Process for the formation of a perovskite layer in particular for a photovoltaic cell

Abstract

Described are a process for forming a perovskite layer (1) on a carrier substrate (3) and a process for manufacturing a photovoltaic cell comprising a perovskite layer of said kind. The process comprises at least the following steps: - mixing a solution containing a first perovskite precursor (7) and a second perovskite precursor (9) at a mixing temperature (T1); - applying the solution (5) to the carrier substrate (3), the temperature of which has optionally been brought to a carrier substrate starting temperature (T2); - moving the carrier substrate (3) along with the applied solution (5) in a two-dimensional movement and simultaneously cooling the carrier substrate (3) along with the applied solution (5) to a deposition temperature (T3) lying below the carrier substrate starting temperature (T2) in order to produce, on the carrier substrate (3), a deposited layer (11) containing the first and second perovskite precursors (7, 9); - optionally: removing a non-deposited portion (13) of the solution (5) from the carrier substrate (3); and - optionally: heating the deposited layer (11) to above a drying temperature (T4) lying above the deposition temperature (T3) in order to initiate a chemical reaction between the first perovskite precursor (7) and the second perovskite precursor (9).

Description

[0001] METHOD FOR FORMING A PEROVSKITE LAYER

[0002] ESPECIALLY FOR A SOLAR CELL

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a method for forming a perovskite layer. Furthermore, the invention relates to a method for manufacturing a solar cell with a perovskite layer formed in this way.

[0005] TECHNICAL BACKGROUND

[0006] Perovskite layers, i.e. thin layers of perovskite material, can exhibit, among other things, interesting electrical and optical properties, which make them suitable for a wide variety of applications.

[0007] In particular, solar cells have recently been developed that utilize an absorber layer made of perovskite material to absorb light and convert the energy contained in the light into electrical energy. These so-called perovskite solar cells promise high efficiencies with low material costs and simple production.

[0008] Various processes are known for the formation of perovskite layers, particularly for solar cells. For example, chemical substances that can react with one another to form a perovskite material and are also referred to herein as perovskite precursors or perovskite educts can be applied to a substrate in a single process step and then caused to react chemically, for example by supplying energy in the form of heat. In such a single-step process, the perovskite layer precursors can be vapor-deposited onto a substrate, for example in a joint vapor deposition process, which is also referred to as co-evaporation. However, such vapor deposition processes are often difficult to implement on an industrial scale, require complex equipment and / or are cost-intensive.Alternatively, wet-chemical deposition processes have been proposed to form a perovskite layer in a single-step process. However, technical difficulties and / or high costs often prevent industrial implementation of these processes.

[0009] Alternatively, perovskite precursors can be applied to a substrate in a two-step process before being subjected to a chemical reaction. This involves first depositing a first perovskite precursor layer onto a substrate, followed by a second perovskite precursor layer on top.

[0010] To form the two perovskite precursor layers, different technologies can be used.

[0011] For example, a perovskite precursor layer can be formed by depositing suitable chemical substances using physical vapor deposition (PVD), such as co-evaporation, or chemical vapor deposition (CVD). However, this often requires complex equipment, and the associated high costs and / or low throughput often make such processes unattractive for industrial implementation. Alternatively, at least one of the perovskite precursor layers can be formed using wet-chemical processes. The use of different wet-chemical deposition processes is conceivable in this case.

[0012] For example, on a laboratory scale, so-called spin coating is often used to apply a viscous solution containing the substances required for the perovskite precursor to a rotating substrate. Centrifugal forces then distribute the solution into a perovskite precursor layer of homogeneous thickness. However, such an approach is usually only applicable to coating small-area substrates and, due to its lack of mass production, is particularly unsuitable for industrial implementation to form perovskite layers.

[0013] Alternatively, perovskite layers can also be applied wet-chemically using so-called slot-die extrusion dies. Such processes are also known as slot-die coating. A solution that should be sufficiently viscous and contains the substances required for the perovskite precursor is extruded through a wide slot die onto the surface of a substrate. However, the relatively high equipment required for this, as well as limitations of the viscous solutions that can be used in this case, make the industrial implementation of such deposition processes for the formation of perovskite layers unattractive.

[0014] In addition, in the two wet-chemical deposition processes mentioned above, the reactants are often dissolved in solvents such as dimethylformamide, which are relatively hazardous substances that are, for example, flammable and / or toxic. This can complicate industrial implementation of these processes, for example due to high costs or the complex equipment required. In particular, many safety-related aspects, such as compliance with regulations (e.g., ATEX), can lead to increased costs when designing a system for this purpose. The solvents themselves are also often expensive, which can increase the manufacturing costs of the entire process.

[0015] In another approach, the reactants are dissolved in a solvent and applied to a substrate using a spraying process, also known as spray coating. However, this generally generates aerosols, which can be difficult to extract and / or prevent a portion of the reactants from reaching the perovskite layer being created, thus reducing the deposition efficiency.

[0016] SUMMARY OF THE INVENTION AND EMBODIMENTS

[0017] There may therefore be a need for an alternative approach by which a perovskite layer can be formed and by which at least some of the aforementioned problems of previous approaches can be avoided or reduced. In particular, there may be a need for a process by which a perovskite layer can be produced at low cost, with low equipment requirements, and / or in an industrially feasible manner. Furthermore, there may be a need for a method for manufacturing a solar cell using such a method for forming a perovskite layer.

[0018] The aforementioned needs can be at least partially met by the subject matter of one of the independent claims of the present application. Advantageous embodiments are specified in the dependent claims and the following description.

[0019] According to a first aspect of the present invention, a method for forming a perovskite layer on a carrier substrate is described. The method comprises at least the following process steps, preferably in the order given: (i) mixing a solution containing a first and a second perovskite precursor at a mixing temperature,

[0020] (ii) applying the solution to the carrier substrate, which is optionally tempered to a carrier substrate initial temperature,

[0021] (iii) moving the carrier substrate together with the applied solution in a two-dimensional movement and simultaneously cooling the carrier substrate together with the applied solution to a deposition temperature below the mixing temperature to produce a deposited layer containing both the first and the second perovskite precursor and / or a reaction product of the two perovskite precursors on the carrier substrate,

[0022] (iv) optionally: removing a non-deposited portion of the solution from the carrier substrate, and

[0023] (v) optionally: heating the deposited layer above a drying temperature above the deposition temperature to dry the solution and / or to initiate a chemical reaction between the first perovskite precursor and the second perovskite precursor and / or a conversion of the reaction product formed therefrom.

[0024] According to a second aspect of the present invention, a method for manufacturing a solar cell is described. The method comprises at least the following process steps, preferably in the specified order:

[0025] - forming a perovskite layer on a surface of a carrier substrate by means of the method according to an embodiment of the first aspect of the invention, and

[0026] - Forming electrical contacts to dissipate electrical charge carriers from the perovskite layer.

[0027] Embodiments of the invention may be considered, among other things and without limiting the invention, to be based on the ideas and findings described below. By way of introduction, a basic idea for embodiments of the invention described herein will be briefly explained, whereby this explanation is to be interpreted as merely a rough summary and not as limiting the invention:

[0028] As already indicated, the aim is to provide an advantageous and, in particular, industrially applicable process for forming perovskite layers, for example for the production of solar cells.

[0029] For this purpose, a preferably single-stage wet-chemical process is proposed herein. A solution in which a first perovskite precursor and a second perovskite precursor are absorbed or dissolved is premixed. The solution is then heated to a mixing temperature that is generally higher than ambient temperature. Preferably, the mixing temperature is selected such that a reaction occurs between the first and second perovskite precursors contained in the solution, whereby a reaction product can correspond to the perovskite to be formed in terms of its chemical composition and possibly also its structural design. This solution is then applied to the carrier substrate, whereby the carrier substrate can also be heated to a so-called carrier substrate initial temperature that is typically higher than ambient temperature.The carrier substrate thus coated with the applied solution is then successively cooled to a lower deposition temperature and simultaneously moved in a special two-dimensional manner. Through the successive cooling, the reaction product formed from the two perovskite precursors can precipitate from the solution and deposit on the surface of the carrier substrate, preferably in the form of a layer and more preferably in a crystalline form. By simultaneously moving the carrier substrate and the solution located thereon, it is possible to achieve a layer formed uniformly and with a homogeneous layer thickness. Once a sufficient layer thickness has been achieved, any excess solution not absorbed into the deposited layer can be removed from the carrier substrate.Finally, the layer deposited in this way can optionally be heated again, for example to evaporate any remaining residues of the solution and / or to convert previously unconverted portions of the first and second perovskite precursors into the reaction product, so that the desired perovskite layer is formed overall.

[0030] The proposed approach can be implemented using a relatively simple plant and / or in an industrially viable manner. Furthermore, hazardous, harmful, and / or expensive solvents can be avoided. Furthermore, the proposed, preferably single-stage, wet-chemical process generally does not generate aerosols.

[0031] Possible features of embodiments of the invention and the advantages to be achieved thereby are described in detail below.

[0032] Perovskite layers can be used for a variety of technical applications. Accordingly, different perovskite materials can be used depending on the application.

[0033] Perovskite solar cells generally consist of several layers. The main layer can be an absorber layer of the ABX3 type, where "A" stands for cesium (Cs), methylammonium (MA), or formamidinium (FA), "B" stands for lead (Pb), and "X" stands for chlorine, bromine, or iodine. For example, MAPbh (methylammonium lead iodide) can be used for the perovskite layer of a solar cell.

[0034] The perovskite layer to be formed using the method described herein can, in principle, be produced with any desired dimensions. For example, the area of ​​the perovskite layer can range from a few square millimeters to several square meters. Preferably, the area of ​​the perovskite layer can be between 5 cm 2and 5 m 2 , more preferably between 200 cm 2 and 2 m 2 The layer thickness can be between 1 nm and 1 mm, preferably between 100 nm and 1 pm. The perovskite layer is generally not self-supporting, but is supported by a carrier substrate.

[0035] The carrier substrate can, in principle, have any dimensions and be made of any material. For example, the carrier substrate can have the same surface area as the perovskite layer to be formed on it. However, the carrier substrate can also be larger than the perovskite layer to be formed, so that the latter only covers partial areas of the carrier substrate. The carrier substrate is usually significantly thicker than the perovskite layer. For example, the thickness of the carrier substrate is usually greater than 0.1 mm, often greater than 0.5 mm, greater than 1 mm, or even greater than 3 mm, but usually less than 2 cm or less than 1 cm.

[0036] The material and geometry of the carrier substrate can be selected to provide sufficient mechanical support for the perovskite layer to withstand the forces acting on it during operation. On the other hand, the carrier substrate should be able to withstand the conditions encountered during the formation of the perovskite layer, such as high temperatures and exposure to chemicals used. Furthermore, the thermal expansion coefficient of the carrier substrate should not differ excessively from that of the perovskite layer formed on it. In practice, thin glass panes have proven suitable for many applications. However, carrier substrates made of semiconductor material, particularly in the form of silicon disks or wafers, can also be used.As described in more detail below, a fully processed solar cell, for example, one constructed from a silicon wafer, can serve as the carrier substrate. In principle, however, carrier substrates made of other materials are also conceivable, such as plastic, ceramic, metal, etc. In the process described here, a solution is first mixed containing both a first and a second perovskite precursor. The two perovskite precursors are typically completely dissolved in and / or mixed with a liquid solvent. One of the perovskite precursors may also be chemically bound in the solvent.The solution can be saturated to a certain extent with the first and / or the second perovskite precursor, for example to more than 10%, more than 30%, more than 60%, more than 80%, more than 90%, more than 95%, or even with complete saturation or even supersaturation. The solution is tempered to a first temperature T1, referred to herein as the mixing temperature T1. This mixing temperature is typically elevated compared to an ambient temperature and is selected such that a reaction occurs between the first and second perovskite precursors to form the desired perovskite or at least a chemically equivalent precursor thereof as a reaction product. The mixing temperature can therefore also be referred to as the reaction temperature. For example, the mixing temperature can be at least 50°C, at least 60°C, or at least 70°C.The mixing temperature depends, among other things, on the properties of the two perovskite precursors and / or the properties of the solvent. The solubility of the perovskite precursors, i.e., the maximum amount of material that can be dissolved in the solution until the solution is completely saturated, typically increases with increasing mixing temperature.

[0037] After the solution has been pre-mixed and tempered in this way, it is applied to a surface of the carrier substrate. For example, the solution can be dripped, poured, poured or applied to the carrier substrate in some other way. In this case, a sufficient amount of solution is preferably applied to wet the entire surface of the carrier substrate or at least a partial surface on which the perovskite layer is to be formed, over the entire area and to a sufficient thickness, with solvent. Preferably, the amount of solvent applied to the carrier substrate or the amount of material of the two perovskite precursors contained therein is greater or even significantly greater (i.e., for example, more than 10%, more than 20% or even more than 50% greater) than the amount of material of the perovskite layer ultimately to be formed on the carrier substrate.In other words, solvent can be applied in abundance to the carrier substrate.

[0038] The carrier substrate is preferably at least initially heated to an elevated second temperature T2, referred to herein as the initial carrier substrate temperature T2. This initial carrier substrate temperature may be similar to the mixing temperature, but need not be identical to the mixing temperature. The initial carrier substrate temperature may be up to 20°C, up to 10°C, or at least up to 5°C higher or lower than the mixing temperature. The initial carrier substrate temperature is preferably slightly lower than the mixing temperature, for example, by between 1°C and 20°C, preferably by between 3°C and 10°C.

[0039] The support substrate covered with the solution in this way is then subjected to a two-dimensional movement. During such a two-dimensional movement, the support substrate is successively displaced transversely in various directions and / or rotated or pivoted about various axes. Such a two-dimensional movement can also be referred to as a tumbling movement or "wobbling." Due to such a two-dimensional movement of the support substrate, the solution applied to its surface can be evenly distributed, ultimately forming a homogeneous layer.

[0040] Simultaneously with the two-dimensional movement, the carrier substrate, together with the solution applied thereto, is successively cooled to a third temperature T3, which is referred to herein as the deposition temperature T3. The deposition temperature is preferably significantly below the initial carrier substrate temperature. For example, the deposition temperature can be at least 10 °C, preferably at least 20 °C, or even at least 30 °C below the initial carrier substrate temperature. For example, the deposition temperature can be lower than 40 °C. The deposition temperature to be achieved depends on the properties of the perovskite precursors or reaction products contained in the solution and the solvent, and in particular on the solubility of the perovskite precursors or reaction products in the solvent of the solution.By successively cooling to the deposition temperature, which is lower than the initial temperature of the carrier substrate, the temperature-dependent solubility of the two perovskite precursors or reaction products in the solution is reduced, so that they at least partially precipitate from the solution and thus deposit as a layer on the surface of the carrier substrate.

[0041] After a desired layer thickness of the layer deposited in this way has been produced from the first and second perovskite precursor and / or the reaction product, a non-deposited residue of the solution is generally removed from the carrier substrate, for example by pouring it off.

[0042] The carrier substrate with the layer produced in this way, which is formed from the two perovskite precursors and / or the reaction product formed from the perovskite precursors, can then be heated again in a targeted manner. In particular, heating is carried out above a predetermined fourth temperature T4, which is referred to herein as the drying temperature T4. This drying temperature can be selected such that any remaining solvent evaporates or vaporizes. Furthermore, the drying temperature can depend on the material-specific properties of the first and second perovskite precursors or the reaction product and can represent a temperature above which a conversion and / or chemical reaction occurs between the two perovskite precursors, so that they ultimately form the desired perovskite layer. The drying temperature can therefore also be referred to as the reaction temperature limit.This reaction temperature limit is usually significantly higher than the deposition temperature, for example, by more than 5 °C or even more than 10 °C. For example, the reaction temperature limit can be above 50 °C, above 60 °C, or above 70 °C, but usually below 150 °C, below 130 °C, or below 90 °C. During the heating mentioned above, the evaporation of residues of the solvent contained in the solution may occur simultaneously.

[0043] According to one embodiment, the solution is aqueous, wherein the first and second perovskite precursors and / or the reaction product are soluble in aqueous solution. The aqueous solution may comprise water as a solvent. Alternatively or additionally, the aqueous solution may comprise an aqueous solution of an acid. An aqueous solution is generally easy to handle and inexpensive to provide. In particular, the aqueous solution should be free of harmful, hazardous, and / or difficult-to-dispose of chemicals. Preferably, both the first and second perovskite precursors and the reaction product should be water-soluble.The solubility of both perovskite precursors and / or the reaction product should be sufficiently high to dissolve a sufficient amount of each of the two perovskite precursors and / or reaction products in the solution to ultimately produce the perovskite layer with the desired thickness. In particular, the solubilities of the perovskite precursors in the solution can vary, but they should be similar to each other within acceptable tolerances. For example, the solubilities of the two perovskite precursors in the solution can differ by less than 50%, preferably less than 20% or less than 10%.

[0044] For example, according to one embodiment, the first perovskite precursor can contain cesium, methylammonium, or formamidinium. In particular, the first perovskite precursor can contain methylammonium iodide, and the second perovskite precursor can contain lead, in particular lead acetate and / or a lead halide. These first and second perovskite precursors have been recognized as suitable for forming a perovskite layer, in particular an ABXs-type perovskite layer. Furthermore, these first and second perovskite precursors exhibit sufficiently high solubility in an aqueous solvent. Accordingly, an easy-to-handle and cost-effective mixture of water and such a perovskite precursor can be used as the solution, to which, for example, no other chemicals or at least only small amounts of other chemicals are added.

[0045] According to one embodiment, the solution may contain hydrogen halide as a solvent. Such hydrogen halide may be provided as hydroiodic acid (HI), hydrochloric acid (HCl, also referred to as hydrochloric acid), or hydrobromic acid (HBr). The solvent may thus be a chemical compound that itself comprises one of the perovskite precursors, for example in the form of a halogen such as iodine, chlorine, or bromine. Mixtures of hydrogen halides may also be used. Aqueous solutions of such hydrogen halides can usually be handled using industrially well-established processes and equipment and can be relatively easily neutralized, for example, by forming salts.

[0046] According to one embodiment, the solution is mixed in a mixing tank separate from the carrier substrate and heated to the mixing temperature. In other words, the first and second perovskite precursors do not come into contact for the first time during or after the solution is applied to the carrier substrate, but are mixed with each other and with the solvent beforehand in a separate mixing tank and heated to the desired mixing temperature. The mixing temperature is preferably selected to be high enough that chemical reactions to form reaction products occur between the perovskite precursors even within the mixing tank. A suitable stirrer or similar device can be provided in the mixing tank for this purpose in order to mix the components of the solution as homogeneously as possible. Furthermore, a heater or similar device can be provided in the mixing tank to heat the entire solution to the mixing temperature.

[0047] In addition, the mixing tank can be pressurised with gas, particularly inert gas. An increased gas pressure can be adjustable, for example to accelerate the dosing of precursors. The solution should be distributed over the substrate as quickly and evenly as possible. For this purpose, the 2-dimensional movement can be initiated as early as the transfer of the solution from the mixing tank to the substrate. In addition, for example, a quantity to be dispensed or a liquid jet can be specifically dispensed into an area of ​​the substrate or divided by a device in order to initially reach several areas of the substrate. In addition, a larger volume can optionally be applied without liquid with high kinetic energy hitting the substrate at specific points. This avoids potential damage to sensitive underlying layers and achieves more homogeneous wetting for initial deposition.

[0048] In addition, a device for providing a required quantity can be provided, for example as a dosing pump, a gravity dosing, a control of a switching time of a valve, etc. The volume can be measured and / or controlled, for example, with an impeller meter or ultrasonic flow meter.

[0049] According to one embodiment, when producing the deposited layer, process parameters, including a process duration and a temporal temperature profile during cooling to the deposition temperature, are selected such that the deposited layer is produced as a crystalline layer. In other words, process parameters that influence the manner in which the deposited layer is produced from the two perovskite precursors and / or the reaction product can be specifically adjusted such that the deposited layer is produced as a crystalline layer, i.e., that crystallization occurs during deposition. Such process parameters include, among other things, the temperature of the solution and, in particular, a temporal profile with which this temperature is reduced during the cooling process.The process duration, during which the previously applied solution is successively cooled from the initial temperature of the carrier substrate to the deposition temperature and then, if necessary, kept stable at this final temperature or at intermediate temperatures, also typically influences the manner in which the perovskite precursors are deposited as a layer and whether crystal formation occurs. The crystalline layer to be produced can, for example, be monocrystalline, multicrystalline, polycrystalline, or nanocrystalline. Such a crystalline layer can subsequently react particularly well upon heating above the reaction temperature limit to form a perovskite layer or be converted into a perovskite layer.

[0050] According to one embodiment, during mixing of the solution, the saturation of the solution with the first and second perovskite precursors is adjusted such that upon subsequent cooling of the solution to the deposition temperature, the solution becomes supersaturated, in particular supersaturated with the reaction product formed from the two perovskite precursors. In other words, during the preparation of the solution, so much of the first and / or second perovskite precursor is dissolved in the solvent that a high saturation of the solution is achieved even at the then prevailing high mixing temperature.The degree of saturation is preferably set so high that upon subsequent cooling of the solution to the lower deposition temperature, the resulting decrease in temperature-dependent solubility leads to supersaturation of the solution, at least with respect to one of the two perovskite precursors and / or preferably with respect to the reaction product formed from the two perovskite precursors. Upon reaching such supersaturation, a portion of the respective perovskite precursor or reaction product contained in the solution precipitates from the solution and preferably deposits on the surface of the carrier substrate or on previously produced portions of the layer deposited there. This allows the deposited layer to grow particularly quickly.

[0051] In order to produce the deposited layer with a high degree of homogeneity and in particular with a consistent layer thickness, the carrier substrate is moved in a targeted manner at the same time as it is cooling. The movement is two-dimensional, i.e. a position and / or orientation of the carrier substrate is changed in at least two dimensions. In particular, the movement should not only take place in a direction orthogonal to a plane of extension of the carrier substrate, but also transverse to this direction. The movement can be translational and / or rotational. The movement can be continuous and / or periodic. In particular, the movement can take place in repeating cycles. For example, the movement can take place in the form of a mixture of a repeating back and forth movement and a repeating up and down movement.Due to such movement, forces act on the solution applied to the carrier substrate in different directions, particularly in different directions parallel to the surface of the carrier substrate, so that the solution is distributed as evenly as possible along this surface. These forces can act as inertial forces and / or gravitational forces.

[0052] According to one embodiment, the two-dimensional movement is a pivoting movement about at least two different axes. In other words, the carrier substrate is repeatedly pivoted about two different axes during cooling to the deposition temperature in order to change its orientation. The two axes run transversely to each other, preferably perpendicular to each other. The two axes can run within the plane of extension of the carrier substrate or parallel to this plane of extension. The pivoting movement caused thereby is also referred to as a tumbling movement or "wobbling" and enables a particularly effective distribution of the solution along the surface of the carrier substrate.According to one embodiment, the carrier substrate is temperature-controlled during the application of the solution, during the generation of the deposited layer, and / or during the heating of the deposited layer by means of a temperature-control device that makes surface contact with the carrier substrate. The temperature-control device can be supplied with power in a controlled manner, in particular with electrical power, in order to be able to heat it to an elevated temperature and / or to cool it to a reduced temperature.For this purpose, a power control can be sufficiently precise to specifically control the carrier substrate to the initial carrier substrate temperature T2 using the temperature control device, then to cool the carrier substrate to the deposition temperature T3 by specifically reducing the heating power, increasing a cooling line, or shutting down the temperature control device, and / or subsequently to heat the carrier substrate beyond the drying temperature T4. The temperature control device and / or its control can be configured to precisely set and / or maintain the aforementioned temperatures within a tolerance of, for example, less than ± 10 °C, preferably less than ± 5 °C or less than ± 3 °C.The technical design of the temperature control device and / or the control system used to supply power to it can be relatively simple, thus enabling cost-effective and / or reliable temperature control of the carrier substrate. For example, the temperature control device can be designed as a simple heating plate. Alternatively, the temperature control device can be configured as a thermostat, in which a liquid medium, heated to a desired temperature, is circulated beneath a plate to heat or cool the plate.

[0053] According to one embodiment, the carrier substrate is covered by a cover during the application of the solution and during the movement of the carrier substrate such that the cover rests annularly sealingly against the carrier substrate along its edges, and a receiving volume is formed between the carrier substrate and the cover, in which the solution applied to the carrier substrate is received. In other words, the cover can be designed such that its edges can rest hermetically sealed against the carrier substrate along a closed annular line. Because the cover rests hermetically sealed against the carrier substrate at its edges, the solution received in the surrounding receiving volume can be prevented from moving away from the surface of the carrier substrate to be coated and, for example, from dripping laterally off the carrier substrate during the movement of the carrier substrate.

[0054] By means of the method according to the first aspect of the invention, a perovskite layer can be formed, which can then be used in the manufacture of a solar cell according to the second aspect of the invention.

[0055] The solar cell can be designed as a pure perovskite solar cell. For this purpose, additional electrical contacts in the form of electrodes must be attached to the formed perovskite layer, with the help of which electrical charge carriers generated by the absorption of light in the perovskite layer can be diverted and fed to an external circuit. In addition to the electrical contacts, further layers or components can be formed on the perovskite layer, for example in the form of an electron conductor layer, a hole conductor layer, or a transparent, electrically conductive oxide layer (TCO). The method described herein is particularly suitable for producing perovskite solar cells based on inorganic perovskite layers (e.g., CsPbBr3). However, it can also be used to produce perovskite solar cells with perovskite layers containing organic compounds, in particular organometallic compounds (e.g.,MAPbl3).

[0056] According to a further embodiment, the carrier substrate can comprise a first solar cell, wherein the perovskite layer, together with the electrical contacts, is formed as a second solar cell. In other words, the carrier substrate can itself be a solar cell or comprise a solar cell, so that a further solar cell can then be formed on this existing solar cell using the perovskite layer formed thereon by the method described herein. The first solar cell can be referred to as a bottom solar cell and the second solar cell as a top solar cell, with both solar cells together forming a tandem solar cell.

[0057] In particular, the first solar cell can be a silicon solar cell, preferably a solar cell formed on a silicon wafer. Such silicon solar cells can be manufactured using long-established technologies, exhibit high efficiencies, and are highly reliable. A perovskite solar cell can be formed on such a silicon solar cell as a top solar cell. The two solar cells complement each other well with regard to their respective absorption spectra.

[0058] Alternatively, the first solar cell may be a thin-film solar cell, for example, based on a 111 V semiconductor. As another example, the first solar cell may be a CdTe solar cell or a CIGS solar cell.

[0059] It should be noted that possible advantages and configurations of embodiments of the invention are described herein partly with reference to a method according to the invention for forming a perovskite layer and partly with reference to a method for manufacturing a solar cell with such a perovskite layer. A person skilled in the art will recognize that the described features can be appropriately transferred, adapted, exchanged, or modified to achieve further embodiments of the invention.

[0060] BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments of the invention will now be described with reference to the accompanying drawings, which are not intended to limit the invention. Figures 1 (a)-(e) show successive stages of a method according to one embodiment of the invention.

[0062] The figures are merely schematic and not to scale. The same reference numerals designate identical or equivalent features in the various figures.

[0063] DESCRIPTION OF PREFERRED EMBODIMENTS

[0064] Fig. 1 shows successive stages of a process for forming a perovskite layer 1, by means of which a solar cell 29 is ultimately formed.

[0065] In a first step (see Fig. 1 (a)), a solution 5 is produced by dissolving methylammonium iodide (CH3NH3I) as the first perovskite precursor 7 and lead acetate trihydrate (Pb(CH3COO)2 -3H2O) as the second perovskite precursor 9 in a mixing tank 15 in an aqueous solution of hydroiodic acid (HI) and heating the solution to a mixing temperature T1 of 70 °C. The three substances mentioned react with each other, with the HI also serving to dissolve the other two substances. Instead of lead acetate, lead iodide can also be used. For this purpose, the mixing tank 15 has a stirrer 31 and a heater 33. A temperature sensor and a controller (not shown) can also be provided.

[0066] In a second step (see Fig. 1 (b)), the solution 5 is applied to the carrier substrate 3 through an outlet 35 on the mixing tank 15. The carrier substrate 3 has optionally already been tempered in advance to an initial carrier substrate temperature T2 of 65 °C. For this purpose, a temperature control device 17, for example in the form of a heating plate, contacts the carrier substrate 3 flatly along its rear surface. On its front surface, a receiving volume 39 is created with the aid of a cover 37, into which the solution 5 is introduced. The cover 37 hermetically seals with its edges 41 against a front surface of the carrier substrate 3. In a third step (see Fig. 1 (c)), the carrier substrate 3 is then moved together with the applied solution 5 in a two-dimensional movement. This is symbolized in the figure by movement arrows 45.At the same time, the carrier substrate 3 and the applied solution 5 are successively cooled to a deposition temperature T3 of below 40 °C. Since the solubility of the two perovskite precursors 7, 9 or the reaction products formed therefrom in the solution 5 decreases with this temperature reduction, their degree of saturation increases until, at the latest when supersaturation is reached, a portion of the perovskite precursors 7, 9 or reaction products contained in the solution 5 precipitate and are deposited on the front surface of the carrier substrate 3. As a result, a deposited layer 11 is formed on the carrier substrate 3. Due to the two-dimensional, preferably tumbling movement of the carrier substrate 3, this deposited layer 11 is produced with a high degree of homogeneity and layer thickness. Process parameters are selected such that the deposited layer 11 is produced as a crystalline layer 12.

[0067] After the deposited layer 11 has reached a sufficient layer thickness, an excess, non-deposited portion 13 of the solution 5 is drained from a drain nozzle 43 and thus removed from the carrier substrate 3.

[0068] Subsequently, in a fourth step (see Fig. 1 (d)), the deposited layer 11 together with the carrier substrate 3 is heated using the temperature control device 17 above a drying temperature T4 of, for example, 50 °C. This evaporates any remaining solvent. Furthermore, a chemical reaction occurs between any remaining residues of the two perovskite precursors 7, 9 and, ultimately, possibly starting from a previously formed intermediate (MA4Pbl6-2H2O), to form the perovskite layer 1 of methylammonium lead iodide (MAPbl3).

[0069] In order to ultimately produce a solar cell 29 with the perovskite layer 1 formed in this way, in a fifth step (see Fig. 1 (e)), electrical contacts 19 in the form of an electrical back contact 21 and an electrical front contact 23 are created, which electrically contact the perovskite layer 1 on opposite sides. In the example shown, the back contact 21 can be applied to a side of the carrier substrate 3 opposite the perovskite layer 1 and electrically connected to a possibly previously produced conductive layer (not shown). Alternatively, and most preferably for practical applications, a back contact 21 can be formed which directly engages such a conductive layer located between the carrier substrate 3 and the perovskite layer 1, or the back side of the perovskite layer 1. The back contact 21 can be provided, for example, in the form of a metal layer.The front contact 23 can be provided in the form of a plurality of thin, finger-like Meta II contacts. Alternatively or additionally, the front contact 23 can be formed using an electrically conductive, transparent layer. Overall, a solar cell 29 in the form of a perovskite solar cell can be formed in this way. The side facing the sun can also be the side covered with the glass substrate. In this case, the metal layer can act as a back contact and can possibly be formed over the entire surface.

[0070] Alternatively, the carrier substrate 3 can be formed from a pre-processed first solar cell 25 instead of a glass substrate. For example, this first solar cell 25 can be an efficient wafer-based silicon solar cell. The perovskite layer 1 can then be created on a front surface of this first solar cell 25, thereby forming a second solar cell 27. The two solar cells 25, 27 are possibly electrically connected to one another via a conductive layer (not shown) formed therebetween and can thus form a solar cell 29 in the form of a tandem solar cell.

[0071] Please note that both the process steps and the resulting structures have been presented and described in a highly simplified manner. In a real-world implementation, additional process steps may be used and / or additional structures may be created, for example, in the form of additional layers, electrodes, or similar.

[0072] Furthermore, it should be noted that the earlier patent DE 10 2006 007 446 B3 describes, among other things, a device that is suitably configured for carrying out embodiments of the method described herein. The method described herein can thus be carried out using such a device. Features described for the device can be applied analogously to the method described herein. The content of the earlier patent is incorporated herein in its entirety by reference.

[0073] It should also be noted that the proposed method can also be carried out as part of a two-stage process. In this case, the proposed method can first be used to create a first partial layer, onto which a further partial layer can then be applied in a second partial process. In this case, the two partial layers can possibly only subsequently be heated to an elevated temperature, which leads to a chemical reaction and / or a transformation of the precursors and / or reaction products contained in the two partial layers, so that the perovskite layer is ultimately formed. The second partial layer can be created using the same or a similar process as the first partial layer. Alternatively, the second partial layer can also be created using a different process such as spinning or rolling.

[0074] Finally, it should be noted that terms such as "having," "comprising," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference symbols in the claims are not to be considered as limiting. LIST OF REFERENCE SYMBOLS

[0075] I Perovskite layer

[0076] 3 Carrier substrate

[0077] 5 Solution

[0078] 7 first perovskite precursor

[0079] 9 second perovskite precursor

[0080] II deposited layer

[0081] 12 crystalline layer

[0082] 13 non-deposited portion of the solution

[0083] 15 Mixing tank

[0084] 17 Heating plate

[0085] 19 electrical contacts

[0086] 21 electrical return contact

[0087] 23 electrical front contact

[0088] 25 first solar cell

[0089] 27 second solar cell

[0090] 29 solar cells

[0091] 31 stirrers

[0092] 33 Temperature control device

[0093] 35 Outlet

[0094] 37 Cover

[0095] 39 recording volume

[0096] 41 edges

[0097] 43 drain sockets

[0098] 45 movement arrows

Claims

AMENDED CLAIMS received by the International Bureau on 07 January 2025 (07.01.2025) 1. A method for forming a perovskite layer (1) on a carrier substrate (3), comprising: - mixing a solution (5) containing a first and a second perovskite precursor (7, 9) at a mixing temperature (TI ), - applying the solution (5) to the carrier substrate (3), - moving the carrier substrate (3) together with the applied solution (5) in a two-dimensional movement in which the carrier substrate is successively displaced transversely in different directions and / or rotated or pivoted about different axes, and simultaneously cooling the carrier substrate (3) together with the applied solution (5) to a deposition temperature (T3) below the mixing temperature (TI ) to produce a deposited layer (11) on the carrier substrate (3) which contains both the first and the second perovskite precursor (7, 9) and / or a reaction product of the two perovskite precursors (7, 9).

2. The method according to claim 1, wherein the solution (5) is aqueous and wherein the first and second perovskite precursor (7, 9) and / or the reaction product are soluble in aqueous solution.

3. Method according to one of the preceding claims, wherein the first perovskite precursor (7) contains cesium, methylammonium or formamidinium.

4. Method according to one of the preceding claims, wherein the first perovskite precursor (7) contains methylammonium iodide.

5. Method according to one of the preceding claims, wherein the second perovskite precursor (9) contains lead.

6. Method according to one of the preceding claims, wherein the second perovskite precursor (9) contains lead acetate and / or a lead halide.

7. Process according to one of the preceding claims, wherein the solution (5) contains hydrogen halide.

8. Method according to one of the preceding claims, wherein the solution (5) is mixed in a mixing tank (15) separately from the carrier substrate (3) and tempered to the mixing temperature (T1).

9. Method according to one of the preceding claims, wherein, when producing the deposited layer (11), process parameters including a process duration and a temporal temperature profile during cooling to the deposition temperature (T3) are selected such that the deposited layer (11) is produced as a crystalline layer (12).

10. Method according to one of the preceding claims, wherein during mixing of the solution (5) a saturation of the solution (5) with the first and the second perovskite precursor (7, 9) is set such that during subsequent cooling of the solution (5) to the deposition temperature (T3) a supersaturation of the solution (5) is set.

11. Method according to one of the preceding claims, wherein the two-dimensional movement is a movement by at least two different Axis pivoting movement.

12. Method according to one of the preceding claims, wherein the carrier substrate (3) is tempered during the application of the solution (5), during the production of the deposited layer (11) and / or during heating of the deposited layer (11) by means of a tempering device (17) which contacts the carrier substrate (3) in a planar manner.

13. Method according to one of the preceding claims, wherein the carrier substrate (3) is covered by a cover (37) during the application of the solution (5) and during the movement of the carrier substrate (3) in such a way that the cover (37) bears against the carrier substrate (3) in an annular sealing manner along its edges (41) and a receiving volume (39) is formed between the carrier substrate (3) and the cover (37), in which the solution (5) applied to the carrier substrate (3) is received.

14. A method for manufacturing a solar cell (29), comprising Forming a perovskite layer (1) on a surface of a carrier substrate (3) by means of the method according to one of the preceding claims, and forming electrical contacts (19) for discharging electrical charge carriers from the perovskite layer (1).

15. The method according to claim 14, wherein the carrier substrate (3) comprises a first solar cell (21) and wherein the perovskite layer (1) is formed together with the electrical contacts (19) as a second solar cell (23).

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