ITO film and laminate

Abstract

Provided is an ITO film 1a in which the work function of a first surface 11 is different from the work function of a second surface 12.

Description

ITO film and laminate

[0001] The present invention relates to an ITO film and a laminate including the same.

[0002] Patent Document 1 discloses a technology for obtaining ITO (indium tin oxide) particles by adding an indium source and a tin source to a solution in which a hydroxide of a quaternary ammonium ion is dissolved in a reducing organic solvent, causing a reaction, and then heating the resulting mixture in an autoclave to mature it under autogenous pressure.

[0003] Patent No. 5706797

[0004] A first aspect of the present invention is an ITO film in which the work function of the first surface is different from the work function of the second surface.

[0005] A second aspect of the present invention is a laminate including the above-mentioned ITO film and an electron transport layer laminated so as to be in contact with the first surface of the ITO film.

[0006] A third aspect of the present invention is a laminate including the above-described ITO film and a hole transport layer laminated so as to be in contact with the second surface of the ITO film.

[0007] FIG. 1 is a conceptual diagram showing an example of an ITO film according to this embodiment. FIG. 2 is a conceptual diagram showing another example of an ITO film according to this embodiment. FIG. 3 is a conceptual diagram showing an example of a laminate according to this embodiment. FIG. 4 is a conceptual diagram showing an example of a solar cell using the laminate according to this embodiment. FIG. 5 is a conceptual diagram showing another example of a laminate according to this embodiment. FIG. 6 is a conceptual diagram showing an example of an EL device using the laminate according to this embodiment. FIG. 7 is a conceptual diagram showing another example of a laminate according to this embodiment. FIG. 8 is a conceptual diagram used to explain the manufacturing method in this embodiment.

[0008] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. In the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0009] <ITO film>

[0010] FIG. 1 is a conceptual diagram showing an example of an ITO film according to this embodiment.

[0011] In the ITO film 1a according to this embodiment, the difference between the work function of the first surface 11 and the work function of the second surface 12 is 0.1 eV or more. The work function of the first surface 11 of the ITO film 1a is greater than the work function of the second surface 12. By using this ITO film 1a, it is possible to omit an adjustment layer for adjusting the work function when forming a laminate for components such as electroluminescence (EL) devices and solar cells. Such components are formed by laminating layers such as an electron transport layer and a hole transport layer on a conductive ITO film as layers for donating and receiving electrons and holes. In this case, if there is a difference in work function between the two surfaces (front and back) of the ITO film, electrons can be efficiently donated and received.

[0012] The Sn concentration of the first surface 11 is preferably lower than the Sn concentration of the second surface 12. In an ITO film, when the content of doped tin is reduced, the ability to emit electrons tends to decrease, and therefore the work function can be relatively reduced.

[0013] The ITO film 1a may have a work function difference of 0.1 eV or more between the two surfaces 11 and 12. For example, the ITO film 1a may have a layer structure including a first layer with a high work function and a second layer with a low work function. The lower limit of the work function difference is preferably 0.1 eV, more preferably 0.2 eV, and even more preferably 0.3 eV. The upper limit is preferably 0.6 eV, more preferably 0.5 eV, and even more preferably 0.4 eV.

[0014] The work function here refers to the minimum energy required to extract electrons into a vacuum, and can be determined in accordance with ultraviolet photoelectron spectroscopy. In this embodiment, the work function can be increased by modifying the surface of the ITO particles using plasma or by controlling the charge distribution. Furthermore, the work function can be decreased by providing a thin metal layer in direct contact with the ITO film. Furthermore, the work function can be increased or decreased by controlling the Sn concentration in the ITO particles.

[0015] The ITO film 1a may have a distinct layer structure, with the first surface 11 as the first layer and the second surface as the second layer. Alternatively, the ITO film 1a may have a structure in which there is no distinct interface between the first and second surfaces, and the work function is gradient from the first surface to the second surface when viewed cross-sectionally. When such a work function gradient is present, the work function gradually decreases (or increases) within the film, thereby slowing the flow of electrons within the film. As a result, the conductivity of the ITO film 1a can be expected to be further improved.

[0016] The ITO film 1a can be manufactured by continuously depositing particles having different work functions, specifically by varying the mixing ratio of particles having different Sn concentrations.

[0017] Regarding the component composition of the ITO particles, the molar ratio of the Sn content to the In content (Sn / In) is not particularly limited, but from the viewpoints of crystal synthesis and conductivity, it is preferably 3.5 to 24, more preferably 3.7 to 23.5, and even more preferably 4 to 23.

[0018] It is preferable that the ITO particles contained in the ITO film 1a satisfy the relationship expressed by the following formula (1): 16×S / P ２ ≦0.330 (1) (wherein S represents the particle area in the TEM photograph, and P represents the circumferential length of the particle.)

[0019] The particle area S and perimeter P in formula (1) refer to the average values ​​of all ITO particles contained in the ITO film 1a, and do not refer only to the ITO particles on the first surface or only to the ITO particles on the second surface. The particle area S and perimeter P are the area and perimeter of a particle in a TEM photograph, and can be determined, for example, in accordance with the following method.

[0020] First, the TEM photograph of the ITO particles is processed using the image processing software "ImageJ 1.5K." For example, the image of the target is first captured and converted to an 8-bit grayscale, and then, in order to make the scale of one pixel correspond to the actual image, the number of nm per pixel is set using "Set Scale."

[0021] Next, to clarify the particle shapes, "Enhance Contrast" is used to set Saturated Pixels to approximately 20-40%. This value also affects the contrast of the entire image, so it should be adjusted as appropriate, but for example, the degree to which the particle outlines are clear can be used as a reference. Furthermore, binarization is performed using "Threshold" to separate the particle shapes from other parts, and an algorithm called "Moments" can be used to set the threshold.

[0022] Then, "Analyze Particles" was selected to measure the particle shape. Contamination and background noise can be eliminated by setting "Size (Pixels^2)" to 1000-Infinity during measurement. Focusing on "Area" and "Perim." from the obtained results, these can be used to represent the particle area S and the particle perimeter P in the TEM photograph, respectively.

[0023] The value of the particle area S in this embodiment is not particularly limited, and is, for example, 100 to 4500 nm ２ 200 to 4300 nm ２ The value of P is not particularly limited, and may be, for example, 100 to 1200 nm, or 120 to 1000 nm.

[0024] The upper limit of the value of the left side of formula (1) may be 0.330 or less, preferably 0.300 or less, more preferably 0.280 or less, even more preferably 0.260 or less, and even more preferably 0.250 or less. By being in this range, the particle shape can be a particle shape that is significantly deformed from a substantially rectangular parallelepiped shape. In addition, the lower limit of the value of the left side of formula (1) is not particularly limited, and may be greater than 0, for example, 0.040 or more, 0.060 or more, 0.070 or more, or 0.100 or more.

[0025] The ITO film 1a having ITO particles having the relationship expressed by formula (1) can be uniformly microparticulated and highly dispersible, and can also meet the requirements for use as a material for various transparent electrodes, etc., such as low resistance, high transmittance, and low turbidity (haze).

[0026] Conventional ITO particles are synthesized by the gel-sol method and have a roughly rectangular parallelepiped shape. In the gel-sol method, nucleation and growth reactions occur within the gel network, so ITO particles produced by the gel-sol method have a rectangular parallelepiped shape that reflects the crystalline phase and have high crystallinity.

[0027] When manufacturing a conductive film using conventional ITO particles with a roughly rectangular parallelepiped shape, if the ITO particles are arranged so that their surfaces are in contact with each other, the film's filling rate will theoretically be 100%. Therefore, it was thought that it would be preferable for ITO particles to approach a rectangular single-crystal structure. However, after extensive research, the inventors discovered that this does not actually occur, and that the particles are randomly packed, resulting in point or line contact between them. Such an arrangement results in fewer conductive paths and higher resistance when used as a transparent conductive film. Furthermore, poor dispersibility leads to agglomeration of particles, resulting in a lower filling rate and loss of film smoothness. The inventors believed that conventional ITO particles could be improved in this respect.

[0028] The inventors further investigated the macroscopic state of ITO particles. As a result, the ITO film 1a according to this embodiment can achieve the above-described effects by satisfying the relationship of formula (1). Although the exact function and effect is unclear, it is believed that this is because the maximum contact area is reduced while maintaining high crystallinity, resulting in good dispersibility in the liquid when the ITO film is made into a dispersion (however, the function and effect according to this embodiment are not limited to these).

[0029] FIG. 2 is a conceptual diagram showing another example of the ITO film according to this embodiment.

[0030] The ITO film 1b according to this embodiment includes an intermediate layer 13 containing ITO particles between the first surface 11 and the second surface 12, and the work function of the intermediate layer 13 is greater than the work function of the second surface 12 but less than the work function of the first surface 11. That is, there is a relationship expressed as work function of the first surface 11 > work function of the intermediate layer 13 > work function of the second surface 12. By providing such an intermediate layer 13, it is possible to suppress an increase in contact resistance between the ITO film and a layer in contact with it due to a sudden change in work function.

[0031] Unless otherwise specified, the same configuration as the ITO film 1a shown in FIG. 1 is permitted to be adopted for the parts common to the ITO film 1a shown in FIG. 1 without any special explanation below.

[0032] The ITO film 1b may have a three-layer structure including a first layer including the first surface 11, an intermediate layer 13, and a second layer including the second surface 14. Such a three-layer structure of ITO particles can suppress an increase in contact resistance between the ITO film and a layer in contact with it due to a sudden change in work function.

[0033] Intermediate layer 13 contains ITO particles, and the Sn concentration therein is preferably greater than the Sn concentration at second surface 12. This can improve the electron carrier concentration. Intermediate layer 13 may contain substances other than ITO particles, or may be a layer made only of ITO particles.

[0034] Furthermore, the concentration of Sn in the intermediate layer 13 is preferably lower than the concentration of Sn in the first surface 12. This can reduce the electron carrier concentration.

[0035] Furthermore, it is more preferable that the relationship expressed by Sn concentration at the first surface > Sn concentration in intermediate layer 13 > Sn concentration at the second surface be satisfied, which allows the work function to be gradually changed and makes it possible to suppress an increase in the contact resistance between the ITO film and layers in contact with it.

[0036] The ITO particles on each surface and layer with different work functions will be described below. The ITO particles on the first surface 11 have the lowest Sn concentration, the ITO particles on the second surface 12 have the highest Sn concentration, and the ITO particles in the intermediate layer 13 have an Sn concentration intermediate between that of the first surface 11 and the second surface 12.

[0037] The ITO films 1a and 1b according to this embodiment can have an electron transport layer or the like laminated on the first surface 11 side. Alternatively, a hole transport layer or the like can be laminated on the second surface. Furthermore, an electron transport layer or the like can be laminated on the first surface 11 side, and a hole transport layer or the like can be laminated on the second surface 12 side. In this way, the ITO films 1a and 1b according to this embodiment can be formed into a laminate with a high degree of freedom in configuration as an electronic component.

[0038] <Laminate>

[0039] FIG. 3 is a conceptual diagram showing an example of a laminate according to this embodiment.

[0040] The laminate 2 according to this embodiment includes the above-described ITO film 1b and an electron transport layer 14 laminated so as to be in contact with the first surface 11 of the ITO film 1b.

[0041] The electron transport layer 14 may be made of, for example, ZnO or TiO. ２ etc. can be used.

[0042] The laminate 2 is a member for which adjustment of the work function can be omitted, and can be suitably used as a member for solar cells.

[0043] FIG. 4 is a conceptual diagram showing an example of a solar cell using the laminate according to this embodiment.

[0044] In the solar cell A, a substrate layer 100 is formed on the ITO film 1b of the laminate 2, and an active layer 300, a hole transport layer 400, and an anode 500 are formed in this order on the electron transport layer 14 of the laminate 2. The ITO film 1b functions as a cathode.

[0045] Solar cell A receives light on the side of the light-transmitting substrate layer 100, and is excited when the light reaches the active layer 300. The electrons and holes generated therein are transported by the electron transport layer 14 and the hole transport layer 400, respectively, and extracted by the cathode (ITO film 1b) and the anode 500. Then, a current can be extracted from an external circuit (not shown) connected to the cathode (ITO film 1b) and the anode 500.

[0046] The substrate layer 100 is a light-transmitting substrate, and may be, for example, a glass substrate, or a film substrate such as a PET substrate or a PEN substrate.

[0047] The active layer 300 can be made of, for example, P3HT (poly(3-hexylthiophene-2,5-diyl)).

[0048] The hole transport layer 400 may be made of, for example, PEDOT:PSS.

[0049] The anode 500 can be made of a metal such as Al.

[0050] The solar cell A using the ITO film 1b can improve the conversion efficiency by reducing the contact resistance between the ITO film and the layer in contact with it.

[0051] FIG. 5 is a conceptual diagram showing another example of the laminate according to this embodiment.

[0052] The laminate 3 according to this embodiment includes the above-described ITO film 1b and a hole transport layer 15 laminated so as to be in contact with the second surface 12 of the ITO film 1b.

[0053] The hole transport layer 15 may be made of, for example, PEDOT:PSS.

[0054] The laminate 3 is a member for which adjustment of the work function can be omitted, and can be suitably used as a member for an EL device.

[0055] FIG. 6 is a conceptual diagram showing an example of an EL device using the laminate according to this embodiment.

[0056] In EL device B, a substrate layer 600 is formed on the ITO film 1b of the laminate 2, and a light-emitting layer 700, an electron transport layer 800, and a cathode 900 are formed in this order on the hole transport layer 15 of the laminate 2. The ITO film 1b functions as an anode. The anode (ITO film 1b) and the cathode 900 are connected to a driving power supply.

[0057] When a voltage is applied from a driving power source to the EL device B, the hole transport layer 15 and the electron transport layer 800 transport holes and electrons, respectively, which then combine in the light-emitting layer 700, thereby emitting light. The light from the light-emitting layer 700 is extracted through the light-transmitting substrate layer 100 and displayed externally.

[0058] The substrate layer 100 is a light-transmitting substrate, and may be, for example, a glass substrate, or a film substrate such as a PET substrate or a PEN substrate.

[0059] The light-emitting layer 700 may be made of, for example, tributyl phosphate (TBP), rubrene, DCM, or the like.

[0060] The electron transport layer 800 may be made of, for example, 2-[4-(9,10-Di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole.

[0061] The cathode 900 can be made of a metal such as Cu, Au, or Ti.

[0062] The EL device B using the ITO film 1b can improve the luminous efficiency by reducing the contact resistance between the ITO film and the layer in contact with it.

[0063] FIG. 7 is a conceptual diagram showing another example of the laminate according to this embodiment.

[0064] The laminate 4 according to this embodiment includes the above-described ITO film 1b, an electron transport layer 14 laminated so as to be in contact with the first surface 11 of the ITO film 1b, and a hole transport layer 15 laminated so as to be in contact with the second surface 12 of the ITO film 1b. The laminate 5 has a sandwich structure in which the ITO film 1b is sandwiched between two other layers.

[0065] Although a three-layer structure is shown here as an example, a multi-layer structure of three or more layers may also be used.

[0066] <Manufacturing Method> The ITO film and the laminate including the ITO film according to this embodiment can be manufactured by a method of sequentially forming ITO films with different work functions on a support layer that will become the electron transport layer 14 and the hole transport layer 15.

[0067] The method for forming the ITO film is not particularly limited, and examples thereof include vacuum deposition, laser deposition, sputtering, plasma CVD, thermal CVD, the sol-gel method, and film-forming methods using mist, spray, and aerosol coating and drying. Among these, film-forming techniques using coating and drying with a nanoparticle dispersion are preferred, from the viewpoint that they allow film formation at low temperatures and can be applied to flexible substrates that generally have a low heat resistance temperature, and among coating methods, mist-forming techniques are more preferred.

[0068] For example, when forming a film by coating and drying, a dispersion liquid in which ITO particles are dispersed in a solvent is supplied onto a support layer, and then the solvent contained in the dispersion liquid is dried, thereby forming an ITO film.

[0069] (Supplying Step) In the step of supplying the dispersion onto the support layer (supplying step), a method of applying or spraying a dispersion in which ITO particles are dispersed in a solvent can be employed.

[0070] The solvent for the dispersion is not particularly limited, but examples thereof include water, alcohols such as methanol, ethanol, and isopropyl alcohol, and mixed solvents thereof. Among these, water and alcohols are preferred, and water is more preferred. That is, the dispersion according to this embodiment can be suitably used as an aqueous dispersion.

[0071] The dispersion may contain other additives as required.

[0072] In particular, when ordinary ITO particles are dispersed in a solvent for a long period of time, a surfactant is required to prevent particle aggregation, but the dispersion liquid used in this embodiment can be a dispersion liquid in which ITO particles can be dispersed for a long period of time without adding a surfactant. Thus, the dispersion liquid according to this embodiment can be one that does not substantially contain a surfactant, i.e., a surfactant-free dispersion liquid.

[0073] The surfactant referred to here refers to a substance that has the function of adsorbing to the particle surface and making the particles dispersible in a dispersion medium, and specific examples include anionic surfactants, cationic surfactants, and nonionic surfactants.

[0074] In the dispersion, the ratio (volume ratio) of ITO particles to the solvent is not particularly limited, but is preferably 40% or less. By setting the ratio in this range, the ITO particles can be stably monodispersed for a long period of time.

[0075] The dispersion method is not particularly limited, and may be a stirring method using a stirrer or the like, or an ultrasonic dispersion method using an ultrasonic bath or the like, or these may be used in combination. Of these, it is preferable to use an ultrasonic bath.

[0076] The dispersion liquid may be applied directly onto the substrate layer, or may be sprayed onto the substrate layer in the form of a mist, and may be applied under atmospheric pressure, reduced pressure, or vacuum, but is preferably applied under atmospheric pressure from the viewpoint of simplicity.

[0077] For example, when manufacturing an ITO film as a conductive film, the ITO film is a material with high conductivity and transparency, and is widely used as a transparent conductive material. Methods for manufacturing ITO films include sputtering and laser deposition, but these techniques make it difficult to form a uniform thin film on a flexible substrate layer, and the performance of ITO, which has excellent surface properties, is not fully utilized. Furthermore, the deposition process requires a large-scale facility configuration, and there is room for improvement in this regard as well.

[0078] In this regard, according to the film formation method using a dispersion, the components of the dispersion do not settle and have high dispersibility, so simple coating techniques or mist techniques can be used when forming an ITO thin film on a substrate layer. Furthermore, restrictions on the substrate material can be relaxed, making it possible to form a film on the flexible type substrate described above. Furthermore, according to this embodiment, even when nano-level ITO particles (ITO nanoparticles) are used, high crystallinity and monodispersity can be stably maintained, so that surface properties such as conductivity and transparency of the thin film can be controlled at a high level.

[0079] The method for producing the mist is not particularly limited, and any method for producing the dispersion liquid in a mist (atom) state can be used. Any known method can be used to produce the mist, such as a pressurized method, a rotating disk method, an ultrasonic method, an electrostatic method, an orifice vibration method, or a steam method. In this embodiment, since the dispersion liquid is an ITO particle dispersion, a physical method for producing the mist is preferred. This facilitates control of the liquid temperature and droplet size. Furthermore, treating the dispersion liquid as a mist provides high controllability and eliminates problems such as distortion during thin film formation, which are common in methods such as the sol-gel method, which involves supplying a liquid.

[0080] In the mist formation, the mist of the dispersion liquid can be carried to the subsequent contact step by using a carrier gas, such as an inert gas such as argon, helium, or nitrogen.

[0081] The mist generation may further include a step of homogenizing the mist using a mist trap and a retention step of providing a retention period (retention portion) for the mist.

[0082] In addition, examples of the spraying method include ultrasonic spraying, mist CVD, a Sonia source method, a hot wall method, etc. These methods can be selected in consideration of the film thickness of the conductive film to be formed on the substrate layer, the size of the droplets to be sprayed, etc.

[0083] Furthermore, by applying or spraying the dispersion onto a masked support layer, fine patterns can be formed. This is particularly suitable for forming a thin film of ITO nanoparticles. This allows for highly accurate dimensional control. For example, when water is used as the solvent for the dispersion, it is preferable to use a water-repellent masking material (water-repellent film) as the masking material. This allows for even more accurate pattern formation.

[0084] (Drying Step) In the step of drying the dispersion liquid supplied onto the support layer (drying step), specifically, the solvent is vaporized by, for example, irradiation with infrared light or the like, heating, or the like, thereby forming a conductive film on the surface of the substrate. The heating temperature can be set taking into consideration the boiling point of the solvent, the softening point of the substrate, and other effects on the physical properties of the conductive film. The softening point of the substrate here refers to the temperature at which the substrate softens and begins to deform when heated, and can be determined, for example, by a test method in accordance with JIS K7191-1.

[0085] After the drying step, if necessary, a step of slowly cooling the substrate on which the conductive film has been formed (slow cooling step) or a UV irradiation step for the purpose of modifying the base material, such as imparting hydrophilicity, may be carried out.

[0086] Furthermore, in this embodiment, when ITO particles satisfying the above-described formula (1) are used, it is preferable to manufacture them by the following method, rather than the gel-sol method: That is, it is preferable that the manufacturing method includes: (a) a reaction step of obtaining ITO particles by reacting in a solution containing 0.09 to 0.9 M (M = mol / L) of an In salt, 0.01 to 0.2 M (M = mol / L) of an Sn salt, a basic compound, and a solvent at 190 to 200°C for 12 to 120 hours; and (b) a step of washing the ITO particles.

[0087] The concentration of the In salt in the reaction solution is preferably 0.09 to 0.9 M, and more preferably 0.09 to 0.45 M. The concentration of the Sn salt in the reaction solution is preferably 0.01 to 0.2 M, and more preferably 0.01 to 0.05 M.

[0088] The concentration of the In salt is preferably 4.5 to 9 times, and more preferably 5 to 9 times, the molar concentration of the Sn salt. By carrying out the particle synthesis reaction at such metal source concentrations, the ITO particles according to this embodiment can be synthesized more easily in one pot.

[0089] The In salt is not particularly limited, and any known In salt can be used as a raw material for ITO. For example, InCl ３ metal salts such as In ２ (C ２ O ４ ) ３ , In(NO ３ ) ３ , In ２ (SO ４ ) ３ and hydrates thereof. Among these, anhydrous salts and metal salts are preferred, metal salts are more preferred, and InCl ３ is more preferred.

[0090] The Sn salt is not particularly limited, and any known Sn salt as a raw material for ITO can be used. For example, SnCl ２ , SnCl ４ , Sn ２ (C ２ O ４ ) ３ , Sn(NO ３ ) ２ , SnSO ４ , InCl ３ metal salts such as In ２ (C ２ O ４ ) ３ , In(NO ３ ) ３ , In ２ (SO ４ ) ３ and hydrates thereof. Among these, anhydrous salts and metal salts are preferred, metal salts are more preferred, and SnCl ２ , SnCl ４ is more preferred.

[0091] The basic compound is not particularly limited as long as it can neutralize the reaction solution and precipitate an In—Sn hydroxide (neutralization coprecipitation). Known basic compounds can be used. Examples include tetramethylammonium hydroxide (TMAH) and sodium hydroxide.

[0092] The concentration of the basic compound in the reaction solution is not particularly limited, but is preferably 1 to 2 M, more preferably 1.5 to 1.7 M, from the viewpoint of particle synthesis.

[0093] The solvent may be any solvent capable of dissolving the In salt, Sn salt, basic compound, and other additives used as needed. Known solvents may be used, and preferred examples include water and alcohols such as methanol, ethanol, and isopropanol.

[0094] (a) In the reaction step, other additives may be added as needed within a range that does not impair the effects of this embodiment.

[0095] The reaction time in the (a) reaction step is preferably 12 to 120 hours, more preferably 24 to 72 hours.

[0096] (a) The reaction temperature in the reaction step is preferably 190 to 200°C.

[0097] The reaction step (a) may be carried out in an open system, but it is preferable to use an autoclave, which can promote the formation of an indium hydroxide-tin hydroxide coprecipitate in the reaction system.

[0098] The mechanism by which ITO particles satisfying the relationship expressed by formula (1) are obtained by the above-mentioned manufacturing method is unclear, but it is thought that factors such as controlling the concentration of metal salt in the reaction system (M = mol / L), reaction temperature, and reaction time may have an effect. While controlling the shape of monodispersed particles can be controlled by the number of nuclei generated in the system and the amount of substance present therein, it is thought that it is necessary to maintain the particles in the gel network and allow further heterogeneous nucleation to occur. Therefore, it is thought that it is best to increase the concentration of the metal source and use a small amount of base relative to the metal source. This allows the concentration of metal oxide precursor capable of nucleation to be maintained for a long period of time. It is thought that synthesis is possible by combining the above-mentioned conditions. (However, the effects of this embodiment are not limited to these.)

[0099] To produce ITO particles that satisfy the relationship expressed by formula (1), it is preferable to increase the concentration of the metal source and to use a relatively low base concentration relative to the metal source, which allows further heterogeneous nucleation to proceed on the generated nuclei rather than allowing particle growth after the initial nucleation reaction, thereby synthesizing ITO particles.

[0100] In this embodiment, a centrifugation step is preferably carried out between the (a) reaction step and the (b) washing step, and the centrifugation step is preferably carried out at 14,000 rpm for 10 minutes.

[0101] In the step (b) of washing the ITO particles, washing is preferably carried out using water, alcohols such as ethanol, etc. When washing with water, it is preferable to use distilled water or pure water such as ion-exchanged water (IEW). It is also preferable to wash the dispersion by treating it with an ultrasonic cleaner.

[0102] Generally, a freeze-drying step and a reduction-baking step are performed after the reaction step, but these steps can be omitted in this embodiment. From this perspective, it is particularly preferable not to perform the baking step after step (b). This prevents the ITO particles from agglomerating and maintains a monodispersed state in the dispersion medium.

[0103] FIG. 8 is a conceptual diagram illustrating the manufacturing method according to this embodiment.

[0104] 8 shows the fabrication of ITO films 2, 3, etc., with a work function gradient, on a support layer L. The support layer L can be the above-mentioned electron transport layer 14 (see FIG. 3) or hole transport layer 15 (see FIG. 4). The support layer L is transported from the bottom to the top in FIG. 8 (see arrow F).

[0105] Nozzles 1 to 5 sequentially apply a dispersion of ITO dispersed in water with Sn concentrations of 4%, 8%, 12%, 16%, and 20% to the support layer L. The application is performed in five stages with a gradient. After spraying a mist of the dispersion at each nozzle, the film may be subjected to a drying process each time to form a film, and then conveyed to the next nozzle. Alternatively, to achieve a smooth concentration gradient, after spraying a mist of the dispersion at each nozzle, the film may be conveyed to the next nozzle without being subjected to a drying process, and after spraying at the final nozzle 5, the film may be subjected to a drying process to form a film.

[0106] The conveyance direction is preferably from bottom to top, which allows dripping of the sprayed mist to be removed from the support layer L, thereby enabling a uniform film to be formed.

[0107] 1a, 1b... ITO film, 2, 3, 4... laminate, 11... first surface, 12... second surface, 13... intermediate layer, 14, 800... electron transport layer, 15, 400... hole transport layer, 100, 600... substrate layer, 300... active layer, 500... anode, 700... light-emitting layer, 900... cathode, A... solar cell, B... EL device, L... support layer

Claims

1. An ITO film, wherein the work function of a first surface is different from the work function of a second surface.

2. The ITO film according to claim 1, wherein the difference between the work function of the first surface and the work function of the second surface is 0.1 eV.

3. The ITO film according to claim 1 or 2, wherein the Sn concentration in the first surface is lower than the Sn concentration in the second surface.

4. The ITO film according to any one of claims 1 to 3, further comprising an intermediate layer containing ITO particles between the first surface and the second surface, wherein a work function of the intermediate layer is greater than a work function of the second surface and less than a work function of the first surface.

5. The ITO film according to claim 4, wherein the Sn concentration in the intermediate layer is greater than the Sn concentration in the second surface.

6. The ITO film according to any one of claims 1 to 5, wherein the ITO particles contained in the ITO film satisfy the relationship represented by the following formula (1): 16×S / P ２ ≦0.330 (1) (wherein S represents the particle area in the TEM photograph, and P represents the peripheral length of the particle.) 7. A laminate comprising: the ITO film according to any one of claims 1 to 6; and an electron transport layer laminated so as to be in contact with the first surface of the ITO film.

8. The laminate according to claim 7, further comprising a hole transport layer laminated in contact with the second surface of the ITO film.

9. A laminate comprising: the ITO film according to any one of claims 1 to 6; and a hole transport layer laminated so as to be in contact with the second surface of the ITO film.

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