JP5430251B2 - Substrate with transparent electrode and method for producing substrate with transparent electrode - Google Patents

Description

  The present invention mainly includes a transparent electrode and a back electrode of a solar cell, a transparent intermediate layer of a multi-junction solar cell, a touch panel, a PDP, an LCD, an electroluminescence (EL) display material, a low dielectric constant film used for a compound semiconductor high-speed device, a surface Elastic wave element, window glass coating for infrared cut, gas sensor, prism sheet using nonlinear optics, transparent magnetic material, optical recording element, optical switch, optical waveguide, optical splitter, photoacoustic material, high temperature heater The present invention relates to a substrate with a transparent electrode capable of achieving high environmental variability in a material such as a material and a method for manufacturing the same.

  As a transparent conductive layer, indium tin oxide (ITO), tin oxide, zinc oxide, and the like are widely used for substrates with transparent electrodes used for solar cells, touch panels, display materials, and the like. Such a transparent conductive layer is formed by a physical vapor deposition method (PVD method) such as magnetron sputtering method or molecular beam epitaxy method or a chemical vapor deposition method (CVD method) such as thermal CVD or plasma CVD, A method formed by an electroless method is known.

  Among them, ITO is a very excellent material as a transparent conductive material, and is currently widely used for a transparent conductive layer. However, there is a possibility that the raw material indium may be depleted, and there is an urgent need to search for a material that can replace ITO in terms of resources and cost.

  A representative example of a material replacing ITO is zinc oxide (ZnO). Non-patent document 1 describes that ZnO is excellent in transparency as compared with ITO, but is inferior in stability to moisture and heat.

  Patent Documents 1 and 2 describe a transparent electrode in which a group III or group IV atom is added to ZnO in addition to chromium or cobalt. In addition, Non-Patent Document 1 describes a mixed oxide of indium oxide and zinc oxide.

  As described above, ZnO as a substitute for ITO has been widely used for transparent conductive layers, but at present, materials superior to ITO, which is currently mainstream, have not been put into practical use.

JP 2002-75061 A JP 2002-75062 A

R. Martins, phys. stat. sol. , 202, 9, R95 (2005)

  An object of the present invention is to provide a substrate with a transparent electrode, which is mainly composed of zinc oxide, which has high durability against environmental fluctuations and is excellent in electrical conductivity, as a substitute for ITO.

  In order to solve the above problems, the present inventors have made extensive studies, and as a result, by adding hydrogen to the structure of zinc oxide in the transparent conductive layer mainly composed of zinc oxide, the conductivity is improved, In addition, it has been found that the environmental variability can be improved.

A method for producing a substrate with a transparent electrode having a transparent conductive oxide layer comprising zinc oxide as a main component and comprising at least one layer on a substrate, wherein the transparent conductive oxide layer is formed by sputtering utilizing plasma discharge. As a carrier gas for sputtering, argon and hydrogen are essential, and one or more selected from oxygen and carbon dioxide are added, and hydrogen is contained in 2 to 30 in all carrier gases. The manufacturing method of the board | substrate with a transparent electrode characterized by containing 1-30 volume% of volume%, oxygen, and / or a carbon dioxide.

Preferred embodiments in the transparent conductive oxide layer, aluminum, gallium, silicon, boron, one or more metals selected and manufacturing method of the transparent electrode-bearing substrate is doped from among niobium, the Doping is a method for producing a substrate with a transparent electrode, which is contained in an amount of 0.5 to 2.75% by weight based on the transparent conductive oxide layer.

In addition, the present invention is a substrate with a transparent electrode manufactured by the method for manufacturing a substrate with a transparent electrode described above, and the transparent conductive oxide layer is c-axis oriented with respect to the substrate when X-ray diffraction measurement is performed. A substrate with a transparent electrode, characterized by having a crystal structure as described above.

  According to the present invention, for example, a transparent conductive layer used for solar cells, a touch panel, an electroluminescent electrode substrate, and the like, which are particularly important elements, such as “conductivity”, “transparency”, and “environmental variability” are transparent. It becomes possible to provide a substrate with electrodes.

It is sectional explanatory drawing of the board | substrate with a transparent electrode which concerns on this invention.

  The present invention is a substrate with a transparent electrode having a transparent conductive oxide layer composed mainly of at least one layer of zinc oxide on a substrate, wherein the transparent conductive oxide layer is c-axis on the surface of the substrate. The transparent conductive oxide layer has an oriented crystal structure and is further doped with hydrogen.

  Zinc oxide is known to be a compound that easily takes a crystal structure even when a thin film is formed at a temperature near room temperature. For this reason, conventionally, aluminum or gallium, which can replace zinc atoms, has been used as a doping atom for improving conductivity. For example, Jpn. J. et al. Appl. Phys. , 24, L781 (1985) (Minami et al.) Discloses that gallium, in particular, exhibits good doping properties because its ionic radius is similar to zinc.

  On the other hand, if too many doping atoms are added, it becomes a carrier scattering source, which may greatly reduce the carrier mobility, and excessive doping atoms are likely to segregate as nonconductors near the surface of the crystal grains. Therefore, there is a possibility that the conductivity is lowered. Furthermore, by doping the above doping atoms, a small amount of electron transition occurs even in the visible light region, which may cause a decrease in transmittance.

  That is, as a method for improving the conductivity of the zinc oxide transparent conductive oxide, doping of impurities as described above is generally used, but there is a limit to the amount of doping of impurities. There is a possibility that the property is impaired. On the other hand, in the present invention, by doping hydrogen into the transparent conductive oxide layer mainly composed of zinc oxide, carrier injection exceeding the case of using the above-described impurities (conventional doping atoms), It has been found that the conductivity can be improved.

  For example, in the literature (Chris G., Physical Review Letters, Vol. 85, No. 5 (2000)), the formation energy of a zinc-hydrogen bond based on the first principle calculation is discussed. However, the above document does not disclose the conductivity and transparency. For example, even when only hydrogen is doped and sputtered, the film-forming zinc is reduced, and the produced film tends to be black. .

  Therefore, the present invention has found that by using oxygen and / or carbon dioxide simultaneously with hydrogen during the doping, the conductivity can be improved by injecting carriers while suppressing the reduction of zinc.

  For example, it has been reported in literature (Youn-Seon Kang, Journal of The Electrochemical Society, Vol. 147 (12), 4625 (2000)) about film formation by magnetron sputtering and improvement of electrical conductivity by high-speed annealing treatment. However, since this method requires annealing at a high temperature of 500 ° C., the types of substrates that can be used are limited. For example, plastic substrates cannot be used. In addition, for example, even when a film is formed on a laminated film, it cannot be used for a substrate that may be reacted or altered by high-temperature treatment.

  On the other hand, in the present invention, since the highly conductive hydrogen-doped zinc oxide transparent conductive oxide layer can be formed at room temperature, the above-described problems due to the high temperature treatment do not occur. It is expected that the form of hydrogen introduction during film formation will differ depending on the difference between the necessity of high temperature treatment in the above document and the present invention. That is, in the present invention, hydrogen is already introduced in an active state as a donor at the time of film formation, whereas in the above document, it is considered that hydrogen is activated only by annealing.

  For example, the patent document (WO2005 / 078154) describes the production of a zinc oxide transparent electrode by a CVD (MOCVD) method using an organic zinc compound as a raw material, and reacts the raw material in gaseous form with hydrogen gas simultaneously. It is described that it is introduced into the system. Hydrogen used here is introduced for the purpose of maintaining the reaction system at a high temperature, preventing the source gas from liquefying, and uniformly diffusing a doping gas such as diborane gas into the reaction system. Is not atomically decomposed and activated as a dopant in zinc oxide. On the other hand, in this invention, it becomes possible to inject | pour as a dopant in zinc oxide by decomposing | disassembling hydrogen into atomic form in plasma.

  Hereinafter, typical embodiments of the substrate with a transparent electrode according to the present invention will be described. FIG. 1 is a cross-sectional view of a substrate with a transparent electrode according to the present invention. A zinc oxide transparent conductive oxide layer 2 is formed on the substrate 1 (FIG. 1).

  About the said base material 1, when using as a base material of a transparent electrode, what is necessary is just a board | substrate transparent at least in visible region, and a hard or soft material is not specifically limited. What is necessary is just to use properly by a use.

  As a hard material used for the base material, for example, glass, sapphire, or the like can be used. Specific examples of the glass include alkali glass, borosilicate glass, and non-alkali glass. The thickness of the substrate when glass or sapphire is used can be arbitrarily selected depending on the purpose of use. However, when the balance between handleability and weight is taken into account, a preferable thickness range is 0.5 mm to 4.5 mm. In general, if it is too thin, the strength is insufficient, so that it tends to break easily due to impact. On the other hand, if the thickness is too thick, the weight becomes heavy and the thickness of the device is affected. Therefore, it tends to be difficult to use the portable device, and it may not be preferable in terms of transparency and cost.

  On the other hand, examples of the soft material used for the substrate include thermoplastic resins and thermosetting resins. Examples of the thermoplastic resin include acrylic resin, polyester, polycarbonate resin, polyolefin, cycloolefin polymer, and examples of the thermosetting resin include polyurethane. Among these, a substrate mainly composed of a cycloolefin polymer (COP) having particularly excellent optical isotropy and water vapor blocking properties is preferable. The thickness of the base material when these soft materials are used is preferably in the range of 0.03 mm to 3.0 mm. Generally, if the thickness is too thin, handling becomes difficult and the strength may be insufficient. On the other hand, if the thickness is too thick, there is a problem in transparency and cost, and the thickness of the device increases, so that it tends to be difficult to use for portable devices.

  Examples of the COP include norbornene polymers, copolymers of norbornene and olefins, and polymers of unsaturated alicyclic hydrocarbons such as cyclopentadiene. From the viewpoint of water vapor barrier properties, it is preferable that the main chain and side chain of the constituent molecules do not contain a functional group having a large polarity, such as a carbonyl group or a hydroxyl group. In addition, from the viewpoint of excellent heat resistance, polyethylene naphthalate (PEN), polyethersulfone (PES), and the like can also be used.

  For example, when the transparent conductive oxide layer is used as an intermediate layer in a solar cell or an EL device, the photoelectric conversion layer or the light emitting layer is used as a base material, and the zinc oxide according to the present invention is a main component thereon. A transparent conductive oxide layer can be formed. As the photoelectric conversion layer in this case, for example, a layer made of amorphous or crystalline silicon or a multi-component compound semiconductor can be used. As the light emitting layer, for example, an organometallic complex having aluminum or rare earth atom as a metal center can be used.

  The transparent conductive oxide layer 2 containing zinc oxide as a main component in the present invention is characterized by containing hydrogen as a dopant. Although details of the hydrogen-containing state in the transparent conductive oxide layer are unknown, a zinc-hydrogen bond state, a zinc-hydrogen-oxygen bond state, an oxygen-hydrogen bond state, and the like are conceivable.

The presence or absence of hydrogen in the transparent conductive oxide layer can be specified by X-ray photoelectron spectroscopy, for example, while observing the binding energy of oxygen on the surface, but can be quantified by Rutherford backscattering method. Most preferred. As an easier method, there is a method of confirming a peak in the region of about 3000 to 3500 cm ⁻¹ by measuring an infrared absorption spectrum.

  The method of doping hydrogen into the transparent conductive oxide layer can be achieved by introducing hydrogen into the sputtering carrier gas. Hydrogen may be the lightest atom, and it is difficult to perform sputtering using only hydrogen as a carrier gas. Furthermore, when sputtering is performed only with argon / hydrogen, the amount of oxygen in the transparent conductive oxide layer is remarkably reduced, the film tends to become black, and the conductivity also deteriorates, so that it does not function as a substrate with a transparent electrode. . In the present invention, the above problem can be overcome by adding oxygen and / or carbon dioxide to argon / hydrogen, which is essential as a carrier gas.

  Furthermore, in the present invention, hydrogen is 2 to 30% by volume, preferably 4 to 10% by volume, and oxygen and / or carbon dioxide is 1 to 30% by volume, preferably 8 to 15% in total in the total carrier gas. It has been found that a substrate with a transparent electrode that is excellent in transparency and conductivity can be produced by containing a volume% (note that argon is 40 to 97 volume%, preferably 75 to 88 volume%). It was. According to the present invention, the transparency in the visible light region is improved. This is because the band gap is shifted to the short wavelength side due to the Bernstein-Moss shift that occurs because hydrogen is injected as a conductive carrier. From this, it is considered that the absorption component decreased. From the above gas range, when there is too much hydrogen, the transparent conductive oxide layer tends to be black. Moreover, when there is too much oxygen, electroconductive oxygen deficiency is also filled and there exists a possibility that electroconductivity may fall. When there is too much carbon dioxide, the oxygen deficiency is eliminated as in the case of oxygen, so that the conductivity may be lowered.

  Sputtering in the present invention can be favorably doped with hydrogen by utilizing plasma discharge. A DC power source or a high frequency power source can be used as a power source for causing plasma discharge. Although the pressure in the system at the time of discharge depends on the exhaust speed of the reaction vessel and the exhaust pump, it is preferably 0.001 Pa to 100 Pa, and more preferably 0.01 Pa to 10 Pa. If the pressure is too high or too low, the discharge tends to be unstable. In sputtering, the gas may be continuously introduced or intermittently introduced, but the argon gas that is an inert gas is preferably continuous in order to stabilize the discharge. Hydrogen, oxygen, and carbon dioxide may be continuous or intermittent.

  The transparent conductive oxide layer 2 mainly composed of zinc oxide in the present invention is preferably oriented in the c-axis with respect to the substrate. This makes it possible to form a zinc oxide transparent conductive oxide layer having a surface that faithfully reproduces the shape of the substrate. The orientation of the crystal can be easily evaluated by performing X-ray diffraction measurement. The c-axis oriented zinc oxide transparent conductive oxide layer exhibits a (0002) oriented peak at 2θ of 33 to 35 degrees. It is estimated that this 2θ shift varies depending on the type and amount of the doping agent.

  In the transparent conductive oxide layer 2 containing zinc oxide as a main component in the present invention, a metal dopant can be added. Examples of the metal dopant to be added include one or more metals selected from aluminum, gallium, silicon, boron, and niobium. These metal dopants may be directly injected into zinc oxide, but it is easier to add them as oxides. Furthermore, it is preferable that the maximum oxidation number is shown regarding the said oxide. For example, niobium has stable oxidation numbers of I, II, and V, but the I value and II value are not preferable from the viewpoint of transparency, and the V value is more preferable. The content of these metal dopants is preferably 0.50 to 2.75% by weight with respect to zinc oxide, and more preferably 0.8 to 2.2% by weight. When there is too much addition amount of a metal dopant, electroconductivity may become a remarkably low thing. It can be explained that when the amount of the metal dopant is increased, the segregation of the dopant at the crystal grain boundary of zinc oxide is increased, and the carrier is less likely to move between the zinc oxide crystal grains.

  The main component in the “transparent conductive oxide layer mainly composed of zinc oxide” of the present invention includes a dopant and the like as a subcomponent other than the main zinc oxide in the transparent conductive oxide layer. It is “having zinc oxide as a main component” and it is sufficient that zinc oxide is contained in an amount of 90% by weight or more.

  The transparent conductive oxide layer 2 according to the present invention can be formed by, for example, a magnetron sputtering method. A target material used for magnetron sputtering can be manufactured by sintering a mixture of an oxide mainly composed of zinc oxide and a dopant and bonding the sintered material to a backing plate by hot pressing or the like. Examples of the dopant here include aluminum oxide, gallium oxide, silicon oxide, boron oxide, and niobium oxide. The amount of dopant mixed with zinc oxide is preferably 0.50 to 2.75% by weight, more preferably 0.8 to 2.2% by weight.

As a power source for magnetron sputtering, a direct current power source or a high frequency power source (RF, VHF) or the like can be used. Power density was 3.5 W / cm ² or more, further it is possible to manufacture the substrate of the present invention by 4W / cm ² or more. It power density is more preferably ^{4W / cm 2 ~15W / cm 2} , particularly more preferably ^{4.5W / cm 2 ~15W / cm 2} , is among others 5W / cm ² ~13W / cm ² Is particularly preferred. If the power density is lower than this, the film-forming speed is not improved, and it is expected to be a problem of crystallinity, but the reliability in a high-temperature and high-humidity environment may not be good. On the other hand, if the power density is too high, the transparent conductive oxide layer is re-sputtered by oxygen ions generated in the plasma, which may result in a substrate with a transparent electrode having poor transparency and conductivity. is there.

  The substrate with a transparent electrode in the present invention may be subjected to hydrogen plasma treatment after forming the transparent conductive oxide layer 2 in order to increase conductivity. By the hydrogen plasma treatment, oxygen defects that greatly contribute to the conductivity of the transparent conductive oxide mainly composed of zinc oxide are formed, and the conductivity is improved.

  In addition, a substrate with a transparent electrode formed on a glass substrate or a soft material having a high softening (melting) temperature can be annealed to increase conductivity and light transmittance. The annealing atmosphere is preferably a vacuum or an inert gas stream. When annealed in an oxygen atmosphere, the transparent conductive oxide may be thermally oxidized and the conductivity may be reduced. The annealing temperature is not less than the temperature at which the crystallinity of zinc oxide is improved, and is preferably not more than the melting temperature of the substrate. Specifically, a good substrate with a transparent electrode is produced by annealing at about 200 to 450 ° C. be able to.

  The film thickness of the transparent conductive oxide layer 2 is preferably 15 to 500 nm, more preferably 20 to 200 nm. By using a transparent conductive oxide layer having a thickness in this range, a substrate with a transparent electrode having both high transparency and conductivity can be produced. When the film thickness is reduced, in the case of film formation by magnetron sputtering, the transparent conductive oxide may be striped and may not be a film. On the other hand, when the film thickness is increased, light absorption by the transparent conductive oxide increases and the transmittance decreases, and cracks tend to occur in the transparent conductive oxide layer due to stress.

  Any method can be used for detecting the doping amount contained in the transparent conductive oxide layer 2 as long as it is a method usually used for elemental analysis. For example, atomic absorption analysis or fluorescent X-ray analysis is possible. Elemental analysis means such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, electron beam microanalyzer, and other methods such as secondary ion mass spectrometry can be used.

  The surface resistance of the substrate with a transparent electrode to be produced varies depending on the intended use, but can be favorably used in the range of 10 to 2000 Ω / □. For example, in the case of a solar cell or an EL element, about 10 to 20 Ω / □ is preferable, and in the case of a touch panel or the like, about 200 to 2000 Ω / □ is preferable.

  In the substrate with a transparent electrode in the present invention, an optical design layer may be provided between the substrate 1 and the transparent conductive oxide layer 2 or on the surface of the transparent conductive oxide layer 2 for the purpose of improving the light transmittance. Specifically, a high refractive index layer such as titanium oxide, hafnium oxide or niobium oxide and a low refractive index layer such as silicon dioxide are provided between the substrate 1 and the transparent conductive oxide layer 2 as “substrate 1 / By laminating like “high refractive index layer / low refractive index layer / transparent conductive oxide layer 2”, reflection of light at the interface from the substrate to the transparent conductive oxide layer is suppressed, and as a result Light transmittance can be improved.

  In the case of providing on the transparent conductive oxide layer 2, the effect of suppressing the reflection of light is large when a layer having a lower refractive index than that of the transparent conductive oxide layer is formed. Specifically, a mixture of poly (3,4-ethylenedioxythiophene (PEDOT), polystyrene sulfonate (PSS), etc. Other than that, a conductive porous carbon material can also be used.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  In the present invention, a scanning electron microscope JSM-6390-LA (manufactured by JEOL Ltd.) was used for the doping amount measurement. For the surface resistance measurement, a resistivity meter Loresta GP MCT-610 (manufactured by Mitsubishi Chemical Corporation) was used. The film thickness of the transparent conductive oxide layer was a spectroscopic ellipsometer VASE (manufactured by JA Woollam). Fitting was performed using the Chaucy model. The light transmittance at a wavelength of 550 nm was measured using an integrating sphere light transmittance measuring device (device name U-4100, manufactured by Hitachi High-Technologies Corporation). The carrier concentration was determined by measuring the Hall effect according to the van der Pauw method.

(Examples 1-9, Comparative Examples 1-3)
A transparent conductive oxide layer was magnetron-sputtered on alkali-free glass (trade name OA-10, film thickness 0.7 mm, manufactured by Nippon Electric Glass Co., Ltd.). The target material, the carrier gas type, and the flow rate were set to the conditions shown in Table 1, and the film was formed to a film thickness of 100 nm under the conditions that the substrate temperature was room temperature and the film forming pressure was 0.2 Pa.

  Table 2 shows the sheet resistance of the substrate with a transparent electrode thus formed, the light transmittance at a wavelength of 550 nm, and the carrier concentration. However, in Comparative Example 3, reduction of zinc by hydrogen occurred, and the formed film turned black, and a transparent electrode could not be formed.

  As a result of X-ray diffraction analysis of Examples 1 to 9 and Comparative Examples 1 and 2, a peak indicating (0002) orientation (c-axis orientation) of zinc oxide was confirmed.

  From the above results, it was found that the conductivity of the transparent electrode can be improved by doping hydrogen into the zinc oxide transparent conductive oxide. Furthermore, even when the film was formed at room temperature, an increase in the carrier concentration was confirmed, and it was found that hydrogen was active as a carrier.

1. Substrate 2. Transparent conductive oxide layer

Claims (4)

A method for producing a substrate with a transparent electrode having a transparent conductive oxide layer mainly composed of zinc oxide consisting of at least one layer on a substrate,
Is film formation by sputtering before Symbol transparent conductive oxide layer using a plasma discharge, as and carrier gas during sputtering, argon and hydrogen as essential, was added one or more selected further oxygen, carbon dioxide What is claimed is: 1. A method for producing a substrate with a transparent electrode, characterized in that the total carrier gas contains 2 to 30% by volume of hydrogen and 1 to 30% by volume of oxygen and / or carbon dioxide. During the transparent conductive oxide layer, aluminum, gallium, silicon, boron, transparent electrode-bearing substrate manufacturing method according to 請 Motomeko 1 1 or more metals selected from among niobium that are doped. The method for producing a substrate with a transparent electrode according to claim 2, wherein the doping is contained in an amount of 0.5 to 2.75 wt% with respect to the transparent conductive oxide layer. A substrate with a transparent electrode manufactured by the method for manufacturing a substrate with a transparent electrode according to claim 1,
The substrate with a transparent electrode, wherein the transparent conductive oxide layer has a crystal structure with c-axis orientation with respect to a base material when X-ray diffraction measurement is performed.

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