JP5424270B2 - Semiconductor solar cell - Google Patents

Description

  The present invention relates to a semiconductor solar cell and a manufacturing method thereof, and more particularly, to a semiconductor solar cell having an electrode / passivation film / semiconductor structure and a manufacturing method thereof.

  In recent years, solar cells have been actively developed as new energy power generation devices. In solar cells, semiconductors are widely used as materials that absorb light and convert it into charges of electrons and holes. In a solar cell, a pn junction shown in FIG. 28 is widely used in order to separate an electron and a hole which are induced by absorbing light and extract a current. FIG. 28 shows a pn junction band diagram of a semiconductor. Since the p-type semiconductor region and the n-type semiconductor region formed by impurity doping have different electron affinity and work function, a potential difference is generated inside the pn junction. When a solar cell having a pn junction is irradiated with light (hν), an electron e and a hole h are generated. The electron e and the hole h are in opposite directions along the potential difference generated inside the pn junction. A flow photoinduced current is generated. That is, electrons e flow to the n-type semiconductor region side, and holes h flow to the p-type semiconductor region side to generate a photo-induced current. In FIG. 23, Eg represents a band gap, Ec represents a conduction band, and Ev represents a valence band.

  And the solar cell characteristic as shown in FIG. 27 is acquired. The output of the solar cell is represented by a correlation curve between the voltage V and the current I generated in the solar cell shown in FIG. 27, and the maximum output is represented by an area Pmp connecting the operating current Imp and the operating voltage Vmp to the origin. Isc indicates a short circuit current and Voc indicates an open circuit voltage.

  As a solar cell, manufacturing with high optical power conversion efficiency and low cost is desired. And the element which converts a photoinduced carrier into an electric current effectively is developed by using the crystal semiconductor of the outstanding quality.

  On the other hand, as a solar cell, a MIS solar cell having a metal / insulating film / semiconductor structure that does not require low manufacturing cost and formation of a pn junction is known. As shown in the conceptual diagram of FIG. 26, a typical MIS type solar cell 41 has a thin insulating film (oxide film) 43 on one surface on the light incident side of an n-type semiconductor substrate 42, for example. A metal electrode 44 is formed, and the other metal electrode 45 is formed directly on the other surface.

  As shown in FIG. 26, a difference in work function between the metal electrode 44 sandwiching the insulating film 43 and the semiconductor substrate 42 causes a potential difference in the semiconductor substrate 42 to induce bending of the band. When light (hν) is incident, electrons e and holes h generated by light irradiation flow in opposite directions along the potential difference, and a photo-induced current is generated. That is, the electrons e pass through the thin insulating film 43 and flow to one metal electrode 44, and the holes h flow to the other metal electrode 45 and a photo-induced current flows. In FIG. 26, Eg represents a band gap, Ec represents a conduction band, Ev represents a valence band, and Ef represents a Fermi level.

  In the case of the MIS type solar cell 41, it is necessary to take out the current by the tunnel effect of the electrons e passing through the insulating film 43 in the example of FIG. It is known that the film thickness of the insulating film 43 needs to be 2 nm or less in order to extract a sufficient current. As shown in the voltage-current density characteristic diagram with the insulating film thickness as a parameter in FIG. 25, it is known that a sufficiently large current flows by applying a voltage of about 1 V in the insulating film 43 having a film thickness of 2 nm or less.

  Patent Document 1 discloses an example of a MIS type or Schottky junction type solar cell.

Japanese Patent Laid-Open No. 11-10380

  By the way, in the conventional MIS type solar cell 41, as shown in FIG. 26, a metal electrode 45 is directly formed on the back side of the semiconductor substrate 42 where no light is incident. At the interface between the metal electrode 45 and the semiconductor substrate 42, crystal defects are likely to occur, and electrons e flowing to the metal electrode 45 on the back side are recombined by the crystal defects at the interface, thereby reducing the photoinduced current. . Further, the metal acts as a killer for recombining the carriers of the electron e and the hole h, and the carrier disappears by the metal electrode 45 formed directly on the semiconductor substrate surface, so that the photoinduced current is reduced.

  On the other hand, in the MIS type structure, for example, on the surface of a silicon substrate covered with a high-quality silicon oxide (SiO 2) film, the density of charge trapping defects is small and no charge is accumulated. Therefore, as shown in FIG. 23, the work function difference between the metal electrode 64 sandwiching the high-quality silicon oxide film 63 and the silicon substrate 62 effectively causes the band in the silicon substrate 62 to bend, thereby forming the built-in potential Ψ. . FIG. 23 is a conceptual diagram of a MIS structure in which a p-type silicon substrate is used as the silicon substrate 62 and a metal electrode 64 is formed on the surface of the p-type silicon semiconductor substrate 62 via an insulating film (SiO 2 film) 63. is there. qψm represents the work function of the metal electrode.

  On the other hand, in FIG. 24, the surface of the silicon substrate 62 covered with the poor-quality silicon oxide (SiO 2) film 65 has a very large number of charge trap defect levels 66 formed mainly in the center of the band gap. Indicates. In this case, the bending of the band in the semiconductor substrate 62 and the internal potential Ψ are determined by the charge trap defect level 66. Since charges are accumulated on the surface of the semiconductor substrate 62 and the work function difference with the metal electrode 64 is consumed as a potential applied to the insulating film 65, the work function difference between the metal electrode 64 and the semiconductor substrate 62 is effectively used. I can't.

  Further, the charge trap defect level 66 on the surface of the semiconductor substrate acts as a recombination level of photoinduced carriers, and the carriers generated by light irradiation disappear, which becomes a major factor for reducing the photoinduced current.

  In view of the above-mentioned points, the present invention provides a semiconductor solar cell that enables high optical power conversion efficiency and low cost, and that can be put into practical use as an electrode / passivation film / semiconductor structure, and a method for manufacturing the same.

A semiconductor solar cell according to the present invention includes a semiconductor substrate, and a steam thermal oxide film in which the thermal oxide film is subjected to steam heat treatment , and the semiconductor substrate has high insulation with respect to the semiconductor substrate and can conduct current by a tunnel effect. It has the 1st electrode and 2nd electrode which are formed through the passivation thin film which consists of, and has different work functions, It is characterized by the above-mentioned.

The first electrode and the second electrode, Ru can be formed together through only the insulating thin film on one surface of the semiconductor substrate.

  In a preferred embodiment of the present invention, the first electrode is formed of a metal having a work function smaller than that of the second electrode and the semiconductor substrate, and the second electrode is formed of a work function of the first electrode and the semiconductor substrate. Form with larger metal.

  In the semiconductor solar cell of the present invention, both the first electrode and the second electrode are formed on the semiconductor substrate via a passivation thin film that is highly insulating with respect to the semiconductor substrate and can conduct current. The so-called double structure, each of which is an electrode / passivation thin film / semiconductor structure, reduces the disappearance of photoinduced carriers as much as possible, and allows electrons and holes to flow efficiently through the first electrode and the second electrode, respectively. .

Method of manufacturing a semi-conductor solar cell has high insulating properties with respect to the semiconductor substrate in a semiconductor substrate, and forming a passivation film made of tunneling current conductible by steam thermal oxide film, work on the insulating film Forming a first electrode and a second electrode having different functions.

In the step of forming a first electrode and a second electrode, a first electrode and a second electrode, Ru can only be formed together via an insulating film on one surface side of the semiconductor substrate.

The first electrode is formed of a metal whose work function is lower than that of the second electrode and the semiconductor substrate, and the second electrode is formed of a metal whose work function is higher than that of the first electrode and the semiconductor substrate.

In the method of manufacturing semi-conductor solar cell, high insulating properties with respect to the semiconductor substrate in a semiconductor substrate, and because it forms a current conducting can passivation film, a passivation effect of the semiconductor surface by the passivation film, the low defect density An interface is formed. In addition, since the first electrode and the second electrode having different work functions are formed on the insulating thin film, a so-called double structure is formed, in which the electrode / passivation thin film / semiconductor structure is formed.

  According to the semiconductor solar cell according to the present invention, it is possible to provide a solar cell that enables high optical power conversion efficiency and low cost and is practical.

  According to the method for manufacturing a semiconductor solar cell according to the present invention, it is possible to manufacture a solar cell that enables high optical power conversion efficiency and low cost and is practical.

It is a schematic block diagram of 1st Embodiment which shows the fundamental structure of the semiconductor solar cell which concerns on this invention. It is a schematic block diagram of the other example of 1st Embodiment which shows the fundamental structure of the semiconductor solar cell which concerns on this invention. It is a graph which shows the lifetime of a photo-induced minority carrier (electron) when an insulating thin film is formed by the steam heat processing provided for description of this invention. It is a graph which shows the relationship between the work function (phi) exp (eV) of various elements and atomic number Z with which it uses for description of this invention. A, B It is the schematic sectional drawing and schematic plan view of 2nd Embodiment of the semiconductor solar cell concerning this invention. AC is a schematic configuration showing a third embodiment of the semiconductor solar cell according to the present invention and its manufacturing process diagram. It is operation | movement explanatory drawing of 3rd Embodiment. A, B It is the schematic sectional drawing and schematic bottom view which show 4th Embodiment of the semiconductor solar cell which concerns on this invention. A, B It is a top view which shows the example of the pattern of the 1st and 2nd electrode of 4th Embodiment. It is a top view which shows other example of the pattern of the 1st and 2nd electrode of 4th Embodiment. A, B It is the schematic sectional drawing and schematic bottom view which show 5th Embodiment of the semiconductor solar cell concerning this invention. It is a schematic block diagram which shows 6th Embodiment of the semiconductor solar cell which concerns on this invention. It is a schematic block diagram which shows the sample of the semiconductor solar cell of this invention for measuring a solar cell characteristic. It is a schematic block diagram of the sample of the solar cell for a comparison. A, B It is an absolute current density-voltage characteristic figure which shows the solar cell characteristic of the semiconductor solar cell which concerns on this invention, and a comparative solar cell. It is an absolute current density-voltage characteristic figure which shows a solar cell characteristic when light is irradiated from the surface and back surface of the semiconductor solar cell concerning the present invention. It is a model figure with which it uses for the setting of the space | interval between electrodes of the semiconductor solar cell concerning this invention, an electrode width, and the board | substrate thickness of a semiconductor substrate. It is a schematic block diagram which shows 7th Embodiment of the semiconductor solar cell which concerns on this invention. It is a schematic block diagram which shows 8th Embodiment of the semiconductor solar cell which concerns on this invention. It is a table | surface figure which shows the potential barrier with respect to the electron and hole of a high dielectric constant material applied to the passivation thin film of 7th, 8th embodiment. A, B It is the schematic block diagram and operation | movement explanatory drawing which show 9th Embodiment of the semiconductor solar cell concerning this invention. It is a schematic block diagram which shows 10th Embodiment of the semiconductor solar cell which concerns on this invention. In the MIS type structure, it is a band diagram when there are few charge trap defect levels on the surface of the semiconductor substrate. In the MIS type structure, it is a band diagram when there are many charge trap defect levels on the surface of the semiconductor substrate. It is a voltage-current density characteristic figure which uses the insulating film of a MIS type solar cell as a parameter. It is a conceptual diagram of the conventional MIS type solar cell. It is a correlation curve figure of voltage V generated in a solar cell, and current I which shows a solar cell characteristic. It is a band figure with which it uses for description of the conventional pn junction type solar cell.

  An embodiment of a semiconductor solar cell according to the present invention is to form a passivation thin film on a first conductivity type, for example, a p-type or n-type semiconductor substrate, which is highly insulative with respect to the semiconductor substrate and capable of current conduction. The first electrode and the second electrode having different work functions are formed on the passivation thin film. The first electrode is formed of a metal whose work function is smaller than that of the second electrode and the semiconductor substrate. The second electrode is formed of a metal having a work function larger than that of the first electrode and the semiconductor substrate. Alternatively, the first electrode and the second electrode can be formed of a combination of a metal having a different work function and a transparent conductive film.

  As described in detail later, the first electrode and the second electrode can be formed on one surface and the other surface of the semiconductor substrate via a passivation thin film, respectively. That is, the first electrode or the second electrode, which becomes one electrode, is formed on one surface of the semiconductor substrate where light is incident via a passivation thin film, and the other surface where light is not incident is formed via the passivation thin film. A second electrode or a first electrode to be the other electrode is formed. Alternatively, as will be described in detail later, the first electrode and the second electrode are formed on the other surface of the semiconductor substrate where no light is incident so as to be separated from each other via a passivation thin film. At this time, a light-transmissive insulating film, that is, a so-called transparent insulating film is formed on one surface of the semiconductor substrate on which light is incident.

  As the semiconductor substrate, a single crystal silicon substrate, a polycrystalline silicon substrate, a compound semiconductor substrate, or another semiconductor substrate can be used.

  As the passivation thin film having higher insulation with respect to the semiconductor substrate and capable of conducting current, an insulating thin film capable of conducting current by the tunnel effect or an intrinsic amorphous semiconductor film can be used. Further, as will be clarified later, as the passivation thin film, an insulating film having a small potential barrier against electrons is used for the passivation thin film on the side where electrons are conducted, and a potential barrier against holes is provided on the passivation thin film on the side where holes are conducted. A small insulating film can be used.

  The passivation thin film according to the present embodiment is a film having high insulating properties with respect to a semiconductor substrate, that is, a film having so-called insulator characteristics. The definition of this insulating property or insulator will be described. In order to generate a built-in potential in a semiconductor such as silicon by utilizing the work function difference between different metals, the charge in the semiconductor moves due to the work function difference between the metal and the semiconductor, and thereby a semiconductor surface layer close to the metal is formed. It must be charged and a potential change must occur. For example, a semiconductor surface near aluminum has more electrons and is negatively charged, and a built-in potential associated therewith is formed. The thin film existing between the semiconductor and the metal governs the passivation of the semiconductor surface. At this time, it is necessary that the mobile charge (carrier) does not exist or is small in the thin film existing between the semiconductor and the metal.

  If there are many mobile charges (carriers) in the thin film between the semiconductor and the metal, the mobile charges (carriers) in the thin film move to balance the work function difference of the metal, creating a large built-in potential in the semiconductor. I can't let you. Therefore, the number of movable charges (carriers) existing in the thin film between the semiconductor and the metal is desirably 1/10 or less of the carrier volume concentration in the semiconductor. This means that when viewed from the semiconductor, the thin film, that is, the above-described passivation thin film is a highly insulating film, that is, has insulating characteristics. In other words, this thin film, that is, the above-described passivation thin film, needs to be a thin film having a larger band gap than the semiconductor.

  For example, when crystalline silicon is used as a semiconductor, the band gap of crystalline silicon is 1.12 eV. Here, the crystalline silicon is single crystal silicon or polycrystalline silicon. The carrier concentration condition of 1/10 or less can be realized if the band gap is 1.18 eV or more at room temperature. Therefore, the band gap of the thin film existing between the semiconductor and the metal may be larger than the semiconductor by 0.006 eV. In the case of silicon, a thin film having a band gap of 1.18 or more may be used. Examples of the thin film having a band gap of 1.18 or more include an insulating film and amorphous silicon. The SiO 2 film has a band gap of 10 eV and is a very excellent insulator, and is suitable for use as a passivation thin film as the insulating thin film of the present invention. Amorphous silicon has a band gap of 1.7 to 2.0 eV and can be used for a passivation thin film as an insulating thin film of the present invention.

  In the present embodiment, for example, when an insulating thin film is used as a passivation thin film that covers the surface on the side of forming an electrode of the semiconductor substrate, the insulating thin film is a high-quality insulating thin film having a charge trap defect level density as low as possible. Must be formed. For this reason, in this embodiment, when the semiconductor substrate is a silicon substrate, a silicon oxide thin film formed by steam heat treatment is preferably used as an insulating thin film as a method for obtaining a high-quality silicon oxide (SiO 2) film / silicon (Si) interface at a low temperature. Use. This steam heat treatment method is known from Document 1. When the semiconductor substrate is a silicon substrate, a high-quality silicon oxide (SiO 2) film can be realized by a thermal oxidation method in which the silicon substrate is heated and oxidized at 1000 ° C.

  Reference 1: T. Sameshima and M. Satoh “Improvement of SiO2 Properties by Heating Treatment in High Pressure H2O Vapor”, Jpn. J. Appl. Phys. 36 (1997) L687-L689

  FIG. 3 shows the minority carrier lifetime when a silicon oxide thin film that becomes an insulating thin film is formed on the p-type silicon surface by steam heat treatment, and shows the minority in the absence of the silicon oxide film immediately after cleaning the silicon surface before the steam heat treatment. Shown in comparison with career lifetime. A of the horizontal axis in FIG. 3 shows a sample immediately after cleaning the silicon surface before the steam heat treatment, and B shows a sample after the silicon oxide thin film is formed by the steam heat treatment.

FIG. 3 shows measured values of the lifetime of photoinduced electron carriers when the p-type silicon surface is oxidized by steam heat treatment at 260 ° C. and 1.3 × 10 ⁶ Pa. A silicon oxide thin film having a thickness of 1.5 nm is formed on the p-type silicon surface by the steam heat treatment, and the lifetime of the photo-induced electron carrier is changed from 20 μs (see point a in the figure) to 700 μs (point in the figure) before the steam heat treatment. b)).

If steam heat treatment is used, the carrier recombination density at the SiO ₂ / Si interface can be significantly reduced even in a low-temperature process, and the minority carrier lifetime is increased. In this embodiment, based on this demonstration, an insulating thin film formed by steam thermal oxidation is used as the insulating thin film between the semiconductor substrate and the electrode in the MIS structure, thereby enabling a more preferable MIS type solar cell configuration. The MIS structure in this embodiment includes a metal (electrode) / insulating thin film / semiconductor structure and a transparent conductive film (electrode) / insulating thin film / semiconductor structure.

FIG. 4 shows the relationship between the work function φ _exp (eV) of various elements and the atomic number Z. Depending on the element, the work function is distributed from 2 eV to 6 eV.

  Since the work function is given by the energy difference between the vacuum energy level and the Fermi level, the semiconductor can change the work function by impurity doping. For example, for silicon, it can vary between 4.05 eV and 5.17 eV. When n-type doping is applied, the Fermi level approaches the conduction band, and the work function becomes small, which is close to 4.05 eV. If the doping amount is increased, the Fermi level further approaches the conduction band, so the work function is further decreased. On the other hand, when p-type doping is performed, the Fermi level approaches the valence band and the work function increases and approaches 5.17 eV. Therefore, if a metal with a low work function and a p-type semiconductor with a high work function are selected, the band bending of the semiconductor can be induced, and the MIS interface turns to n-type. Conversely, if a metal having a high work function and an n-type semiconductor having a low work function are selected, the band bending of the semiconductor can be induced, and the MIS interface turns to p-type.

  Since the solar cell is an element for taking out an electric current, it requires two electrode structures. As described above, the present embodiment is characterized in that the solar cell is configured by using at least two types of electrodes having different work functions. Furthermore, this embodiment is characterized in that a work function difference of an electrode is efficiently used for forming a built-in potential of a semiconductor by forming a MIS structure using a thin high-quality insulating film. For the formation of a thin high-quality insulating film, the above-described steam thermal oxidation method is more preferable. However, in the case of silicon, a high-quality silicon oxide film can be used even if the above-described thermal oxidation method, plasma CVD method or sputtering method is used. Can be formed.

  Next, embodiments of the solar cell and the manufacturing method thereof according to the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 shows a first embodiment of a semiconductor solar cell according to the present invention, that is, a principle configuration example. In this embodiment, a high-quality insulating thin film is used as the passivation thin film. The semiconductor solar cell 1 according to the present embodiment includes a first electrode 4 using a metal having a small work function on one surface (front surface) of a first conductivity type semiconductor substrate 2 via a high-quality insulating thin film 3. And a second electrode 6 using a metal having a high work function is formed on the other surface (back surface) of the semiconductor substrate 2 via a high-quality insulating thin film 5. For example, a p-type silicon semiconductor substrate 2 is used, and a metal having a low work function, such as aluminum (Al) or hafnium, is formed on one surface of the silicon semiconductor substrate 2 via the insulating thin film 3 of the above-described high-quality silicon oxide film. The first electrode 4 using (Hf), tantalum (Ta), indium (In), or zirconium (Zr) is formed. Further, a metal having a high work function, such as gold (Au), nickel (Ni), or platinum, is provided on the other surface opposite to the one surface of the silicon semiconductor substrate 2 through an insulating thin film 5 of a high-quality silicon oxide film. A second electrode 6 using (Pt) or palladium (Pd) is formed. As the insulating thin films 3 and 5, a high-quality insulating thin film having a low density of photoinduced carrier recombination defects is used. It is preferable to use a silicon oxide thin film formed by a steam heat treatment method. Further, a high-quality silicon oxide thin film can be formed by using a thermal oxidation method, a plasma CVD method, or a sputtering method. The silicon oxide thin film has a thickness through which a tunnel current flows, and a thickness of about 0.5 nm to 2.0 nm is preferable. In the present embodiment, a so-called double MIS structure is formed.

  On the other hand, band bending is induced on the semiconductor surface on the first electrode 4 side by aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr), and the MIS interface becomes n-type. Turn. On the other side of the semiconductor surface on the second electrode 6 side by gold (Au), nickel (Ni), platinum (Pt) or palladium (Pd), reverse band bending is induced, and the MIS interface has a stronger p-type. Turn.

  When the semiconductor substrate 2 is irradiated with the light hν, the electrons e, which are minority carriers among the carriers generated by the light irradiation, move to the first electrode 4 side along the built-in potential formed by the band bending, It flows into the first electrode 4 through the insulating thin film 3 made of a silicon oxide film. The hole h, which is a majority carrier among the carriers generated by the light irradiation, moves to the second electrode 6 side and flows into the second electrode 6 through the insulating thin film 5 made of a silicon oxide film.

  Light irradiation can be performed either by light irradiation from the side on which the first electrode 4 is formed or light irradiation from the side on which the second electrode 6 is formed. It is preferable to irradiate light from the side where the work function difference is large. This is because, when light irradiation is performed from the side where the work function difference is small, the distance that minority carriers move along the built-in potential among the generated carriers becomes longer, so the probability that minority carriers disappear during the movement becomes higher. For this reason, it is preferable to irradiate light from the side where the movement distance of minority carriers becomes short and the work function difference is large. In the configuration of FIG. 1, light (hν) is irradiated from the side on which the first electrode 4 is formed.

  FIG. 2 shows a principle configuration example (another example) of a solar cell according to the present invention using an n-type semiconductor substrate. The solar cell 8 according to the present embodiment is a metal having a small work function on one surface (front surface) of the first conductivity type semiconductor substrate 2 via a high-quality insulating thin film 3 in the same manner as the solar cell 1 described above. The first electrode 4 is formed using a metal, and the second electrode 6 using a metal having a high work function is formed on the other surface (back surface) of the semiconductor substrate 2 via a high-quality insulating thin film 5. Is done. In this example, an n-type silicon semiconductor substrate 2 is used. A metal having a small work function, such as aluminum (Al), hafnium (Hf), tantalum (Ta), or indium (In) is formed on one surface of the silicon semiconductor substrate 2 through the insulating thin film 3 of the above-described high-quality silicon oxide film. ) Or the first electrode 4 using zirconium (Zr). Further, a metal having a high work function, such as gold (Au), nickel (Ni), or platinum, is provided on the other surface opposite to the one surface of the silicon semiconductor substrate 2 through an insulating thin film 5 of a high-quality silicon oxide film. A second electrode 6 using (Pt) or palladium (Pd) is formed. As the insulating thin films 3 and 5, a high-quality insulating thin film having a low density of photoinduced carrier recombination defects is used. Also in this case, a high-quality silicon oxide film can be formed by using a steam thermal CVD method or a sputtering method. The silicon oxide thin film has a thickness through which a tunnel current flows, and a thickness of about 0.5 nm to 2.0 nm is preferable.

  Band bending is induced on the semiconductor surface on the second electrode 6 side using gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd), and the MIS interface turns to p-type. On the other hand, the semiconductor surface on the first electrode 4 side using aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr) induces reverse band bending, and MIS. The interface turns into a stronger n-type.

  When the semiconductor substrate 2 is irradiated with the light hν, the electrons e, which are minority carriers among the carriers generated by the light irradiation, move to the first electrode 4 side along the built-in potential formed by the band bending, It flows into the first metal electrode 4 through the insulating thin film 5 formed by silicon oxide. The hole h, which is a majority carrier among the carriers generated by light irradiation, moves to the second electrode 6 side and flows into the second metal electrode 6 through the insulating thin film 3 made of a silicon oxide film. As described in paragraph [0041], when an n-type semiconductor is used, light irradiation is preferably performed from the side on which the second electrode 6 is formed. The minority carrier hole h quickly moves to the second electrode 6 side and contributes to the photoinduced current.

  In this way, the solar cell 1 using the double MIS structure of the first and second electrodes 4 and 6, the insulating thin films 3 and 5, and the semiconductor substrate 2 made of different metals is realized.

  According to the semiconductor solar cell 1 according to the first embodiment, the use of the high-quality insulating thin films 3 and 5, preferably the oxide film formed by steam heat treatment, greatly increases the lifetime of minority carriers among the photo-induced carriers. Increase. Further, a low defect density interface is formed by the passivation effect of the semiconductor interface by the high-quality insulating thin films 3 and 5, and the semiconductor band bending due to the work function difference of the electrode is efficiently induced, and a large built-in potential can be formed. This results in a large open circuit voltage (Voc) of the solar cell.

  Since it has a double MIS structure, the disappearance of photo-induced carriers is reduced as much as possible, and electrons and holes can flow efficiently through both electrodes 4 and 6, respectively. In addition, since the MIS structure is used, an impurity doping process for forming a pn junction is not necessary, and the manufacturing process is simplified. Accordingly, it is possible to provide a MIS type solar cell that has high optical power conversion efficiency, can be reduced in cost, and is practical.

  The principle embodiment has been described above. However, since the metal electrode does not transmit light, a device for making light incident on the semiconductor substrate is necessary. Hereinafter, an embodiment in which light can be efficiently incident on a semiconductor substrate will be described.

[Second Embodiment]
FIG. 5 shows a second embodiment of the semiconductor solar cell according to the present invention. 5A is a cross-sectional view, and FIG. 5B is a plan view. The semiconductor solar cell 11 according to the second embodiment uses the first conductive type semiconductor substrate 2, which is a p-type silicon semiconductor substrate in this example. The semiconductor solar cell 11 is formed with high-quality insulating thin films 3 and 5 on one surface (front surface) and the other surface (back surface) of the semiconductor substrate 2, and the first surface on the insulating thin film 3 on one surface side. The electrode 4 is formed, and the second electrode 6 is formed on the insulating thin film 5 on the other surface side. One surface side of the semiconductor substrate 2 is an irradiation side of the light hν. The insulating thin films 3 and 5 are preferably formed of silicon oxide thin films formed by steam heat treatment. The film thickness of this silicon oxide thin film is preferably about 0.5 nm to 2 nm, which is the thickness through which the tunnel current flows, as described above. By performing this steam heat treatment, a high-quality insulating thin film / semiconductor interface is formed.

  The first electrode 4 on one side where light is incident is formed by arranging a plurality of stripe-shaped electrode portions 4A at a predetermined interval in one direction. The distance d1 between the adjacent electrode portions 4A is selected to be equal to or less than the diffusion distance of the light-induced minority carriers. For example, when a p-type silicon semiconductor substrate is used, when the lifetime of electron minority carriers is 700 μs, the diffusion distance of electron minority carriers is about 1300 μm. Therefore, the light-induced minority carriers can be efficiently injected into the first electrode 4 by making the distance d1 between the electrode portions 4A sufficiently smaller than 1300 μm.

  The first electrode 4 is made of a metal having a work function smaller than that of the semiconductor substrate 2 and the second electrode 6, such as aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr). ) Or the like. The plurality of electrode portions 4A are electrically connected to each other. In this example, the first electrode 4 has a plurality of striped electrode portions 4A, and is formed in a comb-like shape in which the electrode portions 4A are connected to each other at one end. Note that the first electrode 4 can also have a shape in which a plurality of stripe-shaped electrode portions 4A are connected at an intermediate portion in the stripe direction other than the end portions.

  The second electrode 6 on the other surface side where the light hν is not incident is formed uniformly on the entire surface of the insulating thin film 5. The second electrode 6 is a metal having a work function higher than that of the semiconductor substrate 2 and the first electrode 3, such as gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd). It is formed.

  In the second embodiment, the light hν passes between the adjacent electrode portions 4A and enters the semiconductor substrate 2. The light hν is absorbed by the semiconductor substrate 2 and generates photoinduced carriers. At this time, minority carriers (electrons) photoinduced in the region where the electrode portion 4A is not formed reach the upper portion of the electrode portion 4A by diffusion and are insulated according to the built-in potential formed by the work function difference between the electrode portion 4A and the semiconductor. It flows to the first electrode 4 through the thin film 3. The majority carriers (holes) move along the built-in potential formed by the work function difference from the second electrode 6, and flow to the second electrode 6 through the insulating thin film 5. Thus, electrons flow to the first electrode 4 having a low work function, holes flow to the second electrode 6 having a high work function, and the solar cell is driven.

  The manufacturing method of the semiconductor solar cell 11 of 2nd Embodiment is demonstrated. First, high-quality insulating thin films 3 and 5 having film thicknesses through which a tunnel current flows are formed on both surfaces of the semiconductor substrate 2, that is, one surface (front surface) and the other surface (back surface). Passivate. The insulating thin films 3 and 5 are preferably formed of silicon oxide thin films formed by steam heat treatment. The thickness of the silicon oxide thin film is preferably about 0.5 nm to 2 nm as described above. By performing this steam heat treatment, a high-quality insulating thin film / semiconductor interface is formed.

  Next, a first metal film for forming a first electrode is formed on the entire surface of the insulating thin film 3 on one surface of the semiconductor substrate 2 on which light is incident. The first metal film is patterned by, for example, selective etching, and is formed of a plurality of stripe-shaped electrode portions 4A arranged at intervals d1 that are equal to or less than the diffusion distance of minority carriers photoinduced in one direction. The electrode 4 is formed. In this example, the first electrode 4 is formed in a comb-like shape in which a plurality of electrode portions 4A are connected at one end.

  After the formation process of the first electrode 4 or before the formation process of the first electrode 4, the second electrode 6 that is uniform over the entire surface of the insulating thin film 5 on the other surface where the light of the semiconductor substrate 2 is not incident. Form. In this way, the solar cell 11 according to the second embodiment is obtained.

  According to the semiconductor solar cell 11 according to the second embodiment, the light hν is incident on the semiconductor substrate from between the striped electrode portions 4A, so that the light can be efficiently incident. And although a duplicate description is omitted, as described in the first embodiment, it is possible to provide a practical MIS type solar cell that has high optical power conversion efficiency and enables cost reduction.

[Third Embodiment]
FIG. 6 shows a third embodiment of the semiconductor solar cell according to the present invention. 6 shows a solar cell and its manufacturing process, FIGS. 6A and 6B are sectional views, and FIG. 6C is a plan view of FIG. 6B. The semiconductor solar cell 12 according to the third embodiment uses the first conductivity type semiconductor substrate 2, which is a p-type silicon semiconductor substrate in this example. The semiconductor solar cell 12 has a first electrode 4 and a second electrode 6 formed on the other surface (back surface) of the semiconductor substrate 2 via a high-quality insulating thin film 3. A high-quality light-transmissive insulating film 13 is formed on the (surface). One surface side of the semiconductor substrate 2 having the insulating film 13 is an irradiation side of the light hν (see FIG. 6).

  The insulating thin film 3 on the MIS structure side is preferably formed of a silicon oxide thin film by steam heat treatment. The film thickness of this silicon oxide thin film is preferably about 0.5 nm to 2 nm, which is the film thickness through which the tunnel current flows, as described above. This water vapor treatment forms a good quality insulating thin film / semiconductor interface.

  The first electrode 4 is formed by arranging a plurality of stripe-shaped first electrode portions 4A at a predetermined interval in one direction. Similarly, the second electrode 6 is formed by arranging a plurality of striped second electrode portions 6A at a predetermined interval in one direction. The first electrode 4 and the second electrode 6 are formed such that the first electrode portions 4A and the second electrode portions 6A are alternately arranged in one direction. The distance d2 between the adjacent first electrode portion 4A and the second electrode portion 6A is selected to be less than the diffusion distance of the photo-induced minority carriers.

  As described above, when a p-type silicon semiconductor substrate is used, when the lifetime of electron minority carriers is 700 μs, the diffusion distance of electron minority carriers is about 1300 μm. Therefore, the light-induced minority carriers can be efficiently injected into the first electrode 4 by setting the distance d2 between the adjacent first and second electrode portions 4A and 6A to be sufficiently smaller than 1300 μm.

  The first electrode 4 is made of a metal having a work function smaller than that of the semiconductor substrate 2 and the second electrode 6, such as aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr). ) Or the like. The plurality of first electrode portions 4A are electrically connected to each other. The second electrode 6 is a metal having a work function larger than that of the semiconductor substrate 2 and the first electrode 4, for example, a metal such as gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd). It is formed. The plurality of second electrode portions 6A are electrically connected to each other.

  In this example, as shown in FIGS. 6B and 6C, the first electrode 4 has a plurality of stripe-shaped first electrode portions 4A, and the first electrode portion 4A is connected at one end to a comb-teeth shape. Formed. The second electrode 6 has a plurality of striped second electrode portions 6A, and is formed in a comb-like shape in which the second electrode portion 6A is connected at one end. The comb-shaped first electrode 4 and the second electrode 6 are formed by meshing with each other. The transparent insulating film 13 formed on one surface of the semiconductor substrate 2 on which light is incident is formed of a silicon oxide film having a thickness larger than that of the insulating thin film 3 on the MIS structure side using a steam heat treatment method, a thermal oxidation method, or the like. can do.

  In the third embodiment, as shown in FIG. 7, the light hν is incident on the semiconductor substrate 2 from the one surface (front surface) side of the semiconductor substrate 2 through the light-transmissive insulating film 13. Absorbed and photo-induced carriers are generated. Since the first electrode 4 and the second electrode 6 are formed in an intersecting manner on the other surface (back surface) side of the semiconductor substrate 2, the band bending on the left side of FIG. 1 occurs at the MIS interface where the first electrode 4 exists. 1 is induced at the MIS interface where the second electrode 6 is present. Therefore, the electron e which is a minority carrier among the photoinduced carriers moves to the first electrode 4 side and flows into the first electrode 4 through the insulating thin film 3. Moreover, the hole h which is a majority carrier among the photo-induced carriers moves to the second electrode 6 side and flows into the second electrode 6 through the insulating thin film 3. Thus, the electrons e flow to the first electrode 4 having a small work function, the holes h flow to the second electrode 6 having a large work function, and the solar cell 12 is driven. In order for the generated photo-induced minority carriers to efficiently diffuse to the opposite side of the substrate, the thickness of the semiconductor substrate is preferably less than or equal to the minority carrier diffusion distance.

  A method for manufacturing the semiconductor solar cell according to the third embodiment will be described. First, as shown in FIG. 6A, a transparent insulating film 13 and an insulating thin film 3 are formed on both surfaces of the semiconductor substrate 2, that is, one surface (front surface) and the other surface (back surface), respectively, and passivation of the semiconductor substrate surface is performed. Apply. At this time, the insulating thin film 3 on the other surface on which the MIS structure is to be formed has a film thickness through which a tunnel current flows, as described above, and is a high-quality insulating thin film. The insulating thin film 3 is preferably formed of a silicon oxide thin film formed by steam heat treatment. The thickness of the silicon oxide thin film is preferably about 0.5 nm to 2 nm. By performing this steam heat treatment, a high-quality insulating thin film / semiconductor interface is formed.

  The insulating film 13 formed on one surface of the semiconductor substrate 2 can be formed of a silicon oxide film having a thickness larger than that of the insulating thin film 3 on the MIS structure side by using a steam heat treatment method, a thermal oxidation method, or the like. The insulating film 13 can also be formed as the same insulating thin film at the same time as the insulating thin film 3 on the MIS structure side.

  Next, as shown in FIG. 6B and FIG. 6C, the first electrode 4 having a plurality of stripe-shaped first electrode portions 4A on the insulating thin film 3 on the other surface of the semiconductor substrate 2 on which light is incident; The second electrode 6 having a plurality of stripe-shaped second electrode portions 6A is formed. The first electrode portion 4A and the second electrode portion 6A are formed by being alternately arranged at an interval d2 that is equal to or less than the diffusion distance of minority carriers photo-induced in one direction. The first electrode 4 is formed by forming a first metal film on the entire surface of the insulating thin film 3 on the other surface and then patterning it by selective etching. The second electrode 6 is also formed by patterning by selective etching after forming a second metal film on the entire surface of the insulating thin film 3 so as not to affect the first electrode 4. Either the first electrode formation step or the second electrode formation step may be performed first.

  In this example, as shown in FIG. 6C, the first electrode 4 has a plurality of stripe-shaped first electrode portions 4A and has a comb-tooth shape in which the first electrode portions 4A are connected to each other at one end. Form. The second electrode 6 has a plurality of striped second electrode portions 6A, and is formed in a comb-like shape in which the second electrode portions 6A are connected to each other at one end. Moreover, the comb-shaped first electrode 4 and second electrode 6 are formed so as to mesh with each other. In this way, the solar cell 12 according to the third embodiment is obtained.

  According to the semiconductor solar cell according to the third embodiment, the MIS structure is formed on the other surface side of the semiconductor substrate, and the light is irradiated from one surface. Incident light can be used to further increase the power conversion efficiency. And although a duplicate description is omitted, as described in the first embodiment, it is possible to provide a practical MIS type solar cell that has high optical power conversion efficiency and enables cost reduction.

  Solar cells need to achieve both light irradiation and current extraction. Many conventional solar cells use a structure in which transparent electrodes are formed on the top and bottom of a semiconductor substrate having a pn junction to extract current in a direction orthogonal to the light irradiation direction (lateral direction). When a current is taken out in the lateral direction within the surface of the transparent electrode, that is, when a current is taken out from the end of the transparent electrode, the current value is limited by the resistance in the lateral direction. For this reason, the resistance of the transparent electrode must be very small, but the resistance cannot be reduced to ensure transparency, and the resistance of the transparent electrode has a lower limit. Therefore, in practice, the current is taken out by dispersing thin silver electrodes in various places in the transparent electrode. In the transparent electrode, the electrical conductivity and the transparency are in a trade-off relationship.

  In the embodiment of the present invention, it is possible to configure a semiconductor solar cell that achieves both light irradiation and current drawing. In this semiconductor solar cell, a current extraction means is provided on a solar cell body in which first and second electrodes having different work functions are formed on a side opposite to a light incident side of a semiconductor substrate through a high-quality insulating thin film. It is composed by bonding. Next, an embodiment of this semiconductor solar cell will be described.

[Fourth embodiment]
FIG. 8 shows a fourth embodiment of a semiconductor solar cell according to the present invention which achieves both light irradiation and current drawing. FIG. 8A is a cross-sectional view, and FIG. In the semiconductor solar cell 14 according to the fourth embodiment, the first electrode 4 and the second electrode 6 having different work functions are formed on the opposite side of the light incident side of the semiconductor substrate 2 through the high-quality insulating thin film 3. A current extracting means 16 is bonded to the solar cell body 15 formed as described above.

  As the solar cell body 15, the first conductive type semiconductor substrate 2, which is a p-type silicon semiconductor substrate 2 in this example, is used. The solar cell body 15 is formed with the first electrode 4 and the second electrode 6 on the other surface (back surface) of the semiconductor substrate 2 through the high-quality insulating thin film 3. A high-quality light-transmissive insulating film 13 is formed on the surface (surface). One surface (front surface) side of the semiconductor substrate 2 having the insulating film 13 is an irradiation side of the light hν.

  The insulating thin film 3 on the MIS structure side is preferably formed of a silicon oxide thin film by steam heat treatment. The film thickness of this silicon oxide thin film is preferably about 0.5 nm to 2 nm, which is the film thickness through which the tunnel current flows, as described above. This water vapor treatment forms a good quality insulating thin film / semiconductor interface.

  For example, as shown in FIG. 9A, the first electrode 4 and the second electrode 6 are formed so that the plurality of stripe-shaped first electrode portions 4A and the plurality of stripe-shaped second electrode portions 6A face in one direction. Can be alternately arranged. The distance d2 between the adjacent first electrode portion 4A and the second electrode portion 6A is selected to be less than the diffusion distance of the photo-induced minority carriers.

  Alternatively, as shown in FIG. 9B, for example, the first electrode 4 and the second electrode 6 are each formed in a comb shape, and the first electrode portions 4A and the second electrode portions 6A are alternately arranged. Can be formed. That is, the first electrode 4 is formed in a comb-teeth shape in which a plurality of striped first electrode portions 4A arranged in one direction are connected at one end. The second electrode 6 is formed in a comb-like shape in which a plurality of striped first electrode portions 4A arranged in one direction are connected at one end. The comb-shaped first electrode 4 and second electrode 6 are formed by meshing with each other.

  The first electrode 4 is made of a metal having a work function smaller than that of the semiconductor substrate 2 and the second electrode 6, such as aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr). ) Or the like. The second electrode 6 is a metal having a work function larger than that of the semiconductor substrate 2 and the first electrode 4, for example, a metal such as gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd). It is formed. The second electrode 6 can also be formed of a transparent conductive film made of ITO or ZnO described later.

  On the other hand, as shown in FIGS. 8A and 8B, the current extraction means 16 includes an anisotropic conductive sheet 17 in which conductive particles are dispersed in the insulating sheet, and first and second metal block portions 19A in the insulator 18. And 19B embedded in the conductive block body 21. As shown in FIG. 8B, the first and second metal block portions 19A and 19B are arranged so as to mesh with each other as shown in FIG. 8B. The first metal block portion 19A is formed in a comb-like pattern in which a plurality of stripe portions corresponding to the pattern of the stripe-shaped first electrode portion 4A are connected at one end. The second metal block portion 19B is formed in a comb-like pattern in which a plurality of stripe portions corresponding to the pattern of the stripe-shaped second electrode portion 6A are connected at one end. The metal block portions 19A and 19B can be formed of a metal having excellent conductivity, such as copper (Cu).

  In the present embodiment, the conductive block body 21 is bonded to the first and second electrodes 4 and 6 of the solar cell body 15 via the anisotropic conductive sheet 17. In other words, the first metal block portion 19 </ b> A is electrically connected to the first electrode 4 and the second metal block portion 19 </ b> B is electrically connected to the second electrode 6 by pressure bonding via the anisotropic conductive sheet 17. Wirings 22A and 22B are led out to the first metal block portion 19A and the second metal block portion 19B, respectively.

  In the semiconductor solar cell 14 according to the fourth embodiment, as described in the third embodiment, light hν is transmitted from one surface (front surface) side of the semiconductor substrate 2 through the light-transmissive insulating film 13. The light is incident on the substrate 2 and absorbed by the semiconductor substrate 2 to generate photo-induced carriers. Electrons e flow into the first electrode 4 formed on the other surface (back surface) side of the semiconductor substrate 2 through the insulating thin film 3, and holes h flow into the second electrode 6 through the insulating thin film 3.

  The electrons e and holes h flowing into the first and second electrodes 4 and 6 pass through the anisotropic conductive sheet 17 independently of the first and second metal block portions 19A and 19B of the conductive block body 21. Current is taken out from the wirings 22A and 22B as current and driven as a solar cell.

  According to the semiconductor solar cell 14 according to the fourth embodiment, since the anisotropic conductive sheet 17 flows current only in the thickness direction (vertical direction) in FIG. 8A, the first electrode 4 and the second electrode The current of the electrode 6 can be independently guided to the metal block portions 19A and 19B. Currents due to electrons e and holes h flowing into the first and second electrodes 4 and 6 are taken out independently in the vertical direction by the first and second metal block portions 19A and 19B, respectively. On the other hand, the comb-shaped first and second metal block portions 19A and 19B are much thicker than the first and second electrodes 4 and 6 formed of a thin film and have an electric resistance. It is made of a very small metal such as copper (Cu). Since the metal block portions 19A and 19B are formed thick, the lateral resistance in the planar pattern of the metal block portions 19A and 19B becomes very small. Therefore, current can be taken out efficiently. Strictly speaking, it is difficult to obtain flatness on the surfaces of the first and second electrodes 4 and 6 and the connection surface of the conductive block body. However, by connecting via the anisotropic conductive sheet 17, the first and second electrodes 4 and 6 and the first and second metal block portions 19A and 19B can be stably and reliably connected.

  Further, since the light hν is irradiated from the one surface (front surface) side where the electrodes 4 and 6 of the semiconductor substrate 2 are not formed, the light can be incident sufficiently efficiently into the semiconductor substrate 2, and light can be used as power. The conversion efficiency can be further increased. And although a duplicate description is omitted, as described in the first embodiment, it is possible to provide a practical MIS type solar cell that has high optical power conversion efficiency and enables cost reduction. Therefore, it is possible to provide a semiconductor solar cell that achieves both efficient light irradiation and good current extraction.

[Modification]
As the pattern of the first and second electrodes 4 and 6 of the solar cell body 15, various patterns can be considered in addition to the stripe shape. For example, as shown in FIG. 10, it can be formed in a dot shape. In the illustrated example, the first electrodes 4 and 6 are formed in a staggered pattern in which the first and fourth electrodes 4 and 6 are alternately arranged in the vertical and horizontal directions. The distance d2 between each of the first and second electrodes 4 and 6 is selected to be equal to or less than the light-induced minority carrier diffusion distance.

  Corresponding to the pattern of the dot-like first and second electrodes 4 and 6 arranged in this island shape, in the conductive block body 21, the first and second metal block portions 19A and 19B are made to be dot-like. Form into a pattern. Then, the first metal block portions 19A facing the outer surface of the conductive block body 21 and the second metal block portions 19B are electrically connected to lead out the wirings 22A and 22B, respectively.

  By forming the first and second electrodes 4 and 6 in a dot shape, electrons e and holes h generated in the semiconductor substrate 2 can flow into the first and second electrodes 4 and 6 more efficiently. Moreover, the current can be efficiently taken out through the conductive block body 21.

[Fifth Embodiment]
FIG. 11 shows a fifth embodiment of a semiconductor solar cell according to the present invention which achieves both light irradiation and current drawing. 11A is a cross-sectional view, and FIG. 11B is a plan view seen from the opposite side of light irradiation. The semiconductor solar cell 24 according to the fifth embodiment is a solar cell in which first and second electrodes 4 and 6 are formed on a side opposite to the light incident side of the semiconductor substrate 2 via a high-quality insulating thin film 3. The element body 15 is configured by bonding the current extraction means 16 together.

  The semiconductor solar cell 24 according to the present embodiment includes the first and second electrodes 4 and 6 of the solar cell body 21 and the conductive block body directly without using the anisotropic conductive sheet 17, for example, by anodic bonding. 21 first and second metal block portions 19A and 19B are joined together.

Since the configurations of the solar cell body 15 and the conductive block body 21 are the same as those described in the fourth embodiment, the same reference numerals are given to the portions corresponding to those in FIG. To do.
As a modification, the patterns of the first and second electrodes 4 and 6 of the solar cell body 15 and the patterns of the first and second metal block portions 19A and 19B of the conductive block body 21 have various patterns. Conceivable. For example, the first and second electrodes 4 and 6 and the first and second metal block portions 19A and 19B can be formed in a dot pattern as described with reference to FIG.

  According to the semiconductor solar cell 24 according to the fifth embodiment, the first and second electrodes 4 and 6 of the solar cell body 15 and the first and second metal block portions 19A and 19B of the conductive block body 21 are provided. Are directly joined. Thereby, the electric current by the electron e and the hole h which flowed into the 1st and 2nd electrodes 4 and 6 is taken out by the vertical direction by the metal block parts 19A and 19B. On the other hand, each of the first and second metal block portions 19A and 19B having a comb shape is much thicker than the first and second electrodes 4 and 6 formed of a thin film and has an electric resistance. It is made of a very small metal such as copper (Cu). Since the metal block portions 19A and 19B are formed thick, the lateral resistance in the plane pattern of the metal block portions 19A and 19B becomes very small. Therefore, current can be taken out efficiently.

  Further, since the light hν is irradiated from the one surface (front surface) side where the electrodes 4 and 6 of the semiconductor substrate 2 are not formed, the light can be incident sufficiently efficiently into the semiconductor substrate 2, and light can be used as power. The conversion efficiency can be further increased. And although a duplicate description is omitted, as described in the first embodiment, it is possible to provide a practical MIS type solar cell that has high optical power conversion efficiency and enables cost reduction.

[Sixth Embodiment]
FIG. 12 shows a sixth embodiment of the semiconductor solar cell according to the present invention. The semiconductor solar cell 26 according to the sixth embodiment has a high-quality insulation on one surface (front surface) and the other surface (back surface) of the first conductivity type semiconductor substrate 2, in this example, an n-type silicon semiconductor substrate. The thin films 3 and 5 are formed, and the first electrode 4 having a low work function and the second electrode 27 having a high work function are formed on the insulating thin films 3 and 5, respectively. The first and second electrodes 4 and 27 are formed on the entire surface of the semiconductor substrate. The second electrode 27 on the other surface side irradiated with light is formed of a transparent conductive film. The second electrode 27 made of a transparent conductive film has a work function larger than that of the first electrode 4 and the semiconductor substrate 2. The first electrode 4 is formed of a metal having a work function smaller than that of the second electrode 27 and the semiconductor substrate 2 as described above. The insulating thin films 3 and 5 are preferably formed of silicon oxide thin films formed by steam heat treatment. The thickness of the silicon oxide thin film is preferably about 0.5 nm to 2 nm at which the tunnel current flows, as described above. By performing this steam heat treatment, a high-quality insulating thin film / semiconductor interface is formed.

  In the sixth embodiment, the light hν passes through the second electrode 27 made of a transparent conductive film, enters the semiconductor substrate 2, and is absorbed by the semiconductor substrate 2 to generate photoinduced carriers. Among the photo-induced carriers, the electrons e move to the first electrode 4 side and flow to the first electrode 4 through the insulating thin film 3. The hole h moves to the second electrode 27 side and flows to the second electrode 27 through the insulating thin film 5. Thus, the electrons e flow to the first electrode 4 having a small work function, and the holes h flow to the second electrode 27 made of the transparent conductive film having a large work function, and the solar cell is driven.

  A method for manufacturing the semiconductor solar cell 26 according to the sixth embodiment will be described. First, high-quality insulating thin films 3 and 5 are formed on both surfaces of the semiconductor substrate 2, that is, one surface (front surface) and the other surface (back surface), respectively, and the semiconductor substrate surface is passivated. The insulating thin films 3 and 5 are preferably formed of silicon oxide thin films formed by steam heat treatment. The thickness of the silicon oxide thin film is preferably about 0.5 nm to 2 nm as described above. By performing this steam heat treatment, a high-quality insulating thin film / semiconductor interface is formed.

  Next, a second metal electrode 27 made of a transparent conductive film is formed on the entire surface of the insulating thin film 5 on the other surface side where light is incident. Further, the first metal electrode 4 is formed on the entire surface of the insulating thin film 3 on one surface side where no light is incident. Both the second metal electrode 27 and the first metal electrode 4 are formed on the entire surface of both surfaces of the semiconductor substrate 2. In this way, the solar cell 26 according to the sixth embodiment is obtained.

  According to the semiconductor solar cell 26 according to the sixth embodiment, since the light hν is incident on the semiconductor substrate 2 from the second metal electrode 27 side made of the transparent conductive film, the light can be efficiently incident. Then, as described in the first embodiment, a practical MIS type solar cell that has high optical power conversion efficiency and enables cost reduction can be provided.

  Examples of the transparent electrode include InSnO 2 (ITO) or ZnO. The work functions are 4.8 eV and 7.8 eV, respectively. ITO and ZnO have a higher n-type work function than silicon semiconductors. The work function of ZnO is higher than that of a p-type silicon semiconductor. Accordingly, the ITO or ZnO transparent electrode can be used as a substitute for a metal such as gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd).

  That is, since an n-type silicon semiconductor has a work function close to 4.05 eV, an ITO film or a ZnO film can be used as the second electrode having a large work function. In addition, since the work function of the p-type silicon semiconductor is close to 5.17 eV, the ZnO film can be used as the second electrode having a large work function. Furthermore, in a p-type silicon semiconductor, the ITO film can be used as the first electrode having a small work function.

Next, a semiconductor solar cell based on the basic concept of the present invention will be demonstrated. Here, based on the basic concept shown in FIG. 1 (first embodiment), a semiconductor solar cell shown in FIG. 13 was prototyped. As a sample, first, both front and back surfaces of the p-type semiconductor substrate 32 with silicon having a specific resistance of 30 Ωcm and a plate thickness of 520 μm were thermally oxidized to form silicon oxide (SiO ₂ ) films 33 and 35 having a film thickness of 100 nm. The lifetime of the electronic decimal carrier at this time was 185 μs. The surface carrier recombination rate was estimated to be 141 cm / s.

  Next, the silicon oxide film 33 on the surface side was thinned using buffer hydrofluoric acid. By optical measurement, the thickness was reduced to about 1.5 nm. After thinning, the lifetime of the electron minority carrier decreased to 16 μs.

Next, for the purpose of surface passivation, steam heat treatment was performed at 1.3 × 10 ⁶ Pa, 260 ° C. for 3 hours. The film thickness of the silicon oxide film 33 remains unchanged at about 1.5 nm. The film quality of the silicon oxide film is improved by the steam heat treatment. As a result, the lifetime of the electron minority carrier was increased to 47 μs, and the surface carrier recombination rate was estimated to be 970 cm / s.

  Next, a first electrode 34 made of striped aluminum (Al) and a second electrode 36 made of gold (Au) were formed on the silicon oxide film 33 on the surface side of the semiconductor substrate by a vacuum deposition method. The distance d4 between the first electrode 34 made of Al and the second electrode 36 made of Au was 0.29 mm. The width t1 of the first electrode 34 was 0.5 mm, and the width t2 of the second electrode 36 was 1 mm. In this way, a solar cell sample 31 according to the present invention shown in FIG. 13 was prepared.

  For comparison, a comparative solar in which stripe-shaped first electrode 34 'and second electrode 36' made of only aluminum (Al) are formed on the silicon oxide film 33 on the surface side of the semiconductor substrate 32 shown in FIG. A cell sample 37 was prepared. Since the configuration other than the electrodes 34 ′ and 36 ′ is the same as that of FIG. 13, the corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  Each sample 31 and 37 was irradiated with a halogen lamp light having a light intensity of 21.7 mW / cm 2 from the back surface of the semiconductor substrate 32 and the front and back surfaces, and the solar cell characteristics were measured.

  FIG. 15A shows the absolute current density-voltage characteristics of the sample 31 according to the present invention in which the first electrode 34 made of striped Al and the second electrode 36 made of Au (Al—Au electrode) are formed. FIG. 15B shows a sample 37 for comparison in which only an Al electrode, that is, a first electrode 34 'made of striped Al and a second electrode 36' made of striped Al (Al-Al electrode) was formed. Absolute current density vs. voltage characteristics.

  In each of FIGS. 15A and 15B, the vertical axis indicates the absolute current density as a log value, and the horizontal axis indicates a voltage from −1V to + 1V. In normal solar cell characteristics, only positive voltage is measured, but in this measurement, positive / negative voltage is measured. Broken lines b and d indicate characteristics when light is not applied, and solid lines a and c indicate characteristics when light L1 is irradiated from the back side where no electrode is formed.

  In both samples 31, 37, as indicated by broken lines b, d, a current flowed with a small voltage applied in a dark state where no light was applied. This is considered to be an FN current generated because the silicon oxide film 33 on the surface side is thin. In the sample 31 of the present invention in which the Al—Au electrodes 34 and 36 are formed when the light L1 is irradiated from the back side, the zero current (see the valley 30) is a positive side from 0 V as shown in practice a of FIG. 15A. A large current flows at zero voltage (0 V). This indicates that a large photoinduced current has occurred. Furthermore, zero current (see valley 30) appeared at a voltage of 0.49V. This suggests a large open circuit voltage. Note that the measurement was performed by applying a forward voltage between the Al electrode 34 and the Au electrode 36, and the zero current (see the valley 30) corresponds to a position where the voltage is just canceled and the electrode does not flow.

  On the other hand, in the comparative sample 37 in which the Al—Al electrodes 34 ′ and 36 ′ are formed, when the light L 1 is irradiated from the back side, as shown in the practice c in FIG. 15B, at the zero voltage (0 V) The current was small. The voltage of zero current (see valley 30 ') was only 0.02V.

  As a result, the solar cell characteristic of the present invention in FIG. 15A shows that the work function difference between the Al—Au electrodes 34 and 36 causes a potential difference in the silicon semiconductor substrate 32 and generates a photo-induced current.

FIG. 16 shows the solar cell characteristics when the samples 31 of the present invention on which the Al—Au electrodes 34 and 36 are formed are irradiated with light L2 and L1 from the front and back surfaces. In FIG. 16, the vertical axis represents current density [mA / cm ² ] when the log value of the vertical axis in FIG. 15A is a linear value, and the horizontal axis represents 0 V to +0.5 V on the horizontal axis in FIG. 15A. The voltage [V] extracted up to is shown. A curve e indicates a characteristic when the light L2 is irradiated from the front surface, and a curve f indicates a characteristic when the light L1 is irradiated from the back surface. It can be seen from FIG. 16 that typical solar cell characteristics can be obtained. In the case of backside illumination, the short-circuit current density, open-circuit voltage, and efficiency were 5.8 mA / cm ² , 0.49 V, and 7.5%, respectively. In the case of surface irradiation, the current density was small because the metal electrodes 34 and 36 hinder light irradiation.

  The results of the solar cell characteristics in FIG. 15 and FIG. 16 show that the solar cell of the present invention using the work function difference of different electrodes, in this example, different metals, and irradiating light from the back surface where the electrodes are not formed has excellent solar set characteristics. It is proved that it has.

  In the semiconductor solar cell according to the present invention, passivation of the semiconductor (silicon) surface is essential, and various techniques can be applied for this purpose. As the passivation, the steam heat treatment shown in FIG. 3 is effective. A thin thermal oxide film is a promising candidate because a thermal oxide film is also stable and can be well passivated. If a thin film oxide film can be formed by a method such as plasma CVD, it is considered good from the viewpoint of cost reduction. Further, the combination of the thin film oxide film and the steam heat treatment is effective as a surface passivation technique.

  In the above demonstration, a solar cell was formed by thinning the thermal oxide film and performing steam heat treatment. At this time, as described above, a sample having a lifetime of 185 μs with a thermal oxide film was used. The film thickness after the thermal oxide film was thinned was 1.5 nm on average, but the variation is large, and it seems that there are some parts that are completely etched. Therefore, the lifetime has become very small. However, the lifetime was improved to 47 μs after the steam heat treatment. It is thought that the improvement of the lifetime was carried out mainly by the steamed heat treatment, mainly on the etched portion. The principle of the solar cell characteristics of the present invention was able to be demonstrated in the sample having the passivation characteristics with a lifetime of 47 μs. Optimization of passivation is important for the creation of solar cells with better characteristics.

  In the solar cell according to the present invention, the first and second electrodes 4 and 6 are formed on the other surface of the semiconductor substrate 2 via the insulating thin film 3 and light is irradiated from one surface side of the semiconductor substrate 2. In the embodiment, the distance between the electrodes, the electrode width, and the thickness of the semiconductor substrate can be set as follows.

The diffusion length L of minority carriers is expressed by the following equation.
L = √ (D × τ)
D represents a diffusion coefficient, and τ represents a lifetime.

As shown in FIG. 17, when the thickness of the semiconductor substrate 2 is z1, the electrode width t1 of the first electrode 4, the electrode width t2 of the second electrode 6, and the distance d2 between the electrodes, respectively, It is preferable to set it to the diffusion length L or less of the decimal carrier.
d2 <√ (D · τ)
t1 <√ (D · τ)
t2 <√ (D · τ)
z1 <√ (D · τ)

  In the present invention, since the lifetime can take various values depending on the quality of the sample, it is necessary to design the sample accordingly.

On the other hand, the semiconductor solar cell according to the present invention has an advantage that it can be configured regardless of the impurity concentration of the semiconductor substrate 2. The impurity concentration of the semiconductor substrate 2 according to the present invention is preferably a high impurity concentration of 1 × 10 ¹⁵ cm ⁻³ or more. The impurity concentration of the semiconductor substrate 2 according to the present invention can be as low as 1 × 10 ¹⁵ cm ⁻³ or less.

[Seventh embodiment]
FIG. 18 shows a seventh embodiment of the semiconductor solar cell according to the present invention. As a passivation thin film, a silicon oxide (SiO ₂ ) film is an insulator that satisfactorily passivation the surface of a silicon semiconductor substrate. However, the silicon oxide film used as the passivation thin film needs to have a film thickness of about 2 nm or less, preferably 1.5 nm or less, in order to allow a current to flow through the first and second electrodes of metal due to the tunnel effect. When a silicon oxide (SiO ₂ ) film of 1 nm or less is used for passivation, variations in film thickness cannot be ignored. The thinner silicon oxide film may be diffused by the metal formed thereon to contact the silicon substrate and lose the passivation effect. As long as the surface passivation of the semiconductor substrate constituting the semiconductor solar cell can be achieved, the passivation thin film formed on the surface may not be a complete insulating film. For example, an intrinsic amorphous semiconductor having a band gap larger than that of a semiconductor substrate can be used as a passivation film that is highly insulating with respect to the semiconductor substrate and can conduct current.

  The semiconductor solar cell 41 according to the seventh embodiment uses a first conductivity type semiconductor substrate 2 and a semiconductor substrate made of p-type crystalline silicon in this example. The crystalline silicon is single crystal silicon or polycrystalline silicon (hereinafter the same). In the semiconductor solar cell 41, the first electrode 4 and the second electrode 6 are formed on one surface of the semiconductor substrate 2 via an intrinsic amorphous silicon film 42 that becomes a passivation thin film, and the other surface of the semiconductor substrate 2 is formed. An insulating film 44 is formed on the surface. In this configuration, the insulating film 44 is formed via the antireflection film 43 in order to prevent irregular reflection on the other surface irradiated with the light hν of the semiconductor substrate 2. As the insulating film 44, for example, a silicon oxide film or the like having optical transparency can be used. The antireflection film 43 can be formed of, for example, a laminated film of a silicon oxide film and a silicon nitride film.

  As described in the third embodiment, each of the first electrode 4 and the second electrode 6 is formed by arranging a plurality of stripe-shaped electrode portions at a predetermined interval in one direction. The The first electrode 4 and the second electrode 6 are formed in a comb-like shape and are arranged so as to mesh with each other. The distance between the adjacent first electrode 4 and second electrode 6 is set to be equal to or less than the diffusion distance of electron minority carriers.

  The first electrode 4 is made of a metal having a work function smaller than that of the semiconductor substrate 2 and the second electrode 6, such as aluminum (Al), hafnium (Hf), tantalum (Ta), indium (In), or zirconium (Zr). ) Or the like. The second electrode 6 is a metal having a work function larger than that of the semiconductor substrate 2 and the first electrode 4, for example, a metal such as gold (Au), nickel (Ni), platinum (Pt), or palladium (Pd). It is formed.

  The intrinsic amorphous silicon film 42 is a semiconductor having a band gap of 1.5 eV to 1.9 eV. The band gap of the intrinsic amorphous silicon film 42 is larger than the band gap 1.12 eV of the semiconductor substrate 2 made of crystalline silicon, and is a film that is highly insulating with respect to the semiconductor substrate 2 and can conduct current. The intrinsic amorphous silicon film 42 can be used as the passivation film 2 because defects can be reduced by introducing hydrogen. It has been demonstrated in an HIT solar cell that combines crystalline silicon and an amorphous silicon film that amorphous silicon exhibits an excellent passivation effect.

Since the intrinsic amorphous silicon film 42 has a smaller band gap than the silicon oxide (SiO ₂ ) film, a tunnel current can be obtained even if a thick film is used. A suitable film thickness of the intrinsic amorphous silicon film 42 as a passivation thin film is 3 nm to 50 nm. In this embodiment mode, it is sufficient to form a single layer of intrinsic amorphous silicon film.

  The operation of the semiconductor solar cell 41 according to the seventh embodiment is the same as that of the third embodiment described above.

  According to the semiconductor solar cell 41 according to the seventh embodiment, since the intrinsic amorphous silicon film is used as the passivation thin film, the band gap is smaller than the silicon oxide film, and a large tunnel current is obtained even when the film thickness is increased. be able to. Therefore, a practical solar cell with higher optical power conversion efficiency can be provided.

[Eighth Embodiment]
FIG. 19 shows an eighth embodiment of a semiconductor solar cell according to the present invention. This embodiment corresponds to a modification of the seventh embodiment. The semiconductor solar cell 46 according to the eighth embodiment uses a first conductivity type semiconductor substrate 2 and a semiconductor substrate made of p-type crystalline silicon in this example. In the semiconductor solar cell 46, the first electrode 4 and the second electrode 6 are formed on one surface of the semiconductor substrate 2 via a passivation thin film 47, and the antireflection film 43 is interposed on the other surface of the semiconductor substrate 2. An insulating film 44 is formed.

In the present embodiment, the passivation thin film 47 includes a thin silicon oxide film 48 formed on the semiconductor substrate 2 and an intrinsic amorphous silicon film 42 formed on the silicon oxide (SiO ₂ ) film 48. The The thin silicon oxide film 48 is formed with a film thickness having a tunnel effect, for example, a film thickness of 1.5 nm or less, for example, 0.5 nm. As the thin silicon oxide film 48, the above-described steam thermal oxide film is preferably used.

  Since the other configuration is the same as that described in the seventh embodiment, the same reference numerals are given to the portions corresponding to those in FIG.

  According to the semiconductor solar cell 46 according to the eighth embodiment, by forming the intrinsic amorphous silicon film 42 on the thin silicon oxide film 48, the metal that is the first electrode 4 and the second electrode 6. Diffusion can be prevented, and good passivation and tunneling current can be obtained. Therefore, it is possible to provide a practical solar cell with higher reliability and higher optical power conversion efficiency.

  In the seventh and eighth embodiments, the intrinsic amorphous silicon film 42 made of the same semiconductor as the semiconductor substrate is formed on the crystalline silicon semiconductor substrate 2 as the passivation thin film. In addition, an intrinsic amorphous semiconductor film made of a semiconductor other than silicon can be formed as a passivation thin film on the crystalline silicon semiconductor substrate 2. When a crystalline semiconductor substrate made of a different semiconductor material is used as the semiconductor substrate, an intrinsic amorphous semiconductor film made of the same semiconductor as the crystalline semiconductor substrate or a different semiconductor can be used as the passivation thin film as described above. As the passivation thin film, an intrinsic amorphous semiconductor film made of a semiconductor of the same quality as the semiconductor substrate is preferably used.

  The intrinsic amorphous semiconductor film 42 to be a passivation thin film according to the seventh embodiment, or the passivation thin film 47 formed by the intrinsic amorphous semiconductor film 42 and the thin silicon oxide film 48 according to the eighth embodiment is the same as that of the first embodiment to It can be applied to the passivation thin film of the sixth embodiment.

  As the passivation thin film according to the embodiment of the present invention, a diamond-like carbon film having a high insulating property can also be used.

As described above, silicon oxide (SiO ₂ ) has a band gap of 10 eV and is a very excellent insulator, and thus is suitable as a passivation thin film of the present invention. On the other hand, as shown in FIG. 20, various high dielectric constant materials have been developed, and since these all have a band gap of 1.18 eV or more, they are used as a passivation thin film placed between a semiconductor, for example, silicon and metal. Can do.

In particular, when a material having a small potential barrier against electrons and a thin film made of a material having a small potential barrier against holes are combined, a good semiconductor solar cell can be obtained. Materials having a small potential barrier with respect to electrons include Ta ₂ O ₅ , SrTiO ₃ , BaZrO ₃ , ZrO ₂ , HfO ₂ , ZrSiO ₄ , HfSiO _{4 and the} like. Examples of the material having a small potential barrier with respect to holes include LaAlO ₃ and Si ₃ N ₄ .

FIG. 20 shows silicon having a band gap of 1.1 eV (the left end in the figure), a material having a small potential barrier against electrons (solid line), and a material having a small potential barrier against holes (broken line). In FIG. 20, the upper half (E) shows the potential barrier against electrons and the lower half (H) shows the potential barrier against holes across the silicon band gap of 1.1 eV. _{Ta 2 O 5, SrTiO 3,} BaZrO 3, ZrO 2, HfO 2, Zr S iO 4, HfSiO 4 , the potential barrier is less material to electrons. Si ₃ O ₄ and LaAlO ₃ are materials having a small potential barrier against holes. Incidentally, a dashed line _shows a potential barrier _{SiO 2, Al 2 O 3,} Y 2 O 3, La 2 O 3.

  Next, an embodiment of a semiconductor solar cell using a thin film made of a material having a small potential barrier against electrons and a thin film made of a material having a small potential barrier against holes as a passivation thin film under each electrode will be described.

[Ninth Embodiment]
FIG. 21 shows a ninth embodiment of the semiconductor solar cell according to the present invention. The present embodiment is a semiconductor solar cell using the above-described thin film made of a material having a small potential barrier against electrons and the thin film made of a material having a small potential barrier against holes as a passivation thin film under each electrode. . FIG. 21A shows a principle configuration, and FIG. 21B shows an operation explanatory diagram.

A semiconductor solar cell 51 according to the ninth embodiment uses a first conductivity type semiconductor substrate 2 and, in this example, a semiconductor substrate made of p-type crystalline silicon. In the semiconductor solar cell 51, for example, a tantalum oxide (Ta ₂ O ₅ ) film 52 having a small potential barrier against electrons is formed as a passivation thin film on one surface of the semiconductor substrate 2, and the work function of the semiconductor solar cell 51 is on the tantalum oxide film 52. A small first electrode 4 made of, for example, Al is formed. Further, for example, a silicon nitride (Si ₃ N ₄ ) film 53 having a small potential barrier against holes is formed as a passivation thin film on the other surface of the semiconductor substrate 2, and a work function having a large work function is made of, for example, Au on the silicon nitride film 53. A second electrode 6 is formed. Thus, the semiconductor solar cell 51 is configured. The tantalum oxide film 52 and the silicon nitride film 53 to be the passivation thin film can be formed with a film thickness larger than the film thickness of 0.5 nm to 2.0 nm of the silicon oxide thin film described above.

  The operation of the semiconductor solar cell 51 of the ninth embodiment will be described. As shown in FIG. 21B, when the semiconductor 2 is irradiated with the light hν, the electrons e, which are minority carriers among the carriers generated by the light irradiation, are formed along the built-in potential formed by the band bending. 4 flows to the first electrode 4 through the tantalum oxide film 52. At this time, since the tantalum oxide film 52 which is a passivation thin film has a small potential barrier with respect to the electrons e, the electrons e very easily flow to the first electrode 4. Majority carrier holes h out of the carriers generated by the light irradiation move to the second electrode 6 side and flow to the second electrode 6 through the silicon nitride film 53 which is a passivation thin film. At this time, since the silicon nitride film 53 which is a passivation thin film has a small potential barrier with respect to the hole h, the hole h is very likely to flow to the second electrode 6. Therefore, a semiconductor solar cell with low DC resistance can be configured.

  According to the semiconductor solar cell 51 according to the ninth embodiment, since it has a structure with a low direct current resistance, a practical solar cell with higher optical power conversion efficiency can be provided. By using a film with a smaller band gap than electrons and holes as a passivation thin film, a large tunnel current can be obtained even if the film thickness is increased. Reliability is improved.

[Tenth embodiment]
FIG. 22 shows a tenth embodiment of a semiconductor solar cell according to the present invention. The present embodiment is a semiconductor solar cell using the above-described thin film made of a material having a small potential barrier against electrons and the thin film made of a material having a small potential barrier against holes as a passivation thin film under each electrode. .

  The semiconductor solar cell 55 according to the tenth embodiment uses a first conductivity type semiconductor substrate 2 and a semiconductor substrate made of p-type crystalline silicon in this example. In the semiconductor solar cell 55, the first electrode 4 and the second electrode 6 are formed on one surface of the semiconductor substrate 2 via the passivation thin film 56, and the antireflection film 43 is interposed on the other surface of the semiconductor substrate 2. An insulating film 44 is formed. The passivation thin film 56 is formed of the above-described high dielectric constant material film. In the same manner as described in the ninth embodiment, the passivation thin film 56 is formed by forming a passivation thin film corresponding to the lower part of the first electrode 4 with a material film having a small potential barrier with respect to electrons. 6 A corresponding passivation thin film is formed with a material film having a small potential barrier with respect to holes.

  It is known that when a high dielectric constant material film is formed on the surface of a silicon semiconductor substrate 2, a very thin silicon oxide (SiO2) film 57 having a thickness of, for example, about 0.5 nm is formed on the extreme surface of silicon. ing. Accordingly, in the present embodiment, a passivation thin film 58 having a two-layer film structure of the thin silicon oxide film 57 and the passivation thin film 56 made of a high dielectric constant material thereon is formed.

  At this time, the silicon oxide film 57 passivates the surface of the semiconductor substrate, and the passivation thin film 56 made of a high dielectric constant material functions as a passivation and electron / hole transport layer.

  Since other configurations are the same as those described in the seventh embodiment and the eighth embodiment, portions corresponding to those in FIGS. 18 and 21 are denoted by the same reference numerals, and redundant description is omitted.

  According to the semiconductor solar cell 55 according to the tenth embodiment, the surface of the semiconductor substrate is passivated by the thin silicon oxide film 57, and the surface of the semiconductor substrate is further passivated by the passivation thin film 56 made of a high dielectric constant material. Thereby, the passivation of the semiconductor substrate surface becomes good. In addition, the passivation thin film 56 made of a high dielectric constant material is located under the first electrode 4 and the second electrode 6 and serves as an electron transport layer and a hole transport layer. The flow of holes to the second electrode 6 can be facilitated. Therefore, since the reliability of passivation is improved and the direct current resistance is reduced, a practical solar cell with higher optical power conversion efficiency can be provided.

  The configuration of the passivation thin films 52 and 53 of the ninth embodiment or the passivation thin film 58 of the tenth embodiment can be applied to the passivation thin films of the second to sixth embodiments.

  In the second to fifth and seventh to tenth embodiments described above, a p-type silicon semiconductor substrate is used as the semiconductor substrate 2, but an n-type silicon semiconductor substrate can also be used. In the sixth embodiment described above, an n-type silicon semiconductor substrate is used as the semiconductor 2, but a p-type silicon semiconductor substrate can also be used.

  In the above example, a silicon substrate is used as the semiconductor substrate 2, but a germanium substrate, for example, a compound semiconductor substrate such as GaAs or the like can also be used.

  In the above-described embodiment, the first electrode and / or the second electrode can be formed of two or more electrodes having different work functions, for example, metal electrodes. For example, according to the function, the first electrode and / or the second electrode can be configured by combining an electrode for forming a built-in potential and a low-resistance electrode for extracting current.

  1, 8, 11, 12, 21, 41, 46, 51, 55 .. solar cell 2... Semiconductor substrate 3, 5 .. insulating thin film 4, 6. ..Electrode made of transparent conductive film, 42..Intrinsic amorphous silicon film, 47..Passivation thin film,

Claims (3)

A semiconductor substrate;
It is formed on a surface opposite to the light incident surface of the semiconductor substrate, and is made of a water vapor thermal oxide film that is higher in insulation than the semiconductor substrate and capable of current conduction by a tunnel effect, and is obtained by performing a heat treatment on the thermal oxide film. A passivation film,
A first electrode and a second electrode having different work functions formed on the passivation thin film,
The first electrode is formed of a metal having a work function smaller than that of the second electrode and the semiconductor substrate;
The semiconductor solar cell, wherein the second electrode is formed of a metal having a work function larger than that of the first electrode and the semiconductor substrate. The first electrode and the second electrode are photo-induced in one direction and are alternately arranged with an interval equal to or less than the diffusion distance of minority carriers of electrons or holes generated in the semiconductor substrate by light irradiation. And
The first electrodes are electrically connected to each other;
The semiconductor solar cell according to claim 1 , wherein the second electrodes are electrically connected to each other. A conductive block body for taking out a current electrically connected to the first electrode and the second electrode on a surface opposite to the light incident surface of the semiconductor substrate;
The conductive block body includes a first metal block portion embedded in an insulator and electrically connected to the first electrode, and a second metal block electrically connected to the second electrode. The semiconductor solar cell according to claim 1, further comprising: a portion.

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