JP5650057B2 - Transparent electrode substrate and manufacturing method thereof - Google Patents

Description

The present invention relates to a light-transmitting uneven substrate that can be suitably used as, for example, a thin film solar cell substrate, a touch panel substrate, or a photodetector substrate, and a method for manufacturing the same.

The spread of solar cells is rapidly expanding due to the introduction acceleration policy of each country. In particular, thin film solar cells that require less raw materials in order to achieve both cost reduction and high efficiency are attracting attention.

In order to form a thin film solar cell, it is indispensable to provide a transparent electrode in a part thereof. That is, a thin film solar cell is comprised from the structure containing 1 or more photoelectric conversion units between a transparent electrode and a back surface electrode. And light injects from the transparent electrode side. As the transparent electrode, for example, a conductive metal oxide such as tin oxide (SnO ₂ ), zinc oxide (ZnO), indium tin oxide (also referred to as ITO) is used, which is usually chemical vapor deposition (CVD). It is also formed by a method such as sputtering or vapor deposition.

The photoelectric conversion unit is formed of a semiconductor layer including a pn junction or a pin junction. When the photoelectric conversion unit includes a pin junction, the p-type layer, the i-type layer, and the n-type layer are stacked in this order or in reverse order, and the i-type photoelectric conversion layer that occupies the main part of the unit is amorphous. Those of quality are called amorphous photoelectric conversion units, and those of crystalline quality are called crystalline photoelectric conversion units.

As the semiconductor layer, an amorphous silicon layer or a crystalline silicon layer can be used as a silicon-based thin film, and a CIS-based film such as CuInSe ₂ (abbreviated CIS) or a CdTe-CdS-based thin film such as CdTe is used as a compound semiconductor thin film. Can be used. In the specification of the present application, the terms “crystalline” and “microcrystalline” mean those partially containing amorphous.

As a method for improving the conversion efficiency of a thin film solar cell, it is known that two or more photoelectric conversion units are stacked to form a stacked thin film solar cell. In this method, a front unit including a photoelectric conversion layer having a large energy band gap is disposed on the light incident side of the thin film solar cell, and a rear unit including a photoelectric conversion layer having a small band gap is disposed behind the front unit. Thus, photoelectric conversion over a wide wavelength range of incident light is enabled, and the conversion efficiency of the entire solar cell is improved. Among stacked thin film solar cells, a stack of an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit is called a hybrid thin film solar cell.

In the thin film solar cell as described above, the photoelectric conversion layer can be made thinner than the conventional solar cell using a bulk single crystal or polycrystalline silicon substrate, but the light absorption is limited by the film thickness. There is a problem of being. Therefore, in order to more effectively use the light incident on the photoelectric conversion unit including the photoelectric conversion layer, the transparent electrode or the glass substrate on the light incident side as viewed from the photoelectric conversion layer, or the metal layer on the back electrode side. The surface is finely textured (textured). That is, it is intended to increase the amount of light absorption by lengthening the optical path in the photoelectric conversion layer by scattering the light at the fine uneven interface and then entering the photoelectric conversion unit. This surface unevenness (surface texture) technology is also called “light confinement” technology, and is an important basic technology for practical use of a thin film solar cell having high photoelectric conversion efficiency.

The light confinement technology of a solar cell is generally based on a surface uneven structure of a transparent electrode (for example, see Patent Document 1) or a structure in which a glass substrate is made uneven by etching, sandblasting, or fine particle coating (for example, see Patent Documents 2 and 3). Since it is implemented and it is easy to produce uniform irregularities, fine particle coating is often used as a method for forming irregularities on a glass substrate. For example, in Patent Document 2, since the wavelength of the scattered light depends on the size of the unevenness, the particle size of the fine particles used for light confinement of the thin film solar cell is in the range of 0.2 to 1.5 μm. Similarly, Patent Document 3 discloses that the particle diameter of the light-transmitting fine particles is 10 to 100 nm.

JP 2003-253435 A Special Table 2002-529937 JP-A-2005-311292

When the present inventors produced a thin film solar cell using a glass substrate with projections and depressions corresponding to the substrate disclosed in Patent Document 2, an increase in power generation current of the thin film solar cell, that is, a short circuit current density (Jsc) due to the light confinement effect. However, at the same time, a decrease in open-circuit voltage (Voc) and fill factor (FF), which are thought to be caused by the unevenness, was observed, and as a result, a problem that the conversion efficiency of the thin-film solar cell was not improved was confirmed. Therefore, it can be said that there is room for improvement for a glass substrate in which surface irregularities are formed using fine particles.

An object of the present invention is to improve Jsc without lowering Voc and FF of a thin film solar cell caused by the unevenness of the substrate when, for example, the translucent uneven substrate according to the present invention is applied to the thin film solar cell. It is possible to provide a transparent electrode substrate that can improve the conversion efficiency of a thin film solar cell.

As a result of intensive studies based on the above problems, the inventors of the present invention have found that a small surface around a large fine particle does not adhere to the upper surface of the large fine particle on the base surface, which is one main surface of the translucent substrate. It has been found that the conversion efficiency of the thin-film solar cell is improved by fixing the fine particles, and the present invention has been completed.

That is, the first aspect of the present invention is a translucent uneven substrate having at least two kinds of large fine particles and small fine particles, each of which has a base layer fixed on a base surface which is one main surface of the substrate with a binder. A transparent electrode substrate having a transparent electrode layer laminated thereon, wherein the average particle size of the large fine particles is 0.4 μm to 1.5 μm in the transparent electrode substrate having the transparent electrode layer laminated on the underlayer. And the large fine particles are present in a single layer in the underlayer so that the particle coverage of the substrate is 10% or more and 80% or less, and the average particle size of the small fine particles is 50 nm or more and 150 nm or less, and Small particulates are present substantially adjacent to the periphery of the large particulate, and the amount of the small particulate present on top of the large particulate is relative to the amount of small particulate present elsewhere. It is related with a transparent electrode substrate characterized by being 20% or less.
That is, the translucent uneven substrate having at least two kinds of large fine particles and small fine particles, each fine particle having a base layer fixed on a base surface which is one main surface of the substrate with a binder, The average particle diameter of the fine particles is 0.4 μm or more and 1.5 μm or less, and the large fine particles are present in a single layer in the underlayer so that the particle coverage of the substrate is 10% or more and 80% or less. The average particle size of the fine particles is 50 nm or more and 150 nm or less, and the small fine particles are present substantially adjacent to the periphery of the large fine particles. Further, the amount of the small fine particles present on the large fine particles you equal to or less than 20% relative to the amount of small particles present in the parts.

A preferred embodiment relates to the transparent electrode substrate, wherein the light-transmitting concavo-convex substrate is composed of the same material for the large fine particles and the small fine particles .
That is, the large fine particles and the small fine particles are made of the same material .

In a preferred embodiment, the light-transmitting concavo-convex substrate has the small fine particles fixed to one main surface of the substrate opposite to the base surface, and one main surface of the substrate opposite to the base surface. In any one of the said transparent electrode substrates, The reflectance in 2 is below 2% .
That is, the small fine particles are also fixed to one main surface of the substrate opposite to the base surface, and the reflectance on the one main surface of the substrate opposite to the base surface is 2% or less. Features .

A second aspect of the present invention is the method for producing any one of the transparent electrode substrates, wherein when forming the light-transmitting concavo-convex substrate, a large fine particle is fixed on a base surface and then in a solution containing small fine particles. The present invention relates to a method for producing a transparent electrode substrate, wherein the substrate is dipped to fix small fine particles.
That is, in any one of the above methods for producing a light-transmitting uneven substrate, after fixing large particles on the ground of the substrate, the substrate is dipped in a solution containing small particles to fix the small particles. the shall be the feature.

A preferred embodiment relates to the method for producing a transparent electrode substrate, wherein when forming the translucent uneven substrate, the large fine particles are applied to a base surface by dipping and fixed.
That is, the coated large particles to the substrate surface by a dipping method, characterized in that fixed.

ADVANTAGE OF THE INVENTION According to this invention, the conversion efficiency of a thin film solar cell can be improved by using a translucent uneven substrate for a light-incidence side as a board | substrate for thin film solar cells, for example. In particular, in the light-transmitting uneven substrate according to the present invention, since the steep unevenness is relaxed, the main wavelength of sunlight is reduced without lowering Voc and FF of a thin film solar cell formed using the substrate. High diffuse transmittance and total light transmittance can be obtained in the region (400 to 1200 nm), and Jsc can be improved.

It is typical sectional drawing which shows a translucent uneven substrate and a single type thin film solar cell. It is typical sectional drawing which shows a translucent uneven substrate and a hybrid type thin film solar cell. It is a schematic diagram of a laser scribe. It is a SEM image of the board | substrate which dipped and apply | coated the small silica particle to the glass substrate in which the large silica particle was formed. It is a graph which shows the correlation of the unevenness | corrugation (Sq: root mean square) after film formation of a transparent electrode adjusted by changing the adhesion amount of a small microparticle, and the transmittance | permeability before and after film formation of a transparent electrode. It is a cross-sectional TEM image in which a glass substrate, fine particles, and a transparent electrode are sequentially laminated.

The present invention relates to a light-transmitting concavo-convex substrate, in which a base layer in which at least two kinds of specific fine particles of large particles and small particles are fixed with a binder is formed on a base surface which is one main surface of the substrate. is there. In the present invention, the above-mentioned base surface means one main surface of the substrate on the side where a transparent electrode, a photoelectric conversion layer and the like are continuously formed on the surface side.

The substrate that can be used for forming the translucent uneven substrate of the present invention is not particularly limited as long as it has so-called translucency. For example, a known glass plate or a plate-like member made of a transparent resin is used. Or a sheet-like member etc. can be used conveniently. In particular, it is preferable to use a glass substrate as the translucent substrate because it has high transmittance and is inexpensive. That is, when the translucent uneven substrate according to the present invention is used as a substrate for a thin film solar cell, the substrate is located on the light incident side of the thin film solar cell, so that more sunlight is transmitted to the photoelectric conversion layer. In order to absorb light, the substrate is preferably as transparent as possible.

The fine particles that can be used for forming the translucent uneven substrate of the present invention include, for example, silica (also referred to as SiO ₂ ), titanium oxide (also referred to as TiO ₂ ), aluminum oxide (also referred to as Al ₂ O ₃ ), and zirconium oxide. (Also referred to as ZrO ₂ ) and magnesium fluoride (also referred to as MgF ₂ ). The refractive index value of the fine particles is preferably from 1.4 to 2.5, more preferably from 1.4 to 2.0, from the viewpoint of translucency. Since the fine particles are preferably formed on the glass substrate, silica, which is the same material as the glass substrate, is more preferable from the viewpoint of reducing reflection at the interface between the glass substrate and the fine particles.

The average particle size of the large fine particles is preferably in the range of 0.4 μm to 1.5 μm, and more preferably in the range of 0.7 μm to 1.2 μm. On the other hand, the average particle diameter of the small fine particles is preferably in the range of 50 nm to 150 nm, more preferably in the range of 70 nm to 120 nm, from the viewpoint of being suitable for crystal growth of the transparent electrode formed on the large and small fine particle layer. When the average particle size of the small fine particles is larger than 150 nm, the light scattering effect due to the unevenness formed by the large fine particles may be canceled. On the other hand, when the average particle size of the small particles is smaller than 50 nm, the interaction between the particles becomes strong, and the dispersion state of the particles may be deteriorated, and handling difficulty may be increased when forming the underlayer on the substrate. There is concern about the problem of going up. The shape of the large and small fine particles is more preferably spherical in order to uniformly form as fine as possible unevenness.

In the present invention, the average particle diameter is an average of the diameters of each particle observed in a scanning electron microscope (also referred to as SEM) image and includes an error of ± 10%.

The underlayer of the light-transmitting uneven substrate according to the present invention includes at least two types of large particles and small particles, but includes, for example, three or more types of particles having an average particle size of an intermediate size. May be. In that case, the fine particles having the largest average particle size in the range of 0.4 μm or more and 1.5 μm or less are referred to as “large particles” in the present invention, and the fine particles having the smallest average particle size in the range of 50 nm to 150 nm are represented by the present invention. `` Small particles ''.
The large fine particles preferably have a substrate particle coverage of 10% to 80%, more preferably 20% to 60%. This is because outside this range, the effect of forming surface irregularities on the substrate is small, and sufficient diffuse transmittance cannot be obtained. The particle coverage referred to in the present invention is an area occupied by fine particles applied on the substrate surface with respect to the substrate surface. As a calculation method, it can be calculated from an image obtained by observing the substrate surface coated with fine particles from a direction perpendicular to the substrate surface. For example, in an image observed from a direction perpendicular to the substrate surface with a scanning electron microscope (also referred to as SEM), after removing background noise with SPIP manufactured by Image Metrology Co., Ltd., which is image analysis software, For example, the white portion corresponding to the portion is determined from the ratio of the entire image.

The large fine particles are preferably present as a single layer in the underlayer from the viewpoint of suppressing various problems caused by steep irregularities. For example, when large particles are coated using the dipping method, film formation or coating with a single layer of large particles can be achieved by adjusting the particle concentration (coating solution concentration) in the solution containing the large particles and the substrate lifting speed. The rate can be easily controlled.

In the present invention, the small fine particles are preferably present adjacent to the periphery of the substantially large fine particles. This is because the steep unevenness formed by the large fine particles can be relaxed by the small fine particles, and various problems caused by the steep unevenness can be suppressed. For example, when the translucent uneven substrate of the present invention is used as a substrate for a thin film solar cell, there is an effect of suppressing a decrease in Voc and FF of the thin film solar cell. Here, “adjacent” around a large fine particle means that a small fine particle exists within 100 nm from the large fine particle. Further, the fact that small particles are present substantially adjacent to the periphery of the large fine particles is a so-called case in which there are no small particles in the range within 20% of the diameter of the large fine particles from the periphery of the large fine particles. It means that the large fine particles present alone are 10% or less of the whole, preferably 5% or less.

In the present invention, the amount of small fine particles present above the large fine particles is preferably 20% or less, and preferably 5% or less, compared with the amount of small fine particles observed in other portions. More preferably, it is most preferable that none exist. This is because the effect of alleviating the steepness of irregularities due to the presence of small fine particles adjacent to the periphery of the large fine particles is reduced when the small fine particles are present above the large fine particles. In the present invention, the upper part of the large fine particles means a surface having a height of 85% or more when the height of the large fine particles from the substrate surface is used as a reference.

As for the above-described method for forming the underlayer, for example, small particles can be applied by dipping, so that the small particles can be adjacent to each other around the large particles. By adjusting the value, it is possible to prevent the small fine particles from existing on the large fine particles.

The large fine particles and the small fine particles are preferably formed from the same material. This is because the optical properties are the same for the same material, so that the light scattering amount can be easily designed.

In the method for producing a translucent uneven substrate according to the present invention, large fine particles are fixed in advance to a base surface which is one main surface of the substrate, and then small particles are applied by dipping and fixed to the base surface. Is preferred. This is because when a substrate on which large fine particles are fixed is pulled out of a dipping tank containing a solvent, a light-transmitting binder, and a solution containing small fine particles, the solvent applied to the substrate evaporates, and the large particles of the solvent are present. This is because the small particles existing in the solution tend to adhere to and be fixed around the large particles preferentially. From the viewpoint of ease of handling, the solvent is preferably an organic solvent such as isopropanol or methyl ethyl ketone, and the translucent binder is preferably a silicate such as ethyl silicate.

When applying small particles to the base surface on which large fine particles are fixed without applying to the surface opposite to the base surface, which is one main surface of the substrate on which large fine particles are fixed, It is preferable to mask with, for example. The masking material used is resistant to the solvent, and there is no particular limitation as long as no foreign material derived from the masking material's adhesive substance remains on the substrate when the masking material is removed. A high-density polyethylene protective sheet represented by company-made BE705 is preferred.

The method for adhering large fine particles to the substrate is preferably a method of applying a solution containing fine particles together with a translucent binder-forming material containing a solvent from the viewpoint of adhesion to the substrate. For example, a dipping method or a spin coating method. , Bar coating method, spray method, die coating method, roll coating method, flow coating method and the like. Especially, the dipping method which can adjust a particle | grain coverage easily by adjusting the pulling-up speed | rate of the board | substrate from a dipping tank is more preferable. In addition, the solvent similar to the above can be used for the solvent and translucent binder formation material which are contained in the said solution.

When adhering large fine particles to the substrate by dipping, it is necessary to mask the side opposite to the coating surface (base surface) with a film, etc., and the masking material used is resistant to solvents, and the masking material is removed. There is no particular limitation as long as no foreign substance derived from the adhesive material of the masking material remains on the substrate. Similarly to the above, a protective sheet represented by BE705 manufactured by Kaneron Chemical Industries, Ltd. is preferable.

For example, before depositing large fine particles on the substrate surface, it is desirable to clean the substrate in order to remove surface-attached carbon and glass burns and improve the fixed adhesion of the large fine particles. As a cleaning method in the case of using a glass substrate, for example, plasma cleaning, alkali cleaning, celico cleaning, and the like can be raised. From the viewpoint that no foreign matter remains on the surface of the glass substrate and the surface shape does not change, celico cleaning is particularly preferable. . The celico cleaning is a method of polishing and cleaning using a polishing slurry mainly composed of water and cerium oxide.

The steps from the cleaning of the substrate to the application of the large fine particles and the dipping application of the small fine particles are more preferably performed within a time during which the substrate cleaning effect is effective, and more preferably within 2 hours at room temperature in a clean room.

When adhering large fine particles to the glass substrate by dipping, masking is performed on one side of the glass substrate, the other side is washed and dried by air blow, and then the large fine particles are applied by dipping. Thereafter, it is preferable to heat and dry in order to attach large fine particles to the glass substrate in the short term. After heating and drying, after the glass substrate is sufficiently cooled, small particles are applied by dipping, and after removing the masking material, firing is performed by a known method to fix the particles on the lower ground of the substrate.

FIG. 1 is a schematic cross-sectional view of a thin-film solar cell which is one embodiment using the translucent uneven substrate of the present invention. This is a single-type thin film solar cell in which a large and small fine particle layer (underlayer) 2 containing a light-transmitting binder, a transparent electrode layer 3, an amorphous photoelectric conversion unit 4, and a back electrode layer 5 are sequentially laminated on a glass substrate 1. . The amorphous photoelectric conversion unit 4 includes a one conductivity type layer 41, an intrinsic amorphous photoelectric conversion layer 42, and a reverse conductivity type layer 43. The amorphous photoelectric conversion unit 4 can be formed by laminating semiconductor layers by plasma CVD, for example, in the order of pin type. Specifically, for example, a p-type amorphous silicon-based layer doped with 0.01 atomic% or more of boron, which is a conductivity-determining impurity atom, an intrinsic amorphous silicon-based layer that becomes a photoelectric conversion layer, and a conductivity-type determination An n-type amorphous silicon-based layer doped with 0.01 atomic% or more of phosphorus, which is an impurity atom, may be deposited in this order.

Examples of the material of the transparent electrode layer 3 on the large and small fine particle layer 2 include SnO ₂ , ZnO, ITO, and the like, and more preferably ZnO. This is because ZnO has high plasma resistance and can be formed at a low temperature such as a low-pressure thermal CVD method or a sputtering method, so that it can be expected to produce a high-performance thin-film solar cell at a low cost.

For example, when ZnO formed by low-pressure thermal CVD is used for the transparent electrode layer, the substrate temperature, which is the temperature of the underlying glass substrate, is 150 ° C. or higher, the pressure is 5-1000 Pa, and the source gas is diethyl zinc (also referred to as DEZ). ), Water, doping gas, and dilution gas.

As the back electrode layer 5, for example, at least one material selected from Al, Ag, Au, Cu, Pt, and Cr can be formed as at least one metal thin film by sputtering or vapor deposition. In addition, a conductive oxide layer such as ITO, SnO ₂ , or ZnO can be formed as a part of the back electrode layer 5 between one or more photoelectric conversion units. This conductive oxide layer increases the adhesion between one or more photoelectric conversion units and the back electrode layer 5, increases the light reflectance of the back electrode layer 5, and further prevents chemical changes in the photoelectric conversion unit. It has the function to do.

FIG. 2 is a schematic cross-sectional view of a thin film solar cell which is one embodiment using the translucent uneven substrate of the present invention. A tandem-type thin-film solar in which a large and small fine particle layer 2 containing a translucent binder, a transparent electrode layer 3, an amorphous photoelectric conversion unit 4, a crystalline photoelectric conversion unit 6, and a back electrode layer 5 are sequentially laminated on a glass substrate 1. It is a battery.

The crystalline photoelectric conversion unit 6 includes a one conductivity type layer 61, a crystalline intrinsic photoelectric conversion layer 62, and a reverse conductivity type layer 63. The crystalline photoelectric conversion unit 6 preferably has absorption in the main wavelength range of sunlight (400 to 1200 nm). For example, a crystalline silicon photoelectric conversion unit using a crystalline silicon thin film as a crystalline intrinsic photoelectric conversion layer. It may be 6. In addition to silicon, “silicon-based” materials can also include silicon alloy semiconductor materials containing silicon, such as silicon carbide and silicon germanium. In order to obtain a thin film solar cell with high conversion efficiency, an intermediate transparent reflection layer may be formed between the amorphous photoelectric conversion unit and the crystalline photoelectric conversion unit.

In addition, when manufacturing a large-area thin film solar cell capable of generating high output at a high voltage, in order to improve the yield, rather than connecting a plurality of thin film photoelectric conversion devices formed on a substrate in series with wiring. In general, a thin film photoelectric conversion unit layer formed on a large substrate is divided into a plurality of cells, and these cells are integrated in series by patterning, for example, an integrated structure as shown in FIG. Is preferred. For integration, it is convenient to use a laser scribe.

Moreover, the translucent uneven substrate which concerns on this invention can be suitably used also for other uses other than for thin film solar cells, such as a board | substrate for touch panels, a board | substrate for photodetectors, for example.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example, unless the meaning is exceeded.

Example 1
One side of a 4 mm thick white glass substrate manufactured by Asahi Glass Co., Ltd. is masked with a BE705 film manufactured by Kaneron Chemical Industries, Ltd., and the other surface is washed with celico to make the glass surface hydrophilic, and then 6 weights of silica fine particles Silica fine particles having an average particle diameter of 1080 nm were applied at a particle coverage of 20% by dipping under the conditions of% concentration and pulling speed of 100 mm / min. The number average particle diameter of the silica fine particles was determined from the SEM image. The components of the coating solution for dipping are isopropanol, water, ethylsilicate 40 hydrolyzate (average tetramer tetraethoxysilane hydrolyzed partial condensate) and concentrated hydrochloric acid in addition to silica fine particles. The weight of each component is 780 g of silica fine particles, 12 kg of isopropanol, 690 g of water, 240 g of ethyl silicate 40 hydrolyzate, and 24 g of concentrated hydrochloric acid.

After heating and drying in an atmosphere of 80 ° C. for 30 minutes, the substrate was immersed in a coating solution containing silica fine particles having an average particle size of 80 nm at a concentration of 1.5% by weight, and the pulling rate was 275 mm / min. Small silica particles as well as large particles were dipped again. The coating solution components are 12 kg isopropanol, 690 g water, 240 g ethyl silicate 40 hydrolyzate, and 24 g concentrated hydrochloric acid. Then, after removing the masking material, it was heated at 200 ° C. for 2 hours to fix the fine particles to the substrate.

When the surface of the obtained light-transmitting concavo-convex substrate was observed with an SEM, as shown in FIG. 4, adjacent to the periphery of large silica fine particles having an average particle diameter of 1080 nm, silica fine particles having an average particle diameter of 80 nm were substantially deposited. Has been fixed. Moreover, the small silica fine particles adhering to the upper part of the large silica fine particles having an average particle diameter of 1080 nm were within 1% as compared with other portions.

(Examples 2 to 4 and Comparative Example 1)
In the same manner as in Example 1, the pulling speed of the dipping method was changed to 275 mm / min and 1000 mm / min on a 4 mm thick glass substrate coated with large silica fine particles having a particle coverage of 20% and an average particle size of 1080 nm, respectively. Two samples prepared by dipping small silica particles having an average particle size of 80 nm were prepared (Examples 2 and 3), and one sample obtained by repeating dipping coating twice at a lifting speed of 1000 mm / min (Example 4). Produced. When dipping coating was repeated, heating and drying were performed for 30 minutes in an atmosphere at 80 ° C. between the first and second dipping coating. Further, as a comparative example 1, one sample was prepared in which silica fine particles having an average particle diameter of 80 nm were not applied. Water was dropped onto the fine particle layers of these four samples, a cover glass was applied, and the average transmittance from a glass substrate side on the surface opposite to the cover glass to a wavelength of 400 to 1200 nm was measured. In addition, the transmittance | permeability measured by dripping the liquid like this method on an uneven | corrugated | grooved part is hereafter described as immersion liquid transmittance | permeability.

In each of the four samples of Examples 2 to 4 and Comparative Example 1, a deposition temperature of 160 ° C., diethyl zinc (DEZ) and water as source gases, and diborane gas as a dopant gas were used. A transparent conductive film was formed by the CVD method. The sheet resistance of the transparent conductive film was about 18Ω / □. For the samples of Examples 2 to 4 and Comparative Example 1, in-plane roughness Sq (root mean square) was measured with a laser microscope, and immersion liquid transmittance was measured using a methylene iodide solution having a refractive index of 1.7. .

FIG. 5 is a plot when the immersion liquid permeability is taken as the vertical axis and the in-plane roughness (Sq) after forming the transparent electrode is taken along the horizontal axis. The white circle is before the transparent electrode is formed, and the black circle is made of the transparent electrode. The post-membrane is shown. By increasing the coating amount of silica fine particles with an average particle size of 80 nm (increasing the pulling speed in fine particle dipping coating with an average particle size of 80 nm), Sq is reduced by relaxing the irregularities formed with the fine particles with an average particle size of 1080 nm. Decrease. From FIG. 5, in the immersion liquid permeability before film formation of the transparent electrode indicated by white circles, no significant difference is observed depending on Sq. However, in the immersion liquid permeability after film formation of the transparent electrode indicated by black circles, the decrease in Sq An increase in immersion liquid permeability is observed.

(Reference Example 1)
FIG. 6 is a cross-sectional transmission electron microscope (also called TEM) image in which only a fine particle having an average particle diameter of 450 nm, which is a large fine particle, is coated on a glass substrate and a transparent conductive film of ZnO is formed. A cavity can be confirmed. Using 200 g of silica fine particles having an average particle diameter of 450 nm, a weight percent concentration of silica fine particles of 1.5%, isopropanol 12 kg, water 690 g, ethyl silicate 40 hydrolyzate (average tetramer tetraethoxysilane hydrolysis) (Partial condensate) A sample obtained by dipping a coating liquid containing 240 g and hydrochloric acid 24 g under the conditions of a pulling rate of 700 mm / min in the same manner as in Comparative Example 1 to form a transparent conductive film.

From FIG. 5 and FIG. 6, it is possible to fill the cavity after forming the transparent electrode between the large particles by filling the small particles between the large particles with the small particles, which improves the immersion liquid permeability. Conceivable.

(Examples 5 to 7 and Comparative Example 2)
As Examples 5 to 7 and Comparative Example 2, single-type thin film solar cells as shown in FIG. Each of the four transparent electrode substrates produced in Examples 2 to 4 and Comparative Example 1 is a p-type comprising a stack of a p-type microcrystalline silicon layer having a thickness of 10 nm and a p-type amorphous silicon carbide layer having a thickness of 15 nm. A photoelectric conversion unit was formed by sequentially stacking an i-type amorphous silicon photoelectric conversion layer having a thickness of 350 nm and an n-type microcrystalline silicon layer having a thickness of 15 nm by a plasma CVD method. Thereafter, 5 × 5 1 cm square metal masks were attached to the deposited silicon, and an Al-doped ZnO layer having a thickness of 90 nm and an Ag layer having a thickness of 200 nm were sequentially deposited by sputtering. After removing the metal mask, the periphery of the 1 cm square portion formed by sputtering was penetrated to the transparent electrode layer with solder to form a 1 cm square cell. The single-type thin film solar cell thus obtained was irradiated with AM1.5 light at a light quantity of 100 mW / cm ² to measure the output characteristics. The obtained output characteristic results are shown in Table 1.

Each physical property value of the thin-film solar cell is a relative value when each physical property of the sample (Comparative Example 2) having the in-plane roughness Sq = 0.4 is 1. By dipping small silica fine particles on a substrate with large silica fine particles, an increase in Voc and FF can be confirmed as compared with a substrate on which only large silica fine particles are adhered (Comparative Example 2). In addition, the increase in Jsc is caused by the fact that when ZnO is formed as a transparent electrode layer on a glass substrate coated with fine particles, the portion where no ZnO is formed between the large fine particles (cavities) is filled with small fine particles and the immersion liquid permeability is increased. This is probably because

(Example 9 and Comparative Example 3)
As Example 9 and Comparative Example 3, a hybrid thin film solar cell having an antireflection layer (AR coating) on the light incident surface of a glass substrate as shown in FIG. 2 was produced. That is, in Experimental Example 9 and Comparative Example 3, a large and small silica fine particle layer (underlayer) 2, a transparent electrode layer 3, an amorphous silicon photoelectric conversion unit 4, and a crystalline silicon photoelectric conversion unit are formed on a glass substrate 1. 6 and the back surface electrode layer 5 were sequentially formed to produce a hybrid thin film solar cell, and a hybrid thin film solar cell module was produced using laser scribing. Laser scribing was performed as shown in FIG.

In the same manner as in Example 1, a BE705 film made by Kaneron Chemical Industry Co., Ltd. was applied to one side of a 4 mm thick glass substrate, masked, and the other side was washed with serico, and then a large average particle size of 1080 nm was obtained by dipping. Silica fine particles were applied on one side with a particle coverage of 20%. After removing the masking material and heating and drying in an atmosphere of 80 ° C. for 30 minutes, the substrate was immersed in a coating solution containing 1.5% by weight of small silica fine particles having an average particle diameter of 80 nm, and the lifting speed was 275 mm / Dipping was applied under the condition of min. Fine particles having an average particle diameter of 80 nm were applied to both surfaces of the glass substrate and heated at 200 ° C. for 2 hours. In this way, an AR coat was formed on the light incident surface of the substrate. Thereafter, the transparent electrode layer 3 was formed on a large and small fine particle coated glass substrate by a low pressure thermal CVD method using a deposition temperature of 160 ° C., a source gas of diethyl zinc (DEZ), a water source gas, and diborane gas as a dopant gas. The sheet resistance of the transparent electrode layer 3 was about 18Ω / □.

The obtained transparent electrode layer uses a YAG (yttrium, aluminum, garnet) laser with a wavelength of 1064 nm to form a separation groove 101 in the transparent electrode layer 3, and thereafter, the substrate with the transparent electrode layer is washed and dried. It was.

A p-type layer composed of a p-type microcrystalline silicon layer having a thickness of 10 nm and a p-type amorphous silicon carbide layer having a thickness of 15 nm is formed on the laser-processed transparent electrode layer, and an i-type non-layer having a thickness of 300 nm. A crystalline silicon photoelectric conversion layer and a 15-nm-thick n-type microcrystalline silicon layer were sequentially laminated by a plasma CVD method to form a front photoelectric conversion unit. Further, a p-type microcrystalline silicon layer having a thickness of 15 nm, an i-type crystalline silicon photoelectric conversion layer having a thickness of 3.0 μm, and an n-type microcrystalline silicon layer having a thickness of 15 nm are sequentially stacked by plasma CVD to perform backward photoelectric conversion. Unit 7 was formed.

Then, the connection groove | channel 102 which penetrates the front photoelectric conversion unit 4 and the back photoelectric conversion unit 6 was formed using the 2nd harmonic (wavelength: 532 nm) of a YAG laser. After the connection groove 102 was formed, an Al-doped ZnO layer having a thickness of 90 nm and an Ag layer having a thickness of 200 nm were sequentially deposited as the back electrode layer 5 on the rear photoelectric conversion unit 6 by a sputtering method. At this time, the connection groove 102 was filled with the back electrode layer.

Finally, a separation groove 103 penetrating the front photoelectric conversion unit 4, the intermediate transmission reflection layer, the rear photoelectric conversion unit 6, and the back electrode layer 5 was formed using the second harmonic of the YAG laser. The thin film photoelectric conversion module of Experimental Example 9 obtained in this way was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² to measure the output characteristics.

Further, as Comparative Example 3, only silica fine particles having an average particle diameter of 1080 nm were applied to the underlayer at a particle coverage of 20%, and AR coating of silica fine particles having an average particle diameter of 80 nm was applied only to the light incident surface in the same manner as in Example 9. Formed with. Table 2 shows the results of manufacturing the thin-film solar cell module in the same manner as in Example 9 in the steps following the transparent electrode layer, and evaluating the same.

From Table 2, it is confirmed that Voc, FF, Jsc and Eff are increased by filling silica fine particles having an average particle diameter of 80 nm between fine particles having an average particle diameter of 1080 nm.

As described above, since the light-transmitting uneven substrate of the present invention relieves steep unevenness, when used as a substrate for a thin film solar cell, the main light of sunlight is not reduced without lowering Voc and FF. High diffuse transmittance and total light transmittance are obtained in the wavelength range (400 to 1200 nm), and excellent conversion efficiency is obtained.

1 Glass substrate 2 Large and small particle layer (underlayer)
DESCRIPTION OF SYMBOLS 3 Transparent electrode layer 4 Amorphous photoelectric conversion unit 41 One conductivity type layer 42 Intrinsic photoelectric conversion layer 43 Reverse conductivity type layer 5 Back surface electrode layer 6 Crystalline photoelectric conversion unit 61 One conductivity type layer 62 Intrinsic photoelectric conversion layer 63 Reverse conductivity type Layer 101 Separation groove 102 Connection groove 103 Separation groove

Claims (5)

A transparent electrode layer is laminated on a translucent uneven substrate containing at least two kinds of large fine particles and small fine particles, each fine particle being fixed on a base surface which is one main surface of the substrate with a binder. Transparent electrode substrate ,
In the transparent electrode substrate in which the transparent electrode layer is laminated on the base layer,
The average particle size of the large fine particles is 0.4 μm or more and 1.5 μm or less, and the large fine particles are present in a single layer in the underlayer so that the particle coverage of the substrate is 10% or more and 80% or less,
The average particle size of the small particles is 50 nm or more and 150 nm or less, and the small particles are substantially adjacent to the periphery of the large particles;
Further, the transparent electrode substrate is characterized in that the amount of the small particles present above the large particles is 20% or less with respect to the amount of the small particles present in other portions. The transparent electrode substrate according to claim 1, wherein the translucent uneven substrate is made of the same material as the large fine particles and the small fine particles. In the translucent uneven substrate, the small fine particles are also fixed to one main surface of the substrate opposite to the base surface, and the reflectance of the main surface of the substrate opposite to the base surface is 2 The transparent electrode substrate according to claim 1, wherein the transparent electrode substrate is% or less. The method for producing a transparent electrode substrate according to any one of claims 1 to 3, wherein in forming the light-transmitting uneven substrate, after fixing large fine particles to a base surface, in a solution containing small fine particles. A method for producing a transparent electrode substrate , wherein the substrate is dipped to fix small particles. The method for producing a transparent electrode substrate according to claim 4 , wherein when forming the translucent uneven substrate, the large fine particles are applied to a base surface by dipping and fixed.