JP2009302109A - Solar cell and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a method of forming countless irregularities on a surface of a substrate and giving a dispersion to an incident light is considered for improving the efficiency of a solar cell formed on the substrate, however, in irregularity parts formed by a method in the prior art, films are turned up or corner parts are formed, and consequently the reliability of a photoelectric conversion layer formed thereon is spoiled, and moreover the method in the prior art is not fit for industrial utilization because equipment for formation becomes expensive and/or very large. <P>SOLUTION: Part of a substrate material is protruded and a protrusion is formed on a surface of the substrate by rubbing a substrate surface consisting of organic resin with a roller-shaped friction body at high speed. The protrusion has a curved surface shape, and there are irregular irregularities in a flat shape thereof, and a lower electrode film, the photoelectric conversion layer and an upper electrode film are sequentially formed thereon to make the solar cell. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solar cell that converts incident light energy into electrical energy and a method for manufacturing the solar cell.

  Solar cells have been put into practical use as those that directly convert solar energy into electrical energy, but even today, improvements in photoelectric conversion efficiency are always desired. In order to improve the photoelectric conversion efficiency of this solar cell, many materials and manufacturing methods for forming the solar cell have been studied so far, but the increase in efficiency tends to saturate only with the original characteristics of the current silicon-based material. is there.

  The next step is to increase the apparent photoelectric conversion efficiency by capturing more light than before. The tandem method for multilayering photoelectric conversion layers with different absorption wavelengths is This is one method. The other is considered to absorb more light than before by optimizing the internal structure of the solar cell even with light of the same wavelength.

  Therefore, the most effective technique is to texture the substrate surface of the solar cell to improve the photoelectric conversion light rate. When innumerable unevenness is introduced into the surface of the substrate forming the solar cell and textured, the light incident from the opposite surface is scattered by the uneven surface and scattered in various directions. As a result, the light path in the solar cell becomes longer, and light that is not used is reduced by repeating multiple reflections, so that the photoelectric conversion efficiency is increased. Further, since the surface area of the substrate increases due to the formation of irregularities, the area of the photoelectric conversion layer formed thereon also increases, and the photoelectric conversion efficiency also increases.

  However, the concavo-convex shape formed on the surface of the substrate does not provide the effect of improving the photoelectric conversion efficiency even if any concavo-convex shape is simply formed. The concavo-convex shape that can be expected to have an effect must not impair the original characteristics of the film such as a photoelectric conversion layer formed by covering the concavo-convex surface. That is, the formation of the uneven shape should not increase the specific resistance of the photoelectric conversion layer. In addition, the light transmittance should not be reduced by the introduction of the uneven shape on the substrate surface. Furthermore, in consideration of industrial use, it is preferable to be able to manufacture a desired concavo-convex shape on the substrate surface as easily and inexpensively as possible.

Therefore, a method of texturing the substrate surface that solves such a problem has been disclosed (for example, see Patent Document 1). The method described in Patent Document 1 uses a blasting process in which inorganic fine particles are sprayed onto a substrate at a high speed. According to this method, it is possible to reliably roughen the surface without using a very expensive apparatus for blasting, and it is possible to reliably provide unevenness to the film substrate.
As another method, a method of forming irregularities using plasma processing is also disclosed (for example, see Patent Document 2). The method of Patent Document 2 is a technique in which high-frequency plasma is generated in a vacuum chamber into which an inert gas is introduced, and the substrate surface is etched with the plasma gas to form irregularities. According to this document, a pyramid-like unevenness having a size of several hundred nm is formed on the surface of the polyimide substrate.

  As another method, a method of forming a concavo-convex shape on the substrate surface using press working has also been disclosed (for example, see Patent Document 3). In the method of Patent Document 3, a mother die having a desired uneven shape is prepared in advance, and since the plastic substrate is heated and pressed together with the mother die, the uneven shape reversed from the mother die is obtained. It can be introduced into the substrate.

Japanese Patent Laid-Open No. 7-122764 ([0010], FIG. 3) Japanese Patent No. 3216754 ([0007]-[0008], FIG. 1) Japanese Unexamined Patent Publication No. 2003-298085 ([0030]-[0034], FIG. 2)

  As described above, it has been conventionally proposed to form irregularities on an organic resin substrate by various methods, and by forming a photoelectric conversion layer there, conversion efficiency is improved as compared with the case of forming a flat substrate. It is also possible to make a cell. However, each of the conventional methods still has problems.

In the processing by the blast process shown in Patent Document 1, since the processing is performed by spraying fine particles, the formed unevenness becomes a deep and sharp shape. Therefore, in Document 1, the sharpness cannot be alleviated unless an extra process such as etching or SiO ₂ is applied to the processed substrate. Furthermore, when the blasting process is applied to an organic resin substrate, new problems such as the resin being swollen and the sprayed particles embedded therein also occur. For these reasons, in a solar cell in which an upper electrode or a lower electrode of a thin film having a thickness of less than 1 μm is stacked, defects such as disconnection of the film are inevitably generated.

  Further, in the processing by the plasma processing shown in Patent Document 2, the size of the unevenness is smaller than that in the blast processing, but due to the act of scraping off the substrate, protrusions with corners are inevitably formed, and the above-mentioned processing is performed. As is the case, it is likely to cause disconnection of the film. Furthermore, plasma treatment is expensive and difficult to process in large quantities, so it is difficult to say that it is a simple surface treatment.

  Furthermore, in the press work shown in Patent Document 3, it is possible not to form acute-angle protrusions by adjusting the matrix. However, in the first place, it is very difficult to form the matrix itself in the unevenness lined up on the order of several μm. Furthermore, press working can be performed if the area is as small as several centimeters, but if it is several tens of centimeters, it becomes difficult to press unless the pressurizing machine itself to be pressed is very large. In particular, the resin substrate used in solar cells can withstand subsequent processes, so it uses PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), which has high heat resistance and is not easily plastically deformed. Currently, it is difficult to use industrially.

  SUMMARY OF THE INVENTION Accordingly, the present invention is to provide a solar cell that can solve the above-described problems and can improve the conversion efficiency by providing a light scattering effect and a film area increasing effect, and a method for manufacturing the solar cell.

  In order to achieve the above object, the means described below are employed in the solar cell and the manufacturing method thereof of the present invention.

  In a solar cell in which a lower electrode film, a photoelectric conversion layer, and an upper electrode film are sequentially laminated on a flat substrate made of an organic resin, the cross-sectional shape is a curved surface on the surface of the substrate on which the lower electrode film is formed. A solar cell in which a plurality of protrusions having irregularities with irregular planar shapes is formed.

In addition, the protrusions are randomly arranged on the substrate surface, and are formed by raising a part of the material of the substrate, and the protrusions are higher than the width of the planar shape. It is preferable that most of the protrusions are formed on the surface of the substrate on the side on which the lower electrode film is formed.

  Moreover, in the manufacturing method, in the manufacturing method of a solar cell formed by laminating a lower electrode film, a photoelectric conversion layer, and an upper electrode film on a flat substrate made of an organic resin, by rubbing the substrate surface with a friction body, A part of the material of the substrate is raised to form a protrusion on the surface of the substrate, and a lower electrode film, a photoelectric conversion layer, and an upper electrode film are sequentially formed on the surface on which the protrusion is formed.

  The friction body is a cloth material containing fine organic fibers, and the friction body is preferably attached to the surface of a cylindrical roller, and the substrate surface is rubbed by rotating the roller.

  Furthermore, the friction process is preferably performed a plurality of times by changing the friction direction by the rotation of the roller with respect to one substrate.

  A plurality of protrusions are formed on a resin substrate as in the present invention, and upper and lower electrodes and a photoelectric conversion layer are formed on the resin substrate to form a solar cell. It becomes possible to pass a long distance in the conversion layer, and the light conversion efficiency can be improved in the same manner as the power generation region is increased by substantially increasing the film area of the photoelectric conversion layer itself.

  And since the protrusions formed on the solar cell substrate of the present invention are mainly curved and have no corners, there is a risk of disconnection or the like in the thin film comprising the upper electrode or the lower electrode formed thereon. The reliability is higher than the conventional configuration.

  Further, since the projection formed on the substrate of the present invention has irregularities in its planar shape, the length of the outer periphery of the planar shape becomes long, that is, the slope portion of the projection increases. As a result, the probability that incident light is scattered increases as compared with a simple protrusion such as a circle or ellipse, and the solar cell formed thereon can further increase the conversion efficiency.

  In addition, since the irregularities of the planar shape of the protrusions are irregularly formed, the direction of the slope is not anisotropic in any direction in the surface, so a constant conversion efficiency can be obtained anywhere in the solar cell to be formed. It is done.

  On the other hand, according to the method for manufacturing a solar cell of the present invention, the temperature of only the vicinity of the surface is increased by friction, and the substrate material is deformed. It becomes possible to form only. In addition, these protrusions are formed only on one side of the rubbed substrate, but the opposite surface of the substrate remains smooth, so that the amount of light incident from the opposite surface of the smooth substrate is not attenuated here. .

  In addition, the friction process can be performed by rotating a friction body with a simple structure, such as a cloth material affixed to a roller. Therefore, the process is very simple and can be applied to mass production. is there.

Embodiments of the present invention will be described below with reference to the drawings.
First, the structure of the solar cell of this example will be described with reference to FIG. FIG. 1 shows the cross-sectional structure of the main part of the solar cell of this example.

  The substrate 10 is made of an organic resin film such as PET or PEN having a thickness of about 0.1 mm. The substrate 10 is originally a smooth film, but a plurality of protrusions 11 are formed on one side by a method described later. As can be seen from FIG. 1, the cross section of the protrusion 11 has a curved cross section, and has a smooth shape with no sharp corners. The size of the protrusion 11 is several μm to several tens of μm, and the height is smaller than the width. Since the protrusion 11 exists only on one side of the substrate 10, the amount of light incident from the opposite surface of the smooth substrate is not attenuated here.

  A lower electrode film 20 is formed on the surface of the substrate 10 where the protrusions 11 are provided. The lower electrode film 20 is made of a transparent conductive film such as ITO (indium tin oxide). Since the thickness of the lower electrode film 20 is about 0.1 μm, it is much smaller than the size of the protrusion 11.

  A photoelectric conversion layer 30 is formed on the lower electrode film 20. The photoelectric conversion layer 30 has a three-layer structure of a p-type silicon semiconductor, an i-type silicon semiconductor, and an n-type silicon semiconductor. The total thickness is about 0.5 μm to 1 μm.

  An upper electrode film 40 is formed on the photoelectric conversion layer 30. The upper electrode film 40 is made of a metal film such as aluminum, silver, gold, platinum, or titanium, and has a thickness of about 0.5 μm. However, the metal here is desired to be a material having high conductivity and high light reflectivity and is difficult to be absorbed. Each thin film is laminated | stacked on these board | substrates 10, and the solar cell of a present Example is made. As described above, the film formed on the substrate 10 is much thinner than the protrusions 11. However, since the protrusions 11 have a gentle curved surface with a low height, the formed film becomes considerably thin and the resistance increases. There are no worries about breakage.

  In practical use, a protective film is formed on these laminates, and an extraction electrode for external extraction is formed on each of the upper and lower electrode films, but this is not particularly necessary for explaining the present embodiment. So it is not shown.

  Next, a case where power is generated by irradiating the solar cell of this embodiment with light will be described with reference to FIG. FIG. 2 shows a state in which external light enters the solar cell of the present embodiment described above and is scattered in the film as indicated by an arrow.

  When light 45 having a wavelength that is absorbed by the silicon semiconductor is incident on the solar cell of this example, the light 45 is absorbed by the photoelectric conversion layer 30 and causes charge separation. The electrons generated by the charge separation flow into the lower electrode film 20 or the upper electrode film 40 and can be used as a generated current.

  Here, in the solar cell of this example, since the protrusions 11 are formed on the substrate 10, the light 45 is scattered as shown in the figure. As a result, the light 45 enters the photoelectric conversion layer 30 from an oblique direction, and the distance that the light 45 passes through the photoelectric conversion layer 30 becomes long, thereby improving the light confinement effect. Therefore, the current increases because the probability of causing charge separation increases.

  Further, the presence of the protrusions 11 increases the surface area of the film formed thereon, as is apparent from the drawing. In other words, according to this configuration, the region where power generation can be performed is increased, and the current increases from here as well, and the power generation efficiency is improved.

  Furthermore, the planar structure of the protrusion 11 formed on the substrate 10 used in the solar cell of this embodiment will be described with reference to FIG. FIG. 3 shows a part of the substrate 10 viewed in plan, and the planar shape of the plurality of protrusions 11 can be seen.

  As shown in the figure, the protrusion 11 does not have a simple circle or ellipse structure, but has irregular irregularities in its planar structure. As described above with reference to FIG. 2, the light 45 incident from the outside is scattered on the slope of the protrusion 11. Since the planar structure of the projection 11 is uneven as shown in FIG. 3, the outer peripheral length of the projection 11 is increased and the slope portion is increased, so that incident light is further scattered compared to a circular or elliptical projection. This improves the power generation efficiency of the solar cell.

  Further, the size and direction of the planar unevenness is irregular and not constant. As in the prior art, geometrically formed irregularities such as a pyramid structure have a uniform planar shape, so that the scattering direction is constant, and the incident direction dependency of incident light appears. However, as in this embodiment, by making irregularities in the planar structure of the protrusions 11 irregular, it is possible to generate the same power anywhere in the solar cell without dependence on incident light.

  Further, as shown in the figure, the plurality of protrusions 11 are not regular but are randomly arranged on the surface of the substrate 10. By arranging a plurality of projections 11 at random in this way, the incident light described above further increases the degree of scattering.

  Then, the manufacturing method of the solar cell of a present Example is demonstrated. Here, a substrate processing method used in this embodiment will be described with reference to FIG.

  First, a cylindrical roller 51 is prepared, and a cloth material 60 for actually rubbing the surface of the roller 51 is wound and fixed to obtain a friction body 50. The cloth material 60 is preferably made of a material having high heat resistance so as not to be damaged by frictional heat when a frictional force is applied. For example, rayon or the like is used. The friction body 50 can be rotated about the rotation shaft 52. A movable substrate holder 70 is prepared, and a substrate 10 made of an organic resin such as PET or PEN is fixed thereon.

  The friction body 50 applies a force such as a motor from the outside to the rotating shaft 52 and rotates it in the direction of the arrow in FIG. The rotation speed here is about 1000 rotations / minute. Then, the substrate holder 70 is gradually moved in the direction of the arrow toward the friction body 50 so that the cloth material 60 and the surface of the substrate 10 are in contact with each other. After both come into contact and a frictional force starts to be applied to the surface of the substrate 10, the substrate holder 70 is moved at a speed of about 2 mm / second to rub the entire surface of the substrate 10. Since the rotational speed of the friction body 50 is sufficiently faster than the moving speed of the substrate holder 70, the rotational direction may be either direction.

  Through such a treatment, the surface of the substrate 10 made of an organic resin is rubbed so that the temperature of the surface rises, and becomes near or above the glass transition temperature of the material. As a result, the fluidity increases in the vicinity of the surface of the organic resin, and the contained low molecular resin portion expands to form protrusions 11 on the surface. However, since the frictional force generated in this process is continuously applied, the protrusion 11 is crushed to some extent, the cross-sectional shape becomes a gentle convex shape, and irregular irregularities are formed in the planar shape.

  This friction process may be completed by a single process, but in order to make the protrusion 11 more complicated, the direction of the substrate 10 is rotated by 90 degrees with respect to the direction shown in the drawing, and then 2 It is even better to perform the second friction treatment. Through these two friction steps, the substrate 10 on which a plurality of ideal protrusions 11 having a complicated planar shape shown in FIG. 3 are randomly arranged can be obtained.

As described above, since the protrusions 11 can be formed by increasing the temperature of the resin substrate 10, it is conceivable to heat the entire substrate 10 with an electric furnace or the like. However, when the entire laminate is heated, the thin substrate 10 is deformed, and protrusions are formed even on the unnecessary back surface. In the treatment by friction in this embodiment, since the protrusion is formed only on one surface, the opposite surface remains smooth and does not affect the light incidence, and is excellent as a method for forming the local protrusion 11. It is a technique.

  As described above, the process of forming the protrusions 11 on the substrate 10 in the manufacturing method of the present embodiment can be achieved by a very simple structure of the roller 51 and the cloth material 60, and an expensive vacuum device or the like is not necessary. Therefore, the process is simple and can be applied to mass production of solar cells.

  Through the above steps, the lower electrode film 20 is formed on the substrate 10 on which the plurality of protrusions 11 are formed. Although ITO is used for the lower electrode film 20, it is formed as a thin film of about 0.1 μm using a vacuum device such as sputtering.

  Subsequently, the photoelectric conversion layer 30 is formed on the lower electrode film 20. The photoelectric conversion layer 30 is made of the above-described three-layer silicon film. First, a p-type semiconductor layer is formed by introducing a boron-based doping gas using a plasma CVD apparatus into which a silane-based gas is introduced. Subsequently, an i-type semiconductor layer is formed without introducing a doping gas, and finally an n-type semiconductor layer is formed by introducing a phosphorus-based doping gas. The total thickness of the photoelectric conversion layer 30 is about 0.5 μm to 1 μm.

  Finally, the upper electrode film 40 is formed on the photoelectric conversion layer 30. The upper electrode film 40 is formed as a film having a thickness of about 0.5 μm by sputtering using a metal material as a target.

  Although the solar cell of the present embodiment can be produced as described above, it is necessary to form a protective film (not shown) or an extraction electrode on the upper electrode 40 to be incorporated in the device.

It is sectional drawing which showed the solar cell in embodiment of this invention. It is sectional drawing explaining advancing of the light in the solar cell in embodiment of this invention. It is a top view of the protrusion formed in the board | substrate used for the solar cell in embodiment of this invention. It is the perspective view which showed the method of forming a protrusion in the board | substrate used for the solar cell in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Protrusion 20 Lower electrode film 30 Photoelectric conversion layer 40 Upper electrode film 45 Light 50 Friction body 51 Roller 52 Rotating shaft 60 Cloth material 70 Substrate holder

Claims (10)

In a solar cell formed by sequentially laminating a lower electrode film, a photoelectric conversion layer and an upper electrode film on a flat substrate made of an organic resin,
On the surface of the substrate forming the lower electrode film, a plurality of projections having a curved cross-sectional shape and irregular irregularities in a planar shape are formed. .   The solar cell according to claim 1, wherein the protrusions are formed at random on the surface of the substrate. The solar cell according to claim 1, wherein the protrusion is formed by raising a part of a material of the substrate. The solar cell according to any one of claims 1 to 3, wherein the protrusion has a height smaller than a width of the planar shape. 5. The solar cell according to claim 1, wherein most of the protrusions are formed on a surface of the substrate on the side on which the lower electrode film is formed. In a solar cell formed by sequentially laminating a lower electrode film, a photoelectric conversion layer and an upper electrode film on a flat substrate made of an organic resin,
Projections are formed on the surface of the substrate on which the lower electrode film is formed by frictional heat generated by rubbing with a friction body. In a method for manufacturing a solar cell in which a lower electrode film, a photoelectric conversion layer, and an upper electrode film are laminated on a flat substrate made of an organic resin,
Rubbing the surface of the substrate with a friction body to raise a part of the material of the substrate and forming protrusions on the surface of the substrate;
And a step of sequentially forming a lower electrode film, a photoelectric conversion layer, and an upper electrode film on the surface on which the protrusions are formed. A method for manufacturing a solar cell, comprising: The method for manufacturing a solar cell according to claim 7, wherein the friction body is a cloth material including fine organic fibers. The method for manufacturing a solar cell according to claim 8, wherein the friction body is formed by attaching the cloth material to a surface of a cylindrical roller and rubbing the substrate surface by rotating the roller. The method for manufacturing a solar cell according to claim 9, wherein the friction step is performed a plurality of times by changing a friction direction by rotation of the roller with respect to one substrate.

Images