Nickel monoxide as a hole-conducting material, perovskite solar cell and process for producing nickel monoxide as a hole-conducting material

Abstract

The present invention relates to a nickel monoxide as a hole-conducting material and a perovskite solar cell containing the hole-conducting material as a hole-conducting layer, as well as a method for producing the nickel monoxide. The hole-conducting nickel monoxide (NiO) according to the invention x The composition is characterized by the addition of magnesium or of magnesium and lithium together as dopants. The mole fractions of the dopants are in the range of 2% to 4% for magnesium alone and 2% to 4% for magnesium together with 0.75% to 1.25% for lithium, and in particular 2.5% to 3.5% for magnesium and 0.9% to 1.1% for lithium. The NiO doped according to the invention x is of increased stability. A perovskite solar cell, which consists of a NiO doped with magnesium and lithium. xThe inventive method for producing a NiO-doped layer, comprising a hole-conducting layer, exhibits increased stability and improved efficiency. x is based on spray pyolysis in an oxidizing atmosphere. In the process according to the invention, the applied layer is doped with NiO. x First annealed and then cooled, after which further processing or storage is possible.

Description

[0001] The present invention relates to nickel monoxide as a hole transporting material (HTM), such as can be used, for example, in solar cells to form a hole transporting layer (HTL), particularly in perovskite solar cells, but also, for example, in light-emitting diodes, transistors, photoanodes, electrochemical devices, electrodes, and others. Perovskite solar cells in general have recently attracted attention due to their promising efficiency, as described, for example, by D. Li et al. (A Review on Scaling Up Perovskite Solar Cells, Advanced Functional Materials, 31, 2021, 2008621, 1-27). One aspect that still needs to be investigated is the stability of the cells, which, to the applicant's knowledge, is currently below ~1000 h, which is insufficient. The latter is discussed, for example, in the review article by J. Qin et al.(Towards operation-stabilizing perovskite solar cells: Fundamental Materials, device designs, and commercial applications, InfoMat 2024, e 12522, 1-36). The present invention further relates to a method for producing NiO. x as a hole-conducting material.

[0002] Nickel monoxide is frequently used as a high-temperature material (HTM). Nickel monoxide with ideal stoichiometry has the general formula NiO. However, nickel monoxide used as an HTM has an unbalanced oxygen-to-nickel ratio, hence the designation NiO₂. x This is expressed as a value, meaning that the nickel monoxide is non-stoichiometric. The ratio of oxygen to nickel is expressed in the relevant NiO values. x often due to the ratio Ni 3+ / Ni 2+ The occurrence of Ni 3+In nickel monoxide, defects can be caused by two factors: firstly, a depletion of nickel in the crystal structure, and secondly, by (excess) oxygen at interstitial sites. Both defects in the crystal structure can occur simultaneously. The NiO x Consequently, it is depleted of nickel in terms of the amount of oxygen, which at least formally leads to the occurrence of Ni 3+ This leads to charge equalization. A general overview of the properties of NiO x and its diverse application possibilities are given, for example, by M. Napari et al. (Nickel oxide thin films grown by chemical deposition techniques: Potential and challenges in next-generation, rigid and flexible device applications, InfoMat, 2021, 536-576). The implications of such nickel monoxide—with a nickel depletion—in relation to its application in perovskite solar cells are discussed by Md. B. Islam et al. (NiO xHole Transport Layer for Perovskite Solar Cells with Improved Stability and Reproducibility, ACS Omega, 2017, Vol. 2, 2291-2299). Although the correct determination of Ni 3+ / Ni 2+ Since the ratio is difficult to determine, parameters such as electrical conductivity (non-zero for NiO) can be used. x , stoichiometric NiO is an insulator) and the color (stoichiometric NiO is light yellow and initially turns green and then darker, until it becomes darker with increasing amount of Ni 3+ (The fact that it turns black) can be taken as proof that the nickel monoxide material in question is NiO. x , is involved. A fully stoichiometric nickel monoxide, which would mean that the ratio Ni 3+ / Ni 2+While it is possible to achieve a value of zero, this cannot be represented using the usual manufacturing processes for nickel monoxide as HTM, such as atomic layer deposition, spray pyrolysis, spin coating and other deposition processes that use solutions or gels as precursors for the formation of the material.

[0003] Nickel monoxide as an HTM for the construction of a hole-conducting layer (HTL) in solar cells is usually used in direct contact with the absorber layer, for example between the absorber layer and a front contact made of a TCO (Transparent Conductive Oxide).

[0004] Perovskite solar cells are usually described as single-layer or tandem solar cells. The latter are also described as tandems, in which a perovskite is paired with an absorber material other than perovskite or with another type of perovskite. Triple or even multiple solar cells are also being investigated and are described in the literature.

[0005] Perovskite solar cells are generally characterized by at least one absorber layer in which the layer material forms a perovskite crystal structure and is therefore called the perovskite layer, and in which the charge carriers in the solar cell are generated. A halide perovskite layer with the general formula ABX3 has, for example, organic components such as methylammonium (MA) or formamidine (FA) as component A, and / or inorganic components such as cesium (Cs) or rubidium (Rb) as component B, while component B is a metal component, often lead (Pb) or tin (Sn). Component X is, for example, iodine (I), bromine (Br), and / or chlorine (Cl), or a mixture of these elements.

[0006] A perovskite solar cell is typically built on a transparent substrate, such as glass. A front contact layer made of a transparent conductive oxide (TCO), such as indium tin oxide (ITO) or fluorine-doped tin oxide (FTO), is deposited onto the substrate. A perovskite layer system is then applied to the front contact layer. This system comprises at least one electron-conducting layer (ETL), one high-hole layer (HTL), and at least one perovskite layer. The perovskite layer is generally located between the ETL and the HTL. If the ETL is located on the front contact layer, it is called a NIP perovskite layer system; if the HTL is located on the front contact layer, it is called a P-IN perovskite layer system.An absorber layer in such a perovskite solar cell, i.e., the perovskite layer, can be composed of various perovskite components. These components are distinguished by their chemical composition, which may include dopants. The different chemical compositions result in varying physical properties, which can be tailored to increase the efficiency of the absorber layer. In addition to its chemical composition, the perovskite absorber layer's performance is determined by physical properties such as crystallinity and defects in the crystal structure, grain size, layer thickness, surface roughness, and others.

[0007] The object of the present invention is to provide a NiO x to specify a hole-conducting material (HTM) with improved stability compared to the prior art and a perovskite solar cell which incorporates a NiO according to the invention. xin a perovskite-conducting layer, and wherein the perovskite solar cell exhibits an improved lifetime compared to the state of the art, as well as improved efficiency. Furthermore, a method for producing a NiO x The problem is solved by the nickel monoxide as a hole-conducting material according to claim 1, the method according to claim 4, and the perovskite solar cell with the features of claim 7.

[0008] It was demonstrated in the applicant's case that the object of the invention is achieved by a special NiO x as a hole-conducting material (HTM), which according to the invention is specified in that it is at least Mg (magnesium) to improve the stability of the NiO x is self-doped and, together with Li (lithium), leads to perovskite solar cells with improved stability and improved efficiency when the NiO according to the invention is used. xas HTM forms a hole-conducting layer in the perovskite solar cells. According to the invention, the amount of dopants (doping agents) is adjusted with respect to the stoichiometric coefficient in the resulting NiO. x , with the general formula: Mg a Li b Ni 1-a-b O x describe and lies in the range of mole fractions of 2 - 4% for Mg for a well-stabilized NiO x and together with 0.75% - 1.25% for Li, for stabilization and an increase in the efficiency of a perovskite solar cell comprising the HTM according to the invention as HTL. The optimum was achieved at mole fractions of 3% Mg and 1% Li (given by the formula Mg 0,03 Li 0,01 Ni 0,96 Ox) identified, with a range of optimum for mole fractions between 2.5 - 3.5% for Mg and 0.9 - 1.1% for Li to be specified.

[0009] The invention is characterized by the specification of the mole fractions of the dopants magnesium and lithium in NiO. xdetermined. The dopings according to the invention in NiO x lead to a stabilized NiO x itself (at least magnesium as a dopant) and, if the NiO x (Magnesium and lithium together as dopants) is integrated as an HTM in an HTL, resulting in a stabilized perovskite solar cell whose efficiency is even increased. A method for producing the NiO doped according to the invention. x is also indicated.

[0010] A perovskite solar cell with a NiO x , which was doped with magnesium and lithium after the invention, showed no signs of aging even after more than 3150 hours.

[0011] The endowed NiO x According to the invention itself, compared to a NiO x Without the dopants, increased stability against stress caused by light illumination.

[0012] The doped NiO according to the invention xcan be coated by spray pyrolysis using oxygen as a carrier gas in ambient air, which has the advantage that the invention is compatible for upscaling to an industrial process, which is a further advantage of the invention.

[0013] The inventive method for producing a doped NiO according to the invention x The HTM, for example for the construction of an HTL, e.g. in a perovskite solar cell, comprises the following steps: - Providing an initial solution containing magnesium, lithium, and nickel ions in a ratio corresponding to the mole fraction of 2.00–4.00% for Mg and, if applicable, 0.75–1.25% for Li in a NiO solution to be produced x corresponds; - Providing a substrate; - Heating the substrate to a temperature T1 in the range of 450 °C to 550 °C; - Coating of the substrate with the first solution by spray pyrolysis with oxygen as carrier gas. - Glowing of the coated substrate at a temperature in the same temperature range as T1 for a duration of 30 to 50 minutes, followed by - Cooling of the coated substrate to a temperature T2 in the range of 150 °C to 200 °C within 20-30 minutes and then protecting the cooled substrates from contact with oxygen-containing atmospheres or direct further processing.

[0014] This example guarantees a repeatable result for a doped NiO xwith the desired properties and effects and, moreover, has the advantage that it can be easily integrated into the manufacturing process of a perovskite solar cell or into other applications such as water splitting, semiconductor electronics, radiation and light sensors, and catalytic chemistry. The above-mentioned example for the production of NiO according to the invention x The NiO according to the invention is limited x However, this does not indicate that it is a product of this particular method. A doped NiO x A product manufactured according to the invention by methods other than the one given above as an example embodies the invention in the same way and offers the same advantages. Possible alternative methods include, for example, sputtering and spin coating or other solution-based coating methods, as well as physical methods of vapor deposition.

[0015] The first solution to be provided in the process, containing the cations of nickel, magnesium, and lithium in a ratio corresponding to the intended final product, is prepared using precursors containing either nickel or magnesium, or additionally lithium. These precursors are salts soluble in a high-pressure solvent, such as ethanol or other alcohols, provided that all byproducts of the solution and the anions of the salt are volatile at temperature T1. This condition can be easily verified by a person skilled in the art using test coatings.

[0016] The provided substrate is preferably cleaned before use. A suitable method is, for example, the sequential application of the following cleaning steps: application of Mucasol, water, acetone, isopropyl alcohol (IPA), followed by UV-ozone cleaning for 20 minutes.

[0017] For the spray pyrolysis process, oxygen is used as a carrier gas to ensure that the (first) solutions with the precursors react with oxygen at temperature T1, resulting in a high-purity NiO. x -Film guaranteed. An oxygen-rich atmosphere and a high temperature T1 are necessary for the formation of NiO. x and NiO x doped with Li, and Mg is a prerequisite.

[0018] One of the two options in the last step of the inventive method, the protection of the cooled substrates from contact with an oxygen-containing atmosphere, is e.g. by storing the substrate with the doped NiO xThe coating layer is placed in a sealed container for up to two months or, for example, in a glovebox with an inert atmosphere. If the substrate is to be further processed after storage, e.g., to complete a perovskite solar cell, it must be annealed again for about one hour at T1 and then cooled to temperature T2 as in the manufacturing process. The preferred option, which is the second option, is the direct further processing of the coated substrate without intermediate storage.

[0019] In one embodiment, the first solution comprises magnesium, lithium, and nickel ions in a ratio corresponding to the molar fractions of the dopants in the intended product, ranging from 2.5% to 3.5% magnesium and 0.9% to 1.1% lithium. A NiO x doped with magnesium and lithium in the mole fractions of this embodiment corresponds to an optimized NiO x with regard to the stability of NiOx itself as well as a perovskite solar cell with the NiO x in a perforated layer and simultaneously an increase in efficiency for a perovskite solar cell in question.

[0020] In one embodiment of the method, the substrate is a glass substrate with a transparent conductive contact layer for a perovskite solar cell to be manufactured. All other necessary and possible components of the perovskite solar cell to be completed, in particular absorber layers, passivation layers, contact layers and the like, as well as electrical connections and conductors and substrates of a perovskite solar cell, are unaffected by the production of the HTL according to the invention and can therefore follow any arrangement of layers prescribed in the prior art or otherwise desired with regard to chemical position, thickness, application or coating method, introduction of compounds and encapsulations and the like, as well as any method of manufacture and processing prescribed in the prior art or otherwise desired.

[0021] The invention is also implemented in a perovskite solar cell which contains a NiOx It contains a hole-conducting material that forms a hole-conducting layer. The NiO x The material is specified as a hole-conducting material by being doped with magnesium and lithium, with the mole fractions ranging from 2.00% to 4.00% for Mg and 0.75% to 1.25% for Li. In another embodiment, the mole fractions range from 2.5% to 3.5% for magnesium and 0.9% to 1.1% for lithium.

[0022] In another embodiment, the perovskite solar cell with the HTL according to the invention is advantageously a halide perovskite solar cell (i.e. with at least one halide perovskite layer as absorber) in a single-layer or tandem arrangement, either with two or four terminals.

[0023] The halide perovskite can advantageously be represented by the general formula ABX3, for example with the organic components methylammonium (MA), formamidine (FA) and / or inorganic components cesium (Cs), rubidium (Rb) as component A, while component B is a metallic component, often lead (Pb) or tin (Sn). X is, for example, iodine (I), bromine (Br) and / or chlorine (Cl) or a mixture of these elements. Examples

[0024] The invention in exemplary embodiment is described below by one example each for NiO x as a hole-conducting material, the perovskite solar cell, the NiO x as a hole-conducting material in a hole-conducting layer, and the process for producing NiO x depicted as a hole-conducting material together with two figures.

[0025] The figures show: Fig. 1: Stability in terms of efficiency (PCE) at the maximum power point (MPP) of a halide perovskite solar cell with a NiO x According to the invention (3% Mg, 1% Li) as HTM in an HTL --upper curve- over time compared to one with undoped NiO x as an HTM in an HTL -lower curve-. Fig. 2: Stability of a) pure (without dopants) NiO x and b) doped NiO x According to the invention (3% Mg, 1% Li) with respect to the measured density of states (DoS) for the freshly prepared sample (-···-··) and for the same sample after one day of exposure to UV light (-). The data are given for undoped reference samples and for doped NiOx reference samples for the photoemission probe DoS.

[0026] In the example, the doped NiO x According to the invention, doped with mole fractions of 3% for magnesium and 1% for lithium (Mg 0,03 Li 0,01 Ni 0,96 O x ).

[0027] The exemplary doped NiO according to the invention x The following is produced as an example of the inventive method: To obtain a solution, the first solution, containing all the components necessary for the production of the doped NiO according to the invention. x The following substances are provided as precursors if necessary: ​​nickel(II) nitrate hexahydrate, Ni(NO) 32·6H₂O, magnesium acetate tetrahydrate, (CH₃COO)₂Mg·4H₂O, and lithium acetate, CH₃COOLi. First, a 40 mM nickel nitrate solution was prepared by dissolving nickel nitrate in absolute ethanol. Simultaneously, two separate stock solutions were prepared: one containing 0.25 mM lithium acetate and the other containing 0.05 mM magnesium acetate tetrahydrate, both using ethanol as the solvent. Subsequently, 0.4 mM (corresponding to 1% Li in the final product) lithium acetate and 1.2 mM (corresponding to 3% Mg in the final product) magnesium acetate solutions from their respective stock solutions were added to the nickel nitrate solution. Ethanol was used as the solvent for all solutions, and the preparation of the solutions was carried out in an inert atmosphere, for example, in a glovebox filled with nitrogen. For the spray pyrolysis, 20 mL of the first solutions (with or without dopants) prepared in the glovebox are used in the examples, as previously stated.The solutions are preferably used freshly prepared, as they are subject to aging and cannot normally be stored for more than one day. A glass substrate coated with fluorotin oxide (FTO) is provided as the front contact for a perovskite solar cell to be manufactured. This substrate has been cleaned with alkali, water, acetone, and isopropyl alcohol (IPA) and then with UV ozone for 20 minutes. The FTO substrates provided are approximately 100 cm². 2 On the surface and the provision of 20 ml of the solution containing the dopants and nickel - as described above - the following further steps of the process according to the invention are carried out using a heating plate and oxygen as a carrier gas for the spray pyrolysis: - Heating the substrate to 500 °C (T1) within 15 minutes, followed by holding for 15 minutes to stabilize the temperature; - Coating of the substrate by spray pyrolysis using 20 ml of the provided first solution with the dopants (concentrations corresponding to mole fractions of 3% magnesium and 1% lithium in the product) using oxygen as the carrier gas; - Annealing of the coated substrate for 45 minutes at 500 °C (T1); - Cooling of the substrate to 150 °C (T2) within 20 min; - Further processing or storage of the substrate.

[0028] Substrates coated according to the above-described method can be stored for up to two months in a sealed container or in a glove box with an inert atmosphere. The substrate specified in the example for use in perovskite solar cells is not subject to any further (manufacturing) process. The method according to the invention can also be applied to various other possible substrates, such as components of transistors, LEDs, catalysts, and much more.

[0029] Further processing into a halide-perovskite solar cell according to the invention is carried out via the following steps. Before spin-coating the halide-perovskite onto the NiO doped according to the invention. x As HTL, the substrate is doped with NiO xThe substrate is tempered for one hour at 500 °C to remove moisture and other possible volatile contaminants. Without further processing, and in particular without treatment with UV ozone, the freshly coated substrate is transferred to an inert atmosphere, e.g., a nitrogen glove box.

[0030] The subsequent production of the halide-perovskite absorber layer is carried out according to the following steps in this example.

[0031] Dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are used as solvents in a ratio (by volume) of 4:1. A triple cation mixture of formamidinium lead triiodide (FAPbI3) and methylammonium lead bromide (MAPbBr3) in a molar ratio of 85:15 with the addition of 5% Cs1 to the solution is used to form the perovskite. Chlorobenzene is used as an antisolvent. The perovskite is then coated with the NiO according to the invention using the following spin-coating program. x(3% Mg, 1% Li) spin-coated for 30 seconds at 4000 revolutions per minute (rpm), 10 seconds at 4000 rpm, 30 seconds after the start of the spin coating of perovskite to NiO x 200 microliters of chlorobenzene are added as an antisolvens to trigger perovskite crystallization. Immediately after spin-coating the perovskite, the substrate is annealed at 100 °C for 45 to 60 minutes. Subsequently, a layer of C is applied. 60 with a thickness of 23 nm, and then a layer of bathocuproin (BCP) with a thickness of 8 nm is deposited onto the perovskite layer. Then the exposed part of the FTO, the NiO x The free surface is prepared to serve as an electrical contact (payload) for use as a solar cell. Finally, a silver coating with a 100 nm thick mask is applied to complete the halide-perovskite solar cell.

[0032] In Fig. 1 is the stability in terms of efficiency (PCE) at the maximum power point (MPP) of a halide perovskite solar cell containing NiO x according to the invention (3% Mg, 1% Li) as an HTM in an HTL, compared to a halide perovskite solar cell with undoped NiO x as HTM in HTL. The aging of the halide-perovskite solar cell described above is carried out under light cycles similar to those of outdoor sunlight. The doping of NiO x With 3% Mg and 1% Li (upper curve), the stability of the halide perovskite solar cell is significantly increased to > 3000 h without any signs of performance degradation compared to the halide perovskite solar cell with an undoped NiO. x as HTM in HTL (lower curve).

[0033] In Fig. 2 is the stability of a) pure NiO x (without dopants) and b) NiO doped according to the invention x(3% Mg, 1% Li) relative to the DoS of the reference (untreated) for freshly prepared samples and for the same samples after one day of UV light exposure. All samples were coated with CsI to prevent surface degradation of NiO. The advantage of NiO doped with 3% magnesium and 1% lithium x This is clearly evident in a more stable DoS signal of the Mg and Li-doped NiO. x . QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] D. Li et al. (A Review on Scaling Up Perovskite Solar Cells, Advanced Functional Materials, 31, 2021, 2008621, 1-27

[0001] J. Qin et al. (Towards operation-stabilizing perovskite solar cells: Fundamental Materials, device designs, and commercial applications, InfoMat 2024, e 12522, 1-36

[0001] M. Napari et al. (Nickel oxide thin films grown by chemical deposition techniques: Potential and challenges in next-generation, rigid and flexible device applications, InfoMat, 2021, 536-576

[0002] Md. B. Islam et al. (NiO x Hole Transport Layer for Perovskite Solar Cells with Improved Stability and Reproducibility, ACS Omega, 2017, Vol. 2, 2291-2299

[0002]

Claims

[1] Nickel monoxide as a hole-conducting material, characterized by that the nickel monoxide is doped with at least a mole fraction of magnesium in the range of 2% to 4%. [2] Nickel monoxide as a hole-conducting material according to claim 1, characterized by that the nickel monoxide is additionally doped with lithium with a mole fraction in the range of 0.75% to 1.25%. [3] Nickel monoxide as a hole-conducting material according to claim 2, characterized by that the mole fractions are between 2.5% and 3.5% for magnesium and 0.9% and 1.1% for lithium. [4] Method for producing nickel monoxide as a hole-conducting material comprising at least the following steps: - Providing an initial solution containing at least magnesium and nickel ions in a ratio corresponding to the mole fractions in a hypothetical nickel monoxide with 2.00 - 4.00% Mg; - Providing a substrate; - Heating the substrate to a temperature T1 in the range of 450 °C to 550 °C; - Coating of the substrate with the first solution by spray pyrolysis under oxygen-rich conditions; - Annealing of the coated substrate at a temperature in the same temperature range as T1 for a duration of 30 to 50 minutes, followed by - Cooling the coated substrate to a temperature T2 in the range of 150 °C to 200 °C within 20-30 minutes and then starting further processing or storage of the coated substrate. [5] Method for producing nickel monoxide as a hole-conducting material according to claim 4, characterized by , that the first solution contains magnesium, lithium and nickel ions in a ratio corresponding to the mole fractions in a hypothetical nickel monoxide of 2.5% to 3.5% for magnesium and 0.9% to 1.1% for lithium. [6] Method for producing nickel monoxide as a hole-conducting material according to one of claims 4 or 5, characterized by that the substrate is a glass substrate with a transparent contact layer for a perovskite solar cell to be manufactured. [7] Perovskite solar cell comprising at least one layer of perovskite and at least one nickel monoxide as a hole-conducting material according to claim 2 or 3, which forms a hole-conducting layer. [8] Perovskite solar cell according to claim 7, characterized by , the perovskite is a halide perovskite.

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