JP2017045818A - Back electrode type solar battery cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back electrode type solar battery with a high power generation efficiency.SOLUTION: A back electrode type solar battery comprises: a semiconductor substrate; a first conductivity type amorphous semiconductor film and a second conductivity type amorphous semiconductor film provided on a surface at an opposite side to a light-receiving surface of the semiconductor substrate; a first electrode provided on the first conductivity type amorphous semiconductor film; and a second electrode provided on the second conductivity type amorphous semiconductor film. The second electrode consists of a conductive layer substantially coating on the second conductivity type amorphous semiconductor film, and a metal layer formed on the conductive layer. There is no metal layer at an end part of the second electrode. Due to the back electrode type solar battery, the power generation efficiency can be improved.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a back electrode type solar battery cell and a method for manufacturing a back electrode type solar battery cell.

  In recent years, a solar cell that directly converts solar energy into electric energy has been rapidly expected as a next-generation energy source particularly from the viewpoint of global environmental problems. Currently, the most manufactured and sold solar cells have a structure in which electrodes are formed on a light receiving surface that is a surface on which sunlight is incident and a back surface that is opposite to the light receiving surface.

  However, when an electrode is formed on the light receiving surface, sunlight is reflected and absorbed by the electrode, so that the amount of incident sunlight is reduced by the area of the electrode. Therefore, the development of a back electrode type solar cell in which an electrode is formed only on the back surface is being promoted (see, for example, Patent Document 1). In Patent Document 1, a p-type electrode is formed on a p-type semiconductor layer and an n-type electrode is formed on an n-type semiconductor layer on the back surface of a solar cell as a photoelectric conversion element.

International Publication No. 2013/133005

  In order to suppress the leakage current, the p-type electrode and the n-type electrode are formed with an interval. For example, in a back electrode type solar cell as in Patent Document 1, an n-type electrode is provided at the end of the n-type semiconductor layer. It is not done. However, the portion without the n-type electrode has no back-surface reflection effect due to the electrode, and thus power generation efficiency is impaired.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a back electrode type solar cell with high power generation efficiency.

  The back electrode type solar cell of the present invention includes a semiconductor substrate, a first conductive type amorphous semiconductor film and a second conductive type amorphous semiconductor provided on a surface opposite to the light receiving surface of the semiconductor substrate. A first electrode provided on the first conductive type amorphous semiconductor film, and a second electrode provided on the second conductive type amorphous semiconductor film. A conductive layer substantially covering the upper surface of the amorphous semiconductor film, and a metal layer formed on the conductive layer, and has no metal layer at the end of the second electrode.

Moreover, the back surface electrode type solar cell of the present invention includes a material in which the metal layers of the first electrode and the second electrode are different.
Moreover, the back electrode type photovoltaic cell of this invention contains what a conductive layer is Ti or ITO.

  In the back electrode type solar cell of the present invention, the first electrode includes a metal selected from Al, Ni, Co, Pd, and Ag, and an alloy thereof, and the metal layer of the second electrode includes Mn, Mg, A metal selected from Ag, Ta, and Al and alloys thereof are included.

Moreover, the manufacturing method of the back electrode type solar battery cell of the present invention,
The step of selectively forming the first i-type amorphous semiconductor film and the first conductive amorphous semiconductor film on the surface opposite to the light receiving surface of the semiconductor substrate is opposite to the light receiving surface of the semiconductor substrate. Forming a second i-type amorphous semiconductor film and a second conductive amorphous semiconductor film on the entire surface, forming an electrode on the second conductive amorphous semiconductor film, The etching mask includes a step of selectively etching the second i-type amorphous semiconductor film and the second conductive type amorphous semiconductor film in this order.

  According to the present invention, a back electrode type solar cell with high power generation efficiency can be provided.

It is typical sectional drawing which shows the back electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of this invention. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of a comparative example. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of a comparative example. It is typical sectional drawing which shows the manufacturing method of the back surface electrode type solar cell of a comparative example. It is a typical sectional view showing the back electrode type solar cell of a comparative example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

In the present specification, “i-type” means not only a completely intrinsic state but also a sufficiently low concentration (the n-type impurity concentration is less than 1 × 10 ¹⁵ / cm ³ and the p-type impurity concentration is 1 × (Less than 10 ¹⁵ / cm ³ ) is meant to include n-type or p-type impurities. In this specification, “n-type” means a state where the n-type impurity concentration is 1 × 10 ¹⁵ / cm ³ or more, and “p-type” means that the p-type impurity concentration is 1 × 10 ¹⁵ / cm ³ or more. Means the state. The n-type impurity concentration and the p-type impurity concentration can be measured by, for example, secondary ion mass spectrometry.

In this specification, “amorphous silicon” includes not only amorphous silicon in which the dangling bonds of silicon atoms are not terminated with hydrogen, but also dangling bonds of silicon atoms such as hydrogenated amorphous silicon. In which is terminated with hydrogen.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a back electrode type solar cell of the present invention. Although not shown, the back electrode type solar cell 1 has an uneven shape (not shown) formed on the surface 10a of the light receiving surface of the semiconductor substrate 10, and a dielectric film (not shown) on the light receiving surface. ) Is formed. In this embodiment, the semiconductor substrate 10 is an n-type single crystal silicon substrate.

  A first i-type amorphous semiconductor film 11 and a second i-type amorphous semiconductor film 15 are provided on a surface 10 b (back surface) opposite to the light receiving surface of the semiconductor substrate 10. In the present embodiment, the first i-type amorphous semiconductor film 11 and the second i-type amorphous semiconductor film 15 are each formed of an i-type amorphous silicon film.

  A first conductive type amorphous semiconductor film 12 is provided on the first i-type amorphous semiconductor film 11. A second conductivity type amorphous semiconductor film 16 is provided on the second i-type amorphous semiconductor film 15. In the present embodiment, the first conductive amorphous semiconductor film 12 is a p-type amorphous silicon film, and the second conductive amorphous semiconductor film 16 is an n-type amorphous silicon film.

  The side surface of the first i-type amorphous semiconductor film 11 and the side surface of the first conductive type amorphous semiconductor film 12 are covered with the second i-type amorphous semiconductor film 15. A semiconductor film 13 is formed between the upper surface of the first conductive type amorphous semiconductor film 12 and the second i-type amorphous semiconductor film 15. As the semiconductor film 13, n-type amorphous silicon or i-type amorphous silicon can be used.

  On the first conductive type amorphous semiconductor film 12, a metal layer 19 is provided with a thickness of 100 nm or more. In consideration of the low resistance contact property between the first conductive type amorphous semiconductor film 12 and the metal layer 19, the metals used for the metal layer on the p-type amorphous silicon film are Al, Ni, Co, Pd, Ag metals and their alloys can be used. Moreover, it is also possible to laminate | stack these several types of metals. The metal layer 19 functions as a first electrode that is electrically connected to the first conductivity type amorphous semiconductor film 12.

  A conductive layer 17 made of Ti or ITO (Indium Tin Oxide) having a thickness of 1 to 200 nm, preferably 1 to 10 nm is disposed on the second conductive type amorphous semiconductor film 16. A substantially entire upper surface of the second conductive type amorphous semiconductor film 16 is covered with the conductive layer 17. A metal layer 18 is stacked on the upper surface of the conductive layer 17 with a thickness of 100 nm or more.

  In consideration of the low resistance contact property between the conductive layer 17 and the metal layer 18, the metal used for the metal layer 18 may be a metal of Mn, Mg, Ag, Ta, Al or an alloy thereof. . Moreover, it is also possible to laminate | stack these several types of metals. The conductive layer 17 and the metal layer 18 constitute a second electrode.

  When viewed from the back side of the solar cell 1, the metal layer 18 is disposed so as to be surrounded by the conductive layer 17. In the schematic cross-sectional view, the width of the conductive layer 17 is 140 μm to 1200 μm. The width of the conductive layer 17 is the same as the width of the second conductivity type amorphous semiconductor.

  On the other hand, the width of the metal layer 18 is smaller than the width of the conductive layer 17 and is about 100 to 1000 μm, preferably about 300 to 400 μm. The second electrode is composed of the conductive layer 17 and the metal layer 18. When the solar cell 1 is viewed from the back side opposite to the light receiving surface, the end portion of one second electrode has the electrode layer from the conductive layer 17. The metal layer is not formed. Of the second electrode, the end where only the conductive layer 17 is formed has a width of 20 μm or more and 100 μm or less from the end of the second electrode. The central portion of the second electrode surrounded by the end where only the conductive layer 17 is formed is formed of two or more layers including the conductive layer 17 and the metal layer 18.

  Covering the entire surface of the second conductive type amorphous semiconductor layer with the second electrode allows the light passing through the semiconductor substrate to be reflected by the electrode due to the back surface reflection effect and contributes to power generation. The use efficiency of becomes higher. On the other hand, when a thick second electrode is provided on the entire surface of the second conductive type amorphous semiconductor layer, the end portion of the second electrode is close to the first electrode and the first conductive type semiconductor layer, thereby increasing the leakage current.

  Therefore, the end portion of the second electrode is made one layer of only the conductive layer 17, and the end portion of the second electrode is formed thinner than the center portion by laminating the conductive layer 17 and the metal layer 18 at the center portion. become. Therefore, the internal resistance of the electrode at the end increases, and even if the second electrode is provided on the entire surface of the second conductive type amorphous semiconductor layer, the leakage current can be suppressed, so that the power generation efficiency of the solar battery cell is increased. be able to.

  When the solar battery cell 1 is viewed from the back surface opposite to the light receiving surface, the width of the second electrode made of the conductive layer 17 and the metal layer 18 is 100 to 1000 μm, preferably 300 to 400 μm. Of these, the end where the thin conductive layer 17 is exposed has a width of 20 μm or more and 100 μm or less from the end of the stripe-shaped second conductive amorphous semiconductor film 16.

  The width of the first electrode sandwiched between the two second electrodes is 100 to 1000 μm, preferably 600 to 700 μm. Moreover, the outer peripheral part of the photovoltaic cell 1 is surrounded by the first electrode. There is a gap between the first electrode and the second electrode where no electrode having a width of about 100 to 400 μm is provided.

  A solar battery cell having a striped electrode can be placed on a wiring sheet having a wiring pattern and electrically connected to another solar battery cell to form a solar battery module.

(Embodiment 2)
The shape of the electrode may be a comb-like shape in which electrodes arranged in parallel in a stripe shape are connected by electrodes that intersect the electrodes. For example, the first electrode has a comb-teeth shape with a width of 100 to 1000 μm, preferably 600 to 700 μm, and the second electrode has a comb-teeth shape that alternately meshes with the first electrode with a width of 100 to 1000 μm, preferably 300 to 400 μm. May be. The comb-like electrode is an electrode shape suitable for connecting adjacent solar cells with an interconnector.

(Embodiment 3)
Further, the shape of the second electrode may be a shape in which a large number of dots are arranged vertically and horizontally. For example, the second electrode may have a dot shape with a radius of 100 μm to 500 μm, and may be arranged on the back surface of the solar battery cell 1 so that the first electrode surrounds the second electrode. A solar battery cell having a dot-like electrode can be placed on a wiring sheet having a wiring pattern and electrically connected to another solar battery cell to form a solar battery module.

(Embodiment 4)
Hereinafter, an example of the manufacturing method of the back electrode type solar cell of Embodiment 1 is demonstrated with reference to the cross-sectional schematic diagram of FIGS.

  First, as shown in FIG. 2, a first i-type amorphous semiconductor film 11 is formed on the entire surface 10 b opposite to the light receiving surface of the semiconductor substrate 10. Although the formation method of the 1st i-type amorphous semiconductor film 11 is not specifically limited, For example, plasma CVD method can be used.

  Next, a first conductivity type amorphous semiconductor film 12 is formed on the first i-type amorphous semiconductor film 11. Although the formation method of the 1st conductivity type amorphous semiconductor film 12 is not specifically limited, For example, plasma CVD method can be used. Further, a semiconductor film 13 is formed on the first conductive type amorphous semiconductor film 12. The method for forming the semiconductor film 13 is not particularly limited, but for example, a plasma CVD method can be used. The semiconductor film 13 is a second conductivity type amorphous semiconductor film. The semiconductor film 13 may be an i-type amorphous silicon film.

  Next, as shown in FIG. 3, a photoresist mask 14 is formed on the semiconductor film 13. The photoresist mask 14 is formed by applying a photoresist to the entire surface of the semiconductor film, selectively exposing a portion to be etched, and patterning with a developer. In the photoresist mask 14, an opening is formed at a location where the first i-type amorphous semiconductor film 11, the first conductive amorphous semiconductor film 12 and the semiconductor film 13 are etched in the thickness direction. .

  Next, the stacked structure including the first i-type amorphous semiconductor film 11, the first conductive amorphous semiconductor film 12, and the semiconductor film 13 is etched in the thickness direction so that the light-receiving surface of the semiconductor substrate 10 and Exposes a portion of the opposite surface 10b. As the etching method of the laminated structure, for example, wet etching using a hydrofluoric acid aqueous solution, which is a mixed acid of a hydrofluoric acid aqueous solution and a nitric acid aqueous solution, as an etchant may be used. Thereafter, the photoresist mask 14 is removed. In this way, as shown in FIG. 4, the first i-type amorphous semiconductor film 11, the first conductivity-type amorphous semiconductor film 12, and the semiconductor film 13 are surfaces opposite to the light-receiving surface of the semiconductor substrate 10. 10b is selectively formed.

  Further, an etching paste may be used to obtain the structure shown in FIG. As shown in FIG. 5, an etching paste 24 is applied by screen printing to a portion where the first i-type amorphous semiconductor film 11, the first conductive amorphous semiconductor film 12, and the semiconductor film 13 are etched in the thickness direction. Print. As the etching paste, for example, a mixture of phosphoric acid water, N-methyl-2-pyrrolidone, and a thickener can be used.

  Subsequently, the etching paste 24 is reacted with the first i-type amorphous semiconductor film 11, the first conductive amorphous semiconductor film 12, and the semiconductor film 13 by heating, and the etching paste 24 is applied. The surface 10b opposite to the light receiving surface of the semiconductor substrate 10 is exposed. After the heating step, the substrate is dried after ultrasonic cleaning. When using an etching paste, it is preferable to use i-type amorphous silicon for the semiconductor film 13. In this way, using the etching paste, the first i-type amorphous semiconductor film 11, the first conductive amorphous semiconductor film 12, and the semiconductor film 13 are formed on the surface 10 b opposite to the light-receiving surface of the semiconductor substrate 10. It can also be formed selectively.

  Next, as shown in FIG. 6, the exposed surface of the surface 10b opposite to the light receiving surface of the semiconductor substrate 10, the first i-type amorphous semiconductor film 11, the first conductivity-type amorphous semiconductor film 12, and A second i-type amorphous semiconductor film 15 is formed so as to cover the semiconductor film 13. The method for forming the second i-type amorphous semiconductor film 15 is not particularly limited, and for example, a plasma CVD method can be used.

  Next, a second conductivity type amorphous semiconductor film 16 is formed on the second i-type amorphous semiconductor film 15. Although the formation method of the 2nd conductivity type amorphous semiconductor film 16 is not specifically limited, For example, plasma CVD method can be used. In this way, the second i-type amorphous semiconductor film and the second conductive amorphous semiconductor film are formed on the entire surface of the semiconductor substrate 10 opposite to the light receiving surface.

  Next, as shown in FIG. 7, the portion where the semiconductor film 13, the second i-type amorphous semiconductor film 15, and the second conductivity-type amorphous semiconductor film 16 are left, that is, the portion where the second electrode is formed. A first conductive layer 17 is formed on the corresponding second conductive type amorphous semiconductor film 16. For the conductive layer 17, a material having low solubility in an alkaline aqueous solution of 10 wt% or more is used. Specifically, Ti or ITO is vapor-deposited by 1 to 200 nm, preferably 1 to 10 nm, using a shadow mask.

  Subsequently, a metal layer 18 is formed on the first conductive layer 17 by vapor deposition using a shadow mask having an opening smaller than the shadow mask used to form the conductive layer 17. In FIG. 7, the width of the conductive layer 17 is 100 to 1000 μm, preferably 300 to 400 μm, and the width of the metal layer 18 is about 100 to 1000 μm, preferably about 300 to 400 μm.

Next, the second conductive type amorphous semiconductor film 16, the second i-type amorphous semiconductor film 15, and the semiconductor film 13 are selectively etched in the thickness direction using the conductive layer 17 as an etching mask. As shown in FIG. 8, the surface of the first conductive type amorphous semiconductor film 12 is exposed. As an etching method for the second conductivity type amorphous semiconductor film 16, the second i-type amorphous semiconductor film 15, and the semiconductor film 13, an alkaline aqueous solution such as an aqueous potassium borate solution or an aqueous sodium borate solution is used as an etching solution. The wet etching method used is used. Subsequently, the metal layer 19 that is the first electrode is formed using a shadow mask. Thus, the back electrode type solar cell having the configuration shown in FIG. 1 can be formed.
(Comparative example)
FIG. 9 to FIG. 12 are diagrams showing a manufacturing process of the solar battery cell of the comparative example. The first i-type amorphous semiconductor film 51, the first conductive amorphous semiconductor film 52, the semiconductor film 53, and the second i-type amorphous semiconductor film are formed on the semiconductor substrate 50 in the same manner as in the first embodiment. 55, a second conductive type amorphous semiconductor film 56 is stacked.

  Subsequently, as shown in FIG. 10, the first conductive type amorphous semiconductor film 52 is exposed by photolithography. Subsequently, as shown in FIG. 11, a metal layer 57 such as Ag is laminated over the entire back surface of the semiconductor substrate 50.

  Subsequently, among the metal layers stacked on the second conductive type amorphous semiconductor film 56 and the first conductive type amorphous semiconductor film 52, the end of the second conductive type amorphous semiconductor film 56 is formed by photolithography. By removing the metal layer near the portion, the first electrode 60 and the second electrode 61 are formed to obtain the back electrode type solar battery cell shown in FIG.

  As seen from the back surface of the solar battery cell 50 of the comparative example, no electrode exists up to the end on the second conductive type amorphous semiconductor film 56, and the portion where the second conductive type amorphous semiconductor film 56 is exposed is Exists. This contributes to a reduction in leakage current, but it is difficult to improve the power generation efficiency in those portions because light collection of the solar cell by backside reflection cannot be expected and carriers cannot be collected.

  In addition, since the area where the second electrode contacts the second conductivity type amorphous semiconductor is small and the resistance value is increased, it is difficult to improve the power generation efficiency.

  Moreover, since the metal of the first electrode and the second electrode uses the same metal, it is not possible to use a metal having low resistance contact property suitable for each of the first conductive type amorphous semiconductor and the second conductive type amorphous semiconductor. There is a problem.

  In addition, after each amorphous thin film is formed on the back surface of the solar battery cell, a patterning process using photolithography or etching paste is required twice for forming electrodes.

  On the other hand, in the back electrode type solar cells shown in Embodiments 1 and 2, the amorphous semiconductor film is not covered with the conductive layer of the electrode when viewed from the back surface opposite to the rear surface in the figure. The portion is small, the light collection effect of the solar cell by back surface reflection is large, and the power generation efficiency can be improved.

  In addition, a material having a low-resistance contact suitable for the first conductive type amorphous semiconductor and the second conductive type amorphous semiconductor can be used for the first electrode and the second electrode, respectively, so that high power generation efficiency is achieved. Can do.

  In addition, after each amorphous thin film is formed on the back surface of the solar battery cell, a patterning step by photolithography or printing for forming an electrode is not necessary, so that the cost can be reduced.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 ... Solar cell 10 ... Semiconductor substrate 11 ... 1st i type amorphous semiconductor film 12 ... 1st conductivity type amorphous semiconductor film 13 ... Semiconductor film 15 ... 2nd i type amorphous semiconductor film 16 ... Second conductive type amorphous semiconductor film 17 ... conductive layer 18 ... metal layer 19 ... metal layer

Claims (5)

A semiconductor substrate;
A first conductive type amorphous semiconductor film and a second conductive type amorphous semiconductor film provided on a surface opposite to the light receiving surface of the semiconductor substrate;
A first electrode provided on the first conductive type amorphous semiconductor film;
A second electrode provided on the second conductive type amorphous semiconductor film;
The second electrode includes a conductive layer covering the second conductive type amorphous semiconductor film, and a metal layer formed on the conductive layer,
A back electrode type solar cell in which the metal layer is not provided at an end of the second electrode.   The back electrode type solar cell according to claim 1, wherein materials of the metal layers of the first electrode and the second electrode are different.   The back electrode type solar cell according to claim 1, wherein the conductive layer is made of Ti or ITO. The first electrode includes a metal selected from Al, Ni, Co, Pd, and Ag, and alloys thereof.
The back electrode type solar cell according to any one of claims 1 to 3, wherein the metal layer of the second electrode includes a metal selected from Mn, Mg, Ag, Ta, and Al and alloys thereof. Selectively forming a first i-type amorphous semiconductor film and a first conductivity-type amorphous semiconductor film on a surface opposite to the light-receiving surface of the semiconductor substrate;
Forming a second i-type amorphous semiconductor film and a second conductive amorphous semiconductor film on the entire surface opposite to the light-receiving surface of the semiconductor substrate;
Forming an electrode on the second conductive type amorphous semiconductor film;
A method for manufacturing a back electrode type solar cell, comprising the steps of selectively etching the second i-type amorphous semiconductor film and the second conductive amorphous semiconductor film in this order using the electrode as an etching mask.

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