JP2003086817A - Solar battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a solar battery capable of acquiring satisfactory photoelectric conversion characteristics, and reducing dark currents, and improving photoelectric converting efficiency in a simple process without any mask material peeling process. SOLUTION: Mask materials 2 for preventing the formation of pn junction are applied to the edge region of the back face of an almost square semiconductor substrate 1, or the edge region and side face of the back face by using an ink jet method, and then dopant liquid 3 is applied to the surface, and heat treatment is carried out, and the dopant is diffused in the substrate so that the pn junction can be formed on the whole surface side of the substrate. Then, electrodes 6 and 7 are formed in the back region other than the region where the mask materials are applied while the mask materials 2 are allowed to remain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell, a method for manufacturing the same and a manufacturing apparatus therefor, and more particularly to a solar cell with an improved pn junction forming method, a method for manufacturing the same and a manufacturing apparatus therefor.

[0002]

2. Description of the Related Art As a conventional method of manufacturing a solar cell, one having the following steps is known.

(1) First, in order to remove a work-affected layer on a surface produced during manufacturing of a substrate, or to form a textured surface containing fine pyramid-shaped irregularities on the surface of a p-type Si substrate by anisotropic etching, The substrate is etched by immersing it in a solution containing NaOH. Next, a dopant liquid (containing a diffusion source such as P) is applied to the surface of the substrate using a spin coating method.

(2) Next, the substrate coated with the dopant solution is heat-treated in a diffusion furnace. As a result, an n ⁺ layer is formed on the light receiving surface side of the substrate, and a pn junction is generated.

(3) Next, the PSG (phosphorus silica glass) layer generated by the dopant liquid is removed by etching with HF or the like.

(4) Next, an antireflection film of SiN or the like is formed on the light receiving surface side of the substrate by using P-CVD or the like.

(5) Next, an Al electrode and an Ag electrode are formed on the back surface of the substrate by a printing method, while an Ag electrode is formed on the light receiving surface of the substrate, and a heat treatment is performed to separate each electrode from the Si substrate. Make electrical contacts. That is,
During the heat treatment, the Ag electrode on the light receiving surface becomes an electrode that penetrates the antireflection film and is bonded to the n ⁺ diffusion layer. On the other hand, from the Al electrode on the back surface, Al atoms diffuse into the Si substrate to form ap ⁺ diffusion layer.

[0008]

When the above manufacturing method is used, in the step (1), the dopant liquid is
Since it adheres not only to the front surface of the substrate but also to the side surface or the back surface of the substrate that is not desired to be coated, the n ⁺ layer is formed on the side surface or the back surface of the substrate in the step (2). Further, even in the region where the dopant liquid does not adhere, a thin n-type diffusion layer is also formed by the dopant liquid diffused in the atmosphere in the heat treatment furnace. Therefore, in the manufactured solar cell, the n ⁺ diffusion layer portion on the back surface of the cell and the contact portion between the thin n-type diffusion layer and the p ⁺ diffusion layer,
Alternatively, the n ⁺ diffusion layer portion and the thin n-type diffusion layer and Al
A short circuit will occur at the contact portion with the electrode. As a result, there is a problem that the dark current of the solar battery cell increases, the fill factor deteriorates, and the maximum output of the solar battery decreases. Further, when the light has low illuminance, the open-circuit voltage is further affected by the parallel resistance due to the dark current, so that there is a problem that the amount of power generation in the low illuminance of a solar battery cell having a large dark current decreases.

In order to solve such a problem, Japanese Unexamined Patent Publication No. 7-135333 discloses that a mask material for preventing the formation of a pn junction on the back surface of a substrate is applied by spin coating to the back surface of the substrate when a dopant is applied. A method of doing so is disclosed.

According to this method, the occurrence of short circuit can be prevented by applying the mask material to the end portion of the back surface. However, since the spin coating method is used, the shape of the non-coated area is substantially circular, and when the rectangular substrate is used, the mask material application area at the edge of the substrate cannot be formed into a strip shape. Therefore, the coating area of the mask material becomes unnecessarily large, and even if an Al electrode is printed on the back surface and heat treatment is performed in a later step, the p ⁺ diffusion layer is not formed in the back surface side area coated with the mask material. The open circuit voltage drops.

Further, when the back surface Al electrode is formed on the substrate on which the mask material is formed, the adhesiveness is deteriorated as compared with the case where the mask material is not formed. Therefore, a step of peeling the mask material before printing the back surface Al electrode is indispensable, and there arises a problem of increased equipment due to an increase in the step of removing the mask material, and an increase in cost due to an increase in the amount of chemical liquid and processing time. In addition, if the removal of the mask material is insufficient, the p ⁺ diffusion layer is difficult to be formed and the open circuit voltage is lowered.

Further, the spin coating method has a problem in that it takes time to accelerate and decelerate the rotation, and also the rotation moment tends to cause cracks, particularly in the case of a polycrystalline substrate, to lower the yield. Further, the spin coating method has a problem that the chemical liquid is wasted in a large proportion. Further, in the spin coating method, the chemical solution easily wraps around to the opposite surface, and there is a problem of characteristic deterioration due to the mask material wrapping around the surface.
As a result, the photoelectric conversion characteristics of the cell in which such a problem has occurred are deteriorated, and variations in characteristics occur, which may cause a reduction in characteristic yield.

When the mask material is applied to the back surface by the spin coating method as described above, it is difficult to apply the mask material and the dopant liquid substantially at the same time. It is necessary to reverse the front and back of the wafer and apply the dopant liquid on the surface. However, in this case, there are problems that the number of times the wafer is transferred and the rotation is accelerated and decelerated, the probability of breaking the wafer increases, and the processing time increases.

Therefore, an object of the present invention is to provide a solar cell having a sufficient photoelectric conversion characteristic, and a manufacturing method and a manufacturing apparatus capable of realizing such a solar cell relatively easily and at low cost.

[0015]

In order to achieve the above object, the solar cell of the present invention comprises a pn junction formed on the front surface side of a semiconductor substrate and a predetermined end region on the back surface of the semiconductor substrate. Further, it is characterized by including a mask material for preventing the formation of a pn junction and electrodes formed on the front and back surfaces of the semiconductor substrate.

This solar cell can be manufactured by a method of manufacturing a solar cell according to another aspect of the present invention, which is a predetermined end portion of the first surface (the back surface of the substrate) of the semiconductor substrate. A step of applying a mask material for preventing the formation of a pn junction using an inkjet method, a step of applying a dopant liquid to a second surface opposite to the first surface, and a heat treatment to apply a dopant. The second of the semiconductor substrate
By diffusing into the surface (which becomes the surface of the substrate),
The method includes a step of forming a pn junction on the entire surface of the substrate on the second surface side, and a step of removing the dopant on the second surface.

In this method, since the mask material is formed before the heat treatment for diffusing the dopant, the formation of the PN junction on the first surface (back surface) side of the substrate is prevented.

On the other hand, this method does not include a mask material peeling step for preventing the formation of a pn junction. The reason is that since the mask material is applied by the inkjet method, even if the semiconductor substrate is a rectangular substrate, the mask material can be formed in a band shape only in a predetermined end region of the first surface (back surface). is there. That is, in this method, the application area of the mask material can be satisfactorily controlled by using the inkjet method, and as a result, the application area of the mask material can be suppressed to the necessary minimum. Therefore, various problems associated with the conventional manufacturing method in which the mask material is formed by the spin coating method are solved by the manufacturing method of the present invention.

From the above, the solar cell having the above structure of the present invention manufactured by using this manufacturing method becomes a solar cell having a small variation in characteristics and a good characteristic yield.

In the solar cell manufactured by this manufacturing method, the electrode formed on the back surface overlaps the back surface area other than the end area where the mask material is formed, that is, the mask material. Instead, it will be formed.

Desirably, the end region where the mask material is formed is up to 2 mm from the end of the substrate, more specifically 0.1 mm.
It is better to be in the range of 2 mm.

In one embodiment, the semiconductor substrate is a substantially rectangular semiconductor substrate, and the step of applying the mask material using an ink jet method is performed in the steps of facing the substrate.
It includes a step of applying along the side and a step of applying along the other two opposite sides.

The step of applying the mask material using the ink jet method is performed between the step of applying along the two opposing sides of the substrate and the step of applying along the other two opposing sides. The step of rotating the substrate by 90 ° may be included.

By these steps, the four sides of the back surface of the rectangular substrate are
The mask material can be easily and rapidly applied to the end regions of the sides.

The step of applying the mask material using the ink jet method may be performed by making the mask material enter in the direction perpendicular to the first surface,
Alternatively, the mask material may be incident on the first surface in an oblique direction. When the mask material is incident on the first surface in an oblique direction, the mask material can be simultaneously applied to the back surface end portion and the side surface of the semiconductor substrate.

Further, it has a holding means for holding the semiconductor substrate of the solar cell of the present invention and a plurality of nozzles arranged substantially in a row, and has a predetermined surface on the first surface (the back surface of the substrate) of the semiconductor substrate. Ink jet head means for applying a mask material for preventing the formation of a pn junction to the end region, and a second surface opposite to the first surface of the semiconductor substrate (which becomes the substrate surface).
And a moving means for moving the substrate relative to the inkjet head means in a direction orthogonal to the alignment direction of the nozzles, the holding means applying a mask material. It is characterized in that the substrate is held on the first surface side.

In this manufacturing apparatus, since the holding means holds the substrate on the side of the first surface (back surface) on which the mask material is applied, the dopant liquid can be applied without inverting the substrate. . Since it is not necessary to invert the front and back of the substrate as described above, it is possible to reduce the substrate crack caused by the substrate transfer error. Further, since the application of the mask material by the ink jet method does not require acceleration / deceleration of the rotation of the substrate, it is possible to reduce the cracking of the substrate caused by the rotation moment and reduce the processing time.

In one embodiment, the ink jet head means comprises two sets of ink jet heads arranged at a predetermined interval in the moving direction of the substrate, and two ink jet heads forming a set face each other on the substrate. Is arranged at a position where the end regions along the two sides can be coated, and the holding means includes means for rotating the substrate by approximately 90 ° between the two sets of inkjet heads.

In one embodiment, the coating means for the dopant liquid is an ink jet head having a nozzle array that covers the length of one side of the substrate.

In this case, the ink jet head means for the mask material is arranged so as to eject the mask material perpendicularly to the first surface of the substrate, while the ink jet head for the dopant liquid is , So that the dopant liquid is discharged perpendicularly to the second surface of the substrate,
It may be arranged on the side of the substrate opposite the inkjet head means for the mask material.

As an example of such an arrangement, the holding means is arranged vertically below the substrate, holds the first surface of the substrate vertically downward, and ink jet head means for the mask material is provided. Is arranged vertically below the substrate, while the inkjet head for the dopant liquid is arranged vertically above the substrate.

Further, the ink jet head means is
The angle of incidence θ of the mask material on the side surface of the substrate is 20 ° to
The inkjet material for the dopant liquid is arranged such that the mask material is discharged in an oblique direction with respect to the first surface and the side surface of the substrate so as to be 90 °. May be arranged so as to discharge perpendicularly to the second surface of the.

As an example of such an arrangement, the holding means is arranged vertically above the substrate and holds the first surface of the substrate vertically upward, and the ink jet head means is provided on the substrate. The mask material is arranged so as to be discharged obliquely above the first surface, while the inkjet head for the dopant liquid is arranged vertically below the substrate.

The solar cell manufacturing apparatus of the present invention further comprises means for adjusting the position and angle of the substrate upstream of the ink jet head means for applying the mask material in the moving direction of the substrate. May be.

Alternatively, in the solar cell manufacturing apparatus of the present invention, in the moving direction of the substrate, on the upstream side of the inkjet head means for applying the mask material,
A means for measuring the shape of the substrate may be provided, and the operation of the nozzle of the inkjet head means may be controlled based on the information from the means for measuring the shape of the substrate.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION A solar cell, a method for manufacturing the same and a manufacturing apparatus therefor according to the present invention will be described below based on the embodiments shown in the drawings. In all the drawings, the same reference numerals are given to the same parts.

(First Embodiment) First, a solar cell having a mask material is formed only on the end portion of the back surface (the surface where the pn junction is not formed) of the substrate by using the ink jet method which is the gist of the present invention. An example of the method will be described, and the manufacturing apparatus thereof will be described later.

FIGS. 1 (a) to 1 (g) are views showing cross sections in each manufacturing step of a solar cell formed by the method for manufacturing a solar cell according to the present embodiment, and FIG. 1 (h) and FIG. 1
(i) is a bottom view corresponding to FIG. 1 (b) and FIG. 1 (g), respectively. Here, a substantially square p-type polycrystalline Si semiconductor substrate is used as the substrate 1.

In FIG. 1 (a), first, a textured surface including fine pyramid-shaped irregularities is formed on the surface of the substrate 1 in order to remove a work-affected layer on the surface produced during manufacture of the substrate 1 or by anisotropic etching. To do Na
The substrate 1 is immersed in a solution containing OH to etch the substrate. The dashed line in the figure indicates the substrate 1 before processing
Indicates.

Next, as shown in FIGS. 1 (b) and 1 (h),
The mask material 2 is applied along the four sides of the back surface of the substrate 1. In this example, the mask material 2 uses a solution containing titanic acid. However, the material of the dopant liquid is not limited to the titanic acid-containing solution used here as long as it can prevent the diffusion of the dopant liquid from the vapor phase in the diffusion furnace.

Next, as shown in FIG. 1C, the dopant liquid 3 is applied to the entire upper surface of the substrate by an inkjet head, and then the solvent component is dried. Here, a liquid precursor of PSG is used as the dopant liquid 3.

Thereafter, the substrate 1 coated with the mask material 2 and the dopant liquid 3 is heat-treated in a diffusion furnace, so that the n ⁺ layer 4 is formed on the light-receiving surface side of the p-type substrate 1 as shown in FIG. 1D. To form a pn junction. On this occasion,
A thin n-layer is formed by the dopant agent diffused in the atmosphere in the heat treatment furnace even in the region where the dopant liquid 3 is not applied, but it is not formed in the region where the mask material 2 is applied at the end of the back surface. In addition, 3 a in FIG. 1D is a PSG layer generated by the dopant liquid 3.

Thereafter, as shown in FIG. 1 (e), the substrate is dipped in an etching solution containing HF to obtain PSG.
The layer 3a is etched away. In order to remove the mask material 2 containing titanic acid by etching, an etching solution having a higher concentration and a longer etching time than those required to remove the PSG layer 3a by etching are required. Then, since the mask material 2 is arranged so as not to overlap the back surface Al electrode described later, it is not necessary to remove it by etching.

Thereafter, as shown in FIG. 1F, a SiN antireflection film 5 is formed on the pn junction formation surface by P-CVD (plasma CVD) method.

Further, as shown in FIG. 1G, the Al electrode 6 and the Ag electrode 7 are formed on the back surface of the substrate 1 by the printing method, while the light receiving surface of the substrate 1 (more specifically, the antireflection film 5). The Ag electrode 8 is formed on the upper side. Then, heat treatment is performed to form electrical contacts between the electrodes 6, 7 and 8 and the Si substrate 1. That is, during this heat treatment, the Ag electrode 7 on the light receiving surface becomes an electrode that penetrates the antireflection film 5 and is joined to the n ⁺ diffusion layer 4. On the other hand, Al on the back side
Al atoms diffuse from the electrode 6 into the Si substrate to form the p ⁺ diffusion layer 9. At this time, as shown in FIG.
Since the pattern of the mask material 2 is set so as not to overlap the pattern of the back surface Al electrode 6, the mask material 2
Prevents the formation of the p ⁺ diffusion layer 9 and also prevents the back surface Al from forming.
It does not hinder the adhesion between the electrode layer 6 and the substrate 1.

Next, the manufacturing apparatus used in the first embodiment, more specifically, the mask material 2 and the dopant liquid 3
A coating device for coating will be described with reference to FIG. The coating apparatus includes a substrate chuck 11 that holds the substrate 1 from the vertically lower side and can move and rotate the substrate in parallel.
Two sets of four inkjet heads 12a, 12b for applying the mask material 2 to the two side edges of the lower surface of the substrate;
Since the substrate shape measuring devices 13a and 13b arranged in front of the respective inkjet heads in the substrate traveling direction and the dopant liquid 3 are applied to substantially the entire upper surface of the substrate, the inkjets having substantially the same length as one side of the substrate 1 are formed. A head 14 is provided.

Ink jet heads 12a and 12b
And 14, and the substrate shape measuring instruments 13a and 13b are fixed, and the substrate chuck 11 holding the substrate 1 is
The substrate is moved horizontally from left to right in FIG.
The substrate 1 first passes over the substrate shape measuring device 13a, and the outline of the substrate is measured during the passage. Next, the substrate 1 passes over the inkjet head 12a, and the mask material 2 is applied to the opposing two side edges of the lower surface of the substrate during the passage. that time,
Based on the external dimensions of the substrate measured by the shape measuring device 13a in advance, the ejection nozzle that operates among the plurality of ejection nozzles provided in the inkjet heads 12a and 12a so as to apply the mask material 2 to the end region of the back surface of the substrate 1 is selected. By limiting, the mask material 2 can be applied to a desired end region.

When the coating on the end portions of the two sides is completed, the substrate chuck 11 rotates the substrate 1 by 90 ° and then horizontally moves the substrate further to the right. The substrate 1 passes over the substrate shape measuring device 13b, and the two-sided shape of the substrate on which the mask material is not applied is measured during the passage. Next, the substrate 1 passes over the inkjet head 12b, and the mask material 2 is applied to the two side edges of the lower surface of the substrate during the passage.

Here, also in the case of applying the mask material 2, as in the case of applying the dopant liquid 3, by controlling the ejection nozzles by using a head having a length substantially the same as one side of the substrate 1, 9
It is possible to apply the coating to the end portions of the four sides by scanning once without rotating 0 degree. However, in this case, since the substrate chuck 11 cannot hold the mask material application side of the substrate 1, it is necessary to perform chucking again when the mask material 2 is applied and when the dopant liquid 3 is applied. for that reason,
There are problems that cracks are likely to occur at the time of delivery, the processing speed is reduced, or the apparatus price is expensive. On the other hand, the apparatus used in the present embodiment includes the inkjet heads 12 a and 12 for coating the mask material 2.
b is arranged on the side opposite to the inkjet head 14 for applying the dopant in the vertical direction with respect to the substrate, at a position where it can be applied to the end regions of the two sides of the substrate 1, and the substrate 1 is approximately 90 between the two inkjet heads. By providing a means for rotating the substrate 1, the substrate chuck 11 continues to hold the substrate 1 until the mask material 2 is first applied to the two side edges of the back surface of the substrate 1 and then the dopant liquid 3 is applied to the front surface. Therefore, since the substrate 1 is not delivered, the probability that the substrate 1 is broken becomes very small. Also, the substrate chuck 11
Requires that the mask material 2 is first applied to the two side edges of the back surface of the substrate 1 and then the mask material 2 is rotated by 90 ° to apply the mask material 2 to the other two side edges. It does not require a long time for reversing, and it does not require a long time for accelerating and decelerating the rotation as in the spin coating method.

In the first embodiment, the ink jet system is used as the dopant coating method. However,
When the mask material application and the dopant application are not performed substantially at the same time and the substrate is moved and the dopant is applied after the mask material is applied, a spray method may be used. When the spray method is used, the cost of the device can be reduced. However, the spray method is not suitable because the chemical solution is deposited on a place other than the predetermined area, and therefore, when the mask material is applied almost at the same time, the dopant is attached to the inkjet head for mask material application.

(Example 1) Approximately 125 mm on a side and a thickness of 30
Using a 0 μm square-shaped p-type polycrystalline Si semiconductor substrate, a solar cell was prepared by the process and apparatus shown in the first embodiment. Here, the application range of the mask material 2 is 1 mm from the edge of the back surface of the substrate. The solar cell produced in this manner has a pn junction and back electrodes 6, 7 or a pn junction and back p ⁺ diffusion layer 9
There was no short circuit with him. Moreover, when the characteristics of this solar cell were measured, a reverse current of 0.02 A,
Good photoelectric conversion characteristics with a conversion efficiency of 16.5% were obtained.
Furthermore, the photoelectric conversion characteristics of this solar cell are 100
When the 0-sheet test was conducted, 72% showed a photoelectric conversion characteristic of 15.0% or more, showing little characteristic variation and a good characteristic yield. Further, since the mask material manufactured by the inkjet method does not need to be peeled off, the cost can be reduced.

In the first embodiment, 1 from the back end of the substrate.
Although the mask material was formed in the area of mm, but when the coating width of the mask material is as narrow as less than 0.1 mm, the pn junction portion and the back surface electrodes 6 and 7 or the pn junction portion and the p ⁺ diffusion layer 9 on the back surface are short-circuited. Yield is likely to decrease due to. Therefore, it is preferable that the mask width is wide enough not to overlap the Al electrode 6 on the back surface. However, if the mask width is increased to 2 mm or more, the area of the Al electrode is reduced and the area of the p ⁺ diffusion layer is reduced. . Therefore, the mask width is preferably set in the range of 0.1 mm to 2 mm.

(Comparative Example) For comparison, a solar cell having a conventional structure was prepared by using the above-described conventional manufacturing method (using a mask material). The substrate and the material used in each step are the same as in Example 1. This will be described below with reference to FIG.

In FIG. 3A, first, the surface of the substrate 1 is etched by the same method as in the first embodiment.

Next, the mask material 2 was applied to the peripheral portion of the back surface of the substrate 1 by the spin coating method. More specifically, the back surface of the substrate 1 is held so that the back surface is the top surface, and the mask liquid 2 containing titanic acid is discharged through nozzles (not shown) arranged on the peripheral portion of the back surface while rotating at high speed at about 5000 rpm. By doing so, the mask material 2 spreads outward due to the centrifugal force, and is applied to the peripheral portion of the back surface of the substrate 1 as shown in FIGS. 3B and 3H. However, at that time, the mask material 2 also adheres to a region of the substrate surface which is not desired to be coated.

After the application of the mask material 2, the front and back of the substrate 1 are reversed, the substrate 1 is held again, and then about 5000 r
The substrate is rotated at a high speed up to pm, and the dopant liquid 3 is applied to the surface of the substrate 1 as shown in FIG. At this time, it is necessary to hand over the substrate 1 in order to turn the substrate 1 over.
The probability of breaking the substrate 1 at the time of this delivery becomes high, which causes a decrease in yield. Also in this case, the dopant liquid 3 adheres to the side surface or the back surface of the substrate 1 which is not desired to be applied, but the mask material 2 is applied to that portion in advance.

Next, as shown in FIG.
The substrate 1 coated with the dopant solution 3 is heat-treated in a diffusion furnace in the same manner as in 1. to form an n ⁺ layer 4 on the light-receiving surface side of the p-type substrate 1 to form a pn junction.
At this time, the substrate 1 on which the dopant liquid 3 is applied and applied
Since the mask material 2 is applied in advance to a part of the side surface and the back surface of the pn junction, the pn junction does not occur. Further, in the step of applying the mask material 2, the pn junction does not occur even in the area where the mask material is applied around the surface of the substrate 1 so as to wrap around.

After that, as shown in FIG. 3E, the PSG layer 3a generated by the dopant liquid 3 and the mask material layer 2 are removed by etching with HF or the like. In this case, as compared with the PSG layer 3a, the mask material 2 containing titanic acid is less likely to be peeled off, and an etching solution such as a HF solution having a higher concentration than in the case of Example 1 is required.

The subsequent steps are all the same as those of the first embodiment. Also in the case of this comparative example, the contact between the n ⁺ diffusion layer portion and the p ⁺ diffusion layer 9 on the back surface of the substrate 1 or the contact between the n ⁺ diffusion layer portion and the Al electrode 6 tends to occur when the mask material is not used. Although a short circuit due to contact does not occur, the region of the pn junction generated on the surface by the wraparound to the surface (that is, the upper surface) of the mask material 2 is smaller than that in the first embodiment.

When the photoelectric conversion characteristics of the comparative example thus produced were measured, the photoelectric conversion efficiency was 16.0% and the reverse current was 0.02A. Further, when 1000 sheets were tested for photoelectric conversion characteristics of this solar cell, 55 showed a photoelectric conversion characteristic of 15.0% or more.
%there were. Compared with the first embodiment, the characteristic variation is large and the characteristic yield is low. This is because compared with the inkjet method, the spin coating method makes it easier for the chemical solution to reach the opposite side surface, and there are places where the mask material does not completely remove the characteristic deterioration due to the mask material sneaking into the surface. It is thought that this is due to the deterioration of the characteristics.

(Second Embodiment) A solar cell having a mask material on the end portion of the back surface (the surface not subject to pn junction) of the substrate and the side surface of the substrate is manufactured by using the ink jet method which is the gist of the invention of the present invention. The forming method will be described, and the manufacturing apparatus will be described later.

FIGS. 4 (a) to 4 (g) are views showing cross sections in each manufacturing process of the solar cell formed by the method of manufacturing the solar cell according to the present embodiment, and FIG. 4 (h) and FIG. Four
(i) is a bottom view corresponding to FIG. 4 (b) and FIG. 4 (g), respectively. The substrate 1 and the materials and steps used in each step are almost the same as those in the first embodiment, and the detailed description of the same parts will be omitted and the different points will be described.

The difference from the first embodiment is shown in FIG.
As shown in FIG. 5, the mask material 2 is applied to the end portions of the side surface and the back surface of the substrate 1.

The mask material 2 is formed on the side surface and the back surface of the substrate 1.
, The n ⁺ diffusion layer is not formed in that portion. Therefore, when the mask material 2 is not formed on the side surface and the end of the back surface of the substrate 1, the contact portion between the n ⁺ diffusion layer portion and the p ⁺ diffusion layer 9 on the back surface of the substrate 1 or the n ⁺ diffusion layer portion thereof. A short circuit does not occur at the contact portion between the Al electrode 6 and the Al electrode 6.

Next, the manufacturing apparatus used in the second embodiment, more specifically, the mask material 2 and the dopant liquid 3
A coating device for coating will be described with reference to FIG. The coating apparatus includes a substrate chuck 11 that holds the substrate 1 from the vertical upper side and can move and rotate the substrate 1 in parallel.
And two sets of four inkjet heads 12a and 12b for applying the mask material 2 to the two opposite side surfaces of the substrate and the corresponding two side end portions of the upper surface, and the respective inkjet heads 12a and 12b. In order to apply the dopant liquid 3 to the substrate shape measuring instruments 13a and 13b installed in front of the substrate traveling direction and the substantially entire bottom surface of the substrate,
Inkjet head 14 having substantially the same length as one side of the substrate 1
Equipped with.

Ink jet heads 12a and 12b
And 14, and the substrate shape measuring instruments 13a and 13b are fixed, and the substrate chuck 11 holding the substrate 1 is
The substrate 1 is horizontally moved from the left side to the right side in FIG. The substrate 1 first passes under the substrate shape measuring device 13a, and the outline of the substrate is measured during the passage. Substrate 1 is 1
The mask material 2 is passed between the pair of inkjet heads 12a and two side edges of the substrate and two side edges of the upper surface are provided during the passage.
Is applied. Here, as shown in FIGS. 5B and 5D, the inkjet head 12a used for applying the mask material has an incident angle θ of the chemical liquid on the side surface of the substrate formed between the chemical liquid discharge direction and the horizontal direction. Is set to be a constant value.

When the coating on the side surfaces and the edge of the upper surface of the two sides is completed, the substrate chuck 11 rotates the substrate 1 by 90 ° and then horizontally moves the substrate further to the right.

The substrate 1 passes under the substrate shape measuring device 13b, and during the passage, the two-sided shape of the substrate on which the mask material is not applied is measured. Next, the substrate 1 passes between the other set of inkjet heads 12b, and the mask material 2 is applied to the two side edges of the side surface and the upper surface of the substrate during the passage. The direction of ejecting the chemical liquid from the inkjet head 12b is also the same as the direction of the inkjet head 12a. At that time, based on the board external dimensions previously measured by the shape measuring device 13b, the board 1
Among the plurality of ejection nozzles included in the inkjet head 12b so as to apply the mask material 2 to the end region of the, the ejection nozzles that operate are limited.

In this embodiment, the ink jet heads 12a and 12b for applying the mask material are shown in FIG.
Although it is installed so as to be positioned along the side surface of the substrate as shown in FIG. 5, the same effect can be obtained when it is arranged above the substrate as shown in FIG.

By the way, when the mask material 2 is applied using a head having a length substantially the same as one side of the substrate 1 as in the case of applying the dopant liquid 3, the ejection directions of the ejection nozzles arranged in a row form. Is not uniform, the structure of the head becomes very complicated. However, in the apparatus used in the present embodiment, the two sets of inkjet heads 12a and 12b for applying the mask material 2 are arranged at positions where they can be applied to the end regions of the two sides of the substrate 1, and these two sets of inkjet heads are used. By providing a means for rotating approximately 90 ° between them, it becomes possible to accurately apply with a simple head structure.

Further, first, the back side of the substrate 1 is marked on the two side edges.
After applying the disc material 2, the dopant liquid 3 is applied to the surface.
Substrate chuck 11 continues to hold the substrate 1 until
There is no probability that the substrate 1 will break because 1 is not delivered.
Always less. In addition, the substrate chuck 11 is initially attached to the substrate 1
After applying the mask material 2 to the two side edges of the back surface of the
Rotate 90 ° to apply the mask material 2 to the two side edges of the
As the spin coating method
It doesn't take time quickly. (Example 2) Similar to Example 1, one side is approximately 125 mm thick.
P-type polycrystalline Si semiconductor substrate having a substantially square shape with a length of 300 μm
Using the plate, the process and the device shown in the second embodiment are
A solar cell was prepared by placing. Differences from Example 1
Indicates that the coating range of the mask material 2 is 0.5 m from the rear end of the substrate.
The mask material 2 is applied to the point and the side surface defined as the area of m.
That is the point. The inkjet heads 12a and 12b are
The incident angle is 45 ° to the side surface of the substrate, and the side surface and the end surface of the substrate
Are being applied at the same time. The sun created this way
The battery consists of a pn junction and backside electrodes 6, 7 or pn contact.
The mating part and the back ^{P +}No short circuit with the diffusion layer 9 has occurred
won. In addition, the characteristics of this solar cell were measured.
B, good reverse current 0.02A, conversion efficiency 16.5%
A good photoelectric conversion characteristic was obtained. Furthermore, of this solar cell
When 1000 sheets were tested for photoelectric conversion characteristics,
70% had a photoelectric conversion characteristic of 15.0% or more.
Characteristics, there is little variation in characteristics, and the characteristic yield is good.
It was Further, the mask material 2 manufactured by the inkjet method is
Since there is no need for peeling, the cost can be reduced.

In the second embodiment, the ink jet heads 12a, 12 are so arranged that the mask material 2 is discharged in a vertically downward direction.
Although b is arranged, when the mask material 2 is discharged obliquely upward with the substrate 1 arranged upside down, the mask material 2 not applied to the side surfaces adheres to the surface, resulting in deterioration of characteristics. . Therefore, when the mask material 2 is applied also to the side surface of the substrate, the inkjet head 12 for applying the mask material is used.
It is desirable that a and 12b are arranged above the substrate 1 so that the discharge direction of the mask material is obliquely downward. Specifically, when the incident angle θ is less than 20 °, the accuracy of the coating width at the edge of the upper surface (back surface) of the substrate decreases, so the incident angle θ is 20 °.
It is preferable to set to 90 ° (20 ° ≦ θ ≦ 90 °).

Further, the mask material application range is set to 0.5 mm from the back end of the substrate. However, since the mask material is applied to the side surface as well, the mask material is applied more than when the side surface is not applied with the mask material as in the first embodiment. The same characteristics can be obtained even if the width of is small. Therefore, the area of the Al electrode 6 on the back surface can be increased, so that the open circuit voltage can be improved.

Although the solar cell using the polycrystalline semiconductor substrate has been described above, the semiconductor substrate may be a single crystal semiconductor substrate.

Further, regarding the apparatus configurations in the first and second embodiments described above, based on the information from the shape measuring means arranged in front of the ink jet head, the plural ejection nozzles of the ink jet head are The ejection nozzle to be operated was controlled. However, when the variation in the shape of the substrate 1 is sufficiently small, the shape measuring means is not provided, but a means for adjusting the position shift or the angle of the substrate is provided on the upstream side of the ink jet head, so that the mask material or the dopant liquid is predetermined. Can be applied to the area. Specifically, the centers of the substrate chuck 11 and the substrate 1 are aligned by mechanically contacting the front, rear, left, and right of the substrate upstream of the inkjet head, and the two sides of the substrate are parallel to the traveling direction of the substrate. By disposing a mechanism for matching the substrate chuck 11 with each other, the holding operation of the substrate chuck 11 is not performed during the above operation, and the holding operation of the substrate chuck 11 is performed after the matching operation is completed, so that the predetermined area can be applied to the downstream inkjet head. It will be possible. in this case,
Since the device can be simplified, the device price can be reduced. Further, the means for adjusting the position and the angle of the substrate and the board shape measuring means may be provided in combination, and in this case, by providing the means for adjusting the position and the angle of the board on the most upstream side, each is provided independently. Compared with the case, it can be applied more accurately.

In the first and second embodiments, the general case of moving the substrate in the horizontal direction has been described, but the substrate may be moved in the vertical direction.

In the first and second embodiments, two sets of ink heads are provided in a line, and the substrate is rotated 90 ° between these two sets of ink heads. Place vertically and set the direction of travel of the substrate to 9
If it is bent at 0 °, the substrate itself does not have to be rotated at 90 °.

[0078]

As is clear from the above, the solar cell of the present invention is a solar cell in which a pn junction is formed on one surface of a semiconductor substrate. By forming a mask material for prevention by an inkjet method, a solar cell can be created by a simple process without a mask material peeling step, and thus a solar cell with good characteristic yield and less variation in characteristics can be obtained. It is possible to obtain a photoelectric conversion characteristic higher than that of the process.

Further, in the method for manufacturing a solar cell of the present invention, an end region (preferably 0.1 to 2 mm) on the back surface of the semiconductor substrate is used.
Area) or the edge area of the back surface (preferably 0.1
(A region of about 2 mm) and a side face thereof are coated with a mask material for preventing the formation of a pn junction in a region which does not overlap with the back electrode by using an inkjet method, and at the same time as or after that step, a dopant liquid is used, for example, an inkjet method or a spray method A solar cell having good photoelectric conversion characteristics by a simple process without a mask material peeling process, since a pn junction is formed on the front surface side of the substrate surface by applying a heat treatment to the surface of the substrate to diffuse the dopant. Can be manufactured.

In addition, specifically, when the mask material is applied, the mask material can be easily applied simultaneously to the edge and the side surface of the back surface of the substrate by allowing the ink to obliquely enter the back surface of the substrate. Is possible.

When the mask material is applied, it is applied to the ends of the back surface of the two opposite sides of the rectangular substrate, or to the predetermined regions of the ends and the side surfaces, and then the substrate is rotated by about 90 °.
Further, by applying to other end portions of the substrate back surface of the other two parallel sides of the square substrate which relatively moves, or to a predetermined region of the end portion and the side surface, the end portions of the four sides of the back surface of the square substrate or the end portions It becomes possible to easily and rapidly apply the mask material only to the side surface region.

Further, the solar cell manufacturing apparatus of the present invention has a holding means for holding the semiconductor substrate and a plurality of nozzles arranged in a substantially row, and has the first surface of the semiconductor substrate (the back surface of the substrate). Inkjet head means for applying a mask material for preventing the formation of a pn junction to a predetermined end region of FIG.
A coating means for coating the second surface (which becomes the surface of the substrate) opposite to the first surface of the semiconductor substrate with a dopant liquid; and the substrate, which is perpendicular to the inkjet head means, in the alignment direction of the nozzles. Since the holding means holds the substrate on the side of the first surface on which the mask material is applied, the manufacturing apparatus is used to manufacture a solar cell. In the process
It is not necessary to turn the board over. Therefore, it is possible to reduce the breakage of the substrate caused by the substrate transfer error. Further, since application of the mask material by the inkjet method does not require acceleration / deceleration of the substrate rotation required for the spin coating method, it is possible to reduce the substrate breakage caused by the rotation moment and reduce the processing time.

[Brief description of drawings]

1 (a) to 1 (g) are views showing a cross section in each manufacturing step of a solar cell formed by the manufacturing method according to the first embodiment of the present invention, and (h) and (i) ) Are bottom views corresponding to (b) and (g), respectively.

FIG. 2 is a schematic diagram of a solar cell manufacturing apparatus used in the first embodiment of the present invention.

3 (a) to 3 (g) are cross-sectional views in each manufacturing process of a solar cell (comparative example) having a conventional structure formed by a conventional manufacturing method, and FIG. 3 (h) corresponds to (b). FIG.

FIGS. 4 (a) to 4 (g) are views showing a cross section in each manufacturing step of a solar cell formed by the manufacturing method according to the second embodiment of the present invention, and FIGS. ) Are bottom views corresponding to (b) and (g), respectively.

5A is a schematic view of a solar cell manufacturing apparatus used in the second embodiment of the present invention, and FIGS.
FIG. 3A is a diagram illustrating the installation position of the inkjet head with respect to the substrate, and FIG. 7D is a diagram illustrating the ejection angle of the inkjet head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Mask material 3 ... Dopant liquid 3a ... PSG layer 4 ... n ⁺ layer 5 ... Antireflection film 6 ... Al electrode 7, 8 ... Ag electrode 9 ... P ⁺ diffusion layer 11 ... Substrate chuck 12a, 12b ... Mask Inkjet heads for material coating 13a, 13b ... Substrate shape measuring device 14 ... Inkjet head for dopant liquid application

Claims (18)

[Claims] 1. A pn junction formed on the front surface side of a semiconductor substrate and a p-type junction formed on a predetermined end region of the back surface of the semiconductor substrate.
A solar cell comprising an n-junction formation preventing mask material and electrodes formed on the front and back surfaces of the semiconductor substrate. 2. The solar cell according to claim 1, wherein the semiconductor substrate is a substantially rectangular semiconductor substrate. 3. The solar cell according to claim 1, wherein the mask material is also formed on a side surface of the semiconductor substrate. 4. The electrode formed on the back surface is formed on a back surface region other than an end region where the mask material is formed, according to any one of claims 1 to 3. Solar cells. 5. The solar cell according to claim 1, wherein the end region where the mask material is formed is within a range of 2 mm from the end of the substrate. 6. A step of applying a mask material for preventing formation of a pn junction to a predetermined end region of the first surface of the semiconductor substrate by using an ink jet method, and a second step on the opposite side of the first surface. A step of applying a dopant solution to the surface of the semiconductor substrate, and a step of performing a heat treatment to diffuse the dopant into the second surface of the semiconductor substrate to form a pn junction on the entire surface of the substrate on the second surface side. And a step of removing the dopant on the second surface. 7. The semiconductor substrate is a substantially rectangular substrate, and the step of applying the mask material using an ink jet method is a step of applying the mask material along two opposite sides of the substrate, and another step of facing the other side. The method for manufacturing a solar cell according to claim 6, comprising a step of applying along two sides. 8. The step of applying the mask material using an inkjet method is performed between the step of applying along the two opposite sides of the substrate and the step of applying along the other two opposite sides. The method for manufacturing a solar cell according to claim 7, further comprising the step of rotating the substrate by 90 °. 9. The method according to claim 6, wherein the step of applying the mask material using an inkjet method is performed by causing the mask material to enter in a direction perpendicular to the first surface. The method for manufacturing a solar cell according to any one of claims. 10. The method according to claim 6, wherein the step of applying the mask material by using an inkjet method is performed by causing the mask material to enter the first surface in an oblique direction. The method for manufacturing a solar cell according to any one of claims. 11. A mask for holding a semiconductor substrate, and a plurality of nozzles arranged in a line, and a mask for preventing formation of a pn junction in a predetermined end region of the first surface of the semiconductor substrate. An inkjet head means for applying a material; an applying means for applying a dopant liquid to a second surface of the semiconductor substrate opposite to the first surface; and a nozzle for the substrate with respect to the inkjet head means. And a moving means for relatively moving the substrate in a direction orthogonal to the alignment direction, wherein the holding means holds the substrate on the first surface side on which the mask material is applied. 12. The ink jet head means comprises two sets of ink jet heads arranged at a predetermined interval in a moving direction of the substrate, and two ink jet heads forming a set are provided on two opposite sides of the substrate. 7. The holding means is arranged at a position where an end region can be applied, and the holding means includes means for rotating the substrate by approximately 90 ° between the two sets of inkjet heads. 11. The solar cell manufacturing apparatus according to item 11. 13. The coating means for the dopant liquid is an inkjet head having a nozzle row covering a length of one side of the substrate, and the inkjet head means for the mask material includes the mask material on the substrate. The inkjet head for the dopant liquid is arranged to eject the dopant liquid perpendicularly to the second surface of the substrate while being arranged to eject the dopant liquid perpendicularly to the second surface of the substrate. On the other hand, the solar cell manufacturing apparatus according to claim 11 or 12, which is arranged on a side opposite to an inkjet head means for the mask material. 14. The holding means is disposed vertically below the substrate and holds the first surface of the substrate vertically downward, and the ink jet head means for the mask material is vertical to the substrate. The solar cell manufacturing apparatus according to claim 13, wherein the inkjet head for the dopant liquid is arranged vertically upward with respect to the substrate while being arranged downward in the direction. 15. The coating means for the dopant liquid is an inkjet head having a nozzle row covering a length of one side of the substrate, and the inkjet head means is such that the mask material has an incident angle with respect to a side surface of the substrate. The inkjet head for the dopant liquid is arranged so as to discharge the mask material in an oblique direction with respect to the first surface and the side surface of the substrate so that θ becomes 20 ° to 90 °. The solar cell manufacturing apparatus according to claim 10 or 11, wherein the dopant liquid is arranged so as to be discharged perpendicularly to the second surface of the substrate. 16. The holding means is disposed vertically above the substrate and holds the first surface of the substrate vertically upward, and the ink jet head means holds the first surface of the substrate with respect to the first surface. 16. The solar cell according to claim 15, wherein the mask material is arranged so as to be discharged obliquely from above and the inkjet head for the dopant liquid is arranged vertically below the substrate. Manufacturing equipment. 17. A means for adjusting the position and angle of the substrate is further provided on the upstream side of an inkjet head means for applying the mask material with respect to the moving direction of the substrate. 17. The solar cell manufacturing apparatus according to any one of 10 to 16. 18. A means for measuring the shape of the substrate is provided on the upstream side of an inkjet head means for applying the mask material with respect to the moving direction of the substrate, and information from the means for measuring the shape of the substrate is provided. 17. The apparatus for manufacturing a solar cell according to claim 10, wherein the operation of the nozzle of the inkjet head means is controlled based on the above.