JP2011181669A - Method of manufacturing solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell in which an aluminum oxide film is arranged without forming a silicon oxide film on an interface between two silicon film. <P>SOLUTION: The method of manufacturing the solar cell includes a first process of forming a first silicon film as an upper part of a first photoelectric conversion element on a substrate; a second process of forming an aluminum film on the first silicon film; a third process of changing the aluminum film into an aluminum hydroxide oxide film through boehmite treatment; a fourth process of changing the aluminum hydroxide oxide film into an aluminum oxide film through heat treatment; and a fifth process of forming a second silicon film as a lower part of a second photoelectric conversion element differing in band gap from the first photoelectric conversion element on the aluminum oxide film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  A thin film solar cell has a tandem structure in which a plurality of photoelectric conversion elements (subcells) made of materials having different band gaps are stacked on an insulating translucent substrate in order to effectively use the sunlight spectrum widely.

  In Patent Document 1, a lower electrode and a lower photoelectric conversion cell are sequentially formed on an insulating substrate, and then a transparent intermediate layer (Al-doped ZnO film or Ga-doped ZnO film) is formed on the lower photoelectric conversion cell by RF sputtering. In addition, it is described that an integrated tandem solar cell is manufactured by forming an upper photoelectric conversion cell on a transparent intermediate layer. The transparent intermediate layer has a single film specific resistance of 1 Ω · cm to 100 Ω · cm. Thereby, according to patent document 1, it is supposed that the influence of the problem (side leak) which a part of electric current which should flow from an upper photoelectric conversion cell to a lower photoelectric conversion cell leaks through a transparent intermediate | middle layer can be made small. .

JP 2005-322707 A

Patent Document 1 describes that the lower photoelectric conversion cell is formed of amorphous silicon and the transparent intermediate layer is formed of a metal oxide. It is described that the transparent intermediate layer may be formed of aluminum oxide (Al ₂ O ₃ ) instead of the above zinc oxide (ZnO).

  When a transparent intermediate layer of aluminum oxide is formed on an amorphous silicon lower photoelectric conversion cell by RF sputtering, oxygen atoms are always included in the raw material and target. For this reason, when the transparent intermediate layer is formed directly on the lower photoelectric conversion cell, these oxygen atoms oxidize the silicon surface, and the relative dielectric constant is extremely low at the interface between the lower photoelectric conversion cell and the transparent intermediate layer. There is a high possibility that a silicon oxide layer (relative permittivity≈3.8) is formed. In this case, the polarization at the interface between the lower photoelectric conversion cell (silicon film) and the upper photoelectric conversion cell (silicon film) does not occur sufficiently (the energy band does not sufficiently curve), and the lower photoelectric conversion cell and the upper photoelectric conversion It becomes difficult to lower the junction resistance at the interface with the cell.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a method for manufacturing a solar cell capable of arranging an aluminum oxide film without generating a silicon oxide film at the interface between two silicon films. To do.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell according to one aspect of the present invention includes a first silicon film to be an upper part of a first photoelectric conversion element on a substrate. A second step of forming an aluminum film on the first silicon film, and a third step of performing a boehmite treatment on the aluminum film to change it to an aluminum hydroxide oxide film, A fourth step of heat-treating the aluminum hydroxide oxide film into an aluminum oxide film; and a lower portion of the second photoelectric conversion element having a band gap different from that of the first photoelectric conversion element on the aluminum oxide film. And a fifth step of forming a second silicon film to be formed.

  According to the present invention, since the aluminum film is formed in the second step, oxygen atoms are not contained in the raw material or the target. For this reason, when an aluminum film is formed on the first silicon film, a silicon oxide layer is hardly formed at the interface between the first silicon film and the aluminum film. Since the aluminum film is changed to an aluminum hydroxide oxide film in the third step and the aluminum hydroxide oxide film is changed to an aluminum oxide film in the fourth step, the first step is also used in the third step and the fourth step. It is difficult to form a silicon oxide layer at the interface between the silicon film and the aluminum hydroxide oxide film (or aluminum oxide film). As a result, the aluminum oxide film can be disposed at the interface between the two silicon films (the first silicon film and the second silicon film) without generating a silicon oxide film. In other words, an aluminum oxide film is formed directly on the first photoelectric conversion element without generating a low dielectric constant silicon oxide film at the interface between the first photoelectric conversion element and the second photoelectric conversion element. Can do. That is, an aluminum oxide film can be disposed without generating a silicon oxide film at the interface between two silicon films.

FIG. 1 is a diagram showing a cross-sectional configuration of the thin-film silicon solar cell in the first embodiment. FIG. 2 is a diagram illustrating a method for manufacturing the thin-film silicon solar cell according to the first embodiment. FIG. 3 is a diagram illustrating the method for manufacturing the thin-film silicon solar cell according to the first embodiment. FIG. 4 is a diagram illustrating the method for manufacturing the thin-film silicon solar cell according to the first embodiment. FIG. 5 is a diagram illustrating a method for manufacturing the thin-film silicon solar cell according to the first embodiment. FIG. 6 is a diagram showing an electric circuit for evaluating the voltage-capacitance characteristics of the aluminum oxide film in the first embodiment. FIG. 7 is a diagram showing an example of the evaluation result of the voltage-capacitance characteristics of the aluminum oxide film in the first embodiment. FIG. 8 is a diagram showing a capacitor structure sample for evaluating the voltage-current characteristics of the aluminum oxide film in the first embodiment. FIG. 9 is a diagram showing an electric circuit for evaluating the voltage-current characteristics of the aluminum oxide film in the first embodiment. FIG. 10 is a diagram illustrating an example of an evaluation result of voltage-current characteristics of the aluminum oxide film in the first embodiment. FIG. 11 is a diagram illustrating a method for manufacturing the thin-film silicon solar cell according to the second embodiment. FIG. 12 is a diagram illustrating an example of an evaluation result of voltage-capacitance characteristics of the aluminum oxide film in the second embodiment. FIG. 13 is a diagram illustrating an example of an evaluation result of voltage-current characteristics of the aluminum oxide film in the second embodiment.

  Embodiments of a method for manufacturing a thin-film silicon solar cell according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

Embodiment 1 FIG.
A cross-sectional configuration of thin-film silicon solar cell 100 in the first embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a cross-sectional configuration of a thin-film silicon solar cell 100 to be manufactured by the method for manufacturing a thin-film silicon solar cell according to the first embodiment for one cell.

  FIG. 1 shows a tandem thin film silicon solar cell in which three photoelectric conversion elements (subcells) are stacked as an example of the configuration of the thin film silicon solar cell 100. The three photoelectric conversion elements have different band gaps at least between the photoelectric conversion elements adjacent to each other. That is, in the thin film silicon solar cell 100 shown in FIG. 1, on the substrate 1, the surface transparent electrode layer 2, the first photoelectric conversion element 3, the first aluminum oxide film 4, the second photoelectric conversion element 5, the first The aluminum oxide film 6, the third photoelectric conversion element 7, the back transparent electrode layer 8, and the back electrode layer 9 are sequentially stacked. The first photoelectric conversion element 3 and the second photoelectric conversion element 5 have different band gaps. The second photoelectric conversion element 5 and the third photoelectric conversion element 7 have different band gaps.

  The substrate 1 is made of an insulating and translucent substance (for example, glass). The surface transparent electrode layer 2 is formed of a material having conductivity and translucency.

  The first photoelectric conversion element 3 is, for example, a pin type photodiode, and a p-type silicon film 3a, an i-type silicon film 3b, and an n-type silicon film (first silicon film) 3c are sequentially stacked. ing. The p-type silicon film 3a is made of, for example, amorphous silicon or microcrystalline silicon containing a p-type impurity such as boron. The i-type silicon film 3b is made of, for example, amorphous silicon or microcrystalline silicon that does not contain impurities. The n-type silicon film 3c is formed of, for example, amorphous silicon or microcrystalline silicon containing an n-type impurity such as phosphorus or arsenic.

  The first photoelectric conversion element 3 may be a pn type photodiode. In this case, the first photoelectric conversion element 3 has a configuration in which the i-type silicon film 3b is omitted.

  The first aluminum oxide film 4 is made of aluminum oxide. Aluminum oxide is a material having a relatively high relative permittivity (relative permittivity≈10 to 100). The first aluminum oxide film 4 includes an n-type silicon film (first silicon film) 3 c in the first photoelectric conversion element 3 and a p-type silicon film (second silicon film) described later in the second photoelectric conversion element 5. ) By inducing polarization at the interface with 5a and bending the energy band at that interface more greatly to promote tunnel conduction, it functions as an intermediate layer that reduces the junction resistance at that interface. The first aluminum oxide film 4 is a film formed by using boehmite treatment as will be described later. A manufacturing method for forming the first aluminum oxide film 4 will be described later.

  Similar to the first photoelectric conversion element 3, the second photoelectric conversion element 5 is, for example, a pin type photodiode, and includes a p-type silicon film (second silicon film) 5a, an i-type silicon film. 5b and an n-type silicon film (first silicon film) 5c are sequentially stacked. Similar to the first aluminum oxide film 4, the second aluminum oxide film 6 is a film formed by using boehmite treatment. Similarly to the first photoelectric conversion element 3, the third photoelectric conversion element 7 is a pin type photodiode, for example, a p-type silicon film (second silicon film) 7a, an i-type silicon film. 7b and an n-type silicon film 7c are sequentially stacked.

  The back surface transparent electrode layer 8 is formed of a conductive and translucent material. The back electrode layer 9 is formed of a conductive material.

  Here, suppose a case where a silicon oxide film (relative permittivity≈3.8) having an extremely low relative dielectric constant is formed at the interface between the n-type silicon film 3c and the first aluminum oxide film 4. In this case, the polarization at the interface between the n-type silicon film 3c and the p-type silicon film 5a is not sufficiently induced (the energy band is not sufficiently curved), and the n-type silicon film 3c and the p-type silicon film 5a It becomes difficult to lower the junction resistance at the interface (to the target value).

  On the other hand, in the first embodiment, as shown in FIG. 1, the n-type silicon film 3c is formed without forming the silicon oxide film at the interface between the n-type silicon film 3c and the first aluminum oxide film 4. The first aluminum oxide film 4 is disposed at the interface between the p-type silicon film 5a. As a result, the polarization at the interface between the n-type silicon film 3c and the p-type silicon film 5a can be efficiently induced, so that the junction resistance at the interface between the n-type silicon film 3c and the p-type silicon film 5a is reduced to the target. Can be easily reduced). This also applies to the second aluminum oxide film 6.

  Next, the manufacturing method of the thin film silicon solar cell concerning Embodiment 1 is demonstrated using FIGS. 2 to 5 show mainly the steps for forming the first aluminum oxide film 4 in the method for manufacturing the thin-film silicon solar cell according to the first embodiment.

  In the process shown in FIG. 2, first, the surface transparent electrode layer 2 is formed on the substrate 1. Then (first step), a p-type silicon film 3a, an i-type silicon film 3b, and an n-type silicon film (first silicon film) 3c are sequentially laminated on the surface transparent electrode layer 2. The n-type silicon film 3 c is a film that should be an upper part in the first photoelectric conversion element 3. Thereby, the 1st photoelectric conversion element 3 is formed.

  Next (second step), an aluminum film 10 is formed on the n-type silicon film 3c by sputtering or vacuum deposition in a non-oxidizing atmosphere. The aluminum film 10 is formed on the surface of the n-type silicon film 3c with a film thickness of about 2-5 nm, for example.

  In the step shown in FIG. 3 (third step), the aluminum film 10 is subjected to boehmite treatment to be changed to the aluminum hydroxide oxide film 14. Specifically, as shown in FIG. 3 (a), a pure water 13 heated to 80 ° C. or higher is filled in a water tank 11 having a size that can accommodate a glass substrate having a meter angle. Then, the sample 12 having the aluminum film 10 formed on the surface is immersed and boiled. That is, the aluminum film 10 is immersed and boiled in pure water 13 heated to 80 ° C. or higher. Thereby, as shown in FIG. 3B, the aluminum film 10 is transformed into an aluminum hydroxide oxide film 14 (boehmite treatment by boiling).

  Since the surface of the first photoelectric conversion element 3 (that is, the surface of the n-type silicon film 3c) is covered with the aluminum film 10, a natural silicon oxide film is not generated by oxidation in water.

  In the step shown in FIG. 4 (fourth step), the aluminum hydroxide oxide film 14 is heat-treated to change to the aluminum oxide film 4. Specifically, as shown in FIG. 4A, the sample 12 boiled in high-temperature pure water is heated at 200 ° C. in a non-oxidizing atmosphere. Thereby, the aluminum hydroxide oxide film 14 is changed to the aluminum oxide film 4 (the aluminum hydroxide oxide is decomposed by heating at 200 ° C. or more to be changed into aluminum oxide).

  Note that a photoelectric conversion element (amorphous silicon, microcrystalline silicon, or the like) in a thin film silicon solar cell is usually formed at a substrate temperature of about 200 ° C., and the influence of the heat treatment on the photoelectric conversion element There is almost no (damage).

  Next (fifth step), a p-type silicon film (second silicon film) 5a, an i-type silicon film 5b, and an n-type silicon film (first silicon film) 5c are sequentially formed on the aluminum oxide film 4. Laminate. The p-type silicon film 5 a is a film that should be the lower part of the second photoelectric conversion element 5. Thereby, the second photoelectric conversion element 5 is formed.

  Thereafter, in the same manner as described above, the aluminum oxide film 6, the third photoelectric conversion element 7, the back transparent electrode layer 8, and the back electrode layer 9 are sequentially laminated. In the third photoelectric conversion element 7, a p-type silicon film (second silicon film) 7a, an i-type silicon film 7b, and an n-type silicon film 7c are sequentially stacked.

  Here, suppose that an aluminum oxide film is directly formed on the n-type silicon film in the first photoelectric conversion element by a sputtering method or a vacuum evaporation method (hereinafter, this case is referred to as a comparative example). To do). In this comparative example, the raw material and target always contain oxygen atoms. For this reason, when the aluminum oxide film is formed directly on the n-type silicon film, these oxygen atoms oxidize the surface of the n-type silicon film 3c, so that it is compared with the interface between the n-type silicon film 3c and the aluminum oxide film. There is a high possibility that a silicon oxide layer having an extremely low dielectric constant (relative dielectric constant≈3.8) is formed. In this case, polarization at the interface between the n-type silicon film in the first photoelectric conversion element and the p-type silicon film in the second photoelectric conversion element does not occur sufficiently (energy band curvature does not occur sufficiently), and the first It becomes difficult to reduce the junction resistance at the interface between the photoelectric conversion element and the second photoelectric conversion element.

  On the other hand, according to the method for manufacturing the thin-film silicon solar cell according to the first embodiment, since the aluminum film 10 is formed in the second step (see FIG. 2), oxygen atoms are contained in the raw material and the target. Absent. For this reason, when the aluminum film 10 is formed on the n-type silicon film 3 c, it is difficult to form a silicon oxide layer at the interface between the n-type silicon film 3 c and the aluminum film 10. Then, in the third step, the aluminum film 10 is transformed into the aluminum hydroxide oxide film 14, and in the fourth step, the aluminum hydroxide oxide film 14 is changed to the aluminum oxide film 4, so that the third step and the fourth step However, it is difficult to form a silicon oxide layer at the interface between the n-type silicon film 3c and the aluminum hydroxide oxide film 14 (or the aluminum oxide film 4). Thereby, the aluminum oxide film 4 can be disposed at the interface between the two silicon films (n-type silicon film 3c and p-type silicon film 5a) without generating a silicon oxide film. In other words, the aluminum oxide film can be directly formed on the photoelectric conversion element without generating a low dielectric constant silicon oxide film at the interface between the upper and lower photoelectric conversion elements.

  Therefore, the polarization at the interface between the n-type silicon film 3c in the first photoelectric conversion element 3 and the p-type silicon film 5a in the second photoelectric conversion element 5 is efficiently induced (the energy band is bent more greatly to tunnel). Therefore, the junction resistance at the interface between the n-type silicon film 3c and the p-type silicon film 5a can be easily lowered (to a target value).

  In addition, since the aluminum film 10 is formed in a non-oxidizing atmosphere in the second step, it is difficult to form a silicon oxide layer at the interface between the n-type silicon film 3c and the aluminum film 10 from this viewpoint. In the fourth step, since the aluminum hydroxide oxide film 14 is heat-treated in a non-oxidizing atmosphere, a silicon oxide layer is hardly formed at the interface between the n-type silicon film 3c and the aluminum film 10 from this viewpoint.

  Furthermore, in the third step, the aluminum film 10 is soaked in pure water 13 heated to 80 ° C. or higher, thereby transforming the aluminum film 10 into an aluminum hydroxide oxide film 14. Thereby, the aluminum film 10 can be transformed into the aluminum hydroxide oxide film 14 while reducing damage to the photoelectric conversion element (n-type silicon film 3c).

  Next, the relative dielectric constant of the aluminum oxide film manufactured by such a method was evaluated using a sample having a MIS (Metal-Insulator-Semiconductor) structure shown in FIG. FIG. 5 is a diagram showing a sample structure for evaluating voltage-capacitance characteristics of an aluminum oxide film produced by the method for producing a thin-film silicon solar cell according to the first embodiment.

  Here, an n-type silicon film 16 is prepared as a film corresponding to the n-type silicon film 3c, and an aluminum oxide film 15 is formed on the n-type silicon film 16 by the same method as the manufacturing method of the first embodiment. Thereafter, an aluminum electrode 17 was formed by vacuum deposition. That is, the structure in which the n-type silicon film 16, the aluminum oxide film 15, and the aluminum electrode 17 are sequentially stacked is used as the sample of the first embodiment.

  Further, after forming an aluminum oxide film 15 ′ on the n-type silicon film 16 by the same method as in the above comparative example (a method of directly forming an aluminum oxide film on the n-type silicon film by sputtering), vacuum deposition is performed. An aluminum electrode 17 ′ was formed by the method. That is, a structure in which an n-type silicon film 16, an aluminum oxide film 15 ', and an aluminum electrode 17' are sequentially stacked is used as a sample for comparison.

  Furthermore, the electric circuit shown in FIG. 6 was constructed, and the capacitance value was measured while applying a variable voltage to the aluminum electrode 17 (CV characteristics). FIG. 6 is a diagram showing an electric circuit for evaluating the voltage-capacitance characteristics of the aluminum oxide film produced by the method for producing a thin-film silicon solar cell according to the first embodiment. In general, when the CV characteristics of the MIS capacitor are evaluated, the energy band is bent due to the electric charge or the like existing in the insulating film, and the CV curve is Vfb (flat band voltage) along the voltage axis from the ideal curve. ) Is known to shift by minutes. Since Vfb observed here increases as the relative dielectric constant of the inserted insulating film increases, the relative dielectric constant can be evaluated from Vfb appearing in the CV characteristics.

  FIG. 7 shows the results of evaluating the CV characteristics for each of the sample of Embodiment 1 and the sample of the comparative example. That is, FIG. 7 shows the CV characteristic 19 of the aluminum oxide film 15 in the sample of the first embodiment, the CV characteristic 18 of the aluminum oxide film 15 ′ in the sample of the comparative example, and an ideal aluminum oxide film. The CV characteristics 20 of FIG.

  In FIG. 7, when the CV characteristic 18 (comparative example) and the CV characteristic 19 (Embodiment 1) are compared, the value of the flat band voltage is that of the CV characteristic 19 (Embodiment 1). Is higher (Vfb2> Vfb1). This is because the dielectric constant of the insulating film (aluminum oxide film) is higher in the MIS capacitor (sample in the first embodiment) in which the aluminum oxide film is formed by the manufacturing method of the first embodiment. Is shown. That is, according to the manufacturing method of the first embodiment, the generation of silicon oxide on the surface of the n-type silicon film 3c is suppressed, and the high relative dielectric constant possessed by aluminum oxide increases the n-type silicon film 3c and the p-type silicon. It can be seen that this can efficiently contribute to inducing polarization at the interface with the film 5a.

  Next, the junction resistance when the aluminum oxide film produced by the method for manufacturing a thin-film silicon solar cell according to the first embodiment was inserted into the interface between the upper and lower photoelectric conversion elements was evaluated. FIG. 8 is a diagram showing a sample structure for evaluating voltage-current characteristics of an aluminum oxide film produced by the method for producing a thin-film silicon solar cell according to the first embodiment.

  Here, after forming the aluminum electrode 21 by vacuum deposition, the n-type silicon film 16, the aluminum oxide film 15, and the p-type silicon film are formed on the aluminum electrode 21 by the same method as the manufacturing method of the first embodiment. 22 were formed in order. Thereafter, an aluminum electrode 23 was formed by vacuum deposition. That is, the structure in which the aluminum electrode 21, the n-type silicon film 16, the aluminum oxide film 15, the p-type silicon film 22, and the aluminum electrode 23 are sequentially stacked is used as the sample of the first embodiment.

  Further, after forming the aluminum electrode 21 by the vacuum deposition method and forming the n-type silicon film 16, the aluminum oxide film 15 'was formed on the n-type silicon film 16 by the same method as in the above comparative example. Thereafter, a p-type silicon film 22 'was formed, and an aluminum electrode 23' was formed on the p-type silicon film 22 'by vacuum deposition. That is, a structure in which the aluminum electrode 21, the n-type silicon film 16, the aluminum oxide film 15 ', the p-type silicon film 22', and the aluminum electrode 23 'are sequentially stacked is used as a sample for comparison.

  Furthermore, the electric circuit shown in FIG. 9 is configured, the aluminum electrode 21 which is the lower part of the structure is grounded, the variable voltage is applied to the aluminum electrode 23 (23 ′) which is the upper part of the structure, and the current flowing through the circuit Was measured (voltage-current characteristics). FIG. 9 is a diagram illustrating an electric circuit for evaluating voltage-current characteristics of an aluminum oxide film manufactured by the method for manufacturing a thin-film silicon solar cell according to the first embodiment.

  FIG. 10 shows the results of evaluating the voltage-current characteristics for each of the sample of Embodiment 1 and the sample of the comparative example. That is, FIG. 10 shows the voltage-current characteristic 24 of the aluminum oxide film 15 in the sample of the first embodiment and the voltage-current characteristic 25 of the aluminum oxide film 15 ′ in the sample of the comparative example.

  In FIG. 10, when the voltage-current characteristic 25 (comparative example) and the voltage-current characteristic 24 (Embodiment 1) are compared, the current value that flows when a predetermined voltage (A in the figure) is applied is It can be seen that the sample of Embodiment 1 is about one digit higher than the sample of the comparative example. That is, according to the manufacturing method of the first embodiment, the high dielectric constant possessed by aluminum oxide can efficiently contribute to inducing polarization at the interface between the n-type silicon film 3c and the p-type silicon film 5a. Thus, it was confirmed that the junction resistance at the interface between the n-type silicon film 3c and the p-type silicon film 5a can be easily lowered (to a target value).

  As described above, in the tandem-type thin film silicon solar cell in which the aluminum oxide film is formed by the manufacturing method of Embodiment 1, the interface resistance between the upper and lower photoelectric conversion elements (subcells) is changed by the manufacturing method of the comparative example. It is possible to reduce the value to a lower value (for example, about one digit) than when it is formed. As a result, the power generation efficiency of the entire solar cell element can be greatly improved.

Embodiment 2. FIG.
Next, the manufacturing method of the thin film silicon solar cell concerning Embodiment 2 is demonstrated using FIG. Below, it demonstrates focusing on a different point from Embodiment 1. FIG. FIG. 11 shows steps for forming the first aluminum oxide film in the method for manufacturing the thin-film silicon solar cell according to the second embodiment.

  As shown in FIG. 11, the manufacturing method of the thin-film silicon solar cell according to the second embodiment is different from the first embodiment in the specific process in the step of transforming the aluminum film 10 into the aluminum hydroxide oxide film 214. That is, as shown in FIG. 11A, high-temperature and high-pressure water vapor 26 is sprayed onto a sample 212 having an aluminum film 10 formed on the surface to form an aluminum hydroxide oxide film.

  Here, as shown in FIG. 11B, the sample 212 is moved horizontally with respect to the injection direction while injecting the high-temperature and high-pressure water vapor 26 from the injection pipe 27 provided with a plurality of holes, and the sample 212 is moved. Water vapor is sprayed over the entire surface (that is, the aluminum film 10). Alternatively, the injection pipe 27 may be moved while fixing the sample 212 and injecting the high-temperature and high-pressure water vapor 26. Thereby, since the high-temperature and high-pressure water vapor 26 is uniformly sprayed over the entire surface of the sample 212 (that is, the entire aluminum film 10), the aluminum hydroxide oxide film 214 can be uniformly formed over the entire surface of the sample 212. (Boehmite treatment by injection).

  Note that after the aluminum hydroxide oxide film 214 is formed over the entire surface of the sample 212, the entire facility for injecting the high-temperature and high-pressure water vapor 26 shown in FIG. 11 can be heated to 200 ° C. In this case, it is not necessary to separately provide a heating facility for transforming the aluminum hydroxide oxide film into an aluminum oxide film, and the cost for the production facility can be reduced. Further, since the manufacturing process is shortened, the production cost can be reduced.

  Next, the relative dielectric constant of the aluminum oxide film produced by such a method was evaluated using a sample having a MIS structure similar to that shown in FIG.

  Here, an aluminum oxide film was formed on the n-type silicon film by the same method as the manufacturing method of the second embodiment. For example, an aluminum film is formed on an n-type silicon film, and high-temperature and high-pressure steam at 140 ° C. and 0.5 MPa is sprayed from the aluminum film to change the aluminum film into an aluminum hydroxide oxide film. The aluminum hydroxide oxide film was changed to an aluminum oxide film by performing a heat treatment at ° C. Further, an aluminum electrode was formed on the aluminum oxide film by vacuum deposition. That is, a structure in which an n-type silicon film, an aluminum oxide film, and an aluminum electrode are sequentially stacked was used as the sample of the second embodiment.

  FIG. 12 shows the results of evaluating the CV characteristics of the sample of the second embodiment, together with the results of evaluating the CV characteristics of the sample of the first embodiment and the sample of the comparative example. That is, FIG. 12 shows the CV characteristic 29 of the aluminum oxide film in the sample of the second embodiment, the CV characteristic 19 of the aluminum oxide film 15 in the sample of the first embodiment, and the oxidation in the sample of the comparative example. The CV characteristic 18 of the aluminum film 15 'is shown.

  In FIG. 12, when the CV characteristic 18 (comparative example) is compared with the CV characteristic 29 (second embodiment), the value of the flat band voltage is that of the CV characteristic 29 (second embodiment). Is higher (Vfb3> Vfb1). This is because the dielectric constant of the insulating film (aluminum oxide film) is higher in the MIS capacitor (sample in the second embodiment) in which the aluminum oxide film is formed by the manufacturing method of the second embodiment. Is shown. That is, according to the manufacturing method of the second embodiment, the generation of silicon oxide on the surface of the n-type silicon film 3c is suppressed, and the high relative dielectric constant possessed by aluminum oxide increases the n-type silicon film 3c and the p-type silicon. It can be seen that this can efficiently contribute to inducing polarization at the interface with the film 5a.

  When the CV characteristic 29 (Embodiment 2) is compared with the CV characteristic 19 (Embodiment 1), it can be seen that a flat band voltage (Vfb3≈Vfb2) having almost the same magnitude is obtained. .

  Next, the junction resistance when the aluminum oxide film produced by the method for manufacturing a thin-film silicon solar cell according to the second embodiment was inserted into the interface between the upper and lower photoelectric conversion elements was evaluated.

  Here, after forming an aluminum electrode by a vacuum deposition method, an n-type silicon film, an aluminum oxide film, and a p-type silicon film were sequentially formed on the aluminum electrode by the same method as the manufacturing method of the second embodiment. . Thereafter, an aluminum electrode was formed by vacuum deposition. That is, a structure in which an aluminum electrode, an n-type silicon film, an aluminum oxide film, a p-type silicon film, and an aluminum electrode are sequentially stacked is used as the sample of the second embodiment.

  FIG. 13 shows the results of evaluating the voltage-current characteristics for the sample of the second embodiment, together with the results of evaluating the voltage-current characteristics for each of the sample of the first embodiment and the sample of the comparative example. That is, FIG. 13 shows the voltage-current characteristic 30 of the aluminum oxide film in the sample of the second embodiment, the voltage-current characteristic 24 of the aluminum oxide film 15 in the sample of the first embodiment, and the oxidation in the sample of the comparative example. The voltage-current characteristic 25 of the aluminum film 15 ′ is shown.

  In FIG. 13, when the voltage-current characteristic 25 (comparative example) and the voltage-current characteristic 30 (second embodiment) are compared, the value of the current that flows when a predetermined voltage (A in the figure) is applied is It can be seen that the sample of the second embodiment is about one digit higher than the sample of the comparative example. That is, according to the manufacturing method of the second embodiment, the high dielectric constant possessed by aluminum oxide can efficiently contribute to inducing polarization at the interface between the n-type silicon film 3c and the p-type silicon film 5a. Thus, it was confirmed that the junction resistance at the interface between the n-type silicon film 3c and the p-type silicon film 5a can be easily lowered (to a target value).

  When the voltage-current characteristic 30 (Embodiment 2) is compared with the voltage-current characteristic 24 (Embodiment 1), it can be seen that the behavior is almost the same.

  As described above, even in the tandem-type thin film silicon solar cell in which the aluminum oxide film is formed by the manufacturing method of the second embodiment, the interface resistance between the upper and lower photoelectric conversion elements (subcells) is reduced by the manufacturing method of the comparative example. It is possible to lower the value to a lower value (for example, about one digit) than when a film is formed.

  As described above, the method for manufacturing a solar cell according to the present invention is useful for a tandem-type thin film silicon solar cell.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Surface transparent electrode layer 3 1st photoelectric conversion element 3c n-type silicon film 4 1st aluminum oxide film 5 2nd photoelectric conversion element 5a p-type silicon film 5c n-type silicon film 6 2nd aluminum oxide film 7 Third photoelectric conversion element 7a P-type silicon film 8 Back surface transparent electrode layer 9 Back surface electrode layer 10 Aluminum film 11 Water tank 12, 212 Sample 13 Pure water 14, 214 Aluminum hydroxide oxide film 15, 15 'Aluminum oxide film 16 n Type silicon film 17, 17 ′ aluminum electrode 18 CV characteristic of sample of comparative example 19 CV characteristic of sample of embodiment 1 20 ideal CV characteristic 21 aluminum electrode 22 p-type silicon film 23 aluminum electrode 24 Voltage-Current Characteristic of Sample of Embodiment 1 25 Voltage-Current Characteristic of Sample of Comparative Example 2 C-V characteristics 30 voltage of the sample of the second embodiment of the sample of water vapor 27 injection pipe 29 Embodiment 2 - current characteristic

Claims (5)

Forming a first silicon film to be an upper part of the first photoelectric conversion element on the substrate;
A second step of forming an aluminum film on the first silicon film;
A third step of subjecting the aluminum film to a boehmite treatment to change to an aluminum hydroxide oxide film;
A fourth step of heat-treating the aluminum hydroxide oxide film into an aluminum oxide film;
A fifth step of forming, on the aluminum oxide film, a second silicon film to be a lower portion of the second photoelectric conversion element having a band gap different from that of the first photoelectric conversion element;
A method for producing a solar cell, comprising: The method for manufacturing a solar cell according to claim 1, wherein in the second step, the aluminum film is formed in a non-oxidizing atmosphere. 3. The method for manufacturing a solar cell according to claim 1, wherein in the third step, the aluminum film is immersed in pure water heated to 80 ° C. or higher. 3. The method for manufacturing a solar cell according to claim 1, wherein in the third step, water vapor is sprayed onto the aluminum film. 5. The method of manufacturing a solar cell according to claim 1, wherein in the fourth step, the aluminum hydroxide oxide film is heat-treated in a non-oxidizing atmosphere.

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