JP2011009245A - Photoelectric converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric converter having at least one or more photoelectric conversion units and having a structure capable of obtaining high short circuit current density and sufficient conversion efficiency.SOLUTION: The photoelectric converter having at least one or more photoelectric conversion units is characterized in that each photoelectric conversion unit has an uneven structure on a light incident side, and a structure having a cyclic change in refractive index is disposed adjacently on the side opposite to the light incidence in a photoelectric conversion unit disposed furthest from the light incident side out of the one or more photoelectric conversion units.

Description

  The present invention relates to a photoelectric conversion device. More specifically, the present invention relates to a photoelectric conversion device with a high conversion efficiency having a structure that exhibits a high light confinement effect.

  A photoelectric conversion device typified by a solar cell includes a photoelectric conversion layer that generates a pair of electrons and holes (hereinafter also referred to as carriers) by a photoelectric conversion action, and a carrier that generates a pair of diffusion potentials in the photoelectric conversion layer. In general, the photoelectric conversion layer includes a conductive type layer to be collected and is sandwiched between conductive type layers having two different conductive types. This sandwiched structure is called a photoelectric conversion unit.

  The conductive layer is an inactive layer that does not directly contribute to photoelectric conversion, and light absorbed by the impurities doped in the conductive layer results in a loss that does not contribute to power generation. Furthermore, if the conductivity of the conductive layer is low, the series resistance increases and the photoelectric conversion characteristics of the thin film photoelectric conversion device are degraded. Therefore, it is preferable that the conductive layer has a thickness as small as possible within a range in which a sufficient diffusion potential can be generated, that is, is as transparent as possible and has a high conductivity.

  On the other hand, the photoelectric conversion layer is preferably thick in order to increase the light absorption, increase the pair generation of carriers, and increase the photocurrent. However, if the photoelectric conversion layer is too thick for the carrier mobility, the collection of the paired carriers is not collected. It becomes insufficient. Further, since the material cost increases when the photoelectric conversion layer is thick, it is preferable that the photoelectric conversion layer is as thin as possible from the viewpoint of cost. Therefore, it is preferable that the photoelectric conversion layer has a thickness as small as possible within a range in which sufficient pair generation can be caused. Therefore, effective use of incident light is important for improving photoelectric conversion efficiency.

  As a method for effectively using incident light, a method using an antireflection film is known. The antireflection film is formed on the surface of the photoelectric conversion device on the light incident side, and serves to reduce light reflection caused by the difference in refractive index and increase the light incident on the photoelectric conversion device.

  In addition, in order to make effective use of incident light, it is also known that the surface of the photoelectric conversion layer has a minute uneven structure. With this minute uneven structure, incident light is scattered inside the photoelectric conversion layer, the optical path length is extended, and light can be confined. Although this minute uneven structure is formed by various methods, it is general to use random unevenness that is not periodic. Due to this optical confinement effect, more carrier pairs can be generated.

  Further, as a method of effectively using incident light, there is a structure having a high-reflectance back electrode adjacent to a conductive type layer opposite to the light incident side (hereinafter also referred to as a back side). This high-reflectance back electrode prevents light from escaping to the back side, and the reflected light is again incident on the photoelectric conversion layer, so that more pairs of carriers can be generated due to the effect of light confinement.

  As described above, photoelectric conversion devices having various structures having high conversion efficiency by controlling and effectively using incident light have been developed and put into practical use.

  By the way, in recent years, research and development of a photonic crystal, which is a new method for freely controlling light, has been rapidly advanced. A photonic crystal is expressed as a “crystal” but is not necessarily composed of a crystalline material. It is known that an electron wave exhibits a unique behavior in a structure in which atoms are regularly and periodically arranged, that is, in a crystal. Such a structure is widely called a “photonic crystal” because the light wave exhibits a similar behavior in a structure whose refractive index changes regularly and periodically. A more specific definition of the photonic crystal is “a substance having a periodic refractive index change structure having a length of about the wavelength of light”. In the photonic crystal, the light can be localized by the interaction between the light and the particle field and can be kept for a long time, and the controllability of the light is remarkably improved. Various devices such as an optical waveguide, a polarizing filter, and a surface emitting laser using such characteristics have been studied or put into practical use. In addition, depending on the structure and material of the photonic crystal, it is possible to completely prohibit the presence of light in a specific wavelength (energy) band in the photonic crystal. Such a wavelength band is called a photonic band gap, A case having a photonic band gap with respect to incident light from all directions is called a complete photonic band gap.

  Studies are also being conducted on the application of photonic crystals to photoelectric conversion devices. Patent Document 1 discloses a structure of a photoelectric conversion device having a photonic crystal by providing a periodic fine pattern on the side opposite to light incidence (back side) or on the light incidence side. The incident light that has reached the bottom of the photoelectric conversion layer can be efficiently reflected, and the photoelectric conversion efficiency can be increased. However, in Japanese Patent Application Laid-Open No. H11-228707, sufficient characteristics are obtained despite the use of a 10 μm-thick single crystal silicon thin film that has been epitaxially grown and peeled off from porous silicon substantially formed on single crystal silicon. There was a problem that could not be obtained. Furthermore, this formation process also requires a high-temperature process of 1000 ° C. or higher, which is not preferable from the viewpoint of manufacturing a low-cost thin film photoelectric conversion device.

  Non-Patent Document 1 theoretically shows that high photoelectric conversion efficiency can be obtained by arranging various photonic crystal structures on the back side of the photoelectric conversion device. Further, Non-Patent Document 2 shows that a silicon-on-insulator substrate is used. Discloses characteristics of a thin film single crystal silicon photoelectric conversion device in which various photonic crystal structures are formed on the back side of a single crystal silicon thin film having a thickness of 5 μm formed by the peeling method. However, in any case, a sufficient conversion efficiency has not been achieved even though a single crystal silicon thin film having a relatively thick film thickness (5 μm or more) is used as the thin film.

JP 2001-127313 A

P. Bermel et al, OPTICS EXPRESS, Vol.15, No.25, 16986, 10 December 2007 L. Zeng et al, APPLIED PHYSICS LETTERS 93, 221105, 2008

  The present invention provides a structure for obtaining a high light confinement effect that has been insufficient in the prior art by a photoelectric conversion device having a concavo-convex structure on the light incident side and a novel photonic crystal structure on the side opposite to the light incident. The object is to provide a photoelectric conversion device with high conversion efficiency. In particular, non-single-crystal silicon formed on a heterogeneous substrate having a small light absorption coefficient and a high defect density at a low temperature of 500 ° C. or less is preferably used as a photoelectric conversion layer with a thickness of 10 μm or less, more preferably 3 μm or less. In some cases, it is an object to achieve a structure that obtains a high light confinement effect and to provide a photoelectric conversion device with high conversion efficiency.

  As a result of intensive studies, the present inventors have found that the above problem can be solved by the following configuration, and have completed the present invention.

  That is, the present invention is a photoelectric conversion device having at least one or more photoelectric conversion units, wherein the photoelectric conversion unit has a concavo-convex structure on a light incident side, and light among the one or more photoelectric conversion units is light. The present invention relates to a photoelectric conversion device in which a structure having a periodic refractive index change is arranged adjacent to the opposite side of light incidence in a photoelectric conversion unit arranged farthest from the incident side. The term “adjacent” does not necessarily mean that the photoelectric conversion unit and the structure having a periodic refractive index change are strictly adjacent to each other, and the effect of the present invention is lost. This means that it may include a case where something is sandwiched between the photoelectric conversion unit and a structure having a periodic refractive index change within a range that does not exist.

  In a preferred embodiment, the uneven structure has a height difference of 20 to 400 nm, the distance between the vertices of the protrusions is 50 to 1000 nm, and the surface area ratio of the protrusions and recesses is in the range of 20% to 90%. The present invention relates to the photoelectric conversion device.

  In a preferred embodiment, a structure having a periodic refractive index change adjacent to the light incident side opposite to the light incident side in the photoelectric conversion unit disposed farthest from the light incident side is formed by alternating two materials having different refractive indexes. It is comprised from the multilayer alternating film laminated | stacked on the said photoelectric conversion apparatus characterized by the above-mentioned.

  In a preferred embodiment, the multilayer alternating film is obtained by alternately laminating a material having a refractive index of 1.9 or more and a material having a refractive index of less than 1.9 at a wavelength of 600 nm. About.

  In a preferred embodiment, the structure having a periodic refractive index change adjacent to the light incident side opposite to the light incident in the photoelectric conversion unit disposed farthest from the light incident side has a two-dimensional photonic crystal structure. The present invention relates to the photoelectric conversion device.

  In a preferred embodiment, the structure having a periodic refractive index change adjacent to the opposite side of the light incidence in the photoelectric conversion unit arranged farthest from the light incident side has a two-dimensional photonic crystal structure and a wavelength It has a multilayer alternating film in which a material having a refractive index at 600 nm of 1.9 or more and a material having a refractive index of less than 1.9 are alternately laminated, and the two-dimensional photonic crystal structure is on the light incident side The present invention relates to the photoelectric conversion device.

In a preferred embodiment, at least one of the materials having different refractive indexes forming the two-dimensional photonic crystal structure has a conductivity of 10 S / cm or more and 10 ⁶ S / cm or less. The present invention relates to a photoelectric conversion device.

  In a preferred embodiment, the structure having a periodic refractive index change adjacent to the light incident side of the photoelectric conversion unit disposed farthest from the light incident side has a three-dimensional photonic crystal structure. The present invention relates to the photoelectric conversion device.

  A preferred embodiment relates to the photoelectric conversion device, wherein the three-dimensional photonic crystal structure is an opal structure.

In a preferred embodiment, at least one of the materials having different refractive indexes forming the three-dimensional photonic crystal structure has a conductivity of 10 S / cm or more and 10 ⁶ S / cm or less. The present invention relates to a photoelectric conversion device.

  A preferred embodiment relates to the photoelectric conversion device, wherein the photoelectric conversion unit is formed on a transparent insulating substrate, and has a structure in which light is incident through the transparent insulating substrate.

  A preferred embodiment relates to the photoelectric conversion device, wherein the photoelectric conversion unit contains a group 14 element of the periodic table as a main component.

  A preferred embodiment relates to the photoelectric conversion device, wherein the film thickness of at least one of the one or more photoelectric conversion units is 1 μm or more and 10 μm or less.

  In a preferred embodiment, at least one of the one or more photoelectric conversion units is made of a non-single-crystal crystalline material, and the crystal grain size of the crystalline material is 1 nm or more and 10 μm or less. The present invention relates to the photoelectric conversion device.

In a preferred embodiment, in the photoelectric conversion unit disposed farthest from the light incident side, the photoelectric conversion unit includes a photoelectric conversion layer and a conductive type layer, and the conductive type layer is formed on the side opposite to the light incident side. Has a conductivity of 10 S / cm or more and 10 ⁶ S / cm or less.

  In a preferred embodiment, among the one or more photoelectric conversion units, the photoelectric conversion layer of the photoelectric conversion unit disposed on the light incident side is made of an amorphous silicon-based material and is disposed farthest from the light incident side. The photoelectric conversion layer of the photoelectric conversion unit is made of a crystalline silicon-based material.

  According to the present invention, among the one or more photoelectric conversion units of the photoelectric conversion device, the photoelectric conversion unit disposed closest to the light incident side has a concavo-convex structure on the light incident side and is farthest from the light incident side. By having a structure having a periodic refractive index change adjacent to the back side of the photoelectric conversion unit arranged in the far side of combining the effects of using them individually on the light incident side or back side respectively. A high light confinement effect can be obtained. A photoelectric conversion device capable of expressing high conversion efficiency due to these effects can be obtained. In particular, when non-single-crystal silicon formed at a low temperature of 500 ° C. or less on a heterogeneous substrate having a small light absorption coefficient and a high defect density is used as a photoelectric conversion layer with a thickness of preferably 10 μm or less, more preferably 3 μm or less. In this case, since the number of reflections in the film is increased and the angle at the time of reflection is increased, this effect can be exhibited more remarkably.

1 is a cross-sectional view schematically showing a photoelectric conversion device according to a first embodiment of the present invention. It is sectional drawing which shows schematically the photoelectric conversion apparatus by the 2nd Embodiment in this invention. It is sectional drawing which shows roughly an example of the photoelectric conversion apparatus by 3rd Embodiment in this invention. It is sectional drawing which shows roughly an example of the photoelectric conversion apparatus by 3rd Embodiment in this invention. It is sectional drawing which shows roughly an example of the photoelectric conversion apparatus by 3rd Embodiment in this invention. It is sectional drawing which shows schematically the photoelectric conversion apparatus by 4th Embodiment in this invention. It is sectional drawing which shows schematically the photoelectric conversion apparatus by the 5th Embodiment in this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each drawing of the present application, dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Moreover, in each figure, the same referential mark represents the same part or an equivalent part.

(First embodiment)
First, each component of the photoelectric conversion apparatus 1 according to the first embodiment of the present invention will be described with reference to FIG. In addition, in the said 1st Embodiment, it becomes embodiment in the case of one photoelectric conversion unit in a photoelectric conversion apparatus.

For example, a glass plate or a transparent resin film can be used as the transparent insulating substrate 2. For example, as a glass plate, a soda lime plate glass having a smooth main surface, mainly composed of SiO ₂ , Na ₂ O and CaO, which has a large area and can be obtained at low cost, has high transparency and insulation properties, is used. be able to. The transparent conductive film 3, each photoelectric conversion unit, and the like are stacked on one main surface of the transparent insulating substrate, and light such as sunlight incident from the other main surface side is photoelectrically converted. In addition, the main surface on the light incident side of the transparent insulating substrate 2 has a fine concavo-convex structure, a fine particle mainly composed of silica or the like, or MgF ₂ or the like in order to exhibit an antireflection effect. A low refractive index material can also be coated. The main surface on the other transparent conductive film 3 side can also have a minute random uneven structure, can be coated with fine particles mainly composed of silica, or can be coated with silicon nitride.

The transparent conductive film 3 is preferably formed from a conductive metal oxide such as ITO (indium tin oxide), SnO ₂ or zinc oxide (hereinafter also referred to as ZnO), CVD (Chemical Vapor Deposition), sputtering, It is preferably formed using a method such as vapor deposition, electrodeposition or coating. The transparent conductive film 3 can also exhibit an effect of increasing the scattering of incident light by having a minute random uneven structure on the surface thereof. In addition, when the transparent conductive film 3 is formed on the flat transparent insulating substrate 2, a forming method is used in which a minute random uneven structure appears on the surface.

  The photoelectric conversion unit 41 is formed on a minute random concavo-convex structure appearing on the surface of the transparent conductive film 3, and thus has a minute random concavo-convex structure on the surface on the light incident side. The minute random concavo-convex structure preferably has a height difference of 20 to 400 nm, more preferably 100 to 400 nm, and the distance between the vertices of the convex portions is preferably 50 to 1000 nm, more preferably 100 to 600 nm. In addition, the surface area ratio of the unevenness is preferably 20% to 90%, more preferably 30% to 80%. Here, the height difference of the random concavo-convex structure and the distance between the vertices of the convex portions can be measured, for example, by an atomic force microscope. The surface area ratio of the unevenness is specifically the ratio of the surface area of the uneven surface to the flat surface, and it can be said that the larger this value, the more finer unevenness is included. The surface area ratio can be measured by, for example, an atomic force microscope.

  The photoelectric conversion unit 41 includes a photoelectric conversion semiconductor layer 412 that is a photoelectric conversion layer, and a p-type semiconductor layer 411 and an n-type semiconductor layer 413 that are conductive layers, and the p-type semiconductor layer 411 from the transparent conductive film 3 side. The photoelectric conversion semiconductor layer 412 and the n-type semiconductor layer 413 are sequentially stacked. In some cases, the n-type semiconductor layer 413, the photoelectric conversion semiconductor layer 412, and the p-type semiconductor layer 411 are sequentially stacked from the transparent conductive film 3 side. The p-type semiconductor layer 411 and the n-type semiconductor layer 413 can be formed by, for example, CVD, sputtering, vapor deposition, solution growth, coating method, or a composite method thereof.

  The photoelectric conversion semiconductor layer 412 that is the photoelectric conversion layer of the photoelectric conversion unit 41 can be formed of, for example, a Group 14 semiconductor material, a compound semiconductor material, or an organic semiconductor material. Examples of Group 14 semiconductor materials include silicon, germanium, carbon-based materials such as graphite and diamond, and any of them can be used for both amorphous and crystalline materials. The term “crystalline” as used herein includes polycrystals and microcrystals. In addition, the terms “polycrystal” and “microcrystal” are intended to mean those partially containing an amorphous material.

Examples of the compound semiconductor material include Group 14 compound semiconductor materials such as silicon carbide and silicon germanium, gallium arsenide, gallium phosphide, gallium nitride, zinc oxide, titanium oxide, or Cu (InGa) Se _2. . Again, both can be used both amorphous and crystalline.

  As the organic semiconductor material, copper phthalocyanine, perylene dye, methylene blue, pentacene, or the like can be used. Moreover, if these semiconductors have a sufficient photoelectric conversion function, weak p-type or weak n-type semiconductor materials containing a small amount of conductivity determining impurities can be used.

The p-type semiconductor layer 411 can be formed, for example, by doping a silicon alloy such as silicon, silicon carbide, silicon oxide, silicon nitride, or silicon germanium with p-conductivity determining impurity atoms such as boron or aluminum. it can. In addition to these silicon alloys, a compound semiconductor such as Cu (InGa) Se ₂ or an organic semiconductor such as copper phthalocyanine can also be used. The n-type semiconductor 413 can be formed by doping a silicon alloy such as silicon, silicon carbide, silicon oxide, silicon nitride, or silicon germanium with an n-conductivity determining impurity atom such as phosphorus or nitrogen. In addition to these silicon alloys, a compound semiconductor or an organic semiconductor can also be used as in the p-type semiconductor layer 411.

When the p-type semiconductor layer 411 or the n-type semiconductor layer 413 is thin enough to prevent loss due to light absorption and has sufficient conductivity in the direction parallel to the transparent insulating substrate 2, the transparent conductive film 3 is interposed therebetween. It can be directly formed on the transparent insulating substrate 2. At that time, a thin film made of an insulator such as silicon nitride may be formed on the transparent insulating substrate 2 before the p-type semiconductor layer 411 or the n-type semiconductor 413 is formed. In any case, the thickness of the p-type semiconductor layer 411 or the n-type semiconductor layer 413 is preferably in the range of 5 nm to 500 nm, and more preferably in the range of 10 nm to 100 nm. The conductivity is preferably in the range of 10 S / cm or more and 10 ⁶ S / cm or less, more preferably 10 ² S / cm or more and 10 ⁴ S / cm or less. By having the conductivity in this range, the conductive layer 411 or 413 generates a diffusion potential necessary for separating and collecting electrons and holes generated by the photoelectric conversion action in the photoelectric conversion semiconductor layer 412. In addition, the collected electrons or holes can be conducted in a direction parallel to the transparent insulating substrate 2 and can be used as an electrode.

  The multilayer alternating film 51 in which two materials having different refractive indexes are alternately stacked reflects the light incident on the photoelectric conversion unit 41 from the transparent insulating substrate 2 and arriving at the multilayer alternating film 51 to be re-entered in the photoelectric conversion unit 41. It has a function as a reflecting layer to be incident. Here, the multilayer alternating film 51 is composed of two different materials. The “material” in this case is considered to be a different material even if, for example, the same element is in a different phase or has a different film density.

  The refractive indexes of the two materials constituting the multilayer alternating film 51 are different. Preferably, the refractive index of the high refractive index layer 511 at a wavelength of 600 nm is 1.9 or more, and similarly the refractive index of the low refractive index layer 512 is 1.9. It is in the range of less than. The high refractive index layer 511 is made of, for example, a silicon alloy such as silicon, silicon carbide, silicon oxide, silicon nitride, or silicon germanium, p-type conductivity-determining impurity atoms such as boron or aluminum, or n such as phosphorus or nitrogen. It can be formed by doping conductivity type determining impurity atoms. Alternatively, an alloy of a metal such as aluminum or nickel and silicon can be used. Other than these silicon alloys, metal oxides such as ZnO and ITO, simple metals such as Ag and Al, or alloys thereof can be used. However, when a metal is used, light is slightly absorbed by the surface of the metal due to the effect of surface plasmons, and this absorption tends to cause a light reflection loss even though it is small. In these films, the film does not need to be completely filled, and there are cases where there are vacancies in the film in order to adjust the refractive index. The low refractive index layer 512 can be formed using the same material as the high refractive index layer 511. In forming the multilayer alternating film 51, CVD, sputtering, vapor deposition, solution growth, a coating method, or a composite method thereof is preferably used.

  In the multilayer alternating film 51, it is preferable that the combination of the high refractive index layer 511 and the low refractive index layer 512 is in a range of, for example, 2 to 10 layers, and further 4 to 8 layers. The film thickness of the layers is preferably in the range of 20 nm to 500 nm, more preferably 50 nm to 400 nm, for example, and the film thickness of each alternating layer need not be the same. In addition, the order of stacking the high refractive index layer 511 and the low refractive index layer 512 may be either. The multilayer alternating film is electrically insulating or conductive. In the case of the insulating film, a hole that reaches the photoelectric conversion unit 41 is formed in the multilayer alternating film 51 to form an electrical junction. When the multilayer alternating film 51 is conductive, the sheet resistance is in the range of 0.01Ω / □ to 5000Ω / □, preferably in the range of 0.1Ω / □ to 50Ω / □. Alternatively, it is possible to conduct holes in a direction parallel to the transparent insulating substrate 2, and the multilayer alternating film 51 itself can be used as an electrode.

(Second Embodiment)
Each component of the photoelectric conversion device 1 according to the second embodiment of the present invention will be described with reference to FIG. The transparent insulating substrate 2, the transparent conductive film 3, and the multilayer alternating film 51 are the same as those in the first embodiment.

  The photoelectric conversion device 1 according to the second embodiment includes two photoelectric conversion units, and specifically includes a first photoelectric conversion unit 41 and a second photoelectric conversion unit 42. The first photoelectric conversion unit 41 is disposed closer to the light incident side than the second photoelectric conversion unit 42. Both the first photoelectric conversion unit 41 and the second photoelectric conversion unit 42 can use the same material, configuration, and formation method as in the first embodiment, but the first photoelectric conversion unit 41 is the second photoelectric conversion unit 42. It is desirable to have a peak of quantum efficiency on the short wavelength side compared to.

  The first photoelectric conversion unit 41 arranged on the light incident side has a minute random concavo-convex structure on at least the surface on the light incident side, and the minute random concavo-convex structure preferably has a height difference of 20 to 400 nm. Preferably it is 100-400 nm, The distance between the vertexes of this convex part becomes like this. Preferably it is 50-1000 nm, More preferably, it is 100-600 nm. Furthermore, the surface area ratio of the irregularities is preferably in the range of 20% to 90%, more preferably 30% to 80%. However, the surface of the second photoelectric conversion unit 42 on the light incident side is not limited to this range, and may be flat, for example.

As the intermediate transmission / reflection film 6, for example, a transparent conductive oxide layer such as an ITO film, a SnO ₂ film, or a ZnO film, a conductive silicon oxide layer, or a silicon nitride layer is used. The intermediate transmission / reflection film 6 may have a single layer structure, a multilayer structure, or a porous structure. The intermediate transmission / reflection film 6 can be formed by a vapor deposition method known per se such as a vapor deposition method, a CVD method, or a sputtering method. The thickness of the intermediate transmission / reflection film 5 is preferably in the range of 5 nm to 300 nm, for example.

  Thus, the photoelectric conversion device 1 as shown in FIG. 2 is completed.

(Third embodiment)
Each component of the photoelectric conversion apparatus 1 by the 3rd Embodiment of this invention is demonstrated with reference to FIG.3, FIG4 and FIG.5. In the third embodiment, there is one photoelectric conversion unit in the photoelectric conversion device, and the transparent insulating substrate 2 and the transparent conductive film 3 are the same as those in the first embodiment.

  The photoelectric conversion device 1 according to the third embodiment includes a photoelectric conversion unit 41, and the same material as that of the first embodiment can be used. The surface opposite to the light incidence of the photoelectric conversion unit 41 has, for example, a structure in which grooves having a periodic rule are arranged, or a periodic rule having a prismatic, cylindrical, or spherical recess or protrusion. It has the structure. At this time, the period is preferably in the range of 100 nm to 1500 nm, for example, and the height difference is preferably in the range of, for example, more than 400 nm and 1000 nm or less. These periodic structures can be formed by a method such as a photolithography method or a self-assembly method.

The back periodic reflection film 52 has a structure filling periodic depressions and grooves formed on the surface opposite to the light incident side of the photoelectric conversion unit 41, and a material having a refractive index lower than that of the photoelectric conversion unit 41 is used. The refractive index at a wavelength of 600 nm is preferably 1.9 or less. As a material for forming the back periodic reflection film 52, for example, an oxide layer such as an ITO film, a SnO ₂ film, or a ZnO film, a silicon oxide layer, or a silicon nitride layer is used. The back surface periodic reflection film 52 can be formed by a vapor deposition method known per se such as a vapor deposition method, a CVD method, or a sputtering method.

  As a result, a periodic refractive index change equivalent to the wavelength of light occurs two-dimensionally at the interface between the photoelectric conversion unit 41 and the back surface periodic reflection film 52. In the present invention, such a structure is particularly called a “two-dimensional photonic crystal structure”. The two-dimensional photonic crystal structure has a high scattering reflection effect, can reflect vertically incident light at a high angle, and can form a total reflection condition in the photoelectric conversion unit 41 with a high probability. it can. Therefore, a high light confinement effect can be obtained. This effect becomes more prominent as the photoelectric conversion layer becomes thinner.

  The back surface periodic reflection film 52 only needs to fill periodic depressions and grooves formed on the surface opposite to the light incident side of the photoelectric conversion unit 41, and the shape after filling is shown in FIG. It may be flat, and may have a periodic structure as shown in FIG. 4 or may have a random minute uneven structure as shown in FIG. Further, a conductive film such as a metal film may be further formed on the back surface side of the back surface periodic reflection film 52 (not shown).

The back surface periodic reflection film 52 and the n-type conductivity type layer 413 in contact with the back surface periodic reflection film 52 forming a two-dimensional photonic crystal structure (or p-type in the case where the conductivity type layers are stacked in the reverse order) At least one of the conductivity type layers 411) preferably has a conductivity in the range of 10 S / cm to 10 ⁶ S / cm, more preferably in the range of 10 ² S / cm to 10 ⁴ S / cm. . By having a conductivity in this range, the two-dimensional photonic structure itself can conduct collected electrons or holes in a direction parallel to the transparent insulating substrate 2 and can also be used as an electrode.

  Thus, the photoelectric conversion device 1 as shown in FIG. 3 is completed.

(Fourth embodiment)
Each component of the photoelectric conversion device 1 according to the fourth embodiment of the present invention will be described with reference to FIG. The transparent insulating substrate 2, the transparent conductive film 3, the first photoelectric conversion unit 41, and the intermediate transmission / reflection film 6 are the same as those in the second embodiment.

  The photoelectric conversion device 1 according to the fourth embodiment has a second photoelectric conversion unit 42, and the same material as that of the second embodiment can be used. Similar to the photoelectric conversion unit in the third embodiment, the surface opposite to the light incidence of the second photoelectric conversion unit 42 has, for example, a structure in which grooves having periodic rules are arranged, a prismatic shape, a cylindrical shape, It has a structure in which spherical depressions or protrusions are arranged with periodic rules. At this time, the period is preferably in the range of 100 nm to 1500 nm, for example. These periodic structures can be formed by a method such as a photolithography method or a self-assembly method.

  The multilayer alternating film 51 can use the same material, formation method, and the like as in the first embodiment. The multilayer alternating film 51 has a structure that fills periodic depressions and grooves formed on the surface opposite to the light incident side of the second photoelectric conversion unit 42. The refractive indexes of the two materials constituting the multilayer alternating film 51 are different, the refractive index of the high refractive index layer 511 at a wavelength of 600 nm is 1.9 or more, and similarly, the refractive index of the low refractive index layer 512 is less than 1.9. It is preferable that it exists in. In the multilayer alternating film 51, it is preferable that the combination of the high refractive index layer 511 and the low refractive index layer 512 is in a range of, for example, 2 to 10 layers, and further 4 to 8 layers. The film thickness of the layers is preferably in the range of 20 nm to 500 nm, more preferably 50 nm to 400 nm, and the film thickness of each alternating layer need not be the same. In addition, the order of stacking the high refractive index layer 511 and the low refractive index layer 512 may be either. The multilayer alternating film is electrically insulating or conductive, and the sheet resistance in the case of conductivity is preferably in the range of 0.01Ω / □ to 5000Ω / □, more preferably 0.1Ω / □ to 50Ω / □. It is a range.

As a result, a two-dimensional photonic crystal structure is formed in the photoelectric conversion unit 42 and the multilayer alternating film 51, and the photoelectric conversion device as shown in FIG. 4 has the multilayer alternating layer 51 on the back side of the two-dimensional photonic crystal structure. 1 is completed. Of the materials having different refractive indexes forming the two-dimensional photonic crystal structure, at least one material is 10 S / cm or more and 10 ⁶ S / cm or less, more preferably 10 ² S / cm or more and 10 ⁴ S / cm. The same conductivity as described above is preferable.

(Fifth embodiment)
Each component of the photoelectric conversion device 1 according to the fifth embodiment of the present invention will be described with reference to FIG. The transparent insulating substrate 2, the transparent conductive film 3, the first photoelectric conversion unit 41, the second photoelectric conversion unit 42, and the intermediate transmission / reflection film 6 are the same as those in the second embodiment.

  The three-dimensional back surface reflection film 53 can be formed by, for example, a method using a micro mold. The method using a micro mold is to form a face-centered cubic structure by precipitating and arranging microspheres made of silica, resin, etc. in a solution, and forming materials having different refractive indexes in the gaps of the face-centered cubic structure. It is a method to make it. At this time, the material corresponding to the lattice point of the face-centered cubic structure is defined as the lattice point material 531, and the material of the gap portion is defined as the gap material 532. Thereby, a three-dimensional periodic refractive index distribution structure is obtained. In the present invention, in particular, such spheres having a substantially uniform diameter are arranged in a face-centered cubic lattice, and a geometrically generated gap between the spheres is filled with a material having a refractive index different from that of the sphere portion. This structure is called “opal structure”. In this case, for example, the period is preferably in the range of 100 nm to 1500 nm. In the present invention, such a structure is referred to as a “three-dimensional photonic crystal structure”. It is also possible to remove the micro mold to form pores, and such a structure is particularly called “inverted opal structure”. Further, other materials can be formed in the holes of the inverted opal structure. The gap material 532 does not necessarily need to be completely filled in the gap, and the gap may remain. Similar to the two-dimensional photonic crystal structure, the three-dimensional photonic crystal structure has a high scattering reflection effect, can reflect vertically incident light at a high angle, and has a high probability in the photoelectric conversion unit 41. The total reflection condition can be formed. Therefore, a high light confinement effect can be obtained. This effect becomes more prominent as the photoelectric conversion layer becomes thinner.

  The lattice point material 531 and the gap material 532 are composed of two different materials. The “material” at this time is considered to be a different material even when the same element is used, for example, in different phases or in different film densities. The lattice point material 531 and the gap material 532 have different refractive indexes, but either may have a high refractive index. In addition, the high refractive index is preferably in the range of 1.9 or more at the wavelength of 600 nm and the low refractive index in the range of less than 1.9. Examples of the lattice point material 531 include silicon, silicon carbide, silicon oxide, silicon nitride, silicon alloy such as silicon germanium, p-conductivity-type determining impurity atoms such as boron and aluminum, or n such as phosphorus and nitrogen. It can be formed by doping conductivity type determining impurity atoms. Alternatively, an alloy of a metal such as aluminum or nickel and silicon can be used. Other than these silicon alloys, metal oxides such as ZnO and ITO, simple metals such as Ag and Al, or alloys thereof can be used. However, when a metal is used, light is slightly absorbed by the surface of the metal due to the effect of surface plasmons, and this absorption tends to cause a light reflection loss even though it is small. In these films, the film does not need to be completely filled, and there are cases where there are vacancies in the film in order to adjust the refractive index. Furthermore, it may be an organic material such as vacuum or air or a polymer resin. Further, the gap material 532 can be the same material as the lattice point material 531. For the production of each material constituting the three-dimensional back surface reflection film 53, CVD, sputtering, vapor deposition, solution growth, coating method, chemical synthesis or a composite method thereof is preferably used.

The three-dimensional back reflection film 53 is preferably in the range of 5 to 50 cycles, more preferably 10 to 20 cycles in the film thickness direction, and the film thickness of 1 cycle is, for example, 100 nm to 1500 nm, It is preferably in the range of 200 nm to 1000 nm. The three-dimensional back reflecting film 53 is electrically insulating or conductive, and the sheet resistance in the case of conductivity is preferably 0.01Ω / □ to 5000Ω / □, more preferably 0.1Ω / □ to 50Ω / □. It is in the range. At least one of the lattice point material 531 and the gap material 532 preferably has a conductivity in the range of 10 S / cm to 10 ⁶ S / cm, and more preferably in the range of 10 ² S / cm to 10 ⁴ S / cm. It is more preferable. By having a conductivity in this range, the three-dimensional photonic structure itself can conduct collected electrons or holes in a direction parallel to the transparent insulating substrate 2 and can also be used as an electrode.

(Photoelectric conversion unit)
In the present invention, among the one or more photoelectric conversion units, at least one photoelectric conversion unit, preferably the second photoelectric conversion unit 42 has a thickness of 1 μm to 10 μm, and more preferably 1 μm to 3 μm. preferable. Even if it has a light confinement structure as shown in the present invention when the film thickness is 1 μm or less, photoelectric conversion becomes insufficient, and when it is 10 μm or more, it is a trap for carriers in the second photoelectric conversion unit 42. There are cases where the electrical defects to be increased greatly, the diffusion potential inside the second photoelectric conversion unit is lowered, and the output voltage is lowered during the photoelectric conversion.

  In the present invention, a light confinement structure having a concavo-convex structure on the light incident side and a photonic crystal structure on the back surface side is particularly absorbed even in materials such as crystalline silicon having a small light absorption coefficient. Difficult long-wavelength light is also highly confined near the back surface, making it possible to localize the light, and the light leaked from the light confinement near the back surface is reflected again by the uneven structure on the light incident side. It has a remarkable effect that it can be returned to the side and confined in the vicinity of the back surface. The film thickness that maximizes the light confinement effect in the vicinity of the back surface and does not cause a decrease in output voltage is preferably 1 μm or more and 3 μm or less.

  Due to the configuration of the photoelectric conversion device 1, most of the light on the short wavelength side is already absorbed by the first photoelectric conversion unit 41, and the second photoelectric conversion unit 42 needs to absorb light on the long wavelength side that is difficult to absorb. For this purpose, as described above, the second photoelectric conversion unit 42 preferably has a thickness of 1 μm or more from the viewpoint of light confinement. In order to use such a film thickness, sufficient carrier mobility cannot be obtained with an amorphous material, and therefore the second photoelectric conversion unit 42 cannot collect sufficient carriers. Preferably it consists of. At that time, the crystal grains may be 1 nm or more so that sufficient carrier mobility can be obtained, and ideally, the crystal grains are preferably the same size as the film thickness. In the case of the present invention, 10 μm or less, further 3 μm or less This is a preferred range.

  In the present invention, the one or more photoelectric conversion units are appropriately selected. As a preferable example, for example, the first photoelectric conversion semiconductor layer 412 which is the photoelectric conversion layer of the first photoelectric conversion unit 41 is amorphous. A two-stage tandem structure in which the second photoelectric conversion semiconductor layer 422, which is a photoelectric conversion layer of the second photoelectric conversion unit 42, is crystalline silicon, or a photoelectric conversion semiconductor containing a small amount of germanium and tin in the crystalline silicon A single junction structure including a single photoelectric conversion unit 411 including a layer can be given.

  Hereinafter, Examples 1, 2, 3, 4 and 5 will be described as photoelectric conversion devices according to the present invention by comparing with Comparative Examples with reference to the drawings. It is not limited to the description examples.

Example 1
Corresponding to the embodiment described with reference to FIG. 1, a photoelectric conversion device 1 was formed as Example 1. On one main surface of the transparent insulating substrate 2 made of white glass, a transparent conductive film 3 made of ZnO having a thickness of 1.5 μm was formed by a thermal CVD method. The transparent conductive film 3 made of ZnO has a minute random concavo-convex structure on its surface, the height difference is 200 to 400 nm by electron microscope observation, and the distance between the vertices of the convex portions is 200 to 600 nm. . Moreover, the surface area ratio of the unevenness | corrugation of the transparent conductive film 3 which consists of ZnO by atomic force microscope observation was 65%. Moreover, the transmittance | permeability using C light source was 88%, and the sheet resistance by 4 terminal method was 16 ohms / square.

  Next, in order to form the photoelectric conversion unit 41, the transparent insulating substrate 2 on which the transparent conductive film 3 is formed is introduced into a high-frequency plasma CVD apparatus and heated to a predetermined temperature. Further, a p-type crystalline silicon layer 411 having a thickness of 15 nm was formed using silane, hydrogen and diborane as reaction gases. Next, silane and hydrogen are introduced as reaction gases to form an i-type crystalline silicon layer 412 with a set film thickness of 2 μm, and then silane, hydrogen and phosphine are introduced as reaction gases to form an n-type crystalline silicon layer 413 with a set film thickness. Thus, the photoelectric conversion unit 41 was formed. A random uneven structure similar to the minute random uneven structure of the transparent conductive film 3 was formed on the light incident surface of the photoelectric conversion unit 41.

  In addition, the set film thickness of each layer of the photoelectric conversion unit 41 was determined as follows. That is, each layer is formed as a single layer of about 300 nm to 400 nm on a white glass substrate 2 different from that of the photoelectric conversion device 1 in FIG. 1, and the film thickness is calculated from the spectroscopic ellipsometry. The formation rate was calculated with a constant formation rate. For the i-type crystalline silicon layer 412 having a film thickness of 50 nm or more, the film thickness was directly obtained by observing the cross section with an electron microscope. It is assumed that the formation speed of each layer obtained as described above is constant without changing even when it is formed on the transparent conductive film 3 or other films formed on the transparent conductive film 3. The thickness was determined.

In addition, the determination of whether the silicon is crystalline or amorphous is made by measuring the dependence of the scattering intensity on the wave number spectrum of the single layer on the white glass substrate 2 by Raman scattering spectroscopy, and crystal having a peak in the vicinity of 520 cm ^−1. A material having a gentle peak around 480 cm ⁻¹ was made amorphous.

  The multilayer alternating film 51 includes a ZnO layer 511 and a silicon oxide layer 512. The ZnO layer 511 was formed by a sputtering method, and the silicon oxide layer 512 was formed by a high frequency plasma CVD method using silane, hydrogen, carbon dioxide, and phosphine as reaction gases. The thickness of each ZnO layer 511 was 100 nm, and the refractive index at 600 nm was 1.95. Each silicon oxide layer 512 had a thickness of 100 nm and a refractive index at 600 nm of 1.72. Ten alternating layers of ZnO layers 511 and silicon oxide layers 512 were formed. The refractive index was determined by spectroscopic ellipsometry. When the multilayer alternating film 51 was formed on another white glass substrate 2, the sheet resistance by the four-terminal method was 20Ω / □.

After the multilayer alternating film 51 is formed, the film formed on the transparent conductive film 3 made of ZnO is partially removed by a laser scribing method, and separated into a size of 1 cm ² , and single-junction silicon-based thin film photoelectric conversion Device 1 (light receiving area 1 cm ² ) was produced.

When the photoelectric conversion device 1 of Example 1 obtained as described above was irradiated with AM1.5 light at a light amount of 100 mW / cm ^{2 and} the photoelectric conversion characteristics were measured, the open circuit voltage (Voc) was 0.582 V. The short circuit current density (Jsc) was 24.41 mA / cm ² , the fill factor (FF) was 0.712, and the initial conversion efficiency was 10.1%. These values are shown in Example 1 of Table 1.

(Comparative Example 1)
For the structure of the photoelectric conversion device 1 of Example 1, a back reflective layer in which a transparent reflective layer 80 nm made of ZnO formed by sputtering and a metal reflective layer 200 nm made of Ag were laminated instead of the multilayer alternating film 51 was used. . The rest was the same as in Example 1.

The photoelectric conversion device 1 of Comparative Example 1 at this time was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics. As a result, the open circuit voltage (Voc) was 0.573 V, and the short circuit current density ( Jsc) was 23.85 mA / cm ² , fill factor (FF) was 0.718, and initial conversion efficiency was 9.81%. These values are shown in Comparative Example 1 of Table 1.

  In Comparative Example 1, the short-circuit current is lower than in Example 1, and this is considered to be due to light reflection loss due to the plasmon effect by the metal reflective layer made of Ag used for the back surface reflective layer.

(Comparative Example 2)
The transparent conductive film 3 made of ZnO having a thickness of 300 nm formed by a flat sputtering method having no minute random uneven structure on the surface was used for the structure of the photoelectric conversion device 1 of Example 1. At this time, the transparent conductive film 3 made of ZnO had a height difference of 10 nm or less by electron microscope observation, and the distance between the vertices of the convex portions could not be detected. In addition, since the root mean square roughness (RMS) by atomic force microscope observation was 6 nm, it can be said that it is sufficiently flat. Moreover, the transmittance | permeability using C light source was 89%, and the sheet resistance by 4 terminal method was 13 ohms / square. The rest was the same as in Example 1.

At this time, the photoelectric conversion device 1 of Comparative Example 1 was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics. As a result, the open circuit voltage (Voc) was 0.595 V, and the short circuit current density ( Jsc) was 17.83 mA / cm ² , the fill factor (FF) was 0.727, and the initial conversion efficiency was 7.71%. These values are shown in Comparative Example 2 of Table 1.

  In Comparative Example 2, the short-circuit current is clearly lower than that in Example 1, and the surface of the photoelectric conversion unit 41 is flat. Therefore, despite the very high light reflection effect of the multilayer alternating film 51, the photoelectric conversion device 1 It is difficult for the incident light to obtain a total reflection condition inside the photoelectric conversion unit 41, and a lot of light escapes from the light incident side to the outside, that is, light in the photoelectric conversion unit 41 due to light scattering on the light incident side. This is probably because the confinement effect is not obtained so much.

(Example 2)
Corresponding to the embodiment described with reference to FIG. 2, the photoelectric conversion device 1 was formed as Example 2. The transparent insulating substrate 2, the transparent conductive film 3, and the multilayer alternating film 51 are the same as the structure of the photoelectric conversion device 1 of Example 1.

  In order to form the first photoelectric conversion unit 41, the transparent insulating substrate 2 on which the transparent conductive film 3 is formed is introduced into a high-frequency plasma CVD apparatus, heated to a predetermined temperature, and then placed on the transparent conductive film 3 A p-type amorphous silicon carbide layer 411 having a film thickness of 15 nm was formed using silane, hydrogen, diborane and methane as reaction gases. Next, silane and hydrogen are introduced as reaction gases to form an i-type amorphous silicon layer 412 with a set film thickness of 300 nm, and then silane, hydrogen and phosphine are introduced as reaction gases to form an n-type crystalline silicon layer 413 with a set film. The first photoelectric conversion unit 41 was formed by forming a thickness of 20 nm.

  In order to form the intermediate reflection layer 6, the ZnO intermediate reflection layer 6 was formed to a thickness of 60 nm on the n-type crystalline silicon layer 413 by sputtering.

  Next, in order to form the second photoelectric conversion unit 42, the p-type crystalline silicon layer 421 is formed to a thickness of 15 nm on the ZnO intermediate reflection layer 6 using a high-frequency plasma CVD method using silane, hydrogen, and diborane as reactive gases. Formed with. Next, silane and hydrogen are introduced as reaction gases to form an i-type crystalline silicon layer 422 with a set thickness of 2.5 μm, and then silane, hydrogen and phosphine are introduced as reaction gases to set an n-type crystalline silicon layer 423. The second photoelectric conversion unit 42 was formed by forming a film thickness of 20 nm.

At this time, the photoelectric conversion device 1 of Example 2 was irradiated with AM 1.5 light with a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics. As a result, the open-circuit voltage (Voc) was 1.421 V, the short-circuit current density ( Jsc) was 14.21 mA / cm ² , fill factor (FF) was 0.725, and initial conversion efficiency was 14.6%. These values are shown in Example 2 of Table 1.

In the case of a photoelectric conversion device having a structure in which a plurality of photoelectric conversion units are electrically connected in series, the short-circuit current value of the photoelectric conversion device is the lowest short-circuit current value among the photoelectric conversion units. In other words, the sum of the short-circuit currents of the respective photoelectric conversion units is called the total short-circuit current, and indicates the effective photoelectric conversion amount of the photoelectric conversion device, but the total short-circuit current is at least equal to the short-circuit current of the photoelectric conversion device. It will be more than the product of the number of photoelectric conversion units. In Example 2, since the photoelectric conversion device 1 includes the first conversion unit 41 and the second photoelectric conversion unit 42, the total short-circuit current is more than twice the 14.21 mA / cm ² obtained by measuring the photoelectric conversion characteristics, that is, The value is 28.42 mA / cm ² or more. In Example 2, a photoelectric conversion material having different photosensitivity of amorphous silicon and crystalline silicon as compared with Example 1 is laminated, thereby realizing light absorption in a wider wavelength range, and effectively high photoelectric conversion. As a result, it is thought that high conversion efficiency was achieved.

(Comparative Example 3)
For the structure of the photoelectric conversion device 1 of Example 2, a back reflective layer in which a transparent reflective layer 80 nm made of ZnO formed by sputtering and a metal reflective layer 200 nm made of Ag were laminated instead of the multilayer alternating film 51 was used. . The rest was the same as in Example 2.

At this time, the photoelectric conversion device 1 of Comparative Example 3 was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics. As a result, the open-circuit voltage (Voc) was 1.416 V, the short-circuit current density ( Jsc) was 13.52 mA / cm ² , the fill factor (FF) was 0.733, and the initial conversion efficiency was 14.0%. These values are shown in Comparative Example 2 of Table 1.

  In Comparative Example 3, since two photoelectric conversion units were used, high light absorption could be realized, and thus higher conversion efficiency was obtained than in Example 1. However, compared with Example 2 having the same photoelectric conversion unit, the short circuit current A clear decrease is observed in this case, which is considered to be due to the difference in the structure of the back surface reflection layer.

(Example 3)
Corresponding to the embodiment described with reference to FIG. 5, the photoelectric conversion device 1 was formed as Example 3. Note that the transparent insulating substrate 2 and the transparent conductive film 3 were the same as the structure of the photoelectric conversion device 1 of Example 1.

  In order to form the first photoelectric conversion unit 41, the transparent insulating substrate 2 on which the transparent conductive film 3 is formed is introduced into a high-frequency plasma CVD apparatus, heated to a predetermined temperature, and then placed on the transparent conductive film 3 The p-type crystalline silicon layer 411 was formed with a film thickness of 15 nm using silane, hydrogen and diborane as reaction gases. Next, silane and hydrogen were introduced as reaction gases to form an i-type crystalline silicon layer 412 with a set thickness of 2 μm. Thereafter, cylindrical grooves having a diameter of 300 nm and a depth of 500 nm were formed at a pitch of 600 nm using a photolithography method. Thereafter, silane, hydrogen and phosphine were introduced as reaction gases to form an n-type crystalline silicon layer 413 with a set film thickness of 20 nm, whereby the first photoelectric conversion unit 41 was formed.

  In order to form the back surface periodic reflection film 52, the ZnO back surface periodic reflection film 52 was formed in a thickness of 600 nm on the n-type crystalline silicon layer 413 by a thermal CVD method. At this time, the ZnO back surface periodic reflection film 52 filled a groove formed on the back surface side of the first photoelectric conversion unit 41 as shown in FIG. 5 and also inherited a minute random uneven structure on the back surface side. The refractive index of the photoelectric conversion unit 41 and the ZnO back surface periodic reflection film 52 are greatly different. Therefore, a two-dimensional photonic crystal structure is formed at the interface between the photoelectric conversion unit 41 and the ZnO back surface periodic reflection film 52.

The photoelectric conversion device 1 of Example 3 thus obtained was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² and measured for photoelectric conversion characteristics. As a result, the open circuit voltage (Voc) was 0.565 V, The short-circuit current density (Jsc) was 26.66 mA / cm ² , the fill factor (FF) was 0.705, and the initial conversion efficiency was 10.6%. These values are shown in Example 3 of Table 1.

  In Example 3, compared with Example 1, a higher optical confinement effect was obtained by the two-dimensional photonic crystal structure on the back surface side, and as a result, high conversion efficiency was obtained by a high short-circuit current.

Example 4
Corresponding to the embodiment described with reference to FIG. 6, the photoelectric conversion device 1 was formed as Example 4. The transparent insulating substrate 2, the transparent conductive film 3, the first photoelectric conversion unit 41, and the intermediate reflection layer 6 are the same as the structure of the photoelectric conversion device 1 of Example 2.

  In order to form the second photoelectric conversion unit 42, a p-type crystalline silicon layer 421 having a film thickness of 15 nm was formed on the intermediate reflection layer 6 by high frequency plasma CVD using silane, hydrogen, and diborane as reaction gases. Next, silane and hydrogen were introduced as reaction gases to form an i-type crystalline silicon layer 422 with a set thickness of 2 μm. Thereafter, cylindrical grooves having a diameter of 300 nm and a depth of 500 nm were formed at a pitch of 600 nm using a photolithography method. Thereafter, silane, hydrogen and phosphine were introduced as reaction gases to form an n-type crystalline silicon layer 423 with a set film thickness of 20 nm, whereby the second photoelectric conversion unit 42 was formed.

  The multilayer alternating film 51 was composed of a ZnO layer 511 and a silicon oxide layer 512, and was filled with cylindrical grooves formed in the second photoelectric conversion unit 42 as shown in the schematic diagram of FIG. The ZnO layer 511 was formed by a sputtering method, and the silicon oxide layer 512 was formed by a high frequency plasma CVD method using silane, hydrogen, carbon dioxide, and phosphine as reaction gases. The thickness of each ZnO layer 511 was 100 nm, and the refractive index at 600 nm was 1.95. Each silicon oxide layer 512 had a thickness of 100 nm and a refractive index at 600 nm of 1.72. Ten alternating layers of ZnO layers 511 and silicon oxide layers 512 were formed. The refractive index was determined by spectroscopic ellipsometry. When the multilayer alternating film 51 was formed on another white glass substrate 2, the sheet resistance by the four-terminal method was 20Ω / □.

When the photoelectric conversion device 1 of Example 4 obtained as described above was irradiated with AM1.5 light at a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics, the open circuit voltage (Voc) was 1.413 V. The short circuit current density (Jsc) was 15.51 mA / cm ² , the fill factor (FF) was 0.714, and the initial conversion efficiency was 15.6%. These values are shown in Example 4 of Table 1.

  In Example 4, compared with Example 2, it is considered that a higher optical confinement effect was obtained by the two-dimensional photonic crystal structure on the back surface side, and as a result, high conversion efficiency was obtained by a high short-circuit current.

(Example 5)
Corresponding to the embodiment described with reference to FIG. 7, the photoelectric conversion device 1 was formed as Example 5. Note that the transparent insulating substrate 2, the transparent conductive film 3, the first photoelectric conversion unit 41, the second photoelectric conversion unit 42, and the intermediate reflection layer 6 are the same as the structure of the photoelectric conversion device 1 of Example 2.

  As the three-dimensional back reflecting film 53, a silica ZnO opal back reflecting film 53 in which a ZnO film 532 is formed in the gap between the artificial opal structure 531 made of silica was used. The silica ZnO opal back reflecting film 53 was formed as follows. Silica spheres having a diameter of 400 nm were synthesized using tetraethoxysilane (TEOS) and aqueous ammonia. Next, silica spheres were dispersed in ethanol, the solution was uniformly applied onto the second photoelectric conversion unit 42, and then the ethanol was evaporated to form an artificial opal structure 531. Further, a ZnO film 532 was formed in the gap between the artificial opal structures 531 by a thermal CVD method, and a silica ZnO opal back reflecting film 53 was obtained. Since silica has a refractive index of 1.47 at 600 nm and ZnO is 1.95, the silica ZnO opal back reflecting film 53 has a three-dimensional photonic crystal structure having a three-dimensional periodic refractive index change.

The photoelectric conversion device 1 of Example 5 obtained as described above was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² to measure the photoelectric conversion characteristics, and the open circuit voltage (Voc) was 1.423 V. The short circuit current density (Jsc) was 15.43 mA / cm ² , the fill factor (FF) was 0.733, and the initial conversion efficiency was 16.1%. These values are shown in Example 5 of Table 1.

  In Example 5, compared with Example 2, it is considered that a higher light confinement effect was obtained by the three-dimensional photonic crystal structure on the back surface side, and as a result, high conversion efficiency was obtained by a high short-circuit current.

DESCRIPTION OF SYMBOLS 1 Photoelectric conversion apparatus 2 Transparent insulating substrate 3 Transparent electrically conductive film 41 1st thin film photoelectric conversion unit 411 1st p-type semiconductor layer 412 1st photoelectric conversion semiconductor layer 413 1st n-type semiconductor layer 42 2nd thin film photoelectric conversion unit 421 2nd p-type semiconductor Layer 422 Second photoelectric conversion semiconductor layer 423 Second n-type semiconductor layer 51 Multilayer alternating film 511 High refractive index layer 512 Low refractive index layer 52 Back surface periodic reflection film 52
53 Three-dimensional back surface reflective film 531 Lattice material 532 Gap material 6 Intermediate reflective layer

Claims (16)

A photoelectric conversion device having at least one photoelectric conversion unit,
The photoelectric conversion unit has an uneven structure on the light incident side,
And among the one or more photoelectric conversion units, a structure having a periodic refractive index change is disposed adjacent to the opposite side of the light incidence in the photoelectric conversion unit disposed farthest from the light incident side. A photoelectric conversion device.   The height difference of the concavo-convex structure is 20 to 400 nm, the distance between the vertices of the convex portions is 50 to 1000 nm, and the surface area ratio of the concavo-convex portions is in the range of 20% to 90%. The photoelectric conversion device described.   A multilayer structure in which two materials having different refractive indexes are alternately laminated on a structure having a periodic refractive index change that is adjacently arranged on the opposite side of the light incidence in the photoelectric conversion unit arranged farthest from the light incident side. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion device is composed of alternating films.   4. The photoelectric conversion device according to claim 3, wherein the multilayer alternating film is formed by alternately laminating a material having a refractive index of 1.9 or more and a material having a refractive index of less than 1.9 at a wavelength of 600 nm.   The structure having a periodic refractive index change disposed adjacent to the opposite side of the light incidence in the photoelectric conversion unit disposed farthest from the light incident side has a two-dimensional photonic crystal structure. Item 3. The photoelectric conversion device according to Item 1 or 2.   A structure having a periodic refractive index change, which is disposed adjacent to the opposite side of the light incidence in the photoelectric conversion unit disposed farthest from the light incident side, has a two-dimensional photonic crystal structure and a refractive index at a wavelength of 600 nm. 6. A multilayer alternating film in which a material having a refractive index of 1.9 or more and a material having a refractive index of less than 1.9 are alternately stacked, and the two-dimensional photonic crystal structure is on a light incident side. The photoelectric conversion device described. 7. The material according to claim 5, wherein at least one of the materials having different refractive indexes forming the two-dimensional photonic crystal structure has a conductivity of 10 S / cm or more and 10 ⁶ S / cm or less. The photoelectric conversion device described.   The structure having a periodic refractive index change disposed adjacent to the opposite side of the light incidence in the photoelectric conversion unit disposed farthest from the light incident side has a three-dimensional photonic crystal structure. Item 3. The photoelectric conversion device according to Item 1 or 2.   The photoelectric conversion device according to claim 8, wherein the three-dimensional photonic crystal structure is an opal structure. 10. The material according to claim 8, wherein at least one of the materials having different refractive indexes forming the three-dimensional photonic crystal structure has a conductivity of 10 S / cm or more and 10 ⁶ S / cm or less. The photoelectric conversion device described.   The photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit is formed on a transparent insulating substrate and has a structure in which light is incident through the transparent insulating substrate.   The photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit contains a group 14 element of the periodic table as a main component.   13. The photoelectric conversion device according to claim 1, wherein a film thickness of at least one photoelectric conversion unit among the one or more photoelectric conversion units is 1 μm to 10 μm.   Among the one or more photoelectric conversion units, at least one photoelectric conversion unit is made of a non-single-crystal crystalline material, and the crystal grain size of the crystalline material is 1 nm to 10 μm. The photoelectric conversion device according to claim 1. In the photoelectric conversion unit arranged farthest from the light incident side, the photoelectric conversion unit includes a photoelectric conversion layer and a conductive type layer, and the conductive type layer formed on the side opposite to the light incident side is 10 S / cm or more. The photoelectric conversion device according to claim 1, having a conductivity of 10 ⁶ S / cm or less.   Among the one or more photoelectric conversion units, the photoelectric conversion layer of the photoelectric conversion unit disposed on the light incident side is made of an amorphous silicon-based material, and the photoelectric conversion unit disposed farthest from the light incident side The photoelectric conversion device according to claim 1, wherein the conversion layer is made of a crystalline silicon-based material.

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