Transparent electrically conductive film, substrate having transparent electrically conductive film, and photoelectric conversion element

Abstract

The purpose of the present invention is to provide a transparent electrically conductive film which can be formed at a low temperature, has high transparency and high electrical conductivity, and has a low indium content or does not contain indium. This transparent electrically conductive film contains a metal oxide whose primary component is amorphous tin oxide. Among metal elements that constitute the metal oxide, the amount of Sn is 85 atom% or more and the amount of In is 4 atom% or less. The transparent electrically conductive film has a resistivity of 2×10-3 Ω·cm or less.

Description

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

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

[0002] Tin-doped indium oxide (ITO) and other transparent conductive films are used as transparent electrodes on the light-receiving side of optoelectronic devices such as displays and solar cells. ２ O ３ In-based materials are widely known (for example, Patent Document 1). ２ O ３ These materials have the advantage that they can be formed into films using low-temperature processes and also have high transparency and electrical conductivity.

[0003] However, indium is a rare metal and is very expensive. ２ O ３ The replacement of zinc oxide-based materials with other materials has been considered. A film made of zinc oxide (ZnO) is known as a transparent conductive film that is relatively inexpensive and can be formed at low temperatures (see, for example, Patent Document 2). However, transparent conductive films whose main component is zinc oxide have low moisture resistance and chemical resistance. Therefore, it has been difficult to replace transparent conductive films whose main component is zinc oxide with transparent conductive films made of ITO or the like.

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

[0005] International Publication No. 2017 / 057556 Japanese Patent Application Laid-Open No. 2012-117903

[0006] Here, FTO and ATO are polycrystalline, and their conductivity is increased by forming the film at a high temperature to improve the crystallinity. Therefore, FTO and ATO films must be formed at about 500°C by thermal CVD or at 400°C to 500°C by sputtering. However, film formation at a high temperature exceeding 400°C is likely to cause thermal damage to the substrate on which the film is laminated and to each layer of the optoelectronic device. Therefore, it has been difficult to use FTO and ATO as transparent conductive films for optoelectronic devices. For this reason, currently, FTO and ATO, which are mainly composed of rare indium, are used. ２ O ３ Therefore, it was necessary to use a transparent conductive film of this type.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a transparent conductive film that can be formed at low temperatures, has high transparency and high conductivity, and further contains a small amount of indium or is indium-free, as well as a transparent conductive film-coated substrate and a photoelectric conversion element that include the same.

[0008] One embodiment of the present invention is a metal oxide containing amorphous tin oxide as a main component, wherein the amount of Sn among the metal elements constituting the metal oxide is 85 atomic % or more, the amount of In is 4 atomic % or less, and the resistivity is 2×10 －３ A transparent conductive film having a resistivity of Ω·cm or less is provided.

[0009] One embodiment of the present invention also provides a substrate with a transparent conductive film, comprising a substrate and the transparent conductive film disposed on the substrate.

[0010] Furthermore, one embodiment of the present invention also provides a photoelectric conversion element having a photoelectric conversion layer, a first electrode including at least one layer of conductive film arranged adjacent to the photoelectric conversion layer, and a second electrode including at least one layer of conductive film arranged adjacent to the photoelectric conversion layer, wherein at least one of the first electrode and the second electrode includes the above-mentioned transparent conductive film.

[0011] According to the present invention, there is provided a transparent conductive film that can be formed at low temperatures, has high transparency and high conductivity, and further has a low indium content or is indium-free. Furthermore, the transparent conductive film is applicable to various photoelectric conversion elements such as solar cells.

[0012] FIG. 1A is a graph illustrating the correlation between the valence of Sn in a transparent conductive film and the extinction coefficient k, and FIG. 1B is a graph illustrating the correlation between the valence of Sn in a transparent conductive film and the absorption coefficient α. FIG. 2 is a graph showing the relationship between the depth from the surface of a transparent conductive film and the hydrogen atom concentration in the transparent conductive film. FIG. 3 is a schematic diagram of a reactive plasma deposition apparatus capable of forming a transparent conductive film according to one embodiment of the present invention. FIG. 4 is a schematic diagram showing the structure of a Si heterojunction solar cell. FIG. 5 is a schematic diagram showing the structure of a perovskite solar cell. FIG. 6 is a schematic diagram showing the amorphous SnO ２ film, and the a-In film prepared in Reference Example 1 ２ O ３ 7A is a graph showing the extinction coefficient k and refractive index n of the PET substrate alone, the PET substrate and the transparent conductive film (Example 1-3), and the SiO 3 film. ２ FIG. 7B is a graph showing the transmission and reflection spectra of a glass substrate alone and a glass substrate and a transparent conductive film (Examples 1-3 and 1-4). FIG. 8 is a graph showing the external quantum efficiency spectra of the front-junction Si heterojunction solar cells fabricated in Examples 2-1 and 2-2 and Reference Example 2. FIG. 9 is a graph showing the current-voltage characteristics of the rear-junction Si heterojunction solar cells fabricated in Examples 3-1 and 3-2 and Reference Example 3. FIG. 10 is a graph showing the current-voltage characteristics of the rear-junction Si heterojunction solar cells fabricated in Example 3-2a and Reference Example 3. FIG. 11 is a graph showing the series resistance of the Si heterojunction solar cells fabricated in each Example.

[0013] In this specification, a numerical range indicated by "to" means a numerical range including the numerical values ​​written before and after "to".

[0014] 1. Transparent Conductive Film The transparent conductive film of the present invention contains a metal oxide mainly composed of amorphous tin oxide, and 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 is 2×10 －３ The resistivity is Ω·cm or less. In this specification, the term "amorphous" tin oxide in a transparent conductive film means that when X-ray diffraction intensity (XRD intensity) is measured, broad peaks derived from amorphous structures are dominant and no significant peaks derived from crystals are observed. In other words, when a transmission electron microscope (TEM) image is observed, the film may have a microcrystalline structure in which amorphous structures are dominant and crystalline structures are scattered within the amorphous layer. Furthermore, the transparent conductive film may partially contain components other than the metal oxides, for example, may be doped with fluorine, as long as the objectives and effects of the present invention are not impaired. However, it is preferable that 85 mass % or more of the film is the metal oxide, and it is more preferable that the film consists of the metal oxide.

[0015] As mentioned above, polycrystalline FTO (SnO ２ :F) and ATO (SnO ２ It is known that amorphous tin oxide (Sb) and the like have high transparency and high conductivity. However, it has been difficult to form a film of these at low temperatures, making their practical application difficult. In response to this, the inventors have conducted extensive research and found that a film mainly containing amorphous tin oxide not only can be formed at low temperatures, but also has very good transparency and conductivity. The reasons for this are thought to be as follows.

[0016] Tin oxide (especially SnO ２ The conduction band of SnO is mainly composed of Sn5s orbitals. The Sn5s orbitals have a large spatial spread of electrons, and spherical s orbitals overlap with each other. Therefore, even if the bond angle fluctuates due to the amorphous structure, the overlap between orbitals does not decrease so much compared to the crystalline case, and it is thought that high electron mobility is realized. In fact, amorphous SnO ２ The effective mass of an electron in a film made of ０ and crystalline SnO ２Therefore, the carrier conduction path is less affected by the amorphous structure, and the effective mass of the electrons in the film is not significantly different from that of the amorphous tin oxide (especially SnO ２ ) to form crystalline SnO ２ It is believed that high transparency and high conductivity similar to those of the above can be achieved.

[0017] The transparent conductive film of the present invention also has the advantage of having good moisture resistance.

[0018] In order to achieve high transparency and high conductivity of the transparent conductive film, it is sufficient that Sn accounts for 85 atomic % or more of all metal elements constituting the metal oxide, but the amount of Sn is more preferably 90 atomic % or more, and even more preferably 95 atomic % or more. Furthermore, the metal oxide may contain metal elements other than Sn within a range that does not impair the objects and effects of the present invention, but the total amount of metal elements other than Sn is preferably 15 atomic % or less, more preferably 10 atomic % or less, and even more preferably 5 atomic % or less of all metal elements constituting the metal oxide.

[0019] 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., and among these, Zn, Cd, B, Ga, Si, Ge, Pb, Sb, V, Nb, Ta, Mo, W, and Ce are preferred. The metal oxide may contain only one of these, or may contain two or more. When the metal oxide further contains a metal element other than Sn, the processability of the material for forming the transparent conductive film is improved, and depending on the type of metal element, the density, transparency, and conductivity of the transparent conductive film may be further improved.

[0020] However, 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 free of In. The lower the amount of In, the lower the cost of the transparent conductive film. Furthermore, if a metal oxide (transparent conductive film) contains In, which is a specified chemical substance, all work involving the handling of the transparent conductive film becomes subject to regulation. In contrast, if the metal oxide does not contain In, it is not subject to regulation, which has the advantage of improving workability. The amount of each metal element constituting the metal oxide can be determined by, for example, confirming the composition of the transparent conductive film using ICP analysis.

[0021] In addition, in the transparent conductive film (metal oxide), Sn is mainly tetravalent (Sn ４＋ It is preferable that Sn is contained in the state of Sn. ４＋ and Sn ２＋ The Sn in the transparent conductive film can have a mixed valence of ２＋ When the amount of Sn increases, the number of acceptor-type defects increases. As a result, both the carrier concentration and mobility decrease, and as shown in Table 1 below, the resistivity tends to increase. Although it is difficult to directly measure the valence of Sn in a transparent conductive film, 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 of 420 nm to 500 nm. Therefore, the valence of Sn in the transparent conductive film can be evaluated by checking the extinction coefficient k or absorption coefficient α of the transparent conductive film. Figure 1A shows the Sn ４＋ Amount and Sn ２＋ The extinction coefficient k at wavelengths of 200 nm to 1200 nm is shown in FIG. 1B when the ratio of the amount of Sn is changed. ４＋ Amount and Sn ２＋ 1 shows the absorption coefficient α at wavelengths of 400 nm or more and 600 nm or less when the ratio of the amount of fluorine to the amount of fluorine is changed.

[0022] As shown in FIG. 1A, Sn ４＋ In the transparent conductive film containing mainly Sn, the extinction coefficient k is very small in the wavelength range of 420 nm to 500 nm. ２＋As the proportion of increases, the extinction coefficient k at wavelengths of 420 nm to 500 nm increases. Therefore, the maximum value of the extinction coefficient k (maximum extinction coefficient) of the transparent conductive film at wavelengths of 420 nm to 500 nm is preferably 0.033 or less, more preferably 0.025 or less, and even more preferably 0.017 or less. When the maximum extinction coefficient at wavelengths of 420 nm to 500 nm is 0.033 or less, it can be said that the amount of tetravalent Sn in the transparent conductive film is sufficiently large, making it easier to achieve high transparency and high conductivity. The extinction coefficient k can be determined by measuring reflected light at wavelengths of 200 nm to 1200 nm using a spectroscopic ellipsometry device and determining the change in polarization state between the incident light and the reflected light.

[0023] On the other hand, as shown in FIG. ４＋ In the transparent conductive film containing mainly Sn, the absorption coefficient α is very small in the wavelength range of 420 nm to 500 nm. ２＋ When the ratio of α increases, the absorption coefficient α at wavelengths of 420 nm or more and 500 nm or less increases. The maximum value of the absorption coefficient α (maximum absorption coefficient) of the transparent conductive film at wavelengths of 420 nm or more and 500 nm or less is 1×10 ４ cm －１ Preferably, 7.5 x 10 ３ cm －１ Less than 5 x 10 is more preferable. ３ cm －１ It is more preferable that the maximum absorption coefficient α in the wavelength range of 420 nm or more and 500 nm or less is 1×10 ４ cm －１ When the absorption coefficient α is less than 1 / 2, the amount of tetravalent Sn in the transparent conductive film is sufficiently large, and high transparency and high conductivity are more easily achieved. The absorption coefficient α can be determined from the absorption spectrum obtained by measuring the transmittance and reflectance of light having a wavelength of 200 nm or more and 1200 nm or less using a spectrophotometer.

[0024] The method for adjusting the extinction coefficient k or the absorption coefficient α in the transparent conductive film is not limited, but the adjustments can be made by depositing the transparent conductive film in an atmosphere containing a sufficient amount of oxygen, by reducing the partial pressure of water vapor remaining in the film deposition chamber, or by depositing the film by heating at a temperature of about 200°C or less.

[0025] Here, the specific resistance of the transparent conductive film is 2×10 －３ It is sufficient if it is Ω cm or less, but it is 1.5 × 10 －３ Ω cm or less is preferable, and 1×10 －３ The specific resistance of the transparent conductive film is more preferably 2×10 Ω·cm or less. －３ If the resistivity is Ω·cm or less, the transparent conductive film can be used for various purposes, such as a transparent electrode of a photoelectric conversion element, etc. The resistivity can be determined by a Loresta (low resistivity meter).

[0026] Furthermore, the inventors' intensive studies have revealed that a higher film density of the transparent conductive film is preferable in terms of reducing the resistivity of the transparent conductive film. The following four samples were prepared using a method similar to that shown in Example 1-1 described below. The compositions, film densities, and resistivities obtained are shown in Table 1 below. The average compositions were analyzed using Rutherford backscattering spectroscopy (RBS), and the resistivities were measured using a Loresta (low resistivity meter). Furthermore, the film density was calculated from the areal density determined by RBS and the film thickness determined by spectroscopic ellipsometry.

[0027] As shown in Table 1, the resistivity decreases as the film density of the transparent conductive film increases. －３ In the following respects, the film density analyzed by Rutherford backscattering spectroscopy (RBS) is 5.6 g / cm ３ The film density is preferably 6.3 g / cm or more. ３ More preferably, 6.4 g / cm ３The above is more preferable. It is also possible to calculate the film density by X-ray reflectometry (XRR). However, the XRR method calculates the film density by assuming the film composition. Therefore, it is not yet clear which of the RBS method and the XRR method is closer to the true value, since there are no thin film standard samples with known film densities. Therefore, the above results may be values ​​that include an error from the true value, but it is clear that a higher film density of the transparent conductive film is preferable, and when measuring the film density by RBS, it is preferable that the value is equal to or greater than the above value.

[0028] Furthermore, through intensive research by the present inventors, it has become clear that in order to reduce the resistivity of a transparent conductive film, it is preferable to control the hydrogen atom concentration in the transparent conductive film as measured by secondary ion mass spectrometry (SIMS) and adjust the hydrogen atom concentration to a low level. It can also be said that a low hydrogen atom concentration leads to the formation of a dense film, resulting in a film with high film density.

[0029] The following five SnO ２ Films (transparent conductive films) were fabricated. Figure 2 shows the relationship between the depth of the transparent conductive film and the hydrogen atom concentration when the hydrogen atom concentration of these transparent conductive films was measured from one surface using SIMS. It is clear from Figure 2 that hydrogen atoms tend to accumulate on the surface of the transparent conductive film and at the interface between the transparent conductive film and another film (here, a glass substrate), resulting in a higher concentration than inside. Furthermore, SIMS analysis results in a profile that spreads deeper due to the intrusion of elements by sputtering ions. Therefore, the hydrogen atom concentration inside these transparent conductive films (regions 10 nm or more inward from both surfaces (or interfaces)) was determined. The results are shown in Table 2 below. Furthermore, the resistivity of each transparent conductive film was measured using a Loresta (low resistivity meter). The results are shown in Table 2 below.

[0030] As shown in the table above, the lower the hydrogen atom concentration inside the transparent conductive film, the smaller the resistivity. －３ In terms of achieving the above, the concentration of hydrogen atoms in the regions 10 nm or more inward from both surfaces of the transparent conductive film is set to 8×10２１ atoms / cm ３ It is preferable that the density is 7×10 or less. ２１ atoms / cm ３ Less than 6 x 10 is more preferable. ２１ atoms / cm ３ The following is more preferable:

[0031] Here, the thickness of the transparent conductive film is appropriately selected depending on its application. When the transparent conductive film is used as a transparent electrode on the light-receiving side or the light-emitting side of a photoelectric conversion element described below, the thickness is preferably 1 nm or more and 5000 nm or less, and more preferably 10 nm or more and 1000 nm or less. When the thickness of the transparent conductive film is within this range, high transparency and high conductivity required for a transparent electrode can be easily obtained.

[0032] The method for producing the transparent conductive film is not particularly limited as long as the above-mentioned composition and resistivity are satisfied, and the film can be formed by, for example, a film formation method using reactive plasma deposition or a sputtering method. Hereinafter, a film formation method using reactive plasma deposition will be described, but the method for producing the transparent conductive film is not limited to this method. In the examples described later, a method for forming a transparent conductive film by magnetron sputtering will also be shown.

[0033] Film formation by reactive plasma deposition can be performed, for example, by a reactive plasma deposition apparatus 100 shown in the schematic diagram of Fig. 3. However, the configuration of the reactive plasma deposition apparatus 100 is not limited to this configuration.

[0034] The reactive plasma deposition apparatus 100 includes a hearth unit 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 from the plasma gun 20 to the material in the hearth unit 10, and a chamber 40 for accommodating these components. To form the transparent conductive film on a substrate 1 using the reactive plasma deposition method, the material is accommodated in the hearth unit 10, and the substrate 1 is placed in a predetermined position. The interior of the chamber 40 is adjusted to a predetermined atmosphere and pressure. The plasma gun 20 then generates the plasma beam 21 and plasma 22. The plasma beam 21 emitted from the plasma gun 20 is guided to the hearth unit 10 by the plasma beam controller 30 and perpendicularly strikes the material in the hearth unit 10. The material heated by irradiation with the plasma beam 21 sublimes and is ionized in the plasma 22. The ionized material 11 then reaches the substrate 1 in an activated state. This results in the formation of the transparent conductive film on the substrate 1.

[0035] When forming a transparent conductive film by the reactive plasma deposition method, the material to be placed in the hearth 10 is preferably a sintered body having a composition substantially similar to that of the transparent conductive film, a sintered body made of a metal constituting the transparent conductive film, a metal oxide including a suboxide of the metal, or a mixture thereof. The sintered body may be amorphous or crystalline. The sintered body may be SnO ２ Alternatively, it can be obtained by mixing SnO or Sn with other metals or metal oxides as required, and sintering the mixture by a known method such as atmospheric sintering or hot pressing.

[0036] Furthermore, in order to make the tin oxide in the transparent conductor (metal oxide) amorphous, it is preferable to maintain the temperature of the substrate 1 at 300° C. or less. The temperature of the substrate 1 may be around room temperature when not being intentionally heated. Alternatively, it may be intentionally cooled to around 0° C.

[0037] The pressure in the chamber is preferably 0.01 Pa or more and 10 Pa or less from the viewpoint of film formation efficiency, 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 it is preferable to use an inert gas atmosphere in which Sn is tetravalent (Sn ４＋ In order to facilitate this, it is preferable to introduce oxygen into the atmosphere, and the oxygen partial pressure is more preferably 0.01 Pa or more and 10 Pa or less, and even more preferably 0.1 Pa or more and 1 Pa or less. When the oxygen partial pressure is within this range, it becomes even easier to obtain a transparent conductive film having the above-mentioned extinction coefficient and absorption coefficient.

[0038] After the film is formed by the reactive plasma deposition method, it is preferable to perform a heat treatment at 20° C. to 400° C., 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 causes structural relaxation, which tends to stabilize the resulting transparent conductive film and further lower the conductivity.

[0039] 2. Substrate with Transparent Conductive Film The substrate with transparent conductive film of the present invention only needs to have a substrate and the transparent conductive film disposed on the substrate, and there are no particular limitations on the shape of the substrate or the thickness of the transparent conductive film. The transparent conductive film may be disposed over the entire surface of the substrate, or may be disposed only on a partial region of the substrate. Furthermore, the substrate may include components other than the substrate and the transparent conductive film. For example, an optional layer (e.g., a conductive film other than the above, a barrier film, etc.) may be disposed between the substrate and the transparent conductive film, or on the transparent conductive film. The optional layer may be a known layer.

[0040] The material of the substrate may be an inorganic material such as glass, or may be a resin material. That is, the substrate may be a resin film. The substrate may also be composed of multiple layers. The shape of the substrate is not particularly limited, and may be flat or have a three-dimensional shape. Furthermore, the light transmittance of the substrate is appropriately selected depending on the application, and may or may not be light transmittance. The substrate may also be flexible.

[0041] The transparent conductive film described above has high transparency and conductivity. Furthermore, the transparent conductive film can be formed at a relatively low temperature (e.g., 300° C. or less). Therefore, substrates made of various materials can be used.

[0042] Examples of the structure of the substrate with a transparent conductive film include various structures, such as a laminated structure including a substrate / barrier film / the transparent metal film, a laminated structure including a substrate / another conductive film / the transparent conductive film, and a laminated structure including a substrate / the transparent conductive film / another conductive film.

[0043] The applications of the substrate with a transparent conductive film are not limited to photoelectric conversion elements described below, and examples thereof include, but are not limited to, various photodetection elements, displays, wearable devices, thin film transistors (TFTs), transparent heaters, infrared communication devices, infrared sensors, heat ray reflecting materials, electromagnetic wave blocking materials, antistatic agents, and the like.

[0044] 3. Photoelectric Conversion Element The transparent conductive film described above can be used for either or both of the first and second electrodes of a photoelectric conversion element having a photoelectric conversion layer, a first electrode including at least one conductive film disposed adjacent to the photoelectric conversion layer, and a second electrode including at least one conductive film disposed adjacent to the photoelectric conversion layer. The first electrode and the second electrode may be composed of multiple layers. In this case, any layer constituting the first electrode or any layer constituting the second electrode may be the transparent conductive film described above. In this case, two or more layers may be the transparent conductive film described above. Depending on the type of photoelectric conversion element, the layers corresponding to the first and second electrode layers may be referred to as electron transport layers, carrier selection layers, n-type buffer layers, (conductive) cap layers, etc., and the transparent conductive film described above can also be used for these layers.

[0045] In this specification, the term "photoelectric conversion element" refers to an element that converts light energy into electrical energy, or an element that converts electrical energy into light energy. Examples of photoelectric conversion elements include solar cells, organic EL elements, light-emitting diodes, laser diodes, etc. Below, a case where the photoelectric conversion element is a solar cell will be described, but the above-mentioned transparent conductive film can also be used for the transparent electrode or metal electrode on the light-emitting side of an organic EL element, etc.

[0046] Furthermore, the type of solar cell that can use the transparent conductive film is not particularly limited, and can be used for any known type of solar cell. Several solar cell configurations are shown below, but the configurations of solar cells that can use the transparent conductive film described above are not limited to these.

[0047] (Si Heterojunction Solar Cell) An example of the structure of a Si heterojunction solar cell is shown in Figure 4. The Si heterojunction solar cell (hereinafter also simply referred to as "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 the solar cell 200, light is incident from the first electrode 131 side.

[0048] In the solar cell 200, the first electrode 131 is composed of a light-receiving 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 above-mentioned transparent conductive film can be used for either or both of the light-receiving transparent electrode 125 and the back-side transparent electrode 127. Note that when the above-mentioned transparent conductive film is used for only one of the electrodes, 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 above-mentioned transparent conductive film for both the light-receiving transparent electrode 125 and the back-side transparent electrode 127. Furthermore, either or both of the light-receiving transparent electrode 125 and the back-side transparent electrode 127 may be a laminate of multiple conductive films. In this case, the above-mentioned transparent conductive film can be used for either the light-receiving transparent electrode 125 or the back-side transparent electrode 127. For example, a laminate of the above-described transparent conductive film and ITO film may be used as the light-receiving transparent electrode 125 or the back-side transparent electrode 127. Using the above-described transparent conductive film as part of the light-receiving transparent electrode 125 or the back-side transparent electrode 127 has the advantage of reducing the amount of ITO (especially In) used. The grid electrode 126 and the metal electrode 128 are similar to electrodes in known solar cells and are electrodes made of Ag, Cu, composite metals, or the like. While the metal electrode 128 is shown as being formed over the entire surface in FIG. 4 , it may also be grid-shaped like the grid electrode 126. In this case, a bifacial solar cell can be formed in which light incident from the second electrode 132 side also contributes to power generation.

[0049] On the other hand, the photoelectric conversion layer 130 has a structure in which an n-type single crystal silicon layer 120 is sandwiched between a p-type semiconductor layer 122 and an n-type semiconductor layer 124. Between the n-type single crystal silicon layer 120 and the p-type semiconductor layer 122, and between the n-type single crystal silicon layer 120 and the n-type semiconductor layer 124, i-type semiconductor layers 121 and 123 are disposed, respectively.

[0050] The arrangement order of the layers of the photoelectric conversion layer 130 may be reversed, with the n-type semiconductor layer being arranged on the light-receiving surface side and the p-type semiconductor layer being arranged on the back surface side. A structure in which a p-i-n junction structure consisting of a p-type semiconductor layer 122, an i-type semiconductor layer 121, and an n-type single-crystalline silicon layer 120 is arranged on the light-receiving surface side, as shown in FIG. 4, is typically referred to as a front junction type, while a structure in which a p-i-n junction structure is arranged on the back surface side is referred to as a rear junction type. The solar cell of the present invention may be either a front junction type or a rear junction type. Furthermore, although the present specification describes an example in which the photoelectric conversion layer 130 has an n-type single-crystalline silicon layer 120, the photoelectric conversion layer 130 may have a structure in which the n-type single-crystalline silicon layer 120 is replaced with a p-type single-crystalline silicon layer. Furthermore, a structure in which the p-type semiconductor layer and the n-type semiconductor layer are each arranged in a comb-like pattern on the back surface side may also be used. In this case, either a p-type semiconductor layer or an n-type semiconductor layer may be disposed on the light-receiving surface side, or neither of these layers may be disposed on the light-receiving surface side.

[0051] The n-type single-crystalline silicon layer 120 of the photoelectric conversion layer 130 is similar to the n-type single-crystalline silicon layers of known solar cells, and is a layer made of n-type single-crystalline silicon doped with n-type impurities such as phosphorus (P). Here, the light-receiving surface and the back surface of the n-type single-crystalline silicon layer 120 may be flat surfaces formed of (100) planes. However, it is preferable that a random pyramid texture structure formed of silicon (111) facets is formed on one or both surfaces, and it is more preferable that a random pyramid texture structure is formed on both surfaces. When the light-receiving surface and the back surface of the n-type single-crystalline silicon layer 120 are formed with a random pyramid texture structure, light incident on the n-type single-crystalline silicon layer 120 is less likely to be reflected by the surface, and further, the incident light is less likely to exit due to the light trapping effect. This facilitates an increase in the photoelectric conversion efficiency of the solar cell 200.

[0052] On the other hand, examples of the p-type semiconductor layer 122 include a layer made of p-type hydrogen-containing amorphous silicon (also referred to in this specification as "(p)a-Si:H") into which p-type impurities such as boron (B) have been introduced. However, when the above-mentioned transparent conductive film and the p-type semiconductor layer 122 are disposed adjacent to each other, it is preferable that the p-type semiconductor layer 122 be a p-type microcrystalline silicon layer containing p-type microcrystalline silicon in a hydrogenated amorphous silicon layer (also referred to in this specification as "(p)nc-Si:H"). Alternatively, the p-type semiconductor layer 122 may be an alloy layer of p-type microcrystalline silicon, for example, a p-type microcrystalline silicon oxide (also referred to in this specification as "(p)nc-SiO x The higher the oxygen concentration of microcrystalline silicon oxide, the greater the transparency. On the other hand, since the higher the oxygen concentration, the lower the electrical conductivity, it is necessary to select an appropriate range of oxygen concentration, and x is preferably 0.1 or more and 1.5 or less. The microcrystalline silicon phase contained in these layers is composed of minute silicon crystallites, and the crystal size is preferably on the order of nanometers. As will be described in detail in the examples below, when the above-mentioned transparent conductive film and the (p)nc-Si:H film are arranged adjacent to each other, the series resistance of the solar cell 200 may increase. As a result, a decrease in fill factor may be observed compared to when 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 and the (p)nc-Si:H film or the (p)nc-SiO ｘ When the (p)nc-Si:H film is placed adjacent to the (p)a-Si:H film, the series resistance does not increase, and electrical characteristics comparable to those obtained when ITO is used as a transparent electrode are obtained. The reason for such good electrical characteristics is that the (p)nc-Si:H and (p)nc-SiO ｘ The carrier concentration can be increased in the :H film, which is thought to result in a smaller depletion layer at the interface between the transparent conductive film and the p-type layer, allowing carrier movement by the tunneling effect and reducing resistance.

[0053] Furthermore, examples of the n-type semiconductor layer 124 include a layer made of hydrogen-containing amorphous silicon (also referred to in this specification as "(n)a-Si:H") into which n-type impurities such as phosphorus (P) have been introduced. However, when the above-mentioned transparent conductive film and the n-type semiconductor layer 124 are disposed adjacent to each other, it is preferable that the n-type semiconductor layer 124 be an n-type microcrystalline silicon layer containing n-type microcrystalline silicon in a hydrogenated amorphous silicon layer (also referred to in this specification as "(n)nc-Si:H"). Alternatively, the n-type semiconductor layer 124 may be an alloy layer of n-type microcrystalline silicon, for example, n-type microcrystalline silicon oxide (also referred to in this specification as "(n)nc-SiO x The higher the oxygen concentration, the more transparent the microcrystalline silicon oxide becomes. On the other hand, the higher the oxygen concentration, the lower the electrical conductivity becomes, so it is necessary to select an appropriate range of oxygen concentration, and x is preferably 0.1 or more and 1.5 or less. The microcrystalline silicon phase contained in these layers is composed of minute silicon crystallites, and the crystal size is preferably on the order of nanometers. As will be shown in detail in the examples below, even when the above-mentioned transparent conductive film and the (n)nc-Si:H film are arranged adjacent to each other, the series resistance of the solar cell 200 may also increase. In contrast, when the above-mentioned transparent conductive film and the (n)nc-Si:H film or (n)nc-SiO ｘ When the :H film is disposed adjacent to the transparent electrode, the series resistance does not increase, and electrical characteristics that are comparable to those obtained when ITO is used as the transparent electrode are obtained.

[0054] Furthermore, 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 made of intrinsic amorphous silicon doped with hydrogen (also referred to in this specification as "(i) a-Si:H").

[0055] In the solar cell 200, light incident from the grid electrode 126 side 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 crystalline silicon layer 120. Of the light incident on the n-type single crystalline silicon layer 120, the light energy greater than the band gap of silicon excites the n-type crystalline silicon, forming electron-hole pairs. Electrons (e －) moves to the metal electrode 128 side. ＋ ) moves to the grid electrode 126 side, and the solar cell 200 operates.

[0056] The method for manufacturing the solar cell 200 is not particularly limited. 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, respectively. 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 above-mentioned 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 the above-mentioned reactive plasma deposition method or the like. As described above, amorphous SnO ２ A transparent conductive film containing the above can be formed at a relatively low temperature (for example, 300° C. or less). Therefore, even if it is laminated on the photoelectric conversion layer 130, it has the advantage of being less likely to deteriorate the layers in the photoelectric conversion layer 130. After the light-receiving side transparent electrode 125 and the back-side transparent electrode 127 are formed, the grid electrode 126 and metal electrode 128 are formed by a known method.

[0057] (Perovskite Solar Cell) The transparent conductive film described above can also be applied to, for example, perovskite solar cells. An example of the structure of a perovskite solar cell is shown in FIG. 5. The perovskite solar cell 400 has a structure in which a substrate, a first electrode, a first buffer layer, a light-absorbing (halide-based perovskite material) layer, a second buffer layer, and a 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. While it is desirable for the perovskite solar cell to have these layers in order to achieve higher conversion efficiency, this is not essential in embodiments, and one or both of these layers may be omitted. Furthermore, both or either of the first buffer layer and the second buffer layer may have a structure in which different materials are stacked. Light may enter the perovskite solar cell from either the second electrode or the substrate side. The above-described transparent conductive film can be used for either or both of the first electrode and the second electrode of the perovskite solar cell.

[0058] The first electrode and the second electrode may each be a laminate of multiple conductive films, in which case the transparent conductive film may be used for one of the layers. When the first electrode and the second electrode are a laminate of multiple conductive films, the first electrode and 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 / the transparent conductive film. Conventional conductive layers and counter electrodes are generally made of ITO films, but using the transparent conductive film as a part of the electrode has the advantage of reducing the amount of ITO (especially In) used.

[0059] Furthermore, the transparent conductive film can be formed at a relatively low temperature. Therefore, when the transparent conductive film is used as a conductive layer, not only substrates made of inorganic materials such as glass plates but also substrates or films made of resins can be used as the substrate. The materials for each layer of the perovskite-type solar cell are the same as those for each layer of known perovskite-type solar cells.

[0060] (Other Solar Cells) Solar cells other than the above-mentioned Si heterojunction solar cells and perovskite solar cells, for example, TOPCon (Tunnel Oxide Passivated Contact) solar cells, CdTe solar cells, CuInSe solar cells, etc. ２ I-III-VI represented by ２ group compound solar cell, Cu ２ ZnSnS ４ Representative of I ２ -II-IV-VI ４ group compound solar cell, Cu ２ SnS ３ Representative of I ２ -IV-VI ３ group compound solar cell, Cu ２ I represented by S ２The transparent conductive film described above can be used as an electrode for solar cells of any structure, such as a Group VI compound solar cell, a Group II-VI compound solar cell represented by SnS, or a solar cell with a multi-junction structure that combines the perovskite solar cell with a Si-based solar cell or the like. The TOPCon solar cell described here has a structure in which the transparent conductive film described above is laminated on a semiconductor layer on a tunnel oxide film. In any embodiment, the transparent conductive film described above may be used as a single layer electrode, or a laminate of the transparent conductive film described above and a known conductive film such as an ITO film may be used as an electrode.

[0061] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0062] 1. Preparation of Transparent Conductive Film The optical properties and conductivity of the transparent conductive film of the present invention were compared with those of a conventional transparent conductive film (In ２ O ３ The optical properties and electrical conductivity of the film were compared and evaluated using the following methods.

[0063] (Example 1-1) A transparent conductive film was produced by the following reactive plasma deposition method. As substrates, a Si substrate (30 mm x 30 mm) with a thermal oxide film (50 nm thick) and an alkali-free glass substrate (XG manufactured by Corning Incorporated) (100 mm x 100 mm) were prepared and fixed at predetermined positions in a reactive plasma deposition apparatus 100 shown in Figure 3. In addition, the material of the transparent conductive film, SnO ２ A sintered body was prepared and housed in the hearth portion 10 of the reactive plasma deposition apparatus 100. The temperature of the substrate 1 in the chamber 40 was not heated (room temperature). Furthermore, Ar and O were introduced into the chamber 40 of the reactive plasma deposition apparatus 100. ２ Gas was introduced and the pressure inside the chamber 40 was adjusted to 0.4 Pa (oxygen partial pressure 0.3 Pa). Then, a plasma beam 21 was emitted from the plasma gun 20, and the position of the plasma beam 21 was adjusted by the plasma beam controller 30 so that the plasma beam 21 was incident perpendicularly on the material. At this time, the discharge current value was set to 150 mA. Film formation was carried out under these conditions for 0.7 minutes, and a transparent conductive film (SnO ２ A membrane was obtained.

[0064] When the X-ray diffraction intensity (XRD intensity) of the produced transparent conductive film was measured under the following conditions, no peak was observed, and SnO ２ It was confirmed that the sample was amorphous. (Measurement conditions) Apparatus: RIGAKU SmartLab X-ray: Cu Kα ray Output: 9 kW

[0065] Furthermore, when the composition of the produced transparent conductive film was confirmed by ICP analysis, the only constituent metal element was Sn, and the amount of In was below the lower limit of quantification. Furthermore, when the resistivity was measured using a Loresta (low resistivity meter), it was found to be 1.2 × 10 －３ The value was Ω·cm.

[0066] The transparent conductive film on the Si substrate with a thermal oxide film was measured for reflected light with a wavelength of 200 nm to 1200 nm using a spectroscopic ellipsometry device. The change in polarization state between the incident light and the reflected light, and the maximum extinction coefficient k for light with a wavelength of 420 nm to 500 nm were confirmed, and the maximum extinction coefficient k for this range was found to be 0.018. Furthermore, the refractive index n of the transparent conductive film at wavelengths of 420 nm to 500 nm was 2.09 to 2.17.

[0067] Furthermore, the transmission spectrum and reflection spectrum of the transparent conductive film formed on a Corning XG glass substrate were measured using a spectrophotometer for light having a wavelength of 220 nm to 2500 nm. From the obtained spectrum, the maximum absorption coefficient α of light having a wavelength of 420 nm to 500 nm was confirmed. The maximum absorption coefficient α in this range was 3219 cm －１ It was.

[0068] Furthermore, the transparent conductive film was placed in a thermo-hygrostat 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. －３ Ω·cm, and it was confirmed that the moisture resistance was also excellent. For comparison, an FTO coated glass substrate (type-VU manufactured by AGC Fabritech Co., Ltd.) with a specific resistance of 1.1×10 －３ A similar test was also performed on the Ω cm, and the resistivity after the test was 1.1 × 10 －３ Ω·cm. That is, the transparent conductive film (SnO ２It was confirmed that the film had moisture resistance comparable to that of the FTO film.

[0069] (Example 1-2) A 70 nm thick amorphous SnO film was deposited on a substrate by the same reactive plasma deposition method as in Example 1-1. ２ The transparent conductive film was subjected to annealing treatment at 200° C. for 0.5 hours in a nitrogen atmosphere. The resistivity of the transparent conductive film after the annealing treatment was measured using a Loresta (low resistivity meter) and found to be 9.1×10 －４ The value was Ω·cm.

[0070] Furthermore, the transparent conductive film on the Si substrate with a thermally oxidized film after annealing was measured for reflected light with a wavelength of 200 nm or more and 1200 nm or less using a spectroscopic ellipsometry device. The change in polarization state between incident light and reflected light and the maximum extinction coefficient k for light with a wavelength of 420 nm or more and 500 nm or less were confirmed, and the maximum extinction coefficient k in this range was found to be 0.021. Furthermore, the refractive index n of the transparent conductive film in the wavelength range of 420 nm or more and 500 nm or less was 2.08 to 2.16. The transparent conductive film fabricated on a Corning XG glass substrate was measured for the transmission spectrum and reflection spectrum of light with a wavelength of 220 nm or more and 2500 nm or less using a spectrophotometer. The maximum absorption coefficient α for light with a wavelength of 420 nm or more and 500 nm or less was confirmed from the obtained spectrum, and the maximum absorption coefficient α in this range was found to be 5740 cm －１ It was.

[0071] Furthermore, the transparent conductive film was placed in a thermo-hygrostat 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. －４ It was confirmed that the resistance was Ω·cm and the moisture resistance was also excellent.

[0072] (Reference Example 1) Amorphous hydrogen-containing In was deposited by sputtering on a Si substrate (50 mm x 50 mm) with a thermal oxide film (thickness 50 nm). ２ O ３ (a-In ２ O ３ :H) film (transparent conductive film). ２ O ３The thickness of the :H film was 70 nm. The resistivity of the transparent conductive film was measured using a Loresta (low resistivity meter) and found to be 5.4 × 10 －４ The value was Ω·cm.

[0073] The transparent conductive film (a-In ２ O ３ The reflected light of light having a wavelength of 200 nm or more and 1200 nm or less was measured for the SiO2 film (H film) using a spectroscopic ellipsometry device, and the extinction coefficient k within the range was determined from the change in the polarization state between the incident light and the reflected light. Furthermore, the refractive index n within the range was also determined.

[0074] (Evaluation) Fig. 6 shows the extinction coefficient k and refractive index n at wavelengths of 200 nm or more and 1200 nm or less of each transparent conductive film produced in Examples 1-1 and 1-2 and Reference Example 1. As shown in Fig. 6, the amorphous SnO ２ The film has an extinction coefficient k and a refractive index n that are the same as those of the amorphous In of Reference Example 1. ２ O ３ The resistivity of the transparent conductive films prepared in Examples 1-1 and 1-2 was approximately equal to that of the .DELTA. ... －３ The values ​​were Ω·cm or less, and all of them showed excellent conductivity.

[0075] (Example 1-3) A PET (polyethylene terephthalate) substrate (dimensions: 100 mm x 100 mm) and an alkali-free glass substrate (XG manufactured by Corning Incorporated) (dimensions: 100 mm x 100 mm) were prepared as substrates. A 70 nm thick amorphous SnO ２ The resistivity of the obtained transparent conductive film was measured using a Loresta (low resistivity meter), and it was found to be 1.27 × 10 on the PET substrate. －３ Ω cm, and on a glass substrate, 1.37 × 10 －３ The value was Ω·cm.

[0076] (Example 1-4) SiO ２A PET substrate (dimensions: 100 mm x 100 mm) and an alkali-free glass substrate (XG manufactured by Corning Incorporated) (dimensions: 100 mm x 100 mm) were prepared. A 70 nm thick amorphous SnO ２ The resistivity of the obtained transparent conductive film was measured using a Loresta (low resistivity meter), and it was found that the SiO ２ PET substrate 1.34 x 10 －３ Ω cm, and on a glass substrate, 1.34 × 10 －３ The value was Ω·cm.

[0077] (Evaluation) For each substrate with a transparent conductive film, the transmission spectrum and reflection spectrum of light with a wavelength of 220 nm or more and 2500 nm or less were measured. ２ 7A and 7B show the transmission and reflection spectra of the glass substrate alone, the glass substrate and the transparent conductive film (Example 1-3), and the glass substrate and the transparent conductive film (Example 1-4). As shown in FIGS. 7A and 7B, the transmission and reflection spectra of the glass substrate alone, the glass substrate and the transparent conductive film (Example 1-3), and the glass substrate and the transparent conductive film (Example 1-4) are shown. ２ The desired transparent conductive film (a-SnO) was deposited on the PET substrate by reactive plasma deposition without damaging the substrate. ２ As described above, the specific resistance of the transparent conductive films prepared in Examples 1-1 and 1-2 was 1.37×10 －３ The values ​​were Ω·cm or less, and all of them showed excellent conductivity.

[0078] (Examples 1-5 to 1-9) Transparent conductive films were obtained in the same manner as in Example 1-1, except that the material for the transparent conductive film was a sintered body of a metal oxide shown in Table 3 below. The resistivities of the obtained transparent conductive films are also shown in Table 3. Furthermore, the resistivities when the transparent conductive films were annealed in a nitrogen atmosphere at 250°C for 0.5 hours are also shown in Table 3.

[0079] (Example 1-10) A transparent conductive film was obtained in the same manner as in Example 1-1, except that the material for the transparent conductive film was a sintered body of a metal oxide shown in Table 3 below. The resistivity of the obtained transparent conductive film is also shown in Table 3. Furthermore, the resistivity when the transparent conductive film was annealed in a nitrogen atmosphere at 200°C for 0.5 hours is also shown in Table 3.

[0080]

[0081] (Evaluation) As shown in Table 3 above, even when an element other than Sn (Zn, In or Ga) is contained in an amount of 3 atomic % as a metal element constituting the metal oxide, the resistivity can be increased to 2×10 －３ Ω cm or less. Furthermore, in all transparent conductive films, the resistivity was further reduced by annealing (Examples 1-5 to 1-8). Note that when 3 atomic % of W was included as a metal element constituting the metal oxide, the resistivity was 2×10 －３ However, by annealing, the resistivity was reduced to 2 × 10 －３ It was possible to achieve a resistance of less than Ω·cm.

[0082] Similarly, when the metal oxide contains 15 atomic % of an element other than Sn (Ga), the resistivity is 2×10 without annealing. －３ However, by annealing, the resistivity was reduced to 2 × 10 －３ It was possible to achieve a value of Ω·cm or less (Example 1-10).

[0083] 2. Fabrication of Solar Cells (Fabrication of Front-Junction Si Heterojunction Solar Cells) Front-junction Si heterojunction solar cells were fabricated using the transparent conductive film of the present invention as the light-receiving transparent electrode and / or the back-side transparent electrode. The external quantum efficiency of the solar cells was compared with that of conventional Si heterojunction solar cells using ITO films as the light-receiving transparent electrode and the back-side transparent electrode, and the results were evaluated.

[0084] (Example 2-1) Preparation of Photoelectric Conversion Layer An n-type single-crystalline silicon substrate with a thickness of 280 μm and a resistivity of 2 Ωcm, both surfaces of which were (100) planes, was prepared. The surface of the n-type single-crystalline silicon substrate was wet-etched using a solution mainly containing KOH, forming a random texture structure consisting of (111) facets on both surfaces of the n-type single-crystalline silicon substrate. Next, the native oxide films on both surfaces of the n-type single-crystalline silicon substrate were 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 fabricated on the backside of the n-type single-crystalline silicon substrate using plasma-enhanced 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 fabricated on the light-receiving surface side of the n-type single-crystalline silicon substrate using PECVD. As a result, a photoelectric conversion layer was obtained in which a p-type a-Si:H layer / i-type a-Si:H layer / n-type single crystal silicon layer / i-type a-Si:H layer / n-type a-Si:H layer were stacked in this order from the light-receiving surface side.

[0085] Preparation of the first electrode and the second electrode Amorphous SnO ２ A transparent electrode made of a film was formed. Each of these had a thickness of 75 nm. Furthermore, a grid electrode (width 100 μm, thickness 2 μm) made of Ag was fabricated by sputtering on the transparent conductive film on the light-receiving surface side (light-receiving-side transparent electrode). A metal electrode made of Ag was formed on the entire surface of the transparent conductive film on the back surface side (on the back-side transparent electrode) by sputtering. Subsequently, annealing was performed at 160°C to obtain a front-junction Si heterojunction solar cell.

[0086] (Example 2-2) The transparent electrode on the light-receiving surface side was made of amorphous SnO ２ A front junction Si heterojunction solar cell was obtained in the same manner as in Example 2-1, except that the rear transparent electrode was an ITO film (75 nm thick, prepared by sputtering).

[0087] Reference Example 2 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 surface side and the back surface side were each an ITO film (75 nm thick, prepared by sputtering).

[0088] (Evaluation) 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. 8. As shown in Fig. 8, the transparent electrodes on the light-receiving surface side and the back surface side were made of amorphous SnO ２ Film / amorphous SnO ２ The solar cell of Example 2-1 in which the transparent electrodes on the light-receiving surface side and the back surface side were made of amorphous SnO ２ The external quantum efficiency of the solar cell of Example 2-2, which had a structure of a ZnO film / ITO film, was comparable to the external quantum efficiency of the solar cell of the conventional type (Reference Example 2).

[0089] 3. Fabrication of Solar Cell (Fabrication of Rear-Junction Si Heterojunction Solar Cell) A rear-junction Si heterojunction solar cell was fabricated using the transparent conductive film of the present invention as the light-receiving transparent electrode and / or the back-side transparent electrode. 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 the light-receiving transparent electrode and the back-side transparent electrode.

[0090] In addition, the transparent conductive film (a-SnO ２ We also fabricated rear-junction Si heterojunction solar cells in which the type of semiconductor layer adjacent to the rear-junction Si heterojunction solar cell was changed, and compared the current-voltage characteristics of these solar cells with those of conventional rear-junction Si heterojunction solar cells.

[0091] Example 3-1 A rear junction Si heterojunction solar cell was fabricated by carrying out the same steps as in Example 2-1, except that the photoelectric conversion layer was formed in the following order from the light-receiving surface side: n-type a-Si:H layer / i-type a-Si:H layer / n-type single-crystalline silicon layer / i-type a-Si:H layer / p-type a-Si:H layer.

[0092] (Example 3-2) The transparent electrode on the light-receiving surface side was made of amorphous SnO ２A rear junction Si heterojunction solar cell was obtained in the same manner as in Example 3-1, except that the rear electrode was an ITO film (75 nm thick, prepared by sputtering).

[0093] Reference Example 3 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 surface side and the back surface side were each an ITO film (75 nm thick, prepared by sputtering).

[0094] Example 3-2a 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 changed to an n-type nc-SiOx:H film (thickness: 10 nm).

[0095] (Evaluation) Figure 9 shows the current-voltage characteristics of the rear-junction Si heterojunction solar cells obtained in Examples 3-1 and 3-2, and Reference Example 3. The solar cells of Examples 3-1 and 3-2, in which the transparent conductive film of the present invention was used in the light-receiving-side transparent electrode and / or the back-side transparent electrode, exhibited good current-voltage characteristics, but compared with a conventional solar cell (Reference Example 3), the fill factor (FF) decreased with an increase in series resistance.

[0096] Therefore, a similar evaluation was carried out 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. 10. As shown in FIG. 10, the transparent conductive film (a-SnO ２ When the layer adjacent to the n-type nc-SiOx:H layer was an n-type nc-SiOx:H layer, the fill factor (FF) did not decrease, and current-voltage characteristics very close to those of the conventional solar cell (Reference Example 3) were obtained.

[0097] 4. Preparation of Contact Resistance Evaluation Samples Based on the results described above, to clarify the cause of the decrease in fill factor (FF), the contact resistance of the n-type and p-type contact structures was evaluated using the TLM (transmission line measurement) method. The n-type and p-type contact resistance evaluation samples had the exact same layer structure as the light-incident side of rear-junction and front-junction Si heterojunction solar cells, respectively. That is, the n-type contact resistance evaluation sample was composed 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 light-incident side n-type contact structure of the rear-junction Si heterojunction solar cell was evaluated using this n-type contact resistance evaluation sample. The p-type contact resistance evaluation sample was composed 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 light-incident side p-type contact structure of the front-junction Si heterojunction solar cell was evaluated using this p-type contact resistance evaluation sample. The differences between the contact resistance evaluation sample and the solar cell are that the laminated portion of Ag / transparent conductive film that serves as the electrode is patterned into a strip shape, and that the p-type contact resistance evaluation sample uses p-type crystalline silicon. ２ A contact resistance evaluation sample (Example 2-2a below) was fabricated by changing the type of semiconductor layer adjacent to the ITO film, and the contact resistance value was evaluated. Furthermore, for the p-type contact structure of the solar cell (Reference Examples 2 and 3) using a conventional ITO film, a contact resistance evaluation sample (Reference Examples 2a and 3a below) was fabricated by changing the type of semiconductor layer adjacent to the ITO film, and the contact resistance value was confirmed.

[0098] Example 2-2a 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 changed to a p-type nc-Si:H layer (thickness: 20 nm).

[0099] Reference Example 2a 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 changed to a p-type nc-Si:H layer (thickness: 20 nm).

[0100] Reference Example 3a 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 changed to an n-type nc-SiOx:H layer (thickness 10 nm).

[0101] (Evaluation) FIG. 11 shows 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 cells fabricated in Example 3-2a, Reference Example 3a, Example 3-2, and Reference Example 3. Similarly, FIG. 11 also shows 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 cells obtained in Example 2-2a, Reference Example 2a, Example 2-2, and Reference Example 2. As is clear from FIG. 11, in both the front junction type (p-type contact on the light incident side) and the rear junction type (n-type contact on the light incident side) configurations, the transparent conductive film (a-SnO ２ The semiconductor layer adjacent to the a-Si:H layer is changed to an nc-Si:H layer or an nc-SiO ｘ By changing the material to H, the series resistance was significantly reduced (Examples 3-2a and 2-2a). Furthermore, by adopting such a configuration, it was possible to achieve a series resistance that was equivalent to or lower than that of conventional solar cells (Reference Examples 3 and 2).

[0102] 5. Preparation of Transparent Conductive Film by Magnetron Sputtering (Example) A transparent conductive film was prepared by RF magnetron sputtering in the following manner. First, an alkali-free glass substrate (XG manufactured by Corning Incorporated) (dimensions: 50 mm x 50 mm) was prepared as a substrate. Furthermore, a 3-inch diameter SnO target was prepared. ２ A sintered body was prepared, and the substrate temperature was set to room temperature. Ar gas and O２ The oxygen flow rate ratio was set to 0.25% or 0.375%, and the chamber pressure was set to 0.5 Pa. Then, film formation was carried out for 20 minutes at a sputtering input power of 100 W, and a transparent conductive film (SnO ２ The obtained transparent conductive film was subjected to annealing treatment at 200° C. for 0.5 hours in a nitrogen atmosphere.

[0103] The X-ray diffraction intensity (XRD intensity) of the produced transparent conductive films was measured in the same manner as in Example 1-1. As a result, it was found that all the thin films were composed of SnO ２ Although a slight diffraction peak due to the oxygen flow rate was observed, it was confirmed that the amorphous structure was the dominant structure. Furthermore, when the resistivity of the transparent conductive film was measured using a Loresta (low resistivity meter), the resistivity 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 was 2.0×10 －３ On the other hand, the resistivity of the transparent conductive film prepared at an oxygen flow rate of 0.375% before annealing was 7.0×10 －３ Ω cm, and the resistivity after annealing was 1.9×10 －３ The resistivity was Ω·cm. Furthermore, when the composition of the produced transparent conductive film was confirmed by ICP analysis in the same manner as in Example 1-1, the only constituent metal element was Sn, and In was below the lower limit of quantification. In other words, the transparent conductive film (SnO ２ The film is then annealed to form a metal oxide film containing amorphous tin oxide as the main component (among the metal elements, Sn is 85 atomic % or more and In is 4 atomic % or less) and having a resistivity of 2×10 －３ A transparent conductive film having a resistivity of Ω·cm or less was obtained.

[0104] The transmission spectrum and reflection spectrum of light having a wavelength of 220 nm or more and 2500 nm or less were measured using a spectrophotometer for each transparent conductive film that had undergone annealing. The maximum absorption coefficient α of light having a wavelength of 420 nm or more and 500 nm or less was confirmed from the obtained reflection spectrum. The maximum absorption coefficient α of the transparent conductive film fabricated with an oxygen flow rate ratio of 0.25% was 1059 cm －１The maximum absorption coefficient α of the transparent conductive film fabricated at an oxygen flow rate of 0.375% is 2585 cm －１ It was.

[0105] 6. Preparation of a substrate with a transparent conductive film A (Example a1) A PI (polyimide) substrate (thickness: 125 μm, dimensions: 100 mm×100 mm) was prepared as a substrate. Then, amorphous SnO was deposited on the PI substrate by reactive plasma deposition under the same conditions as in Example 1-1. ２ A transparent conductive film containing the above as a main component was produced. The sheet resistance of the obtained transparent conductive film was measured using a Loresta (low resistivity meter). The film thickness, sheet resistance, and specific resistance at this time are shown in Table 4. Although not shown in Table 4, when the composition of the transparent conductive film was confirmed by ICP analysis in the same manner as in Example 1-1, it was found that the only constituent metal element was Sn, and the amount of In was below the lower limit of quantitation.

[0106] Example a2 The substrate with the transparent conductive film produced in Example (a1) was annealed for 0.5 hours at 250° C. The sheet resistance and specific resistance at this time are shown in Table 4.

[0107] (Examples a3, a5, a7, and a9) In was deposited on a PI substrate by reactive plasma deposition. ２ O ３ In-based transparent conductive film containing Ce and H ２ O ３ A transparent conductive film of SnO :Ce, H was then deposited. ２ Transparent conductive films containing amorphous SnO as the main component were prepared. The film thickness, sheet resistance, and specific resistance of each transparent conductive film are shown in Table 4. The specific resistances shown in Table 4 are specific resistances (reference data) assuming that the electrical properties of each transparent conductive film are uniform in the film thickness direction. Although not shown in Table 4, amorphous SnO ２ The only metal element constituting the transparent conductive film mainly composed of Sn was Sn, and the amount of In was below the lower limit of quantification. ２ The resistivity of the transparent conductive film containing the －３ It is clear from the resistivity of Example a1 that it is Ω·cm or less.

[0108] (Examples a4, a6, a8, and a10) The substrates with transparent conductive films produced in Examples a3, a5, a7, and a9 were each annealed for 0.5 hours at 250° C. The sheet resistance and specific resistance at this time are shown in Table 4.

[0109]

[0110] (Results) As shown in Table 4 above, In ２ O ３ : Ce, H Amorphous SnO on transparent conductive film ２ When a transparent conductive film containing In as the main component is laminated, ２ O ３ By increasing the proportion of the Ce, H transparent conductive film, the sheet resistance of the substrate with the transparent conductive film monotonically decreased (Examples a3 to a10). ２ O ３ The substrate having the transparent conductive film (amorphous SnO ２ It has been confirmed that by laminating a transparent conductive film on the substrate, a very useful substrate with a transparent conductive film can be obtained.

[0111] 7. Preparation of Substrate with Transparent Conductive Film B (Examples b1, b3, b5, and b7) A PI (polyimide) substrate (thickness: 125 μm, dimensions: 100 mm×100 mm) was prepared as the substrate. Then, amorphous SnO ２ A transparent conductive film containing amorphous SnO as the main component was then prepared. ２ ) by reactive plasma deposition in the same manner as in Example a3. ２ O ３ :Ce, H transparent conductive film was deposited. Furthermore, under the same conditions as in Example 1-1, an amorphous SnO ２ Transparent conductive films containing amorphous SnO as the main component were prepared. The film thickness, sheet resistance, and specific resistance of each transparent conductive film are shown in Table 5. The specific resistances shown in Table 5 are specific resistances (reference data) assuming that the electrical properties of each transparent conductive film are uniform in the film thickness direction. Although not shown in Table 5, amorphous SnO ２The only metal element constituting the transparent conductive film mainly composed of Sn was Sn, and the amount of In was below the lower limit of quantification. ２ The resistivity of the transparent conductive film containing the －３ It is clear from the resistivity of Example a1 described above that it is Ω·cm or less.

[0112] (Examples b2, b4, b6, and b8) The substrates with transparent conductive films produced in Examples b1, b3, b5, and b7 were annealed for 0.5 hours at 250° C. The sheet resistance and specific resistance at this time are shown in Table 5.

[0113]

[0114] (Results) As shown in Table 5 above, amorphous SnO ２ Transparent conductive film mainly composed of In ２ O ３ : Ce, H film / amorphous SnO ２ When a transparent conductive film containing In as the main component is laminated, ２ O ３ By increasing the ratio of the Ce, H film, the sheet resistance of the substrate with the transparent conductive film monotonically decreased. ２ film) and a known transparent conductive film (In ２ O ３ It was confirmed that by laminating a transparent conductive film (Ce, H film) on the substrate, a very useful substrate with a transparent conductive film can be obtained.

[0115] This application claims priority from Japanese Patent Application No. 2023-026205, filed February 22, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0116] According to the present invention, a transparent conductive film is provided that can be formed at low temperatures, has high transparency and high conductivity, and further has a low indium content. The transparent conductive film can be applied to various devices as a film that can replace conventional ITO films.

[0117] 1 Substrate 10 Hearth part 11 Material 20 Plasma gun 21 Plasma beam 22 Plasma 30 Plasma controller 40 Chamber 100 Reactive plasma deposition apparatus 120 n-type single crystal silicon layer 121, 123 i-type semiconductor layer 122 p-type semiconductor layer 124 n-type semiconductor layer 125 Light-receiving side transparent electrode 126 Grid electrode 127 Back side transparent electrode 128 Metal electrode 130 Photoelectric conversion layer 131 First electrode 132 Second electrode 200 Si heterojunction solar cell 400 Perovskite solar cell

Claims

1. It contains a metal oxide whose main component is amorphous tin oxide, Among the metal elements constituting the metal oxide, the amount of Sn is 95 atomic % or more and the amount of In is 4 atomic % or less; and Resistivity is 1.9 x 10 －３ A transparent conductive film having a resistivity of Ω·cm or less.

2. The maximum absorption coefficient at wavelengths of 420 nm or more and 500 nm or less is 1 x 10 ４ cm －１ Below is the The transparent conductive film according to claim 1 .

3. At least one element 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, and Zr, The transparent conductive film according to claim 1 .

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

5. A substrate; The transparent conductive film according to any one of claims 1 to 4, which is disposed on the substrate; A substrate with a transparent conductive film comprising:

6. The substrate is a resin film. The transparent conductive film-attached substrate according to claim 5 .

7. a photoelectric conversion layer; a first electrode including at least one conductive film disposed adjacent to the photoelectric conversion layer; a second electrode including at least one conductive film disposed adjacent to the photoelectric conversion layer; and At least one of the first electrode and the second electrode comprises the transparent conductive film according to any one of claims 1 to 4. Photoelectric conversion element.

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

9. 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 disposed adjacent to the p-type microcrystalline silicon layer or its alloy layer and / or the n-type microcrystalline silicon layer or its alloy layer; The photoelectric conversion element according to claim 8 .