JP2011003663A - Thin-film photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film photoelectric conversion device that is configured by improving utilization efficiency of converted light and preventing a series resistive component from being increased by utilizing an up conversion material.SOLUTION: In this thin-film photoelectric conversion device, a transparent conductive layer 2, photoelectric conversion layers 32, 42, 62, a transparent conductive layer 7 and a back reflecting electrode layer 9 are sequentially laminated on an insulating transparent substrate 1. The thin-film photoelectric conversion device includes a wavelength conversion layer 8 between the transparent conductive layer 7 and the back reflecting electrode layer 9, wherein the wavelength conversion layer 8 contains a material for converting the wavelength of light having entered from the insulating transparent substrate 1 and having passed through the photoelectric conversion layers 32, 42, 62 to further small wavelength, and includes conductive parts 10 for electrically connecting the transparent conductive layer 7 to the back reflecting electrode layer 9 in the layer.

Description

  The present invention relates to a thin film photoelectric conversion device such as a thin film solar cell.

  In recent years, thin-film solar cells have been vigorously developed in order to achieve both low cost and high efficiency of solar cells, and multi-junction thin-film photoelectric conversion devices have attracted attention. In general, the configuration of a multi-junction photoelectric conversion device includes a transparent conductive layer, a photoelectric conversion layer, a conductive type layer, an intermediate layer, and a back reflective electrode layer. The primary absorption of incident light in the photoelectric conversion layer, the intermediate layer, Power generation is performed by higher-order absorption of reflected light by the back surface reflective electrode layer or the like.

  However, depending on the material or crystallinity used for the photoelectric conversion layer, light may not be sufficiently absorbed with respect to the incident light spectrum. For example, when amorphous silicon or microcrystalline silicon is used for the photoelectric conversion layer, absorption of visible light in a region near visible light is significant, but a region excluding a part of ultraviolet light or infrared light. Absorption of light does not sufficiently absorb incident light due to its material, crystallinity, and the like. For this reason, non-absorbing light is generated in the photoelectric conversion layer, which is an item to be considered in improving the photoelectric conversion efficiency of the multi-junction photoelectric conversion device.

  On the other hand, in Patent Document 1, an effort has been made regarding a composition that converts light in a region excluding a part of infrared light into light in the near visible region, and is effective for upconversion at low excitation (irradiation) intensity and at room temperature. Active materials and compositions are disclosed. The material and the composition function as a photoreceptor of the composition, function as a light emitter of the composition, a first component that absorbs energy in the first wavelength range w ≦ λ1 ≦ x, and a second wavelength. Including at least two components, a second component that absorbs energy in the region y ≦ λ2 ≦ z, λ2 ≦ λ1, and the second component during energy absorption in the first wavelength region λ1 by the first component Emits energy in the second wavelength region λ2, and the first component and / or the second component is an organic compound. As an application of such a material and composition, it is described as “an up-conversion device characterized by being a label in a photovoltaic element, particularly a solar cell or LED”.

JP-A-2005-49824

  In the thin film photoelectric conversion device, since the photoelectric conversion layer and the conductive layer are thin, it is particularly important to increase the utilization efficiency of light and decrease the electric resistance of the conductive layer in order to improve the photoelectric conversion efficiency. However, Patent Document 1 describes the application of the above materials and compositions to solar cells, but does not show a specific structure on how to apply them.

  The present invention has been made in view of the above, and by using an up-conversion material, a thin-film photoelectric conversion device that improves the utilization efficiency of converted light and does not increase the series resistance component is obtained. With the goal.

  In order to solve the above-described problems and achieve the object, a thin film photoelectric conversion device according to the present invention includes a first transparent conductive layer, a photoelectric conversion layer, a second transparent conductive layer, and a back surface reflection on a translucent substrate. A thin-film photoelectric conversion device in which electrode layers are sequentially stacked, having a wavelength conversion layer between the second transparent conductive layer and the back reflective electrode layer, wherein the wavelength conversion layer is the translucent substrate Containing a material that converts the wavelength of light that has entered through the photoelectric conversion layer into a shorter wavelength, and electrically connects the second transparent conductive layer and the back reflective electrode layer within the layer It has a conductive part.

  According to this invention, the wavelength conversion containing the material which converts into a shorter wavelength the wavelength of the light which injected from the translucent board | substrate and passed the photoelectric converting layer between the 2nd transparent conductive layer and the back surface reflective electrode layer. Since it has a layer, light having a wavelength that has passed without being absorbed by the photoelectric conversion layer can be converted into light having a wavelength that is easily absorbed, and reflected and absorbed by the photoelectric conversion layer, and thus the efficiency of use of the converted light In this case, since the second transparent conductive layer electrically connected to the back surface reflective electrode layer by the conductive portion is disposed on the back side of the photoelectric conversion layer, the series when taking out the electric power from the photoelectric conversion layer is improved. There is an effect that the resistance component can be reduced.

FIG. 1 is a schematic cross-sectional view illustrating a multi-junction thin film photoelectric conversion device according to a first embodiment. FIG. 2 is a schematic cross-sectional view illustrating a multi-junction thin film photoelectric conversion device according to the second embodiment. FIG. 3 is a schematic cross-sectional view illustrating a multi-junction thin-film photoelectric conversion device according to the third embodiment. FIG. 4 is a schematic cross-sectional view illustrating a multi-junction thin film photoelectric conversion device according to the fourth embodiment.

  Embodiments of a thin film photoelectric conversion device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to these embodiments. In addition, the cross-sectional views of the thin film photoelectric conversion device described in the following embodiments are schematic, and the relationship between the thickness and width of the layers, the ratio of the thicknesses of the layers, and the like are different from the actual ones.

Embodiment 1 FIG.
FIG. 1 is a schematic cross-sectional view showing a multi-junction thin-film photoelectric conversion device according to the first embodiment. The multi-junction thin film photoelectric conversion device according to the first embodiment includes a transparent conductive layer 2, a front photoelectric conversion cell 3, an intermediate photoelectric conversion cell 4, an intermediate layer 5, and a rear photoelectric conversion cell 6 on an insulating transparent substrate 1. , A three-junction photoelectric conversion device in which a transparent conductive layer 7, a wavelength conversion layer 8, and a back reflective electrode layer 9 are sequentially stacked. In FIG. 1, light is incident from the insulating transparent substrate 1 side and has the above-described laminated structure. However, the present invention has no particular limitation on the number of junctions, and a single photoelectric conversion device such as polycrystalline silicon is used. Or a photoelectric conversion device made of thin-film amorphous silicon, a photoelectric conversion device having two or more junctions, for example, a two-junction photoelectric conversion device made of amorphous silicon and microcrystalline silicon, and amorphous silicon germanium added thereto Although the case where it applies also to a three junction photoelectric conversion apparatus etc. is mentioned, a combination is not this limitation. The wavelength conversion layer 8 may be a single layer photoelectric conversion device made of amorphous silicon or the like.

Glass, resin film, etc. are used for the insulating transparent substrate 1 which is a translucent board | substrate. It is desirable that the transparent conductive layer 2 as the first transparent conductive layer made of SnO ₂ , ZnO or the like is formed on the insulating transparent substrate 1 by using a method such as CVD, sputtering, or vapor deposition. The transparent conductive layer 2 desirably has a concavo-convex structure that increases the scattering of incident light.

  Further, the front photoelectric conversion cell 3, the intermediate photoelectric conversion cell 4, and the rear photoelectric conversion cell 6 each have a pin junction. That is, the front photoelectric conversion cell 3 includes a conductive layer 31, a photoelectric conversion layer 32, and a conductive layer 33, and the intermediate photoelectric conversion cell 3 includes a conductive layer 41, a photoelectric conversion layer 42, and a conductive layer 43. The rear photoelectric conversion cell 6 includes a conductive type layer 61, a photoelectric conversion layer 62, and a conductive type layer 63. In this case, a material having a relatively wide band gap, such as amorphous silicon, is used for the front photoelectric conversion cell 3, and a material having a relatively narrow band gap, such as microcrystalline silicon or microcrystalline silicon germanium, is used for the rear photoelectric conversion cell 6. Is preferably used.

  The intermediate layer 5 is a thin film having a low refractive index, a high transmittance and a high reflectance with respect to a desired wavelength, and a conductivity. For example, even when the photoelectric conversion device as shown in FIG. 1 is formed with a refractive index of about 1.5 to 2.5 and a film thickness of about 20 to 100 nm, there is no electrical loss due to the intermediate layer 5, and the intermediate layer 5 is a thin film that reflects light of a desired wavelength to the photoelectric conversion cells 3 and 4 on the incident side of 5 and transmits light of the desired wavelength to the photoelectric conversion cell 6 on the opposite side.

The back reflective electrode layer 9 is preferably formed of a metal thin film such as Ag, Al, or Cu by sputtering or vapor deposition. In addition, it is preferable to form the transparent conductive layer 7 that is a second transparent conductive layer made of SnO ₂ , ZnO, or the like between the photoelectric conversion cell 6 and the back surface reflective electrode layer 9.

  The wavelength conversion layer 8 of the first embodiment has an up-conversion action that converts part of the light that has passed through the three-junction photoelectric conversion device in FIG. 1 to the back side into light having a short wavelength. Thereby, the light of the wavelength which can be absorbed by the front photoelectric conversion cell 3, the intermediate photoelectric conversion cell 4, and the back photoelectric conversion cell 6 can be generated. Therefore, it is possible to improve the photoelectric conversion efficiency by effectively using the wavelength region that could not be used in conventional multi-junction photoelectric conversion devices.

The wavelength conversion layer 8 is, for example, an organic material as disclosed in Patent Document 1 or an inorganic material having an upconversion action. For example, it may have a compound such as porphyrin or phthalocyanine and a fluorene-based luminescent polymer as a pigment having the two-photon absorption property. Further, a rare earth element such as _{Er Y 2 O 3, YAO 3} , YF 3 may be a sintered particles obtained by adding the like. In a thin film photoelectric conversion device containing silicon as a main component, light having a wavelength of 800 to 1200 nm is relatively transmitted to the back surface side, so that light in these wavelength regions is converted to 400 to 700 nm that is easily absorbed by silicon. It is desirable. These up-conversion materials may be dispersed in a material such as a transparent polymer such as an acrylic resin or a silicone resin. It can be formed as a solution with an appropriate solvent by sputtering, printing, spray coating, or the like.

  In the thin film photoelectric conversion device, since the photoelectric conversion layer 62 and the transparent conductive layer 7 are thin, not only the light use efficiency is increased but also the electric resistance of the transparent conductive layer 7 is decreased in order to improve the photoelectric conversion efficiency. Of particular importance. In Embodiment 1, the wavelength conversion layer 8 is disposed on the back side of the transparent conductive layer 7 and the reflected light including the wavelength-converted light is used for photoelectric conversion, so that the utilization efficiency can be improved. On the other hand, when the transparent conductive layer 7 is thickened to prevent an increase in the electrical resistance of the transparent conductive layer 7, light on the long wavelength side such as the near infrared region is absorbed by the transparent conductive layer 7 and the use efficiency of reflected light is reduced. Resulting in. Therefore, in the first embodiment, the wavelength conversion layer 8 electrically connects the transparent conductive layer 7 and the back surface reflective electrode layer 9 in the layer so that the electrical resistance can be lowered even if the transparent conductive layer 7 is thinned to some extent. The conductive part 10 to be connected was formed. The transparent conductive layer 7 has a little higher resistance, but is electrically connected to the back reflective electrode layer 9 by the conductive portion 10, so that power can be extracted from the photoelectric conversion layer 62 with high efficiency.

  In the first embodiment, as shown in FIG. 1, the penetrating portion 8a is formed in the wavelength conversion layer 8, and the conductive portion 10 is formed by allowing a part of the back surface reflecting electrode layer 9 to enter the penetrating portion 8a. The transparent conductive layer 7 and the back reflective electrode layer 9 are in electrical contact with each other. In FIG. 1, since a part of the back surface reflective electrode layer 9 enters the penetrating portion 8 a in the wavelength conversion layer 8, the transparent conductive layer 7 and the back surface reflective electrode layer 9 are in direct contact with each other. Although it is the simplest, another conductive material may be inserted into the penetrating portion 8a to form the conductive portion. Further, instead of the penetrating portion 8a, the wavelength conversion layer 8 is divided into a plurality of island-shaped patterns, and the transparent conductive layer 7 and the back surface reflective electrode layer 9 are electrically connected through gaps between the island-shaped patterns. It may be.

  The penetrating portion 8a and the island pattern of the wavelength conversion layer 8 can be formed by wet or dry etching of a layer-coated film using a mask. Further, it can be easily formed by forming a layer in which a pattern is directly processed by a printing method.

  The wavelength conversion layer 8 may have a thickness of 1 to 750 nm, for example. If the coverage of the wavelength conversion layer 8 with respect to the underlying layer is approximately 80% or less, it is desirable because the connection resistance between the transparent conductive layer 7 and the back reflective electrode layer 9 decreases. On the other hand, from the viewpoint of the efficiency of wavelength conversion, it is preferable that the coverage of the wavelength conversion layer 8 with respect to the underlying layer is approximately 50% or more.

  In addition, if the irregularities on the surface of the wavelength conversion layer 8 have an irregular structure such as 1 to 50 nm using RMS measured by an atomic force microscope as an index, the reflection at the back reflective electrode layer 9 is scattered. Use efficiency of reflected light increases.

Embodiment 2. FIG.
FIG. 2 is a schematic cross-sectional view showing a multi-junction thin-film photoelectric conversion device according to the second embodiment. The thin film photoelectric conversion device according to the second embodiment is different from the first embodiment in the shapes of the wavelength conversion layer 8 and the back surface reflective electrode layer 9. In the second embodiment, the wavelength conversion layer 8 is formed such that the surface has a convex curved surface on the back side such as a spherical surface or a cylindrical surface. Further, the back reflective electrode layer 9 thereon is formed in a shape having a concave curved surface 9 a on the wavelength conversion layer 8 side, following the surface shape of the wavelength conversion layer 8. For this reason, the inner reflective surface of the back surface reflective electrode layer 9 has a condensing function for condensing the reflected light in the wavelength conversion layer 8.

  The wavelength conversion layer 8 is made of, for example, an organic material or a resin material. The shape of the wavelength conversion layer 8 can be easily created by applying and spraying a solution so that particles are scattered, and it is softened by heat treatment after a discrete layered pattern is formed by mask processing. It is also possible to smooth the edges by doing so.

  When the back surface reflective electrode layer 9 is formed on such a wavelength conversion layer 8 by sputtering or the like, the film adheres along the surface shape of the wavelength conversion layer 8, so that the wavelength conversion layer 8 as shown in FIG. The curved surface is concave on the side.

  Thus, the back surface reflective electrode layer 9 has the concave curved surface 9 a on the wavelength conversion layer 8 side, and the light incident from the front side and transmitted through the photoelectric conversion layer 62 passes through the wavelength conversion layer 8 and is behind the concave curved surface 9 a. Thus, the light is reflected so as to be condensed in the wavelength conversion layer 8. That is, when the light reflected by the back surface reflective electrode layer 9 passes through the wavelength conversion layer 8 again, it is condensed, so that the wavelength conversion efficiency is improved. In the case where the concave curved surface 9a is a curved surface having a focal point such as a spherical surface or a cylindrical surface, it is further desirable that the focal point be in the wavelength conversion layer 8. By improving the wavelength conversion efficiency, it is possible to increase the wavelength component that is easily absorbed by the photoelectric conversion layer 62 out of the wavelength components of the light reflected by the back surface reflective electrode layer 9, thereby improving the photoelectric conversion efficiency. .

Embodiment 3 FIG.
Next, Embodiment 3 will be described. The material that converts infrared light into visible light is not limited to two-photon absorption, and may be a material that performs infrared-visible conversion by a multi-stage transition type. As such a material, for example, according to Japanese Patent Laid-Open No. 2005-82770, an infrared-visible conversion phosphor having a minute particle size of about several microns is shown. In phosphors containing Er3 +, Tm3 +, Ho3 +, etc., these ions in the excited state further absorb light and cause a multi-step excitation that rises to a higher excitation level, thereby converting infrared to visible light. . The wavelength conversion layer can be easily formed by dispersing fine particles made of such a material in an insulating transparent resin solution and spraying the liquid by printing or spraying. In addition to the multi-stage excitation type, a fine powder of an infrared stimulable phosphor whose main component is a sulfide or selenide of an alkaline earth metal may be used.

  FIG. 3 is a schematic cross-sectional view illustrating a multi-junction thin-film photoelectric conversion device according to the third embodiment. Although the shape of the wavelength conversion layer 8 and the back surface reflecting electrode layer 9 is the same as in the case of the second embodiment, the wavelength conversion layer 8 of the third embodiment is made of a transparent resin material 8c and phosphor fine particles such as sulfides. 8b. The phosphor fine particles 8b are dispersed in the resin material 8c, and can be produced in the same manner as in the second embodiment. The size of the phosphor fine particles 8b is, for example, 1 to 5 μm.

  The phosphor fine particles 8b are generally horny materials, but are dispersed in the resin material 8c, so that the adhesion to the base is good, and the back surface reflective electrode layer 9 is smooth on the phosphor fine particle 8b side. The concave curved surface 9a can be created. Since the condensing performance is improved by such a concave curved surface 9a, the photoelectric conversion efficiency is improved as in the case of the second embodiment.

Embodiment 4 FIG.
FIG. 4 is a schematic cross-sectional view illustrating a multi-junction thin film photoelectric conversion device according to the fourth embodiment. In the fourth embodiment, the conductive particles 12 serving as the conductive part are dispersed in the wavelength conversion layer 8. The conductive particles 12 are particles made of metal particles or a transparent conductive material. For example, it is good also as a particle | grain of about 1-5 micrometers. For this reason, the back reflective electrode layer 9 and the transparent conductive layer 7 can be electrically connected by the conductive particles 12 without forming a through hole or an opening in the wavelength conversion layer 8.

  As described above, the conductive particles 12 are dispersed in the wavelength conversion layer 8 to facilitate the production. Moreover, the dispersion | distribution of the electroconductive particle 12 increases the scattering effect in the wavelength conversion layer 8, and the light reflected by the back surface reflective electrode layer 9 is absorbed by the back photoelectric conversion cell 6 (photoelectric conversion layer 62). It becomes easy and photoelectric conversion efficiency improves.

  Although not shown in particular, the wavelength conversion phenomenon such as multiphoton absorption dramatically increases the efficiency when the light intensity is increased. It is even better if the solar cell is made to receive light that has been condensed.

  As described above, the thin film photoelectric conversion device according to the present invention is useful for improving the photoelectric conversion efficiency when generating power by primary absorption of incident light in the photoelectric conversion layer and high-order absorption of reflected light by the back surface reflective electrode layer or the like. It is.

DESCRIPTION OF SYMBOLS 1 Insulating transparent substrate 2 Transparent conductive layer 7 Transparent conductive layer 8 Wavelength conversion layer 9 Back surface reflective electrode layer 9a Concave surface 10 Conductive part 12 Conductive particle 32, 42, 62 Photoelectric conversion layer

Claims (4)

A thin film photoelectric conversion device in which a first transparent conductive layer, a photoelectric conversion layer, a second transparent conductive layer, and a back surface reflective electrode layer are sequentially laminated on a translucent substrate,
Between the second transparent conductive layer and the back reflective electrode layer, a wavelength conversion layer is provided,
The wavelength conversion layer contains a material that converts the wavelength of light incident from the translucent substrate and passed through the photoelectric conversion layer into a shorter wavelength, and the second transparent conductive layer and the layer are included in the layer. A thin film photoelectric conversion device comprising a conductive portion that electrically connects a back surface reflective electrode layer.   The thin film photoelectric conversion device according to claim 1, wherein the back reflective electrode layer has a concave curved surface on the wavelength conversion layer side.   The thin film photoelectric conversion device according to claim 1, wherein the conductive portion is made of conductive particles dispersed in the wavelength conversion layer.   The thin film photoelectric conversion according to any one of claims 1 to 3, wherein a coverage of the wavelength conversion layer with respect to a layer serving as a base of the wavelength conversion layer is approximately 80% or less and 50% or more. apparatus.

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