JP5961094B2 - Organic thin film solar cell - Google Patents

Description

  The present invention relates to an organic thin film solar cell, and more particularly to an organic thin film solar cell having at least two hole transport layers satisfying a predetermined ionization potential relationship.

In recent years, flexible electronic devices as soft matter have attracted attention. In particular, there is an increasing expectation for flexible organic electronic devices, particularly organic thin-film solar cells, that can be expected to be lightweight and cost-effective.
As a configuration of the organic thin film solar cell, an organic thin film having electron conductivity and / or hole conductivity is generally arranged between two different electrodes, at least one of which is transparent. Such an organic thin film solar cell is easy to manufacture as compared with an inorganic device using silicon or the like, and has an advantage that it can be manufactured at a low cost.

For example, Patent Document 1 discloses an organic photoelectric conversion element having a highly conductive layer having a conductivity of 1 to 10 ⁷ S / cm between at least one electrode and a charge transport layer. ing. More specifically, in the example of Japanese Patent Laid-Open Publication No. 2003-259542, a hole transport layer (layer thickness: 100 nm) including PEDOT-PSS (conductivity 1 × 10 ⁻³ S / cm) and PEDOT- with higher conductivity are used. An organic photoelectric conversion element having a high conductive layer (layer thickness: 100 nm) including PSS (conductivity 3 × 10 ² S / cm) is disclosed.

JP 2012-23126 A

On the other hand, in recent years, for organic thin-film solar cells, it shows excellent photoelectric conversion efficiency even after being bent because it is used by pasting it on curved surfaces other than flat surfaces and complex shapes such as automobile bodies and building roofs. It is demanded.
The present inventors refer to the description in the Example column of Patent Document 1, and an organic thin-film solar cell having two hole transport layers (corresponding to a hole transport layer and a highly conductive layer in Patent Document 1) Was used to measure the photoelectric conversion efficiency after a predetermined bending test (bending test). As a result, it was found that the photoelectric conversion efficiency was greatly reduced as compared with that before the bending test.
In the first place, in the organic thin-film solar cell described in Patent Document 1, the photoelectric conversion efficiency and dark current characteristics in a state before being bent have not yet reached the required levels, and further improvement is necessary.

  In view of the above circumstances, the present invention provides an organic thin-film solar cell that exhibits high photoelectric conversion characteristics and low dark current characteristics before being subjected to bending treatment, and that suppresses deterioration in photoelectric conversion performance before and after the bending treatment. The purpose is to do.

As a result of intensive studies on the problems of the prior art, the present inventors have found that a desired effect can be obtained by using two hole transport layers having a predetermined ionization potential relationship. .
That is, the present inventors have found that the problem can be solved by the following configuration.

(1) An organic thin film solar cell having at least a transparent electrode layer, a photoelectric conversion layer, a first hole transport layer, a second hole transport layer, and a counter electrode layer in this order on a plastic support. Because
The photoelectric conversion layer contains at least an electron donating compound and an electron accepting compound,
The ionization potential of the first hole transport layer is smaller than the ionization potential of the second hole transport layer;
The ionization potential of the electron donating compound is smaller than the ionization potential of the second hole transport layer;
The organic thin-film solar cell whose ratio (T1 / T2) of thickness T1 of a 1st positive hole transport layer and thickness T2 of a 2nd positive hole transport layer is 0.6 or less.

(2) The organic thin-film solar cell according to (1), wherein the first hole transport layer includes poly-3,4-ethylenedioxythiophene / polystyrene sulfonate (PEDOT / PSS).

(3) The first hole transport layer is formed using the first hole transport layer forming composition having a contact angle with respect to the photoelectric conversion layer of 20 ° or less, according to (1) or (2) Organic thin film solar cell.

(4) The organic thin-film solar cell according to any one of (1) to (3), wherein the second hole transport layer includes a conjugated polymer.

(5) The organic thin-film solar cell according to any one of (1) to (4), wherein the transparent electrode layer includes a metal pattern layer and a transparent conductive resin layer.

(6) The organic thin-film solar cell according to any one of (1) to (5), further including an electron transport layer between the transparent electrode layer and the photoelectric conversion layer.

(7) The organic thin-film solar cell according to (6), wherein the electron transport layer includes metal oxide particles having at least one metal atom selected from the group consisting of zinc, titanium, tin, and tungsten.

(8) The 2nd metal oxidation in which an electron carrying layer is formed from the 1st metal oxide layer formed from a metal oxide particle with an average particle diameter of 1-10 nm, and the metal oxide particle with an average particle diameter of 20-100 nm The organic thin-film solar cell according to (6) or (7), comprising at least two layers with a physical layer.

  ADVANTAGE OF THE INVENTION According to this invention, while performing a bending process, while exhibiting a high photoelectric conversion characteristic and a low dark current characteristic, the deterioration of the photoelectric conversion performance before and behind a bending process can be provided. .

It is a schematic sectional drawing which shows 1st Embodiment of the organic thin-film solar cell of this invention. It is a schematic sectional drawing which shows 2nd Embodiment of the organic thin-film solar cell of this invention. It is an arrow top view along the AA line in FIG. It is a schematic plan view of other embodiment of the metal pattern layer in 2nd Embodiment of the organic thin-film solar cell of this invention. It is a schematic sectional drawing which shows 3rd Embodiment of the organic thin film solar cell of this invention. It is a schematic sectional drawing which shows the modification of 3rd Embodiment of the organic thin-film solar cell of this invention.

Below, the suitable form of the organic thin-film solar cell of this invention is explained in full detail.
First, one of the features of the present invention compared to the prior art is that it has at least two hole transport layers satisfying a predetermined ionization potential relationship. More specifically, the ionization potential of the first hole transport layer is smaller than the ionization potential of the second hole transport layer, and the ionization potential of the electron donating compound in the photoelectric conversion layer is ionization of the second hole transport layer. By being smaller than the potential, photoelectric conversion characteristics and dark current characteristics are further improved. Moreover, the improvement of flexibility is also achieved by adjusting the thickness relationship between the first hole transport layer and the second hole transport layer.

[First Embodiment]
FIG. 1 is a cross-sectional view schematically showing the layer configuration of the first embodiment of the organic thin-film solar cell of the present invention. The organic thin film solar cell 10 includes a plastic support 12, a transparent electrode layer 14, a photoelectric conversion layer 16, a first hole transport layer 18, a second hole transport layer 20, and a counter electrode layer 22 in this order. The organic thin film solar cell 10 is a so-called reverse organic thin film solar cell, and the surface on the plastic support 12 side is a light receiving surface, and the transparent electrode layer 14 on the side close to the plastic support 12 corresponds to the negative electrode. . That is, light is irradiated from the plastic support 12 side, and the light reaches the photoelectric conversion layer 16 through the plastic support 12 and the transparent electrode layer 14.
In the following, first, the first hole transport layer 18 and the second hole transport layer 20 will be described in detail, and then other configurations (plastic support 12, transparent electrode layer 14, photoelectric conversion layer 16, counter electrode layer 22). ) Will be described in detail.
In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

(First hole transport layer 18 and second hole transport layer 20)
The first hole transport layer 18 and the second hole transport layer 20 are formed so that holes can be easily transported from the photoelectric conversion layer 16 to the counter electrode layer 22. It is a layer provided between. The first hole transport layer 18 and the second hole transport layer 20 also have a function of blocking electrons from moving from the photoelectric conversion layer 16 to the counter electrode layer 22.

The ionization potential (Ip1) of the first hole transport layer 18 is smaller than the ionization potential (Ip2) of the second hole transport layer 20. That is, the relationship of Ip1 <Ip2 is satisfied. In other words, the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the first hole transport layer 18 is greater than the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the second hole transporting layer 20. Is also small. By satisfy | filling the said relationship, the high photoelectric conversion characteristic and low dark current characteristic of an organic thin film solar cell are achieved.
The ionization potential (Ip1) of the first hole transport layer 18 and the ionization potential (Ip2) of the second hole transport layer 20 are not particularly limited as long as the above relationship is satisfied, but the difference between Ip1 and Ip2 (Ip2 -Ip1) is preferably more than 0 and 1.0 eV or less, more preferably 0.1 to 0.5 eV.
When the ionization potential (Ip1) of the first hole transport layer 18 and the ionization potential (Ip2) of the second hole transport layer 20 do not satisfy the above relationship, the photoelectric conversion characteristics and dark current characteristics of the organic thin film solar cell are inferior. .
The ionization potential Ip of the first hole transport layer 18 and the second hole transport layer 20 is measured using an atmospheric photoelectron spectrometer (AC-2 manufactured by Riken Keiki Co., Ltd.) (measurement light quantity: 20 nW, step: 0.1 eV). ). In addition, the 1st positive hole transport layer 18 and the 2nd positive hole transport layer 20 which are measured are formed into a film on a quartz substrate, and thickness is 50 nm.

An ionization potential (Ip3) of an electron donating compound in the photoelectric conversion layer 16 described later is smaller than an ionization potential (Ip2) of the second hole transport layer 20. That is, the relationship of Ip3 <Ip2 is satisfied. In other words, the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron donating compound is smaller than the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the second hole transport layer 20. By satisfy | filling the said relationship, the high photoelectric conversion characteristic and low dark current characteristic of an organic thin film solar cell are achieved.
The ionization potential (Ip3) of the electron donating compound and the ionization potential (Ip2) of the second hole transport layer 20 are not particularly limited as long as the above relationship is satisfied, but the difference between Ip3 and Ip2 (Ip2-Ip3) Is preferably more than 0 and 1 eV or less, more preferably 0.1 to 0.5 eV.
When the ionization potential (Ip3) of the electron donating compound and the ionization potential (Ip2) of the second hole transport layer 20 do not satisfy the above relationship, the photoelectric conversion characteristics and the dark current characteristics of the organic thin film solar cell are inferior.
The method for measuring the ionization potential is as described above.

The relationship between the ionization potential (Ip3) of the electron donating compound in the photoelectric conversion layer 16 described later and the ionization potential (Ip1) of the first hole transport layer 18 is not particularly limited, but various characteristics of the organic thin film solar cell (photoelectric It is preferable that the ionization potential (Ip3) of the electron donating compound is larger than the ionization potential (Ip1) of the first hole transport layer 18 in terms of more excellent conversion characteristics and dark current characteristics. That is, the relationship of Ip3> Ip1 is satisfied. In other words, the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron donating compound is larger than the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the first hole transport layer 18.
The ionization potential (Ip3) of the electron donating compound and the ionization potential (Ip1) of the first hole transport layer 18 are not particularly limited as long as the above relationship is satisfied, but the difference between Ip3 and Ip1 (Ip3-Ip1) Is preferably more than 0 and 1 eV or less, more preferably 0.1 to 0.3 eV.

The ionization potential (Ip1) of the first hole transport layer 18 is not particularly limited as long as the above relationship is satisfied, but it is 4 in terms of more excellent characteristics (photoelectric conversion characteristics and dark current characteristics) of the organic thin film solar cell. .2 to 5.2 eV is preferable, and 4.7 to 5.2 eV is more preferable.
The ionization potential (Ip1) of the second hole transport layer 20 is not particularly limited as long as the above relationship is satisfied, but it is 5 in that the various characteristics (photoelectric conversion characteristics and dark current characteristics) of the organic thin film solar cell are more excellent. 0.0 to 5.5 eV is preferable, and 5.2 to 5.5 eV is more preferable.

The ratio (T1 / T2) between the thickness T1 of the first hole transport layer 18 and the thickness T2 of the second hole transport layer 20 is 0.6 or less, and various characteristics of the organic thin film solar cell (photoelectric conversion characteristics and darkness). 0.4 or less is preferable and 0.3 or less is more preferable in terms of more excellent current characteristics. Although a minimum in particular is not restrict | limited, Usually, 0.1 or more is preferable.
When the ratio (T1 / T2) is more than 0.6, the characteristics (photoelectric conversion characteristics and dark current characteristics) of the organic thin film solar cell are inferior.

The thickness of the first hole transport layer 18 is not particularly limited as long as the above relationship is satisfied, but it is 10 to 100 nm in that various characteristics (photoelectric conversion characteristics, dark current characteristics, and flexibility) of the organic thin film solar cell are more excellent. Is preferable, and 20 to 60 nm is more preferable.
The thickness of the second hole transport layer 20 is not particularly limited as long as the above relationship is satisfied, but it is 20 to 170 nm in that various characteristics (photoelectric conversion characteristics, dark current characteristics, and flexibility) of the organic thin film solar cell are more excellent. Is preferable, and 30-100 nm is more preferable.

  The material used in the first hole transport layer 18 and the second hole transport layer 20 is not particularly limited as long as the above relationship is satisfied, and a known material can be used. Examples thereof include conjugated polymers such as polyaniline, polythiophene, and polypyrrole, aromatic amine derivatives, thiophene derivatives, condensed aromatic ring compounds, and carbazole derivatives. In addition, Chem. Rev. A group of compounds described as Hole Transport material in 2007, 107, 953-1010 is also applicable.

The material contained in the first hole transport layer 18 is preferably a conductive polymer (hereinafter abbreviated as PEDOT-PSS) composed of poly (3,4-ethylenedioxythiophene) and polystyrenesulfonic acid.
The material contained in the second hole transport layer 20 may be a conjugated polymer that may have a substituent (for example, polythiophenes, polypyrroles, polyindoles, polycarbazoles, polyanilines, polyacetylene). , Polyfurans, polyparaphenylene vinylenes, polyazulenes, polyparaphenylenes, polyparaphenylene sulfides, polyisothianaphthenes, polythiazyl) are preferable, and various characteristics of organic thin film solar cells (photoelectric conversion characteristics and darkness) A sulfonated polythiophene (polythiophene having a sulfonic acid group) is preferable in terms of more excellent current characteristics.

The manufacturing method of the first hole transport layer 18 and the second hole transport layer is not particularly limited, and various wet film forming methods, dry film forming methods such as vapor deposition and sputtering, transfer methods, printing methods, etc. Also, it can be suitably formed.
Especially, as a manufacturing method of the 1st positive hole transport layer 18, it is excellent with respect to the photoelectric converting layer 14 mentioned later at the point which is excellent in the film-forming property of the 1st positive hole transport layer 18, and the flexibility of an organic thin film solar cell is more excellent. It is preferable to form the first hole transport layer forming composition having a contact angle of 30 ° or less. More specifically, it is preferable to form the first hole transport layer 18 by applying a composition for forming the first hole transport layer on the photoelectric conversion layer 14 and performing a heat treatment as necessary.
When the contact angle of the composition is within the above range, a first hole transport layer having excellent thickness and uniform thickness on the photoelectric conversion layer 14 can be formed. Among these, the contact angle is preferably 20 ° or less from the viewpoint that the film formation property of the first hole transport layer 18 is excellent and the flexibility of the organic thin film solar cell is more excellent. The lower limit is not particularly limited, but is usually 0 ° or more.

The material contained in the composition for forming the first hole transport layer only needs to contain the material for forming the first hole transport layer described above, and a solvent is included in terms of excellent coating properties. preferable. The type of the solvent used is not particularly limited, but an alcohol solvent is preferable and isopropyl alcohol is more preferable in that the contact angle relationship is easily satisfied.
Examples of the first hole transport layer forming composition include H.P. C. For example, CPP 105D from Starck.

(Plastic support)
The plastic support 12 is a support that holds various layers including the first hole transport layer 18 and the second hole transport layer 20 and imparts flexibility to the organic thin film solar cell 10. There is no restriction | limiting in particular etc., According to the objective, it can select suitably.

  Examples of the material for the plastic support 12 include polyester resin, methacrylic resin, methacrylic acid-maleic acid copolymer, polystyrene resin, transparent fluororesin, polyimide resin, fluorinated polyimide resin, polyamide resin, polyamideimide resin, and polyether. Imide resin, cellulose acylate resin, polyurethane resin, polyether ether ketone resin, polycarbonate resin, alicyclic polyolefin resin, polyarylate resin, polyether sulfone resin, polysulfone resin, cycloolefin copolymer, fluorene ring-modified polycarbonate resin, alicyclic ring Examples thereof include thermoplastic resins such as modified polycarbonate resins, fluorene ring-modified polyester resins, and acryloyl compounds.

The plastic support 12 is preferably made of a heat resistant material. Specifically, the glass transition temperature (Tg) has heat resistance satisfying at least one of the physical properties of 60 ° C. or higher and the linear thermal expansion coefficient of 40 ppm / ° C. or lower, and is higher with respect to the exposure wavelength. A support formed from a transparent material is preferable.
The Tg and linear expansion coefficient of the plastic support 12 are measured by the plastic transition temperature measurement method described in JIS K 7121 and the linear expansion coefficient test method by thermomechanical analysis of plastic described in JIS K 7197. In the present invention, values measured by this method are used for the Tg and the linear expansion coefficient of the plastic support 12.

As a thermoplastic resin having excellent heat resistance, for example, polyethylene terephthalate (PET: 65 ° C.), polyethylene naphthalate (PEN: 120 ° C.), polycarbonate (PC: 140 ° C.), alicyclic polyolefin (for example, manufactured by Nippon Zeon Co., Ltd.) ZEONOR 1600: 160 ° C., polyarylate (PAr: 210 ° C.), polyethersulfone (PES: 220 ° C.), polysulfone (PSF: 190 ° C.), cycloolefin copolymer (COC: compound of JP 2001-150584 A: 162 ° C.), fluorene ring-modified polycarbonate (BCF-PC: compound of JP 2000-227603 A: 225 ° C.), alicyclic modified polycarbonate (IP-PC: compound of JP 2000-227603 A: 205 ° C.), Acryloyl compounds 2002-80616 compound: 300 [deg.] C. or higher), polyimide, and the like (the numerical values written in abbreviated parenthesis in the parentheses indicate Tg of the resin). Especially, it is preferable to use alicyclic polyolefin etc. for the use for which transparency is especially required.
The Tg and the linear expansion coefficient of the plastic support 12 can be adjusted with an additive or the like.

  The plastic support 12 is preferably transparent to light. In other words, a transparent plastic support is preferred. More specifically, the light transmittance for light in the wavelength range of 400 to 1000 nm is usually preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The light transmittance is determined by measuring the total light transmittance and the amount of scattered light using the method described in JIS-K7105, that is, an integrating sphere light transmittance measuring device, and subtracting the diffuse transmittance from the total light transmittance. Can be calculated. In this specification, the value using this method is adopted as the light transmittance.

Although there is no restriction | limiting in particular regarding the thickness of the plastic support body 12, Typically, it is 1-800 micrometers, Preferably it is 10-300 micrometers.
A known functional layer may be provided on the back surface of the plastic support 12 (the surface on which the transparent electrode layer 14 is not provided). Examples of the functional layer include a gas barrier layer, a matting agent layer, an antireflection layer, a hard coat layer, an antifogging layer, and an antifouling layer, which will be described later. In addition, the functional layer is described in detail in paragraph numbers [0036] to [0038] of JP-A-2006-289627.

(Transparent electrode layer)
The transparent electrode layer 14 is an electrode layer disposed on the plastic support 12 and functions as a negative electrode in the organic thin film solar cell 10.
The transparent electrode layer 14 is a layer containing at least a transparent conductive material. The transparent electrode layer 14 is usually required to be excellent in light transmittance from visible light to near infrared light. Specifically, when a layer having a thickness of 0.1 μm is formed of a transparent conductive material, the average light transmittance of the formed layer in the wavelength region of 400 nm to 800 nm is preferably 50% or more, and 75% or more. More preferably, it is more preferably 85% or more.

The transparent conductive material used for the transparent electrode layer 14 is required to have high conductivity, and the specific resistance after film formation is preferably 8 × 10 ⁻³ Ω · cm or less. As the transparent conductive material that realizes such a specific resistance, for example, the transparent conductive material is a metal oxide (indium-tin oxide, antimony oxide, aluminum-zinc oxide, boron-zinc oxide, tin fluoride oxide). Etc.), conductive nanomaterials (for example, silver nanowires, carbon nanotubes, graphene, etc.) dispersed in acrylic polymers, conductive polymers (for example, polythiophene, polypyrrole, polyaniline, polyphenylene vinylene, polyphenylene, polyacetylene, polyquinoxaline) , Polyoxadiazole, polybenzothiadiazole, and the like, and polymers having a plurality of these conductive skeletons).

  Although the thickness in particular of the transparent electrode layer 14 is not restrict | limited, It is preferable that it is 50 nm-1 micrometer, and it is more preferable that it is 100 nm-300 nm by the point which is excellent in the electroconductive property and transparency balance.

(Photoelectric conversion layer)
The photoelectric conversion layer 16 is a layer that contributes to charge separation of the organic thin-film solar cell 10 and has a function of transporting the generated electrons and holes toward electrodes in opposite directions.
The photoelectric conversion layer 16 has a bulk heterostructure in which an electron donating compound (hole transport material) that is an organic material and an electron accepting compound (electron transport material) are mixed.
The kind of the electron donating compound used is not particularly limited as long as it satisfies a predetermined relationship with the ionization potential of the second hole transport layer described above. For example, various arenes (for example, thiophene, carbazole, fluorene) Conjugated polymers, phenylene vinylene-based polymers, porphyrins, phthalocyanines, and the like, which are coupled to each other), silafluorene, thienopyrazine, thienobenzothiophene, dithienosilole, quinoxaline, benzothiadiazole, thienothiophene, and the like. In addition, Chem. Rev. The compound group described as Hole Transport material in 2007, 107, 953-1010, and the porphyrin derivative described in Journal of the American Chemical Society vol. 131, page 16048 (2009) are also applicable.
Among these, a conjugated polymer obtained by coupling a structural unit selected from the group consisting of thiophene, carbazole, fluorene, silafluorene, thienopyrazine, thienobenzothiophene, dithienosilole, quinoxaline, benzothiadiazole, and thienothiophene is particularly preferable. Specific examples include poly-3-hexylthiophene, poly-3-octylthiophene, various polythiophene derivatives described in Journal of the American Chemical Society, Volume 130, page 3020 (2008), Advanced Materials, Volume 19, pages 2295 ( PCDTBT described in 2007), Journal of the American Chemical Society, Volume 130, page 732 (2008), PCDTQx, PCDTPP, PCDTPT, PCDTBX, PCDTPX, Nature Photonics Volume 3, page 649 (2009) PBDTTTT-E, PBDTTTC, PBDTTTT-CF, and PTB7 described in Advanced Materials, Vol. 22, pages 1-4 (2010).

  The ionization potential (in other words, the absolute value of the HOMO level) of the electron donating compound is preferably 4.5 to 5.4 eV, and more preferably 5.0 to 5.4 eV.

  The kind of the electron-accepting compound used is not particularly limited, but a π-electron conjugated compound having a LUMO level of −3.5 eV to −4.5 eV is preferable. Specifically, fullerene, a derivative thereof, and a phenylene vinylene polymer. , Naphthalene tetracarboxylic imide derivatives, perylene tetracarboxylic imide derivatives, and the like. Of these, fullerene derivatives are preferred. Specific examples of fullerene derivatives include C60, phenyl-C61-methyl butyrate (fullerene derivatives referred to as PCBM, [60] PCBM, or PC61BM in literature), C70, phenyl-C71-methyl butyrate (in many literatures, etc.) Fullerene derivatives referred to as PCBM, [70] PCBM, or PC71BM), and fullerene derivatives described in Advanced Functional Materials Vol. 19, pages 779-788 (2009), Journal of the American Chemical Society, Vol. 131. 16048 (2009) and the fullerene derivative SIMEF.

  The mixing ratio of the electron donating compound and the electron accepting compound contained in the photoelectric conversion layer 16 is adjusted so that the conversion efficiency is the highest. The mixing ratio of the electron donating compound and the electron accepting compound is usually selected from the range of 10:90 to 90:10 in terms of mass ratio. As a method for forming such a mixed organic layer, for example, a co-evaporation method by vacuum deposition may be mentioned. Alternatively, the mixed organic layer can be formed by solvent coating using a solvent in which both organic materials of the electron donating compound and the electron accepting compound are dissolved.

The layer thickness of the photoelectric conversion layer 16 is preferably 10 nm to 500 nm, particularly preferably 20 nm to 300 nm.
In the bulk hetero photoelectric conversion layer 16, the electron-donating compound and the electron-accepting compound may be completely uniformly mixed, or may be phase-separated so as to have a domain size of 1 nm to 1 μm. . The phase separation structure may be an irregular structure or a regular structure. When forming an ordered structure, it may be a top-down ordered structure such as a nanoimprint method or a bottom-up such as self-organization.

In FIG. 1, the photoelectric conversion layer 16 has been described in detail for a bulk hetero type, but is not limited to this form.
The photoelectric conversion layer may have a planar heterostructure composed of an electron donating layer containing an electron donating compound (hole transport layer) and an electron accepting layer containing an electron accepting compound (electron transport layer). When a planar heterostructure is adopted, an electron donating layer is arranged on the positive electrode side, and an electron accepting layer is also arranged on the negative electrode side. Moreover, the hybrid structure which has a bulk hetero layer as an intermediate | middle layer of a planar heterostructure may be sufficient.
In the case of a planar heterostructure, the electron-donating compound and the electron-accepting compound used in the electron-donating layer and the electron-accepting layer are as described above.

When the photoelectric conversion layer 16 has a planar heterostructure, the thickness of the electron donating layer is not particularly limited, but is preferably 5 to 500 nm, and particularly preferably 10 to 200 nm, from the viewpoint of photoelectric conversion performance.
When the photoelectric conversion layer 16 has a planar heterostructure, the thickness of the electron-accepting layer is not particularly limited, but is preferably 5 to 500 nm, and particularly preferably 10 to 200 nm from the viewpoint of photoelectric conversion performance.

(Counter electrode layer 22)
The counter electrode layer 22 is an electrode layer disposed on the second hole transport layer 20 and plays a role of a positive electrode in the organic thin film solar cell 10.
The counter electrode layer 22 is usually a metal electrode layer, and is preferably composed of a metal having a relatively low work function. Examples thereof include aluminum, magnesium, silver, and a silver-magnesium alloy.

Although the layer thickness in particular of the counter electrode layer 22 is not restrict | limited, 10-500 nm is preferable from the point of photoelectric conversion performance, and 50-300 nm is more preferable.
The counter electrode layer 22 can be formed by any of various wet film forming methods, dry film forming methods such as vapor deposition and sputtering, transfer methods, and printing methods. Among these, a printing method, an inkjet method, and a vapor deposition method are preferable.
Examples of the patterning for forming the counter electrode layer 22 include printing, ink jetting, and the like. Chemical etching by photolithography or the like may be performed, physical etching by a laser or the like may be performed, and vacuum deposition or sputtering may be performed by overlapping a mask.
In the present invention, the formation position of the counter electrode layer 22 is not particularly limited, and may be formed on the entire second hole transport layer 20 or a part thereof.

(Any constituent layer)
The organic thin film solar cell 10 shown in FIG. 1 has the plastic support 12, the transparent conductive layer 14, the photoelectric conversion layer 16, the first hole transport layer 18, the second hole transport layer 20, and the counter electrode layer 22 described above. However, it is not limited to this form, You may have layers other than the above as needed.
An example is shown below.

(Upper sealing member)
The organic thin film solar cell may further have an upper sealing member on the counter electrode layer 22. By arrange | positioning an upper sealing member, an organic thin-film solar cell is isolated from the atmosphere of the external field, and photoelectric conversion performance improves more.
The upper sealing member may include a protective layer, a gas barrier layer, a contact material layer, or a plastic support. As a preferred configuration example of the upper sealing member, a laminate in which a protective layer, an adhesive layer, a gas barrier layer, and a plastic support are laminated in this order from the counter electrode layer 22 side can be mentioned. Below, the structure of each layer is explained in full detail.

Protective layer is _{typically, MgO, SiO, SiO 2,} Al 2 O 3, Y 2 O 3, TiO metal oxides such as _2, metal nitrides such as SiN _x, metal nitride oxide such as SiN _x O _{y, MgF 2, LiF, AlF 3,} CaF 2 , etc. of the metal fluoride, polyethylene, polypropylene, polyvinylidene fluoride, or a polymer such as poly-para-xylylene and the like. Of these, metal oxides, nitrides, and nitride oxides are preferable, and silicon, aluminum oxides, nitrides, and nitride oxides are particularly preferable. The protective layer may be a single layer or a multilayer structure of different materials selected from the above.

  The method for forming the protective layer is not particularly limited, and for example, vacuum deposition, sputtering, reactive sputtering, MBE (molecular beam epitaxy), cluster ion beam, ion plating, plasma polymerization (high frequency) Excited ion plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, vacuum ultraviolet CVD method, coating method, printing method, transfer method and the like can be applied.

The gas barrier layer is not particularly limited as long as it has a gas barrier property. Usually, the gas barrier layer is an inorganic layer (sometimes referred to as an inorganic layer). Typical examples of the inorganic substance contained in the inorganic layer include boron, magnesium, aluminum, silicon, titanium, zinc, tin oxide, nitride, oxynitride, carbide, hydride, and the like. These may be pure substances, or may be a mixture of multiple compositions or a gradient material layer. Among these, aluminum oxide, nitride or oxynitride, or silicon oxide, nitride or oxynitride is preferable.
As the gas barrier layer, an organic layer can be used, and a polymer of (meth) acrylate is preferable because it is low in cost, ready for production, and has high transparency.

The inorganic layer as the gas barrier layer may be a single layer or a laminate of a plurality of layers. When the gas barrier layer has a laminated structure, it may be a laminate of an inorganic layer and an organic layer, or may be an alternating laminate of a plurality of inorganic layers and a plurality of organic layers. Specific examples of the organic layer and the inorganic layer and the lamination method are described in JP 2010-87339 A. The term “organic polymer layer” in this publication corresponds to the term organic layer in the present invention.
Although there is no limitation in particular about the thickness of the inorganic layer as a gas barrier layer, it is attached to 1 layer, and is in the range of 5-500 nm normally, Preferably it is 10-200 nm. The inorganic layer may have a laminated structure including a plurality of sublayers. In this case, each sublayer may have the same composition or a different composition.
Although there is no limitation in particular regarding the thickness of the organic layer as a gas barrier layer, 300-3000 nm is preferable per one layer.
Further, as disclosed in US Patent Publication No. 2004-46497, the interface between the inorganic layer and the organic layer adjacent thereto is not clear, and the composition is a layer whose composition changes continuously in the layer thickness direction. Also good.

The adhesive is not particularly limited, and for example, an emulsion type adhesive, an adhesive for wax hot melt lamination, an adhesive for dry lamination, and the like are preferable.
Examples of the emulsion type adhesive include a coating agent in which thermoplastic elastomer, LDPE, IO (ionomer), PVDC, PE (polyethylene) wax and the like are dispersed.
Examples of the wax hot melt lamination adhesive include PVDC (OPP (biaxially stretched polypropylene film, nylon film, PET film, PVA film) coated with polyvinylidene chloride resin).
Examples of adhesives for dry lamination include vinyl chloride / vinyl acetate copolymer, EVA (ethylene / vinyl acetate copolymer), ionomer copolymer, polyvinylidene chloride, ethylene / vinyl alcohol copolymer, nitrocellulose, Examples include cellulose acetate and silicone.

  The definition of the plastic support is similar to that already described.

  The installation method of the upper sealing member described above is not particularly limited. For example, first, a protective layer is provided on the counter electrode layer 22. Then, the sealing film (plastic support) which installed the gas barrier layer on the plastic support body is produced, and a sealing film is adhere | attached on the said protective layer through an adhesive agent. When transparency is not required on the upper part, a method of adhering a gas barrier film in which a metal foil is laminated on a protective layer may be used.

  Further, the above-described gas barrier layer may be disposed on the surface of the plastic support 12 on the counter electrode layer 22 side. In other words, a gas barrier layer may be disposed between the plastic support 12 and the counter electrode layer 22. The form of the gas barrier layer is as described above.

[Second Embodiment]
FIG. 2 is a cross-sectional view schematically showing the layer configuration of the second embodiment of the organic thin-film solar cell of the present invention.
The organic thin film solar cell 100 includes a plastic support 12, a transparent conductive layer 140, a photoelectric conversion layer 16, a first hole transport layer 18, a second hole transport layer 20, and a counter electrode layer 22 in this order. The transparent electrode layer 140 includes the metal pattern layer 24 and the transparent conductive resin layer 26. The organic thin film solar cell 100 is a so-called inverted organic thin film solar cell, similar to the organic thin film solar cell 10, and the surface on the plastic support 12 side is a light receiving surface and is closer to the plastic support 12. The transparent conductive layer 140 corresponds to the negative electrode.
The organic thin film solar cell 100 shown in FIG. 2 has the same configuration as that of the organic thin film solar cell 10 shown in FIG. 1 except that the transparent conductive layer 140 is provided. The reference numerals are attached and the description thereof is omitted, and the transparent conductive layer 140 will be described in detail below.

(Transparent electrode layer)
The transparent electrode layer 140 is an electrode layer disposed on the plastic support 12 and includes the metal pattern layer 24 and the transparent conductive resin layer 26. The metal pattern layer 24 includes a plurality of metal wiring layers 28. When the transparent electrode layer 140 includes the metal pattern layer 24 and the transparent conductive resin layer 26 having excellent ductility, the organic thin-film solar cell 10 having more flexibility is obtained.

  The transparent electrode layer 140 is preferably highly transparent and highly conductive. For high transparency, it is preferable that the area of the opening of the metal pattern layer 24 is large (the opening ratio is large). On the other hand, for high conductivity, the cross-sectional area of the metal wiring layer 28 is preferably large when compared with the same metal.

FIG. 3 is a plan view taken along the line AA in FIG. 2. The metal pattern layer 24 is composed of a plurality of thin metal wiring layers 28, and the metal wiring layers 28 are arranged in stripes. . In addition, the pattern shape of the metal pattern layer 24 is not limited to the form of FIG. 3, and can be arbitrarily designed, such as a mesh, a honeycomb, and a rhombus.
The opening ratio of the opening defined by the metal pattern layer 24 is preferably 70% or more and more preferably 80% or more from the viewpoint of transparency. Since the light transmittance and the conductivity are in a trade-off relationship, the larger the aperture ratio, the better. However, in practice, it becomes 95% or less. The opening means the opening region 30 in which the metal pattern layer 24 is not formed. More specifically, the transparent electrode layer in which the metal pattern layer 24 is not formed and the transparent conductive resin layer 26 described later is provided. 14 is intended as an area. The aperture ratio means the area ratio of the opening region 30 [area of the opening region 30 / (area of the opening region 30 + area of the metal pattern layer 24)].

The material of the metal wiring layer 28 of the metal pattern layer 24 is not particularly limited as long as it is a highly conductive metal or alloy, but is preferably made of a metal or alloy having a specific resistance of 1 × 10 ⁻⁵ Ω · cm or less. . More specifically, examples of such metals or alloys include gold, platinum, iron, copper, silver, nickel, aluminum, and alloys containing these metals. More preferred examples include copper, silver, or alloys containing these. Copper is preferable from the viewpoint of cost reduction of the metal material itself and migration resistance.

The line width W in plan view of the metal wiring layer 28 is preferably 0.1 to 1 mm or less from the viewpoint of transparency, and the distance D between the metal wiring layers 28 is preferably 3 to 30 mm from the viewpoint of transparency.
The resistance value of the metal wiring layer 28 is preferably 50 Ω / cm or less, more preferably 20 Ω / cm or less, and further preferably 10 Ω / cm or less. In order to realize such conductivity (low resistance), there is a method of increasing the cross-sectional area of the metal wiring layer 28. Further, in order to increase the aperture ratio, it is advantageous that the length (line width) in the film plane direction is short and the length (layer thickness) in the layer thickness direction is large as the cross-sectional shape.
However, when the metal wiring layer 28 having such a cross section is installed, a large step is likely to occur. In the organic thin film solar cell 10, the layer thickness of the photoelectric conversion layer 16 is often relatively thin, and if the step formed by the metal wiring layer 28 is large, a short circuit (failure) is likely to occur at the corner of the convex portion of the metal wiring layer 28. For this reason, reducing the level difference caused by the metal wiring layer 28 and making the corners of the metal wiring layer 28 convex are more important than increasing the aperture ratio, and a design that sacrifices the aperture ratio to some extent is required. In some cases, it must be taken. That is, a design having a long line width and a thin layer thickness is selected as the cross-sectional shape of the metal wiring layer 28. A preferable ratio between the line width and the layer thickness is in the range of 20000: 1 to 200: 1. Here, the value of the thickest part in the line width is used as the layer thickness.

The cross-sectional shape of the metal wiring layer 28 is a rectangle in FIG.
However, the cross-sectional shape of the metal wiring layer 28 is not limited to this form, and may be an isosceles trapezoid, an obtuse isosceles triangle, a semicircle, a figure surrounded by an arc and a chord, a figure obtained by deforming these, and the like. At this time, a tapered isosceles trapezoid or an obtuse isosceles triangle is more preferable than a cross section in which the angle of the convex portion is a right angle, such as a rectangle, because a short circuit does not occur. In addition, a cross-sectional shape in which a step is smoothed by a curve or a slope is more preferable than a cross-section having a clear corner because a short circuit is less likely to occur.

  The installation method of the metal pattern layer 24 is not particularly limited, and examples thereof include a vapor deposition method, a sputtering method, a printing method, and an ink jet method, and are appropriately selected. When the metal pattern layer 24 is formed by a printing method or an inkjet method, a binder may be added as long as desired conductivity is not impaired. Examples of binders include polyester resin, methacrylic resin, methacrylic acid-maleic acid copolymer, polystyrene resin, transparent fluororesin, polyimide resin, fluorinated polyimide resin, polyamide resin, polyamideimide resin, polyetherimide resin, cellulose acylate. Rate resin, polyurethane resin, polyether ether ketone resin, polycarbonate resin, alicyclic polyolefin resin, polyarylate resin, polyether sulfone resin, polysulfone resin, cycloolefin copolymer, fluorene ring modified polycarbonate resin, alicyclic modified polycarbonate resin, fluorene Thermoplastic resins such as ring-modified polyester resins and acryloyl compounds, gelatin, polyvinyl alcohol, polyacrylic acid, polyacrylamide, and polyvinyl Pyrrolidone, polyvinyl pyridine, hydrophilic polymers such as polyvinyl imidazole, and the like. These polymers may have a cross-linked structure to increase the film strength.

The configuration of the metal pattern layer 24 is not limited to that shown in FIG. 3, and may have a bus line 32 that intersects the metal wiring layer 28 as shown in FIG. 4.
The bus line 32 is a wiring formed from the viewpoint of ensuring conductivity necessary for the entire operation surface. A preferable line width of the bus line 32 is preferably 1 to 5 mm, more preferably 1 to 3 mm.
The line width of the bus line 32 is not necessarily uniform. The bus line 32 and the metal wiring layer 28 may be made of the same material or different materials. The bus line 32 is normally installed so as to be orthogonal to the metal wiring layer 28, but may intersect with an angle other than 90 degrees. The same definition as the metal wiring layer 28 is applied to the thickness, cross-sectional shape, and material of the bus line 32.

The interval (pitch) of the bus lines 32 is selected as the optimum condition as a compromise between the large area conductivity and the light transmittance, as in the metal wiring layer 28. Specifically, it is determined by the conductivity of the metal wiring layer 28 that connects the adjacent bus lines 32. Typically, it is preferable to select an interval at which the resistance value of the metal wiring layer 28 connecting two adjacent bus lines 32 is 50Ω or less per line. The resistance value is preferably 20Ω or less, particularly preferably 10Ω or less.
The pitch of the bus lines 32 is preferably 40 to 200 mm.

  The bus line 32 may be formed by an evaporation method, or may be formed by a method such as a printing method or an inkjet method. It is advantageous from the viewpoint of cost to form the metal wiring layer 28 and the bus line 32 simultaneously using materials having the same composition. When the metal wiring layer 28 and the bus line 32 are simultaneously manufactured by roll-to-roll using a mask vapor deposition method, generally, a fixed mask for manufacturing the metal wiring layer 28 and the bus line 32 are manufactured. A facility having a movable mask is required.

  The transparent conductive resin layer 26 is a layer that covers the metal pattern layer 24 and is filled in the opening region 30 of the metal pattern layer 24. The transparent conductive resin layer 26 needs to be transparent in the emission spectrum or action spectrum range of the organic thin-film solar cell, and usually needs to be excellent in light transmittance from visible light to near infrared light. Specifically, when the layer thickness is 0.1 μm, the average light transmittance in the wavelength region of 400 nm to 800 nm is preferably 50% or more, more preferably 75% or more, and 85% or more. Is more preferable.

Although the thickness in particular of the transparent conductive resin layer 26 is not restrict | limited, 20-500 nm is preferable, 30-300 nm is more preferable, 50-200 nm is further more preferable.
The transparent conductive resin layer 26 is not particularly limited as long as it has the above-described transparency and conductivity. However, the transparent conductive resin has a specific resistance of 8 × 10 ⁻³ Ω · cm or less after film formation. It is preferable to use a resin as a main component. Here, the main component means a component having a content of 80% or more based on the total amount of the transparent conductive resin layer 26.
Transparent conductive resins that realize such specific resistance include dispersions of conductive nanomaterials in acrylic polymers (eg, silver nanowires, carbon nanotubes, graphene, etc.), conductive polymers (eg, polythiophene, polypyrrole). Polyaniline, polyphenylene vinylene, polyphenylene, polyacetylene, polyquinoxaline, polyoxadiazole, polybenzothiadiazole, and the like, and polymers having a plurality of these conductive skeletons).

Among these, polythiophene is preferable, and polyethylenedioxythiophene is particularly preferable. These polythiophenes are usually partially oxidized in order to obtain conductivity. The conductivity of the conductive polymer can be adjusted by the degree of partial oxidation (doping amount), and the higher the doping amount, the higher the conductivity. Since polythiophene becomes cationic by partial oxidation, it has a counter anion to neutralize the charge. An example of such a polythiophene is polyethylene dioxythiophene (PEDOTPSS) having polystyrene sulfonic acid as a counter ion.
PEDOT-PSS may contain an organic solvent having a high boiling point for the purpose of increasing conductivity. Examples of the high boiling point organic solvent include ethylene glycol, diethylene glycol, dimethyl sulfoxide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like.
Specific product examples for realizing the specific resistance include Orgacon (Orgacon) S-305, manufactured by Agfa Co., Ltd. C. A Stark company make and Clevios (Clebios) PH-1000 etc. are mentioned.

Other polymers may be added to the transparent conductive resin layer 26 as long as the desired conductivity is not impaired. Other polymers are added for the purpose of improving coatability and increasing the film strength.
Examples of other polymers include polyester resin, methacrylic resin, methacrylic acid-maleic acid copolymer, polystyrene resin, transparent fluororesin, polyimide, fluorinated polyimide resin, polyamide resin, polyamideimide resin, polyetherimide resin, cellulose Acylate resin, polyurethane resin, polyether ether ketone resin, polycarbonate resin, alicyclic polyolefin resin, polyarylate resin, polyether sulfone resin, polysulfone resin, cycloolefin copolymer, fluorene ring modified polycarbonate resin, alicyclic modified polycarbonate resin, Thermoplastic resins such as fluorene ring-modified polyester resins and acryloyl compounds, gelatin, polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyvinyl pyrone Pyrrolidone, polyvinyl pyridine, hydrophilic polymers such as polyvinyl imidazole, and the like. These polymers may have a cross-linked structure to increase the film strength.

The transparent conductive resin layer 26 is preferably formed by a known means after the above-described metal pattern layer 24 is formed, because the step formed by the metal pattern layer 24 is smoothed by the transparent conductive resin. .
In addition, as a suitable form of the film-forming method of the transparent conductive resin layer 26, the composition containing the transparent conductive resin is applied on the plastic support 12 on which the metal pattern layer 24 is disposed, and heated as necessary. Examples of the method include performing a treatment to form the transparent conductive resin layer 26.

[Third Embodiment]
FIG. 5 is a cross-sectional view schematically showing the layer configuration of the second embodiment of the organic thin-film solar cell of the present invention.
The organic thin film solar cell 200 includes a plastic support 12, a transparent conductive layer 14, an electron transport layer 34, a photoelectric conversion layer 16, a first hole transport layer 18, a second hole transport layer 20, and a counter electrode layer 22 in this order. Have in. The organic thin film solar cell 200 is a so-called inverted organic thin film solar cell, similar to the organic thin film solar cell 10, and the surface on the plastic support 12 side is a light receiving surface and is closer to the plastic support 12. The transparent conductive layer 14 corresponds to the negative electrode.
The organic thin-film solar cell 200 shown in FIG. 5 has the same configuration as the organic thin-film solar cell 10 shown in FIG. 1 except that the electron-transport layer 34 is provided. The reference numerals are attached and the description thereof is omitted, and the electron transport layer 34 will be described in detail below.

(Electron transport layer)
The electron transport layer 34 is a layer provided between the transparent electrode layer 14 and the photoelectric conversion layer 16 so that electrons are easily transported from the photoelectric conversion layer 16 to the transparent electrode layer 14. The electron transport layer 16 also has a function of blocking the movement of holes from the photoelectric conversion layer 16 to the transparent electrode layer 14.

  Examples of the electron transport material that can be used for the electron transport layer 34 include those described above and Chem. Rev. Examples include those described as Electron Transport Materials in 2007, 107, 953-1010, and n-type inorganic oxide semiconductors having an electron transporting property (for example, titanium oxide, zinc oxide, tin oxide, tungsten oxide, and the like). Among these, titanium oxide and zinc oxide are preferable.

Although the film thickness of the electron carrying layer 34 is not specifically limited, 20-1000 nm is preferable and 20-200 nm is more preferable.
The electron transport layer 34 can be suitably formed by any of various wet film forming methods, dry film forming methods such as vapor deposition and sputtering, transfer methods, and printing methods. In particular, the method of forming a zinc oxide layer described in Journal of Physical Chemistry Vol. 114, pages 6849 to 6853 (2010), Thin Solid Film Vol. 517, pages 3766 to 3769 (2007), Advanced Materials No. 19 The method for forming a titanium oxide layer described in Volume 2, pages 2445 to 2449 (2007) is particularly suitable.

As a preferred form of the electron transport layer 34, as shown in FIG. 6, a first metal oxide layer 34a formed from metal oxide particles having an average particle diameter of 1 to 10 nm, and metal oxide having an average particle diameter of 20 to 100 nm. Examples thereof include an electron transport layer 340 including at least two layers including a second metal oxide layer 34b formed from physical particles. The organic thin film solar cell 300 including the electron transport layer 340 is superior in photoelectric conversion characteristics and flexibility.
Hereinafter, the first metal oxide layer 34a and the second metal oxide layer 34b will be described in detail.

The first metal oxide layer 34a is a layer formed of metal oxide particles having an average particle diameter of 1 to 10 nm (hereinafter also referred to as metal oxide particles A as appropriate). That is, the first metal oxide layer 34a is mainly composed of metal oxide particles, and is usually a so-called porous layer.
The kind of the metal oxide particle A used is not limited, for example, the metal oxide particle which has the property of an n-type semiconductor can be used conveniently. Examples thereof include metal oxide particles having at least one metal atom selected from the group consisting of zinc, titanium, tin, and tungsten. Among these, metal oxide particles having at least one metal atom selected from the group consisting of zinc and titanium are preferable in that the initial photoelectric conversion performance before bending is more excellent.

The average particle diameter of the metal oxide particles A is 1 to 10 nm. Especially, 2-8 nm is preferable and 3-6 nm is more preferable at the point which the photoelectric conversion performance after bending is more excellent.
The average particle diameter of the metal oxide particles A is measured by observing the cross section of the first metal oxide layer 34a with an electron microscope, measuring the diameter of at least 100 metal oxide particles, and calculating them. Find on average. In addition, when the metal oxide particle A is not spherical, the major axis is handled as the diameter. For simplicity, the diameter may be obtained from the surface irregularity period using an atomic force microscope (AFM).

  Although the layer thickness in particular of the 1st metal oxide layer 34a is not restrict | limited, 5-200 nm is preferable and 10-100 nm is more preferable at the point which the photoelectric conversion performance after a bending is more excellent.

The second metal oxide layer 34b is a layer formed of metal oxide particles having an average particle diameter of 20 to 100 nm (hereinafter also referred to as metal oxide particles B as appropriate). That is, the second metal oxide layer 34b is mainly composed of metal oxide particles, and is usually a so-called porous layer.
The kind of the metal oxide particle B is synonymous with the kind of the metal oxide particle A described above.
The average particle diameter of the metal oxide particles B is 20 to 100 nm. When the average particle diameter is within this range, excellent photoelectric conversion performance can be obtained. Especially, 20-80 nm is preferable and 30-60 nm is more preferable at the point which photoelectric conversion performance is more excellent.
The average particle diameter of the metal oxide particles B is measured by observing the cross section of the second metal oxide layer 34b with an electron microscope, measuring the diameter of at least 100 metal oxide particles, and calculating them. Find on average. In addition, when the metal oxide particle B is not spherical, the major axis is handled as the diameter.

  The layer thickness of the second metal oxide layer 34b is not particularly limited, but is preferably 10 to 500 nm and more preferably 20 to 300 nm in terms of more excellent initial photoelectric conversion performance before bending.

The manufacturing method of the 1st metal oxide layer 34a and the 2nd metal oxide layer 34b will not be restrict | limited especially if the layer formed from the metal oxide particle mentioned above can be manufactured.
For example, the method of using the composition for coating-film formation containing a metal oxide particle is mentioned. For example, a coating film-forming composition containing metal oxide particles having an average particle diameter of 1 to 10 nm is applied on the transparent electrode layer 14 and subjected to heat treatment as necessary, so that the first metal oxide layer 34a is applied. The method of producing is mentioned. In addition, when producing the 2nd metal oxide layer 34b, the composition for coating-film formation containing a metal oxide particle with an average particle diameter of 20-100 nm is apply | coated on the 1st metal oxide layer 34a, and it is the same as the above. The second metal oxide layer 34b is produced by the procedure described above.

In addition to the metal oxide particles, the coating film forming composition may contain various solvents as necessary. By including the solvent, it becomes easier to adjust the thickness of the first metal oxide layer 34a or the second metal oxide layer 34b.
The kind in particular of solvent used is not restrict | limited, Water or an organic solvent is mentioned. Examples of organic solvents include alcohol solvents (eg, methanol, ethanol, isopropanol), ketone solvents (eg, acetone, methyl ethyl ketone, cyclohexanone), aromatic hydrocarbon solvents (eg, toluene, xylene), amide solvents. (Eg, formamide, dimethylacetamide, N-methylpyrrolidone), nitrile solvents (eg, acetonitrile, propionitrile), ester solvents (eg, methyl acetate, ethyl acetate), carbonate solvents (eg, dimethyl carbonate, diethyl) Carbonate), ether solvents, halogen solvents and the like. Two or more of these solvents may be mixed and used.

  The heat treatment, which is an optional step performed after the coating film-forming composition is applied on the transparent electrode layer 14, easily removes the solvent from the formed coating film and bonds between the metal oxide particles. Will be strengthened. The conditions for the heat treatment are not particularly limited, and optimum conditions are selected according to the type of metal oxide particles used. Especially, it is preferable to implement the heat processing for 5 minutes-4 hours (more preferably 10 minutes-2 hours) at 50-250 degreeC (more preferably 80-180 degreeC).

As another manufacturing method of the first metal oxide layer 34a and the second metal oxide layer 34b, in addition to the coating film forming composition including the metal oxide particles described above, the coating film formation including the metal oxide precursor is performed. A method of using the composition for use is also mentioned. For example, a coating film-forming composition containing a metal oxide precursor capable of forming metal oxide particles of a predetermined size is applied on the transparent electrode layer 14 and subjected to heat treatment as necessary to obtain average particles. A method of forming the first metal oxide layer 34a by forming metal oxide particles having a diameter of 1 to 10 nm may be mentioned.
In addition, when producing the 2nd metal oxide layer 34b, the coating-film formation composition containing a metal oxide precursor is apply | coated on the 1st metal oxide layer 34a, and it is 2nd in the procedure similar to the above. A metal oxide layer 34b is produced.

The type of the metal oxide precursor to be used is not particularly limited as long as it is a compound capable of preparing the above-described metal oxide particles having a predetermined size under predetermined conditions. Examples thereof include β-diketonate complexes and metal complexes such as metal chelates.
Examples of the β-diketonate complex include complexes of metal atoms (for example, metal atoms contained in the metal oxide particles described above) and acetylacetone, benzoylacetone, benzoyltrifluoroacetone, benzoyldifluoroacetone, or benzoylfluoroacetone. It is done. More specifically, Zn (acac) _{2 and the} like can be mentioned.
More specifically, when a coating film-forming composition containing Zn (acac) ₂ is applied onto the transparent electrode layer 14 and subjected to heat treatment, the metal oxide particles having the above-mentioned predetermined average particle diameter ( ZnO) is formed, and the desired first metal oxide layer 34a or second metal oxide layer 34b is obtained.
In addition, when using a metal alkoxide as a metal oxide precursor, it is difficult to manufacture the desired 1st metal oxide layer 34a and the 2nd metal oxide layer 34b depending on the kind. For example, when titanium alkoxide or the like is used, it is difficult to control the hydrolysis rate, and the desired first metal oxide layer 34a and second metal oxide layer 34b cannot be obtained.

  In FIG. 6, the first metal oxide layer 34a is disposed on the transparent electrode layer 14, and the second metal oxide layer 34b is disposed on the first metal oxide layer 34a. The stacking order of the metal oxide layer 34a and the second metal oxide layer 34b may be reversed. That is, the second metal oxide layer 34b may be disposed on the transparent electrode layer 14, and the first metal oxide layer 34a may be disposed on the second metal oxide layer 34b.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

<Example 1>
A gas barrier layer is formed on one surface of a 100 μm thick polyethylene naphthalate film (hereinafter abbreviated as a PEN film), which is a plastic support, and a transparent conductive layer, an electron transport layer, a photoelectric conversion layer, and a first hole transport layer are formed on the gas barrier layer. The organic thin film solar cell of Example 1 was produced by laminating | stacking a layer, a 2nd positive hole transport layer, and a counter electrode layer.
The detailed procedure is shown below.

[Formation of gas barrier layer]
On the PEN film, using a wire bar, a polymerizable composition (EB-3702 (13 g) manufactured by Daicel Cytec Co., Ltd., light acrylate TMP-A (6 g) manufactured by Kyoeisha Chemical Co., Ltd.), KAYAMER PM-21 (1 g) manufactured by Nippon Kayaku Co., Ltd. Lambberti UV polymerization initiator ESACURE KTO-46 (0.5 g), 2-butanone 190 g mixed solution) was applied. After drying, the organic layer is cured by irradiating with ultraviolet rays from a high-pressure mercury lamp (accumulated dose 1 J / cm ² ) in a chamber in which the oxygen concentration is 0.1% by the nitrogen substitution method. A 5 μm organic layer was formed.
An inorganic layer (aluminum oxide layer) was formed on the organic layer using a sputtering apparatus. Aluminum was used as a target, argon was used as a discharge gas, and oxygen was used as a reaction gas. The film forming pressure was 0.1 Pa, and the reaching layer thickness was 40 nm.
On the obtained laminated body, the said polymeric composition was apply | coated and hardened by the method similar to the above, and the organic layer whose layer thickness was 1.5 micrometers was formed.
Thus, the gas barrier layer which consists of three layers, an organic layer, an inorganic layer, and an organic layer, was formed on the PEN film. When the water vapor transmission rate at 40 ° C. and 90% relative humidity of the PET film having the gas barrier layer was measured using a water vapor transmission rate measuring device (manufactured by MOCON, PERMATRAN-W3 / 31), the detection limit value of this measurement (0.005 g / m ² / day) or less.

[Formation of metal pattern layer]
Each PEN film on which a gas barrier layer is formed is cut into 25 mm squares, a mask for a 25 mm square substrate is set in a vacuum deposition apparatus, and a silver metal wiring layer is deposited on the gas barrier layer by a resistance heating method to a thickness of 100 nm. A pattern layer was formed. Deposition is performed by deposition, and the deposition pattern is a parallel stripe having a line width of 0.3 mm, a line length of 20 mm, and a line interval of 4 mm. In order to form this pattern, a stainless steel mask having a thickness of 0.1 mm was set below the PEN film with a clearance of 1 mm.
Next, the ends of the metal wiring layers in the metal pattern layer were brought into contact with each other using a silver paste.

[Formation of transparent conductive resin layer]
Next, an aqueous dispersion of polyethylene dioxythiophene / polystyrene sulfonic acid (abbreviation: PEDOT-PSS) (manufactured by Agfa, Olgacon S-305) was spin-coated from the upper surface of the surface on which the metal pattern layer was formed. Next, this film was heat-dried at 110 ° C. for 20 minutes to form a transparent conductive resin layer made of a transparent conductive resin. At this time, the thickness of the transparent conductive resin layer was 100 nm.

[Formation of electron transport layer]
A solution containing ZnO particles (Aldrich, 721085-100G) diluted 80-fold with pure water was spin-coated on a transparent conductive resin layer with a spin coater (500 rpm, 120 seconds), and a film was formed. An electron transport layer was formed.

[Formation of photoelectric conversion layer]
A bulk hetero layer was formed as the photoelectric conversion layer. 20 mg of P3HT (poly-3-hexylthiophene, Lisicon SP-001 (trade name), manufactured by Merck) and 14 mg of ICBA (indene C60 bis-adduct, manufactured by Aldrich) were dissolved in 1 ml of chlorobenzene to obtain a bulk hetero layer coating solution. . This was spin-coated on the electron transport layer to form a bulk hetero layer. The rotation speed of the spin coater was 500 rpm, and the dry layer thickness was 180 nm.
Then, it heated for 15 minutes at 130 degreeC using the hotplate.

[Formation of first hole transport layer]
An organic solvent dispersion (manufactured by HC Starck, CPP 105D) of polyethylenedioxythiophene / polystyrenesulfonic acid (abbreviation: PEDOT-PSS) was spin-coated on the photoelectric conversion layer. Next, this was heat-dried at 140 ° C. for 15 minutes to form a first hole transport layer. The thickness of the first hole transport layer was 40 nm.
In addition, the contact angle of the organic solvent dispersion (CPP 105D) with respect to the surface of the photoelectric conversion layer was less than 20 °.

[Formation of Second Hole Transport Layer]
On the first hole transport layer, a sulfonated polythiophene (OC1200) (manufactured by Sigma-Aldrich, 699799-25ML, Poly (thiophene-3- [2- (2-methoxyethoxy) ethoxy] -2,5-diyl), A sulfonated solution (electronic grade) was spin-coated, and this was heat-dried at 130 ° C. for 15 minutes to form a second hole transport layer. The thickness of the second hole transport layer was 100 nm.

[Formation of counter electrode layer]
Aluminum was deposited on the second hole transport layer so as to have a thickness of 100 nm to form a counter electrode layer. At this time, mask vapor deposition was performed so that the effective area of photoelectric conversion was 1 cm ² .

[Measurement of photoelectric conversion efficiency and dark current]
The organic thin-film solar cell obtained above was irradiated with simulated sunlight of AM1.5G and 80 mW / cm ² using a Pexel Technologies L12 solar simulator, while measuring the source measure unit (SMU2400, manufactured by KEITHLEY) ) Was used to measure the generated current value in the voltage range of −0.1 V to 1.0 V. The obtained current-voltage characteristics were evaluated using a Pexel Technologies IV curve analyzer, and the conversion efficiency (%), which is the initial battery characteristics, was calculated as a characteristic parameter. The measurement results are shown in Table 1 below.
Further, the same measurement as described above was performed in a state where light was blocked, and the dark current was measured. The dark current value was -0.5V.

[Measurement of ionization potential (Ip)]
The ionization potentials of P3HT, the first hole transport layer, and the second hole transport layer in the photoelectric conversion layer were measured with an AC-2 apparatus manufactured by Riken Keiki.
The ionization potentials of P3HT, the first hole transport layer, and the second hole transport layer were 4.9 eV, 4.7 eV, and 5.2 eV, respectively. That is, the ionization potential Ip1 of the first hole transport layer is smaller than the ionization potential Ip2 of the second hole transport layer, and the ionization potential Ip3 of the electron donating compound P3HT is smaller than the ionization potential Ip2 of the second hole transport layer. It was.

[Evaluation of flexibility]
After preparing 10 samples of the above organic thin film solar cells, wrapping each sample around a 20 mmφ cylindrical stainless steel by 180 ° and returning it 100 times, it was evaluated whether the sample was short-circuited and short-circuited. The proportion of organic thin film solar cells that did not exist was calculated.
[Ratio (%)] = (Number of organic thin-film solar cells not short-circuited / 10 samples) × 100

<Example 2>
Except having changed the thickness of the 1st positive hole transport layer from 40 nm to 60 nm, the organic thin film solar cell was manufactured according to the procedure similar to Example 1, and various measurements were performed.

<Example 3>
Except having changed the manufacturing method of the electron carrying layer into the following procedures, the organic thin film solar cell was manufactured according to the procedure similar to Example 1, and various measurements were performed.
[Formation of electron transport layer]
Next, an ethanol solution containing Zn (acac) ₂ (manufactured by Wako Pure Chemical Industries, Ltd.) was applied on the transparent conductive resin layer and subjected to heat treatment at 160 ° C. for 20 minutes to form a first metal oxide layer. . The content of Zn (acac) ₂ in the ethanol solution was 0.5 parts by mass with respect to 100 parts by mass of ethanol.
When the surface of the obtained first metal oxide layer was observed with an atomic force microscope, it was confirmed that the first metal oxide layer was a layer formed of ZnO particles having an average particle diameter of 5 nm. The layer thickness of the first metal oxide layer was 80 nm.
Next, a solution obtained by diluting an ethanol solution containing ZnO particles (manufactured by Aldrich) eight times with ethanol was applied onto the first metal oxide layer and dried as it was to form a second metal oxide layer. In addition, the average particle diameter of the ZnO particle | grains in a solution was 40 nm, and the content was 5 mass parts with respect to 100 mass parts of ethanol solvents.
When the obtained second metal oxide layer was observed with an electron microscope, it was confirmed that the second metal oxide layer was a porous layer formed of ZnO particles having an average particle diameter of 40 nm as a starting material. . The layer thickness of the second metal oxide layer was 100 nm.

<Example 4>
Except having changed the manufacturing method of the counter electrode layer into the following procedures, the organic thin film solar cell was manufactured according to the procedure similar to Example 3, and various measurements were performed.
[Formation of counter electrode layer]
An Ag electrode was formed by an inkjet method using Harima Kasei NPS-JL ink (Ag nanoparticle dispersion solution).

<Comparative Example 1>
Except for changing the thickness of the first hole transport layer from 40 nm to 100 nm, an organic thin film solar cell was produced according to the same procedure as in Example 1, and various measurements were performed.

<Comparative example 2>
An organic thin-film solar cell was manufactured according to the same procedure as in Example 1 except that the thickness of the first hole transport layer was changed from 40 nm to 200 nm and the second hole transport layer was not formed. went.

In Table 1, in the “electron transport layer” column, “ZnO-np” represents a single-layer electron transport layer formed of ZnO particles, and “Zn (acea) ₂ / ZnO-np” represents Zn (acea) _2. This represents an electron transport layer having a layer formed by ZnO particles and a layer formed by ZnO particles.
In the “counter electrode” column, the case of being produced by vapor deposition is represented as “deposition Ag”, and the case of being produced by the inkjet method is represented as “IJ-Ag”.

As can be seen from Table 1, the organic thin film solar cell of the present invention was excellent in dark current characteristics and photoelectric conversion efficiency, and also in flexibility. In particular, in Examples 3 and 4 in which the electron transport layer is two layers, it was confirmed that the dark current characteristics were further suppressed and the flexibility was excellent.
On the other hand, in Comparative Example 1 relating to the layer thickness specifically disclosed in Patent Document 1, it was confirmed that all of the dark current characteristics, photoelectric conversion efficiency, and flexibility were inferior to those of Examples. . Moreover, also in the comparative example 2 which did not form the 2nd hole transport layer, it was confirmed that it is inferior to an Example in all the items, and especially a dark current characteristic and flexibility are inferior.

10, 100, 200, 300 Organic thin film solar cell 12 Plastic support 14, 140 Transparent electrode layer 16 Photoelectric conversion layer 18 First hole transport layer 20 Second hole transport layer 22 Counter electrode layer 24 Metal pattern layer 26 Transparent conductive Resin layer 28 Metal wiring layer 30 Open region 32 Bus line 34,340 Electron transport layer 34a First metal oxide layer 34b Second metal oxide layer

Claims (8)

An organic thin-film solar cell having at least a transparent electrode layer, a photoelectric conversion layer, a first hole transport layer, a second hole transport layer, and a counter electrode layer in this order on a plastic support. ,
The photoelectric conversion layer contains at least an electron donating compound and an electron accepting compound;
An ionization potential of the first hole transport layer is smaller than an ionization potential of the second hole transport layer;
An ionization potential of the electron donating compound is smaller than an ionization potential of the second hole transport layer;
The organic thin-film solar cell, wherein the ratio (T1 / T2) of the thickness T1 of the first hole transport layer to the thickness T2 of the second hole transport layer is 0.6 or less.   The organic thin-film solar cell according to claim 1, wherein the first hole transport layer comprises poly-3,4-ethylenedioxythiophene / polystyrene sulfonate (PEDOT / PSS).   The organic thin film solar according to claim 1 or 2, wherein the first hole transport layer is formed using a first hole transport layer forming composition having a contact angle with respect to the photoelectric conversion layer of 20 ° or less. battery.   The organic thin-film solar cell according to any one of claims 1 to 3, wherein the second hole transport layer includes a conjugated polymer.   The organic thin-film solar cell according to any one of claims 1 to 4, wherein the transparent electrode layer includes a metal pattern layer and a transparent conductive resin layer.   The organic thin-film solar cell according to any one of claims 1 to 5, further comprising an electron transport layer between the transparent electrode layer and the photoelectric conversion layer.   The organic thin-film solar cell according to claim 6, wherein the electron transport layer includes metal oxide particles having at least one metal atom selected from the group consisting of zinc, titanium, tin, and tungsten.   The electron transport layer includes a first metal oxide layer formed from metal oxide particles having an average particle diameter of 1 to 10 nm, and a second metal oxide layer formed from metal oxide particles having an average particle diameter of 20 to 100 nm. The organic thin-film solar cell of Claim 6 or 7 containing at least 2 layers.

Images