JP2675174B2 - Solar cell manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a solar cell, and more particularly to a method for manufacturing a solar cell having good energy conversion efficiency.

[Conventional technology]

Conventionally, a solar cell has been used as a driving energy source in various devices. This solar cell uses a pn junction in the functional portion, and silicon is generally used as a semiconductor forming the pn junction. From the viewpoint of the efficiency of converting light energy into electromotive force, it is preferable to use single crystal silicon, but from the viewpoint of increasing the area and reducing the cost, amorphous silicon is advantageous.

In recent years, the use of polycrystalline silicon has been studied for the purpose of obtaining low cost as amorphous silicon and high energy conversion efficiency as single crystal. However, in the conventionally proposed method, it is difficult to make a thin plate by slicing a lumpy polycrystal into a plate, and therefore, the thickness is not less than a film thickness sufficient to absorb the amount of light. The energy conversion efficiency was not sufficient.

Therefore, attempts have been made to form a thin film of polycrystalline silicon by using a thin film forming technique such as chemical vapor deposition (CVD), but the crystal grain size is only about a few hundredths of a micron, and the bulk polycrystalline The energy conversion efficiency is inferior to the case of the silicon slice method.

Further, attempts have been made to increase the crystal grain size by irradiating the polycrystalline silicon thin film formed by the CVD method with a laser beam to melt and recrystallize the thin film, but cost reduction is not sufficient, and stable production is possible. Have difficulty.

Furthermore, in the above CVD method, the thin film manufacturing process temperature is 6
Since the temperature ranges from 00 ° C to 1000 ° C, the characteristics of the solar cell are deteriorated due to the diffusion of the dopant through the junction surface in the solar cell. Furthermore, if a low-cost metal substrate is used as the substrate, silicide will be formed at high temperatures and surface levels will be created, degrading the solar cell characteristics, so expensive substrates such as SiO and SiN must be used. First of all, the manufacturing cost must be high.

Therefore, for the purpose of making it possible to form a thin film polycrystal on an inexpensive metal substrate, the molten silicon is directly deposited on the substrate by a method (rotation method and horizontal pulling method) of about 10
Although a polycrystalline silicon thin film having a thickness of 0 μm to 30 μm has been formed, the fact is that a good solar cell has not been produced due to the strong influence of impurities in the manufacturing process.

On the other hand, Japanese Patent Application Laid-Open No. 62-241326 discloses a proposal for improving the quality by lowering the thin film manufacturing process temperature. This method of forming a deposited film is the same as the active species (A) obtained by decomposing a compound containing a silicon atom and a halogen, and the active species (A).
And the activated species (B) capable of chemically interacting with each other are separately introduced into the film formation space to form a deposited film on the substrate provided in the film formation space by a chemical reaction. By this method, a deposited film can be formed at about 200 ° C. to 300 ° C., and a problem that has been a problem in a high temperature process, that is, a problem of interdiffusion of dopants through a bonding surface is being solved.

However, in the production of a semiconductor layer by vapor phase growth, in order to obtain good crystallinity, a crystalline base material of the same type (homoepitaxial growth) or a different type (heteroepitaxial growth) with a close lattice constant is used as the base material. , This is used as a Seed substrate for crystal growth. Therefore, in order to manufacture a solar cell by this deposited film forming method, it is necessary to use an expensive single crystal substrate, and if a simple metal substrate is used, a good crystalline solar cell cannot be obtained. This has been one of the causes for increasing the manufacturing cost of solar cells.

In addition, there are methods such as vapor deposition and sputtering in the method for manufacturing the silicon polycrystalline electrode substrate, but the film forming rate is significantly inferior to the method in which molten silicon is directly contacted with the substrate and rapidly cooled. In reality, the increase in substrate manufacturing cost due to speed cannot be avoided.

[Problems to be solved by the invention]

An object of the present invention is a manufacturing method capable of good crystal growth and having a reduced manufacturing cost, which has good characteristics such as crystallinity and energy conversion efficiency, and can be used for stable practical solar cells. It is to provide a method that can be manufactured.

[Means for solving the problem]

In the present invention, an active species (A) obtained by decomposing a compound containing silicon and halogen and an active species (B) capable of chemically interacting with the active species (A) are separately introduced into a film formation space. In a method for manufacturing a solar cell, which comprises a step of forming a deposited film on a substrate placed in the film formation space by a chemical reaction, a metal substrate or a metal substrate coated with a refractory metal is used as the substrate, A solar cell characterized by using a substrate having a silicon polycrystal electrode layer obtained by forming a polycrystal silicon layer by growing a doping material and molten silicon by a rotating method or a horizontal pulling method, and carrying out a heat treatment. It is a method of manufacturing a battery.

First, one mode for obtaining a substrate (silicon polycrystalline electrode substrate) used in the present invention. The rotation method will be described in detail.

This rotation method is, for example, a method in which a metal substrate or a metal substrate coated with a high melting point metal is rotated at a high speed, molten silicon is dropped in an appropriate amount onto the metal substrate, and it is spread thinly and crystallized on the substrate by centrifugal force. . This crystal grows upward from the surface of the substrate rotating at high speed to form a columnar structure. In the present invention, the metal substrate and the refractory metal are not particularly limited, but examples of the metal substrate include SUS material, Fe and the like, and examples of the refractory metal include Cr, W, Mo and the like.

When performing this rotation method, it is also effective to perform heating of the substrate, ultrasonic vibration or a combination of heating and vibration for the purpose of improving the adhesion between the metal substrate or the refractory metal coating substrate and silicon. . Further, the amount of molten silicon dropped by this rotation method may be appropriately determined according to the desired film thickness. At a rotation speed of about 1000 revolutions per minute, a polycrystal of about 30 to 20 μm can be formed, and this polycrystal film is sufficient for use as an electrode. Furthermore, it is possible to reduce the film thickness by adjusting the rotation speed.

Next, the horizontal drawing method, which is another embodiment of the method for obtaining the silicon polycrystalline electrode substrate used in the present invention, will be described in detail.

This horizontal pulling method is, for example, a method of inserting a metal base or a metal base coated with a refractory metal into a nozzle and continuously horizontal pulling while growing a silicon crystal on the base in the nozzle. . This crystal grows from the surface of the substrate toward the upper surface of the nozzle to form a columnar structure.

If impurities are introduced into the silicon polycrystal layer formed on the substrate by the above-mentioned rotation method or horizontal pulling method, the resistivity of the silicon polycrystal layer in the thin film direction is significantly reduced, and the silicon polycrystal layer can sufficiently function as an electrode. In the present invention, a doping material composed of this impurity is provided in advance on the metal substrate or the like before forming the silicon polycrystal layer, or after forming the silicon polycrystal layer, the doping material is formed thereon, Impurities are introduced into the silicon polycrystal by heat treatment to obtain a silicon polycrystal electrode substrate. As the impurity introduction method, a solid phase epitaxy method or a photochemical formation method, which can easily lower the temperature of the process, is desirable. This method is usually a method of forming a P-type Si layer with a dopant such as Al, and when this method is used on a thick Si wafer, n-P
Bonding is possible, but P-
This is a method for producing Si, and typical examples of the impurities include Al and Cr. The heat treatment temperature for introducing this impurity is preferably 400 ° C or higher, and preferably 400 ° C to 600 ° C.
The temperature is more preferably 00 ° C to 500 ° C, and the heat treatment time is preferably about 2 hours.

On the silicon polycrystalline electrode substrate obtained as described above, a substantially single crystal layer of a semiconductor of the first conductivity type and a second
A solar cell can be obtained by forming a substantially single crystal layer of a conductive type semiconductor. The first-conductivity-type semiconductor layer is formed so that the surrounding crystal orientations are the same, and the second-conductivity-type semiconductor layer is on the first semiconductor layer and has the same peripheral crystal orientation. Is formed as. Hereinafter, this step will be described in detail.

In the manufacturing method of the present invention, the above-mentioned first and second
As a deposited film forming method for forming a semiconductor layer, an active species (A) obtained by decomposing a compound containing silicon and halogen, and an active species (B) capable of chemically interacting with the active species (A). Is separately introduced into the film forming space, and a deposited film is formed on the substrate placed in the film forming space by a chemical reaction. In this deposited film forming method, the compound containing silicon and halogen is decomposed by being supplied with activation energy in an activation space (a) different from the film formation space and decomposed to generate active species (A). Further, the active species (B) is also generated in the activation space (b) different from the film formation space. Then, in the film formation space, a chemical interaction is caused in the coexistence of the active species (A) and the active species (B) to form a deposited film. Therefore, it is not necessary to generate plasma or the like in the film formation space, and the deposited film is not adversely affected by sputtering or electrons due to plasma or generated ions. Furthermore, a more stable CVD method can be achieved by controlling the atmospheric temperature of the film formation space and the substrate temperature as desired. In addition, here, since the active species previously activated in the activation space different from the film formation space is used, the film formation speed is dramatically increased, and the substrate temperature during the formation of the deposited film is further improved. It is possible to reduce the temperature. In the present invention, by using the silicon polycrystalline electrode substrate obtained by the above-mentioned special method for such a special CVD method, the respective advantages of the both have a synergistic effect, and as a result, It is possible to obtain a solar cell that is extremely excellent in terms of function, cost, and the like. In other words, the combination of the series of steps described above is a very suitable manufacturing method for manufacturing a solar cell.

The active species (A) introduced into the film formation space has a life of 0.1 seconds or more, more preferably 1 second or more, and most preferably 10 seconds or more, selected from the viewpoints of productivity and ease of handling. Has been used.

As the compound containing silicon and halogen for generating the active species (A), for example, a compound obtained by substituting a part or all of hydrogen atoms of a chain or cyclic silane compound with a halogen atom is used. Specifically, for example, Si _u Y
_{2U + 2} (u represents an integer of 1 or more, Y represents at least one element selected from the group consisting of F, Cl, Br and I)
A chain silicon halide represented by Si _v Y _2V (v is a positive number of 3 or more, Y is the same as above), and Si _U H _x Y _y (u and Y are as described above). Which have the same meaning, x + y = 2u or 2u + 2), and the like. More specifically, for example, SiF ₄ , (SiF ₂ ) ₅ , (SiF ₂ ) ₆ , (SiF ₂ ) ₄ , SiF _{2
F 6, Si 3 F 8,} SiHF 3, SiH 2 F 2, SiCl 4, (SiCl 2) 5, SiBr
₄ , (SiBr ₂ ) ₅ , Si ₂ Cl ₆ , Si ₂ Br ₆ , SiHl ₃ , SiH ₃ Cl, SiH
Examples thereof include compounds in a gas state or easily gasifiable such as ₂ Cl ₂ , SiHBr ₃ , SiH ₃ , and Si ₂ Cl ₃ F ₃ .

When generating the active species (A), in addition to the compound containing silicon and halogen, if necessary, elemental silicon or another silicon compound, hydrogen, a halogen compound (for example, F ₂ gas, Cl
₂ gas, gasified Br ₂ , I ₂ etc.) can be used together.

As a method for generating the active species (A) in the activation space (a), microwave, R
Electric energy such as F, low frequency, DC, etc., heat energy by heater heating, infrared heating, etc., and activation energy such as light energy are used.

As the chemical substance for generating the active species (B),
Hydrogen gas and / or halogen gas (eg F ₂ gas, Cl ₂
Gas, gasified Br ₂ , I ₂ etc.) are advantageously used. In addition to these compounds for film formation, an inert gas such as helium, argon or neon can be used. When a plurality of these chemical substances are used, they can be mixed in advance and introduced into the activation space (b) in a gas state, or these chemical substances can be introduced in a gas state from respective independent sources. They can be individually introduced into the activation space (b), or they can be introduced into independent activation spaces and activated individually.

In the present invention, the ratio of the amount of the active species (A) and the amount of the active species (B) introduced into the film forming space depends on the film forming conditions,
The type of active species and the like are appropriately determined as desired, but the ratio is preferably 10: 1 to 1:10 (introduction flow rate ratio), and more preferably 8: 2 to 4: 6.

The deposited film formed by the above method can be doped with an impurity element in the so-called semiconductor field during or after film formation. The impurity element used is p
As a type impurity, an element of Group IIIA of the periodic table, for example,
B, Al, Ga, In, Tl and the like are preferred, and n
As the type impurities, elements of Group V group A of the periodic table, for example, P, As, Sb, Bi and the like can be preferably mentioned. Particularly, B, Ga, P, Sb, etc. are most suitable. The amount of the impurity to be doped is appropriately determined according to the desired electrical and optical characteristics.

As the substance containing such an impurity element as a component (impurity introducing substance), a compound which is in a gas state at normal temperature and normal pressure or is a gas at least under activation conditions and which can be easily vaporized by an appropriate vaporizer is used. It is preferable to select it. Such compounds include PH ₃ , P ₂ H ₄ , PF ₃ and P
F ₅ , PCl ₃ , AsH ₃ , AsF ₃ , AsF ₅ , AsCl ₃ , SbH ₃ , SbF ₅ , SiH
_{3, BF 3, BCl 3,} BBr 3, B 2 H 6, B 4 H 10, B 5 H 9, B 5 H 11, B 6 H
₁₀ , B ₆ H ₁₂ , AlCl _{3 and the} like can be mentioned. The compound containing an impurity element may be used alone or in combination of two or more.

The compound containing an impurity element as a component may be directly introduced into the film formation space in a gas state, or in advance, the activation space (a) to the activation space (b), or the third activation space ( It can also be activated in c) and then introduced into the film formation space.

The term “active species” as used in the present invention means not only a substance that can be a raw material of a deposited film but also a chemical interaction with a substance that can be a raw material of a deposited film, for example, giving energy or chemically reacting. It is also meant to include a substance that plays a role of making the substance into a state capable of forming a deposited film. Therefore, the active species may or may not include the constituents of the deposited film.

〔Example〕

Next, a method for manufacturing the solar cell of the present invention will be described with reference to examples.

FIG. 1 is a schematic diagram of the configuration of the solar cell manufactured in this example. In this embodiment, 101 is a SUS substrate, 10
2 is a P-type silicon polycrystal electrode formed by heat treatment of Al and a silicon polycrystal layer, 103 is a first conductive layer, which is an n ^- silicon crystal layer, 104 is a second conductive layer, which is a P ⁺ silicon crystal layer, 1
Reference numeral 05 is a transparent conductive layer, and 106 is a collector electrode.

Example 1 (Production of Silicon Polycrystalline Electrode Substrate) FIG. 2 is a schematic view of the apparatus used in this example.
In the figure, 201 is a crucible, 202 is a high-frequency coil for heating,
203 is molten silicon, 204 is polycrystalline silicon deposited by spraying molten silicon 203, 205 is an Al layer previously deposited by an electron beam evaporation method as a doping impurity, 206 is a substrate made of SUS-316 material, 207 Is a substrate support provided with a heater for heating the substrate, 208 is the shaft for rotating the substrate, 209 is an ultra-high speed motor for rotating the substrate, 210 is an ultrasonic vibration unit for transmitting ultrasonic vibration to the substrate through the rotating shaft. Is.

First, a 1 μm Al layer 205 was deposited on a substrate 206 made of a SUS-316 material by an electron beam evaporation method. This substrate was placed in the apparatus shown in FIG. 2, and a silicon block was put into a crucible 201 in an Ar atmosphere and heated by a high frequency coil 202 to raise the temperature until the silicon block was sufficiently melted. Next, the ultra-high speed motor 209 is rotated at a speed of 1000 revolutions per minute and the substrate heater 207 is used to rotate the substrate 206 and the Al layer 20.
5 was heated to 400 ° C., ultrasonic vibration was also applied, and a 30 μm silicon polycrystal layer was deposited. This was heat-treated at 400 ° C. for 2 hours to form a P-type silicon polycrystalline electrode 102.

(Production of First and Second Conductive Layers) FIG. 3 is a schematic view of the apparatus used in this example. In the figure, 301 is a gas introduction tube for introducing a compound containing silicon and halogen, 302 is a gas introduction tube for introducing a substance that produces active species (B), 303 is a substrate, and 304 is a holder for holding the substrate 303. A heater is built in so that the substrate temperature can be set appropriately. Each gas introduced through the gas introduction pipes 301 and 302 is exhausted by a vacuum pump (not shown) including unreacted or reaction products.

On the electrode 102 obtained by the above-mentioned method, using the apparatus shown in FIG. 3, SiF ₄ gas and PH ₃ gas were introduced from the gas introduction pipe 301 according to the production conditions of crystalline silicon shown in Table 1 below. Further, H ₂ and Ar gas were introduced through the gas introduction pipe 302, and an exhaust valve (not shown) was adjusted so that the film formation space pressure was 400 mTorr.

High frequency power 2.45GHz was adjusted to 400W and the substrate temperature was 400 ℃
As a result, deposition was started to form an n ^- silicon polycrystalline layer 103 having a film thickness of 50 μm.

Next, an exhaust valve (not shown) was fully opened in the film formation space in FIG. 3 to sufficiently exhaust the residual gas.

After that, the gas introduced from the gas introduction pipe 301 under the above conditions was added with SiF ₄ gas at a concentration of 4 ppm of BF ₃ gas for 76 s.
The deposited film was formed under the same conditions except that it was ccm, and the thickness
A 0.5 μm P ⁺ silicon polycrystalline layer 104 was formed.

The semiconductor element thus obtained was taken out and the transparent conductive layer
800 Å of 105 (In, Sn, O) was deposited by vacuum deposition by a predetermined method. Then, chromium (1
00Å), silver (500Å), and chromium (100Å) were deposited in this order by vacuum evaporation.

Conversion efficiency of light electromotive force by AM 1.5, 100 mW / cm ² solar spectrum simulator of the solar cell obtained by this example was 8.5%, it is excellent in practical use as a characteristic of the polycrystalline silicon solar cell Was confirmed.

Example 2 FIG. 4 is a schematic view of the film forming apparatus used in this example. In the figure, 401 is a gas introduction ring for introducing a compound mainly containing silicon and halogen into the vacuum chamber 409. Reference numeral 402 denotes a gas introduction pipe, which is mainly used as a raw material of the activated species (B) for the quartz cavity.
It is for introduction into 403. A microwave is generated from a microwave oscillator (not shown), propagates in the waveguide 405, and by appropriately adjusting the squeeze 406, a standing wave is generated between the squeeze 406 and the mesh 404 to generate a quartz cavity 403.
The gas present therein can be turned into plasma. 407
Is a holder with a built-in heater, and is capable of heating and holding the substrate 408 at a desired temperature.

In this example, the same silicon polycrystalline electrode substrate as the substrate used in Example 1 was used. That is, the substrate was heat treated at 400 ° C. for 2 hours. 25 sccm of hydrogen gas and 50 sccm of He gas were introduced into the quartz cavity 403 through the gas introduction pipe 402. Also, 15 sccm of Si ₂ F ₆ gas was introduced toward the substrate 408 from the gas introduction ring 401 as shown in FIG. By adjusting the electric power of the microwave oscillator to 250 W and adjusting the narrowing 406, it is possible to turn hydrogen and He gas in the quartz cavity 403 into plasma. The manufacturing conditions in this example are shown in Table 2.

Microwave power = 250w Substrate temperature = 300 ° C. The hydrogen radicals generated in this way chemically react with the Si ₂ F ₆ gas ejected from the gas introduction ring 401, and a silicon crystal layer can be deposited on the substrate 408. However, Si ₂ F
_An n ⁻ silicon crystal layer was deposited on the substrate 408 by 50 μm by mixing 0.6 ppm of PH ₃ gas with ₆ gases, and the output of the microwave oscillator was stopped at zero. Then, the supply of each gas was stopped, the vacuum chamber 409 was sufficiently evacuated, and the residual gas was completely evacuated. After that, 1.2 ppm of BF ₃ gas was mixed into Si ₂ F ₆ gas, and P ⁺ silicon crystal layer was continuously deposited by 0.5 μm under the same manufacturing conditions.

Next, the substrate 408 thus obtained is taken out,
A transparent conductive layer 405 (In, Sn, O) having a thickness of 800 Å was deposited by vacuum deposition by a predetermined method. Then, the collector electrode 406
As chrome (100Å), silver (500Å), chrome (100
Å) was deposited by vacuum deposition in this order.

The solar cell obtained in this way has an AM1.5, 100mw / cm ² photovoltaic spectrum simulator with a photovoltaic conversion efficiency of 8.7%, which is a practically excellent characteristic of polycrystalline silicon solar cells. I was able to confirm.

Example 3 W was deposited on the SUS substrate 101 as a refractory metal by an electron beam deposition method by 5000 Å, and then an Al layer for doping was deposited by 1 μm. A P-type silicon polycrystalline electrode 102 was formed on this W-coated metal substrate in the same manner as in Example 1.

Using the silicon polycrystalline electrode substrate thus obtained, 50 μm of n ⁻ silicon polycrystalline layer 103 and P ⁺ polycrystalline layer 104 were deposited in the same manner as in Example 1, and the transparent conductive layer 10 was formed.
5, the collector electrode 106 was formed to obtain a solar cell.

The conversion efficiency of photovoltaic power of this solar cell by AM1.5, 100 mw / cm ² solar spectrum simulator was 8.9%, and it was confirmed that it is practically excellent as the characteristics of the silicon solar cell.

Example 4 (Production of Silicon Polycrystalline Electrode Substrate) FIG. 5 is a schematic view of the apparatus used in this example. In the figure, 501 is a crucible, 502 is a high-frequency coil for heating,
503 is molten silicon, 504 is a deposited silicon epitaxial layer, 505 is an Al layer, 506 is a substrate made of SUS-316 material, 50
7 is a heater for heating, and 508 is a nozzle for quenching gas.

First, in an Ar atmosphere, a silicon block was put into a crucible 501 and heated and melted by a high frequency coil 502.

Next, the SUS substrate 506 on which Al was vapor-deposited by 1 μm was continuously drawn horizontally in the direction of the arrow at about 10 cm / sec. Subsequently, a heater 507 is heated from above the substrate surface, a cooling gas is flown from a cooling gas nozzle 508 below the substrate surface to grow crystals upward from the substrate surface, and a silicon polycrystal layer 504 having a columnar structure with a thickness of about 50 μm is formed. Got

Next, the substrate in which the silicon polycrystal layer 504 was deposited on this Al layer was heat-treated at 400 ° C. for 2 hours in an Ar atmosphere to form a eutectic of Al and silicon to obtain P ⁺ silicon. .

(Production of First and Second Semiconductor Layers) Under the same conditions as in Example 1, an n ⁺ silicon polycrystal layer 103 and a P ⁺ polycrystal layer 104 were deposited, and a transparent conductive layer 105 (In, Sn, O)
800 Å vapor-deposited, and chromium (100 Å) as the collecting electrode 106,
Silver (500Å) and chromium (100Å) were deposited in this order respectively.

The conversion efficiency of photovoltaic power of the solar cell thus obtained by AM1.5, 100mw / cm ² solar spectrum simulator is
It was 8.9%, and it was confirmed that the characteristics of the silicon solar cell were practically excellent.

(Reference example)

In the present invention, the condition of the heat treatment for introducing the impurities may be such that the impurities can be introduced so as to exhibit a sufficient conductivity as the silicon electrode, and is not limited to a specific value. However, suitable conditions have been clarified by the following experiments, and are listed below as reference examples.

Reference Experimental Example 1 In the same manner as in Example 1, a silicon polycrystalline layer was formed on a substrate made of a SUS-316 material by a rotation method. Then, within the range of 300-600 ℃ in Ar atmosphere (shown in Fig. 6)
By changing the set temperature with, and performing heat treatment for 2 hours, a eutectic of Al and silicon was formed to form a P ⁺ silicon layer. The results are shown as a graph in FIG. In this figure, the abscissa represents the heat treatment temperature, and the ordinate represents the ratio of the resistivity measured in the thin film direction at 400 ° C. to 1.

In this experimental example, at a heat treatment temperature of 400 ° C or higher, A
It is clear that l is a dopant that efficiently enters the polycrystal of silicon and forms a eutectic, and that the doping effect does not appear effectively below 400 ° C. Further, when the heat treatment was performed at 600 ° C. or higher, slight cracks were generated at the four-corner edge portions of the square silicon polycrystal surface. Although the cause is not clear, it is considered that in the case of a quadrangular substrate shape, strain is likely to occur at the four-sided corners on the metal substrate having large thermal strain during the process of substrate expansion by heating and the process of contraction by cooling.

From this result, in this experimental example, the heat treatment was 400 to 6
It turns out that 00 ° C is suitable.

Reference Experimental Example 2 A P ⁺ silicon layer was formed in exactly the same manner as Reference Experimental Example 1 except that the heat treatment temperature was kept constant at 450 ° C. and the treatment time was changed (illustrated in FIG. 7). The results are shown in FIG. In this figure, the heat treatment time is shown on the horizontal axis, and the vertical axis shows the ratio of the resistivity measured in the thin film direction to the resistivity at 2 hours as 1.

From this result, it is understood that Al is efficiently introduced into the silicon polycrystal as a dopant and forms a eutectic crystal by the heat treatment for 2 hours. Further, since the resistivity ratio is almost constant and does not change even after the heat treatment for 2 hours or more, it is considered that the heat treatment time of 2 hours is sufficient to reduce the production cost.

As described above, the silicon polycrystalline electrode substrate obtained by heat treatment at 400 ° C. or higher for 2 hours or longer has a resistivity in the thin film direction of 2 × 10 ⁻² (Ωcm), which is suitable for solar cells. It was found that sufficient electrodes can be obtained.

Then, on this silicon polycrystalline electrode substrate, as in Example 1, the apparatus shown in FIG. 3 was used to set as a substrate 303, and silicon was epitaxially grown. The film thickness is 50 μm.

The silicon epitaxial film thus formed was subjected to Seccoething in order to make the defect sensible pressure from above, and the number of defects in a square of 50 μm was visually observed to compare the film quality. The result is shown as (a) in FIG.

In the graph of FIG. 8A, the vertical axis represents the defect density ratio, and the defect density at 400 ° C. is 1. The horizontal axis represents the heat treatment temperature.

As can be seen from the graph, when the heat treatment temperature is lower than 400 ° C, the number of polycrystalline defects deposited on the heat treatment temperature increases. This is because the crystal growth reflects the crystallinity of the underlayer, and since the insufficient heat treatment was performed while a sufficient crystal was not obtained by the rotation method alone, the grain size of the silicon polycrystalline layer thereon was It is thought that it could not grow large, resulting in more defects.

From the above results, by providing a silicon polycrystalline electrode layer on a metal substrate, it is possible to deposit a high-quality polycrystalline film having a high orientation and a large grain size having only a fixed crystal orientation. .

Reference Experimental Example 3 On a silicon polycrystalline electrode substrate prepared under the same conditions and formulation as in Reference Experimental Example 1, except that W was deposited on the SUS substrate by the electron beam evaporation method at 5000Å and then Al was vapor-deposited at 1 μm. , Epitaxial growth of silicon,
The defect sensible pressure treatment performed in Reference Experimental Example 2 was performed to investigate the defect density. As a result, as shown in FIG. 8 (b), almost the same result as in Reference Experimental Example 1 was obtained.

Reference Experimental Example 4 In the same manner as in Example 4, SUS-3 in which Al was deposited to a thickness of 1 μm.
A polycrystalline silicon layer was deposited on a substrate made of 16 materials.

Next, in the Ar atmosphere, the set temperature is changed within the range of 300 to 600 ° C. (shown in FIG. 9), and heat treatment is performed for 3 hours.
A eutectic of Al and silicon was formed to make P ⁺ silicon.

FIG. 9 shows a graph in which the heat treatment temperature and the resistivity measured in the thin film direction are plotted as a ratio with the resistivity at 400 ° C. being 1. From this result, as in Reference Experimental Example 1, 40
It was found that Al was not doped efficiently unless it was above 0 ° C.

Reference Experimental Example 5 Heat treatment temperature within the range of 300 to 600 ° C (shown in Fig. 10)
A solar cell was prepared in the same manner as in Example 1 or Example 4, except that the setting was made in step 1 above and the operation was performed for 2 hours. Its conversion efficiency is
Figure 10 shows. In this figure, the horizontal axis represents the heat treatment temperature, the vertical axis represents the conversion efficiency of the solar cell, (a) shows the one produced in the same manner as in Example 1, and (b) shows the same as in Example 4. Shown in Fig.

As shown in FIG. 10, in the heat treatment temperature range of 300 ° C to 390 ° C, the conversion efficiency is as low as 3 to 5% and 410 ° C to 6 ° C.
The conversion efficiency never exceeded 5% even at 00 ° C.

It is considered that this is because when the heat treatment temperature is low, Al is not sufficiently doped in the gyricon polycrystal electrode layer and the function as an electrode is not sufficiently performed. At a heat treatment temperature of 410 ° C or higher, cracks were generated on the silicon polycrystal electrode substrate, and the n ⁻ polycrystal layer and P ⁺ polycrystal layer deposited on the cracks grew abnormally, so a sufficient crystal grain size was also obtained. This is because the conversion efficiency is lowered due to deterioration of diode characteristics and the like.

Reference Experimental Example 6 Heat treatment temperature within the range of 300 to 600 ° C (shown in Fig. 11)
A solar cell was prepared in the same manner as in Example 2 except that the setting was made in step 1 and the operation was performed for 2 hours. The conversion efficiency is shown in FIG. No.
As shown in Fig. 10, the conversion efficiency is as low as 3 to 5% in the heat treatment temperature range of 300 ℃ to 390 ℃, and 410 ℃ to 600 ℃.
The conversion efficiency never exceeded 6%.
This is considered to be the same as the reason described in Reference Experimental Example 5.

〔The invention's effect〕

As described above, in the manufacturing method of the present invention, the active species (A) and the active species (B) are separately introduced into the film formation space to form the chemical reaction deposited film, and the specific silicon content is increased. Since the crystal electrode substrate is used, good crystal growth is possible and the manufacturing cost is reduced. Furthermore, the characteristics such as crystallinity and energy conversion efficiency are good, and a practical solar cell can be stably manufactured.

Therefore, according to the manufacturing method of the present invention, it is possible to provide a mass-produced, inexpensive, high-quality thin-film solar cell to the market.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a solar cell manufactured by the method of the present invention, FIGS. 2 to 5 are schematic diagrams of respective film forming apparatuses used in Examples, and FIGS. 6 to 11 are 3 is a graph showing the data obtained in the reference experimental example. 101 ... Substrate 102 ... Polycrystalline silicon electrode layer 103 ... First conductive layer, 104 ... Second conductive layer 105 ... Transparent electrode film, 106 ... Current collecting electrode 201,501 ... Crucible, 202,502 ... High frequency coil 203,503 …… Melted silicon 204,504 …… Polycrystalline silicon layer 205,505 …… Doping material 206,506 …… Metal substrate, 207,507 …… Heater 208 …… Rotating shaft, 508 …… Cooling nozzle 209 …… Motor, 210 …… Ultrasonic generator 301 ... Gas introduction pipe, 302 ... Gas introduction pipe 303 ... Substrate, 304 ... Holder 305 ... Meeting space 401 ... Gas introduction ring, 402 ... Gas introduction pipe 403 ... Quartz cavity, 404 ... Mesh 405 ... Microwave waveguide 406 ... Squeezing, 407 ... Holder 408 ... Substrate, 409 ... Vacuum chamber

Claims (1)

(57) [Claims] 1. An active species (A) obtained by decomposing a compound containing silicon and halogen and an active species (B) capable of chemically interacting with the active species (A) are separately introduced into a film forming space. In the method for manufacturing a solar cell, which comprises a step of forming a deposited film on a substrate installed in the film formation space by a chemical reaction, a metal substrate or a metal substrate coated with a refractory metal is used as the substrate. Characterized by using a substrate having a silicon polycrystalline electrode layer obtained by forming a polycrystalline silicon layer formed by growing a doping material and molten silicon by a rotating method or a horizontal pulling method and performing a heat treatment. Method for manufacturing solar cell.