WO2023190142A1

WO2023190142A1 - Semiconductor device, solar cell, and method for manufacturing semiconductor device

Info

Publication number: WO2023190142A1
Application number: PCT/JP2023/011781
Authority: WO
Inventors: 卓矢松井; 均齋
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2022-03-30
Filing date: 2023-03-24
Publication date: 2023-10-05

Abstract

The present invention addresses the problem of providing a semiconductor device, a solar cell, and a method for manufacturing a semiconductor device, wherein cost reduction can be achieved with a simple configuration. A semiconductor device resolving the problem comprises: a crystalline silicon layer 10 having a first surface and a second surface on the reverse side from the first surface; a titanium oxide film 11 disposed in contact with the first surface or the second surface of the crystalline silicon layer 10; and a metal electrode 14 disposed in contact with the surface of the titanium oxide film and serving as a positive electrode. In addition, a semiconductor device manufacturing method resolving the problem comprises the steps of: forming a titanium oxide film 11 on a crystalline silicon layer 10; subjecting the titanium oxide film 11 to a hydrogen plasma treatment; and forming a metal electrode 14 as a positive electrode directly on the surface of the titanium oxide film 11.

Description

Semiconductor device, solar cell, and method for manufacturing semiconductor device

The present invention relates to a semiconductor device, a solar cell, and a method for manufacturing a semiconductor device, and for example, to a technique that is effective when applied to a semiconductor device that constitutes a solar cell and a manufacturing technique thereof.

Non-Patent Document 1 states that a titanium oxide film (TiOx film) formed on a buffer layer made of hydrogen-doped amorphous silicon functions as an electron-selective film or a hole-selective film depending on the manufacturing conditions. is listed.

For example, in recent years, development of carrier selective membranes having carrier selectivity has been progressing. In order to obtain a hole-selective film that has both good hole selectivity and good passivation properties, Patent Document 1 discloses that a titanium oxide film is formed directly on the surface of crystalline silicon by thermal atomic layer deposition, and the titanium oxide film is A manufacturing method is described in which a titanium film is subjected to hydrogen plasma treatment, a light-transmitting electrode (ITO electrode) is formed on the titanium oxide film, and further annealing is performed in an atmosphere containing oxygen.

Also, in Non-Patent Document 2, similarly to Patent Document 1, a structure is described in which a titanium oxide film is formed on the surface of crystalline silicon, an ITO electrode is further formed on the surface, and a metal is placed on the surface of the ITO electrode. It is described that it is used for the positive electrode side.

International Publication No. 2021/010127

In order to commercialize a semiconductor device using such a configuration, many other layers must be stacked on the surface of crystalline silicon, which complicates the manufacturing process and increases costs. There was a problem.

Therefore, an object of the present invention is to provide a semiconductor device, a solar cell, and a method for manufacturing a semiconductor device that has a simple configuration and can reduce costs.

In one embodiment, a semiconductor device includes a crystalline silicon layer having a first surface and a second surface on the back surface thereof, and a titanium oxide film provided in contact with the first surface or the second surface of the crystalline silicon layer. and a metal electrode that is provided in contact with the surface of the titanium oxide film and serves as a positive electrode.

Furthermore, a solar cell in one embodiment includes the semiconductor device.

Furthermore, a method for manufacturing a semiconductor device in one embodiment includes a step of forming a titanium oxide film on a crystalline silicon layer, a step of performing hydrogen plasma treatment on the titanium oxide film, and a step of oxidizing a metal that will become a positive electrode. The method includes a step of forming the titanium film directly on the surface of the titanium film.

According to one embodiment, it is possible to provide a semiconductor device, a solar cell, and a method for manufacturing a semiconductor device that have a simple configuration and can reduce manufacturing costs.

FIG. 1(A) is a diagram showing a schematic device structure of a carrier-selective solar cell of this embodiment, and FIG. 1(B) is a diagram showing a schematic device structure of a carrier-selective solar cell of a comparative example. It is a figure showing a structure. It is a flowchart explaining the manufacturing process of the carrier selection type solar cell of this embodiment. 1 is a graph showing current-voltage characteristics of a carrier-selective solar cell. FIG. 4(A) and FIG. 4(B) are diagrams showing a device structure for investigating the influence of a metal material in contact with a titanium oxide film on solar cell performance. It is a graph showing the solar cell performance when the metal material in contact with the titanium oxide film is changed, and is a diagram showing the short circuit current density. It is a graph showing the solar cell performance when the metal material in contact with the titanium oxide film is changed, and is a diagram showing the open circuit voltage. It is a graph showing the solar cell performance when the metal material in contact with the titanium oxide film is changed, and is a diagram showing the fill factor. It is a graph showing the solar cell performance when the metal material in contact with the titanium oxide film is changed, and is a diagram showing the conversion efficiency. It is a graph showing the relationship between the wavelength of incident light and external quantum efficiency. It is a device structure of a device having a p-type crystalline silicon layer, and an external photograph of a light-receiving surface and a non-light-receiving surface. 2 is a photograph of the device structure of a device having an n-type crystalline silicon layer, and the appearance of a light-receiving surface and a non-light-receiving surface. 8(A) is a photoluminescence (PL) emission image when the type of metal film in FIG. 7A is changed, and FIG. 8(B) is a PL emission image when the type of metal film in FIG. 7B is changed. It is a statue. Schematic device structures of the carrier selective solar cell (p-type crystal silicon layer) of the embodiment (FIG. 9(A)) and the carrier selective solar cell of the comparative example (FIGS. 9(B)-(D)) FIG. It is a graph showing the relationship between the wavelength of incident light and the external quantum efficiency of carrier selective solar cells of the embodiment (FIG. 10(A)) and the comparative example (FIG. 10(B)). Schematic device structures of the carrier selective solar cell (n-type crystal silicon layer) of the embodiment (FIG. 11(A)) and the carrier selective solar cell of the comparative example (FIGS. 11(B)-(D)) FIG. 12 is a graph showing the relationship between the wavelength of incident light and the external quantum efficiency of the carrier selective solar cells of the embodiment (FIG. 12(A)) and the comparative example (FIG. 12(B)). 13(A) and 13(B) are diagrams showing a typical device structure of a carrier selective solar cell according to another embodiment 1. FIG. 3 is a flowchart illustrating a manufacturing process of a carrier selective solar cell according to another embodiment 1. FIG. FIG. 7 is a diagram showing a schematic device structure of a carrier selective solar cell according to another embodiment 2. FIG. 12 is a flowchart illustrating a manufacturing process of a carrier selective solar cell according to another embodiment 2. FIG. 1 is a diagram showing the structure of a PERC type solar cell that is generally commercially available.

FIG. 1(A) shows a schematic device structure of a carrier-selective solar cell of this embodiment, and FIG. 1(B) shows a schematic device structure of a carrier-selective solar cell of a comparative example. shows. Note that in this specification, a carrier-selective solar cell may be simply referred to as a solar cell or a device.
The device structure shown in FIG. 1(A) and the device structure shown in FIG. 1(B) differ from each other in that in the device structure shown in FIG. On the other hand, the device structure shown in FIG. 1(B) is different in that a transparent electrode 23 (ITO electrode) is present between the titanium oxide film 11 and the metal electrode 14, but other than that, the device structure shown in FIG. They have the same structure. A carrier-selective solar cell has a hole-selective film and an electron-selective film sandwiched between a light absorber (generally a semiconductor of a single conductivity type), and conducts a hole current through the hole-selective film. At the same time, the electron current is extracted through an electron selective membrane, thereby operating as a solar cell.

In FIGS. 1(A) and 1(B), carrier selective

solar cells

100 and 200 have a crystalline silicon layer 10. This crystalline silicon layer 10 is composed of, for example, a p-type silicon layer into which a p-type impurity such as boron (B) is introduced. A random texture structure is formed on the surface (second main surface) of the crystalline silicon layer 10. On the other hand, the back surface (first main surface) of the crystalline silicon layer 10 is a flat surface.

In the carrier selective solar cell 100 of this embodiment, as shown in FIG. is formed. Further, as shown in FIG. 1A, an electron selection film 12 is formed on the surface of the crystalline silicon layer 10 so as to be in direct contact with the crystalline silicon layer 10. That is, the crystalline silicon layer 10 is sandwiched between the hole selection film 11 and the electron selection film 12. At this time, the hole selection film 11 is made of a titanium oxide film. On the other hand, the electron selection film 12 is made of, for example, an amorphous silicon film containing hydrogen or a titanium oxide film having electron selectivity, but is not particularly limited in this embodiment.

As shown in FIG. 1(A), a light-transmitting electrode 13 is arranged on the electron selection film 12. The light-transmitting electrode 13 is made of a light-transmitting film that is transparent to at least visible light contained in sunlight and has electrical conductivity. On the other hand, a metal electrode 14 is arranged so as to be in contact with the hole selection film 11 which is a titanium oxide film. Although it is sufficient that the metal electrode 14 is in contact with a part of the hole selection membrane 11, it is preferable that the metal electrode 14 be in contact with the entire surface of the hole selection membrane 11 from the viewpoint of simplicity of the metal electrode formation process. The metal electrode 14 is made of a metal material such as aluminum (Al), titanium (Ti), silver (Ag), copper (Cu), nickel (Ni), gold (Au), or platinum (Pt). There is. For example, it is preferable to apply a film of gold, silver, copper, or the like, which has a relatively large work function, to the metal electrode 14 because it has the effect of increasing the open-circuit voltage and conversion efficiency of the solar cell. Further, the metal material may be an alloy or a laminated film made of two or more types of metals. For example, the film thickness of expensive Ag may be set to the minimum required thickness, and the rest may be laminated with an inexpensive metal such as Al.

In the carrier-selective solar cell 100 configured as described above, light is incident on the carrier-selective solar cell 100 from above the transparent electrode 13, for example. Then, this light passes through the light-transmitting electrode 13 having light-transmitting properties and the electron-selective film 12 having light-transmitting properties (for example, an amorphous silicon film), and enters the crystalline silicon layer 10 . Of the light incident on the crystalline silicon layer 10, electrons are excited from the valence band to the conduction band of the crystalline silicon layer 10 by light having optical energy larger than the band gap of silicon. As a result, electron-hole pairs are formed inside the crystalline silicon layer 10. Of the pair of electrons and holes generated, the hole (h+) passes through the titanium oxide film, which is the hole selection film 11, and reaches the metal electrode 14. On the other hand, among the pair-generated electrons and holes, electrons (e ⁻ ) pass through the electron selection film 12 and reach the transparent electrode 13 . This creates a potential difference between the transparent electrode 13 and the metal electrode 14. That is, when the carrier selective solar cell 100 is irradiated with light, an electromotive force is generated between the transparent electrode 13 and the metal electrode 14. A metal electrode 16 such as a silver film is formed on the transparent electrode 13, and is processed into a grid shape to ensure a region through which light can pass. Therefore, when a load is connected between the metal electrode 14 serving as the positive electrode and the grid-shaped metal electrode 16 serving as the negative electrode, the load can be driven by the electromotive force. In this manner, the carrier selective solar cell 100 operates. Furthermore, the grid-shaped metal electrode 16 may penetrate through the transparent electrode 13 and be in contact with the electron selective membrane 12 .

Although the surface of the crystalline silicon layer 10 may be a flat surface, in the carrier selective solar cell 100 shown in FIG. 1(A), a random texture structure is formed on the surface of the crystalline silicon layer 10. Thereby, in the carrier selective solar cell 100, the conversion efficiency can be improved due to the reflection reduction effect and light confinement effect resulting from the random texture structure. Note that a random texture structure may be formed on both the front and back surfaces of the crystalline silicon layer 10.

Next, a method for manufacturing the carrier selective solar cell 100 shown in FIG. 1(A) will be described. FIG. 2 shows a flowchart illustrating the manufacturing process of the carrier selective solar cell 100.
First, a p-type silicon substrate that will become the crystalline silicon layer 10 is prepared. This silicon substrate has, for example, a (100) plane as a surface, a specific resistivity of 2 Ωcm, and a thickness of 280 μm. Next, a silicon nitride film (SiNx film) with a thickness of approximately 140 nm is formed on one side of the silicon substrate (Side 1, the lower side in FIG. 1A) by plasma-assisted chemical vapor deposition (plasma CVD) (S1 ). Next, the other surface of the silicon substrate (surface 2, the upper surface in FIG. 1A) is anisotropically etched to form a random texture structure on the silicon substrate (S2). At this time, the SiNx film formed on surface 1 acts as a protective film for the etching solution, and a random texture structure can be formed only on surface 2. In the embodiment, for the sake of clarity, surface 1 refers to the surface on the non-light-receiving side, and surface 2 refers to the surface on the light-receiving side.

After that, the SiNx film is removed with dilute hydrofluoric acid (S3). Although it is possible to form a random texture structure on only one side of the crystalline silicon layer 10 using these processes, it is also possible to form a random texture structure on both sides once and then etching the crystalline silicon layer 10 on one side as a more industrial method. It is possible to create a board for This is a method for reducing recombination loss on the back surface, and is also used in solar cells with a general PERC (Passivated Emitter Rear Cell) structure (FIG. 17).

Next, after cleaning the silicon substrate (crystalline silicon layer 10), the natural oxide film formed on surfaces 1 and 2 of the silicon substrate is removed by using dilute hydrofluoric acid (S4). Thereafter, an electron selective film 12 with good passivation properties is formed on the surface 2 of the silicon substrate (S5). Here, the electron selective film 12 with good passivation properties is made of, for example, a laminated film (a-Si:H i-n layer film) of an intrinsic amorphous silicon film doped with hydrogen and an n-type amorphous silicon film doped with hydrogen. Can be configured. The thickness of the film is 10 nm or less. The hydrogen-doped intrinsic amorphous silicon film and the hydrogen-doped n-type amorphous silicon film can be formed, for example, by using a plasma CVD (Chemical Vapor Deposition) method. At this time, the hydrogen-doped intrinsic amorphous silicon film functions as a passivation film, while the hydrogen-doped n-type amorphous silicon film functions as an electron selection film. As a result, the laminated film of the hydrogen-doped intrinsic amorphous silicon film and the hydrogen-doped n-type amorphous silicon film becomes an electron-selective film with good passivation properties.

Note that in this embodiment, an amorphous silicon film commonly used in heterojunction solar cells is used as the electron selective film 12 with good passivation properties. However, the present invention is not limited to this, and the electron selective film 12 with good passivation properties in this embodiment may be made of a film other than an amorphous silicon film. For example, as the electron selective film 12 with good passivation properties in this embodiment, an electron selective film known from PERC solar cells may be used. That is, by combining an n-type silicon layer in which phosphorus (P) is diffused on the light-receiving surface of surface 2, a passivation film such as a SiNx film, and a point contact of a metal electrode such as silver (Ag), an amorphous silicon film can be used as an electron-selective film. Similar functions can be provided.

Next, by using dilute hydrofluoric acid again on the silicon substrate (crystalline silicon layer 10), the natural oxide film on surface 1 is removed (S6). Thereafter, a titanium oxide film, which is the hole selection film 11, is formed on surface 1, which is the non-light-receiving surface of the silicon substrate (S7). The titanium oxide film is formed by thermal atomic layer deposition. In this embodiment, FLexAL manufactured by Oxford Instruments is used as the atomic layer deposition apparatus. At this time, TTIP (Titanium isopropoxide) is used as a titanium precursor, and water vapor (H ₂ O) is used as an oxygen source. In this embodiment, the TTIP dose time per cycle is 1.2 seconds, and the water dose of 1.2 seconds is repeated three times. Further, the film forming temperature of titanium oxide is set in the range of 120-350°C. By repeating this ALD cycle 128 times, a titanium oxide film having a thickness of about 5 nm is formed on the surface of the silicon substrate.

Next, after forming a titanium oxide film on the surface of the silicon substrate (crystalline silicon layer 10), hydrogen plasma treatment is performed within 60 minutes to irradiate the surface of the titanium oxide film with hydrogen plasma (S8). . In this embodiment, hydrogen plasma is generated using an inductively coupled plasma source attached to the above-described atomic layer deposition apparatus under conditions of a hydrogen flow rate of 50 sccm, a pressure of 10 Pa, and a discharge power of 600 W. Note that, in order to shorten the hydrogen plasma treatment time, a discharge power of 15 W was also applied to the substrate tray.
Thereafter, the transparent electrode 13 is formed on the electron selective film 12 on the surface 2 by, for example, a sputtering method (S9). The light-transmitting electrode 13 is transparent to at least visible light and is made of, for example, indium-tin oxide (ITO) with a thickness of 60 nm to 150 nm. Thereafter, annealing is performed in an oven at a temperature of 180° C. for 2 hours (S10). Here, the annealing is performed in an atmosphere containing oxygen, such as under reduced pressure or in the atmosphere. This annealing is performed not only for the purpose of reducing silicon defects generated during the ITO film formation, but also for the purpose of supplying oxygen to the titanium oxide film (hole selection film 11).

Then, a metal film with a thickness of about 700 nm, which will become the positive metal electrode 14, is formed on the titanium oxide film (hole selection film 11) on the surface 1 by DC discharge magnetron sputtering (S11). For example, metals such as aluminum (Al), titanium (Ti), silver (Ag), copper (Cu), nickel (Ni), gold (Au), and platinum (Pt) may be used alone or in combination in the metal film. It's okay. When forming the metal electrode 14, different types of metal films may be laminated, or an alloy metal film may be formed. This is also common to other embodiments. Note that the metal film may be formed by other methods, such as electron beam evaporation, resistance heating evaporation, screen printing, electrodeposition, or the like. Thereafter, a silver film that will become the negative metal electrode 16 is formed on the surface of the transparent electrode 13 formed on the surface 2 of the electron selection film 12 by direct current magnetron sputtering (S12). Note that other forming methods may be used, such as electron beam evaporation, resistance heating evaporation, screen printing, electrodeposition, etc. At this time, the silver film formed on the light incident side is processed into a grid shape to ensure a region through which light passes. For example, the area of the silver film in the cell area is about 4%. Note that the cell area of the carrier selective solar cell 100 having p-type silicon is the translucent electrode on the emitter side surface 2 where the junction between the electron selective film 12 and the p-type silicon (crystalline silicon layer 10) is formed. It is defined by the area of 13. Finally, annealing is performed at a temperature of 180° C. in a reduced pressure atmosphere containing oxygen (S13) to reduce defects in silicon generated during metal film formation. Note that the annealing in S10 may be omitted and only the annealing in S13 may be performed. However, if the annealing in S10 is omitted and the annealing in S13 is performed only after forming the metal electrode 14, it is necessary to supply oxygen in the atmosphere to the titanium oxide film by passing through the metal. Therefore, it is necessary to adjust the oxygen concentration of the atmosphere, annealing temperature, and annealing time depending on the type and film thickness of the metal electrode.
In this embodiment, in order to prevent the metal electrode 14 from deteriorating due to contact with the atmosphere when storing the fabricated solar cell for a long period of time, a 20 nm thick ITO film is formed on the metal electrode 14 as a protective film. However, since it does not affect the characteristics of the solar cell, it is not shown in FIG. 1(A) or the flowchart of FIG. 2. This also applies to other embodiments. Note that this protective film is not necessary because solar cells used in actual products are sealed with glass or a sealant.

As described above, the carrier selective solar cell of this embodiment can be manufactured. In the carrier selective solar cell manufactured in this way, the titanium oxide film (hole selective film 11) formed directly on the surface of the silicon substrate (crystalline silicon layer 10) has good hole selectivity. This results in a hole-selective film having the same properties and good passivation properties. That is, in this embodiment mode, (1) a titanium oxide film is directly formed on the surface of a crystalline silicon layer by thermal atomic layer deposition, and (2) a hydrogen plasma treatment is performed on the titanium oxide film. , (3) After forming the titanium oxide film, annealing is performed in an atmosphere where oxygen exists, and (4) an electrode made of silver or the like is formed on the surface of the titanium oxide film. ing. As a result, the titanium oxide film formed directly on the crystalline silicon layer becomes a hole selective film having good hole selectivity and good passivation properties. In addition, by not forming a transparent electrode between the titanium oxide film and the metal electrode, the structure is simple, shortening the manufacturing process and reducing manufacturing costs. It has the advantage of suppressing the consumption of rare metals such as.

Note that when a titanium oxide film is formed by an atomic layer deposition method such as a thermal atomic layer deposition method, silicon element (Si), titanium element (Ti), and oxygen element ( A film (about 1 nm thick) containing O) is formed, but this film is naturally formed and can be regarded as the same as a titanium oxide film. Furthermore, an n-type silicon layer may be used as the silicon substrate that becomes the crystalline silicon layer 10. For example, it is an n-type silicon layer into which an n-type impurity such as phosphorus (P) is introduced.

(Solar cell performance evaluation 1)
A carrier selective solar cell 100 (FIG. 1(A)) was manufactured by the method described above (FIG. 2). Further, as Comparative Example 1, a carrier selective solar cell 200 (FIG. 1(B)) having a light-transmitting electrode 23 between a titanium oxide film and a metal electrode was manufactured. Note that the carrier selective solar cell 200 of Comparative Example 1 has the same structure as the light-transmitting electrode 23 on the titanium oxide film side (surface 1 side) in step S9 of FIG. , was manufactured by the same method as carrier selective solar cell 100. A boron-doped FZ silicon wafer manufactured by TOPSIL (thickness: approximately 280 μm, plane orientation (100), resistivity: approximately 4 Ωcm) was used as the p-type silicon substrate, and silver (manufactured by Mitsubishi Materials Corporation) was used for the metal electrode 14. , the thickness was about 700 nm. The thickness of the electron selective film 12 (amorphous silicon film) is approximately 10 nm, the thickness of the titanium oxide film (hole selective film 11) is approximately 5 nm, and the thickness of the transparent electrode 13 (ITO electrode) is approximately 10 nm. , about 70 nm.

FIG. 3 shows the current-voltage characteristics of the carrier selective solar cell 100.
Here, in FIG. 3, the solid line indicates the current-voltage characteristic of the carrier-selective solar cell 100, and the broken line indicates the current-voltage characteristic of the carrier-selective solar cell 200 of Comparative Example 1. A Keithley Sourcemeter 2400 was used to measure the current-voltage characteristics of the solar cell. In addition, a solar simulator (manufactured by WACOM Corporation) consisting of two lamps, Xe and halogen, was used as a light source, and the solar cell was irradiated with standard sunlight of 100 mW/cm ² at an air mass of 1.5 global.
According to the carrier selective solar cell 100, even if the titanium oxide film 11 and the metal electrode 14 do not have a translucent electrode, the carrier selective solar cell of Comparative Example 1 can be used at a voltage of less than 0.54 V. It was confirmed that the battery cell had the same performance as battery cell 200. Moreover, it can be seen that when the voltage is 0.54 V or more, the performance of the carrier-selective solar cell 100 is conversely improved over that of the carrier-selective solar cell 200 of Comparative Example 1. Therefore, according to the carrier selective solar cell 100, the performance is good, the structure is simple, the manufacturing process is not complicated, and the manufacturing cost can be reduced.

Generally, in a semiconductor device, as shown in FIG. 14 of Patent Document 1 and FIG. 1 of Non-Patent Document 2, there is a gap between a crystalline silicon hole selective film (titanium oxide film) and a metal electrode. , ITO electrodes are arranged. In Non-Patent Document 2, annealing is performed after forming an ITO electrode, but it is stated that if annealing is performed in the absence of an ITO electrode, the performance of solar cells and the like will be extremely degraded. This is because when the titanium oxide film is annealed, if too much oxygen is supplied from the atmosphere to the titanium oxide film, the electrical resistance of the titanium oxide film or the contact resistance of the interface with silicon or ITO in contact with it increases. It has been reported that the ITO electrode film plays a role in adjusting the amount of oxygen supplied to the titanium oxide film. Therefore, in order to use a titanium oxide film as a hole-selective film and achieve a certain level of performance, it was assumed that the use of an ITO electrode would be essential. However, according to the present embodiment, it was confirmed that even when there is no ITO electrode, performance equivalent to or higher than when there is an ITO electrode can be obtained. This is because the conductivity of the metal constituting the metal electrode is sufficiently higher than that of ITO, and even if the supply of oxygen to the titanium oxide film during annealing is excessive, at least the contact resistance between the metal and titanium oxide is This is thought to be due to the fact that it is kept lower than that of ITO and titanium oxide.

(Study of metal electrode materials 1)
Next, using carrier selective

solar cells

110 and 120 shown in FIGS. 4(A) and 4(B), the influence of the metal material in contact with the titanium oxide film on solar cell performance was investigated. The carrier-selective solar cell 110 in FIG. 4(A) has a hole-selective film 11 (titanium oxide film) and a first metal electrode 18 (silver It has a structure in which a second metal electrode 17 (50 nm) is sandwiched between the two metal electrodes (film). That is, the metal electrode 14 has a double structure of a first metal electrode 18 and a second metal electrode 17 made of a silver film. As materials for the second metal electrode 17, seven types of metals were used: aluminum, titanium, silver, copper, nickel, gold, and platinum. Note that these metals were used as highly pure as possible within the available range. Further, the second metal electrode 17 was formed as follows.

In the flowchart of FIG. 2, in S11 of the above method, before forming the above-mentioned silver film (in this configuration, the silver film that becomes the first metal electrode 18), a second metal electrode 17 with a thickness of about 50 nm is formed. It was formed by electron beam vacuum evaporation. That is, the step of forming a metal electrode on the hole selection film 11 (titanium oxide film) on the surface 1 was performed twice. However, among the second metal electrodes 17, silver and copper were formed by direct current magnetron sputtering. Here, the reason why the metal electrodes were formed using a method different from electron beam vacuum evaporation for silver and copper was simply due to the convenience of the experimental equipment. This is sufficiently small compared to the influence of

Further, the carrier selective solar cell 120 in FIG. 4(B) has a structure in which the crystalline silicon layer 10 of the carrier selective solar cell 110 in FIG. 4(A) is changed from a p-type silicon layer to an n-type silicon layer (manufactured by TOPSIL). This is a phosphorus-doped FZ silicon wafer, approximately 280 μm thick, (100) plane orientation, and approximately 3 Ωcm resistivity. In this case as well, like the carrier selective solar cell 110, a second metal electrode 17 (50 nm) is provided between the hole selective film 11 (titanium oxide film) and the first metal electrode 18 (silver film). Sandwiched. The method for manufacturing this carrier selective solar cell 120 is the same as the method for manufacturing the solar cell 110 having a p-type silicon layer described above, except that the type of silicon layer is different. However, in order to define the solar cell area, in the solar cell 110 having a p-type silicon substrate, the electrode on the light-receiving surface side where the junction (emitter) is located is patterned, and in the solar cell having an n-type silicon layer, the junction (emitter) is patterned. The difference is that the electrodes on the non-light-receiving surface are patterned. This is a technique for fabricating multiple small-area experimental solar cells on the same substrate, and in actual crystalline silicon solar cell products, the entire surface of the silicon substrate becomes one solar cell, so such electrodes are used. No patterning is required.

The results are shown in FIGS. 5A to 5D and FIG. 6. 5A to 5D, each graph shows the results of measurement for each type of second metal electrode 17, and the number below the element symbol of each metal indicates the work function of that metal. For the work functions of metals, Reference 1 (HB Michaelson, Journal of Applied Physics 48, 4729 (1977)) was referred to. Note that the work function of Ag described in Source 1 is very small and varies greatly depending on the literature, so Reference 2 (RP Winch, Phys. Rev. 37, 1269 (1931)) was referred to for the work function of Ag. Further, FIG. 5A shows the short circuit current density (Jsc), FIG. 5B shows the open circuit voltage (Voc), FIG. 5C shows the fill factor (FF), and FIG. 5D shows the conversion efficiency (Eff). ing. In each graph, the circle mark (shown on the left side of each metal's graph) is for a device 110 having a p-type silicon layer, and the triangle mark (shown on the right side of each metal graph) is for a device 110 having an n-type silicon layer. 120 is shown. In addition, to the right of the circle and triangle marks, the range of the circle and triangle marks is shown in a boxplot.The border of the box closest to zero represents the 25% point, and the border of the box furthest from zero represents the 25% point. represents the 75% point. Also, the whiskers (error bars) above and below the box indicate the 90% point and 10% point, respectively. Further, FIG. 6 shows the relationship between the wavelength of incident light and the external quantum efficiency of each second metal electrode 17. Regarding the solar cell performance in FIGS. 5A to 5D, the current-voltage characteristics were measured under the same conditions as in FIG. 3, and the parameters Jsc, Voc, FF, and Eff were extracted from the current-voltage characteristics. The external quantum efficiency spectrum in Figure 6 was measured using CEP-97 manufactured by Bunko Keiki Co., Ltd., using air mass 1.5 global, unmodulated white bias light of 100 mW/cm ² and monochromatic light modulated by a mechanical chopper (82 Hz). The sample was irradiated with monochromatic light, and the modulated photocurrent generated by the irradiation was measured by lock-in detection.

As the metal used for the metal electrode, a metal with a work function of 4.2 eV or more (the work function of aluminum) is suitable. Here, referring to FIG. 5A, it can be seen that a high short-circuit current density can be obtained when aluminum, silver, copper, nickel, gold, or platinum is used as the material of the second metal electrode 17. Furthermore, from FIGS. 5B to 5D, when silver, copper, nickel, gold, or platinum is used as the material for the second metal electrode 17, all of the open circuit voltage, fill factor (excluding copper), and conversion efficiency are A high value was obtained, indicating that the solar cell has good performance. In particular, with regard to open circuit voltage and conversion efficiency, silver and nickel, which have a relatively large work function, are used as the material for the second metal electrode 17, compared to aluminum and titanium, which have a relatively small work function. The effect was more pronounced when gold, platinum, and copper were used. In particular, the open-circuit voltage, which reflects hole selectivity, and the conversion efficiency, which is an important index of solar cell performance, depend on the work function of the metal (metal electrode 14) in contact with the titanium oxide film, which is the hole-selective film 11. It can be said that this shows that

Also, when copper was used as the material for the second metal electrode 17, high values were obtained for short circuit current density and open circuit voltage, as described above. Note that although the fill factor is slightly low, it is known that the cause is the annealing (S13). In fact, by simply omitting the annealing process (S13), the fill factor can be improved by about 0.05-0.08, and the conversion efficiency can be improved by about 1-2% from the values shown in Figure 5D. can. Copper is also suitable from the viewpoint of reducing the use of rare metals.

Furthermore, from FIG. 6, silver, copper (partially overlapped with silver on the long wavelength side), and gold exhibit high values regarding the external quantum efficiency of incident light in the near-infrared region with a wavelength of 900 nm to 1200 nm. I understand that. Solar cells absorb sunlight over a wide range of wavelengths, from short wavelengths (ultraviolet rays) to long wavelengths (infrared rays), but crystalline silicon layers are difficult to absorb the long wavelengths of near-infrared and infrared light. These long wavelength incident lights reach the outermost metal electrode 14 from the crystalline silicon layer. Here, if the reflectance of the metal electrode 14 is low, the long wavelength light will be absorbed as is, but if the reflectance of the metal electrode 14 is high, the long wavelength light will be reflected and absorbed into the crystalline silicon layer again. This contributes to improving external quantum efficiency and conversion efficiency. For example, as shown in Figure 5 of Non-Patent Document 3, metals such as gold, silver, and copper have high reflectance in the near-infrared region (wavelength 900-1200 nm), and in air at room temperature (25°C). The reflectance is 90% or more. In particular, according to this result, the sensitivity in the near-infrared region with a wavelength of 1000 nm or more depends on the type of the second metal electrode 17, and it is recommended to select a metal with high reflectance in the near-infrared region, such as silver, copper, or gold. This shows that high sensitivity can be obtained. Therefore, it can be said that using silver, copper, and gold for the metal electrode 14 of the carrier type battery cell 100 (FIG. 1(A)) of this embodiment is effective in improving external quantum efficiency and conversion efficiency. In particular, copper is less expensive than gold and silver, and is preferable from the perspective of reducing rare metals.

(Study of metal electrode materials 2)
Furthermore, the PL (Photoluminescence) emission of the device shown in FIG. 4 was also investigated regarding the influence of the metal material in contact with the titanium oxide film on the solar cell performance. The seven types of metals described above were used as the metal materials.

FIG. 7A shows the device structure (Front emitter) of the device 130 having the p-type crystalline silicon layer 10 and an external photograph of the prepared sample ((lower left) light-receiving surface and (lower right) non-light-receiving surface). FIG. 7B shows a device structure (rear emitter) of the device 140 having the n-type crystalline silicon layer 10 and an external photograph of the sample ((lower left) light-receiving surface and (lower right) non-light-receiving surface). The external photo of the sample shows a total of 7 devices, 3 on the top, 3 on the middle, and 1 on the bottom (the remaining 2 are samples for evaluation), each measuring approximately 10mm x 10mm, on a 50mm x 50mm crystalline silicon substrate. These are photographs of the light-receiving surface and non-light-receiving surface when the device is placed. That is, these are photographs taken from above and from below of a sample in which a total of nine devices, including two evaluation samples, were arranged in a 3x3 arrangement on a 50 mm x 50 mm plane. The structures of the device 130 having a p-type crystalline silicon layer and the device 140 having an n-type crystalline silicon layer are the same except for the crystalline silicon layer 10. However, the patterns of the light-transmitting electrode (ITO electrode) 13 on the light-receiving surface and the metal electrode 14 on the non-light-receiving surface are different. As mentioned above, this is for the purpose of defining the area of a small-area solar cell.In the device 130 having a p-type crystalline silicon layer, the ITO film 13 on the light-receiving surface side where the junction is formed is patterned, and the n-type silicon layer is In the device 140 having the above structure, the metal electrode 14 on the non-light-receiving surface side where the junction is located is patterned.
8(A) is a PL emission image when the type of second metal electrode 17 in FIG. 7A is changed, and FIG. 8(B) is a PL emission image when the type of second metal electrode 17 in FIG. 7B is changed. This is a PL emission image of the case. For the PL emission image, PVX1000+POPLI-Λ manufactured by ITES Co., Ltd. was used, a laser with a wavelength of 850 nm and an output of 15 W was used as the excitation light, and a highly sensitive silicon CCD camera was used as the detector. 8(A) and FIG. 8(B) show PL emission images taken from the light-receiving surface of each sample by irradiating excitation light from the light-receiving surface. The principle of PL emission imaging is to measure the intensity distribution of light emitted when electron-hole pairs generated by light irradiation undergo radiative recombination, but if the proportion of non-radiative recombination through defects increases, radiation The rate of recombination decreases and the emission becomes weaker. That is, in these PL emission images, bright parts indicate long carrier lifetimes and dark parts indicate short carrier lifetimes, and it can be seen that the brightness differs depending on the metal in contact with the titanium oxide film. For example, when aluminum or titanium is brought into contact, the PL emission becomes weaker, indicating that the passivation characteristics of the titanium oxide film differ depending on the metal in contact. Comparing the brightness of this PL emission (degree of passivation performance) and the solar cell characteristics shown in Figures 5A to 5D, we find that aluminum and titanium, which have dark PL emission, have a low open circuit voltage, while silver, copper, and nickel, which have bright PL emission, have a low open circuit voltage. It can be seen that gold and platinum have high open circuit voltages. In other words, it has become clear that the type of metal in contact with the titanium oxide film affects the passivation characteristics of the backside, and that this particularly affects the open-circuit voltage of the solar cell.

In particular, from the PL emission image of the device 140 having an n-type crystalline silicon layer in which the metal electrode 14 on the non-light-receiving surface side is patterned, it is clear that when a metal with a low work function (aluminum, titanium) and a titanium oxide film come into contact, the metal It can be seen that the PL emission is significantly weak only at the contact area. That is, in this case, the passivation characteristics of the back surface of the solar cell deteriorate only at the portion where aluminum or titanium and titanium oxide come into contact, and the recombination loss increases. On the other hand, it can be seen that when a metal with a high work function (silver, copper, nickel, gold, platinum) contacts a titanium oxide film, PL light emission is strong at the metal contact portion. In particular, in the case of metals such as silver, gold, and copper, which have high reflectance in the near-infrared region, the brightness of the emitted light is remarkable. Since titanium oxide, which is the hole-selective film 11, has a negative fixed charge, it is thought to have passivation properties due to the electric field effect. However, when titanium oxide comes into contact with a metal with a low work function, It is presumed that the electric field applied thereto becomes weaker and the carrier recombination rate on the surface (back surface) on the metal film side increases.

(Solar cell performance evaluation 2)
Furthermore, the solar cell performance of the carrier selective solar cell 100 (FIG. 1(A)) and the carrier selective solar cell having another structure (Comparative Example 2-4) was evaluated. FIG. 9(A) shows the device structure of a carrier selective solar cell (device having a p-type crystalline silicon layer) 100, and FIGS. 2 shows device structures of carrier selective

solar cells

210, 220, and 230. Note that the device structure in FIG. 9(A) is the same as that shown in FIG. 1(A), so a description thereof will be omitted. In FIG. 9B, a laminated film of i-type and p-type amorphous silicon films (a-Si:H i-p layer film, 16 nm thick) is used as the hole selection film 15, and a transparent electrode (ITO electrode) is used. 9(C) is a device structure of a heterojunction solar cell 210 in which ITO electrodes 23 and metal electrodes 14 are laminated, and FIG. FIG. 9D shows a device structure of a solar cell 230 without the ITO electrode 23 or hole selection film 15 on the back surface.
A solar cell 210 shown in FIG. 9(B) is obtained by replacing steps S7 and S8 in the manufacturing process shown in FIG. 2 with a hole-selective membrane of a heterojunction solar cell. Specifically, an i-type (film thickness: 8 nm) and a p-type amorphous silicon film (film thickness: 8 nm) are laminated by plasma CVD (a-Si:H i-p layer film) as the hole selective film 15. Manufactured. Then, in S9, following the formation of the ITO electrode 13 on the electron selection film 12, the ITO electrode 23 was also formed on the hole selection film 15 by sputtering. Furthermore, the solar cell 220 shown in FIG. 9(C) was manufactured by omitting the step of forming the ITO electrode 23 on the hole selection film 15 side from the manufacturing process of the device shown in FIG. 9(B). . Furthermore, the solar cell 230 shown in FIG. 9(D) was manufactured by omitting the film forming steps S7 and S8 from the manufacturing process shown in FIG.

Table 1 shows the carrier-selective solar cell 100 and the carrier-selective solar cells (devices having a p-type crystal silicon layer) 210, 220, and 230 of Comparative Example 2-4 under light irradiation (air mass 1.5 global , 100 mW/cm ² ), and FIGS. 10(A) and 10(B) show the relationship between the wavelength of incident light and the external quantum efficiency of the embodiment and the comparative example. Note that FIG. 10(B) is an enlarged view of FIG. 10(A) on the long wavelength side. These figures were measured using the same apparatus as in FIGS. 3 and 6 under the same conditions.

As can be seen from Table 1, the conversion efficiency was highest in the order of Comparative Example 2 (high), Embodiment, Comparative Example 3, and Comparative Example 4 (low). The carrier selective solar cell 210 of Comparative Example 2 is generally commercially available, and has an ITO electrode 23 inside the metal electrode 14. Due to the presence of the ITO electrode 23, the carrier selective solar cell 100 exhibits a slightly higher conversion efficiency than the device of the embodiment, but the carrier selective solar cell 100 is different from the carrier selective solar cell 220 of Comparative Example 3-4, which does not have an ITO electrode. , 230, the conversion efficiency is higher. In particular, it has been confirmed that the performance is higher than that of the carrier selective solar cell 220 of Comparative Example 3, which has a buffer layer (hole selective film 15) made of amorphous silicon with excellent passivation properties, and is therefore practical. It can be said. Generally, amorphous silicon is formed using a specific high-pressure gas such as silane (SiH ₄ ), but these gases tend to require large equipment investment and maintenance costs in order to be used safely. Therefore, it is of great industrial significance to replace amorphous silicon with titanium oxide, which can be formed using a cheaper and safer process.

Further, as shown in FIG. 10, it can be seen that the carrier selective solar cell 100 has the highest external quantum efficiency in the near-infrared wavelength region, and the light absorption loss is the lowest. In particular, the carrier-selective solar cell 100 had high sensitivity on the long wavelength side, which was remarkable compared to the

solar cells

210, 220, and 230 of Comparative Example 2-4. As described above, long-wavelength light is difficult to be absorbed by the crystalline silicon layer, but according to the carrier selective solar cell 100, long-wavelength light is also effectively used, and the effect of improving conversion efficiency is high. It can be said. In addition, the reason why the sensitivity on the long wavelength side was low in the solar cell 210 in which the ITO electrode 23 of Comparative Example 2 is arranged is that the ITO electrode 23 has a low sensitivity in the near-infrared wavelength region due to free electron absorption. It is thought that absorption loss occurred due to the lack of transparency.

(Solar cell performance evaluation 3)
A carrier selective solar cell 150 was prepared in which the crystalline silicon layer of the carrier selective solar cell 100 was an n-type crystalline silicon layer, and the solar cell performance was evaluated. Note that the carrier selective solar cell 150 is the same as the carrier selective solar cell 100 described above, except that the crystalline silicon layer is an n-type crystalline silicon layer, so a detailed description thereof will be omitted. Further, Comparative Example 5-7 also corresponds to Comparative Example 2-4, and is the same except that the crystalline silicon layer is an n-type crystalline silicon layer, so a description thereof will be omitted. FIG. 11(A) shows the device structure of a carrier selective solar cell (device having an n-type crystalline silicon layer) 150, and FIGS. 2 shows device structures of carrier selective

solar cells

240, 250, and 260. Table 2 shows the carrier selective solar cell 150 and the carrier selective solar cell of Comparative Example 5-7 (device having an n-type crystalline silicon layer) under light irradiation (air mass 1.5 global, 100 mW/cm ² ), and FIGS. 12(A) and 12(B) show the relationship between the wavelength of incident light and the external quantum efficiency of the embodiment and the comparative example. Note that FIG. 12(B) is an enlarged view of FIG. 12(A) on the long wavelength side.

As can be seen from Table 2, the conversion efficiency was highest in the order of Comparative Example 5 (high), Embodiment, Comparative Example 6, and Comparative Example 7 (low). The carrier-selective solar cell 240 of Comparative Example 5 is generally commercially available, and the carrier-selective solar cell 150 had a conversion efficiency comparable to that. Comparative Example 6 is a solar cell of Comparative Example 5 in which the back ITO electrode 23 is removed, and a comparison of the solar cells without the ITO electrode 23 on the back side clearly shows the superiority of the carrier-selective solar cell 150. Ta. The conversion efficiency of Comparative Example 7 is significantly low, but this is due to the fact that no hole selection film (junction/emitter) is formed on either the front or back surface of the n-type silicon layer. From this comparison, it is clear that titanium oxide exhibits excellent hole selectivity.

Further, as shown in FIG. 12, it can be seen that the carrier selective solar cell 150 has the highest external quantum efficiency in the near-infrared wavelength region, and the light absorption loss is the lowest. From these results, it was confirmed that the above-mentioned carrier-selective solar cell has a similar effect of improving external quantum efficiency regardless of whether the crystalline silicon layer is of n-type or p-type.

(Another Embodiment 1)
13(A) and 13(B) show a carrier selective solar cell 160 (FIG. 13(A)) and a carrier selective solar cell 170 (FIG. 13(B)) according to another embodiment 1. ) shows a schematic device structure. Further, FIG. 14 shows a flowchart illustrating the manufacturing process of the carrier selective solar cell 160. Note that detailed explanations of parts that overlap with the flowchart of FIG. 2 will be omitted.

A method for manufacturing carrier selective solar cell 160 shown in FIG. 13(A) will be described. First, a p-type silicon substrate that will become the crystalline silicon layer 10 is prepared. Then, by performing anisotropic etching on both surfaces (Surface 1 and Surface 2) of the silicon substrate, a random texture structure is formed on the silicon substrate (S21). Next, after cleaning the silicon substrate, the natural oxide film formed on surfaces 1 and 2 of the silicon substrate is removed by using dilute hydrofluoric acid (S22). Subsequently, an n ⁺ layer 35 (n: n-type semiconductor; + indicates high concentration) is formed on the surface 2 of the silicon substrate (S23). The n ⁺ layer can be formed, for example, by using POCl ₃ containing phosphorus as an n-type dopant as a raw material and thermally diffusing phosphorus into the p-type crystalline silicon layer.

Then, silicon nitride films (SiNx films) 33 are formed to a thickness of about 80 nm on both sides of the silicon substrate by plasma-assisted chemical vapor deposition (plasma CVD) (S24). Thereafter, a silver film (grid shape) that will become the negative metal electrode 16 is formed on the surface of the n ⁺ layer 35 by screen printing (S25). At this time, the silver film is formed by screen printing, for example. Then, annealing is performed in an oven at a temperature of 500° C. or higher (S25). At this time, the silver film of the metal electrode 16 diffuses and penetrates (fires through) the SiNx film 33, so that the silver film contacts the n ⁺ layer 35 and forms a negative electrode. Subsequently, one surface of the silicon substrate (surface 1, the lower surface in FIG. 13) is flattened by single-sided etching and cleaned (S26). Then, a titanium oxide film, which is the hole selection film 11, is formed on surface 1, which is the non-light-receiving surface of the silicon substrate (S27). The titanium oxide film is formed by thermal atomic layer deposition. Thereafter, a hydrogen plasma treatment is performed to irradiate the surface of the titanium oxide film with hydrogen plasma for up to 60 minutes (S28), and annealing is performed in an oven at a temperature of 180° C. for 2 hours (S29). Here, the annealing is performed in a low vacuum or in an atmosphere containing oxygen, such as the atmosphere.

Then, a metal film (first electrode 18 and second electrode 17 made of silver or copper, etc.) with a thickness of about 700 nm is applied to the titanium oxide film (hole selection film 11) on surface 1 as the metal electrode 14 of the positive electrode by direct current discharge. It is formed by magnetron sputtering method (S30). Finally, annealing is performed (S31) to reduce silicon defects generated during metal film formation. Further, the carrier selective solar cell 170 can be manufactured by the same method as shown in FIG. 14 except that the crystalline silicon layer 10 is replaced with an n-type silicon substrate. A carrier selective solar cell having such a device structure also provides the same effects as the carrier selective solar cell of the other embodiments. The carrier selective cell thus obtained can simplify the back electrode structure of the generally commercially available PERC solar cell 300 shown in FIG. 17, and can also be expected to improve performance. That is, since the PERC type solar cell has a structure in which the non-light-receiving surface is passivated with an insulator such as the aluminum oxide film 37, a process of forming a contact hole for bringing metal and silicon into contact is required. Further, the distance for carriers (holes) to reach the metal electrode 14 on the back surface is long, which may lead to performance deterioration depending on the quality of the wafer. In addition, passivation is not applied at the point where silicon and metal come into contact (point contact area), and there is a problem in that carrier recombination loss occurs due to contact between metal and silicon. That is, the carrier selection type cell obtained in another embodiment 1 can solve these problems of commercially available PERC type solar cells. In addition, in such a PERC type solar cell, an aluminum electrode is used for the p-type silicon layer in order to obtain ohmic contact between silicon and metal and to form a p ⁺ layer, but aluminum has a lower electrode density than silver. Since the reflectance is low and the optical loss on the back surface is large, it can be said that the above-mentioned alternative embodiment 1, in which a metal with a high reflectance can be selected, is more preferable.

(Another Embodiment 2)
FIG. 15 shows a schematic device structure of a carrier selective solar cell 180 according to another embodiment 2. Further, FIG. 16 shows a flowchart illustrating the manufacturing process of the carrier selective solar cell 180. Note that detailed explanations of parts that overlap with the flowchart of FIG. 2 will be omitted. This carrier selection type solar cell 180 differs from the carrier selection type solar cells of other embodiments in that the structures of the positive electrode side and the negative electrode side are different. That is, the upper side of the drawing in FIG. 15 is the positive electrode (surface 2), and the lower side is the negative electrode (surface 1).

A method for manufacturing carrier selective solar cell 180 will be described. First, a p-type silicon substrate that will become the crystalline silicon layer 10 is prepared. Then, by performing anisotropic etching on both surfaces (Surface 1 and Surface 2) of the silicon substrate, a random texture structure is formed on the silicon substrate (S41). Next, after cleaning the silicon substrate, the natural oxide film formed on surfaces 1 and 2 of the silicon substrate is removed by using dilute hydrofluoric acid (S42). Subsequently, a silicon oxide film 43 and an a-Si n layer film are formed on surface 1 (lower surface in FIG. 15) of the silicon substrate (S43). The silicon oxide film 43 can be obtained, for example, by immersing a p-type silicon layer in an oxidizing solution. Further, the a-Si n layer film can be formed by, for example, plasma CVD. Furthermore, a silicon nitride film (SiNx film) is formed to a thickness of about 140 nm on the surface 2 of the silicon substrate by plasma CVD (S44). Then, annealing is performed in an oven at a temperature of 800° C. or higher (S45). By performing the annealing, the a-Si n layer film is crystallized and becomes a poly-Si n layer film (polycrystalline silicon layer film) 45.
Thereafter, a metal film with a thickness of about 700 nm, which will become the metal electrode 14 of the negative electrode, is formed by screen printing (S46). Next, after removing and cleaning the SiNx film from one surface (surface 2, the upper surface in FIG. 15) of the silicon substrate (S47), a titanium oxide film 11 is formed (S48). The subsequent steps (S49-S52) are the same as those in the flowchart of FIG. 14, so their description will be omitted. Note that the carrier selective solar cell 180 has a different structure on the positive electrode side and the negative electrode side from the carrier selective solar cell of other embodiment 1, so in S51, the positive electrode side surface which is the light incident side A grid-shaped metal electrode 16 such as a silver film or a copper film is formed on the second side.
Furthermore, by replacing the p-type crystal silicon layer 10 of the carrier selective solar cell 180 with an n-type crystal silicon substrate, a solar cell with an n-type crystal silicon layer can be manufactured in the same manner as described above.

This application claims priority based on Japanese Patent Application No. 2022-056473 filed on March 30, 2022. All contents described in the application specification and drawings are incorporated herein by reference.

According to the invention according to the present invention, it can be used in various devices using solar cells.

10 Crystalline silicon layer 11 Hole selection film (titanium oxide film)
12 Electron

selective membranes

13, 23 Transparent electrode 14 Metal electrode 15 Hole selective membrane 16 Grid-shaped metal electrode 17 Second metal electrode 18 First metal electrode 33 Silicon nitride film 35 N ⁺ layer 37 Aluminum oxide film 43 Oxidation Silicon film 45 Poly-Si

n layer film

100, 110, 120, 130, 140, 150, 160, 170, 180 Carrier selection

solar cell

200, 210, 220, 230, 240, 250, 260 Carrier selection solar cell Cell (comparative example)
300 General PERC type solar cell

Claims

a crystalline silicon layer having a first surface and a second surface behind the first surface;
a titanium oxide film provided in contact with the first surface or the second surface of the crystalline silicon layer;
A semiconductor device comprising: a metal electrode that is provided in contact with the surface of the titanium oxide film and serves as a positive electrode.
The semiconductor device according to claim 1, wherein the titanium oxide film and the metal electrode are formed on the entire surface of the positive electrode side of the semiconductor device.
2. The semiconductor device according to claim 1, wherein the titanium oxide film is formed on the entire surface of the positive electrode side of the semiconductor device, and the metal electrode is laminated on a part of the titanium oxide film.
4. The semiconductor device according to claim 1, wherein the metal electrode is made of a metal having a work function of 4.2 eV or more.
4. The semiconductor device according to claim 1, wherein the metal electrode is made of at least one metal selected from gold, silver, and copper.
Any one of claims 1 to 5, wherein the metal electrode is formed of a metal having a reflectance of 90% or more in air and at room temperature in a near-infrared region with a wavelength range of 900 to 1200 nm. The semiconductor device according to item 1.
A solar cell comprising the semiconductor device according to any one of claims 1 to 6.
forming a titanium oxide film on the crystalline silicon layer;
a step of performing hydrogen plasma treatment on the titanium oxide film;
1. A method for manufacturing a semiconductor device, comprising the step of directly forming a metal to serve as a positive electrode on the surface of a titanium oxide film.
9. The method of manufacturing a semiconductor device according to claim 8, further comprising the step of performing an annealing treatment immediately before or after the step of directly forming the metal to be the positive electrode on the surface of the titanium oxide film.