JP2015191967A - Solar battery cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solar battery cell that utilizes effects of electric field effect passivation using a polarization material having spontaneous polarization derived from a crystal structure.SOLUTION: Provided is a solar battery cell that has a second conductivity type semiconductor layer 12 formed on a light-receiving surface 11A of a first conductivity type semiconductor substrate 11. Between at least a part of this second conductivity type semiconductor layer 12 and a light-receiving surface electrode 15 as a first electrode, or between at least a part of the second principal surface of the first conductivity type semiconductor substrate 11 and a rear face electrode 18 as a second electrode contacted with this, the solar battery cell comprises a polarization material layer 13 that has spontaneous polarization whose polarization axial direction is not parallel to the first principal surface or the second principal surface, and that consists of a polycrystal film. This polarization material layer 13 is formed of a material having a crystal structure that belongs to any one in a crystallization point group of 1, 2, m, mm2, 4, 4mm, 3, 3m, 6, and 6mm.

Description

  The present invention relates to a solar battery cell and a method for manufacturing the same, and more particularly to a solar battery cell utilizing the effect of field effect passivation using a polarization material in a crystalline silicon solar battery.

  In general, in a solar cell, pairs of electrons and holes are generated inside the semiconductor of the solar cell by light entering from the outside, and the electrons are n-type due to the electric field generated at the pn junction in the generated pairs of electrons and holes. Moving to the semiconductor, holes move to the p-type semiconductor to generate electric power.

  In the present crystalline silicon solar cell, a diffusion type solar cell in which an impurity semiconductor layer by diffusion is formed on the light receiving surface side of the most general structure is manufactured at a mass production level. A diffusion type solar cell usually uses a p-type crystalline silicon substrate having a thickness of about 200 μm, and has a surface texture that increases light absorption, an n-type diffusion layer, an antireflection film, and a surface electrode (for example, a comb-type Ag electrode). Are sequentially formed on the light-receiving surface side of the substrate, and a back electrode (for example, an Al electrode) is formed on the non-light-receiving surface side of the substrate by screen printing, followed by baking at a high temperature of about 800 ° C. In such firing, the solvent components of the front electrode and the back electrode are volatilized, and the comb-shaped Ag electrode breaks through the antireflection film and is connected to the n-type diffusion layer on the light receiving surface side of the substrate by fire-through. Also, a part of the Al electrode diffuses into the substrate on the non-light-receiving surface side of the substrate to form a back surface field layer (BSF: Back Surface Field). As a result, recombination on the back surface can be suppressed and a high open circuit voltage can be obtained.

  Thus, in order to increase the solar cell conversion efficiency, it is important to reduce recombination at the silicon substrate interface on the light receiving surface or the back surface. Recombination can be reduced by terminating the dangling bond at the interface (chemical passivation). For example, dangling bonds at the silicon substrate interface can be terminated by hydrogen introduced during film formation or heat treatment.

  In addition, recombination can be reduced by applying an electric field in the vicinity of the interface, which is called field effect passivation. This can be realized by introducing a fixed charge into the passivation film / crystalline silicon interface.

  Field effect passivation can also be obtained by laminating a polarizing material at the crystalline silicon interface. For example, in Patent Document 1, a p (or n) type silicon substrate having a lower electrode formed on the back surface, an n (or p) type injection layer formed on the silicon substrate and a comb electrode having a metal laminated thereon, and A field-effect photoelectric energy conversion device that includes a ferroelectric layer formed on an upper surface and induces an electric field on the upper portion of the silicon substrate by the spontaneous polarization effect of the ferroelectric to improve the characteristics of the solar cell is disclosed. .

  In Patent Document 2, at least one of a first conductivity type substrate, a second conductivity type semiconductor layer formed on the upper surface of the substrate and having an opposite conductivity type, a pn junction formed at an interface, and at least a second conductivity type semiconductor layer. Shown is a solar cell with a front electrode in contact with a portion and a back electrode in contact with at least a portion of the substrate. This solar cell includes a ferroelectric layer formed on at least one of the front and rear surfaces, and a poling electrode formed on the ferroelectric layer, and the ferroelectric layer is formed on the semiconductor surface. By using a strong electric field, the surface recombination can be prevented and the open-circuit voltage can be improved, thereby greatly improving the efficiency.

  Note that the solar cells described in Patent Document 1 and Patent Document 2 are provided with a polling electrode, and a ferroelectric is subjected to a poling process (polarization process), that is, an electric field is applied, and the polarization of the ferroelectric is aligned in the direction of the electric field. It needs to be processed.

  For example, ZnO, which is a pyroelectric material, has spontaneous polarization in the c-axis direction, is an Al-added polycrystalline film formed on glass, has c-axis orientation, and the polarity of the crystal that influences the direction of polarization. It is shown that they are aligned in one direction (Non-Patent Document 1).

Japanese Patent No. 3585621 JP 2003-78153 A

Yutaka Adachi et al. Thin Solid Films 519 (2011) 5875-5881

  However, according to the conventional techniques (Patent Documents 1 and 2), it is necessary to provide a polling electrode on the solar cell substrate and perform a polling process (polarization process) on the ferroelectric material, and the structure and process are complicated. There was a problem that there was.

In addition, the polarization of the ferroelectric polycrystalline thin film subjected to the poling process has been confirmed only up to 10 ⁶ seconds (about 2 years) in high-quality crystals of limited materials. In addition, in the case of a ferroelectric having a low Curie temperature of 200 ° C. or lower, polarization is thermally scattered due to the influence of the operating temperature of the solar cell, so that even if the amount of polarization decreases and the solar cell becomes low temperature The amount of polarization does not return to the original, and the solar cell operation becomes unstable. From the above, over 20 years, which is a general use period of a solar cell, there is a problem in reliability that it is difficult to maintain polarization and the characteristics of the solar cell deteriorate.

  This invention is made | formed in view of the above, Comprising: While simplifying a structure and a process, it aims at obtaining a reliable solar cell.

  In order to solve the above-described problems and achieve the object, the present invention provides a second conductive material formed on a first main surface of a first conductivity type semiconductor substrate having a first main surface and a second main surface facing each other. It is a photovoltaic cell which has a type semiconductor layer. Between at least a part of the second conductivity type semiconductor layer and the first electrode, or between at least a part of the second main surface of the first conductivity type semiconductor substrate and the second electrode in contact therewith. And a polarization material layer made of a polycrystalline film having spontaneous polarization and whose polarization axis direction is not parallel to the first main surface or the second main surface. This polarization material layer is a material having a crystal structure belonging to any of point groups of 1, 2, m, mm2, 4, 4 mm, 3, 3 m, 6, and 6 mm.

  According to the present invention, it is possible to simplify the structure of the solar cell and improve the reliability by using a polarization material that does not require a poling treatment.

1A and 1B are diagrams schematically showing a solar battery cell according to Embodiment 1 of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. 2A to 2D are schematic cross-sectional views showing the polarization direction of the polarization material layer. FIG. 3 is a flowchart showing a method for manufacturing the solar battery cell according to the first embodiment. 4A to 4C are process cross-sectional views illustrating the method for manufacturing the solar battery cell according to the first embodiment. 5A to 5C are process cross-sectional views illustrating the method for manufacturing the solar battery cell according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing the structure of the solar battery cell according to the second embodiment. FIG. 7 is a schematic cross-sectional view showing the structure of the solar battery cell according to the third embodiment.

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

Embodiment 1 FIG.
1A and 1B are diagrams schematically showing Embodiment 1 of a solar battery cell according to the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. In the solar cell 10 according to the first embodiment, a concavo-convex structure having a texture 11T for reducing light reflection is formed on a first main surface (hereinafter referred to as a light receiving surface 11A) of a first conductive type semiconductor substrate 11. . A second conductive semiconductor layer 12 is formed on the concavo-convex structure, and a polarization material layer 13 and an antireflection film 14 are sequentially stacked on the second conductive semiconductor layer 12. As the polarization material layer 13, for example, a polycrystalline film of zinc oxide belonging to a point group of 6 mm is used. This polycrystalline film is a polycrystalline film whose orientation direction is not parallel to the light receiving surface 11A. Thereby, the polarization material layer 13 having the polarization derived from the polarity of the crystal unit cell can be obtained simply by forming the film without performing the polarization treatment. A light receiving surface electrode 15 is formed at an arbitrary position of the antireflection film 14, and the light receiving surface electrode 15 is in contact with the second conductivity type semiconductor layer 12. A texture 11T is formed on the second main surface (hereinafter referred to as back surface 11B) facing the light receiving surface 11A of the first conductive type semiconductor substrate 11 in the same manner as the light receiving surface 11A, and in order, the first conductive type semiconductor layer 16 and the reflection An anti-reflection film 17 is formed, and a back electrode 18 is formed at an arbitrary position of the anti-reflection film 17. Electron-hole pairs that attempt to reach the surface are separated by the electric field of the polarization material layer 13, thereby suppressing surface recombination and obtaining a high open circuit voltage. Here, also in the peripheral region 1 where the light receiving surface electrode 15 is not formed, the polarization material layer 13 is formed so that an electric field is applied to the entire surface.

As the solar cell substrate (first conductive semiconductor substrate 11) according to the present embodiment, for example, an n-type single crystal or polycrystalline silicon substrate can be used. In this case, the second conductivity type semiconductor layer 12 is an impurity diffusion layer (p-type impurity diffusion layer) in which, for example, boron is diffused on the light receiving surface of the first conductivity type semiconductor substrate 11. Furthermore, the light receiving surface electrode 15 is formed using, for example, a mixture of aluminum and silver. The antireflection film 14 is, for example, a silicon nitride film (SiN _x ) to which hydrogen is added. On the other hand, the first conductive semiconductor layer 16 on the back surface is, for example, an impurity diffusion layer (n-type impurity diffusion layer) in which phosphorus is diffused. For example, SiN _x is used for the antireflection film 17. The back electrode 18 is made of, for example, silver. The first conductivity type semiconductor substrate 11 is not limited to this, and a p-type silicon substrate may be used. Similarly, phosphorus is diffused into the second conductivity type semiconductor layer 12, and the first conductivity type semiconductor substrate 11 is used. Boron may be diffused into the layer 16. The light receiving surface 11A or the back surface 11B of the first conductivity type semiconductor substrate 11 is preferably a concavo-convex structure in order to reduce the reflectivity, but is not limited to the concavo-convex structure, for example, a flat structure or a combination of concavo-convex and flat Any one of the structures may be used in accordance with the application. Further, although the polarization material layer 13 is used only on the light receiving surface side, it may be used on the back surface side.

  The polarization material layer 13 is not limited to zinc oxide belonging to the crystal point group 6 mm, and in addition to the crystal point groups 1, 2, m, mm2, 4, 4 mm, 3, 3 m, 6, 6 mm. A material having a crystal structure to which it belongs is used.

  Materials having spontaneous polarization include not only ferroelectric materials but also pyroelectric materials. The pyroelectric material has a crystal structure belonging to a crystal point group represented by 1,2, m, mm2,4,4mm, 3,3m, 6,6mm, and a crystal structure having polarity in the crystal unit cell. Therefore, it is a group of materials having spontaneous polarization. Since the spontaneous polarization of the pyroelectric material is derived from the crystal structure, the spontaneous polarization tends to be small in a randomly oriented polycrystalline film. On the other hand, a relatively large spontaneous polarization can be obtained when the orientation direction of the film matches the polarization direction. Here, zinc oxide is used as the polarization material layer 13. By interposing such a polarizing material layer 13 between the electrode and the semiconductor layer, recombination is suppressed and the characteristics of the solar battery cell are improved.

  In order to have spontaneous polarization of a certain size and to obtain the effect of field effect passivation, a polycrystalline film whose polarization axis is not parallel to the surface of the first conductivity type semiconductor substrate 11 is preferable (FIG. 2). . This will be described with reference to FIGS.

  2A to 2D are schematic cross-sectional views of a polarizing material layer 13 made of zinc oxide formed by aligning crystal grains 20 in a certain crystal orientation with respect to the surface of the second conductivity type semiconductor layer 12. It is. The polarization material layer 13 made of zinc oxide belongs to a point group of 6 mm and has a wurtzite crystal structure. In order to facilitate understanding, a small number of differently oriented crystal grains 20 are omitted. A material having a crystal structure belonging to a crystal point group of 1, 2, m, mm2, 4, 4 mm, 3, 3 m, 6, 6 mm has a polarization derived from the polarity of the crystal structure.

FIG. 2A illustrates an example in which the crystal is oriented with a certain crystal orientation perpendicular to the surface of the second conductivity type semiconductor layer 12 and the polarization axis direction P _d is the same as the orientation direction O _d . In this case, surface charge according to the amount of polarization is induced. Obliquely to FIG. 2 (b), the surface of the second conductive type semiconductor layer 12, aligned with a certain crystal orientation, the polarization axis direction P _d is an example of the same direction as the alignment direction O _d. In this case, a surface charge according to a component perpendicular to the surface of the second conductivity type semiconductor layer 12 having a polarization amount is induced. FIG. 2C shows an example in which the crystal is oriented with a certain crystal orientation obliquely with respect to the surface of the second conductivity type semiconductor layer 12, and the polarization axis direction _Pd is not the same direction as the orientation direction _Od . Also in this case, a surface charge corresponding to a component perpendicular to the surface of the second conductivity type semiconductor layer 12 having a polarization amount is induced as in FIG. FIG. 2D shows an example in which the crystal is oriented with a certain crystal orientation perpendicular to the surface of the second conductivity type semiconductor layer 12 and the polarization axis direction P _d is a direction perpendicular to the orientation direction O _d . In this example, the polarization axis direction is parallel to the surface of the second conductivity type semiconductor layer 12. In this case, no surface charge is induced at the interface between the polarization material layer 13 and the second conductivity type semiconductor layer 12.

As described above, any polycrystalline film whose polarization axis direction _Pd is not parallel to the surface of the second conductivity type semiconductor layer 12 may be used. Further, it is randomly oriented and the polarization axis of each crystal grain 20 is random. Even so, it may be a polycrystalline film in which the polarization direction of the entire film is not parallel to the surface of the second conductivity type semiconductor layer 12 when viewed macroscopically. That is, any polycrystalline film having a component in which the polarization direction of the entire film is non-parallel to the surface of the second conductivity type semiconductor layer 12 may be used.

At this time, the surface charge induced on the surface of the polarization material layer 13 is preferably 10 ¹² cm ² or more, and the vertical component of the polarization amount of the polarization amount of the polarization material layer 13 with respect to the surface of the second conductivity type semiconductor layer 12 is 0.1 μC / cm ² or more is preferable.

  Moreover, the use temperature of a solar cell is generally −30 ° C. to 100 ° C., and the electrode is baked at 700 ° C. or higher in the electrode baking step. Therefore, the polarization material layer 13 is preferably capable of maintaining polarization in a temperature range of −30 ° C. to 800 ° C. For this purpose, it is preferable that the crystal structure does not change in the above temperature range, that is, there is no melting point and no phase transition point.

Furthermore, it is preferable that the amount of polarization, that is, the induced surface charge does not change when the solar cell is used outdoors, and the pyroelectric coefficient at −30 ° C. to 100 ° C. is preferably 10 nC / cm ² K or less.

  Also, the amount of polarization can be confirmed by forming metal electrodes on both surfaces of the polarizing material thin film by sputtering vapor deposition or the like to form a capacitor structure and measuring the temperature dependence of the pyroelectric current. In addition, the induced surface charge may be measured. In that case, a metal electrode is formed on the bottom surface of the semiconductor substrate and the top surface of the polarization material layer in a structure in which a polarization material layer is laminated on the semiconductor substrate to form a capacitor structure. It can be obtained by analyzing the CV characteristics.

  Further, since it is used for the light receiving surface 11A, a transparent material having a band gap of 2.5 eV or more is preferable. Further, even a material having a band gap of 2.5 eV or less may be used with a film thickness that does not significantly reduce the transmittance. Moreover, when using only for a back surface, it does not need to be transparent.

As a preferable material for such a polarization material layer 13, for example, zinc oxide (ZnO) is mentioned as described above. The polarization material layer 13 will be described in detail using ZnO as an example. ZnO belongs to a point group of 6 mm and has a wurtzite crystal structure. The melting point of ZnO crystal is 1975 ° C., and the pyroelectric coefficient from room temperature to 100 ° C. is about ² nC / cm ² K. The band gap is 3.37 eV. The unit cell of the ZnO crystal has polarity, and the c-axis direction is the polarization axis. Further, a c-axis oriented polycrystalline film can be obtained relatively easily on an amorphous substrate, for example, a glass substrate, by using a sputter deposition method or the like. Furthermore, as described in Non-Patent Document 1, for example, the polarity in the crystal can be controlled by adding an impurity such as Al. That is, it is possible to easily control the polarization axis direction. ZnO is known to have a spontaneous polarization of about 6 μC / cm ^{2 in a} single crystal. In order to have spontaneous polarization, either a crystal grain having an oxygen polar face or a crystal grain having a zinc polar face is required. It is necessary to increase the number of one side and to have polarization as a whole. In a polycrystalline alignment film with controlled polarity, almost the same spontaneous polarization can be obtained.

The thicknesses of the polarization material layer 13 and the antireflection film 14 depend on each other in order to design the field effect passivation and the antireflection effect to the maximum. The thickness of the polarizing material layer 13 is preferably equal to or greater than the thickness at which spontaneous polarization is exhibited, and is preferably a thickness that allows fire-through during electrode firing, and is preferably 10 nm to 100 nm. If the thickness of the polarization material layer 13 is less than 10 nm, spontaneous polarization does not appear. On the other hand, if the thickness of the polarization material layer 13 exceeds 100 nm, fire-through becomes difficult. If the total film thickness of the polarization material layer 13 and the antireflection film 14 is too thick, for example, hydrogen diffusion from SiN _x that can be used as the antireflection film 14 to the semiconductor substrate 11 will be hindered. The chemical passivation effect cannot be obtained. Therefore, it is necessary to consider the total film thickness of the polarization material layer 13 and the antireflection film 14. The total film thickness of the polarization material layer 13 and the antireflection film 14 is desirably about 120 nm or less. If the total film thickness exceeds 120 nm, a sufficient passivation effect cannot be obtained.

  An example of the manufacturing method of the solar battery cell of the first embodiment having the above structure will be described according to the flowchart shown in FIG. 3 and FIGS. 4 (a) to (c) and FIGS. 5 (a) to (c). To do.

  First, etching for removing a damaged layer and forming a concavo-convex shape of an n-type single crystal silicon substrate as the first conductive type semiconductor substrate 11 is performed. The pre-cleaning of the n-type single crystal silicon substrate is performed by removing the damaged layer of the substrate with an alkali solution. FIG. 4 (a))). In the case of a polycrystalline substrate, etching with an acid may be used.

  Next, boron diffusion is performed to form a p-type diffusion layer as the second conductivity type semiconductor layer 12 (FIG. 3: step S2). Boron diffusion with a sheet resistance of 50 to 150Ω / □ is performed at a temperature of 850 ° C. to 1000 ° C. At this time, a boron silicate glass (BSG) film of 50 to 200 nm is formed on the boron diffusion surface.

Next, the back surface is etched (FIG. 3: Step S3). Boron diffusion causes back diffusion to the back surface, so an in-line single-sided etching device is used. Preferably, the substrate is moved horizontally to a roller-type transport system, and a system in which an HF / HNO ₃ solution is applied to the back surface side is applied. It is preferable to etch only the back surface with an HF / HNO ₃ solution. In this way, as shown in FIG. 4B, the second conductivity type semiconductor layer 12 composed of the p-type diffusion layer obtained by boron diffusion is formed on the light receiving surface 11A side.

Next, in order to form a BSF layer composed of an n-type diffusion layer as the first conductivity type semiconductor layer 16, back surface phosphorus diffusion is performed (FIG. 3: step S4). Phosphorus diffusion is performed at a temperature of 800 ° C. to 900 ° C. using POCl ₃ gas as a diffusion source with the boron diffusion surfaces facing each other. The sheet resistance is preferably 40-100 Ω / □.

  Next, BSG removal and phosphorus silicate glass (PSG) removal of the light receiving surface are performed (FIG. 3: Step S5 (FIG. 4C)). Etching is performed to the extent that water repellency can be confirmed on both sides using an HF solution.

Next, the polarization material layer 13 is formed (FIG. 3: Step S6 (FIG. 5A)). Here, description will be made using ZnO. The polarization material layer 13 is formed on the upper surface of the second conductivity type semiconductor layer 12 by using a DC magnetron sputtering method. The formation conditions are a substrate temperature of 100 ° C. to 800 ° C. and a sputtering gas using a mixed gas of Ar gas and O ₂ gas. The flow ratio O ₂ / Ar between Ar gas and O ₂ gas is preferably 1% to 10%. The pressure is 0.1 Pa to 1 Pa, the DC power is 0.1 W / cm ^{2 to 2} W / cm, and the film thickness is preferably 10 to 100 nm. Further, H, N, Al, Li, Mg, Mn, Co, Ni, or the like may be added.

  Examples of methods other than the above include RF magnetron sputtering, thermal CVD, plasma CVD, ion plating vapor deposition, electron beam vapor deposition, pulse laser deposition, sol-gel method, and chemical solution growth. In addition, in order to prevent damage to the film formation surface, silicate glass opposite to the film formation surface, that is, BSG on the light receiving surface and PSG on the back surface may be left. In that case, the silicate glass may be removed only on one side before the polarization material layer 13 is formed.

Next, the antireflection films 14 and 17 are formed on the light receiving surface 11A side and the back surface 11B side (FIG. 3: Step S7 (FIG. 5B)). The antireflection film 14 and the antireflection film 17 on the back surface are formed at a substrate temperature of 400 ° C. to 550 ° C. by plasma CVD. The material gas is formed using a mixed gas of SH ₃ and NH ₄ . The polarization material layer 13 may also serve as an antireflection film, and in this case, this step is omitted.

  Next, the light-receiving surface electrode 15 and the back surface electrode 18 are formed (FIG. 3: Step S8 (FIG. 5C)). A comb-shaped electrode is printed using a screen printing method. It is preferable to use a paste in which Al, Ag, and frit glass are mixed in a solvent for the electrode on the light receiving surface, and a paste in which Ag and frit glass are mixed in the solvent for the electrode on the back surface.

  And after making it dry at 100 to 200 degreeC, it bakes with a temperature profile with a peak temperature of 700 to 850 degreeC in a belt-type baking furnace (FIG. 3: step S9). By this baking, the light receiving surface electrode 15 fires through the antireflection film 14 and the polarization material layer 13 and contacts the first conductivity type semiconductor layer 12. On the other hand, the back electrode 18 contacts the second conductive semiconductor layer 16 through the antireflection film 17 through fire. In this way, the solar battery cell shown in FIGS. 1A and 1B is formed. In addition, crystallization of the polarization material layer 13 is further promoted during electrode firing, and spontaneous polarization can be increased.

  Next, a laser scriber scribes the periphery of the light receiving surface of the solar battery cell to perform junction separation (FIG. 3: step S10). Junction separation may be performed only on the end face of the solar battery cell using a plasma etcher with a plurality of solar battery cells stacked. In this way, the solar battery cell 10 shown in FIGS. 1A and 1B is formed.

  In the solar battery cell 10 according to the first embodiment configured as described above, the action (field effect passivation) of the polarization material layer 13 will be described in detail. In general, pyroelectric materials generate polarization charges on the surface by spontaneous polarization. A strong electric field is formed inside the first conductivity type semiconductor substrate 11 by this polarization charge. Therefore, when the polarization material layer 13 is formed on the light receiving surface, surface recombination can be suppressed. The reason is as follows. If a pair of electrons and holes is formed inside the semiconductor by light entering from the outside of the solar cell, the electrons and holes are separated by the potential difference generated at the pn junction. For example, when an n-type semiconductor is used as a substrate and a pn junction is formed by diffusion, the electric field direction at the pn junction is directed from the n-type semiconductor to the p-type semiconductor, and the generated electron-hole pair is Under the influence of the electric field at the junction, as a result, electrons move to the n-type semiconductor side, and holes move to the p-type semiconductor side, thereby generating effective power. At this time, there are generally many dangling bonds and impurities that could not be involved in bonding on the semiconductor surface, and they act as recombination centers for electron-hole pairs. That is, when an electron-hole pair that is not affected by the electric field at the pn junction portion reaches impurities on such a surface, recombination is likely to occur, and thus cannot contribute to output. However, if the polarization material layer 13 is formed on the light receiving surface to form a strong electric field on the semiconductor surface, the electron-hole pairs that are to reach the surface are separated by the electric field formed by the polarization material layer, and the surface It becomes possible to suppress recombination. As a result, a high open circuit voltage can be obtained.

  As described above, in the solar cell according to the first embodiment, the polycrystalline alignment film made of a material having a crystal structure belonging to the crystal point group of 1,2, m, mm2,4,4mm, 3,3m, 6,6mm is provided. When used, the polarization material layer has a polarization derived from the polarity of the crystal unit cell. Therefore, the polling process is not required, and the above-described field effect passivation effect can be obtained, a high open-circuit voltage can be obtained, and the cell characteristics can be improved. Furthermore, it becomes possible to omit the complicated polling electrode and its formation process. Further, since the polarization is derived from the crystal structure, the polarization material has a high Curie point, and has a small pyroelectric coefficient, the solar cell operation does not become unstable due to thermal scattering of the polarization. Therefore, it becomes possible to hold spontaneous polarization for 20 years or more, which is a general use period of a solar battery, and there is an effect that the reliability of the solar battery cell can be improved.

Embodiment 2. FIG.
In the first embodiment, the antireflection film 14 is formed on the surface of the polarization material layer 13. However, it is not necessary to diffuse hydrogen from the antireflection film 14 to the semiconductor substrate 11, and the polarization material layer 13 is antireflection. In the case of fulfilling the role, the antireflection film 14 may be omitted. FIG. 6 shows a schematic cross-sectional view of a solar battery cell that does not have the antireflection film 14. Since it is the same as that of the solar cell of the first embodiment except that the antireflection film 14 is not provided, the description is omitted, but the same portions are denoted by the same reference numerals. The polarization material layer 13 is a polycrystalline alignment film made of a material having a crystal structure belonging to a crystal point group of 1, 2, m, mm2, 4, 4 mm, 3, 3 m, 6, 6 mm, as in the first embodiment. Needless to say, is used. Thereby, the polarization material layer 13 has polarization derived from the polarity of the crystal unit cell.

  According to this configuration, it is possible to reduce the loss of incident light and improve the photoelectric conversion efficiency. For example, when the refractive index of the polarizing material layer 13 is smaller than that of silicon and larger than the refractive index of the antireflection film 14, reflection occurs at the interface between the polarizing material layer 13 and the antireflection film 14 and the incident light is lost. Sometimes. For this reason, when the refractive index of the polarization material layer 13 is smaller than that of silicon and larger than the refractive index of the antireflection film 14, it is preferable that the antireflection film 14 be absent.

Embodiment 3 FIG.
In the solar cell of the first embodiment, since the polarization material layer 13 is directly laminated on the second conductivity type semiconductor layer 12, the termination of dangling bonds on the surface is insufficient. Further, the interface was likely to be defective due to damage caused by the deposition of the polarization material layer 13. Therefore, the solar cell characteristics may be deteriorated.

  Therefore, in this embodiment, as shown in FIG. 7, a passivation layer 19 made of a thin silicon oxide film having a thickness of about 20 nm is inserted between the second conductive type semiconductor layer 12 on the light receiving surface 11A side and the polarizing material layer 13. ing. Others are the same as the solar cell of Embodiment 1 shown in FIG. Here, the same parts are denoted by the same reference numerals.

The passivation layer 19 is preferably made of a material such as SiO ₂ , SiO _x , AlO _x , hydrogenated amorphous silicon (a-Si: H), or MgO. These materials are formed using thermal oxidation, chemical oxidation, plasma CVD, ALD, or sputter deposition.

  As described above, in the solar cell according to the third embodiment, it is possible to suppress the dangling bond termination on the surface and damage due to the deposition of the polarization material layer, thereby suppressing recombination and high openness. A voltage can be obtained.

Also in manufacturing, prior to the formation of the p-type diffusion layer or the amorphous silicon p-layer as the second conductive semiconductor layer 12, it is only necessary to add a step of forming a passivation film 19 such as SiO ₂ and the manufacturing is easy. .

  In the above-described embodiment, a diffusion type called a double-sided light receiving (bifacial) structure has been described. However, the present invention is not limited to this, and a single-sided light receiving structure or electrode in which a metal electrode is disposed on the entire back surface 11B. The back contact structure may be arranged only on the back surface 11B. In addition, a crystalline silicon solar cell such as a heterojunction solar cell in which an amorphous thin film or the like is formed on a crystalline silicon substrate such as a single crystal silicon substrate or a polycrystalline silicon substrate to form a pn junction. It can be applied to anything.

  In any of the solar cells of the above-described embodiments, the polarization material layer may be formed only on the back surface side, or may be formed on both the light receiving surface side and the back surface side.

  In any of the embodiments, the first conductive semiconductor substrate can be applied to a semiconductor substrate such as a compound semiconductor substrate in addition to a crystalline silicon substrate such as a single crystal silicon substrate or a polycrystalline silicon substrate. .

  Moreover, although the said embodiment demonstrated the solar cell, it is applicable to various photoelectric conversion devices including light receiving elements, such as an image sensor, without being limited to a solar cell.

  Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 Perimeter area | region, 10 photovoltaic cell, 11 1st conductivity type semiconductor substrate, 11A light-receiving surface, 11B back surface, 11T texture, 12 2nd conductivity type semiconductor layer, 13 Polarization material layer, 14, 17 Antireflection film, 15 Light reception surface Electrode, 16 1st conductivity type semiconductor layer, 18 Back electrode, 20 Crystal grain, 19 Passivation layer.

Claims (9)

A first conductivity type semiconductor substrate having a first main surface and a second main surface facing each other;
A second conductivity type semiconductor layer formed on the first main surface of the first conductivity type semiconductor substrate and having a conductivity type opposite to the first conductivity type semiconductor substrate;
A first electrode in contact with at least a portion of the second conductivity type semiconductor layer;
A second electrode in contact with at least a portion of the second main surface of the first conductivity type semiconductor substrate;
Formed on at least one of the first main surface side of the second conductivity type semiconductor layer or the second main surface side of the semiconductor substrate, and a crystal point group of 1, 2, m, mm2, 4, 4 mm, A material having a crystal structure belonging to any of 3, 3 m, 6 and 6 mm, which is made of a polycrystalline film having spontaneous polarization and whose polarization axis direction is not parallel to the first main surface or the second main surface A polarizing material layer;
A solar battery cell.   The solar cell according to claim 1, wherein the polarization material layer is formed on the second conductive semiconductor layer via a passivation film. A first conductivity type semiconductor layer on the second main surface of the semiconductor substrate;
The solar cell according to claim 1, wherein the polarization material layer is formed on the first conductive semiconductor layer via a passivation film.   The solar cell according to claim 2 or 3, wherein an antireflection film is formed on an outer surface of the polarization material layer.   The solar cell according to claim 2, wherein the passivation film includes any one of silicon oxide, aluminum oxide, and amorphous silicon film. The solar cell according to claim 4, wherein the antireflection film is hydrogenated silicon nitride. 2. The polarization material layer is a zinc oxide-based material that is c-axis oriented with respect to the first main surface, and includes either one of crystal grains having an oxygen polar face and crystal grains having a zinc polar face. The solar battery cell according to any one of 1 to 6. The solar cell according to claim 7, wherein the zinc oxide-based material is added with at least one of H, N, Al, Li, Mg, Mn, Co, and Ni. A second conductivity type semiconductor layer having a conductivity type opposite to that of the first conductivity type semiconductor substrate is formed on the first or second major surface of the first conductivity type semiconductor substrate having the first and second major surfaces facing each other. And a process of
Forming a first electrode in contact with at least a portion of the second conductivity type semiconductor layer;
Forming a second electrode in contact with at least a portion of the second main surface of the first conductivity type semiconductor substrate;
Forming a solar cell by performing pn separation on the first conductivity type semiconductor substrate,
Prior to the step of forming the first or second electrode, a crystal point is formed on at least one of the first main surface side of the second conductivity type semiconductor layer or the second main surface side of the semiconductor substrate. A material having a crystal structure belonging to any of the groups 1, 2, m, mm2, 4, 4 mm, 3, 3 m, 6, 6 mm, and having spontaneous polarization, the polarization direction of which is the first main surface or A method for manufacturing a solar cell, comprising a step of forming a polarization material layer made of a polycrystalline film that is not parallel to the second main surface.

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