JP5472939B2 - Thin film solar cell module - Google Patents

Description

  Embodiments described herein relate generally to a thin film solar cell module.

  An organic thin film solar cell is a solar cell using an organic thin film semiconductor, for example, a mixture of a conductive polymer and fullerene. The organic thin-film solar cell has an advantage that it can be produced by a simple method and is low in cost as compared with a solar cell using an inorganic material such as silicon, CIGS, and CdTe. On the other hand, the organic thin film solar cell has a problem that the photoelectric conversion efficiency and the lifetime are low as compared with the inorganic solar cell. Therefore, various ideas have been made to improve the photoelectric conversion efficiency of the organic thin film solar cell.

  The following items can be cited as factors that lower the efficiency of the organic thin film solar cell module.

  Since the moving distance of carriers in the photoelectric conversion layer made of an organic thin film is short, it is necessary to form the photoelectric conversion layer as thin as about 100 nm. As a result, the received light is not sufficiently absorbed, and part of it escapes to the outside as reflected light.

  Further, due to the material properties of the organic thin film, the voltage dependence of the leakage current of the solar battery cell is high, so that it is necessary to limit the potential difference generated between the anode and the cathode along the current direction. For this reason, in order to operate the device in a desired voltage range, a plurality of solar cells having a narrow width are formed in a stripe shape with a gap therebetween, and adjacent solar cells are connected in series. However, in the organic thin-film solar cell module, the area ratio of the gap region to the cell region is high due to restrictions on the manufacturing process, so that the aperture ratio cannot be increased as much as solar cell modules of other materials. As a result, the power generation efficiency of the organic thin-film solar battery module is extremely low compared to the efficiency of a small area solar battery cell.

  An object of the present invention is to provide a thin film solar cell module having high photoelectric conversion efficiency.

  The thin film solar cell module according to the embodiment has a plurality of solar cells formed in parallel in a striped manner on a transparent substrate with a gap therebetween, and each of the solar cells has a transparent electrode, a photoelectric conversion layer, and The adjacent solar cells including a counter electrode are connected in series, and reflect light incident from the transparent substrate side toward the solar cell corresponding to a gap between the adjacent solar cells. It has a solar cell submodule on which a light reflecting layer is formed. The pair of solar cell sub-modules are such that the main surfaces of their transparent substrates are inclined non-parallel with a positive inclination and a negative inclination, respectively, along one direction, and facing each other so as to have a close end and an open end. Has been placed.

Sectional drawing of the thin film solar cell module which concerns on 1st Embodiment. Sectional drawing of the thin film solar cell module which concerns on 2nd Embodiment. Sectional drawing which shows an example of the photovoltaic cell in the thin film photovoltaic module which concerns on 1st Embodiment. Sectional drawing which shows the other example of the photovoltaic cell in the thin film photovoltaic module which concerns on 1st Embodiment. Sectional drawing which shows an example of the photovoltaic cell in the thin film photovoltaic module which concerns on 2nd Embodiment. Sectional drawing which shows the other example of the photovoltaic cell in the thin film photovoltaic module which concerns on 2nd Embodiment. Sectional drawing which shows the other example of the photovoltaic cell in the thin film photovoltaic module which concerns on 2nd Embodiment. Sectional drawing which shows a bulk heterojunction type organic thin-film solar cell roughly. Sectional drawing of the thin film solar cell module which concerns on 3rd Embodiment. Sectional drawing which shows an example of the photovoltaic cell in the thin film photovoltaic module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment. The top view which shows the manufacturing process of the thin film solar cell module which concerns on 3rd Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the thin film solar cell module according to the first embodiment. In FIG. 1, the thin film solar cell module 100 is formed of a pair of solar cell submodules 50. One solar cell sub-module 50 has a plurality of solar cells 30 formed in parallel in a striped pattern on one transparent substrate 10 with a gap therebetween. As will be described later, each solar battery cell 30 includes a transparent electrode, a photoelectric conversion layer, and a counter electrode, and adjacent solar battery cells 30 are connected in series. The photoelectric conversion layer of the organic thin film solar cell is of a bulk heterojunction type including, for example, a p-type organic semiconductor and an n-type organic semiconductor.

  The pair of solar cell submodules 50 has their principal surfaces of the transparent substrate 10 inclined non-parallel with a positive inclination and a negative inclination along one direction (x direction in FIG. 1), respectively, and the adjacent end E1 and the opening It arrange | positions so that it may have the edge E0. A plurality of pairs of solar cell submodules 50 are arranged along one direction (the x direction in FIG. 1).

In FIG. 1, the surface of the transparent substrate 10 of each solar cell submodule 50 on which the solar cells 30 are formed (hereinafter referred to as the back surface) reflects light corresponding to the gap between the adjacent solar cells 30. Layer 20 is formed. The light reflectance of the light reflecting layer 20 is preferably in the range of 90 to 100%. As will be described later, the light reflection layer 20 in FIG. 1 is used as a wiring for connecting adjacent solar cells 30.

  Light enters the thin film solar cell module from the opening end E0 side, and enters each solar cell submodule 50 from the front surface side of the transparent substrate 10 toward the solar cell 30 on the back surface. Here, if there is no light reflection layer 20, the probability that light will not be utilized through the gap between the adjacent photovoltaic cells 30 increases. On the other hand, in the first embodiment, since the light reflecting layer 20 is formed corresponding to the gap between the adjacent solar battery cells 30, the sun facing the light reflected by the light reflecting layer 20. It can be used in the battery submodule 50. Therefore, it is possible to effectively increase the aperture ratio of the thin film solar cell module and increase the photoelectric conversion efficiency.

  FIG. 2 is a cross-sectional view of the thin film solar cell module according to the second embodiment. 2 is different from FIG. 1 in that the light reflecting layer 20 formed corresponding to the gap between the adjacent solar cells 30 is not on the back side of the transparent substrate 10 but on the surface side of the transparent substrate 10. It is formed. That is, the light reflection layer 20 is formed on the main surface of the transparent substrate 10 that faces the main surface on which the solar battery cells 30 are provided.

  Also in the second embodiment, similarly to the first embodiment, the aperture ratio of the thin film solar cell module can be effectively increased, and the photoelectric conversion efficiency can be increased.

  In the solar cell submodule according to the embodiment, the average inclination angle θ of the solar cells 30 with respect to the one direction (x direction) or the opening end surface (a surface perpendicular to the incident direction of light having the highest intensity) is 40 °. It is preferably 50 ° or 55 ° to 65 °. By tilting the solar cell with respect to the incident direction of light, the light reflected by one cell can be received by the opposing cell and reused, and the light utilization rate can be increased. The range where the angle θ is 40 to 50 ° is a peripheral condition with the number of reflections of 1 and is an angle at which the power generation efficiency with respect to the cell area is maximized, and thus is excellent in cost performance. The range in which the angle θ is 55 to 65 ° is a peripheral condition with the number of reflections of 2 and the light utilization rate approaches 1. At higher angles, the light utilization rate increases but tends to saturate. On the other hand, the power generation efficiency with respect to the cell area rapidly decreases, so an appropriate angle is around 60 °. When the number of reflections is 2, the amount of invalid light becomes 10% or less. When the transparent substrate 10 is curved, the inclination angle θ of the tangent of the transparent substrate 10 or the tangent of the transparent substrate 10 where the solar cells 30 are provided is 40 ° to 50 ° or 55 ° to 65 °. Preferably there is.

  Next, the structure of the solar battery cell in the thin film solar battery module according to the first embodiment will be described with reference to FIGS.

  FIG. 3 is a cross-sectional view showing an example of a solar battery cell in the thin-film solar battery module according to the first embodiment. As shown in FIG. 3, the solar battery cell 30 is formed on a transparent substrate 10 made of glass, for example, and includes a transparent electrode (anode) 11, a photoelectric conversion layer 12 made of an organic thin film, and a counter electrode (cathode) 13. The stacked structure is the basic structure. As shown in FIG. 3, when the transparent electrode 11, the photoelectric conversion layer 12, and the counter electrode 13 are stacked so as to partially overlap, the transparent electrode 11, the photoelectric conversion layer 12, and the counter electrode 13 are The stacked portion is referred to as a solar battery cell 30.

Here, of two adjacent solar cells 30, a region between the transparent electrode 11 of one solar cell 30 and the counter electrode 13 of the other solar cell 30 is defined as a gap (gap) G. .

In FIG. 3, the light reflecting layer 20 is formed corresponding to the gap G on the back surface of the transparent substrate 10 on which the array of solar battery cells 30 is formed. That is, the light reflecting layer 20 is formed on the back surface of the transparent substrate 10 corresponding to the gap G, and the insulating layer 21 made of an inorganic material such as SiO ₂ is formed thereon. A contact hole is formed in the insulating layer 21, and the transparent electrode 11 having a pattern such as indium tin oxide (ITO) and the extraction electrode 22 of the counter electrode 13 are formed on the insulating layer 21 and connected to the light reflecting layer 20. ing. A photoelectric conversion layer 12 made of an organic thin film applied on the transparent electrode 11 is formed. A counter electrode 13 made of a metal such as Al is formed on the photoelectric conversion layer 12 and connected to the extraction electrode 22. Thus, the light reflection layer 20 in FIG. 3 is used as the wiring of the solar battery cell 30.

  The portion where the counter electrode 13 is connected to the extraction electrode 22 and does not cover the photoelectric conversion layer 12 is not included in the solar battery cell 30. Further, the portion connected to the extraction electrode 22 of the transparent electrode 11 and not covered by the counter electrode 13 is not included in the solar battery cell 30. That is, a gap (gap) G is a region between portions where the transparent electrode 11, the photoelectric conversion layer 12, and the counter electrode 13 are stacked.

  Although not shown in FIG. 3, a hole transport layer is generally provided between the transparent electrode 11 and the photoelectric conversion layer 12, and an electron transport layer is generally provided between the photoelectric conversion layer 12 and the counter electrode 13. . Moreover, it is common to provide a sealing film in the back surface of a photovoltaic cell.

  FIG. 4 is a cross-sectional view showing another example of the solar battery cell in the thin film solar battery module according to the first embodiment. The solar battery cell of FIG. 4 has the same structure as that of FIG. On the surface of the transparent substrate 10, a light diffusion reflection layer 23 as a light reflection layer is formed at a position facing the gap G, and a non-reflection film 24 is formed at a position facing the solar battery cell 30.

  FIG. 5 is a cross-sectional view showing an example of a solar battery cell in the thin-film solar battery module according to the second embodiment. Unlike FIG. 3 in which the light reflecting layer 20 is formed on the back surface of the transparent substrate 10 corresponding to the gap G, in FIG. 5, the transparent electrode (anode) 11, the photoelectric conversion layer 12 made of an organic thin film, and A counter electrode (cathode) 13 is sequentially stacked. On the surface of the transparent substrate 10, a light diffusion reflection layer 23 as a light reflection layer is formed facing the gap G. As a material for the light diffusion reflection layer 23, for example, a foamed PET film is used because of its high reflectance and low cost. Although not shown, a non-reflective film may be formed so as to cover the entire surface of the transparent substrate 10.

  FIG. 6 is a cross-sectional view showing another example of the solar battery cell in the thin film solar battery module according to the second embodiment. In the solar battery cell of FIG. 6, the light reflection layer 20 and the light transmission diffusion layer 23 are laminated on the surface of the transparent substrate 10 so as to face the gap G as a light reflection layer. Other than that, it has the same structure as FIG.

  FIG. 7: is sectional drawing which shows the other example of the photovoltaic cell in the thin film solar cell module which concerns on 2nd Embodiment. In the solar battery cell of FIG. 7, the non-reflective film 24 is formed on the entire surface of the transparent substrate 10, and the light reflecting layer 20 is formed so as to face the gap G thereon. Other than that, it has the same structure as FIG. The structure of FIG. 7 can be produced by attaching a stripe film on which a metal is vapor-deposited so as to form a stripe pattern on the non-reflective film to the transparent substrate 20.

  A structure in which a film produced by alternately integrating light reflecting layers and non-reflecting layers is added to the light incident surface of the transparent substrate 10 is also effective. For example, a film in which a thin film of silver or aluminum is formed in a stripe shape by vapor deposition (or sputtering) on a non-reflective film typified by a moth-eye film, which will be described later, is arranged at a position facing the cell and the gap, respectively. A desired structure can be manufactured by pasting.

  Hereinafter, each structural member of the organic thin film photovoltaic cell which concerns on embodiment is demonstrated.

(Transparent substrate)
The transparent substrate 10 is for supporting other components. The transparent substrate 10 is preferably one that forms an electrode and does not deteriorate due to heat or an organic solvent. Examples of the material of the transparent substrate 10 include inorganic materials such as alkali-free glass and quartz glass, polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide, polyamideimide, liquid crystal polymer, cycloolefin polymer, and the like. And plastics and polymer films. The thickness of the substrate is not particularly limited as long as it has sufficient strength to support other components.

  By installing an antireflection film having a moth-eye structure on the light incident surface of the transparent substrate 10, for example, light can be efficiently taken in and the energy conversion efficiency of the cell can be improved. The moth-eye structure has a structure having a regular protrusion arrangement of about 100 nm on the surface, and the refractive index in the thickness direction is continuously changed by this protrusion structure. By interposing the non-reflective film, there is no discontinuous change surface of the refractive index, so that reflection of light is reduced and cell efficiency is improved.

(Transparent electrode)
The transparent electrode (anode) 11 is formed on the back surface of the transparent substrate 10. The material for the transparent electrode (anode) is not particularly limited as long as it has conductivity. Usually, a transparent conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. Examples of the transparent electrode material include a conductive metal oxide film and a translucent metal thin film. Specifically, conductive glass composed of indium oxide, zinc oxide, tin oxide, and indium tin oxide (ITO), fluorine-doped tin oxide (FTO), indium zinc oxide, etc., which are composites thereof. A film (NESA or the like) manufactured by using gold, platinum, silver, copper, or the like is used. In particular, ITO or FTO is preferable. Further, as an electrode material, an organic conductive polymer such as polyaniline and a derivative thereof, polythiophene and a derivative thereof may be used. In the case of ITO, the film thickness of the anode 11 is preferably 30 to 300 nm. If it is thinner than 30 nm, the conductivity is lowered, the resistance is increased, and the photoelectric conversion efficiency is lowered. If it is thicker than 300 nm, ITO becomes inflexible and cracks when stress is applied. The sheet resistance of the anode 11 is preferably as low as possible, and is preferably 10Ω / □ or less. The anode 11 may be a single layer or may be a laminate of layers made of materials having different work functions.

(Hole transport layer)
The hole transport layer is arbitrarily disposed between the transparent electrode 11 and the photoelectric conversion layer 12. The function of the hole transport layer is to level the unevenness of the lower electrode to prevent a short circuit of the solar cell element, to efficiently transport only holes, and to excitons generated near the interface of the photoelectric conversion layer 12 For example, to prevent disappearance. As a material for the hole transport layer, a polythiophene polymer such as PEDOT / PSS (poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate)), or an organic conductive polymer such as polyaniline or polypyrrole should be used. Can do. Typical products of the polythiophene-based polymer include, for example, Clevios PH500, CleviosPH, CleviosPV P Al 4083, and CleviosHIL1.1 from Starck. For inorganic materials, molybdenum oxide is a suitable material.

  When Clevios PH500 is used as the material for the hole transport layer, the film thickness is preferably 20 to 100 nm. If it is too thin, the effect of preventing the short-circuit of the lower electrode is lost, and a short circuit occurs. If it is too thick, the film resistance increases and the generated current is limited, so that the light conversion efficiency decreases.

  The method for forming the hole transport layer is not particularly limited as long as it is a method capable of forming a thin film. For example, the hole transport layer can be applied by spin coating. After applying the material for the hole transport layer to a desired film thickness, it is heated and dried with a hot plate or the like. Heat drying at 140 to 200 ° C. for several minutes to 10 minutes is preferable. As the solution to be applied, it is desirable to use a solution that has been filtered in advance.

(Photoelectric conversion layer)
The photoelectric conversion layer 12 is disposed between the transparent electrode 11 and the counter electrode 13. A bulk heterojunction solar cell has a micro-layer separation structure in which a p-type semiconductor and an n-type semiconductor are mixed in a photoelectric conversion layer. In the bulk heterojunction type, a mixed p-type semiconductor and n-type semiconductor form a pn junction having a nano-order size in the photoelectric conversion layer, and a current is obtained by utilizing photocharge separation generated at the junction surface. A p-type semiconductor is composed of a material having an electron donating property. On the other hand, the n-type semiconductor is made of a material having an electron accepting property. In the embodiment, at least one of the p-type semiconductor and the n-type semiconductor may be an organic semiconductor.

  Examples of p-type organic semiconductors include polythiophene and derivatives thereof, polypyrrole and derivatives thereof, pyrazoline derivatives, arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, oligothiophene and derivatives thereof, polyvinylcarbazole and derivatives thereof, polysilane and derivatives thereof. Polysiloxane derivatives having aromatic amines in the side chain or main chain, polyaniline and derivatives thereof, phthalocyanine derivatives, porphyrin and derivatives thereof, polyphenylene vinylene and derivatives thereof, polythienylene vinylene and derivatives thereof, and the like can be used, These may be used in combination. These copolymers may be used, and examples thereof include a thiophene-fluorene copolymer, a phenylene ethynylene-phenylene vinylene copolymer, and the like.

  A preferred p-type organic semiconductor is polythiophene which is a conductive polymer having π conjugation and derivatives thereof. Polythiophene and its derivatives can ensure excellent stereoregularity and have relatively high solubility in a solvent. Polythiophene and derivatives thereof are not particularly limited as long as they are compounds having a thiophene skeleton. Specific examples of polythiophene and derivatives thereof include polyalkylthiophenes such as poly-3-methylthiophene, poly-3-butylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, poly-3-decylthiophene, poly-3-dodecylthiophene Polyarylthiophenes such as poly-3-phenylthiophene and poly-3- (p-alkylphenylthiophene); poly-3-butylisothionaphthene, poly-3-hexylisothionaphthene, poly-3-octylisothionaphthene, poly-3- Polyalkylisothionaphthene such as decylisothionaphthene; polyethylenedioxythiophene and the like.

  In recent years, PCDTBT (poly [N-9 "-hepta-decanyl-2,7-carbazole-alt-5,5- (4 ', 7'-di ()), which is a copolymer of carbazole, benzothiadiazole and thiophene. Derivatives such as -2-thienyl-2 ′, 1 ′, 3′-benzothiadiazole)]) are known as compounds capable of obtaining excellent photoelectric conversion efficiency.

  These conductive polymers can be formed by applying a solution dissolved in a solvent. Therefore, there is an advantage that a large-area organic thin film solar cell can be manufactured at low cost with inexpensive equipment by a printing method or the like.

  As the n-type organic semiconductor, fullerene and derivatives thereof are preferably used. The fullerene derivative used here is not particularly limited as long as it is a derivative having a fullerene skeleton. Specific examples include derivatives composed of C60, C70, C76, C78, C84, etc. as the basic skeleton. In the fullerene derivative, carbon atoms in the fullerene skeleton may be modified with an arbitrary functional group, and these functional groups may be bonded to each other to form a ring. Fullerene derivatives also include fullerene bonded polymers. A fullerene derivative having a functional group with high affinity for the solvent and high solubility in the solvent is preferred.

  Examples of the functional group in the fullerene derivative include hydrogen atom; hydroxyl group; halogen atom such as fluorine atom and chlorine atom; alkyl group such as methyl group and ethyl group; alkenyl group such as vinyl group; cyano group; methoxy group and ethoxy group. An aromatic hydrocarbon group such as a phenyl group and a naphthyl group, and an aromatic heterocyclic group such as a thienyl group and a pyridyl group. Specific examples thereof include hydrogenated fullerenes such as C60H36 and C70H36, oxide fullerenes such as C60 and C70, and fullerene metal complexes.

  Among the above-described compounds, it is particularly preferable to use 60PCBM ([6,6] -phenyl C61 butyric acid methyl ester) or 70PCBM ([6,6] -phenyl C71 butyric acid methyl ester) as the fullerene derivative.

  When using unmodified fullerene, it is preferable to use C70. Fullerene C70 has high photocarrier generation efficiency and is suitable for use in organic thin-film solar cells.

  The mixing ratio of the n-type organic semiconductor and the p-type organic semiconductor in the photoelectric conversion layer is preferably about n: p = 1: 1 when the p-type semiconductor is a P3HT system. When the p-type semiconductor is a PCDTBT system, it is preferable that n: p = 4: 1.

  In order to apply an organic semiconductor, it is necessary to dissolve in a solvent. Examples of the solvent used therefor include toluene, xylene, tetralin, decalin, mesitylene, n-butylbenzene, sec-butylbenzene, and tert-butylbenzene. Unsaturated hydrocarbon solvents such as, halogenated aromatic hydrocarbon solvents such as chlorobenzene, dichlorobenzene, and trichlorobenzene, carbon tetrachloride, chloroform, dichloromethane, dichloroethane, chlorobutane, bromobutane, chloropentane, chlorohexane, bromohexane, Halogenated saturated hydrocarbon solvents such as chlorocyclohexane and ethers such as tetrahydrofuran and tetrahydropyran. In particular, a halogen-based aromatic solvent is preferable. These solvents can be used alone or in combination.

  As a method of applying a solution to form a film, spin coating, dip coating, casting, bar coating, roll coating, wire bar coating, spraying, screen printing, gravure printing, flexographic printing, offset Examples thereof include a printing method, gravure / offset printing, dispenser coating, nozzle coating method, capillary coating method, and inkjet method, and these coating methods can be used alone or in combination.

(Electron transport layer)
The electron transport layer is arbitrarily disposed between the photoelectric conversion layer 12 and the counter electrode 13. The electron transport layer has a function of blocking holes and efficiently transporting only electrons, and a function of preventing the disappearance of excitons generated at the interface between the photoelectric conversion layer 12 and the electron transport layer.

  Examples of the material for the electron transport layer include metal oxides such as amorphous titanium oxide obtained by hydrolyzing titanium alkoxide by a sol-gel method. The film forming method is not particularly limited as long as it is a method capable of forming a thin film, and examples thereof include a spin coating method. When titanium oxide is used as the material for the electron transport layer, the film thickness is preferably 5 to 20 nm. When the film thickness is thinner than the above range, the hole blocking effect is reduced, so that the generated excitons are deactivated before dissociating into electrons and holes, and current cannot be efficiently extracted. When the film thickness is too thick, the film resistance increases, and the light conversion efficiency decreases because the generated current is limited. It is desirable to use a coating solution that has been filtered with a filter in advance. After applying to a specified film thickness, it is heated and dried using a hot plate or the like. Heat drying at 50 to 100 ° C. for several minutes to 10 minutes while promoting hydrolysis in the air. For inorganic materials, a metal calcium film formed by vapor deposition is suitable.

(Counter electrode)
The counter electrode (cathode) 13 is stacked on the photoelectric conversion layer 12 (or the electron transport layer). A conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. Examples of the electrode material include a conductive metal thin film and a metal oxide film. When the transparent electrode 11 is formed using a material having a high work function, it is preferable to use a material having a low work function for the counter electrode 13. Examples of the material having a low work function include alkali metals and alkaline earth metals. Specific examples include Li, In, Al, Ca, Mg, Sm, Tb, Yb, Zr, Na, K, Rb, Cs, Ba, and alloys thereof.

  The counter electrode 13 may be a single layer or may be a laminate of layers made of materials having different work functions. Alternatively, an alloy of one or more of the materials having a low work function with gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, tin, or the like may be used. Examples of the alloy include lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, magnesium-silver alloy, magnesium-indium alloy, magnesium-aluminum alloy, indium-silver alloy, calcium-aluminum alloy and the like.

  The thickness of the counter electrode 13 is 1 nm to 500 nm, preferably 10 nm to 300 nm. When the film thickness is smaller than the above range, the resistance becomes too large and the generated charge cannot be sufficiently transmitted to the external circuit. When the film thickness is thick, it takes a long time to form the counter electrode 13, so that the material temperature rises and the organic layer is damaged to deteriorate the performance. Further, since a large amount of material is used, the occupation time of the film forming apparatus becomes longer, leading to an increase in cost.

(Light reflecting layer)
The light reflecting layer 20 formed on the back surface by being integrated with the solar battery is formed by depositing, sputtering, ion, or a metal film having a high reflectance such as silver, silver alloy, or aluminum on the bottom layer of the cell forming surface of the transparent substrate. It is formed by a method such as plating. Since the light reflection layer made of an Ag alloy thin film has high conductivity, it can also be used for wiring between cells. In order to prevent a short circuit between cells, it is preferable to coat a part thereof with an inorganic transparent insulator typified by alumina, silica, and silicon nitride.

  The light reflecting layer formed on the surface of the transparent substrate 10 is a material having a highly reflective surface. For example, the surface is reflected by a well-polished aluminum, a metal such as chromium, glass or resin by silver plating or the like. A mirror-like reflection plate provided with a film, a reflection plate in which aluminum is vapor-deposited on the surface of glass or resin, various metal foils, an organic reflection sheet with an adjusted refractive index, and the like can be used. As a specific organic reflective sheet, for example, a reflective film having a reflectivity of 97% or more can be produced by selecting a reflective film Vicuity ESR manufactured by 3M or a Ruir mirror manufactured by Reiko. Further, as the scatterer (light diffusive reflection layer) having a high reflectance, a material having a light reflectance lower than that of the light reflection layer can be used. For example, a micro-foamed film (98% or more diffuse reflection) typified by Furukawa Electric's MCPET can be applied. As the antireflective film, a film having a moth-eye structure, a single layer film of magnesium fluoride, or the like can be used. For example, when the light reflecting layer is formed with a single film, a stripe film in which a non-reflective film typified by a moth-eye structure and a light scattering complete reflective layer typified by a micro foam structure are alternately formed on the film, You may affix on the back surface of a board | substrate according to the position of a photovoltaic cell and a space | gap (a non-reflective film | membrane is arrange | positioned in a cell position, and a perfect reflection film | membrane is arrange | positioned in a gap position). Further, as a different reflective layer configuration, a light diffusion sheet may be laminated on the reflecting mirror surface. This laminated structure includes a structure in which the mirror surface is directly laminated and a structure in which the mirror surface and the light diffusion sheet are opposed to each other with a transparent substrate interposed therebetween.

When the transparent substrate is a resin-based flexible transparent substrate, an inorganic insulating material is used as a shielding film (moisture-proof / oxygen-proof film) that shields oxygen and water from the outside in order to suppress deterioration of the organic thin film constituting the photoelectric conversion layer. A surface coating layer or intermediate layer is formed. Since the reflective layer and the inorganic insulating layer formed on the back surface of the transparent substrate have a function of a shielding film against oxygen and water, they are effective as an auxiliary shielding film for the flexible transparent substrate. In general, in order to increase the storage stability of the organic thin film solar cell module, moisture and oxygen resistance characteristics better than the order of 10 ⁻⁴ are desired.

FIG. 8 is a diagram for explaining the operation mechanism of a bulk heterojunction solar cell. In FIG. 8, reference numerals 1 and 2 represent a p-type semiconductor and an n-type semiconductor, respectively. Reference symbols _CP and _CE represent holes and electrons, respectively.

  The photoelectric conversion process of an organic thin film solar cell includes: a) a process in which an organic molecule absorbs light to generate exciton, b) a process of exciton migration and diffusion, c) a process of exciton charge separation, d) It can be roughly divided into charge transport processes.

  In step a), excitons are generated by absorption of light by the p-type organic semiconductor or the n-type organic semiconductor. Let this generation efficiency be η1. In step b), the generated excitons move to the p / n junction surface by diffusion. This diffusion efficiency is assumed to be η2. Since excitons have a lifetime, they can only move about the diffusion length. In step c), the exciton that has reached the p / n junction is separated into electrons and holes. The efficiency of this exciton separation is η3. In step d), each optical carrier is transported through the p / n material to the electrode and taken out to an external circuit. This transport efficiency is assumed to be η4.

The external extraction efficiency of the generated carriers with respect to the irradiated photons can be expressed by the following equation. This value corresponds to the quantum efficiency of the solar cell.
ηEQE = η1, η2, η3, η4.

  In order to improve the photoelectric conversion efficiency, an organic thin film solar cell element may be produced in view of the characteristics a) to d). That is, in step a), the photoelectric conversion layer absorbs 100% of incident photons; in steps b) and c), the mobility of the organic semiconductor material is high, and the p / n junction is reliably performed. It should be noted that in step d), carrier paths to both poles are formed, the distance to the electrodes is short, and there are no defects that become traps.

  If an organic thin film solar cell is manufactured based on such a premise, a highly efficient element can be realized, but the present materials and film forming methods are far from the ideal form. Organic thin-film solar cells have a problem that the exciton dissociation probability is low, the exciton diffusion length is short, and the carrier mobility is low as compared with conventional inorganic solar cells. This is because organic semiconductors have many parameters that are difficult to control, such as purity, molecular weight distribution, and orientation.

  In order to improve the step a), means for increasing the photon absorption rate by increasing the thickness of the photoelectric conversion layer can be considered. Increasing the thickness of the photoelectric conversion layer increases the optical path length, so that the absorption rate of photons increases. However, as the thickness of the photoelectric conversion layer increases, the electrical resistance increases and carriers are easily trapped. Therefore, the generated carrier cannot reach the electrode, and the photoelectric conversion efficiency is lowered.

  In order to improve the step d), a means for reducing the distance between the electrodes by thinning the photoelectric conversion layer can be considered. By shortening the distance between the electrodes, the generated carriers are likely to reach the electrodes, and the electrical resistance of the film is also reduced. Therefore, it seems that the photoelectric conversion efficiency is improved. However, when the film thickness of the photoelectric conversion layer is thin, the amount of exciton generated in step a) is reduced. This is because the material used for the photoelectric conversion layer is not so light-absorbing, and if the film thickness is small, all the photons are not absorbed by the photoelectric conversion layer and escape to the outside. For this reason, the number of carriers decreases and the current decreases. As a result, the photoelectric conversion efficiency decreases.

  When the film thickness of the photoelectric conversion layer is thus increased, the number of excitons generated increases, but the transport ability of carriers to the electrode deteriorates. On the other hand, when the film thickness of the photoelectric conversion layer is reduced, the transport property of the carrier to the electrode is excellent, but generated exciton is reduced. Accordingly, the photoelectric conversion efficiency ultimately decreases under either condition.

  FIG. 9 is a cross-sectional view of a thin film solar cell module manufactured using a flexible transparent substrate according to the third embodiment. A flexible substrate containing a resin is used as the substrate 10. The thin-film solar cell module 100 is folded when housed, and opened and opened to the left and right when used to receive light. As shown in FIG. 9, this module is called a Y-shaped module based on a shape that is opened to the left and right and viewed from the side.

  Adjacent solar cell sub-modules 50 are connected by alternately performing valley folding and mountain folding along one direction (x direction). The pairs of solar cell submodules 50 are preferably connected in series, but can be connected in parallel. In FIG. 9, since the electrodes on the back surface of the flexible transparent substrate 10F are connected by the highly conductive conductive tape 54 in the valley fold, assembly troubles such as disconnection due to folding are unlikely to occur. By adhering the adhesive surface of the flexible transparent substrate 10F in the valley fold with a double-sided adhesive tape, a module in which the power generation region reaches the bottom of the valley can be configured. At the mountain fold, the surface of the flexible transparent substrate is connected by a reflective tape 55 such as a 3M company's Vicuity film or aluminum film. A highly conductive double-sided adhesive tape for bonding electrodes (tab wires) is arranged on the back surface of the flexible transparent substrate 10F in the mountain folded portion, and the thickness of the reflective region in the mountain folded portion is ensured while ensuring conduction between the submodules. Reduce.

  FIG. 10: is sectional drawing which shows an example of the photovoltaic cell in the thin film photovoltaic module concerning 3rd Embodiment. The array of photovoltaic cells 30 in FIG. 10 is the same as the structure shown in FIG. 3 except that a flexible transparent substrate 10F made of a resin sheet is used.

  Although not shown in FIG. 10, the back surface of the solar cell array is covered with a sealing sheet (film) on which a moisture-proof / oxygen-proof layer made of an inorganic insulating material is formed. The reflective layer 20 formed on the back surface of the flexible transparent substrate 10F and the insulating layer 21 made of an inorganic material also have a shielding property against oxygen and water, but when the shielding property by these is not sufficient, the surface of the flexible transparent substrate 10F ( Alternatively, a shielding layer made of a transparent inorganic material may be formed on the intermediate layer.

  Next, an example of a method (assembly process) for manufacturing a thin-film solar cell module according to the third embodiment will be described with reference to FIGS. FIGS. 11-15 is the figure which looked at the thin film solar cell module from the back surface in which the photovoltaic cell is formed. FIG. 16 is a perspective view of a thin film solar cell module.

  As shown in FIG. 11, the solar cell array 51, the cathode extraction electrode 52, and the anode extraction electrode 53 corresponding to the solar cell submodule 50 are formed on the back surface of the flexible transparent substrate made of one resin sheet. This figure includes six solar cell submodules 50. The resin sheet is accurately cut and juxtaposed at each predetermined position of the valley fold V and the mountain fold M.

  As shown in FIG. 12, a conductive tape 54 (a highly conductive copper foil tape or a tab wire connection tape for solar cells) is attached to the back surface of the valley folding position V of the solar cell submodule 50, and the adjacent solar cell sub The cathode extraction electrode 52 and the anode extraction electrode 53 are bonded and connected in series between the modules 50.

  As shown in FIG. 13, a reflective tape 55 (for example, an aluminum foil adhesive tape or a 3M vicuity adhesive sheet) is attached to the surface of the mountain fold position M of the solar cell submodule 50, and the adjacent solar cell submodules 50 are bonded.

  As shown in FIG. 14, a double-sided adhesive conductive tape 56 (a highly conductive copper foil tape or a tab line connecting tape for solar cells) is attached to the back surface of the mountain folding position M of the solar cell submodule 50, and adjacent solar cells. The cathode extraction electrode 52 and the anode extraction electrode 53 are bonded and connected in series between the submodules 50.

  As shown in FIG. 15, the double-sided adhesive tape 57 is attached to the surface of the valley folding position V of the solar cell submodule 50, and the adjacent solar cell submodules 50 are bonded.

  As shown in FIG. 16, the folded thin film solar cell module 100 is manufactured by repeating valley folding and mountain folding. This thin-film solar cell module 100 is spread left and right and used in the form of a Y-shaped module shown in FIG. 9 to obtain photovoltaic power.

  Thus, the thin film solar cell module produced using the flexible transparent substrate can be used, for example, as a charging power source at the time of disaster by putting it in an emergency carry-out bag. The folded flexible solar cell module is sealed with nitrogen in a moisture-proof package. As a result, even a module using a film having a relatively low shielding property can store a solar cell with only a slight deterioration in characteristics over several years. Since the power generation efficiency gradually decreases after opening the package, the module may be discarded after 2 to 3 months of use, but it can still be used for the purpose of securing the minimum necessary power supply in an emergency.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... P-type semiconductor, 2 ... N-type semiconductor, 10 ... Transparent substrate, 10F ... Flexible transparent substrate, 11 ... Transparent electrode, 12 ... Photoelectric conversion layer, 13 ... Opposite electrode, 20 ... Light reflection layer, 21 ... Insulating layer, DESCRIPTION OF SYMBOLS 22 ... Extraction electrode, 23 ... Light diffusive reflection layer, 24 ... Non-reflective film, 30 ... Solar cell, 50 ... Solar cell submodule, 51 solar cell array, 52 cathode extraction electrode, 53 anode extraction electrode, 54 ... Conductive tape 55 ... reflective tape, 56 ... conductive tape, 57 ... double-sided adhesive tape, 100 ... thin film solar cell module.

Claims (4)

It has a plurality of solar cells formed on a transparent substrate via gaps, and each of the solar cells comprises a laminated transparent electrode, a photoelectric conversion layer, and a counter electrode, and the adjacent solar cells are A solar cell submodule connected in series and having a light reflecting layer formed corresponding to the gap between adjacent solar cells,
The photoelectric conversion layer includes an organic thin film, and the light reflecting layer is formed of a metal film that connects a transparent electrode of one solar battery cell and a counter electrode of the other solar battery cell in a gap between the adjacent solar battery cells. is, pairs of the solar cell sub-module, the main surface thereof a transparent substrate is not parallel inclined with a positive slope and negative slope respectively in one direction, opposite to have a proximal end and an open end A thin film solar cell module that is arranged. The thin film solar cell module according to claim 1 , wherein the transparent substrate is a flexible substrate containing a resin, and one main surface of the transparent substrate is covered with the light reflecting layer and an inorganic insulating layer covering a part thereof. . The thin film solar cell module according to claim 1 or 2 , wherein a plurality of pairs of the solar cell submodules are arranged along the one direction. The thin film solar cell module according to any one of claims 1 to 3, wherein an average inclination angle of the transparent electrode of the solar cell submodule with respect to the one direction is 40 ° to 50 ° or 55 ° to 65 °.

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