JP2013183004A - Method for manufacturing solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solar cell, capable of manufacturing a rear-surface junction solar cell having excellent photoelectric conversion efficiency.SOLUTION: A method for manufacturing a solar cell includes the steps of; forming an impurity diffusion layer of a second conductivity type on the entire rear surface of a semiconductor substrate; forming an insulating layer on the impurity diffusion layer of the second conductivity type; forming a plurality of first island-shaped recesses reaching the semiconductor substrate from a surface of the insulating layer on the insulating layer in a dispersed manner in a surface direction of the semiconductor substrate; forming an impurity diffusion layer of a first conductivity type on a surface layer of the semiconductor substrate on a bottom surface of the first recess and on a surface layer of the impurity diffusion layer of the second conductivity type on a side surface of the first recess by diffusing an impurity of the first conductivity type on a rear surface of the semiconductor substrate via the first recess using the insulating layer as a mask; forming a first electrode electrically connected to the impurity diffusion layer of the first conductivity type through the insulating layer on one surface side of the semiconductor substrate; and forming a second electrode electrically connected to the impurity diffusion layer of the second conductivity type through the insulating layer on the one surface side of the semiconductor substrate.

Description

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

  In a general crystalline silicon solar cell, an electrode is connected to a diffusion layer (emitter) on the light receiving surface side. For this reason, the sunlight irradiated to the electrode is reflected by the electrode, becomes a loss (reflection loss) without being used for photoelectric conversion, and power generation efficiency is limited. On the other hand, the photoelectric conversion efficiency of the crystalline silicon solar cell can be improved by forming the electrode on the light receiving surface side to be thin and high. However, there is a limit to thinning the electrodes.

  Therefore, while a pn junction is usually formed on the light receiving surface side, a pn junction is arranged in the surface direction of the substrate on the back surface of the crystalline silicon solar cell for the purpose of increasing the photoelectric conversion efficiency of the crystalline silicon solar cell. A structure (back junction solar cell) has been proposed. The diffusion length in the crystalline silicon solar cell is about several hundred μm. For this reason, in the case of a back junction solar cell, it is necessary to arrange a plurality of pn junctions in the surface direction of the substrate on the back surface of the solar cell, but since there is no electrode on the light receiving surface side, there is no ideal reflection loss described above. Various structures are being studied.

  Usually, as a pattern of the impurity diffusion layer on the back surface of the back junction solar cell, each of the n-type impurity diffusion layer and the p-type impurity diffusion layer is alternately arranged in a continuous line (for example, Non-Patent Document 1). reference). Here, for example, as shown in Non-Patent Document 1, it is known that when an n-type wafer is used as the substrate of the back junction solar cell, the quantum efficiency of the n-type impurity diffusion layer is lowered. For this reason, on the back surface of the n-type wafer, the width of the n-type impurity diffusion layer region needs to be narrower than the width of the p-type impurity diffusion layer region. This is considered to be one of the reasons that the n-type impurity diffusion layer region (nn +) has a lower barrier and has a larger influence of surface recombination than the p-type impurity diffusion layer region (np +). Therefore, in the back junction solar cell, high photoelectric conversion efficiency can be achieved by shortening the width of the n-type impurity diffusion layer region relative to the width of the p-type impurity diffusion layer region.

JP 2004-71828 A

F.Granek, et al, “HIGH-EFFICIENCY BACK-CONTACT BACK-JUNCTION SILICON SOLAR CELL” 23rd European Photovoltaic Solar Energy Conference, 1-5 September 2008, Valencia, Spain, pp.991-995

  However, if the width of the n-type impurity diffusion layer region is too narrow, there is a problem that it is difficult to align the n-type impurity diffusion layer region and the electrode when forming the electrode. In the mass production process of solar cells, high-precision alignment such as photolithography is difficult to apply due to problems of mass productivity and cost. For this reason, in electrode formation, it is necessary to align by a method using screen printing or the like, and there is a limit to the alignment accuracy between the n-type impurity diffusion layer region and the electrode. For this reason, in the line-shaped n-type impurity diffusion layer region pattern, the pattern of the n-type impurity diffusion layer region must be designed with a dimension limited to the alignment accuracy, and sufficient high photoelectric conversion efficiency cannot be achieved. .

  For example, Patent Document 1 discloses a back junction solar cell having a dot-shaped back surface impurity diffusion layer. According to such a back-junction solar cell, for example, when an n-type wafer is used as a semiconductor substrate, such a dot-shaped back-surface impurity diffusion layer is used, thereby reducing the quantum efficiency of the n-type impurity diffusion layer. Can be reduced, and high photoelectric conversion efficiency can be achieved.

  However, Patent Document 1 shows a dot-shaped backside impurity diffusion layer, but does not mention a method for forming the dot-shaped backside impurity diffusion layer.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the manufacturing method of the solar cell which can manufacture the back junction solar cell excellent in the photoelectric conversion efficiency.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell according to the present invention includes a first conductivity type impurity diffusion layer on a back surface opposite to a light receiving surface of a first conductivity type semiconductor substrate. A method of manufacturing a solar cell having a second conductivity type impurity diffusion layer formed thereon, the first step of forming the second conductivity type impurity diffusion layer on the entire back surface of the semiconductor substrate, and the second step. A second step of forming an insulating layer on the impurity diffusion layer of the conductive type, and a plurality of island-shaped first recesses reaching the semiconductor substrate from the surface of the insulating layer are dispersed in the insulating layer in the plane direction of the semiconductor substrate And forming the first conductivity type impurity concentration on the back surface of the semiconductor substrate by diffusing the first conductivity type impurity through the first recess using the insulating layer as a mask. Impurities of the first conductivity type higher than the substrate A fourth step of forming a diffusion layer on the surface layer of the semiconductor substrate on the bottom surface of the first recess and on the surface layer of the second conductivity type impurity diffusion layer on the side surface of the first recess; A fifth step of forming a first electrode electrically connected to the first conductivity type impurity diffusion layer on one surface side of the semiconductor substrate; and an electrical connection to the second conductivity type impurity diffusion layer through the insulating layer. And a sixth step of forming a second electrode to be connected on one side of the semiconductor substrate.

  According to the present invention, an impurity diffusion layer of the same first conductivity type as that of a semiconductor substrate can be formed in an island shape, so that the area of the impurity diffusion layer of the first conductivity type can be reduced and the photoelectric conversion efficiency of the solar cell can be increased. It is possible to produce a back junction solar cell excellent in photoelectric conversion efficiency.

1-1 is principal part sectional drawing which shows typically schematic structure of the solar cell produced by the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. 1-2 is principal part bottom view which shows typically schematic structure of the solar cell produced by the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. FIGS. 2-1 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. FIGS. 2-2 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. FIGS. 2-3 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. 2-4 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. 2-5 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. 2-6 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. 2-7 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. 2-8 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. 2-9 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. 2-10 is principal part sectional drawing which shows typically an example of the process sequence of the manufacturing method of the solar cell concerning embodiment of this invention. FIG. 3 is a diagram showing a formation pattern of the recesses on the back surface of the n-type silicon substrate. FIG. 4 is a diagram showing a formation pattern of the recesses on the back surface of the n-type silicon substrate.

  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 FIG. 1-1 is a main part sectional view schematically showing a schematic configuration of a solar cell manufactured by a method for manufacturing a solar cell according to an embodiment of the present invention. FIGS. 1-2 is principal part bottom view which shows typically schematic structure of the solar cell produced by the manufacturing method of the solar cell concerning embodiment of this invention. FIGS. FIG. 1-1 is a main part sectional view taken along line AA in FIG. In FIG. 1-1, attention is paid to the arrangement of the p-type impurity diffusion layer 102 and the back-side n-type impurity diffusion layer 106, and the description of other members is omitted.

  In this solar cell, an uneven texture structure 108 is formed on the light receiving surface side of an n-type silicon substrate 101 as a crystalline semiconductor substrate for the purpose of reducing light reflection on the surface. The n-type silicon substrate 101 is a crystalline silicon substrate that exhibits an n-type conductivity type by being doped with, for example, an n-type dopant (for example, P (phosphorus)). Crystalline silicon substrates include single crystal silicon substrates and polycrystalline silicon substrates. Note that although an n-type silicon substrate is used here, a p-type crystalline silicon substrate can also be used as the crystalline silicon substrate.

On the light receiving surface side of the n-type silicon substrate 101, a light-receiving surface side n-type impurity diffusion layer 109, which is a region having a higher n-type impurity concentration than the n-type silicon substrate 101, is formed, and minority carriers generated on the surface side ( In this case, a surface electric field layer called FSF (Front Surface Field) that directs holes) to the surface side is formed. Further, a silicon oxide (SiO ₂ ) film 110 is formed on the upper surface of the light-receiving surface side n-type impurity diffusion layer 109 for the purpose of preventing carrier recombination on the silicon surface on the light-receiving surface side, and this serves as a passivation film. It is functioning. On the silicon oxide film 110, an antireflection film 111 that prevents reflection of incident light to the light receiving surface of the n-type silicon substrate 101 is formed.

  On the other hand, the surface layer on the back surface of the n-type silicon substrate 101 is provided with a plurality of island-shaped recesses 105 arranged in a line extending in a predetermined direction in a dispersed manner. An n-type impurity diffusion layer 106 is formed. That is, the back surface side n-type impurity diffusion layers 106 are distributed and arranged in a line extending in a predetermined direction on the back surface of the n-type silicon substrate 101. The back-side n-type impurity diffusion layer 106 is a region having an n-type impurity concentration higher than that of the n-type silicon substrate 101, and recombination at the substrate interface of minority carriers (in this case, holes) flowing to the back side. It functions as a back surface field layer (BSF: Back Surface Field) for forming an electric field layer for preventing the above.

  A p-type impurity diffusion layer 102 is formed on the almost entire surface of the back surface of the n-type silicon substrate 101 except for the region of the back-side n-type impurity diffusion layer 106, and a pn junction is formed between the n-type silicon substrate 101 and the n-type silicon substrate 101. Form.

A silicon oxide (SiO ₂ ) film 103 and a silicon nitride (SiN) film 104 which are insulating layers are formed on the back-side n-type impurity diffusion layer 106 and the p-type impurity diffusion layer 102 on the back surface of the n-type silicon substrate 101. They are stacked in order. The back surface n-type impurity diffusion layer 106 has an n-layer extraction electrode 113 via an island-shaped recess 105 provided from the surface of the silicon nitride (SiN) film 104 to the back surface n-type impurity diffusion layer 106. Is connected. A p-layer extraction electrode 114 is connected to the p-type impurity diffusion layer 102 via an island-shaped recess 112 provided from the surface of the silicon nitride (SiN) film 104 to the p-type impurity diffusion layer 102. .

  That is, this solar cell is a back electrode type solar cell in which the n layer extraction electrode 113 and the p layer extraction electrode 114 are arranged only on the back surface side of the solar cell. Thereby, in this solar cell, the optical loss resulting from the reflection of the light by the electrode in the light-receiving surface side is prevented, and the photoelectric conversion efficiency is improved.

  In the solar cell thus configured, when sunlight L is irradiated from the light receiving surface side of the solar cell (the antireflection film 111 side of the n-type silicon substrate 101), holes and electrons are formed in the n-type silicon substrate 101. And generate. Electrons generated by light absorption move toward the back-side n-type impurity diffusion layer 106, and holes move toward the p-type impurity diffusion layer 102. As a result, electrons are excessive in the back side n-type impurity diffusion layer 106, holes are excessive in the p-type impurity diffusion layer 102, and photovoltaic power is generated. As a result, the n-layer extraction electrode 113 formed connected to the back surface side n-type impurity diffusion layer 106 becomes a negative pole, and the p layer formed connected to the p-type impurity diffusion layer 102 forming the pn junction on the back surface. The extraction electrode 114 becomes a positive electrode, and a current flows through an external circuit (not shown).

  Next, a method for manufacturing a solar cell having such a structure will be described with reference to FIGS. 2-1 to 2-10. FIGS. 2-1 to 2-10 are principal part cross-sectional views schematically showing an example of the processing procedure of the method for manufacturing the solar cell according to the present embodiment.

  First, an n-type silicon substrate 101 containing, for example, phosphorus (P) as an n-type impurity atom at a predetermined concentration is prepared as a semiconductor substrate (FIG. 2-1). Since the n-type silicon substrate 101 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, first, the n-type silicon substrate 101 is immersed in an acid or a heated alkaline solution, for example, an aqueous solution of sodium hydroxide and etched to etch the surface. Remove existing damage areas.

  Next, the n-type silicon substrate 101 is heated in an atmosphere containing an acceptor such as boron (B), for example, and boron (B) is diffused on the surface of the n-type silicon substrate 101 to serve as an emitter. 102 is formed on the entire surface of the n-type silicon substrate 101 (FIG. 2-2). When a p-type semiconductor substrate is used as the semiconductor substrate, a donor such as phosphorus (P) may be diffused on the surface of the semiconductor substrate.

  Next, for the purpose of preventing carrier recombination on the silicon surface on the back side of the substrate, a thermal oxidation process is performed on the n-type silicon substrate 101 to form a silicon oxide film 103 that is a thermal oxide film as a passivation film. (FIG. 2-2). The thermal oxidation method for the n-type silicon substrate 101 may be either wet oxidation or dry oxidation.

  Next, on the silicon oxide film 103 on the back surface side of the n-type silicon substrate 101, a silicon nitride film 104 that serves as a diffusion mask in a later step is formed by a plasma CVD (Chemical Vapor Deposition) method (FIG. 2-3). Here, the thickness of the silicon nitride film 104 only needs to be greater than or equal to a thickness that functions as a diffusion mask in a later process.

  Next, part of the silicon nitride film 104 and the silicon oxide film 103 is removed and patterned by laser irradiation, for example, to form a recess 105a that reaches the p-type impurity diffusion layer 102 from the surface of the silicon nitride film 104 (FIG. 2-). 4). Further, by performing wet etching using a solution such as alkali, the p-type impurity diffusion layer 102 below the recess 105a is removed, and the recess 105 reaching the n-type silicon substrate 101 from the surface of the silicon nitride film 104 is formed. (Fig. 2-5). The recess 105 becomes a diffusion window and an electrode contact hole for diffusing impurities in a later step.

  Here, the concave portions 105 are formed in an island shape, and are distributed and arranged at predetermined intervals in a line shape extending in a predetermined direction. FIG. 3 is a diagram showing a formation pattern of the recesses 105 on the back surface of the n-type silicon substrate 101. The shape of the recess 105 in the surface direction of the n-type silicon substrate 101 is, for example, a rectangular shape with dimensions of about 30 μm in the longitudinal direction and about 20 μm in the lateral direction. However, the shape of the recess 105 is not limited to this. The method for forming the recess 105a is not limited to laser irradiation, but by forming the recess 105a by laser irradiation, the recess 105a can be accurately formed at a desired position, and the recess 105 can be accurately formed at a desired position.

  Next, a donor such as phosphorus (P) is diffused into the bottom surface of the recess 105 and the side surface of the p-type impurity diffusion layer 102 through the recess 105. As a result, the back-side n-type impurity diffusion layer 106 is formed on the bottom surface of the recess 105 and the side surface of the p-type impurity diffusion layer 102, and the p-type impurity diffusion layer and the n-type impurity diffusion layer are formed on the back surface of the substrate ( Fig. 2-6). For example, phosphorus (P) is diffused by heating the n-type silicon substrate 101 in an atmosphere containing phosphorus (P), and using the silicon nitride (SiN) film 104 as a diffusion mask and the bottom surface of the recess 105 and the p This is performed by diffusing phosphorus (P) on the side surface of the type impurity diffusion layer 102. When a p-type semiconductor substrate is used as the semiconductor substrate, for example, an acceptor such as boron (B) is diffused.

Next, by thermally oxidizing the surface of the back surface side n-type impurity diffusion layer 106, a silicon oxide (SiO ₂ ) film 107, which is an oxide film, is formed on the surface of the back surface side n type impurity diffusion layer 106 at the bottom of the recess 105. Form. As a result, the bottom of the recess 105 is filled with the silicon oxide film 107, and the recess 105a reaching the p-type impurity diffusion layer 102 from the surface of the silicon nitride film 104 is formed again. By forming the silicon oxide film 107 on the surface of the back-side n-type impurity diffusion layer 106, phosphorus (P) in the back-side n-type impurity diffusion layer 106 diffuses into the silicon oxide film 107, and the back-side n-type The phosphorus (P) concentration in the impurity diffusion layer 106 is lowered. The silicon oxide film 107 is used as a mask when forming the light receiving surface side texture in the next process. In this case, in order to obtain a necessary thickness as a mask, the silicon oxide film 107 is preferably formed by wet oxidation.

  Here, as described above, the formation pattern of the island-shaped recesses 105 on the back surface of the n-type silicon substrate 101 is formed in a line shape that is dispersedly arranged at a predetermined interval and extends in a predetermined direction. Photoelectric conversion efficiency can be improved. As shown in Non-Patent Document 1, when an n-type wafer is used for the substrate of the back junction solar cell, the n-type impurity diffusion region has a lower quantum efficiency than the p-type impurity diffusion region. This is considered to be one of the reasons that the n-type impurity diffusion region (nn +) has a lower barrier than the p-type impurity diffusion region (np +) and has a large influence of surface recombination. For this reason, when an n-type wafer is used for the substrate of the back junction solar cell, it is possible to increase the photoelectric conversion efficiency of the solar cell by reducing the area occupied by the n-type impurity diffusion region on the back surface of the substrate. For the same reason, it is considered that the quantum efficiency of the p-type impurity diffusion layer 102 is lowered when a p-type semiconductor substrate is used as the semiconductor substrate.

  However, as shown in Non-Patent Document 1, when a general continuous line pattern is used for the pattern of the back surface n-type impurity diffusion layer, the positional accuracy of the back surface n-type impurity diffusion layer and the back surface during electrode formation Due to the problem of alignment accuracy between the n-type impurity diffusion layer and the electrode, there is a limit to narrowing the width of the back surface n-type impurity diffusion layer.

  Therefore, in the present embodiment, phosphorus (P) is diffused through the island-shaped recess 105 formed at a desired position with high accuracy as described above to form the back-side n-type impurity diffusion layer 106. . As a result, the back-side n-type impurity diffusion layer 106 can be accurately formed at a desired position, and the area of the back-side n-type impurity diffusion layer 106 can be accurately controlled by adjusting the phosphorus (P) diffusion conditions. Thus, the area occupied by the back surface side n-type impurity diffusion layer 106 on the back surface of the substrate can be reduced.

  Next, the texture structure 108 is formed on the light receiving surface side of the n-type silicon substrate 101 (FIGS. 2-7). First, only the light-receiving surface side of the n-type silicon substrate 101 is immersed in a hydrogen fluoride (HF) solution to remove the silicon oxide film 103 on the light-receiving surface side. Next, only the light-receiving surface side of the n-type silicon substrate 101 is etched using an alkaline solution such as a potassium hydroxide (KOH) solution or a sodium hydroxide (NaOH) solution, so that only the light-receiving surface side of the n-type silicon substrate 101 is etched. The texture structure 108 is formed. At this time, the p-type impurity diffusion layer 102 on the light receiving surface side is removed. Etching does not proceed on the back surface of the n-type silicon substrate 101 because the silicon nitride film 104, the silicon oxide film 103, and the silicon oxide film 107 serve as a mask. The flat back surface of the n-type silicon substrate 101 is important for reducing the surface area with a high recombination speed as much as possible.

  Next, a light-receiving surface side n-type impurity diffusion layer 109 functioning as an FSF is formed by diffusing a donor such as phosphorus (P) on the light-receiving surface side of the n-type silicon substrate 101 (FIG. 2-8). When a p-type semiconductor substrate is used as the semiconductor substrate, an acceptor such as boron (B) is diffused.

Next, for the purpose of surface passivation, a silicon oxide (SiO ₂ ) film 110 that is an oxide film is formed on the light-receiving surface side n-type impurity diffusion layer 109 as a passivation film by, for example, thermal oxidation treatment (FIG. 2-8). . When the silicon oxide film 110 used as the passivation film is thick, it hinders the reduction of the reflectance of the incident light. Therefore, it is necessary to balance the surface passivation effect and the reflectance of the incident light.

Next, a silicon nitride (SiN) film, a titanium oxide (TiO ₂ ) film, or the like is formed on the silicon oxide film 110 as the antireflection film 111 (FIG. 2-8). Examples of the method for forming the antireflection film 111 include a CVD method, a sputtering method, and a vapor deposition method.

  Next, in order to form a contact hole connected to the p-type impurity diffusion layer 102 on the back surface side, the silicon nitride film 104 and the silicon oxide film 103 are partially removed by laser irradiation, for example, and the silicon nitride film 104 and the silicon oxide film are removed. A recess 112 that penetrates 103 and reaches the p-type impurity diffusion layer 102 is formed (FIG. 2-9). Here, since the junction between the p-type impurity diffusion layer 102 and the electrode has a high surface recombination rate, it is preferable to reduce the bottom region of the contact hole to such an extent that the fill factor (FF) does not decrease.

  The recesses 112 are formed between the adjacent recesses 105 in a distributed manner in a line extending in a predetermined direction on the back surface of the n-type silicon substrate 101 in the same direction as the recesses 105. Thereby, the line in which the recessed part 105 is distributed and the line in which the recessed part 112 is distributed are alternately arranged. FIG. 4 is a diagram showing a formation pattern of the recess 112 on the back surface of the n-type silicon substrate 101. The shape of the recess 112 in the surface direction of the n-type silicon substrate 101 is, for example, a rectangular shape with dimensions of about 30 μm in the longitudinal direction and about 20 μm in the short direction. However, the shape of the recess 112 is not limited to this. Moreover, although the formation method of the recessed part 112 is not limited to laser irradiation, the recessed part 112 can be accurately formed in a desired position by forming the recessed part 112 by laser irradiation.

  Next, the silicon oxide film 107 on the back side n-type impurity diffusion layer 106 is removed with a hydrogen fluoride (HF) solution (FIG. 2-9). In the removal of the silicon oxide film 107, the silicon oxide film 107 can be selectively removed by using, for example, lithography and etching. Thereby, the recess 105 reaching the n-type silicon substrate 101 from the surface of the silicon nitride film 104 is formed again, and a contact hole connected to the back-side n-type impurity diffusion layer 106 is formed.

  Next, on the back side of the n-type silicon substrate 101, an n-layer extraction electrode 113 electrically connected to the back-side n-type impurity diffusion layer 106 and a p-layer extraction electrode electrically connected to the p-type impurity diffusion layer 102 114 is formed (FIG. 2-10). As the electrode material of the n-layer extraction electrode 113 and the p-layer extraction electrode 114, for example, a high reflectivity material such as silver (Ag) or aluminum (Al) is preferable. By configuring the n-layer extraction electrode 113 and the p-layer extraction electrode 114 with a high reflectivity material, sunlight L that has been transmitted without being absorbed by the n-type silicon substrate 101 is reflected and returned to the n-type silicon substrate 101 again. Thus, the photoelectric conversion efficiency can be improved.

  The n-layer extraction electrode 113 and the p-layer extraction electrode 114 are formed by, for example, printing and drying an electrode material paste by a screen printing method, and then baking it. The n-layer extraction electrode 113 is formed by printing an electrode material paste so as to cover the silicon nitride (SiN) film 104 in the recess 105 and adjacent to the recess 105. The p-layer extraction electrode 114 is formed by printing an electrode material paste over the silicon nitride (SiN) film 104 in the recess 112 and adjacent to the recess 112 so as not to be connected to the n-layer extraction electrode 113. The Further, the n-layer extraction electrode 113 and the p-layer extraction electrode 114 can be formed by sputtering or vapor deposition in addition to screen printing.

  In the formation of the n-layer extraction electrode 113, it is only necessary to embed the recess 105 and precise alignment is not required. Therefore, when a method suitable for mass production is used, such as a screen printing method, although the alignment accuracy is low. However, the n-type region can be reduced and high photoelectric conversion efficiency can be achieved.

  Further, the insulating mask (silicon nitride film 104, silicon oxide film 103) used when forming the back-side n-type impurity diffusion layer 106 is left as it is and used as an insulating film, so that the p-type impurity diffusion layer 102 is formed at the time of electrode formation. And the back surface n-type impurity diffusion layer 106 are not covered with electrodes. Further, since the recess 105 formed in the insulating mask (silicon nitride film 104, silicon oxide film 103) when forming the back side n-type impurity diffusion layer 106 is used as it is as a contact hole for forming the n-layer extraction electrode 113, the process is performed. It is simple and the positioning of the electrodes is easy.

  Also, an electrode material paste containing aluminum (Al) is printed as an electrode material for the p-layer extraction electrode 114, and the aluminum (Al) of the p-layer extraction electrode 114 is converted into the p-type impurity diffusion layer 102 by heat treatment (firing) after the electrode formation. Can diffuse. As a result, the BSF can be formed by increasing the impurity concentration of only the p-type impurity diffusion layer 102 located below the contact portion in the recess 112 in the p-type impurity diffusion layer 102, and the p-type impurity diffusion The contact resistance between the layer 102 and the p-layer extraction electrode 114 can be reduced. In this case, it is possible to design the impurity concentration when forming the p-type impurity diffusion layer 102 to be lower than the condition for reducing the contact resistance with the p-layer extraction electrode 114.

As described above, in the method for manufacturing a solar cell according to the present embodiment, the p-type impurity diffusion layer 102 is formed on the back surface side of the n-type silicon substrate 101, and silicon oxide (SiO _{2) as} an insulating layer is formed thereon. ) A film 103 and a silicon nitride (SiN) film 104 are formed. Then, recesses 105 reaching the p-type impurity diffusion layer 102 from the surface of the insulating layer are formed in an island shape, and a donor such as phosphorus (P) is diffused through the recesses 105 to diffuse n-type impurity diffusion on the back surface side. Layer 106 is formed. Thereby, the area of the back surface side n-type impurity diffusion layer 106 on the back surface of the n-type silicon substrate 101 can be reduced, and high photoelectric conversion efficiency can be achieved.

  Further, in forming the n-layer extraction electrode 113, it is only necessary to embed the concave portion 105, and precise alignment is not required. Therefore, a method suitable for mass production, such as a screen printing method, with low alignment accuracy is used. Even in the case where n is present, the n-type region can be reduced and high photoelectric conversion efficiency can be achieved.

  Therefore, according to this Embodiment, there exists an effect that the back junction solar cell excellent in the photoelectric conversion efficiency is obtained.

  As described above, the method for manufacturing a solar cell according to the present invention is useful for manufacturing a back junction solar cell excellent in photoelectric conversion efficiency, and is particularly suitable for mass production.

101 n-type silicon substrate 102 p-type impurity diffusion layer 103 silicon oxide (SiO ₂ ) film 104 silicon nitride (SiN) film 105 recess 105 a recess 106 back side n-type impurity diffusion layer 107 silicon oxide (SiO ₂ ) film 108 texture structure 109 Light-receiving-side n-type impurity diffusion layer 110 Silicon oxide (SiO ₂ ) film 111 Antireflection film 112 Recess 113 N layer extraction electrode 114 p layer extraction electrode L Sunlight

Claims (4)

A method of manufacturing a solar cell, wherein a first conductivity type impurity diffusion layer and a second conductivity type impurity diffusion layer are formed on a back surface opposite to a light receiving surface of a first conductivity type semiconductor substrate,
Forming a second conductivity type impurity diffusion layer on the entire back surface of the semiconductor substrate;
A second step of forming an insulating layer on the second conductivity type impurity diffusion layer;
A third step of dispersing and forming a plurality of island-shaped first recesses reaching the semiconductor substrate from the surface of the insulating layer in the surface direction of the semiconductor substrate;
The first conductivity type impurity concentration is higher than that of the semiconductor substrate by diffusing impurities of the first conductivity type through the first recess using the insulating layer as a mask on the back surface of the semiconductor substrate. Forming a first impurity diffusion layer on a surface layer of the semiconductor substrate on a bottom surface of the first recess and on a surface layer of the second conductivity type impurity diffusion layer on a side surface of the first recess;
A fifth step of forming a first electrode penetrating the insulating layer and electrically connected to the impurity diffusion layer of the first conductivity type on the one surface side of the semiconductor substrate;
A sixth step of forming a second electrode penetrating the insulating layer and electrically connected to the second conductivity type impurity diffusion layer on one surface side of the semiconductor substrate;
The manufacturing method of the solar cell characterized by including. In the third step, laser irradiation is used to form the first recess for the insulating layer;
The manufacturing method of the solar cell of Claim 1 characterized by these. Forming the first electrode electrically connected to the impurity diffusion layer of the first conductivity type through the first recess in the fifth step;
The method for producing a solar cell according to claim 1 or 2. In the sixth step, after forming a second recess that penetrates the insulating layer and reaches the impurity diffusion layer of the second conductivity type, the electrode material paste containing aluminum is printed by filling the second recess. Forming the second electrode by performing a heat treatment and diffusing aluminum in the impurity diffusion layer of the second conductivity type in contact with the second electrode;
The manufacturing method of the solar cell as described in any one of Claims 1-3 characterized by these.

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