Transparent conductive film, substrate with transparent conductive film, and photoelectric conversion element

Abstract

The purpose of the present invention is to provide a transparent conductive film which can be formed at low temperatures, has high transparency and high conductivity, and has a low indium content or does not contain indium. The transparent conductive film contains a metal oxide having amorphous tin oxide as the main component, the amount of Sn is 85 at% or more and the amount of In is 4 at% or less among the metal elements constituting the metal oxide, and the specific resistance of the transparent conductive film is 2 * 10 <-3 > Omega * cm or less.

Description

Technical Field

[0001] The present invention relates to a transparent conductive film, a substrate with a transparent conductive film, and a photoelectric conversion element. Background Art

[0002] In2O3-based materials such as ITO (tin-doped indium oxide) are widely known as transparent conductive films for light-receiving side transparent electrodes in optoelectronic devices such as displays and solar cells (e.g., Patent Document 1). In2O3-based materials have the advantages of being able to form films using low-temperature processes and having both high transparency and conductivity.

[0003] However, since indium is a rare metal and very expensive, there is a consideration of replacing In2O3-based materials with other materials. As a relatively inexpensive transparent conductive film that can be formed at low temperatures, films made of ZnO (zinc oxide) are known (e.g., Patent Document 2). However, transparent conductive films primarily composed of zinc oxide have low moisture and chemical resistance. Therefore, transparent conductive films primarily composed of zinc oxide have difficulty replacing transparent conductive films made of, for example, ITO.

[0004] On the other hand, films containing SnO 2 (tin dioxide), such as FTO (fluorine-doped tin oxide) and ATO (antimony-doped tin oxide), are known as transparent conductive films having high transparency and excellent stability and chemical resistance.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2017 / 057556

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-117903 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] Here, FTO and ATO are polycrystalline, and their conductivity is improved by forming films at high temperatures and improving their crystallinity. Therefore, FTO and ATO films need to be formed at around 500°C using a thermal CVD method or at 400°C to 500°C using a sputtering method. However, forming films at high temperatures exceeding 400°C can easily cause thermal damage to the substrate on which the film is stacked or the layers of the optoelectronic device. Therefore, it is difficult to use FTO or ATO as transparent conductive films for optoelectronic devices. Therefore, currently, In2O3-based transparent conductive films with rare indium as the main component have to be used.

[0011] The present invention has been developed in view of the above-mentioned problems. An object of the present invention is to provide a transparent conductive film that can be formed at low temperatures, has high transparency and high conductivity, and contains little or no indium, as well as a substrate with a transparent conductive film and a photoelectric conversion element containing the film.

[0012] Solutions to the Problem

[0013] One embodiment of the present invention provides a transparent conductive film comprising a metal oxide having amorphous tin oxide as a main component, wherein the amount of Sn in the metal oxide is 85 atomic % or more and the amount of In is 4 atomic % or less, and the resistivity of the transparent conductive film is 2×10 -3 Ω·cm or less.

[0014] One embodiment of the present invention further provides a substrate with a transparent conductive film, which includes a substrate and the transparent conductive film disposed on the substrate.

[0015] In addition, one embodiment of the present invention also provides a photoelectric conversion element, which includes: a photoelectric conversion layer; a first electrode, arranged adjacent to the photoelectric conversion layer, comprising at least one conductive film; and a second electrode, arranged adjacent to the photoelectric conversion layer, comprising at least one conductive film; at least one of the first electrode and the second electrode comprises the above-mentioned transparent conductive film.

[0016] Effects of the Invention

[0017] According to the present invention, a transparent conductive film can be formed at low temperatures, has high transparency and high conductivity, and contains little or no indium. Furthermore, the transparent conductive film can be applied to various photoelectric conversion elements such as solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A is a graph for explaining the correlation between the valence of Sn in the transparent conductive film and the extinction coefficient k. Figure 1B This is a graph for explaining the correlation between the valence of Sn in the transparent conductive film and the absorption coefficient α.

[0019] Figure 2 This is a graph showing the relationship between the depth from the surface of the transparent conductive film and the hydrogen atom concentration in the transparent conductive film.

[0020] Figure 3 FIG. 1 is a schematic diagram of a reactive plasma deposition apparatus capable of forming a transparent conductive film according to an embodiment of the present invention.

[0021] Figure 4 Schematic diagram showing the structure of a Si heterojunction solar cell.

[0022] Figure 5 Schematic diagram showing the structure of a perovskite solar cell.

[0023] Figure 6 It is a graph showing the extinction coefficient k and refractive index n of the amorphous SnO2 film prepared in Examples 1-1 and 1-2 and the a-In2O3:H film prepared in Reference Example 1 for each wavelength.

[0024] Figure 7A Graphs showing transmission and reflection spectra of a PET substrate alone, a PET substrate and a transparent conductive film (Examples 1-3), and a PET substrate and a transparent conductive film with SiO2 (Examples 1-4). Figure 7B Graphs showing transmission spectra and reflection spectra of only a glass substrate and a glass substrate and a transparent conductive film (Example 1-3, Example 1-4).

[0025] Figure 8 Spectra of the external quantum efficiency of the front-junction Si heterojunction solar cells prepared in Examples 2-1, 2-2 and Reference Example 2 are shown.

[0026] Figure 9 3-1, 3-2, and Reference Example 3 are graphs showing the current-voltage characteristics of the rear-junction Si heterojunction solar cells prepared.

[0027] Figure 10 3-2a and Reference Example 3 are graphs showing the current-voltage characteristics of the rear-junction Si heterojunction solar cells prepared in Example 3-2a and Reference Example 3.

[0028] Figure 11 It is a graph showing the series resistance value of the Si heterojunction solar cell prepared in each example. DETAILED DESCRIPTION

[0029] In this specification, the numerical range expressed with "to" means a numerical range including the numerical values ​​described before and after "to".

[0030] 1. Transparent conductive film

[0031] The transparent conductive film of the present invention comprises a metal oxide containing amorphous tin oxide as a main component, wherein the amount of Sn in the metal elements constituting the metal oxide is 85 atomic % or more and the amount of In is 4 atomic % or less, and the resistivity of the transparent conductive film is 2×10 -3Ω·cm or less. In this specification, the tin oxide in the transparent conductive film is "amorphous" means that: when measuring the X-ray diffraction intensity (XRD intensity), the broad peak originating from the amorphous is dominant and the peak originating from the crystal is not significantly confirmed. That is to say, it can also have a microcrystallinity to the extent that the amorphous structure is dominant when observing the transmission electron microscope image (TEM image) and the crystals are scattered in the amorphous layer. In addition, within the scope of not impairing the purpose and effect of the present invention, the transparent conductive film may also contain trace amounts of components other than the above-mentioned metal oxides, for example, it may be doped with fluorine, etc., but it is preferred that more than 85% by mass of the transparent conductive film is the above-mentioned metal oxide, and it is more preferred that the transparent conductive film is composed of the above-mentioned metal oxide.

[0032] As mentioned above, polycrystalline FTO (SnO2:F) and ATO (SnO2:Sb) are known to have high transparency and high conductivity. However, these materials are difficult to form into films at low temperatures, hindering their practical application. The inventors of the present invention, through intensive research, have discovered that films primarily composed of amorphous tin oxide can not only be formed at low temperatures but also exhibit excellent transparency and conductivity. The reasons for this can be understood as follows.

[0033] The conduction band of tin oxide (especially SnO2) is mainly composed of Sn5s orbitals. Moreover, in the Sn5s orbital, the spatial expansion of the electron is large, and the s orbitals of the spherical shape overlap with each other. Therefore, it can be understood that even if the bond angle fluctuates due to the amorphous structure, the overlap between the orbitals is not much reduced compared to the crystalline case, so that the high mobility of the electrons is achieved. In fact, the effective mass of the electrons in the film composed of amorphous SnO2 is 0.35m0, which is not much different from the effective mass of the electrons in the film composed of crystalline SnO2. Therefore, it can be understood that the carrier transport path is not easily affected by the amorphous structure, so that the amorphous tin oxide (especially SnO2) achieves the same high transparency and high conductivity as the crystalline SnO2.

[0034] Furthermore, the transparent conductive film of the present invention has the advantage of being excellent in moisture resistance.

[0035] Here, from the perspective of achieving high transparency and high conductivity of the transparent conductive film, the Sn content is sufficient to be 85 atomic % or greater relative to the total metal elements constituting the metal oxide. Preferably, the Sn content is 90 atomic % or greater, and more preferably, 95 atomic % or greater. Furthermore, the metal oxide may contain metal elements other than Sn, to the extent that the objects and effects of the present invention are not impaired. However, preferably, the total content of metal elements other than Sn is 15 atomic % or less, more preferably 10 atomic % or less, and even more preferably 5 atomic % or less relative to the total metal elements constituting the metal oxide.

[0036] Examples of metal elements other than Sn contained in the metal oxide include In, Zn, Cd, Nb, Ta, B, Ga, Ba, Mo, Pb, Rb, Re, Sb, W, Ce, Cs, Dy, Er, Ge, Hf, Ho, La, Lu, Nd, Pr, Sc, Si, Sm, Tb, V, Y, Al, Ti, Zr, etc., among which Zn, Cd, B, Ga, Si, Ge, Pb, Sb, V, Nb, Ta, Mo, W, and Ce are more preferred. The metal oxide may contain only one of these elements or two or more. When the metal oxide further contains metal elements other than Sn, the processability of the material used to form the transparent conductive film may be improved. When the metal oxide contains certain metal elements, the density, transparency, and conductivity of the transparent conductive film may be further improved.

[0037] In addition, the amount of In relative to the total amount of metal elements constituting the metal oxide is 4 atomic % or less, preferably 3 atomic % or less, preferably 0.09 atomic % or less, and more preferably substantially no In is contained. The less the amount of In, the lower the cost of the transparent conductive film. In addition, if the metal oxide (transparent conductive film) contains In as a specific chemical substance, all operations for processing the transparent conductive film will become the subject of supervision. In contrast, if the metal oxide does not contain In, it will not become the subject of supervision, and has the advantage of improved operability. The amount of each metal element constituting the metal oxide can be determined by confirming the composition of the transparent conductive film using an ICP analysis method or the like.

[0038] Furthermore, preferably, in the transparent conductive film (metal oxide), Sn is mainly in the form of tetravalent (Sn 4+ ) state exists. Sn may have Sn 4+ and Sn 2+ Mixed atomic valence, but if the transparent conductive film Sn 2+ As the amount of Sn increases, acceptor defects increase. As a result, both carrier concentration and mobility decrease, leading to an increasing specific resistance as shown in Table 1 below. Directly measuring the valence of Sn in a transparent conductive film is difficult, but there is a correlation between the valence of Sn and the extinction coefficient k or absorption coefficient α of the transparent conductive film at wavelengths between 420 nm and 500 nm. Therefore, by determining the extinction coefficient k or absorption coefficient α of the transparent conductive film, the valence of Sn in the transparent conductive film can be estimated. Figure 1A Shows the change in Sn 4+ Quantity and Sn 2+ When the ratio of the amount of light is greater than or equal to 1,200 nm, the extinction coefficient k is calculated at a wavelength of 200 nm to 1,200 nm. Figure 1B Shows the change in Sn 4+ and Sn 2+When the ratio of the amount is greater than or equal to 0.05, the absorption coefficient α is calculated at a wavelength of 400 nm to 600 nm.

[0039] like Figure 1A As shown, if it mainly contains Sn 4+ The extinction coefficient k of the transparent conductive film is very small within the wavelength range of 420nm to 500nm. 2+ becomes larger, the extinction coefficient k at a wavelength of not less than 420 nm and not more than 500 nm becomes larger. Here, the maximum value of the extinction coefficient k of the transparent conductive film when the wavelength is not less than 420 nm and not more than 500 nm (maximum extinction coefficient) is preferably not more than 0.033, more preferably not more than 0.025, and further preferably not more than 0.017. When the maximum extinction coefficient at a wavelength of not less than 420 nm and not more than 500 nm is not more than 0.033, it can be said that the amount of tetravalent Sn in the transparent conductive film is sufficient, and it is easier to achieve high transparency and high conductivity. It should be noted that the reflected light of light with a wavelength of not less than 200 nm and not more than 1200 nm can be measured by an elliptical polarization spectrometer, and the extinction coefficient k can be obtained based on the change in the polarization state of the incident light and the reflected light.

[0040] On the other hand, Figure 1B As shown, if it mainly contains Sn 4+ The absorption coefficient α of the transparent conductive film is very small within the wavelength range of 420nm to 500nm. 2+ As the ratio of increases, the absorption coefficient α at a wavelength of 420 nm to 500 nm increases. The maximum value (maximum absorption coefficient) of the absorption coefficient α of the transparent conductive film at a wavelength of 420 nm to 500 nm is preferably 1×10 4 cm -1 Below, more preferably 7.5×10 3 cm -1 Below, more preferably 5×10 3 cm -1 The maximum absorption coefficient α when the wavelength is 420 nm or more and 500 nm or less is 1×10 4 cm -1 When the amount of tetravalent Sn in the transparent conductive film is sufficiently high, it can be said that high transparency and high conductivity are more easily achieved. It should be noted that the absorption coefficient α can be determined from the absorption spectrum obtained by measuring the transmittance and reflectance of light with a wavelength of 200 nm to 1200 nm using a spectrophotometer.

[0041] In addition, there is no restriction on the method for adjusting the extinction coefficient k or absorption coefficient α in the transparent conductive film. Adjustment can be achieved by forming the transparent conductive film in an atmosphere with sufficient oxygen, reducing the residual water vapor partial pressure in the film forming chamber, or heating the film at a temperature below 200°C.

[0042] Here, the specific resistance of the transparent conductive film is 2×10 -3 Ω·cm or less, but preferably 1.5×10 -3 Ω·cm or less, more preferably 1×10 -3 Ω·cm or less. If the specific resistance of the transparent conductive film is 2×10 -3 If the specific resistance is less than Ω·cm, the transparent conductive film can be used for various applications such as transparent electrodes of photoelectric conversion elements. The above-mentioned specific resistance can be determined using Loresta (low resistivity meter).

[0043] In addition, through in-depth research by the inventors of the present invention, it was found that if the resistivity of the transparent conductive film is to be reduced, the higher the film density of the transparent conductive film, the more preferred it is. The following four samples were prepared in the same manner as shown in Example 1-1 described later. The composition, film density and resistivity at this time are shown in Table 1. It should be noted that the average composition is analyzed by Rutherford backscattering analysis (RBS) and the resistivity is measured using Loresta (low resistivity meter). In addition, the film density is calculated based on the surface density determined by the RBS method and the film thickness determined by ellipsometry.

[0044] [Table 1]

[0045]

[0046] As shown in Table 1, as the film density of the transparent conductive film increases, the specific resistance decreases. Considering this result, the specific resistance of the transparent conductive film is reduced to 2.0×10 -3 From the following perspective, the film density analyzed by Rutherford backscattering analysis (RBS) is preferably 5.6 g / cm 3 Above, the film density is 6.3g / cm 3 The above is more preferred, if 6.4g / cm 3 The above is further preferred. In addition, the film density can also be calculated by the X-ray reflection (XRR) method. However, the XRR method calculates the film density assuming the film composition. Since there is no standard sample that is a thin film and has a known film density, it is not clear which of the RBS method and the XRR method is closer to the true value. Therefore, the above results may contain errors from the true value, but it is obvious that the higher the film density of the transparent conductive film, the more preferred it is. It can be said that when the film density is measured using the RBS method, it is preferred that the film density is above the above value.

[0047] Furthermore, the inventors of the present invention have discovered through extensive research that, in order to reduce the resistivity of a transparent conductive film, it is preferable to control the hydrogen atomic concentration in the transparent conductive film, as measured by secondary ion mass spectrometry (SIMS), and to lower the hydrogen atomic concentration. This lowering of the hydrogen atomic concentration results in a denser film, resulting in a film with a higher film density.

[0048] The following five SnO2 films (transparent conductive films) were prepared by the same method as that shown in Examples 1-1 and 1-2 described later. When the hydrogen atom concentration of these transparent conductive films was measured from one surface by SIMS, the relationship between the depth of the transparent conductive film and the hydrogen atom concentration was as follows: Figure 2 As shown. Figure 2 It is clear that hydrogen atoms are easily accumulated on the surface of the transparent conductive film and at the interface between the transparent conductive film and other films (here, the glass substrate), and the concentration is higher than that inside the transparent conductive film. In addition, due to the intrusion of elements caused by sputtering ions in SIMS analysis, a profile extending to the depth is formed. Therefore, the concentration of hydrogen atoms inside these transparent conductive films (the area inside of which is more than 10 nm from the surface (or interface) on both sides) was determined. The results are shown in Table 2. In addition, the specific resistance of each transparent conductive film was measured using Loresta (low resistivity meter). The results are shown in Table 2.

[0049] [Table 2]

[0050]

[0051] As shown in the table above, the specific resistance decreases as the hydrogen atom concentration inside the transparent conductive film decreases. -3 From the following perspective, it is preferable that the concentration of hydrogen atoms in the region 10 nm or more inside the transparent conductive film from both side surfaces is 8×10 21 atoms / cm 3 Below, more preferably 7×10 21 atoms / cm 3 Below, more preferably 6×10 21 atoms / cm 3 the following.

[0052] The thickness of the transparent conductive film is appropriately selected depending on its intended use. When used as a transparent electrode on the light-receiving or light-emitting side of a photoelectric conversion element (described later), the transparent conductive film preferably has a thickness of 1 nm to 5000 nm, more preferably 10 nm to 1000 nm. When the thickness of the transparent conductive film falls within this range, the high transparency and high conductivity required for a transparent electrode are easily achieved.

[0053] The method for producing the transparent conductive film is not particularly limited as long as the aforementioned composition and resistivity conditions are met. For example, the film can be formed by reactive plasma deposition or sputtering. While the reactive plasma deposition method will be described below, the method for producing the transparent conductive film is not limited to this method. A method for forming a transparent conductive film by magnetron sputtering will also be demonstrated in the examples described below.

[0054] Film formation using reactive plasma deposition can be achieved, for example, by Figure 3 The reactive plasma deposition apparatus 100 is shown in the schematic diagram of FIG. However, the structure of the reactive plasma deposition apparatus 100 is not limited to this structure.

[0055] This reactive plasma deposition apparatus 100 includes a crucible 10 for maintaining a material at a predetermined temperature, a plasma gun 20 for generating a plasma beam 21 and plasma 22, a plasma beam controller 30 for directing the plasma beam 21 generated by the plasma gun 20 to the material within the crucible 10, and a chamber 40 for housing these components. To form the aforementioned transparent conductive film on a substrate 1 using this reactive plasma deposition method, the material is placed in the crucible 10 and the substrate 1 is positioned at a predetermined location. Furthermore, the interior of the chamber 40 is adjusted to a predetermined atmosphere and pressure. Then, the plasma beam 21 and plasma 22 are generated from the plasma gun 20. The plasma beam 21 emitted from the plasma gun 20 is directed by the plasma beam controller 30 to the crucible 10 and perpendicularly incident on the material within the crucible 10. The material, heated by the irradiation of the plasma beam 21, sublimates and ionizes in the plasma 22. The ionized material 11 then reaches the substrate 1 in an activated state. This forms the aforementioned transparent conductive film on the substrate 1.

[0056] When forming a transparent conductive film using the reactive plasma deposition method, a sintered body having a composition substantially similar to that of the transparent conductive film, a sintered body composed of a metal constituting the transparent conductive film and a metal oxide including a suboxide of the metal, and a mixture thereof are preferably used as the material contained in the crucible portion 10. The sintered body may be amorphous or crystalline. The sintered body can be obtained by mixing SnO2, SnO, or Sn with other metals or metal oxides as needed and sintering the mixture using a known method such as pressureless sintering or hot pressing.

[0057] Furthermore, in order to render the tin oxide in the transparent conductor (metal oxide) amorphous, the temperature of the substrate 1 is preferably maintained at 300°C or lower. It is possible to maintain the substrate 1 at approximately room temperature without intentionally heating it. Alternatively, it may be intentionally cooled to approximately 0°C.

[0058] Furthermore, from the perspective of film formation efficiency, it is preferable to set the pressure in the chamber to be 0.01 Pa or more and 10 Pa or less, and more preferably 0.1 Pa or more and 1 Pa or less. The atmosphere in the chamber 40 may be an inert gas atmosphere such as nitrogen or argon, but in order to easily make Sn into tetravalent (Sn 4+ ), preferably, oxygen is introduced into the atmosphere, more preferably, the oxygen partial pressure is from 0.01 Pa to 10 Pa, and even more preferably, from 0.1 Pa to 1 Pa. When the oxygen partial pressure is within this range, a transparent conductive film having the aforementioned extinction coefficient and absorption coefficient is more easily obtained.

[0059] Furthermore, after film formation by the reactive plasma deposition method, it is preferably subjected to heat treatment at a temperature of 20°C to 400°C, more preferably 100°C to 300°C. The heat treatment time is preferably 0.1 seconds to 24 hours, more preferably 0.1 seconds to 1 hour. Annealing treatment causes structural relaxation, which tends to stabilize the resulting transparent conductive film and further reduce its conductivity.

[0060] 2. Substrate with transparent conductive film

[0061] The substrate with a transparent conductive film of the present invention only needs to include a substrate and the transparent conductive film disposed on the substrate. There are no particular restrictions on the shape of the substrate and the thickness of the transparent conductive film. In addition, the transparent conductive film can be disposed on the entire surface of the substrate or only on a portion of the substrate. In addition, a structure other than the substrate and the transparent conductive film can also be included. For example, an arbitrary layer (for example, a conductive film other than the above, a barrier film, etc.) can be provided between the substrate and the transparent conductive film, or on the transparent conductive film. The arbitrary layer can be a well-known layer.

[0062] The substrate can be made of an inorganic material such as glass, or a resin material. Specifically, the substrate can be a resin film. Furthermore, the substrate can be composed of multiple layers. Furthermore, there are no particular limitations on the shape of the substrate; it can be flat or three-dimensional. Furthermore, the light transmittance of the substrate can be appropriately selected depending on its intended use; it may or may not be light-transmissive. The substrate can be flexible.

[0063] The transparent conductive film has high transparency and conductivity. In addition, the transparent conductive film can be formed at a relatively low temperature (eg, below 300° C.). Therefore, substrates made of various materials can be used as the substrate.

[0064] Examples of the structure of the substrate with a transparent conductive film include various structures such as the following stacked structure, wherein the stacked structure includes: substrate / barrier film / stacked structure including the above-mentioned transparent metal film, substrate / conductive film other than the above-mentioned / stacked structure including the above-mentioned transparent conductive film, substrate / the above-mentioned transparent conductive film / conductive film other than the above-mentioned.

[0065] The use of the substrate with a transparent conductive film is not limited to the photoelectric conversion element described later. Examples of its use include various light detection elements, displays, wearable devices, thin film transistors (TFTs), transparent heaters, infrared communication equipment, infrared sensors, infrared reflective materials, electromagnetic wave shielding materials, antistatic agents, etc., but are not limited to these.

[0066] 3. Photoelectric conversion element

[0067] The above-mentioned transparent conductive film can be used for one or both of the first electrode and the second electrode of a photoelectric conversion element, which includes a photoelectric conversion layer, a first electrode comprising at least one conductive film arranged adjacent to the photoelectric conversion layer, and a second electrode comprising at least one conductive film arranged adjacent to the photoelectric conversion layer. It should be noted that the first electrode and the second electrode can also be composed of multiple layers. In this case, one of the layers constituting the first electrode or one of the layers constituting the second electrode can be the above-mentioned transparent conductive film. In addition, at this time, two or more layers can also be the above-mentioned transparent conductive film. In addition, depending on the type of photoelectric conversion element, the layer equivalent to the first electrode layer or the second electrode layer is sometimes called an electron transport layer, a carrier selection layer, an n-type buffer layer, a (conductive) cap layer, etc., and the above-mentioned transparent conductive film can also be used for these layers.

[0068] In this specification, the term "photoelectric conversion element" refers to an element that converts light energy into electrical energy, or vice versa. Examples of photoelectric conversion elements include solar cells, organic EL elements, light-emitting diodes, and laser diodes. While the following description will describe a solar cell as the photoelectric conversion element, the transparent conductive film described above can also be used as a transparent electrode or metal electrode on the light-emitting side of an organic EL element or the like.

[0069] Furthermore, there are no particular limitations on the types of solar cells that can use the transparent conductive film, and the transparent conductive film can be used in all known types of solar cells. Several solar cell structures are shown below, but the structures of solar cells that can use the transparent conductive film are not limited thereto.

[0070] (Si heterojunction solar cell)

[0071] Figure 4An example of the structure of a Si heterojunction solar cell is shown. This Si heterojunction solar cell (hereinafter also referred to as a "solar cell") 200 has a structure in which a photoelectric conversion layer 130 is sandwiched between a first electrode 131 and a second electrode 132. In this solar cell 200, light is incident from the first electrode 131 side.

[0072] In this solar cell 200, the first electrode 131 is composed of a light-receiving-side transparent electrode 125 and a grid electrode 126, and the second electrode 132 is composed of a back-side transparent electrode 127 and a metal electrode 128. The transparent conductive film can be used for one or both of the light-receiving-side transparent electrode 125 and the back-side transparent electrode 127. If the transparent conductive film is used for only one of the two, the other can be a known transparent conductive film such as ITO. From the perspective of reducing the cost of the solar cell 200, it is preferable to use the transparent conductive film for both the light-receiving-side transparent electrode 125 and the back-side transparent electrode 127. Alternatively, one or both of the light-receiving-side transparent electrode 125 and the back-side transparent electrode 127 can be a laminate of multiple conductive films. In this case, the transparent conductive film can be used for either of the layers forming the light-receiving-side transparent electrode 125 or the back-side transparent electrode 127. For example, a laminate of the transparent conductive film and an ITO film can be used as either the light-receiving-side transparent electrode 125 or the back-side transparent electrode 127. The advantage is that the use of the transparent conductive film in a portion of the light-receiving side transparent electrode 125 or the back side transparent electrode 127 can reduce the amount of ITO (especially In). In addition, the grid electrode 126 and the metal electrode 128 are the same as the electrodes of the known solar cell and are made of Ag, Cu, composite metal, etc. In addition, the metal electrode 128 is Figure 4 Although it is formed on the entire surface, it can also be grid-shaped like the grid electrode 126. In this case, light incident from the second electrode 132 side also contributes to power generation, and it can become a double-sided light-receiving solar cell.

[0073] Meanwhile, photoelectric conversion layer 130 has a structure in which n-type single crystal silicon layer 120 is sandwiched between p-type semiconductor layer 122 and n-type semiconductor layer 124. I-type semiconductor layers 121 and 123 are disposed between n-type single crystal silicon layer 120 and p-type semiconductor layer 122, and between n-type single crystal silicon layer 120 and n-type semiconductor layer 124, respectively.

[0074] The arrangement order of the layers of the photoelectric conversion layer 130 may also be opposite to the above, and the n-type semiconductor layer may be arranged on the light-receiving side and the p-type semiconductor layer may be arranged on the back side. Figure 4As shown, a structure in which a pin junction structure consisting of a p-type semiconductor layer 122, an i-type semiconductor layer 121, and an n-type single crystal silicon layer 120 is arranged on the light-receiving surface side is generally referred to as a front junction type, while a structure in which a pin junction structure is arranged on the back side is referred to as a back junction type. The solar cell of the present invention can be a front junction type or a back junction type. In addition, in this specification, the case where the photoelectric conversion layer 130 has an n-type single crystal silicon layer 120 is used as an example for explanation, but the photoelectric conversion layer 130 can also be a structure in which the n-type single crystal silicon layer 120 is replaced by a p-type single crystal silicon layer. In addition, a structure in which the p-type semiconductor layer and the n-type semiconductor layer are arranged in a comb-tooth shape on the back side can also be adopted. In this case, one of the p-type semiconductor layer and the n-type semiconductor layer can be arranged on the light-receiving surface side, or these semiconductor layers can be not arranged on the light-receiving surface side.

[0075] The n-type single crystal silicon layer 120 of the photoelectric conversion layer 130 is the same as the n-type single crystal silicon layer of a known solar cell, and is a layer composed of n-type single crystal silicon into which n-type impurities such as phosphorus (P) are introduced. Here, the surfaces of the light-receiving side and the back side of the n-type single crystal silicon layer 120 can be flat surfaces composed of (100) planes, but preferably, a random pyramid texture structure composed of silicon (111) facets is formed on one or both surfaces, and more preferably, a random pyramid texture structure is formed on both surfaces. If a random pyramid texture structure is formed on the light-receiving side and the back side of the n-type single crystal silicon layer 120, light incident on the n-type single crystal silicon layer 120 is not easily reflected on its surface, and due to the light trapping effect, the incident light is not easily emitted. Therefore, the photoelectric conversion efficiency of the solar cell 200 is easily improved.

[0076] On the other hand, examples of the p-type semiconductor layer 122 include a layer composed of p-type hydrogenated amorphous silicon (also referred to as "(p)a-Si:H" in this specification) into which p-type impurities such as boron (B) are introduced. However, when the transparent conductive film is arranged adjacent to the p-type semiconductor layer 122, the p-type semiconductor layer 122 is preferably configured as a p-type microcrystalline silicon (also referred to as "(p)nc-Si:H" in this specification) layer containing p-type microcrystalline silicon in a hydrogenated amorphous silicon layer. Alternatively, the p-type semiconductor layer 122 may be configured as an alloy layer of p-type microcrystalline silicon, such as a p-type microcrystalline silicon oxide (also referred to as "(p)nc-Si:H" in this specification) in which oxygen is added to the hydrogenated amorphous silicon layer. x:H”) layer. The higher the oxygen concentration of the microcrystalline silicon oxide, the stronger the transparency. On the other hand, since the higher the oxygen concentration, the lower the conductivity, it is necessary to select an appropriate range of oxygen concentration, and x is preferably greater than 0.1 and less than 1.5. The microcrystalline silicon phase contained in these layers is composed of tiny silicon crystals, and the crystal size thereof is preferably in the nanometer order. As described in detail in the embodiments described later, when the above-mentioned transparent conductive film is arranged adjacent to the (p)a-Si:H film, the series resistance of the solar cell 200 may increase. As a result, a decrease in the curve factor may be observed compared to the case where an ITO film is used as the transparent electrode (here, the light-receiving side transparent electrode 125). In contrast, when the above-mentioned transparent conductive film is arranged adjacent to the (p)nc-Si:H film or the (p)nc-SiO x When (p)a-Si:H films are arranged adjacent to each other, the series resistance does not increase, and the electrical characteristics obtained are comparable to those obtained when ITO is used as a transparent electrode. It is believed that the reason for such good electrical characteristics is that (p)nc-Si:H or (p)nc-SiO is better than (p)a-Si:H. x The H film increases the carrier concentration. As a result, the thickness of the depletion layer formed at the interface between the transparent conductive film and the p-type layer is reduced, enabling carrier migration based on the tunneling effect, thereby reducing resistance.

[0077] In addition, examples of the n-type semiconductor layer 124 include a layer composed of hydrogenated amorphous silicon (also referred to as "(n)a-Si:H" in this specification) into which n-type impurities such as phosphorus (P) are introduced. However, when the above-mentioned transparent conductive film is arranged adjacent to the n-type semiconductor layer 124, it is preferable that the n-type semiconductor layer 124 is set as an n-type microcrystalline silicon (also referred to as "(n)nc-Si:H" in this specification) layer containing n-type microcrystalline silicon in a hydrogenated amorphous silicon layer. Alternatively, the n-type semiconductor layer 124 can be set as an alloy layer of n-type microcrystalline silicon, such as n-type microcrystalline silicon oxide (also referred to as "(n)nc-SiO x :H”) layer. The higher the oxygen concentration of the microcrystalline silicon oxide, the stronger its transparency. On the other hand, since the higher the oxygen concentration, the lower the conductivity, it is necessary to select an appropriate range of oxygen concentration, and x is preferably greater than or equal to 0.1 and less than or equal to 1.5. The microcrystalline silicon phase contained in these layers is composed of tiny silicon crystals, and the crystal size thereof is preferably nanometer-sized. As described in detail in the embodiments described later, when the above-mentioned transparent conductive film is arranged adjacent to the (n)a-Si:H film, the series resistance of the solar cell 200 may increase. In contrast, when the above-mentioned transparent conductive film is arranged adjacent to the (n)nc-Si:H film or the (n)nc-SiO x : When the H films are arranged adjacent to each other, the series resistance does not increase, and the electrical characteristics obtained are not inferior to those when ITO is used as the transparent electrode.

[0078] The i-type semiconductor layers 121 and 123 are similar to the i-type semiconductor layers of known solar cells, and are, for example, layers composed of intrinsic amorphous silicon doped with hydrogen (also referred to as “(i)a-Si:H” in this specification).

[0079] In the solar cell 200, light incident from the grid electrode 126 passes through the transparent electrode 125, the p-type semiconductor layer 122, and the i-type semiconductor layer 121 and enters the n-type single crystal silicon layer 120. Of the light incident on the n-type single crystal silicon layer 120, the light energy greater than the band gap of silicon excites the n-type crystalline silicon to form electron-hole pairs. - ) migrate to the metal electrode 128 side. On the other hand, holes (h + ) migrates to the grid electrode 126 side, so that the solar cell 200 operates.

[0080] There are no particular restrictions on the manufacturing method of the solar cell 200. For example, the photoelectric conversion layer 130 is formed by a known method, and the light-receiving side transparent electrode 125 and the back-side transparent electrode 127 are formed on the photoelectric conversion layer 130. When an ITO film is formed as the light-receiving side transparent electrode 125 or the back-side transparent electrode 127, it can be formed by a sputtering method or the like. On the other hand, when the transparent conductive film is formed as the light-receiving side transparent electrode 125 or the back-side transparent electrode 127, it can be formed by a reactive plasma deposition method or the like. As described above, a transparent conductive film containing amorphous SnO2 can be formed at a relatively low temperature (e.g., below 300°C). Therefore, it has the advantage that even if it is stacked on the photoelectric conversion layer 130, the various layers in the photoelectric conversion layer 130 are not easily degraded. In addition, after the light-receiving side transparent electrode 125 and the back-side transparent electrode 127 are prepared, the grid electrode 126 and the metal electrode 128 are prepared by a known method.

[0081] (Perovskite solar cells)

[0082] The above-mentioned transparent conductive film can also be applied to perovskite solar cells. Figure 5An example of the structure of a perovskite solar cell is shown. The perovskite solar cell 400 has a structure in which a substrate / first electrode / first buffer layer / light absorption (halide-based perovskite material) layer / second buffer layer / second electrode are stacked in this order. One of the first buffer layer and the second buffer layer functions as a hole transport layer, and the other functions as an electron transport layer. Although it is desirable to have these layers in order to achieve a better conversion efficiency for the perovskite solar cell, it is not necessary in the embodiment, and one or both of them may not be present. In addition, it may be that both or one of the first buffer layer and the second buffer layer has a structure in which different materials are stacked. In the perovskite solar cell, light can be incident from the second electrode or from the substrate side. The above-mentioned transparent conductive film can be used for one or both of the first electrode and the second electrode of the perovskite solar cell.

[0083] Alternatively, the first electrode and the second electrode may be a stack of multiple conductive films. In this case, the transparent conductive film may be used in only one layer. When the first electrode or the second electrode is a stack of multiple conductive films, the first electrode or the second electrode may have a two-layer structure of the transparent conductive film and an ITO film, or a three-layer structure of the transparent conductive film / ITO film / transparent conductive film. Conventionally, the conductive layer and the counter electrode are typically formed of an ITO film. By using the transparent conductive film in a portion of the structure, the amount of ITO (particularly In) used can be reduced.

[0084] Furthermore, the transparent conductive film can be formed at a relatively low temperature. Therefore, when the transparent conductive film is used as the conductive layer, the substrate can be composed not only of inorganic materials such as glass plates but also of resin substrates or films. Furthermore, the materials used for the various layers of the perovskite solar cell are the same as those used for conventional perovskite solar cells.

[0085] (Other solar cells)

[0086] Solar cells other than the above-mentioned Si heterojunction solar cells and perovskite solar cells, such as TOPCon (Tunnel Oxide Passivated Contact) solar cells, CdTe solar cells, I-III-VI2 compound solar cells represented by CuInSe2, I2-II-IV-VI4 compound solar cells represented by Cu2ZnSnS4, I2-IV-VI3 compound solar cells represented by Cu2SnS3, I2-VI compound solar cells represented by Cu2S, II-VI compound solar cells represented by SnS, multi-junction solar cells in which the above-mentioned perovskite solar cells are combined with Si-based solar cells, etc., can use the above-mentioned transparent conductive film as the electrode for any structure of the solar cell. It should be noted that the TOPCon solar cell here has a structure in which the above-mentioned transparent conductive film is stacked on a semiconductor layer on a tunnel oxide film. In any method, a single layer of the above-mentioned transparent conductive film can be used as an electrode, and a laminate of a well-known conductive film such as an ITO film and the above-mentioned transparent conductive film can also be used as an electrode.

[0087] [Example]

[0088] Hereinafter, the present invention will be described in more detail by way of examples, but the scope of the present invention is not limited thereto.

[0089] 1. Preparation of transparent conductive film

[0090] The optical properties and electrical conductivity of the transparent conductive film of the present invention were compared and evaluated with those of a conventional transparent conductive film (In2O3 film) by the following method.

[0091] (Example 1-1)

[0092] The transparent conductive film was prepared by the following reactive plasma deposition method.

[0093] As substrates, a Si substrate (size 30 mm × 30 mm) with a thermal oxide film (thickness 50 nm) and an alkali-free glass substrate (XG produced by Corning) (size 100 mm × 100 mm) were prepared and fixed on Figure 3The reactive plasma deposition apparatus 100 is placed at a designated position of the reactive plasma deposition apparatus 100 shown. In addition, a SnO2 sintered body, which is the material of the transparent conductive film, is prepared and housed in the crucible portion 10 of the reactive plasma deposition apparatus 100. In the chamber 40, the temperature of the substrate 1 is set to no heating (room temperature). In addition, Ar and O2 gases are introduced into the chamber 40 of the reactive plasma deposition apparatus 100, and the pressure in the chamber 40 is adjusted to 0.4 Pa (oxygen partial pressure 0.3 Pa). Then, a plasma beam 21 is emitted from the plasma gun 20, and the position of the plasma beam 21 is adjusted by the plasma beam controller 30 so that the plasma beam 21 is vertically incident on the material. At this time, the discharge current value is set to 150 mA. Film formation is performed under this condition for 0.7 minutes to obtain a transparent conductive film (SnO2 film) with a thickness of 70 nm.

[0094] The X-ray diffraction intensity (XRD intensity) of the prepared transparent conductive film was measured under the following conditions, but no peak was detected, confirming that SnO 2 was amorphous.

[0095] (Measurement conditions)

[0096] Device: RIGAKU SmartLab

[0097] X-rays: Cu Kα rays

[0098] Output: 9kW

[0099] In addition, the composition of the prepared transparent conductive film was confirmed by ICP analysis. The results showed that the metal element constituting the transparent conductive film was only Sn, and the In content was below the quantitative limit. In addition, the specific resistance was measured using Loresta (low resistivity meter) and the measurement result was 1.2×10 -3 Ω·cm.

[0100] Ellipsometry was used to measure the reflected light of this transparent conductive film on a Si substrate with a thermal oxide film for wavelengths between 200 nm and 1200 nm. The polarization state of the incident and reflected light, as well as the maximum extinction coefficient k for wavelengths between 420 nm and 500 nm, were determined. The results showed that the maximum extinction coefficient k within this range was 0.018. Furthermore, the refractive index n of the transparent conductive film ranged from 2.09 to 2.17 at wavelengths between 420 nm and 500 nm.

[0101] Furthermore, the transmission and reflection spectra of this transparent conductive film, fabricated on an XG glass substrate manufactured by Corning, were measured using a spectrophotometer for light with a wavelength of 220 nm to 2500 nm. The maximum absorption coefficient α for light with a wavelength of 420 nm to 500 nm was determined from the obtained spectra and was found to be 3219 cm-1. -1 .

[0102] Furthermore, the transparent conductive film was placed in a constant temperature and humidity chamber at 85°C and 85% for 1000 hours, and the resistivity was measured in the same manner as above. The result was 1.1×10 -3 Ω·cm, confirming that its moisture resistance is also excellent. In addition, for comparison, the FTO coated glass substrate (type-VU manufactured by AGC Fabritec) (specific resistance of 1.1×10 -3 Ω·cm), and the same test was carried out. The specific resistance after the test was 1.1×10 -3 That is, it was confirmed that the transparent conductive film (SnO2 film) has moisture resistance comparable to that of the FTO film.

[0103] (Example 1-2)

[0104] A 70 nm thick amorphous SnO2 film (transparent conductive film) was deposited on a substrate using the same reactive plasma deposition method as in Example 1-1. The film was then annealed at 200°C for 0.5 hours in a nitrogen atmosphere. The resistivity of the annealed film was measured using a Loresta (low resistivity meter) and was found to be 9.1 × 10 -4 Ω·cm.

[0105] In addition, for the transparent conductive film on the Si substrate with a thermal oxidation film after annealing, the reflected light of light with a wavelength of more than 200nm and less than 1200nm was measured using an ellipsometry spectrometer. The changes in the polarization state of the incident light and the reflected light, the maximum extinction coefficient k of the light with a wavelength of more than 420nm and less than 500nm were confirmed, and the results showed that the maximum extinction coefficient k in this range was 0.021. In addition, the refractive index n of the transparent conductive film is 2.08 to 2.16 when the wavelength is more than 420nm and less than 500nm. For the transparent conductive film prepared on the XG glass substrate produced by Corning, the transmission spectrum and reflection spectrum of light with a wavelength of more than 220nm and less than 2500nm were measured using a spectrophotometer. The maximum absorption coefficient α of light with a wavelength of more than 420nm and less than 500nm was confirmed from the obtained spectrum, and the results showed that the maximum absorption coefficient α in this range is 5740cm -1 .

[0106] Furthermore, the transparent conductive film was placed in a constant temperature and humidity chamber at a temperature of 85°C and a humidity of 85% for 1000 hours, and the resistivity was measured in the same manner as above. The result was 9.6×10 -4 Ω·cm, and it was confirmed that the moisture resistance was also excellent.

[0107] (Reference Example 1)

[0108] An amorphous hydrogenated In2O3 (a-In2O3:H) film (transparent conductive film) was deposited by sputtering on a Si substrate (50 mm x 50 mm) with a thermal oxide film (50 nm thick). The thickness of the a-In2O3:H film was 70 nm. Furthermore, the resistivity of the transparent conductive film was measured using a Loresta (low resistivity meter) and the result was 5.4 × 10 -4 Ω·cm.

[0109] For this transparent conductive film (a-In2O3:H film), we measured the reflected light of light with a wavelength between 200 nm and 1200 nm using spectroscopic ellipsometry. We determined the extinction coefficient k within this range based on the changes in the polarization state of the incident and reflected light. Furthermore, we also determined the refractive index n within this range.

[0110] (evaluate)

[0111] Figure 6 The extinction coefficient k and the refractive index n of each transparent conductive film prepared in the above-mentioned Examples 1-1 and 1-2 and Reference Example 1 are shown at a wavelength of 200 nm to 1200 nm. Figure 6 As shown in FIG. 1 , the extinction coefficient k and refractive index n of the amorphous SnO2 films prepared in Examples 1-1 and 1-2 are substantially the same as those of the amorphous In2O3:H film in Reference Example 1, indicating that the transparent conductive film of the present invention has excellent optical properties. In addition, as described above, the specific resistivity of the transparent conductive films prepared in Examples 1-1 and 1-2 is 1.2×10 -3 Ω·cm or less, showing excellent electrical conductivity.

[0112] (Examples 1-3)

[0113] As substrates, a PET (polyethylene terephthalate) substrate (size 100 mm × 100 mm) and an alkali-free glass substrate (XG manufactured by Corning) (size 100 mm × 100 mm) were prepared. A 70 nm thick amorphous SnO2 film (transparent conductive film) was deposited on the substrate by reactive plasma deposition in the same manner as in Example 1-1. The specific resistivity of the resulting transparent conductive film was measured using a Loresta (low resistivity meter) and was found to be 1.27 × 10-3 Ω·cm, 1.37×10 on a glass substrate -3 Ω·cm.

[0114] (Examples 1-4)

[0115] As substrates, a PET substrate with SiO2 (size 100 mm × 100 mm) and an alkali-free glass substrate (XG manufactured by Corning) (size 100 mm × 100 mm) were prepared. A 70 nm thick amorphous SnO2 film (transparent conductive film) was deposited on the substrates by reactive plasma deposition in the same manner as in Example 1-1. The specific resistivity of the resulting transparent conductive film was measured using a Loresta (low resistivity meter). The results showed that the specific resistivity of the PET substrate with SiO2 was 1.34 × 10 -3 Ω·cm, 1.34×10 on a glass substrate -3 Ω·cm.

[0116] (evaluate)

[0117] For each substrate with a transparent conductive film, the transmission spectrum and reflection spectrum of light with a wavelength of 220 nm to 2500 nm were measured. Figure 7A The transmission spectra and reflection spectra of only the PET substrate, the PET substrate and the transparent conductive film (Examples 1-3), and the PET substrate and the transparent conductive film with SiO2 (Examples 1-4) are shown. Figure 7B The transmission and reflection spectra of only the glass substrate, the glass substrate and the transparent conductive film (Examples 1-3), and the glass substrate and the transparent conductive film (Examples 1-4) are shown. Figure 7A and Figure 7B As shown in FIG. 1 , the desired transparent conductive film (a-SnO2 film) can be formed on a PET substrate or a PET substrate with SiO2 by reactive plasma deposition without damaging the substrate. Furthermore, as described above, the specific resistance of the transparent conductive films prepared in Examples 1-1 and 1-2 was 1.37×10 -3 Ω·cm or less, showing excellent electrical conductivity.

[0118] (Example 1-5 to Example 1-9)

[0119] A transparent conductive film was obtained in the same manner as in Example 1-1, except that the material of the transparent conductive film was changed to a sintered body of a metal oxide as shown in Table 3 below. The specific resistivity of the resulting transparent conductive film is summarized in Table 3. In addition, the specific resistivity of the transparent conductive film after annealing at 250°C for 0.5 hours in a nitrogen atmosphere is also shown in Table 3.

[0120] (Examples 1-10)

[0121] A transparent conductive film was obtained in the same manner as in Example 1-1, except that the material of the transparent conductive film was changed to a sintered body of metal oxides as shown in Table 3 below. The specific resistivity of the resulting transparent conductive film is summarized in Table 3. In addition, the specific resistivity of the transparent conductive film after annealing at 200°C for 0.5 hours in a nitrogen atmosphere is also shown in Table 3.

[0122] [Table 3]

[0123]

[0124] (evaluate)

[0125] As shown in Table 3 above, even when an element other than Sn (Zn, In, or Ga) is contained at 3 atomic % as a metal element constituting the metal oxide, the specific resistance can be made 2×10 -3 Ω·cm or less. In addition, all transparent conductive films have their specific resistance reduced by annealing (Examples 1-5 to 1-8). In addition, when 3 atomic % of W is contained as a metal element constituting the metal oxide, the specific resistance without annealing exceeds 2×10 -3 , but by annealing, the specific resistance can be reduced to 2×10 -3 Ω·cm or less.

[0126] Similarly, when the metal oxide contains 15 atomic % of an element other than Sn (Ga) as a metal element, the specific resistance before annealing exceeds 2×10 -3 , but by annealing, the specific resistance can be reduced to 2×10 -3 Ω·cm or less (Examples 1-10).

[0127] 2. Preparation of solar cells (preparation of front-junction Si heterojunction solar cells)

[0128] A front-junction Si heterojunction solar cell was fabricated using the transparent conductive film of the present invention as the light-receiving and / or back-side transparent electrodes. The external quantum efficiency of this solar cell was compared and evaluated with that of a conventional Si heterojunction solar cell using an ITO film as both the light-receiving and back-side transparent electrodes.

[0129] (Example 2-1)

[0130] Preparation of photoelectric conversion layer

[0131] A 280μm-thick n-type single-crystalline silicon substrate with (100) faces on both sides and a resistivity of 2Ωcm was prepared. The surface of the n-type single-crystalline silicon substrate was wet-etched with a solution primarily composed of KOH, forming a random texture structure consisting of (111) facets on both sides of the substrate.

[0132] Subsequently, the natural oxide film on both sides of the n-type single-crystalline silicon substrate was removed using dilute hydrofluoric acid. Then, an i-type a-Si:H layer (approximately 5 nm thick) and an n-type a-Si:H layer (approximately 7 nm thick) were deposited on the back side of the n-type single-crystalline silicon substrate using plasma-assisted chemical vapor deposition (PECVD). Furthermore, an i-type a-Si:H layer (approximately 5 nm thick) and a p-type a-Si:H layer (approximately 5 nm thick) were deposited on the light-receiving side of the n-type single-crystalline silicon substrate using PECVD. This resulted in a photoelectric conversion layer stacked in the order of p-type a-Si:H layer / i-type a-Si:H layer / n-type single-crystalline silicon layer / i-type a-Si:H layer / n-type a-Si:H layer from the light-receiving side.

[0133] Preparation of the first electrode and the second electrode

[0134] On both sides of the above-mentioned photoelectric conversion layer, transparent electrodes composed of amorphous SnO2 films were formed using the same method as in the above-mentioned Example 1-1. The thickness of each of them was 75nm. In addition, on the transparent conductive film on the light-receiving side (transparent electrode on the light-receiving side), a grid electrode composed of Ag (width 100μm, thickness 2μm) was prepared by sputtering. On the transparent conductive film on the back side (on the back side transparent electrode), a metal electrode composed of Ag was formed on the entire surface by sputtering. After that, annealing treatment was carried out at 160°C to obtain a front-junction Si heterojunction solar cell.

[0135] (Example 2-2)

[0136] A front-junction Si heterojunction solar cell was obtained in the same manner as in Example 2-1 above, except that the transparent electrode on the light-receiving side was set to an amorphous SnO2 film (thickness 75 nm) and the transparent electrode on the back side was set to an ITO film (thickness 75 nm, prepared by sputtering).

[0137] (Reference Example 2)

[0138] A front-junction Si heterojunction solar cell was obtained in the same manner as in Example 2-1, except that the transparent electrodes on the light-receiving side and the back side were each formed of an ITO film (75 nm thick, prepared by sputtering).

[0139] (evaluate)

[0140] The external quantum efficiency spectra of the front-junction Si heterojunction solar cells obtained in Examples 2-1 and 2-2 and Reference Example 2 are shown in FIG. Figure 8 .like Figure 8 As shown, the external quantum efficiency of the solar cell of Example 2-1 in which the transparent electrodes on the light-receiving side / back side are set as amorphous SnO2 film / amorphous SnO2 film, and the external quantum efficiency of the solar cell of Example 2-2 in which the transparent electrodes on the light-receiving side / back side are set as amorphous SnO2 film / ITO film, are not inferior to the external quantum efficiency of the solar cell of the previous type (Reference Example 2).

[0141] 3. Preparation of solar cells (preparation of rear junction Si heterojunction solar cells)

[0142] A rear-junction Si heterojunction solar cell was fabricated using the transparent conductive film of the present invention as the light-receiving and / or back-side transparent electrodes. The current-voltage characteristics of this solar cell were compared and evaluated with those of a conventional rear-junction Si heterojunction solar cell using an ITO film as both the light-receiving and back-side transparent electrodes.

[0143] In addition, a rear-junction Si heterojunction solar cell was prepared in which the type of semiconductor layer adjacent to the transparent conductive film (a-SnO2 film) of the present invention was changed, and the current-voltage characteristics of the solar cell were compared with the current-voltage characteristics of the previous type of rear-junction Si heterojunction solar cell.

[0144] (Example 3-1)

[0145] A rear-junction Si heterojunction solar cell was prepared by following the same procedures as in Example 2-1, except that the photoelectric conversion layer was arranged as n-type a-Si:H layer / i-type a-Si:H layer / n-type single crystal silicon layer / i-type a-Si:H layer / p-type a-Si:H layer from the light-receiving side.

[0146] (Example 3-2)

[0147] A rear-junction Si heterojunction solar cell was obtained in the same manner as in Example 3-1, except that the transparent electrode on the light-receiving side was made of an amorphous SnO2 film (75 nm thick) and the transparent electrode on the back side was made of an ITO film (75 nm thick, prepared by sputtering).

[0148] (Reference Example 3)

[0149] A rear-junction Si heterojunction solar cell was obtained in the same manner as in Example 3-1 except that the transparent electrodes on the light-receiving side and the back side were each formed of an ITO film (75 nm thick, prepared by sputtering).

[0150] (Example 3-2a)

[0151] A rear-junction Si heterojunction solar cell was obtained in the same manner as in Example 3-2, except that the n-type a-Si:H film of the photoelectric conversion layer was replaced with an n-type nc-SiOx:H film (thickness 10 nm).

[0152] (evaluate)

[0153] The current-voltage characteristics of the rear-junction Si heterojunction solar cells obtained in Examples 3-1 and 3-2 and Reference Example 3 are shown in FIG. Figure 9 The solar cells of Examples 3-1 and 3-2 using the transparent conductive film of the present invention as the light-receiving side transparent electrode and / or the back side transparent electrode exhibited good current-voltage characteristics, but compared with the conventional type of solar cell (Reference Example 3), the fill factor (FF) decreased as the series resistance increased.

[0154] Then, the same evaluation was conducted on a solar cell (Example 3-2a) in which the n-type semiconductor layer adjacent to the transparent conductive film of the present invention was changed from an a-Si:H layer to an n-type nc-SiOx:H layer. The current-voltage characteristics of the solar cell of Example 3-2a and the current-voltage characteristics of the solar cell of Reference Example 3 are shown in FIG. Figure 10 .like Figure 10 As shown, when the layer adjacent to the transparent conductive film (a-SnO2 film) of the present invention is an n-type nc-SiOx:H layer, the curve factor (FF) does not decrease, and a current-voltage characteristic very close to that of the previous type of solar cell (Reference Example 3) is obtained.

[0155] 4. Preparation of Contact Resistance Evaluation Samples

[0156] According to the above results, in order to clarify the reason for the decrease in the curve factor (FF), the contact resistance of the n-type and p-type contact structures was evaluated by the TLM (transmission line measurement) method. The n-type and p-type contact resistance evaluation samples were set to have the same layer structure as the light incident side of the rear junction and front junction Si heterojunction solar cells, respectively. That is, the n-type contact resistance evaluation sample consists of Ag / transparent conductive film / n-type semiconductor layer / i-type a-Si:H layer / n-type crystalline silicon layer, and the series resistance of the n-type contact structure on the light incident side of the rear junction Si heterojunction solar cell was evaluated using the n-type contact resistance evaluation sample. In addition, the p-type contact resistance evaluation sample consists of Ag / transparent conductive film / p-type semiconductor layer / i-type a-Si:H layer / p-type crystalline silicon layer, and the series resistance of the p-type contact structure on the light incident side of the front junction Si heterojunction solar cell was evaluated using the p-type contact resistance evaluation sample. The contact resistance evaluation sample differs from the solar cell in the following two points: the laminated portion of the Ag / transparent conductive film serving as the electrode is patterned into a strip shape, and p-type crystalline silicon is used in the p-type contact resistance evaluation sample. With respect to the p-type contact structure of the front-junction Si heterojunction solar cell (the structure of Example 2-2), a contact resistance evaluation sample (Example 2-2a below) was prepared in which the type of semiconductor layer adjacent to the transparent conductive film (a-SnO2 film) of the present invention was changed, and the contact resistance value was evaluated. In addition, with respect to the p-type contact structure of the conventional type of solar cell using an ITO film (Reference Examples 2 and 3), a contact resistance evaluation sample (Reference Examples 2a and 3a below) was prepared in which the type of semiconductor layer adjacent to the ITO film was changed, and its contact resistance value was confirmed.

[0157] (Example 2-2a)

[0158] A p-type contact resistance evaluation sample having the same structure as Example 2-2 was obtained, except that the p-type a-Si:H layer of the photoelectric conversion layer was replaced with a p-type nc-Si:H layer (thickness 20 nm).

[0159] (Reference Example 2a)

[0160] A p-type contact resistance evaluation sample having the same structure as Reference Example 2 was obtained, except that the p-type a-Si:H layer of the photoelectric conversion layer was replaced with a p-type nc-Si:H layer (thickness 20 nm).

[0161] (Reference Example 3a)

[0162] An n-type contact resistance evaluation sample having the same structure as Reference Example 3 was obtained, except that the n-type a-Si:H layer of the photoelectric conversion layer was replaced with an n-type nc-SiOx:H layer (thickness 10 nm).

[0163] (evaluate)

[0164] The contact resistance values ​​of each n-type contact structure (Ag / transparent conductive film / n-type semiconductor layer / i-type a-Si:H layer / n-type crystalline silicon layer) corresponding to the contact structure on the light incident side of the rear-junction Si heterojunction solar cell prepared in Example 3-2a, Reference Example 3a, Example 3-2 and Reference Example 3 are shown in FIG. Figure 11 Similarly, the contact resistance values ​​of each p-type contact structure (Ag / transparent conductive film / p-type semiconductor layer / i-type a-Si:H layer / p-type crystalline silicon layer) corresponding to the contact structure on the light incident side of the front-junction Si heterojunction solar cell obtained in Example 2-2a, Reference Example 2a, Example 2-2, and Reference Example 2 are also shown. Figure 11 .from Figure 11 It is obvious that, regardless of the structure of the front junction type (the light incident side is the p-type contact) or the rear junction type (the light incident side is the n-type contact), by changing the semiconductor layer adjacent to the transparent conductive film (a-SnO2 film) of the present invention from the a-Si:H layer to the nc-Si:H layer or the nc-SiO x :H, the series resistance value is greatly reduced (Example 3-2a and Example 2-2a). In addition, by adopting this structure, a series resistance value equivalent to or lower than that of conventional solar cells (Reference Example 3 and Reference Example 2) can be achieved.

[0165] 5. Preparation of Transparent Conductive Film by Magnetron Sputtering (Example)

[0166] A transparent conductive film was prepared by RF magnetron sputtering as follows. First, an alkali-free glass substrate (XG manufactured by Corning Incorporated) (size 50 mm × 50 mm) was prepared as a substrate. In addition, a 3-inch A SnO2 sintered body was used as the target, and the substrate temperature was set to unheated (room temperature). Ar gas and O2 gas were introduced into the sputtering apparatus, with the oxygen flow ratio set to 0.25% or 0.375%, and the chamber pressure was set to 0.5 Pa. Then, sputtering was performed for 20 minutes at a sputtering input power of 100 W, resulting in a transparent conductive film (SnO2 film) with a thickness of 70 nm. The resulting transparent conductive film was annealed at 200°C for 0.5 hours in a nitrogen atmosphere.

[0167] The X-ray diffraction intensity (XRD intensity) of the prepared transparent conductive films was measured in the same manner as in Example 1-1. The results showed that, although diffraction peaks due to rutile SnO2 were observed in all films, it was confirmed that the amorphous structure was dominant in all films. Furthermore, the specific resistance of the transparent conductive films was measured using a Loresta (low resistivity meter). The results showed that the specific resistance of the transparent conductive film prepared at an oxygen flow rate of 0.25% before annealing was 4.7×10-3 Ω·cm, and the resistivity after annealing is 2.0×10 -3 Ω·cm. On the other hand, the specific resistance of the transparent conductive film prepared with an oxygen flow rate of 0.375% before annealing was 7.0×10 -3 Ω·cm, and the resistivity after annealing is 1.9×10 -3 Ω·cm. In addition, the composition of the prepared transparent conductive film was confirmed by the same ICP analysis method as in Example 1-1. The results showed that the metal element constituting the transparent conductive film was only Sn, and the In content was below the quantitative lower limit. In other words, by forming a transparent conductive film (SnO2 film) by magnetron sputtering and performing annealing, a metal oxide containing amorphous tin oxide as the main component (Sn is 85 atomic % or more and In is 4 atomic % or less among the metal elements) and having a specific resistance of 2×10 -3 Transparent conductive film with a resistance of less than Ω·cm.

[0168] Furthermore, the transmission and reflection spectra of each annealed transparent conductive film were measured using a spectrophotometer for light with a wavelength of 220 nm to 2500 nm. The maximum absorption coefficient α for light with a wavelength of 420 nm to 500 nm was determined from the obtained reflection spectra. The results showed that the maximum absorption coefficient α for the transparent conductive film prepared at an oxygen flow rate of 0.25% was 1059 cm -1 The maximum absorption coefficient α of the transparent conductive film prepared with an oxygen flow rate of 0.375% is 2585 cm -1 .

[0169] 6. Preparation of substrate with transparent conductive film A

[0170] (Example a1)

[0171] A PI (polyimide) substrate (thickness 125 μm, size 100 mm × 100 mm) was prepared as a substrate. Then, on the PI substrate, a transparent conductive film with amorphous SnO2 as the main component was prepared by reactive plasma deposition under the same conditions as in Example 1-1. The sheet resistance of the obtained transparent conductive film was measured using Loresta (low resistivity meter). The film thickness, sheet resistance and resistivity at this time are shown in Table 4, respectively. In addition, although not recorded in Table 4, the composition of the transparent conductive film was confirmed by ICP analysis in the same way as in Example 1-1. The results showed that the metal element constituting the transparent conductive film was only Sn, and In was below the quantitative lower limit.

[0172] (Example a2)

[0173] The substrate with a transparent conductive film prepared in Example (a1) was annealed at 250° C. for 0.5 hours. Table 4 shows the sheet resistance and specific resistance at this time.

[0174] (Examples a3, a5, a7 and a9)

[0175] On a PI substrate, a transparent conductive film of In2O3:Ce,H to which Ce and H were added, which is one of the transparent conductive films of the In2O3 system, was deposited by reactive plasma deposition. Subsequently, a transparent conductive film with amorphous SnO2 as the main component was prepared in the same manner as in Example a1. The film thickness, sheet resistance and specific resistance of each transparent conductive film are shown in Table 4. In addition, the specific resistance shown in Table 4 is the specific resistance (reference data) assuming that the electrical properties of each transparent conductive film are uniform in the film thickness direction. In addition, although it is not described in Table 4, the constituent metal element of the transparent conductive film with amorphous SnO2 as the main component is only Sn, and In is below the quantitative lower limit. In addition, although it is not described in Table 4, it is obvious from the specific resistance of Example a1 that the specific resistance is 2×10 -3 Ω·cm or less.

[0176] (Examples a4, a6, a8 and a10)

[0177] The substrates with transparent conductive films prepared in Examples a3, a5, a7, and a9 were annealed at 250° C. for 0.5 hours. Table 4 shows the sheet resistance and specific resistance at this time.

[0178] [Table 4]

[0179]

[0180]

[0181] (result)

[0182] As shown in Table 4 above, when a transparent conductive film primarily composed of amorphous SnO2 is stacked on an In2O3:Ce,H transparent conductive film, increasing the ratio of the In2O3:Ce,H transparent conductive film monotonically decreases the sheet resistance of the substrate with the transparent conductive film (Examples a3 to a10). This demonstrates that a very useful substrate with a transparent conductive film can be obtained by further stacking the transparent conductive film of the present invention (amorphous SnO2 film) on a substrate with a known transparent conductive film (In2O3:Ce,H film).

[0183] 7. Preparation of substrate with transparent conductive film B

[0184] (Examples b1, b3, b5 and b7)

[0185] A PI (polyimide) substrate (thickness 125 μm, size 100 mm × 100 mm) was prepared as a substrate. Subsequently, a transparent conductive film with amorphous SnO2 as the main component was prepared by reactive plasma deposition under the same conditions as in Example 1-1. Next, an In2O3:Ce,H transparent conductive film was deposited on the transparent conductive film (amorphous SnO2) by reactive plasma deposition in the same manner as in Example a3. Furthermore, a transparent conductive film with amorphous SnO2 as the main component was prepared by reactive plasma deposition under the same conditions as in Example 1-1. The film thickness, sheet resistance and resistivity of each transparent conductive film are shown in Table 5. In addition, the resistivity shown in Table 5 is the resistivity (reference data) assuming that the electrical properties of each transparent conductive film are uniform in the film thickness direction. In addition, although not listed in Table 5, the constituent metal element of the transparent conductive film with amorphous SnO2 as the main component is only Sn, and In is below the quantitative lower limit. In addition, although not shown in Table 5, it is clear from the specific resistance of Example a1 that the specific resistance of the transparent conductive film containing only amorphous SnO2 as the main component is 2×10 -3 Ω·cm or less.

[0186] (Examples b2, b4, b6 and b8)

[0187] The substrates with transparent conductive films prepared in Examples b1, b3, b5, and b7 were annealed at 250° C. for 0.5 hours. Table 5 shows the sheet resistance and specific resistance at this time.

[0188] [Table 5]

[0189]

[0190] (result)

[0191] As shown in Table 5 above, when stacking a transparent conductive film primarily composed of amorphous SnO2, an In2O3:Ce,H film, and a transparent conductive film primarily composed of amorphous SnO2, the sheet resistance of the substrate with the transparent conductive film decreases monotonically as the ratio of the In2O3:Ce,H film increases. This confirms that stacking the transparent conductive film of the present invention (amorphous SnO2 film) with a known transparent conductive film (In2O3:Ce,H film) yields a very useful substrate with a transparent conductive film.

[0192] This application is based on the priority of Japanese Patent Application No. 2023-026205, filed on February 22, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0193] Industrial Applicability

[0194] According to the present invention, a transparent conductive film having high transparency and high conductivity and a low indium content can be provided, which can be formed at low temperatures and can be used in various devices as a film that can replace conventional ITO films.

[0195] Description of Reference Numerals

[0196] 1 substrate

[0197] 10 Crucible

[0198] 11 Materials

[0199] 20 Plasma Gun

[0200] 21 Plasma beam

[0201] 22 Plasma

[0202] 30 Plasma Controller

[0203] 40 chambers

[0204] 100 Reactive Plasma Deposition Device

[0205] 120n-type single crystal silicon layer

[0206] 121, 123i type semiconductor layer

[0207] 122 p-type semiconductor layer

[0208] 124 n-type semiconductor layer

[0209] 125 Light-receiving side transparent electrode

[0210] 126 Grid Electrode

[0211] 127 Back side transparent electrode

[0212] 128 Metal Electrode

[0213] 130 Photoelectric conversion layer

[0214] 131 first electrode

[0215] 132 second electrode

[0216] 200 Si heterojunction solar cells

[0217] 400 Perovskite solar cells.

Claims

1. A transparent conductive film, characterized in that: Contains a metal oxide with amorphous tin oxide as a main component, Among the metal elements constituting the metal oxide, the amount of Sn is 85 atomic % or more, the amount of In is 4 atomic % or less, and, The specific resistance of the transparent conductive film is 2×10 -3 Ω·cm or less.

2. The transparent conductive film according to claim 1, wherein When the wavelength is between 420nm and 500nm, the maximum absorption coefficient is 1×10 4 cm -1 the following.

3. The transparent conductive film according to claim 1, wherein Contains at least one selected from the group consisting of In, Zn, Cd, Nb, Ta, B, Ga, Ba, Mo, Pb, Rb, Re, Sb, W, Ce, Cs, Dy, Er, Ge, Hf, Ho, La, Lu, Nd, Pr, Sc, Si, Sm, Tb, V, Y, Al, Ti, Zr, and Si.

4. The transparent conductive film according to claim 1, wherein The concentration of hydrogen atoms in the region 10 nm or more from both sides of the surface measured by secondary ion mass spectrometry was 8×10 21 atoms / cm 3 the following.

5. A substrate with a transparent conductive film, characterized in that: include: substrate; The transparent conductive film according to any one of claims 1 to 4, disposed on the substrate.

6. The substrate with a transparent conductive film according to claim 5, wherein The substrate is a resin film.

7. A photoelectric conversion element, characterized in that: include: Photoelectric conversion layer; A first electrode, disposed adjacent to the photoelectric conversion layer, comprising at least one conductive film; as well as a second electrode, disposed adjacent to the photoelectric conversion layer, comprising at least one conductive film; At least one of the first electrode and the second electrode includes the transparent conductive film according to any one of claims 1 to 4.

8. The photoelectric conversion element according to claim 7, wherein The photoelectric conversion element is a solar cell, The photoelectric conversion layer includes: a single crystal silicon layer doped to n-type or p-type; a p-type semiconductor layer disposed on one side of the single crystal silicon layer; and an n-type semiconductor layer disposed on the other side or the same side of the single crystal silicon layer.

9. The photoelectric conversion element according to claim 8, wherein The p-type semiconductor layer is a p-type microcrystalline silicon layer or an alloy layer thereof, and / or the n-type semiconductor layer is an n-type microcrystalline silicon layer or an alloy layer thereof, The transparent conductive film is arranged adjacent to the p-type microcrystalline silicon layer or its alloy layer and / or the n-type microcrystalline silicon layer or its alloy layer.

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