JP3628108B2 - Manufacturing method of solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystalline solar cell and a method for manufacturing the same.
[0002]
[Prior art]
A conventional crystalline silicon solar cell is manufactured as follows, for example. A polycrystalline or single crystal silicon ingot (bulk crystal) produced by a pulling method or a casting method is cut into a thin wafer. Then, a pn junction is formed on the surface of the wafer by a diffusion method or an ion implantation method, and an electrode is further formed by a vacuum deposition method, a printing firing method, or a plating method.
[0003]
[Problems to be solved by the invention]
In the above conventional method for manufacturing a crystalline silicon solar cell, a cutting margin is generated when a wafer is cut out from a polycrystalline or single crystal silicon ingot. For example, when a wafer having a thickness of several hundreds μm is cut out from a silicon ingot having a diameter of 15 cm or a square of 15 cm, a cutting margin of the same thickness as the wafer, that is, a thickness of several hundreds of μm is generated. For this reason, waste of silicon having the same thickness as that of the silicon wafer actually used occurs.
[0004]
Moreover, although the thickness which contributes to photoelectric conversion in a crystalline silicon solar cell is 100 μm or less, it is difficult to cut the silicon ingot into a wafer having a thickness of 100 μm or less. For this reason, an actual crystalline silicon solar cell uses silicon having a thickness greater than necessary, resulting in waste.
[0005]
An object of the present invention is to provide a method capable of manufacturing a crystalline solar cell at a low cost without causing waste of a crystalline semiconductor .
[0006]
The method for manufacturing a solar cell according to the present invention includes a first step of ion-implanting a predetermined element into a predetermined depth of a first conductivity type crystalline semiconductor, and a predetermined element being implanted in the first step. A second step of bonding the crystalline semiconductor on the band-shaped substrate, a third step of depositing a predetermined element from the crystalline semiconductor by heat treatment to form vacancies distributed in layers in the crystalline semiconductor, and a crystal of the crystal by heat treatment A fourth step of forming a first conductivity type semiconductor layer on the band-shaped substrate by cutting the semiconductor in a layer-distributed void region; and in the first conductivity type semiconductor layer or the first conductivity type semiconductor layer And a fifth step of forming a second conductivity type semiconductor layer thereon, and the second, third, fourth and fifth steps are successively performed in independent reaction chambers while transferring the belt-like substrate. The crystal semiconductor cut from the first conductivity type semiconductor layer in the fourth step is It is intended to be reused in the process.
[0007]
In the method for manufacturing a solar cell according to the present invention, vacancy distributed in a layered manner is formed in the crystalline semiconductor by precipitating from the crystalline semiconductor a predetermined element injected in a layered manner to a predetermined depth of the crystalline semiconductor, A semiconductor layer of the first conductivity type can be formed on the substrate by cutting the crystalline semiconductor at the region of the holes distributed in the layer shape. Since the thickness of the first conductivity type semiconductor layer corresponds to the implantation depth of the predetermined element, the first conductivity type semiconductor layer having an arbitrary thickness is formed on the substrate by adjusting the implantation depth. can do.
[0008]
Therefore, the first conductivity type semiconductor layer can be easily formed to a thin thickness necessary for photoelectric conversion. Further, the remaining portion of the crystalline semiconductor cut in the region of the holes distributed in layers can be reused for manufacturing another solar cell. Therefore, the crystal semiconductor is not wasted, and the manufacturing cost of the solar cell is reduced.
[0009]
In particular, it is a great advantage that the crystalline semiconductor cut from the first conductivity type semiconductor layer in the fourth step can be reused in the first step. Thereby, the crystal semiconductor is not wasted, and the manufacturing cost of the solar cell is reduced.
[0010]
In addition, since the second, third, fourth, and fifth steps are continuously performed in independent reaction chambers while transferring the strip substrate, a plurality of solar cells can be continuously formed on the strip substrate. It becomes possible.
[0011]
The crystalline semiconductor may be a single crystal semiconductor or a polycrystalline semiconductor. The predetermined element is preferably hydrogen or a rare gas. Thus, the predetermined element can be easily precipitated from the crystalline semiconductor by heat treatment in the third step, and vacancies distributed in layers in the crystalline semiconductor can be easily formed.
[0012]
The predetermined depth is preferably 100 μm or less. In particular, when the crystalline semiconductor is silicon, the predetermined depth is preferably 20 μm or more and 100 μm or less. When the crystalline semiconductor is gallium arsenide, the predetermined depth is preferably 2 μm or more and 10 μm or less. As a result, it is possible to form the first conductivity type semiconductor layer with a thin thickness that contributes sufficiently to photoelectric conversion and does not cause waste on the substrate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic process diagram showing a method for manufacturing a solar cell in one embodiment of the present invention.
[0014]
In FIG. 1, a belt-shaped stainless steel substrate 1 having a thickness of about 0.2 mm and a width of about 900 mm is wound around a roll 101. As shown by the arrow A, the stainless steel substrate 1 is transferred between the two rolls 101 and 102, and the steps (a) to (h) are performed in separate reaction chambers. Inter-mixing of process gases is prevented by blocking each reaction chamber with an air curtain or differential exhaust.
[0015]
In step (i), for example, H (hydrogen) is ion-implanted into a p-type cast polycrystalline silicon ingot 2 of 15 cm square, for example. Thereby, an implantation region of atomic hydrogen 4 is formed in the polycrystalline silicon ingot 2. The specific resistance of the polycrystalline silicon ingot 2 is 10 ⁻¹ Ω · cm to several Ω · cm. As ion implantation conditions, the acceleration energy of hydrogen ions (H ⁺ ) is 2 MeV, and the dose is 1 × 10 ¹⁷ cm ⁻² . In this case, the implantation depth D is about 50 μm, and the thickness t of the implantation region is about 0.7 μm.
[0016]
On the other hand, in the step (a), the surface of the stainless steel substrate 1 is cleaned by ion sputtering cleaning with Ar (argon) using the sputtering apparatus 10. Or you may clean with an organic solvent or / and an acid solution. Next, in the step (b), the polycrystalline silicon ingot 2 into which the atomic hydrogen 4 has been implanted is applied to the surface of the stainless steel substrate 1 at 200 ° C. using the conductive adhesive 3 made of a low melting point metal such as Sn (tin). Glue with. Or you may adhere | attach with the electroconductive adhesive which disperse | distributed the metal particle to the organic solvent.
[0017]
Next, heat treatment is performed at 300 ° C. in step (c). As a result, the atomic hydrogen 4 is precipitated as a hydrogen molecular gas inside the polycrystalline silicon ingot 2, and a large number of holes 4 a distributed in layers at a depth of about 50 μm of the polycrystalline silicon ingot 2 are formed. Next, in step (d), heat treatment is performed at 500 ° C., and the polycrystalline silicon ingot 2 is cut in the region of the holes 4 a by thermal shock. Thereby, a p-type silicon layer 2 a having a thickness of about 50 μm is formed on the stainless steel substrate 1. The surface of the p-type silicon layer 2a has a roughness of about 0.01 to 0.1 μm.
[0018]
Next, in step (e), P (phosphorus) as n-type dopant is doped into the p-type silicon layer 2a by ion implantation to a depth of about 0.06 μm. As ion implantation conditions, the acceleration energy of phosphorus ions (P ⁺ ) is 50 keV, and the dose is 1 × 10 ¹⁶ cm ⁻² .
[0019]
Further, in the step (f), a short-time heat treatment (Fush annealing) is performed using the Xe (xenon) lamp 11. Thereby, P doped in the p-type silicon layer 2a is activated, and an n-type silicon layer 5 having a thickness of about 0.06 μm is formed on the surface of the p-type silicon layer 2a.
[0020]
Next, in step (g), an electrode 6 is formed on the surface of the n-type silicon layer 5 by screen printing. Finally, in step (h), an antireflection film 7 made of a silicon nitride film or the like is formed on the n-type silicon layer 5 by a CVD method (chemical vapor deposition method) or the like. In this way, solar cells 8 are formed on the stainless steel substrate 1.
[0021]
On the other hand, the polycrystalline silicon ingot 2 cut in step (d) is reused in step (i) after the surface is polished.
In this way, a plurality of solar cells 8 are continuously manufactured on the stainless steel substrate 1 by a dry process. In this solar cell 8, the stainless steel substrate 1 serves as a back electrode, and the electrode 6 serves as a front electrode.
[0022]
In the solar cell 8 manufactured as described above, the p-type silicon layer 2a is as thin as about 50 μm, and the remaining portion of the polycrystalline silicon ingot 2 cut in the step (d) is repeatedly processed in the step (i). Is also reused, so that the polycrystalline silicon ingot 2 is not wasted. Therefore, the manufacturing cost of the photovoltaic cell 8 is reduced.
[0023]
Moreover, since the surface of the p-type silicon layer 2a formed in the step (d) has a roughness of about 0.01 to 0.1 [mu] m, sunlight incident on the solar cells 8 is p-type silicon layer 2a. Are reflected multiple times on the surface of the solar cell 8 and reenter the entire solar cell 8 to be used. Therefore, the effective incident light reflectance is reduced regardless of the wavelength, and the conversion efficiency is improved. For example, when a <100> plane single crystal ingot is used, hydrogen gas is selectively deposited on the (111) plane, so that the cut surface has a textured structure with irregularities on the (111) plane, and the effective reflectance is reduced to 1 /. Can be reduced to two.
[0024]
Before the step (a), as shown in FIG. 2, an insulating layer 1 ′ made of a silicon oxide film or the like is formed on the stainless steel substrate 1 by a CVD method or the like by the step (a ′). The solar cells 8 can be insulated from each other, and the plurality of solar cells 8 can be connected in series. Thereby, the output voltage can be increased.
[0025]
FIG. 3A is a schematic cross-sectional view of a hybrid solar cell module using the solar cell of FIG. 1, and FIG. 3B is a cross-sectional view taken along the line XX of FIG.
As shown in FIG. 3, a plurality of solar cells 8 are formed on the upper surface of the stainless steel substrate 1 by the method shown in FIG. A plurality of metal pipes 31 are disposed on the lower surface of the stainless steel substrate 1. Water circulates inside the metal pipe 31.
[0026]
In the hybrid solar cell module of FIG. 3, the solar energy is converted into electric energy by the solar cells 8, and the solar energy is converted into thermal energy in the metal pipe 31 and hot water is supplied.
[0027]
In this hybrid solar cell module, by using the solar cell of FIG. 1, the manufacturing cost can be reduced and the added value can be improved by using hot water.
The conversion efficiency of solar cells decreases with increasing temperature. In the hybrid solar cell module of FIG. 3, the water circulating in the metal pipe 31 also works as cooling water for cooling the solar cells 8, so that energy can be effectively used.
[0028]
In the above embodiment, H is ion-implanted in the step (a) in order to form the holes 4a in the step (c), but a rare gas such as He (helium) is used instead of H. You can also. When He ions are implanted, the acceleration energy is set to about 10 MeV.
[0029]
A single crystal silicon ingot may be used instead of the polycrystalline silicon ingot 2. Further, plate-like silicon may be used instead of the silicon ingot. Further, a gallium arsenide (GaAs) ingot having a large light absorption coefficient may be used instead of the silicon ingot. In this case, since the light absorption coefficient is larger than that of silicon, the semiconductor layer can be made 2 μm or more and 10 μm or less thinner than silicon, so that the usage fee of the semiconductor is further reduced, and the hydrogen ion implantation energy is a fraction of that of silicon. Can be reduced.
[0030]
Further, a glass substrate may be used instead of the stainless steel substrate 1. When sunlight is incident from the glass substrate side, a transparent electrode is formed between the glass substrate and the silicon layer.
[0031]
Further, in the above embodiment, a p-type polycrystalline silicon ingot is used. However, an n-type silicon layer is formed using an n-type polycrystalline or single-crystal silicon ingot, and a p-type is formed on the n-type silicon layer. A silicon layer may be formed.
[Brief description of the drawings]
FIG. 1 is a schematic process diagram showing a method for manufacturing a solar cell in an embodiment of the present invention.
FIG. 2 is a diagram showing a process that can be added before the first process in FIG. 1;
3 is a schematic cross-sectional view of a hybrid solar cell module using the solar cell of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Stainless steel substrate 1 'Insulating film 2 Polycrystalline silicon ingot 2a P-type silicon layer 3 Conductive adhesive 4 Atomic hydrogen 4a Hole 5 N-type silicon layer 6 Electrode 7 Antireflection film 8 Solar cell

Claims (3)

A first step of ion-implanting a predetermined element into a predetermined depth to a predetermined depth of a crystalline semiconductor of the first conductivity type;
A second step of bonding the crystalline semiconductor into which the predetermined element has been implanted in the first step onto a strip substrate;
A third step of depositing the predetermined element from the crystalline semiconductor by heat treatment to form vacancies distributed in layers in the crystalline semiconductor;
A fourth step of forming a first conductivity type semiconductor layer on the band-shaped substrate by cutting the crystalline semiconductor in the layered hole regions by heat treatment;
And a fifth step of forming a second conductivity type semiconductor layer in the first conductivity type semiconductor layer or on the first conductivity type semiconductor layer,
The second, third, fourth and fifth steps are continuously performed in independent reaction chambers while transferring the strip substrate,
A method for manufacturing a solar cell, wherein the crystal semiconductor cut from the semiconductor layer of the first conductivity type in the fourth step is reused in the first step . Method of manufacturing a solar cell according to claim 1, wherein said predetermined element is characterized in that it consists of hydrogen or a noble gas. According to claim 1 or 2 for producing a solar cell, wherein said predetermined depth is 100μm or less.

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