JP2013225583A - Method of manufacturing solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery in which a formation region for a rear surface electrode is expanded for excellent light-electron conversion efficiency while preventing characteristic deterioration caused by protrusion of a rear surface electrode from a rear surface.SOLUTION: A step for forming a rear surface side electrode which is electrically connected to the other surface side of a first conductive type semiconductor substrate which contains, on one surface side, a second conductive type impurity diffusion layer, on the other surface side of the semiconductor substrate, includes a step for forming a recessed part that extends in the direction along extension direction of an outer peripheral part, in an outer edge region near the outer peripheral part of the other surface side of the semiconductor substrate, a step for applying an electrode material paste to a place inner than the recessed part on the other surface side of the semiconductor substrate, a step in which the electrode material paste applied on the other surface side of the semiconductor substrate is expanded to its periphery and the electrode material paste is dammed with the recessed part so that an application area of the electrode material paste is expanded to a range of the recessed part and the inside of it, and a step for baking the electrode material paste.

Description

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

  In a conventional solar cell, an n-type impurity diffusion layer is formed on the entire light-receiving surface of a polycrystalline silicon or single-crystal silicon p-type silicon substrate, and minute unevenness is provided on the surface on the light-receiving surface side. An antireflection film is formed on the minute irregularities, and a surface electrode is provided in a comb shape thereon. Further, on the back side of the p-type silicon substrate, electrodes are provided on the entire back side.

  Such a conventional solar cell is manufactured as follows. For example, using a wet etching process using a mixed solution of an alkali solution and alcohol, a mixed acid solution of hydrofluoric acid and nitric acid, or a dry etching process such as a reactive ion etching (RIE) method, a p-type single layer is used. Micro unevenness is formed on the surface of a crystalline silicon substrate (hereinafter referred to as a substrate). The fine irregularities on the surface are formed in order to suppress light reflection from the outside, confine the light in the substrate, and increase the light-electron conversion efficiency for converting the light into electricity.

Next, an n-type impurity diffusion layer is formed on the surface layer of the substrate by a vapor phase diffusion method in phosphorus oxychloride (POCl ₃ ) gas. After the oxide film formed on the surface of the substrate is removed by immersion in hydrogen fluoride, silicon nitride as an antireflection film is formed on the surface on the light receiving surface side of the substrate by a plasma CVD (chemical vapor deposition) method. Next, a surface electrode is formed on the surface of the substrate on the light-receiving surface side, which is patterned into a comb shape by a printing method using a silver paste. On the back surface side of the substrate, an aluminum electrode is formed on almost the entire back surface using an aluminum paste, and a silver electrode is formed on a part of the substrate as an external extraction electrode by a printing method. And after drying an electrode paste at the temperature of 200 degreeC, an electrode paste is baked at the temperature of 700 to 800 degreeC, and a solar cell element is completed.

  As described above, generally, the aluminum electrode on the back surface is formed by printing an aluminum paste containing aluminum on the back surface of the substrate by a printing method using a printing apparatus (see, for example, Patent Document 1). Moreover, although the aluminum electrode on the back surface is printed on almost the entire back surface of the substrate, the photo-electron conversion efficiency can be improved by extending the printing area to the outer peripheral portion (end portion) of the back surface of the substrate. .

JP-A-6-209115

  However, according to the above-described conventional technique, in forming the aluminum electrode on the back surface, the aluminum paste is applied to an area smaller than the outer shape of the back surface of the substrate. That is, in the formation of the aluminum electrode on the back surface, the aluminum paste does not protrude from the back surface of the substrate, considering the substrate dimensional accuracy, alignment accuracy, print mask elongation, etc. ) Was printed as the outermost position at a position 1 mm or more away from the inside.

  When the aluminum paste wraps around and adheres to the side surface (edge) of the substrate or the light-receiving surface of the substrate due to misalignment during printing, the aluminum paste fires through the diffusion layer on the light-receiving surface of the substrate. In some cases, the aluminum electrode on the back surface and the diffusion layer on the light receiving surface side are short-circuited to deteriorate the photo-electron conversion efficiency. That is, in the printing area of the aluminum paste, if the design tolerance is not provided about 1 mm to 2 mm from the outer peripheral portion (end) of the substrate, the printed aluminum electrode is photoelectrically converted when it protrudes from the back surface of the substrate. In some cases, the efficiency deteriorated. For this reason, it has been difficult to improve the photoelectric conversion efficiency by expanding the printing area of the aluminum electrode on the back surface.

  The present invention has been made in view of the above, and expands the formation region of the back electrode while preventing characteristic deterioration due to protrusion of the back electrode from the back surface, and is excellent in photoelectric conversion efficiency. It aims at obtaining the manufacturing method of the solar cell which can manufacture.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell according to the present invention comprises diffusing a second conductivity type impurity element on one surface side of a first conductivity type semiconductor substrate, and thereby said semiconductor substrate. A first step of forming an impurity diffusion layer on one surface side, a second step of forming a light receiving surface side electrode electrically connected to the impurity diffusion layer on one surface side of the semiconductor substrate, and the other surface of the semiconductor substrate A third step of forming, on the other side of the semiconductor substrate, a back-side electrode that is electrically connected to the side, wherein the third step is performed in an outer edge region near the outer peripheral portion on the other side of the semiconductor substrate. Forming a recess extending in a direction along the extending direction of the outer peripheral portion, applying an electrode material paste inside the recess on the other surface side of the semiconductor substrate, and the other surface of the semiconductor substrate Around the electrode material paste applied to the side And the step of damaging the electrode material paste by the recesses to expand the application area of the electrode material paste to the recesses and the range inside the recesses, and the step of firing the electrode material paste. .

  According to the present invention, there is an effect that a solar cell excellent in photo-electron conversion efficiency can be obtained by expanding the formation region of the back electrode while preventing characteristic deterioration due to protrusion of the back electrode from the back surface.

1-1 is principal part sectional drawing which shows schematic structure of the photovoltaic cell produced by the manufacturing method of the solar cell concerning Embodiment 1 of this invention. 1-2 is a top view of a solar battery cell when the solar battery cell manufactured by the method for manufacturing a solar battery according to the first embodiment of the present invention is viewed from the light-receiving surface side. 1-3 is a bottom view of the solar battery when the solar battery cell produced by the method for manufacturing a solar battery according to Embodiment 1 of the present invention is viewed from the side opposite to the light receiving surface (back surface side). FIGS. 2-1 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-2 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-3 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-4 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 2-5 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 2-6 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 2-7 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. 2-8 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIG. 3 is a flowchart for explaining an example of the manufacturing process of the solar battery cell according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing a first modification of the shape of the recess. FIG. 5 is a cross-sectional view showing a second modification of the shape of the recess. FIG. 6A is a cross-sectional view illustrating a second modification of the shape of the recess. FIG. 6B is a bottom view of the third modification of the shape of the recess.

  Embodiments of a method for manufacturing a solar cell according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings. Further, even a plan view may be hatched to make the drawing easy to see.

Embodiment 1 FIG.
1-1 is principal part sectional drawing which shows schematic structure of the photovoltaic cell 1 produced by the manufacturing method of the solar cell concerning Embodiment 1 of this invention. FIG. 1-2 is a top view of the solar battery cell 1 as viewed from the light-receiving surface side of the solar battery cell 1 manufactured by the method for manufacturing the solar battery according to the first embodiment of the present invention. 1-3 is a bottom view of the solar battery cell 1 when the solar battery cell 1 manufactured by the method for manufacturing a solar battery according to the first embodiment of the present invention is viewed from the side opposite to the light receiving surface (back surface side). . FIG. 1-1 is a cross-sectional view of an essential part taken along line AA in FIGS. 1-2 and 1-3.

  In the solar cell 1 according to the present embodiment, the second conductivity type n-type impurity diffusion layer 3 is formed by phosphorous diffusion on the light-receiving surface side of the p-type polycrystalline silicon substrate which is the first conductivity type semiconductor substrate 2. Is formed with a thickness of about 0.2 μm, and a semiconductor substrate 11 having a pn junction is formed. An antireflection film 4 made of a silicon nitride film (SiN film) is formed on the n-type impurity diffusion layer 3. The first conductivity type semiconductor substrate 2 is not limited to a p-type polycrystalline silicon substrate, but may be a p-type single crystal silicon substrate, an n-type polycrystalline silicon substrate, or an n-type single crystal silicon substrate. It may be used.

In addition, on the surface of the semiconductor substrate 11 (n-type impurity diffusion layer 3) on the light receiving surface side, minute unevenness 2a is formed as a texture structure with a depth of about 10 μm in order to improve the light utilization rate. The minute unevenness 2a has a structure that increases the area for absorbing light from the outside on the light receiving surface, suppresses the reflectance on the light receiving surface, and confines light. The antireflection film 4 is made of an insulating film such as a silicon nitride film (SiN film), a silicon oxide film (SiO ₂ film), or a titanium oxide film (TiO ₂ film).

  Further, a plurality of long and narrow surface silver grid electrodes 5 are provided side by side on the light receiving surface side of the semiconductor substrate 11, and a thick surface silver bus electrode 6 electrically connected to the surface silver grid electrode 5 is connected to the surface silver grid electrode 5. They are provided so as to be substantially orthogonal to each other, and are electrically connected to the n-type impurity diffusion layer 3 at the bottom portions. The front silver grid electrode 5 and the front silver bus electrode 6 are made of a silver material. The front silver grid electrode 5 and the front silver bus electrode 6 are formed so as to be surrounded by the antireflection film 4.

  The front silver grid electrodes 5 are arranged substantially in parallel with a predetermined width and interval, and collect electricity generated inside the semiconductor substrate 11. Further, the front silver bus electrode 6 has a predetermined width larger than that of the front silver grid electrode 5 and is arranged, for example, two to three per solar cell, and collects electricity collected by the front silver grid electrode 5. Take it out. The front silver grid electrode 5 and the front silver bus electrode 6 constitute a light receiving surface side electrode 12 as a first electrode. Since the light receiving surface side electrode 12 blocks sunlight incident on the semiconductor substrate 11, it is desirable to reduce the area as much as possible from the viewpoint of improving the power generation efficiency.

  On the other hand, a back aluminum electrode 7 made of an aluminum material is provided on the entire back surface (surface opposite to the light receiving surface) of the semiconductor substrate 11 and extends in substantially the same direction as the front silver bus electrode 6. A back silver electrode 8 made of is provided as an extraction electrode. The back aluminum electrode 7 and the back silver electrode 8 constitute a back electrode 13 as a second electrode.

  A recess 2b is formed in an outer edge region within a certain distance from the outer peripheral portion of the substrate on the back surface of the semiconductor substrate 11, that is, in the vicinity of the outer edge portion. For example, when the outer shape of the semiconductor substrate 11 is a substantially square shape, four recesses 2b are formed along the four sides of the outer shape of the semiconductor substrate 11, and each recess 2b is formed between the adjacent recess 2b and the back surface of the semiconductor substrate 11. They are connected in the vicinity of the four corners and surround the inner side of the back surface of the semiconductor substrate 11. The back aluminum electrode 7 is formed in the four recesses 2b and in the region surrounded by the four recesses 2b including the upper part. Accordingly, the back aluminum electrode 7 is formed without protruding from the back surface of the semiconductor substrate 11 to the side surface or the light receiving surface side. In addition, the recessed part 2b should just be formed in the shape along the external shape of the semiconductor substrate 11. FIG.

  Further, an alloy layer of aluminum (Al) and silicon (Si) is formed by firing on the surface layer part on the back surface (surface opposite to the light receiving surface) side of the semiconductor substrate 11 and below the back aluminum electrode 7. Underneath, a p + layer (BSF (Back Surface Field)) (not shown) containing high concentration impurities by aluminum diffusion is formed. The p + layer (BSF) is provided to obtain the BSF effect, and the electron concentration in the p-type layer (semiconductor substrate 2) is increased by an electric field having a band structure so that electrons in the p-type layer (semiconductor substrate 2) do not disappear. To.

  In the solar cell 1 configured as described above, sunlight is applied to the pn junction surface (the junction surface between the semiconductor substrate 2 and the n-type impurity diffusion layer 3) of the semiconductor substrate 11 from the light receiving surface side of the solar cell 1. Then, holes and electrons are generated. Due to the electric field at the pn junction, the generated electrons move toward the n-type impurity diffusion layer 3 and the holes move toward the p + layer. As a result, electrons are excessive in the n-type impurity diffusion layer 3 and holes are excessive in the p + layer, resulting in generation of photovoltaic power. This photovoltaic power is generated in the direction in which the pn junction is forward-biased, the light receiving surface side electrode 12 connected to the n-type impurity diffusion layer 3 becomes a negative pole, and the back aluminum electrode 7 connected to the p + layer becomes a positive pole. Thus, a current flows through an external circuit (not shown).

  Hereinafter, the manufacturing method of the photovoltaic cell 1 concerning this Embodiment comprised as mentioned above is demonstrated along drawing. FIGS. 2-1 to 2-8 are cross-sectional views for explaining an example of the manufacturing process of the solar battery cell 1 according to the first embodiment of the present invention. FIG. 3 is a flowchart for explaining an example of the manufacturing process of the solar battery cell 1 according to the first embodiment of the present invention.

  First, a p-type polycrystalline silicon substrate having a thickness of, for example, several hundred μm is prepared as the semiconductor substrate 2 and the substrate is cleaned. Since a p-type polycrystalline silicon substrate is manufactured by slicing an ingot formed by cooling and solidifying molten silicon with a wire saw, damage on the surface remains on the surface. Therefore, the p-type polycrystalline silicon substrate is generated when the silicon substrate is cut out by immersing the p-type polycrystalline silicon substrate in an acid such as hydrofluoric acid or a heated alkaline solution, for example, an aqueous sodium hydroxide solution and etching the surface. Remove damaged areas near the surface of the substrate. Then, it wash | cleans with a pure water (step S10, FIGS. 2-1). The external dimensions of the p-type polycrystalline silicon substrate are 156 mm square.

  Following the removal of the damage, for example, the p-type polycrystalline silicon substrate is immersed in a mixed solution of sodium hydroxide and isopropyl alcohol (IPA), and anisotropic etching is performed on the p-type polycrystalline silicon substrate. A textured structure is formed by forming minute irregularities 2a with a depth of about 10 μm on the light receiving surface side surface of the silicon substrate (step S20, FIG. 2-2). By providing such a texture structure on the light-receiving surface side of the p-type polycrystalline silicon substrate, multiple reflection of light is generated on the surface side of the solar battery cell 1, and the light incident on the solar battery cell 1 is efficiently semiconductorized. The light can be absorbed in the substrate 11, and the conversion efficiency can be improved by effectively reducing the reflectance. When the damaged layer is removed and the texture structure is formed with an alkaline solution, the concentration of the alkaline solution may be adjusted to a concentration according to each purpose, and continuous treatment may be performed. Further, the fine unevenness 2a having a depth of about 1 μm to 3 μm may be formed on the surface of the p-type polycrystalline silicon substrate by a dry etching process such as reactive ion etching (RIE).

Next, a diffusion process is performed to form a pn junction in the semiconductor substrate 2 (step S30, FIG. 2-3). That is, a group V element such as phosphorus (P) is diffused into the semiconductor substrate 2 to form the n-type impurity diffusion layer 3 having a thickness of several hundred nm. Here, a pn junction is formed by diffusing phosphorus by thermal diffusion at a high temperature in a phosphorus oxychloride (POCl ₃ ) gas at a high temperature by a vapor phase diffusion method on a p-type polycrystalline silicon substrate having a textured structure formed on the surface. . Thus, the semiconductor substrate 2 made of p-type polycrystalline silicon which is the first conductivity type layer, and the n-type impurity diffusion layer 3 which is the second conductivity type layer formed on the light receiving surface side of the semiconductor substrate 2. A semiconductor substrate 11 having a pn junction is obtained.

The concentration of phosphorus diffused at this time can be controlled by the concentration of phosphorus oxychloride (POCl ₃ ) gas, the temperature atmosphere, and the heating time. The sheet resistance of the n-type impurity diffusion layer 3 formed on the surface of the semiconductor substrate 2 is, for example, 40Ω / □ to 60Ω / □.

  Here, a glassy (phosphosilicate glass, PSG: Phospho-Silicate Glass) layer deposited on the surface during the diffusion treatment is formed on the surface immediately after the formation of the n-type impurity diffusion layer 3. Is removed using a hydrofluoric acid solution or the like.

  Although not shown in the figure, the n-type impurity diffusion layer 3 is formed on the entire surface of the semiconductor substrate 2. Therefore, in order to remove the influence of the n-type impurity diffusion layer 3 formed on the back surface or the like of the semiconductor substrate 2, the n-type impurity diffusion layer 3 is left only on the light-receiving surface side of the semiconductor substrate 2, and n in other regions is left. The type impurity diffusion layer 3 is removed.

Next, in order to improve photoelectric conversion efficiency, the antireflection film 4 is formed with a uniform thickness on one surface of the light receiving surface of the semiconductor substrate 11, that is, on the n-type impurity diffusion layer 3 (step S40, FIG. 2-3). ). The film thickness and refractive index of the antireflection film 4 are set to values that most suppress light reflection. The antireflection film 4 is formed by using, for example, a plasma CVD method, using a mixed gas of silane (SiH ₄ ) gas and ammonia (NH ₃ ) gas as a raw material, for example, at 300 ° C. or higher and under reduced pressure. A silicon nitride film is formed as the film 4. The refractive index is, for example, about 2.0 to 2.2, and the film thickness is, for example, about 60 nm to 80 nm. Note that two or more films having different refractive indexes may be laminated as the antireflection film 4. In addition to the plasma CVD method, the antireflection film 4 may be formed by vapor deposition, thermal CVD, or the like. It should be noted that the antireflection film 4 formed in this way is an insulator, and simply forming the light receiving surface side electrode 12 thereon does not act as a solar cell.

  Next, on one surface of the semiconductor substrate 11 opposite to the light-receiving surface side, that is, on the back surface opposite to the side where the n-type impurity diffusion layer 3 is formed, the outer edge is within a certain distance from the outer periphery of the substrate to the inside. The recess 2b is formed in the region, that is, the region near the outer edge (step S50, FIG. 2-4). Examples of the processing method for forming the recess 2b include an etching method, a laser processing method, a blast method, a dicing method, and the like. Here, the formation method of the recessed part 2b by the laser processing method is demonstrated.

  The semiconductor substrate 11 is placed on an XY stage of a laser processing apparatus, and the semiconductor substrate 11 is positioned with respect to the XY stage by using, for example, image processing with the center of the semiconductor substrate 11 as a reference position. Next, a laser is processed in a direction parallel to the outer side of the semiconductor substrate 11 by, for example, a YAG laser so that the processing end by the laser is positioned 50 μm (0.05 mm) inside from the outer periphery of the semiconductor substrate 11 whose image has been recognized. The silicon is blown off to form four line-shaped recesses 2b having a width of 200 μm and a depth of 50 μm along the four sides of the semiconductor substrate 11. That is, the recess 2 b extends in a direction along the extending direction of the outer peripheral portion of the back surface of the semiconductor substrate 11. The four recesses 2b are connected in the vicinity of the four corners on the back surface of the semiconductor substrate 11 and the adjacent recesses 2b. The position on the outer peripheral side of the semiconductor substrate 11 in each recess 2b is 50 μm (0.05 mm) from the outer peripheral side of the semiconductor substrate 11.

  The recess 2b is preferably formed with a width of 100 μm to 500 μm and a depth of 50 μm to 100 μm, for example. Here, regarding the shape of the recess 2b, on the back surface of the semiconductor substrate 11, the direction parallel to the outer side of the semiconductor substrate 11 is defined as the longitudinal direction of the recess 2b, and the direction perpendicular to the longitudinal direction of the recess 2b is defined as the width direction. .

  The wider the recess 2b, the more effective it is to suppress and prevent the aluminum paste from spreading to the outer peripheral side when the aluminum paste is expanded and the coating area of the aluminum paste is expanded during the formation of the back side electrode 13 described later. However, if the width of the concave portion 2b is too wide, the strength of the substrate is lowered, and a problem that it is easy to break occurs. Therefore, the width of the recess 2b is preferably 100 μm or more so that the aluminum paste does not spread to the end of the back surface of the semiconductor substrate 11, and is preferably 500 μm or less so that the semiconductor substrate 11 is not damaged.

  Further, when the depth of the recess 2b is deeper than 100 μm with respect to the thickness 180 to 230 μm of the semiconductor substrate 11 to be used, the mechanical strength in the vicinity of the recess 2b in the semiconductor substrate 11 is lowered, and the semiconductor substrate 11 is easily cracked by carrying the device. . Further, when the depth of the recess 2b is less than 50 μm, when the back surface side electrode 13 to be described later is formed, the aluminum paste is expanded to expand the coating area of the aluminum paste, thereby suppressing the aluminum paste from spreading to the outer peripheral side. The effect to prevent becomes small.

  Next, front and back electrodes are formed. The electrode is formed by printing an electrode paste on the electrode pattern by screen printing, drying and baking. In screen printing, an electrode paste containing silver particles or aluminum particles is pressed with a squeegee into a printing mask in which a resin film having an opening corresponding to the electrode pattern is formed on a metal mesh, and the electrode paste is transmitted through the opening of the mask. To do.

  First, the back side electrode 13 (before firing) is formed by screen printing. That is, the silver paste 8a, which is an electrode material paste containing silver particles, is printed on the back surface of the semiconductor substrate 11 in a pattern of the back silver electrode 8 that is an external extraction electrode that is electrically connected to the outside, and dried (step S60, FIG. 2). -5). Here, the silver paste 8a is printed in a line at predetermined intervals.

  Next, an aluminum paste 7a, which is an electrode material paste containing aluminum particles, is applied to the shape of the back aluminum electrode 7 by screen printing on the back surface of the semiconductor substrate 11 excluding the pattern portion of the back silver electrode 8 (step). S70, FIG. 2-5). Here, the aluminum paste 7a is printed in a pattern in which the outer position is 0.5 mm from the outer peripheral portion (substrate end portion) of the semiconductor substrate 11 in the width direction of the concave portion 2b. That is, the aluminum paste 7a is printed on the back surface side of the semiconductor substrate 11 inside the recess 2b.

  The aluminum paste 7a used at this time preferably has a lower viscosity or a lower thixotropy than a normally used paste so that the aluminum paste 7a can easily spread in the subsequent process. For example, while the back aluminum electrode 7 is usually formed using an aluminum paste having a viscosity of 35 Pa · s to 50 Pa · s, in the present embodiment, the viscosity of the aluminum paste 7a is set to 20 Pa · s to 40 Pa · s. By using s, the aluminum paste 7a can easily spread to the surroundings. If the viscosity of the aluminum paste 7a is less than 20 Pa · s, the viscosity is too low to make it difficult to control the spread of the aluminum paste 7a around. When the viscosity of the aluminum paste 7a is greater than 40 Pa · s, the aluminum paste 7a is difficult to spread to the surroundings.

  Next, after the application of the aluminum paste 7a, a coating area expansion process is performed in which the aluminum paste 7a is spread to the vicinity of the outer peripheral portion (substrate end) of the semiconductor substrate 11 to expand the coating area of the aluminum paste 7a (step). S80, FIG. 2-6). Examples of a method of spreading the aluminum paste 7a to the vicinity of the outer peripheral portion (edge) include performing spin coating, substrate swinging, air blowing, ultrasonic vibration, etc. on the semiconductor substrate 11 after the application of the aluminum paste 7a. Here, a method using ultrasonic vibration will be described as a method for easily controlling the spread of the aluminum paste 7a.

  First, the ultrasonic oscillator 21 is disposed on a table on which the semiconductor substrate 11 coated with the aluminum paste 7a is placed on the back surface of the semiconductor substrate 11 from the outer peripheral portion (substrate end portion) to a position 0.5 mm inside. Move to another position. Then, a table on which the semiconductor substrate 11 is placed is arranged at a position where the ultrasonic wave generated by the ultrasonic oscillator 21 hits the outer peripheral edge of the application part of the aluminum paste 7a.

  Next, ultrasonic waves are oscillated in the ultrasonic oscillator 21. Thereby, an ultrasonic wave hits the outer peripheral edge part of the application part of the aluminum paste 7a, and the aluminum paste 7a spreads to the periphery by the vibration. The aluminum paste 7a spreads around the periphery due to the vibration of the ultrasonic waves, but when the aluminum paste 7a spread outside (substrate end side) enters the recess 2b formed in the outer edge region of the back surface of the semiconductor substrate 11, the aluminum paste 7a is more than that. It does not spread outside (board end side). That is, the aluminum paste 7a spreads around by the vibration of the ultrasonic wave, but is dammed by the recess 2b and surrounded by the four recesses 2b including the inside of the four recesses 2b and the upper part thereof on the back surface of the semiconductor substrate 11. The application area is expanded only in the inner region. This suppresses or prevents the back aluminum electrode 7 from protruding from the back surface of the semiconductor substrate 11 to the side surface or the light receiving surface side without the aluminum paste 7a protruding from the back surface of the semiconductor substrate 11 to the side surface or the light receiving surface side. Is done. As a result, the aluminum paste 7 a is applied in a substantially square region having an outer shape at a position of 50 μm (0.05 mm) from the outer peripheral side of the semiconductor substrate 11.

  Therefore, the aluminum paste 7a spreads to the peripheral portion due to the vibration of the ultrasonic waves and oscillates ultrasonic waves for a predetermined time to enter the recess 2b, and at that time, the ultrasonic oscillation in the ultrasonic oscillator 21 is stopped. Set the timer. Thereby, the aluminum paste 7a can be reliably spread in the minimum necessary processing time. Thereafter, the aluminum paste 7a is dried.

  Next, the light receiving surface side electrode 12 composed of a plurality of front silver grid electrodes 5 and several front silver bus electrodes 6 is formed by screen printing using an electrode material paste (silver paste) 6a containing silver ( Before firing (step S90, FIG. 2-7)). The light-receiving surface side electrode 12 has a function of collecting electrons generated on the surface of the solar battery cell 1, but is a part that blocks sunlight and does not contribute to power generation. For this reason, it is desirable to reduce the area by reducing the width of the light receiving surface side electrode 12 as much as possible. Next, the silver paste 6a is dried.

  Next, the printed and dried electrode material paste is fired (step S100, FIG. 2-8). The baking treatment is performed at a temperature of 750 ° C. to 800 ° C. or more using, for example, an infrared heating furnace. Thereby, on the light receiving surface side of the semiconductor substrate 11, the light receiving surface side electrode 12 is formed on the n-type impurity diffusion layer 3 on the light receiving surface of the semiconductor substrate 11. In this baking process, the glass contained in the silver paste 6 a is melted, erodes the insulating film that is the antireflection film 4 formed on the light receiving surface, and reaches the semiconductor substrate 11. That is, in the portion where the antireflection film 4 is formed on the n-type impurity diffusion layer 3, the light-receiving surface side electrode 12 is connected to the n-type impurity diffusion layer 3 by a so-called fire-through and is made conductive.

  On the other hand, on the back surface (surface opposite to the light receiving surface) of the semiconductor substrate 11, the silver paste 8 a becomes the back silver electrode 8 by baking, and the aluminum paste 7 a becomes the back aluminum electrode 7. Further, the aluminum (Al) of the back aluminum electrode 7 and the silicon (Si) of the semiconductor substrate 11 react with each other by firing to form an aluminum alloy layer below the back aluminum electrode 7, and an aluminum diffusion layer is formed below the aluminum alloy layer. A p + layer (BSF) (not shown) is formed.

  By performing the steps as described above, the solar battery cell 1 according to the present embodiment shown in FIGS. 1-1 to 1-3 is completed.

  The solar battery cell 1 of an Example was produced with the manufacturing method of the above solar cells. Further, according to a conventional method, an opening of 1.5 mm from the outer peripheral portion (substrate end portion) of the semiconductor substrate on each side of the back surface of the semiconductor substrate is opened to a position inside the semiconductor substrate having the same outer dimension of 156 mm square as in the embodiment. The back side electrode 13 was formed by screen printing using a printing mask plate having a printed pattern (153 mm square), and a solar cell of a comparative example was produced. The manufacturing process of the solar cell of the comparative example is the same as that of the example except for the formation method of the back surface side electrode 13 and the area of the back aluminum electrode 7.

  When the characteristics of the solar battery cells of the example and the comparative example were examined, it was confirmed that the fill factor (FF) was improved by 0.005 and the photoelectric conversion efficiency was improved. In the solar cell 1 of the example, the printing area of the aluminum paste 7a is increased by printing the aluminum paste 7a from the outer periphery (substrate end) to a position 0.5 mm inside on the back surface of the semiconductor substrate 11. This is because 2.3% larger than the solar cell of the comparative example.

  In the first embodiment as described above, the recess 2b is formed in the outer edge region within a certain distance from the outer periphery of the back surface of the semiconductor substrate 11 toward the inside, and the aluminum paste 7a is printed inside the recess 2b. To do. Thereafter, the aluminum paste 7a is spread to the vicinity of the outer peripheral portion (substrate end) of the semiconductor substrate 11 to perform a coating area expansion process for expanding the coating area of the aluminum paste 7a. For this reason, the aluminum paste 7a does not protrude from the back surface of the semiconductor substrate 11 to the side surface or the light receiving surface side, and the back aluminum electrode 7 is suppressed or prevented from protruding from the back surface of the semiconductor substrate 11 to the side surface or the light receiving surface side. Is done. Thereby, the formation area of the back aluminum electrode 7 can be expanded and the photo-electron conversion efficiency can be improved while preventing deterioration of characteristics due to the back aluminum electrode 7 protruding from the back surface of the semiconductor substrate 11.

  In addition, it is possible to reduce the rate of occurrence of defects due to the back aluminum electrode 7 protruding from the back surface of the semiconductor substrate 11 and to prevent a decrease in manufacturing yield.

  Therefore, according to the first embodiment, a solar cell excellent in manufacturing yield and photoelectric conversion efficiency can be obtained by expanding the formation region of the back electrode while preventing characteristic deterioration due to the protrusion of the back electrode from the back surface. The effect is obtained.

Embodiment 2. FIG.
In the second embodiment, a modified example of the shape of the recess 2b described above will be described. FIG. 4 is a cross-sectional view showing a first modification of the shape of the recess 2b, and corresponds to FIG. 2-4. As for the concave portion 2b, as a first modified example of an effective shape for preventing the aluminum paste 7a from protruding from the back surface and spreading to the periphery, as shown in FIG. A shape in which the opening in the depth direction) is widened. By setting the shape of the recess 2b to such a shape, it is possible to suppress and prevent the aluminum paste 7a that has spread to the recess 2b from spreading outside the recess 2b.

  As a method for forming such a recess 2b, an acid-resistant masking agent is applied to the outer edge region of the semiconductor substrate 11 in addition to the region where the recess 2b is to be formed, and then the back surface of the semiconductor substrate 11 isotropic with a hydrofluoric acid solution or the like. Etching is performed. Thereby, the recessed part 2b by which the opening inside the hole was made wider than the surface vicinity of the back surface of the semiconductor substrate 11, and the cross-sectional shape along the width direction was made into the semicircle can be formed.

  FIG. 5 is a cross-sectional view showing a second modification of the shape of the recess 2b and corresponds to FIG. 2-4. As for the concave portion 2b, as a second modification example of an effective shape for preventing the aluminum paste 7a from protruding from the back surface and spreading to the periphery, as shown in FIG. The shape opened in the diagonal direction is mentioned. That is, the shape opened in the diagonal direction which inclines outside as it goes to the bottom part of a recessed part from the back surface of the semiconductor substrate 11 is mentioned. By setting the shape of the recess 2b to such a shape, it is possible to suppress and prevent the aluminum paste 7a that has spread to the recess 2b from spreading outside the recess 2b.

  As a method of forming such a recess 2b, as in the case of the first modification, an acid-resistant masking agent is applied to the outer edge region of the semiconductor substrate 11 other than the region where the recess 2b is formed, and then the semiconductor substrate The semiconductor substrate 11 is formed so as to be inclined obliquely, and the back surface of the semiconductor substrate 11 is etched obliquely outward with respect to the thickness direction of the semiconductor substrate 11 by dry etching such as reactive ion etching. Thereby, the recessed part 2b opened in the diagonal direction toward the outer side with respect to the thickness direction of the semiconductor substrate 11 can be formed.

  FIG. 6A is a cross-sectional view illustrating a third modification of the shape of the recess 2b, and corresponds to FIG. FIG. 6B is a bottom view of the third modification of the shape of the recess 2b. As a third modification example of the effective shape for preventing the aluminum paste 7a from protruding from the back surface and spreading to the periphery of the recess 2b, as shown in FIGS. 6A and 6B, the outer edge region of the semiconductor substrate 11 In FIG. 3, a shape in which three substantially parallel recesses 2 b-1, recesses 2 b-2, and recesses 2 b-3 are formed surrounding the inner region of the semiconductor substrate 11 is mentioned. By setting the shape of the recess 2b to such a shape, it is possible to suppress and prevent the aluminum paste 7a that has spread to the recess 2b from spreading outside the recess 2b.

  For example, by forming three recesses 2b having a width of 100 μm substantially in parallel at a predetermined interval, the spread of the aluminum paste 7a to the outside is more effectively suppressed than when one recess 2b having a width of 300 μm is formed. Can be prevented. Such a recess 2b can be formed by the method shown in the first embodiment. In addition, the number of the recessed parts 2b is not limited to three, What is necessary is just two or more.

  In addition, the above-described modifications can be used in combination with each other as far as possible.

  Moreover, the solar cell module excellent in photo-electron conversion efficiency is realizable by forming several photovoltaic cells which have the structure demonstrated in said embodiment, and electrically connecting adjacent photovoltaic cells. . In this case, what is necessary is just to electrically connect one light-receiving surface side electrode 12 and the other back surface side electrode 13 of an adjacent photovoltaic cell.

  As described above, the method for manufacturing a solar cell according to the present invention is useful for realizing a solar cell excellent in photo-electron conversion efficiency in which deterioration of characteristics due to protrusion of the back electrode from the back surface is prevented.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Semiconductor substrate 2a Minute unevenness 2b Recessed part 3 N-type impurity diffusion layer 4 Antireflection film 5 Front silver grid electrode 6 Front silver bus electrode 6a Silver paste 7 Back aluminum electrode 7a Aluminum paste 8 Back silver electrode 8a Silver paste 11 Semiconductor substrate 12 Light receiving surface side electrode 13 Back surface side electrode 21 Ultrasonic oscillator

Claims (8)

A first step of diffusing a second conductivity type impurity element on one surface side of the first conductivity type semiconductor substrate to form an impurity diffusion layer on the one surface side of the semiconductor substrate;
A second step of forming a light receiving surface side electrode electrically connected to the impurity diffusion layer on one surface side of the semiconductor substrate;
A third step of forming, on the other surface side of the semiconductor substrate, a back surface side electrode electrically connected to the other surface side of the semiconductor substrate;
Including
The third step includes
Forming a recess extending in a direction along the extending direction of the outer peripheral portion in an outer edge region in the vicinity of the outer peripheral portion on the other surface side of the semiconductor substrate;
Applying an electrode material paste on the inner side of the recess on the other side of the semiconductor substrate;
Spreading the electrode material paste applied to the other surface side of the semiconductor substrate around and expanding the application area of the electrode material paste to the recess and the area inside the recess by blocking the electrode material paste by the recess; and
Firing the electrode material paste;
The manufacturing method of the solar cell characterized by including. By applying ultrasonic waves to the electrode material paste applied to the other surface side of the semiconductor substrate, to vibrate the electrode material paste and to spread the electrode material paste around,
The manufacturing method of the solar cell of Claim 1 characterized by these. The viscosity of the electrode material paste is in the range of 20 Pa · s to 40 Pa · s,
The method for producing a solar cell according to claim 1 or 2. The concave portion has an opening size inside the concave portion larger than an opening size on a surface of the other surface of the semiconductor substrate;
The manufacturing method of the solar cell as described in any one of Claims 1-3 characterized by these. The recess is formed to be inclined toward the outer peripheral side of the semiconductor substrate from the surface of the other surface of the semiconductor substrate toward the bottom of the recess;
The manufacturing method of the solar cell as described in any one of Claims 1-4 characterized by these. A plurality of the recesses are formed in parallel;
The manufacturing method of the solar cell as described in any one of Claims 1-5 characterized by these. The recess is formed so as to surround an inner side of the other surface of the semiconductor substrate;
The method for manufacturing a solar cell according to claim 1, wherein: The electrode material paste is an aluminum paste containing aluminum particles;
The manufacturing method of the solar cell as described in any one of Claims 1-7 characterized by these.

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