JP2011086715A - Electrode for organic solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible type electrode for organic solar cell which uses a plastic film and has superior bending resistance, and ensures high photovoltaic power generation efficiency when used for an organic solar cell, and hardly cause cracking. <P>SOLUTION: The electrode for organic solar cell comprises a base film and a laminate transparent conductive layer provided thereupon. The laminate transparent conductive layer comprises a dielectric layer being in contact with the base film, a metal layer being in contact with the dielectric layer, and a dielectric layer being in contact with the metal layer, wherein surface resistivity of the laminate transparent conductor layer is equal to or less than 40 Ω/sq. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode used for an organic solar cell, that is, an electrode used for an organic thin film solar cell and a dye-sensitized solar cell, and more specifically, a flexible type organic solar cell having high photovoltaic efficiency can be manufactured. The present invention relates to an electrode for an organic solar cell.

  Organic solar cells include organic thin-film solar cells and dye-sensitized solar cells, which can be manufactured by a coating method, and are attracting attention as solar cells that can be manufactured at low cost because of low material costs. ing.

  Dye-sensitized solar cells have been attracting attention as a new solar cell replacing silicon-based solar cells since the proposal of photoelectric conversion elements using dye-sensitized semiconductor fine particles. Sensitive solar cells can be made flexible and light, and many studies have been made.

  And when using a plastic film as a base material of an organic solar cell, since a power generation layer can be formed by coating and a solar cell can be manufactured by a continuous process, a solar cell can be manufactured at low cost. Can do.

  The solar cell electrode is generally provided with a transparent conductive layer of metal oxide such as ITO, IZO, or FTO. However, when a plastic film is used as a substrate, there is a problem that a high-temperature process cannot be performed, the film quality of the transparent conductive layer is lowered, and the carrier moving speed is lowered.

  In order to suppress a decrease in the moving speed of the carrier, the resistivity of the transparent conductive layer may be lowered. For that purpose, the transparent conductive layer may be thickened. However, when a plastic film is used as the base material, the transparent conductive layer is used. When the film thickness is increased, cracks are likely to occur in the transparent conductive layer. Further, since the transparent conductive layer is generally expensive, there is a problem that the cost increases when the transparent conductive layer is thickened.

  By the way, there is a metal as a highly conductive material. Since the metal thin film has high light reflectivity, it is difficult to use the metal thin film as a window layer electrode on the light incident side. Furthermore, metals generally corrode easily and are difficult to use as they are.

JP-A-11-288745 JP 2001-160426 A JP 2002-50413 A

  The present invention solves the problems of the prior art, is a flexible type solar cell electrode with excellent bending resistance using a plastic film, and can obtain high photovoltaic efficiency when used in an organic solar cell, It is an object of the present invention to provide an organic solar cell electrode that is difficult to crack.

  That is, the present invention is an organic solar cell electrode comprising a base film and a laminated transparent conductive layer provided thereon, wherein the laminated transparent conductive layer is a dielectric layer in contact with the base film, and a metal layer in contact with the dielectric layer. An organic solar cell electrode comprising: a dielectric layer in contact with the metal layer; and a surface resistivity of the laminated transparent conductor layer of 40Ω / □ or less.

  ADVANTAGE OF THE INVENTION According to this invention, it is a flexible type solar cell electrode which is excellent in bending tolerance using a plastic film, can obtain high photovoltaic power generation efficiency when used for an organic solar cell, and is not easily cracked. An electrode can be provided.

[Base film]
The base film in the present invention is a flexible transparent thermoplastic resin film, preferably a crystalline polymer film, and has heat resistance capable of forming a vapor deposition layer by sputtering or vacuum vapor deposition. It is preferably a transparent thermoplastic resin film.

  Examples of the thermoplastic resin film include aromatic polyester represented by polyethylene terephthalate and polyethylene-2,6-naphthalate, aliphatic polyamide represented by nylon 6 and nylon 66, aromatic polyamide, polyethylene and polypropylene. Polyolefin and polycarbonate films can be used. Of these, aromatic polyesters are preferable, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferable, and polyethylene terephthalate film is particularly preferable.

Moreover, since a mechanical strength is high as a thermoplastic resin film, a biaxially stretched film is preferable. A preferred biaxially stretched film is a biaxially stretched polyethylene terephthalate film or a biaxially stretched polyethylene-2,6-naphthalate film because of its excellent heat resistance and mechanical strength, and a biaxially stretched polyethylene terephthalate film is particularly preferred.
The thermoplastic resin film can be obtained on the market, and can be produced by a conventionally known method.

[Laminated transparent conductive layer]
The electrode for organic solar cells of the present invention is an electrode for organic solar cells in which a laminated transparent conductive layer is provided on one side of the base film described above.
The laminated transparent conductive layer is composed of a dielectric layer in contact with the metal layer and the base film, a metal layer in contact with the dielectric layer, and a dielectric layer in contact with the metal layer and positioned on the outermost surface.

  Many layers may be laminated | stacked alternately with the metal layer and the transparent conductive layer. In that case, the laminated transparent conductive layer is preferably a laminated transparent conductive layer in which a dielectric layer and metal layers in contact with the dielectric layer are alternately laminated in a total of 5 to 17 layers. For example, in the case of a laminated transparent conductive layer in which a dielectric layer and a metal layer in contact with the dielectric layer are alternately laminated in total 5 layers, the laminated transparent conductive layer is formed from the side in contact with the base film from the dielectric layer, A metal layer, a dielectric layer, a metal layer, and an outermost dielectric layer are used.

[Dielectric layer]
The dielectric layer in the present invention is made of a dielectric, and preferably made of a transparent and high refractive index dielectric. As the dielectric, can be exemplified for example _{TiO 2, Ta 2 O 5,} ZrO 2, SnO 2, SiO, SiO 2, In 2 O 3, ITO, IZO, GZO, AZO, FTO, the ZnO. A preferable dielectric is TiO ₂ or ZrO ₂ derived from an organic compound obtained by hydrolysis of alkyl titanate or alkyl zirconium. Use of these is preferable because of excellent workability. Further, as the dielectric, indium oxide, tin oxide, or a dielectric doped with these can be used.

  The dielectric layer can obtain good transparency by taking a laminated structure in which the metal layer is sandwiched. The thickness of the dielectric layer should be set together with the metal layer so as to satisfy the optical properties of the base film, but the thickness of the dielectric layer is preferably 2 to 1000 nm as a single layer.

[Metal layer]
Examples of the metal constituting the metal layer include Au, Ag, Cu, and Al. Among these, Ag that hardly absorbs visible light and Al that has relatively low corrosivity are preferable. For the metal layer, an alloy composed of a plurality of metals may be used as necessary. The thickness of the metal layer is preferably in the range of 5 to 1000 nm as a single layer thickness. When the thickness is in this range, high visible light transmittance can be obtained while obtaining sufficient conductivity.

[Surface resistance]
The surface resistivity of the laminated transparent conductive layer is 40Ω / □ or less, preferably 30Ω / □ or less, more preferably 20Ω / □ or less. When it exceeds 40Ω / □, when the solar cell is produced using the organic solar cell electrode of the present invention to generate electric power, the internal resistance is high and the efficiency is not sufficiently increased.

[Light transmittance]
The light transmittance of the organic solar cell electrode of the present invention is such that the light transmittance at 400 to 800 nm for absorbing light is preferably 60% or more, more preferably 65% or more, and particularly preferably 70% or more. By being 60% or more, a sufficient amount of light reaching the photovoltaic layer can be secured, and good photovoltaic efficiency can be obtained when a solar cell is created and generated.

[Easily adhesive layer]
In order to improve the adhesion between the base film and the laminated transparent conductive layer, an easy adhesion layer may be provided between the base film and the laminated transparent conductive layer. The thickness of the easy adhesion layer is preferably 10 to 8000 nm, and more preferably 80 to 6000 nm. If the thickness of the easy-adhesion layer is less than 10 nm, the effect of improving the adhesiveness is poor, and if it exceeds 8000 nm, the easy-adhesion layer tends to cause cohesive failure, resulting in a decrease in adhesion.

  As the constituent material of the easy-adhesion layer, a substance that exhibits excellent adhesion to both the base film and the laminated transparent conductive layer is used. For example, when a polyester film is used as the base film, for example, a polyester resin, an acrylic resin, a urethane acrylic resin, a silicon acrylic resin, a melamine resin, or a polysiloxane resin can be used. These resins can be used alone or as a mixture of two or more.

[Antireflection layer]
The organic solar cell electrode of the present invention may be provided with an antireflection layer on the surface opposite to the laminated transparent conductive layer for the purpose of improving the light transmittance and enhancing the photovoltaic power generation efficiency. For this antireflection layer, a method of laminating a material having a refractive index different from the refractive index of the base film into a single layer or two or more layers can be used. In the case of a single layer structure, it is better to use a material having a refractive index smaller than that of the base film, and in the case of a multilayer structure of two or more layers, the layer adjacent to the laminate is larger than the base film. It is preferable to select a material having a refractive index smaller than this as a material having a refractive index and a layer laminated thereon.

As a material constituting the antireflection layer, any of an organic material and an inorganic material can be used as long as the above refractive index relationship is satisfied. Preferred examples _include a dielectric such as _{CaF 2, MgF 2, NaAlF 4} , SiO 2, ThF 4, ZrO 2, Nd 2 O 3, SnO 2, TiO 2, CeO 2, ZnS, In 2 O 3 .

[Production method]
A commercially available base film can be used. For example, when a biaxially stretched film of polyethylene terephthalate is used, Teijin Tetron O3 made by Teijin DuPont Film can be used.

  The transparent conductive layer can be formed on the base film by vapor deposition. Preferably, a vacuum evaporation method, a sputtering method, or a plasma CVD method is used. The metal layer can be formed on the transparent conductive layer by a vapor deposition method. Preferably, a vacuum evaporation method, a sputtering method, or a plasma CVD method is used. The easy-adhesion layer can be applied and provided by a conventional method after the base film is manufactured or formed. The antireflection layer can be provided by, for example, a dry coating method such as a vacuum deposition method, a sputtering method, a CVD method, or an ion plating method, or a wet coating method such as a gravure method, a reverse method, or a die method. Prior to the lamination of the antireflection layer, a known pretreatment such as corona discharge treatment, plasma treatment, sputter etching treatment, electron beam irradiation treatment, ultraviolet ray irradiation treatment, primer treatment, and easy adhesion treatment may be applied to the base film.

Hereinafter, the present invention will be described in detail by way of examples. The film characteristics were measured according to the following method.
(1) Surface resistivity It measured using the surface resistance measuring device loresta-GP (MCD-T600) by Mitsubishi Chemical Corporation.
(2) Light transmittance Measured using a spectrophotometer MPC3100 manufactured by Shimadzu Corporation.
(3) Bending resistance The electrode film was cut into a 2.5 cm × 20 cm strip, a 250 g weight was fixed to one of the long pieces, and the remaining one was fixed to metal bars having different diameters of 10 mm to 50 mm. The metal rod was rotated and completely wound up, and then rewound. The change in surface resistivity was evaluated before and after this operation. The diameter at which the surface resistivity was maintained at 1.5 times or less was defined as the critical bending radius.
(4) IV characteristics (photocurrent-voltage characteristics)
A 25 mm ² large dye-sensitized solar cell was formed, and the photovoltaic power generation efficiency was calculated by the following method. A 500 W xenon lamp (made by USHIO ELECTRIC CO., LTD.) Is equipped with a correction filter for sunlight simulation (AM1.5 Global made by Oriel), and simulated solar light with an incident light intensity of 100 mW / cm ² is applied to the above photovoltaic power generation device. Irradiation was performed by changing the incident angle with respect to the horizontal plane. The system was left indoors at a temperature of 18 ° C. and a humidity of 50%. Using a current-voltage measuring device (Keutley source measure unit 238 type), the DC voltage applied to the system is scanned at a constant speed of 10 mV / second, and the photocurrent output from the device is measured, so that photocurrent-voltage The characteristics were measured, and the photovoltaic power generation efficiency was calculated.
(5) Film thickness Using a micrometer (K-402B type manufactured by Anritsu Co., Ltd.), measurements are made at 10 cm intervals in the continuous film forming direction and the width direction of the film, and a total of 300 film thicknesses are measured. did. The average value of the film thicknesses of the obtained 300 locations was calculated and used as the film thickness.

[Example 1]
<Creation of polyester film>
Polyethylene naphthalene dicarboxylate (intrinsic viscosity: 0.61) was melt extruded onto a rotating cooling drum maintained at 60 ° C. to obtain an unstretched film. Next, the film was stretched 3.3 times in the longitudinal direction at 140 ° C., then stretched 3.5 times in the transverse direction at 145 ° C., heat-fixed by shrinking 2% in the width direction at 240 ° C., and a polyester film having a thickness of 125 μm. Got.

<Formation of laminated transparent conductive layer>
A titanium oxide layer (dielectric layer; first layer) having a thickness of 31 nm is provided on one side of the film, a silver / copper alloy layer (metal layer; second layer) having a thickness of 12 nm is provided thereon, and further thereon A titanium oxide layer (dielectric layer; third layer) having a thickness of 22 nm was provided on the laminated transparent conductive layer. All the three layers were formed by sputtering under vacuum.
The surface resistivity of the laminated transparent conductive layer of the organic solar cell electrode thus obtained was 11Ω / □, and the light transmittance at 400 to 800 nm was 60% or more. Further, as a result of bending test with the transparent conductive layer unwound, no cracks could be visually confirmed even for a diameter of 10 mm, and no increase in resistivity was observed.

[Example 2]
<Creation of polyester film>
Molten polyethylene terephthalate (intrinsic viscosity (orthochlorophenol, 35 ° C.) = 0.65) is extruded from a die, cooled with a cooling drum by a conventional method to form an unstretched film, and then, in the longitudinal direction, 3.6 times at 95 ° C. After stretching, the film was subsequently stretched 3.8 times in the transverse direction at 120 ° C. and then heat-set at 220 ° C. to obtain a biaxially stretched polyethylene terephthalate film having a thickness of 50 μm.

<Formation of laminated transparent conductive layer>
An indium oxide layer (dielectric layer; first layer) having a thickness of 38 nm is provided on one surface of the film, and a silver / gold alloy layer (metal layer; second layer) having a thickness of 10 nm is provided thereon, and further thereon An indium oxide layer (dielectric layer; third layer) having a thickness of 279 nm, a silver / gold alloy layer (metal layer; fourth layer) having a thickness of 6 nm, and an indium oxide layer having a thickness of 38 nm thereon. (Dielectric layer; fifth layer) was provided to form a laminated transparent conductive layer. All the five layers were formed by sputtering under vacuum.
The surface resistance of the laminated transparent conductive layer of the organic solar cell electrode thus obtained was 7Ω / □, and the light transmittance at 400 to 800 nm was 60% or more. Further, as a result of bending test with the transparent conductive layer unwound, no cracks could be visually confirmed even for a diameter of 10 mm, and no increase in resistivity was observed.

<Creation of dye-sensitized solar cell>
A commercially available paste for forming a low temperature forming porous titanium dioxide layer (SP-200 made by Showa Denko) is applied on the laminated transparent conductive layer with a bar coater, and heat treatment is performed at 200 ° C. for 60 minutes in the atmosphere. A porous titanium dioxide layer was formed to a thickness of 3 μm, and an electrode of a dye-sensitized solar cell was created.
This electrode was immersed in a 300 μM ethanol solution of a ruthenium complex (Ru535bisTBA, Solaronix) for 24 hours to adsorb the ruthenium complex on the surface of the photoactive electrode.

Further, a counter electrode was formed by depositing a Pt film on the transparent conductive layer of the laminate by sputtering.
The electrode and the counter electrode are overlapped via a thermocompression-resistant polyethylene film frame spacer (thickness 20 μm), the spacer part is heated to 120 ° C., and both electrodes are pressure-bonded. It was left and sealed with an epoxy resin adhesive. Then, from the unsealed portion, an electrolyte solution (3-methoxypropyl containing 0.5% lithium iodide, 0.05M iodine, 0.5M tert-butylpyridine, 3% by weight of nylon beads having an average particle diameter of 20 μm is used. After injecting a (pionitrile solution), it was sealed with an epoxy adhesive.
The completed dye-sensitized solar cell was subjected to IV measurement (effective area 25 mm ² ) after 1000 hours in an environment of a temperature of 23 ° C. and a humidity of 50%. The open circuit voltage, short circuit current density, and fill factor were 0.75 V, 6.0 mA / cm ² , and 0.69, respectively, and the photovoltaic generation efficiency was 3.1%.

  The electrode for organic solar cells of the present invention can be suitably used as an electrode for organic solar cells.

Claims (6)

  An organic solar cell electrode comprising a substrate film and a laminated transparent conductive layer provided thereon, wherein the laminated transparent conductive layer is a dielectric layer in contact with the substrate film, a metal layer in contact with the dielectric layer, and the metal layer An electrode for an organic solar cell comprising a dielectric layer in contact with the laminated transparent conductor layer and having a surface resistivity of 40Ω / □ or less.   The electrode for organic solar cells according to claim 1, wherein the laminated transparent conductive layer comprises a dielectric layer in contact with the base film, a metal layer in contact with the dielectric layer, and a dielectric layer in contact with the metal layer and located on the outermost surface. .   The electrode for organic solar cells according to claim 1, wherein the laminated transparent conductive layer is a laminated transparent conductive layer in which a dielectric layer and metal layers in contact with the dielectric layer are alternately laminated in a total of 5 to 17 layers.   The electrode for organic solar cells according to claim 1, wherein the metal layer is a layer made of one or more metals selected from the group consisting of Au, Ag, Cu and Al. The dielectric layer is at least one selected from the group consisting of TiO ₂ , Ta ₂ O ₅ , ZrO ₂ , SnO ₂ , SiO, SiO ₂ , In ₂ O _3, ITO, IZO, GZO, AZO, FTO and ZnO. The electrode for organic solar cells according to claim 1, which is a layer made of a dielectric.   The electrode for organic solar cells according to claim 1, wherein the base film is a crystalline polymer film.