Source: https://patents.google.com/patent/JP2006148155A/en
Timestamp: 2020-04-05 02:03:18
Document Index: 525176080

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JP2006148155A - Manufacturing method of solar cell and the solar cell - Google Patents
Manufacturing method of solar cell and the solar cell Download PDF
JP2006148155A
JP2006148155A JP2006012789A JP2006012789A JP2006148155A JP 2006148155 A JP2006148155 A JP 2006148155A JP 2006012789 A JP2006012789 A JP 2006012789A JP 2006012789 A JP2006012789 A JP 2006012789A JP 2006148155 A JP2006148155 A JP 2006148155A
JP2006012789A
Toru Nunoi
浩明 中弥
徹 布居
1994-07-21 Priority to JP16931894 priority Critical
2006-01-20 Application filed by Sharp Corp, シャープ株式会社 filed Critical Sharp Corp
2006-01-20 Priority to JP2006012789A priority patent/JP2006148155A/en
2006-06-08 Publication of JP2006148155A publication Critical patent/JP2006148155A/en
150000003609 titanium compounds Chemical class 0 abstract 2
<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a solar cell, capable of manufacturing the solar cell in a simple process with few process steps and obtaining high short-circuiting current. <P>SOLUTION: Irregularities 22a, 22b are formed on the surface 1a of a p-type silicon crystal substrate 1. Titanium compound and phosphorus compound in gaseous conditions are supplied to the surface 1a of the substrate 1 that is heated at a predetermined temperature to form a titanium oxide film 2, containing phosphorus consisting of a reactant of the titanium compound and phosphorus compound. The substrate is thermally processed at a predetermined temperature to form a p-n junction by dispersing phosphorus from the film 2 and form an antireflection coating comprising the film 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI
The present invention relates to a solar cell manufacturing method and a solar cell, and more specifically, a solar cell manufacturing method for manufacturing a crystalline silicon solar cell having a titanium oxide film containing phosphorus as an antireflection film, and such a manufacturing method. Related to the solar cell.
As a method for manufacturing a crystalline silicon solar cell, a process as shown in FIG. 12 can be considered. First, minute irregularities or grooves having a height difference of several μm to several tens of μm are formed on the surface of the silicon substrate (S101). As a method of forming the irregularities and grooves, for example, etching is performed using a mixed solution of several percent NaOH aqueous solution and alcohol, and texture etching, dicing apparatus, or laser is used to form a micro pyramid with a height of several μm on the substrate surface. In addition, there are a method of forming many grooves having a depth of several tens of μm in parallel on the surface of the substrate, dry etching, and the like. These irregularities and grooves (hereinafter simply referred to as “irregularities”) are for reducing the surface reflection and improving the short-circuit current during the operation of the completed solar cell. Next, in a state where the silicon substrate is placed in a quartz tube heated to about 800 to 1100 ° C., a liquid impurity source such as POCl 2 contained in a bubbler container is put into the quartz tube by a carrier gas such as N 2 . Introduce. At this time, a phosphor oxide layer is formed on the substrate surface. At the same time, the phosphorus oxide layer serves as a diffusion source to diffuse phosphorus in the silicon substrate, thereby forming a pn junction on the substrate surface side portion (S102). After this diffusion step, a hygroscopic oxide film containing phosphorus as a main component remains on the substrate surface, and this film is removed with hydrofluoric acid (S103). Thereafter, in order to further reduce surface reflection, an antireflection film is formed on the substrate surface (S104). As the antireflection film at this time, a TiO 2 film formed using an atmospheric pressure CVD (chemical vapor deposition) method, an SiN film formed using a plasma CVD method, or the like is used. For example, when forming a TiO 2 film by the atmospheric pressure CVD method, a carrier gas such as N 2 is sent into a bubbler containing titanium alkoxide and water, and each raw material is conveyed to the substrate surface by these carrier gases. A TiO 2 film is deposited by causing a hydrolysis reaction on the surface. Next, the light-receiving surface side of the substrate is protected with an acid-resistant tape or resist, and unnecessary bonding formed on the back surface side of the substrate in the diffusion step is removed using an HNO 3 -HF mixed solution (S105). Next, an aluminum paste is printed on the back side of the substrate and baked at about 700 to 800 ° C. to form a back electrode and a P + layer. Thereafter, a silver paste is printed in a fishbone shape on the substrate surface (light receiving surface) side and fired to form a light receiving surface electrode (S107).
As an atmospheric pressure CVD apparatus capable of forming the antireflection film, for example, as shown in FIG. 17, a continuous normal product manufactured by Watkins-Johnson Co. or BTU International (BTU International) is used. A pressure CVD apparatus has been put into practical use. This type of continuous atmospheric pressure CVD apparatus includes a conveyor belt 201 for placing and moving a substrate, a belt driving mechanism 202 having rollers 202A and 202B, and a horizontal portion of the conveyor belt 201 (rollers 202A and 202A). A dispersion head 206 having a heater plate 203 for substrate heating disposed under the portion between the roller 202B and a head assembly 208 disposed above the heater plate 203 and the conveyor belt 201; An assembly 208 and a cover 205 that covers the horizontal portion of the conveyor belt 201 are provided. A portion of the cover 205 that covers the head assembly 208 is formed in a convex shape with a gap with respect to the head assembly 208, and an exhaust port 207 is provided at an upper portion thereof. When film formation is performed, the substrate is placed on the transfer belt 201 at the load position 201a, and the substrate is moved in the horizontal direction (leftward in FIG. 17) at a constant speed by the belt driving mechanism 202. When the substrate passes under the head assembly 208, the heater plate 203 has already heated the substrate to a predetermined temperature. Then, the source gas is blown out toward the surface of the substrate from an outlet provided on the lower surface of the head assembly 208, and a desired film is formed on the surface of the substrate. The remaining gas or the like passes through the gap between the head assembly 208 and the convex portion of the cover 205 and is discharged from the exhaust port 207 to the outside. Thereafter, the substrate is further moved leftward by the conveying belt 201 and collected at the unloading position 201b. In some cases, the substrate is reciprocated in the horizontal direction and collected at the load position 201a.
Further, as a method for producing a crystalline silicon solar cell, as shown in FIG. 13, in order to form a pn junction, instead of POCl 3 diffusion described above, PSG (phosphosilicate glass (Phosphosilicate Glass) .SiO 2 In addition, a process in which phosphorus is doped, etc.) and this is used as an impurity source is also known. In this case, first, as in the process of FIG. 12, minute irregularities are formed on the surface of the silicon substrate (S201). Next, a PSG film is formed on the uneven substrate surface (S202). Subsequently, the substrate is heated to about 800 to 1100 ° C. to diffuse phosphorus from PSG into the silicon substrate, thereby forming a pn junction on the surface side of the substrate (S203). The PSG film remaining on the substrate surface after this diffusion step has a refractive index of about 1.4 to 1.5 and is not suitable as an antireflection film. Therefore, after removing the PSG film with HF (S204), an antireflection film such as TiO 2 or SiN is formed on the substrate surface (S205). Thereafter, as in the process of FIG. 12, a back electrode and a light receiving surface electrode are formed (S206, S207).
As a typical PSG film forming method,
A method of applying a coating solution comprising an organosilicon compound, an organic solvent, and a phosphorus compound;
-CVD method using SiH 4 and PH 3 and O 2 or N 2 O,
· SiH 4 and an organic phosphorus compound and a CVD method using O 2,
A CVD method using Si (OC 2 H 5 ) 4 , an organophosphorus compound and O 2 ;
A CVD method using Si (OC 2 H 5 ) 4 , an organophosphorus compound and O 3 is known.
Further, as a process in which the two processes shown in FIGS. 12 and 13 are simplified, a process of simultaneously forming a pn junction and an antireflection film using a coating liquid is known as shown in FIG. For example, see Patent Document 1 (Japanese Patent Laid-Open No. 54-76629). In this case, first, similarly to the above two processes, minute irregularities are formed on the surface (light receiving surface side) of the silicon substrate (S301). Next, a TiO 2 film containing an impurity having a conductivity type different from that of the substrate is formed on the surface of the substrate on which the unevenness has been formed using a coating liquid (S302). Subsequently, heat treatment is performed to form a pn junction on the substrate surface side portion, and at the same time, an antireflection film made of a TiO 2 film containing the impurities is formed (S303). Since the TiO 2 film containing impurities after heating has a low hygroscopic property and a refractive index of about 1.7 to 2, it can be used as it is as an antireflection film. Thereafter, similarly to the processes of FIGS. 12 and 13, the back electrode and the light receiving surface electrode are formed (S304, S305).
The coating solution used in the process of FIG. 14 is made from a titanium alkoxide such as tetra-i-propoxy titanium, a compound containing an impurity element such as phosphorus or boron, a carboxylic acid and an alcohol. The coating on the substrate surface is performed by spin coating, dipping or spraying. Patent Document 2 (Japanese Patent Laid-Open No. 56-60075) discloses that when the content of B 2 O 3 in the antireflection film formed from such a coating solution is changed from 10% by weight to 50% by weight. If the refractive index of the antireflection film changes from about 2.5 to about 2.0, and if the content of B 2 O 3 is 30% by weight or more, the carrier concentration and bonding when heat-treated at the same temperature Depth is shown to saturate.
In order to form the pn junction and the antireflection film at the same time, a doped SiO 2 , TiOx or Ta 2 O 5 (doped layer) is formed thinly as a diffusion source for forming the pn junction and doping the antireflection film. In addition, a method of forming SiO 2 , TiOx or Ta 2 O 5 thereon is known (for example, see Patent Document 3 (Japanese Patent Laid-Open No. 60-1113915)). In this case, the dope layer is formed by spin coating, spraying, dipping, deposition, printing, and the like, and the antireflection layer thereon is formed by vapor deposition, chemical deposition from the gas phase, and printing. The purpose of this method is that it is difficult to uniformly form a doped layer on a semiconductor surface that is not smooth compared to a chemically polished surface. Therefore, by forming a thin doped layer, the optical properties of the antireflection layer formed thereon are reduced. It is intended to reduce the environmental impact.
JP 54-76629 A Japanese Patent Laid-Open No. 56-60075 Japanese Patent Application Laid-Open No. 60-113915
Compared with the process of first forming a pn junction and removing the oxide film on the substrate surface as shown in FIG. 12 or 13 and then forming the antireflection film, the titanium oxide film containing impurities as shown in FIG. Is formed from a coating solution, a pn junction is formed using this film as an impurity source, and the remaining film is used as an antireflection film, which has an advantage that the number of steps is small and simple.
However, as shown in FIG. 15, the process of obtaining the pn junction and the antireflection film of FIG. 14 at the same time was applied to the silicon substrate 17 in which fine unevenness of several μm to several tens μm in height difference was formed on the substrate surface. In this case, the following problem occurs.
That is, when the coating liquid 18 is applied to the substrate 17 by the spin coating method or the dipping method, the coating liquid 18 accumulates on the concave portion 17b on the surface of the substrate and becomes thick, but on the convex portion 17a, the coating liquid 18 becomes thin. Also in the case of applying by the spray method, since the size of the spray particles is about several hundred μm, similarly, the coating liquid 18 is accumulated on the concave portion 17b on the surface of the substrate and becomes thick, but conversely on the convex portion 17a. getting thin. For this reason, the film thickness of the antireflection film formed from the coating liquid 18 through the heat treatment (S303) becomes nonuniform.
As is known, the refractive index of the material surrounding the solar cell is n 0 (for example, n 0 = 1 in air), the refractive index of silicon is n s , the wavelength of incident light is λ, and the refractive index of the antireflection film is n, where d is the thickness of the antireflection film, and the antireflection film is formed so as to satisfy the conditional expressions n 2 = n 0 · ns and d = λ / 4n, the surface reflectance at the wavelength λ is Can be minimized. However, if the film thickness of the antireflection film is not uniform as described above, this conditional expression cannot be satisfied, so that the surface reflection cannot be reduced sufficiently.
FIG. 16 shows the surface reflectance of a solar cell (conventional example 1) produced by forming an antireflection film (titanium oxide film) by CVD after pn junction formation according to the process of FIG. 12, and impurities according to the process of FIG. The surface reflectance of a solar cell (conventional example 2) produced by forming a titanium oxide film containing a coating solution by spin coating and forming a pn junction and an antireflection film simultaneously is shown. In Conventional Example 1, a minimum value of reflectance is recognized in the vicinity of a wavelength of 600 nm, but in Conventional Example 2, a clear minimum value of reflectance is not seen. This indicates that the film thickness of the antireflection film of Conventional Example 2 is not uniform. In addition, the light receiving surface of the solar cell of Conventional Example 1 appears blue due to the interference effect of the antireflection film, whereas the light receiving surface of the solar cell of Conventional Example 2 remains the ground color (gray) of the silicon substrate. It is clear that there is no effect.
As a result, the solar cell (conventional example 2) produced by the process of simultaneously obtaining the pn junction and the antireflection film using the coating liquid is a solar cell in which an antireflection film having a uniform film thickness is formed using the CVD method or the like. There is a problem that the short-circuit current is lower than that of (conventional example 1).
In addition, according to the CVD method, a TiO 2 film and a PSG film having a uniform film thickness can be formed on the substrate surface having the above-described minute irregularities. However, a uniform film is formed of a film containing impurities sufficient to form a pn junction and capable of being used as an antireflection film after diffusion, that is, a phosphorus-doped titanium oxide film, on the substrate surface having the unevenness. A method for forming a thick film has not yet been reported.
Accordingly, an object of the present invention includes a process for forming a titanium oxide film containing phosphorus so that a titanium oxide film containing phosphorus can be formed in a uniform film thickness on a substrate surface having minute irregularities, and the number of steps An object of the present invention is to provide a method for manufacturing a solar cell capable of producing a solar cell capable of obtaining a high short-circuit current with a small and simple process. Moreover, the subject of this invention is providing the solar cell produced by the manufacturing method of such a solar cell.
The crystalline silicon solar cell is often incorporated in a so-called super straight type module. This module is composed of the solar cell, glass and filler for protecting its light receiving surface (generally EVA (ethylene vinyl acetate) is used), a back surface material, a peripheral sealing material, and a frame material surrounding the periphery. Composed. When incorporated in such a module, glass and EVA are provided on the light receiving surface of the solar cell, and thus an antireflection film having a refractive index different from that when the light receiving surface of the solar cell is in direct contact with air is required. . That is, when the refractive index of the antireflection film is n, the refractive index of silicon is n s , and the refractive index of the substance on the antireflection film is n 0 , the optimum refractive index of the antireflection film is n = (N 0 · n s ) 1/2 . Here, in the wavelength region of the sensitive λ = 600~1100nm of the solar cell, the refractive index n s of silicon is about 3.5 to 4, if the light-receiving surface of the solar cell is air in contact directly ( n 0 = 1) has an optimum refractive index of the antireflection film of 1.8 to 2, but when glass and EVA are present on the light receiving surface of the solar cell (n 0 = 1.4 to 1.5), The optimum refractive index of the antireflection film is 2.2 to 2.5. As can be seen from this analysis result, the titanium oxide film (refractive index of about 1.7 to 2) formed by the process of FIG. 14 has a slightly lower refractive index as an antireflection film of the solar cell for the module, There is a problem that surface reflection cannot be effectively reduced.
In the process of FIG. 14, a pn junction and a titanium oxide film are simultaneously formed using a coating solution, and then a film having a high refractive index such as Si 3 N 4 or TiO 2 is uniformly formed thereon by a CVD method or the like. Even if deposited, the underlying titanium oxide film is not uniform in thickness, so that a good antireflection film showing an interference effect could not be obtained.
Then, another subject of this invention includes the formation process of the titanium oxide film containing phosphorus so that the titanium oxide film containing phosphorus can be formed in a uniform film thickness on the substrate surface with minute unevenness, An object of the present invention is to provide a method of manufacturing a solar cell that can produce a solar cell suitable for modularization by a simple process with a small number of steps. Moreover, the subject of this invention is providing the solar cell produced by the manufacturing method of such a solar cell.
The process of forming a titanium oxide film containing phosphorus, which is the basis of the present invention, supplies a titanium compound and a phosphorus compound in a gas state to the surface of a substrate heated to a predetermined temperature, It is characterized in that a titanium oxide film containing phosphorus composed of a reaction product of a titanium compound and a phosphorus compound is formed.
In the step of forming the titanium oxide film containing phosphorus, a titanium compound and a phosphorus compound are supplied in a gas state to the surface of the substrate heated to a predetermined temperature. Each supplied compound is thermally decomposed at or near the substrate surface. The titanium compound is decomposed into titanium oxide, and the phosphorus compound is decomposed into phosphorus oxide. The titanium oxide and phosphorus oxide form a network, and a titanium oxide film containing phosphorus is formed on the substrate surface. This forming method belongs to the CVD method because a titanium compound and a phosphorus compound are supplied in a gas state to the surface of the substrate. Therefore, even on the substrate surface having minute irregularities, the titanium oxide film containing phosphorus is formed to have a uniform thickness.
Then, in order to solve the above-mentioned subject, the manufacturing method of the solar cell of this invention,
forming a predetermined height difference unevenness on the surface of the p-type silicon crystal substrate;
Forming a titanium oxide film containing phosphorus on the surface of the substrate on which the irregularities are formed;
The substrate is heat-treated at a predetermined temperature, and phosphorus is diffused from the titanium oxide film containing phosphorus on the surface side portion of the substrate to form a pn junction, and an antireflection film made of the titanium oxide film containing phosphorus Forming a step,
In the step of forming the titanium oxide film containing phosphorus, a titanium compound and a phosphorus compound are supplied in a gas state to the surface of the substrate heated to a predetermined temperature, and the titanium compound and the phosphorus compound are supplied to the surface of the substrate. A titanium oxide film containing phosphorus made of a reaction product is formed.
In the method for manufacturing a solar cell according to the present invention, the titanium oxide film containing phosphorus is formed on the surface of the substrate, that is, the titanium oxide film containing phosphorus is formed by a CVD method. Even so, the titanium oxide film containing phosphorus is formed on the substrate surface in a uniform film thickness, and thus an antireflection film having a uniform film thickness is obtained after the heat treatment. As a result, a high short-circuit current is obtained after the solar cell is completed. In addition, since the pn junction and the antireflection film are formed simultaneously by the heat treatment, the solar cell is manufactured by a simple process with a small number of steps.
In another aspect, the method for producing a solar cell of the present invention includes:
Heat-treating the substrate at a predetermined temperature, diffusing phosphorus from the titanium oxide film containing phosphorus on the surface side portion of the substrate to form a pn junction;
Forming a film having a refractive index of 2.2 to 2.5 having a higher refractive index than that of the film on the titanium oxide film containing phosphorus to a uniform thickness;
In the method for manufacturing a solar cell according to the present invention, a film having a refractive index of 2.2 to 2.5 having a higher refractive index than that of the film is formed on the titanium oxide film containing phosphorus to have a uniform film thickness. As a reflection preventing film, a film having an optimum refractive index of 2.2 to 2.5 when glass and EVA are present on the light receiving surface is produced. That is, when modularized, the surface reflectance can be effectively reduced, and a solar cell suitable for modularization is produced. This manufacturing method has more steps of forming the film having the refractive index of 2.2 to 2.5 than the manufacturing method described above, but still has fewer steps than the processes of FIGS. It is a simple process.
The titanium oxide film containing phosphorus and the film having a refractive index of 2.2 to 2.5 are both formed to have a uniform film thickness. Therefore, a good antireflection film showing an interference effect by the two films. Is obtained.
In one embodiment of the method for producing a solar cell, in the step of forming the titanium oxide film containing phosphorus, a carrier gas is passed through each of the liquid titanium compound and the phosphorus compound, and the titanium compound and the phosphorus compound are made to correspond to the vapor pressure. And is supplied to the surface of the substrate together with the carrier gas.
In the method for manufacturing a solar cell according to this embodiment, the above-mentioned respective compounds are obtained by controlling the vapor pressure according to the set temperature of a bubbler container containing each compound in the liquid state or by changing the flow rate of the carrier gas passed through the bubbler container. Is accurately controlled. As a result, the film thickness uniformity of the titanium oxide film containing phosphorus increases, and the phosphorus concentration is reliably controlled. Further, the phosphorus concentration in the film is variously set by changing the mixing ratio of the titanium compound and the phosphorus compound. By changing the mixing ratio of the titanium compound and the phosphorus compound during film formation, the phosphorus concentration can also be changed in the film thickness direction.
In one embodiment of the method for manufacturing a solar cell, the method includes the steps of forming a back electrode on the back side of the substrate and forming a light receiving surface electrode on the surface side of the substrate after all the steps. .
The solar cell of this invention is
A p-type silicon crystal substrate having unevenness of a height difference of several μm to several tens of μm on the surface;
An n-type impurity region formed on the surface of the p-type silicon substrate,
The surface of the n-type impurity region is provided with a titanium oxide film containing phosphorus having a substantially uniform thickness to the extent that an interference effect is exhibited.
In another aspect, the solar cell of the present invention is:
A titanium oxide film containing phosphorus having a substantially uniform thickness on the surface of the n-type impurity region;
A surface of the titanium oxide film containing phosphorus is provided with a titanium oxide film having a substantially uniform thickness not containing phosphorus having a refractive index of 2.2 to 2.5.
A solar cell manufacturing apparatus suitable for carrying out the manufacturing method of the present invention includes a transport belt having a horizontal portion arranged horizontally so that a substrate on which a film is to be formed can be placed, and the transport belt Belt driving means capable of moving the horizontal portion of the belt in the horizontal direction, and the horizontal portion of the conveying belt is provided in a specific region in a moving path moved by the belt driving means, and is disposed on the horizontal portion. A first film-forming part that heats a substrate that is placed and moves to a predetermined temperature, supplies a titanium compound and a phosphorus compound in a gas state to the surface of the substrate, and forms a titanium oxide film containing phosphorus; A heat treatment part that is provided in a region following the first film forming unit in the movement path and that holds the substrate at a temperature higher than a temperature at which the first film forming part heats; In the following area It is characterized in that a second film forming unit for forming a large film of the refractive index than the film on the titanium oxide film containing the phosphorus.
According to the solar cell manufacturing apparatus, the first film forming unit, the heat treatment unit, and the second film forming unit form the titanium oxide film containing phosphorus in the solar cell manufacturing method, and the substrate. The step of forming the pn junction by heat treatment at a predetermined temperature and the step of forming the film having the refractive index of 2.2 to 2.5 on the titanium oxide film containing phosphorus are automatically performed by belt conveyance. It is executed continuously. As a result, the time for cooling the substrate and raising the temperature between these three steps is shortened. In other words, when performing these processes with independent devices, in order to carry the substrate from the place where the apparatus for the previous process is installed in the factory to the place where the apparatus for the next process is installed, It is necessary to cool the substrate to near room temperature. On the other hand, according to this manufacturing apparatus, since the above three steps are performed continuously, there is no need to cool the substrate to near room temperature, and the temperature from the previous step to the temperature for the next step. What is necessary is just to change temperature directly. Therefore, the time required for manufacturing the solar cell is shortened. Further, according to this manufacturing apparatus, unlike the case where these three steps are performed by independent apparatuses, the operation of transferring the substrate between the apparatuses becomes unnecessary. Therefore, the manufacturing cost of the solar cell can be reduced.
Furthermore, a solar cell manufacturing apparatus suitable for carrying out the manufacturing method of the present invention includes a bubbler container filled with a liquid titanium compound and a liquid phosphorus compound in the solar cell manufacturing apparatus. A bubbler container, a temperature adjusting part for adjusting the temperature of each bubbler container, and a pipe for transporting the titanium compound and phosphorus compound evaporated in each bubbler container to the first film forming part, The first film forming section has a dispersion head in which a titanium compound and a phosphorus compound in a gas state received through the pipe are mixed and blown toward the surface of the substrate.
According to the solar cell manufacturing apparatus, by controlling the vapor pressure by the set temperature of the bubbler container containing each compound in the liquid state, or by controlling the flow rate of the carrier gas passed through the bubbler container, The supply amount is controlled with high accuracy. As a result, the film thickness uniformity of the titanium oxide film containing phosphorus increases, and the phosphorus concentration is reliably controlled. Further, the phosphorus concentration in the film is variously set by changing the mixing ratio of the titanium compound and the phosphorus compound.
As is clear from the above, the solar cell manufacturing method of the present invention can produce a solar cell capable of obtaining a high short-circuit current by a simple process with a small number of steps.
In another aspect, the solar cell manufacturing method of the present invention can produce a solar cell suitable for modularization by a simple process with a small number of steps.
Moreover, the solar cell of this invention is preferably produced with the manufacturing method of those solar cells.
FIG. 2 shows a CVD apparatus for carrying out a method for forming a titanium oxide film containing phosphorus.
This apparatus includes a heater block 8 for placing and heating the substrate 7 in the growth chamber 20, and a gas dispersion head 13 facing the upper surface of the heater block 8. A gas supply pipe 21 is connected to the gas dispersion head 13 through the wall surface of the growth chamber. The gas supply pipe 21 is a combination of the atmospheric gas supply pipe 14, the titanium compound supply pipe 15b, and the phosphorus compound supply pipe 16b.
A bubbler container 11 containing tetra-i-propoxy titanium 9 is connected to the titanium compound supply pipe 15b, while a bubbler container 12 containing triethoxy phosphorus 10 is connected to the phosphorus compound supply pipe 16b. A carrier gas is introduced into the bubbler containers 11 and 12 through carrier gas supply pipes 15a and 16a, respectively. The introduced carrier gas contains the above tetra-i-propoxy titanium 9 and triethoxy phosphorus 10 up to a partial pressure corresponding to the vapor pressure. The tetra-i-propoxy titanium 9 and triethoxy phosphorus 10 in a gas state together with the carrier gas merge with the atmospheric gas in the gas supply pipe 21 through the titanium compound supply pipe 15b and the phosphorus compound supply pipe 16b. These gases are supplied to the substrate surface on the heater block 8 through the gas supply pipe 21 and the gas dispersion head 13.
The two bubbler containers 11 and 12 are provided with a heater and a temperature controller (not shown) so that the liquid raw materials in the bubbler containers 11 and 12 can be heated and kept at a constant temperature. The supply pipe between the outlets of the bubbler containers 11 and 12 and the gas dispersion head 13 is heated by a tape heater (not shown) in order to prevent the source gas from being liquefied in the pipe.
Formation of the titanium oxide film containing phosphorus is performed as follows.
First, a p-type silicon substrate 7 having a specific resistance of 1 Ω · cm and a single-sided mirror is placed on the heater block 8. The substrate is heated by the heater block 8, and supply of the source gas is started through the gas supply pipe 21 when the substrate temperature becomes constant.
That is, the temperature of the bubbler container 11 containing the tetra-i-propoxy titanium 9 is maintained at about 60 ° C. (vapor pressure is about 1 Torr). N 2 carrier gas is supplied to the carrier gas supply pipe 15a at a flow rate of 0.5 l / min, and the tetra-i-propoxy titanium 9 is included in the N 2 carrier gas up to a partial pressure corresponding to the vapor pressure to supply a titanium compound. The gas is supplied to the gas supply pipe 21 through the pipe 15b. On the other hand, the temperature of the bubbler container 12 containing the triethoxy phosphorus 10 is kept at about 50 ° C. (vapor pressure about 4 Torr). The N 2 carrier gas is supplied to the carrier gas supply pipe 16 at a flow rate of 0.25 l / min, and the triethoxy phosphorus 10 is included in the N 2 carrier gas up to a partial pressure corresponding to the vapor pressure, and the gas is passed through the phosphorus compound supply pipe 16b. Supply to the supply pipe 21. Further, N 2 is supplied to the atmosphere gas supply pipe 14 as an atmosphere gas at a flow rate of 2.5 l / min, and O 2 is supplied at a flow rate of 0.5 l / min. All these gases are supplied to the substrate surface on the heater block 8 through the gas supply pipe 21 and the gas dispersion head 13.
Tetra-i-propoxy titanium 9 and triethoxy phosphorus 10 supplied to the substrate surface are thermally decomposed at or near the substrate surface. Tetra-i-propoxy titanium 9 is decomposed to titanium oxide, and triethoxy phosphorus 10 is decomposed to phosphorus oxide. The titanium oxide and phosphorus oxide form a network, and a titanium oxide film containing phosphorus is formed on the substrate surface.
In this case, the supply amount of each of the compounds 9 and 10 can be accurately controlled by controlling the vapor pressure according to the set temperature of the bubbler containers 11 and 12 and changing the flow rate of the N 2 carrier gas passed through the bubbler containers 11 and 12. It can be controlled well. Therefore, the film thickness uniformity of the titanium oxide film containing phosphorus to be formed can be improved, and the phosphorus concentration can be reliably controlled.
Here, the substrate temperature was changed between about 200 ° C. and 500 ° C. by the heater block 8, and an experiment for forming a titanium oxide film containing phosphorus was performed.
FIG. 3 shows an IR absorption spectrum of the titanium oxide film containing phosphorus thus formed (Example 1). Also, in FIG. 3, the IR absorption spectrum of a non-doped TiO 2 film (Comparative Example 1) formed by supplying only tetra-i-propoxytitanium 9 with the apparatus of FIG. The IR absorption spectrum of a titanium oxide film containing phosphorus formed by spin-coating (propoxytitanium, P 2 O 5 , carboxylic acid, isopropyl alcohol) and drying at about 300 ° C. (Comparative Example 2) is also shown. . As can be seen, the IR absorption spectrum of the TiO 2 film of Comparative Example 1 does not show a peak in the vicinity of about 1000 cm −1 . On the other hand, the IR absorption spectrum of the titanium oxide film containing phosphorus in Example 1 has a peak in the vicinity of about 1000 cm −1 , and shows almost the same characteristics as the IR absorption spectrum of the film from the coating liquid in Comparative Example 2. ing. From this, it can be seen that the film of Example 1 is certainly a titanium oxide film containing phosphorus.
FIG. 4 shows the refractive index of the titanium oxide film containing phosphorus when the substrate temperature is changed. The refractive index was measured with an ellipsometer. As the substrate temperature increased from 250 ° C. to 450 ° C., the refractive index changed from 2.0 to 1.6. This suggests that the phosphorus concentration in the film can be set higher as the temperature rises.
FIG. 5 shows the formation of an n-layer when a titanium oxide film containing phosphorus is formed on the surface of the silicon substrate 7 by changing the substrate temperature, and is further subjected to a heat treatment at about 900 ° C. for 30 minutes in an N 2 atmosphere. The sheet resistance value is shown. The sheet resistance was measured by a four-probe method after dissolving a titanium oxide film containing phosphorus with hot concentrated sulfuric acid. As the substrate temperature increases to 250 ° C. or 450 ° C., the sheet resistance value becomes 5 × 10 2 Ω / sq. To 5 × 10 1 Ω / sq. Changed. This suggests that the phosphorus concentration in the film can be set higher as the temperature rises. This result corresponds to the result obtained from the refractive index.
As the carrier gas, not only N 2 but also an inert gas such as He or Ar can be used.
As the titanium compound, not only the tetra-i-propoxy titanium 9 but also a titanium alkoxide that is liquid at room temperature, for example, tetra-n-propoxy titanium, tetra-n-butoxy titanium, tetra-i-butoxy titanium, tetra-sec- Butoxy titanium or the like can be used.
As the phosphorus compound, not only the above triethoxy phosphorus 10 but also a phosphate ester or phosphite ester which is liquid at room temperature, for example, trimethyl phosphate, triethyl phosphate, tri-n-propoxy phosphate, tri-i-propoxy phosphate Trimethoxyline and the like can be used.
FIG. 1 shows a manufacturing process of a solar cell embodying the present invention.
i) First, as shown in FIG. 1A, the p-type single crystal silicon substrate 1 having a thickness of about 400 μm and a specific resistance of about 1 Ω · cm is cleaned. Subsequently, texture etching is performed at a liquid temperature of about 90 ° C. using a mixed solution of NaOH aqueous solution and isopropyl alcohol. As a result, microscopic pyramid irregularities (recesses are indicated by 22 b and protrusions by 22 a) having a height difference of several μm are formed on the surface 1 a of the substrate 1.
ii) Next, as shown in FIG. 1B, the substrate 1 is placed on the heater block 8 of the CVD apparatus shown in FIG. 2, and the substrate 1 is heated to about 400 ° C. and kept at a constant temperature. The temperature of the bubbler container 11 containing tetra-i-propoxy titanium 9 is about 60 ° C. (vapor pressure is about 1 Torr), the N 2 carrier gas flow rate is 0.5 l / min, and the temperature of the bubbler container 12 containing triethoxy phosphorus 10 is About 50 ° C. (vapor pressure: about 4 Torr), N 2 carrier gas flow rate is set to 0.25 l / min, N 2 flow rate as atmospheric gas is set to 2.5 l / min, and O 2 flow rate is set to 0.5 l / min. Under these conditions, a titanium oxide film 2 containing phosphorus having a thickness of about 70 to 90 nm is formed on the substrate surface 1a. Since the raw material is formed on the substrate surface 1a by a CVD method in which a raw material is supplied in a gas state, the titanium oxide film 2 containing phosphorus can be formed with a uniform thickness even on the substrate surface 1a having minute irregularities. .
iii) Next, as shown in FIG. 1 (c), the substrate 1 is transferred to a quartz tube furnace, and heat treatment is performed at about 900 ° C. for 30 minutes in an N 2 atmosphere. As a result, phosphorus is diffused from the titanium oxide film 2 containing phosphorus to the surface 1a of the substrate 1 so that the sheet resistance is about 60 to 80Ω / sq. The n + layer 3 is formed (a p-type portion inside the substrate 1 and the n + layer 3 form a pn junction). At the same time, an antireflection film made of the titanium oxide film 2 containing phosphorus is formed on the substrate surface 1a. Since the titanium oxide film 2 containing phosphorus is formed in a uniform film thickness in step ii), an antireflection film having a uniform film thickness can be formed. Since this antireflection film has low hygroscopicity and a refractive index of about 1.6 to 2.1, it is suitable as an antireflection film for a solar cell used alone.
Note that the temperature and time of the heat treatment are set according to the required surface concentration and junction depth of the n + layer. Further, the surface concentration and the junction depth of the n + layer can be controlled by the phosphorus concentration contained in the titanium oxide film, the heat treatment temperature, and the heat treatment time. In order to obtain an n + layer suitable for a solar cell, the heat treatment temperature is preferably set in the range of about 800 ° C. to about 1000 ° C.
iv) Next, as shown in FIG. 1 (d), an aluminum paste is printed on the back surface 1b of the substrate by a screen printing method and baked at about 700 ° C. to form a back electrode 4 made of the aluminum paste, and aluminum Aluminum is diffused from the paste into the back surface 1b of the substrate to form the p + layer 5.
v) Finally, as shown in FIG. 1 (e), a silver paste is printed on the light receiving surface 1a in a comb shape or fish bone shape by screen printing, and baked at about 700 ° C. to form the light receiving surface electrode 6. . At this time, the light-receiving surface electrode 6 is in contact with the n + layer 3 through the titanium oxide film 2 containing phosphorus by the action of glass frit in the silver paste.
The firing temperature for the light-receiving surface electrode 6 is preferably set in the range of about 600 ° C to about 800 ° C. The light receiving surface electrode 6 can also be formed by plating or vapor deposition.
Thus, according to this formation method, the titanium oxide film 2 containing phosphorus can be formed with a uniform film thickness by the CVD method, and thus an antireflection film with a uniform film thickness can be obtained after the heat treatment. As a result, a high short-circuit current can be obtained after the solar cell is completed. In addition, since the pn junction and the antireflection film are formed simultaneously by the heat treatment, a solar cell can be manufactured by a simple process with a small number of steps.
FIG. 6 shows the surface reflectance of the solar cell thus fabricated (Example 3). For comparison, in FIG. 6, a titanium oxide film containing phosphorus is formed using a coating solution according to the process shown in FIG. 14, and heat treatment is performed to simultaneously form a pn junction and an antireflection film. The surface reflectance of the solar cell (Comparative Example 3) is also shown. In the solar cell of Comparative Example 3, a titanium oxide coating solution containing phosphorus is spin-coated on the texture-etched substrate surface, dried at about 300 ° C. for 15 minutes, and then subjected to heat treatment at 900 ° C. for 30 minutes to form an n + layer. Formed. The subsequent process conditions were the same as in Example 3.
As is apparent from FIG. 6, since the titanium oxide film 2 containing phosphorus is formed with a uniform film thickness by the CVD method, an antireflection film with a uniform film thickness is formed even on the substrate surface 1a having irregularities. The surface reflectance could be reduced as compared with Comparative Example 3 using a coating solution. As a result, the short-circuit current could be improved as compared with Comparative Example 3.
FIG. 8 shows a solar cell manufacturing apparatus embodying the present invention.
This apparatus includes a belt driving means 116 including rollers 116A, 116B,..., 116G, and a conveying belt 110 surrounding the rollers 116A, 116B,. The rollers 116A and 116B are horizontally disposed at right and left positions in the drawing, and the rollers 116C and 116G are horizontally disposed at positions obliquely below them. As a result, the portion of the conveyor belt 110 between the rollers 116A and 116B constitutes a horizontal portion for placing a substrate on which a film is to be formed. The rollers 116D and 116F are disposed relatively close to the rollers 116C and 116G, and the roller 116E is disposed below the rollers 116D and 116F. The conveyor belt 110 passes through the inside of the rollers 116D and 116F and the outside of the roller 116E, and the portion around which the roller 116E is wound is cleaned by the belt cleaning unit 114.
A first film-forming part 111 for forming a titanium oxide film containing phosphorus, a heat treatment part 112, and a film having a higher refractive index than the titanium oxide film containing phosphorus, in order from the right along the horizontal part of the conveyor belt 110. A second film forming part 113 is formed. Heater plates 115 </ b> A, 115 </ b> B, and 115 </ b> C are provided in the first film forming unit 111, the heat treatment unit 112, and the second film forming unit 113, respectively, below the transfer belt 110. The first film forming part 111, the heat treatment part 112, and the second film forming part 113 are covered with a cover 124 that is integrally formed in a substantially U-shaped cross section. The first film forming part 111 and the second film forming part 113 are provided with dispersion heads 125 and 128 each having a head assembly 130. The portions of the cover 124 that cover the head assembly 130 of the first film forming unit 111 and the second film forming unit 113 are formed in a convex shape with a gap with respect to the head assembly 130. At portions covering the heat treatment section 112, an atmosphere gas inlet 127 is provided on the second film forming section 113 side, and an atmosphere gas discharge port 126 is provided on the first film forming section 111 side. Further, the first film forming unit 111 and the heat treatment unit 112 and the heat treatment unit 112 and the second film forming unit 113 are partitioned by partition plates 129A and 129B formed integrally with the cover 124, respectively. .
The dispersion heads 125 and 128 are configured in detail as shown in FIG. That is, the head assembly 130 is fixed between a top plate 135, four side plates 134 (only the left and right side plates are shown) extending downward from the periphery of the top plate 135, and the left and right side plates 134, 134. It has many partition plates 133 arranged with a gap. Two gas inlets 131 and 132 are provided in a portion corresponding to the back side plate between the top plate 135 and the upper end of the partition plate 133. Further, a cooling plate 138 having a built-in pipe for flowing air as a refrigerant is attached to the outer surface of each side plate 134. During operation, gas containing raw materials is introduced into the space between the top plate 135 and the upper end of the partition plate 133 through the gas inlets 131 and 132 and mixed there. The mixed gas G is blown downward along the partition plate 133, and is supplied to the surface of the substrate 101 passing on the transport belt 110 and passing below the head assembly 130. The gas G is decomposed on the surface of the substrate 101, and a film having a composition corresponding to the type of the raw material is formed on the surface of the substrate 101. The remaining gas or the like passes through the gap 139 between the head assembly 130 and the cover convex portion 136 and is discharged to the outside through the exhaust port 137. The temperature of the head assembly 130 is adjusted to a temperature not lower than the temperature at which the raw material does not condense (the temperature of the bubbler container described later) and lower than the lower limit temperature at which the raw material decomposes by flowing air through the cooling plate 135 at an appropriate flow rate. Is done.
FIG. 10 shows a piping system for supplying a gas containing a raw material to the head assembly 130 of the dispersion head (each of the head assemblies 130 of the first film forming section 111 and the second film forming section 113). This piping system is connected). A gas supply pipe 150 is connected to the gas inlet 132 of the head assembly 130, while a gas supply pipe 151 is connected to the gas inlet 131.
The gas supply pipe 150 is a combination of a dilution N 2 gas supply pipe 146 and a first source gas supply pipe 145b, and the gas supply pipe 151 includes a dilution N 2 gas supply pipe 147 and an O 2 gas supply pipe. 148 and the second source gas supply pipe 149b merge. The first raw material gas supply pipe 145b is connected to a bubbler container 161 accommodated in a thermostatic chamber 163 with a temperature regulator as a temperature adjustment unit, and a carrier gas supply pipe 145a is connected to the bubbler container 161. On the other hand, the second raw material gas supply pipe 149b is connected to a bubbler container 162 accommodated in a thermostatic chamber 164 with a temperature controller as a temperature adjustment unit, and a carrier gas supply pipe 149a is connected to the bubbler container 162. Yes. The carrier gas supply pipes 145a and 149a are provided with flow rate controllers 142A and 142B, the dilution N 2 gas supply pipes 146 and 147 are provided with flow rate controllers 143A and 143B, and the O 2 gas supply pipe 148 is provided with a flow rate controller 143C. The flow rate of gas passing through the pipeline can be adjusted (each pipeline can be shut off by an on-off valve not shown). The first source gas supply pipe 145b, the second source gas supply pipe 149b, and the gas supply pipes 150 and 151 are heated by a heater (not shown) in order to prevent the source gas from being liquefied in the pipe.
During operation, each of the bubbler containers 161 and 162 is filled with the first raw material 159 and the second raw material 160 in a liquid state and maintained at a predetermined temperature. A predetermined flow rate of carrier gas is introduced into each of the bubbler containers 161 and 162 through the carrier gas supply pipes 145a and 149a, and the first raw material 159 and the second raw material 160 are introduced into the introduced carrier gas up to a partial pressure corresponding to the vapor pressure, respectively. included. Then, the first raw material and the second raw material in the gas state together with the carrier gas flow through the first raw material gas supply pipe 145b and the second raw material gas supply pipe 149b, and diluted N 2 gas and O 2 gas are respectively supplied through the gas supply pipes 150 and 151. And is supplied to the head assembly 130.
According to this manufacturing apparatus, the vapor pressure control by the set temperature of the bubbler containers 161 and 162 containing the first raw material 159 and the second raw material 160 in the liquid state, and the flow rate control of the carrier gas passed through the bubbler containers 161 and 162 are performed. By performing the above, the supply amount of each raw material can be controlled with high accuracy. As a result, for example, when a titanium compound is used as the first raw material 159 and a phosphorus compound is used as the second raw material 160 to form a titanium oxide film containing phosphorus, the film thickness uniformity of the formed film is increased and the phosphorus concentration is increased. Can be reliably controlled. Moreover, various phosphorus concentrations in the film can be set by changing the mixing ratio of the titanium compound and the phosphorus compound.
FIG. 7 shows a solar cell manufacturing process performed using the solar cell manufacturing apparatus. Here, a solar cell having an antireflection film having a refractive index of 2.2 to 2.5 and suitable for a super straight type module is manufactured.
i) First, as shown in FIG. 7A, the p-type single crystal silicon substrate 101 having a thickness of about 400 μm and a specific resistance of about 1 Ω · cm is cleaned. Subsequently, texture etching is performed at a liquid temperature of about 90 ° C. using a mixed solution of NaOH aqueous solution and isopropyl alcohol. Thus, minute pyramid-shaped irregularities (represented by a concave portion 122b and a convex portion 122a) having a height difference of several μm are formed on the surface 101a of the substrate 101.
In addition, it is preferable that the height difference of the unevenness is in the range of several μm to several tens of μm.
ii) Next, using the solar cell manufacturing apparatus shown in FIG. 8, the titanium oxide film 102A containing phosphorus shown in FIG. 7B and the n + layer (pn junction) 103 shown in FIG. 7C. Then, a titanium oxide film (not including phosphorus) 102B having a refractive index of 2.2 to 2.5 shown in FIG. 7D is continuously formed as follows.
First, as a setting condition of the apparatus, in the first film forming unit 111, the heating temperature of the substrate 101 by the heater plate 115A is set to 400 ° C., and the head assembly temperature is set to 100 to 120 ° C. A bubbler container 161 (FIG. 10) connected to the first film forming unit 111 is filled with tetra-i-propoxytitanium as the first raw material 159, and this bubbler container 161 is maintained at a temperature of 85 ° C. by a temperature controller. The flow rate of N 2 gas serving as the carrier gas flowing through the carrier gas supply pipe 145a is set to 1 l / min, and the flow rate of dilution N 2 gas flowing through the dilution gas supply pipe 146 is set to 4 l / min. Further, the bubbler container 162 connected to the first film forming unit 111 is filled with triethoxy phosphorus as the second raw material 160, and the bubbler container 162 is maintained at a temperature of 45 ° C. by the temperature controller. O flowing N 2 gas flow as a carrier gas flowing through the carrier gas supply pipe 149a 0.5 l / min, diluted N 2 flow rate flowing through the diluent N 2 gas supply pipe 147 5l / min, the O 2 gas supply pipe 148 2 Set the flow rate to 7 l / min.
Further, in the heat treatment unit 112, N 2 gas as an atmospheric gas is introduced into the cover through the atmospheric gas introduction port 127 shown in FIG. 8 and exhausted through the atmospheric gas exhaust port 126. At the same time, the heating temperature of the substrate 101 by the heater plate 115B is set to 950 ° C. In addition, when the moving speed of the board | substrate by the belt 110 for conveyance is 300 mm / min, it sets so that a board | substrate may be hold | maintained for 10 minutes at the temperature of 950 degreeC.
In the second film forming section 113, the heating temperature of the substrate 101 by the heater plate 115C is set to 300 ° C., and the head assembly temperature is set to 100 to 120 ° C. A bubbler container 161 (FIG. 10) connected to the second film forming unit 113 is filled with tetra-i-propoxy titanium as the first raw material 159, and this bubbler container 161 is maintained at a temperature of 85 ° C. by a temperature controller. The flow rate of N 2 gas as the carrier gas flowing through the carrier gas supply pipe 145a is set to 1.5 l / min, and the flow rate of dilution N 2 gas flowing through the dilution gas supply pipe 146 is set to 4 l / min. Moreover, the bubbler container 162 connected to the second film forming unit 113 is filled with water as the second raw material 160, and the bubbler container 162 is maintained at a temperature of 40 ° C. by the temperature controller. Set N 2 gas flow rate 0.2 l / min as a carrier gas flowing through the carrier gas supply pipe 149a, the diluted N 2 flow rate flowing through the diluent N 2 gas supply pipe 147 to 8l / min.
Under such setting conditions, the substrate 101 is placed on the transport belt 110 at the load position 110a shown in FIG. 8, and the substrate is moved to the left at a constant speed of 300 mm / min by the belt driving mechanism 116. As a result, as shown in FIG. 7B, a titanium oxide film 102 </ b> A containing phosphorus is formed on the surface of the substrate 101 in the first film forming portion 111. Subsequently, as shown in FIG. 7C, in the heat treatment section 112, heat treatment is performed at a maximum temperature of 950 ° C. for 10 minutes to diffuse phosphorus from the titanium oxide film 102A containing phosphorus to the substrate surface 101a. Thus, the n + layer 103 is formed (a pn junction is formed by the p-type portion inside the substrate 101 and the n + layer 103). Subsequently, as shown in FIG. 7 (d), a titanium oxide film (refractive index 2.2 to 2.5 having a higher refractive index than this film) is formed on the surface of the titanium oxide film 102A containing phosphorus. 102B) is formed. In this way, the three steps are automatically and continuously formed by belt conveyance.
Here, since the first film forming unit 111 is formed by a CVD method in which a raw material is supplied in a gas state to the substrate surface 101a, the titanium oxide film 102A containing phosphorus is formed even on the substrate surface 101a having minute unevenness. Can be formed in a uniform film thickness. When the refractive index and film thickness of the titanium oxide film 102A containing phosphorus after the heat treatment were measured with an ellipsometer, the refractive index was 1.7 to 1.8 and the film thickness was about 30 to 40 nm. The sheet resistance value of the obtained n + layer 103 was about 60 to 80 Ω / cm 2 . The titanium oxide film containing phosphorus is formed with a film thickness of about 100 nm so that the surface reflectance is minimized in the vicinity of a wavelength of about 600 nm when the surface of the solar cell is in direct contact with air. When producing a solar cell suitable for modularization as in the example, it is preferable to make the film thickness as thin as possible within a range that can be an impurity diffusion source.
In addition, since the second film forming unit 113 is formed by a CVD method in which the raw material is supplied in a gas state as in the first film forming unit 111, the titanium oxide film can be formed with a uniform film thickness. When the refractive index and film thickness of the obtained titanium oxide film 102B were measured with an ellipsometer, the refractive index was 2.2 to 2.5, and the film thickness was about 50 to 60 nm. As a result, the antireflection films 120A and 102B having a uniform film thickness and showing a good interference effect could be produced. The main reason for adopting the titanium oxide film 102B as the film having a refractive index of 2.2 to 2.5 is that the heating temperature of the substrate is set to 150 to 350 as disclosed in JP-A-62-140881. This is because the refractive index can be changed to about 1.8 to 2.4 by changing in the range of ° C.
Further, since the above three steps are automatically and continuously executed by belt conveyance, the time for cooling the substrate 101 and raising the temperature between these three steps can be shortened. That is, when these processes are performed by independent apparatuses, the substrate 101 is transported from the place where the apparatus for the previous process is installed in the factory to the place where the apparatus for the next process is installed. The substrate 101 needs to be once cooled to near normal temperature. On the other hand, according to the manufacturing apparatus of FIG. 8, since the above three steps can be executed continuously, there is no need to cool the substrate 101 to near normal temperature, and the temperature for the next step can be changed from the temperature for the previous step. It is sufficient to change the temperature directly up to the temperature. That is, as shown in FIG. 11, the temperature is directly changed from 400 ° C. of the first film forming part 111 to 950 ° C. of the heat treatment part 112 and from 950 ° C. of the heat treatment part 112 to 300 ° C. of the second film forming part 113. You can do it. Therefore, the time required for manufacturing the solar cell can be shortened. In addition, unlike the case where the above three steps are performed by independent devices, the operation of transferring the substrate 101 between the devices becomes unnecessary, and the manufacturing cost of the solar cell can be reduced.
The heating temperature of the substrate in the first film forming unit 111 is 350 to 450 ° C., the heating temperature of the substrate in the heat treatment unit 112 is 800 to 1000 ° C., and the heating temperature of the substrate in the second film forming unit 113 is 200 to 400 ° C. It is preferable to set within the range.
iii) Next, as shown in FIG. 7 (e), an aluminum paste is printed on the back surface 101b of the substrate by a screen printing method and baked at about 700 ° C. to form a back electrode 104 made of the aluminum paste, and aluminum A p + layer 105 is formed by diffusing aluminum from the paste to the substrate back surface 101b.
iv) Next, as shown in FIG. 7 (f), a silver paste is printed on the light receiving surface 101a in a comb shape or a fishbone shape by screen printing, and baked at about 700 ° C. to form the light receiving surface electrode 106. . At this time, the light-receiving surface electrode 106 passes through the titanium oxide film 102 containing phosphorus and contacts the n + layer 103 by the action of glass frit in the silver paste.
The firing temperature for the light-receiving surface electrode 106 is preferably set in the range of about 600 ° C to about 800 ° C. The light receiving surface electrode 106 can also be formed by plating or vapor deposition.
The solar cell thus produced is solder coated and stringed with lead wires. By sandwiching the solar cell in this state with EVA and thermocompression bonding the glass and the back surface protection sheet from above and below, a super straight type module can be produced.
In this module, the surface of the solar cell has a titanium oxide film 102A containing phosphorus and a titanium oxide film 102B not containing phosphorus having a refractive index of 2.2 to 2.5 as an antireflection film. Compared with the case of having an antireflection film consisting only of a titanium oxide film, the surface reflectance of the solar cell can be reduced and the short-circuit current can be improved.
The manufacturing process of the solar cell described here has many steps of forming the titanium oxide film 102B having the refractive index of 2.2 to 2.5 as compared with the manufacturing process of FIG. It is a simple process with fewer steps than the process. In addition, the titanium oxide film 102A containing phosphorus, the n + layer (pn junction) 103, and the titanium oxide film (not containing phosphorus) 102B having a refractive index of 2.2 to 2.5 are continuously formed in one apparatus. Therefore, the actual amount of work can be reduced as compared with the process of FIG.
It is a figure which shows the manufacturing process of the solar cell of embodiment of this invention. It is a figure which shows the CVD apparatus for enforcing the formation method of the titanium oxide film containing phosphorus of embodiment of this invention. It is a figure which shows the IR absorption spectrum of the titanium oxide film containing phosphorus formed by applying this invention together with a comparative example. It is a figure which shows the relationship between the substrate temperature when forming the titanium oxide film containing the said phosphorus, and the refractive index of the formed film. It is the figure which showed the relationship between the substrate temperature when forming the said titanium oxide film containing phosphorus, and the surface resistance of the board | substrate after heat processing. It is a figure which shows the surface reflectance of the solar cell produced by the manufacturing process of the said solar cell together with a comparative example. It is a figure which shows the manufacturing process of the solar cell of embodiment of this invention. It is a figure which shows the structure of the 1st film forming part in the solar cell manufacturing apparatus of embodiment of this invention, the heat processing part, and the 2nd film forming part. It is a figure which shows the cross-section of the dispersion head provided in the said 1st film forming part and the 2nd film forming part. It is a figure which shows the piping system connected to each dispersion head of the said solar cell manufacturing apparatus. It is a figure which shows the temperature profile of the 1st film forming part in the said solar cell manufacturing apparatus, the heat processing part, and the 2nd film forming part. It is a figure which shows the manufacturing process of the conventional solar cell. It is a figure which shows the manufacturing process of another conventional solar cell. It is a figure which shows the manufacturing process of another conventional solar cell. It is a figure which shows a state when the titanium oxide film containing an impurity is formed in the substrate surface with an unevenness | corrugation using a coating liquid. It is a figure which shows the surface reflectance of the conventional solar cell. It is a figure which shows the structure of the head vicinity of the conventional atmospheric pressure CVD apparatus.
1,101 p-type silicon substrate 2,102A titanium oxide film containing phosphorus 102B titanium oxide film 3,103 n + layer 4,104 back electrode 5,105 p + layer 6,106 light-receiving surface electrode 7,107 substrate 8 heater block 9 Tetra-i-propoxy titanium 10 Triethoxyline 11, 12, 161, 162 Bubbler container 13 Gas dispersion head 110 Belt 116 Belt drive mechanism 115A, 115B, 115C Heater 111 First film forming part 112 Heat treatment part 113 Second film formation Part 114 Belt cleaning part 125, 128 Dispersion head 130 Head assembly
In the step of forming the titanium oxide film containing phosphorus, a titanium compound and a phosphorus compound are supplied in a gas state to the surface of the substrate heated to a predetermined temperature, and the titanium compound and the phosphorus compound are supplied to the surface of the substrate. A method for manufacturing a solar cell, comprising forming a titanium oxide film containing phosphorus comprising a reaction product of
In the manufacturing method of the solar cell of Claim 1 or 2,
In the step of forming the titanium oxide film containing phosphorus, a carrier gas is passed through the liquid titanium compound and the phosphorus compound, respectively, and the titanium compound and the phosphorus compound are included in the carrier gas according to the vapor pressure, and the carrier gas A method for producing a solar cell, characterized by being supplied to the surface of the substrate.
A method for producing a solar cell comprising the steps of forming a back electrode on the back side of the substrate and forming a light receiving surface electrode on the surface side of the substrate after all the steps.
A solar cell comprising a titanium oxide film containing phosphorus having a substantially uniform thickness to the extent that an interference effect is exhibited on the surface of the n-type impurity region.
A solar cell comprising a titanium oxide film having a substantially uniform thickness not containing phosphorus having a refractive index of 2.2 to 2.5 on a surface of the titanium oxide film containing phosphorus.
JP2006012789A 1994-07-21 2006-01-20 Manufacturing method of solar cell and the solar cell Pending JP2006148155A (en)
JP16931894 1994-07-21
JP2006012789A JP2006148155A (en) 1994-07-21 2006-01-20 Manufacturing method of solar cell and the solar cell
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JP2006148155A true JP2006148155A (en) 2006-06-08
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JP2006012789A Pending JP2006148155A (en) 1994-07-21 2006-01-20 Manufacturing method of solar cell and the solar cell
JP (1) JP2006148155A (en)
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WO2010134673A1 (en) * 2009-05-22 2010-11-25 동국대학교 산학협력단 Apparatus and method for fabricating anti-reflection film of solar battery cell
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