JP2011222819A - Solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell with good quality which has an organic thin film voltaic layer.SOLUTION: An organic thin film voltaic layer 4, an upper electrode 5 consisting of thin film, and an auxiliary electrodes 6 are successively provided on a metal foil 1. The circumference of the metal foil 1 is framed by a sealing material 7, the inner side region of which has a sealing material 8. The arithmetic surface roughness Ra of the surface of the metal foil 1 is less than half the thickness of the organic thin film voltaic layer.

Description

  The present invention relates to a solar cell having a photoelectric conversion layer (photovoltaic layer) made of an organic thin film formed on a metal substrate.

Patent Documents 1 and 2 below describe solar cells in which unit cells are formed on a metal substrate and the unit cells are connected in series. In Patent Document 1, a SiO ₂ insulating layer is formed on a 50 μm-thick stainless steel sheet, and a Mo layer (back electrode layer), CuSe layer (p layer), CdS layer, ZnO layer, ITO layer (transparent conductive layer) is formed thereon. Layer) are sequentially formed, and the Mo layer and the ITO layer of the adjacent unit cells are made conductive to connect the unit cells in series (paragraphs 0057 to 0058).

  In Patent Document 2, a lower conductive layer made of Mo, a metal semiconductor film layer, and an upper transparent conductive layer such as ITO are stacked on a stainless steel plate having a thickness of 0.1 mm, and the lower conductive layer of one adjacent unit cell is laminated. The unit cells are connected in series by conducting the layer and the upper transparent conductive layer of the other unit cell. In Patent Documents 1 and 2, the photovoltaic layer is a silicon layer, but in recent years, development of an organic thin-film solar cell in which the photovoltaic layer is formed of an organic thin film has been promoted (for example, Patent Document 3). 4). In Patent Documents 3 and 4, the organic thin film is formed on a glass substrate.

JP 2004-146435 A JP 2006-185979 A JP2008-201819 JP2009-99805

  In the solar cells of Patent Documents 1 and 2, the photovoltaic layer is made of a metal semiconductor. Generally, the surface of a metal substrate is rougher than a glass substrate, and the surface roughness is large. Since the metal semiconductor is generally thicker than the organic thin film, even if the substrate surface is rough, the characteristics of the photovoltaic layer are hardly affected. On the other hand, since the organic thin film photovoltaic layer has a smaller thickness than a metal semiconductor, if the surface roughness of the base material is large, defects such as pinholes may occur and the characteristics may be deteriorated.

  An object of the present invention is to provide a high-performance solar cell in which an organic thin-film photovoltaic layer is formed on a metal substrate.

  The solar cell according to claim 1 is a solar cell in which at least an electromotive force layer and an upper electrode are formed on a metal substrate, the electromotive force layer is an organic thin film electromotive force layer, and the surface of the metal substrate is smooth. It is characterized by having been processed.

  The solar cell of claim 2 is characterized in that, in claim 1, the value of the arithmetic average surface roughness Ra of the surface of the metal substrate is ½ or less of the thickness of the organic thin film electromotive force layer. is there.

  The solar cell of claim 3 is characterized in that, in claim 1 or 2, the surface of the metal substrate is smoothed by physical polishing treatment and / or chemical polishing treatment.

  According to a fourth aspect of the present invention, there is provided a solar cell according to any one of the first to third aspects, wherein a lower electrode is provided between the metal substrate and the organic thin film electromotive force layer.

  The solar cell of claim 5 is characterized in that, in claim 4, an insulating layer is provided between the metal substrate and the lower electrode.

  In the solar cell of the present invention, an organic thin film electromotive force layer is formed on a smooth surface of a metal substrate through a lower electrode layer as necessary.

  In the present invention, since the surface of the metal substrate is smooth, the organic thin film electromotive force layer can be formed uniformly without causing defects such as pinholes. Thereby, the characteristics of the organic thin film electromotive force layer are improved, and a short circuit between the metal substrate or the lower electrode and the upper electrode is prevented through a pinhole or the like.

  In the present invention, since the organic thin film photovoltaic layer and the electrode are formed on a metal substrate having high heat resistance, it is possible to give sufficient thermal energy for the formation of the electrode material and the organic semiconductor material. The characteristics and life of the power layer are improved.

  In addition, since the metal base material adopted as the base base material has low oxygen and moisture permeability, the demand for oxygen and moisture resistance of the electrode material and organic semiconductor material is relaxed, and the characteristics and life of the organic thin film photovoltaic layer are reduced. improves. Moreover, since application | coating of a barrier material and a getter material can be reduced, the thickness and rigidity of a solar cell module are reduced, and a lightweight and flexible solar cell module is realizable.

  Since the metal substrate is conductive, charging of the solar cell module is prevented, failure such as electrostatic breakdown is avoided, and the reliability of the solar cell module is improved.

  Moreover, since the metal substrate has high penetration resistance, the organic thin-film photovoltaic layer that is weak against the action of external force can be protected from damage during transportation and construction, and the reliability of the solar cell module is improved.

  In the present invention, since the organic thin film photovoltaic layer can be connected in series with a monolithic structure, no element connection parts or processing (cutting or bonding) is required, and a lightweight and flexible solar cell module can be realized. It becomes.

It is sectional drawing of the solar cell which concerns on embodiment. It is sectional drawing of the solar cell which concerns on another embodiment. It is sectional drawing of the solar cell which concerns on another embodiment.

  A first embodiment will be described with reference to FIG.

  As for the metal foil 1 as a base metal, the surface (upper surface of the figure) is smoothed. An organic thin film electromotive force layer 4 is provided on the metal foil 1, and an upper electrode 5 made of a thin film is provided thereon. An auxiliary electrode 6 is provided on the upper electrode 5. The thickness of the organic thin film electromotive force layer 4 is preferably about 50 to 500 nm, particularly about 100 to 300 nm.

  A sealing material 7 is arranged in a frame shape on the periphery of the metal foil 1. The sealing material 8 exists in the inner region of the sealing material 7. The sealing material 7 consists of photocurable resin, and the synthetic resin film 9 has adhered to the upper side.

  The generated power of the solar cell is taken out from the metal foil 1 and the auxiliary electrode 6.

  In this embodiment, the arithmetic mean surface roughness (Ra) of the surface on the upper surface side of the metal foil 1 in the drawing is ½ or less of the thickness of the organic thin film electromotive force layer 4, preferably 50 nm or less. 30 nm or less. Thus, since the surface roughness of the metal foil 1 is small, the organic thin-film electromotive force layer 4 formed on the metal foil 1 is uniformly formed and has excellent characteristics. Moreover, it is prevented that defects, such as a pinhole, arise in the organic thin film electromotive force layer 4, and it is prevented that the metal foil 1 and the upper electrode 5 are short-circuited via a pinhole.

  In addition, since the base material is a metal foil, as described in the above-mentioned column of effects, effects such as improvement in characteristics and life, lightness and flexibility, and improvement in reliability are exhibited.

[Another embodiment]
In the above embodiment, the organic thin-film electromotive force layer 4 is formed directly on the metal foil 1, but a conductive layer (lower electrode) is provided on the metal foil 1 using the same material as the upper electrode described later. The organic thin film electromotive force layer 4 may be formed thereon.

  Also in this case, by making the surface roughness of the metal foil 1 small as described above, the surface roughness of the lower electrode becomes small, and the same effect as the first embodiment is exhibited.

  In the present invention, as shown in FIG. 2, the insulating layer 2 is provided on the metal foil 1, the lower electrode 3 is provided on the insulating layer 2, and the organic thin film electromotive force layer 4 is provided on the lower electrode 3. It may be provided.

  Also in this case, by making the surface roughness of the metal foil 1 small as described above, the surface roughness of the lower electrode becomes small, and the same effect as the first embodiment is exhibited.

  In the present invention, when an insulating layer is formed on the metal foil 1, a plurality of unit cells may be formed on the metal foil 1 and connected in series. An example is shown in FIG.

  An insulating layer 2 is provided on the entire surface of the metal foil 1, and a plurality of lower electrodes 3 made of a thin film are provided on the insulating layer 2 at intervals.

  An organic thin film electromotive force layer 4 is provided on the lower electrode 3, and an upper electrode 5 made of a thin film is provided thereon. The upper electrode 5 is connected to one end of the adjacent lower electrode 3. An auxiliary electrode 6 is provided on the upper electrode 5.

  As in the case of FIGS. 1 and 2, the sealing material 7 is arranged in a frame shape on the periphery of the metal foil 1. The sealing material 8 exists in the inner area | region of the sealing material 7, and the synthetic resin film 9 has adhered to the upper side.

  As shown in the figure, the unit cell includes a lower electrode 3, an organic thin film electromotive force layer 4, an upper electrode 5, and an auxiliary electrode 6. The upper electrode 5 of the left unit cell in the figure is connected to the lower electrode 3 of the right unit cell, and both unit cells are connected in series.

  The generated electric power of the solar cell is taken out from the lower electrode 3 of the left unit cell and the lower auxiliary electrode 3A that conducts to the upper electrode 5 of the right unit cell.

  Also in this embodiment, the arithmetic average surface roughness (Ra) of the surface on the upper surface side of the metal foil 1 is set to ½ or less of the thickness of the organic thin film electromotive force layer 4, and the characteristics of each unit cell Is good.

  Next, suitable constituent materials, thicknesses, and the like of the main components of the solar cell will be described.

[Aspect of metal foil]
The material of the metal foil is preferably iron, copper, aluminum, zinc, tin, chrome, nickel or an alloy thereof, and particularly preferably an aluminum alloy or stainless steel. The thickness is preferably 10 μm to 300 μm. As the surface roughness, it is usually preferable that the arithmetic average surface roughness (Ra) is ½ or less of the thickness of the organic thin film electromotive force layer, for example, 50 nm or less, particularly about 30 nm or less. The linear thermal expansion coefficient is usually preferably about 5 to 40 ppm / ° C.

  The treatment for smoothing the surface of the metal foil may be a physical polishing treatment or a chemical polishing treatment, or a plurality of them may be used in combination. Examples of the processing method include, but are not limited to, physical polishing processing such as buffing, belts, and barrels, chemical polishing processing, electrolytic polishing processing, and plasma polishing processing.

[Insulation layer]
The insulating layer may be a metal oxide film (for example, an oxide film formed by oxidizing the surface of a metal foil), a synthetic resin film, or a film made of other materials. . Examples of other materials include organic-inorganic hybrid materials.

  Hereinafter, these coating films will be described in more detail.

i) Metal Oxide Film An alumite film excellent in insulation is particularly suitable as a film obtained by anodizing the metal foil itself. The oxides of other species metal on metal foil _{(Si0 2, Ti0 2, ZrO} 2, Ta 2 O 3) which was precipitated also suitable. The thickness is preferably 0.1 μm to 1 μm, particularly preferably 0.2 μm to 0.5 μm. The linear thermal expansion coefficient is usually preferably about 5 to 20 ppm / ° C.

ii) Synthetic resin film The types of synthetic resin are PC, PS, PE, PP, PET, PEN, PAI, PPS, PFA, ETFE and other thermoplastic resins, PI, PF, UF, MF, UP, EP, PDAP, etc. The thermosetting resin is preferably a radical polymerization system such as acrylate or unsaturated polyester, or a cationic polymerization system photocurable resin such as epoxy, oxetane or vinyl ether. Among these, a photo-curing resin or a thermoplastic resin is preferable because it is possible to form a coating on a metal foil continuously and easily.

  The thickness of the synthetic resin film is preferably 0.01 μm to 5 μm, and particularly preferably 0.1 μm to 3 μm. The linear thermal expansion coefficient is usually preferably about 20 to 200 ppm / ° C.

iii) Organic-inorganic hybrid material A nanocomposite material in which inorganic particles such as silica, alumina, titania and zirconia are nano-dispersed in a polymer is preferable, and a nanocomposite of silica gel is particularly preferable. An organic-inorganic hybrid material such as polysiloxane or polyphosphazene is also suitable, and a hybrid polymer in which an organic functional group is introduced into siloxane having excellent heat resistance is particularly suitable. These can be satisfactorily formed by a sol-gel method.

  The thickness of the organic-inorganic hybrid film is preferably 0.1 μm to 5 μm, and particularly preferably 0.5 μm to 3 μm. The linear thermal expansion coefficient is usually preferably about 10 to 100 ppm / ° C.

  In the present invention, the thickness of the insulating layer is preferably ½ or less of the thickness of the metal foil, for example, 10 to 20%, and 5 times or more of the thickness of the organic thin film electromotive force layer, for example, 10 to 100 times. When the thickness of the insulating layer is set in this way, when the solar cell module is bent by an external force, between the metal foil, the insulating layer, and the organic thin film photovoltaic layer, and between the insulating layer, the organic thin film photovoltaic layer, Since the peeling due to strain is less likely to occur, the reliability of the solar cell module is improved.

  Moreover, it is preferable that the difference of the linear thermal expansion coefficient of an insulating layer and the said metal foil shall be 100 ppm / degrees C or less. In this case, since the difference in thermal expansion between the metal foil and the insulating layer when the environmental temperature changes is reduced, the insulating layer is prevented from being destroyed and warping deformation is suppressed. Will improve.

[Organic thin film electromotive force layer]
The organic thin film electromotive force layer is formed of an organic semiconductor. Organic semiconductors are classified into p-type and n-type depending on semiconductor characteristics. The p-type and n-type indicate whether it is a hole or an electron that contributes to electrical conduction, and depends on the electronic state, doping state, and trap state of the material. Therefore, there are cases where p-type and n-type cannot always be clearly classified, and there are cases where the same substance exhibits both p-type and n-type characteristics.

  Examples of p-type semiconductors include porphyrin compounds such as tetrabenzoporphyrin, tetrabenzocopper porphyrin, tetrabenzozinc porphyrin; phthalocyanine compounds such as phthalocyanine, copper phthalocyanine, zinc phthalocyanine; naphthalocyanine compounds; polyacenes of tetracene and pentacene; Examples thereof include oligothiophene and derivatives containing these compounds as a skeleton. Furthermore, polymers such as polythiophene, polyfluorene, polyphenylene vinylene, polytriallylamine, polyacetylene, polyaniline, polypyrrole and the like including poly (3-alkylthiophene) are exemplified.

  Examples of n-type semiconductors include fullerenes (C60, C70, C76); octaazaporphyrins; perfluoro compounds of the above p-type semiconductors; naphthalenetetracarboxylic acid anhydrides, naphthalenetetracarboxylic acid diimides, perylenetetracarboxylic acid anhydrides, perylenes And aromatic carboxylic acid anhydrides such as tetracarboxylic acid diimide and imidized products thereof; and derivatives containing these compounds as a skeleton.

  The specific configuration of the organic semiconductor layer is arbitrary as long as at least a p-type semiconductor and an n-type semiconductor are contained. It may be constituted only by a single layer film or may be constituted by two or more laminated films. For example, an n-type semiconductor and a p-type semiconductor may be contained in separate films, or an n-type semiconductor and a p-type semiconductor may be contained in the same film. In addition, each of the n-type semiconductor and the p-type semiconductor may be used alone or in combination of two or more in any combination and ratio.

  Specific examples of the structure of the organic semiconductor layer include a bulk heterojunction type having a layer (i layer) in which a p-type semiconductor and an n-type semiconductor are phase-separated in the layer, a layer containing a p-type semiconductor (p layer), and n, respectively. Examples include a stacked type (hetero pn junction type) in which a layer containing a p-type semiconductor (p layer) has an interface, a Schottky type, and a combination thereof. Among these, a bulk heterojunction type and a combination of a bulk heterojunction type and a stacked type (p-i-n junction type) are preferable because they exhibit high performance.

  Although there is no restriction | limiting in the thickness of p layer of an organic-semiconductor layer, i layer, and n layer, Usually, it is preferable to set it as 3 nm or more, especially 10 nm or more, and usually 200 nm or less, especially 100 nm or less. Increasing the layer thickness tends to increase the uniformity of the film, and decreasing the thickness tends to improve the transmittance and decrease the series resistance.

  A hole transport layer and an electron transport layer may be provided between the organic thin film electromotive force layer and the electrode.

  Examples of the constituent material of the hole transport layer include phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, triphenylamines, aromatic diamine compounds, polysilanes, PEDTO-PSS (poly (ethylenedioxythiophene) -poly (styrenesulfonic acid) ) And the like.

Examples of the constituent material of the electron transport layer include organic compounds such as phenanthroline derivatives and silole derivatives, and inorganic semiconductors such as TiO ₂ .

[Lower and upper electrodes]
The lower electrode and the upper electrode can be formed of a conductive material, for example, a metal such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium, sodium, or the like Metal oxides such as indium oxide, zinc oxide, tin oxide, ITO, indium zinc oxide (IZO); polyaniline, polypyrrole, polythiophene, polyacetylene, PEDOT-PSS (poly (ethylenedioxythiophene) -poly (styrene) A conductive polymer such as sulfonic acid)); an acid such as hydrochloric acid, sulfuric acid or sulfonic acid; a Lewis acid such as FeCl _3; a halogen atom such as iodine; a metal atom such as sodium or potassium; Containing dopant: metal particles, carbon black, hula Examples thereof include conductive composite materials in which conductive particles such as fullerene and carbon nanotubes are dispersed in a matrix such as a polymer binder. Especially, the material which has deep work functions, such as Au and ITO, is preferable for the electroconductive base material or electrode which collects a hole. On the other hand, a material having a shallow work function such as Al is preferable for the conductive base material or electrode for collecting electrons. By optimizing the work function, there is an advantage of favorably collecting holes and electrons generated by light absorption.

  It is preferable that at least the upper electrode on the light-receiving surface side has light transmittance for power generation. However, even if the electrode is not transparent, it does not necessarily have to be transparent if the power generation performance is not significantly adversely affected. Examples of transparent electrode materials include oxides such as ITO, zinc oxide, tin oxide, and indium zinc oxide (IZO); and metal thin films. In this case, the specific range of the light transmittance is not limited, but considering the power generation efficiency of the solar cell element, 80% or more is preferable except for the loss due to partial reflection at the optical interface.

  Since these require transparency, the film thickness cannot be increased, and as a result, it is difficult to reduce the resistance value to a required value.

  Therefore, a configuration is used in which an electrode made of a metal material is formed as an auxiliary electrode above the upper electrode to reduce the resistance value of the upper electrode. As a material for the auxiliary electrode, a metal material such as a silver paste or an aluminum vapor deposition film is generally used. A silver paste is a conductive paste in which silver particles are mixed in a resin.

  The auxiliary electrode may include a current collector that collects the current collected by the auxiliary electrode into one.

  In addition, the material of a lower electrode and an upper electrode may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  In addition, there is no restriction | limiting in the formation method of a lower electrode and an upper electrode. For example, it can be formed by a dry process such as vacuum deposition or sputtering. Further, for example, it can be formed by a wet process using a conductive ink or the like. At this time, any conductive ink can be used. For example, a conductive polymer, a metal particle dispersion, or the like can be used.

  Furthermore, two or more electrodes may be laminated, and characteristics (electric characteristics, wetting characteristics, etc.) due to surface treatment may be improved.

[Other layers]
The solar cell of the present invention may include layers other than the above, such as a buffer layer.

  The buffer layer is a layer provided at the electrode interface facing the organic semiconductor layer for improving electrical characteristics and the like. For example, poly (ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS), molybdenum oxide, lithium fluoride, 2,9dimethyl-4,7-diphenyl-1,10-phenanthroline, and the like can be given.

  Hereinafter, an example of a method capable of easily producing the solar cell of the present invention will be described.

  First, the surface of the metal foil 1 is polished by buffing so that the arithmetic average surface roughness is 100 nm or less. An organic thin film electromotive force layer (organic semiconductor layer) 4 is pattern-printed on the metal foil 1 by flexographic printing. As the organic semiconductor, a 1: 1 mixture by weight of polythiophene (P3HT; poly-3-hexylthiophene) and fullerene (PCBM; 1- (3-methoxycarbonyl) -propyl-1-phenyl (6.6) -C61) is preferable. If this is made into a chlorobenzene solution of about 1.0 wt%, it can be satisfactorily applied, and the thickness is preferably about 50 to 100 nm.

  Next, the upper electrode 5 is formed by sputtering of ITO (indium tin oxide). The thickness of ITO is preferably about 100 to 200 nm. Patterning of the upper electrode 5 can be performed by a mask sputtering method or a laser ablation method. Alternatively, the upper electrode 5 can be formed into a film by wet coating using a transparent conductive ink such as ITO nanoparticles, conductive polymer (PEDOT / PSS, etc.), graphene, or CNT.

  Next, the auxiliary electrode 6 is formed on the upper electrode 5. As the auxiliary electrode material, a silver paste is suitable, and it can be printed favorably by a screen printing method. A line width of about 20 to 100 μm and a thickness of about 20 to 100 μm are suitable.

  Next, the sealing material 8 is applied to the sealing region with a dispenser or the like. As the sealing material, a gel-like transparent getter material is suitable, and it can be adjusted by mixing a viscosity adjusting agent such as aerosol or a dehydrating agent such as calcium oxide powder with an inert liquid such as fluorinate.

  Next, in order to form the sealing material 7, a photo-curable sealing material is applied by a dispenser or the like so as to surround the sealing region, and after that, the transparent flexible film 9 is laminated, and then cured by UV irradiation, Complete sealing.

  For example, a PET film with a barrier film having a thickness of about 100 μm is suitable as the flexible film 9. For example, an acrylic UV adhesive is suitable as the sealing material.

  As described above, a solar cell module having an organic thin film electromotive force layer is produced.

DESCRIPTION OF SYMBOLS 1 Metal foil 2 Insulating layer 3 Lower electrode 4 Organic thin-film electromotive force layer 5 Upper electrode 6 Auxiliary electrode 7 Sealing material 8 Sealing material 9 Film

Claims (5)

  In a solar cell in which at least an electromotive force layer and an upper electrode are formed on a metal substrate, the electromotive force layer is an organic thin film electromotive force layer, and the surface of the metal substrate is smoothed. A solar cell.   2. The solar cell according to claim 1, wherein the value of the arithmetic average surface roughness Ra of the surface of the metal substrate is ½ or less of the thickness of the organic thin film electromotive force layer.   3. The solar cell according to claim 1, wherein the surface of the metal substrate is smoothed by physical polishing treatment and / or chemical polishing treatment.   4. The solar cell according to claim 1, wherein a lower electrode is provided between the metal substrate and the organic thin film electromotive force layer.   The solar cell according to claim 4, wherein an insulating layer is provided between the metal base and the lower electrode.

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