Additive for the coating of hydrophobic surfaces with halogenide perovskites

Abstract

The invention relates to a method for producing a coating, containing one or more Pb-(II) compounds, on a hydrophobic surface by applying a precursor solution, which contains one or more Pb-(II) compounds in an organic solvent; optionally then applying an organic anti-solvent; and then annealing, characterised in that the precursor solution contains a polymer additive containing polar groups, which is PMMA. The invention also relates to a solar cell which contains a Pb-(II) perovskite layer obtained in accordance with the method according to the invention, and the use of PMMA to produce perovskite layers on hydrophobic surfaces.

Description

[0001] Additive for coating hydrophobic surfaces with halide perovskites

[0002] Description

[0003] In recent decades, solar cells have been increasingly used to generate electricity. Initially, the focus was primarily on silicon solar cells (monocrystalline or polycrystalline). However, since further increases in efficiency, or rather, the efficiency ratio (which currently stands at 26.7%), no longer seemed readily possible, there was a growing search for other ways of generating electricity using photovoltaics.

[0004] The development of perovskite-based solar modules is considered very promising due to their low cost of production. The cells can be built significantly thinner than silicon cells. However, problems remain, in some cases, with limited durability, moisture protection, and the necessary amount of lead in all efficient perovskite cells.

[0005] Although it is in principle possible to replace lead with other elements such as tin, as of 2016 such attempts have been largely unsuccessful because tin gradually oxidizes and thus the crystal structure of the perovskite is lost.

[0006] Following the steady efficiency improvements in recent years, perovskite modules must be considered a serious potential challenger to other solar technologies. Efficiency was already at 20.1% in 2015, over 25% since 2020, and is expected to continue rising in the coming years (https: / / www.nrel.gov / pv / cell-efficiency.html). Furthermore, the technology is inexpensive. The efficiencies mentioned refer to pure perovskite solar cells. Although they are still in their early stages of development, perovskite-based solar cells have demonstrated outstanding potential for sustainability. They exhibit a very short energy payback time and could potentially become the most environmentally friendly photovoltaic technology if further development can increase utilization and durability (J. Gong et al., Perovskite photovoltaics: life-cycle assessment of energy and environmental impacts).Energy and Environmental Science 8, (2015), 1953-1968, doi:10.1039 / c5ee00615e). At the beginning of 2022, several manufacturers announced that they were close to series production of silicon perovskite tandem solar cells, with cell efficiency already at approximately 31% in the laboratory.

[0007] Perovskites are a class of materials that encompasses an extremely large number of different substances, all of which share the same crystal structure. They are capable of raising solar cells' efficiency far beyond the limits of conventional silicon cells.

[0008] While a simple silicon-based solar cell can only optimally utilize light in a specific wavelength range (red-yellow), a cell with a second semiconductor layer can be optimized so that each layer optimally converts a different part of the light spectrum (green-blue) into electricity. These are then referred to as tandem cells.

[0009] Some of today's perovskite cells have such a dual structure, for example, with perovskite layers and silicon layers as semiconductor layers (also called absorber layers, e.g., in Figs. 1 and 2). These are therefore referred to as silicon-perovskite tandem solar cells. They typically contain a 140 to 160 micrometer-thick conventional silicon wafer, onto which a perovskite layer of a few micrometers is applied (along with other layers described below).

[0010] Materials with a perovskite structure—perovskite is originally the name of the natural mineral calcium titanate (CaTiCh)—have been known for a long time. In the 1980s, oxide perovskites formed the basis for the further development of so-called superconductors.

[0011] In fact, research into solar cells made of metal halide perovskites, which differ greatly from oxide perovskites in their electronic, optical, and mechanical properties, has only begun since the late 2000s. The first report dates back to 2009 (A. Kojima et al., J. Am Chem. Soc. 2009, 131 17, 6050-6051). One reason for the pace—and further potential—of research into perovskite solar cells is the low non-radiative recombination coefficients in certain lead halide perovskites, as well as the possibility of depositing these materials with good electronic quality from the liquid phase. Semiconductors for good solar cells and light-emitting diodes must normally be highly pure to achieve high efficiency. One example of this is single-crystal Si, which lacks any grain boundaries. GaAs has been proposed as an alternative, which is produced epitaxially at high temperatures and requires very complex equipment.With perovskites, however, you can mix an "ink" from inexpensive chemicals, then apply (or print) it to a substrate at room temperature, and in this very simple way, you obtain a good semiconductor. This means that the lead halide perovskites obtained in this way are semiconductors with numerous crystallographic defects, which apparently have no serious consequences and therefore still allow the production of good solar cells.

[0012] In the early days of perovskite solar cells, the lifetime was unclear. One challenge is that different perovskites can have very different stability levels depending on their chemical composition.

[0013] Metal halide perovskites in particular have been intensively investigated in recent years with regard to their suitability for solar cells.

[0014] Metal halide perovskites grow in the perovskite structure, but what is important for their function in solar cells is not primarily the structure itself, but rather the lead-halide bond. The Pb-I or Pb-Br bonds have special properties that make them suitable for use in solar cells. However, PbI2 alone would not be a good solar cell material. It has been shown that the lead and iodine must be combined into a crystal structure—the perovskite structure—that is suitable for solar cells.

[0015] Typical metal halide perovskites for photovoltaic applications are made of a mixture of different cations (e.g. methylammonium MA, formamidinium FA, Cs, Rb etc.) with oxidation state +1, of cations with oxidation state +2 (almost exclusively Pb 2+) and anions (I; Br, Cl'). A "triple cation" perovskite is widely used, which contains Cs, FA, and MA. Its formula can be written as Cs0.os MAiyFAssjgsPbOssBriy. It is also called CsMAFA (A. Al-Ashouri et al., Energy Environ. Sci. 2019, D0l:10.1039 / c9ee02268f). The properties of a perovskite are influenced by the anion ratio Br / I. For example, a Br / I ratio >20% achieves a larger band gap. On the other hand, at high Br / I ratios, phase instabilities arise due to light-induced halide segregation.

[0016] A typical structure of a perovskite solar cell with a pin structure (positively doped layer - intrinsically conducting layer - negatively doped layer) consists of a glass substrate with a transparent conductive oxide layer applied on it, e.g. B. made of ITO (indium tin oxide), as an electrode and a conductive hole transport layer applied on top, usually made of an organic polymer such as PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] or polyTPD (poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine]). On top of this there is a perovskite layer as a semiconducting absorber layer. Ceo (fullerene), for example, is applied to the perovskite layer as an electron-selective contact. The last layer acts as an electrode, which often consists of two layers. First comes a thin layer of an organic semiconductor with a strong dipole (e.g. bathocuproine) and then an approximately 100 nm thick metal electrode made of Ag or Cu.One example is a bathocuproine electrode ((BCP) / Cu or BCP / Ag). Such a perovskite solar cell is shown schematically in Fig. 2.

[0017] Such solar cells are often combined with silicon solar cells to create so-called tandem solar cells. For example, a perovskite solar cell constructed as described above is "stacked" on top of a silicon solar cell with, for example, a pinine structure. The silicon solar cell then has no metal contact on the light-facing side. For this, the BCP / Ag contact in the perovskite solar cell must be replaced by several transparent layers. These typically consist of a thin layer of SnC>2 as protection against sputter damage, followed by a layer of indium tin oxide and a metal grid.

[0018] The individual layers of perovskite solar cells are sometimes deposited (printed) on top of one another using liquid-phase processes. While some of the layers are well-suited for solar cells due to their electronic properties, they are too hydrophobic to allow for even application of the subsequent layer. Therefore, the surface is only partially covered by the perovskite layer, rendering the solar cell unusable.

[0019] Solutions to this problem have already been proposed, such as ultraviolet ozone treatment (X. Xu, et al., J. Power Sources 360, 157 (2017)) or the use of poly[(9,9-bis(3-( / V, / V-Dimethylamino)propyl)-2,7-fluorene)-a / t-2,7-(9,9-dioctyl-fluorene)] (PFN) as an amphiphilic interfacial compatibilizer (J. Lee et al., Adv. Mater.

[0020] 29, 1606363 (2017)). A specific two-step process has also been proposed, namely a two-step heat-assisted interdiffusion method (J. Höcker et al., Zeitschr. Naturforsch. 2019, 74, 665-672). The same article also reports that polyTPD was used as a hole-transport layer in combination with vacuum-sublimated MAPbh perovskite, but that the hydrophobic nature of the polyTPD layer poses a challenge.

[0021] P. Tockhorn et al., Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells, Nature Nanotechnology, publication date 24.10.2022, https: / / doi.org / 10.1038 / s41565-022-012228-8) propose to avoid the formation of macroscopic holes in perovskite layers on planar Me-4PACz surfaces by using nanotextured silicon cells with a Me-4PACz coating as substrates. The nanotexturing, which takes the form of sinusoidal protrusions in the submicrometer range, forms perovskite layers that do not exhibit holes visible to the naked eye.

[0022] US 2022 / 0108847 A1 discloses an electronic device, such as a solar cell, comprising a layer of a perovskite material. In the disclosed solar cell arrangement, an additional layer of an oxysalt is provided between the perovskite layer and the hole-transport layer. The hole-transport layer used here is PTAA. The additional oxysalt layer is formed by applying a solution of the oxysalt to the perovskite layer, and a reaction takes place between the salt and the perovskite. The oxysalt layer influences the electronic properties and increases the stability of the perovskite film.

[0023] Polymethyl methacrylate (PMMA), better known as acrylic, is a transparent and rigid thermoplastic. PMMA, or acrylic, is a widely used transparent plastic material known for its applications in a variety of fields, from car windows to smartphone screens to aquariums. It is a durable plastic that is easily molded and offers an alternative to expensive and less durable glass.

[0024] In perovskite solar cells, PMMA has previously been used as a separate interlayer to passivate surface defects of the perovskite layer. However, the thickness of the PMMA layer must be extremely thin (referred to as “ultrathin” in the publication, but not specified) due to the low conductivity of PMMA, i.e., probably a few nanometers thick (J. Peng et al., Nanoscale localized contacts for high fill factors in polymer-passivated perovskite solar cells. Science 2021 , 371 (6527), 390 — 395; J. Peng et al., A Universal Double-Side Passivation for High Open-Circuit Voltage in Perovskite Solar Cells: Role of Carbonyl Groups in Poly(methyl methacrylate). Advanced Energy Materials 2018, 8 (30); H. Kim et al., Polymethyl Methacrylate as an Interlayer Between the Halide Perovskite and Copper Phthalocyanine Layers for Stable and Efficient Perovskite Solar Cells. Advanced Functional Materials 2021, 32 (13)).

[0025] In another case, PMMA was incorporated into CsPbXs quantum dots (QDs-CsPbXs) to improve their stability and maintain their excellent optical properties (LC Chen, Influence of PMMA on All-Inorganic Halide Perovskite CsPbBr(3) Quantum Dots Combined with Polymer Matrix. Materials (Basel) 2019, 72 (6)).

[0026] PMMA has also been added to perovskite solutions to control perovskite crystal size and morphology in perovskite layers.

[0027] S. Masi et al., Multiscale morphology design of hybrid halide perovskites through a polymeric template, Nanoscale 2015, 7, 18569 describe the influence of different polymers, namely poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly(methyl methacrylate) (PMMA), poly[(9,9-bis(3'-(V,V-dimethylamino)propyl)-2,7-fluorene-a / t-2,7-(9,9-diocytlfluorene)] (PFN), 2,4-dimethyl-poly(triarylamine) (PTAA) and polystyrene (PS) on the formation of MAPbh perovskite. The influence on self-aggregation as well as the influence on film growth were investigated by adding the different polymers to a perovskite precursor solution in DMF, which was then spin-coated onto (PEDOT:PSS) / glass substrates and then heated to 100 °C for 10 minutes. MEH-PPV and PFN, due to their basic functional groups, led to a base-acid equilibrium between the polymer and MA. +-cation. The resulting improved complexing ability led to smooth perovskite films with uniformly distributed aggregates of a few 10 nm. PMMA, PS and PTAA show a significantly poorer affinity in solution to MA + and Pblß' ions, leading to severe phase separation during the film formation process and causing stronger aggregation of the perovskite domains. The polymer was added to the perovskite precursor solution in a less polar solvent (THF), which strongly influenced the film formation step. MAPbh:PMMA blend films exhibited uneven surface coverage and high roughness due to the unfavorable polymer environment, which impairs the uniform growth of the perovskite phase.

[0028] D. Bi et al., Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency > 21%, Nature Energy 2016, 9, 2609) describes the formation of a mixed organic-inorganic Pb perovskite from FAI, PbI2, MABr, and PbBr2 in a mixed solvent of DMF, DMSO, and N-methylpyrrolidone (NMP). PMMA is added to the perovskite precursor solution in a chlorobenzene / toluene mixture (9:1 volume ratio) during spin coating. The solution is spin-coated onto a substrate made of FTO / compact TiO2 / mesoporous TiO2, i.e., onto a hydrophilic surface. The publication specifically investigates the influence of PMMA concentration on the perovskite film properties. A PMMA concentration of 0.6 mg / ml was found to be optimal.

[0029] Lead halide perovskite layers have already been deposited on various coatings, some of which are also hydrophobic (see, for example, A. Al-Ashouri, op. cit., A. Al-Ashouri et al., Science 2020, 1300-1309, J. Höcker et al., op. cit.). However, the publications do not describe the proportion of rejects obtained with the processes used.

[0030] PTAA and Me-4PACz are not as hydrophobic as poly-TPD and P3HT, so it may be possible in some labs to spin-coat them with perovskites because the environment, such as temperature and humidity, is very precisely controlled. Therefore, some labs may be able to spin-coat perovskites onto Me-4PACz. However, this is not yet possible on poly-TPD, at least not for large areas.

[0031] There are currently no published processes that allow the coating of hydrophobic surfaces with a Pb perovskite layer with high reproducibility and good surface coverage. The object of the invention was therefore to provide a process for the production of Pb(II)-containing layers on hydrophobic substrates, which results in a complete, gapless coating.

[0032] The object is achieved by the method according to claim 1. It is characterized in that the Pb(II)-containing solution contains a polymer additive which has polar groups, namely polymethyl methacrylate (PMMA).

[0033] Furthermore, the invention provides a method for producing a perovskite layer on a hydrophobic layer and a solar cell comprising such a perovskite layer. The use of PMMA as an additive for producing a Pb(II)-containing layer, in particular a Pb(II)-containing perovskite layer on a hydrophobic surface, is also disclosed.

[0034] Fig. 1 is a schematic diagram of a perovskite-based tandem solar cell.

[0035] Fig. 2 is a schematic diagram of a perovskite solar cell.

[0036] Fig. 3 shows the film quality of a perovskite layer according to the invention on a Me-4PACz surface as a function of the PMMA concentration of the perovskite precursor solution.

[0037] Description of the preferred embodiments

[0038] According to the invention, PMMA is used as the polymer additive.

[0039] Tests have shown that monomeric methyl methacrylate and polyethylene oxide are unsuitable as polymer additives according to the invention.

[0040] The PMMA typically has an average weight-average molecular weight of approximately 10,000 to approximately 200,000 g / mol, preferably approximately 15,000 to approximately 100,000 g / mol.

[0041] Any commercially available PMMA, e.g., from Sigma Aldrich, is suitable. The average weight-average molecular weight (determined by GC) is approximately 10,000 to approximately 120,000 g / mol, preferably approximately 15,000 to approximately 100,000 g / mol. In experiments, both PMMA with an average weight-average Mw of approximately 15,000 g / mol and PMMA with an average weight-average Mw of approximately 120,000 g / mol showed very good results, i.e., perovskite layers completely covering the hydrophobic surface were obtained. It is assumed that PMMA with a too high weight average molecular weight, i.e. higher than approximately 120,000 g / mol, does not dissolve completely in the solvent of the precursor solution, so that too high weight average molecular weights appear unsuitable.

[0042] The polymer additive PMMA is added to the Pb(II)-containing solution, which is then applied to the hydrophobic surface. The polymer additive dissolves completely in the Pb(II)-containing or perovskite precursor solution, forming a clear, viscous solution.

[0043] The solvent is any solvent commonly used for Pb(II) compounds or perovskite precursors, in particular dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), 2-methoxyethanol, or γ-butyrolactone, and mixtures thereof. DMF or a mixture of DMF / DMSO in a volume ratio of 3:1 to 5:1, e.g., 4:1, is particularly preferred.

[0044] Chlorobenzene and toluene are not suitable solvents for perovskite precursors. Rather, they are used as antisolvents, as described below.

[0045] The concentration of PMMA added to the Pb(II)-containing solution is generally 0.01 mg / ml to 1.5 mg / ml, preferably 0.03 to 1.2 mg / ml, particularly preferably 0.5 to 1.0 mg / ml, based on the Pb(II)-containing solution. The higher the PMMA concentration in the perovskite precursor solution, the better the quality of the resulting perovskite film, measured in terms of the uninterrupted area. This is clearly evident from Figure 3.

[0046] The hydrophobic surface, which according to the invention functions as a hole conductor or transport layer in the case of solar cells, can be any hydrophobic surface. According to the invention, a surface is particularly hydrophobic if the constituent polymer or molecule has numerous alkyl groups and / or longer-chain alkyl groups and / or aryl groups, as is the case, for example, with Me6-PACz or PTAA, whereas, for example, Me-2PACz, 2PACz, and V1036 are not classified as hydrophobic and Me-4-PACz is only weakly hydrophobic. According to the invention, surfaces are considered to be hydrophobic in particular if their constituent polymer or molecule has one or more alkyl groups with a number of >3 carbon atoms and / or aryl groups.

[0047] For example, the hydrophobic surface is made of poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (polyTPD). PolyTPD is transparent and colorless, so it has no influence on the absorption behavior of the solar cell and is particularly suitable for perovskite solar cells.

[0048] In addition to polyTPD, surfaces made of polytriarylamine (PTAA), poly(3-hexylthiophene-2,5-diyl) (P3HT), [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) and 6-(3,6-dimethyl-9H-carbazol-9-yl)hexyl)phosphonic acid (Me-6PACz) are also suitable according to the invention.

[0049] The polymer or molecule forming the hydrophobic surface is selected according to the perovskite layer to be deposited. The choice of material depends on the ionization potential of the molecule or polymer and the subsequently deposited perovskite, or rather, on the position of its valence band. These data are already known from the literature for perovskites and hole conductors (e.g., A. Al-Ashouri et al., Conformal monolayer contacts with lossless interfaces for perovskite single junction and monolithic tandem solar cells, Energy and Environ. Sci. 2019, 12, 3356; S. Tao et al., Absolute energy level positions in tin-and lead-based halide perovskites, Nature Comm. 2019, 10, 2560) or can be determined by ultraviolet irradiation.

[0050] Photoelectron spectroscopy can be used to measure the hole conductors. However, since this method has significant measurement uncertainty, hole conductors are often selected by fabricating perovskite solar cells and measuring the current-voltage characteristics.

[0051] According to the invention, the surface to be coated with the precursor solution, or the hole conductor, is not made of PEDOT:PSS (poly-3,4-ethylenedioxythiophene: sodium polystyrenesulfonate). This polymer is hygroscopic and therefore hydrophilic.

[0052] The hydrophobic surface is prepared by any conventional method, e.g. by applying a solution containing the constituent polymer, e.g. in toluene, chlorobenzene, dichlorobenzene, isopropanol, ethanol or another conventional solvent known to those skilled in the art, onto a substrate, e.g. glass / ITO or plastic / ITO, by e.g. spin coating, and subsequent drying.

[0053] According to the invention, all Pb(II) salts are suitable as Pb(II)-containing compounds, in particular lead(II) halides and lead acetate, particularly preferably Pbl2, PbBr2, and Pb(OAc)2.

[0054] According to the invention, the perovskite precursor compounds are selected from halides of metals, in particular Pb and Cs, and halides of organic cations, in particular methylammonium (MA) and formamidinium (FA). The halides are selected from bromide, iodide, and chloride and are preferably iodide and / or bromide, particularly preferably iodide or both iodide and bromide. According to the invention, the perovskite precursors are particularly preferably PbI2, PbBr2, MAI, FAI, and CsI.

[0055] The molar ratio of iodide to bromide, when both are present, in the perovskite precursor solution is arbitrary. It determines the size of the band gap and is therefore appropriately selected to achieve the desired band gap. It is, for example, 5:1 to 1:5, 4:1 to 1:4, 3.5:1 to 1:3.5, or 3.5:1.

[0056] For example, the molar ratio of the cations Pb : MA : FA : Cs in the perovskite precursor solution is 1.2 : 0.26 : 0.88 : 0.06.

[0057] The Pb-(II) compound is preferably selected from Pbl2, PbBr2 and Pb(CH3COO)2. The perovskite obtained according to the claimed process is preferably FAPbh, MAPbh, Cs x FAi. x Pbl3 or Cs x FA y May. x.y Pb(l z Bri. z )3, where x + y < 1 , 0 < x < 1 , 0 < y < 1 and 0 < z < 1 , and x means the proportion of Cs in all cations with oxidation state + 1, y means the proportion of FA in all cations with oxidation state +1 and z means the proportion of iodine in all anions.

[0058] Particularly preferred according to the invention is the perovskite Cso,o5MAo,22FAo.73Pb(10,78Bro,2)3 or Cso,o5(MAi7FA83)o,95Pb(183Bri7)3. These have proven particularly suitable for use in perovskite solar cells in experiments conducted.

[0059] The precursor solution is obtained by dissolving the Pb(II) compounds or perovskite precursors in a suitable solvent, especially a polar aprotic solvent, for example in dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), 2-methoxyethanol, or γ-butyrolactone. DMF or a mixture of DMF / DMSO, e.g., in a volume ratio of 3:1 to 5:1, especially 4:1, is preferred.

[0060] The Pb-(II) and any other compounds are dissolved in the solvent by stirring, e.g. at room temperature for 2 hours, and the solution is usually filtered before further use, e.g. with a 0.45 pm PTFE filter.

[0061] The precursor solution is then applied to the hydrophobic surface using a conventional process, e.g., spin coating, slot die coating, blade coating, inkjet printing, or roller coating. For example, spin coating involves a two-step process at different rotational speeds, e.g., 1400 rpm for 15 seconds with a ramp rate of 350 rpm / second, followed by 6000 rpm for 30 seconds with a ramp rate of 767 rpm / second.

[0062] Some time before the end of the second step, an antisolvent is applied, if desired, preferably by dropwise application. The antisolvent is, for example, anisole. However, other common antisolvents are also suitable, such as chlorobenzene, dichlorobenzene, toluene, or trimethylbenzene. The antisolvent initiates the crystallization of the perovskite (see AD Taylor et al., Nature Communications https: / / doi.org / 10.1038 / s41467-021-22049-8). The amount and duration of application of the antisolvent are known to the person skilled in the art and can be suitably selected, for example, based on the aforementioned publication by Taylor.

[0063] Immediately after application with a doctor blade, the precursor solution according to the invention containing the polymer additive forms a liquid film on the hydrophobic surface that is visible to the naked eye. When applied at an angle, this film does not run off but adheres to the surface. A drop of the additive-containing precursor solution according to the invention applied with a pipette cannot be completely removed from the surface with the pipette because the solution adheres too strongly.

[0064] In contrast, if a precursor solution without additive is applied to the hydrophobic surface in the same way using a squeegee, no film forms. Instead, the solution forms a droplet on the surface and runs off completely when the surface is tilted. A droplet of the precursor solution without additive applied with a pipette can be completely reabsorbed, as the solution without additive adheres poorly to the hydrophobic surface.

[0065] After applying the precursor solution, the resulting film is dried and then heated. Heating is carried out, for example, at 80 to 120°C, preferably 90 to 110°C, particularly preferably approximately 100°C, for 15 to 45 minutes, preferably 25 to 35 minutes, particularly preferably approximately 30 minutes.

[0066] The layer thickness of the resulting Pb(II) layer or perovskite layer is, for example, approximately 500 to 600 nm. The layer thickness can be increased by increasing the concentration of the perovskite precursor solution, e.g., up to 1.0 pm. The layer thickness can be determined, for example, by electron microscopic measurement of a section of the resulting sample. The layer thickness can be determined in a known manner, e.g., by scanning electron microscopic examination of a section. The layer thickness can also be determined using a profilometer, in which the height of a section through the layer is scanned with a needle that is slowly moved over the sample.

[0067] No special environmental conditions are required for the production of the perovskite layer. Typically, the coatings are produced on a laboratory scale in a glove box at 18 to 25 °C and in a nitrogen atmosphere with a maximum of 1% relative humidity. However, this is primarily done to prevent lead from escaping into the environment and to protect the personnel performing the process from lead. Experts are familiar with the appropriate conditions. For example, the process is carried out at a room temperature of 18 to 25 °C and a relative humidity of 30 to 80%.

[0068] The resulting Pb(II)-containing layer or perovskite layer completely covers the hydrophobic surface. This means that no holes or gaps in the perovskite coating are visible to the naked eye. Holes and even very small holes (so-called pinholes) are particularly clearly visible when the coated substrate is held against a light source, for example. The perovskite layer is black in color and its completeness is therefore easily visible to the naked eye. Cracks may be present in the edge region, as can be seen in Fig. 3, for example; however, the entire area covered by the perovskite layer is sufficiently large to achieve the solar cell sizes specified below, and these covered areas exhibit no holes or pinholes.

[0069] The coating quality can also be confirmed using an optical microscope or a scanning electron microscope. This allows for clear visualization of the complete coverage of the hydrophobic layer.

[0070] X-ray diffraction can confirm the presence of a perovskite crystal structure in a manner known to those skilled in the art. Sharp peaks in the X-ray diffraction spectrum indicate the presence of polycrystalline perovskite films. The formation of the perovskite structure is already evident in known perovskites due to the black coloration of the coating.

[0071] The area of ​​the uncoated substrate is typically up to 2 cm x 2 cm on a laboratory scale. On such a substrate, one can mount either one solar cell with an area of ​​1 cm x 1 cm or four solar cells with an area of ​​4 mm x 4 mm each.

[0072] For industrial application scale, substrates of up to 150 cm x 150 cm, e.g. 100 cm x 100 cm, 40 cm x 40 cm or 30 cm x 30 cm are coated.

[0073] Furthermore, a perovskite solar cell is claimed, which contains a perovskite layer produced by the method according to the invention. Otherwise, the solar cell contains the usual layers found in perovskite solar cells or tandem solar cells, which are produced in the usual way.

[0074] The perovskite solar cell comprises, in particular, a transparent substrate, a transparent anode applied thereon, an organic polymeric hole transport layer provided thereon, the perovskite layer obtained according to the invention applied thereon, and thereon, in this order, an electron transport layer, a buffer layer and a cathode.

[0075] The transparent substrate is made of glass or a transparent plastic, such as PET (polyethylene terephthalate), PI (polyimide), or PEN (polyethylene naphthalate). Depending on the material and the intended use of the solar cell, the substrate can be planar or curved. It can be rigid or flexible.

[0076] The transparent electrode consists, for example, of a transparent conductive metal oxide, preferably of antimony-doped tin oxide (ATO), indium-tin oxide (ITO), fluorine-doped tin oxide (FTO) or aluminum-doped zinc oxide (AZO), preferably of indium-tin oxide (ITO).

[0077] The hole transport layer (hole conductor) is preferably a hydrophobic layer as defined above, for example a polyTPD layer or PTAA layer.

[0078] The electron transport layer consists, for example, of Ceo or PCBM ([6,6]-phenyl-Cei-butyric acid methyl ester), ICBA (T, 1 ", 4',4"-tetrahydro-di[1 ,4]methanonaphthaleno[1 ,2:2',3',56,60:2",3"][5,6]fullerene-C6o, also known as indene-Ceo-bisadduct, molecular formula CysH ) or ZnO.

[0079] The buffer layer consists of e.g. 2,9-dimethyl-4,7-diphenyl-1 ,10-phenathroline (BCP), LiF, polyethyleneimine (PEIE), tris-(8-hydroxyquinoline)aluminum (Alq3), SnO x , or Ti(Nb)O x .

[0080] The cathode is made of a metal such as silver, copper, or gold, or alloys of these metals. Alternatively, cathodes made of common non-metallic materials such as graphite, ITO, FTO, and the like are also suitable.

[0081] The use of polymethyl methacrylate as an additive for producing a perovskite layer on a hydrophobic surface is also claimed.

[0082] EXAMPLES

[0083] A typical process for producing perovskite solar cells according to the invention is as follows:

[0084] Example 1 The pre-structured ITO substrates (2.0 x 2.0 cm 2 ) were cleaned successively with soap (Hellmanex III), deionized water, acetone, and isopropanol (IPA) by ultrasonication for 10 minutes. The cleaned ITO substrates were treated with oxygen plasma for 12 minutes and placed in a glove box filled with N2. 80 μl of 75 °C poly-TPD [poly (N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine, 1.5 mg / ml in toluene] solution were applied with a step program at 4000 rpm for 30 s (with a ramp rate of 800 rpm s -1 ) was applied to the ITO substrates by spin coating, then the samples were thermally annealed at 100 °C for 10 min and subsequently cooled to room temperature.

[0085] The perovskite precursor solution, prepared by mixing PbI (0.80 mmol), PbBr (0.4 mmol), MAI (0.26 mmol), FAI (0.88 mmol), and CsI (0.06 mmol) in 1 mL of DMF, was mixed with 0.5 mg / mL of PMMA, based on the perovskite precursor solution, and stirred for 2 hours at room temperature. The solution was filtered through a 0.45 μm PTFE filter before use. To prepare the perovskite layer, 120 μl of the perovskite precursor solution was spin-coated onto the hydrophobic poly-TPD layer in two consecutive steps at 1400 rpm for 15 s (with a ramp rate of 350 rpm). -1 ) and 6000 rpm for 30 s with a ramp rate of 767 rpm s -1 Ten seconds before the end of the program, 300 μl of anisole was added dropwise to the film as an antisolvent. The samples were immediately annealed on a hot plate at 100 °C for 30 min.

[0086] Subsequently, 20 nm of Ceo were deposited at a speed of 0.15 Ä s -1thermally deposited onto the perovskite film. Finally, BCP (8 nm) and Ag (80 nm) were sequentially deposited in a separate vacuum chamber (<5X10 -6 Pa) thermally evaporated.

[0087] 2 to 4

[0088] The procedure was carried out exactly as in Example 1 with the exception that the following hydrophobic polymers, solvents and concentrations were used for applying the hydrophobic layer: Example 2: P3HT [poly(3-hexylthiophene)] 1.5 mg / ml in chlorobenzene Example 3: Me-4PACz 1 mmol / ml (0.331 mg / ml) in ethanol Example 4: PTAA, 1.5 mg / ml in toluene Example 5: Me-4PACz 1 mmol / ml (0.331 g / ml) in ethanol, various concentrations of PMMA, namely 0.05 mg / ml, 0.1 mg / ml, 0.15 mg / ml and 0.2 mg / ml, each in DMF. The results are shown in Fig. 3.

[0089] Embodiments

[0090] The present application discloses the following embodiments:

[0091] 1. A process for producing a coating containing one or more Pb(II) compounds on a hydrophobic surface by applying a precursor solution containing one or more Pb(II) compounds in an organic solvent; optionally subsequently applying an organic anti-solvent; and subsequently heating, characterized in that the precursor solution contains a polymer additive containing polar groups.

[0092] 2. The method according to [1], wherein the precursor solution contains perovskite precursors, at least one of which is a Pb(II) compound, and the coating is a perovskite layer.

[0093] 3. Process according to [1] or [2] , wherein the polymer additive is selected from polyalkyl methacrylate, polyalkyl acrylate, polyacrylate or a copolymer of polyalkyl methacrylate, polyalkyl acrylate and / or polyacrylate.

[0094] 4. Process according to one or more of the preceding embodiments, wherein the polymer additive is selected from polymethyl methacrylate (PMMA) and polyethyl methacrylate and is preferably PMMA.

[0095] 5. Method according to one or more of the preceding embodiments, wherein the polymer additive is present in the perovskite precursor solution in a concentration of 0.01 mg / ml to 2.0 mg / ml, preferably 0.05 mg / ml to 1.0 mg / ml, based on the perovskite precursor solution.

[0096] 6. The process according to one or more of the preceding embodiments, wherein the solvent of the precursor solution is a polar aprotic solvent, preferably dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), 2-methoxyethanol or γ-butyrolactone or a mixture thereof, particularly preferably DMF. 7. The process according to one or more of [2] to [6], wherein the perovskite precursors are selected from halides of metals, in particular Pb and Cs, and halides of organic cations, in particular methylammonium (MAI) and formamidinium (FAI), wherein the halides are preferably selected from bromide, iodide and chloride, particularly preferably iodide and / or bromide, and most preferably iodide and bromide.

[0097] 8. The process according to one or more of [2] to [7], wherein the perovskite precursors are Pbl2, PbBr2, MAI, FAI and Csl.

[0098] 9. Method according to one or more of [2] to [8], wherein the Pb(II) compound is selected from Pbl2, PbBr2 and Pb(CH3COO)2 or the perovskite is selected from FAPbh, MAPbh, Cs x FAi. x Pbl3 and Cs x FA y May. x.y Pb(l z Bri. z )3, where x + y < 1 , 0 < x < 1 , 0 < y < 1 and 0 < z < 1 , and x is the proportion of Cs in all cations with oxidation state + 1 , y is the proportion of FA in all cations with oxidation state +1 and z is the proportion of iodine in all anions.

[0099] 10. The method according to one or more of the preceding embodiments, wherein the hydrophobic layer is selected from electrically conductive hydrophobic polymers, preferably from P3HT, polyTPD (poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine], PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), Me-4PACz ([4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid and Me-6PACz ([6-3,6-dimethyl-9H-carbazol-9-yl)hexyl]phosphonic acid.

[0100] 11. Process according to one or more of the preceding embodiments, wherein the perovskite obtained has the molecular formula Cso.o5MAo. 22 FAo.73Pb(lo.78Bro.2)30 which has Cso,o5(MAi7FA83)o,95Pb(ls3Bri7)3.

[0101] 12. A perovskite solar cell, characterized in that it contains a perovskite layer produced by the process according to one or more of [2] to

[0011] .

[0102] 13. Use of polymethyl methacrylate as an additive for the preparation of a Pb(II) perovskite layer on a hydrophobic surface.

Claims

Patent claims 1. A process for producing a coating containing one or more Pb(II) compounds on a hydrophobic surface by applying a precursor solution containing one or more Pb(II) compounds in an organic solvent; optionally subsequently applying an organic anti-solvent; and subsequently heating, characterized in that the precursor solution contains a polymer additive containing polar groups, wherein the polymer additive is polymethyl methacrylate (PMMA).

2. The method of claim 1, wherein the precursor solution contains perovskite precursors, at least one of which is a Pb(II) compound, and the coating is a perovskite layer.

3. The method according to one or more of the preceding claims, wherein the polymer additive is present in the perovskite precursor solution in a concentration of 0.01 mg / ml to 2.0 mg / ml, preferably 0.05 mg / ml to 1.0 mg / ml, based on the perovskite precursor solution.

4. The process according to one or more of the preceding claims, wherein the solvent of the precursor solution is a polar aprotic solvent, preferably dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), 2-methoxyethanol or γ-butyrolactone or a mixture thereof, particularly preferably DMF.

5. The method according to one or more of claims 2 to 4, wherein the perovskite precursors are selected from halides of metals, in particular Pb and Cs, and halides of organic cations, in particular methylammonium (MAI) and formamidinium (FAI), wherein the halides are preferably selected from bromide, iodide and chloride, particularly preferably iodide and / or bromide, and most preferably iodide and bromide.

6. The method according to one or more of claims 2 to 5, wherein the perovskite precursors are Pbl2, PbBr2, MAI, FAI and Csl. Method according to one or more of claims 2 to 6, wherein the Pb(II) compound is selected from Pbl2, PbBr2 and Pb(CH5COO)2 or the perovskite is selected from FAPbh, MAPbh, Cs x FAi. x Pbl3 and Cs x FA y May. x.y Pb(l z Bri. z)3, where x + y < 1 , 0 ^ x 5 1 , 0 y 1 and 0 z 1 , and x is the proportion of Cs in all cations with oxidation state + 1 , y is the proportion of FA in all cations with oxidation state +1 and z is the proportion of iodine in all anions. Method according to one or more of the preceding claims, wherein the hydrophobic layer is selected from electrically conductive hydrophobic polymers, preferably from P3HT, polyTPD (poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine], PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), Me-4PACz ([4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid and Me-6PACz ([6-3,6-dimethyl-9H-carbazol-9-yl)hexyl]phosphonic acid). Method according to one or more of the preceding claims, wherein the perovskite obtained has the empirical formula C50.o5MAo.22FAo.73Pb(10.78Bro.2)30der Oso,o5(MAi7FA83)o,95Pb(l83Bri7)3 has.Perovskite solar cell, characterized in that it contains a perovskite layer produced by the process according to one or more of claims 2 to 9.

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