JP2000101113A - Manufacture of solar battery substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a solar battery substrate whose photoelectric conversion efficiency is high, in which the peeling of a transparent conductive film or an amorphous silicon thin film does not peeled, and which has minute rugged structure and is formed of glass-like carbon. SOLUTION: Liquid thermosetting resin whose viscosity is 0.5-5 poises is injected into a frame where a plate, in which an uneven surface is formed is arranged on one face and is cured. Alternatively, the frame is peeled, the obtained resin cured plate is burnt and is made into glass-like carbon or the frame, where the substrate in which the uneven surface is formed is arranged on one face is filled with powder-like thermosetting resin. It is hot-pressed and molded with a pressure of 0.2-20 Ton/cm2, and the resin cured plate is generated. After that, the frame is peeled, the obtained resin cured plate is burnt, and it may be made into glass-like carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solar cell substrate.

[0002]

2. Description of the Related Art As a solar cell using an amorphous semiconductor material such as amorphous silicon, SnO on glass is used.
_2. It is known to use a substrate on which a transparent electrode layer made of a light-transmitting conductive oxide such as ITO is deposited, and form an amorphous semiconductor layer on the substrate by a plasma CVD method. Conventionally, in order to improve the conversion efficiency by using the light confinement effect, the transparent electrode layer is formed into a shape having many irregularities on the surface by controlling the deposition conditions within an appropriate range. However, when depositing a transparent electrode layer having such a surface shape, 5
Since it is formed by a thermal CVD process at about 50 ° C., it accounts for a large proportion of the manufacturing cost, which hinders the cost reduction of the amorphous solar cell.

[0003] Further, as described in Japanese Patent Application Laid-Open No. 1-246816, the use of a general carbon material as a substrate for a solar cell has been studied. There is a drawback that causes a reduction in yield in the production of solar cells. In addition, when a general carbon material is used for the substrate, a concavo-convex structure (texture structure) formed to improve the light confinement effect cannot be formed, so that the obtained photoelectric conversion efficiency is low and the performance as a solar cell is low. And it was difficult to put it to practical use.

Further, when a general carbon material is used as a substrate for a solar cell, the carbon powder detached from the carbon material itself when depositing amorphous silicon by CVD becomes dust and is taken in the amorphous silicon thin film. Battery yield is low. Further, if dust is present on the surface layer of the carbon substrate, the adhesion of the CVD thin film to the substrate is poor, and the formed thin film is easily peeled off from the carbon substrate, causing a reduction in reliability.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. That is, the present invention provides a manufacturing method that can easily form a glassy carbon solar cell substrate having a high degree of photoelectric conversion efficiency and a precise uneven structure without peeling of a transparent conductive film or an amorphous silicon thin film. It is.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a mold in which a plate having an uneven surface is arranged on one surface and has a viscosity of 0.5 to 0.5.
A method for manufacturing a solar cell substrate, comprising casting and curing a 5-poise liquid thermosetting resin, peeling off a mold, and firing the resulting resin-cured plate to form a glassy carbon. About. The present invention also provides a mold in which a substrate having the above-mentioned uneven surface is formed on one surface, a powdery thermosetting resin is filled, and hot-pressed at a pressure of 0.2 to 20 Ton / cm ^2. The present invention relates to a method for manufacturing a solar cell substrate, comprising: after forming a cured resin plate by heating, removing a mold, and firing the resulting cured resin plate to form a glassy carbon.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A solar cell substrate manufactured by the present invention is made of glassy carbon having a concavo-convex structure formed on the surface of a substrate forming the solar cell. Glassy carbon has properties such as light weight, heat resistance, corrosion resistance, electric conductivity, and high purity that common carbon materials have. Because of its low characteristics, it is being used in a wide range of applications in various fields such as the electronics industry, nuclear power industry, and aviation industry. The above uneven structure can increase the optical path length of light in the amorphous silicon film formed thereon, thereby increasing the photoelectric conversion efficiency. The specific shape of the uneven structure is not particularly limited. For example, an inverted pyramid-shaped depression having a side of 0.2 to 50 μm is arranged innumerably regularly or irregularly, and has a width of 0.2. There may be mentioned, for example, those in which grooves of up to 50 μm are formed in countless stripes or lattices, and those in which hemispherical depressions are formed innumerably. The unevenness level difference (level difference) on the surface on which the uneven structure is formed is 0.2
It is preferably from 50 to 50 μm.

The material is made of glassy carbon. By this material, when the amorphous silicon is deposited by CVD, the carbon powder does not become dust and is not desorbed, so that the yield of the solar cell can be improved. The amorphous silicon thin film formed with good adhesion of the CVD thin film to the substrate is less likely to peel off from the substrate, and the reliability is improved.

The glassy carbon can be obtained by firing and carbonizing a thermosetting resin. As a method for forming the uneven structure (texture structure) on the glassy carbon, a mold using a substrate on which a concavo-convex structure that can transfer a desired uneven structure is formed on a surface on which a solar cell is formed is formed. However, it can be performed by molding using this mold.

There is no particular limitation on the method of forming the concave-convex structure on a substrate serving as a mold. For example, a single-crystal silicon substrate is etched with an etchant to form a substrate on which a large number of large and small pyramid-shaped protrusions are formed. The method used (Figure 1
Figure 1 shows an electron micrograph of an example of the substrate), a method of mechanically forming grooves in a glass or metal substrate, a method of forming irregularities by sandblasting the surface of a glass or metal substrate using abrasive grains, etc. Is mentioned. Among these,
It is preferable to use a substrate on which a single crystal silicon substrate is etched with an etching solution and an infinite number of large and small pyramid-shaped projections are formed, since an uneven structure can be formed easily and accurately. There are no particular restrictions on the etching conditions,
For example, after cleaning the surface of a single crystal silicon substrate on which a concavo-convex structure is formed with a cleaning liquid,
% At 70-80 ° C.
It can be formed by etching for about 0 to 80 minutes.

The method for transferring differs depending on the type of the thermosetting resin. When a liquid thermosetting resin (liquid thermosetting resin itself and a solution of the thermosetting resin) is used,
It can be cast and transferred to the substrate, and in the case of a powdery thermosetting resin, it can be transferred by hot pressing. The thermosetting resin is not particularly limited, and examples thereof include a phenol resin, an epoxy resin, an unsaturated polyester resin, a furan resin, a melamine resin, an alkyd resin, and a xylene resin. Also, a mixture of these resins can be used. Among these resins, it is preferable to use a furan resin, a phenol resin, or a mixed resin thereof because a vitreous carbon having good characteristics can be obtained.

Further, when a curing agent such as p-toluenesulfonic acid, phenolsulfonic acid or trichloroacetic acid is dissolved in a solvent such as ethanol, acetone or ethylene glycol and added to the thermosetting resin, the curing time can be shortened. preferable. When a curing agent is used, its amount is preferably 0.1 to 10% by weight based on the thermosetting resin in terms of controlling the curing reaction.

When a liquid thermosetting resin is used, the substrate having the uneven structure is fixed in a dish-shaped container or mold made of aluminum, iron, or the like using an adhesive or the like, if necessary. This is preferable because the mold can be easily separated and reused. In the production method of the present invention, the viscosity of the liquid thermosetting resin (when a curing agent is blended, the viscosity before blending) is 0.5 to 5 poise (25 ° C.). Outside this range, the uneven structure cannot be transferred accurately.
From the same viewpoint, a preferable viscosity is 0.8 to 2.5 poise. In this case, in order to accurately transfer the uneven structure, after casting the liquid thermosetting resin, it is preferable that the uncured stage be placed under a reduced pressure of preferably 0.01 to 10 Torr and returned to normal pressure. A method in which the treatment is repeated several times, preferably 2 to 10 times, is preferred. After the treatment under reduced pressure, the resin is cured at preferably 30 to 90C, more preferably 40 to 70C, and preferably for 30 minutes to 15 hours. After the resin is cured, the cured product of the resin is separated from the silicon substrate, preferably at 90 to 230 ° C, more preferably at 100 to 21 ° C.
Cure at 0 ° C. for 1-50 hours. FIG. 2 shows an electron micrograph of an example of a cured resin manufactured using a liquid thermosetting resin using the silicon substrate of FIG. 1 as a mold.

When a powdery thermosetting resin is used, a method of forming a concavo-convex structure on glassy carbon may be a hot-press molding method. In order to form the concavo-convex structure by the hot-press molding method, the substrate having the concavo-convex structure is fixed to a mold of a hot-press molding machine by welding or bonding, or the concavo-convex structure is directly formed on one surface of the mold of the hot-press molding machine. A structure can be formed and used as a mold. After filling the mold with the powdery thermosetting resin, in the present invention, molding is performed at a pressure of 0.2 to 20 Ton / cm ² . Outside this range, the uneven structure may not be transferred with high accuracy, or the mold may be broken. From the same viewpoint, a preferable pressure is 0.5 to 5 To.
n / cm ² . The temperature of hot pressing is preferably 50 to 2
00 ° C, more preferably 80 to 160 ° C. After the hot pressing, the obtained resin molded plate is preferably cured again at 80 to 230 ° C. to obtain a resin cured plate.

The cured resin plate obtained by each of the above methods can then be fired in a non-oxidizing atmosphere to obtain glassy carbon. Firing is preferably at 0.5 to 10 ° C.
/ Hour, preferably at a temperature of 800 ° C. or higher, more preferably at a temperature of 1000 ° C. or higher.
It can be carried out by holding for 0 hour. When the maximum heat treatment temperature is lower than 800 ° C., carbonization is insufficient, and atoms other than carbon atoms contained in the raw material thermosetting resin, such as hydrogen, oxygen, and nitrogen, tend to remain in the obtained glassy carbon. is there. If the element other than carbon atoms is used for the substrate of the solar cell while remaining, the element other than carbon is released during the thin film CVD of silicon and the like, enters the silicon thin film and becomes a defect, deteriorating the reliability of the solar cell. May be.

Further, the glassy carbon obtained by firing at a heat treatment temperature of 800 ° C. or higher may be subjected to a high temperature treatment in a non-oxidizing atmosphere at a temperature in the range of 800 to 3000 ° C. Further, after cutting into an arbitrary size, a high purity treatment can be performed by blowing a purified gas such as chlorine or freon with a decalcification furnace or the like. FIG. 3 shows an electron micrograph of the surface of a solar cell substrate obtained by converting the cured resin of FIG. 2 into glassy carbon.

On a glassy carbon substrate having an uneven structure formed on the surface obtained as described above, a conventional method is used.
An amorphous silicon thin film or the like can be formed. The substrate thus obtained has a high light confinement effect because of having a precise uneven structure, and by using this, a solar cell with high photoelectric conversion efficiency can be obtained.
In addition, since the uneven structure also has a function of preventing peeling of a thin film of amorphous silicon or the like, there is no peeling of the thin film, and a solar cell with good yield and high reliability can be obtained.

[0018]

Embodiments of the present invention will be described below. Example 1 A single-crystal silicon substrate formed by the etching process with the concavo-convex structure shown in FIG. 1 was bonded to an aluminum Petri dish using an adhesive. An initial condensate of a furan resin having a viscosity of 1 poise (measured with a B-type viscometer at 25 ° C. and a rotor rotation speed of 60 rpm) (Hitafuran V, manufactured by Hitachi Chemical Co., Ltd.)
F-302), trichloroacetic acid was added as a curing agent to the resin at 7% by weight, and the mixture was cast into a petri dish.
After resin injection, degassing was performed twice at room temperature to reduce the pressure to 0.1 Torr for 2 minutes, then the pressure was returned to normal pressure, and curing was performed at 40 ° C. for 7 hours. After curing, the semi-cured resin was peeled off from the single crystal silicon, and cured at 120 ° C. for 10 hours between stainless steel plates. The obtained hardened plate is heated in a non-oxidizing atmosphere to 900 ° C. at a rate of 2 ° C./hour, kept at 1000 ° C. for 3 hours to be baked and carbonized, and further up to 2800 at a rate of 5 ° C./min. The temperature was raised to 70 ° C. to perform graphitization.

FIG. 3 shows an electron micrograph of the formed concavo-convex structure. As is clear from this figure,
Precise uneven structure (inverted pyramid type or hemispherical shape with one side in the range of 1 to 50 μm, unevenness step (height difference) is 1 to 50 μm
m) was formed over the entire surface. After forming a tungsten back electrode film on the obtained glassy carbon substrate by sputtering, the plasma CV
A thin film of amorphous silicon was deposited by Method D, a transparent electrode film on the surface side and a comb-shaped collector electrode were formed, lead wires were attached, and the photoelectric conversion efficiency was evaluated.

Example 2 Single-crystal silicon having the concavo-convex structure shown in FIG. 1 was welded to the bottom of a mold of a hot press molding machine. A powdery phenol resin (Kanebo Co., Ltd., S800) was used as a raw material resin, and was charged into a hot-press molding machine. After loading the resin, 150 ℃ at ² Ton / cm ² pressure
For 3 minutes. After molding, the semi-cured resin was separated from the single crystal silicon, and cured at 230 ° C. for 3 hours between SUS plates. The obtained cured plate was heated to 1000 ° C. at a rate of 2 ° C./hour in a non-oxidizing atmosphere,
It was kept at 000 ° C. for 3 hours for carbonization, and further graphitized by heating up to 2800 ° C. at a rate of 5 ° C./min.

On the surface of the formed substrate, the same fine uneven structure as shown in FIG. 3 (an inverted pyramid type or hemispherical shape having a side of 1 to 50 μm, a step of unevenness (difference in height) of 1 to 50 μm).
m) was formed over the entire surface. After forming a tungsten back electrode film on the obtained glassy carbon substrate by sputtering, the plasma CV
A thin film of amorphous silicon was deposited by Method D, a transparent electrode film on the surface side and a comb-shaped collector electrode were formed, lead wires were attached, and the photoelectric conversion efficiency was evaluated.

Comparative Example 1 Trichloroacetic acid as a curing agent was added to a furan resin precondensate (Hitafuran VF-302, manufactured by Hitachi Chemical Co., Ltd.) as a curing agent in an amount of 7% by weight and cast into a petri dish. After resin injection, degassing was performed twice at room temperature to reduce the pressure to 0.1 Torr for 2 minutes, then the pressure was returned to normal pressure, and molding was performed at 90 ° C. for 7 hours. The obtained cured plate is heated in a non-oxidizing atmosphere at a heating rate of 2 ° C.
/ Hour at 900 ° C., and hold at 900 ° C. for 3 hours to form carbonized carbon, and at a rate of 5 ° C./min.
The temperature was raised to 0 ° C. to perform graphitization. After forming a tungsten backside electrode film on the obtained glassy carbon substrate by a sputtering method and further depositing an amorphous silicon thin film by a plasma CVD method, the amorphous silicon thin film was peeled off. I could not do it.

Comparative Example 2 After forming a tungsten back electrode film on a glass substrate having no uneven structure by a sputtering method, a thin film of amorphous silicon was further deposited by a plasma CVD method, and a transparent electrode film on the front side and a comb shape were formed. Was formed, lead wires were attached, and the photoelectric conversion efficiency was evaluated. Using the above substrate, the photoelectric conversion efficiency was evaluated. Substrate size is 1cm
^{And 2} . Table 1 shows the evaluation results. In addition, the photoelectric conversion efficiency indicates that the larger the number is, the higher the efficiency is.

[0024] ☆

[Table 1] Table 1 ★

[0025]

According to the method for manufacturing a solar cell substrate of the present invention, it is possible to easily form a precise uneven structure and to produce a solar cell having high photoelectric conversion efficiency. A solar cell substrate made of glassy carbon that does not generate can be manufactured.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing an example of the surface structure of a mold substrate used for forming a concavo-convex structure in a method for manufacturing a solar cell substrate of the present invention.

FIG. 2 is an electron micrograph showing an example of the surface structure of a cured resin that becomes a solar cell substrate in the method for manufacturing a solar cell substrate of the present invention.

FIG. 3 is an electron micrograph showing an example of a concavo-convex structure on the surface of a solar cell substrate obtained by the production method of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 87/00 C04B 35/52 A (72) Inventor Kojiro Ota 3-1-1 Ayukawacho, Hitachi City, Ibaraki Prefecture No. Hitachi Chemical Industry Co., Ltd. Yamazaki Plant (72) Inventor Takayuki Suzuki 3-3-1 Ayukawacho, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Plant (72) Inventor Mikiro Taguchi Keihan Motodori, Moriguchi City, Osaka Prefecture 2-5-5 Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A liquid thermosetting resin having a viscosity of 0.5 to 5 poise is poured into a mold in which a plate having an uneven surface is arranged on one side, and the mold is cured. A method for manufacturing a solar cell substrate, comprising peeling off a resin cured plate and firing the resin cured plate to form a glassy carbon. 2. A mold in which a substrate having an uneven surface formed on one side is filled with a thermosetting resin in powder form,
After forming a resin-cured plate by hot-press molding at a pressure of ~ 20 Ton / cm ² , the mold is peeled off, and the obtained resin-cured plate is baked to be glassy carbonized. Production method.