JP2003298086A - Solar cell and its fabricating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a texture structure contributive to enhancement of conversion efficiency of a solar cell inexpensively with high reproducibility. <P>SOLUTION: The solar cell comprises a texture layer 3 having a texture structure on the upper surface thereof, a lower electrode 4, a photoelectric conversion layer 5 and an upper electrode 6 formed sequentially on a substrate 2 of flexible film wherein the texture structure has protrusions and recesses arranged regularly. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solar cell having a structure in which a photoelectric conversion layer is provided on a substrate and a method for manufacturing the solar cell.

[0002]

2. Description of the Related Art Solar cells are used in various electronic devices as a power source to replace dry cells and the like. In particular, low-power electronic devices such as electronic desk calculators, clocks, portable electronic devices (cameras, mobile phones, consumer radar detectors), remote controllers, etc. can be sufficiently driven by the electromotive force of the solar cell, and It has attracted attention because it requires no replacement and can be operated semi-permanently, and is environmentally clean.

The structure of a solar cell is generally one in which a lower electrode made of metal, a photoelectric conversion layer and a transparent electrode are provided in this order on the surface of a rigid or flexible substrate. A Si layer formed by a plasma CVD method is generally used as the photoelectric conversion layer. An organic flexible substrate is often used as the substrate. The organic flexible substrate has flexibility and can be wound and developed, and therefore has the following advantages in production. When manufacturing a solar cell, a step of stacking a functional thin film such as a photoelectric conversion layer or an electrode layer by a vacuum process, a wiring electrode or an interlayer insulating film is patterned on the functional thin film surface by a screen printing method or the like. A step of forming, a step of providing a protective layer on the outermost surface of the solar cell, etc. are provided. In each of these processes, if the long organic flexible substrate is used in roll-to-roll, that is, in the process of unwinding the long organic flexible substrate from the unwinding roll and winding it up to the winding roll, the function is performed on the substrate. By forming a thin film, an electrode, an insulating film, or the like, the tact time can be shortened, the substrate need not be carried, and the substrate can be easily handled, and the throughput can be improved. Further, similar effects can be obtained even when the integration degree of solar cells is improved and large-scale mass production is aimed at.

In the solar cell, in order to improve efficiency, attempts have been made to improve the conversion efficiency of the photoelectric conversion layer itself and to increase the amount of light incident on the photoelectric conversion layer. Specifically, a so-called texture structure exhibiting a light diffusion effect is provided on the surface of the substrate facing the photoelectric conversion layer.

Factors that hinder the high efficiency of solar cells include:
(1) Loss due to reflection of sunlight on the surface of the photoelectric conversion layer, and (2) loss due to incomplete collection of light incident on the photoelectric conversion layer. Regarding (1), it is improved by the texture structure of the light incident side surface of the photoelectric conversion layer,
Regarding (2), it is improved by the texture structure of the lower electrode surface and the photoelectric conversion layer surface. For example, when fine pyramidal unevenness is formed as a texture structure on the substrate surface, this unevenness is reflected on the surface properties of the lower electrode and the photoelectric conversion layer. Therefore, light that reaches the uneven surface of the photoelectric conversion layer from the outside and is reflected by the inclined surface of the unevenness hits the other inclined surface of the unevenness, enters the photoelectric conversion layer, and is absorbed by the photoelectric conversion layer. In addition, among the incident light, the light that reaches the back surface of the photoelectric conversion layer without being absorbed by the photoelectric conversion layer is
Since the light is scattered and reflected at the uneven interface between the lower electrode and the photoelectric conversion layer and obliquely returns to the inside of the photoelectric conversion layer, the distance that the reflected light travels in the photoelectric conversion layer becomes long and is efficiently absorbed. further,
Of the light that has returned to the inside of the photoelectric conversion layer, the light that has not reached the surface of the photoelectric conversion layer and has reached the surface of the photoelectric conversion layer again is reflected obliquely again on the uneven surface of the photoelectric conversion layer. Due to such repeated reflection, light is efficiently absorbed in the photoelectric conversion layer, and the efficiency of the battery is increased.

As a conventional texture producing method, there are the following methods, for example. In the case of a crystalline silicon solar cell, isopropyl alcohol is added to a heated sodium hydroxide (NaOH) or potassium hydroxide (KOH) aqueous solution, and a Si (100) wafer is dipped in the resulting mixed solution to form a quadrangular pyramid. A textured structure is obtained which has ridge-like protrusions. In addition, sodium carbonate (Na ₂ C
A method has also been proposed in which an O ₃ ) aqueous solution is used as an etching solution and a silicon substrate is dipped in the aqueous solution to form fine irregularities on the surface of the silicon substrate (Japanese Patent Laid-Open No. 2000-
183378).

On the other hand, in the case of a thin film solar cell, an aluminum target containing 0.1 to 6.0 mass% of silicon is used as the lower electrode, and the temperature of the substrate is raised to 50 to 200 ° C. to perform sputtering. It has been proposed to obtain an aluminum film having a textured structure (Japanese Patent Laid-Open No. 9-
69642). Also, titanium oxide on the metal substrate,
By coating a heat-resistant resin having electrical insulation with a pigment such as alumina or silica, the surface roughness Rma
It has also been proposed to form a substrate having irregularities with x of 0.3 to 1.5 μm (JP-A-11-177111).

[0008]

However, the above-described conventional texture structure forming method has the following problems.

1) Method of using wet etching in crystalline silicon solar cell i) Fabrication of a textured structure by wet etching utilizes the fact that the etching rate of Si differs depending on the crystal plane (anisotropic etching). The etching rate of Si is highest in the (100) plane and lowest in the (111) plane. Therefore, when etching is performed with the (100) plane as the initial surface, the (111) plane having a slow etching rate is preferentially left on the surface. Since the (111) plane has an inclination of about 54 degrees with respect to the (100) plane, both the convex portion and the concave portion formed by etching have a quadrangular pyramid shape, that is, a sharply pointed shape. Therefore, when the photoelectric conversion layer is formed on the unevenness, the thickness of the photoelectric conversion layer becomes thin on the convex portion, so that a leak is likely to occur and a defect is likely to occur on the concave portion, which rather lowers the conversion efficiency. There is. Further, since the etching does not proceed completely uniformly, the unevenness distribution is not uniform, and as a result, the texture effect varies, which does not sufficiently contribute to the improvement of the conversion efficiency. ii) Wet etching with an acid or an alkali is not preferable because it has high running costs associated with equipment and waste liquid treatment, and has problems such as environmental problems.

2) Fabrication of Textured Structure by Sputtering The textured structure is produced by controlling the crystal growth of the Al film by raising the substrate temperature and introducing an additive, but the obtained shape is a grain with facets. Therefore, the shape is steep with respect to the substrate surface. Therefore, the same problem as in the case of wet etching occurs,
On the other hand, since the in-plane distribution is not uniform, the texture effect varies and does not sufficiently contribute to the improvement of conversion efficiency.

3) Fabrication of textured structure by CVD method i) Equipment is expensive, the manufacturing process is complicated, and the manufacturing cost is increased. ii) When the CVD method is used, the SnO ₂ electrode film has a special manufacturing method as compared with a general ITO electrode film, which causes an increase in cost. In addition, the reaction temperature is high, and in order to obtain an effective texture structure, it is necessary to increase the film thickness to several hundreds to several thousands of nanometers, which also increases the cost. Further, since it is not possible to form a texture structure composed of concavities and convexities that are perfectly regularly arranged, the texture effect varies and does not sufficiently contribute to the improvement of conversion efficiency.

4) Titanium oxide in the paint to impart a coating texture effect by the paint,
When fine particles such as alumina and silica are blended, the shape and in-plane distribution of the texture formed on the surface of the insulating film will vary, and it will not sufficiently contribute to the improvement of conversion efficiency.
In addition, since the fine particles protruding on the surface of the insulating film and the holes formed by dropping of the fine particles from the surface of the insulating film form a steep slope with respect to the surface of the insulating film, the photoelectric conversion layer formed on this surface Defects such as film breakage are likely to occur.

An object of the present invention is to provide a texture structure which contributes to improvement of conversion efficiency of a solar cell with good reproducibility and at low cost.

[0014]

[Means for Solving the Problems] The above-mentioned object is as follows (1)
It is achieved by the present invention of (14). (1) A solar cell having a textured layer having a textured structure on the upper surface, a lower electrode, a photoelectric conversion layer, and an upper electrode in this order on a substrate made of a film having flexibility, wherein the textured structure has a regular structure. A solar cell comprising unevenness having concave and convex portions arranged in a regular pattern. (2) The solar cell according to (1), wherein the top of the convex portion is a flat surface or a convex curved surface. (3) The solar cell according to (1) or (2), wherein the bottom of the recess is a flat surface or a concave curved surface. (4) The solar cell according to any one of the above (1) to (3), wherein the convex portion has a truncated pyramid shape or a truncated cone shape, or the apex portion has a convex curved surface. (5) The solar cell according to any one of the above (1) to (4), wherein the concave portion has a truncated pyramid shape or a truncated cone shape, or the bottom portion has a pyramidal shape or a cone shape having a concave curved surface. (6) The above (1) in which the texture layer is made of resin.
The solar cell according to any one of to (5). (7) The solar cell according to any one of (1) to (5) above, wherein the texture layer is made of polyimide. (8) The substrate is a metal foil, polyethylene naphthalate,
The solar cell according to any one of (1) to (7) above, which is made of polyether sulfone, polyimide, polyamide, polyimide amide, or polyarylate. (9) The solar cell according to any one of (1) to (8), wherein the texture layer has a thickness of 0.1 to 5 μm. (10) The method for producing the solar cell according to any one of (1) to (9), wherein a texture roll having the uneven master pattern on the peripheral surface is used as a gravure printing roll, and the coating is applied by gravure printing. Is applied to form a textured layer on the substrate surface. (11) The paint has a resin as a main component,
The solid content concentration in the paint is 5 to 30% by mass (1)
The method for manufacturing a solar cell according to 0). (12) A method for manufacturing the solar cell according to any one of (1) to (9) above, which comprises forming a coating film on the substrate surface,
A method for manufacturing a solar cell, comprising the step of pressing the coating film with a texture roll on which the matrix pattern of the projections and depressions is formed to form the projections and depressions on the surface of the coating film to form a texture layer. (13) The method for manufacturing a solar cell according to any one of (10) to (12), wherein in the mother die pattern, the top of the concave portion serving as the mother die of the convex portion is a flat surface or a concave curved surface. (14) The method for manufacturing a solar cell according to any one of (10) to (13), wherein, in the mother die pattern, a top of a protrusion serving as a mother die of the recess is a flat surface or a convex curved surface.

[0015]

In the first aspect of the present invention, the texture layer is formed on the surface of the substrate by gravure printing using a texture roll having a master pattern as a gravure printing roll. In the second aspect, after forming a coating film on the surface of the substrate, the coating film is pressed by a texture roll to transfer the master pattern to the coating film to obtain the texture layer.

Since the texture roll used in the present invention can be manufactured by using the plate-making technique, a fine pattern can be formed with high precision. Further, in the plate-making technique, unlike the above-mentioned conventional technique, it is possible to accurately form a regularly arranged uneven pattern. Further, since the texture layer can be continuously formed while feeding a long film, the texture structure can be formed at high speed and with good reproducibility, and the size of the film is not substantially limited, so that mass processing is possible. Therefore, in the present invention, a high conversion efficiency can be obtained with good reproducibility, and an inexpensive solar cell can be realized.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A structural example of a solar cell of the present invention is shown in FIG. 1 as a partial sectional view. This solar cell has a texture layer 3, a lower electrode 4, a photoelectric conversion layer 5, and an upper electrode 6 on a substrate 2 in this order. Although not shown, in order to suppress mechanical damage, oxidation, corrosion, etc. of the solar cell, it is preferable to provide a sealing member made of resin or the like on at least the surface of the illustrated solar cell on which the upper electrode 6 is formed. . Further, such a sealing member is preferably provided also on the back surface side of the substrate 2.

Incidentally, FIG. 1 shows a solar battery cell, and the solar battery is usually constructed by connecting a plurality of cells in series. In that case, on the upper electrode 6 of each cell,
Usually, a collecting electrode and a wiring electrode are provided. The collecting electrode is an electrode for collecting the electric power generated in each cell from the surface of the upper electrode 6 having a relatively high specific resistance. The wiring electrode is an electrode for connecting the collecting electrode of each cell and the lower electrode of the adjacent cell. In addition, positive and negative lead electrodes are provided at both ends of the series connection of the cells.

The present invention is highly effective when applied to a solar cell having a structure in which light is incident on the photoelectric conversion layer 5 through the upper electrode 6, but a solar cell having a structure in which light is incident on the photoelectric conversion layer 5 through the substrate 2. Can also be applied to.

The structure of each part of the solar cell of the present invention will be described in detail below.

Substrate 2 The substrate 2 is made of a flexible film. The material for forming the film is not particularly limited, but a material having relatively good heat resistance in order to withstand heating during the formation of the photoelectric conversion layer is preferable, and specifically, a metal foil or a resin film is preferable. As the resin film, polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, polyamide or polyimide amide, especially PEN
Alternatively, PES is preferred. These have excellent performance in terms of heat resistance during plasma CVD film formation, heat resistance during long-term use, Young's modulus (stiffness), mechanical properties, and the like. PEN and PES also have excellent transparency. In addition to these, polyarylate is also preferable.

When light is incident on the photoelectric conversion layer 5 through the substrate 2, the substrate 2 must have a light-transmitting property.

The thickness of the substrate 2 may be appropriately determined according to the required strength, bending rigidity, etc., but in the case of a resin film, it is usually preferable that the thickness is 25 to 100 μm. If the substrate 2 is too thin, it may be difficult to handle, and defective products may occur due to breakage. On the other hand, if the substrate 2 is too thick, the amount of light transmission will be small and the solar cell characteristics will be degraded when light is made to enter through the substrate 2.

[0024] On the surface opposite to the photoelectric conversion layer 5 Texture layer 3 texture layer 3, a texture structure made of irregularities with depressions and protrusions regularly arranged respectively exists. “Regularly arrayed” means that the unit concavo-convex structure composed of convex parts of a specific shape and concave parts of a specific shape is repeatedly arranged.
The shape of the unevenness is not particularly limited. For example, the shape (cross-sectional shape) of the concave portion and the convex portion in a cross section perpendicular to the substrate surface may be any of a wedge shape, a rectangle, a trapezoid, a concave lens shape (in the case of a concave portion), a convex lens shape (in the case of a convex portion), and the like. Of course, the concave portion and the convex portion may have different shapes.

The unevenness may be composed of an isolated concave portion independent of each other and a convex portion surrounding the concave portion, or may be formed of an isolated convex portion independent of each other and a concave portion surrounding the isolated convex portion, and are independent from each other. The isolated concave portions and the isolated convex portions independent of each other may be arranged adjacent to each other, or a large number of grooves may be arranged substantially parallel to each other.

However, in order to prevent defects such as film breakage from occurring in the photoelectric conversion layer 5 formed on the textured structure, it is preferable that the tops of the projections are flat or have a convex curved surface. It is preferable that the bottom surface of the is flat or has a concave curved surface. Further, in order to enhance the effect as a texture structure, that is, in order to enhance the light utilization efficiency, the convex portion has a truncated pyramid shape or a truncated cone shape, or the apex portion has a convex curved surface or a truncated pyramid shape, respectively. It is preferably conical. Further, it is preferable that the recess has a truncated pyramid shape or a truncated cone shape, or a pyramid shape or a cone shape with a concave surface at the bottom. If the convex portion and / or the concave portion has such a shape, the improvement in light utilization efficiency due to the texture structure is less likely to depend on the incident angle of light, so that stable efficiency improvement is realized.

The size of the concavities and convexities and the arrangement density thereof are not particularly limited, and may be determined experimentally so that the degree of improvement in power generation efficiency is high, but normally the depth of the concavities (height of the convexities) is It is preferably 0.05 μm or more and less than the thickness of the texture layer, and the arrangement pitch of the concave portions or the arrangement pitch of the convex portions is preferably 0.1 to 60 μm.

The above description regarding the unevenness is for the solar cell in which light is incident from above in FIG. When the present invention is applied to a solar cell in which light is incident from below in FIG. 1, the terms “concave” and “convex” are replaced with “convex” in the above description.

The texture structure may be provided at least in a region that contributes to power generation, but may be provided wider than this region or may be provided so as to cover the entire surface of the substrate. However, when the wiring electrode is formed on the textured structure, the wiring electrode may have uneven thickness, and the wiring resistance may increase, resulting in deterioration or variation in characteristics. Further, in the manufacturing process of a solar cell, laser scribing is performed to form a cell structure. However, if a textured structure exists at the scribing location, the laser light may be diffusely reflected to cause processing defects. Therefore, if such a problem may occur, it is preferable not to provide it in a region that does not contribute to power generation, such as immediately below the wiring electrode or a scribing process location.

The constituent material of the texture layer 3 is not particularly limited, but it is preferable to use a resin because the master pattern can be easily and highly accurately transferred from a mold having an uneven master pattern. The type of resin is not particularly limited, but a resin having high heat resistance so that it can withstand heating during formation of the photoelectric conversion layer 5 and having a texture structure that can be formed by a method described later is preferable, and for example, polyimide is preferable. It should be noted that the texture layer 3 may be mixed with a filler such as an inorganic particle for adjusting the thermal expansion coefficient, but for forming a texture structure having a smooth surface in order to prevent the photoelectric conversion layer 5 from being broken. It is preferable that no filler is mixed in the above.

The thickness of the texture layer 3 is preferably 0.1.
-5 μm, preferably 0.5-4 μm. If the texture layer 3 is too thin, it becomes difficult to form a texture structure having a depth that can obtain a sufficient texture effect. On the other hand, if the texture layer 3 is too thick, cracks are likely to occur in the texture layer 3 or the texture layer 3 is likely to peel off from the substrate 2. Further, in the case where light is incident through the substrate 2, if the texture layer is too thick, the amount of light transmission decreases, resulting in poor solar cell characteristics.

Usually, the lower electrode 4 has a structure divided into cell units, and the texture layer 3 is provided uniformly on the substrate 2. Therefore, in order to prevent the adjacent lower electrodes 4 from being short-circuited, the texture layer 3 is It must have insulating properties.
The sheet resistance of the texture layer 3 is preferably 100 kΩ / □ or more, and particularly preferably 1 MΩ / □ or more.

Next, a method of forming the texture layer 3 will be described.

In the first aspect of the present invention, the texture roll having the uneven master pattern formed on the texture layer on the peripheral surface is used as a gravure printing roll, and the texture layer 3 is formed by utilizing gravure printing. To do. Figure 2
2 shows an example of the configuration of the device used in the first aspect. In the apparatus shown in FIG. 2, the film 21 wound around the pay-out roll 11 is paid out, passed between the texture roll 10 (gravure printing roll) and the backup roll 15 to form a coating film, and then dried. It passes through a furnace 31 and is then wound on a winding roll 13. The texture roll 10 is rotated with a part thereof immersed in a liquid tank 33 containing the coating liquid 32. The coating liquid adhering to the peripheral surface of the texture roll 10 is scraped off by a doctor blade and then applied to the surface of the film 21. At the same time, the master pattern on the peripheral surface of the texture roll 10 is transferred to the coating film. To be done. The film 21 having the coating film formed thereon is dried in a drying oven 31 to obtain a substrate having a texture layer.

In the first aspect, when the coating material contains a resin as a main component, the solid content concentration in the coating material is 5 to 5.
It is preferably 30% by mass. If the paint concentration is too low, the amount of the diluting solvent is large, so that the drying process after coating becomes complicated and the drying equipment becomes large, and the cost increases due to the increase in the amount of energy required for drying. In addition, since the viscosity of the paint is low, the paint is likely to be scattered during application, and scattered substances may scatter on the product, which may cause defective products. When the viscosity of the paint becomes low, a liquid flow (leveling) phenomenon occurs due to the influence of the surface tension and the transportation of the coating line until the transferred paint dries.
The transfer pattern is likely to collapse. On the other hand, when the paint concentration is too high, the viscosity of the paint is too high, which makes it difficult to perform accurate transfer such as faint print.

In the second aspect of the present invention, after a coating film is formed on the surface of the substrate, the matrix pattern is transferred to the coating film by pressing the coating film with the texture roll to obtain a texture layer. FIG. 3 shows a configuration example of the device used in the second mode. In the apparatus shown in FIG. 3, the film 21 wound around the pay-out roll 11 is paid out, a coating film is formed on the surface of the film 21 by the coating machine 41, and then, the film 21 is passed through a drying furnace 31, and then the texture roll 10 is applied. It passes between a pair of press rolls composed of a smooth roll 12 and a smooth roll 12, and is then wound around a winding roll 13. Film 2
When 1 passes between the texture roll 10 and the smooth roll 12, the matrix pattern is transferred to the coating film and a texture structure is formed.

In the second aspect, it is preferable that the coating film is in a heated state so as to be easily deformed when it is pressed by the texture roll. For that purpose, it is preferable to provide a means for heating the texture roll and / or the smooth roll to heat the roll surface. The temperature of the coating film when pressed by the texture roll is 30 to
It is preferably 450 ° C., particularly 50 to 400 ° C.
If the heating temperature is too low, the coating film is unlikely to be deformed, and it becomes difficult to accurately transfer the uneven pattern. On the other hand, if the heating temperature is too high, the film is distorted, and the shape and dimensions are likely to be distorted. Since the specific optimum heating temperature differs depending on the constituent material of the coating film, it may be experimentally determined. Since the film and the coating film are thin, the film and the coating film are instantly heated to the same temperature as the roll temperature when brought into contact with a heated roll.

The pressure at which the texture roll presses the coating film is preferably 40 to 150 MPa, particularly 50 to 120 MPa. If the pressure is too low, the coating film is less likely to be deformed, and it becomes difficult to accurately transfer the uneven pattern. On the other hand, if the pressure is too high, the film is likely to be distorted and the shape and dimensions are likely to be distorted.

The texture roll 10 and the smooth roll 12 may not be heated, and a heater such as an electric heater may be provided immediately before them to heat the coating film.

When light is incident through the substrate 2, it is preferable that textured structures are formed on both surfaces of the substrate 2. Therefore, in both the first and second aspects, the film may be formed as necessary. Texture layers may be formed on both sides of 21. Further, in the second embodiment shown in FIG. 3, if a texture roll is provided instead of the smooth roll 12 and the film 21 is sandwiched between the pair of texture rolls, the surface opposite to the coating film forming surface is pressed by the texture roll. Since it is formed, the texture structure can be formed on both surfaces of the film 21 at the same time.

The first aspect and the second aspect are not particularly inferior and superior, and in both cases, transferability is good and a texture layer with high dimensional accuracy can be obtained. In particular, in the first aspect,
Since the pattern transfer is carried out at the same time as the formation of the coating film, there is no return of the shape due to the release of the stress of the coating film, and the transferability becomes extremely good. However, even in the second mode, the shape hardly returns.

The feeding speed of the film is not particularly limited, and it is possible to transfer the master pattern even if it is fed at a high speed. However, if the feeding speed is too fast, scattering of the paint is likely to occur, so 1 to 1 is preferable. 200 m / min, more preferably 3
~ 100 m / min.

Next, a method for manufacturing the texture roll will be described. It is preferable to use a plate making technique for forming the master pattern on the peripheral surface of the texture roll. As the plate making technique, direct plate making or electronic engraving plate making is preferable.

In direct plate making, first, an underlayer made of Ni or the like is provided on the peripheral surface of a roll base material made of iron or the like by plating, and then a Cu layer is formed by plating. Then, if necessary, the surface of the Cu layer is polished so that the cross section of the roll is a perfect circle, and then a photosensitive solution is applied to the surface of the Cu layer to form a photosensitive layer. Next, the film on which the master block pattern is transferred is exposed to ultraviolet rays or the like in a state of being brought into close contact with the photosensitive layer to form a latent image on the photosensitive layer, and then development is performed. Then, Cu exposed from the patterned photosensitive layer
After etching the layer with a cupric chloride solution or the like, the photosensitive layer is peeled off.

In electronic engraving plate making, after forming a Cu layer in the same manner as in direct plate making, CAD (computer-aided d)
C using data created by esign) or image processing
The surface of the u layer is directly shaped. A diamond needle or a laser beam is used for shape processing.

A protective layer is formed on the surface of the Cu layer patterned by the above-mentioned method to improve hardness and durability. The protective layer is usually Cr formed by plating.
Layers and / or Ni layers are used. The thickness of the protective layer is preferably 10 to 50 μm. If the protective layer is too thin,
The protective layer may become non-uniform due to uneven plating, and if the protective layer is too thick, cracks may occur in the protective layer.

As the mother die pattern, it is preferable that the tops of the concave portions which are the mother die of the convex portions of the substrate are flat or concave. In addition, it is preferable that the top of the convex portion that is the mother die of the concave portion of the substrate is a flat surface or a convex curved surface. In addition,
As shown in FIG. 4, in the mother die pattern of the peripheral surface of the texture roll 10, each surface such as a slope, a top surface, and a bottom surface that form the unevenness is a substantially flat surface, and the boundaries (edges) of these surfaces are sharp. However, when the master pattern is transferred to the texture layer 3 by pressing, the edges of the transferred pattern are usually blunt. For example, even if the concave portion of the matrix pattern is a truncated pyramid, the convex portion of the texture layer 3 formed by the transfer often has a smooth convex surface instead of a flat top portion.

When light is incident on the photoelectric conversion layer 5 through the lower electrode 4 and the upper electrode 6, the lower electrode 4 is usually made of metal. The metal forming the lower electrode is not particularly limited, and for example, Al, stainless steel, Ti or the like may be used, but Al is preferably used.
To use. Since Al has a low specific resistance, there is little deterioration in characteristics due to an increase in series resistance. By the way, in the solar cell, the light reflected by the lower electrode 4 through the photoelectric conversion layer 5 enters the photoelectric conversion layer 5 again, and this reflected light is also converted into electric energy. Therefore, the lower electrode 4 preferably has a high reflectance, but Al having a high light reflectance is also excellent in this respect.
Furthermore, Al is inexpensive. The thickness of the lower electrode 4 made of metal is not particularly limited, but is preferably 0.01
10 μm. The lower electrode 4 is preferably formed by a vacuum film forming method such as a sputtering method.

On the other hand, when light is incident on the photoelectric conversion layer 5 through the substrate 2, the lower electrode 4 is made of a transparent conductive material. The transparent conductive material used is not particularly limited, but a material having excellent transparency and conductivity, such as SnO ₂ or ITO.
(Indium tin oxide) and ZnO are preferable. However, since the lower electrode 4 may be exposed to hydrogen plasma when the photoelectric conversion layer 5 is formed, and the translucency thereof may be deteriorated, a material excellent in hydrogen plasma resistance, such as SnO ₂ or Zn.
It is more preferable to use O. The thickness of the lower electrode made of a transparent conductive material is usually preferably 10 to 100 nm.

When the lower electrode 4 of the diffusion prevention layer is made of a metal, it prevents the constituent components of the lower electrode 4 from diffusing into the photoelectric conversion layer 5 between the lower electrode 4 and the photoelectric conversion layer 5. It is preferable to provide a diffusion prevention layer made of a metal such as stainless steel, Ti, or Cr in order to reduce the resistance of the interface. The thickness of the diffusion barrier layer is preferably 3 to 5 nm. The diffusion prevention layer may be usually formed by a vacuum film forming method such as a sputtering method.

Photoelectric conversion layer 5 The photoelectric conversion layer 5 has a pn junction or a pin junction, preferably a pin junction. Since the effect of the present invention is the improvement of the light utilization efficiency by providing the texture structure, the structure of the photoelectric conversion layer 5 is not particularly limited, and the effect of the present invention is realized no matter what kind of photoelectric conversion layer is provided. To do. For example, Si is often used as a material for forming the photoelectric conversion layer.
Besides, any of GaAs, InP, Cd / CdTe, or the like may be used. Further, in order to expand the usable wavelength range, a tandem photoelectric conversion layer in which layers made of different compounds are laminated may be used. The thickness of the photoelectric conversion layer 5 is
Usually, it is about 0.2 to 50 μm.

The photoelectric conversion layer 5 is preferably formed by a vacuum film forming method such as a plasma CVD method. The formation conditions are not particularly limited and may be set appropriately according to the constituent materials.

[0053] the material of the upper electrode 6 upper electrode 6, depending on whether the optical transparency is required, may be suitably selected from a transparent conductive material or a metal material similarly to the lower electrode 4. However, the upper electrode 6 constituent material is not required to have hydrogen plasma resistance. Further, the thickness of the upper electrode 6 may be determined according to the constituent material thereof, similarly to the lower electrode 4.

[0054]

Example A solar cell was manufactured by the following procedure and its characteristics were evaluated.

Substrate 2 On one surface of a substrate 2 made of a stainless steel foil having a thickness of 50 μm, an apparatus having the structure shown in FIG. 2 was used. Coating liquid: polyimide resin was used as a solvent (N-methyl-2-pyrrolidone). Diluted product (solid content: 17% by mass), film running speed: 2 m / min, and drying temperature: 110 ° C. A texture layer 3 having a thickness of 2 μm was formed. The texture roll 10 was produced using the electronic engraving process described above. The surface of the texture roll 10 was composed of a Cr plating layer having a thickness of 20 μm. A plan view of the peripheral surface of the texture roll 10 is shown in FIG.
It shows in (B). In the matrix pattern shown in FIGS. 5A and 5B, the truncated pyramid-shaped isolated concave portion 10D is the convex portion 10P.
It is a structure surrounded by. The isolated recess 10D has a depth D,
The array pitch P, the width W of the bottom surface and the inclination angle θ of the side surface are D = 3 μm, P = 28 μm, W = 18 μm, and θ = 60 °.

Lower electrode 4 Next, a lower electrode 4 consisting of an Al layer having a thickness of 300 nm and a Ga-doped ZnO layer having a thickness of 90 nm was formed by DC sputtering. The ZnO layer is a layer for obtaining the effect of increasing reflection due to optical interference. The sputtering conditions are as follows: Al layer, used gas: Ar, pressure: 66.7 Pa, input power: 2.2 W / cm ² , substrate temperature: room temperature, ZnO layer, used gas: Ar, pressure: 66.7 Pa, input power : 0.5 W / cm ² , substrate temperature: room temperature.

Photoelectric Conversion Layer 5 Next, a polycrystalline Si photoelectric conversion layer consisting of an n layer, an i layer and ap layer was formed on the lower electrode 4 by the plasma CVD method under the following conditions.

N layer Gas used and flow rate: PH ₃ / H ₂ / SiH ₄ = 0.06 s
ccm / 800sccm / 5sccm, pressure: 133.3Pa, input power: 50mW / cm ² , substrate temperature: 220 ° C, thickness: 50nm

I layer Gas used and flow rate: H ₂ / SiH ₄ = 1000 sccm / 2
0sccm, pressure: 26.7Pa, input power: 600mW / cm ² , substrate temperature: 220 ° C, thickness: 1600nm

P layer Gas used and flow rate: B ₂ H ₆ / H ₂ / SiH ₄ = 0.02
sccm / 900sccm / 4sccm, pressure: 66.7Pa, input power: 180mW / cm ² , substrate temperature: 120 ° C, thickness: 15nm

Upper Electrode 6 Next, the upper electrode 6 made of ITO and having a thickness of 60 nm is DC
It was formed by the sputtering method. The sputtering conditions are: gas and pressure used: Ar / O ₂ = 0.4Pa / 0.08P
a, input power: 0.3 W / cm ² , substrate temperature: room temperature.

Next, a wiring electrode and an extraction electrode were formed to obtain a solar cell.

Evaluation With respect to the above solar cell, the solar cell characteristics were measured by irradiating light from the upper electrode 6 side using a solar simulator. As a result, the open circuit voltage Voc was 0.508 V, the short circuit current Isc was 24.3 mA / cm ² , the form factor FF was 0.652, and the conversion efficiency Eff was 8.05%.

On the other hand, a comparative cell was prepared in the same manner as the above solar cell except that the texture layer was not provided, and the solar cell characteristics were measured. The open circuit voltage Voc: 0.51 V, the short circuit current Isc: 19 It was 0.8 mA / cm ² , form factor FF: 0.645, and conversion efficiency Eff: 6.51%.

From these results, it can be seen that the provision of the texture layer increased the photoelectric current and improved the conversion efficiency by about 24%.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a configuration example of a solar cell of the present invention.

FIG. 2 is a diagram showing a configuration example of a texture layer forming apparatus.

FIG. 3 is a diagram showing another configuration example of a texture layer forming apparatus.

FIG. 4 is a cross-sectional view showing a state where a coating film is pressed by a texture roll.

5A and 5B show a surface structure of a texture roll used for forming a texture layer, FIG. 5A is a plan view, and FIG.

[Explanation of symbols]

2 substrates 21 film 3 texture layers 4 Lower electrode 5 Photoelectric conversion layer 6 Upper electrode 10 texture rolls 11 Roll out 12 smooth roll 13 Take-up roll

Continued front page    (72) Inventor Masaru Takayama             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 5F051 BA15 GA03 GA05 GA16

Claims (14)

[Claims] 1. A textured layer having a textured structure on an upper surface of a substrate made of a flexible film,
A solar cell having a lower electrode, a photoelectric conversion layer, and an upper electrode in this order, wherein the textured structure is unevenness having regularly arranged recesses and protrusions, respectively. 2. The solar cell according to claim 1, wherein the top of the convex portion is a flat surface or a convex curved surface. 3. The solar cell according to claim 1, wherein the bottom of the concave portion is a flat surface or a concave curved surface. 4. The solar cell according to claim 1, wherein the convex portion has a truncated pyramid shape or a truncated cone shape, or a pyramid shape or a cone shape having a convex curved surface at the top. 5. The solar cell according to claim 1, wherein the recess has a truncated pyramid shape or a truncated cone shape, or a pyramid shape or a cone shape with a concave curved surface at the bottom. 6. The solar cell according to claim 1, wherein the texture layer is made of resin. 7. The solar cell according to claim 1, wherein the texture layer is composed of polyimide. 8. The solar cell according to claim 1, wherein the substrate is made of metal foil, polyethylene naphthalate, polyether sulfone, polyimide, polyamide, polyimide amide or polyarylate. 9. The solar cell according to claim 1, wherein the texture layer has a thickness of 0.1 to 5 μm. 10. The method for manufacturing a solar cell according to claim 1, wherein a texture roll having the concave-convex mother die pattern on its peripheral surface is used as a gravure printing roll, and a paint is applied by gravure printing. A method for manufacturing a solar cell, which comprises a step of applying to form a texture layer on a substrate surface. 11. The method of manufacturing a solar cell according to claim 10, wherein the coating material contains a resin as a main component, and a solid content concentration in the coating material is 5 to 30 mass%. 12. The method of manufacturing a solar cell according to claim 1, wherein a coating film is formed on the surface of the substrate, and then the coating film is formed by a texture roll on which the uneven master pattern is formed. A method of manufacturing a solar cell, comprising the step of forming a texture layer by forming the unevenness on the surface of the coating film by pressing. 13. The method for manufacturing a solar cell according to claim 10, wherein, in the master pattern, the top of the recess serving as the master of the protrusion is a flat surface or a concave curved surface. 14. The method of manufacturing a solar cell according to claim 10, wherein, in the master pattern, the top of the convex that serves as the master of the concave is a flat surface or a convex curved surface.