Method of forming a perovskite layer of a photovoltaic solar cell

Abstract

The invention relates to a photovoltaic solar cell, comprising a starting layer structure, a perovskite layer disposed on the starting layer structure, and a charge transport layer disposed on the side of the perovskite layer facing away from the starting layer structure. It is an essential feature that an intermediate urea element is disposed between the charge transport layer and the perovskite layer, where the intermediate urea element partly covers the perovskite layer such that the charge transport layer partly directly adjoins the perovskite layer at the interface between charge transport layer and perovskite layer, and one or more urea layers of the intermediate urea element are partly disposed between charge transport layer and perovskite layer. The invention further relates to a method of forming a perovskite layer of a photovoltaic solar cell.

Description

[0001] Method for forming a perovskite layer of a photovoltaic solar cell

[0002] Description

[0003] Photovoltaic solar cells based on perovskite semiconductors have been researched for several years. Perovskite solar cell structures are being developed, as are solar cell structures in which perovskite is used to form a sub-cell of a multi-junction solar cell. In particular, the combination of perovskite and silicon to form a perovskite-silicon tandem solar cell promises lower electricity generation costs and lower resource consumption than conventional silicon solar cells. Efficiencies of over 30% are possible. Pure perovskite multi-junction solar cells also offer great potential, as they can be realized with lower manufacturing costs.

[0004] To create a photovoltaic perovskite solar cell, either as a single-junction solar cell or as a multi-junction solar cell, it is known to form the perovskite layer in a multi-step synthesis on a starting layer structure. In the so-called hybrid route for producing perovskite layers, the inorganic precursors are applied in a first step. Subsequently, additional, preferably organic precursors in the form of a halide solution are added in a second step to form a crystalline perovskite layer on the starting layer structure by heating in an annealing step. Subsequently, additional layers are applied, in particular selective contact layers and electrodes for charge transport.

[0005] It is known that a small grain size of the crystalline perovskite layer leads to reduced electronic quality due to high non-radiative recombination. By increasing the temperature during the annealing step, the grain size can be increased, but a higher temperature typically has a detrimental effect on other layers of the solar cell's layered structure, as shown in

[0006] Er-raji, O.; Rustam, L.; Kore, B.P.; Glunz, SW; Schulze, PSC Insights into Perovskite Film Formation Using the Hybrid Evaporation / Spin-Coating Route: An In Situ XRD Study. ACS Appt. Energy Matter. 2023, 6 (11), 6183-6193. DOI: 10.1021 / acsaem.3c00698.

[0007] The present invention is therefore based on the object of providing a method for forming a perovskite layer of a photovoltaic solar cell, which enables a high electronic quality of the perovskite layer without leading to high recombination losses at the interface of the perovskite layer to a neighboring charge transport layer and additionally reducing damage to other layers of the layer structure of the solar cell due to the effect of temperature and, in the case of the formation of a multi-junction solar cell, layers of other partial solar cells.

[0008] This object is achieved by a method for forming a perovskite layer of a photovoltaic solar cell according to claim 1 and a photovoltaic solar cell according to claim 14. Advantageous embodiments can be found in the dependent claims 2 to 13 and 15.

[0009] The method according to the invention is preferably designed to form a photovoltaic solar cell according to the invention, in particular a preferred embodiment thereof. The photovoltaic solar cell according to the invention is preferably formed by means of the method according to the invention, in particular a preferred embodiment thereof.

[0010] The method according to the invention for forming a perovskite layer of a photovoltaic solar cell comprises the following method steps:

[0011] A) Providing an initial layer structure of the solar cell;

[0012] B) applying a first precursor, which has inorganic components for the formation of perovskite, to the initial layer structure;

[0013] C) adding a halide solution as a second precursor to the first precursor on the starting layer structure, wherein the second precursor comprises an additive, and preferably an organic precursor is used as the second precursor, and

[0014] Carrying out an annealing step to form a crystalline perovskite layer on the initial layer structure D) Applying a charge transport layer to the perovskite layer

[0015] It is essential that the annealing in step C takes place at a temperature of less than 110°C, preferably less than or equal to 100°C, that the second precursor comprises urea as an additive, and in step C, by means of the second precursor, when forming the crystalline perovskite layer on the side facing away from the starting layer structure, the perovskite layer is partially covered with urea, so that in process step D, a urea intermediate element, which has one or more separate urea regions (one or more urea elements), is formed between the charge transport layer and the perovskite layer.

[0016] The invention is based on the finding that by using urea as an additive in the second precursor, the annealing step in process step C can be carried out at temperatures below 110°C, while still achieving a good crystal structure of the perovskite layer, which enables high electronic quality. Furthermore, the additive urea is used to form a urea intermediate element, which is arranged between the perovskite layer and a charge transport layer arranged on the perovskite layer. The urea intermediate element has one or more separate urea regions, so that the perovskite layer is partially covered with urea on the side facing the charge transport layer. The charge transport layer thus only directly borders the perovskite layer in some regions; in other regions, the urea intermediate element is interposed between the charge transport layer and the perovskite layer.

[0017] This combination achieves grain sizes of the crystalline perovskite layer that enable good electronic quality despite the comparatively low temperature of the annealing step in process step C. Likewise, the comparatively low temperature of the annealing step leads to less damage to other layers of the solar cell's layer structure and allows for greater choice in the selection of the layers of the solar cell's layer structure. In addition, the urea intermediate element reduces charge carrier recombination at the interface between the perovskite layer and the charge transport layer, thus achieving better electronic quality of the solar cell, in particular higher efficiency. The object stated at the outset is further achieved by a photovoltaic solar cell according to the invention as claimed in claim 14.

[0018] The photovoltaic solar cell according to the invention has an initial layer structure, a perovskite layer arranged on the initial layer structure and a charge transport layer arranged on the side of the perovskite layer facing away from the initial layer structure.

[0019] It is essential that a urea intermediate element is arranged between the charge transport layer and the perovskite layer, wherein the urea intermediate element partially covers the perovskite layer, so that at the interface between the charge transport layer and the perovskite layer, the charge transport layer partially adjoins the perovskite layer and partially one or more urea layers of the urea intermediate element is / are arranged between the charge transport layer and the perovskite layer.

[0020] This results in the advantages previously explained in the explanation of the method according to the invention.

[0021] The annealing in step C preferably takes place at a temperature in the range of 50°C to 110°C, preferably 80°C to 105°C, in particular at 100°C. This further reduces the risk of impairing the quality of further layers of the initial layer structure of the solar cell and / or, when formed as a multi-junction solar cell, the layers of further partial solar cells, while still enabling the formation of a perovskite layer with high electronic quality.

[0022] The annealing in process step C is preferably carried out for a period of time in the range of 5 minutes to 15 minutes, in particular 10 minutes, preferably at a temperature in the range of 50°C to 110°C, in particular in the range of 80°C to 105°C, preferably at 100°C. This achieves an advantageous thermal budget to achieve the aforementioned advantages.

[0023] As described above, the urea intermediate element partially covers the perovskite layer, so that there is partial direct contact between the charge-transport layer and the perovskite layer, and a partial urea region of the urea intermediate element is interposed. It is within the scope of the invention for the urea intermediate element to have a urea region, in particular a urea region formed from several contiguous urea surfaces. It is also within the scope of the invention for the urea intermediate element to have several separate urea regions.

[0024] To achieve partial coverage of the perovskite layer with urea in process step C for the formation of the urea intermediate element in process step D, urea is advantageously used in an excess amount by means of the second precursor, so that partial coverage of the perovskite layer with urea is achieved. It is particularly advantageous to use urea in the second precursor in a concentration that not only achieves the crystallization kinetics of perovskite formation toward larger, fewer-defect grains, but also to use an excess of urea as an additive to further achieve partial coverage with urea on the surface of the perovskite layer.

[0025] To form the perovskite layer partially covered with urea, it is advantageous for the second precursor to contain urea in the range of at least 2 mg / ml, in particular at least 3 mg / ml, in particular to achieve the aforementioned excess. In particular, it is advantageous for the second precursor to contain urea in the range of at least 3.5 mg / ml, in particular at least 4 mg / ml, in order to achieve the aforementioned excess.

[0026] To achieve coverage of the perovskite layer with urea on the one hand, and to use resources economically on the other, it is advisable for the precursor to contain urea in the range of 2 mg / ml to 7 mg / ml, preferably in the range of 4 mg / ml to 5 mg / ml. In particular, it is advantageous for the second precursor to contain urea in the range of 3.5 mg / ml to 7 mg / ml, preferably in the range of 3.5 mg / ml to 5 mg / ml. Furthermore, it is advantageous for the precursor to contain urea in the range of 4 mg / ml to 7 mg / ml, preferably in the range of 4 mg / ml to 5 mg / ml.

[0027] Studies show that covering the perovskite layer with urea reduces charge carrier recombination at the interface between the perovskite layer and the charge transport layer, and in particular, improves the open-circuit voltage of the solar cell. Excessive surface coverage of the perovskite layer with urea could lead to losses due to significant series resistance during charge carrier transport between the perovskite layer and the charge transport layer. It is therefore advantageous to form the urea intermediate element on the side of the perovskite layer facing away from the initial layer structure with a coverage in the range of 10% to 40%, particularly 20% to 30%. The coverage indicates the percentage of the surface of the perovskite layer facing the charge transport layer that is covered with urea.The covering can be effected by a urea intermediate element which is designed as a continuous urea element, in particular with recesses, in particular not simply connected, or by a urea intermediate element which has several separate urea elements.

[0028] The charge transport layer, which is preferably applied after formation of the perovskite layer, is preferably an electron conductor (ETL electron transport layer).

[0029] The charge transport layer preferably comprises one or more of the following layers:

[0030] - C60 layer

[0031] - C70 layer

[0032] - PCBM layer.

[0033] It is within the scope of the invention for the charge transport layer to be formed in multiple parts, in particular in multiple layers. The charge transport layer is preferably formed as one of the layers listed above. In particular, it is advantageous to form the charge transport layer as a C60 layer.

[0034] Advantageously, as described above, the charge transport layer is applied to the perovskite layer as a first charge transport layer. The starting layer structure preferably has a further charge transport layer, correspondingly preferably formed as a hole conductor (HTL hole transport layer), and the perovskite layer is preferably formed directly or indirectly on the second charge transport layer, particularly preferably directly on the second charge transport layer, so that the perovskite layer is arranged between the first and second charge transport layers.

[0035] Both charge-transport layers are preferably formed as charge-selective layers, with the first charge-transport layer preferably having a charge selectivity opposite to that of the second charge-transport layer. The charge selectivity can be electron-selective or, inversely, hole-selective.

[0036] Preferably, the previously described first charge-transport layer applied to the perovskite layer is electron-selective, and the previously described second charge-transport layer is hole-selective. The designations "first" and "second" refer only to the order in which they are mentioned. These layers are preferably produced in the reverse order of their mention, i.e., the second charge-transport layer, preferably a hole conductor, is preferably produced before the first charge-transport layer, preferably an electron conductor.

[0037] In particular, it is advantageous to form the second charge transport layer as one of the layers:

[0038] - SpiroTTB (2,2',7,7'-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene) layer

[0039] - TaTm (N4,N4,N4",N4"-tetra([1,1'-biphenyl]-4-yl)-[1,1':4',1"-terphenyl]-4,4"-diamine) layer

[0040] - Layers of self-assembling molecules, preferably with an acid anchor group and a carbazole unit, such as 2PACz ([2-(9H-carbazol-9-yl)ethyl]phosphonic acid), Me-4PACz ([4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid), MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid)

[0041] - Nickel oxide

[0042] Electrodes for discharging charges to an external circuit or adjacent solar cells are preferably arranged on the side of the first charge-carrier-selective layer facing away from the perovskite layer and on the side of the second charge-carrier-selective layer facing away from the perovskite layer, indirectly with the interposition of further layers or in particular directly without the interposition of further layers.

[0043] Advantageously, the initial layer structure therefore comprises a second electrode and the second charge-carrier-selective layer. The first charge-transport layer is applied to the perovskite layer in process step D. Advantageously, in a subsequent process step, a first electrode is applied indirectly or preferably directly to the first charge-transport layer.

[0044] It is within the scope of the invention that the starting layer structure comprises a substrate, in particular to ensure the stability of the solar cell. The substrate can be a radiation-transmissive substrate, in particular a glass substrate. Likewise, the substrate can be a semiconductor substrate, in particular a silicon substrate. This substrate can be either planar or textured.

[0045] As mentioned at the beginning, a perovskite layer is particularly suitable for forming a multi-junction solar cell. Advantageously, the solar cell formed using the perovskite layer is therefore a multi-junction solar cell, preferably a tandem solar cell.

[0046] In an advantageous embodiment, the starting layer structure comprises a silicon substrate, in particular to form a multi-junction solar cell, in particular to form a tandem solar cell. It is advantageous that a first charge carrier separation occurs by means of the perovskite layer and charge-selective layers, and a second charge carrier separation occurs by means of a PN junction in or on the silicon substrate.

[0047] Advantageously, an interconnection layer structure is arranged between the silicon substrate and the perovskite layer, which comprises at least one hole transport layer, preferably at least one of the hole transport layers

[0048] - SpiroTTB (2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene) layer - TaTm (N4, N4, N4", N4" tetra([1 , 1 '-biphenyl]-4-yl)-[1 , 1 ':4', 1 "-terphenyl]- 4,4" diamine) layer

[0049] - 2PACz layer

[0050] - Me-4PACz layer

[0051] - MeO-2PACz layer

[0052] - nickel oxide. The interconnection layer structure is preferably formed as an electrical connection layer, in particular as a recombination layer or tunnel diode.

[0053] In particular, it is advantageous for the interconnection layer structure to have a carrier layer, preferably a recombination layer made of a transparent conductive oxide such as indium tin oxide (ITO), and for the hole-transport layer to be arranged on the carrier layer, in particular on the side of the carrier layer facing the perovskite layer. In an alternative preferred embodiment to the recombination layer, silicon-based tunnel diodes can also electrically connect the subcells to one another. This results in an advantageous, compact monolithic structure for forming a multi-junction solar cell, in particular a tandem solar cell.

[0054] The starting layer structure thus preferably has a partial solar cell in order to form a multi-junction solar cell, preferably a tandem solar cell, with the perovskite layer and preferably at least a first, preferably a first and a second charge carrier-selective layer.

[0055] A particularly high electrical quality is achieved by forming a PN junction as a pin junction. It is therefore advantageous for the partial solar cell of the initial layer structure to have a pin structure, in particular for a pin structure to be formed adjacent to the perovskite layer. The pin structure preferably has a p-doped layer, an n-doped layer, and between these layers a lightly doped or intrinsic i-layer. The pin structure can be formed directly or indirectly (with the interposition of additional layers) adjacent to the perovskite layer. An increase in efficiency through total internal reflection within a substrate and / or longer light paths can be achieved by a structured, in particular a pyramid-like texture.

[0056] In an advantageous embodiment, the starting layer structure is therefore textured on the side facing the perovskite layer. In particular, the starting layer structure preferably has a pyramid-like texture on the side facing the perovskite layer, with the pyramids of the texture preferably having a base area with an edge length in the range of 0.2 pm to 10 pm, preferably 1 pm to 4 pm, in particular 1 pm to 2 pm.

[0057] The second precursor preferably contains formamidinium iodide (FAI) and / or formamidinium bromide (FABr). This has the advantage that perovskite compounds containing FA are more stable than the alternative methylammonium (MA), and that the use of both FAI and FABr allows the ratio of iodide to bromide in the final perovskite layer to be adjusted, thus controlling the band gap of the perovskite material.

[0058] The solar cell according to the invention is preferably formed by means of the method according to the invention, in particular a preferred embodiment thereof, and thus preferably has a structure according to the previously described layers and / or the previously described layer structure in the method according to the invention, in particular a preferred embodiment of the method according to the invention.

[0059] In particular, it is advantageous that the charge transport layer comprises one or more of the following layers

[0060] - C60 layer

[0061] - C70 layer

[0062] - PCBM layer.

[0063] In particular, it is advantageous for the charge-transport layer to be formed as one of the previously listed layers. The starting layer structure preferably comprises a substrate, particularly preferably a silicon substrate, further preferably a silicon substrate with a texturally textured surface, in particular pyramid-like textured surfaces.

[0064] In a further preferred embodiment, the starting layer structure comprises a glass substrate, in particular a glass substrate coated with at least one indium tin oxide layer.

[0065] In an advantageous embodiment, the starting layer structure comprises a non-textured substrate, in particular a flat substrate, preferably a glass substrate.

[0066] Perovskite layers are suitable for forming flexible solar cells. In an advantageous embodiment, the starting layer structure therefore comprises a flexible substrate, particularly preferably a plastic film.

[0067] Advantageously, the first precursor and / or the second precursor is applied by means of one of the methods

[0068] - evaporation;

[0069] - inkjet printing;

[0070] - spray coating;

[0071] - Blade coating (knife and / or squeegee coating);

[0072] - Spin coating (rotational coating);

[0073] - Slot-die coating.

[0074] In particular, the following combinations for applying the first precursor and the second precursor are advantageous: Further advantageous features and embodiments are explained below using exemplary embodiments and the figures. Herein:

[0075] Figure 1 shows an embodiment of a solar cell according to the invention as a single solar cell and

[0076] Figure 2 shows an embodiment of a solar cell according to the invention as a tandem solar cell.

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

[0078] Fig. 1 shows an embodiment of a solar cell according to the invention as a single-layer solar cell. In the illustration according to Fig. 1, the layers are formed from bottom to top, with the last layer formed forming the back of the solar cell. Thus, in the illustration according to Fig. 1, the front side, which faces the radiation during use, is shown at the bottom.

[0079] The structure of the embodiment of a solar cell according to the invention shown in Fig. 1 is explained using a first embodiment of a method according to the invention for forming a perovskite layer of a photovoltaic solar cell.

[0080] In a method step A, a starting layer structure 9 is provided. The starting layer structure 9 comprises a carrier substrate 8, which in this case is designed as a glass substrate. A transparent, conductive layer, in this case an indium tin oxide (ITO) layer, is arranged on the carrier substrate. A hole-transport layer 6, which in this case is designed as a 2PACz layer, is arranged on the ITO layer.

[0081] The hole transport layer 6 (hole-selective transport layer HTL) is generated by static spin coating from a 4 mol solution at 3000 rpm (revolutions per minute) for 35 s and subsequent annealing at 100 °C for 10 min.

[0082] Subsequently, in process steps B and C, a perovskite layer 5 and a urea intermediate element 4 are formed using a hybrid evaporation spin coating method:

[0083] In process step B, a first precursor, which contains inorganic components for the formation of perovskite, is applied to the initial visible structure 9, in this case to the hole transport layer 6. For this purpose, lead iodide and cesium iodide (Pbl2 / Csl) are co-evaporated as the first precursor until a 550 nm thick layer structure is formed.

[0084] In process step C, a halide solution is added as a second precursor to the first precursor on the initial visible structure 9, wherein the second precursor comprises an additive, and an annealing step is carried out to form the crystalline perovskite layer 5. The second precursor comprises urea as an additive. In this case, a 0.67 molar solution of formamidinium iodide (FAI) and formamidinium bromide (FABr) with a volume ratio of 65 / 35 is prepared, and then 5 mg / ml of the additive urea is added. This solution is applied as a second precursor by spin coating onto the Pb / Csl framework structure (the previously described 550 nm thick layer structure) at 2200 rpm for 30 s. The tempering in step C takes place at a temperature < 100 °C; in this case, a heating step is carried out at 100 °C for 10 min in ambient air (with a humidity of about 35%).This forms the perovskite layer 5 with a layer thickness of approximately 650 nm, as well as the urea intermediate element 4. The urea intermediate element 4 only partially covers the side of the perovskite layer 5 facing away from the starting layer structure 9, in this case with a surface area (i.e., a degree of coverage by urea) in the range of 20% to 30%, in this case 25%. The urea intermediate element consists of several non-contiguous urea elements, whose total surface coverage forms the aforementioned surface area.

[0085] In a process step D, a first charge transport layer 3 is applied to the perovskite layer 5. The first charge transport layer 3 is formed as an electron-selective charge transport layer (ETL), in this case as a Ceo layer. It is produced by thermal evaporation, with the first charge transport layer 3 being formed with a thickness of 20 nm.

[0086] The previously described hole transport layer 6 represents a second transport layer in the previously chosen order of naming the transport layers.

[0087] A 20 nm thick SnO x -layer is applied. On the SnO x A first electrode 1 is applied to the layer 2, which in this case is made of silver with a thickness of 200 nm by means of thermal evaporation.

[0088] The carrier substrate 8 is embodied as a glass substrate with a 200 nm thick transparent conductive layer 7. The transparent conductive layer 7 is embodied as an indium tin oxide coating on the carrier substrate 8 and is arranged between the carrier substrate 8 and the hole transport layer 6.

[0089] A second electrode 1a, which is also designed as a silver electrode, is formed on the carrier substrate 8 at a distance from the further layers.

[0090] The embodiment shown in Fig. 1 is manufactured starting from the carrier substrate 8, which is formed as a planar glass substrate. Accordingly, the starting layer structure 9 has a planar surface on the side facing the perovskite layer 5.

[0091] Fig. 2 shows a second embodiment of a solar cell according to the invention, which is designed as a tandem solar cell with an upper sub-cell 16 and a lower sub-cell 17.

[0092] The structure of the second exemplary embodiment of a solar cell according to the invention is explained using a second exemplary embodiment of a method according to the invention. In method step A, a starting layer structure 9a of the solar cell is provided. In this case, the starting layer structure 9a comprises the lower sub-cell 17 (except for the electrode 1c), which is designed as a silicon solar cell. To produce the starting layer structure 9a, a p-doped silicon substrate with a thickness of 250 μm is provided, which is treated with potassium hydroxide (KOH) to create a 1-2 μm thick pyramidal texture on both sides. Subsequently, amorphous intrinsic silicon layers 12 and 14 are formed on both sides. Doped amorphous silicon layers are applied to the intrinsic silicon layers 12 and 14: an n-doped silicon layer 11 and a p-doped silicon layer 15.The amorphous silicon layers 11, 12, 14, and 15 are deposited by plasma-enhanced physical vapor deposition. The thickness of the p- and n-doped layers 15 and 11 is 12 nm. The thickness of the intrinsic layers 12 and 14 is 6 nm.

[0093] On the side of the n-doped amorphous silicon layer 11 facing away from the silicon substrate 13, a transparent, conductive carrier layer 7b is created, which in this case is formed as an indium tin oxide layer. Such a layer is also referred to as a recombination ITO layer. The transparent, conductive layer 7b is formed by sputtering with a thickness of 30 nm.

[0094] On the side of the p-doped amorphous silicon layer 15 facing away from the silicon substrate, a 195 nm thick transparent conductive layer c is formed by sputtering, which is also formed as an indium tin oxide layer (ITO).

[0095] As the second electrode 1c, a 1000 nm thick silver layer is applied by sputtering to the side of the transparent conductive layer 7c facing away from the silicon substrate 13. The second electrode 1c represents the backside electrode of the solar cell.

[0096] Subsequently, analogous to the first embodiment, process steps B and C are carried out to form the transparent conductive layer 7b, the hole transport layer 6a, the perovskite layer 5a, the urea intermediate element 4a and the SnO x -Layer 2a. These layers are formed, as described in the first embodiment, identical to the transparent, conductive layer 7, hole transport layer 6, perovskite layer 5, urea intermediate element 4, first charge transport layer 3, and SnOx layer 2.

[0097] It is therefore also essential here that the urea intermediate element 4a only partially covers the surface of the perovskite layer 5a facing the first charge transport layer 3a, in this case also with an area proportion in the range of 20% to 30%, in this case 25%. In both exemplary embodiments, at the interface between the charge transport layer 3, 3a and the perovskite layer 5, 5a, the charge transport layer is partially formed directly adjacent to the perovskite layer, and a urea layer of the urea intermediate element 4, 4a is partially arranged between the charge transport layer 3, 3a and the perovskite layer 5, 5a.

[0098] On the side of the SnOx layer 2a facing away from the perovskite layer 5a, a transparent, conductive layer 7a is applied by sputtering, which is designed as an indium tin oxide layer with a thickness of 25 nm. On the side of the transparent, conductive layer 7a facing away from the perovskite layer 5a, a first electrode 1b is formed, which is designed as a silver electrode and covers only a partial area of ​​the surface of the transparent, conductive layer 7a in order to reduce losses due to shadowing in a manner known per se. On the surface of the transparent, conductive layer 7a not covered by the first electrode, an anti-reflection layer 10 is applied by thermal evaporation, which in the present case is designed as MgF x -layer with a thickness of 100 nm.

[0099] Due to the texturing of the silicon substrate 13, the structure determined by the texture is also continued in the layers of the upper subcell 16.

[0100] The method according to the invention can be applied to both textured and planar starting layer structures, in particular to starting layer structures based on planar silicon substrates and to starting layer structures based on textured silicon substrates. When forming a multi-junction solar cell, the starting layer structure can comprise one or more semiconductor sub-solar cells, in particular one or more of the following solar cells: silicon solar cell, perovskite solar cell, or CIGS solar cell.

[0101] In the embodiment shown in Fig. 2, the upper subcell 16 and the lower subcell 17 are interconnected by means of an interconnection layer structure 18, wherein the interconnection layer structure is partially a component of the subcells. The interconnection layer structure 18 comprises the hole transport layer 6a, the transparent, conductive carrier layer 7b, the n-doped silicon layer

[0102] 11 and the intrinsic silicon layer 12.

[0103] List of reference symbols

[0104] 1 , 1 b first electrode

[0105] 1a, 1c second electrode

[0106] 2, 2a SnOx layer

[0107] 3, 3a first charge transport layer

[0108] 4, 4a Urea intermediate element

[0109] 5, 5a Perovskite layer

[0110] 6, 6a Hole transport layer

[0111] 7, 7a, 7c transparent, conductive layer

[0112] 7b transparent, conductive carrier layer

[0113] 8 Carrier substrate

[0114] 9, 9a Initial layer structure

[0115] 10 Anti-reflective coating

[0116] 11 n-doped silicon layer

[0117] 12 intrinsic silicon layer

[0118] 13 Silicon substrate

[0119] 14 intrinsic silicon layer

[0120] 15 p-doped silicon layer

[0121] 16 upper subcell

[0122] 17 lower subcell

[0123] 18 Interconnection layer structure

Claims

Claims 1. Method for forming a perovskite layer of a photovoltaic solar cell, comprising the process steps A) providing an initial layer structure (9, 9a) of the solar cell; B) applying a first precursor, which has inorganic components for the formation of perovskite, to the starting layer structure (9, 9a); C) adding a halide solution as a second precursor to the first precursor on the starting layer structure (9, 9a), wherein the second precursor comprises an additive, and preferably an organic precursor is used as the second precursor, and carrying out an annealing step to form a crystalline perovskite layer (5, 5a) on the starting layer structure (9, 9a); D) Applying a charge transport layer (3, 3a) to the perovskite layer (5, 5a), characterized in that the tempering in step C takes place at a temperature of less than 110°C, preferably less than or equal to 100°C, that the second precursor comprises urea as an additive, and in step C, by means of the second precursor, during formation of the crystalline perovskite layer (5, 5a) on the side facing away from the starting layer structure (9, 9a), the perovskite layer (5, 5a) is partially covered with urea, so that in process step D, a urea intermediate element (4, 4a), which has one or more separate urea regions, is formed between the charge transport layer (3, 3a) and the perovskite layer (5, 5a).

2. The method according to claim 1, characterized in that the tempering in step C is carried out at a temperature in the range 50°C to 110°C, preferably 80°C to 105°C, in particular at 100°C.

3. Method according to one of the preceding claims, characterized in that the tempering in step C is carried out for a period of time in the range of 5 minutes to 15 minutes, in particular 10 minutes, preferably at a temperature in the range of 50°C to 110°C, preferably 80°C to 105°C, in particular at 100°C.

4. Method according to one of the preceding claims, characterized in that the second precursor contains urea in the range of at least 2 mg / ml, in particular at least 3 mg / ml and / or that the second precursor contains urea in the range of 2 mg / ml to 7 mg / ml, preferably 4 mg / ml to 5 mg / ml.

5. Method according to one of the preceding claims, characterized in that the urea intermediate element (4, 4a) covers the side of the perovskite layer facing away from the starting layer structure (9, 9a) with a degree of coverage in the range 10% to 40%, in particular 20% to 30%, in particular that the urea intermediate element has several unconnected urea elements and the degree of coverage of all urea elements of the urea intermediate element is in the range 10% to 40%, in particular 20% to 30%.

6. Method according to one of the preceding claims, characterized in that the charge transport layer (3, 3a) comprises one or more of the following layers: - C60 layer - C70 layer - PCBM layer, in particular that the charge transport layer is formed as one of the listed layers.

7. Method according to one of the preceding claims, characterized in that the starting layer structure (9, 9a) comprises a silicon substrate (13).

8. The method according to claim 7, characterized in that an interconnection layer structure (18) is arranged between the silicon substrate (13) and the perovskite layer (5a), which interconnection layer structure (18) comprises at least one of the hole transport layers (6a) - SpiroTTB (2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene) layer - TaTm (N4,N4,N4",N4"-tetra([1,1'-biphenyl]-4-yl)-[1,1':4',1"-terphenyl]-4,4"-diamine) layer - 2PACz layer - Me-4PACz layer - MeO-2PACz layer - contains nickel oxide.

9. The method according to claim 8, characterized in that the interconnection layer structure (18) has a carrier layer (7b), preferably a transparent conductive layer, in particular an indium tin oxide layer, and the hole transport layer (6a) is arranged on the carrier layer (7b), in particular on the side of the carrier layer (7b) facing the perovskite layer (5a).

10. Method according to one of the preceding claims, characterized in that the starting layer structure (9a) has a partial solar cell (17) in order to form a multi-junction solar cell, preferably a tandem solar cell, with the perovskite layer (5a).

11. Method according to one of the preceding claims, characterized in that a pin structure is formed directly or indirectly adjacent to the perovskite layer (5a).

12. Method according to one of the preceding claims, characterized in that the starting layer structure (9, 9a) is planar or textured on the side facing the perovskite layer (5, 5a), in particular is textured and preferably has a pyramid-like texture, wherein the pyramids of the texture preferably have a base area with an edge length in the range 0.2 pm to 10 pm, preferably 1 pm to 4 pm, in particular 1 pm to 2 pm.

13. Process according to one of the preceding claims, characterized in that the second precursor contains formamidinium iodide (FAI) and / or formamidinium bromide (FABr).

14. Photovoltaic solar cell, preferably manufactured according to one of the preceding claims, with an initial layer structure (9, 9a), a perovskite layer (5, 5a) arranged on the initial layer structure (9, 9a) and a charge transport layer (3, 3a) arranged on the side of the perovskite layer (5, 5a) facing away from the initial layer structure (9, 9a), characterized in that a urea intermediate element (4, 4a) is arranged between the charge transport layer (3, 3a) and the perovskite layer (5, 5a), wherein the urea intermediate element (4, 4a) partially covers the perovskite layer (5, 5a), so that at the interface between the charge transport layer (3, 3a) and the perovskite layer (5, 5a), the charge transport layer partially adjoins the perovskite layer and partially one or more urea layers of the urea intermediate element (4, 4a) between Charge transport layer (3, 3a) and perovskite layer (5, 5a) arranged is / are.

15. The method according to claim 14, characterized in that the charge transport layer (4, 4a) comprises one or more of the following layers: - C60 layer - C70 layer - PCBM layer, in particular that the charge transport layer (3, 3a) is formed as one of the listed layers.

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