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

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

[Technical Field]

[0001] The present invention relates to a semiconductor device, a solar cell, and a method for manufacturing a semiconductor device, and more particularly to a technology that is effective when applied to a semiconductor device constituting a solar cell, for example, and a manufacturing technology for the semiconductor device. [Background technology]

[0002] Non-Patent Document 1 describes that a titanium oxide film (TiOx film) formed on a buffer layer made of hydrogen-added amorphous silicon functions as an electron-selective film or a hole-selective film depending on the fabrication conditions, etc.

[0003] For example, in recent years, development of carrier selective films with carrier selectivity has been progressing. In order to obtain a hole selective film that combines good hole selectivity and good passivation properties, Patent Document 1 describes a manufacturing method in which a titanium oxide film is formed directly on the surface of crystalline silicon by thermal atomic layer deposition, the titanium oxide film is subjected to hydrogen plasma treatment, a transparent electrode (ITO electrode) is formed on the titanium oxide film, and then annealing is performed in an atmosphere containing oxygen.

[0004] Similarly to Patent Document 1, Non-Patent Document 2 also describes the use of a structure on the positive electrode side in which a titanium oxide film is formed on the surface of crystalline silicon, an ITO electrode is further formed on the surface of the titanium oxide film, and a metal is disposed on the surface of the ITO electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2021 / 010127 [Non-patent literature]

[0006] [Non-Patent Document 1] T. Matsui et al., Energy Procedia 124 (2017) 628 [Non-patent document 2] T. Matsui et al., ACS Appl. Mater. Interfaces 2020, 12, 49777-49785 [Non-patent document 3] D. Aisa et al., 2017 JINST 12 P12017 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to put such a structure into practical use in semiconductor devices, it was necessary to stack several other layers on the surface of the crystalline silicon, which created problems such as a complicated manufacturing process and high costs.

[0008] Therefore, an object of the present invention is to provide a semiconductor device and a solar cell, as well as a method for manufacturing a semiconductor device, which have a simple configuration and can be manufactured at low cost. [Means for solving the problem]

[0009] In one embodiment, the semiconductor device comprises a crystalline silicon layer having a first surface and a second surface opposite to the first surface, a titanium oxide film provided in contact with the first surface or the second surface of the crystalline silicon layer, and a metal electrode serving as a positive electrode provided in contact with the surface of the titanium oxide film.

[0010] In one embodiment, a solar cell includes the semiconductor device.

[0011] Furthermore, in one embodiment, a method for manufacturing a semiconductor device includes the steps of forming a titanium oxide film on a crystalline silicon layer, performing a hydrogen plasma treatment on the titanium oxide film, and forming a metal that will serve as a positive electrode directly on the surface of the titanium oxide film. [Effects of the Invention]

[0012] According to one embodiment, it is possible to provide a semiconductor device and a solar cell, as well as a method for manufacturing a semiconductor device, which have a simple configuration and can also reduce manufacturing costs. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1(A) is a diagram showing a schematic device structure of a carrier selection solar cell of this embodiment, and FIG. 1(B) is a diagram showing a schematic device structure of a carrier selection solar cell of a comparative example. [Figure 2] 1 is a flowchart illustrating a manufacturing process of a carrier selection solar cell according to the present embodiment. [Figure 3] 1 is a graph showing current-voltage characteristics of a carrier selection solar cell. [Figure 4] 4(A) and 4(B) are diagrams showing a device structure for investigating the influence of a metal material in contact with a titanium oxide film on the solar cell performance. [Figure 5A] FIG. 10 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. [Figure 5B] FIG. 10 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. [Figure 5C] FIG. 10 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. [Figure 5D] FIG. 10 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. [Figure 6] 1 is a graph showing the relationship between the wavelength of incident light and external quantum efficiency. [Figure 7A] 1 shows the device structure of a device having a p-type crystalline silicon layer, and photographs of the light-receiving surface and non-light-receiving surface. [Figure 7B] 1 shows the device structure of a device having an n-type crystalline silicon layer, and photographs of the light-receiving surface and non-light-receiving surface. [Figure 8] FIG. 8(A) is a photoluminescence (PL) image when the type of metal film in FIG. 7A is changed, and FIG. 8(B) is a PL image when the type of metal film in FIG. 7B is changed. [Figure 9] 9A to 9D are diagrams showing schematic device structures of a carrier selection type solar cell (p-type crystalline silicon layer) according to an embodiment (FIG. 9A) and a carrier selection type solar cell according to a comparative example (FIGS. 9B to 9D). [Figure 10] 10 is a graph showing the relationship between the wavelength of incident light and the external quantum efficiency of the carrier selection solar cell of the embodiment (FIG. 10(A)) and the comparative example (FIG. 10(B)). [Figure 11] 11A and 11B are diagrams showing schematic device structures of a carrier selection type solar cell (n-type crystalline silicon layer) according to an embodiment (FIG. 11A) and a carrier selection type solar cell of a comparative example (FIGS. 11B-11D). [Figure 12] 12(A) is a graph showing the relationship between the wavelength of incident light and the external quantum efficiency of the carrier selection solar cell of the embodiment (FIG. 12(A)) and the comparative example (FIG. 12(B)). [Figure 13] 13(A) and 13(B) are diagrams showing a schematic device structure of a carrier selection solar cell according to another embodiment 1. FIG. [Figure 14] 10 is a flowchart illustrating a manufacturing process of the carrier selection solar cell according to another embodiment 1. [Figure 15] FIG. 10 is a diagram showing a schematic device structure of a carrier selection solar cell according to another embodiment 2. [Figure 16] 10 is a flowchart illustrating a manufacturing process of a carrier selection solar cell according to another embodiment 2. [Figure 17] FIG. 1 is a diagram showing the structure of a commonly available PERC solar cell. DETAILED DESCRIPTION OF THE INVENTION

[0014] Fig. 1(A) shows a schematic device structure of a carrier selection solar cell of this embodiment, and Fig. 1(B) shows a schematic device structure of a carrier selection solar cell of a comparative example. In this specification, a carrier selection solar cell may be simply referred to as a solar cell or a device. The device structure shown in Figure 1(A) and the device structure shown in Figure 1(B) differ in that the titanium oxide film (TiOx film) 11 and the metal electrode 14 are in direct contact with each other in the device structure shown in Figure 1(A), whereas the device structure shown in Figure 1(B) has a transparent electrode 23 (ITO electrode) between the titanium oxide film 11 and the metal electrode 14, but otherwise they have the same structure. A carrier selection solar cell is configured by forming a hole selective film and an electron selective film to sandwich a light absorber (generally a semiconductor of a single conductivity type), and operates as a solar cell by extracting hole current through the hole selective film and electron current through the electron selective film.

[0015] 1(A) and 1(B), carrier selection solar cells 100 and 200 have a crystalline silicon layer 10. This crystalline silicon layer 10 is composed of a p-type silicon layer doped with p-type impurities such as boron (B). A random texture structure is formed on the front 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 flat.

[0016] In the carrier selection solar cell 100 of this embodiment, as shown in FIG. 1(A), a hole selection film 11 is formed on the back surface of the crystalline silicon layer 10 so as to be in direct contact with the crystalline silicon layer 10. Also, as shown in FIG. 1(A), an electron selection film 12 is formed on the front 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. In this case, the hole selection film 11 is made of a titanium oxide film. In contrast, 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 this is not particularly limited in this embodiment.

[0017] As shown in FIG. 1A, a translucent electrode 13 is disposed on the electron selective film 12. This translucent electrode 13 is composed of a translucent film that is transparent to at least visible light contained in sunlight and is conductive. Meanwhile, a metal electrode 14 is disposed in contact with the hole selective film 11, which is a titanium oxide film. While the metal electrode 14 may be in contact with only a portion of the hole selective film 11, it is preferable for the metal electrode 14 to be in contact with the entire surface of the hole selective film 11 from the viewpoint of ease of the metal electrode formation process. The metal electrode 14 is formed from a metal material such as aluminum (Al), titanium (Ti), silver (Ag), copper (Cu), nickel (Ni), gold (Au), or platinum (Pt). For example, using a film of gold, silver, or copper, which has a relatively large work function, for the metal electrode 14 is preferable because it increases the open-circuit voltage and conversion efficiency of the solar cell. The metal material may also be an alloy or a laminated film made of two or more metals. For example, costly Ag may be used to a minimum thickness, and the remaining portion may be made of an inexpensive metal such as Al.

[0018] In the carrier selection solar cell 100 configured as described above, for example, light is incident on the carrier selection solar cell 100 from above the translucent electrode 13. This light then passes through the translucent electrode 13 and the translucent electron selective film 12 (e.g., an amorphous silicon film), and enters 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 a light energy greater than the band gap of silicon among the light incident on the crystalline silicon layer 10. As a result, electron-hole pairs are formed inside the crystalline silicon layer 10. Of the electron-hole pairs generated, the hole (h+) passes through the titanium oxide film, which is the hole selective film 11, and reaches the metal electrode 14. On the other hand, of the electron-hole pairs generated, the electron (e - ) passes through the electron selection membrane 12 and reaches the translucent electrode 13. This generates a potential difference between the translucent electrode 13 and the metal electrode 14. In other words, when light is irradiated onto the carrier selection solar cell 100, an electromotive force is generated between the translucent electrode 13 and the metal electrode 14. A metal electrode 16 such as a silver film is formed on the translucent electrode 13 and is processed into a grid shape to ensure an area through which light passes. Therefore, when a load is connected between the metal electrode 14, which serves as the positive electrode, and the grid-shaped metal electrode 16, which serves as the negative electrode, the load can be driven by the electromotive force. In this way, the carrier selection solar cell 100 operates. The grid-shaped metal electrode 16 may also penetrate the translucent electrode 13 and be in contact with the electron selection membrane 12.

[0019] The surface of the crystalline silicon layer 10 may be flat, but in the carrier selection solar cell 100 shown in Figure 1(A), a random texture structure is formed on the surface of the crystalline silicon layer 10. This allows the carrier selection solar cell 100 to improve its conversion efficiency due to the reflection reduction effect and light trapping effect resulting from the random texture structure. The random texture structure may be formed on both the front and back surfaces of the crystalline silicon layer 10.

[0020] Next, a method for manufacturing the carrier selection type solar cell 100 shown in Fig. 1(A) will be described. Fig. 2 shows a flowchart illustrating the manufacturing process of the carrier selection type solar cell 100. First, a p-type silicon substrate for the crystalline silicon layer 10 is prepared. This silicon substrate has, for example, a (100) surface, a resistivity of 2 Ωcm, and a thickness of 280 μm. Next, a silicon nitride film (SiNx film) 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) to a thickness of approximately 140 nm (S1). Subsequently, the other side of the silicon substrate (side 2, the upper side 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 side 1 acts as a protective film against the etching solution, allowing the random texture structure to be formed only on side 2. Note that in the embodiment, for ease of understanding, side 1 refers to the non-light-receiving side, and side 2 refers to the light-receiving side.

[0021] The SiNx film is then removed with dilute hydrofluoric acid (S3). These processes allow the formation of a random texture structure on only one side of the crystalline silicon layer 10, but a more industrially viable method is to first form a random texture structure on both sides and then etch the crystalline silicon layer 10 on one side to create an equivalent substrate. This is a method for reducing recombination loss on the back side, and is also used in solar cells with a common PERC (Passivated Emitter Rear Cell) structure (Figure 17).

[0022] Next, the silicon substrate (crystalline silicon layer 10) is cleaned, and then the native oxide film formed on surfaces 1 and 2 of the silicon substrate is removed using dilute hydrofluoric acid (S4). An electron selective film 12 with excellent passivation properties is then formed on surface 2 of the silicon substrate (S5). Here, the electron selective film 12 with excellent passivation properties can be composed of, for example, a stacked film (a-Si:H in layer) of a hydrogenated intrinsic amorphous silicon film and a hydrogenated n-type amorphous silicon film. The film thickness is 10 nm or less. The hydrogenated intrinsic amorphous silicon film and the hydrogenated n-type amorphous silicon film can be formed, for example, by using plasma CVD (Chemical Vapor Deposition). In this case, the hydrogenated intrinsic amorphous silicon film functions as a passivation film, while the hydrogenated n-type amorphous silicon film functions as an electron selective film. As a result, the stacked film of the hydrogenated intrinsic amorphous silicon film and the hydrogenated n-type amorphous silicon film becomes an electron selective film with good passivation properties.

[0023] In this embodiment, an amorphous silicon film, which is commonly used in heterojunction solar cells, is used as the electron selective film 12 with good passivation properties. However, the electron selective film 12 with good passivation properties in this embodiment is not limited to this, and can also be composed of a film other than an amorphous silicon film. For example, the electron selective film 12 with good passivation properties in this embodiment may be an electron selective film such as that known in PERC solar cells. That is, by combining an n-type silicon layer in which phosphorus (P) is diffused on the light-receiving surface of surface 2 with a passivation film such as a SiNx film and point contacts of metal electrodes such as silver (Ag), it is possible to provide the same functionality as an electron selective film made of an amorphous silicon film.

[0024] Next, the native oxide film on surface 1 of the silicon substrate (crystalline silicon layer 10) is removed again using dilute hydrofluoric acid (S6). A titanium oxide film, which serves as the hole-selective film 11, is then formed on surface 1, the non-light-receiving surface of the silicon substrate (S7). The titanium oxide film is formed by thermal atomic layer deposition. In this embodiment, a FLexAL atomic layer deposition system from Oxford Instruments is used. TTIP (titanium isopropoxide) is used as the titanium precursor, and water vapor (HO) is used as the oxygen source. In this embodiment, the TTIP dose time per cycle is 1.2 seconds, and three 1.2-second doses of water are repeated. The titanium oxide film formation temperature is in the range of 120–350°C. This ALD cycle is repeated 128 times to form a titanium oxide film with a thickness of approximately 5 nm on the surface of the silicon substrate.

[0025] Next, after forming a titanium oxide film on the surface of the silicon substrate (crystalline silicon layer 10), a hydrogen plasma treatment is performed for 60 minutes or less (S8), in which the surface of the titanium oxide film is irradiated with hydrogen plasma. In this embodiment, the hydrogen plasma is generated using an inductively coupled plasma source attached to the 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. In addition, a discharge power of 15 W is also applied to the substrate tray in order to shorten the hydrogen plasma treatment time. Thereafter, a transparent electrode 13 is formed on the electron selective film 12 on the surface 2 by, for example, sputtering (S9). This transparent 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. Then, annealing is performed in an oven at a temperature of 180°C for two hours (S10). Here, the annealing is performed in an oxygen-containing atmosphere, such as reduced pressure or air. This annealing is performed to reduce silicon defects generated during the ITO film formation and to supply oxygen to the titanium oxide film (hole selective film 11).

[0026] Then, a metal film having a thickness of approximately 700 nm, which will become the positive metal electrode 14, is formed on the titanium oxide film (hole selective film 11) on surface 1 by DC discharge magnetron sputtering (S11). The metal film may be made of a single or multiple metals, such as aluminum (Al), titanium (Ti), silver (Ag), copper (Cu), nickel (Ni), gold (Au), or platinum (Pt). When forming the metal electrode 14, different types of metal films may be stacked, or a metal alloy film may be formed. This also applies to other embodiments. Note that other methods for forming the metal film may also be used, such as electron beam evaporation, resistance heating evaporation, screen printing, or electrodeposition. Thereafter, a silver film, which will become the negative metal electrode 16, is formed on the surface of the translucent electrode 13 formed on surface 2 of the electron selective film 12 by DC magnetron sputtering (S12). Other methods may also be used for the formation, such as electron beam evaporation, resistance heating evaporation, screen printing, and electrodeposition. The silver film formed on the light-incident side is processed into a grid pattern to ensure a light-transmitting area. For example, the area of the silver film accounts for approximately 4% of the cell area. The cell area of a carrier-selective solar cell 100 having p-type silicon is determined by the area of the translucent electrode 13 on the emitter-side surface 2, where the electron-selective film 12 and the p-type silicon (crystalline silicon layer 10) are junctioned. Finally, annealing is performed at 180°C in a reduced-pressure atmosphere containing oxygen (S13) to reduce silicon defects that occur during metal film formation. 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 the formation of the metal electrode 14, oxygen from the atmosphere must be passed through the metal to be supplied to the titanium oxide film. Therefore, it is necessary to adjust the oxygen concentration of the atmosphere, the annealing temperature, and the annealing time depending on the type and film thickness of the metal electrode. In this embodiment, to prevent deterioration of the metal electrode 14 due to contact with the atmosphere when the fabricated solar cell is stored for a long period of time, a protective film of 20 nm ITO is formed on the metal electrode 14. However, since this does not affect the characteristics of the solar cell, it is not shown in FIG. 1(A) or the flowchart in FIG. 2. This is also common to the other embodiments. However, solar cells used in actual products are sealed with glass or a sealant, so this protective film is not necessary.

[0027] In this manner, the carrier selection solar cell of this embodiment can be manufactured. In the carrier selection solar cell manufactured in this manner, the titanium oxide film (hole-selective film 11) formed directly on the surface of the silicon substrate (crystalline silicon layer 10) serves as a hole-selective film with excellent hole selectivity and passivation properties. Specifically, this embodiment has the following manufacturing method features: (1) forming a titanium oxide film directly on the surface of the crystalline silicon layer by thermal atomic layer deposition; (2) subjecting the titanium oxide film to hydrogen plasma treatment; (3) annealing the titanium oxide film in an oxygen-containing atmosphere after its formation; and (4) forming an electrode such as silver on the surface of the titanium oxide film. As a result, the titanium oxide film formed directly on the crystalline silicon layer serves as a hole-selective film with excellent hole selectivity and passivation properties. Furthermore, by not forming a translucent electrode between the titanium oxide film and the metal electrode, the structure is simplified, shortening the manufacturing process and reducing manufacturing costs, while also reducing consumption of rare metals such as indium (In), which is the raw material for the ITO electrode.

[0028] When a titanium oxide film is formed by atomic layer deposition such as thermal atomic layer deposition, a film (approximately 1 nm thick) containing silicon (Si), titanium (Ti), and oxygen (O) is formed at the interface between the titanium oxide film and the crystalline silicon layer. This film is formed naturally and can be considered the same as the titanium oxide film. An n-type silicon layer may also be used as the silicon substrate that becomes the crystalline silicon layer 10. For example, this may be an n-type silicon layer doped with n-type impurities such as phosphorus (P).

[0029] (Solar cell performance evaluation 1) A carrier selection solar cell 100 (FIG. 1(A)) was manufactured by the above-described method (FIG. 2). As Comparative Example 1, a carrier selection solar cell 200 (FIG. 1(B)) having a translucent electrode 23 between a titanium oxide film and a metal electrode was manufactured. The carrier selection solar cell 200 of Comparative Example 1 was manufactured by the same method as the carrier selection solar cell 100, except that a translucent electrode 23 similar to the translucent electrode 13 was also formed on the titanium oxide film side (face 1 side) in S9 of FIG. 2. A boron-doped FZ silicon wafer (thickness: approximately 280 μm, plane orientation (100), resistivity: approximately 4 Ωcm) manufactured by TOPSIL was used as the p-type silicon substrate, and silver (manufactured by Mitsubishi Materials Corporation) was used for the metal electrode 14, with a thickness of approximately 700 nm. The thickness of the electron selective film 12 (amorphous silicon film) was about 10 nm, the thickness of the titanium oxide film (hole selective film 11) was about 5 nm, and the thickness of the translucent electrode 13 (ITO electrode) was about 70 nm.

[0030] FIG. 3 shows the current-voltage characteristics of the carrier selection solar cell 100. 3, the solid line indicates the current-voltage characteristics of the carrier selection solar cell 100, and the dashed line indicates the current-voltage characteristics of the carrier selection solar cell 200 of Comparative Example 1. A Keithley Source Meter 2400 was used to measure the current-voltage characteristics of the solar cell. A solar simulator (manufactured by WACOM Corporation) consisting of two lamps, one Xe and one halogen, was used as the light source, and the light was measured at an air mass of 1.5 global and 100 mW / cm. 2The solar cell was irradiated with reference sunlight. It was confirmed that the carrier selection solar cell 100 had performance equivalent to that of the carrier selection solar cell 200 of Comparative Example 1 at a voltage of less than 0.54 V, even though it did not have a translucent electrode between the titanium oxide film 11 and the metal electrode 14. Conversely, it was found that the carrier selection solar cell 100 had better performance than the carrier selection solar cell 200 of Comparative Example 1 at a voltage of 0.54 V or higher. Therefore, the carrier selection solar cell 100 not only has good performance, but also has a simple configuration, does not require a complex manufacturing process, and can achieve low manufacturing costs.

[0031] Generally, in semiconductor devices, an ITO electrode is disposed between a crystalline silicon hole-selective film (titanium oxide film) and a metal electrode, as shown in Figure 14 of Patent Document 1 and Figure 1 of Non-Patent Document 2. Non-Patent Document 2 describes annealing after the deposition of the ITO electrode, but describes that annealing without the ITO electrode significantly reduces the performance of solar cells and other devices. This is because, when the titanium oxide film is annealed, if too much oxygen is supplied to the titanium oxide film from the atmosphere, the electrical resistance of the titanium oxide film or the contact resistance at the interface with the silicon or ITO that contacts it increases. It has been reported that the ITO electrode film plays a role in regulating the amount of oxygen supplied to the titanium oxide film. Therefore, it was assumed that the use of an ITO electrode was essential to achieve a certain level of performance when using a titanium oxide film as a hole-selective film. However, according to the present embodiment, it was confirmed that performance equivalent to or better than that with an ITO electrode could be achieved even without an ITO electrode. This is thought to be because the conductivity of the metal that makes up the metal electrode is significantly higher than that of ITO, and even if there is an excess supply of oxygen to the titanium oxide film during annealing, the contact resistance between the metal and titanium oxide remains lower than that between ITO and titanium oxide.

[0032] (Study of metal electrode materials 1) Next, we investigated the effect of metal materials in contact with the titanium oxide film on solar cell performance using carrier selection solar cells 110 and 120 shown in Figures 4(A) and 4(B). The carrier selection solar cell 110 in Figure 4(A) has a structure similar to that of the carrier selection solar cell 100 shown in Figure 1(A), except that a second metal electrode 17 (50 nm) is sandwiched between the hole selection film 11 (titanium oxide film) and the first metal electrode 18 (silver film). In other words, the metal electrode 14 has a double structure consisting of the first metal electrode 18 made of a silver film and the second metal electrode 17. Seven metals were used for the second metal electrode 17: aluminum, titanium, silver, copper, nickel, gold, and platinum. These metals were selected to be as pure as possible within the available range. The second metal electrode 17 was formed as follows.

[0033] In the flowchart of FIG. 2, in S11 of the above method, before forming the above-mentioned silver film (the silver film that becomes the first metal electrode 18 in this configuration), a second metal electrode 17 with a thickness of approximately 50 nm was formed by electron beam vacuum deposition. That is, the process of forming a metal electrode on the hole selective film 11 (titanium oxide film) on surface 1 was performed twice. However, the silver and copper of the second metal electrode 17 were formed by DC magnetron sputtering. The reason why the silver and copper metal electrodes were formed by a method other than electron beam vacuum deposition here was simply due to the convenience of the experimental equipment, and the effect of differences in the metal electrode formation method on the solar cell characteristics is significantly smaller than the effect of the type of metal.

[0034] 4(B) is a carrier selection solar cell 120 in which the crystalline silicon layer 10 of the carrier selection solar cell 110 in FIG. 4(A) is replaced from a p-type silicon layer to an n-type silicon layer (phosphorus-doped FZ silicon wafer manufactured by TOPSIL, thickness approximately 280 μm, surface orientation (100), resistivity approximately 3 Ωcm). In this case, as with the carrier selection solar cell 110, a second metal electrode 17 (50 nm) is sandwiched between the hole selection film 11 (titanium oxide film) and the first metal electrode 18 (silver film). The manufacturing method of this carrier selection solar cell 120 is the same as the manufacturing method of the solar cell 110 having the p-type silicon layer described above, except for the type of silicon layer. However, there is a difference in that, in order to define the solar cell area, the electrode on the light-receiving surface side where the junction (emitter) is located is patterned for solar cells 110 with a p-type silicon substrate, while the electrode on the non-light-receiving surface side where the junction (emitter) is located is patterned for solar cells with an n-type silicon layer. This is a technique for producing multiple small-area solar cells for experiments on the same substrate, and in actual crystalline silicon solar cell products, the entire surface of the silicon substrate becomes a single solar cell, so such electrode patterning is not required.

[0035] The results are shown in Figures 5A-5D and 6. In Figures 5A-5D, each graph shows the results of measurements for each type of second metal electrode 17. The numbers below each metal's element symbol indicate the work function of that metal. The work functions of the metals were referenced in Source 1 (H.B. Michaelson, Journal of Applied Physics 48, 4729 (1977)). Because the work function of Ag described in Source 1 is very small and varies significantly depending on the literature, the work function of Ag was referenced in Source 2 (R.P. Winch, Phys. Rev. 37, 1269 (1931)). Figure 5A shows the short-circuit current density (Jsc), Figure 5B shows the open-circuit voltage (Voc), Figure 5C shows the fill factor (FF), and Figure 5D shows the conversion efficiency (Eff). In each graph, the circles (shown on the left side of each metal graph) represent the device 110 with a p-type silicon layer, and the triangles (shown on the right side of each metal graph) represent the device 120 with an n-type silicon layer. The range of the circles and triangles is shown as a box-and-whisker plot to the right of the circles and triangles. The boundary of the box closest to zero represents the 25th percentile, and the boundary of the box furthest from zero represents the 75th percentile. The whiskers (error bars) above and below the boxes represent the 90th and 10th percentiles, respectively. Figure 6 also shows the relationship between the wavelength of incident light and the external quantum efficiency for each second metal electrode 17. For the solar cell performance shown in Figures 5A-5D, the current-voltage characteristics were measured under the same conditions as in Figure 3, and the parameters Jsc, Voc, FF, and Eff were extracted from the current-voltage characteristics. The external quantum efficiency spectra shown in Figure 6 were measured using a CEP-97 manufactured by Bunkoukeiki Co., Ltd., using an air mass of 1.5 global and 100 mW / cm. 2 The sample was irradiated with unmodulated white bias light and monochromatic light modulated (82 Hz) by a mechanical chopper, and the modulated photocurrent generated by the monochromatic light irradiation was measured by lock-in detection.

[0036] Metals with a work function of 4.2 eV or higher (the work function of aluminum) are suitable for use in metal electrodes. Referring to FIG. 5A, it can be seen that high short-circuit current densities can be obtained when aluminum, silver, copper, nickel, gold, or platinum is used as the material for the second metal electrode 17. Furthermore, FIGS. 5B-5D show that when silver, copper, nickel, gold, or platinum is used as the material for the second metal electrode 17, high values are obtained for the open-circuit voltage, fill factor (excluding copper), and conversion efficiency, indicating good solar cell performance. In particular, the open-circuit voltage and conversion efficiency were significantly improved when silver, nickel, gold, platinum, or copper, which have relatively large work functions, were used as the material for the second metal electrode 17 compared to when aluminum or titanium, which have relatively small work functions. This indicates that the open-circuit voltage, which reflects hole selectivity, and the conversion efficiency, which is an important indicator of solar cell performance, depend on the work function of the metal (metal electrode 14) in contact with the titanium oxide film serving as the hole-selective film 11.

[0037] Furthermore, when copper was used as the material for the second metal electrode 17, high values were obtained for the short-circuit current density and open-circuit voltage, as described above. Although the fill factor was slightly low, it was found that this was due to the annealing (S13). In fact, simply omitting the annealing treatment (S13) could improve the fill factor by approximately 0.05-0.08, and the conversion efficiency could be improved by approximately 1-2% compared to the value shown in Figure 5D. Copper is also suitable from the perspective of reducing the use of rare metals.

[0038] Figure 6 also shows that silver, copper (which partially overlaps with silver on the long-wavelength side), and gold exhibit high external quantum efficiency values for incident light in the near-infrared region, which has wavelengths of 900-1200 nm. Solar cells absorb a wide range of wavelengths, from short-wavelength sunlight (ultraviolet) to long-wavelength sunlight (infrared). However, the crystalline silicon layer has difficulty absorbing long-wavelength near-infrared and infrared light. These long-wavelength incident light beams reach the outermost metal electrode 14 through the crystalline silicon layer. If the metal electrode 14 has low reflectivity, the long-wavelength light is absorbed as is. However, if the metal electrode 14 has high reflectivity, the long-wavelength light is reflected and reabsorbed by the crystalline silicon layer, contributing to improved 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 reflectivity in the near-infrared region (wavelengths of 900-1200 nm), with reflectivity of 90% or more in air at room temperature (25°C). In particular, these results indicate that sensitivity in the near-infrared region, wavelengths of 1000 nm or more, depends on the type of second metal electrode 17, and that high sensitivity can be achieved by selecting a metal with high reflectivity in the near-infrared region, such as silver, copper, or gold. Therefore, using silver, copper, or 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. Copper, in particular, is less expensive than gold or silver and is also preferable from the perspective of reducing the use of rare metals.

[0039] (Study of metal electrode materials 2) Furthermore, to investigate the effect of metal materials in contact with the titanium oxide film on solar cell performance, we also investigated the PL (Photoluminescence) emission of the device shown in Figure 4. The seven types of metals mentioned above were used as metal materials.

[0040] FIG. 7A shows the device structure (front emitter) of device 130 having a p-type crystalline silicon layer 10, and photographs of the exterior of the fabricated sample (light-receiving surface (lower left) and non-light-receiving surface (lower right)). FIG. 7B shows the device structure (rear emitter) of device 140 having an n-type crystalline silicon layer 10, and photographs of the exterior of the sample (light-receiving surface (lower left) and non-light-receiving surface (lower right)). The photographs of the exterior of the sample are photographs of the light-receiving surface and non-light-receiving surface when a total of seven devices, each approximately 10 mm x 10 mm in size, are arranged on a 50 mm x 50 mm crystalline silicon substrate: three on the top row, three in the middle row, and one on the bottom row (the remaining two are evaluation samples). In other words, the photographs are taken from above and below of a sample in which a total of nine devices, including two evaluation samples, are arranged in a 3 x 3 pattern on a 50 mm x 50 mm plane. The structures of device 130 with a p-type crystalline silicon layer and device 140 with 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 the small-area solar cell; in device 130 with a p-type crystalline silicon layer, the ITO film 13 on the light-receiving surface side where the junction is located is patterned, and in device 140 with an n-type silicon layer, the metal electrode 14 on the non-light-receiving surface side where the junction is located is patterned. Figure 8(A) shows PL images obtained by varying the type of second metal electrode 17 in Figure 7A, and Figure 8(B) shows PL images obtained by varying the type of second metal electrode 17 in Figure 7B. PL images were obtained using a PVX1000+POPLI-Λ (ITES Corporation) with an 850 nm wavelength, 15 W output laser as the excitation light and a high-sensitivity silicon CCD camera as the detector. Figures 8(A) and 8(B) show PL images obtained by irradiating the light-receiving surface of each sample with excitation light. PL images are based on measuring the intensity distribution of light emitted when electron-hole pairs generated by light irradiation undergo radiative recombination. As the proportion of non-radiative recombination via defects increases, the proportion of radiative recombination decreases, resulting in weaker light emission. In other words, in these PL images, bright areas indicate long carrier lifetimes, while dark areas indicate short carrier lifetimes. The brightness and darkness vary depending on the metal in contact with the titanium oxide film. For example, when aluminum or titanium is in contact with the film, the PL emission weakens, indicating that the passivation characteristics of the titanium oxide film differ depending on the metal it is in contact with. Comparing the brightness of this PL emission (degree of passivation performance) with the solar cell characteristics shown in Figures 5A-5D, we can see that aluminum and titanium, which have dim PL emission, have low open-circuit voltages, while silver, copper, nickel, gold, and platinum, which have bright PL emission, have high open-circuit voltages. This means that the type of metal in contact with the titanium oxide film affects the passivation characteristics of the backside, and this in turn determines the open-circuit voltage of the solar cell.

[0041] Furthermore, PL images of a device 140 with an n-type crystalline silicon layer and a patterned metal electrode 14 on the non-light-receiving side reveal that when a low-work-function metal (aluminum, titanium) contacts a titanium oxide film, PL emission is significantly weaker only at the metal contact points. This indicates that the passivation characteristics of the solar cell backside are reduced only at the contact points between the aluminum or titanium and titanium oxide, resulting in increased recombination loss. On the other hand, when a high-work-function metal (silver, copper, nickel, gold, platinum) contacts a titanium oxide film, PL emission is stronger at the metal contact points. Metals with high near-infrared reflectance, such as silver, gold, and copper, exhibit particularly pronounced brightness. Titanium oxide, which is the hole-selective film 11, has a negative fixed charge and is therefore thought to have passivation properties due to the electric field effect. However, when titanium oxide contacts a low-work-function metal, the electric field induced in the crystalline silicon layer 10 weakens, presumably increasing the carrier recombination rate on the metal film side (backside).

[0042] (Solar cell performance evaluation 2) Furthermore, the solar cell performance of the carrier selection solar cell 100 (FIG. 1(A)) and carrier selection solar cells having other structures (Comparative Examples 2-4) was evaluated. FIG. 9(A) shows the device structure of the carrier selection solar cell 100 (device having a p-type crystalline silicon layer), and FIGS. 9(B)-(D) show the device structures of the carrier selection solar cells 210, 220, and 230 of Comparative Examples 2-4, respectively. Note that the device structure in FIG. 9(A) is the same as that shown in FIG. 1(A), and therefore a description thereof will be omitted. Figure 9(B) shows the device structure of a heterojunction solar cell 210 in which a laminated film of i-type and p-type amorphous silicon films (a-Si:H p-layer film 16 nm thick) is used as the hole selective film 15, and a transparent electrode (ITO electrode) 23 and a metal electrode 14 are laminated on top of it. Figure 9(C) shows the device structure of a solar cell 220 in which the ITO electrode 23 on the back side has been removed from the structure of Figure 9(B). Figure 9(D) shows the device structure of a solar cell 230 in which the ITO electrode 23 on the back side and the hole selective film 15 are not present. The solar cell 210 shown in FIG. 9(B) is a solar cell obtained by replacing steps S7 and S8 in the manufacturing process shown in FIG. 2 with a hole selective film of a heterojunction solar cell. Specifically, an i-type (thickness: 8 nm) and a p-type amorphous silicon film (thickness: 8 nm) were laminated by plasma CVD (a-Si:H p-layer film) to form the hole selective film 15. Then, in step S9, an ITO electrode 23 was formed on the hole selective film 15 by sputtering, following the formation of the ITO electrode 13 on the electron selective film 12. The solar cell 220 shown in FIG. 9(C) was manufactured by omitting the film formation step of the ITO electrode 23 on the hole selective film 15 side from the manufacturing process of the device shown in FIG. 9(B). The solar cell 230 shown in FIG. 9(D) was manufactured by omitting the film formation steps S7 and S8 from the manufacturing process shown in FIG. 2.

[0043] Table 1 shows the thermal conductivity of the carrier selection solar cell 100 and the carrier selection solar cells 210, 220, and 230 of Comparative Examples 2-4 (devices having a p-type crystalline silicon layer) under light irradiation (air mass 1.5 global, 100 mW / cm 2 ) shows the solar cell performance, and Fig. 10(A) and Fig. 10(B) show the relationship between the wavelength of incident light and the external quantum efficiency for the embodiment and the comparative example. Note that Fig. 10(B) is an enlarged view of the long wavelength side of Fig. 10(A). These figures were measured using the same equipment as Figs. 3 and 6 under the same conditions.

[0044] [Table 1]

[0045] As can be seen from Table 1, the conversion efficiency was highest in Comparative Example 2 (high), followed by the embodiment, Comparative Example 3, and Comparative Example 4 (low). The carrier-selection solar cell 210 of Comparative Example 2 is a commercially available product, and has an ITO electrode 23 inside the metal electrode 14. Due to the presence of the ITO electrode 23, the carrier-selection solar cell 100 exhibits a slightly higher conversion efficiency than the device of the embodiment. However, the carrier-selection solar cell 100 exhibits a higher conversion efficiency than the carrier-selection solar cells 220 and 230 of Comparative Examples 3-4, which do not have an ITO electrode. In particular, the performance was confirmed to be higher than that of the carrier-selection solar cell 220 of Comparative Example 3, which has a buffer layer (hole-selection film 15) made of amorphous silicon with excellent passivation properties, demonstrating its practicality. Generally, amorphous silicon is formed using a specific high-pressure gas, such as silane (SiH4), but these gases tend to require large capital investments and maintenance costs to ensure their safe use. Therefore, replacing amorphous silicon with titanium oxide, which can be formed using a cheaper and safer process, is of great industrial significance.

[0046] Furthermore, as shown in Figure 10, the carrier selection solar cell 100 had the highest external quantum efficiency in the near-infrared wavelength region and the lowest light absorption loss. In particular, the carrier selection solar cell 100 had high sensitivity on the long wavelength side, which was significantly higher than that of the solar cells 210, 220, and 230 of Comparative Examples 2-4. As described above, long wavelength light is not easily absorbed by crystalline silicon layers. However, the carrier selection solar cell 100 effectively utilizes long wavelength light, resulting in a significant improvement in conversion efficiency. The solar cell 210 of Comparative Example 2, which had an ITO electrode 23, had low sensitivity on the long wavelength side, possibly because the ITO electrode 23 was not completely transparent in the near-infrared wavelength region due to free electron absorption, resulting in absorption loss.

[0047] (Solar cell performance evaluation 3) A carrier selection solar cell 150 was prepared in which the crystalline silicon layer of the carrier selection solar cell 100 was replaced with an n-type crystalline silicon layer, and solar cell performance was evaluated. The carrier selection solar cell 150 is similar to the carrier selection solar cell 100 described above except that the crystalline silicon layer is replaced with an n-type crystalline silicon layer, and therefore a detailed description will be omitted. Comparative Examples 5-7 also correspond to Comparative Examples 2-4, respectively, and are similar except that the crystalline silicon layer is replaced with an n-type crystalline silicon layer, and therefore a description will be omitted. Figure 11(A) shows the device structure of the carrier selection solar cell 150 (device having an n-type crystalline silicon layer), and Figures 11(B)-(D) show the device structures of the carrier selection solar cells 240, 250, and 260 of Comparative Examples 5-7, respectively. Table 2 shows the optical transmittance (O / D) of the carrier selection solar cell 150 and the carrier selection solar cells (devices having an n-type crystalline silicon layer) of Comparative Examples 5-7 under light irradiation (air mass 1.5 global, 100 mW / cm 2 12(A) and 12(B) show the relationship between the wavelength of incident light and the external quantum efficiency for the embodiment and the comparative example. Note that FIG. 12(B) is an enlarged view of the long wavelength side of FIG. 12(A).

[0048] [Table 2]

[0049] As can be seen from Table 2, the conversion efficiency was highest for Comparative Example 5 (high), followed by the embodiment, Comparative Example 6, and Comparative Example 7 (low). The carrier-selective solar cell 240 of Comparative Example 5 is a commonly available product, and the carrier-selective solar cell 150 achieved a conversion efficiency comparable to that of Comparative Example 5. Comparative Example 6 is a solar cell of Comparative Example 5 with the backside ITO electrode 23 removed. A comparison of solar cells without the ITO electrode 23 on the backside clearly demonstrated the superiority of the carrier-selective solar cell 150. The conversion efficiency of Comparative Example 7 is significantly low, but this is due to the absence of a hole-selective film (junction emitter) on either the front or back side of the n-type silicon layer. This comparison clearly demonstrates that titanium oxide exhibits excellent hole selectivity.

[0050] 12, it can be seen that the carrier selection solar cell 150 has the highest external quantum efficiency in the near-infrared wavelength region and the lowest light absorption loss. These results confirm that the carrier selection solar cell has a high effect of improving external quantum efficiency, whether the crystalline silicon layer is n-type or p-type.

[0051] (Another embodiment 1) 13(A) and 13(B) show schematic device structures of a carrier selection solar cell 160 (FIG. 13(A)) and a carrier selection solar cell 170 (FIG. 13(B)) according to another embodiment 1. FIG. 14 shows a flowchart illustrating the manufacturing process of the carrier selection solar cell 160. Note that detailed explanations of parts that overlap with the flowchart in FIG. 2 will be omitted.

[0052] A method for manufacturing the carrier selection 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, anisotropic etching is performed on both sides (side 1 and side 2) of the silicon substrate to form a random texture structure on the silicon substrate (S21). Next, the silicon substrate is cleaned, and then, using dilute hydrofluoric acid, the native oxide films formed on sides 1 and 2 of the silicon substrate are removed (S22). Subsequently, n-type silicon oxide is formed on side 2 of the silicon substrate. + A layer 35 (n: n-type semiconductor. + indicates high concentration) is formed (S23). + The layer is formed by using POCl3 containing phosphorus as an n-type dopant as a raw material and thermally diffusing phosphorus into a p-type crystalline silicon layer.

[0053] Then, a silicon nitride film (SiNx film) 33 is formed on both sides of the silicon substrate to a thickness of about 80 nm by plasma-assisted chemical vapor deposition (plasma CVD) (S24). +A silver film (grid-shaped) that will become the negative metal electrode 16 is formed on the surface of the layer 35 (S25). At this time, the silver film is formed by, for example, screen printing. 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 becomes n + A negative electrode is formed in contact with layer 35. Next, one side of the silicon substrate (side 1, the lower side in FIG. 13) is subjected to single-sided etching to flatten and clean (S26). Then, a titanium oxide film, which serves as hole-selective film 11, is formed on side 1, the non-light-receiving side of the silicon substrate (S27). The titanium oxide film is formed by thermal atomic layer deposition. Thereafter, a hydrogen plasma treatment is performed for 60 minutes or less (S28), in which the surface of the titanium oxide film is irradiated with hydrogen plasma, and annealing is performed in an oven at a temperature of 180°C for 2 hours (S29). Here, annealing is performed in an oxygen-containing atmosphere, such as in a low vacuum or in the air.

[0054] Then, a metal film (first electrode 18 or second electrode 17, such as silver or copper) approximately 700 nm thick is formed on the titanium oxide film (hole-selective film 11) on surface 1 by DC discharge magnetron sputtering (S30) as the positive metal electrode 14. Finally, annealing is performed (S31) to reduce silicon defects that occur when the metal film is formed. A carrier-selective solar cell 170 can be manufactured using a method similar to that shown in FIG. 14, except that the crystalline silicon layer 10 is replaced with an n-type silicon substrate. A carrier-selective solar cell with this device structure also achieves the same effects as the carrier-selective solar cells of other embodiments. The carrier-selective solar cell obtained in this manner can simplify the back electrode structure of the commonly available PERC solar cell 300 shown in FIG. 17 and is expected to achieve improved performance. In other words, because the non-light-receiving surface of a PERC solar cell is passivated with an insulator such as an aluminum oxide film 37, a process for forming contact holes to connect the metal and silicon was previously required. In addition, the distance that carriers (holes) have to travel to reach the metal electrode 14 on the backside is long, which can lead to a decrease in performance depending on the quality of the wafer. Also, there is a problem that passivation is not applied at the point contact portion where silicon and metal come into contact, which causes carrier recombination loss due to contact between metal and silicon. In other words, the carrier selection cell obtained in another embodiment 1 can solve these problems of commercially available PERC solar cells. Note that in such PERC solar cells, in order to obtain ohmic contact between silicon and metal or p + To form a layer, an aluminum electrode is used for the p-type silicon layer. However, aluminum has a lower reflectivity than silver and causes a large optical loss on the back surface. Therefore, the above-mentioned alternative embodiment 1, which allows selection of a metal with a high reflectivity, is more preferable.

[0055] (Another embodiment 2) Fig. 15 shows a schematic device structure of a carrier selection solar cell 180 according to another embodiment 2. Fig. 16 shows a flowchart illustrating the manufacturing process of the carrier selection solar cell 180. Note that detailed explanations of parts that overlap with the flowchart in Fig. 2 will be omitted. This carrier selection solar cell 180 differs from the carrier selection solar cells of the other embodiments in that the structures of the positive and negative electrode sides are different. That is, the upper side of Fig. 15 is the positive electrode (surface 2), and the lower side is the negative electrode (surface 1).

[0056] A method for manufacturing the carrier selection solar cell 180 will be described. First, a p-type silicon substrate that will become the crystalline silicon layer 10 is prepared. Then, anisotropic etching is performed on both sides (sides 1 and 2) of the silicon substrate to form a random texture structure on the silicon substrate (S41). Next, the silicon substrate is cleaned, and then the native oxide films formed on sides 1 and 2 of the silicon substrate are removed using dilute hydrofluoric acid (S42). Next, a silicon oxide film 43 and an a-Si n-layer film are formed on side 1 of the silicon substrate (the lower surface in FIG. 15) (S43). The silicon oxide film 43 can be obtained, for example, by immersing a p-type silicon layer in an oxidizing solution. The a-Si n-layer film can be formed, for example, by plasma CVD. Furthermore, a silicon nitride film (SiNx film) is formed to a thickness of approximately 140 nm on side 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 annealing, the a-Si n-layer film is crystallized to become a poly-Si n-layer film (polycrystalline silicon layer film) 45 . Thereafter, a metal film having a thickness of approximately 700 nm is formed by screen printing to become the negative metal electrode 14 (S46). Next, the SiNx film is removed and cleaned from one surface (surface 2, the upper surface in FIG. 15) of the silicon substrate (S47), and then a titanium oxide film 11 is formed (S48). The subsequent steps (S49-S52) are the same as those in the flowchart of FIG. 14, and therefore their explanation will be omitted. Note that the carrier selection solar cell 180 differs from the carrier selection solar cell of the first embodiment in the structure of the positive and negative sides, and therefore in S51, a grid-shaped metal electrode 16 such as a silver film or copper film is formed on the positive side (surface 2) which is the light incident side. Furthermore, by replacing the p-type crystalline silicon layer 10 of the carrier selection solar cell 180 with an n-type crystalline silicon substrate, a solar cell with an n-type crystalline silicon layer can be manufactured in the same manner as above.

[0057] This application claims priority from Japanese Patent Application No. 2022-056473, filed March 30, 2022. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety. [Industrial Applicability]

[0058] The present invention has applicability to various devices that use solar cells. [Explanation of symbols]

[0059] 10 crystalline silicon layer 11 Hole selective film (titanium oxide film) 12 Electron-selective membrane 13, 23 Translucent 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 35n + layer 37 Aluminum oxide film 43 Silicon oxide film 45 poly-Si n-layer film 100, 110, 120, 130, 140, 150, 160, 170, 180 Carrier-selective solar cell 200, 210, 220, 230, 240, 250, 260 Carrier selection solar cell (comparison example) 300 Typical PERC solar cell

Claims

1. a crystalline silicon layer having a first surface and a second surface opposite to the first surface; a titanium oxide film provided in contact with the first surface or the second surface of the crystalline silicon layer; a metal electrode that serves as a positive electrode and is provided in contact with the surface of the titanium oxide film; Equipped with the titanium oxide film is a film to which hydrogen has been added, A semiconductor device, wherein the metal electrode comprises silver.

2. 2. 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.

3. 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. A solar cell comprising the semiconductor device according to any one of claims 1 to 3.

5. forming a titanium oxide film on the crystalline silicon layer; performing a hydrogen plasma treatment on the titanium oxide film; forming a metal electrode serving as a positive electrode directly on the surface of the titanium oxide film after the hydrogen plasma treatment; Equipped with the metal electrode comprises silver; and A method for manufacturing a semiconductor device, comprising the step of performing an annealing treatment immediately before or immediately after the step of forming the metal electrode to be the positive electrode directly on the surface of the titanium oxide film.

Images