WO2019220949A1 - Structure for photoelectric conversion element, method for manufacturing same, photoelectric conversion element, and method for manufacturing said photoelectric conversion element - Google Patents

Structure for photoelectric conversion element, method for manufacturing same, photoelectric conversion element, and method for manufacturing said photoelectric conversion element Download PDF

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WO2019220949A1
WO2019220949A1 PCT/JP2019/018234 JP2019018234W WO2019220949A1 WO 2019220949 A1 WO2019220949 A1 WO 2019220949A1 JP 2019018234 W JP2019018234 W JP 2019018234W WO 2019220949 A1 WO2019220949 A1 WO 2019220949A1
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convex
photoelectric conversion
silicon
conversion element
layer
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PCT/JP2019/018234
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French (fr)
Japanese (ja)
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紘太郎 大
啓 篠塚
直樹 深田
ウイパコーン ジェバスワン
ティヤグ スブラマニ
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王子ホールディングス株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells

Definitions

  • the present invention relates to a photoelectric conversion element such as a solar cell, a structure for a photoelectric conversion element, and a method for manufacturing the structure.
  • a photoelectric conversion element such as a solar cell
  • a structure for a photoelectric conversion element and a method for manufacturing the structure.
  • Solar cells include inorganic semiconductor systems such as silicon and compound semiconductor systems and organic semiconductor systems. Silicon systems, particularly crystalline silicon systems using crystalline silicon, are the mainstream. Crystalline silicon solar cells are formed from two or more semiconductors of silicon doped n-type or p-type, and solar energy is converted into electrical energy by using a junction surface (pn junction) between different semiconductors. Convert.
  • a pn junction is provided inside or on the surface of a silicon layer in which many fine wire structures are erected in a comb-like shape (Patent Document 1).
  • the pn junction is formed by doping by thermal diffusion. Doping has the advantage of not having defects such as unpaired electrons in the pn junction, but the thermal control of the doping method itself by thermal diffusion is very difficult, and doping doping is performed on one wire structure and the entire wire structure layer. Since the thickness of the layer varies, it is difficult to uniformly form the p layer or the n layer. There may be a portion where a pn junction is not formed. In that case, the pn junction does not function as an element, so that there is a disadvantage that it is not suitable for production.
  • a pn junction is formed by depositing a different semiconductor layer (silicon shell layer) by a thin film manufacturing method such as vapor deposition or sputtering. To do. Unlike the doping method, this method has an advantage that the formation of the silicon shell layer can be stably controlled.
  • the silicon shell layer may accumulate on the top of the structure and fill the gap between the wire structures, and the shell forming gas may not reach the root between the wire structures. is there. As a result, a uniform pn junction cannot be formed, and the function as an element may be reduced. Therefore, when a fine wire structure is provided, the area of the pn junction can be increased and the effect of improving the conversion efficiency can be expected, but the features of the wire structure have not been fully utilized.
  • the present invention provides a structure for a photoelectric conversion element for obtaining a photoelectric conversion element capable of obtaining excellent photoelectric conversion efficiency, a method for producing the same, and a photoelectric conversion element capable of obtaining excellent photoelectric conversion efficiency. It is an object to provide a manufacturing method.
  • a photoelectric conversion element structure including a silicon core layer made of silicon doped in n-type or p-type, The silicon core layer has a first surface and a second surface opposite the first surface;
  • the first surface is a concavo-convex structure (I) having a number of convex surfaces,
  • a large number of convex surfaces in the concavo-convex structure (I) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second surface.
  • a structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1000 nm.
  • L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained.
  • the bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  • a silicon core layer made of silicon doped n-type or p-type, and a silicon shell made of silicon doped p-type or n-type provided to form a pn junction with the silicon core layer A structure for a photoelectric conversion element comprising a layer, The silicon core layer has a first surface and a second surface opposite the first surface; The silicon shell layer is provided to form the pn junction on the first surface; The surface of the silicon shell layer is a concavo-convex structure (II) having a large number of convex surfaces, A large number of convex surfaces in the concavo-convex structure (II) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second
  • a structure for a photoelectric conversion element wherein the average height L1a is 100 to 1000 nm.
  • L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained.
  • the bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  • the first surface of the silicon core layer has an uneven structure, and the uneven structure (II) follows the uneven structure on the first surface of the silicon core layer.
  • the structure for a photoelectric conversion element according to any one of to [6].
  • a photoelectric conversion element structure comprising a layer and a transparent conductive layer covering the surface of the silicon shell layer,
  • the silicon core layer has a first surface and a second surface opposite the first surface;
  • the silicon shell layer is provided to form the pn junction on the first surface;
  • the surface of the transparent conductive layer is a concavo-convex structure (III) having a large number of convex surfaces, A number of convex surfaces in the concavo-convex structure (III) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut by a plane perpendicular to the second surface.
  • a structure for a photoelectric conversion element wherein the average height L1a is 100 to 1100 nm.
  • L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained.
  • the bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  • the first surface of the silicon core layer has an uneven structure
  • the surface of the silicon shell layer has an uneven structure following the uneven structure of the first surface of the silicon core layer.
  • the uneven structure (III) follows the uneven structure on the first surface of the silicon core layer and the uneven structure on the surface of the silicon shell layer, according to any one of [8] to [10].
  • the structure for photoelectric conversion elements [12]
  • a doped silicon material opposite to the silicon core layer is deposited on the first surface of the photoelectric conversion element structure according to any one of [1] to [3] to form a silicon shell layer.
  • a method for producing a structure for a photoelectric conversion element comprising: forming the structure.
  • a doped silicon material opposite to the silicon core layer is deposited on the first surface of the photoelectric conversion element structure according to any one of [1] to [3] to form a silicon shell layer. Forming, Furthermore, the back surface electrode is provided directly or indirectly on the second surface of the silicon core layer. [21] The method for manufacturing a photoelectric conversion element according to [20], further including providing a surface electrode that is in electrical contact with the silicon shell layer.
  • the photoelectric conversion element structure of the present invention a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained. Moreover, the photoelectric conversion element of this invention is excellent in photoelectric conversion efficiency.
  • the photoelectric conversion element structure 10 of the present embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type.
  • the dopant for doping n-type include phosphorus and arsenic.
  • An example of the dopant for p-type doping is boron.
  • the silicon core layer is preferably composed of crystalline silicon. Among these, single crystal silicon is preferable because a photoelectric conversion element having excellent conversion efficiency can be obtained. On the other hand, polycrystalline silicon is inferior to single crystal silicon in terms of conversion efficiency, but is preferable in that a low-cost structure for a photoelectric conversion element can be obtained.
  • the thickness of the silicon core layer 1 is preferably 100 ⁇ m to 1000 ⁇ m, more preferably 100 ⁇ m to 525 ⁇ m, and particularly preferably 100 ⁇ m to 300 ⁇ m.
  • the silicon core layer 1 has a first surface 1A and a second surface 1B opposite to the first surface 1A, and macroscopically, the first surface 1A and the first surface 1A opposite to the first surface 1A. It may be a plate having two surfaces 1B.
  • the first surface 1A is observed microscopically, as shown in FIGS. 1 and 2, it has a large number of convex portions 1a. That is, the silicon core layer 1 has a plate-like shape having a fine uneven structure, particularly an uneven structure (I) described later, on the first surface 1A.
  • the surface of the convex portion 1a is referred to as a convex surface 1b.
  • 1 and 2 show an example in which a flat surface 1c exists between adjacent convex surfaces 1b. That is, in the example of FIG. 1 and FIG. 2, the first surface 1A is composed of a plurality of convex surfaces 1b and a flat surface 1c existing between them.
  • the flat surface is a straight line connecting the surface height at the midpoint in the region and the surface height of any point in the region based on the measurement result of AFM (atomic force microscope).
  • the inclination with respect to the substrate surface is ⁇ 10 ° or less.
  • the convex surface 1b may include a flat surface.
  • the vicinity of the apex may be a flat surface.
  • the flat surface 1c does not need to exist in all or a part between the adjacent convex surfaces 1b.
  • the 1st surface 1A in case the flat surface 1c does not exist at all is comprised by the some convex surface 1b. Since it is easy to form a layer following the convex surface 1b on the silicon core layer 1, it is preferable that the first surface 1A has a flat surface 1c.
  • the photoelectric conversion element structure 10 of the present embodiment has a concavo-convex structure (I) in which the first surface 1A has a large number of convex surfaces 1b.
  • the average height L1a of the convex surface 1b in the concavo-convex structure (I) is 100 to 1000 nm.
  • the average height L1a of the convex surface in the concavo-convex structure (I) is preferably from 100 to 800 nm, more preferably from 100 to 650 nm.
  • the photoelectric conversion element structure of the present embodiment has a concavo-convex structure (I) having an average height L1a of the convex surface 1b of 100 to 1000 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
  • the average height L1a of the convex surface (the convex surface 1b in this embodiment) is obtained as follows. First, the structure (photoelectric conversion element structure 10 in this embodiment) is cut to obtain a small square sample having a side of approximately 10 mm. The cutting is performed using, for example, a microtome or a focused ion beam apparatus (FIB) so that the cut surface is perpendicular to the second surface 1B.
  • FIB focused ion beam apparatus
  • the cutting direction for obtaining the small sample is preferably different from the lattice direction.
  • the direction different from the lattice direction it becomes easy to observe the cross-sectional shape of the plurality of convex surfaces.
  • the cutting directions for obtaining small piece samples are cut in the directions shown as s1 to s3 in FIG.
  • the cutting directions for obtaining the small sample are cut in the directions shown as s11 to s12 in FIG.
  • the cut surface of the obtained small piece sample is observed with a scanning electron microscope (SEM), and a cross-sectional image is obtained at a magnification capable of measuring approximately three convex surfaces per image from the cut surface.
  • SEM scanning electron microscope
  • 10 or more cross-sectional images having the same magnification are obtained, a total of 30 convex surfaces are selected, and the height L1 of each convex surface is obtained.
  • L2 to L7 described later are also obtained by observing each convex surface for which the height L1 has been obtained.
  • each convex surface 1b is the height of the vertex T of the convex surface 1b with reference to the lowest part of the convex surface. Since the lowest part of the convex surface that can be observed from the cut surface can be grasped between the convex surfaces of the adjacent convex parts, the intermediate height between them is the lowest part of the convex surface. If there is a flat surface between the convex surface of both adjacent convex portions, and the flat surface exists between the adjacent convex surfaces, the boundary between the flat surface and the convex surface is the lowermost portion between the adjacent convex surfaces It is. When there is no flat surface between the adjacent convex surfaces, the lowest point between the adjacent convex surfaces is the lowest portion between the adjacent convex surfaces.
  • a flat surface 1c exists between the convex surface 1b of one convex portion 1a (center in the case of FIG. 3) and the convex surface 1b adjacent to the convex surface 1b (right side in the case of FIG. 3).
  • the point Ba which is the boundary between the flat surface 1c and the convex surface 1b is the lowermost portion between the adjacent convex surface 1b.
  • the lowest point Bb between the adjacent convex surface 1b is the lowermost portion between the adjacent convex surface 1b.
  • the average height L1a is obtained by averaging the heights L1 of the 30 convex surfaces thus obtained.
  • the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm.
  • the photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
  • the average pitch P1a of the convex surface (the convex surface 1b in the present embodiment) is obtained as follows. First, the structure (photoelectric conversion element structure 10 in this embodiment) is cut to obtain a small square sample having a side of approximately 10 mm. The cutting is performed using, for example, a microtome or a focused ion beam apparatus (FIB) so that the cut surface is perpendicular to the second surface 1B.
  • FIB focused ion beam apparatus
  • An adjacent convex surface is a convex surface adjacent along the lattice direction. For example, when a large number of convex surfaces 1b are arranged in a triangular lattice pattern, adjacent convex surfaces are adjacent convex surfaces along the directions indicated by t1 to t3 in FIG.
  • the adjacent convex surfaces are adjacent convex surfaces along the directions indicated by t11 to t12 in FIG.
  • the average pitch P1a is obtained by averaging the 30 distances P1 thus obtained.
  • the aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (I) is preferably 0.1 to 10, more preferably 0.5 to 5.0, and particularly preferably 0.7 to 3.0. preferable. Since the structure for photoelectric conversion elements of this embodiment has a preferable aspect ratio, the antireflection effect is enhanced and a large amount of sunlight can be taken in. Further, the shell forming gas reaches the base of the wire structure, and the silicon shell layer can be uniformly deposited without filling between the wire structures. Furthermore, the conversion efficiency can be improved by increasing the pn junction area.
  • convex surfaces in the concavo-convex structure (I) satisfy the following condition X.
  • Condition X When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
  • L1a is the average height of the above-mentioned convex surface
  • L2a, L3a, L4a, L5a, L6a, and L7a are the average of L2, L3, L4, L5, L6, and L7, respectively, and L2 calculates
  • the bottom width, L3, L4, L5, L6, and L7 of the convex surface at the bottom of the convex surface are 1/4, 1/2, 3/4, It is the width of the convex surface at 7/8 and 15/16
  • the condition X more preferably satisfies the following formulas (1-1) to (6-1) and (7), and further satisfies the following formulas (1-2) to (6-2) and (7).
  • L1a / L2a 0.4 to 7.5
  • (1-1) L3a / L2a 0.75 to 0.98
  • L4a / L2a 0.42 to 0.89
  • (3-1) L5a / L2a 0.25 to 0.71
  • (4-1) L6a / L2a 0.13 to 0.59
  • (5-1) L7a / L2a 0.05 to 0.5 (6-1) L2a ⁇ L3a ⁇ L4a ⁇ L5a ⁇ L6a ⁇ L7a (7)
  • the height L1 of each convex surface is the height of the apex of the convex surface with reference to the lowest part of the convex surface.
  • L2 is the bottom width of the convex surface at the bottom of the convex surface for which L1 was obtained.
  • the lowermost part is the intermediate height of the lowermost part that is grasped between the adjacent convex surfaces. Therefore, as long as the heights that can be grasped do not completely coincide, the convex surface at the lowermost portion exists only on one side, and the other convex surface exists only above the lowermost portion. Therefore, the position of the other convex surface is obtained by extrapolating to the lowest part.
  • the position of one convex surface 1b at the lowermost part of the convex surface 1b is 1ba
  • the position of the other convex surface 1b is obtained by extrapolating the convex surface 1b from the point Bb and reaching the lowest position. It is position 1bb.
  • the distance between the position 1ba and the position 1bb is L2.
  • L3, L4, L5, L6, and L7 are respectively 1/4, 1/2, 3/4, 7/8, and 15/16 of the height L1 with respect to the lowest part of the convex surface for which L1 and L2 are obtained. 4 is a distance indicated by an arrow in FIG. L30, L3, L4, L5, L6, L7 are obtained in this way for each of the 30 convex surfaces selected when the average height L1a is obtained, and these are averaged to obtain L2a, L3a, L4a, L5a, L6a and L7a are obtained.
  • L1a / L2a is substantially equal to the aspect ratio of the concavo-convex structure (I).
  • the convex surface 1b in the cross section is circular or nearly circular.
  • the convex surface 1b satisfying the condition X is a columnar shape, a truncated cone shape, a bell shape, a cone shape, a side surface.
  • the shape becomes a conical shape or a truncated cone shape.
  • a large number of convex surfaces 1b are two-dimensionally arranged on the first surface 1A.
  • the arrangement of the multiple convex surfaces 1b may be periodic or aperiodic. In the case of non-periodic arrangement, it is particularly preferable that the structure is a polycrystalline structure in which there are a plurality of areas arranged periodically and the arrangement of the areas is not uniform.
  • “Many convex surfaces 1b are periodically arranged in two dimensions” means a state in which many convex surfaces 1b are periodically arranged in at least two directions on the first surface 1A.
  • the orientation direction is two directions and the intersection angle is 90 ° (square lattice), the orientation direction is three directions and the intersection angle is 60 ° ( Triangular lattice, hexagonal lattice) and the like.
  • the photoelectric conversion element structure 10 of the present embodiment can be manufactured by dry-etching a silicon wafer that has been doped n-type or p-type in advance using an etching mask.
  • the etching mask include a particle mask, a resist mask by photolithography and nanoimprinting.
  • it is preferable to use a particle mask because a concavo-convex structure having an appropriate periodicity can be formed at low cost and can easily cope with a large area. That is, the photoelectric conversion element structure of the present embodiment is obtained by arranging particles on a silicon wafer doped n-type or p-type in advance (particle arranging step) and performing dry etching as an arranged particle mask. It is preferable to manufacture (etching process).
  • the particles used as the mask are preferably inorganic particles, but organic polymer materials can also be used depending on the conditions.
  • inorganic particles for example, particles composed of oxides, nitrides, carbides, borides, sulfides, selenides, metals and the like, metal particles, and the like can be used.
  • organic particles thermoplastic resins such as polystyrene and PMMA, thermosetting resins such as phenol resins and epoxy resins, and the like can be used.
  • a single particle film mask with a single layer As a method for forming a single-layer, uniform single-particle film mask, a dropping step of dropping a dispersion in which particles are dispersed in a solvent having a specific gravity smaller than that of water on the surface of water in a water tank; A method having a single particle film forming step of forming a single particle film composed of the particles on the liquid surface of water by volatilization and a transfer step of transferring the single particle film onto a silicon wafer (for example, (See Japanese Patent No. 6036830). After the transfer step, a fixing step for fixing the transferred single particle film to the silicon wafer may be performed.
  • the single particle film forming step is preferably performed under ultrasonic irradiation conditions.
  • the solvent of the dispersion liquid is volatilized while irradiating ultrasonic waves from the lower water to the water surface, the closest packing of particles is promoted, and a single particle film in which each particle is two-dimensionally closely packed with higher accuracy is obtained. It is done.
  • the output of the ultrasonic wave is preferably 1 W to 1200 W, and more preferably 50 W to 600 W.
  • it is preferable to employ a so-called LB trough method see Journal of Materials and Chemistry, Vol. 11, 3333 (2001), Journal of Materials and Chemistry, Vol. 12, 3268 (2002), etc.).
  • the following method may be adopted. 1) A silicon wafer is immersed in a suspension of colloidal particles, and then the second and higher particle layers are removed leaving only the first particle layer electrostatically bonded to the substrate (particle adsorption method). Thus, an etching mask made of a single particle film is provided on the substrate (see Japanese Patent Laid-Open No. 58-120255). 2) A binder layer is formed on a silicon wafer, a particle dispersion is applied thereon, and then the binder layer is softened by heating, so that only the first particle layer is embedded in the binder layer. A method of washing away excess particles (see JP-A-2005-279807).
  • the particles are dry-etched under a condition that the silicon wafer is substantially less likely to be etched than the particles (particle-etching process). Wafer etching step). Thereby, it becomes easy to make the uneven structure in which the flat surface 1c exists.
  • the shape control for forming the concavo-convex structure becomes easier when the dry etching rate of the silicon wafer exceeds the etching rate of the particles, and therefore the dry etching selectivity of the formula (9) needs to be larger than 100%.
  • the dry etching selectivity of the formula (9) in the wafer etching process is preferably 150% or more, and more preferably 200% or more.
  • the dry etching selection ratio can be adjusted by appropriately selecting an etching gas (see, for example, Japanese Patent No. 6036830).
  • the termination treatment include a method of annealing with nitrogen or hydrogen.
  • the annealing temperature is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C.
  • the annealing time depends on the annealing temperature, but is preferably 5 to 60 minutes, more preferably 10 to 45 minutes.
  • a natural oxide film having a thickness of about 1 to 2 nm is formed on the surface of the silicon wafer.
  • Annealing with nitrogen or hydrogen is performed without removing the natural oxide film.
  • the presence of the natural oxide film can prevent the concavo-convex structure from being brittle and easily broken by the slite etching with nitrogen or hydrogen.
  • hydrogen diffuses and permeates through the layer of the natural oxide film and reaches the SiO 2 / Si interface, even if there is a natural oxide film, the termination process is not hindered.
  • Chemical polishing etching is performed using, for example, a mixed solution of hydrofluoric acid and nitric acid.
  • CPE Chemical polishing etching
  • the convex portion 1a itself is thinned and the distance between the convex surfaces 1b is widened because the surface between the convex surface 1b and the surface of the convex surface 1b is etched.
  • deposits on the surface of the structure may be removed with hydrofluoric acid, a mixed solution of sulfuric acid and hydrogen peroxide (piranha solution), or the like.
  • FIG. 5 shows a photoelectric conversion element structure 20 according to the second embodiment.
  • the photoelectric conversion element structure 20 of this embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, and a silicon shell layer 2 formed on the first surface A of the silicon core layer 1. I have.
  • the silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the silicon shell layer 2 is provided so as to form a pn junction with the silicon core layer 1 and is made of silicon doped p-type or n-type. That is, when the silicon core layer 1 is doped n-type, the silicon shell layer 2 is doped p-type. When the silicon core layer 1 is doped p-type, the silicon shell layer 2 is doped n-type. As the dopant of the silicon shell layer 2, the same dopants as those described as the dopant of the silicon core layer 1 can be used.
  • the photoelectric conversion element structure 20 of the present embodiment has a concavo-convex structure (II) in which the surface 2A of the silicon shell layer 2 has a large number of convex surfaces 2b.
  • the concavo-convex structure (II) is composed of a plurality of convex surfaces 2b and a flat surface 2c between adjacent convex surfaces 2b.
  • the average height L1a of the convex surface 2b in the concavo-convex structure (II) is 100 to 1000 nm.
  • the average height L1a is preferably 150 to 900 nm, more preferably 200 to 750 nm.
  • the photoelectric conversion element structure of the present embodiment has a concavo-convex structure (II) having an average height L1a of the convex surface 2b of 100 to 1000 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
  • the method for obtaining the average height L1a is the same as the method for obtaining the average height of the concavo-convex structure (I) of the first embodiment, and the height of the apex of the convex surface 2b with reference to the lowest part of the convex surface 2b. Obtained by averaging L1.
  • the flat surface 2c does not need to exist in all or a part between the adjacent convex surfaces 2b.
  • the surface 2A of the silicon shell layer 2 when the flat surface 2c does not exist at all is constituted by a plurality of convex surfaces 2b. Since a layer that follows the convex surface 2 b is easily formed on the silicon shell layer 2, it is preferable that a flat surface 2 c exists on the surface 2 A of the silicon shell layer 2.
  • the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm.
  • the photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
  • the method for obtaining the average pitch P1a is the same as the method for obtaining the average pitch P1a of the convex surface 1b in the concavo-convex structure (I) of the first embodiment, and the apexes of adjacent convex surfaces 2b forming a triangular lattice or a square lattice. Is obtained by averaging the distance P1 between the two.
  • the aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (II) is preferably 0.1 to 10, more preferably 0.3 to 7, and particularly preferably 0.5 to 5.
  • the aspect ratio when the aspect ratio is in a preferable range, the carrier movement distance in the vertical direction is shortened, and the probability of recombination can be reduced.
  • the multiple convex surfaces 2b in the concavo-convex structure (II) satisfy the condition X.
  • a preferable aspect in the condition X is the same as that in the first embodiment.
  • the convex surface 2b in the cross section is circular or nearly circular.
  • the convex surfaces 2b are arranged two-dimensionally.
  • sequence of the convex surface 2b is the same as the preferable aspect regarding the arrangement
  • the thickness of the silicon shell layer 2 is preferably 20 to 300 nm, and more preferably 50 to 200 nm.
  • the thickness of the silicon shell layer 2 can be determined by observation with a transmission electron microscope (TEM).
  • the concavo-convex structure on the surface of the silicon core layer 1 on the silicon shell layer 2 side is preferably the concavo-convex structure (I) of the first embodiment, and the preferable form of the concavo-convex structure (I) is the same as that of the first embodiment. .
  • a certain layer (tentatively referred to as a “first layer” in this paragraph) follows the uneven structure of another certain layer (referred to as a “second layer” in this paragraph). Then, although the concavo-convex structure that matches the concavo-convex structure of the second layer is not obtained, the first layer is formed with a uniform thickness with respect to the concavo-convex structure of the second layer. It means that the concavo-convex structure of the layer is formed.
  • the thickness of the first layer (the length of the perpendicular from the point on the surface of the first layer to the surface of the concavo-convex structure of the second layer) ) Is constant with respect to the concave-convex structure of the second layer.
  • uniform thickness includes “substantially uniform thickness”
  • Thickness is constant includes “thickness is substantially constant”. . “Having substantially uniform thickness” or “thickness is almost constant” may mean that the error in thickness is 100 nm or less, preferably 30 nm or less.
  • the photoelectric conversion element structure 20 of the present embodiment is preferably manufactured by forming the silicon shell layer 2 on the photoelectric conversion element structure 10 of the first embodiment.
  • Examples of the method for forming the silicon shell layer 2 on the photoelectric conversion element structure 10 include the following methods (i) and (ii), and the following method (i) is preferable.
  • Ii A method of forming the silicon shell layer 2 by drive-in diffusion of a doped dopant opposite to the photoelectric conversion element structure 10 on the first surface 1A of the photoelectric conversion element structure 10.
  • the deposition of the doped silicon material opposite to the photoelectric conversion element structure 10 in the method (i) is preferably performed by a dry process.
  • the dry process includes a chemical vapor deposition method (CVD method: chemical vapor deposition) and a physical vapor deposition method (PVD method: physical vapor deposition), and the CVD method is preferred. Since the CVD method is highly versatile and easy to control, it is easy to stably form a uniform silicon shell layer.
  • CVD method is highly versatile and easy to control, it is easy to stably form a uniform silicon shell layer.
  • the silicon shell layer 2 After forming the silicon shell layer 2 by depositing a doped silicon material opposite to the photoelectric conversion element structure 10, damage (dangling of the silicon surface) occurring on the surface of the concavo-convex structure of the silicon shell layer 2 is formed. It is preferable to perform termination treatment to remove the bond. In addition, since the annealing effect can be obtained also by the BSF process described later, the termination process at this stage may be omitted.
  • Examples of the termination treatment include a method of annealing with nitrogen or hydrogen.
  • the annealing temperature with nitrogen or hydrogen is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C.
  • the hydrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
  • a natural oxide film having a thickness of about 1 to 2 nm is formed on the surface of the formed silicon shell layer 2, and annealing with nitrogen or hydrogen is performed without removing the natural oxide film.
  • the presence of the natural oxide film can prevent the concavo-convex structure from being brittle and easily broken by the slite etching with nitrogen or hydrogen.
  • hydrogen diffuses and permeates through the layer of the natural oxide film and reaches the SiO 2 / Si interface, even if there is a natural oxide film, the termination process is not hindered.
  • the method (ii) is advantageous in that the pn junction cannot be made of defects such as unpaired electrons.
  • the heat during drive-in diffusion careful adjustment is required.
  • FIG. 6 shows a photoelectric conversion element structure 30 according to the third embodiment.
  • the photoelectric conversion element structure 30 of this embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and A transparent conductive layer 3 covering the surface of the silicon shell layer 2 opposite to the silicon core layer 1 is provided.
  • the silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the transparent conductive layer 3 is a layer formed of a transparent conductive material.
  • a transparent conductive material known materials can be used. For example, indium tin oxide (Indium Tin Oxide (ITO)), indium zinc oxide (Indium Zinc Oxide (IZO)), zinc oxide (Zinc Oxide (ZnO)), zinc-tin oxide (Zinc Tin Oxide (ZTO)) ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
  • the photoelectric conversion element structure 30 of the present embodiment has a concavo-convex structure (III) in which the surface 3A of the transparent conductive layer 3 has a large number of convex surfaces 3b.
  • the average height L1a of the convex surface 3b in the concavo-convex structure (III) is 100 to 1100 nm.
  • the average height L1a is preferably 200 to 1000 nm, and more preferably 250 to 800 nm.
  • the photoelectric conversion element structure of the present embodiment has a concavo-convex structure (III) having an average height L1a of the convex surface 3b of 100 to 1100 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
  • the method for obtaining the average height L1a is the same as the method for obtaining the average height of the concavo-convex structure (I) of the first embodiment, and the height of the apex of the convex surface 3b with reference to the lowest part of the convex surface 3b. Obtained by averaging L1.
  • a flat surface may exist in all or a part between the adjacent convex surfaces 3b. From the viewpoint of enhancing the antireflection effect and increasing the area of the pn junction, it is preferable that the surface 3A of the transparent conductive layer 3 has no flat surface.
  • the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm.
  • the photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
  • the method for obtaining the average pitch P1a is the same as the method for obtaining the average pitch P1a of the concavo-convex structure (I) of the first embodiment, between the vertices of adjacent convex surfaces 3b forming a triangular lattice or a square lattice. It is obtained by averaging the distance P1.
  • the aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (III) is preferably from 0.1 to 10, more preferably from 0.3 to 7, and particularly preferably from 0.5 to 5. Since the structure for photoelectric conversion elements of this embodiment has a preferable aspect ratio, the antireflection effect is enhanced and a large amount of sunlight can be taken in. It is preferable that the multiple convex surfaces 3b in the concavo-convex structure (III) satisfy the condition X. A preferable aspect in the condition X is the same as that in the first embodiment.
  • the convex surface 3b in the cross section thereof is circular or nearly circular.
  • the convex surfaces 3b are arranged two-dimensionally.
  • sequence of the convex surface 3b is the same as the preferable aspect regarding the arrangement
  • An uneven structure is formed on the surface (first surface) of the silicon core layer 1 on the silicon shell layer 2 side, and the silicon shell layer 2 is formed so as to follow the uneven structure of the silicon core layer 1.
  • the thickness of the silicon shell layer 2 is preferably 20 to 300 nm, and more preferably 50 to 200 nm.
  • the transparent conductive layer 3 is formed so as to follow the uneven structure of the silicon shell layer 2.
  • the thickness of the transparent conductive layer 3 is preferably 10 to 200 nm, more preferably 20 to 100 nm.
  • the thickness of the transparent conductive layer 3 can be determined by observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM).
  • the concavo-convex structure on the surface of the silicon core layer 1 on the silicon shell layer 2 side is preferably the concavo-convex structure (I) of the first embodiment, and the preferable form of the concavo-convex structure (I) is the same as that of the first embodiment.
  • the concavo-convex structure on the surface of the silicon shell layer 2 on the transparent conductive layer 3 side is preferably the concavo-convex structure (II) of the second embodiment, and the preferable aspect of the concavo-convex structure (II) is the same as that of the second embodiment. .
  • the photoelectric conversion element structure 30 of the present embodiment is preferably manufactured by forming the transparent conductive layer 3 on the photoelectric conversion element structure 20 of the second embodiment.
  • the formation of the transparent conductive layer 3 is preferably performed by a dry process.
  • the dry process includes a chemical vapor deposition method (CVD method: chemical vapor deposition) and a physical vapor deposition method (PVD method: physical vapor deposition), and the CVD method is preferred.
  • CVD method chemical vapor deposition method: chemical vapor deposition
  • PVD method physical vapor deposition
  • FIG. 7 shows a photoelectric conversion element 40 according to the fourth embodiment.
  • the photoelectric conversion element 40 of this embodiment includes a silicon core layer 1 made of silicon doped in n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and a silicon shell layer. 2, a transparent conductive layer 3 covering the surface opposite to the silicon core layer 1, a back barrier layer (BSF layer) 4 and a back electrode 5 sequentially formed on the second surface 1 B of the silicon core layer 1. .
  • BSF layer back barrier layer
  • the silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the transparent conductive layer 3 is preferably the same as the transparent conductive layer 3 of the photoelectric conversion element structure 30 of the third embodiment, and a preferable aspect thereof is also the same, and thus detailed description thereof is omitted.
  • the back barrier layer 4 is a layer provided between the silicon core layer 1 and the back electrode 5 in order to improve conversion efficiency.
  • the back barrier layer 4 is a densely doped n + layer that blocks holes by a barrier between nn + and near the back electrode 5 It plays a role of suppressing recombination.
  • the back barrier layer 4 is a densely doped p + layer, blocks electrons by the barrier between pp + , and closes the back electrode 5 It plays a role of suppressing recombination.
  • the back electrode 5 is an n-electrode that extracts electrons when the silicon core layer 1 is doped n-type, and a p-electrode that extracts holes when the silicon core layer 1 is doped p-type.
  • Examples of the material for the back electrode 5 include aluminum, silver, titanium, and alloys thereof.
  • the back surface barrier layer 4 is not essential and may be omitted. That is, the back electrode 5 may be directly formed on the second surface 1B of the silicon core layer 1.
  • the photoelectric conversion element 40 of this embodiment can be manufactured by performing the BSF process on the photoelectric conversion element structure 30 of the third embodiment to form the back barrier layer 4 and then forming the back electrode 5. preferable.
  • the thickness of the back barrier layer 4 can be selected within a range obvious to those skilled in the art.
  • Examples of the BSF treatment for forming the n + layer include a method in which a phosphorus-based concentrated solution is spin-coated on the second surface 1B of the silicon core layer 1 and sintered, followed by nitrogen annealing.
  • a phosphorus-based concentrated solution for example, an OCD (registered trademark) solution manufactured by Tokyo Ohka Kogyo Co., Ltd. can be used.
  • the temperature of nitrogen annealing is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C. Further, the nitrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
  • Examples of the BSF treatment for forming the p + layer include a method in which the second surface 1B of the silicon core layer 1 is coated with a conductive paste containing aluminum or silver and sintered.
  • a conductive paste containing aluminum or silver and sintered For example, Alsolar (registered trademark) manufactured by Toyo Aluminum Co., Ltd. can be used as the conductive paste.
  • the temperature of nitrogen annealing is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C. Further, the nitrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
  • the back electrode 5 can be formed by a method such as vapor deposition or sputtering. The thickness of the back electrode 5 can be selected within a range obvious to those skilled in the art.
  • FIG. 8 shows a photoelectric conversion element 50 according to the fifth embodiment.
  • the photoelectric conversion element 50 of the present embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and a silicon shell layer A transparent conductive layer 3 covering the surface opposite to the silicon core layer 1, a back barrier layer (BSF layer) 4 formed on the second surface 1 B of the silicon core layer 1, a back electrode 5, and a transparent conductive layer A surface electrode 6 is provided in contact with the layer 3 in an electrically conductive state.
  • BSF layer back barrier layer
  • the silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
  • the transparent conductive layer 3 is preferably the same as the transparent conductive layer 3 of the photoelectric conversion element structure 30 of the third embodiment, and a preferable aspect thereof is also the same, and thus detailed description thereof is omitted.
  • the back surface barrier layer 4 and the back surface electrode 5 are preferably the same as the back surface barrier layer 4 and the back surface electrode 5 of the photoelectric conversion element 40 of the fourth embodiment, and preferable aspects are also the same, and thus detailed description thereof is omitted. To do.
  • the surface electrode 6 is a p-electrode for extracting holes when the silicon core layer 1 is doped n-type, and an n-electrode for extracting electrons when the silicon core layer 1 is doped p-type. .
  • the surface electrode 6 is preferably composed of thin grid lines. Thereby, sufficient electrical continuity with the transparent conductive layer 3 can be achieved without hindering the arrival of light to the pn junction surface.
  • Examples of the material of the back electrode 6 include aluminum, silver, titanium, and alloys thereof.
  • the back barrier layer 4 is not essential and may be omitted. That is, the back electrode 5 may be directly formed on the second surface 1B of the silicon core layer 1.
  • the photoelectric conversion element 50 of the present embodiment is preferably manufactured by forming the surface electrode 6 on the photoelectric conversion element 40 of the fourth embodiment.
  • the surface electrode 6 is formed on the photoelectric conversion element structure 30 of the third embodiment, and then the back surface barrier layer 4 is formed by performing the BSF treatment. You may manufacture by forming.
  • the surface electrode 6 can be formed by a method such as vapor deposition or sputtering.
  • FIG. 9 shows a photoelectric conversion element 60 according to the sixth embodiment.
  • the photoelectric conversion element 60 of this embodiment is the same as the photoelectric conversion element 50 according to the fifth embodiment except that the transparent conductive layer 3 is not provided.
  • the photoelectric conversion element 60 of this embodiment can be manufactured in the same manner as the photoelectric conversion element 50 according to the fifth embodiment, except that the transparent conductive layer 3 is not formed.
  • the interface between the silicon core layer and the silicon shell layer constituting the pn junction is a convex surface having a sufficient height.
  • carrier collection at the pn junction occurs not only in the vertical direction but also in the horizontal direction (radial direction of the concavo-convex structure), so that the conversion efficiency can be improved.
  • the convex surface satisfies the condition X, it is considered that carrier collection occurs more efficiently in the horizontal direction (radial direction of the concavo-convex structure).
  • the relatively low height of the convex surface shortens the vertical carrier movement distance, thereby reducing the probability of recombination.
  • Example 1 A 20% by mass aqueous dispersion of spherical colloidal silica having an average particle size of 600 nm and a particle size variation coefficient of 1.72% was prepared. The average particle diameter and the coefficient of variation of the particle diameter were determined from peaks obtained by fitting the particle size distribution determined by the particle dynamic light scattering method to a Gaussian curve. As a measuring device, Zetasizer Nano-ZS manufactured by Malvern Instruments Ltd. which can measure particles having a particle size of about 10 nm to 3 ⁇ m by a dynamic light scattering method was used.
  • This aqueous dispersion was filtered through a membrane filter having a pore diameter of 1.2 ⁇ m ⁇ .
  • An aqueous solution of a hydrolyzate of phenyltriethoxysilane having a concentration of 1.0% by mass was added to the aqueous dispersion that passed through the membrane filter and reacted at about 40 ° C. for 3 hours to obtain a reaction solution.
  • the aqueous dispersion and the hydrolyzate aqueous solution were mixed so that the mass of phenyltriethoxysilane was 0.02 times the mass of the colloidal silica particles.
  • reaction liquid methyl isobutyl ketone having a volume 4 times the volume of this reaction liquid was added and stirred sufficiently, and the hydrophobized colloidal silica was subjected to oil phase extraction to obtain a hydrophobic concentration of 0.91% by mass. A colloidal silica dispersion was obtained.
  • Water tank (LB trough device) provided with a hydrophobized colloidal silica dispersion thus obtained, a surface pressure sensor for measuring the surface pressure of the single particle film, and a movable barrier for compressing the single particle film in the direction along the liquid surface
  • the solution was added dropwise to the inside liquid surface (water was used as the lower layer water, water temperature 25 ° C.) at a dropping rate of 0.01 mL / second.
  • An n-type Si substrate (15 mm ⁇ 15 mm, thickness: 0.525 mm) having a flat surface was immersed in a substantially vertical direction in advance in the lower layer water of the water tank.
  • ultrasonic waves (output: 300 W, frequency: 950 kHz) are irradiated from the lower layer water toward the water surface for 10 minutes to volatilize methyl isobutyl ketone, which is the solvent of the dispersion, while urging the particles to be two-dimensionally closely packed.
  • the single particle film was compressed by a movable barrier until the diffusion pressure became 25 mNm ⁇ 1 , the substrate was pulled up at a speed of 5 mm / min, and transferred onto one side of the substrate to obtain a substrate with a single particle film.
  • dry etching was performed on the substrate with the single particle film. Specifically, dry etching was performed using a mixed gas of CF 4 and O 2 as a particle etching process. Etching conditions were an antenna power of 1700 W, a bias power of 1500 W, a gas flow rate of 150 sccm, an etching selectivity of 90%, and an etching time of 250 seconds. Thereafter, dry etching was performed using a mixed gas of BCl 3 and Ar as a wafer etching process. Etching conditions were an antenna power of 1700 W, a bias power of 700 W, a gas flow rate of 150 sccm, an etching selectivity of 120%, and an etching time of 280 seconds.
  • H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 1 was obtained.
  • Example 1 A part of the structure (1) of Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. When these values were averaged, the following uneven structure (I) was formed.
  • a silicon shell layer 2 having a thickness of 100 nm is formed by CVD, and has a large number of convex surfaces 2b forming a triangular lattice.
  • the structure (2) of Example 1 in which the concavo-convex structure (II) was formed was obtained.
  • the CVD conditions silane gas and diborane were used as source gases, the flow rate was 20 sccm, the pressure in the chamber was 800 Pa, and the film formation time was 3 minutes.
  • the structure (2) of Example 1 had a good p / n junction interface between the silicon core layer 1 and the silicon shell layer 2.
  • a part of the structure (2) of Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. When these values were averaged, the following uneven structure (II) was formed.
  • Example 2 The structure (2) of Example 2 was obtained by the same process and method as the structure (2) of Example 1. Thereafter, an OCD (registered trademark) solution manufactured by Tokyo Ohka Kogyo Co., Ltd. is spin-coated on the second surface 1B of the silicon core layer 1, sintered at 450 ° C. for 30 minutes, and further annealed at 850 ° C. for 30 minutes in a nitrogen atmosphere.
  • the back barrier layer 4 (BSF layer) was formed. Further, the back electrode 5 having a thickness of 250 nm was formed by the same processing method as in Example 1, and the solar cell of Example 2 was produced. When the solar cell of Example 2 was evaluated in the same manner as in Example 1, a conversion efficiency of 8.2% was obtained.
  • Example 3 The structure (2) of Example 3 was obtained by the same process and method as the structure (2) of Example 1. Thereafter, ITO is deposited by sputtering, the transparent conductive layer 3 having a thickness of 30 nm is formed, and the concavo-convex structure (III) having a large number of convex surfaces 3b forming a triangular lattice is formed (3) )
  • Example 3 A part of the structure (3) of Example 3 was cut perpendicularly to the surface by using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
  • the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same processing method as in Example 2.
  • a solar cell was produced.
  • the solar cell of Example 3 was evaluated in the same manner as in Example 1, a conversion efficiency of 10.1% was obtained.
  • Example 4 A substrate with a single particle film was obtained in the same manner as in Example 1 except that Si substrates having different thicknesses (thickness: 0.280 mm) were used. Thereafter, dry etching was performed with a mixed gas of CF 4 and O 2 as a particle etching process. Etching conditions were an antenna power of 1700 W, a bias power of 1500 W, a gas flow rate of 150 sccm, an etching selectivity of 90%, and an etching time of 300 seconds. Thereafter, dry etching was performed using a mixed gas of BCl 3 and Ar as a wafer etching process. Etching conditions were an antenna power of 1700 W, a bias power of 500 W, a gas flow rate of 150 sccm, an etching selectivity of 120%, and an etching time of 240 seconds.
  • H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 4 was obtained.
  • Example 4 Thereafter, a silicon shell layer 2 having a thickness of 100 nm is formed by the same process and method as in Example 1, and a transparent conductive layer 3 having a thickness of 30 nm is formed by the same process and method as in Example 3 The structure (3) of Example 4 was obtained.
  • Example 4 A part of the structure (3) of Example 4 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
  • the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same processing method as in Example 2.
  • a solar cell was produced.
  • the solar cell of Example 4 was evaluated in the same manner as in Example 1, a conversion efficiency of 13.7% was obtained.
  • Example 5 Similar to Example 1 except that Si substrates (thickness: 0.280 mm) having different thicknesses were used, and spherical colloidal silica having an average particle size of 300 nm and a particle size variation coefficient of 3.44% was used. A substrate with a single particle film was obtained by various methods. Thereafter, dry etching was performed with a mixed gas of BCl 3 and Cl 2 . Etching conditions were an antenna power of 1500 W, a bias power of 700 W, a gas flow rate of 100 sccm, an etching selectivity of 160%, and an etching time of 230 seconds.
  • H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 5 was obtained.
  • Example 2 a silicon shell layer 2 having a thickness of 100 nm is formed by the same process and method as in Example 1, and a transparent conductive layer 3 having a thickness of 30 nm is formed by the same process and method as in Example 3 to form a triangle.
  • Example 5 A part of the structure (3) of Example 5 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
  • the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same treatment method as in Example 2.
  • a solar cell was produced.
  • the solar cell of Example 5 was evaluated in the same manner as in Example 1, a conversion efficiency of 11.7% was obtained.
  • Example 1 A substrate with a single particle film was obtained in the same manner as in Example 1 except that spherical colloidal silica having an average particle size of 300 nm and a particle size variation coefficient of 3.44% was used. Thereafter, dry etching was performed with a mixed gas of CHF 3 and Cl 2 . Etching conditions were an antenna power of 1700 W, a bias power of 700 W, a gas flow rate of 100 sccm, an etching selectivity of 460%, and an etching time of 260 seconds.
  • H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Furthermore, as chemical polishing etching, a concavo-convex structure (I ′) having a convex surface 1b that forms a triangular lattice is formed on the first surface 1A by treatment with a mixed solution (1: 1) of nitric acid and hydrofluoric acid for 30 seconds. The structure (1) of Comparative Example 1 was obtained.
  • a silicon shell layer 2 having a thickness of 100 nm is formed by CVD, and a large number of convex surfaces 2b forming a triangular lattice are formed.
  • the structure (2) of Comparative Example 1 in which the concavo-convex structure (II ′) was formed was obtained.
  • the CVD conditions silane gas and diborane were used as source gases, the flow rate was 20 sccm, the pressure in the chamber was 800 Pa, and the film formation time was 6 minutes.
  • the structure (2) of Comparative Example 1 had a good p / n junction interface between the silicon core layer 1 and the silicon shell layer 2.
  • a portion of the structure (2) of Comparative Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (II ') was formed.
  • the photoelectric conversion element using the photoelectric conversion element of the present invention and the structure for photoelectric conversion element of the present invention can be used as a solar cell, a sensor using a pn junction, a high-sensitivity sensor for molecular adsorption identification, and the like.

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Abstract

Provided are: a structure for a photoelectric conversion element by which a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained; a method for manufacturing the same; a photoelectric conversion element; and a method for manufacturing said photoelectric conversion element. According to the present invention, a structure for a photoelectric conversion element is characterized by being provided with a silicon core layer 1 comprising n-type or p-type doped silicon, wherein the silicon core layer 1 has a first surface 1A and a second surface 1B on an opposite side to the first surface 1A, the first surface 1A has an uneven structure (I) having a plurality of convex surfaces 1b, and the average height L1a of the plurality of convex surfaces 1b in the uneven structure (I), which is the average of the heights L1 of the apexes of the convex surfaces 1b from the lowermost portions of the convex surfaces when the silicon layer 1 is cut along a plane that is perpendicular to the second surface 1B, is 100 to 1000 nm.

Description

光電変換素子用構造体とその製造方法及び光電変換素子とその製造方法STRUCTURE FOR PHOTOELECTRIC CONVERSION ELEMENT AND ITS MANUFACTURING METHOD, AND PHOTOELECTRIC CONVERSION ELEMENT AND ITS MANUFACTURING METHOD
　本発明は太陽電池等の光電変換素子、及び光電変換素子用の構造体とこれらの製造方法に関する。
　本願は、２０１８年５月１５日に、日本に出願された特願２０１８－０９４０３２号に基づき優先権を主張し、その内容をここに援用する。 The present invention relates to a photoelectric conversion element such as a solar cell, a structure for a photoelectric conversion element, and a method for manufacturing the structure.
This application claims priority on May 15, 2018 based on Japanese Patent Application No. 2018-094032 for which it applied to Japan, and uses the content here.
　太陽電池には、シリコン系、化合物半導体系等の無機半導体系と有機半導体系があるが、シリコン系、中でも結晶シリコンを使用する結晶シリコン系が主流である。
　結晶シリコン系の太陽電池は、ｎ型又はｐ型にドープされたシリコンの２種以上の半導体から形成され、異なる半導体同士の接合面（ｐｎ接合）を利用して、太陽光エネルギーを電気エネルギーに変換する。 Solar cells include inorganic semiconductor systems such as silicon and compound semiconductor systems and organic semiconductor systems. Silicon systems, particularly crystalline silicon systems using crystalline silicon, are the mainstream.
Crystalline silicon solar cells are formed from two or more semiconductors of silicon doped n-type or p-type, and solar energy is converted into electrical energy by using a junction surface (pn junction) between different semiconductors. Convert.
　結晶シリコン系の太陽電池においては、微細なワイヤー構造が櫛の歯状に多数立設したシリコン層の内部又は表面にｐｎ接合を設けることが行われている（特許文献１）。
　ワイヤー構造を有するシリコン層の内部にｐｎ接合を設ける場合は、熱拡散によるドーピングによってｐｎ接合を形成する。ドーピングにはｐｎ接合に不対電子などからなる欠陥ができない利点があるが、熱拡散によるドーピング方法自体の熱コントロールが非常に困難であり、また、ワイヤー構造１本及びワイヤー構造層全体でドーピングドープ層の厚さにバラつきが生じるため、均一にｐ層又はｎ層を作製することが困難である。ｐｎ接合が形成されていない箇所が生じる場合もあり、その場合は、素子として機能しないので、生産には不向きである欠点がある。 In a crystalline silicon-based solar cell, a pn junction is provided inside or on the surface of a silicon layer in which many fine wire structures are erected in a comb-like shape (Patent Document 1).
When a pn junction is provided inside a silicon layer having a wire structure, the pn junction is formed by doping by thermal diffusion. Doping has the advantage of not having defects such as unpaired electrons in the pn junction, but the thermal control of the doping method itself by thermal diffusion is very difficult, and doping doping is performed on one wire structure and the entire wire structure layer. Since the thickness of the layer varies, it is difficult to uniformly form the p layer or the n layer. There may be a portion where a pn junction is not formed. In that case, the pn junction does not function as an element, so that there is a disadvantage that it is not suitable for production.
　一方、ワイヤー構造を有するシリコン層（シリコンコア層）の表面にｐｎ接合を設ける場合は、蒸着やスパッタ等の薄膜製造法により、異なる半導体層（シリコンシェル層）を堆積することによってｐｎ接合を形成する。この方法はドーピング方法とは異なり、シリコンシェル層の形成が安定的にコントロール可能である利点がある。しかし、シリコンシェル層を積層する際に、ワイヤー構造の形状によっては構造頂部にシリコンシェル層が堆積してワイヤー構造間を埋めてしまい、シェル形成ガスがワイヤー構造間の根元まで届かない可能性がある。その結果、均一なｐｎ接合の形成ができず、素子としての機能が低下する恐れがある。
　したがって、微細なワイヤー構造を設けると、ｐｎ接合の面積を増加させることができ変換効率を向上させる効果が期待できるものの、ワイヤー構造の特長を充分に活かし切れていなかった。 On the other hand, when providing a pn junction on the surface of a silicon layer (silicon core layer) having a wire structure, a pn junction is formed by depositing a different semiconductor layer (silicon shell layer) by a thin film manufacturing method such as vapor deposition or sputtering. To do. Unlike the doping method, this method has an advantage that the formation of the silicon shell layer can be stably controlled. However, when laminating the silicon shell layer, depending on the shape of the wire structure, the silicon shell layer may accumulate on the top of the structure and fill the gap between the wire structures, and the shell forming gas may not reach the root between the wire structures. is there. As a result, a uniform pn junction cannot be formed, and the function as an element may be reduced.
Therefore, when a fine wire structure is provided, the area of the pn junction can be increased and the effect of improving the conversion efficiency can be expected, but the features of the wire structure have not been fully utilized.
特許第５６６９８３０号公報Japanese Patent No. 5669830
　近年自然エネルギーの活用が望まれる中、太陽電池等の光電変換素子においては、さらなる変換効率の向上が求められている。
　上記事情に鑑みて、本発明は、優れた光電変換効率が得られる光電変換素子を得るための光電変換素子用構造体とその製造方法、及び優れた光電変換効率が得られる光電変換素子とその製造方法を提供することを課題とする。 While utilization of natural energy is desired in recent years, further improvement in conversion efficiency is required for photoelectric conversion elements such as solar cells.
In view of the above circumstances, the present invention provides a structure for a photoelectric conversion element for obtaining a photoelectric conversion element capable of obtaining excellent photoelectric conversion efficiency, a method for producing the same, and a photoelectric conversion element capable of obtaining excellent photoelectric conversion efficiency. It is an object to provide a manufacturing method.
　上記の課題を達成するために、本発明は以下の構成を採用した。
［１］ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層を備える光電変換素子用構造体であって、
　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
　前記第１の表面が、多数の凸面を有する凹凸構造（Ｉ）とされており、
　前記凹凸構造（Ｉ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１０００ｎｍであることを特徴とする光電変換素子用構造体。
［２］前記凹凸構造（Ｉ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している［１］に記載の光電変換素子用構造体。
［３］前記凹凸構造（Ｉ）における多数の凸面が、下記条件Ｘを満たす［１］又は［２］に記載の光電変換素子用構造体。
（条件Ｘ）
　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。
［４］ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層と、前記シリコンコア層とｐｎ接合を形成するように設けられた、ｐ型又はｎ型にドープされたシリコンからなるシリコンシェル層とを備える光電変換素子用構造体であって、
　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
　前記シリコンシェル層は前記第１の表面に前記ｐｎ接合を形成するように設けられ、
　前記シリコンシェル層の表面が、多数の凸面を有する凹凸構造（ＩＩ）とされており、
　前記凹凸構造（ＩＩ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１０００ｎｍであることを特徴とする光電変換素子用構造体。
［５］前記凹凸構造（ＩＩ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している［４］に記載の光電変換素子用構造体。
［６］前記凹凸構造（ＩＩ）における多数の凸面が、下記条件Ｘを満たす［４］又は［５］に記載の光電変換素子用構造体。
（条件Ｘ）
　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。
［７］前記シリコンコア層の前記第１の表面が凹凸構造とされており、前記凹凸構造（ＩＩ）は、前記シリコンコア層の前記第１の表面の凹凸構造に追従している［４］～［６］のいずれかに記載の光電変換素子用構造体。
［８］ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層と、前記シリコンコア層とｐｎ接合を形成するように設けられた、ｐ型又はｎ型にドープされたシリコンからなるシリコンシェル層と、前記シリコンシェル層の表面を覆う透明導電層とを備える光電変換素子用構造体であって、
　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
　前記シリコンシェル層は前記第１の表面に前記ｐｎ接合を形成するように設けられ、
　前記透明導電層の表面が、多数の凸面を有する凹凸構造（ＩＩＩ）とされており、
　前記凹凸構造（ＩＩＩ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１１００ｎｍであることを特徴とする光電変換素子用構造体。
［９］前記凹凸構造（ＩＩＩ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している［８］に記載の光電変換素子用構造体。
［１０］前記凹凸構造（ＩＩＩ）における多数の凸面が、下記条件Ｘを満たす［８］又は［９］に記載の光電変換素子用構造体。
（条件Ｘ）
　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。
［１１］前記シリコンコア層の前記第１の表面が凹凸構造とされており、前記シリコンシェル層の表面は、前記シリコンコア層の前記第１の表面の凹凸構造に追従した凹凸構造とされており、前記凹凸構造（ＩＩＩ）は、前記シリコンコア層の前記第１の表面の凹凸構造及び前記シリコンシェル層の表面の凹凸構造に追従している［８］～［１０］のいずれかに記載の光電変換素子用構造体。
［１２］［８］～［１１］のいずれかに記載の光電変換素子用構造体と、前記シリコンコア層の前記第２の表面に、直接又は間接的に設けられた裏面電極を備えることを特徴とする光電変換素子。
［１３］さらに、前記透明導電層に、電気的に導通可能な状態で接触する表面電極を備える［１２］に記載の光電変換素子。
［１４］［４］～［７］のいずれかに記載の光電変換素子用構造体と、前記シリコンコア層の前記第２の表面に、直接又は間接的に設けられた裏面電極を備えることを特徴とする光電変換素子。
［１５］さらに、前記シリコンシェル層に、電気的に導通可能な状態で接触する表面電極を備える［１４］に記載の光電変換素子。
［１６］［１］～［３］のいずれかに記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成することを特徴とする光電変換素子用構造体の製造方法。
［１７］前記形成したシリコンシェル層の表面に、さらに透明導電材料を堆積させて透明導電層を形成する［１６］に記載の光電変換素子用構造体の製造方法。
［１８］［１］～［３］のいずれかに記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成し、前記形成したシリコンシェル層の表面に、透明導電材料を堆積させて透明導電層を形成し、
　さらに、前記シリコンコア層の前記第２の表面に、直接又は間接的に裏面電極を設けることを特徴とする光電変換素子の製造方法。
［１９］さらに、前記透明導電層と電気的に導通可能な状態で接触する表面電極を設ける［１８］に記載の光電変換素子の製造方法。
［２０］［１］～［３］のいずれかに記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成し、
　さらに、前記シリコンコア層の前記第２の表面に、直接又は間接的に裏面電極を設けることを特徴とする光電変換素子の製造方法。
［２１］さらに、前記シリコンシェル層と電気的に導通可能な状態で接触する表面電極を設ける［２０］に記載の光電変換素子の製造方法。 In order to achieve the above object, the present invention employs the following configuration.
[1] A photoelectric conversion element structure including a silicon core layer made of silicon doped in n-type or p-type,
The silicon core layer has a first surface and a second surface opposite the first surface;
The first surface is a concavo-convex structure (I) having a number of convex surfaces,
A large number of convex surfaces in the concavo-convex structure (I) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1000 nm.
[2] The photoelectric conversion element structure according to [1], wherein a large number of convex surfaces in the concavo-convex structure (I) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
[3] The photoelectric conversion element structure according to [1] or [2], in which a number of convex surfaces in the uneven structure (I) satisfy the following condition X.
(Condition X)
When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
L1a / L2a = 0.1 to 10.0 (1)
L3a / L2a = 0.7 to 1.0 (2)
L4a / L2a = 0.4 to 0.9 (3)
L5a / L2a = 0.15 to 0.8 (4)
L6a / L2a = 0.07 to 0.7 (5)
L7a / L2a = 0.03 to 0.6 (6)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
[4] A silicon core layer made of silicon doped n-type or p-type, and a silicon shell made of silicon doped p-type or n-type provided to form a pn junction with the silicon core layer A structure for a photoelectric conversion element comprising a layer,
The silicon core layer has a first surface and a second surface opposite the first surface;
The silicon shell layer is provided to form the pn junction on the first surface;
The surface of the silicon shell layer is a concavo-convex structure (II) having a large number of convex surfaces,
A large number of convex surfaces in the concavo-convex structure (II) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1000 nm.
[5] The photoelectric conversion element structure according to [4], wherein a large number of convex surfaces in the concavo-convex structure (II) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
[6] The photoelectric conversion element structure according to [4] or [5], wherein a large number of convex surfaces in the uneven structure (II) satisfy the following condition X.
(Condition X)
When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
L1a / L2a = 0.1 to 10.0 (1)
L3a / L2a = 0.7 to 1.0 (2)
L4a / L2a = 0.4 to 0.9 (3)
L5a / L2a = 0.15 to 0.8 (4)
L6a / L2a = 0.07 to 0.7 (5)
L7a / L2a = 0.03 to 0.6 (6)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
[7] The first surface of the silicon core layer has an uneven structure, and the uneven structure (II) follows the uneven structure on the first surface of the silicon core layer. The structure for a photoelectric conversion element according to any one of to [6].
[8] A silicon core layer made of silicon doped n-type or p-type, and a silicon shell made of silicon doped p-type or n-type provided to form a pn junction with the silicon core layer A photoelectric conversion element structure comprising a layer and a transparent conductive layer covering the surface of the silicon shell layer,
The silicon core layer has a first surface and a second surface opposite the first surface;
The silicon shell layer is provided to form the pn junction on the first surface;
The surface of the transparent conductive layer is a concavo-convex structure (III) having a large number of convex surfaces,
A number of convex surfaces in the concavo-convex structure (III) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut by a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1100 nm.
[9] The photoelectric conversion element structure according to [8], wherein a large number of convex surfaces in the concavo-convex structure (III) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
[10] The photoelectric conversion element structure according to [8] or [9], wherein a number of convex surfaces in the uneven structure (III) satisfy the following condition X.
(Condition X)
When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
L1a / L2a = 0.1 to 10.0 (1)
L3a / L2a = 0.7 to 1.0 (2)
L4a / L2a = 0.4 to 0.9 (3)
L5a / L2a = 0.15 to 0.8 (4)
L6a / L2a = 0.07 to 0.7 (5)
L7a / L2a = 0.03 to 0.6 (6)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
[11] The first surface of the silicon core layer has an uneven structure, and the surface of the silicon shell layer has an uneven structure following the uneven structure of the first surface of the silicon core layer. The uneven structure (III) follows the uneven structure on the first surface of the silicon core layer and the uneven structure on the surface of the silicon shell layer, according to any one of [8] to [10]. The structure for photoelectric conversion elements.
[12] The photoelectric conversion element structure according to any one of [8] to [11], and a back electrode provided directly or indirectly on the second surface of the silicon core layer. A characteristic photoelectric conversion element.
[13] The photoelectric conversion element according to [12], further comprising a surface electrode that is in contact with the transparent conductive layer in an electrically conductive state.
[14] The photoelectric conversion element structure according to any one of [4] to [7], and a back electrode provided directly or indirectly on the second surface of the silicon core layer. A characteristic photoelectric conversion element.
[15] The photoelectric conversion element according to [14], further comprising a surface electrode in contact with the silicon shell layer in an electrically conductive state.
[16] A doped silicon material opposite to the silicon core layer is deposited on the first surface of the photoelectric conversion element structure according to any one of [1] to [3] to form a silicon shell layer. A method for producing a structure for a photoelectric conversion element, comprising: forming the structure.
[17] The method for producing a structure for a photoelectric conversion element according to [16], further comprising depositing a transparent conductive material on the surface of the formed silicon shell layer to form a transparent conductive layer.
[18] A doped silicon material opposite to the silicon core layer is deposited on the first surface of the photoelectric conversion element structure according to any one of [1] to [3] to form a silicon shell layer. Forming a transparent conductive layer by depositing a transparent conductive material on the surface of the formed silicon shell layer;
Furthermore, the back surface electrode is provided directly or indirectly on the second surface of the silicon core layer.
[19] The method for producing a photoelectric conversion element according to [18], further comprising providing a surface electrode in contact with the transparent conductive layer in an electrically conductive state.
[20] A doped silicon material opposite to the silicon core layer is deposited on the first surface of the photoelectric conversion element structure according to any one of [1] to [3] to form a silicon shell layer. Forming,
Furthermore, the back surface electrode is provided directly or indirectly on the second surface of the silicon core layer.
[21] The method for manufacturing a photoelectric conversion element according to [20], further including providing a surface electrode that is in electrical contact with the silicon shell layer.
　本発明の光電変換素子用構造体によれば、光電変換効率に優れる光電変換素子を得ることができる。また、本発明の光電変換素子は、光電変換効率に優れる。 According to the photoelectric conversion element structure of the present invention, a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained. Moreover, the photoelectric conversion element of this invention is excellent in photoelectric conversion efficiency.
本発明の第１実施形態に係る光電変換素子用構造体の表面構造を示す斜視図である。It is a perspective view which shows the surface structure of the structure for photoelectric conversion elements which concerns on 1st Embodiment of this invention. 本発明の第１実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 1st Embodiment of this invention. 本発明における平均高さ等の求め方の説明図である。It is explanatory drawing of how to obtain | require average height etc. in this invention. 本発明における条件Ｘの説明図である。It is explanatory drawing of the condition X in this invention. 本発明の第２実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 2nd Embodiment of this invention. 本発明の第３実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 3rd Embodiment of this invention. 本発明の第４実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 4th Embodiment of this invention. 本発明の第５実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 5th Embodiment of this invention. 本発明の第６実施形態に係る光電変換素子用構造体の縦断面図である。It is a longitudinal cross-sectional view of the structure for photoelectric conversion elements which concerns on 6th Embodiment of this invention. 平均高さと平均ピッチの求め方に関する説明図である。It is explanatory drawing regarding the method of calculating | requiring an average height and an average pitch. 平均高さと平均ピッチの求め方に関する説明図である。It is explanatory drawing regarding the method of calculating | requiring an average height and an average pitch.
　以下、本発明の実施形態について、図面を参照しつつ説明する。なお、各図面では、説明の便宜上表面の凹凸を強調しており、凹凸部分とそれ以外の部分の比率は正確ではない。また、各層の厚さの比率も正確ではない。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the unevenness on the surface is emphasized for convenience of explanation, and the ratio of the uneven part to the other part is not accurate. Also, the ratio of the thickness of each layer is not accurate.
［第１実施形態］
　図１、２に第１実施形態に係る光電変換素子用構造体１０を示す。本実施形態の光電変換素子用構造体１０は、ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層１で構成されている。
　ｎ型にドープする場合のドーパントとしては、例えば、リン、ヒ素が挙げられる。ｐ型にドープする場合のドーパントとしては、例えば、ホウ素が挙げられる。
　シリコンコア層は、結晶シリコンで構成されていることが好ましい。中でも単結晶シリコンは変換効率に優れる光電変換素子が得られるため好ましい。一方、多結晶シリコンは、変換効率の点では単結晶シリコンに劣るが、低コストの光電変換素子用構造体を得られる点で好ましい。
　シリコンコア層１の厚みは、１００μｍ～１０００μｍであることが好ましく、１００μｍ～５２５μｍであることがより好ましく、１００μｍ～３００μｍが特に好ましい。 [First Embodiment]
1 and 2 show a photoelectric conversion element structure 10 according to the first embodiment. The photoelectric conversion element structure 10 of the present embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type.
Examples of the dopant for doping n-type include phosphorus and arsenic. An example of the dopant for p-type doping is boron.
The silicon core layer is preferably composed of crystalline silicon. Among these, single crystal silicon is preferable because a photoelectric conversion element having excellent conversion efficiency can be obtained. On the other hand, polycrystalline silicon is inferior to single crystal silicon in terms of conversion efficiency, but is preferable in that a low-cost structure for a photoelectric conversion element can be obtained.
The thickness of the silicon core layer 1 is preferably 100 μm to 1000 μm, more preferably 100 μm to 525 μm, and particularly preferably 100 μm to 300 μm.
　シリコンコア層１は、第１の表面１Ａと第１の表面１Ａの反対側の第２の表面１Ｂを有し、巨視的には第１の表面１Ａと第１の表面１Ａの反対側の第２の表面１Ｂを有する板状とされていてよい。また、第１の表面１Ａを微視的に観察すると図１、図２に示すように、多数の凸部１ａを有している。すなわち、シリコンコア層１は、微細な凹凸構造、特に後述する凹凸構造（Ｉ）を第１の表面１Ａに有する板状とされている。凸部１ａの表面を凸面１ｂと称する。図１、図２では、隣り合う凸面１ｂの間に、平坦面１ｃが存在する例を示している。すなわち、図１、図２の例では、第１の表面１Ａは、複数の凸面１ｂと、それらの間に存在する平坦面１ｃとで構成されている。 The silicon core layer 1 has a first surface 1A and a second surface 1B opposite to the first surface 1A, and macroscopically, the first surface 1A and the first surface 1A opposite to the first surface 1A. It may be a plate having two surfaces 1B. When the first surface 1A is observed microscopically, as shown in FIGS. 1 and 2, it has a large number of convex portions 1a. That is, the silicon core layer 1 has a plate-like shape having a fine uneven structure, particularly an uneven structure (I) described later, on the first surface 1A. The surface of the convex portion 1a is referred to as a convex surface 1b. 1 and 2 show an example in which a flat surface 1c exists between adjacent convex surfaces 1b. That is, in the example of FIG. 1 and FIG. 2, the first surface 1A is composed of a plurality of convex surfaces 1b and a flat surface 1c existing between them.
　本明細書において、平坦面とは、ＡＦＭ（原子間力顕微鏡）の測定結果に基づき、その領域内の中点における表面高さと、その領域内における任意の点の表面高さとを結ぶ直線の、基板面に対する傾きが±１０゜以下である領域である。なお、凸面１ｂは平坦面を含んでいてもよい。例えば、頂点付近が平坦面であってもよい。
　本実施形態において、隣り合う凸面１ｂの間の全部又は一部には、平坦面１ｃが存在していなくてもよい。平坦面１ｃが全く存在しない場合の第１の表面１Ａは、複数の凸面１ｂで構成される。
　シリコンコア層１上に、凸面１ｂに追従する層を形成しやすいことから、第１の表面１Ａには平坦面１ｃが存在することが好ましい。 In this specification, the flat surface is a straight line connecting the surface height at the midpoint in the region and the surface height of any point in the region based on the measurement result of AFM (atomic force microscope). In this region, the inclination with respect to the substrate surface is ± 10 ° or less. The convex surface 1b may include a flat surface. For example, the vicinity of the apex may be a flat surface.
In this embodiment, the flat surface 1c does not need to exist in all or a part between the adjacent convex surfaces 1b. The 1st surface 1A in case the flat surface 1c does not exist at all is comprised by the some convex surface 1b.
Since it is easy to form a layer following the convex surface 1b on the silicon core layer 1, it is preferable that the first surface 1A has a flat surface 1c.
　本実施形態の光電変換素子用構造体１０は、第１の表面１Ａが多数の凸面１ｂを有する凹凸構造（Ｉ）とされている。凹凸構造（Ｉ）における凸面１ｂの平均高さＬ１ａは１００～１０００ｎｍである。凹凸構造（Ｉ）における凸面の平均高さＬ１ａは１００～８００ｎｍが好ましく１００～６５０ｎｍがより好ましい。本実施形態の光電変換素子用構造体は、凸面１ｂの平均高さＬ１ａが１００～１０００ｎｍの凹凸構造（Ｉ）を有することにより、光電変換効率に優れる光電変換素子を得ることができる。 The photoelectric conversion element structure 10 of the present embodiment has a concavo-convex structure (I) in which the first surface 1A has a large number of convex surfaces 1b. The average height L1a of the convex surface 1b in the concavo-convex structure (I) is 100 to 1000 nm. The average height L1a of the convex surface in the concavo-convex structure (I) is preferably from 100 to 800 nm, more preferably from 100 to 650 nm. The photoelectric conversion element structure of the present embodiment has a concavo-convex structure (I) having an average height L1a of the convex surface 1b of 100 to 1000 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
　凸面（本実施形態では凸面１ｂ）の平均高さＬ１ａは、次のように求める。
　まず、構造体（本実施形態では光電変換素子用構造体１０）を切断し、１辺が１０ｍｍ程度の略正方形の小片サンプルを得る。
　切断は、例えばミクロトームや集束イオンビーム装置（ＦＩＢ）を用い、切断面が前記第２の表面１Ｂに対して垂直になるように切断する。 The average height L1a of the convex surface (the convex surface 1b in this embodiment) is obtained as follows.
First, the structure (photoelectric conversion element structure 10 in this embodiment) is cut to obtain a small square sample having a side of approximately 10 mm.
The cutting is performed using, for example, a microtome or a focused ion beam apparatus (FIB) so that the cut surface is perpendicular to the second surface 1B.
　多数の凸面が格子状に配列している場合、小片サンプルを得るための切断方向は、格子方向と異なる方向であることが好ましい。格子方向と異なる方向とすることにより、複数の凸面の断面形状を観察しやすくなる。
　例えば、多数の凸面１ｂが三角格子状に配列している場合、小片サンプルを得るための切断方向は、図１０にｓ１～ｓ３として示す方向で切断することが好ましい。
　また、多数の凸面１ｂが正方格子状に配列している場合、小片サンプルを得るための切断方向は、図１１にｓ１１～ｓ１２として示す方向で切断することが好ましい。 When a large number of convex surfaces are arranged in a lattice pattern, the cutting direction for obtaining the small sample is preferably different from the lattice direction. By making the direction different from the lattice direction, it becomes easy to observe the cross-sectional shape of the plurality of convex surfaces.
For example, when a large number of convex surfaces 1b are arranged in a triangular lattice shape, it is preferable that the cutting directions for obtaining small piece samples are cut in the directions shown as s1 to s3 in FIG.
Further, when a large number of convex surfaces 1b are arranged in a square lattice pattern, it is preferable that the cutting directions for obtaining the small sample are cut in the directions shown as s11 to s12 in FIG.
　そして、得られた小片サンプルの切断面を走査電子顕微鏡（ＳＥＭ）で観察し、切断面から全体を観察できる凸面が１画像あたり約３個測定できる倍率で断面画像を得る。同様にして１０枚以上の同じ倍率の断面画像を得て、計３０個の凸面を選択し、これら各凸面の高さＬ１を求める。
　なお、後述のＬ２～Ｌ７も、高さＬ１を求めた各凸面を観察することにより求める。 Then, the cut surface of the obtained small piece sample is observed with a scanning electron microscope (SEM), and a cross-sectional image is obtained at a magnification capable of measuring approximately three convex surfaces per image from the cut surface. Similarly, 10 or more cross-sectional images having the same magnification are obtained, a total of 30 convex surfaces are selected, and the height L1 of each convex surface is obtained.
Note that L2 to L7 described later are also obtained by observing each convex surface for which the height L1 has been obtained.
　各凸面１ｂの高さＬ１は、当該凸面の最下部を基準とする当該凸面１ｂの頂点Ｔの高さである。
　切断面から観察できる当該凸面の最下部は、両隣の凸部の凸面との間において各々把握できるので、それらの中間高さが、当該凸面の最下部となる。
　両隣の凸部の凸面との間における最下部は、隣の凸面との間に平坦面が存在する場合は、その平坦面と当該凸面との境目が、その隣の凸面との間における最下部である。隣の凸面との間に平坦面が存在しない場合は、隣の凸面との間で最も低い点が、その隣の凸面との間における最下部である。 The height L1 of each convex surface 1b is the height of the vertex T of the convex surface 1b with reference to the lowest part of the convex surface.
Since the lowest part of the convex surface that can be observed from the cut surface can be grasped between the convex surfaces of the adjacent convex parts, the intermediate height between them is the lowest part of the convex surface.
If there is a flat surface between the convex surface of both adjacent convex portions, and the flat surface exists between the adjacent convex surfaces, the boundary between the flat surface and the convex surface is the lowermost portion between the adjacent convex surfaces It is. When there is no flat surface between the adjacent convex surfaces, the lowest point between the adjacent convex surfaces is the lowest portion between the adjacent convex surfaces.
　例えば、図３に示すように、１つの凸部１ａの凸面１ｂ（図３の場合中央）と該凸面１ｂの隣の凸面１ｂ（図３の場合右側）との間に平坦面１ｃが存在する場合は、平坦面１ｃと当該凸面１ｂとの境目である点Ｂａが隣の凸面１ｂとの間における最下部である。隣の凸面１ｂ（図３の場合左側）との間に平坦面１ｃが存在しない場合は、隣の凸面１ｂとの間で最も低い点Ｂｂが、隣の凸面１ｂとの間における最下部である。
　点Ｂａを基準とする頂点Ｔの高さをＬａ、点Ｂｂを基準とする頂点Ｔの高さをＬｂとすると、図３の中央の凸部１ａの凸面１ｂの高さＬ１は、Ｌ１＝（Ｌａ＋Ｌｂ）／２で求められる。
　このようにして求めた３０個の凸面の高さＬ１を平均したものが、平均高さＬ１ａである。 For example, as shown in FIG. 3, a flat surface 1c exists between the convex surface 1b of one convex portion 1a (center in the case of FIG. 3) and the convex surface 1b adjacent to the convex surface 1b (right side in the case of FIG. 3). In this case, the point Ba which is the boundary between the flat surface 1c and the convex surface 1b is the lowermost portion between the adjacent convex surface 1b. When the flat surface 1c does not exist between the adjacent convex surface 1b (left side in FIG. 3), the lowest point Bb between the adjacent convex surface 1b is the lowermost portion between the adjacent convex surface 1b. .
Assuming that the height of the vertex T relative to the point Ba is La and the height of the vertex T relative to the point Bb is Lb, the height L1 of the convex surface 1b of the central convex portion 1a in FIG. (La + Lb) / 2.
The average height L1a is obtained by averaging the heights L1 of the 30 convex surfaces thus obtained.
　凹凸構造（Ｉ）における凸面１ｂが三角格子又は正方格子を形成する場合の平均ピッチＰ１ａは１００～１０００ｎｍが好ましく、１００～８００ｎｍがより好ましく、１００～６５０ｎｍが特に好ましい。本実施形態の光電変換素子用構造体は、平均ピッチＰ１ａが好ましい範囲であることにより、可視光領域の波長において、反射防止機能を設けることができ、可視光領域の太陽光を多く取り込むことが可能となる。 When the convex surface 1b in the concavo-convex structure (I) forms a triangular lattice or a tetragonal lattice, the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm. The photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
　凸面（本実施形態では凸面１ｂ）の平均ピッチＰ１ａは、次のように求める。
　まず、構造体（本実施形態では光電変換素子用構造体１０）を切断し、１辺が１０ｍｍ程度の略正方形の小片サンプルを得る。
　切断は、例えばミクロトームや集束イオンビーム装置（ＦＩＢ）を用い、切断面が前記第２の表面１Ｂに対して垂直になるように切断する。 The average pitch P1a of the convex surface (the convex surface 1b in the present embodiment) is obtained as follows.
First, the structure (photoelectric conversion element structure 10 in this embodiment) is cut to obtain a small square sample having a side of approximately 10 mm.
The cutting is performed using, for example, a microtome or a focused ion beam apparatus (FIB) so that the cut surface is perpendicular to the second surface 1B.
　そして、得られた小片サンプルを上面から走査電子顕微鏡（ＳＥＭ）で観察し、観察できる凸面が１画像あたり２０～３０個測定できる倍率で表面画像を得る。同様にして複数枚の同じ倍率の表面画像を得て、計３０対の隣接する凸面を選択して各々の凸面の頂点Ｔの間の距離Ｐ１を求める。
　隣接する凸面とは、格子方向に添って隣接する凸面である。
　例えば、多数の凸面１ｂが三角格子状に配列している場合、隣接する凸面は、図１０にｔ１～ｔ３として示す方向に添って隣接する凸面である。
　また、多数の凸面１ｂが正方格子状に配列している場合、隣接する凸面は、図１１にｔ１１～ｔ１２として示す方向に添って隣接する凸面である。
　このようにして求めた３０個の距離Ｐ１を平均したのが、平均ピッチＰ１ａである。 Then, the obtained small sample is observed from the upper surface with a scanning electron microscope (SEM), and a surface image is obtained at a magnification capable of measuring 20 to 30 convex surfaces per image. Similarly, a plurality of surface images having the same magnification are obtained, a total of 30 pairs of adjacent convex surfaces are selected, and a distance P1 between the vertices T of the respective convex surfaces is obtained.
An adjacent convex surface is a convex surface adjacent along the lattice direction.
For example, when a large number of convex surfaces 1b are arranged in a triangular lattice pattern, adjacent convex surfaces are adjacent convex surfaces along the directions indicated by t1 to t3 in FIG.
Further, when a large number of convex surfaces 1b are arranged in a square lattice shape, the adjacent convex surfaces are adjacent convex surfaces along the directions indicated by t11 to t12 in FIG.
The average pitch P1a is obtained by averaging the 30 distances P1 thus obtained.
　凹凸構造（Ｉ）のアスペクト比（平均高さＬ１ａを平均ピッチＰ１ａで割った値）は０．１～１０が好ましく０．５～５．０がより好ましく、０．７～３．０が特に好ましい。
　本実施形態の光電変換素子用構造体は、アスペクト比が好ましい範囲であることにより、反射防止効果が高くなり、太陽光を多く取り込むことが可能となる。また、シェル形成ガスがワイヤー構造の根元まで行き届き、シリコンシェル層はワイヤー構造間を埋めることなく均一に堆積することが可能となる。さらにｐｎ接合面積が増加することによって変換効率の向上が期待できる。 The aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (I) is preferably 0.1 to 10, more preferably 0.5 to 5.0, and particularly preferably 0.7 to 3.0. preferable.
Since the structure for photoelectric conversion elements of this embodiment has a preferable aspect ratio, the antireflection effect is enhanced and a large amount of sunlight can be taken in. Further, the shell forming gas reaches the base of the wire structure, and the silicon shell layer can be uniformly deposited without filling between the wire structures. Furthermore, the conversion efficiency can be improved by increasing the pn junction area.
　凹凸構造（Ｉ）における多数の凸面は、また、下記条件Ｘを満たすことが好ましい。
（条件Ｘ）
　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
　ただし、Ｌ１ａは前述の凸面の平均高さであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。 It is preferable that many convex surfaces in the concavo-convex structure (I) satisfy the following condition X.
(Condition X)
When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
L1a / L2a = 0.1 to 10.0 (1)
L3a / L2a = 0.7 to 1.0 (2)
L4a / L2a = 0.4 to 0.9 (3)
L5a / L2a = 0.15 to 0.8 (4)
L6a / L2a = 0.07 to 0.7 (5)
L7a / L2a = 0.03 to 0.6 (6)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
However, L1a is the average height of the above-mentioned convex surface, L2a, L3a, L4a, L5a, L6a, and L7a are the average of L2, L3, L4, L5, L6, and L7, respectively, and L2 calculates | requires said L1. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the bottom of the convex surface are 1/4, 1/2, 3/4, It is the width of the convex surface at 7/8 and 15/16.
　条件Ｘは、下記式（１－１）～（６－１）、（７）を満たすことがより好ましく、下記式（１－２）～（６－２）、（７）を満たすことがさらに好ましい。
　　Ｌ１ａ／Ｌ２ａ＝０．４～７．５　・・・（１－１）
　　Ｌ３ａ／Ｌ２ａ＝０．７５～０．９８　・・・（２－１）
　　Ｌ４ａ／Ｌ２ａ＝０．４２～０．８９　・・・（３－１）
　　Ｌ５ａ／Ｌ２ａ＝０．２５～０．７１　・・・（４－１）
　　Ｌ６ａ／Ｌ２ａ＝０．１３～０．５９　・・・（５－１）
　　Ｌ７ａ／Ｌ２ａ＝０．０５～０．５　・・・（６－１）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７） The condition X more preferably satisfies the following formulas (1-1) to (6-1) and (7), and further satisfies the following formulas (1-2) to (6-2) and (7). preferable.
L1a / L2a = 0.4 to 7.5 (1-1)
L3a / L2a = 0.75 to 0.98 (2-1)
L4a / L2a = 0.42 to 0.89 (3-1)
L5a / L2a = 0.25 to 0.71 (4-1)
L6a / L2a = 0.13 to 0.59 (5-1)
L7a / L2a = 0.05 to 0.5 (6-1)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
　　Ｌ１ａ／Ｌ２ａ＝０．７～５．０　・・・（１－２）
　　Ｌ３ａ／Ｌ２ａ＝０．８～０．９６　・・・（２－２）
　　Ｌ４ａ／Ｌ２ａ＝０．５～０．８７　・・・（３－２）
　　Ｌ５ａ／Ｌ２ａ＝０．３４～０．６３　・・・（４－２）
　　Ｌ６ａ／Ｌ２ａ＝０．２～０．５　・・・（５－２）
　　Ｌ７ａ／Ｌ２ａ＝０．０６～０．４　・・・（６－２）
　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７） L1a / L2a = 0.7 to 5.0 (1-2)
L3a / L2a = 0.8 to 0.96 (2-2)
L4a / L2a = 0.5 to 0.87 (3-2)
L5a / L2a = 0.34 to 0.63 (4-2)
L6a / L2a = 0.2 to 0.5 (5-2)
L7a / L2a = 0.06 to 0.4 (6-2)
L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
　前述のように、各凸面（本実施形態では凸面１ｂ）の高さＬ１は、当該凸面の最下部を基準とする当該凸面の頂点の高さである。
　Ｌ２はＬ１を求めた凸面の最下部における当該凸面の底部幅である。前述のように、最下部は、両隣の凸面との間において各々把握される最下部の中間高さである。そのため、各々把握できる高さが完全に一致していない限り、最下部における凸面は一方にのみ存在し、他方の凸面は最下部よりも上方にしかない。そこで、他方の凸面の位置は、最下部まで外挿して求める。
　例えば、図３の場合、凸面１ｂの最下部における一方の凸面１ｂの位置は１ｂａであり、他方の凸面１ｂの位置は、凸面１ｂを点Ｂｂから外挿し、最下部の位置まで達したときの位置１ｂｂである。そして、位置１ｂａと位置１ｂｂとの距離がＬ２である。 As described above, the height L1 of each convex surface (the convex surface 1b in the present embodiment) is the height of the apex of the convex surface with reference to the lowest part of the convex surface.
L2 is the bottom width of the convex surface at the bottom of the convex surface for which L1 was obtained. As described above, the lowermost part is the intermediate height of the lowermost part that is grasped between the adjacent convex surfaces. Therefore, as long as the heights that can be grasped do not completely coincide, the convex surface at the lowermost portion exists only on one side, and the other convex surface exists only above the lowermost portion. Therefore, the position of the other convex surface is obtained by extrapolating to the lowest part.
For example, in the case of FIG. 3, the position of one convex surface 1b at the lowermost part of the convex surface 1b is 1ba, and the position of the other convex surface 1b is obtained by extrapolating the convex surface 1b from the point Bb and reaching the lowest position. It is position 1bb. The distance between the position 1ba and the position 1bb is L2.
　Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、Ｌ１、Ｌ２を求めた凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅なので、図４に矢印で示す距離となる。
　平均高さＬ１ａを求めた際に選択した３０個の各凸面について、このようにしてＬ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７を求め、これらを各々平均してＬ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａを求める。
　第１の表面１Ａに平坦面１ｃが存在しない場合、Ｌ１ａ／Ｌ２ａは、凹凸構造（Ｉ）のアスペクト比に略等しい。 L3, L4, L5, L6, and L7 are respectively 1/4, 1/2, 3/4, 7/8, and 15/16 of the height L1 with respect to the lowest part of the convex surface for which L1 and L2 are obtained. 4 is a distance indicated by an arrow in FIG.
L30, L3, L4, L5, L6, L7 are obtained in this way for each of the 30 convex surfaces selected when the average height L1a is obtained, and these are averaged to obtain L2a, L3a, L4a, L5a, L6a and L7a are obtained.
When the flat surface 1c does not exist on the first surface 1A, L1a / L2a is substantially equal to the aspect ratio of the concavo-convex structure (I).
　各凸部１ａは、第２の表面１Ｂに対して水平な任意の平面で切断した際、その断面における凸面１ｂが円形又は円形に近いことが好ましい。
　第２の表面１Ｂに対して水平な任意の平面で切断した断面における凸面１ｂが円形又は円形に近い場合、条件Ｘを満たす凸面１ｂは、円柱状、円錐台状、釣り鐘状、円錐状、側面が窪んだ円錐状ないし円錐台状等の形状となる。
　このような形状を有する場合、ｐｎ接合におけるキャリア収集が垂直方向だけでなく水平方向（半径方向）にも生じるため変換効率向上の点で好ましい。 When each convex part 1a cut | disconnects by the arbitrary horizontal planes with respect to the 2nd surface 1B, it is preferable that the convex surface 1b in the cross section is circular or nearly circular.
When the convex surface 1b in the cross section cut by an arbitrary plane parallel to the second surface 1B is circular or nearly circular, the convex surface 1b satisfying the condition X is a columnar shape, a truncated cone shape, a bell shape, a cone shape, a side surface. The shape becomes a conical shape or a truncated cone shape.
When such a shape is used, carrier collection at the pn junction occurs not only in the vertical direction but also in the horizontal direction (radial direction), which is preferable in terms of improving conversion efficiency.
　多数の凸面１ｂは第１の表面１Ａに二次元的に配列されている。多数の凸面１ｂの配列は、周期的であっても非周期的であってもよい。非周期的に配列する場合は、周期的に配列されているエリアが複数あり、エリア同士の配列は揃っていない多結晶構造体であることが特に好ましい。
　「多数の凸面１ｂが周期的に二次元に配置」とは、多数の凸面１ｂが第１の表面１Ａ上の少なくとも２方向に周期的に配置されている状態をいう。周期的な二次元構造の好ましい具体例として、配向方向が２方向で、その交差角度が９０°であるもの（正方格子）、配向方向が３方向で、その交差角度が６０°であるもの（三角格子、六方格子）等が挙げられる。 A large number of convex surfaces 1b are two-dimensionally arranged on the first surface 1A. The arrangement of the multiple convex surfaces 1b may be periodic or aperiodic. In the case of non-periodic arrangement, it is particularly preferable that the structure is a polycrystalline structure in which there are a plurality of areas arranged periodically and the arrangement of the areas is not uniform.
“Many convex surfaces 1b are periodically arranged in two dimensions” means a state in which many convex surfaces 1b are periodically arranged in at least two directions on the first surface 1A. As a preferable specific example of the periodic two-dimensional structure, the orientation direction is two directions and the intersection angle is 90 ° (square lattice), the orientation direction is three directions and the intersection angle is 60 ° ( Triangular lattice, hexagonal lattice) and the like.
　本実施形態の光電変換素子用構造体１０は、予め、ｎ型又はｐ型にドープされたシリコンウエハを、エッチングマスクを用いてドライエッチングすることにより製造できる。
　エッチングマスクとしては、粒子マスク、フォトリソグラフィーやナノインプリントによるレジストマスクが挙げられる。中でも、適度な周期性を有する凹凸構造を安価に形成でき、かつ、大面積にも対応しやすいことから、粒子マスクを用いることが好ましい。
　すなわち、本実施形態の光電変換素子用構造体は、予め、ｎ型又はｐ型にドープされたシリコンウエハに粒子を配列させ（粒子配列工程）、配列させた粒子マスクとして、ドライエッチングすることにより製造（エッチング工程）することが好ましい。 The photoelectric conversion element structure 10 of the present embodiment can be manufactured by dry-etching a silicon wafer that has been doped n-type or p-type in advance using an etching mask.
Examples of the etching mask include a particle mask, a resist mask by photolithography and nanoimprinting. Among them, it is preferable to use a particle mask because a concavo-convex structure having an appropriate periodicity can be formed at low cost and can easily cope with a large area.
That is, the photoelectric conversion element structure of the present embodiment is obtained by arranging particles on a silicon wafer doped n-type or p-type in advance (particle arranging step) and performing dry etching as an arranged particle mask. It is preferable to manufacture (etching process).
　マスクとして使用する粒子は無機粒子であることが好ましいが、条件によっては有機高分子材料なども使用できる。
　無機粒子としては、例えば、酸化物、窒化物、炭化物、硼化物、硫化物、セレン化物及び金属等の化合物からなる粒子及び金属粒子等を使用することができる。有機粒子としては、ポリスチレン、ＰＭＭＡ等の熱可塑性樹脂、フェノール樹脂、エポキシ樹脂等の熱硬化性樹脂等が使用可能である。 The particles used as the mask are preferably inorganic particles, but organic polymer materials can also be used depending on the conditions.
As the inorganic particles, for example, particles composed of oxides, nitrides, carbides, borides, sulfides, selenides, metals and the like, metal particles, and the like can be used. As the organic particles, thermoplastic resins such as polystyrene and PMMA, thermosetting resins such as phenol resins and epoxy resins, and the like can be used.
　粒子配列工程では、単層で均一な単粒子膜マスクを製膜することが好ましい。単層で均一な単粒子膜マスクを製膜する方法としては、水槽内の水の液面に水よりも比重が小さい溶剤中に粒子が分散した分散液を滴下する滴下工程と、前記溶剤を揮発させることにより前記粒子からなる単粒子膜を水の液面上に形成する単粒子膜形成工程と、前記単粒子膜をシリコンウエハ上に移し取る移行工程とを有する方法が挙げられる（例えば、特許第６０３６８３０号公報参照）。移行工程の後には、移行した単粒子膜をシリコンウエハに固定するための固定工程を行ってもよい。 In the particle arranging step, it is preferable to form a single particle film mask with a single layer. As a method for forming a single-layer, uniform single-particle film mask, a dropping step of dropping a dispersion in which particles are dispersed in a solvent having a specific gravity smaller than that of water on the surface of water in a water tank; A method having a single particle film forming step of forming a single particle film composed of the particles on the liquid surface of water by volatilization and a transfer step of transferring the single particle film onto a silicon wafer (for example, (See Japanese Patent No. 6036830). After the transfer step, a fixing step for fixing the transferred single particle film to the silicon wafer may be performed.
　単粒子膜形成工程は、超音波照射条件下で実施することが好ましい。下層水から水面に向けて超音波を照射しながら分散液の溶剤を揮発させると、粒子の最密充填が促進され、各粒子がより高精度で２次元に最密充填した単粒子膜が得られる。この際、超音波の出力は１Ｗ～１２００Ｗが好ましく、５０Ｗ～６００Ｗがより好ましい。
　移行工程においては、いわゆるＬＢトラフ法を採用することが好ましい（Journal of Materials and Chemistry, Vol.11, 3333 (2001)、Journal of Materials and Chemistry, Vol.12, 3268 (2002)など参照。）。 The single particle film forming step is preferably performed under ultrasonic irradiation conditions. When the solvent of the dispersion liquid is volatilized while irradiating ultrasonic waves from the lower water to the water surface, the closest packing of particles is promoted, and a single particle film in which each particle is two-dimensionally closely packed with higher accuracy is obtained. It is done. At this time, the output of the ultrasonic wave is preferably 1 W to 1200 W, and more preferably 50 W to 600 W.
In the transition process, it is preferable to employ a so-called LB trough method (see Journal of Materials and Chemistry, Vol. 11, 3333 (2001), Journal of Materials and Chemistry, Vol. 12, 3268 (2002), etc.).
　粒子配列工程では、以下の方法を採用してもよい。
１）シリコンウエハをコロイド粒子の懸濁液中に浸漬し、その後、基板と静電気的に結合した第１層目の粒子層のみを残し第２層目以上の粒子層を除去する（粒子吸着法）ことで、単粒子膜からなるエッチングマスクを基板上に設ける方法（特開昭５８－１２０２５５号公報参照）。
２）シリコンウエハ上にバインダー層を形成し、その上に粒子の分散液を塗布し、その後バインダー層を加熱により軟化させることで、第１層目の粒子層のみをバインダー層中に包埋させ、余分な粒子を洗い落とす方法（特開２００５－２７９８０７号公報参照）。 In the particle arranging step, the following method may be adopted.
1) A silicon wafer is immersed in a suspension of colloidal particles, and then the second and higher particle layers are removed leaving only the first particle layer electrostatically bonded to the substrate (particle adsorption method). Thus, an etching mask made of a single particle film is provided on the substrate (see Japanese Patent Laid-Open No. 58-120255).
2) A binder layer is formed on a silicon wafer, a particle dispersion is applied thereon, and then the binder layer is softened by heating, so that only the first particle layer is embedded in the binder layer. A method of washing away excess particles (see JP-A-2005-279807).
　エッチング工程では、粒子よりもシリコンウエハが実質的にエッチングされにくい条件で粒子をドライエッチングし（粒子エッチング工程）、ある程度粒子を小さくしてから、シリコンウエハが実質的にエッチングされる条件でエッチング（ウエハエッチング工程）してもよい。これにより、平坦面１ｃが存在する凹凸構造とすることが容易になる。 In the etching process, the particles are dry-etched under a condition that the silicon wafer is substantially less likely to be etched than the particles (particle-etching process). Wafer etching step). Thereby, it becomes easy to make the uneven structure in which the flat surface 1c exists.
　粒子エッチング工程で、シリコンウエハが粒子よりも実質的にエッチングされにくい条件としては、下記式（９）のドライエッチング選択比が１００％以下の条件であることが好ましく、９０％以下の条件であることが好ましく、８０％以下の条件であることが、さらに好ましい。
ドライエッチング選択比［％］＝（シリコンウエハのドライエッチング速度／粒子のドライエッチング速度）×１００・・・（９） As a condition that the silicon wafer is substantially less likely to be etched than the particle in the particle etching step, the dry etching selectivity of the following formula (9) is preferably 100% or less, and is preferably 90% or less. Preferably, the condition is 80% or less.
Dry etching selectivity [%] = (Dry etching rate of silicon wafer / Dry etching rate of particles) × 100 (9)
　ウエハエッチング工程はシリコンウエハのドライエッチング速度が粒子のエッチング速度を上回る方が、凹凸構造作製の形状コントロールが容易となるため、前記式（９）のドライエッチング選択比が１００％より大きいことを要する。ウエハエッチング工程の前記式（９）のドライエッチング選択比は、１５０％以上であることが好ましく、２００％以上であることがより好ましい。
　ドライエッチング選択比は、エッチングガスを適切に選択することにより調整できる（例えば、特許第６０３６８３０号公報参照）。 In the wafer etching process, the shape control for forming the concavo-convex structure becomes easier when the dry etching rate of the silicon wafer exceeds the etching rate of the particles, and therefore the dry etching selectivity of the formula (9) needs to be larger than 100%. . The dry etching selectivity of the formula (9) in the wafer etching process is preferably 150% or more, and more preferably 200% or more.
The dry etching selection ratio can be adjusted by appropriately selecting an etching gas (see, for example, Japanese Patent No. 6036830).
　ドライエッチング後は、凹凸構造の表面に発生しているダメージを取り除くことが好ましい。シリコン表面のダングリングボンドを取り除く場合は、終端処理を行うことが好ましい。また、凹凸構造表面が荒れている場合は、化学研磨エッチングを行うことが好ましい。
　終端処理としては、窒素又は水素によるアニールを行う方法が挙げられる。
　アニールの温度は、７００～１０００℃が好ましく８００～９５０℃がより好ましい。
また、アニールの時間は、アニール温度にもよるが、５～６０分が好ましく１０～４５分がより好ましい。 After dry etching, it is preferable to remove damage generated on the surface of the concavo-convex structure. When removing dangling bonds on the silicon surface, it is preferable to perform termination treatment. Moreover, when the uneven structure surface is rough, it is preferable to perform chemical polishing etching.
Examples of the termination treatment include a method of annealing with nitrogen or hydrogen.
The annealing temperature is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C.
The annealing time depends on the annealing temperature, but is preferably 5 to 60 minutes, more preferably 10 to 45 minutes.
　ドライエッチング後、シリコンウエハ表面には、約１～２ｎｍの厚さの自然酸化膜が形成されているが、窒素又は水素によるアニールは、この自然酸化膜を除去せずに行う。自然酸化膜があることで、窒素又は水素によるスライトエッチングによって凹凸構造が脆く壊れやすくなることを防止できる。特に、水素は自然酸化膜の層を拡散透過してＳｉＯ２／Ｓｉ界面に到達するので、自然酸化膜があっても終端処理に支障は生じない。 After dry etching, a natural oxide film having a thickness of about 1 to 2 nm is formed on the surface of the silicon wafer. Annealing with nitrogen or hydrogen is performed without removing the natural oxide film. The presence of the natural oxide film can prevent the concavo-convex structure from being brittle and easily broken by the slite etching with nitrogen or hydrogen. In particular, since hydrogen diffuses and permeates through the layer of the natural oxide film and reaches the SiO 2 / Si interface, even if there is a natural oxide film, the termination process is not hindered.
　化学研磨エッチング（ＣＰＥ：Ｃｈｅｍｉｃａｌ　ｐｏｌｉｓｈｉｎｇ　ｅｔｃｈｉｎｇ）は、例えばフッ酸と硝酸の混合液で行う。化学研磨エッチングを行うと、凸面１ｂと凸面１ｂの間及び凸面１ｂの表面がエッチングされるため、凸部１ａ自体は細くなり、また凸面１ｂ間の距離も広がる。
　化学研磨エッチングの前には、フッ酸や、硫酸と過酸化水素の混合溶液（ピラニア溶液）等により構造体表面のデポ物を除去してもよい。 Chemical polishing etching (CPE) is performed using, for example, a mixed solution of hydrofluoric acid and nitric acid. When chemical polishing etching is performed, the convex portion 1a itself is thinned and the distance between the convex surfaces 1b is widened because the surface between the convex surface 1b and the surface of the convex surface 1b is etched.
Before chemical polishing etching, deposits on the surface of the structure may be removed with hydrofluoric acid, a mixed solution of sulfuric acid and hydrogen peroxide (piranha solution), or the like.
［第２実施形態］
　図５に第２実施形態に係る光電変換素子用構造体２０を示す。本実施形態の光電変換素子用構造体２０は、ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層１と、シリコンコア層１の第１の表面Ａに形成されたシリコンシェル層２を備えている。
　シリコンコア層１は、第１実施形態の光電変換素子用構造体１０のシリコンコア層１と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。 [Second Embodiment]
FIG. 5 shows a photoelectric conversion element structure 20 according to the second embodiment. The photoelectric conversion element structure 20 of this embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, and a silicon shell layer 2 formed on the first surface A of the silicon core layer 1. I have.
The silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
　シリコンシェル層２は、シリコンコア層１とｐｎ接合を形成するように設けられ、ｐ型又はｎ型にドープされたシリコンから構成されている。すなわち、シリコンコア層１がｎ型にドープされている場合、シリコンシェル層２はｐ型にドープされている。また、シリコンコア層１がｐ型にドープされている場合、シリコンシェル層２はｎ型にドープされている。
　シリコンシェル層２のドーパントとしては、シリコンコア層１のドーパントとして挙げたものと同様のものが使用できる。 The silicon shell layer 2 is provided so as to form a pn junction with the silicon core layer 1 and is made of silicon doped p-type or n-type. That is, when the silicon core layer 1 is doped n-type, the silicon shell layer 2 is doped p-type. When the silicon core layer 1 is doped p-type, the silicon shell layer 2 is doped n-type.
As the dopant of the silicon shell layer 2, the same dopants as those described as the dopant of the silicon core layer 1 can be used.
　本実施形態の光電変換素子用構造体２０は、シリコンシェル層２の表面２Ａが多数の凸面２ｂを有する凹凸構造（ＩＩ）とされている。凹凸構造（ＩＩ）は、複数の凸面２ｂと、隣り合う凸面２ｂの間の平坦面２ｃとから構成されている。凹凸構造（ＩＩ）における凸面２ｂの平均高さＬ１ａは１００～１０００ｎｍである。平均高さＬ１ａは１５０～９００ｎｍが好ましく２００～７５０ｎｍがより好ましい。本実施形態の光電変換素子用構造体は、凸面２ｂの平均高さＬ１ａが１００～１０００ｎｍの凹凸構造（ＩＩ）を有することにより、光電変換効率に優れる光電変換素子を得ることができる。
　平均高さＬ１ａの求め方は、第一の実施形態の凹凸構造（Ｉ）の平均高さの求め方と同様にして、当該凸面２ｂの最下部を基準とする当該凸面２ｂの頂点の高さＬ１を平均することにより求める。 The photoelectric conversion element structure 20 of the present embodiment has a concavo-convex structure (II) in which the surface 2A of the silicon shell layer 2 has a large number of convex surfaces 2b. The concavo-convex structure (II) is composed of a plurality of convex surfaces 2b and a flat surface 2c between adjacent convex surfaces 2b. The average height L1a of the convex surface 2b in the concavo-convex structure (II) is 100 to 1000 nm. The average height L1a is preferably 150 to 900 nm, more preferably 200 to 750 nm. The photoelectric conversion element structure of the present embodiment has a concavo-convex structure (II) having an average height L1a of the convex surface 2b of 100 to 1000 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
The method for obtaining the average height L1a is the same as the method for obtaining the average height of the concavo-convex structure (I) of the first embodiment, and the height of the apex of the convex surface 2b with reference to the lowest part of the convex surface 2b. Obtained by averaging L1.
　本実施形態において、隣り合う凸面２ｂの間の全部又は一部には、平坦面２ｃが存在していなくてもよい。平坦面２ｃが全く存在しない場合のシリコンシェル層２の表面２Ａは、複数の凸面２ｂで構成される。
　シリコンシェル層２上に、凸面２ｂに追従する層を形成しやすいことから、シリコンシェル層２の表面２Ａには平坦面２ｃが存在することが好ましい。 In this embodiment, the flat surface 2c does not need to exist in all or a part between the adjacent convex surfaces 2b. The surface 2A of the silicon shell layer 2 when the flat surface 2c does not exist at all is constituted by a plurality of convex surfaces 2b.
Since a layer that follows the convex surface 2 b is easily formed on the silicon shell layer 2, it is preferable that a flat surface 2 c exists on the surface 2 A of the silicon shell layer 2.
　凹凸構造（ＩＩ）における凸面２ｂが三角格子又は正方格子を形成する場合の平均ピッチＰ１ａは１００～１０００ｎｍが好ましく、１００～８００ｎｍがより好ましく、１００～６５０ｎｍが特に好ましい。本実施形態の光電変換素子用構造体は、平均ピッチＰ１ａが好ましい範囲であることにより、可視光領域の波長において、反射防止機能を設けることができ、可視光領域の太陽光を多く取り込むことが可能となる。
　平均ピッチＰ１ａの求め方は、第一の実施形態の凹凸構造（Ｉ）における凸面１ｂの平均ピッチＰ１ａの求め方と同様にして、三角格子又は正方格子を形成している隣り合う凸面２ｂの頂点の間の距離Ｐ１を平均することにより求める。 When the convex surface 2b in the concavo-convex structure (II) forms a triangular lattice or a square lattice, the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm. The photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
The method for obtaining the average pitch P1a is the same as the method for obtaining the average pitch P1a of the convex surface 1b in the concavo-convex structure (I) of the first embodiment, and the apexes of adjacent convex surfaces 2b forming a triangular lattice or a square lattice. Is obtained by averaging the distance P1 between the two.
　凹凸構造（ＩＩ）のアスペクト比（平均高さＬ１ａを平均ピッチＰ１ａで割った値）は、０．１～１０が好ましく０．３～７がより好ましく、０．５～５が特に好ましい。本実施形態の光電変換素子用構造体は、アスペクト比が好ましい範囲であることにより、垂直方向のキャリアの移動距離が短くなり、再結合の確率を低下させることができる。
　凹凸構造（ＩＩ）における多数の凸面２ｂは、また、前記条件Ｘを満たすことが好ましい。条件Ｘにおける好ましい態様は第１の実施形態と同様である。 The aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (II) is preferably 0.1 to 10, more preferably 0.3 to 7, and particularly preferably 0.5 to 5. In the photoelectric conversion element structure of the present embodiment, when the aspect ratio is in a preferable range, the carrier movement distance in the vertical direction is shortened, and the probability of recombination can be reduced.
It is preferable that the multiple convex surfaces 2b in the concavo-convex structure (II) satisfy the condition X. A preferable aspect in the condition X is the same as that in the first embodiment.
　シリコンコア層１の第２の表面１Ｂに対して水平な任意の平面で切断した際、その断面における凸面２ｂは円形又は円形に近いことが好ましい。
　凸面２ｂは二次元的に配列されている。凸面２ｂの配列に関する好ましい態様は、第１の実施形態における凸面１ｂの配列に関する好ましい態様と同様である。 When cut along an arbitrary plane parallel to the second surface 1B of the silicon core layer 1, it is preferable that the convex surface 2b in the cross section is circular or nearly circular.
The convex surfaces 2b are arranged two-dimensionally. The preferable aspect regarding the arrangement | sequence of the convex surface 2b is the same as the preferable aspect regarding the arrangement | sequence of the convex surface 1b in 1st Embodiment.
　シリコンコア層１のシリコンシェル層２側の表面（第１の表面Ａ）には凹凸構造が形成されており、シリコンシェル層２は、シリコンコア層１の凹凸構造に追従するように形成されている。シリコンシェル層２の厚みは、２０～３００ｎｍが好ましく５０～２００ｎｍがより好ましい。
　シリコンシェル層２の厚みは、透過型電子顕微鏡（ＴＥＭ）による観察によって求めることができる。
　シリコンコア層１のシリコンシェル層２側の表面の凹凸構造は、第１実施形態の凹凸構造（Ｉ）であることが好ましく、凹凸構造（Ｉ）の好ましい態様も第１実施形態と同様である。
　なお、本発明において、ある層（本段落において、仮に「第１の層」と言う。）が別のある層（本段落において、仮に「第２の層」と言う。）の凹凸構造に追従するとは、第２の層の凹凸構造と一致する凹凸構造とはならないが、第２の層の凹凸構造に対して、均一の厚みをもって第１の層が製膜されることによって、第１の層の凹凸構造が形成されることを意味する。したがって、第１の層が第２の層に追従していれば、第１の層の厚み（第１の層の表面のある点から第２の層の凹凸構造の表面への垂線の長さ）は、第２の層の凹凸構造に対して一定である。
　また、上記に係る「追従する」の説明において、「均一の厚み」には「ほぼ均一の厚み」を含み、「厚みが一定であること」には「厚みがほぼ一定であること」を含む。「ほぼ均一の厚みを有すること」や「厚みがほぼ一定であること」とは、厚みの誤差が最大１００ｎｍ以下であること、好ましくは最大３０ｎｍ以下であることを意味してもよい。 An uneven structure is formed on the surface (first surface A) of the silicon core layer 1 on the silicon shell layer 2 side, and the silicon shell layer 2 is formed so as to follow the uneven structure of the silicon core layer 1. Yes. The thickness of the silicon shell layer 2 is preferably 20 to 300 nm, and more preferably 50 to 200 nm.
The thickness of the silicon shell layer 2 can be determined by observation with a transmission electron microscope (TEM).
The concavo-convex structure on the surface of the silicon core layer 1 on the silicon shell layer 2 side is preferably the concavo-convex structure (I) of the first embodiment, and the preferable form of the concavo-convex structure (I) is the same as that of the first embodiment. .
In the present invention, a certain layer (tentatively referred to as a “first layer” in this paragraph) follows the uneven structure of another certain layer (referred to as a “second layer” in this paragraph). Then, although the concavo-convex structure that matches the concavo-convex structure of the second layer is not obtained, the first layer is formed with a uniform thickness with respect to the concavo-convex structure of the second layer. It means that the concavo-convex structure of the layer is formed. Therefore, if the first layer follows the second layer, the thickness of the first layer (the length of the perpendicular from the point on the surface of the first layer to the surface of the concavo-convex structure of the second layer) ) Is constant with respect to the concave-convex structure of the second layer.
In the description of “follow” according to the above, “uniform thickness” includes “substantially uniform thickness”, and “thickness is constant” includes “thickness is substantially constant”. . “Having substantially uniform thickness” or “thickness is almost constant” may mean that the error in thickness is 100 nm or less, preferably 30 nm or less.
　本実施形態の光電変換素子用構造体２０は、第１の実施形態の光電変換素子用構造体１０に、シリコンシェル層２を形成することにより製造することが好ましい。
　光電変換素子用構造体１０に、シリコンシェル層２を形成する方法としては、下記（ｉ）、（ｉｉ）の方法が挙げられ、下記（ｉ）の方法が好ましい。
（ｉ）光電変換素子用構造体１０の第１の表面１Ａに、光電変換素子用構造体１０と反対のドープ型のシリコン材料を堆積させてシリコンシェル層２を形成する方法。
（ｉｉ）光電変換素子用構造体１０の第１の表面１Ａに、光電変換素子用構造体１０と反対のドープ型のドーパントをドライブイン拡散させてシリコンシェル層２を形成する方法。 The photoelectric conversion element structure 20 of the present embodiment is preferably manufactured by forming the silicon shell layer 2 on the photoelectric conversion element structure 10 of the first embodiment.
Examples of the method for forming the silicon shell layer 2 on the photoelectric conversion element structure 10 include the following methods (i) and (ii), and the following method (i) is preferable.
(I) A method of forming a silicon shell layer 2 by depositing a doped silicon material opposite to the photoelectric conversion element structure 10 on the first surface 1A of the photoelectric conversion element structure 10.
(Ii) A method of forming the silicon shell layer 2 by drive-in diffusion of a doped dopant opposite to the photoelectric conversion element structure 10 on the first surface 1A of the photoelectric conversion element structure 10.
　前記（ｉ）の方法における光電変換素子用構造体１０と反対のドープ型のシリコン材料の堆積は、ドライプロセスによることが好ましい。ドライプロセスには化学気相成長法（ＣＶＤ法：化学的蒸着）と物理気相成長法（ＰＶＤ法：物理的蒸着）とあるが、ＣＶＤ法によることが好ましい。
　ＣＶＤ法は、汎用性が高く、制御がしやすいため、均一なシリコンシェル層を安定的に形成しやすい。
　前記（ｉ）の方法を行う際は、その直前に、光電変換素子用構造体１０の第１の表面１Ａにある自然酸化膜を必ず除去しなければならない。 The deposition of the doped silicon material opposite to the photoelectric conversion element structure 10 in the method (i) is preferably performed by a dry process. The dry process includes a chemical vapor deposition method (CVD method: chemical vapor deposition) and a physical vapor deposition method (PVD method: physical vapor deposition), and the CVD method is preferred.
Since the CVD method is highly versatile and easy to control, it is easy to stably form a uniform silicon shell layer.
When the method (i) is performed, the natural oxide film on the first surface 1A of the photoelectric conversion element structure 10 must be removed immediately before the method (i).
　光電変換素子用構造体１０と反対のドープ型のシリコン材料を堆積させてシリコンシェル層２を形成した後は、シリコンシェル層２の凹凸構造の表面に発生しているダメージ（シリコン表面のダングリングボンド）を取り除く、終端処理を行うことが好ましい。
　なお、後述のＢＳＦ処理によってもアニール効果を得られるため、この段階での終端処理は省略してもよい。 After forming the silicon shell layer 2 by depositing a doped silicon material opposite to the photoelectric conversion element structure 10, damage (dangling of the silicon surface) occurring on the surface of the concavo-convex structure of the silicon shell layer 2 is formed. It is preferable to perform termination treatment to remove the bond.
In addition, since the annealing effect can be obtained also by the BSF process described later, the termination process at this stage may be omitted.
　終端処理としては、窒素又は水素によるアニールを行う方法が挙げられる。
　窒素又は水素によるアニールの温度は、７００～１０００℃が好ましく８００～９５０℃がより好ましい。また、水素アニールの時間は、アニール温度にもよるが、５～６０分が好ましく１０～４５分がより好ましい。 Examples of the termination treatment include a method of annealing with nitrogen or hydrogen.
The annealing temperature with nitrogen or hydrogen is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C. Further, the hydrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
　形成したシリコンシェル層２の表面には、約１～２ｎｍの厚さの自然酸化膜が形成されているが、窒素又は水素によるアニールは、この自然酸化膜を除去せずに行う。自然酸化膜があることで、窒素又は水素によるスライトエッチングによって凹凸構造が脆く壊れやすくなることを防止できる。特に、水素は自然酸化膜の層を拡散透過してＳｉＯ２／Ｓｉ界面に到達するので、自然酸化膜があっても終端処理に支障は生じない。 A natural oxide film having a thickness of about 1 to 2 nm is formed on the surface of the formed silicon shell layer 2, and annealing with nitrogen or hydrogen is performed without removing the natural oxide film. The presence of the natural oxide film can prevent the concavo-convex structure from being brittle and easily broken by the slite etching with nitrogen or hydrogen. In particular, since hydrogen diffuses and permeates through the layer of the natural oxide film and reaches the SiO 2 / Si interface, even if there is a natural oxide film, the termination process is not hindered.
　一方、前記（ｉｉ）の方法は、ｐｎ接合部に不対電子などからなる欠陥ができない点が有利である。ただし、ドライブイン拡散させる際の熱のコントロールが難しいため、慎重な調整が必要である。 On the other hand, the method (ii) is advantageous in that the pn junction cannot be made of defects such as unpaired electrons. However, since it is difficult to control the heat during drive-in diffusion, careful adjustment is required.
［第３実施形態］
　図６に第３実施形態に係る光電変換素子用構造体３０を示す。本実施形態の光電変換素子用構造体３０は、ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層１と、シリコンコア層１の第１の表面に形成されたシリコンシェル層２と、シリコンシェル層２のシリコンコア層１と反対側の表面を覆う透明導電層３を備えている。 [Third Embodiment]
FIG. 6 shows a photoelectric conversion element structure 30 according to the third embodiment. The photoelectric conversion element structure 30 of this embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and A transparent conductive layer 3 covering the surface of the silicon shell layer 2 opposite to the silicon core layer 1 is provided.
　シリコンコア層１は、第１実施形態の光電変換素子用構造体１０のシリコンコア層１と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。
　シリコンシェル層２は、第２実施形態の光電変換素子用構造体２０のシリコンシェル層２と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。 The silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
The silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
　透明導電層３は、透明導電材料により形成された層である。透明導電材料としては、公知のものが使用できる。例えばインジウム－スズ酸化物（Ｉｎｄｉｕｍ　Ｔｉｎ　Ｏｘｉｄｅ（ＩＴＯ））、インジウム－亜鉛酸化物（Ｉｎｄｉｕｍ　Ｚｉｎｃ　Ｏｘｉｄｅ（ＩＺＯ））、酸化亜鉛（Ｚｉｎｃ　Ｏｘｉｄｅ（ＺｎＯ））、亜鉛－スズ酸化物（Ｚｉｎｃ　Ｔｉｎ　Ｏｘｉｄｅ（ＺＴＯ））等が挙げられる。 The transparent conductive layer 3 is a layer formed of a transparent conductive material. As the transparent conductive material, known materials can be used. For example, indium tin oxide (Indium Tin Oxide (ITO)), indium zinc oxide (Indium Zinc Oxide (IZO)), zinc oxide (Zinc Oxide (ZnO)), zinc-tin oxide (Zinc Tin Oxide (ZTO)) )) And the like.
　本実施形態の光電変換素子用構造体３０は、透明導電層３の表面３Ａが多数の凸面３ｂを有する凹凸構造（ＩＩＩ）とされている。凹凸構造（ＩＩＩ）における凸面３ｂの平均高さＬ１ａは１００～１１００ｎｍである。平均高さＬ１ａは２００～１０００ｎｍが好ましく２５０～８００ｎｍがより好ましい。本実施形態の光電変換素子用構造体は、凸面３ｂの平均高さＬ１ａが１００～１１００ｎｍの凹凸構造（ＩＩＩ）を有することにより、光電変換効率に優れる光電変換素子を得ることができる。
　平均高さＬ１ａの求め方は、第一の実施形態の凹凸構造（Ｉ）の平均高さの求め方と同様にして、当該凸面３ｂの最下部を基準とする当該凸面３ｂの頂点の高さＬ１を平均することにより求める。 The photoelectric conversion element structure 30 of the present embodiment has a concavo-convex structure (III) in which the surface 3A of the transparent conductive layer 3 has a large number of convex surfaces 3b. The average height L1a of the convex surface 3b in the concavo-convex structure (III) is 100 to 1100 nm. The average height L1a is preferably 200 to 1000 nm, and more preferably 250 to 800 nm. The photoelectric conversion element structure of the present embodiment has a concavo-convex structure (III) having an average height L1a of the convex surface 3b of 100 to 1100 nm, whereby a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained.
The method for obtaining the average height L1a is the same as the method for obtaining the average height of the concavo-convex structure (I) of the first embodiment, and the height of the apex of the convex surface 3b with reference to the lowest part of the convex surface 3b. Obtained by averaging L1.
　本実施形態において、隣り合う凸面３ｂの間の全部又は一部には、平坦面が存在していてもよい。
　反射防止効果を高め、ｐｎ接合の面積を増やす観点から、透明導電層３の表面３Ａには平坦面が存在しない方が好ましい。 In this embodiment, a flat surface may exist in all or a part between the adjacent convex surfaces 3b.
From the viewpoint of enhancing the antireflection effect and increasing the area of the pn junction, it is preferable that the surface 3A of the transparent conductive layer 3 has no flat surface.
　凹凸構造（ＩＩＩ）における凸面２ｂが三角格子又は正方格子を形成する場合の平均ピッチＰ１ａは１００～１０００ｎｍが好ましく１００～８００ｎｍがより好ましく、１００～６５０ｎｍが特に好ましい。本実施形態の光電変換素子用構造体は、平均ピッチＰ１ａが好ましい範囲であることにより、可視光領域の波長において、反射防止機能を設けることができ、可視光領域の太陽光を多く取り込むことが可能となる。
　平均ピッチＰ１ａの求め方は、第一の実施形態の凹凸構造（Ｉ）の平均ピッチＰ１ａの求め方と同様にして、三角格子又は正方格子を形成している隣り合う凸面３ｂの頂点の間の距離Ｐ１を平均することにより求める。 When the convex surface 2b in the concavo-convex structure (III) forms a triangular lattice or a tetragonal lattice, the average pitch P1a is preferably 100 to 1000 nm, more preferably 100 to 800 nm, and particularly preferably 100 to 650 nm. The photoelectric conversion element structure of the present embodiment can provide an antireflection function at a wavelength in the visible light region and can take in a large amount of sunlight in the visible light region because the average pitch P1a is in a preferable range. It becomes possible.
The method for obtaining the average pitch P1a is the same as the method for obtaining the average pitch P1a of the concavo-convex structure (I) of the first embodiment, between the vertices of adjacent convex surfaces 3b forming a triangular lattice or a square lattice. It is obtained by averaging the distance P1.
　凹凸構造（ＩＩＩ）のアスペクト比（平均高さＬ１ａを平均ピッチＰ１ａで割った値）は０．１～１０が好ましく０．３～７がより好ましく、０．５～５が特に好ましい。本実施形態の光電変換素子用構造体は、アスペクト比が好ましい範囲であることにより、反射防止効果が高くなり、太陽光を多く取り込むことが可能となる。
　凹凸構造（ＩＩＩ）における多数の凸面３ｂは、また、前記条件Ｘを満たすことが好ましい。条件Ｘにおける好ましい態様は第１の実施形態と同様である。 The aspect ratio (value obtained by dividing the average height L1a by the average pitch P1a) of the concavo-convex structure (III) is preferably from 0.1 to 10, more preferably from 0.3 to 7, and particularly preferably from 0.5 to 5. Since the structure for photoelectric conversion elements of this embodiment has a preferable aspect ratio, the antireflection effect is enhanced and a large amount of sunlight can be taken in.
It is preferable that the multiple convex surfaces 3b in the concavo-convex structure (III) satisfy the condition X. A preferable aspect in the condition X is the same as that in the first embodiment.
　シリコンコア層１の第２の表面１Ｂに対して水平な任意の平面で切断した際、その断面における凸面３ｂは円形又は円形に近いことが好ましい。
　凸面３ｂは二次元的に配列されている。凸面３ｂの配列に関する好ましい態様は、第１の実施形態における凸面１ｂの配列に関する好ましい態様と同様である。 When cut along an arbitrary plane horizontal to the second surface 1B of the silicon core layer 1, it is preferable that the convex surface 3b in the cross section thereof is circular or nearly circular.
The convex surfaces 3b are arranged two-dimensionally. The preferable aspect regarding the arrangement | sequence of the convex surface 3b is the same as the preferable aspect regarding the arrangement | sequence of the convex surface 1b in 1st Embodiment.
　シリコンコア層１のシリコンシェル層２側の表面（第１の表面）には凹凸構造が形成されており、シリコンシェル層２は、シリコンコア層１の凹凸構造に追従するよう形成されている。シリコンシェル層２の厚みは、２０～３００ｎｍが好ましく５０～２００ｎｍがより好ましい。透明導電層３は、シリコンシェル層２の凹凸構造に追従するように形成されている。透明導電層３の厚みは、１０～２００ｎｍが好ましく２０～１００ｎｍがより好ましい。
　透明導電層３の厚みは、走査電子顕微鏡（ＳＥＭ）や透過型電子顕微鏡（ＴＥＭ）による観察によって求めることができる。 An uneven structure is formed on the surface (first surface) of the silicon core layer 1 on the silicon shell layer 2 side, and the silicon shell layer 2 is formed so as to follow the uneven structure of the silicon core layer 1. The thickness of the silicon shell layer 2 is preferably 20 to 300 nm, and more preferably 50 to 200 nm. The transparent conductive layer 3 is formed so as to follow the uneven structure of the silicon shell layer 2. The thickness of the transparent conductive layer 3 is preferably 10 to 200 nm, more preferably 20 to 100 nm.
The thickness of the transparent conductive layer 3 can be determined by observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM).
　シリコンコア層１のシリコンシェル層２側の表面の凹凸構造は、第１実施形態の凹凸構造（Ｉ）であることが好ましく、凹凸構造（Ｉ）の好ましい態様も第１実施形態と同様である。
　シリコンシェル層２の透明導電層３側の表面の凹凸構造は、第２実施形態の凹凸構造（ＩＩ）であることが好ましく、凹凸構造（ＩＩ）の好ましい態様も第２実施形態と同様である。 The concavo-convex structure on the surface of the silicon core layer 1 on the silicon shell layer 2 side is preferably the concavo-convex structure (I) of the first embodiment, and the preferable form of the concavo-convex structure (I) is the same as that of the first embodiment. .
The concavo-convex structure on the surface of the silicon shell layer 2 on the transparent conductive layer 3 side is preferably the concavo-convex structure (II) of the second embodiment, and the preferable aspect of the concavo-convex structure (II) is the same as that of the second embodiment. .
　本実施形態の光電変換素子用構造体３０は、第２の実施形態の光電変換素子用構造体２０に、透明導電層３を形成することにより製造することが好ましい。
　透明導電層３の形成は、ドライプロセスによることが好ましい。ドライプロセスには化学気相成長法（ＣＶＤ法：化学的蒸着）と物理気相成長法（ＰＶＤ法：物理的蒸着）とあるが、ＣＶＤ法によることが好ましい。
　透明導電層３を形成する際は、その直前に、光電変換素子用構造体２０の表面２Ａにある自然酸化膜を必ず除去しなければならない。 The photoelectric conversion element structure 30 of the present embodiment is preferably manufactured by forming the transparent conductive layer 3 on the photoelectric conversion element structure 20 of the second embodiment.
The formation of the transparent conductive layer 3 is preferably performed by a dry process. The dry process includes a chemical vapor deposition method (CVD method: chemical vapor deposition) and a physical vapor deposition method (PVD method: physical vapor deposition), and the CVD method is preferred.
When the transparent conductive layer 3 is formed, the natural oxide film on the surface 2A of the photoelectric conversion element structure 20 must be removed immediately before that.
［第４実施形態］
　図７に第４実施形態に係る光電変換素子４０を示す。本実施形態の光電変換素子４０は、ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層１と、シリコンコア層１の第１の表面に形成されたシリコンシェル層２と、シリコンシェル層２のシリコンコア層１と反対側の表面を覆う透明導電層３と、シリコンコア層１の第２の表面１Ｂに順次形成された裏面障壁層（ＢＳＦ層）４と裏面電極５を備えている。 [Fourth Embodiment]
FIG. 7 shows a photoelectric conversion element 40 according to the fourth embodiment. The photoelectric conversion element 40 of this embodiment includes a silicon core layer 1 made of silicon doped in n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and a silicon shell layer. 2, a transparent conductive layer 3 covering the surface opposite to the silicon core layer 1, a back barrier layer (BSF layer) 4 and a back electrode 5 sequentially formed on the second surface 1 B of the silicon core layer 1. .
　シリコンコア層１は、第１実施形態の光電変換素子用構造体１０のシリコンコア層１と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。
　シリコンシェル層２は、第２実施形態の光電変換素子用構造体２０のシリコンシェル層２と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。
　透明導電層３は、第３実施形態の光電変換素子用構造体３０の透明導電層３と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。 The silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
The silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
The transparent conductive layer 3 is preferably the same as the transparent conductive layer 3 of the photoelectric conversion element structure 30 of the third embodiment, and a preferable aspect thereof is also the same, and thus detailed description thereof is omitted.
　裏面障壁層４は、変換効率を改善するためにシリコンコア層１と裏面電極５との間に設けられる層である。
　シリコンコア層１がｎ型にドープされている場合、裏面障壁層４は、高密度にドープされたｎ＋層であり、ｎ－ｎ＋間の障壁によってホールをブロックし、裏面電極５付近での再結合を抑える役割を果たす。
　シリコンコア層１がｐ型にドープされている場合、裏面障壁層４は、高密度にドープされたｐ＋層であり、ｐ－ｐ＋間の障壁によって電子をブロックし、裏面電極５付近での再結合を抑える役割を果たす。 The back barrier layer 4 is a layer provided between the silicon core layer 1 and the back electrode 5 in order to improve conversion efficiency.
When the silicon core layer 1 is doped n-type, the back barrier layer 4 is a densely doped n + layer that blocks holes by a barrier between nn + and near the back electrode 5 It plays a role of suppressing recombination.
When the silicon core layer 1 is doped p-type, the back barrier layer 4 is a densely doped p + layer, blocks electrons by the barrier between pp + , and closes the back electrode 5 It plays a role of suppressing recombination.
　裏面電極５は、シリコンコア層１がｎ型にドープされている場合は、電子を取り出すｎ電極であり、シリコンコア層１がｐ型にドープされている場合は、ホールを取り出すｐ電極である。
　裏面電極５の材質としては、アルミニウム、銀、チタン、又はそれぞれの合金が挙げられる。
　第４実施形態において、裏面障壁層４は必須ではなく省略してもよい。すなわち、裏面電極５は、シリコンコア層１の第２の表面１Ｂに直接形成されていてもよい。 The back electrode 5 is an n-electrode that extracts electrons when the silicon core layer 1 is doped n-type, and a p-electrode that extracts holes when the silicon core layer 1 is doped p-type. .
Examples of the material for the back electrode 5 include aluminum, silver, titanium, and alloys thereof.
In the fourth embodiment, the back surface barrier layer 4 is not essential and may be omitted. That is, the back electrode 5 may be directly formed on the second surface 1B of the silicon core layer 1.
　本実施形態の光電変換素子４０は、第３の実施形態の光電変換素子用構造体３０にＢＳＦ処理を施して裏面障壁層４を形成し、その後裏面電極５を形成することにより製造することが好ましい。裏面障壁層４の厚みは、当業者に自明の範囲で選択することができる。
　ｎ＋層とするＢＳＦ処理としては、シリコンコア層１の第２の表面１Ｂにリン系の濃溶液をスピンコートし、焼結させた後に、窒素アニールする方法が挙げられる。リン系の濃溶液としては、例えば、東京応化工業社製ＯＣＤ（登録商標）溶液を用いることができる。窒素アニールの温度は、７００～１０００℃が好ましく８００～９５０℃がより好ましい。また、窒素アニールの時間は、アニール温度にもよるが、５～６０分が好ましく１０～４５分がより好ましい。 The photoelectric conversion element 40 of this embodiment can be manufactured by performing the BSF process on the photoelectric conversion element structure 30 of the third embodiment to form the back barrier layer 4 and then forming the back electrode 5. preferable. The thickness of the back barrier layer 4 can be selected within a range obvious to those skilled in the art.
Examples of the BSF treatment for forming the n + layer include a method in which a phosphorus-based concentrated solution is spin-coated on the second surface 1B of the silicon core layer 1 and sintered, followed by nitrogen annealing. As the phosphorus-based concentrated solution, for example, an OCD (registered trademark) solution manufactured by Tokyo Ohka Kogyo Co., Ltd. can be used. The temperature of nitrogen annealing is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C. Further, the nitrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
　ｐ＋層とするＢＳＦ処理としては、シリコンコア層１の第２の表面１Ｂをアルミニウム又は銀を含む導電ペーストを塗布し焼結する方法が挙げられる。導電ペーストとしては、例えば、東洋アルミニウム社製のアルソーラー（登録商標）を用いることができる。窒素アニールの温度は、７００～１０００℃が好ましく８００～９５０℃がより好ましい。また、窒素アニールの時間は、アニール温度にもよるが、５～６０分が好ましく１０～４５分がより好ましい。
　裏面電極５は、蒸着やスパッタ等の方法で形成することができる。裏面電極５の厚みは、当業者に自明の範囲で選択することができる。 Examples of the BSF treatment for forming the p + layer include a method in which the second surface 1B of the silicon core layer 1 is coated with a conductive paste containing aluminum or silver and sintered. For example, Alsolar (registered trademark) manufactured by Toyo Aluminum Co., Ltd. can be used as the conductive paste. The temperature of nitrogen annealing is preferably 700 to 1000 ° C., more preferably 800 to 950 ° C. Further, the nitrogen annealing time is preferably 5 to 60 minutes, more preferably 10 to 45 minutes, although it depends on the annealing temperature.
The back electrode 5 can be formed by a method such as vapor deposition or sputtering. The thickness of the back electrode 5 can be selected within a range obvious to those skilled in the art.
［第５実施形態］
　図８に第５実施形態に係る光電変換素子５０を示す。本実施形態の光電変換素子５０は、ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層１と、シリコンコア層１の第１の表面に形成されたシリコンシェル層２と、シリコンシェル層２のシリコンコア層１と反対側の表面を覆う透明導電層３と、シリコンコア層１の第２の表面１Ｂに順次形成された裏面障壁層（ＢＳＦ層）４と裏面電極５と、透明導電層３と電気的に導通可能な状態で接触する表面電極６を備えている。 [Fifth Embodiment]
FIG. 8 shows a photoelectric conversion element 50 according to the fifth embodiment. The photoelectric conversion element 50 of the present embodiment includes a silicon core layer 1 made of silicon doped n-type or p-type, a silicon shell layer 2 formed on the first surface of the silicon core layer 1, and a silicon shell layer A transparent conductive layer 3 covering the surface opposite to the silicon core layer 1, a back barrier layer (BSF layer) 4 formed on the second surface 1 B of the silicon core layer 1, a back electrode 5, and a transparent conductive layer A surface electrode 6 is provided in contact with the layer 3 in an electrically conductive state.
　シリコンコア層１は、第１実施形態の光電変換素子用構造体１０のシリコンコア層１と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。
　シリコンシェル層２は、第２実施形態の光電変換素子用構造体２０のシリコンシェル層２と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。 The silicon core layer 1 is preferably the same as the silicon core layer 1 of the photoelectric conversion element structure 10 of the first embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
The silicon shell layer 2 is preferably the same as the silicon shell layer 2 of the photoelectric conversion element structure 20 of the second embodiment, and a preferable aspect is also the same, and thus detailed description thereof is omitted.
　透明導電層３は、第３実施形態の光電変換素子用構造体３０の透明導電層３と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。
　裏面障壁層４及び裏面電極５は、第４実施形態の光電変換素子４０の裏面障壁層４及び裏面電極５と同じであることが好ましく、好ましい態様も同一であるため、その詳細な説明を省略する。 The transparent conductive layer 3 is preferably the same as the transparent conductive layer 3 of the photoelectric conversion element structure 30 of the third embodiment, and a preferable aspect thereof is also the same, and thus detailed description thereof is omitted.
The back surface barrier layer 4 and the back surface electrode 5 are preferably the same as the back surface barrier layer 4 and the back surface electrode 5 of the photoelectric conversion element 40 of the fourth embodiment, and preferable aspects are also the same, and thus detailed description thereof is omitted. To do.
　表面電極６は、シリコンコア層１がｎ型にドープされている場合は、ホールを取り出すｐ電極であり、シリコンコア層１がｐ型にドープされている場合は、電子を取り出すｎ電極である。
　表面電極６は、細い格子状の線で構成することが好ましい。これにより、ｐｎ接合面への光の到達を妨げることなく、透明導電層３との電気的導通を充分にとることができる。
　裏面電極６の材質としては、アルミニウム、銀、チタン、又はそれぞれの合金が挙げられる。
　第５実施形態において、裏面障壁層４は必須ではなく省略してもよい。すなわち、裏面電極５は、シリコンコア層１の第２の表面１Ｂに直接形成されていてもよい。 The surface electrode 6 is a p-electrode for extracting holes when the silicon core layer 1 is doped n-type, and an n-electrode for extracting electrons when the silicon core layer 1 is doped p-type. .
The surface electrode 6 is preferably composed of thin grid lines. Thereby, sufficient electrical continuity with the transparent conductive layer 3 can be achieved without hindering the arrival of light to the pn junction surface.
Examples of the material of the back electrode 6 include aluminum, silver, titanium, and alloys thereof.
In the fifth embodiment, the back barrier layer 4 is not essential and may be omitted. That is, the back electrode 5 may be directly formed on the second surface 1B of the silicon core layer 1.
　本実施形態の光電変換素子５０は、第４の実施形態の光電変換素子４０に、表面電極６を形成することにより製造することが好ましい。
　本実施形態の光電変換素子５０は、第３の実施形態の光電変換素子用構造体３０に表面電極６を形成し、その後ＢＳＦ処理を施して裏面障壁層４を形成し、さらに裏面電極５を形成することにより製造してもよい。
　表面電極６は、蒸着やスパッタ等の方法で形成することができる。 The photoelectric conversion element 50 of the present embodiment is preferably manufactured by forming the surface electrode 6 on the photoelectric conversion element 40 of the fourth embodiment.
In the photoelectric conversion element 50 of the present embodiment, the surface electrode 6 is formed on the photoelectric conversion element structure 30 of the third embodiment, and then the back surface barrier layer 4 is formed by performing the BSF treatment. You may manufacture by forming.
The surface electrode 6 can be formed by a method such as vapor deposition or sputtering.
［第６実施形態］
　図９に第６実施形態に係る光電変換素子６０を示す。本実施形態の光電変換素子６０は、透明導電層３を有しない他は、第５実施形態に係る光電変換素子５０と同様である。
　本実施形態の光電変換素子６０は、透明導電層３を形成しない他は、第５実施形態に係る光電変換素子５０と同様にして製造することができる。 [Sixth Embodiment]
FIG. 9 shows a photoelectric conversion element 60 according to the sixth embodiment. The photoelectric conversion element 60 of this embodiment is the same as the photoelectric conversion element 50 according to the fifth embodiment except that the transparent conductive layer 3 is not provided.
The photoelectric conversion element 60 of this embodiment can be manufactured in the same manner as the photoelectric conversion element 50 according to the fifth embodiment, except that the transparent conductive layer 3 is not formed.
［作用機序］
　本発明の光電変換素子及び本発明の光電変換素子用構造体を用いた光電変換素子は、ｐｎ接合を構成するシリコンコア層とシリコンシェル層との界面が、充分な高さを有する凸面とされていることにより、ｐｎ接合におけるキャリア収集が垂直方向だけでなく水平方向（凹凸構造の半径方向）にも生じるため変換効率を向上させることができる。特に凸面が条件Ｘを満たす場合、キャリア収集が、より効率的に水平方向（凹凸構造の半径方向）に生じるものと考えられる。
　さらに、前記凸面の高さが比較的低いことにより、垂直方向のキャリアの移動距離が短くなり、再結合の確率を低下させることができたものと考えられる。 [Mechanism of action]
In the photoelectric conversion element using the photoelectric conversion element of the present invention and the photoelectric conversion element structure of the present invention, the interface between the silicon core layer and the silicon shell layer constituting the pn junction is a convex surface having a sufficient height. As a result, carrier collection at the pn junction occurs not only in the vertical direction but also in the horizontal direction (radial direction of the concavo-convex structure), so that the conversion efficiency can be improved. In particular, when the convex surface satisfies the condition X, it is considered that carrier collection occurs more efficiently in the horizontal direction (radial direction of the concavo-convex structure).
Furthermore, it is considered that the relatively low height of the convex surface shortens the vertical carrier movement distance, thereby reducing the probability of recombination.
　以下、実施例により本発明を詳細に説明するが、本発明は下記実施例に限定されるものではない。なお、％は特に断りのない限り質量％である。また、原料の「質量部」は、分散媒体を含む質量である。 Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples. In addition,% is the mass% unless there is particular notice. The “mass part” of the raw material is the mass including the dispersion medium.
［実施例１］
　平均粒径が６００ｎｍで、粒径の変動係数が１．７２％である球形コロイダルシリカの２０質量％水分散体を用意した。なお、平均粒径及び粒径の変動係数は、粒子動的光散乱法により求めた粒度分布をガウス曲線にフィッティングさせて得られるピークから求めた。測定器としては、動的光散乱法によって、粒径１０ｎｍ以下～３μｍ程度の粒子を測定することができるＭａｌｖｅｒｎ　Ｉｎｓｔｒｕｍｅｎｔｓ　Ｌｔｄ社製　Ｚｅｔａｓｉｚｅｒ　Ｎａｎｏ－ＺＳを使用した。 [Example 1]
A 20% by mass aqueous dispersion of spherical colloidal silica having an average particle size of 600 nm and a particle size variation coefficient of 1.72% was prepared. The average particle diameter and the coefficient of variation of the particle diameter were determined from peaks obtained by fitting the particle size distribution determined by the particle dynamic light scattering method to a Gaussian curve. As a measuring device, Zetasizer Nano-ZS manufactured by Malvern Instruments Ltd. which can measure particles having a particle size of about 10 nm to 3 μm by a dynamic light scattering method was used.
　この水分散体を孔径１．２μｍφのメンブランフィルターでろ過した。メンブランフィルターを通過した水分散体に、濃度１．０質量％のフェニルトリエトキシシランの加水分解物水溶液を加え、約４０℃で３時間反応させて反応液を得た。この際、フェニルトリエトキシシランの質量がコロイダルシリカ粒子の質量の０．０２質量倍となるように水分散体と加水分解物水溶液とを混合した。
　得られた反応液に、この反応液の体積の４倍の体積のメチルイソブチルケトンを加えて十分に攪拌して、疎水化されたコロイダルシリカを油相抽出し、濃度０．９１質量％の疎水化コロイダルシリカ分散液を得た。 This aqueous dispersion was filtered through a membrane filter having a pore diameter of 1.2 μmφ. An aqueous solution of a hydrolyzate of phenyltriethoxysilane having a concentration of 1.0% by mass was added to the aqueous dispersion that passed through the membrane filter and reacted at about 40 ° C. for 3 hours to obtain a reaction solution. At this time, the aqueous dispersion and the hydrolyzate aqueous solution were mixed so that the mass of phenyltriethoxysilane was 0.02 times the mass of the colloidal silica particles.
To the obtained reaction liquid, methyl isobutyl ketone having a volume 4 times the volume of this reaction liquid was added and stirred sufficiently, and the hydrophobized colloidal silica was subjected to oil phase extraction to obtain a hydrophobic concentration of 0.91% by mass. A colloidal silica dispersion was obtained.
　こうして得られた疎水化コロイダルシリカ分散液を、単粒子膜の表面圧を計測する表面圧力センサーと、単粒子膜を液面に沿う方向に圧縮する可動バリアとを備えた水槽（ＬＢトラフ装置）中の液面（下層水として水を使用、水温２５℃）に滴下速度０．０１ｍＬ／秒で滴下した。水槽の下層水にはあらかじめ、基板として、表面が平坦なｎ型Ｓｉ基板（１５ｍｍ×１５ｍｍ、厚さ：０．５２５ｍｍ）を略鉛直方向に浸漬しておいた。
　その後、超音波（出力３００Ｗ、周波数９５０ｋＨｚ）を下層水中から水面に向けて１０分間照射して粒子が二次元的に最密充填するのを促しつつ、分散液の溶剤であるメチルイソブチルケトンを揮発させ、単粒子膜を形成させた。
　ついで、この単粒子膜を可動バリアにより拡散圧が２５ｍＮｍ－１になるまで圧縮し、基板を５ｍｍ／分の速度で引き上げ、基板の片面上に移し取り、単粒子膜付き基板を得た。 Water tank (LB trough device) provided with a hydrophobized colloidal silica dispersion thus obtained, a surface pressure sensor for measuring the surface pressure of the single particle film, and a movable barrier for compressing the single particle film in the direction along the liquid surface The solution was added dropwise to the inside liquid surface (water was used as the lower layer water, water temperature 25 ° C.) at a dropping rate of 0.01 mL / second. An n-type Si substrate (15 mm × 15 mm, thickness: 0.525 mm) having a flat surface was immersed in a substantially vertical direction in advance in the lower layer water of the water tank.
Thereafter, ultrasonic waves (output: 300 W, frequency: 950 kHz) are irradiated from the lower layer water toward the water surface for 10 minutes to volatilize methyl isobutyl ketone, which is the solvent of the dispersion, while urging the particles to be two-dimensionally closely packed. To form a single particle film.
Next, the single particle film was compressed by a movable barrier until the diffusion pressure became 25 mNm −1 , the substrate was pulled up at a speed of 5 mm / min, and transferred onto one side of the substrate to obtain a substrate with a single particle film.
　ついで、前記単粒子膜付き基板に対して、ドライエッチングを行った。具体的には、粒子エッチング工程としてＣＦ４及びＯ２の混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１７００Ｗ、バイアス電力１５００Ｗ、ガス流量１５０ｓｃｃｍ、エッチング選択比９０％、エッチング時間２５０秒とした。
　その後、ウエハエッチング工程としてＢＣｌ３及びＡｒの混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１７００Ｗ、バイアス電力７００Ｗ、ガス流量１５０ｓｃｃｍ、エッチング選択比１２０％、エッチング時間２８０秒であった。 Next, dry etching was performed on the substrate with the single particle film. Specifically, dry etching was performed using a mixed gas of CF 4 and O 2 as a particle etching process. Etching conditions were an antenna power of 1700 W, a bias power of 1500 W, a gas flow rate of 150 sccm, an etching selectivity of 90%, and an etching time of 250 seconds.
Thereafter, dry etching was performed using a mixed gas of BCl 3 and Ar as a wafer etching process. Etching conditions were an antenna power of 1700 W, a bias power of 700 W, a gas flow rate of 150 sccm, an etching selectivity of 120%, and an etching time of 280 seconds.
　その後、構造体表面に発生しているダメージ（Ｓｉ表面のダングリングボンド）を取り除く（終端処理）ため、電気炉でＨ２アニール処理（９００℃／１０分）を行った。さらに、化学研磨エッチングとして、硝酸とフッ酸の混合溶液（１：１）で３０秒間処理し、三角格子を形成する多数の凸面１ｂを有する凹凸構造（Ｉ）が、第１の表面１Ａに形成された実施例１の構造体（１）を得た。 Thereafter, in order to remove damage (dangling bonds on the Si surface) generated on the surface of the structure (termination treatment), H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 1 was obtained.
　実施例１の構造体（１）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（Ｉ）が形成されていた。 A part of the structure (1) of Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. When these values were averaged, the following uneven structure (I) was formed.
　平均ピッチＰ１ａ：６００ｎｍ
　平均高さＬ１ａ：６２０ｎｍ
　Ｌ２ａ：４２０ｎｍ
　Ｌ１ａ／Ｌ２ａ＝１．４８
　Ｌ３ａ／Ｌ２ａ＝０．８１
　Ｌ４ａ／Ｌ２ａ＝０．６２
　Ｌ５ａ／Ｌ２ａ＝０．３８
　Ｌ６ａ／Ｌ２ａ＝０．２４
　Ｌ７ａ／Ｌ２ａ＝０．１４ Average pitch P1a: 600 nm
Average height L1a: 620 nm
L2a: 420 nm
L1a / L2a = 1.48
L3a / L2a = 0.81
L4a / L2a = 0.62
L5a / L2a = 0.38
L6a / L2a = 0.24
L7a / L2a = 0.14
　こうして得られた実施例１の構造体（１）の凹凸構造（Ｉ）の上に、ＣＶＤにて厚さ１００ｎｍのシリコンシェル層２を成膜し、三角格子を形成する多数の凸面２ｂを有する凹凸構造（ＩＩ）が形成された実施例１の構造体（２）を得た。ＣＶＤ条件は、原料ガスとしてシランガスとジボランを使用し、流量を２０ｓｃｃｍ、チャンバー内圧力を８００Ｐａ、成膜時間を３分間とした。
　実施例１の構造体（２）は、シリコンコア層１とシリコンシェル層２の間に、良好なｐ/ｎ接合界面を有していた。 On the concavo-convex structure (I) of the structure (1) of Example 1 obtained in this way, a silicon shell layer 2 having a thickness of 100 nm is formed by CVD, and has a large number of convex surfaces 2b forming a triangular lattice. The structure (2) of Example 1 in which the concavo-convex structure (II) was formed was obtained. As the CVD conditions, silane gas and diborane were used as source gases, the flow rate was 20 sccm, the pressure in the chamber was 800 Pa, and the film formation time was 3 minutes.
The structure (2) of Example 1 had a good p / n junction interface between the silicon core layer 1 and the silicon shell layer 2.
　実施例１の構造体（２）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（ＩＩ）が形成されていた。 A part of the structure (2) of Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. When these values were averaged, the following uneven structure (II) was formed.
　平均ピッチＰ１ａ：６００ｎｍ
　平均高さＬ１ａ：７２０ｎｍ
　Ｌ２ａ：５８０ｎｍ
　Ｌ１ａ／Ｌ２ａ＝１．２４
　Ｌ３ａ／Ｌ２ａ＝０．９６
　Ｌ４ａ／Ｌ２ａ＝０．８０
　Ｌ５ａ／Ｌ２ａ＝０．５７
　Ｌ６ａ／Ｌ２ａ＝０．４０
　Ｌ７ａ／Ｌ２ａ＝０．２８ Average pitch P1a: 600 nm
Average height L1a: 720 nm
L2a: 580 nm
L1a / L2a = 1.24
L3a / L2a = 0.96
L4a / L2a = 0.80
L5a / L2a = 0.57
L6a / L2a = 0.40
L7a / L2a = 0.28
　その後、実施例１の構造体（２）のシリコンコア層１の第２の表面１Ｂに、Ｔｉ／Ａｇのスパッタを行って、厚さ２５０ｎｍの裏面電極５を形成し、実施例１の太陽電池を作製した。
　作成した太陽電池をソーラーシミュレーター、ソースメーターを使用して評価したところ、変換効率７．４％が得られた。 Thereafter, Ti / Ag sputtering is performed on the second surface 1B of the silicon core layer 1 of the structure (2) of Example 1 to form the back electrode 5 having a thickness of 250 nm. The solar cell of Example 1 Was made.
When the created solar cell was evaluated using a solar simulator and a source meter, a conversion efficiency of 7.4% was obtained.
［実施例２］
　実施例１の構造体（２）と同様な処理及び手法で実施例２の構造体（２）を得た。その後、シリコンコア層１の第２の表面１Ｂに東京応化工業社製ＯＣＤ（登録商標）溶液をスピンコートし、４５０℃で３０分間焼結し、さらに窒素雰囲気下で８５０℃３０分アニール処理し、裏面障壁層４（ＢＳＦ層）を形成した。さらに、実施例１と同様な処理方法で、厚さ２５０ｎｍの裏面電極５を形成し、実施例２の太陽電池を作製した。
　実施例２の太陽電池を実施例１と同様に評価したところ、変換効率８．２％が得られた。 [Example 2]
The structure (2) of Example 2 was obtained by the same process and method as the structure (2) of Example 1. Thereafter, an OCD (registered trademark) solution manufactured by Tokyo Ohka Kogyo Co., Ltd. is spin-coated on the second surface 1B of the silicon core layer 1, sintered at 450 ° C. for 30 minutes, and further annealed at 850 ° C. for 30 minutes in a nitrogen atmosphere. The back barrier layer 4 (BSF layer) was formed. Further, the back electrode 5 having a thickness of 250 nm was formed by the same processing method as in Example 1, and the solar cell of Example 2 was produced.
When the solar cell of Example 2 was evaluated in the same manner as in Example 1, a conversion efficiency of 8.2% was obtained.
［実施例３］
　実施例１の構造体（２）と同様な処理及び手法で実施例３の構造体（２）を得た。その後、ＩＴＯをスパッタにて堆積し、厚さ３０ｎｍの透明導電層３を形成し、三角格子を形成する多数の凸面３ｂを有する凹凸構造（ＩＩＩ）が形成された実施例３の構造体（３）を得た。 [Example 3]
The structure (2) of Example 3 was obtained by the same process and method as the structure (2) of Example 1. Thereafter, ITO is deposited by sputtering, the transparent conductive layer 3 having a thickness of 30 nm is formed, and the concavo-convex structure (III) having a large number of convex surfaces 3b forming a triangular lattice is formed (3) )
　実施例３の構造体（３）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（ＩＩＩ）が形成されていた。 A part of the structure (3) of Example 3 was cut perpendicularly to the surface by using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
　平均ピッチＰ１ａ：６００ｎｍ
　平均高さＬ１ａ：７６０ｎｍ
　Ｌ２ａ：６９０ｎｍ
　Ｌ１ａ／Ｌ２ａ＝１．１０
　Ｌ３ａ／Ｌ２ａ＝０．９２
　Ｌ４ａ／Ｌ２ａ＝０．７７
　Ｌ５ａ／Ｌ２ａ＝０．５８
　Ｌ６ａ／Ｌ２ａ＝０．４３
　Ｌ７ａ／Ｌ２ａ＝０．３３ Average pitch P1a: 600 nm
Average height L1a: 760 nm
L2a: 690 nm
L1a / L2a = 1.10
L3a / L2a = 0.92
L4a / L2a = 0.77
L5a / L2a = 0.58
L6a / L2a = 0.43
L7a / L2a = 0.33
　得られた、実施例３の構造体（３）に対し、実施例２と同様な処理方法で、裏面障壁層４（ＢＳＦ層）と厚さ２５０ｎｍの裏面電極５を形成し、実施例３の太陽電池を作製した。
　実施例３の太陽電池を実施例１と同様に評価したところ、変換効率１０．１％が得られた。 With respect to the structure (3) obtained in Example 3, the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same processing method as in Example 2. A solar cell was produced.
When the solar cell of Example 3 was evaluated in the same manner as in Example 1, a conversion efficiency of 10.1% was obtained.
［実施例４］
　厚さの異なるＳｉ基板（厚さ：０．２８０ｍｍ）を使用した以外、実施例１と同様な手法で単粒子膜付の基板を得た。その後、粒子エッチング工程としてＣＦ４及びＯ２の混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１７００Ｗ、バイアス電力１５００Ｗ、ガス流量１５０ｓｃｃｍ、エッチング選択比９０％、エッチング時間３００秒とした。その後、ウエハエッチング工程としてＢＣｌ３及びＡｒの混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１７００Ｗ、バイアス電力５００Ｗ、ガス流量１５０ｓｃｃｍ、エッチング選択比１２０％、エッチング時間２４０秒とした。 [Example 4]
A substrate with a single particle film was obtained in the same manner as in Example 1 except that Si substrates having different thicknesses (thickness: 0.280 mm) were used. Thereafter, dry etching was performed with a mixed gas of CF 4 and O 2 as a particle etching process. Etching conditions were an antenna power of 1700 W, a bias power of 1500 W, a gas flow rate of 150 sccm, an etching selectivity of 90%, and an etching time of 300 seconds. Thereafter, dry etching was performed using a mixed gas of BCl 3 and Ar as a wafer etching process. Etching conditions were an antenna power of 1700 W, a bias power of 500 W, a gas flow rate of 150 sccm, an etching selectivity of 120%, and an etching time of 240 seconds.
　その後、構造体表面に発生しているダメージ（Ｓｉ表面のダングリングボンド）を取り除く（終端処理）ため、電気炉でＨ２アニール処理（９００℃／１０分）を行った。さらに、化学研磨エッチングとして、硝酸とフッ酸の混合溶液（１：１）で３０秒間処理し、三角格子を形成する多数の凸面１ｂを有する凹凸構造（Ｉ）が、第１の表面１Ａに形成された実施例４の構造体（１）を得た。
　その後、実施例１と同様な処理及び手法で厚さ１００ｎｍのシリコンシェル層２を成膜し、実施例３と同様な処理及び手法にて厚さ３０ｎｍの透明導電層３を成膜し、実施例４の構造体（３）を得た。 Thereafter, in order to remove damage (dangling bonds on the Si surface) generated on the surface of the structure (termination treatment), H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 4 was obtained.
Thereafter, a silicon shell layer 2 having a thickness of 100 nm is formed by the same process and method as in Example 1, and a transparent conductive layer 3 having a thickness of 30 nm is formed by the same process and method as in Example 3 The structure (3) of Example 4 was obtained.
　実施例４の構造体（３）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（ＩＩＩ）が形成されていた。 A part of the structure (3) of Example 4 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
　平均ピッチＰ１ａ：６００ｎｍ
　平均高さＬ１ａ：５４０ｎｍ
　Ｌ２ａ：６９０ｎｍ
　Ｌ１ａ／Ｌ２ａ＝０．７８
　Ｌ３ａ／Ｌ２ａ＝０．９３
　Ｌ４ａ／Ｌ２ａ＝０．７５
　Ｌ５ａ／Ｌ２ａ＝０．５５
　Ｌ６ａ／Ｌ２ａ＝０．４０
　Ｌ７ａ／Ｌ２ａ＝０．３０ Average pitch P1a: 600 nm
Average height L1a: 540 nm
L2a: 690 nm
L1a / L2a = 0.78
L3a / L2a = 0.93
L4a / L2a = 0.75
L5a / L2a = 0.55
L6a / L2a = 0.40
L7a / L2a = 0.30
　得られた、実施例４の構造体（３）に対し、実施例２と同様な処理方法で、裏面障壁層４（ＢＳＦ層）と厚さ２５０ｎｍの裏面電極５を形成し、実施例４の太陽電池を作製した。
　実施例４の太陽電池を実施例１と同様に評価したところ、変換効率１３．７％が得られた。 With respect to the structure (3) obtained in Example 4, the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same processing method as in Example 2. A solar cell was produced.
When the solar cell of Example 4 was evaluated in the same manner as in Example 1, a conversion efficiency of 13.7% was obtained.
［実施例５］
　厚さの異なるＳｉ基板（厚さ：０．２８０ｍｍ）を使用し、平均粒径が３００ｎｍで、粒径の変動係数が３．４４％である球形コロイダルシリカを使用した以外、実施例１と同様な手法で単粒子膜付の基板を得た。その後、ＢＣｌ３及びＣｌ２混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１５００Ｗ、バイアス電力７００Ｗ、ガス流量１００ｓｃｃｍ、エッチング選択比１６０％、エッチング時間２３０秒とした。 [Example 5]
Similar to Example 1 except that Si substrates (thickness: 0.280 mm) having different thicknesses were used, and spherical colloidal silica having an average particle size of 300 nm and a particle size variation coefficient of 3.44% was used. A substrate with a single particle film was obtained by various methods. Thereafter, dry etching was performed with a mixed gas of BCl 3 and Cl 2 . Etching conditions were an antenna power of 1500 W, a bias power of 700 W, a gas flow rate of 100 sccm, an etching selectivity of 160%, and an etching time of 230 seconds.
　その後、構造体表面に発生しているダメージ（Ｓｉ表面のダングリングボンド）を取り除く（終端処理）ため、電気炉でＨ２アニール処理（９００℃／１０分）を行った。さらに、化学研磨エッチングとして、硝酸とフッ酸の混合溶液（１：１）で３０秒間処理し、三角格子を形成する多数の凸面１ｂを有する凹凸構造（Ｉ）が、第１の表面１Ａに形成された実施例５の構造体（１）を得た。
　その後、実施例１と同様な処理及び手法で厚さ１００ｎｍのシリコンシェル層２を成膜し、実施例３と同様な処理及び手法にて厚さ３０ｎｍの透明導電層３を成膜し、三角格子を形成する多数の凸面３ｂを有する凹凸構造（Ｉ）が形成された実施例５の構造体（３）を得た。 Thereafter, in order to remove damage (dangling bonds on the Si surface) generated on the surface of the structure (termination treatment), H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Further, as chemical polishing etching, a concavo-convex structure (I) having a large number of convex surfaces 1b forming a triangular lattice is formed on the first surface 1A by treatment with a mixed solution of nitric acid and hydrofluoric acid (1: 1) for 30 seconds. A structure (1) of Example 5 was obtained.
Thereafter, a silicon shell layer 2 having a thickness of 100 nm is formed by the same process and method as in Example 1, and a transparent conductive layer 3 having a thickness of 30 nm is formed by the same process and method as in Example 3 to form a triangle. The structure (3) of Example 5 in which the concavo-convex structure (I) having a large number of convex surfaces 3b forming the lattice was obtained.
　実施例５の構造体（３）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（ＩＩＩ）が形成されていた。 A part of the structure (3) of Example 5 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (III) was formed.
　平均ピッチＰ１ａ：３００ｎｍ
　平均高さＬ１ａ：５４０ｎｍ
　Ｌ２ａ：２９５ｎｍ
　Ｌ１ａ／Ｌ２ａ＝１．８３
　Ｌ３ａ／Ｌ２ａ＝０．９４
　Ｌ４ａ／Ｌ２ａ＝０．７９
　Ｌ５ａ／Ｌ２ａ＝０．５８
　Ｌ６ａ／Ｌ２ａ＝０．４６
　Ｌ７ａ／Ｌ２ａ＝０．３６ Average pitch P1a: 300 nm
Average height L1a: 540 nm
L2a: 295 nm
L1a / L2a = 1.83
L3a / L2a = 0.94
L4a / L2a = 0.79
L5a / L2a = 0.58
L6a / L2a = 0.46
L7a / L2a = 0.36
　得られた、実施例５の構造体（３）に対し、実施例２と同様な処理方法で、裏面障壁層４（ＢＳＦ層）と厚さ２５０ｎｍの裏面電極５を形成し、実施例５の太陽電池を作製した。
　実施例５の太陽電池を実施例1と同様に評価したところ、変換効率１１．７％が得られた。 With respect to the structure (3) obtained in Example 5, the back barrier layer 4 (BSF layer) and the back electrode 5 having a thickness of 250 nm were formed by the same treatment method as in Example 2. A solar cell was produced.
When the solar cell of Example 5 was evaluated in the same manner as in Example 1, a conversion efficiency of 11.7% was obtained.
［比較例１］
　平均粒径が３００ｎｍで、粒径の変動係数が３．４４％である球形コロイダルシリカを使用した以外、実施例１と同様な手法で単粒子膜付の基板を得た。その後、ＣＨＦ３及びＣｌ２の混合ガスによりドライエッチングを行った。エッチング条件は、アンテナ電力１７００Ｗ、バイアス電力７００Ｗ、ガス流量１００ｓｃｃｍ、エッチング選択比４６０％、エッチング時間２６０秒とした。 [Comparative Example 1]
A substrate with a single particle film was obtained in the same manner as in Example 1 except that spherical colloidal silica having an average particle size of 300 nm and a particle size variation coefficient of 3.44% was used. Thereafter, dry etching was performed with a mixed gas of CHF 3 and Cl 2 . Etching conditions were an antenna power of 1700 W, a bias power of 700 W, a gas flow rate of 100 sccm, an etching selectivity of 460%, and an etching time of 260 seconds.
　その後、構造体表面に発生しているダメージ（Ｓｉ表面のダングリングボンド）を取り除く（終端処理）ため、電気炉でＨ２アニール処理（９００℃／１０分）を行った。さらに、化学研磨エッチングとして、硝酸とフッ酸の混合溶液（１：１）で３０秒間処理し、三角格子を形成する凸面１ｂを有する凹凸構造（Ｉ’）が、第１の表面１Ａに形成された比較例１の構造体（１）を得た。 Thereafter, in order to remove damage (dangling bonds on the Si surface) generated on the surface of the structure (termination treatment), H 2 annealing treatment (900 ° C./10 minutes) was performed in an electric furnace. Furthermore, as chemical polishing etching, a concavo-convex structure (I ′) having a convex surface 1b that forms a triangular lattice is formed on the first surface 1A by treatment with a mixed solution (1: 1) of nitric acid and hydrofluoric acid for 30 seconds. The structure (1) of Comparative Example 1 was obtained.
　こうして得られた比較例１の構造体（１）の凹凸構造（Ｉ’）の上に、ＣＶＤにて厚さ１００ｎｍのシリコンシェル層２を成膜し、三角格子を形成する多数の凸面２ｂを有する凹凸構造（ＩＩ’）が形成された比較例１の構造体（２）を得た。ＣＶＤ条件は、原料ガスとしてシランガスとジボランを使用し、流量を２０ｓｃｃｍ、チャンバー内圧力を８００Ｐａ、成膜時間を６分間とした。
　比較例１の構造体（２）は、シリコンコア層１とシリコンシェル層２の間に、良好なｐ/ｎ接合界面を有していた。 On the concavo-convex structure (I ′) of the structure (1) of Comparative Example 1 thus obtained, a silicon shell layer 2 having a thickness of 100 nm is formed by CVD, and a large number of convex surfaces 2b forming a triangular lattice are formed. The structure (2) of Comparative Example 1 in which the concavo-convex structure (II ′) was formed was obtained. As the CVD conditions, silane gas and diborane were used as source gases, the flow rate was 20 sccm, the pressure in the chamber was 800 Pa, and the film formation time was 6 minutes.
The structure (2) of Comparative Example 1 had a good p / n junction interface between the silicon core layer 1 and the silicon shell layer 2.
　比較例１の構造体（２）の一部を、ミクロトームを用いて表面に対して垂直に切断して１辺が１０ｍｍ程度の略正方形の小片サンプルを得て、その切断面と表面の走査電子顕微鏡（ＳＥＭ）画像を各々複数枚得た。これらの画像から、前記した方法で、３０個の凸面１ｂのＬ１～Ｌ７、及び３０対の凸面１ｂピッチＰ１を求めた。これらの値を平均して求めたところ以下のような凹凸構造（ＩＩ’）が形成されていた。 A portion of the structure (2) of Comparative Example 1 was cut perpendicularly to the surface using a microtome to obtain a small square sample having a side of about 10 mm, and scanning electrons on the cut surface and the surface. A plurality of microscope (SEM) images were obtained. From these images, L1 to L7 of 30 convex surfaces 1b and 30 pairs of convex surface 1b pitches P1 were obtained by the method described above. As a result of averaging these values, the following uneven structure (II ') was formed.
　平均ピッチＰ１ａ：３００ｎｍ
　平均高さＬ１ａ：１４００ｎｍ
　Ｌ２ａ：３００ｎｍ
　Ｌ１ａ／Ｌ２ａ＝１．２４
　Ｌ３ａ／Ｌ２ａ＝０．９６
　Ｌ４ａ／Ｌ２ａ＝０．９１
　Ｌ５ａ／Ｌ２ａ＝０．８２
　Ｌ６ａ／Ｌ２ａ＝０．７４
　Ｌ７ａ／Ｌ２ａ＝０．６７ Average pitch P1a: 300 nm
Average height L1a: 1400nm
L2a: 300 nm
L1a / L2a = 1.24
L3a / L2a = 0.96
L4a / L2a = 0.91
L5a / L2a = 0.82
L6a / L2a = 0.74
L7a / L2a = 0.67
　その後、比較例１の構造体（２）のシリコンコア層１の第２の表面１Ｂに、Ｔｉ／Ａｇのスパッタを行って裏面電極５を形成し、比較例１の太陽電池を作製した。
　比較例１の太陽電池を実施例１と同様に評価したところ、変換効率３．２％が得られた。 Thereafter, Ti / Ag was sputtered on the second surface 1B of the silicon core layer 1 of the structure (2) of Comparative Example 1 to form the back electrode 5, and the solar cell of Comparative Example 1 was fabricated.
When the solar cell of Comparative Example 1 was evaluated in the same manner as in Example 1, a conversion efficiency of 3.2% was obtained.
　本発明の光電変換素子及び本発明の光電変換素子用構造体を用いた光電変換素子は、太陽電池、ｐｎ接合を利用したセンサー、分子吸着識別用の高感度センサー等として利用可能である。 The photoelectric conversion element using the photoelectric conversion element of the present invention and the structure for photoelectric conversion element of the present invention can be used as a solar cell, a sensor using a pn junction, a high-sensitivity sensor for molecular adsorption identification, and the like.
　１　シリコンコア層
　２　シリコンシェル層
　３　透明導電層
　４　裏面障壁層
　５　裏面電極
　６　表面電極
１０、２０、３０　光電変換素子用構造体
４０、５０、６０　光電変換素子 DESCRIPTION OF SYMBOLS 1 Silicon core layer 2 Silicon shell layer 3 Transparent conductive layer 4 Back surface barrier layer 5 Back surface electrode 6 Surface electrode 10, 20, 30 Structure 40, 50, 60 for photoelectric conversion elements Photoelectric conversion element

Claims (21)

  1. 　ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層を備える光電変換素子用構造体であって、
    　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
    　前記第１の表面が、多数の凸面を有する凹凸構造（Ｉ）とされており、
    　前記凹凸構造（Ｉ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１０００ｎｍであることを特徴とする光電変換素子用構造体。     A structure for a photoelectric conversion element including a silicon core layer made of silicon doped in n-type or p-type,
    The silicon core layer has a first surface and a second surface opposite the first surface;
    The first surface is a concavo-convex structure (I) having a number of convex surfaces,
    A large number of convex surfaces in the concavo-convex structure (I) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1000 nm.
  2. 　前記凹凸構造（Ｉ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している請求項１に記載の光電変換素子用構造体。 2. The photoelectric conversion element structure according to claim 1, wherein a number of convex surfaces in the concavo-convex structure (I) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
  3. 　前記凹凸構造（Ｉ）における多数の凸面が、下記条件Ｘを満たす請求項１又は２に記載の光電変換素子用構造体。
    （条件Ｘ）
    　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
    　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
    　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
    　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
    　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
    　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
    　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
    　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
    　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。     The structure for photoelectric conversion elements according to claim 1, wherein a number of convex surfaces in the uneven structure (I) satisfy the following condition X.
    (Condition X)
    When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
    L1a / L2a = 0.1 to 10.0 (1)
    L3a / L2a = 0.7 to 1.0 (2)
    L4a / L2a = 0.4 to 0.9 (3)
    L5a / L2a = 0.15 to 0.8 (4)
    L6a / L2a = 0.07 to 0.7 (5)
    L7a / L2a = 0.03 to 0.6 (6)
    L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
    However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  4. 　ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層と、前記シリコンコア層とｐｎ接合を形成するように、ｐ型又はｎ型にドープされたシリコンからなるシリコンシェル層を備える光電変換素子用構造体であって、
    　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
    　前記シリコンシェル層は前記第１の表面に前記ｐｎ接合を形成するように設けられ、
    　前記シリコンシェル層の表面が、多数の凸面を有する凹凸構造（ＩＩ）とされており、
    　前記凹凸構造（ＩＩ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１０００ｎｍであることを特徴とする光電変換素子用構造体。     A photoelectric conversion element comprising: a silicon core layer made of silicon doped n-type or p-type; and a silicon shell layer made of silicon doped p-type or n-type so as to form a pn junction with the silicon core layer A structure for
    The silicon core layer has a first surface and a second surface opposite the first surface;
    The silicon shell layer is provided to form the pn junction on the first surface;
    The surface of the silicon shell layer is a concavo-convex structure (II) having a large number of convex surfaces,
    A large number of convex surfaces in the concavo-convex structure (II) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut along a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1000 nm.
  5. 　前記凹凸構造（ＩＩ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している請求項４に記載の光電変換素子用構造体。 The photoelectric conversion element structure according to claim 4, wherein a number of convex surfaces in the concavo-convex structure (II) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
  6. 　前記凹凸構造（ＩＩ）における多数の凸面が、下記条件Ｘを満たす請求項４又は５に記載の光電変換素子用構造体。
    （条件Ｘ）
    　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
    　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
    　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
    　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
    　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
    　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
    　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
    　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
    　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。     The structure for photoelectric conversion elements according to claim 4 or 5, wherein a number of convex surfaces in the uneven structure (II) satisfy the following condition X.
    (Condition X)
    When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
    L1a / L2a = 0.1 to 10.0 (1)
    L3a / L2a = 0.7 to 1.0 (2)
    L4a / L2a = 0.4 to 0.9 (3)
    L5a / L2a = 0.15 to 0.8 (4)
    L6a / L2a = 0.07 to 0.7 (5)
    L7a / L2a = 0.03 to 0.6 (6)
    L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
    However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  7. 　前記シリコンコア層の前記第１の表面が凹凸構造とされており、前記凹凸構造（ＩＩ）は、前記シリコンコア層の前記第１の表面の凹凸構造に追従している請求項４～６のいずれか一項に記載の光電変換素子用構造体。 The first surface of the silicon core layer has an uneven structure, and the uneven structure (II) follows the uneven structure of the first surface of the silicon core layer. The structure for photoelectric conversion elements according to any one of the above.
  8. 　ｎ型又はｐ型にドープされたシリコンからなるシリコンコア層と、前記シリコンコア層とｐｎ接合を形成するように、ｐ型又はｎ型にドープされたシリコンからなるシリコンシェル層と、前記シリコンシェル層の表面を覆う透明導電層を備える光電変換素子用構造体であって、
    　前記シリコンコア層は、第１の表面と前記第１の表面の反対側の第２の表面を有し、
    　前記シリコンシェル層は前記第１の表面に前記ｐｎ接合を形成するように設けられ、
    　前記透明導電層の表面が、多数の凸面を有する凹凸構造（ＩＩＩ）とされており、
    　前記凹凸構造（ＩＩＩ）における多数の凸面は、前記第２の表面に対して垂直な平面で切断したときに、各凸面の最下部を基準とする当該凸面の頂点の高さＬ１の平均である平均高さＬ１ａが１００～１１００ｎｍであることを特徴とする光電変換素子用構造体。     a silicon core layer made of n-type or p-type doped silicon, a silicon shell layer made of p-type or n-type doped silicon so as to form a pn junction with the silicon core layer, and the silicon shell A photoelectric conversion element structure comprising a transparent conductive layer covering the surface of the layer,
    The silicon core layer has a first surface and a second surface opposite the first surface;
    The silicon shell layer is provided to form the pn junction on the first surface;
    The surface of the transparent conductive layer is a concavo-convex structure (III) having a large number of convex surfaces,
    A number of convex surfaces in the concavo-convex structure (III) are averages of the heights L1 of the vertices of the convex surfaces with respect to the lowest part of each convex surface when cut by a plane perpendicular to the second surface. A structure for a photoelectric conversion element, wherein the average height L1a is 100 to 1100 nm.
  9. 　前記凹凸構造（ＩＩＩ）における多数の凸面が、平均ピッチＰ１ａが１００～１０００ｎｍの三角格子又は正方格子を形成している請求項８に記載の光電変換素子用構造体。 The photoelectric conversion element structure according to claim 8, wherein a number of convex surfaces in the concavo-convex structure (III) form a triangular lattice or a square lattice having an average pitch P1a of 100 to 1000 nm.
  10. 　前記凹凸構造（ＩＩＩ）における多数の凸面が、下記条件Ｘを満たす請求項８又は９に記載の光電変換素子用構造体。
    （条件Ｘ）
    　前記第２の表面に対して垂直な平面で切断したときに、前記切断面から観察される多数の凸面の形状が下記式（１）～（７）を満たす。
    　　Ｌ１ａ／Ｌ２ａ＝０．１～１０．０　・・・（１）
    　　Ｌ３ａ／Ｌ２ａ＝０．７～１．０　・・・（２）
    　　Ｌ４ａ／Ｌ２ａ＝０．４～０．９　・・・（３）
    　　Ｌ５ａ／Ｌ２ａ＝０．１５～０．８　・・・（４）
    　　Ｌ６ａ／Ｌ２ａ＝０．０７～０．７　・・・（５）
    　　Ｌ７ａ／Ｌ２ａ＝０．０３～０．６　・・・（６）
    　　Ｌ２ａ≧Ｌ３ａ≧Ｌ４ａ≧Ｌ５ａ≧Ｌ６ａ≧Ｌ７ａ　・・・（７）
    　ただし、Ｌ１ａは前記と同じであり、Ｌ２ａ、Ｌ３ａ、Ｌ４ａ、Ｌ５ａ、Ｌ６ａ、Ｌ７ａはそれぞれ、Ｌ２、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７の平均であり、Ｌ２は前記Ｌ１を求めた凸面の最下部における当該凸面の底部幅、Ｌ３、Ｌ４、Ｌ５、Ｌ６、Ｌ７はそれぞれ、当該凸面の最下部を基準とする高さがＬ１の１／４、１／２、３／４、７／８、１５／１６における当該凸面の幅である。     The structure for photoelectric conversion elements according to claim 8 or 9, wherein a number of convex surfaces in the uneven structure (III) satisfy the following condition X.
    (Condition X)
    When cut along a plane perpendicular to the second surface, the shape of many convex surfaces observed from the cut surface satisfies the following formulas (1) to (7).
    L1a / L2a = 0.1 to 10.0 (1)
    L3a / L2a = 0.7 to 1.0 (2)
    L4a / L2a = 0.4 to 0.9 (3)
    L5a / L2a = 0.15 to 0.8 (4)
    L6a / L2a = 0.07 to 0.7 (5)
    L7a / L2a = 0.03 to 0.6 (6)
    L2a ≧ L3a ≧ L4a ≧ L5a ≧ L6a ≧ L7a (7)
    However, L1a is the same as the above, L2a, L3a, L4a, L5a, L6a, and L7a are averages of L2, L3, L4, L5, L6, and L7, respectively, and L2 is the maximum of the convex surface from which L1 is obtained. The bottom width, L3, L4, L5, L6, and L7 of the convex surface at the lower part are 1/4, 1/2, 3/4, 7/8, The width of the convex surface at 15/16.
  11. 　前記シリコンコア層の前記第１の表面が凹凸構造とされており、前記シリコンシェル層の表面は、前記シリコンコア層の前記第１の表面の凹凸構造に追従した凹凸構造とされており、前記凹凸構造（ＩＩＩ）は、前記シリコンコア層の前記第１の表面の凹凸構造及び前記シリコンシェル層の表面の凹凸構造に追従している請求項８～１０のいずれか一項に記載の光電変換素子用構造体。 The first surface of the silicon core layer has an uneven structure, and the surface of the silicon shell layer has an uneven structure following the uneven structure of the first surface of the silicon core layer, 11. The photoelectric conversion according to claim 8, wherein the concavo-convex structure (III) follows the concavo-convex structure on the first surface of the silicon core layer and the concavo-convex structure on the surface of the silicon shell layer. Element structure.
  12. 　請求項８～１１のいずれか一項に記載の光電変換素子用構造体と、前記シリコンコア層の前記第２の表面に、直接又は間接的に設けられた裏面電極を備えることを特徴とする光電変換素子。 A structure for a photoelectric conversion element according to any one of claims 8 to 11, and a back electrode provided directly or indirectly on the second surface of the silicon core layer. Photoelectric conversion element.
  13. 　さらに、前記透明導電層に、電気的に導通可能な状態で接触する表面電極を備える請求項１２に記載の光電変換素子。 Furthermore, the photoelectric conversion element of Claim 12 provided with the surface electrode which contacts the said transparent conductive layer in the state which can be electrically conducted.
  14. 　請求項４～７のいずれか一項に記載の光電変換素子用構造体と、前記シリコンコア層の前記第２の表面に、直接又は間接的に設けられた裏面電極を備えることを特徴とする光電変換素子。 A structure for a photoelectric conversion device according to any one of claims 4 to 7, and a back electrode provided directly or indirectly on the second surface of the silicon core layer. Photoelectric conversion element.
  15. 　さらに、前記シリコンシェル層に、電気的に導通可能な状態で接触する表面電極を備える請求項１４に記載の光電変換素子。 Furthermore, the photoelectric conversion element of Claim 14 provided with the surface electrode which contacts the said silicon shell layer in the state which can be electrically conduct | electrically_connected.
  16. 　請求項１～３のいずれか一項に記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成することを特徴とする光電変換素子用構造体の製造方法。 A silicon shell layer is formed by depositing a doped silicon material opposite to the silicon core layer on the first surface of the photoelectric conversion element structure according to any one of claims 1 to 3. A method for producing a structure for a photoelectric conversion element, comprising:
  17. 　前記形成したシリコンシェル層の表面に、さらに透明導電材料を堆積させて透明導電層を形成する請求項１６に記載の光電変換素子用構造体の製造方法。 The method for producing a structure for a photoelectric conversion element according to claim 16, wherein a transparent conductive layer is formed by further depositing a transparent conductive material on the surface of the formed silicon shell layer.
  18. 　請求項１～３のいずれか一項に記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成し、前記形成したシリコンシェル層の表面に、透明導電材料を堆積させて透明導電層を形成し、
    　さらに、前記シリコンコア層の前記第２の表面に、直接又は間接的に裏面電極を設けることを特徴とする光電変換素子の製造方法。     A silicon shell layer is formed by depositing a doped silicon material opposite to the silicon core layer on the first surface of the photoelectric conversion element structure according to any one of claims 1 to 3. On the surface of the formed silicon shell layer, a transparent conductive material is deposited to form a transparent conductive layer,
    Furthermore, the back surface electrode is provided directly or indirectly on the second surface of the silicon core layer.
  19. 　さらに、前記透明導電層と電気的に導通可能な状態で接触する表面電極を設ける請求項１８に記載の光電変換素子の製造方法。 Furthermore, the manufacturing method of the photoelectric conversion element of Claim 18 which provides the surface electrode which contacts the said transparent conductive layer in the state which can be electrically conducted.
  20. 　請求項１～３のいずれか一項に記載の光電変換素子用構造体の前記第１の表面に、前記シリコンコア層と反対のドープ型のシリコン材料を堆積させてシリコンシェル層を形成し、
    　さらに、前記シリコンコア層の前記第２の表面に、直接又は間接的に裏面電極を設けることを特徴とする光電変換素子の製造方法。     A silicon shell layer is formed by depositing a doped silicon material opposite to the silicon core layer on the first surface of the photoelectric conversion element structure according to any one of claims 1 to 3.
    Furthermore, the back surface electrode is provided directly or indirectly on the second surface of the silicon core layer.
  21. 　さらに、前記シリコンシェル層と電気的に導通可能な状態で接触する表面電極を設ける請求項２０に記載の光電変換素子の製造方法。 Furthermore, the manufacturing method of the photoelectric conversion element of Claim 20 which provides the surface electrode which contacts the said silicon shell layer in the state which can be electrically conducted.
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