A method for producing a semiconductor film of an organic-inorganic metal halide compound having a perovskite-like structure

Abstract

The present invention relates to the field of material science, in particular, to a method for producing a film of a semiconductor material based on an organic-inorganic metal halide compound having a perovskite-like structure, which can be used as a light-absorbing layer in solar cells, including thin-film solar cells, flexible solar cells and tandem solar cells, and can be applied to optoelectronic devices, in particular light-emitting diodes. The method of producing a semiconductor film of an organic-inorganic metal halide compound having a perovskite-like structure comprises the following steps: (a) applying a layer of precursors of component B on a substrate, (b) applying a layer of a complexing reagent onto the surface of the layer of precursors of component B, and (c) treating the applied layer on the substrate by a reagent X2 during a time necessary and sufficient for completing the chemical reaction of the applied reagents and precursors of component B, resulting in the formation of an organic-inorganic metal halide perovskite-like compound, characterized in that the complexing reagent applied in step b) comprises a mixture of AX reagent and X2 reagent, wherein the molar ratio of [X2] / [AX] is in the range of 0 < [X2] / [AX] < 1, and the film obtained after step b) comprises seeds of phases having a perovskite-like structure, wherein component B comprises cations M of different metals (including Pb, Sn, Bi) selected from Pb, Sn, Bi and mixtures thereof n+ , the reagent AX is a salt comprising a cation A + and an anion X ‑ ; wherein the cation A + is a monocharged organic or inorganic cation selected from methylammonium CH3NH3 + , formamidinium (NH2)2CH + , guanidinium C(NH2)3 + , Cs + , Rb + and unsubstituted ammonium cation (NH4 + ) or substituted ammonium cation comprising mono-, or di-, or tri-, or tetra-substituted ammonium cation, and combinations thereof; and the anion X ‑ is a monocharged anion selected from Cl ‑ , Br ‑ , I ‑ or pseudohalide anion and combinations thereof; the reagent X2 is a molecular halogen. The present invention provides a simpler and more efficient method of producing a thin film of a semiconductor film of an organic-inorganic metal halide compound having a perovskite-like structure, which can be used as a light-absorbing layer of a perovskite solar cell and ensures an increase in its efficiency compared to analogues.

Description

Field of the Invention

[0001] The present invention relates to the field of materials science, and in particular to a method for producing a film of a semiconductor material based on an organic-inorganic metal halide compound having a perovskite-like structure, which film can be used as a light-absorbing layer in solar cells including thin-film solar cells, flexible solar cells and tandem solar cells, and can be used in optoelectronic devices, in particular light-emitting diodes. Background of the Invention

[0003] To date, several methods for producing semiconductor films of light-absorbing materials having a perovskite-like structure are known.

[0004] Perovskite CH3NH3PbI3 thin layer or film is prepared in one step by applying the solution of perovskite in an organic mixed solvent to a substrate (substrate) with a thin layer via rotating it at high speed around an axis perpendicular to the layer plane [Saliba M. et al. Incorporation of rubidium cations intoperovskite solar cells improves photovoltaic performance / / Science (80-.). 2016. Vol. 354, No. 6309, pp. 206-209]. In this case, the resulting perovskite film combined with other layers in the composition of the solar cell serves as a light absorbing material. Specifically, the article describes the generation of a perovskite solar cell consisting of five main functional layers applied to a glass substrate: a transparent conductive electrode (such as FTO), an electron transport layer (such as TiO2 blocking layer), a light absorbing layer (perovskite) and a hole transport layer (such as Spiro MeOTAD), a reverse electrode (reverse electrode) (Au). Light is absorbed by the perovskite layer, which results in the formation of nonequilibrium charge carriers—electrons and holes—in it. Furthermore, the electrons and holes migrate to the electron transport layer and the hole transport layer, respectively, and further migrate to the corresponding electrodes.

[0005] A disadvantage of the above methods is the difficulty in preparing perovskite layers from solution on large-area substrates, and therefore the inability to fabricate large-area perovskite solar cells.

[0006] The known documents that are particularly relevant to the claimed invention are:

[0007] Published WO2018124938A1 "Methods for producing light-absorbing materials with perovskite structure and liquid polyhalides of variable composition for their implementation",

[0008] Patent RU2685296 "method for producing a film of light-absorbing material with a perovskite-like structure",

[0009] And the patent RU2675610 "a method for producing a film of a light-absorbing material with a perovskite-like structure".

[0010] The method described in publication WO2018124938A1 involves mixing a reagent of composition AX-nX2 with a reagent containing B, where n is greater than or equal to 1, component A is a singly charged organic or inorganic cation or a mixture thereof, and component X2 is Cl2, Br2, I2, or a mixture thereof, wherein the reagent containing B is used as a film of Sn, Pb, or Bi of a given thickness in the form of a metal, alloy, oxide, or salt. The reagent composition AX-nX2 is applied to the reagent B. The reaction proceeds: B + AX ​​+ X2 = ABX3, producing the perovskite ABX3, and excess reagent is removed if necessary.

[0011] A disadvantage of this known method is the impossibility of dosing the polyiodide (polyhalide) reagent in a stoichiometric amount relative to component B per unit area of ​​the film. This impossibility is a consequence of the high reactivity and high viscosity of the liquid composition AX-nX2. An AX3 / B ratio that differs significantly (over 5%) from the stoichiometric ratio corresponding to pure ABX3 inevitably leads to a deterioration in the quality of the resulting film of semiconductor material (in particular, thickness uniformity and phase purity), which negatively affects the efficiency of solar cells based on the resulting film.

[0012] The method described in patent RU 2685296 C1 includes forming a uniform layer of component B on a substrate, preparing a mixture of reagents that react with component B under predetermined conditions, and a reaction inhibitor that inhibits the reaction under these conditions, applying the prepared mixture in a stoichiometric or greater amount to the layer of component B, and removing the reaction inhibitor from the mixture so that a chemical reaction between the mixture of reagents and component B is activated to form a film of a perovskite-like material (ABX3).

[0013] The above method allows the formation of perovskite layers on surfaces of almost any size. However, a disadvantage is the low efficiency of the films obtained using this method (no higher than 5%). [Stepanov NM, Petrov AA, Belich NA, Tarasov AB, Study of the reactivity of the ternary system MAI-I2-i-PrOH with metallic lead to obtain MAPbI3 films (MA=CH3NH3), abstracts at the conference XXVInternational Conference of Students, Graduate Students and Young Scientists "Lomonosov", Russia, April 9-13, 2018], [Rakita Y. et al. Metal to Halide Perovskite (HaP): An Alternative Route to HaP Coating, Directly from Pb(0) or Sn(0) Films / / Chem. Mater. 2017. Vol. 29, No. 20, pp. 8620-8629]. This problem is the result of fundamental flaws inherent in this method, in particular:

[0014] 1) It is difficult to precisely control the conditions and rate of the perovskite layer formation process in the above-mentioned method, and therefore, it is difficult to precisely control the morphology and size of the grains and crystallites of the resulting perovskite film. This problem is caused by the high reactivity of the AX-nX2 compositions of the polyiodide melt formed after inhibitor removal and their increased recrystallization ability relative to the perovskite layer.

[0015] 2) Phase separation during the formation of mixed-cation perovskites containing cesium and formamidinium (FA+) cations, as the process of chemical conversion at low temperature leads to the irreversible formation of non-perovskite low-temperature phases such as δ-CsPbI3, δ-FAPbI3.

[0016] The method for producing a film of a light-absorbing material having a perovskite structure with the structural formula ADE3 disclosed in patent RU 2675610 (in the terminology of the claimed invention, component D is identical to component B, and component E is identical to component X) is most relevant to the claimed invention in terms of technical essence. The method is implemented by applying a layer of reagent D and a layer of reagent AE to a substrate in succession, after which the substrate with the deposited layers is placed in a liquid or gaseous medium containing reagent B2 for a period of time necessary and sufficient for the reaction to proceed: C + AE + E2 = ADE3 + X, with CH3NH3 + or (NH2)2CH + or C(NH2)3 + or Cs + or a mixture thereof as component A, Cl or Br as component E or I or a mixture thereof, Sn, Pd or Bi metal or its alloy or oxide or salt serves as component D, and when an oxide or salt is used as component D, X represents a decomposition product of component D.

[0017] The main disadvantage of the above methods is the difficulty in controlling the deposition of a layer of reagent AE on the surface of the substrate provided with a layer of component D. In particular, in the case of organic cations A, deposition of thin layers of AE reagents by vapor phase or thermal evaporation methods is difficult, since they may thermally decompose and deposit uncontrollably in areas of the substrate where their deposition is undesirable or unacceptable.

[0018] The use of vacuum deposition for applying the reagents AE allows achieving a high dosage of the reagents AE per unit area, however, requires the use of expensive equipment.

[0019] Furthermore, the bilayer AE@D structures formed by any possible method exhibit extreme sensitivity to atmospheric moisture due to the high moisture sensitivity (hygroscopicity) of the AE reagents. The latter requires the use of special conditions, techniques, and solutions when handling the resulting bilayer structures.

[0020] These two factors significantly reduce the technological advantages of this approach for large-scale production of perovskite films and devices based on them.

[0021] Terminology of the present invention

[0022] In the context of the present invention, a perovskite-like structure means both a perovskite structure and any structure derived from a perovskite structure. Thus, the terms "perovskite-like compound" and "perovskite-like phase" as used herein refer to a compound having a perovskite-like structure and a phase having a perovskite-like structure, respectively.

[0023] In particular, in the context of the present invention, the term "halide perovskite" means a phase having the formula ABX3 with a cubic system or any lower crystal system (e.g., tetragonal system, orthorhombic system), as well as mixtures of different phases of halide perovskites. The structure of halide perovskites consists of a three-dimensional network of corner-connected regular or distorted octahedra [BX6], which is composed of a central atom - component B (cation B n+ ) and six X atoms (anion X - )composition.

[0024] Specifically, as used herein, "perovskite-like structure" refers to a collection of structures of so-called layered or two-dimensional or low-dimensional perovskite-related compounds, which contain layers (perovskite layers) of octahedrons [BX6] connected at corners alternating with layers of another motif (e.g., Aurivillius phase, Ruddlesden-Popper phase, Dion-Jacobson phase) [Mitzi D.B. Synthesis, Structure, and Properties of Organic-Inorganic Perovskites and Related Materials / / Progress in Inorganic Chemistry, Vol. 48. Wiley Online Library, 2007. Pages 1-121]. Perovskite-like compounds and perovskite-like phases refer to compounds having a perovskite-like structure and phases having a perovskite-like structure, respectively.

[0025] The halide perovskites and halide-like perovskite phases described above belong to complex halide salts including halogenated lead salts, halogenated stannates and halogenated bismuth salts (complex metal-halide salts of lead, tin and bismuth, respectively), and therefore, generally, such materials are referred to as organic-inorganic metal halide compounds having a perovskite-like structure.

[0026] As used herein, the term "seed" refers to a core of a small grain or crystallite of a perovskite-like phase having a size of no more than 100 nm in any direction.

[0027] Disclosure of the Invention

[0028] A technical problem is the need to overcome the disadvantages inherent in known analogues and prototypes by inventing a simpler and more technologically advanced method for producing semiconductor films of organic-inorganic metal halide compounds with a perovskite-like structure, which semiconductor films can be used as light-absorbing layers in perovskite solar cells in order to improve their power conversion efficiency (PCE or efficiency) compared to analogues.

[0029] The technical result obtained by using the claimed invention is the ability to form films of a perovskite-like phase with an increased average grain size compared to related methods, due to the introduction of an intermediate step that provides for the formation of a film comprising seeds of a phase having a perovskite-like structure and a precursor of the initial reagent AX and component B (hereinafter "precursor B"), which ensures an increase in the efficiency (PCE) of solar cells based on the obtained film of perovskite-like material as a light-absorbing layer.

[0030] An additional technical result is that the electronic and optical properties of the perovskite films obtained using the proposed method are improved compared to related methods involving the conversion of component precursor B into organic-inorganic metal halide compounds with a perovskite-like structure through the action of reagents AX and X2.

[0031] Another advantage of the proposed method is the possibility of its implementation without the use of specialized expensive equipment and complex technical requirements, which makes the claimed method more suitable for industrial large-scale production.

[0032] The formation of the film comprising the seed of the phase having a perovskite structure and the initial reagent AX and the precursor B in the intermediate step is necessary to increase the grain size of the film of the organic-inorganic metal halide compound having a perovskite structure or a perovskite-like structure. The increase in grain size improves the electronic and optoelectronic properties of the film of the polycrystalline semiconductor material, in particular leading to a reduction in the recombination of charge carriers at the grain boundaries, which leads to an increase in the efficiency (PCE) of the device based on the film of the same material with larger grains (see Table 1 in the embodiment section of the present invention). When the film comprising the seed of the phase having a perovskite structure and the initial reagent AX and the precursor B is treated with halogen, the seed grows, and the initial reagent AX and the precursor B and other seeds are consumed by the chemical reaction between the reagent AX, the precursor B and X2 (for example, B + AX ​​+ X2 = ABX3), ultimately resulting in a film of the perovskite-like phase having large grains (average size 500 nm or more). The treatment with halogen is performed at a given temperature and a given halogen partial pressure (or a given concentration), which provides control over the chemical reaction rate and grain size of the perovskite film, ensuring that the shortcomings of analogs and prototypes are overcome.

[0033] In the context of the present invention, chemical conversion means a chemical process that results in the formation of halide perovskite ABX3 or a halide perovskite-like compound of the composition A n+1 B n X 3n+1 where 1 < n < 100, due to the reaction between a precursor of component B (metal, alloy, oxide), reagent AX, and reagent X2. In general, the reaction can be represented by the equation below:

[0034] nB'+(n + 1)AX+((3n + 1) / 2)X2 = A n+1 B n X 3n+1 +Y, where B'- is the precursor of component B and Y- is the by-product released in the case of using an oxide or a salt as the precursor of component B.

[0035] Chemical conversion can occur as a result of both simultaneous addition and multiple sequential addition of the components. In the context of the present invention, the complete chemical conversion of the starting reagents (AX, X2) and the precursor (B) into an organic-inorganic metal halide compound having a perovskite-like structure means that more than 90% (mole fraction) of the starting materials (reagents and precursor) have reacted. Brief description of the drawings:

[0037] Figure 1 Shows a micrograph of the top surface of a film using a scanning electron microscope (SEM). Figure 1 (a) (left) shows a micrograph of the surface of a film obtained after applying a solution of a mixture containing reagent MAX and X2 to the surface of metallic lead (precursor of component B), where the ratio of [X2] / [MAX] = 0.5. On the surface of the film, perovskite grains MAPbI3 and MAI with dimensions of approximately 20 nm - 100 nm can be seen. Figure 1 (b) (right) is a micrograph of the surface of the final perovskite film obtained after treating the film shown in Figure 1 (a) with iodine (X2) vapor and after its complete chemical conversion to perovskite MAPbI3. The resulting film contains microcrystals with dimensions in the range from 200 nm to 1 μm or larger.

[0038] Figure 2 Shows a graph reflecting the dependence of the average grain size of the obtained MAPbI3 perovskite film on the composition of the solution for forming the intermediate film in step II and the PCE (%) of a solar cell, said solar cell including a film made using these perovskite films as the light-absorbing layer. Detailed Description of the Invention

[0040] The method for producing a semiconductor film of an organic-inorganic metal halide compound having a perovskite structure or a perovskite-like structure described in the present invention is a process comprising the following main steps:

[0041] Step-I: Forming a layer of a precursor of component B, where B = Pb, Sn, Bi, on the surface of a substrate.

[0042] Step II: Apply to the surface of the layer of the precursor of component B a + ] / [X - ]<10 molar ratio of component A + and X - mixture or having 0<[X - [X2] < 1 or 0 < [X2] / [AX] < 1, and forming a film containing seeds of a perovskite-like phase and components AX and B. This step may include an additional step of post-processing (heating, annealing, light irradiation) the obtained film without changing its chemical composition.

[0043] Step-III: Treating (exposing) a previously formed film comprising a seed crystal of a perovskite phase or a perovskite-like phase and a precursor of a reagent AX and a component B with a reagent X2 results in the formation of a semiconductor film of an organic-inorganic metal halide compound having a perovskite structure or a perovskite-like structure, or a film of a material having the same composition as the target phase of an organic-inorganic metal halide compound having a perovskite structure or a perovskite-like structure, or a mixture thereof. In the last two cases, an auxiliary step of post-processing the film of the obtained material is introduced to ensure that any impurity phase of the film material is completely converted into the target phase of an organic-inorganic metal halide compound having a perovskite structure or a perovskite-like structure.

[0044] In a first step (step I), a layer of a precursor of component B is formed on the surface of a carrier substrate. In this case, glass, transparent conductive silicon oxides, polymers (including transparent and conductive polymers), and any other material that is inert with respect to the reagents used and the final material (perovskite halides or perovskite-like compounds) are used as carrier substrates. Experiments have shown that the physicochemical processes that take place in all three main steps of the proposed process are independent of the properties of the inert material of the carrier substrate. An inert material in the sense of the claimed invention is any material that does not undergo any chemical interaction with the final material, its components, the reagents and solvents used in its synthesis. hereinafter, we refer to the base material as the material of the upper layer of the substrate, to which the precursor of component B is directly applied.

[0045] In one embodiment of the present invention, the carrier substrate material is selected to be the same as that used to construct perovskite solar cells and similar photovoltaic devices. Typically, in such devices, the ABX3 layer is applied to the surface of a layer of transparent conductive material (transparent conductive oxide, conductive polymer) deposited on top of glass or a transparent polymer. In general, it is assumed that the carrier substrate contains all the functional layers required to produce the finished device (solar cell, LED), except for the layer of light-absorbing material ABX3 and the covering functional layers.

[0046] In one embodiment of the present invention, a layer of lead, tin or bismuth having a thickness of 5 nm to 500 nm is sprayed onto a substrate of the following materials: fluorine-doped tin oxide (FTO) glass, indium-doped tin oxide (ITO), tin oxide SnO2 (on FTO, ITO) or titanium oxide TiO2 (planar and mesoporous layers), polyethylene terephthalate, polytriarylamine (PTAA).

[0047] Before applying the layer of the precursor of component B, the surfaces of the support substrates are thoroughly cleaned of contaminants. In particular, they are purified using ultrasound in an aqueous solution of surface-active substances (surfactants), washed with distilled water and purified with ozone plasma.

[0048] The precursor of component B is applied in the form of a metal film - Pb, Sn, Bi or their alloys or a layered structure comprising several metal (Pb, Sn, Bi) layers one above the other. In addition, lead salts and oxides, such as PbI2 and PbO, can also be used as precursors of component B.

[0049] The precursor of component B is applied by vacuum deposition, electrochemical deposition, chemical vapor deposition, decomposition of a previously applied solid phase compound comprising component B or by other methods.

[0050] The most convenient and technically advanced is to use as precursor the metal component B. Methods for applying metal films of a given thickness are well known, widely distributed and available.

[0051] In one embodiment, a film of the precursor of component B in the form of a metal (tin, lead, bismuth) is deposited by thermal sputtering or magnetron sputtering in a vacuum. At the same time, the cleaned substrate is placed in a vacuum chamber, fixed at a predetermined distance from the heated crucible or magnetron target, and sputtering is performed while the thickness of the sprayed coating is controlled by a quartz thickness sensor.

[0052] In the second step (step II), a complexing agent is applied to the surface of the layer of the precursor of component B, the complexing agent comprising a 0.5<[A+ ] / [X - ]<10 molar ratio of component A + and X - mixture or having 0<[X - ] / [X2]<1 or 0<[X2] / [AX]<1, and form a film containing seeds of a perovskite-like phase and the reagent AX and the precursor B.

[0053] The composition comprising reagent AX or component A is coated using inkjet printing, screen printing, spin coating and immersion coating aerosol spraying methods, in particular ultrasonic spraying, atomization through a nozzle, electrospraying, aerosol inkjet printing or other methods. + and X - The mixture of and the complex reagent of reagent X2 is distributed in a uniform thin layer on the surface of the layer of the precursor of component B.

[0054] As a complexing agent, a + 、Anion X - and halogen X2, as well as solutions or solvent-diluted melts, and colloids or suspensions or emulsions comprising these components in the liquid or solid phase in a mixture with one or more solvents.

[0055] In order to combine component A in the necessary stoichiometric ratio + and X - In the composition added to the complex reagent, both the AX salt itself and any mixture of salts can be used, at least one of which contains component A + , and any other components X - As a result of mixing, component A + and component X - In one embodiment of the present invention, acetate, formate, fluoride, oxalate of a singly charged organic cation mixed with ammonium, potassium halide or hydrogen halide is used as an anion halide source to prepare the complex reagent, and the organic cation salt and the anion halide source are obtained in a ratio close to unit.

[0056] In one embodiment of the present invention, methylammonium iodide (CH3NH3I), methylammonium bromide (CH3NH3Br), formamidinium iodide (FAI), formamidinium bromide (FABr), cesium iodide (CsI) and various halide salts of substituted (primary, secondary, tertiary or quaternary) ammonium cations and other stoichiometric halides with suitable singly charged cations are used as AX salts.

[0057] In order to successfully carry out the proposed method, the concentrations of reagents AX and X2 in the applied reagent complex are selected in such a way as to ensure that component A is applied in a stoichiometric amount relative to component B per unit area of ​​the membrane.

[0058] In particular, this condition is met when the precursor component A of the reagent AX is applied to the membrane surface in a stoichiometric amount per unit area of ​​membrane. In this case, deviations of up to 10% from the optimal A / B ratio of the resulting material may be acceptable.

[0059] For 3D halide perovskites, the optimal ratio is A / B = 1, as it corresponds to the stoichiometry of the final material ABX3 and produces a single-phase film after the conversion is complete. For other perovskite-like compounds, this ratio can vary depending on the desired compound. In particular, it was shown that the ratio A / B = (n + 1) / n is optimal for layered halide perovskites.

[0060] In one embodiment, layered halide perovskites BA2PbI4, PEA2PbI4, BDAPbI4 (BA + is the butylammonium cation, PEA + is the phenylethylammonium cation, BDA 2+ is the butanediammonium cation). Similarly, the optimal A / B ratio for any given perovskite-like compound can be readily calculated based on its chemical formula.

[0061] The most convenient and technically simple way to apply a given amount of reagents AX and X2 to a film of precursor B per unit area is to distribute their solutions on the surface of the layer of precursor of component B. In this case, acetone, alcohol, tetrahydrofuran, dioxane, acetonitrile or a mixture of these solvents is used in any ratio, and any other organic or inorganic neutral solvent can also be used. In this context, a neutral solvent is any solvent that is unable to dissolve the compound of component B in a concentration greater than 0.3 M.

[0062] In different embodiments of the present invention, the compound reagent that comprises reagent AX and X2 can be applied on substrate by any means.Typically, in order to provide the uniform distribution of the thin layer of reagent AX and X2 on the surface of substrate, spin coating method is convenient, because it is fast and needs a small amount of solution.Usually, in the situation of large area substrate, compound reagent is applied on substrate by spin coating, spraying (aerosol spraying), slot die coating (slot-die coating) or vapor deposition.

[0063] In order to successfully implement the claimed method, it is necessary to obtain after step-II a film that not only has an A / B ratio corresponding to the chemical formula of the desired perovskite compound, but also contains seeds of the perovskite phase (perovskite phase nuclei) as well as residual reagent AX and precursor B.

[0064] The fundamentally important condition for the formation of perovskite phase nuclei is the possibility of chemical reaction of the reagent solutions AX and X2 with the precursors of component B to form perovskites. In this case, only a portion of the initial precursors of component B should undergo chemical conversion to perovskites, and a portion thereof should remain in order to react with the excess applied reagent AX during the treatment with the halogen in the next step (III) and form perovskites.

[0065] The amount of the perovskite phase in the form of seed crystals after step-II is determined by the amount of halogen X2 in the composite reagent applied. For this reason, the process is carried out under such conditions: when the precursor of component B interacts with reagent AX and X2, only the chemical reaction (chemical conversion) of the precursor of component B to perovskite occurs, and when the precursor of component B interacts with AX, no perovskite is formed. These conditions are achieved because reagent AX and X2 together form a highly reactive polyiodide melt [Petrov AA et al. A new formation strategy of hybrid perovskites via roomtemperature reactive polyiodide melts / / Mater. Horiz. 2017. Vol. 4, pp. 625-632], which reacts with the precursor of component B and forms perovskite even at low temperature within a few seconds or tens of seconds, while the reaction of component B with reagent AX can only be carried out at a significant rate at high temperature or during about a few hours.

[0066] Thus, in the case of applying a stoichiometric amount of AX to the precursor of component B, the amount of perovskite will be determined by the ratio [X2] / [AX] or the proportion of the halogen - δ.

[0067] Therefore, the general equation for the chemical process occurring in Step II can be written as follows:

[0068] B'+AX+δX2→δABX3+(1-δ)B”@AX+Y↑

[0069] Where B' is the initial precursor of component B (usually in the form of a metal), B" is the final precursor of component B (neither a perovskite compound nor a perovskite-like compound), which is usually the same as the original precursor B', and Y is a by-product (which can then be removed by post-processing).

[0070] Pb+MAI+δI2→δMAPbI3+(1-δ)Pb@MAI

[0071] {Pb 0.8 Sn 0.2}+MAI+δI2→δMAPb 0.8 Sn 0.2 I3+(1-δ){Pb 0.8 Sn 0.2}@MAI

[0072] Pb+2BAI+δI2→δBA2PbI4+(1-δ)Pb@2BAI

[0073] In one embodiment of the present invention, a solution of reagents AX and X2 in an organic solvent is applied to the surface of the precursor of component B by spin coating (or spin-coating) in an organic solvent to form a film containing cores of grains of a halide perovskite phase.

[0074] -paper( http: / / konf.x-pdf.ru / 18fizika / 632895-1-fotovoltaicheskie- strukturi- osnove-organicheskih-poluprovodnikov-kvantovih-tochek-cdse.php);

[0075] -GOST R ISO 27911-2015 "State system for ensuring the uniformity ofmeasurements(GSI).Chemical analysis of the surface.Scanning probemicroscopy.Determination and calibration of the lateral resolution of a near-field optical microscope"(http: / / docs.cntd.ru / document / 1200119068);

[0076] - https: / / www.msu.ru / science / main_themes / v-mgu-razrabotali-novuyu-(disclosed in [strategy-polucheniya-perovskitnykh-solnechnykh-yacheek.html]), the solution is distributed over the surface in a uniform thin layer, while the solvent begins to evaporate. As a result, the concentrations of reagents AX and X2 increase in the thin layer above the film of component B's precursor, and a rapid chemical reaction of AX and X2 with the precursor of component B begins. If the ratio [X2] / [AX] is greater than 0 and less than 1, the result is a film containing cores of grains of a perovskite or perovskite-like phase and AX and B. When this process is carried out at a temperature of 10°C to 40°C, such a film forms within approximately 5 to 100 seconds. In the absence of X2, perovskite formation does not occur under these conditions. However, when the ratio [X2] / [AX] is greater than 1, the reaction completely converts component B into a halide perovskite via the precursor.

[0077] Therefore, if the ratio [X2] / [AX] is in the range greater than 0 and less than 1, and this optimal ratio is close to 0.5, the key step of the proposed method (forming a film containing perovskite or perovskite-like phase nuclei and reagent AX and precursor B) can be achieved (see the Examples section of the present invention and Table-1).

[0078] In the particular case of the present invention, the film obtained in step II may undergo additional post-processing. Post-processing may include annealing (heat treatment), treatment in an atmosphere of a given composition (inert gas, dry air, humid air, solvent fumes), irradiation with visible light, ultraviolet light or infrared light. Post-processing is performed to remove residual solvents or other auxiliary reagents, remove possible by-products of the reaction to form halide perovskites (or perovskite-like compounds), and complete the desired reaction to the desired degree of progress. In most cases, in an embodiment of the present invention, the post-processing in step II includes a short-term (1 second -3600 seconds) annealing at a given temperature (30°C -300°C).

[0079] In the third step (step III), the formed film containing the seeds of the perovskite phase or perovskite-like phase and reagents AX and B is treated by X2 until the precursor of component B and reagent AX are completely reacted to produce a film of a halide material having a perovskite structure or a perovskite-like structure.

[0080] In one embodiment, the treatment or "halogenation" by X2 (halogen) is carried out in the gas phase or in the liquid phase. In the first case, a halogen vapor is used; in the second case, a solution of the halogen in a neutral solvent is used. In this context, a neutral solvent is understood to mean any solvent that does not dissolve the final material (e.g., perovskite ABX3) and does not chemically interact with it, and also does not dissolve the reagent AX and the precursor B and does not chemically interact with them.

[0081] In one embodiment, alkanes (heptane, octane, decane), halogenated alkanes (chloroform, dichloromethane), toluene, chlorobenzene, ethers and esters and other slightly polar or non-polar solvents and any mixtures thereof are used as solvents for the halogen X2. Experiments have shown that when the halogen is exposed to a halide perovskite phase or a perovskite-like phase, the properties of the neutral solvent do not affect the chemical transformation of the reagent AX and the precursor of the component B, so in principle any neutral solvent can be used.

[0082] In one embodiment, the halogenation from the gas phase is carried out at room temperature in an atmosphere of air or a neutral gas in a closed thermostatic container into which the film formed in step II is placed.

[0083] During the treatment of the film formed in step-II with the halogen (X2), the reagent AX and the precursor B contained in the film react with the halogen previously present near the seeds of the perovskite-like phase, which results in the growth of the seeds of the perovskite-like phase and the formation of large grains (typically >500 nm) of the perovskite-like phase. In general, "large grains" of a polycrystalline thin film are defined herein as grains whose average size is greater than or equal to the film thickness. The optimal thickness of the perovskite-like phase film is in the range of 200 nm to 1000 nm, which generally ensures that more than 90% of the incident light is absorbed by the film.

[0084] The optimal conditions for chemical conversion to obtain a film of a halide perovskite of a given composition and thickness are selected by varying the temperature and time of the process (the time of the chemical conversion), as well as the pressure of the halogen vapor or the concentration of the halogen in the solution. In different embodiments of the present invention, the parameters are varied as follows: temperature from 0°C to 300°C, process time from 5s to 3600s, and partial pressure of the halogen vapor from 0.01mmHg to 500mmHg (see Table 1).

[0085] Processing with halogen at a given temperature and a given halogen partial pressure (or, in the case of solutions, a given concentration) allows you to control the rate of halogen influx into the film surface, thereby controlling the conversion reaction rate and the grain size of the resulting perovskite film. Increasing the temperature and / or partial pressure accelerates the conversion reaction. Crystallite size increases with increasing duration of the conversion reaction. However, starting from a certain processing time, when complete conversion of the film has been achieved, further processing can lead to degradation of the morphology and optoelectronic properties of the perovskite halide film.

[0086] It should be noted that during the treatment with the halogen X2, the formation of the reactive polyhalide melt follows the reaction AX+nX2→AX 2n+1[Petrov AA et al. A new formation strategy of hybrid perovskites via roomtemperature reactive polyiodide melts / / Mater. Horiz. 2017. Vol. 4, No. 4 pp. 625-632] occurs. The polyhalide melt facilitates the chemical conversion of the precursor of component B into a halide perovskite phase or a perovskite-like phase. The key feature of the proposed method is the ability to control the rate at which the halogen flows into the film, which contains the reagents and components necessary for the reaction formation in the presence of a halide perovskite or perovskite-like compound. The perovskite formed by the reaction B+AX+X2=ABX3 in this case does not form many small crystallites or grains, but ensures the growth or reaction growth of the small perovskite phase present in the halogen-treated film. Therefore, the entire process implemented in the second and third steps of the proposed method can be reflected in the case of halide perovskites by the following equation:

[0087] B'+AX+δX2→δABX3+(1-δ)B"@AX+Y↑(Step-II)

[0088] {δABX3+(1-δ)B”@AX}+X2→ABX3 (Step-III)

[0089] The reagents shown in the brackets {} are part of the film formed in the second step.

[0090] Thus, compared to the method described in patent RU 2685296 C1, the claimed solution provides for a delayed formation of the perovskite halide during the chemical conversion with halogen, which facilitates the possibility of growing the crystallites to larger sizes, and a necessary condition for this is the formation of a film of the above-mentioned composition during the second (intermediate) step of perovskite film formation. The slower formation of the perovskite under conditions close to equilibrium, and therefore the slower growth of the crystals, not only makes it possible to produce films with larger crystallites, but also provides for a lower defect concentration in the crystals.

[0091] In one embodiment of the present invention, after the chemical transformation under the influence of the halogen is completed, the film of the halide perovskite phase or perovskite-like phase undergoes additional post-processing. Post-processing may include annealing (temperature treatment), treatment in an atmosphere of a given composition (inert gas, dry air, humid air, solvent vapor), irradiation with visible light, ultraviolet light or infrared light, and treatment with a solution or solvent of the desired composition. Post-processing is performed to remove excess halogen adsorbed by the film, to remove possible by-products of the chemical transformation, or to improve the functional properties of the perovskite layer.

[0092] In one embodiment, during the prolonged (5 minutes or more) treatment by the halogen reaction, a post-treatment is used to remove excess halogen X2, which includes annealing the film at a given temperature or within a certain temperature range, or reducing the pressure above the film to below atmospheric pressure, or using both of the effects shown. In addition, the higher the temperature and the lower the pressure, the higher the rate of halogen removal. The optimal post-processing temperature for such a material is one that ensures rapid removal of excess halogen (in less than 10 minutes) without causing decomposition of the material or degradation of its properties (even partial degradation). For example, for FAPbI3 halide perovskite, the upper temperature limit is 190°C, for MAPbI3 perovskite -150°C, and for CsPbBr3 perovskite -450°C.

[0093] The most technologically advanced and efficient post-processing method is high temperature annealing for a period of time ranging from a few minutes to 1 hour. The annealing is performed in a temperature range that is optimal for a given material (perovskite ABX3 or perovskite-like phase) D and does not exceed the thermal stability range of the material.

[0094] Annealing was also performed during the formation and chemical conversion of phases consistent with the perovskite halide stoichiometry but with different structures. For example, a film composed of FAPbI3, including the hexagonal phase of FAPbI3 after chemical conversion, was annealed at 160°C for 30 minutes.

[0095] In one embodiment of the present invention, E2A can be obtained. (n-1) B n X 3n+1 Layered halide perovskites containing organic cations E as spacers or interlayers + , the organic cation E + Selected from a variety of substituted ammonium cations, including primary ammonium cations (monosubstituted, R-NH3 + ), secondary ammonium cation (R1(R2)NH2 + ), tertiary ammonium cation ([R1(R2)(R3)NH] + ) and quaternary ammonium cations ([([R1(R2)(R3)NR4] + ). In this case, the corresponding cation halide or other salt or mixture thereof is added to the complexing agent and then applied to the surface of the layer of precursor of component B in step-II of the process.

[0096] The ratio of component E to component A in the composite reagent is selected to approximate their ratio in the resulting layered perovskite. The concentrations of the components vary from 0.1 M to 7 M. When producing a film of the layered perovskite, the halogen treatment in the third step of the process is performed at a temperature ranging from 25°C to 150°C. The optimal processing temperature for layered perovskites containing such bulky cations is close to the minimum temperature that provides melting of the desired polyhalide of the substituted ammonium cation.

[0097] In one embodiment of the present invention, a thin film of a layered halide perovskite having a composition of BA2PbI4, PEA2PbI4, BDAPbI4, (BMA)2PbI4, or BA2MAPb2I7 is obtained by applying liquid composite reagents of different compositions through chemical conversion of a pre-deposited film of Pb having a thickness of about 60 nm. In particular, in step-III, in the case of BA2PbI4, a solution of butylammonium iodide having a concentration of [BAI] = 0.9M-1.1M and a molar ratio of [I2] / [BAI] = 0.5 is used as a composite reagent; in the case of PEA2PbI4, a solution of iodine and phenylethylammonium iodide (PEAI) having a concentration of [PEAI] = 1.1M and a molar ratio of [I2] / [PEAI] = 0.5 is used as a composite reagent; in the case of BDAPbI4, a solution of iodine and phenylethylammonium iodide (PEAI) having a concentration of 1.2M and a molar ratio of [I2] / [BDAI] = 0.5 is used. In the case of (BMA)2PbI4, a solution of iodine and butylmethylammonium (or butyl(methyl)azonium) iodide (BMAI) with a [BMAI] = 1.1 M and a [I2] / [BMAI] = 0.5 was used as a complexing reagent; in the case of BA2MAPb2I7, a solution of iodine and butylammonium and methylammonium (MAI) iodide with a BAI concentration of 0.6 M and a MAI concentration of 0.3 M and a total iodine to iodide ratio close to 0.5 was used as a complexing reagent. In step-III, the film obtained as described above was treated with halogen vapor at a temperature of 50°C or above for 5 minutes. These examples show that layered halide perovskites containing a variety of substituted ammonium cations can be obtained under almost the same conditions. It should be noted that the conditions required for preparing layered perovskites are also independent of the type of substituents of the organic cations.

[0098] Embodiments of the present invention

[0099] The following table shows typical conditions for forming films and the efficiency of devices based on these conditions, if the devices were fabricated.

[0100] The first column "P[D]" indicates the precursor of component B. The optimal thickness of its layer is about 60-65 nm in the case of a metal film - Pb, Sn, Bi or their alloys or a layered structure comprising several metal (Pb, Sn, Bi) layers one above the other.

[0101] The second column indicates the ratio [X2] / [AX] and the concentration of AX in the applied complexing reagent. In all cases, except for the application of pure AX applied from the vapor, the complexing reagent was used in the form of a solution of X2 and AX in an organic solvent.

[0102] The third column shows the conditions for post-processing (eg, annealing) of a film obtained by applying the reagents shown in the second column to a film of Precursor B.

[0103] The fourth column indicates the conditions under which the film of the precursor formed after step-II is treated by halogen (X2).

[0104] The fifth column shows the conditions of the final treatment (annealing) of the film obtained after completing step-III (treatment by X2), which is necessary to remove excess halogen and complete the formation of the ABX3 layer.

[0105] The sixth column indicates the phase of the material obtained from x-ray phase analysis.

[0106] The seventh column indicates the average grain size of the obtained film of the organic-inorganic metal halide-based perovskite compound.

[0107] The eighth column indicates the PCE (%) of the manufactured solar cell including the obtained film of the organic-inorganic metal halide-based perovskite compound as a light absorbing layer.

[0108] Table 1

[0109]

[0110]

[0111] Table 1 and Figure 2 Data are presented on the average size of perovskite grains in MAPbI3 films and on the efficiency of solar cells comprising corresponding perovskite films as light-absorbing layers, depending on the conditions used for their preparation. The following conclusions can be drawn from the data presented:

[0112] When MAI is applied to the lead surface in step II without the iodine additive, no chemical reaction occurs, and no nucleation of perovskite grains occurs. The iodine treatment results in the formation of a polyiodide melt, which immediately reacts with metallic lead and forms a large number of small perovskite grains. Consequently, when the resulting perovskite films are used as light-absorbing layers in solar cells, they have relatively small grain sizes and exhibit relatively low efficiency values.

[0113] When a composite reagent with a ratio [X2] / [AX] = 1 was applied to the lead surface in step II, a MAPbI3 perovskite film with a given grain size was immediately formed, and subsequent treatment with halogen did not result in its reactive growth. As a result, when used as a light-absorbing layer in solar cells, the obtained perovskite film had an average grain size of approximately 500 nm and exhibited relatively low efficiency values ​​(up to 12%).

[0114] When a complex reagent having a molar ratio of [X2] / [AX] = 0.5 is applied to the surface of the metal (Pb) layer in step II, a "precursor film" containing seeds (nuclei) of a perovskite-like phase is formed. After the precursor film is then treated with iodine, perovskite grains grow due to a chemical reaction. As a result, the resulting perovskite film has a large average grain size (approximately 700nm-800nm) and exhibits high efficiency values ​​(up to 16%) when used as a light-absorbing layer in solar cells.

[0115] Therefore, the experimental data obtained directly indicate that the introduction of an intermediate step in the processing of perovskite compound films, ensuring the formation of films containing seeds of the perovskite phase as well as precursors of the initial reagents AX and B, is a key step in the formation of perovskite films with increased average grain size and provides an increase in the efficiency of the resulting perovskite solar cells.

[0116] In order to obtain a + Cation and X - For the perovskite-like compounds of the anions (Table 1), it is not only the ratio [X2] / [AX] that is important, but also the ratio of the different cations and anions in the applied complex reagent. In one embodiment, in order to obtain a composition of MA 0.25 FA 0.75 PbI3 film, using [MA + ] / [FA + ] a molar ratio of about 3 complex reagents; in order to obtain a composition of MA 0.25 FA 0.75 PbBr 0.5 I 2.5 The membrane used was about 3 [MA + ] / [FA +] and a molar ratio of about 5 [I - ] / [Br - ] molar ratio, that is, the different A + The ratio of cations and different X - The ratio of anions should be selected to be close to their desired ratio in the resulting film of the organic-inorganic metal halide compound having a perovskite-like structure.

Claims

1. A method for preparing a semiconductor film of an organic-inorganic metal halide compound having a perovskite-like structure, comprising the following steps: a) applying a layer of a precursor of component B to a substrate, b) applying a layer of the complex reagent onto the surface of the layer of the precursor of component B, and c) treating the applied layer on said substrate with a reagent X2 during the time necessary and sufficient for completion of the chemical reaction of the applied reagent and the precursor of said component B, resulting in the formation of an organic-inorganic metal halide perovskite compound, Characterized in that the composite reagent applied in the step b) comprises a mixture of an AX reagent and an X2 reagent, wherein the molar ratio of [X2] / [AX] is in the range of 0 < [X2] / [AX] < 1, and the film obtained after the step b) comprises seeds of a phase having a perovskite-like structure, in The component B comprises cations M of different metals selected from Pb, Sn, Bi and mixtures thereof. n+ , The reagent AX is a cation containing + and anion X - A salt wherein the cation A + is selected from methylammonium CH3NH3 + 、Formamidinium (NH2)2CH + , Guanidinium C(NH2)3 + 、Cs + , Rb + and unsubstituted ammonium cations (NH4 + ) or a singly charged organic or inorganic cation including a monosubstituted, disubstituted, trisubstituted or tetrasubstituted ammonium cation, and combinations thereof; and the anion X - Is selected from Cl - Br - , I - or pseudohalide anions and singly charged anions of combinations thereof, The reagent X2 is a molecular halogen. 2 . The method according to claim 1 , wherein in a step prior to the treatment by the reagent X2, the film containing seeds of the perovskite-like phase is subjected to a heat treatment at a temperature of 30° C. to 300° C. for 1 s to 3600 s.

3. The method according to claim 1, wherein after completing step (c), the obtained film of the organic-inorganic metal halide compound having a perovskite-like structure is subjected to an additional post-treatment, wherein the additional post-treatment includes heat treatment at a temperature of 30°C to 400°C for 1 second to 7200 seconds, or exposure to an inert gas, dry air, humid air, solvent vapor, or exposure to visible light, ultraviolet light or infrared light, or treatment by solution or solvent, or a combination of these types of post-treatments.

4. The method according to claim 1, wherein the film in step b) is formed by repeatedly applying a complexing agent of a mixture of AX and X2 from solutions having equal or different molar ratios of AX and X2.

5. The method according to claim 1, wherein the composite agent applied in step (b) is uniformly distributed on the surface of the layer of the precursor of component B using inkjet printing, screen printing, spin coating, dip coating, aerosol spraying, wherein the composite agent is component A + and X - or solutions or melts of reagent AX and reagent X2, as well as colloids or suspensions or emulsions containing these substances in the liquid phase or solid phase and with the addition of one or more solvents.

6. The method according to claim 5, wherein the complexing agent applied in step (b) is uniformly distributed on the surface of the layer of the precursor of component B using ultrasonic spraying, atomization through a nozzle, electrospraying, jet printing.

7. The method according to claim 1 , wherein the film of the precursor of component B in step (a) is obtained in the form of a metal selected from Pb, Sn, Bi or their alloys or in the form of a layered structure comprising layers of several metals selected from Pb, Sn, Bi located one above the other, and also in the form of a film of an oxide or a lead salt, the precursor of component B being applied by vacuum deposition or by electrochemical deposition of component B or by chemical vapor deposition or by decomposition of a previously applied solid-phase compound containing component B.

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