JP5975841B2 - Manufacturing method of photovoltaic device and photovoltaic device - Google Patents

Description

  The present invention relates to a photovoltaic device manufacturing method and a photovoltaic device, and more particularly to a heterojunction photovoltaic device in which a p layer is disposed on one surface of a crystalline silicon substrate and an n layer is disposed on the other surface. The present invention relates to a method for manufacturing a power element and a photovoltaic element.

  2. Description of the Related Art In recent years, development of crystalline silicon photovoltaic devices (hereinafter sometimes simply referred to as photovoltaic devices) using crystalline silicon substrates such as single crystal silicon substrates and polycrystalline silicon substrates has been actively conducted. . In particular, the one using a single crystal silicon substrate has excellent photovoltaic efficiency, and the spread of silicon wafers has been progressing with the price reduction. Further improvement in photovoltaic efficiency is required for residential use in urban areas with limited installation area.

  The heterojunction cell is a combination of a crystalline silicon substrate and an amorphous silicon thin film, and has a higher open-circuit voltage and higher photovoltaic efficiency than a general crystalline silicon photovoltaic device. . Since a thin film amorphous silicon is formed on a crystalline silicon substrate, this technique is also called a hybrid type.

  Specifically, for example, an i-type amorphous silicon layer on the surface side of an n-type single crystal silicon substrate, a p-type amorphous silicon layer serving as a positive electrode thereon, a light-transmitting light-receiving surface-side electrode, and a current collector The electrodes are sequentially formed, and an n-type amorphous silicon layer serving as a negative electrode, a back electrode, and a collecting electrode are sequentially formed on the back surface side.

  In general, in a photovoltaic device having a structure in which a semiconductor layer for generating photovoltaic power is sandwiched between two electrodes, the semiconductor layer absorbs more light, so the electrodes formed on both sides of the semiconductor layer are A translucent electrode material is used. Of course, the light receiving surface side electrode formed on the light receiving surface side of the photovoltaic element must be translucent, but a translucent material is also used for the back electrode formed on the back surface side. This is to prevent the metal component of the collecting electrode made mainly of metal from diffusing into the semiconductor layer, and to efficiently confine light that has passed through the semiconductor layer without being absorbed by the semiconductor layer.

A photovoltaic device having a laminated structure of a translucent electrode, an amorphous or microcrystalline conductive semiconductor layer, and a crystalline semiconductor substrate at least on the light receiving surface side of the substantially plate-like photovoltaic element from the surface on the surface side. In a power element, a technique using a translucent material having a carrier density of less than 6 × 10 ²⁰ / cm ³ as a translucent electrode is disclosed (for example, Patent Document 1).

  This is because the carrier density of the translucent electrode is related to the light absorptance of the translucent electrode, particularly the infrared light absorption of 800 nm or more. Generally, when the carrier density of the translucent electrode increases, the light absorption rate of infrared light of 800 nm or more increases. Therefore, when using a translucent electrode for a photovoltaic element, it is necessary to reduce carrier density as much as possible.

JP 2002-299658 A

  However, when the carrier density is reduced, there is a problem that the resistivity of the translucent electrode increases. If the resistivity of the transparent electrode used in the photovoltaic element increases, the series resistance of the photovoltaic element increases and the fill factor decreases, so the conversion efficiency of the photovoltaic element decreases. There was a problem of doing.

  The present invention has been made in view of the above, and reduces the increase in series resistance while reducing the light absorption of the translucent electrode, and obtains a photovoltaic device having high conversion efficiency and a method for manufacturing the photovoltaic device. With the goal.

In order to solve the above-described problems and achieve the object, the present invention provides a process of forming a second conductive type amorphous or microcrystalline semiconductor layer on a first surface of a first conductive type crystalline semiconductor substrate. Forming a first electrode on the second conductive type amorphous or microcrystalline semiconductor layer; and forming a second electrode on the second surface of the first conductive type crystalline semiconductor substrate. A process for forming a photovoltaic device, wherein at least one of the steps of forming the first and second electrodes is a step of forming a translucent electrode and a step of forming a collecting electrode The step of forming the translucent electrode includes: forming a translucent initial layer using zinc oxide as a base material; and using the translucent initial layer as a seed, the same zinc oxide as the seed. A translucent conductive film having a crystal grain size larger than that of the translucent initial layer is obtained by crystal growth of a translucent conductive film as a base material. Characterized in that it comprises a step of forming.

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that the resistivity and light absorption of the translucent electrode used for a photovoltaic element can be reduced, and the conversion efficiency of a photovoltaic element can be improved by it. .

FIG. 1 is a cross-sectional view showing the structure of the photovoltaic element according to the first embodiment of the present invention. FIGS. 2-1 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 1 of this invention. FIGS. FIGS. 2-2 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 1 of this invention. FIGS. FIGS. 2-3 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 1 of this invention. FIGS. FIGS. 2-4 is sectional drawing which shows the manufacturing process of the photovoltaic device concerning Embodiment 1 of this invention. FIGS. FIGS. 2-5 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 1 of this invention. FIGS. FIG. 3 is a flowchart showing manufacturing steps of the photovoltaic element according to the first embodiment of the present invention. FIG. 4 is a flowchart showing a main part of the manufacturing process of the photovoltaic element according to the first embodiment of the present invention. FIG. 5 is a flowchart showing a main part of the manufacturing process of the photovoltaic element according to the second embodiment of the present invention. FIG. 6 is a sectional view showing the structure of the photovoltaic element according to the third embodiment of the present invention. FIGS. 7-1 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 3 of this invention. FIGS. 7-2 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 3 of this invention. 7-3 is sectional drawing which shows the manufacturing process of the photovoltaic element concerning Embodiment 3 of this invention. FIG. 8 is a flowchart showing manufacturing steps of the photovoltaic element according to the third embodiment of the present invention.

  Below, the manufacturing method of the photovoltaic device concerning this invention and embodiment of a photovoltaic device are demonstrated in detail based on drawing. 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.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing the structure of the photovoltaic element according to the first embodiment of the present invention. In contrast to the n-type single crystal silicon substrate 1 having a concavo-convex structure called texture on the surface of the substrate, the amorphous silicon layer 2 and the first electrode 4 are sequentially formed on the first surface 1A on the light receiving surface side. The amorphous silicon layer 3 and the second electrode 5 are sequentially laminated on the second surface 1B on the back surface side. Here, the first electrode 4 is formed by sequentially laminating a first translucent electrode 4t and a grid-shaped first collector electrode 4m, and the second electrode 5 is composed of a second translucent electrode 5t, And the 2nd current collection electrode 5m is laminated | stacked and formed one by one. The amorphous silicon layer 2 on the first surface 1A side includes an i-type amorphous silicon layer 2i and a p-type amorphous silicon layer 2p, and the amorphous silicon layer 3 on the second surface 1B side is an i-type. It consists of an amorphous silicon layer 3i and an n-type amorphous silicon layer 3n. Light to be subjected to photoelectric conversion is incident from the first surface 1A side where the p-type amorphous silicon layer 2p and the i-type amorphous silicon layer 2i are formed. The translucent conductive film 4t formed on the light receiving surface side 1A is formed of a two-layer film, and the movement of the translucent conductive film 4t2 on the upper layer side compared to the translucent initial layer 4t1 on the substrate side, that is, the lower layer side. It is characterized by a large degree.

  In the photovoltaic device configured as described above, the pn junction surface (the n-type single crystal silicon substrate 1 and the p-type amorphous silicon layer 2p between the n-type single crystal silicon substrate 1 and the p-type amorphous silicon layer 2p) from the surface side of the photovoltaic device. When light is irradiated onto the bonding surface, holes and free electrons are generated. Due to the action of the electric field at the pn junction, the generated free electrons move toward the n-type single crystal silicon substrate 1, and the holes move toward the p-type amorphous silicon layer 2p. As a result, the n-type single crystal silicon substrate 1 has excessive electrons, and the p-type amorphous silicon layer 2p has excessive holes to generate photovoltaic power. This photovoltaic power is generated in the direction in which the pn junction is forward-biased, and the second translucent electrode 5t on the back surface side connected to the n-type amorphous silicon layer 3n becomes a negative pole, and the p-type amorphous The first translucent electrode 4t connected to the silicon layer 2p becomes a positive electrode, and a current flows through an external circuit (not shown).

  According to the above configuration, the light in the first translucent electrode 4t is increased without increasing the contact resistance between the first translucent electrode 4t on the first surface 1A side and the p-type amorphous silicon layer 2p. A photovoltaic device that reduces the amount of absorption and increases the current density can be obtained.

Hereinafter, the manufacturing process of the photovoltaic element according to the first embodiment of the present invention will be described.
First, an i-type amorphous silicon layer 2i and a p-type amorphous silicon layer 2p are sequentially formed on the light-receiving surface side 1A of an n-type single crystal silicon substrate 1 having a texture formed on the surface of the substrate. The i-type amorphous silicon layer 2i has a passivation function of the n-type single crystal silicon substrate 1, and dopants are mixed between the amorphous silicon layer formed thereon and the single crystal silicon substrate. To prevent this.

  Subsequently, an i-type amorphous silicon layer 3 i and an n-type amorphous silicon layer 3 n are sequentially formed on the back side 1 </ b> B of the n-type single crystal silicon substrate 1. As a method for forming the i-type amorphous silicon layer 2i, the i-type amorphous silicon layer 3i, the p-type amorphous silicon layer 2p, and the n-type amorphous silicon film 3n, a plasma CVD method is suitable.

  Next, a translucent initial layer 4t1 and a translucent conductive film 4t2 are sequentially formed on the p-type amorphous silicon layer 2p. As a method for forming the translucent initial layer 4t1 and the translucent conductive film 4t2, sputtering, ion plating, vapor deposition, or the like can be used. Then, recrystallization occurs through the annealing step, and the light-transmitting conductive layer 4t2 having a larger particle diameter grows using the light-transmitting initial layer 4t1 as a seed. The translucent initial layer 4t1 becomes a contact layer electrically connected to the p-type amorphous silicon layer 2p.

  Next, the second translucent electrode 5t is formed on the n-type amorphous silicon layer 3n. As a method for forming the second light-transmissive electrode 5t, sputtering, ion plating, vapor deposition, or the like can be used. The second translucent electrode 5t becomes a contact layer electrically connected to the n-type amorphous silicon layer 3n.

  Next, a grid-shaped first current collecting electrode 4m and a second current collecting electrode 5m are formed immediately above the light transmissive conductive film 4t2 and the second light transmissive electrode 5t, respectively. By forming the first current collecting electrode 4m and the second current collecting electrode 5m, a heterojunction photovoltaic element (solar cell) is completed.

  Hereafter, the manufacturing process of the photovoltaic element of Embodiment 1 of this invention is demonstrated in detail. FIGS. 2-1 to 2-5 are manufacturing process diagrams of this photovoltaic element, and FIG. 3 is a flowchart showing the manufacturing process of the photovoltaic element.

  Here, the n-type single crystal silicon substrate 1 is used as the substrate, but since it is usually cut out by slicing an ingot obtained by pulling, a natural oxide film and structural defects on the surface, It is contaminated with metal. Therefore, the n-type single crystal silicon substrate 1 used here is cleaned and damaged layer etched (S1001).

  After cleaning and damage layer etching are performed on the n-type single crystal silicon substrate 1, gettering is performed to remove impurities in the n-type single crystal silicon substrate 1 (S1002). In the gettering step, impurities are segregated in a phosphorus glass layer formed by thermal diffusion of phosphorus at a processing temperature of about 1000 ° C., and the phosphorus glass layer is etched with hydrogen fluoride or the like.

  After gettering, anisotropic etching is performed by immersing in an alkaline aqueous solution such as KOH (potassium hydroxide), NaOH (sodium hydroxide), TMAH (tetramethylammonium hydroxide) for the purpose of reducing light reflection loss on the substrate surface. By using this method, fine pyramidal irregularities are formed on the surface of the n-type single crystal silicon substrate 1 (S1003). In FIGS. 1, 2-1 to 2-5, the concavo-convex shape is not drawn but is made flat to facilitate understanding of the configuration of the present embodiment.

  After texture formation, substrate cleaning is performed to remove particles, organic matter contamination, and metal contamination on the surface of the n-type single crystal silicon substrate 1 serving as a heterojunction interface (S1004). For the cleaning, so-called RCA cleaning, SPM cleaning (sulfuric acid hydrogen peroxide water cleaning), HPM cleaning (hydrochloric acid hydrogen peroxide water cleaning), DHF cleaning (dilute hydrofluoric acid cleaning), alcohol cleaning, and the like are used.

In the RCA cleaning, first, the n-type single crystal silicon substrate 1 is put in a dilute hydrofluoric acid aqueous solution (HF) to elute a thin silicon oxide film. At this time, the silicon oxide film is eluted, and at the same time, many foreign substances adhering to the silicon oxide film are removed at the same time. Further, organic substances, particles and the like are removed with ammonia (NH ₄ OH) + hydrogen peroxide (H ₂ O ₂ ). Next, the metal is removed with hydrochloric acid (HC1) + hydrogen peroxide (H ₂ O ₂ ), and finally, finishing is performed with ultrapure water.

After performing substrate cleaning using any of the above-described cleaning methods, in order to form a heterojunction and a pn, nn ⁺ junction, a semiconductor of each conductivity type is sequentially formed on the n-type single crystal silicon substrate 1. Form a layer. The n-type single crystal silicon substrate 1 obtained through the texture forming step and the cleaning step had a thickness of 100 to 500 μm.

First, as shown in FIG. 2A, an i-type amorphous silicon layer 2i having a thickness of about 1 to 10 nm is formed on the first main surface 1A of the n-type single crystal silicon substrate 1 using a plasma CVD method, and A p-type amorphous silicon layer 2p having a thickness of about 5 to 50 nm is deposited in this order (S1005: i-type amorphous silicon layer formation, S1006: p-type amorphous silicon layer formation). In forming the i-type amorphous silicon layer 2i, SiH ₄ (silane) gas and H ₂ (hydrogen) gas are introduced into the vacuum chamber. In forming the p-type amorphous silicon layer 2p, SiH ₄ gas, H ₂ gas, and B ₂ H ₆ (diborane) gas are introduced into the vacuum chamber. Here, the i-type amorphous silicon layer 2i and the p-type amorphous silicon layer 2p are each amorphous, but microcrystalline silicon may be used. Here, the i-type amorphous silicon layer 2i has a passivation action of the n-type single crystal silicon substrate 1, and also includes a p-type amorphous silicon layer 2p formed on the n-type single crystal silicon substrate 1 and the n-type single crystal silicon substrate 1. This prevents dopants from being mixed with each other.

Subsequently, as shown in FIG. 2B, an i-type amorphous silicon layer 3i having a thickness of about 1 to 10 nm is formed on the second surface 1B side of the n-type single crystal silicon substrate 1 using a plasma CVD method. An n-type amorphous silicon layer 3n having a thickness of about 5 to 50 nm is formed in this order (S1007: i-type amorphous silicon layer formation, S1008: n-type amorphous silicon layer formation). In forming the i-type amorphous silicon layer 3i, SiH ₄ (silane) gas and H ₂ (hydrogen) gas are introduced into the vacuum chamber. In forming the n-type amorphous silicon layer 3n, SiH ₄ gas, H ₂ gas, and PH ₃ (phosphine) gas are introduced into the vacuum chamber. Further, although the i-type amorphous silicon layer 3i and the n-type amorphous silicon layer 3n are each amorphous, microcrystalline silicon may be used. The order of forming the p-type amorphous silicon layer 2p and the n-type amorphous silicon layer 3n may be switched.

  Next, as shown in FIG. 2-3, a light-transmitting initial layer 4t1 is formed on the p-type amorphous silicon layer 2p (S1009a: light-transmitting initial layer formation). Then, as shown to FIGS. 2-4, the translucent conductive film 4t2 is formed (S1009b: Translucent conductive film formation). In this way, the first translucent electrode 4t composed of the two-layer film of the translucent initial layer 4t1 and the translucent conductive film 4t2 is formed (S1009: first translucent electrode formation). The first translucent electrode 4t serves as a contact layer electrically connected to the p-type amorphous silicon layer 2p.

As a material of the translucent initial layer 4t1 and the translucent conductive film 4t2, metal oxide such as ZnO (zinc oxide), In ₂ O ₃ (indium oxide), SnO ₂ (tin oxide) and TiO ₂ (titanium oxide) is used. A material is desirable, but ZnO is most desirable in view of the cost of the translucent electrode. These oxides have n-type semiconductor properties. Moreover, in order to improve electroconductivity to the said metal oxide, you may use what contained the dopant. The types of dopants are Al, Ga, In, Ti, B and F for ZnO, Sn, Ti, Zn, Zr, Hf and W for In ₂ O ₃ , and In, Ti, Sb and F for SnO _2. TiO ₂ is preferably Nb, Ta and W. As a method for forming the light-transmitting conductive film 4t2, there are a chemical vapor phase method such as plasma CVD and a physical vapor phase method such as sputtering and ion plating. In mass production, sputtering, ion plating and vapor deposition are used. Is desirable. Further, it is desirable to remove the natural oxide film formed on the surface of the p-type amorphous silicon layer 2p with a hydrofluoric acid-based solution or the like before forming the translucent initial layer 4t1.

  Next, as shown in FIG. 2-5, a second translucent electrode 5t made of a translucent conductive film is formed on the n-type amorphous silicon layer 3n (S1010: second translucent light). Electrode formation). The second translucent conductive film 5t becomes a contact electrode layer electrically connected to the n-type amorphous silicon layer 3n. Similarly, sputtering, ion plating, vapor deposition, or the like can be used to form the second light-transmissive electrode 5t. Here, nitrogen may be introduced into the vacuum chamber at the time of forming the second translucent electrode 5t on the second surface 1B side. In the introduction method, the flow rate of nitrogen is gradually increased so that the introduction amount increases from the start to the end of the formation of the second translucent electrode 5t. By this method, the carrier concentration of the second translucent electrode 5t can be reduced without oxidizing the surface of the n-type amorphous silicon layer 3n. Thereby, it is possible to reduce the contact resistance while improving the translucency on the second surface 1B side.

  Next, the first light-collecting electrode 4m and the second current-collecting electrode 5m in the form of a grid are respectively formed on the first light-transmissive electrode 4t located on the light-receiving surface side and the second light-transmissive electrode 5t on the back surface side. Form. The heterojunction photovoltaic element (solar cell) shown in FIG. 1 is formed by forming the grid-like first collector electrode 4m and the second collector electrode 5m (S1011: collector electrode formation). Cell) is completed.

  Here, as shown in the flowchart of FIG. 4, in the first translucent electrode forming process on the light-receiving surface side, first, in the first sputtering process S1091a, the first layer that becomes the translucent initial layer 4t1 is formed. In the second sputtering step S1091b, a second layer to be a light-transmitting conductive film is formed. Then, through the second translucent electrode forming step S1010, the first collector electrode 4m and the second collector electrode 5m are screen-printed with silver paste (silver paste coating: S1011a) and fired. In the annealing step for firing the current collecting electrode, the zinc oxide is recrystallized using the light-transmitting initial layer 4t1 as a seed to form a light-transmitting conductive film 4t2 (annealing: S1011S).

  In this way, the first light-transmitting electrode 4t positioned on the light-receiving surface side, the second light-transmitting electrode 5t on the back surface side, and the grid-shaped first current collecting electrode 4m and second current collecting electrode, respectively. At the same time as 5 m is formed, the translucent initial layer 4t1 and the translucent conductive film 4t2 are improved in film quality by recrystallization and become electrodes having excellent contact properties.

  In the embodiment, the plasma CVD method is used to form the i-type amorphous silicon layer 2i and the i-type amorphous silicon layer 3i. However, other methods such as a CatCVD method may be used. The CatCVD method is effective in that the plasma damage is small compared to the plasma CVD method. Before forming the i-type amorphous silicon layer 2i and the i-type amorphous silicon layer 3i, it is desirable to remove the natural oxide film formed on the n-type single crystal silicon substrate 1 with a hydrofluoric acid-based solution.

By the way, as a material of the translucent conductive film 4t2 and the translucent initial layer 4t1, metals such as ZnO (zinc oxide), In ₂ O ₃ (indium oxide), SnO ₂ (tin oxide) and TiO ₂ (titanium oxide) are used. Although an oxide is desirable, ZnO is most desirable in view of the cost as a translucent electrode. These oxides have n-type semiconductor properties. Moreover, in order to improve electroconductivity to the said metal oxide, you may use what contained the dopant. As the kind of dopant, Zn, Al, Ga, In, Ti, B and F are desirable. Further, Sn, Ti, Zn, Zr, Hf and W are desirable for In ₂ O ₃ , and In, Ti, Sb and F are desirable for SnO ₂ . Furthermore, Nb, Ta and W are desirable for TiO ₂ . As a method for forming the light-transmitting conductive film 4t2, there are a chemical vapor phase method such as plasma CVD and a physical vapor phase method such as sputtering and ion plating. In mass production, sputtering, ion plating and vapor deposition are used. Is desirable. Further, it is desirable to remove the natural oxide film formed on the surface of the p-type amorphous silicon layer 2p with a hydrofluoric acid-based solution or the like before forming the translucent initial layer 4t1.

  As the material of the second light transmissive electrode 5t, the same material as that of the light transmissive conductive film 4t2 and the light transmissive initial layer 4t1 is desirable. As a method for forming the second light-transmissive electrode 5t, there are a chemical vapor deposition method such as plasma CVD and a physical vapor deposition method such as sputtering and ion plating. In mass production, sputtering and ion plating are used. And vapor deposition is desirable.

  In general, it is known that a film formed by a chemical vapor phase method and a physical vapor phase method is strongly influenced by a base substrate. For example, the zinc oxide film formed by the above formation method is known to have (002) plane preferred orientation, but when formed on a substrate such as glass or other amorphous and different orientation, Due to the influence, the initial layer portion of the film does not have (002) plane preferred orientation and the crystal grain size becomes small. Then, the crystal grain boundary increases and the mobility of the film decreases. In addition, when a substrate having an orientation close to that of zinc oxide, such as a sapphire substrate, is used, the crystal grain size of the initial layer portion of the film is large, the crystal grain boundary is reduced, and the mobility of the film is increased. Further, there is a method of increasing the formation temperature in order to increase the mobility of the film. However, since the amorphous silicon layer on the photovoltaic element is recrystallized at 220 ° C. or higher, the transparent electrode is set at 220 ° C. In the following, it is desirable to grow the crystal at 200 ° C. or lower.

  Further, in the case where a light-transmitting conductive film is formed on an amorphous substrate such as glass and a substrate having different orientation under conditions that increase the grain boundary, the metal oxide metal that becomes the light-transmitting conductive film It is necessary to bring the oxygen ratio close to the ideal value. For example, in the case of zinc oxide, oxygen is more likely to escape from the film than zinc, so it is necessary to add oxygen during the formation of the film. However, adding oxygen significantly reduces the carrier density, and light The series resistance of the electromotive force element increases, and the conversion efficiency decreases.

  For this reason, in the present embodiment, a light-transmitting initial layer 4t1 is formed on the p-type amorphous silicon layer 2p of the photovoltaic element, and the light-transmitting initial layer 4t1 is used as a seed for the light-transmitting conductive film. Grow 4t2. The crystal grain size and mobility of the first translucent electrode 4t are increased. As for the formation conditions of the light-transmitting initial layer 4t1, in the case of film formation by sputtering, the atmospheric pressure, the oxygen concentration in the atmosphere, the impurity doping concentration, and the like are changed as compared with the light-transmitting conductive film 4t2. Specifically, the atmospheric pressure is increased during the formation of the light-transmitting initial layer 4t1, a dense film is formed, and the light-transmitting initial layer 4t1 is used as a seed to reduce the atmospheric pressure, so that the light-transmitting conductive film is formed. 4t2 is formed. Alternatively, the oxygen concentration is increased during the formation of the translucent initial layer 4t1, and is decreased in the translucent conductive film 4t2. Alternatively, a method of decreasing the impurity doping concentration when forming the light-transmitting initial layer 4t1 and increasing the impurity doping concentration is used for the light-transmitting conductive film 4t2.

  The grid-shaped first current collecting electrode 4m is formed directly on the first translucent electrode 4t using a method such as sputtering vapor deposition, electron beam vapor deposition, or screen printing. Since the first light transmitting electrode 4t also has a function as a current collecting electrode, the first current collecting electrode 4m is not necessarily formed on the entire surface of the first light transmitting electrode 4t. As a material of the metal electrode, Ag (silver), Al (aluminum), Ti (titanium), Mo (molybdenum), W (tungsten), or the like is desirable.

  Further, after the first current collecting electrode 4m is formed, an antireflection film may be formed on the translucent electrode 4t in order to reduce the light reflectance of the light receiving surface. As the antireflection film, a silicon nitride film, a silicon oxide film, a magnesium fluoride film, or the like is used. In this case, the film thicknesses of the antireflection film and the translucent electrode 4t are adjusted so that the short-circuit current of the photovoltaic element is maximized. The antireflection film may be directly formed on the translucent electrode 4t in advance before forming the first current collecting electrode 4m.

  The second current collecting electrode 5m is formed directly on the second light transmitting electrode 5t by using a method such as sputtering vapor deposition, electron beam vapor deposition, or screen printing. Since the second light transmitting electrode 5t also has a function as a current collecting electrode, the second current collecting electrode 5m is not necessarily formed on the entire surface of the second light transmitting electrode 5t. As a material of the metal electrode, Ag (silver), Al (aluminum), Ti (titanium), Mo (molybdenum), W (tungsten), or the like is desirable.

  In this case, when the light incident from the light receiving surface of the photovoltaic element reaches the back surface side, the reflected light cannot be used without the second current collecting electrode 5m. For this reason, it is desirable to install a reflective member such as a white plate on the back side when modularizing the photovoltaic element in which the second current collecting electrode 5m is partially formed.

  According to the photovoltaic device of this embodiment, since the resistance at the junction interface between the p-type amorphous silicon layer 2p and the light-transmitting initial layer 4t1 is small, the series resistance of the photovoltaic device is reduced and the fill factor Will increase. Furthermore, since the carrier concentration is reduced, the amount of light absorbed by the photovoltaic device is increased and the current density is increased. As a result, the photoelectric conversion efficiency of the photovoltaic element is improved.

  Hereinafter, the present invention will be specifically described by way of examples.

Example 1.
In Example 1, a photovoltaic device was produced by the method of Embodiment 1, and the characteristics were evaluated. The structure of the photovoltaic element according to Example 1 of the present invention is as shown in the cross-sectional view of FIG. As the n-type single crystal silicon substrate 1, a square wafer having a crystal orientation of the first surface 1A of (100) and dimensions of 10 cm × 10 cm × t 200 μm was used. The manufacturing process is as follows.

  First, a pyramidal texture structure was formed on the substrate surface with NaOH aqueous solution. After the substrate cleaning, an i-type amorphous silicon layer 2i and a p-type amorphous silicon layer 2p are sequentially formed on the first surface 1A side of the n-type single crystal silicon substrate 1 by the CVD method, and the second surface 1B On the side, an i-type amorphous silicon layer 3i and an n-type amorphous silicon layer 3n were sequentially formed by a CVD method. Table 1 is a list of the composition, pressure, and input power of the gas introduced into the deposition chamber under the deposition conditions of the formation film.

  Next, a second translucent electrode 5t made of zinc oxide was formed on the n-type amorphous silicon layer 3n by RF sputtering to a thickness of 70 nm. Table 2 shows doping conditions and other formation conditions for zinc oxide.

  Next, a light-transmitting initial layer 4t1 and a light-transmitting conductive film 4t2 made of zinc oxide were sequentially formed by RF sputtering on the p-type amorphous silicon layer 2p on the first surface 1A side. Table 2 shows the formation conditions. Table 3 shows conditions for forming the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2. As shown in Table 3, in Example 1, only the oxygen concentration of the translucent initial layer 4t1 was changed. In addition, Comparative Example 1 is obtained by forming only the translucent conductive film 4t2 without forming the translucent initial layer 4t1. In Examples 1-1, 1-2, and 1-3, the oxygen concentration of the translucent initial layer 4t1 was changed to 0%, 3%, and 10%, respectively. All the Al doping concentrations of the light-transmitting initial layer were 1%, the chamber pressure was 0.3 Pa, and the film thickness was 10 nm. All the translucent conductive films 4t2 had an oxygen concentration of 0%, an Al doping concentration of 1%, a chamber pressure of 0.16 Pa, and a film thickness of 60 nm.

  Finally, the grid-shaped first collector electrode 4m and the second collector electrode 5m were formed by screen printing. The material was Ag paste, and after printing, it was dried at 200 ° C. for 1 hour in a drying furnace. In addition, in order to evaluate the single-film characteristics of the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 in Examples and Comparative Examples, the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 were formed on a glass substrate. . After the formation, annealing was performed at 200 ° C. for 1 hour in an argon atmosphere.

  Table 4 is a table | surface which shows the single film | membrane characteristic on a glass substrate in Example 1-1, 1-2, 1-3, and the comparative example 1, and a photovoltaic element characteristic. All values described as normalization are standardized with the value of Comparative Example 1 as 1.

  As a single film characteristic on a glass substrate, Hall effect measurement was performed, and resistivity, carrier density, and hole mobility were evaluated. Furthermore, the half-width (FWHM) of the 002 plane which is the preferential orientation plane of zinc oxide was measured using an X-ray diffractometer.

  As photovoltaic device characteristics, short-circuit current density (Jsc), fill factor (FF), and conversion efficiency (Eff) were evaluated using a solar simulator.

  As shown in Table 4, the normalized mobility exceeds 1 in Examples 1-2 and 1-3. Further, FWHM is reduced as compared with Comparative Example 1. From the above, it is presumed that the formation of the translucent initial layer 4t1 increases the crystal grain size of the translucent conductive film 4t2 and increases the mobility. In addition, the carrier concentration is lower than that of the comparative example 1 by forming the translucent initial layer 4t1. This is considered to be because it was formed at a higher pressure than the translucent conductive film 4t2.

  As described above, the resistivity and carrier concentration in Examples 1-2 and 1-3 are lower than those in Comparative Example 1, and the short-circuit current density and curve exceeding Comparative Example 1 in terms of photovoltaic element characteristics. Factors and conversion efficiency could be obtained. Also in Example 1-1, the fill factor and the conversion efficiency were slightly lowered, but a short-circuit current density exceeding Comparative Example 1 could be obtained.

Example 2
In Example 2, a photovoltaic device was produced by the method of Embodiment 1, and the characteristics were evaluated. Except for the formation conditions of the translucent conductive film 4t2 and the translucent initial layer 4t1, all the formation conditions were the same as in Example 1. A zinc oxide light-transmitting initial layer 4t1 and a light-transmitting conductive film 4t2 were sequentially formed on the p-type amorphous silicon layer 2p by RF sputtering. Table 5 shows conditions for forming the translucent initial layer 4t1 and the translucent electrode 4t2. As shown in Table 5, in Example 2, only the Al doping concentration of the translucent initial layer 4t1 was changed. In addition, a comparative example 1 is the same as the first example except that the transparent initial layer 4t1 is not formed and only the transparent conductive film 4t2 is formed.

  In addition, in order to evaluate the single-film characteristics of the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 in Examples and Comparative Examples, the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 were formed on a glass substrate. . After the formation, annealing was performed at 200 ° C. for 1 hour in an argon atmosphere. Table 6 is a table | surface which shows the single film | membrane characteristic on a glass substrate and photovoltaic element characteristic in Examples 2-1, 2-2, 2-3 and Comparative Example 1. All values described as normalization are standardized with the value of Comparative Example 1 as 1.

  As shown in Table 6, the normalized mobility exceeded 1 in Examples 2-1, 2-2, and 2-3. Further, FWHM is reduced as compared with Comparative Example 1. From the above, it is presumed that the formation of the translucent initial layer 4t1 increases the crystal grain size of the translucent conductive film 4t2 and increases the mobility. In addition, the carrier concentration is lower than that of the comparative example 1 by forming the translucent initial layer 4t1. This is considered to be because it was formed at a higher pressure and a higher oxygen concentration than the translucent conductive film 4t2.

  From the above, the resistivity and carrier concentration in Examples 2-1, 2-2, and 2-3 are lower than those in Comparative Example 1, and the short-circuit current density that exceeds Comparative Example 1 in terms of photovoltaic device characteristics. The curve factor and the conversion efficiency were obtained. In particular, in Example 2-3 in which the Al doping concentration of the translucent initial layer 4t1 was 3%, the conversion efficiency was improved by 7% compared with Comparative Example 1.

Example 3
In Example 3, a photovoltaic device was produced by the method of Embodiment 1, and the characteristics were evaluated. Except for the formation conditions of the translucent conductive film 4t2 and the translucent initial layer 4t1, all the formation conditions were the same as in Example 1.

  A zinc oxide light-transmitting initial layer 4t1 and a light-transmitting conductive film 4t2 were sequentially formed on the p-type amorphous silicon layer 2p by RF sputtering. Table 7 shows conditions for forming the translucent initial layer 4t1 and the translucent conductive film 4t2. As shown in Table 7, in Example 3, only the pressure at the time of forming the translucent initial layer 4t1 was changed. In addition, a comparative example 1 is the same as the first example except that the transparent initial layer 4t1 is not formed and only the transparent conductive film 4t2 is formed.

  In Table 7, the formation pressure of the translucent conductive film 4t2 is set to be the same as or lower than the formation pressure of the translucent initial layer 4t1. In film formation by sputtering, it is said that a dense film can be formed as the pressure is lowered. For this reason, the translucent conductive film 4t2 formed at a high pressure on the translucent initial layer 4t1 formed at a low pressure is a dense film compared to the translucent conductive film 4t2 formed without a translucent initial layer. Therefore, high mobility of the translucent electrode film cannot be expected. For this reason, in all the examples, the light-transmitting conductive film 4t2 formed at a low pressure was formed on the light-transmitting initial layer 4t1 formed at a high pressure.

  In addition, in order to evaluate the single-film characteristics of the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 in Examples and Comparative Examples, the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 were formed on a glass substrate. . After the formation, annealing was performed at 200 ° C. for 1 hour in an argon atmosphere.

  Table 8 is a table | surface which shows the single film | membrane characteristic on a glass substrate and photovoltaic element characteristic in Examples 3-1, 3-2, 3-3, and the comparative example 1. FIG. All values described as normalization are standardized with the value of Comparative Example 1 as 1.

  As shown in Table 8, the normalized mobility exceeds 1 in Examples 3-2 and 3-3. Further, FWHM is reduced as compared with Comparative Example 1. From the above, it is presumed that the formation of the translucent initial layer 4t1 increases the crystal grain size of the translucent conductive film 4t2 and increases the mobility. In addition, the carrier concentration is lower than that of the comparative example 1 by forming the translucent initial layer 4t1. This is considered to be because it was formed at a higher pressure and a higher oxygen concentration than the translucent electrode of Comparative Example 1.

  As described above, in Examples 3-2 and 3-3, the resistivity is lower than that in Comparative Example 1, and in Examples 3-1, 3-2, and 3-3, the carrier concentration is compared with Comparative Example 1. It is falling. Therefore, the short-circuit current density and the conversion efficiency exceeding Comparative Example 1 were obtained in the photovoltaic device characteristics.

  Note that the annealing temperature for recrystallization is 150 to 220 ° C., preferably 200 ° C. or less. In order to prevent deterioration of the amorphous silicon layer, the upper limit is preferably low. Indium oxide is crystallized at a relatively low temperature (150 ° C. or more). However, regarding zinc oxide, the higher the temperature, the higher the crystallinity, so it is desirable to increase the annealing temperature.

Embodiment 2. FIG.
In the first embodiment, in forming the first light-transmitting electrode, both the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 are formed by the sputtering method, and recrystallized in the annealing step of the current collecting electrode. However, in this embodiment, as shown in the flowchart of the main part in FIG. 5, both the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 are formed by the CVD method. Is.

  That is, as shown in FIG. 5, after the formation of the n-type amorphous silicon layer, in the first translucent electrode forming step S1009, first, the oxygen concentration is set to 3% and the Al doping concentration is set to 1.00%. The optical initial layer 4t1 is formed (first CVD process: S1092a).

  Next, a light-transmitting conductive film 4t2 having an oxygen concentration of 0% and an Al doping concentration of 1.00% is formed using the light-transmitting initial layer 4t1 as a seed (second CVD step: S1092b). At this time, the translucent conductive film 4t2 having good orientation and large particle size is formed using the translucent initial layer 4t1 as a seed. The translucent conductive film 4t formed on the light receiving surface side 1A is formed of a two-layer film, and the movement of the translucent conductive film 4t2 on the upper layer side compared to the translucent initial layer 4t1 on the substrate side, that is, the lower layer side. It is characterized by increasing degrees. Therefore, the point which can obtain the translucent electrode of a desired characteristic without an annealing process is a point different from the 1st translucent electrode of Embodiment 1. FIG. Since the formation of the second light-transmitting electrode (S1010) and the formation of the collecting electrode (S1011) are the same as those in Embodiment 1, the description thereof is omitted here. The whole is the same as the solar cell shown in FIG. 1, and the process cross-sectional views are also the same as those shown in FIGS. 2-1 to 2-5.

  According to the embodiment, the resistivity and light absorption of the translucent electrode can be reduced, and thereby the conversion efficiency of the photovoltaic element can be improved.

  In this step, the collector electrode includes an annealing step as in the first embodiment. However, the collector electrode may be used by forming a metal electrode by a sputtering method without using the annealing step. .

  Also in the second embodiment, as in the first embodiment, the conditions of the light-transmitting conductive film are changed with respect to the light-transmitting initial layer for various conditions such as oxygen concentration, Al doping concentration, and atmospheric pressure. Thus, desired characteristics can be obtained.

  Furthermore, the first CVD step S1092a for forming the light-transmitting initial layer 4t1 and the second CVD step S1092b for forming the light-transmitting conductive film 4t2 are gradually performed without breaking the vacuum in the same chamber. The composition gradient layer 4g corresponding to the translucent initial layer 4t1 and the translucent conductive film 4t2 may be formed by changing the composition.

Embodiment 3 FIG.
In the first and second embodiments, a two-layer structure of the light-transmitting initial layer 4t1 and the light-transmitting conductive film 4t2 is used for forming the first light-transmitting electrode. In this embodiment, FIG. As shown in the overall configuration, a gradient composition layer 4g having a different composition in the film thickness direction is formed in place of the light-transmitting electrode having a two-layer structure.

  Hereafter, the manufacturing process of the photovoltaic element of Embodiment 3 of this invention is demonstrated in detail. FIGS. 7-1 to 7-3 are manufacturing process diagrams of this photovoltaic element, and FIG. 8 is a flowchart showing the manufacturing process of the photovoltaic element.

  That is, as shown in the flowchart in FIG. 8, the process up to the step of forming an n-type amorphous silicon layer in step S1008 is the same as that in the first embodiment, and after step S1008, the first transparent electrode forming step S1009 is performed. Then, a composition gradient layer is formed (S1009g). In this step, first, the oxygen concentration is 3%, the oxygen concentration is gradually decreased, and finally the oxygen is 0%, the Al doping concentration is 1.00%, and the first light-transmitting property composed of the composition gradient layer 4g of 70 nm. A conductive film is formed (formation of a composition gradient layer: S1009g).

  That is, as shown in FIG. 7A, an i-type amorphous silicon layer 2i having a thickness of about 1 to 10 nm is formed on the first main surface 1A of the n-type single crystal silicon substrate 1 using a plasma CVD method. A p-type amorphous silicon layer 2p having a thickness of about 5 to 50 nm is deposited in this order (S1005: i-type amorphous silicon layer formation, S1006: p-type amorphous silicon layer formation).

  Subsequently, as shown in FIG. 7B, an i-type amorphous silicon layer 3i having a thickness of about 1 to 10 nm is formed on the second surface 1B side of the n-type single crystal silicon substrate 1 using a plasma CVD method. An n-type amorphous silicon layer 3n having a thickness of about 5 to 50 nm is formed in this order (S1007: i-type amorphous silicon layer formation, S1008: n-type amorphous silicon layer formation).

  Next, as shown in FIG. 7C, the composition gradient layer 4g is formed on the p-type amorphous silicon layer 2p (formation of the composition gradient layer: S1009g). At this time, since the composition is gradually changed, a translucent conductive film 4g having good orientation and a large particle size is formed. Thus, the translucent electrode 4t formed on the light receiving surface side 1A is composed of the composition gradient layer, and the mobility of the translucent conductive film on the upper layer side is higher than that on the substrate side, that is, the lower layer side. . Since the formation of the second light-transmissive electrode 5t (S1010) and the formation of the current collecting electrodes 4m and 5m (S1011) are the same as those in the first embodiment, the description thereof is omitted here.

  Also in Embodiment 3, the resistivity and light absorption of the translucent electrode can be reduced, thereby improving the conversion efficiency of the photovoltaic element.

  In this step, the collector electrode includes an annealing step as in the first embodiment. However, the collector electrode may be used by forming a metal electrode by a sputtering method without using the annealing step. .

  In the third embodiment, as in the first and second embodiments, the conditions of the light-transmitting conductive film with respect to the light-transmitting initial layer are also set for various conditions such as oxygen concentration, Al doping concentration, and atmospheric pressure. By changing it, it is possible to obtain desired characteristics.

  As the crystalline semiconductor substrate, in addition to a crystalline silicon substrate such as a single crystal silicon substrate or a polycrystalline silicon substrate, a silicon compound such as a silicon carbide substrate can be used as long as it is a photovoltaic device having a structure using a light-transmitting conductive film. The present invention can also be applied to crystalline silicon substrates such as substrates. The intrinsic or conductive amorphous silicon layer can also be applied to crystalline thin films such as microcrystalline silicon thin films and polycrystalline silicon thin films as long as the photovoltaic element has a structure using a transparent conductive film. Is possible.

  Moreover, in the said embodiment, although it was set as the 2 layer structure of the translucent initial layer and the translucent conductive film only with respect to the 1st translucent electrode located in the light-receiving surface side, it is located in a back surface side. The second light-transmitting electrode or both may have a two-layer structure.

  As described above, the method for manufacturing a photovoltaic device element and the photovoltaic device element according to the present invention increase the light absorption amount without increasing the contact resistance between the light-transmitting electrode on the light-receiving surface side and the semiconductor layer. It is useful for realizing a photovoltaic device that is reduced and increases current density, and has excellent fill factor and photovoltaic efficiency.

1 n-type single crystal silicon substrate, 2i i-type amorphous silicon layer, 2pp p-type amorphous silicon layer, 3i i-type amorphous silicon layer, 3n n-type amorphous silicon layer, 4t1 translucent initial layer 4t2 Translucent conductive film, 4t translucent electrode, 4m first collector electrode, 5t translucent electrode, 5m second collector electrode.

Claims (21)

Forming a second conductivity type amorphous or microcrystalline semiconductor layer on the first surface of the first conductivity type crystalline semiconductor substrate;
Forming a first electrode on the amorphous or microcrystalline semiconductor layer of the second conductivity type;
Forming a second electrode on the second surface of the first conductive type crystalline semiconductor substrate, comprising:
At least one of the steps of forming the first and second electrodes comprises:
Forming a translucent electrode;
Forming a current collecting electrode,
Forming the translucent electrode comprises:
Forming a light-transmitting initial layer based on zinc oxide ;
Crystal-growing a translucent conductive film using the same zinc oxide as that of the seed as a base material using the translucent initial layer as a seed, and forming a translucent conductive film having a crystal grain size larger than that of the translucent initial layer Forming the photovoltaic element. The crystal growth step includes:
Forming the translucent conductive film;
The method for manufacturing a photovoltaic device according to claim 1, further comprising: recrystallizing the light-transmitting conductive film by heat treatment. The step of forming the translucent conductive film includes
The method for producing a photovoltaic element according to claim 2, wherein the process is a step of forming the translucent conductive film by a sputtering method. The recrystallization step includes:
4. The method for manufacturing a photovoltaic device according to claim 3, wherein the method is a heat treatment at 150 to 220 [deg.] C. The crystal growth step includes:
The method for manufacturing a photovoltaic element according to claim 1, further comprising a step of forming a light-transmitting conductive film by using the light-transmitting initial layer as a seed by a CVD method. Forming the translucent initial layer;
The method of manufacturing a photovoltaic element according to claim 1, wherein the step of forming the translucent conductive film is continuously performed in the same chamber. 7. The photovoltaic device according to claim 1, wherein the crystalline semiconductor substrate of the first conductivity type, which is a base layer of the translucent initial layer, is a crystalline silicon substrate. A method for manufacturing a power element. Underlying layer of the light-transmitting initial layer, prior Symbol amorphous or microcrystalline semiconductor layer of the second conductivity type, claim 1, wherein the amorphous or microcrystalline silicon layer 6 of The manufacturing method of the photovoltaic element of any one . The step of forming the translucent initial layer includes
9. The method of manufacturing a photovoltaic element according to claim 6, wherein the supply amount of oxygen is larger than that in the step of forming the translucent conductive film. The step of forming the translucent initial layer includes
The method for manufacturing a photovoltaic element according to any one of claims 6 to 9, wherein the method is a step of forming at a higher doping concentration than the step of forming the light-transmitting conductive film. The step of forming the translucent initial layer includes
The method for manufacturing a photovoltaic element according to any one of claims 6 to 10, wherein the method is a step of forming at a higher atmospheric pressure than a step of forming the light-transmitting conductive film. Forming the translucent initial layer;
The step of forming the light-transmitting conductive film is a sputtering method, and the step of forming the light-transmitting initial layer is performed by continuously reducing the amount of oxygen supplied from the step of forming the light-transmitting initial layer. The manufacturing method of the photovoltaic element of any one of 6 to 8.   The step of forming the translucent conductive film is a step of continuously increasing the dope concentration from the step of forming the translucent initial layer. The manufacturing method of the photovoltaic element of description.   The step of forming the translucent conductive film is a step of continuously forming the translucent initial layer at a low atmospheric pressure from the step of forming the translucent initial layer. 14. The method for producing a photovoltaic element according to any one of items 13 to 13. The first electrode is disposed on the light receiving surface side,
Forming the first electrode includes forming the translucent initial layer and forming the translucent conductive film;
15. The method for manufacturing a photovoltaic element according to claim 1, wherein the step of forming the second electrode is a step of forming a single-layer translucent conductive film. . A first conductive type crystalline semiconductor substrate;
A second conductivity type amorphous or microcrystalline semiconductor layer formed on the first surface of the crystalline semiconductor substrate;
A first electrode formed on the amorphous or microcrystalline semiconductor layer of the second conductivity type;
A photovoltaic device including a second electrode formed on a second surface of the crystalline semiconductor substrate,
At least one of the first and second electrodes is
Including a translucent electrode and a collecting electrode;
The translucent electrode is
It is composed of a laminated film of a translucent initial layer using zinc oxide as a base material and a translucent conductive film composed of a crystal growth layer formed on the translucent initial layer,
The photovoltaic element, wherein the crystal growth layer is a crystal layer having the same zinc oxide as that of the translucent initial layer as a base material and a crystal grain size larger than that of the translucent initial layer.   The photovoltaic device according to claim 16, wherein the first conductive type crystalline semiconductor substrate serving as a base layer of the translucent initial layer is a crystalline silicon substrate.   The light according to claim 16, wherein the second conductive type amorphous or microcrystalline semiconductor layer serving as a base layer of the translucent initial layer is an amorphous or microcrystalline silicon layer. Electromotive force element.   The photovoltaic device according to any one of claims 16 to 18, wherein the translucent initial layer has a higher oxygen content than the translucent conductive film.   20. The photovoltaic element according to claim 16, wherein the light-transmitting initial layer has a higher doping concentration than the light-transmitting conductive film. The first electrode is disposed on the light receiving surface side,
The first electrode includes the translucent initial layer and the translucent conductive film,
21. The photovoltaic element according to claim 16, wherein the second electrode is a translucent electrode made of a single translucent conductive film.

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