Aqueous solution precursors for making oxide thin films, and composition and method for making conductive oxide thin films therefrom

Abstract

To provide an aqueous solution for solution processing for forming a conductive oxide thin film having high density, high optical transmittance, low surface roughness, and good electronic properties, as well as the formed thin film and a method for forming the thin film.SOLUTION: A precursor solution for producing a conductive oxide thin film is prepared from metal salts comprising indium, tin, titanium, and cadmium salts, and numerous combinations thereof. These salts have purity levels of at least 99% to at least 99.999%. These salts may be metal nitrates, or they may be metal halides such as chlorides. The solution is aqueous. The solution may be an aqueous solution comprising In(NO3)3, and at least one of SnCl2 and SnF2. The solution may be an aqueous solution comprising In(NO3)3 and TiCl3. The solution may be an aqueous solution comprising Cd(NO3)2, and at least one of SnCl2 and SnF2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 62 / 862,43 9, filed on June 17, 2019, and the entire disclosure thereof is incorporated herein by reference.

[0002] (Technical Field) The present invention relates to methods for making conductive metal oxides such as Sn:In2O3, Ti:In2O3, and Cd2SnO4, and for forming conductive films comprising metal oxide semiconductors using high - purity solution compositions containing tin and indium reagents.

[0003] (Confirmation of Government Support) This invention was made with government support under Grant No. CHE1606982 awarded by the National Science Foundation of the United States. The government has certain rights in this invention.

Background Art

[0004] The preparation of conductive thin - film materials is currently mainly carried out by vacuum processes, such as chemical vapor deposition or sputtering. These processes require highly specialized equipment and are costly to operate due to high energy requirements. Solution processing is simpler and less expensive compared to the current vacuum - processing methods currently used for the preparation of conductive thin - film materials.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Unfortunately, the prior solution - processing techniques have not been satisfactory. For example, known In the solution treatment method, there has been a failure to produce a high-density film. Density is important for the electronic properties of the film. A low-density or porous film can exhibit lower conductivity, lower light transmittance, and greater surface roughness than an equivalent high-density film. and. light transmittance and greater surface roughness may be exhibited. **Means for Solving the Problems**

[0006] The disclosed embodiments relate to conductive oxide thin films having high density, high light transmittance, low surface roughness, and good electronic properties. Embodiments for producing such conductive oxide thin films using appropriate precursor solutions and solution treatment are also disclosed. These precursor solutions are prepared from metal salts including indium, tin, titanium, and cadmium salts and numerous combinations thereof. In certain embodiments, these salts have a purity level of at least 99% to at most 99.999%. In certain embodiments, these salts can be metal nitrates, or they can be metal halides such as chlorides. In certain embodiments, the solution is aqueous. In a specific disclosed embodiment, the solution is an aqueous solution containing at least one of In(NO3)3 and SnCl2 or SnF2. In another disclosed embodiment, the solution is an aqueous solution containing In(NO3)3 and TiCl3. In yet another disclosed embodiment, the solution is an aqueous solution containing at least one of Cd(NO3)2 and SnCl2 or SnF2. A film can be prepared by first preparing a suspension, more typically a solution, of one or more selected metal salts. Next, the solution is applied to a substrate to form a film. In some embodiments and. um, tin, titanium, and cadmium salts and numerous combinations thereof. In certain embodiments, these salts have a purity level of at least 99% to at most 99.999%. at least. In certain embodiments, these salts can be metal nitrates, or they can be metal halides such as chlorides. In certain embodiments, the solution is aqueous. In a specific disclosed embodiment, the solution is an aqueous solution containing at least one of In(N O3)3 and SnCl2 or SnF2. In another disclosed embodiment, the solution is an aqueous solution containing In(NO3)3 and TiCl3. solution. In yet another disclosed embodiment, the solution is an aqueous solution containing at least one of Cd(NO3)2 and SnCl

[0007] First, a film can be prepared by preparing a suspension, more typically a solution, of one or more selected metal salts. Next, the solution is applied to a substrate to form a film. In some embodiments thereby. In this state, the solution is applied by spin coating, roll coating, spray coating, inkjet printing, mist deposition, die slot coating, dip coating, doctor blade coating or a combination thereof. Next, the film is annealed to form a thin film of a conductive metal oxide. In some embodiments, the thin films obtained from these solutions are Sn:In2O Ti:In2O3, Cd2SnO4 or a combination thereof. In the first disclosed aspect, the invention relates to a solution comprising an aqueous solvent, high purity SnCl2 and high purity In(NO3)3. In a second disclosed aspect, the invention relates to an aqueous solution comprising perovskite titanate clusters and high purity In(NO3)3. In a third aspect, the invention relates to an aqueous solution comprising high purity Cd(NO3)2, high purity SnCl2 and high purity 3、 SnF2. In a final aspect, these solutions function as precursors for depositing highly conductive thin films that exhibit very smooth surfaces with thicknesses in the range of 3 nm to 3,0 00 nm, and certain embodiments have thicknesses greater than 300 nm.

[0008] The films created by this process can be incorporated into many useful devices. Those skilled in the art will understand how to assemble these useful devices. These devices can include, for example, light emitting diodes, solar cells, and printed circuits. The foregoing and other objects, features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The films created by this process can be incorporated into many useful devices. Those skilled in the art will understand how to assemble these useful devices. These devices can include, for example, light emitting diodes, solar cells, and printed circuits.

[0009] The foregoing and other objects, features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. These devices can include, for example, light emitting diodes, solar cells, and printed circuits.

[0010] The foregoing and other objects, features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011]

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DETAILED DESCRIPTION OF THE INVENTION

[0012] (I. Terms) The following explanations of terms and abbreviations are provided to better explain the present disclosure and as a guide for those skilled in the art in implementing the present disclosure. As used herein, "comprising" means "including", and the singular forms "a", "an", or "the" include references to the plural form unless the context clearly dictates otherwise. The term "or" refers to a single one of the recited alternative elements or a combination of two or more of the elements unless the context clearly dictates otherwise.

[0013] ​​​​​Unless otherwise indicated, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described in this specification can be used to practice or test the present disclosure, suitable methods and materials are described below. The disclosed materials, methods, and examples are illustrative only and not limiting. Other features of the present disclosure will be apparent from the following detailed description and claims.

[0014] Unless otherwise specified, all numerical values representing amounts, molecular weights, percentages, temperatures, times, etc. of components used in the specification or claims are to be understood as being modified by the term "about." Accordingly, the recited numerical parameters are approximations that may depend, implicitly or explicitly, on the desired properties and / or the detection limits under standard test conditions / methods as required, for example. When distinguishing embodiments directly and explicitly from the prior art being discussed, the numerical values of the embodiments are not approximations unless the word "about" is cited.

[0015] The arithmetic average roughness, Ra, is the arithmetic average of the absolute values of the profile heights over the measurement length or area.

[0016] The RMS roughness is the root mean square of the square of the film height over the measurement length or area.

[0017] As used herein with respect to a thin film or thin layer, "thin" typically means from 200 nm to 700 nm or from 400 nm to 600 nm or from greater than 0 to 500 nm, from greater than 0 to 2 50 nm or from greater than 0 to 100 nm, including from greater than 0 to 3,000 nm, from greater than 0 to 2,00 Refers to a film or layer having a film thickness or layer thickness of 0 nm, greater than 0 to 1,000 nm.

[0018] As used herein with respect to thin films or thin layers, "ultrasmooth" typically refers to a film or layer having an RMS roughness of greater than 0 nm to 5 nm or less, such as greater than 0 nm to 3 nm or less, greater than 0 nm to 2 nm or less. In certain embodiments, it has a roughness of greater than 0 nm to 1 nm or less, greater than 0 to 0.75 nm, 0.1 nm to 0.7 nm, 0.2 nm to 0.6 nm, 0.3 nm to 0.6 nm, 0.4 nm to 0.6 nm, or 0.4 nm to 0.5 nm. A film having such a smooth surface provides advantages in end - use applications. For example , the small surface roughness prevents a decrease in light transmittance due to photon scattering. Additionally, a small surface roughness reduces the likelihood of electrical short - circuits due to insufficient surface contact, resulting in further improved electrical performance.

[0019] (II. Description) (A. Compositions, Precursor Reagents, Precursor Reagent Compositions Used to Make Compositions, and Films Comprising Compositions) The disclosed embodiments relate to these oxide compositions such as indium oxide (In2O3) compositions, tin oxide (SnO2) compositions, indium:tin oxide (Sn:In2O3) compositions, titanium:indium oxide (Ti:In2O3) compositions, cadmium:tin oxide (Cd2SnO4) compositions, doped indium oxide compositions, and doped tin oxide compositions, and the doped versions of such compositions, and precursor reagents and compositions used to make such compositions. The present invention also relates to In2O3, Sn:In2O3, Ti:In 2O3, Cd2SnO4, doped In2O3, doped SnO2, doped Sn:In2O3 , and doped Ti:In2O3 and doped Cd2SnO4, to produce films, particularly thin films, even more preferably very thin ultra-smooth films. Embodiments of a method for producing are related. Certain embodiments include doped conductive In2O3 films or doped Sn:In2O3 films, and doped conductive films such as doped Ti:In2O3 and doped Cd2SnO4 compositions,

[0020] Those skilled in the art will understand that a composition comprising two or more metal species can have metal ions in various ratios. For the specific embodiments disclosed, in the case of Sn:In2O3 films, the Sn:In ratio is from about 0.05:1 to about 0.25:1, in the case of Ti:In2O3 films, the Ti:In ratio is from about 0.05:1 to about 0.2:1 and in the case of Cd2SnO4 films, the Cd:Sn ratio is up to about 3.5:1.

[0021] Suitable In2O3 precursors include any precursor that can be used to produce the desired indium oxide thin film. In the case of the specific embodiments disclosed, water-soluble precursors are preferred. Soluble indium oxide precursors can be, for example, indium nitrate or indium halide. The amount of indium oxide precursor used is selected to produce a concentration of In in solution suitable for facilitating the production of a thin film having the desired properties such as the desired density, desired thickness, desired refractive index, 3+ and / or RMS surface roughness. In some embodiments, the amount of indium oxide precursor is from 0.1M to 0.9M, from 0.2M to 0.8M or 0.4 In in a solution from 0 to greater than 1 M, such as from 0.8 M to 1 M, from M 3+ is selected to produce a concentration of is selected to produce a concentration of

[0022] Suitable SnO2 precursors include any precursor that can be used to produce a desired film, such as SnO2 or Sn:Sn:In2O3 films. In the case of the specific embodiments disclosed, water soluble precursors are preferred. Soluble tin oxide precursors can be, for example, tin complexes or salts . In some embodiments, the tin compound is tin fluoride, tin chloride, tin bromide or iodine tin halides such as tin iodide, tin chloride hydrate, tin nitrate, tin nitrate hydrate, tin acetate , tin sulfate or combinations thereof. The amount of tin oxide precursor used is such that the desired density, desired thickness, desired refractive index, and / or desired properties such as RMS surface roughness is suitable for facilitating the production of a thin film having the concentration of Sn in the solution is selected to produce 2+ the concentration of Sn in the solution is selected to produce is selected. In some embodiments, the amount of tin oxide precursor is from 0.1 M to 0.9 M, 0.2 M to 0.8 M or 0.4 M to 0.8 M, etc., from greater than 0 to 1 M or greater than that the concentration of Sn in the solution is selected to produce 2+ is selected.

[0023] Suitable titanium precursors include any precursor that can be used to produce a desired film, such as Ti:In2O3 films. In the case of the specific embodiments disclosed, water-soluble precursors or aqueous solutions thereof are preferred. Soluble titanium precursors can be, for example, titanium complexes or salts . In some embodiments, the titanium compound is titanium fluoride, titanium chloride, titanium bromide or titanium iodide or combinations thereof such as titanium halides. is selected to produce a concentration of

[0024] Suitable cadmium precursors include any precursor that can be used to produce a desired cadmium oxide film such as a Cd2SnO4 thin film. For the specific embodiments disclosed, water-soluble precursors are preferred. Soluble cadmium precursors can be, for example, cadmium complexes or salts. In some embodiments, the cadmium compound is cadmium fluoride, cadmium chloride, cadmium bromide, cadmium iodide, or a combination thereof, such as cadmium halides.

[0025] For the specific embodiments disclosed, the In2O3, Sn:In2O3, Ti:In2O3, and Cd2SnO4 precursor compositions include doping reagents selected to impart cadmium or titanium dopants to the resulting In2O3, Sn:In2O3, Ti:In2O3, and Cd2SnO4 compositions. The doping reagents can include thiocyanate. + 4 + 5 + and 6

[0026] The data presented herein demonstrates that the electrical properties of In2O3, Sn:In2O3, Ti:In2O3, and Cd2SnO4 films, including doped composition films, are substantially affected even by trace contaminants. Thus, the specific embodiments disclosed relate to the use of high-purity precursor reagents, including reagents having a purity of at least 99%, such as 99.5%, 99.9%, 99.99%, and 99.999%. In the exemplary embodiments disclosed, In(NO3)3 (99.999%, Alfa-Aesar), SnCl2 (99.999%, Sigma-Aldrich), SnF2 (99.999%, S Sigma - Aldrich), TiCl3 (20% w / v Fisher), and Cd reagents such as (NO3)3 (Alfa - Aesar, 99.99%) were used.

[0027] Methods for fabricating In2O3, Sn:In2O3, Ti:In2O3, and Cd2SnO4 compositions generally involve dissolving one or more suitable precursors in water to form a solution. Stirring, such as by stirring, shaking, sonication, or a combination thereof, can be used to facilitate the formation of the desired precursor composition. Additionally or alternatively, the precursor / solvent mixture can be heated to assist in the formation of the solution. The mixture can be heated to a temperature suitable for facilitating the formation of the solution, usually from 30°C to 100°C, from 50°C to 90°C, or from 70°C to 90°C, for example, up to reflux at 25 °C to 100°C or higher. Heating and / or stirring can proceed for an appropriate time, from a few minutes to 48 hours, from less than 1 hour to 48 hours or more, from 6 hours to 36 hours, from 12 hours to 30 hours hours, or from 18 hours to 24 hours, etc., to form an acceptable composition. In some embodiments, the precursor / solvent mixture is heated and / or stirred in a sealed container, for example, to reduce evaporation.

[0028] (B. Formation of thin films) In2O3, Sn:In2O3, Ti:In2O3, and Cd2SnO4 compositions, as well as their doped variants, are deposited on a substrate, and then the film - coated substrate is used to form a device or a component of a device, such as an electrical device. The substrate can be silicon containing silica (SiO2), glass, metal, metal alloy, optical crystals including non - linear optical crystals Substrates comprising crystals, laser crystals, ceramic substrates, and combinations of such materials, and any substrate on which a thin film can be formed. In some embodiments, the substrate is a silicon substrate such as a silicon wafer. In other embodiments, the substrate is a hydrophobic or hydrophilic glass such as silicate glass, i.e., glass containing silicon dioxide.

[0029] The thin film can be deposited on the substrate by any suitable technique. Suitable techniques include spin coating, roll coating, spray coating, inkjet printing, mist deposition, slot die coating, dip coating, doctor blade coating, and combinations thereof, but are not limited thereto. Certain embodiments of the present invention use spin coating to form a film on a suitable substrate. In large-scale commercial production, other techniques such as roll coater or doctor blade applications may be used. In the case of spin coating, the selected composition and its amount are dropped as droplets onto the substrate surface, and then the surface is rotated at a suitable rotational speed to effectively coat the substrate surface within a time suitable to provide the desired film thickness. For example, spin coating can be performed at about 500 rpm to about 6,000 rpm, such as 1,000 rpm to 5,000 rpm, 2,000 rpm to 4,000 rpm, and 4,000 rpm is used to form the specific exemplary embodiments disclosed. The processing period is typically on the order of seconds, but depends on the rotational speed, and the typical processing time is from about 1 to about 60 seconds, and specific operational embodiments use spin processing

[0030] For the specific embodiments disclosed, the thin film is a dense film, i.e., substantially non-porous membrane. The dense membrane can have a density from greater than 80% to 100% of the theoretical single crystal density of the material.

[0031] The thin films produced by the disclosed method have a substantially smooth surface, preferably a surface with an RMS roughness value greater than 0 and less than 1 nm, greater than 0 and less than 0.75 nm, from 0.1 nm to 0.7 nm, from 0.2 nm to 0. 6 nm, from 0.3 nm to 0.6 nm, from 0.4 nm to 0.6 nm, or from 0.4 nm to 0 .5 nm, etc., such as an ultrasmooth surface with an RMS roughness value greater than 0 and less than 1 nm. The value of the RMS roughness can be determined by AFM measurements taken over an area of 1×1 μm 2 . Alternatively, the RMS surface roughness can be estimated by the presence of Kiessig fringes at low values of 2θ. FIG. 3 shows X-ray reflectivity data for the case of a thermal process such as annealing of a Sn:In2O3 thin film at 500 °C. As can be seen from the presence of Kiess ig fringes extending up to 2θ of 6° in FIG. 3, the film surface is substantially smooth and has a root mean square (RMS) value of 0.4 nm. Such a smooth surface can be advantageous, for example, to enhance the antireflection properties of the film, reduce electrical short circuits, and / or provide an enhanced interface with a second film or layer deposited on top of the thin film.

[0032] After deposition, the thin film is usually heat-treated as necessary. The disclosed embodiments can first be exposed to a temperature lower than the annealing temperature of the film, for example, to evaporate some or substantially all of any residual solvent. The first heating or "soft baking" is from 50 °C to 250 °C. It may include exposing the film to a suitable temperature such as from 100°C to 200°C, for a time greater than 0 and up to 5 minutes or from 1 minute to 2 minutes, etc., up to the time necessary to achieve the desired result. The film can be processed at a first temperature for a first time and then at a second temperature, usually a second time at a higher temperature than the first. In some embodiments the film is processed at a temperature of from 80°C to 120°C for a time greater than 0 and up to 3 minutes, such as from 1 to 2 minutes, and then exposed to a temperature of from 150°C to 250°C, such as from 180°C to 220°C, for a time greater than 0 and greater than 3 minutes, such as from 1 to 2 minutes.

[0033] The thin film can be exposed to a temperature suitable for producing a film having one or more desired properties, such as annealing the film and promoting oxide formation and / or improving the surface smoothness, film thickness, electrical properties and / or refractive index. The annealing temperature can be selected to ensure the removal of substantially all residual components from the precursor, such as nitrate salts and any additional processing aids. Additionally or alternatively, the annealing temperature can be selected to promote crystallization such as desired for the final product or to substantially eliminate crystallization of the film. The film can begin to crystallize as the annealing temperature approaches the crystallization temperature of the film. When the film begins to crystallize, the refractive index and / or surface RMS roughness can begin to increase. Therefore, an appropriate annealing temperature is selected to balance these elements required for the final product.

[0034] The film is annealed at a temperature of from 400°C to 1,000°C, from 450°C to 900°C, from 45 0°C to 800°C, from 450°C to 700°C, from 450°C to 600°C or from 500°C to 6 It can be processed at an annealing temperature of 350 °C to 1,000 °C or higher, such as 0 °C. In certain disclosed exemplary embodiments, the film was annealed at a temperature of about 500 °C. A time sufficient to anneal the film can be from 5 minutes to 6 hours, from 15 minutes to 4 hours, from 30 minutes to 2 hours, or from 45 minutes to 90 minutes, etc., more than 1 minute to 12 hours or more. In the specific embodiments disclosed, the film was exposed to a suitable annealing temperature, such as 500 °C, for 1 hour.

[0035] Annealing can occur in any suitable environment, including air, nitrogen, noble gas, hydrogen, or a suitable mixture thereof. In the specific embodiments disclosed, annealing was performed in a controlled atmosphere of mixed hydrogen and argon gas. In some embodiments, the annealing atmosphere was 5% hydrogen gas and 95% argon gas.

[0036] The conductive oxide film thus produced can have high optical transparency in some embodiments. In the specific examples disclosed, the light transmittance exceeds 85% across the visible spectrum. The light transmittance can be affected by the surface roughness, thickness, and total density of the film. Figure 6 provides the UV-visible light transmittance of a solution-deposited Sn:In2O3 film, which is equivalent to or better than commercially produced films prepared by vacuum processing methods.

[0037] The thickness of the film after annealing can be affected by selecting the concentration of the precursor, such as the concentration of the indium-containing precursor, tin-containing precursor, titanium-containing precursor and / or cadmium-containing precursor (if present). By selecting the spin speed, the thickness of the film can be further affected. It is possible to control it, and generally a thicker film can be obtained by reducing the speed. The disclosed In some embodiments, a speed of 3000 rpm for 30 seconds is selected. Thus The deposited film layer can have a thickness of up to about 50 nm in some embodiments. If a film thicker than that produced by a single spin coating process is desired, the desired thickness can be achieved by successively stacking multiple films.

[0038] (C. Multilayer film comprising multiple thin films) The multilayer film can comprise multiple thin films, and at least one, some or all of the films have the composition and / or physical properties of the films as disclosed herein, and each thin film is a layer in the multilayer film. The multilayer film can comprise two or more layers, such as 2 to 50 layers, more typically 2 to 10 layers, such as 3, 4, 5, 6, 7, 8, 9, 10 or more layers. The continuous and / or discontinuous layers can have the same or different compositions, such as dopant amount or metal ion ratio, and / or physical and / or optical properties such as refractive index. The multilayer film can have a composition change and / or gradient across the layers from the substrate to the surface layer. For example, there can be a dopant whose amount increases or decreases across the layers from the substrate to the surface layer. In some embodiments, different layers are selected to provide a change and / or gradient in physical and / or optical properties. As used herein with respect to composition or physical and / or optical properties, a gradient across a layer refers to a change from a first layer having a first composition and / or properties to a second layer having a second composition and / or properties, where the first and second layers together define a change from the first composition and / or properties to the second composition and / or properties, and where the first and second layers together with the first composition and / or properties One having an intermediate composition and / or property that gradually changes to an article and / or property There are a plurality of intermediate layers, such as one intermediate layer or two, three, four, five, six, seven, eight or more intermediate layers The layer can be selected to provide an increase or decrease in electrical properties or refractive index across the layer from the substrate to the surface layer change or gradient. In some embodiments, the multilayer film has a plurality of compositional and / or property changes and / or gradients across the layer from the substrate to the surface. For example, the layer can be selected to provide a first change and / or gradient that increases a property such as the refractive index of the layer, and then, conversely, can be selected to provide a second change and / or gradient that decreases a property such as the refractive index of the layer.

[0039] The multilayer film can be fabricated by depositing a first layer on a substrate and heating this layer for a time suitable to form a non-annealed layer at a first temperature lower than the annealing temperature as described herein. Next, a second layer can be deposited on the surface of the first layer. Next, the second layer can be heated at a second temperature lower than the annealing temperature, where the second temperature is the same or different from the first temperature. If the second layer is the desired outer or surface layer, heating at the second temperature can be omitted if desired. Next, additional layers can be deposited by repeating the deposition and heating process until all desired layers are deposited. The multilayer film can be annealed at an annealing temperature as described herein when the desired outer or surface layer is deposited . The outer or surface layer can be heated at a temperature lower than the annealing temperature prior to annealing if desired . The outer or surface layer can be annealed at an annealing temperature as described herein when the desired outer or surface layer is deposited . The outer or surface layer can be heated at a temperature lower than the annealing temperature prior to annealing if desired .

[0040] In some embodiments of the present invention, the layer of the conductive oxide film has a desired thickness of up to 1 micron and is added until the desired thickness is obtained. In a specific example, the total film thickness is 250 nm to 350 nm .

[0041] (III. Schematic Diagram of the Device) Those skilled in the art will understand that many useful devices can be fabricated using products such as the thin films fabricated herein . For example, such products can be used to form light-emitting diodes such as organic light-emitting diodes. FIG. 1 provides a schematic diagram showing an exemplary OLED100 . The OLED100 includes a substrate such as a glass substrate 102. The thin-film conductive oxide (TCO) layer 104 according to the present application is formed on the glass substrate 102. Next, the organic layer 106 is positioned adjacent to the TCO layer 104. The OLED100 also includes a cathode 108 and a barrier layer 110 . . . .

[0042] FIG. 2 illustrates an embodiment of a device 200 with a TCO according to the present application that is useful for solar applications . The device 200 includes a back electrical contact layer 202, a CdTe layer 204, and a CdS layer 206 positioned adjacent to the CdTe layer 204. The TCO layer 208 according to the present application is positioned adjacent to the CdS layer 206. The device 200 also includes a diffusion barrier 210 and a glass substrate 212 . . .

Examples

[0043] (IV. Examples) The following examples are provided to illustrate the features of certain exemplary embodiments according to the present invention . Those skilled in the art will understand that the scope of the present invention is not limited to these specific features .

[0044] ​​​​​​​Example 1 In(NO3)3 (99.999%, Alfa-Aesar) and SnCl2 (99 .999%, Sigma-Alrich) with an Sn:In atomic ratio of 0.05 to 0.25 The solution was dissolved in 1000 ml of deionized water. The solution was then dropwise deposited on a SiO2 substrate and rotated at 3,000 RPM. The thin films were formed by spin coating at 200°C for 30 seconds. The film was subjected to heat treatment such as annealing at temperatures between 1000 and 1000°C. The film shows a very smooth surface. Figure 1 shows the X-ray reflectivity data for a film annealed at 550 °C for 1 h. The derived low surface roughness The surface roughness (RMS surface roughness = 0.4 nm) is characterized by Kiessig fringes extending to 2θ of 6o. This is visually confirmed by the presence of

[0045] The electrical resistivity of the films as a function of annealing temperature was measured. The lowest resistivity was ρ = 6 × 1 0 -4 ohm cm is the Sn concentration of 1 for a film annealed at 500oC in 5%H2 / Ar. Figure 4 shows the annealing results for ITO films annealed in 5% H2 / Ar. The effect of the Neel temperature is shown. The Hall mobility of one embodiment of the film according to the present invention is 21 cm 2 V -1 s -1 It was measured that the sputter I after annealing at 500 °C in 5% H2 / Ar It's similar to that of TO.

[0046] Films produced by this method and annealed at temperatures above 500°C have X-ray diffraction patterns as shown in Figure 5. It is crystalline as indicated by the presence of a turn peak. The films obtained for this purpose were 350 nm thick, and such films were The surface roughness is less than 1 nm as measured by X-ray reflectivity as shown in FIG. The data was confirmed.

[0047] The film produced by this method further exhibits a high light transmittance across the visible spectrum. . Figure 6 shows that the transmittance of the solution-deposited Sn:In2O3 was over 85% between 400 and 1000 nm, i.e., equivalent to or higher than that of a commercially available Sn:In2O3 film deposited by the vapor-phase sputtering method. This indicates that it was equal to or better than. (Example 2)

[0048] In(NO3)3 (99.999%, Alfa-Aesar) was dissolved in water, and an aqueous mixture of H2O2 and TiCl3 (20% w / v, Fisher) was added to produce a Ti:In atomic ratio of 0. 05:1 to 0.2:1. The 10% doped Ti:In2O3 film annealed at 500 °C for 1 hour had a resistivity of 2.1×10 ohm·cm or less, a thickness of 3 -3 00 nm to 1 μm, and a low RMS surface roughness of 0.5 nm. The film is crystalline at an annealing temperature of 500 °C or higher. The film has a low RMS surface roughness of 0.5 nm or less at a thickness in the range of 300 nm to 1 μm. The film is crystalline at an annealing temperature of 500 °C or higher.

[0049] (Example 3) Cd(NO3)2 (99.999%, Alfa-Aesar) was dissolved in water together with SnCl2 (99. 999%, Sigma-Alrich) and / or SnF2 (99.99%, Sig ma-Alrich). A normal solution was prepared at a Cd:Sn ratio of 2.5:1. The Cd2SnO4 film annealed at 500 °C for 1 hour had a resistivity of 17×10 -4 ohm ·cm or less and a high mobility of 35 cm 2 V -1 s -1 . The film has a low RMS surface roughness of less than 0.5 nm at a thickness in the range of 300 nm to 1 μm. The film has a low RMS surface roughness of less than 0.5 nm at a thickness in the range of 300 It is crystalline at an annealing temperature of 0 °C or higher.

[0050] Considering the many possible embodiments to which the principles of the disclosed invention can be applied, the illustrated embodiments are merely preferred examples of the invention and should not be regarded as limiting the scope of the invention. Rather, the scope of the invention is defined by the appended claims. Therefore, all that falls within the scope and concept of these claims is claimed as the invention. ​

Claims

1. An aqueous solution for solution treatment for forming a metal oxide film, wherein the solution contains indium salt, tin salt, titanium salt, cadmium salt or any combination thereof, and one or more of the metal salts have a purity of more than 99%, an aqueous solution for solution treatment for forming a metal oxide film.

2. The solution according to claim 1, wherein the metal salt is a nitrate or a halide.

3. The solution according to claim 2, wherein the metal salt is a chloride metal salt.

4. In(NO ３ ) ３ and SnCl ２ or SnF ２ at least one of, In(NO ３ ) ３ and TiCl ３ or, Cd(NO ２ ) ２ and at least one of SnCl ２ or SnF ２ ​ The solution according to claim 1, comprising

5. Sn:In ２ O ３ 、Ti:In ２ O ３ 、Cd ２ SnO ４ or combinations thereof A thin film produced from an aqueous solution obtained

6. A method for forming a conductive metal oxide thin film, comprising: preparing an aqueous solution containing a metal salt selected from indium salt, tin salt, titanium salt, cadmium salt or any combination thereof; coating the solution on a substrate to form a thin film; heating the substrate to form a conductive metal oxide thin film; A method for forming a conductive metal oxide thin film, comprising the above steps.

7. The method according to claim 6, wherein one or more of the metal salts have a purity of more than 99%.

8. The method according to claim 6, wherein one or more of the metal salts are nitrates or halides.

9. The method according to claim 6, wherein one or more of the metal salts are chloride In(NO ３ ) ３ and SnCl ２ or SnF ２ at least one of, In(NO ３ ) ３ and TiCl ３ or Cd(NO ３ ) ２ and at least one of SnCl ２ or SnF ２ ​ metal salts.

10. The aqueous solution contains The method according to claim 6, wherein the substrate is coated by spin coating, roll coating, spray coating, inkjet printing, mist deposition, die slot coating, dip 。 coating, doctor blade coating or any combination thereof. The metal oxide film is Sn:In ２ O ３ , Ti:In ２ O ３ , Cd ２ SnO ４ Or it

11. The method according to claim 6, comprising any combination of these.

12. A conductive metal thin film produced by the method according to claim 6, having an RMS roughness value of more than 0 nm and up to 3 nm.

13. The conductive metal thin film according to claim 13, having an RMS roughness value of 1 nm or less.

14. The conductive metal thin film according to claim 13, having a density of 80% to 100% of the theoretical single crystal density of the material. preparing an aqueous solution containing a metal salt having a purity of more than 99% selected from indium salt, tin salt, titanium salt, cadmium salt or any combination thereof; Spin coating, roll coating, spray coating, inkjet printing, mist deposition, die slot coating, dip coating, doctor blade coating, or a combination thereof to apply the solution to a substrate and form a thin film, a step of and, heating the substrate to form a conductive metal oxide thin film, and assembling a device comprising the substrate and the conductive metal oxide thin film, A method comprising:

17. The solution is In(NO ３ ) ３ and SnCl ２ or SnF ２ of at least one aqueous solution liquid, In(NO ３ ) ３ and an aqueous solution of TiCl ３ or, Cd(NO ３ ) ２ and SnCl ２ or SnF ２ of at least one aqueous solution liquid The method according to claim 16, comprising:

18. The metal oxide film is Sn:In ２ O ３ , Ti:In ２ O ３ , Cd ２ SnO ４ or it The method according to claim 16, comprising these combinations.

19. A device manufactured according to the method according to claim 16.

20. The device according to claim 19, wherein the device is a light emitting diode, a solar cell or a printed circuit. device.

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