a layer between the KMA3 perovskite layer. n denotes the number of KMA3 perovskite layers, as well as perovskite-inspired materials. K is preferably selected from the group consisting of CH3NH3. 4 ; CH5N2 + , Li + , N / a + , K + , Rb + , Cs+ , Imidazolium cations, ammonium cations, sulfonium cations, pyridinium cations, bipyridyls, Ca2 + and Mg2 + , M is preferably selected from the group consisting of Pb, Sn, Bi, Fe, Mn, Cu, Co, W, Ti and Zn, and A is preferably selected from the group consisting of |-, C , F-, Br, SCN-, BF4OTf MnO4', O2Sf and SO4 2 '.

[0073] Further examples of preferred perovskite-inspired materials can be found in Yi-Teng Huang et al, “Perovskite-inspired materials for photovoltaics and beyond— from design to devices”, 2021 Nanotechnology 32, 132004, DOI 10.1088 / 1361-6528 / abcf6d.

[0074] Further advantageous features and designs are described below with reference to exemplary embodiments and figures. These show:

[0075] Figure 1 shows a schematic representation of an intermediate stage of the process before joining the subcell and backside contact structure.

[0076] Figure 2 shows a schematic representation of an intermediate stage of the process after joining the partial cell and backside contact structure.

[0077] The figures are schematic representations, not to scale. Identical reference symbols within the figures indicate identical or equivalent elements.

[0078] The following is an example of fabricating a solar cell in a nip configuration (in the nip configuration, counting from the first deposited contact, the electron-selective contact 'n' is deposited first. The perovskite 'i' then follows on the layer stack, and then the hole-selective contact). It is also within the scope of the invention to form a pin configuration.

[0079] 34511-P-WO Di / co 08.10.2025 First, a subcell 1 is formed, as described in Zouhair et al. DOI: 10.1002 / aenm.202200837, especially Fig. 1 there.:

[0080] For this process, a compact TiO2 layer is first applied to a glass substrate coated with fluorinated tin oxide (FTO). This layer is produced by spray pyrolytic deposition of titanium diisopropoxide bis(acetylacetonate) in isopropanol (1:15, v / v) at 450 °C. A mesoporous TiO2 layer is then applied by spin-coating a paste containing TiO2 nanoparticles. This paste is subsequently baked at 500 °C for 30 minutes. The perovskite layer is then applied, in this case by spin-coating a liquid precursor solution under a nitrogen atmosphere. The precursor solvent is then driven off at 150 °C for 13 minutes. This process forms a porous perovskite layer within the porous TiO2 and a compact perovskite layer above it. In this case, a solution containing salts of large organic cations such as octylammonium iodide is flung onto the perovskite layer.

[0081] This results in the formation of a 70 nm thick charge-selective passivation layer made of 2D perovskite. In this embodiment, a back-side charge-selective sub-cell layer is thus formed as a charge-selective passivation layer made of 2D perovskite.

[0082] This layered structure forms subcell 1 according to Figure 1. Subcell 1 thus comprises the charge-selective passivation layer made of 2D perovskite as a charge-selective front-side contact structure and the porous perovskite layer as the (essential) absorber structure for the incident electromagnetic radiation.

[0083] It is essential that a separate training of a backside contact structure 2 continues to take place.

[0084] In this embodiment, the backside contact structure 2 is formed on the basis of a backside graphite layer 3 designed as graphite paper:

[0085] Graphite paper with a thickness of 100 pm is used; in this case, graphite paper as described in Huiyin Zhang et al., op. cit. The graphite paper is then coated by dipping with water-soluble PEDOT:PSS in ethanol (10% w / v).

[0086] 34511-P-WO Di / co 08.10.2025 coated. The PEDOT:PSS is then baked out at 100°C. This forms the backside contact structure, comprising the graphite paper as the backside graphite layer and the PEDOT:PSS layer as the charge-selective backside contact layer.

[0087] The arrangement of the backside contact structure 2 on the subcell 1 then takes place:

[0088] The back-side contact structure is pressed onto the subcell with the back-side contact layer facing the subcell at 15 MPa at 60°C for 1 minute. To improve the adhesion properties, a nonpolar solvent such as ethanol or o-xylene is then applied to the graphite paper layer, followed by a second hot-pressing step at 15 MPa at 60°C for 2 minutes. After this process step, the back-side contact structure is thus arranged on the subcell, with the back-side contact layer positioned between the back-side graphite layer and the subcell.

[0089] In a modification of the embodiment, the graphite paper is functionalized with self-organizing monolayers (SAM): The graphite paper is dipped into a solution of 2PACz in ethanol (2% w / v) and thus coated by dipping. This graphite paper is then pressed onto the subcell at 15 MPa at 60°C for 3 minutes. In this modification, the charge-selective backside contact layer is thus formed as self-organizing monolayers (SAM).

[0090] In a further modification of the embodiment, a nickel oxide layer is formed on the graphite paper. For this purpose, a nickel layer is first formed by electroplating by electrically contacting the graphite paper and immersing it in an aqueous electrolyte solution consisting of 300 g / L NiCl₂ and 30 g / L H₃BO₃. A counter electrode is also placed in the electrolyte solution, and a voltage of -IV is applied between the graphite paper and the counter electrode. This causes nickel ions to be deposited onto the graphite paper. The coated graphite paper is then baked in air at 120 °C for 30 minutes to oxidize the nickel to nickel oxide. In this modification, the charge-selective backside contact layer is thus formed as a nickel oxide layer.

[0091] 34511-P-WO Di / co 08.10.2025 In a further modification, a layer of SAM is applied to the nickel oxide layer by immersing the NiO-coated graphite paper in a solution of 2PACz in ethanol (0.3 mg / ml). In this modification, the charge-selective backside contact layer is thus formed as a layer system consisting of the nickel oxide layer and SAM.

[0092] In a further alternative embodiment of the exemplary process, the graphite paper is coated by spin coating with a hole-selective contact such as spiro-OMeTAD as a charge-selective backside contact layer. In this process, 70 mg of spiro-OMeTAD solution, in 896 ml of chlorobenzene, 28 pL of tBP, 16 pL of Li-TFSI solution (from 517 mg / mL dissolved in acetonitrile), and 13 pL of Co-TFSI solution (from 376 mg / mL dissolved in acetonitrile), are added to the partial cell. Subsequently, 40 pL of this spiro-OMeTAD solution is spin coated onto the graphite paper.

[0093] In a further alternative embodiment of the exemplary embodiment, a hole-selective contact is deposited on the subcell as a charge-selective backside contact layer by adding 70 mg of spiro-OMeTAD solution in 896 ml of chlorobenzene, 28 pL of tBP, 16 pL of Li-TFSI solution (from 517 mg / mL dissolved in acetonitrile), and 13 pL of Co-TFSI solution (from 376 mg / mL dissolved in acetonitrile). Subsequently, 40 pL of this spiro-OMeTAD solution is spin-deposited onto the 2D perovskite.

[0094] In a further alternative embodiment of the exemplary embodiment, the graphite paper can be coated with TiO2 as a charge-selective backside contact layer by means of spray pyrolytic deposition of titanium diisopropoxide bis(acetylacetonate) in isopropanol (1:15, v / v) at 450 °C.

[0095] 34511-P-WO Tue / co 08.10.2025 Reference number:

[0096] 1 subcell

[0097] 2 Backside contact structure

[0098] 3 Backside graphite layer

[0099] 4 charge-selective backside contact layer

[0100] 34511-P-WO Tue / co 08.10.2025

Claims

Claims 1. A method for manufacturing a solar cell for converting incident electromagnetic radiation into electrical power, comprising a layered structure with at least one charge-selective front contact structure, at least one charge-selective back contact structure, and an absorber structure comprising at least perovskite, wherein the back contact structure is formed having at least one back graphite layer, characterized in that a subcell comprising at least the front contact structure and the absorber structure is formed, that the back contact structure, which comprises at least the back graphite layer and a charge-selective back contact layer, is initially formed separately from the subcell, and that after forming the back contact structure, the back contact structure is arranged on the subcell.so that the charge-selective backside contact layer is arranged between the backside graphite layer and the subcell.

2. Method according to claim 1, characterized in that, prior to arranging the backside contact structure on the subcell, the backside contact structure, in particular the charge-selective backside contact layer, is processed, which comprises at least one of the following process steps. Heating to a temperature of at least 150°C, in particular at least 200°C, preferably at least 400°C; Oxidation; wet chemical processing, in particular the use of solvents incompatible with perovskite such as water, aqueous solutions, Application of acids and / or alkalis. 34511-P-WO Tue / co 08.10.2025 3. Method according to one of the preceding claims, characterized in that the charge-selective backside contact layer is formed by means of one or more of the following method steps. Galvanic deposition, Formation as an oxygen-containing layer by means of oxidation, in particular as a metal oxide layer, Training using a water-based solution, in particular using water-based PEDOT:PSS or water-soluble SnOj nanoparticles.

4. Method according to one of the preceding claims, characterized in that the formation of the charge-selective backside contact layer comprises at least one of the following method steps: Use of a polar solvent, in particular PEDOT:PSS dissolved in water or SnO2 nanoparticles dissolved in water; Electroplating, especially in water baths; spray pyrolytic deposition.

5. Method according to one of the preceding claims, characterized in that the charge-selective layer is formed having nickel oxide, preferably by electroplating of nickel and subsequent oxidation.

6. Method according to one of the preceding claims, characterized in that, prior to arranging the backside contact structure on the subcell, a backside charge-selective subcell layer is formed on a backside of the subcell, preferably by wet chemical means. 34511-P-WO Tue / co 08.10.2025 7. Method according to one of the preceding claims, characterized in that the backside contact structure is formed having a backside perovskite layer, wherein the charge-selective backside contact layer is preferably arranged between the backside perovskite layer and the graphite layer.

8. Method according to one of the preceding claims, characterized in that the backside graphite layer, in particular a backside graphite layer formed from graphite paper, is used as a support substrate for forming the backside contact structure.

9. Method according to any one of the preceding claims 1 to 6, characterized in that a carrier substrate is used to form the backside contact structure, on which at least the backside graphite layer and the backside contact layer are arranged, wherein the backside graphite layer is preferably arranged between the carrier substrate and the backside contact layer.

10. Method according to claim 8, characterized in that the carrier substrate is removed after arranging the backside contact structure on the subcell.

11. Method according to claim 8, characterized in that the carrier substrate is not removed after arranging the backside contact structure on the subcell. 34511-P-WO Tue / co 08.10.2025

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