Solar cell element, solar cell module, and method for manufacturing solar cell element

Abstract

An embodiment of a solar cell element comprises a first electrode part (106), a photoelectric conversion unit (104), and a first carrier transport unit (105). The first carrier transport unit (105) is positioned between the first electrode part (106) and the photoelectric conversion unit (104). The first carrier transport unit (105) has a first surface (CF1) in contact with the photoelectric conversion unit (104) and a second surface (CF2) in contact with the first electrode part (106). In the first carrier transport unit (105), a first level (EL1), which is an energy level of the highest occupied molecular orbit of a first interface region (Ab1) along the first surface (CF1), is lower than a second level (EL2), which is an energy level of the highest occupied molecular orbit of a second interface region (Ab2) along the second surface (CF2).

Description

Solar cell element, solar cell module, and method for manufacturing solar cell element CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Application No. 2022-141521 (filed September 6, 2022), the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to a solar cell element, a solar cell module, and a method for manufacturing a solar cell element.

[0003] A technique relating to the energy level of an electron transport layer in a solar cell element is described in Patent Document 1. In recent years, there has been an increasing demand for improved power generation efficiency in solar cell elements and solar cell modules.

[0004] JP 2022-31990 A

[0005] One aspect of the solar cell element includes a first electrode, a photoelectric conversion unit, and a first carrier transport unit located between the first electrode and the photoelectric conversion unit. The first carrier transport unit has a first surface in contact with the photoelectric conversion unit and a second surface in contact with the first electrode. In the first carrier transport unit, a first level, which is an energy level of a highest occupied molecular orbital (HMO) in a first interface region along the first surface, is lower than a second level, which is an energy level of a highest occupied molecular orbital (HMO) in a second interface region along the second surface.

[0006] One aspect of the solar cell element includes a first electrode, a photoelectric conversion unit, and a first carrier transport unit located between the first electrode and the photoelectric conversion unit. The first carrier transport unit has a first surface in contact with the photoelectric conversion unit and a second surface in contact with the first electrode. In the first carrier transport unit, a carrier density in a first interface region along the first surface is greater than a carrier density in a second interface region along the second surface.

[0007] One aspect of a solar cell module includes a first electrode, a photoelectric conversion unit, and a first carrier transport unit located between the first electrode and the photoelectric conversion unit. The first carrier transport unit has a first surface in contact with the photoelectric conversion unit and a second surface in contact with the first electrode. In the first carrier transport unit, a first level, which is an energy level of a highest occupied molecular orbital (HOL) in a first interface region along the first surface, is lower than a second level, which is an energy level of a highest occupied molecular orbital (HOL) in a second interface region along the second surface.

[0008] One aspect of a method for manufacturing a solar cell element includes a first step of forming a photoelectric conversion section, a second step of forming a first carrier transport section on the photoelectric conversion section, and a third step of forming a first electrode section on the first carrier transport section. The second step includes a step 2A, a step 2B, and a step 2C. In the step 2A, a first layer is formed on the photoelectric conversion section. In the step 2B, a second layer is formed on the first layer. In the step 2C, the first layer and the second layer are heated to diffuse a dopant contained in the first layer into the second layer, thereby generating the first carrier transport section from the first layer and the second layer. The first layer has a higher dopant concentration than the second layer. The second layer has a lower dopant concentration than the first layer or does not contain a dopant. The second layer contains a semiconductor material that constitutes the first carrier transport section.

[0009] FIG. 1 is a diagram schematically showing a first example of the cross-sectional configuration of a solar cell element according to the first embodiment. FIG. 2 is an energy band diagram showing a first example of the relationship between energy levels among the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the first embodiment. FIG. 3 is a diagram schematically showing a second example of the cross-sectional configuration of a solar cell element according to the first embodiment. FIG. 4 is an energy band diagram showing a second example of the relationship between energy levels among the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the first embodiment. FIG. 5 is a diagram schematically showing a third example of the cross-sectional configuration of a solar cell element according to the first embodiment. FIG. 6 is an energy band diagram showing a third example of the relationship between energy levels among the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the first embodiment. FIG. 7 is a diagram schematically showing a fourth example of the cross-sectional configuration of a solar cell element according to the first embodiment. FIG. 8 is an energy band diagram showing a fourth example of the relationship between the energy levels of the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the first embodiment. FIG. 9 is a flowchart showing an example of a flow of a method for manufacturing a solar cell element according to the first embodiment. FIG. 10 is a diagram schematically showing an example of a cross-sectional configuration of a solar cell module according to the first embodiment. FIG. 11 is a diagram schematically showing a first example of a cross-sectional configuration of a solar cell element according to the second embodiment. FIG. 12 is an energy band diagram showing a first example of the relationship between the energy levels of the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the second embodiment. FIG. 13 is a flowchart showing an example of a flow of a method for manufacturing a solar cell element according to the second embodiment. FIG. 14 is a diagram schematically showing a second example of the cross-sectional configuration of a solar cell element according to the second embodiment. FIG. 15 is an energy band diagram showing a second example of the relationship between the energy levels of the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the second embodiment. FIG. 16 is a diagram schematically showing a third example of the cross-sectional configuration of the solar cell element according to the second embodiment.Fig. 17 is an energy band diagram showing a third example of the relationship between the energy levels of the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the second embodiment. Fig. 18 is a diagram schematically showing a fourth example of the cross-sectional configuration of the solar cell element according to the second embodiment. Fig. 19 is an energy band diagram showing a fourth example of the relationship between the energy levels of the first electrode portion, the first carrier transport portion, the photoelectric conversion portion, and the second carrier transport portion of the solar cell element according to the second embodiment.

[0010] For example, there is a solar cell element having a structure in which a first electrode section, a first carrier transport section for transporting holes, a photoelectric conversion section, a second carrier transport section for transporting electrons, and a second electrode section are stacked in this order. Typically, the Fermi level and the highest occupied molecule orbital (HOMO) energy level (hereinafter also referred to as the HOMO level) in the first carrier transport section are constant or approximately constant in the thickness direction of the first carrier transport section.

[0011] Regarding the solar cell element, for example, a viewpoint of reducing energy loss due to an energy barrier (hereinafter also simply referred to as an energy barrier) occurring at the contact between a semiconductor and an electrode such as a metal or at the contact between semiconductors can be considered. From this viewpoint, ideally, it can be considered that the Fermi level in the first electrode section, the Fermi level or the energy level of the highest occupied molecular orbital (HOMO level) in the first carrier transport section, and the energy level of the top of the valence band (VBM) (hereinafter also referred to as the VBM level) or the energy level of the highest occupied molecular orbital (HOMO level) in the photoelectric conversion section are matched.

[0012] However, there are cases where these energy levels cannot be made to coincide. In such cases, it is possible to reduce the difference in energy levels at the interface between the first electrode unit and the first carrier transport unit and the difference in energy levels at the interface between the first carrier transport unit and the photoelectric conversion unit. Here, the Fermi level and the HOMO level of the first carrier transport unit are set to be equal to or lower than the Fermi level of the first electrode unit and equal to or higher than the VBM level or the HOMO level of the photoelectric conversion unit.

[0013] Here, in order to improve the conversion efficiency of a solar cell element, it is considered to increase the photovoltaic power of the solar cell element. The photovoltaic power is determined by the difference between the Fermi level of the material of the second carrier transport part and the Fermi level of the material of the first carrier transport part, assuming that the second carrier transport part, the photoelectric conversion part, the first carrier transport part, and the first electrode part are not joined. Therefore, in order to increase the photovoltaic power of a solar cell element, it is considered to lower the Fermi level and the HOMO level of the material of the first carrier transport part so that they approach the VBM level or the HOMO level of the material of the photoelectric conversion part.

[0014] However, lowering the Fermi level and HOMO level of the material of the first carrier transporting part increases the difference between the Fermi level and HOMO level of the material of the first carrier transporting part and the Fermi level of the material of the first electrode part. This may increase the energy barrier at the interface between the first carrier transporting part and the first electrode part in the solar cell element. As a result, the power generation efficiency of the solar cell element may decrease.

[0015] In addition, in a solar cell element, in order to reduce the energy barrier at the interface between the first carrier transport part and the first electrode part, it is conceivable to bring the Fermi level and the HOMO level of the material of the first carrier transport part closer to the Fermi level of the material of the first electrode part. In this case, the difference between the Fermi level of the material of the second carrier transport part and the Fermi level of the material of the first carrier transport part may be reduced. As a result, the photovoltaic power of the solar cell element may be reduced.

[0016] In summary, the Fermi level and the HOMO level in the first carrier transporting portion usually have a constant or approximately constant distribution in the thickness direction of the first carrier transporting portion. Therefore, it has not been easy to simultaneously increase the photovoltaic power of the solar cell element and reduce the energy loss due to the energy barrier at the interface between the first carrier transporting portion and the first electrode portion. Therefore, there is room for improvement in solar cell elements and solar cell modules in terms of increasing the power generation efficiency.

[0017] Therefore, the inventors of the present disclosure have created a technology for improving the power generation efficiency of solar cell elements in solar cell elements and solar cell modules.

[0018] Various embodiments will be described below with reference to the drawings. In the drawings, parts having the same or substantially the same configuration and function are designated by the same reference numerals. Therefore, redundant explanations will be omitted in the following description. The drawings are schematic. Figures 1, 3, 5, 7, 10, 11, 14, 16, and 18 each illustrate a right-handed XYZ coordinate system. In this XYZ coordinate system, the normal direction of the first element surface F1 of the solar cell element 10, 40 is the +Z direction. One direction along the first element surface F1 is the +X direction. A direction along the first element surface F1 that is perpendicular to both the +X direction and the +Z direction is the +Y direction.

[0019] <1. First embodiment> <1-1. Solar cell element 10> A solar cell element 10 according to a first embodiment will be described with reference to Figs. 1 to 8. As shown in Fig. 1, the solar cell element 10 has a surface F1 onto which light is mainly incident (also referred to as a first element surface) and a surface F2 located on the opposite side of the first element surface F1 (also referred to as a second element surface). In the first embodiment, the first element surface F1 faces the +Z direction. The second element surface F2 faces the -Z direction. For example, the +Z direction may be set to a direction toward the sun at its zenith moment.

[0020] 1 , the solar cell element 10 includes a first electrode unit 106, a first carrier transport unit 105, a photoelectric conversion unit 104, a second carrier transport unit 103, a second electrode unit 102, and a substrate unit 101. In the first embodiment, the second electrode unit 102, the second carrier transport unit 103, the photoelectric conversion unit 104, the first carrier transport unit 105, and the first electrode unit 106 are stacked in this order on the substrate unit 101. Therefore, the first carrier transport unit 105 is located between the first electrode unit 106 and the photoelectric conversion unit 104.

[0021] Although not shown, an anti-reflection film may be positioned on the surface of the solar cell element 10. For example, an insulating film made of silicon nitride or the like is used as the anti-reflection film. Furthermore, although not shown, a passivation film may be positioned between the solar cell element 10 and the anti-reflection film. For example, a thin film made of an oxide such as aluminum oxide or a nitride is used as the passivation film.

[0022] <1-1-1. Substrate Unit 101> The substrate unit 101 is, for example, a translucent insulating substrate. The substrate unit 101 is, for example, translucent to light in a specific wavelength range. The specific wavelength range includes, for example, a wavelength range of light that the photoelectric conversion unit 104 can absorb and cause photoelectric conversion. Specifically, the specific wavelength range may include, for example, a wavelength range of visible light from approximately 400 nanometers (nm) to 700 nm and a wavelength range of infrared light from approximately 700 nm to 1200 nm. This allows, for example, light irradiated onto the first element surface F1 to pass through the substrate unit 101 toward the photoelectric conversion unit 104. Here, for example, if the specific wavelength range includes wavelengths of light with high irradiation intensity that constitute sunlight, the power generation efficiency of the solar cell element 10 can be improved. Examples of materials used for the substrate unit 101 include glass, acrylic, and polycarbonate. The substrate unit 101 may have, for example, a flat plate, sheet, or film shape. The thickness of the substrate portion 101 is, for example, about 0.01 millimeters (mm) to 5 mm.

[0023] <1-1-2. Second electrode portion 102> The second electrode portion 102 is located on the substrate portion 101. The second electrode portion 102 is located on the second element surface F2 side of the substrate portion 101. In other words, the second electrode portion 102 is located on the −Z direction side of the substrate portion 101.

[0024] The second electrode unit 102 can collect carriers generated by photoelectric conversion in response to light irradiation of the photoelectric conversion unit 104 described below. The second electrode unit 102 can, for example, function as an electrode (also referred to as a negative electrode) that collects electrons as carriers. The second electrode unit 102 may be formed on the substrate unit 101 by a vacuum process such as sputtering.

[0025] The second electrode unit 102 is made of a transparent conductive oxide (TCO) that is transparent to light in a specific wavelength range. Examples of TCO include, but are not limited to, indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), titanium-doped indium oxide (ITiO), indium zinc oxide (Indium Zinc Oxide (IZO), Indium Gallium Zinc Oxide (IGZO), Tantalum-doped Tin Oxide (SnO ２ :Ta), niobium-doped tin oxide (SnO ２ : Nb), tungsten-doped tin oxide (SnO ２ : W), molybdenum-doped tin oxide (SnO ２ :Mo), fluorine-doped tin oxide (SnO ２The second electrode unit 102 may include an oxide such as indium oxide (IOH) or hydrogen-doped indium oxide (IOH). The second electrode unit 102 may be composed of a transparent conductive oxide film. The transparent conductive oxide film may be a stacked film having a plurality of films. For example, the above-mentioned oxide film may be applied to each of the plurality of films. Furthermore, in addition to the above-mentioned oxide film, an oxide film such as tin oxide containing a dopant may be applied to the plurality of films. As the dopant, one or more elements selected from the group consisting of indium (In), silicon (Si), germanium (Ge), titanium (Ti), copper (Cu), antimony (Sb), niobium (Nb), fluorine (F), tantalum (Ta), tungsten (W), molybdenum (Mo), bromine (Br), iodine (I), and chlorine (Cl) may be used.

[0026] <1-1-3. Second carrier transport section 103> The second carrier transport section 103 is located on the second electrode section 102. The second carrier transport section 103 is located on the second element surface F2 side of the second electrode section 102. In other words, the second carrier transport section 103 is located on the −Z direction side of the second electrode section 102.

[0027] The second carrier transport section 103 may be made of, for example, a semiconductor made of an inorganic material (also referred to as an inorganic semiconductor) having a higher electrical resistance than the second electrode section 102. This makes it less likely that electrical contact will occur between the second electrode section 102 and the photoelectric conversion section 104.

[0028] In the first embodiment, for example, a semiconductor having n-type conductivity (also referred to as an n-type semiconductor) may be used as the inorganic semiconductor material. In this case, the second carrier transport unit 103 functions as, for example, a so-called hole blocking layer and an electron transport layer (Electron Transport Layer: ETL). The electron transport layer can, for example, collect and output electrons.

[0029] The second carrier transport region 103 is made of a metal oxide that is transparent to light in a specific wavelength range. For example, titanium dioxide (TiO ２), tin dioxide (SnO ２ ), zinc oxide (ZnO) or indium oxide (In ２ O ３ ) or the like is applied. This metal oxide may be doped with, for example, an n-type dopant. For example, if the metal oxide is ZnO, aluminum (Al) or boron (B) or the like may be applied as the n-type dopant. The thickness of the second electrode unit 102 may be, for example, approximately 10 nm to 50 nm. The second carrier transport unit 103 may be formed on the second electrode unit 102 by applying a raw material solution prepared by dissolving a raw material such as a metal chloride or a metal isopropoxide in a polar solution onto the second electrode unit 102 and hydrolyzing the raw material to generate a metal oxide. Here, examples of the metal chloride include titanium chloride, tin chloride, zinc chloride, or indium chloride. Examples of the metal isopropoxide include titanium isopropoxide, tin isopropoxide, zinc isopropoxide, or indium isopropoxide.

[0030] <1-1-4. Photoelectric conversion section 104> The photoelectric conversion section 104 is located above the second carrier transport section 103. The photoelectric conversion section 104 is located on the second element surface F2 side of the second carrier transport section 103. In other words, the photoelectric conversion section 104 is located on the −Z direction side of the second carrier transport section 103.

[0031] The photoelectric conversion unit 104 can absorb light that has passed through the substrate unit 101, the second electrode unit 102, and the second carrier transport unit 103. In the first embodiment, for example, an intrinsic semiconductor (also referred to as an i-type semiconductor) is applied to the photoelectric conversion unit 104. For example, a semiconductor having a perovskite structure (also referred to as a perovskite semiconductor) may be applied to the i-type semiconductor.

[0032] The perovskite semiconductor may include, for example, a halide-based organic-inorganic perovskite semiconductor. ３ It is a semiconductor having a perovskite structure with the composition of ABX. ３ A in the formula (I) can be, for example, methylammonium (CH ３ NH３ ), formamidinium (CH(NH ２ ) ２ ), cesium (Cs), rubidium (Rb) and potassium (K) ions are applied. ３ In the above, B is, for example, one or more ions of lead (Pb) and tin (Sn). ３ In the formula, X is, for example, one or more ions of iodine (I), bromine (Br), and chlorine (Cl). Specifically, ABX ３ The semiconductor having a perovskite structure with the composition is, for example, CH ３ NH ３ PbI ３ or (CH(NH ２ ) ２ ,Cs)Pb(I,Br) ３ The photoelectric conversion unit 104 may be formed of an organic perovskite such as a crystalline perovskite. The organic perovskite may be formed, for example, by applying a first raw material liquid onto the second carrier transport unit 103 and then drying the applied first raw material liquid. Here, the organic perovskite may be a crystalline thin film. The first raw material liquid may be generated, for example, by dissolving raw materials, such as an alkylamine halide and a lead halide, in a solvent. The thickness of the photoelectric conversion unit 104 may be, for example, approximately 100 nm to 2000 nm. Hereinafter, the VBM energy level (VBM level) of the photoelectric conversion unit 104 is referred to as a third level EL3.

[0033] <1-1-5. First carrier transport section 105> The first carrier transport section 105 is located above the photoelectric conversion section 104. The first carrier transport section 105 is located on the second element surface F2 side of the photoelectric conversion section 104. In other words, the first carrier transport section 105 is located on the −Z direction side of the photoelectric conversion section 104.

[0034] In the first embodiment, for example, a semiconductor having p-type conductivity (also referred to as a p-type semiconductor) may be applied to the first carrier transport unit 105. In this case, the first carrier transport unit 105 functions as, for example, a so-called electron blocking layer and a hole transport layer (HOLE TRANSPORT LAYER: HTL). The HTL can, for example, collect and output holes.

[0035] As a material for the first carrier transport region 105, for example, a soluble diamine derivative such as [2,2',7,7'-tetrakis(N,N-di-P-methoxyphenylamino)-9,9'-spirobifluorene] (2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene: spiro-OMeTAD) may be used. The first carrier transport region 105 may be formed, for example, by applying a second raw material liquid onto a layer of a perovskite semiconductor as the photoelectric conversion region 104 and then drying the applied second raw material liquid. The thickness of the carrier transport layer may be, for example, approximately 50 nm to 200 nm.

[0036] Other materials that may be used for the first carrier transport unit 105 include, for example, poly[bis(4-phenyl)(2,4,6-triphenylmethyl)amine] (Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]: PTAA), poly(3-hexylthiophene-2,5-diyl) (Poly(3-hexylthiophene-2,5-diyl): P3HT), or poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) (PEDOT / PSS).

[0037] The first carrier transport unit 105 has a surface (also referred to as a first surface) CF1 in contact with the photoelectric conversion unit 104 and a surface (also referred to as a second surface) CF2 in contact with the first electrode unit 106. Hereinafter, the energy level of the highest occupied molecular orbital (HOMO) in a region (also referred to as a first interface region) Ab1 of the first carrier transport unit 105 along the first surface CF1 will be referred to as a first level EL1. Furthermore, the energy level of the highest occupied molecular orbital (HOMO) in a region (also referred to as a second interface region) Ab2 of the first carrier transport unit 105 along the second surface CF2 will be referred to as a second level EL2.

[0038] Here, the first interface region Ab1 may be a region of the first carrier transport part 105 that forms the first surface CF1 along the first surface CF1. This first interface region Ab1 may have a predetermined thickness along the −Z direction, which is a first direction from the first surface CF1 toward the second surface CF2. This predetermined thickness may be determined, for example, based on the spatial resolution of the device that measures the HOMO level. Furthermore, when the device that measures the HOMO level measures the HOMO level in the depth direction of the sample to be measured while performing a predetermined etching on the surface of the sample to be measured, this predetermined thickness may be determined based on an error in the etching rate or the time resolution of the etching operation. The predetermined thickness may be, for example, 5 nm, 3 nm, 1 nm, 0.5 nm, 0.3 nm, or 0.1 nm.

[0039] The second interface region Ab2 may be a region of the first carrier transport part 105 that forms the second surface CF2 along the second surface CF2. The second interface region Ab2 may have a predetermined thickness along the +Z direction, which is a second direction opposite to the first direction. This predetermined thickness may be determined, for example, based on the spatial resolution of the device that measures the HOMO level. Furthermore, when the device that measures the HOMO level measures the HOMO level in the depth direction of the sample while performing a predetermined etching on the surface of the sample, this predetermined thickness may be determined based on an error in the etching rate or the time resolution of the etching operation. The predetermined thickness may be, for example, 5 nm, 3 nm, 1 nm, 0.5 nm, 0.3 nm, or 0.1 nm.

[0040] <1-1-6. First electrode portion 106> The first electrode portion 106 is located on the first carrier transport portion 105. The first electrode portion 106 is located on the second element surface F2 side of the first carrier transport portion 105. In other words, the first electrode portion 106 is located on the −Z direction side of the first carrier transport portion 105.

[0041] The first electrode unit 106 can collect carriers generated by photoelectric conversion in response to light irradiation of the photoelectric conversion unit 104. The first electrode unit 106 may be made of a highly conductive metal such as gold (Au) or a TCO. Examples of TCO include ITO, FTO, and ZnO. The first electrode unit 106 may be made of a layered electrode (also referred to as a first electrode layer). The thickness of the first electrode unit 106 may be approximately 10 nm to 1000 nm. The first electrode unit 106 may be formed on the first carrier transport unit 105 by a vacuum process such as sputtering. When the first electrode unit 106 is made of a TCO, the first electrode unit 106 is translucent to light in a specific wavelength range. In this case, light irradiating the second element surface F2 may pass through the first electrode unit 106 and reach the photoelectric conversion unit 104. As a result, both surfaces of the solar cell element 10, including not only the first element surface F1 but also the second element surface F2, can serve as light-receiving surfaces. Hereinafter, the Fermi level in the first electrode portion 106 will be referred to as a fourth level EL4.

[0042] Wiring 20, such as a lead wire, may be electrically connected to each of the first electrode portion 106 and the second electrode portion 102. Specifically, for example, a first wiring 20a may be electrically connected to the first electrode portion 106, and a second wiring 20b may be connected to the second electrode portion 102. Each wiring 20 may be joined to each of the first electrode portion 106 and the second electrode portion 102 by, for example, soldering. In the solar cell element 10, output obtained by photoelectric conversion may be extracted by, for example, the first wiring 20a and the second wiring 20b.

[0043] <1-2. Energy Band Structure of the First Carrier Transport Section 105> The first carrier transport section 105 of the solar cell element 10 according to the first embodiment may have, for example, an energy band structure as shown in Fig. 2. In Fig. 2, the horizontal axis indicates the position in the -Z direction, and the vertical axis indicates the energy level. Also, in Fig. 2, from left to right, the energy level of the forbidden band B103 in the second carrier transport section 103, the energy level of the forbidden band B104 in the photoelectric conversion section 104, the energy level of the forbidden band B105 in the first carrier transport section 105, and the Fermi level in the first electrode 106 are shown in this order.

[0044] In the first carrier transport section 105, a first level EL1, which is the HOMO level in a first interface region Ab1 along a first face CF1, which is the face in contact with the photoelectric conversion section 104, is different from a second level EL2, which is the HOMO level in a second interface region Ab2 along a second face CF2, which is the face in contact with the first electrode section 106.

[0045] Here, it is assumed that the HOMO level in the first carrier transport section 105 is approximately constant in the thickness direction. In this case, assuming that the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined together in order to increase the photovoltaic power, if the HOMO level in the material of the first carrier transport section 105 is brought closer to the VBM level in the material of the photoelectric conversion section 104, the difference between the HOMO level in the material of the first carrier transport section 105 and the Fermi level in the material of the first electrode section 106 may become large. As a result, in the state of the solar cell element 10, the energy barrier between the first carrier transport section 105 and the first electrode section 106 may increase. Furthermore, in order to reduce the energy barrier between the first carrier transport section 105 and the first electrode section 106 of the solar cell element 10, assuming that the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined, if the HOMO level of the material of the first carrier transport section 105 is brought closer to the Fermi level of the first electrode section 106, the difference between the HOMO level of the material of the first carrier transport section 105 and the Fermi level of the material of the second carrier transport section 103 may be reduced. In other words, the difference between the Fermi level of the material of the first carrier transport section 105 and the Fermi level of the material of the second carrier transport section 103 may be reduced. This may reduce the photovoltaic power of the solar cell element 10.

[0046] In contrast, as described above, assume that the first level EL1 and the second level EL2 are different. In this case, for example, the second level EL2 can be changed without changing the first level EL1. Furthermore, for example, the first level EL1 can be changed without changing the second level EL2. In other words, for example, the first level EL1 can be brought closer to the third level EL3, which is the VBM level of the photoelectric conversion unit 104, while the second level EL2 is brought closer to the third level EL3, which is the VBM level of the photoelectric conversion unit 104, while the first level EL1 is brought closer to the third level EL3, which is the VBM level of the photoelectric conversion unit 104. This allows the photovoltaic power to be increased without increasing the energy barrier between the first carrier transport unit 105 and the first electrode unit 106. From another perspective, the energy barrier between the first carrier transporting section 105 and the first electrode section 106 can be lowered without reducing the photovoltaic power.

[0047] The HOMO level in the first carrier transport unit 105 can be measured using, for example, ultraviolet photoelectron spectroscopy (UPS). When UPS is used, the HOMO level can be estimated from the position where the spectrum of detected photoelectrons rises. This allows the HOMO level to be identified. The VBM level in the photoelectric conversion unit 104 can also be measured using, for example, UPS, like the HOMO level. In this case, the VBM level can be estimated from the position where the spectrum of detected photoelectrons rises. This allows the VBM level to be identified. The HOMO level and VBM level of each unit may also be measured by other measurement methods, such as X-ray photoelectron spectroscopy (XPS). Furthermore, for example, the distribution of the HOMO level in the depth direction of the sample can be measured by performing measurements using UPS or XPS while etching the surface of the sample with a gas cluster ion beam (GCIB). The Fermi level at the first electrode unit 106 can be measured using, for example, UPS. When using UPS, the Fermi level can be estimated from the position where the spectrum of detected photoelectrons rises. This allows the Fermi level to be identified. The Fermi level at the first electrode unit 106 may also be measured using other measurement methods, such as X-ray photoelectron spectroscopy (XPS).

[0048] In the present disclosure, "two energy levels are different" means that the absolute value of the difference between the two energy levels is equal to or greater than a predetermined value. Alternatively, "two energy levels are equal" may be considered when the absolute value of the difference between the two energy levels is smaller than a predetermined value. Alternatively, "two energy levels are approximately the same" may be considered when the absolute value of the difference between the two energy levels is smaller than a predetermined value. "Two energy levels are approximately the same" may be considered to be synonymous with "two energy levels are substantially the same." The predetermined value may be determined based on the measurement error of a measurement device that measures energy levels, such as UPS or XPS. In this case, for example, 0.1 eV (electron volt) may be used as the predetermined value. In other words, "two energy levels are approximately the same" may be synonymous with "the absolute value of the difference between the two energy levels is less than a predetermined value of 0.1 eV."

[0049] In the first carrier transport unit 105, the HOMO level of the first carrier transport unit 105 can be changed by changing the dopant concentration. In other words, in the first carrier transport unit 105, the HOMO level of the first carrier transport unit 105 can be changed by changing the carrier density. From another perspective, the carrier density of the first carrier transport unit 105 may be changed by changing the dopant concentration in the first carrier transport unit 105. The dopant concentration in the first carrier transport unit 105 may change, for example, in a manner in which the dopant concentration decreases from the first surface CF1 toward the second surface CF2. More specifically, the dopant concentration in the first carrier transport unit 105 may change, for example, in a manner in which the dopant concentration decreases from the first interface region Ab1 along the first surface CF1 toward the second interface region Ab2 along the second surface CF2. In other words, when the solar cell element 10 is observed in an X-Z cross section as shown in FIG. 1 , the dopant concentration in the first carrier transport section 105 may change, for example, in a manner that the dopant concentration decreases along the −Z direction. The dopant concentration may be expressed, for example, as the number of dopant atoms per unit volume or the number of moles (mol) of dopant per unit volume. The change in the dopant concentration in the first carrier transport section 105 may be achieved, for example, by the dopant diffusing through the layer of semiconductor material constituting the first carrier transport section 105 from the first surface CF1 to the second surface CF2. The change in the dopant concentration in the first carrier transport section 105 may be controlled, for example, by selecting the dopant material or by the conditions for diffusing the dopant through the layer of semiconductor material when forming the first carrier transport section 105. In other words, the change in the dopant concentration in the first carrier transport section 105 may be controlled, for example, by the conditions for forming the first carrier transport section 105.

[0050] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, the first level EL1 is lower than the second level EL2. Generally, the third level EL3 of the photoelectric conversion section 104 is lower than the fourth level EL4 of the first electrode section 106. Therefore, by making the first level EL1 of the first carrier transport section 105 lower than the second level EL2, it is possible to reduce the difference between the first level EL1 and the third level EL3 while also reducing the difference between the second level EL2 and the fourth level EL4. In other words, by making the first level EL1 of the first carrier transport section 105 lower than the second level EL2, it is possible to reduce the difference between the first level EL1 and the third level EL3 while reducing the difference between the second level EL2 and the fourth level EL4. This allows the photovoltaic power of the solar cell element 10 to be increased while reducing the energy barrier between the first carrier transport section 105 and the first electrode section 106. From another perspective, it is possible to increase the photovoltaic power in the solar cell element 10 while reducing the energy barrier between the first carrier transport part 105 and the first electrode part 106. As a result, it is possible to improve the power generation efficiency in the solar cell element 10.

[0051] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, the HOMO level in the first carrier transport section 105 may increase along a first direction from the first surface CF1 to the second surface CF2. In other words, in the first carrier transport section 105, for example, the HOMO level may increase along the first direction from the first interface region Ab1 along the first surface CF1 to the second interface region Ab2 along the second surface CF2. Here, the HOMO level of the first carrier transport section 105 may increase continuously or discretely. For example, when the distribution of the HOMO level of the first carrier transport section 105 along the first direction is represented on a graph, the HOMO level of the first carrier transport section 105 may increase monotonically along the first direction. In this case, the rate of change of the HOMO level in the first direction may be constant or not. The rate of change of the HOMO level in the first direction may be a value obtained by dividing the amount of change in the HOMO level with respect to the amount of change in position in the first direction by the amount of change in position in the first direction. Furthermore, for example, when the distribution of the HOMO level of the first carrier transporter 105 along the first direction is represented on a graph, the HOMO level of the first carrier transporter 105 may increase stepwise along the first direction. If the HOMO level of the first carrier transporter 105 increases along the first direction, the shape of the graph showing the distribution of the HOMO level of the first carrier transporter 105 along the first direction does not have a concave shape in the direction of increasing energy level from the first surface CF1 to the second surface CF2. If the shape of the graph showing the distribution of the HOMO level of the first carrier transporter 105 along the first direction has a concave portion in the direction of increasing energy level, carrier movement may be hindered in this concave portion, which may reduce the power generation efficiency of the solar cell element 10. In contrast, since the HOMO level in the first carrier transport part 105 increases along the first direction, holes, which are carriers, can move more easily within the first carrier transport part 105. This can reduce the decrease in power generation efficiency in the solar cell element 10.

[0052] In the first carrier transport portion 105 of the solar cell element 10 according to the first embodiment, for example, the first level EL1 may be substantially equal to the third level EL3. That is, the absolute value of the difference between the first level EL1 and the third level EL3 may be equal to or less than a predetermined value. As described above, this predetermined value may be determined based on the measurement error of a measurement device that measures energy levels, such as UPS or XPS. In this case, for example, 0.1 eV may be used as the predetermined value. If the first level EL1 and the third level EL3 are substantially equal to each other, the energy barrier between the first carrier transport portion 105 and the photoelectric conversion portion 104 may be reduced.

[0053] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, the first level EL1 may be greater than the third level EL3 and may be substantially the same as the third level EL3. In this case, the first level EL1 is greater than the third level EL3. This facilitates the movement of carrier holes from the photoelectric conversion section 104 to the first carrier transport section 105. This is because electrons with a negative charge have the tendency to move toward lower energy levels, whereas holes with a positive charge opposite to the negative charge have the tendency to move toward higher energy levels.

[0054] In the first carrier transport portion 105 of the solar cell element 10 according to the first embodiment, for example, the second level EL2 may be substantially equal to the fourth level EL4. That is, the absolute value of the difference between the second level EL2 and the fourth level EL4 may be equal to or less than a predetermined value. As described above, this predetermined value may be determined based on the measurement error of a measurement device that measures energy levels, such as UPS or XPS. In this case, for example, 0.1 eV may be used as the predetermined value. If the second level EL2 and the fourth level EL4 are substantially equal to each other, the energy barrier between the first carrier transport portion 105 and the first electrode portion 106 may be reduced.

[0055] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, the second level EL2 may be smaller than the fourth level EL4 and substantially the same as the fourth level EL4. In this case, the fourth level EL4 is larger than the second level EL2. This makes it easier for holes, which are carriers, to move from the first carrier transport section 105 to the first electrode section 106. This is because electrons with a negative charge have the tendency to move toward lower energy levels, whereas holes with a positive charge opposite to the negative charge have the tendency to move toward higher energy levels.

[0056] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, as shown in FIG. 3 , the first carrier transport section 105 may include a first region 1051 located along the first surface CF1. The first region 1051 has a first predetermined thickness from the first surface CF1 along the −Z direction as a first direction. The first region 1051 is a region that forms the first surface CF1. The first region 1051 is in contact with the photoelectric conversion section 104 at the first surface CF1. In this case, the first carrier transport section 105 of the solar cell element 10 according to the first embodiment may have an energy band structure as shown in FIG. 4 , for example. 4 is an energy band diagram based on the energy band diagram of FIG. 2 , in which, instead of the energy level of the forbidden band B105 of the first carrier transport region 105, the energy level of the forbidden band B1051 of the first region 1051, the energy level of the forbidden band B1053 of the third region 1053 (described later), and the energy level of the forbidden band B1052 of the second region 1052 (described later) are shown in this order from left to right. Here, the HOMO level in the first region 1051 may be substantially equal to the third level EL3. In other words, in the first carrier transport region 105, the HOMO level is substantially equal to the third level EL3 for a first predetermined thickness from the first face CF1 along the first direction. In other words, the HOMO level in the first region 1051 may be said to be substantially the same as the third level EL3 along the −Z direction as the first direction. Here, for example, by having the first region 1051 in the first carrier transport part 105, even if the HOMO level in the first carrier transport part 105 increases along the −Z direction as the first direction, the amount of decrease in the photovoltaic power of the solar cell element 10 may be smaller than when the first region 1051 is not present.

[0057] As described above, the photovoltaic power of the solar cell element 10 is determined in proportion to the difference between the Fermi level of the material of the first carrier transport section 105 and the Fermi level of the material of the second carrier transport section 103. Here, assuming that the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined, the Fermi level of the material of the first carrier transport section 105, which contributes to determining the photovoltaic power, may be approximated to, for example, the average value of the Fermi levels in a region of the first carrier transport section 105 that contacts the photoelectric conversion section 104 (also referred to as a first contact region). The thickness of the first contact region along the −Z direction, which is the first direction, may be, for example, 1 nm or more and less than 100 nm. Therefore, for example, in the first contact region, if the HOMO level in the first carrier transport section 105 increases along the −Z direction as the first direction, the Fermi level in the first carrier transport section 105 may also increase along the −Z direction as the first direction, similar to the HOMO level. This may increase the average value of the Fermi level in the region of the first carrier transport section 105 that contacts the photoelectric conversion section 104 (first contact region). As a result, assuming that the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined, the difference between the Fermi level in the first carrier transport section 105 and the Fermi level in the second carrier transport section 103, which contributes to determining the photovoltaic power, may become smaller. This may result in a smaller photovoltaic power of the solar cell element 10.

[0058] In contrast, for example, if the first carrier transport section 105 has the first region 1051, the average value of the Fermi level in the region of the first carrier transport section 105 that contacts the photoelectric conversion section 104 (first contact region) can be substantially the same as the third level EL3. As a result, even if the HOMO level in the first carrier transport section 105 increases along the −Z direction as the first direction, if the first carrier transport section 105 has the first region 1051, assuming a state in which the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined, the amount by which the difference between the Fermi level in the first carrier transport section 105 and the Fermi level in the second carrier transport section 103, which contributes to determining the photovoltaic power, becomes smaller. Therefore, the amount of decrease in the photovoltaic power of the solar cell element 10 can be reduced.

[0059] The first predetermined thickness may be, for example, 10 nm or more. As such, if the first predetermined thickness is not too small, the average value of the Fermi level in the region (first contact region) of the first carrier transport section 105 that is in contact with the photoelectric conversion section 104 can be approximately equal to the third level EL3. Furthermore, the first predetermined thickness may be, for example, 100 nm or less. As such, if the first carrier transport section 105 has a second region 1052 described below, as long as the first predetermined thickness is not too large, the thickness of the second region 1052 will not be too small, and an increase in the energy barrier between the first carrier transport section 105 and the first electrode section 106 can be reduced.

[0060] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, as shown in FIG. 3 , the first carrier transport section 105 may include a second region 1052 located along the second surface CF2. The second region 1052 has a second predetermined thickness from the second surface CF2 along the +Z direction, which is a second direction opposite to the first direction. The second region 1052 is a region forming the second surface CF2. The second region 1052 contacts the first electrode section 106 at the second surface CF2. In this case, for example, as shown in FIG. 4 , the HOMO level in the second region 1052 may be substantially equal to the fourth level EL4. In other words, in the first carrier transport section 105, the HOMO level is substantially equal to the fourth level EL4 for the second predetermined thickness along the second direction from the second surface CF2. In other words, the HOMO level in the second region 1052 may be said to be substantially the same as the fourth level EL4 along the +Z direction as the second direction. Here, for example, by having the second region 1052 in the first carrier transport part 105, even if the HOMO level in the first carrier transport part 105 increases along the −Z direction as the first direction, the magnitude of the energy barrier between the first carrier transport part 105 and the first electrode part 106 may be smaller than in the case where the second region 1052 is not provided.

[0061] As described above, the magnitude of the energy barrier between the first carrier transport section 105 and the first electrode section 106 is determined depending on the difference between the HOMO level of the material of the first carrier transport section 105 and the Fermi level of the material of the first electrode section 106, assuming a state in which the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined together. Here, assuming a state in which the second carrier transport section 103, the photoelectric conversion section 104, the first carrier transport section 105, and the first electrode section 106 are not joined together, the HOMO level of the material of the first carrier transport section 105, which contributes to determining the magnitude of the energy barrier between the first carrier transport section 105 and the first electrode section 106, may be approximated to, for example, the average value of the HOMO levels in a region of the first carrier transport section 105 that contacts the first electrode section 106 (also referred to as a second contact region). The thickness of the second contact region along the +Z direction (the second direction) may be, for example, 1 nm or more and less than 100 nm. Therefore, for example, in the second contact region, when the HOMO level of the first carrier transport portion 105 increases along the −Z direction (the first direction), the average value of the HOMO level of the first carrier transport portion 105 may decrease. As a result, assuming that the second carrier transport portion 103, the photoelectric conversion portion 104, the first carrier transport portion 105, and the first electrode portion 106 are not joined, the difference between the HOMO level in the region of the first carrier transport portion 105 that contacts the first electrode portion 106 (the second contact region) and the Fermi level in the first electrode portion 106 may become large. Therefore, the magnitude of the energy barrier between the first carrier transport section 105 and the first electrode section 106 can increase as the difference between the HOMO level in the region (second contact region) of the first carrier transport section 105 that contacts the first electrode section 106 and the Fermi level in the first electrode section 106 increases.

[0062] In contrast to this, for example, if the first carrier transport part 105 has the second region 1052, the average value of the HOMO level in a region (second contact region) of the first carrier transport part 105 that contacts the first electrode part 106 can be substantially equal to the fourth level EL4. As a result, even if the HOMO level in the first carrier transport part 105 increases along the −Z direction as the first direction, if the first carrier transport part 105 has the second region 1052, the amount by which the difference between the HOMO level in the first carrier transport part 105 and the Fermi level in the first electrode part 106 increases, which contributes to determining the magnitude of the energy barrier between the first carrier transport part 105 and the first electrode part 106, can be reduced, assuming a state in which the second carrier transport part 103, the photoelectric conversion part 104, the first carrier transport part 105, and the first electrode part 106 are not joined. Therefore, in the solar cell element 10, the magnitude of the energy barrier between the first carrier transport part 105 and the first electrode part 106 can be reduced.

[0063] The second predetermined thickness may be, for example, 10 nm or more. Thus, if the second predetermined thickness is not too small, the average value of the HOMO level in the region (second contact region) of the first carrier transport unit 105 that contacts the first electrode unit 106 can be approximately equal to the fourth level EL4. Furthermore, the second predetermined thickness may be, for example, 100 nm or less. Thus, if the second predetermined thickness is not too large, when the first carrier transport unit 105 has the above-described first region 1051, the thickness of the first region 1051 does not become too small, and the decrease in the photovoltaic power of the solar cell element 10 can be reduced.

[0064] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, as shown in FIG. 3 , the first carrier transport section 105 may include a third region 1053 located between the first region 1051 and the second region 1052. In this case, for example, as shown in FIG. 4 , the HOMO level in the third region 1053 may increase along the −Z direction as the first direction. The HOMO level in the first carrier transport section 105 may increase continuously or discretely. For example, when the distribution of the HOMO level of the first carrier transport section 105 along the first direction is represented on a graph, the HOMO level in the first carrier transport section 105 may increase monotonically along the first direction. Furthermore, for example, when the distribution of the HOMO level of the first carrier transport section 105 along the first direction is represented on a graph, the HOMO level in the first carrier transport section 105 may increase stepwise along the first direction. If the HOMO level in the first carrier transport section 105 increases along the first direction, the shape of the graph showing the distribution of the HOMO level in the first direction of the first carrier transport section 105 does not have a concave shape in the direction of increasing energy level from the first region 1051 side to the second region 1052 side. If the shape of the graph showing the distribution of the HOMO level in the first direction of the first carrier transport section 105 has a concave portion in the direction of increasing energy level, carrier movement may be hindered in this concave portion, resulting in a decrease in the conversion efficiency of the solar cell element 10. In contrast, since the HOMO level in the third region 1053 of the first carrier transport section 105 increases along the first direction, holes, which are carriers, can move more easily within the first carrier transport section 105. This can reduce a decrease in the conversion efficiency of the solar cell element 10.

[0065] In the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, as shown in FIG. 5 , the first carrier transport section 105 does not have to have the second region 1052 located between the third region 1053 and the first electrode section 106. In other words, for example, the first carrier transport section 105 may include the third region 1053 located between the first region 1051 and the first electrode section 106. In this case, the first carrier transport section 105 of the solar cell element 10 according to the first embodiment may have an energy band structure as shown in FIG. 6 . The energy band diagram of FIG. 6 is an energy band diagram based on the energy band diagram of FIG. 4 , with the energy level of the forbidden band B 1052 of the second region 1052 deleted.

[0066] Furthermore, in the first carrier transport section 105 of the solar cell element 10 according to the first embodiment, for example, as shown in FIG. 7 , the first carrier transport section 105 does not have to have the first region 1051 located between the photoelectric conversion section 104 and the third region 1053. In other words, for example, the first carrier transport section 105 may include the third region 1053 located between the second region 1052 and the photoelectric conversion section 104. In this case, the first carrier transport section 105 of the solar cell element 10 according to the first embodiment may have, for example, an energy band structure as shown in FIG. 8 . The energy band diagram of FIG. 8 is an energy band diagram based on the energy band diagram of FIG. 4 , in which the energy level of the forbidden band B 1051 of the first region 1051 has been deleted.

[0067] In the above description, the HOMO level in the first carrier transport part 105 has been used for explanation, but this is not limiting. For example, a relatively small HOMO level in the first carrier transport part 105 may be rephrased as a relatively large carrier density in the first carrier transport part 105. Furthermore, a relatively large HOMO level in the first carrier transport part 105 may be rephrased as a relatively small carrier density in the first carrier transport part 105.

[0068] For example, the fact that the first level EL1 and the second level EL2 in the first carrier transport part 105 are different may be rephrased as the fact that the carrier density in the first interface region Ab1 along the first surface CF1 and the carrier density in the second interface region Ab2 along the second surface CF2 in the first carrier transport part 105 are different. Furthermore, the fact that the first level EL1 is smaller than the second level EL2 in the first carrier transport part 105 may be rephrased as the fact that the carrier density in the first interface region Ab1 along the first surface CF1 in the first carrier transport part 105 is higher than the carrier density in the second interface region Ab2 along the second surface CF2 in the first carrier transport part 105. Furthermore, the fact that the HOMO level of the first carrier transport part 105 is increasing along the first direction may be rephrased as the carrier density of the first carrier transport part 105 is decreasing along the first direction. Furthermore, the fact that the HOMO level of the first carrier transport part 105 increases along the first direction from the first interface region Ab1 to the second interface region Ab2 can also be rephrased as the carrier density of the first carrier transport part 105 decreasing along the first direction from the first interface region Ab1 to the second interface region Ab2.

[0069] 9, the solar cell element 10 according to the first embodiment illustrated in Fig. 1 and the like can be manufactured by performing the processes of steps S1 to S5 in the order shown. Here, for example, step S3 corresponds to the first step of the present disclosure, step S4 corresponds to the second step of the present disclosure, and step S5 corresponds to the third step of the present disclosure.

[0070] In step S1, the second electrode unit 102 is formed on the substrate unit 101. Here, the second electrode unit 102 can be formed on the substrate unit 101 by depositing the material of the second electrode unit 102 on the substrate unit 101 using a vacuum process such as sputtering. The material of the second electrode unit 102 may be, for example, a TCO such as ITO, FTO, or ZnO. When the first electrode unit 106 is translucent to light in a specific wavelength range, the material of the second electrode unit 102 may be, for example, a metal with excellent conductivity such as Au.

[0071] In step S2, the second carrier transport region 103 is formed on the second electrode region 102. The material of the second carrier transport region 103 is, for example, TiO ２ , SnO ２ , ZnO or In ２ O ３ A metal oxide such as TiO 4 is applied. Here, for example, a raw material solution prepared by dissolving a raw material such as a metal chloride or a metal isopropoxide in a polar solution may be applied to the second electrode portion 102, and the raw material may be hydrolyzed to generate a metal oxide, thereby forming the second carrier transport portion 103 on the second electrode portion 102. Examples of metal chlorides include titanium chloride, tin chloride, zinc chloride, or indium chloride. Examples of metal isopropoxides include titanium isopropoxide, tin isopropoxide, zinc isopropoxide, or indium isopropoxide. Specifically, for example, an aqueous solution of titanium tetrachloride is applied to the second electrode portion 102 by spin coating or the like and dried. Thereafter, for example, the titanium tetrachloride is hydrolyzed by heating on a hot plate at about 150°C, thereby forming TiO 4 on the second electrode portion 102. ２ The second carrier transport region 103 can be formed. Here, for example, an n-type dopant may be added to the metal oxide. For example, if the metal oxide is ZnO, an element such as Al or B may be used as the n-type dopant. In this case, the raw material solution may be doped with the n-type dopant.

[0072] In this case, for example, an organic material may be used as the material of the second carrier transport part 103. For example, PCBM ([6,6]-Phenyl-C ６１A fullerene derivative such as butylic acid methyl ester (PBMC) may also be used. In this case, for example, a source solution prepared by dissolving the fullerene derivative in a chlorobenzene solvent may be used. Here, 1 milliliter (1 ml) of the source solution may contain, for example, approximately 5 milligrams (mg) to 20 mg of the fullerene derivative. In other words, for example, a source solution may be used in which the solvent is chlorobenzene and the concentration of the fullerene derivative is approximately 5 milligrams per milliliter (mg / ml) to 20 mg / ml. The source solution applied to the second electrode 102 may then be dried and annealed to form the second carrier transport region 103 of PCBM on the second electrode 102. Furthermore, the organic material used as the material for the second carrier transport region 103 may have its solubility in organic solvents and physical properties changed, for example, by changing the functional group. In this case, the organic material may also contain, for example, an n-type dopant.

[0073] In step S3, the photoelectric conversion section 104 is formed on the second carrier transport section 103. In other words, in step S3, the photoelectric conversion section 104 is formed. Here, the photoelectric conversion section 104 can be formed, for example, by applying a raw material liquid onto the second carrier transport section 103 and annealing the applied raw material liquid. The raw material liquid can be generated, for example, by dissolving a halogenated alkylamine and a lead halide or a tin halide, which are raw materials for the photoelectric conversion section 104, in a solvent. In this case, the photoelectric conversion section 104 can be formed of a thin film of a crystalline halogenated perovskite semiconductor.

[0074] In step S4, the first carrier transport unit 105 is formed on the photoelectric conversion unit 104. Here, for example, by performing the processes of step S4a, step S4b, and step S4c in this order, the first carrier transport unit 105 can be formed on the photoelectric conversion unit 104. Here, for example, step S4a corresponds to step 2A of the present disclosure, step S4b corresponds to step 2B of the present disclosure, and step S4c corresponds to step 2C of the present disclosure.

[0075] In step S4a, a first layer is formed on the photoelectric conversion unit 104. In step S4b, a second layer is formed on the first layer. In step S4c, the first and second layers are heated to diffuse the dopant contained in the first layer into the second layer, thereby generating the first carrier transport unit 105 from the first and second layers. Here, the first layer has a higher dopant concentration than the second layer. The second layer has a lower dopant concentration than the first layer or does not contain a dopant. The second layer contains a semiconductor material that constitutes the first carrier transport unit 105. Here, the dopant may be a p-type dopant that makes the semiconductor a p-type semiconductor. The first layer may be a layer containing a material or element that serves as a dopant in the first carrier transport unit 105. The first layer may or may not contain a semiconductor material that constitutes the semiconductor of the first carrier transport unit 105. The second layer is a layer containing a semiconductor material for constituting the semiconductor of the first carrier transport section 105, and may or may not contain a material or element that serves as a dopant in the first carrier transport section 105.

[0076] For example, if the first layer does not contain a semiconductor material for forming the semiconductor of the first carrier transport unit 105, in step S4a, a dopant layer is formed as the first layer on the photoelectric conversion unit 104. The dopant layer may be a layer that does not contain a semiconductor material for forming the semiconductor of the first carrier transport unit 105, but contains a material or element that serves as a dopant in the first carrier transport unit 105. Here, for example, a raw material liquid is applied to the photoelectric conversion unit 104, and the raw material liquid is dried or annealed, thereby forming the dopant layer on the photoelectric conversion unit 104. For example, a raw material solution may be used that is prepared by dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or 4-tert-butylpyridine (TBP) in a chlorobenzene solution. Here, LiTFSI and TBP are materials that serve as dopants in the first carrier transport part 105.

[0077] For example, if the first layer includes a semiconductor material for constituting the semiconductor of the first carrier transport unit 105, in step S4a, a highly doped layer is formed as the first layer on the photoelectric conversion unit 104. The highly doped layer may be a layer including the semiconductor material for constituting the semiconductor of the first carrier transport unit 105 and a material or element that serves as a dopant in the first carrier transport unit 105. Here, for example, a raw material liquid is applied to the photoelectric conversion unit 104, and the raw material liquid is dried and annealed to form a highly doped layer on the photoelectric conversion unit 104. Examples of the semiconductor material for constituting the semiconductor of the first carrier transport unit 105 include organic semiconductor materials such as spiro-OMeTAD, P3HT, PTAA, and Poly-TPD (4-Butyl-N,N-diphenylaniline homopolymer). Here, for example, a source solution can be prepared by dissolving spiro-OMeTAD and LiTFSI or TBP, which serves as a dopant in the first carrier transport unit 105, in chlorobenzene. Here, for example, 1 ml of source solution may contain approximately 10 mg to 85 mg of spiro-OMeTAD. In other words, for example, a source solution may be used in which the solvent is chlorobenzene and the spiro-OMeTAD concentration is approximately 10 mg / ml to 85 mg / ml. Alternatively, for example, a source solution may be prepared by dissolving P3HT and LiTFSI or TBP, which serves as a dopant in the first carrier transport unit 105, in dichlorobenzene. Here, for example, 1 ml of source solution may contain approximately 5 mg to 20 mg of P3HT. In other words, for example, a source solution may be used in which the solvent is dichlorobenzene and the P3HT concentration is approximately 5 mg / ml to 20 mg / ml. Alternatively, for example, the raw material solution may be prepared by dissolving PTAA and LiTFSI or TBP, which serves as a dopant in the first carrier transport part 105, in toluene. Here, for example, 1 ml of the raw material solution may contain approximately 5 mg to 20 mg of PTAA. In other words, for example, a raw material solution may be used in which the solvent is toluene and the concentration of PTAA is 5 mg / ml to 20 mg / ml.Alternatively, for example, a source solution may be prepared by dissolving Poly-TPD and LiTFSI or TBP, which serves as a dopant in the first carrier transporting part 105, in chlorobenzene. Here, for example, 1 ml of the source solution may contain approximately 5 mg to 20 mg of Poly-TPD. In other words, for example, a source solution may be used in which the solvent is chlorobenzene and the concentration of Poly-TPD is 5 mg / ml to 20 mg / ml.

[0078] For example, if the second layer contains a material or element that serves as a dopant in the first carrier transport section 105, step S4b involves forming a low-doped layer as the second layer on the first layer. The low-doped layer may be a layer containing a semiconductor material for constituting the semiconductor of the first carrier transport section 105 and a material or element that serves as a dopant in the first carrier transport section 105. For example, if the first layer is a highly doped layer, the low-doped layer as the second layer may be a layer based on the highly doped layer, with a reduced concentration of the material or element that serves as a dopant in the first carrier transport section 105. Here, for example, a raw material liquid may be applied to the first layer and then dried to form the low-doped layer on the first layer. The semiconductor material for constituting the semiconductor of the first carrier transport section 105 may be, for example, an organic semiconductor material such as spiro-OMeTAD, P3HT, PTAA, or Poly-TPD. Here, for example, a source solution can be prepared by dissolving spiro-OMeTAD and LiTFSI or TBP, which serves as a dopant in the first carrier transport unit 105, in chlorobenzene. Here, for example, a source solution in which the solvent is chlorobenzene and the spiro-OMeTAD concentration is approximately 10 mg / ml to 85 mg / ml may be used. Alternatively, for example, a source solution can be prepared by dissolving P3HT and LiTFSI or TBP, which serves as a dopant in the first carrier transport unit 105, in dichlorobenzene. Here, for example, a source solution in which the solvent is dichlorobenzene and the P3HT concentration is approximately 5 mg / ml to 20 mg / ml may be used. Alternatively, for example, a source solution can be prepared by dissolving PTAA and LiTFSI or TBP, which serves as a dopant in the first carrier transport unit 105, in toluene. Here, for example, a source solution may be used in which the solvent is toluene and the concentration of PTAA is 5 mg / ml to 20 mg / ml. Alternatively, for example, the source solution may be prepared by dissolving Poly-TPD and LiTFSI or TBP as a material to be a dopant in the first carrier transporting part 105 in chlorobenzene.Here, for example, a raw material solution may be used in which the solvent is chlorobenzene and the concentration of Poly-TPD is 5 mg / ml to 20 mg / ml.

[0079] For example, if the second layer does not contain a material or element that serves as a dopant in the first carrier transport section 105, an undoped layer is formed as the second layer on the first layer in step S4b. The undoped layer may be a layer that contains a semiconductor material for constituting the semiconductor of the first carrier transport section 105 but does not contain a material or element that serves as a dopant in the first carrier transport section 105. For example, if the first layer is a highly doped layer, the undoped layer as the second layer may be a layer based on the highly doped layer from which the material or element that serves as a dopant in the first carrier transport section 105 has been removed. Here, for example, an undoped layer can be formed on the first layer by applying a raw material solution onto the first layer and drying the raw material solution. Examples of the semiconductor material for constituting the semiconductor of the first carrier transport section 105 include organic semiconductor materials such as spiro-OMeTAD, P3HT, PTAA, and Poly-TPD. Here, for example, a source solution can be prepared by dissolving spiro-OMeTAD in chlorobenzene. Here, for example, a source solution in which the solvent is chlorobenzene and the concentration of spiro-OMeTAD is approximately 10 mg / ml to 85 mg / ml may be used. Alternatively, for example, a source solution can be prepared by dissolving P3HT in dichlorobenzene. Here, for example, a source solution in which the solvent is dichlorobenzene and the concentration of P3HT is approximately 5 mg / ml to 20 mg / ml may be used. Alternatively, for example, a source solution can be prepared by dissolving PTAA in toluene. Here, for example, a source solution in which the solvent is toluene and the concentration of PTAA is approximately 5 mg / ml to 20 mg / ml may be used. Alternatively, for example, a source solution can be prepared by dissolving Poly-TPD in chlorobenzene. Here, for example, a source solution in which the solvent is chlorobenzene and the concentration of Poly-TPD is approximately 5 mg / ml to 20 mg / ml may be used.

[0080] In step S4c, the first layer and the second layer are heated to diffuse the dopant contained in the first layer into the second layer. This generates the first carrier transport unit 105 from the first layer and the second layer. Here, the heating of the first layer and the second layer may be annealing of the first layer and the second layer. The temperature and time for heating the first layer and the second layer may be appropriately set depending on, for example, the semiconductor material and the dopant material in the first layer and the second layer. Here, for example, if the first layer is a dopant layer that does not contain a semiconductor material for forming the semiconductor of the first carrier transport unit 105, diffusion of the semiconductor material for forming the semiconductor of the first carrier transport unit 105 from the second layer toward the first layer may also occur.

[0081] In step S5, the first electrode portion 106 is formed on the first carrier transport portion 105. Here, the first electrode portion 106 can be formed by depositing a material for the first electrode portion 106 on the first carrier transport portion 105 using a vacuum process such as sputtering. The material for the first electrode portion 106 may be, for example, a metal with excellent conductivity such as Au, or a TCO such as ITO, FTO, or ZnO. Alternatively, the first electrode portion 106 may be formed by, for example, applying a metal paste as a coating liquid by screen printing or the like, and then drying the applied metal paste to solidify it.

[0082] Here, in step S4, for example, a dopant layer or a highly doped layer may be employed as the first layer, and a lightly doped layer or an undoped layer may be employed as the second layer. The thicknesses of the first and second layers and the temperature and time conditions for heating the first and second layers may be appropriately set. This may result in, for example, a first carrier transport portion 105 in which the dopant concentration decreases along the −Z direction as the first direction from the first interface region Ab1 along the first surface CF1 to the second interface region Ab2 along the second surface CF2. In other words, for example, a first carrier transport portion 105 in which the HOMO level increases along the −Z direction as the first direction from the first interface region Ab1 along the first surface CF1 to the second interface region Ab2 along the second surface CF2 may be formed. In this case, for example, the first carrier transport portion 105 may have an energy band structure such as that shown in FIG. 2 . In other words, in the first carrier transport portion 105, for example, a first level EL1, which is the HOMO level in the first interface region Ab1, can be smaller than a second level EL2, which is the HOMO level in the second interface region Ab2. Furthermore, in the first carrier transport portion 105, for example, the HOMO level can increase from the first interface region Ab1 to the second interface region Ab2 along the −Z direction as a first direction. Here, for example, by appropriately setting the semiconductor material in the first carrier transport portion 105 and the dopant concentration in the dopant layer or highly doped layer as the first layer, the first level EL1, which is the HOMO level in the first interface region Ab1, can be made substantially equal to a third level EL3, which is the VBM level of the photoelectric conversion portion 104. Furthermore, for example, by appropriately setting the semiconductor material in the first carrier transport portion 105 and the dopant concentration in the lightly doped layer or undoped layer as the second layer, the second level EL2, which is the HOMO level in the second interface region Ab2, may be made substantially equal to the fourth level EL4, which is the Fermi level in the first electrode portion 106.

[0083] In step S4, for example, a highly doped layer may be used as the first layer, and a lightly doped or undoped layer may be used as the second layer. The thicknesses of the first and second layers and the temperature and time conditions for heating the first and second layers may be appropriately set. As a result, for example, as shown in FIGS. 3 and 5 , the first carrier transport unit 105 including the first region 1051 may be formed. Here, for example, by appropriately setting the semiconductor material of the first carrier transport unit 105 and the dopant concentration in the highly doped layer as the first layer, the HOMO level in the first region 1051 may be made substantially equal to the third level EL3, which is the VBM level in the photoelectric conversion unit 104. Furthermore, for example, by appropriately setting the temperature and time conditions in heating the first layer and the second layer, the first carrier transport section 105 including the first region 1051, the second region 1052, and the third region 1053 may be formed as shown in Fig. 3, or the first carrier transport section 105 including the first region 1051 and the third region 1053 may be formed as shown in Fig. 5. When the first carrier transport section 105 including the first region 1051, the second region 1052, and the third region 1053 is formed as shown in Fig. 3, the first carrier transport section 105 may have, for example, the energy band structure shown in Fig. 4. In this case, for example, by appropriately setting the semiconductor material of the first carrier transport section 105 and the dopant concentration in the low-doped layer or undoped layer as the second layer, the HOMO level in the second region 1052 may be made substantially equal to the fourth level EL4, which is the Fermi level of the first electrode section 106. When the first carrier transport region 105 including the first region 1051 and the third region 1053 is formed as shown in Fig. 5, for example, the first carrier transport region 105 may have an energy band structure as shown in Fig. 6. In this case, for example, by appropriately setting the semiconductor material in the first carrier transport region 105 and the dopant concentration in the lightly doped layer or undoped layer as the second layer, the second level EL2 which is the HOMO level in the second interface region Ab2 may be made substantially equal to the fourth level EL4 which is the Fermi level in the first electrode region 106.

[0084] In step S4, for example, a dopant layer or a highly doped layer may be used as the first layer, and a lightly doped layer or an undoped layer may be used as the second layer. The thicknesses of the first and second layers and the temperature and time conditions for heating the first and second layers may be appropriately set. As a result, for example, as shown in FIG. 7 , the first carrier transport unit 105 including the second region 1052 may be formed. Here, for example, by appropriately setting the semiconductor material of the first carrier transport unit 105 and the dopant concentration in the lightly doped or undoped layer as the second layer, the HOMO level in the second region 1052 may be made substantially equal to the fourth level EL4, which is the Fermi level of the first electrode unit 106. Furthermore, for example, by appropriately setting the semiconductor material in the first carrier transport section 105 and the dopant concentration in the dopant layer or highly doped layer as the first layer, the first level EL1, which is the HOMO level in the first interface region Ab1, may be made substantially equal to the third level EL3, which is the VBM level of the photoelectric conversion section 104.

[0085] 10 , for example, the solar cell module 1 includes a plurality of solar cell elements 10 and a power collecting portion 30. In the solar cell module 1 according to the first embodiment, the plurality of solar cell elements 10 share a single substrate portion 101. In other words, in the solar cell module 1 according to the first embodiment, a plurality of second electrode portions 102 are formed on a single substrate portion 101.

[0086] The current collecting section 30 functions as an extraction electrode. The current collecting section 30 may be, for example, an aluminum or copper wiring. The current collecting section 30 is connected to, for example, a terminal for extracting electricity generated by the solar cell element 10.

[0087] 2. Other Embodiments The present disclosure is not limited to the first embodiment described above, and various modifications and improvements can be made without departing from the gist of the present disclosure.

[0088] 2-1. Second Embodiment A second embodiment will be described below, focusing mainly on the differences from the first embodiment.

[0089] Fig. 11 is a diagram schematically showing a first example of a cross-sectional configuration of the solar cell element 40 according to the second embodiment. Fig. 12 is an energy band diagram showing a first example of the relationship between energy levels among the first electrode portion 106, the first carrier transport portion 105, the photoelectric conversion portion 104, and the second carrier transport portion 103 of the solar cell element 40 according to the second embodiment.

[0090] As shown in FIG. 11 , the solar cell element 40 according to the second embodiment is based on the example of the solar cell element 10 according to the first embodiment shown in FIG. 3 , but has a configuration in which the first carrier transport region 105 includes a fourth region 1054 instead of the third region 1053. The fourth region 1054 is located between the first region 1051 and the second region 1052. In this case, the first carrier transport region 105 of the solar cell element 40 according to the second embodiment may have an energy band structure as shown in FIG. 12 , for example. The energy band diagram of FIG. 12 is based on the energy band diagram of FIG. 4 , but shows the energy level of the forbidden band B1054 of the fourth region 1054 instead of the energy level of the forbidden band B1053 of the third region 1053. The HOMO level in the fourth region 1054 is substantially the same as a fifth level EL5, which is an energy level between the first level EL1 and the second level EL2. In other words, the HOMO level of the fourth region 1054 of the first carrier transporter 105 is approximately equal to the fifth level EL5 over a fourth predetermined thickness from the first region 1051 to the second region 1052. In other words, the HOMO level of the fourth region 1054 is approximately equal to the fifth level EL5 along the −Z direction as the first direction. In this case, the HOMO level of the first carrier transporter 105 increases discretely from the first surface CF1 to the second surface CF2. In other words, the HOMO level of the first carrier transporter 105 increases discretely from the first interface region Ab1 along the first surface CF1 to the second interface region Ab2 along the second surface CF2. More specifically, the HOMO level in the first carrier transport part 105 increases stepwise from the first surface CF1 to the second surface CF2. In other words, the HOMO level in the first carrier transport part 105 increases stepwise from the first interface region Ab1 along the first surface CF1 to the second interface region Ab2 along the second surface CF2. Note that the difference between the first level EL1 and the fifth level EL5 and the difference between the second level EL2 and the fifth level EL5 may be the same or different.

[0091] 11 can be manufactured by, for example, performing the processes of steps S1 to S3 in the order described above, as in the first embodiment, followed by the process of step S4A, and then performing the process of step S5 in the same manner as in the first embodiment, as shown in Fig. 13. In step S4A, the processes of steps S41, S42, and S43 are performed in the order described above.

[0092] In step S41, the first region 1051 of the first carrier transport section 105 is formed on the photoelectric conversion section 104. Here, for example, a second-A raw material liquid is applied to the photoelectric conversion section 104, and the applied second-A raw material liquid is dried and annealed, thereby forming the first region 1051 on the photoelectric conversion section 104. The material for the second-A raw material liquid may be, for example, a material in which a dopant is added to an organic semiconductor material such as spiro-OMeTAD, P3HT, PTAA, or Poly-TPD. Here, the concentration of the dopant in the second-A raw material liquid is greater than the concentration of the dopant in each of the second-B raw material liquid and the second-C raw material liquid, which will be described later. For example, LiTFSI or TBP may be used as the dopant.

[0093] In step S42, a fourth region 1054 of the first carrier transport unit 105 is formed on the first region 1051 of the first carrier transport unit 105. Here, for example, a second-B source liquid is applied to the first region 1051, and the applied second-B source liquid is dried and annealed to form the fourth region 1054 on the first region 1051. The material for the second-B source liquid may be, for example, a material in which a dopant is added to an organic semiconductor material such as spiro-OMeTAD, P3HT, PTAA, or Poly-TPD. Here, the concentration of the dopant in the second-B source liquid is greater than the concentration of the dopant in the second-C source liquid described below. For example, LiTFSI or TBP may be used as the dopant.

[0094] In step S43, the second region 1052 of the first carrier transport unit 105 is formed on the fourth region 1054 of the first carrier transport unit 105. Here, for example, a second C source liquid is applied onto the fourth region 1054, and the applied second C source liquid is dried and annealed, thereby forming the second region 1052 on the fourth region 1054. The material for the second C source liquid may be, for example, a material in which a dopant is added to an organic semiconductor material such as spiro-OMeTAD, P3HT, PTAA, or Poly-TPD. Examples of the dopant that may be used include LiTFSI and TBP.

[0095] By employing the first carrier transport part 105 having such a structure, it is possible to control the thicknesses of the first region 1051 and the second region 1052 without controlling the conditions for diffusing the dopant. This makes it easier to control the thicknesses of the first region 1051 and the second region 1052 even when the thickness of the first carrier transport part 105 is large.

[0096] In the above description of the second embodiment, the first carrier transport unit 105 is configured by three regions, namely, the first region 1051, the fourth region 1054, and the second region 1052. However, the first carrier transport unit 105 is not limited to this structure. For example, the first carrier transport unit 105 may include, between the first region 1051 and the second region 1052, a plurality of regions having mutually different HOMO levels between the first level EL1 and the second level EL2.

[0097] 14 , for example, the first carrier transport portion 105 of the solar cell element 40 according to the second embodiment may include a first interface layer 1055 located between the first region 1051 and the fourth region 1054. In this case, even if the material of the first region 1051 and the material of the fourth region 1054 are different, the presence of the first interface layer 1055 can reduce deterioration of one or more of the materials of the first region 1051 and the fourth region 1054 due to contact between the materials of the first region 1051 and the fourth region 1054. In this case, the first carrier transport portion 105 of the solar cell element 40 according to the second embodiment may have an energy band structure as shown in FIG. 15 is an energy band diagram in which the energy level of a forbidden band B1055 of a first interface layer 1055 is added between the energy level of a forbidden band B1051 of a first region 1051 and the energy level of a forbidden band B1054 of a fourth region 1054, based on the energy band diagram of FIG. 12 . For example, as shown in FIG. 15 , the HOMO level of the first interface layer 1055 may be equal to or higher than the HOMO level of the first region 1051 and equal to or lower than the HOMO level of the fourth region 1054. In other words, the HOMO level of the first interface layer 1055 may be equal to or higher than a first level EL1 that is substantially the same as the HOMO level of the first region 1051 and equal to or lower than a fifth level EL5 that is substantially the same as the HOMO level of the fourth region 1054. The material of the first interface layer 1055 may be, for example, a material that is translucent to light in a specific wavelength range. The material of the first interface layer 1055 may be, for example, a transparent conductive oxide (TCO) or a material used in a buffer layer of a tandem solar cell. The first interface layer 1055 may be formed, for example, by applying a raw material solution containing the material of the first interface layer 1055 onto the first region 1051 and then drying and annealing the applied raw material solution. Alternatively, the first interface layer 1055 may be formed by a vacuum process such as sputtering.

[0098] 16 , for example, the first carrier transport portion 105 of the solar cell element 40 according to the second embodiment may include a second interface layer 1056 located between the second region 1052 and the fourth region 1054. In this case, even if the material of the second region 1052 and the material of the fourth region 1054 are different, the presence of the second interface layer 1056 can reduce deterioration of one or more of the materials of the second region 1052 and the fourth region 1054 due to contact between the materials of the second region 1052 and the fourth region 1054. In this case, the first carrier transport portion 105 of the solar cell element 40 according to the second embodiment may have an energy band structure as shown in FIG. 17 is an energy band diagram in which the energy level of a forbidden band B1056 of a second interface layer 1056 is added between the energy level of a forbidden band B1052 of the second region 1052 and the energy level of a forbidden band B1054 of the fourth region 1054, based on the energy band diagram of FIG. 12 . For example, as shown in FIG. 17 , the HOMO level of the second interface layer 1056 may be higher than the HOMO level of the fourth region 1054 and lower than the HOMO level of the second region 1052. In other words, the HOMO level of the second interface layer 1056 may be higher than a fifth level EL5 that is substantially the same as the HOMO level of the fourth region 1054 and lower than a second level EL2 that is substantially the same as the HOMO level of the second region 1052. The material of the second interface layer 1056 may be, for example, a material that is translucent to light in a specific wavelength range. The material of the second interface layer 1056 may be, for example, a transparent conductive oxide (TCO) or a material used in a buffer layer of a tandem solar cell. The second interface layer 1056 may be formed, for example, by applying a raw material solution containing the material of the second interface layer 1056 onto the fourth region 1054 and then drying and annealing the applied raw material solution. Alternatively, the second interface layer 1056 may be formed by a vacuum process such as sputtering.

[0099] 18 , the first carrier transport part 105 of the solar cell element 40 according to the second embodiment may include the first interface layer 1055 and the second interface layer 1056. The first interface layer 1055 is located between the first region 1051 and the fourth region 1054. The second interface layer 1056 is located between the second region 1052 and the fourth region 1054. In this case, the first carrier transport part 105 of the solar cell element 40 according to the second embodiment may have an energy band structure as shown in FIG. 19 , for example. 12 , the energy band diagram of Fig. 19 is an energy band diagram in which the energy level of the forbidden band B1055 of the first interface layer 1055 is added between the energy level of the forbidden band B1051 of the first region 1051 and the energy level of the forbidden band B1054 of the fourth region 1054, and the energy level of the forbidden band B1056 of the second interface layer 1056 is added between the energy level of the forbidden band B1052 of the second region 1052 and the energy level of the forbidden band B1054 of the fourth region 1054. For example, as shown in Fig. 19 , the HOMO level of the first interface layer 1055 may be higher than the HOMO level of the first region 1051 and lower than the HOMO level of the fourth region 1054. 19 , the HOMO level of the second interface layer 1056 may be equal to or higher than the HOMO level of the fourth region 1054 and equal to or lower than the HOMO level of the second region 1052. In other words, the HOMO level of the second interface layer 1056 may be equal to or higher than the HOMO level of the fourth region 1054, i.e., a fifth level EL5, which is approximately the same as the HOMO level of the fourth region 1054, and equal to or lower than the HOMO level of the second region 1052. In other words, the HOMO level of the second interface layer 1056 may be equal to or higher than the fifth level EL5, which is approximately the same as the HOMO level of the fourth region 1054, and equal to or lower than the second level EL2, which is approximately the same as the HOMO level of the second region 1052.

[0100] <2-2. Other Embodiments> In the first and second embodiments, the third level EL3 is the VBM level in the photoelectric conversion unit 104, but is not limited to this. For example, when the i-type semiconductor applied to the photoelectric conversion unit 104 is an organic semiconductor, the third level EL3 may be the energy level of the highest occupied molecular orbital (HOMO level) in the photoelectric conversion unit 104.

[0101] Although the present disclosure has been described based on various drawings and various embodiments, those skilled in the art may make various modifications and alterations based on the present disclosure. Therefore, these modifications and alterations are within the scope of the present disclosure. For example, functions included in each functional unit and step may be rearranged in a logically consistent manner, and multiple functional units and steps may be combined or divided into one. Furthermore, the present disclosure is not limited to faithfully implementing each of the above-described embodiments. Some features of each embodiment may be combined, or parts of each embodiment may be omitted, as appropriate.

[0102] <2-3. Summary of the present disclosure> The present disclosure includes the following contents.

[0103] In one embodiment, (1) a solar cell element includes a first electrode unit, a photoelectric conversion unit, and a first carrier transport unit located between the first electrode unit and the photoelectric conversion unit, wherein a first level of the first carrier transport unit, which is an energy level of a highest occupied molecular orbital (HMO) at a first surface that is in contact with the photoelectric conversion unit, is lower than a second level of the HMO at a second surface that is in contact with the first electrode unit.

[0104] (2) In the solar cell element of (1) above, the energy level of the highest occupied molecular orbital of the first carrier transport part increases from the first surface to the second surface along a first direction from the first surface to the second surface.

[0105] (3) In the solar cell element of any one of (1) and (2) above, the first energy level is substantially the same as a third energy level, which is the energy level at the top of the valence band of the photoelectric conversion section.

[0106] (4) In the solar cell element according to any one of (1) to (3) above, the second level is substantially the same as a fourth level, which is the Fermi level of the first electrode portion.

[0107] (5) In the solar cell element of any one of (1) to (4), the first carrier transport part includes a first region having a first predetermined thickness along the first direction from the first surface, and an energy level of the highest occupied molecular orbital of the first carrier transport part in the first region is substantially the same as the third level.

[0108] (6) In the solar cell element of any one of (1) to (5), the first carrier transporting part further includes a second region having a second predetermined thickness from the second surface along a direction opposite to the first direction, and an energy level of the highest occupied molecular orbital of the first carrier transporting part in the second region is substantially the same as the fourth level.

[0109] (7) In the solar cell element of any one of (1) to (6), the first carrier transport part further includes a third region between the first region and the first electrode part, and an energy level of the highest occupied molecular orbital of the first carrier transport part in the third region increases along the first direction.

[0110] (8) In the solar cell element of any one of (1) to (7), the first carrier transporting part further includes a fourth region between the first region and the second region, and the energy level of the highest occupied molecular orbital of the first carrier transporting part in the fourth region is substantially equal to a fifth level that is an energy level not lower than the first level and not higher than the second level.

[0111] (9) In any of the solar cell elements (1) to (8) above, the first carrier transport part comprises a first interface layer between the first region and the fourth region, and a second interface layer between the second region and the fourth region.

[0112] In one embodiment, (10) a solar cell module includes a first electrode unit, a photoelectric conversion unit, and a first carrier transport unit located between the first electrode unit and the photoelectric conversion unit, wherein a first level of the first carrier transport unit, which is an energy level of a highest occupied molecular orbital (HMO) at a first surface that is in contact with the photoelectric conversion unit, is lower than a second level of the HMO at a second surface that is in contact with the first electrode unit.

[0113] (11) In the solar cell module of (10) above, the energy level of the highest occupied molecular orbital of the first carrier transport part increases from the first surface to the second surface along a first direction from the first surface to the second surface.

[0114] (12) In the solar cell module of any one of (10) to (11) above, the first energy level is substantially the same as a third energy level, which is the energy level at the top of the valence band of the photoelectric conversion section.

[0115] (13) In the solar cell module of any one of (10) to (12) above, the second level is substantially the same as a fourth level, which is a Fermi level of the first electrode portion.

[0116] (14) In the solar cell module of any one of (10) to (13), the first carrier transport part includes a first region having a first predetermined thickness along the first direction from the first surface, and an energy level of the highest occupied molecular orbital of the first carrier transport part in the first region is substantially the same as the third level.

[0117] (15) In the solar cell module of any one of (10) to (14), the first carrier transporting part further includes a second region having a second predetermined thickness from the second surface along a direction opposite to the first direction, and an energy level of the highest occupied molecular orbital of the first carrier transporting part in the second region is substantially the same as the fourth level.

[0118] (16) In the solar cell module of any one of (10) to (15), the first carrier transport part further includes a third region between the first region and the first electrode part, and an energy level of the highest occupied molecular orbital of the first carrier transport part in the third region increases along the first direction.

[0119] (17) In the solar cell module of any one of (10) to (16), the first carrier transport part further includes a fourth region between the first region and the second region, and the energy level of the highest occupied molecular orbital of the first carrier transport part in the fourth region is substantially equal to a fifth level that is an energy level not lower than the first level and not higher than the second level.

[0120] (18) In any of the solar cell modules (10) to (17) above, the first carrier transport part comprises a first interface layer between the first region and the fourth region, and a second interface layer between the second region and the fourth region.

[0121] In one embodiment, (11) a method for manufacturing a solar cell element includes a first step of forming a photoelectric conversion section, a second step of forming a dopant layer on the photoelectric conversion section, a third step of forming a first carrier transport section on the dopant layer, and a fourth step of forming a first electrode section on the first carrier transport section.

[0122] 1: Solar cell module 10: Solar cell element 101: Substrate portion 102: Second electrode portion 103: Second carrier transport portion 104: Photoelectric conversion portion 105: First carrier transport portion 1051: First region 1052: Second region 1053: Third region 1054: Fourth region 1055: First interface layer 1056: Second interface layer 106: First electrode portion F1: First element surface F2: Second element surface CF1: First surface CF2: Second surface EL1: First level EL2: Second level EL3: Third level EL4: Fourth level EL5: Fifth level 20: Conducting wire 30: Current collecting portion 40: Solar cell element

Claims

1. a first electrode portion, a photoelectric conversion portion, a first carrier transport portion positioned between the first electrode portion and the photoelectric conversion portion, and comprising: the first carrier transport portion has a first surface in contact with the photoelectric conversion portion and a second surface in contact with the first electrode portion; in the first carrier transport portion, a first level, which is the energy level of the highest occupied orbital in a first interface region along the first surface, is smaller than a second level, which is the energy level of the highest occupied orbital in a second interface region along the second surface, a solar cell element.

2. The energy level of the highest occupied orbital of the first carrier transport portion increases from the first interface region to the second interface region along a first direction from the first surface to the second surface, the solar cell element according to claim 1.

3. The first level is substantially the same as a third level, which is the energy level of the upper end of the valence band in the photoelectric conversion portion, the solar cell element according to claim 1 or claim 2.

4. The first carrier transport portion includes a first region positioned along the first surface, the first region has a first predetermined thickness from the first surface along a first direction from the first surface to the second surface, the energy level of the highest occupied orbital in the first region is substantially the same as the third level, the solar cell element according to claim 3.

5. The first carrier transport portion includes a third region positioned between the first region and the first electrode portion, the energy level of the highest occupied orbital in the third region increases along the first direction, the solar cell element according to claim 4.

6. The second level is substantially the same as a fourth level, which is the Fermi level in the first electrode portion, the solar cell element according to claim 1 or claim 2.

7. The first carrier transport portion includes a second region positioned along the second surface, the second region has a second predetermined thickness from the second surface along a second direction opposite to the first direction from the first surface to the second surface, the energy level of the highest occupied orbital in the second region is substantially the same as the fourth level, the solar cell element according to claim 6.

8. The first carrier transport portion includes a third region between the second region and the photoelectric conversion portion, the energy level of the highest occupied orbital in the third region increases along the first direction, the solar cell element according to claim 7.

9. The solar cell device according to claim 4, wherein the second level is substantially the same as the fourth level which is the Fermi level in the first electrode portion.

10. The first carrier transport portion includes a second region located along the second surface, The second region has a second predetermined thickness from the second surface along a second direction opposite to the first direction, The energy level of the highest occupied orbital in the second region is substantially the same as the fourth level, the solar cell device according to claim 9.

11. The first carrier transport portion includes a third region located between the first region and the second region, The energy level of the highest occupied orbital in the third region increases along the first direction, the solar cell device according to claim 10.

12. The first carrier transport portion further includes a fourth region located between the first region and the second region, The energy level of the highest occupied orbital in the fourth region is substantially the same as the fifth level which is the energy level between the first level and the second level, the solar cell device according to claim 10.

13. The first carrier transport portion includes a first interface layer located between the first region and the fourth region, The energy level of the highest occupied orbital in the first interface layer is equal to or higher than the energy level of the highest occupied orbital in the first region and equal to or lower than the energy level of the highest occupied orbital in the fourth region, the solar cell device according to claim 12.

14. The first carrier transport portion includes a second interface layer located between the second region and the fourth region, The energy level of the highest occupied orbital in the second interface layer is equal to or higher than the energy level of the highest occupied orbital in the fourth region and equal to or lower than the energy level of the highest occupied orbital in the second region, the solar cell device according to claim 12.

15. A first electrode portion, A photoelectric conversion portion, A first carrier transport portion located between the first electrode portion and the photoelectric conversion portion, The first carrier transport portion has a first surface in contact with the photoelectric conversion portion and a second surface in contact with the first electrode portion, In the first carrier transport portion, the carrier density in the first interface region along the first surface is higher than the carrier density in the second interface region along the second surface, the solar cell device.

16. A first electrode portion, A photoelectric conversion portion, A first carrier transport part positioned between the first electrode part and the photoelectric conversion part, The first carrier transport part has a first surface in contact with the photoelectric conversion part and a second surface in contact with the first electrode part, In the first carrier transport part, a first level, which is the energy level of the highest occupied orbital in a first interface region along the first surface, is smaller than a second level, which is the energy level of the highest occupied orbital in a second interface region along the second surface. A solar cell module.

17. A first step of forming a photoelectric conversion part, A second step of forming a first carrier transport part on the photoelectric conversion part, A third step of forming a first electrode part on the first carrier transport part, and having, The second step includes a second A step of forming a first layer on the photoelectric conversion part, a second B step of forming a second layer on the first layer, and a second C step of generating the first carrier transport part from the first layer and the second layer by heating the first layer and the second layer to diffuse a dopant contained in the first layer into the second layer, The first layer has a higher dopant concentration than the second layer, The second layer has a lower dopant concentration than the first layer or does not contain a dopant, and includes a material of a semiconductor constituting the first carrier transport part. A method for manufacturing a solar cell element.