JP6003071B2 - Tandem organic photoelectric conversion device - Google Patents

Description

  The present invention relates to a tandem organic photoelectric conversion element.

  In recent years, in order to cope with global warming, reduction of carbon dioxide emissions has been strongly desired. In addition, fossil fuels such as oil, coal, and natural gas are expected to be depleted in the near future, and there is an urgent need to secure alternative earth-friendly energy resources. Thus, development of power generation technology using sunlight, wind power, geothermal energy, nuclear power, and the like has been actively conducted, and among them, solar power generation is particularly attracting attention because of its high safety.

  In solar power generation, light energy is directly converted into electric power using a photoelectric conversion element utilizing the photovoltaic effect. Generally, a photoelectric conversion element has a structure in which a photoelectric conversion layer (light absorption layer) is sandwiched between a pair of electrodes, and light energy is converted into electric energy in the photoelectric conversion layer. The photoelectric conversion element is a silicon-based photoelectric conversion element using single-crystal / polycrystalline / amorphous Si, GaAs, CIGS (copper (Cu), indium (In), depending on the material used for the photoelectric conversion layer and the form of the element. Compound-based photoelectric conversion elements using a compound semiconductor such as gallium (Ga) and selenium (Se)), dye-sensitized photoelectric conversion elements (Gretzel cells), and the like have been proposed and put to practical use.

  However, the power generation cost when these solar cells are used is still higher than the cost when generating and transmitting power using fossil fuels, which hinders the spread of solar power generation. In addition, since heavy glass must be used for the substrate, reinforcement work is required when it is installed on a roof or the like, which has also contributed to the increase in power generation costs.

  As a technique for reducing the power generation cost in solar power generation, an electron-donating organic compound (p-type organic semiconductor) and an electron-accepting organic compound (between a transparent electrode and a counter electrode) and an electron-accepting organic compound ( A bulk heterojunction (BHJ) type photoelectric conversion element including a mixture with an n-type organic semiconductor as a photoelectric conversion layer has been proposed (see, for example, Non-Patent Document 1 and Patent Document 1).

  Bulk heterojunction organic photoelectric conversion elements are lightweight and flexible, and are expected to be applied to various products. In addition, since the structure is relatively simple and a photoelectric conversion layer can be formed by applying a p-type organic semiconductor and an n-type organic semiconductor, cost reduction can be expected by mass production on a roll-to-roll basis. It is possible that the problem of power generation cost can be solved. Further, unlike the production of conventional silicon-based photoelectric conversion elements, compound-based photoelectric conversion elements, dye-sensitized photoelectric conversion elements, etc., it does not necessarily involve a manufacturing process at a temperature higher than 160 ° C. It is expected that it can be formed on a lightweight plastic substrate.

  Note that the power generation cost needs to take into consideration the photoelectric conversion efficiency and durability of the element in addition to the initial manufacturing cost, and research for improving these has been actively conducted.

  In order to further improve the photoelectric conversion efficiency, it is necessary to more efficiently convert solar energy into electric energy. Specifically, (1) expanding the wavelength range of the sunlight spectrum that can be used for photoelectric conversion; (2) increasing the absorptance of a specific wavelength is required. In the said nonpatent literature 1, it has reached the conversion efficiency exceeding 5% by using the organic polymer which can absorb to about 900 nm as a photoelectric conversion material mainly for the said (1) objective.

  Further, a tandem technology is expected as a technology capable of achieving both of the above (1) and (2). This is a technique for stacking a plurality of solar cells (cells) (that is, providing a plurality of photoelectric conversion layers in one element). If the photoelectric conversion materials of the stacked photoelectric conversion layers are the same, light absorption is achieved. The rate (absorbance) is expected to increase, and if a photoelectric conversion layer composed of photoelectric conversion layers that absorb different wavelengths is laminated, an improvement in the usable wavelength region can be expected.

Such a tandem organic photoelectric conversion element (hereinafter also simply referred to as “tandem type element”) has different element performance depending on how the bottom cell and the top cell are electrically connected. In theory, when connected in series, The open circuit voltage V _oc is the sum of the upper and lower cells, and when connected in parallel, the short-circuit current density J _sc is the sum of the upper and lower cells, and the fill factor FF may be approximately the same as the value of a single cell in any case. Are known. However, in practice, unless the resistance of the intermediate layer connecting the bottom cell and the top cell is sufficiently low, the FF is remarkably lowered and it is difficult to obtain the efficiency as theoretically.

  Up to now, an intermediate layer formed by vapor-depositing a metal on PEDOT-PSS as an intermediate layer of a parallel-connected tandem element (for example, Cr is 1 nm and Au is 5 nm in Patent Document 1; Au in Non-Patent Document 2 is Au) And an intermediate layer formed by laminating PEDOT-PSS after forming an ultrathin metal layer by vapor deposition. On the other hand, in the serial connection type tandem element, as in Non-Patent Documents 3 and 4 and Patent Document 4, a layer made of an inorganic material such as titanium oxide is used as an intermediate layer.

International Publication No. 008/066933 Pamphlet US Patent Application Publication No. 2009/0211633 US Patent Application Publication No. 2010/326497 JP 2010-192862 A

A. Heeger, Nature Mat. , Vol. 6 (2007), p497 Adv. Mater. , 2010, 22, E77 Science, 317, p222, 2007 Adv. Mater. , 2011, 23, 3465

  However, each of the intermediate layers in the above-mentioned tandem type parallel connection device has a problem in terms of increasing the efficiency of the production process because it is necessary to form a metal layer by vapor deposition under vacuum.

  Further, the metal layer included in the intermediate layer in the parallel connection type tandem element and the layer made of an inorganic material such as titanium oxide that is the intermediate layer of the direct connection type tandem element are adjacent to the layer made of the organic substance.・ It is joined. Since inorganic materials (metals) and organic materials have different linear expansion coefficients and elastic moduli, peeling due to temperature cycle tests (JIS C8938-1995 etc.) and bending tests occur, electrical connections are cut, and photoelectric conversion efficiency is reduced. There was a risk of causing.

  Furthermore, in order to efficiently and inexpensively produce photoelectric conversion elements, it is required that they can be produced continuously on a roll-to-roll basis using an inexpensive plastic film substrate. In forming the layer, the non-patent document 3 requires an annealing process at 160 ° C. for 5 minutes, and the non-patent document 4 requires an annealing process at 150 ° C. for 30 minutes. It was a problem that it is not a process that can be adapted to below ℃.

  Therefore, the present invention provides a tandem organic photoelectric conversion element that can be manufactured by a manufacturing method that does not require a vacuum process and a process at a high temperature exceeding 120 ° C. and that has sufficient photoelectric conversion efficiency and durability. The purpose is to provide.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. And a specific emulsion-forming compound, that is, a self-dispersing polymer that is dispersible in an aqueous solvent without the need for a surfactant (commonly referred to as “self-emulsifying polymer” or “soap-free polymer”); It has been found that by forming an intermediate layer using molecules, it has desired transparency and can solve the above problems.

  That is, the tandem organic photoelectric conversion element of the present invention includes a first electrode, a first photoelectric conversion layer, a second photoelectric conversion layer, and a second electrode laminated in this order, and the first photoelectric An intermediate layer containing both a conductive polymer and a self-dispersing polymer dispersible in an aqueous solvent is provided between the conversion layer and the second photoelectric conversion layer.

  According to the present invention, a tandem organic photoelectric conversion element that can be manufactured by a manufacturing process that does not require a vacuum process and a process at a high temperature exceeding 120 ° C. and that has sufficient photoelectric conversion efficiency and durability. Can be provided.

It is the cross-sectional schematic which represented the normal layer type single type organic photoelectric conversion element typically. It is the cross-sectional schematic which represented typically the reverse layer type single type organic photoelectric conversion element. It is the cross-sectional schematic which represented typically the tandem type | mold organic photoelectric conversion element of the normal layer and series connection type which concerns on one Embodiment of the reference example of this invention. It is the cross-sectional schematic which represented typically the tandem type | mold organic photoelectric conversion element of the normal layer and parallel connection type which concerns on other one Embodiment of the reference example of this invention.

  Hereinafter, preferred embodiments of the present invention will be described.

<Organic photoelectric conversion element>
In one embodiment of the present invention, a first electrode, a first photoelectric conversion layer, a second photoelectric conversion layer, and a second electrode are stacked in this order, and the first photoelectric conversion layer and the second photoelectric conversion layer are stacked. The present invention relates to a tandem organic photoelectric conversion element having an intermediate layer containing both a conductive polymer and a self-dispersing polymer that can be dispersed in an aqueous solvent between the conversion layer.

  According to the study by the present inventors, since the self-dispersing polymer has high adhesiveness and excellent dispersibility even at a low temperature, it is considered that a microphase separation structure is formed when mixed with a conductive polymer. That is, it is possible to form a morphology in which the conductive polymer fills the gaps between the particles formed from the self-dispersing polymer. As a result, the density of the conductive polymer is reduced as the whole intermediate layer, and the transparency is improved. Also, the conductive polymer has a domain structure while improving the adhesion between the intermediate layer and the adjacent layer. Therefore, a decrease in conductivity can be suppressed. Furthermore, the present inventors have found that the intermediate layer can be formed at a low temperature of 120 ° C. or lower, and have completed the present invention.

  By tandemizing the element using the intermediate layer, two subcells such as the top cell and the bottom cell can be connected with good electrical characteristics, and the intermediate layer itself is highly transparent, so that the bottom cell (light incidence It is possible to transmit light having sufficient intensity to a cell that is not on the side. Moreover, since adhesiveness and flexibility are high, it can show the durability excellent also with respect to the temperature cycle test.

  Such an effect can also be obtained when a metal grid is arranged as an auxiliary extraction electrode in the intermediate layer as will be described later. By providing a metal grid in the intermediate layer, a higher fill factor and photoelectric conversion efficiency can be obtained.

  Hereinafter, the structure and each member of the tandem organic photoelectric conversion element of this embodiment will be described in detail.

[Structure of tandem organic photoelectric conversion device]
The organic photoelectric conversion element of this embodiment is a tandem type. A tandem organic photoelectric conversion element has a configuration in which a plurality of so-called single-type elements made of a single cell are electrically stacked in series or in parallel. Note that the structure of the single-type element also functions so that the first electrode (transparent electrode) formed on the substrate functions as an anode (anode) and the second electrode (counter electrode) functions as a cathode (cathode). There is a layer type element and a so-called reverse layer type element in which a first electrode (transparent electrode) functions as a cathode (cathode) and a second electrode (counter electrode) functions as an anode (anode). Therefore, for example, in the case of a tandem element in which two subcells are stacked, the following four types of tandem organic photoelectric conversion elements are conceivable in consideration of the above-described series / parallel and forward / reverse layers.
(1) Normal layer / series tandem type element: first electrode (anode) / first photoelectric conversion layer / intermediate layer (charge recombination layer) / second photoelectric conversion layer / second electrode (cathode)
(2) Reverse layer / series tandem type element: first electrode (cathode) / first photoelectric conversion / intermediate layer (charge recombination layer) / second photoelectric conversion layer / second electrode (anode)
(3) Normal layer / parallel tandem type element: first electrode (anode) / first photoelectric conversion layer / intermediate layer (extraction electrode; cathode) / second photoelectric conversion layer / second electrode (anode)
(4) Reverse layer / parallel tandem type element: first electrode (cathode) / first photoelectric conversion layer / intermediate layer (extraction electrode; anode) / second photoelectric conversion layer / second electrode (cathode)
In the present invention and the reference example of the present invention, any of the above-mentioned four types of structures can be used. From the viewpoint of improving the durability of the element, the reverse layer type (2) and (4) In addition, the configuration (4) is more preferable from the viewpoint of improving the resistance to the temperature cycle test.

  First, in order to describe the normal layer type and the reverse layer type of the element, the structure of a single type organic photoelectric conversion element will be described.

  FIG. 1 is a schematic cross-sectional view schematically showing a normal layer type single-type organic photoelectric conversion element. The organic photoelectric conversion element 10 is formed by laminating a first electrode 12, a hole transport layer 17, a photoelectric conversion layer 14, an electron transport layer 18, and a second electrode 13 on a substrate 11 in this order.

  In FIG. 1, the substrate 11 and the first electrode 12 are made of a transparent material, and light used for photoelectric conversion is irradiated from the side of the substrate 11, passes through the first electrode 12 and the hole transport layer 17, and It reaches the conversion layer 14. The photoelectric conversion layer 14 is a layer that converts light energy into electrical energy, and contains a p-type organic semiconductor and an n-type organic semiconductor as a photoelectric conversion material.

  The p-type organic semiconductor functions relatively as an electron donor (donor), and the n-type organic semiconductor functions relatively as an electron acceptor (acceptor). In addition, the electron donor and the electron acceptor referred to here are “when electrons are absorbed, electrons move from the electron donor to the electron acceptor to form a hole-electron pair (charge separation state)”. It has a function, and does not simply donate or accept electrons like an electrode, but donates or accepts electrons by a photoreaction.

  In FIG. 1, light incident from the first electrode 12 through the substrate 11 is absorbed by an electron acceptor or an electron donor (p-type organic semiconductor and n-type organic semiconductor) in the photoelectric conversion layer 14, and the electron donor. The electrons move from the electron acceptor to the electron acceptor, and a hole-electron pair (charge separation state) is formed.

  The generated electric charge is generated between the electron acceptors due to the internal electric field, for example, when the work functions of the first electrode 12 and the second electrode 13 are different, due to the potential difference between the first electrode 12 and the second electrode 13. And the holes pass between the electron donors and are carried to different electrodes, and a photocurrent is detected.

  In the example of FIG. 1, the work function of the first electrode 12 is deeper (larger) than the work function of the second electrode 13, and electrons are easily carried between the first electrode 12 and the photoelectric conversion layer 14. The hole transport layer 17 that does not easily transport holes is formed, and the electron transport layer 18 that does not easily transport holes and easily transports electrons is formed between the second electrode 13 and the photoelectric conversion layer 14. The electrons are transported to one electrode 12 and the electrons are transported to the second electrode 13. That is, the first electrode functions as an anode (anode) and the second electrode functions as a cathode (cathode). In this case, as the second electrode 13, a metal having a shallow (small) work function and relatively easily oxidized can be used. Note that the work functions of the first electrode and the second electrode are relative work functions when the photoelectric conversion layer 14 is used as a reference, and are, for example, Advanced Materials, 2011 (Vol. 23, no. 40), When a dipole layer is formed as in p4636-4463, it is necessary to determine the magnitude of the work function in consideration of the level shift caused by them.

  FIG. 2 is a schematic cross-sectional view schematically showing a reverse layer type single type organic photoelectric conversion element. In the reverse layer type single type organic photoelectric conversion element 20 of FIG. 2, the work function of the first electrode 12 is relatively shallower than that of the second electrode 13, contrary to the case of the forward layer type of FIG. (Made small). In addition, an electron transport layer 18 that easily carries electrons between the first electrode 12 and the photoelectric conversion layer 14 is formed, and it is difficult to carry electrons between the second electrode 13 and the photoelectric conversion layer 14. Since the hole transport layer 17 that easily transports holes is formed, electrons are transported to the first electrode 12, and holes are transported to the second electrode 13. That is, the first electrode functions as a cathode (cathode) and the second electrode functions as an anode (anode). In the reverse layer type, a metal, metal oxide, or conductor having a work function equivalent to or deeper than that of the first electrode (transparent electrode, electrode made of metal oxide) can be used as the second electrode. The stability of the second electrode with respect to oxygen and moisture is higher than that of the layer type element, and the durability of the element can be increased.

  Next, the structure of the tandem organic photoelectric conversion element according to this embodiment will be described. The tandem organic photoelectric conversion element of this embodiment has a configuration in which a plurality of the above normal layer type or reverse layer type subcells are stacked. The tandem organic photoelectric conversion element can increase the absorption wavelength of sunlight and / or increase the amount of absorption as compared with a single-type element having only one photoelectric conversion layer. High photoelectric conversion efficiency can be expected.

  As described above, four types of tandem organic photoelectric conversion elements can be considered in consideration of series / parallel and forward / reverse layers. In the following, (1) forward / series tandem type is considered. The elements and (3) forward layer / parallel tandem elements will be described in detail. Other than these, (2) reverse layer / series tandem type elements and (4) reverse layer / parallel tandem type reverse layer type elements, as described in the single type element, the first electrode and the second layer It can be produced by appropriately selecting the relationship between the work functions of the electrodes and the positions where the hole transport layer 17 and the electron transport layer 18 are arranged.

  In the following description, a tandem organic photoelectric conversion element including two subcells will be mainly described. However, the present invention may be a tandem organic photoelectric conversion element including three or more subcells. Absent. The cell located on the transparent electrode side or the light incident side of the two subcells is referred to as the “top cell” (or the first photoelectric conversion layer) and the reflective electrode (counter electrode) side or the light incident side. The other cell is referred to as a “bottom cell” (or a second photoelectric conversion layer).

FIG. 3 is a schematic cross-sectional view schematically showing a normal layer / series connection type tandem organic photoelectric conversion device according to an embodiment of a reference example of the present invention. According to FIG. 3, the tandem organic photoelectric conversion element 30 includes a first electrode 22a, a first hole transport layer 27a, a first photoelectric conversion layer 24a, a first electron transport layer 28a, It has an intermediate layer 29 including a metal grid 25 and a transparent conductive layer 26, and further includes a second hole transport layer 27b, a second photoelectric conversion layer 24b, a second electron transport layer 28b, and a second electrode 23. It has a configuration in which the layers are laminated in order. That is, in the form of FIG. 3, two forward layer type elements (subcells) are connected in series by the intermediate layer 29 to be tandem. At this time, the intermediate layer 29 functions as a charge recombination layer. In this embodiment, since the work function of the first electrode 22 is deeper (larger) than the work function of the second electrode 23, holes are transported to the first electrode 22 and electrons are transported to the second electrode 23. The In this case, the first electrode functions as an anode (anode) and the second electrode functions as a cathode (cathode).

  Further, as in the single-type element described with reference to FIGS. 1 and 2 described above, the work function of the second electrode 23 is made deeper (larger) than the work function of the first electrode 22, so that It can also be designed to transport holes to one electrode 22 to the second electrode 23 (reverse layer / series tandem element). In this case, the first electron transport layer 28a in FIG. 3 is disposed between the first electrode 22 and the first photoelectric conversion layer 24a, and the first hole transport layer 27a is the first photoelectric conversion layer. The second electron transport layer 28b is disposed between the intermediate layer 29 and the second photoelectric conversion layer 24b, and the second hole transport layer 27b is disposed between the second layer 24a and the intermediate layer 29. It arrange | positions between the photoelectric converting layer 24b and the 2nd electrode 23. FIG. At this time, the first electrode functions as a cathode (cathode) and the second electrode functions as an anode (anode). In this embodiment, two reverse layer elements (subcells) are connected in series by the intermediate layer 29 to be tandem, and the intermediate layer 29 functions as a charge recombination layer.

An element in which such normal layer and reverse layer subcells are tandemly connected in series has electrons (or holes) generated in the top cell and holes (or electrons) generated in the bottom subcell, By being recombined in the intermediate layer 29, the output open-circuit voltage (V _oc ) becomes a total value obtained by adding the voltage of the top cell and the voltage of the bottom cell. However, since the short-circuit current value (J _sc ) is limited to the lower of the two subcells, the film thicknesses of the two subcells are set so that the currents of the top cell and the bottom cell are substantially equal in order to obtain higher efficiency. Is preferably controlled.

FIG. 4 is a schematic cross-sectional view schematically showing a forward-layer / parallel-connected tandem organic photoelectric conversion device according to another embodiment of the reference example of the present invention. The tandem organic photoelectric conversion element 40 in FIG. 4 includes a first electrode 22a, a first hole transport layer 27a, a first photoelectric conversion layer 24a, a first electron transport layer 28a, a metal grid on a substrate 21. 25 and an intermediate layer 29 including a transparent conductive layer 26, and further a second electron transport layer 28b, a second photoelectric conversion layer 24b, a second hole transport layer 27b, and a second electrode 23 are laminated in this order. It has the structure formed. In the form of FIG. 4, the forward layer type element (subcell) is used as the top cell, and the reverse layer type element (subcell) is used as the bottom cell, which is tandemized by being connected in parallel by the intermediate layer 29. At this time, the intermediate layer 29 functions as an extraction electrode. In this embodiment, the work functions of the first electrode 22 and the second electrode 23 are designed to be deep (large), and the work function of the intermediate layer 29 is designed to be shallow (small). 22 and the second electrode 23 are transported, and the electrons are transported to the intermediate layer 29. In this case, the first electrode 22 and the second electrode 23 function as an anode (anode), and the intermediate layer 29 functions as a cathode (cathode).

  Further, as in the single-type element described with reference to FIGS. 1 and 2, the work function of the first electrode 22 and the second electrode 23 is shallow (small), and the work function of the intermediate layer 29 is deep (large). ) So that electrons can be transported to the first electrode 22 and the second electrode 23, and holes can be transported to the intermediate layer 29 (reverse layer / parallel type tandem element) ). In this case, the electron transport layer 28a in FIG. 4 is disposed between the first electrode 22 and the first photoelectric conversion layer 24a, and the first hole transport layer 27a is the first photoelectric conversion layer 24a. The second hole transport layer 27b is disposed between the intermediate layer and the second photoelectric conversion layer 24b, and the second electron transport layer 28b is disposed between the second photoelectric conversion layer and the intermediate layer 29. Arranged between the layer 24 b and the second electrode 23. At this time, the first electrode 22 and the second electrode 23 function as a cathode (cathode), and the intermediate layer 29 functions as an anode (anode). In this embodiment, two reverse layer elements (subcells) are connected in parallel by the intermediate layer 29 to be tandem, and the intermediate layer 29 functions as an extraction electrode.

In the element tandemized by such parallel connection, holes (or electrons) generated in the top cell and holes (or electrons) generated in the bottom cell are respectively output from the intermediate layer 29, and at the same time, Electrons (or holes) generated in the cell and electrons (or holes) generated in the bottom cell are output from the first electrode 22 and the second electrode 23, so that there is a gap between the top cell and the bottom cell. Thus, an electrical parallel connection is formed, and the external circuit 200 is driven by the connection as shown in FIG. When this parallel connection is efficiently performed, the output short-circuit current density (J _sc ) is a total value obtained by adding the current of the top cell and the current of the bottom cell. However, since the open circuit voltage (V _oc ) is limited to the lower of the two subcells, in order to obtain high efficiency, the photoelectric conversion materials of the two subcells should be set so that the voltages of the top cell and the bottom cell are substantially equal. It is preferable to select appropriately. In addition, since the voltage by the photoelectric conversion material is mainly determined by the HOMO level of the p-type organic semiconductor and the LUMO level of the n-type organic semiconductor included in the photoelectric conversion layer described later, each subcell has a desired V _oc and A combination of a p-type organic semiconductor and an n-type organic semiconductor may be selected. This is because the series-type tandem element has more control over the thickness of the first and second photoelectric conversion layers in order to match the J _sc between the sub-cells than the series-connected tandem-type element. There is an advantage that optimization is easy.

  Note that in both the series tandem element (FIG. 3) and the parallel tandem element (FIG. 4), the second photoelectric conversion layer 24b has the same spectrum as the absorption spectrum of the first photoelectric conversion layer 24a. It may be a layer made of a photoelectric conversion material that absorbs light or a layer made of a photoelectric conversion material that absorbs light of different spectra, but efficiently converts light in a wider wavelength range into electricity. For this purpose, a layer made of a photoelectric conversion material that absorbs light having different spectra is preferable.

  Hereinafter, each member of the tandem organic photoelectric conversion element of this embodiment will be described in detail.

[Middle layer]
The intermediate layer according to the present invention plays a role of taking in and recombining both holes and electrons extracted from two subcells in a series-connected tandem element. Further, the intermediate layer in the tandem element connected in parallel has a function of extracting holes or electrons extracted from the two subcells to an external circuit. Therefore, the intermediate layer needs to be configured with sufficient conductivity in both the series and parallel forms. Moreover, it is preferable that these intermediate | middle layers can be formed by the process by the apply | coating method.

  Also, as shown in FIGS. 3 and 4 described above, since the intermediate layer 29 is formed between the two photoelectric conversion layers (24a, 24b), the second photoelectric conversion layer 24b generates power with high photoelectric conversion efficiency. In order to be able to do so, it is desirable that the intermediate layer has high transparency. In addition, in order to be able to form an element on an inexpensive plastic substrate, it is also required to form the element at a low temperature of 120 ° C. or less, which is the upper limit temperature of plastic heat resistance.

  These issues are generally in a trade-off relationship. For example, in order to obtain high conductivity, it is necessary to increase the thickness of the intermediate layer to some extent as in Non-Patent Document 2, but organic conductive materials such as PEDOT-PSS are used even if the material used is a metal. Even so, transparency usually decreases.

  Further, when using PEDOT-PSS or the like, it is necessary to anneal at a certain high temperature (about 150 ° C.) as in Non-Patent Document 2 in order to obtain high conductivity.

  In the present invention, a plurality of problems in such a trade-off relationship have been solved by using a conductive polymer and a self-dispersing polymer. In other words, by mixing a conductive polymer and a self-dispersing polymer, the conductive polymer retains a continuous domain structure and forms a structure in which self-dispersing polymer particles fill the gap. It is done. As a result, the present inventors succeeded in forming an intermediate layer excellent in transparency while ensuring sufficient conductivity. Furthermore, because of the domain structure in which the conductive polymer is finely dispersed, sufficient conductivity can be obtained even at low temperature annealing. As a further effect, since the self-dispersing polymer generally has a property of high adhesiveness, when the layer adjacent to the intermediate layer is a layer made of an inorganic material, it seems that the intermediate layer has a metal grid. Even if it is a form, high adhesiveness can be ensured and it became able to exhibit high durability with respect to a temperature cycle test.

In the present specification, the “metal grid” means that the resistance of the intermediate layer is very low (less than 10 Ω / cm ² square) when the intermediate layer is connected to an external circuit as an extraction electrode in a tandem element connected in parallel. Otherwise, the fill factor (FF) decreases and the photoelectric conversion efficiency decreases. However, this refers to a mesh-like metal pattern introduced to prevent this. By forming such an auxiliary electrode in the intermediate layer, the conductivity can be further increased while maintaining transparency. Therefore, the intermediate layer in this embodiment includes, for example, a conductive layer containing a conductive polymer and a self-dispersing polymer, and a metal grid (metal fine wire) disposed as necessary, as in the embodiment shown in FIG. ) And may be formed. The metal grid may be provided in the intermediate layer of the series-connected tandem elements as shown in FIG.

(Self-dispersing polymer)
In the present invention, a polymer dispersion that can be dispersed in an aqueous solvent is a state in which nanometer-scale fine particles are stably suspended in a medium without the need for a surfactant or an emulsifier that assists micelle formation. A colloid-forming polymer.

  As used herein, the term “dispersion” relates to a liquid medium containing a suspension of microparticles. In accordance with the present invention, the “medium” is typically an aqueous liquid, such as water. As used herein, “aqueous” means a liquid (greater than 50% by weight) with a significant portion of water. “Colloid formation” refers to substances that form microparticles when dispersed in an aqueous solution, ie, “colloid formation” polymers are not water soluble.

  That is, the water-insoluble polymer can stably maintain the particle size of nanometer-scale fine particles in a solvent containing 50% by weight or more of water without a surfactant or an emulsifier (for one week or more) (increase). In this case, a self-dispersing polymer dispersion that can be dispersed in an aqueous solvent is defined.

  The size (diameter) of the colloidal particles is usually about 0.001 to 1 μm (1 to 1000 nm), but preferably 3 to 500 nm, more preferably 5 to 500 nm from the viewpoint of the transparency of the obtained intermediate layer. It is 100 nm, More preferably, it is 10-50 nm. The size of the colloidal particles can be measured with a light scattering photometer. The particle size here refers to the particle size of the primary particles.

  Such self-dispersing polymers are mainly classified into ionic ones and nonionic ones. In other words, an ionic polymer of a type that can dissociate by dissociating a dissociable group (such as a carboxylic acid group) in an aqueous solvent and becoming charged, and a nonion that is self-dispersed by a hydrophilic group such as polyethylene oxide. There are sex polymers. In this embodiment, both ionic and nonionic polymers can be used, but from the viewpoint of durability of the resulting device, it is preferable to use a polymer having a dissociable group (ionic polymer). By using a self-dispersing polymer having a dissociable group, the conductivity and adhesion of the intermediate layer obtained can be improved. In particular, it is preferable to use a polymer having an anionic dissociative group.

  Basically, even when a composition containing these self-dispersing polymers is applied to form a thin film, the particle size in the above dispersion is also observed in the film as it is, preferably 5 to 100 nm. More preferably, the particle diameter is 8 to 80 nm, and more preferably 10 to 50 nm. If the particle size is 5 nm or more, the compatibility with the conductive polymer does not become too high. It can be formed well. On the other hand, when the particle size is 100 nm or less, the compatibility with the conductive polymer does not become too low, and thus transparency and conductivity can be maintained well. The particle size in the thin film of the self-dispersing polymer can be measured with an atomic force microscope (AFM).

  The glass transition temperature (Tg) of the self-dispersing polymer is preferably 25 ° C to 80 ° C, more preferably 30 to 75 ° C, and still more preferably 50 to 70 ° C. When the glass transition temperature is 25 ° C. or higher, sufficient heat resistance can be imparted to the intermediate layer. On the other hand, if the glass transition temperature (Tg) is 80 ° C. or lower, the durability can be improved by a temperature cycle test. Glass transition temperature The glass transition temperature (Tg) is measured at a rate of temperature increase of 20 ° C./min using a differential scanning calorimeter (DTC-7 manufactured by Perkin Elmer), and can be determined according to JIS K7121 (1987). it can.

When the self-dispersing polymer has a dissociable group, examples of the dissociable group include an anionic group (sulfo group (—SO ₃ H) and a salt thereof (—SO ₃ X; X = cation, the same shall apply hereinafter), carboxyl Group (—COOH) and its salt (—COOX), phosphoric acid group (—OPO ₃ H ₂ ) and its salt (—OPO ₃ HX, —OPO ₃ X ₂ ), etc., cationic group (ammonium salt (—NH) ₃ X) and the like. Although there is no particular limitation, the dissociable group is preferably an anionic group from the viewpoint of compatibility with the conductive polymer. The amount of the dissociable group is not particularly limited as long as the self-dispersing polymer can be dispersed in an aqueous solvent, but is preferably as small as possible because the drying time is shortened. The counter species (cation X) used for the anionic group and the cationic group is not particularly limited, but is preferably a halide ion from the viewpoint of dispersion stability.

  The structure of the self-dispersing polymer is not particularly limited, but polyethylene, polyethylene-polyvinyl alcohol (PVA) copolymer, polyethylene-polyvinyl acetate copolymer, polyethylene-polyurethane copolymer, polybutadiene, polybutadiene-polystyrene copolymer. , Polyamide (nylon), polyvinylidene chloride, polyester, polyacrylate, polyacrylate-polyester copolymer, polyacrylate-polystyrene copolymer, polyvinyl acetate, polyurethane-polycarbonate copolymer, polyurethane-polyether copolymer, Polyurethane-polyacrylate copolymer, silicone copolymer, silicone-polyurethane copolymer, silicone-polyacrylate copolymer, polyvinylidene fluoride-polyacrylate copolymer It preferably has polyvinyl ether copolymer as a main skeleton - polyfluoro olefins. Further, a copolymer obtained by copolymerizing with other monomers based on these skeletons may be used. Among them, a polymer having a polyester skeleton (polyester-based polymer, polyester-acrylic resin-based polymer) or a polyethylene resin polymer having an ethylene skeleton is preferable.

  As these self-dispersing polymers, those synthesized by themselves may be used, or commercially available products may be used. An example of a commercial product is shown below. For example, as a self-dispersing polymer having an anionic dissociative group, Polysol (registered trademark) FP3000 (polyester resin, anion, core: acrylic, shell: polyester, Showa Denko), Vironal (registered trademark) MD1480 (polyester) Resin, anion, manufactured by Toyobo Co., Ltd., Vironal (registered trademark) MD1245 (polyester resin, anion, manufactured by Toyobo Co., Ltd.), Vironal (registered trademark) MD1500 (polyester resin, anion, manufactured by Toyobo Co., Ltd.), Vironal (registered trademark) MD2000 ( Polyester resin, anion, manufactured by Toyobo Co., Ltd., Vironal (registered trademark) MD 1930 (polyester resin, anion, manufactured by Toyobo Co., Ltd.), plus coat RZ105 (polyester resin, anion, manufactured by Toyobo Co., Ltd.), plus coat RZ5 1 (polyester resin, anion, manufactured by Kyoyo Chemical Co., Ltd.), Plus Coat RZ570 (polyester resin, anion, manufactured by Kyogo Chemical Co., Ltd.), Plus Coat RZ571 (polyester resin, anion, manufactured by Kyogo Chemical Co., Ltd.), Hitec S-9242 (polyethylene resin) , Anion, manufactured by Toho Chemical Co., Ltd.).

  Vironal (registered trademark) is a high molecular weight polyester obtained by copolymerizing a small amount of a monomer having a hydrophilic functional group, and has a hydroxyl group at the molecular end. Pluscoat (registered trademark) is a saturated copolymerized polyester resin containing terephthalic acid as a main component, and is a resin characterized by including a hard segment and a soft segment in the polymer.

  Examples of the self-dispersing polymer having a cationic dissociable group include UW-319SX, UW-223SX, UW-550CS (acrylic resin, manufactured by Taisei Fine Chemical Co., Ltd.), Rikabond (registered trademark) AW71-L, Aquatex EC. -1200, EC-1700, AC-3100, FK-854, ES-330 (polyolefin, manufactured by Chuo Rika Kogyo Co., Ltd.), NS-600X, NS-620X, NS-650X (acrylic resin, manufactured by Takamatsu Yushi Co., Ltd.), etc. Can be mentioned.

  On the other hand, as a nonionic (non-dissociable) self-dispersing polymer having no dissociable group, Movinyl (registered trademark) 7720 (acrylic resin, nonion, manufactured by Nippon Synthetic Chemical Co., Ltd.), Movinyl (registered trademark) 7820 ( Acrylic resin, nonion, manufactured by Nippon Synthetic Chemical Co., Ltd.), Ricabond (registered trademark) BA-10L, AW-18LK, AW-919, BE-812H, BE-814, BC-331 (polyolefin, manufactured by Chuo Rika Kogyo Co., Ltd.) Etc.

  Among these, a self-dispersing polymer of a type having a dissociable group is preferable. When the self-dispersing polymer has a dissociable group, a more optimal domain size can be obtained. In particular, when an anionic material such as PSS is used for the conductive polymer, an optimum intermediate layer with excellent temporal stability can be obtained by using a self-dispersing polymer having an anionic dissociative group. .

(Conductive polymer)
In this specification, “conductive polymer” means a sheet resistance of 10 × ⁸ Ω / cm measured by a method according to JIS K 7194 “Resistivity test method of conductive plastic by four-probe method”. ^It refers to a polymer material lower than ² square.

  The conductive polymer is preferably a conductive polymer having a π-conjugated conductive polymer and a polyanion. Such a conductive polymer can be easily obtained by chemical oxidative polymerization of a precursor monomer that forms a π-conjugated conductive polymer described later, an appropriate oxidizing agent, and an oxidation catalyst in the presence of a poly anion described later. Can be manufactured.

  The π-conjugated conductive polymer is not particularly limited, but is substituted or unsubstituted polythiophenes, polypyrroles, polyindoles, polycarbazoles, polyanilines, polyacetylenes, polyfurans, polyparaphenylene vinylenes, Chain conductive polymers such as polyazulenes, polyparaphenylenes, polyparaphenylene sulfides, polyisothianaphthenes, and polythiazyl compounds can be used. Of these, polythiophenes and polyanilines are preferable from the viewpoint of conductivity, transparency, stability, and the like, polythiophenes are more preferable, and polyethylenedioxythiophene is most preferable.

  Precursor monomers used in the formation of π-conjugated conductive polymers have a π-conjugated system in the molecule, and even when polymerized by the action of an appropriate oxidant, a π-conjugated system is formed in the main chain. It is what is done. Examples thereof include pyrroles and derivatives thereof, thiophenes and derivatives thereof, anilines and derivatives thereof, and the like.

  Specific examples of the precursor monomer include pyrrole, 3-methylpyrrole, 3-ethylpyrrole, 3-n-propylpyrrole, 3-butylpyrrole, 3-octylpyrrole, 3-decylpyrrole, 3-dodecylpyrrole, 3, 4-dimethylpyrrole, 3,4-dibutylpyrrole, 3-carboxylpyrrole, 3-methyl-4-carboxylpyrrole, 3-methyl-4-carboxyethylpyrrole, 3-methyl-4-carboxybutylpyrrole, 3-hydroxypyrrole 3-methoxypyrrole, 3-ethoxypyrrole, 3-butoxypyrrole, 3-hexyloxypyrrole, 3-methyl-4-hexyloxypyrrole, thiophene, 3-methylthiophene, 3-ethylthiophene, 3-propylthiophene, 3 -Butylthiophene, 3-hexylchi Phen, 3-heptylthiophene, 3-octylthiophene, 3-decylthiophene, 3-dodecylthiophene, 3-octadecylthiophene, 3-bromothiophene, 3-chlorothiophene, 3-iodothiophene, 3-cyanothiophene, 3-phenyl Thiophene, 3,4-dimethylthiophene, 3,4-dibutylthiophene, 3-hydroxythiophene, 3-methoxythiophene, 3-ethoxythiophene, 3-butoxythiophene, 3-hexyloxythiophene, 3-heptyloxythiophene, 3- Octyloxythiophene, 3-decyloxythiophene, 3-dodecyloxythiophene, 3-octadecyloxythiophene, 3,4-dihydroxythiophene, 3,4-dimethoxythiophene, 3,4-diethoxythiol 3,4-dipropoxythiophene, 3,4-dibutoxythiophene, 3,4-dihexyloxythiophene, 3,4-diheptyloxythiophene, 3,4-dioctyloxythiophene, 3,4-didecyloxy Thiophene, 3,4-didodecyloxythiophene, 3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, 3,4-butenedioxythiophene, 3-methyl-4-methoxythiophene, 3-methyl -4-ethoxythiophene, 3-carboxythiophene, 3-methyl-4-carboxythiophene, 3-methyl-4-carboxyethylthiophene, 3-methyl-4-carboxybutylthiophene, aniline, 2-methylaniline, 3-isobutyl Aniline, 2-aniline sulfonic acid, 3-aniline A sulfonic acid etc. are mentioned.

  The poly anion is a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, a substituted or unsubstituted polyester, and a copolymer thereof. And it is preferable that it consists of a structural unit which has an anionic group, and a structural unit which does not have an anionic group.

  In the conductive polymer, the poly anion has a function of solubilizing the π-conjugated conductive polymer in a solvent. Further, the anionic group of the polyanion functions as a dopant for the π-conjugated conductive polymer, and can improve the conductivity and heat resistance of the π-conjugated conductive polymer.

  The anionic group of the polyanion may be any functional group that can undergo chemical oxidation doping to the π-conjugated conductive polymer. Among them, from the viewpoint of ease of production and stability, a monosubstituted sulfate ester Group, monosubstituted phosphate group, phosphate group, carboxyl group, sulfo group and the like are preferable. Furthermore, from the viewpoint of the doping effect of the functional group on the π-conjugated conductive polymer, a sulfo group, a monosubstituted sulfate group, and a carboxyl group are more preferable.

  Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid ethyl sulfonic acid, polyacrylic acid butyl sulfonic acid, poly-2-acrylamido-2-methylpropane sulfonic acid, poly Isoprene sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacryl carboxylic acid, polymethacryl carboxylic acid, poly-2-acrylamido-2-methylpropane carboxylic acid, polyisoprene carboxylic acid, polyacrylic acid, etc. Can be mentioned. Further, these may be homopolymers or the above two or more kinds of copolymers.

  The polyanion may further have F (fluorine atom) in the compound. Specifically, Nafion (registered trademark) containing a perfluorosulfonic acid group (manufactured by Dupont), Flemion (registered trademark) made of perfluoro vinyl ether containing a carboxylic acid group (made by Asahi Glass Co., Ltd.), etc. Can do.

  Among these polyanions, when a compound having a sulfonic acid group is used, it is formed by applying and drying a layer containing a conductive polymer and a self-dispersing polymer, and then before irradiation with microwaves. You may heat-dry for 5 minutes or more at 120 degreeC.

  Furthermore, among these poly anions, polystyrene sulfonic acid, polyisoprene sulfonic acid, polyacrylic acid ethyl sulfonic acid, and polybutyl acrylate sulfonic acid that can obtain high conductivity are preferable.

  The polymerization degree of the polyanion is preferably 10 to 100,000, and more preferably in the range of 50 to 10,000 from the viewpoint of solvent solubility and conductivity. The degree of polymerization can be measured (confirmed) by gel permeation chromatography (GPC).

  Examples of the method for producing a polyanion include a method of directly introducing an anionic group into a polymer having no anionic group using an acid, a method of sulfonating a polymer having no anionic group with a sulfonating agent, an anion And a method of producing the polymerizable group-containing polymerizable monomer by polymerization.

  More specifically, in the method for producing an anionic group-containing polymerizable monomer by polymerization, the anionic group-containing polymerizable monomer is produced by oxidative polymerization or radical polymerization in a solvent in the presence of an oxidizing agent and / or a polymerization catalyst. The method of doing is mentioned. Specifically, a predetermined amount of the anionic group-containing polymerizable monomer is dissolved in a solvent, this is maintained at a constant temperature, and a solution in which a predetermined amount of an oxidizing agent and / or a polymerization catalyst is dissolved in the solvent is added to the solvent. The reaction is performed for a predetermined time. The polymer obtained by the reaction is adjusted to a certain concentration by the solvent. In this production method, a polymerizable monomer having no anionic group may be copolymerized with the anionic group-containing polymerizable monomer.

  When the obtained polymer is a polyanionic salt, it is preferably transformed into a polyanionic acid. Examples of the method for transforming into polyanionic acid include ion exchange method using an ion exchange resin, dialysis method, ultrafiltration method and the like, and among these, ultrafiltration method is preferable from the viewpoint of easy work.

  Ratio of π-conjugated conductive polymer and polyanion contained in conductive polymer “π-conjugated conductive polymer”: “polyanion” is preferably 1: 1 to 20 in mass ratio. From the viewpoint of conductivity and dispersibility, the range of 1: 2 to 10 is more preferable.

Examples of the oxidizing agent used for obtaining the conductive polymer according to the present invention by chemical oxidative polymerization of a precursor monomer that forms a π-conjugated conductive polymer in the presence of a polyanion include, for example, J. Org. Am. Soc. 85, 454 (1963), and is preferably any oxidizing agent suitable for oxidative polymerization of pyrrole. For practical reasons, cheap and easy to handle oxidants, such as iron (III) salts, eg FeCl ₃ , Fe (ClO ₄ ) ₃ , organic acids and iron (III) salts of inorganic acids containing organic residues Or use hydrogen peroxide, potassium dichromate, alkali persulfate (eg potassium persulfate, sodium persulfate) or ammonium, alkali perborate, potassium permanganate and copper salts such as copper tetrafluoroborate preferable. In addition, air or oxygen in the presence of catalytic amounts of metal ions, such as iron, cobalt, nickel, molybdenum or vanadium ions, can be used as an oxidizing agent. Persulfates and the iron (III) salts of inorganic acids containing organic acids and organic residues are not corrosive and are preferably used.

  Examples of iron (III) salts of inorganic acids containing organic residues include iron (III) salts of sulfuric acid half esters of alkanols having 1 to 20 carbon atoms, such as lauryl sulfate; alkyl sulfonic acids having 1 to 20 carbon atoms, For example, methanesulfonic acid or dodecanesulfonic acid; carboxylic acid having 1 to 20 aliphatic carbon atoms such as 2-ethylhexylcarboxylic acid; aliphatic perfluorocarboxylic acid such as trifluoroacetic acid and perfluorooctanoic acid; aliphatic dicarboxylic acid; For example oxalic acid; and especially aromatic, optionally substituted alkyl sulfonic acids having 1 to 20 carbon atoms, such as Fe (III) salts of benzenesulfonic acid, p-toluenesulfonic acid and dodecylbenzenesulfonic acid; It is done.

  Commercially available materials can be preferably used for these conductive polymers. For example, a conductive polymer (abbreviated as PEDOT-PSS) made of poly (3,4-ethylenedioxythiophene) and polystyrenesulfonic acid is H.264. C. It is commercially available from Starck as the Clevios® series, from Aldrich as PEDOT-PSS 483095, 560596, from Nagase Chemtex as the Denatron series. Polyaniline is commercially available from Nissan Chemical as the ORMECON (registered trademark) series.

  The conductive polymer may contain an organic compound as the second dopant for the purpose of further improving the conductivity. There is no restriction | limiting in particular in the organic compound which can be used by this invention, It can select suitably from well-known things, For example, an oxygen containing compound is mentioned suitably. The oxygen-containing compound is not particularly limited as long as it contains oxygen, and examples thereof include a hydroxy group-containing compound, a carbonyl group-containing compound, an ether group-containing compound, and a sulfoxide group-containing compound. Examples of the hydroxy group-containing compound include ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, glycerin and the like. Among these, ethylene glycol and diethylene glycol are preferable. Examples of the carbonyl group-containing compound include isophorone, propylene carbonate, cyclohexanone, γ-butyrolactone, and the like. Examples of the ether group-containing compound include diethylene glycol monoethyl ether. Examples of the sulfoxide group-containing compound include dimethyl sulfoxide. Among these, it is preferable to use at least one selected from dimethyl sulfoxide, ethylene glycol, and diethylene glycol. Moreover, these may be used individually by 1 type and may use 2 or more types together.

  The transparent conductive layer contains a self-dispersing polymer as described above, but also has a polar solvent such as dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF), which has a conductivity enhancing effect on the conductive polymer, a hydroxyl group A contained non-conductive polymer can be included. Thereby, high electroconductivity, high transparency, water resistance, and smoothness can be satisfy | filled simultaneously.

  As the transparent non-conductive polymer, a natural polymer resin or a synthetic polymer resin can be widely selected and used, and a water-soluble polymer or an aqueous polymer emulsion is particularly preferable. Examples of water-soluble polymers include natural polymers such as starch, gelatin, and agar, semi-synthetic polymers such as hydroxypropylmethylcellulose, carboxymethylcellulose, and hydroxyethylcellulose, cellulose derivatives, synthetic polymers such as polyvinyl alcohol, and polyacrylic acid polymers. , Polyacrylamide, polyethylene oxide, polyvinylpyrrolidone and the like. Examples of the aqueous polymer emulsion include acrylic resins (acrylic silicon-modified resins, fluorine-modified acrylic resins, urethane-modified acrylic resins, epoxy-modified acrylic resins, etc.), polyester resins, urethane resins, vinyl acetate resins, and the like.

  In addition, as the synthetic polymer resin, a transparent thermoplastic resin (for example, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, vinylidene fluoride) A transparent curable resin (for example, melamine acrylate, urethane acrylate, epoxy resin, polyimide resin, silicone resin such as acrylic-modified silicate) that can be cured by heat, light, electron beam, or radiation can be used. The following polymer (A) is also a synthetic polymer resin that is a preferred second dopant.

  In this embodiment, a method for forming a transparent conductive layer containing a conductive polymer and a self-dispersing polymer is not particularly limited. However, as an example, a conductive polymer and a self-dispersing polymer are formed as shown in the examples. It can be formed by preparing a coating solution dispersed in an aqueous solvent, coating and drying the coating solution.

  The aqueous solvent is not particularly limited as long as it contains 50% by volume or more of water. Besides pure water (including distilled water and deionized water), an aqueous solution containing acid, alkali, salt, etc., hydrophilic An organic solvent or the like may be contained. Specifically, pure water (including distilled water and deionized water), alcohol solvents such as methanol and ethanol, aprotic water-soluble such as dimethyl sulfoxide (DMSO), DMF, hexamethylphosphoramide (HMPA) Examples thereof include organic solvents, mixed solvents of water and alcohol solvents or aprotic water-soluble organic solvents.

  The compounding ratio of the conductive polymer contained in the coating solution and the self-dispersing polymer is not particularly limited, but is 10:90 by mass from the viewpoint of achieving both transparency and conductivity of the resulting intermediate layer. It is preferable that it is -90: 10, and it is more preferable that it is 25: 75-75: 25.

  In addition, the ratio of the aqueous solvent contained in the coating liquid is determined from the viewpoint of the stability of the coating liquid in terms of the total solid concentration (conducting polymer and self-dispersing polymer, and all solids including other components optionally added). The fractional concentration) is preferably 2 to 20% by mass, and more preferably 5 to 15% by mass. It is more preferable that

  The pH of the coating solution is desirably within a range exhibiting high conductivity, specifically, preferably 0.1 to 4.0, more preferably 0.5 to 3.0, and even more preferably 1. 0.0-2.0.

  Moreover, it is preferable that the said coating liquid does not contain a plasticizer etc. which control surfactant (emulsifier) and film forming temperature from a durable viewpoint of an organic thin-film solar cell.

  The method for applying the coating solution is not particularly limited, but the casting method, spin coating method, blade coating method, wire bar coating method, gravure coating method, spray coating method, dipping (dipping) coating method, bead coating method, air knife Ordinary methods such as a coating method, a curtain coating method, an ink jet method, a screen printing method, a relief printing method, an intaglio printing method, an offset printing method, a flexographic printing method, and a Langmuir-Blodgett (LB) method may be used. it can. Among these, it is particularly preferable to use a spin coating method or a blade coating method. Further, the temperature of the coating liquid and / or the coating surface during coating is not particularly limited, but is preferably 20 to 80 ° C. from the viewpoint of preventing precipitation and unevenness due to temperature fluctuations during coating and drying. Preferably it is 50-70 degreeC. Furthermore, there is no restriction | limiting in particular also about the specific form of drying, A conventionally well-known knowledge can be referred suitably. An example of drying (heat treatment) conditions is exemplified by conditions of about 50 to 120 ° C. and about 1 to 20 minutes. Examples of the apparatus used for drying include a hot plate, hot air drying, an infrared heater, a microwave, and a vacuum dryer. Of course, other drying apparatuses can be used.

(Metal grid)
The intermediate layer in the present invention may further include a metal grid (also referred to as “metal fine line” or “metal fine line pattern”) made of metal or metal oxide. By having a metal grid in the intermediate layer, the conductivity of the intermediate layer is improved, and a higher fill factor and photoelectric conversion efficiency can be obtained. This is particularly useful when the element size is large or in the case of tandem elements connected in parallel. In addition, when arrange | positioning these metal grids to an intermediate | middle layer, after forming the 1st photoelectric converting layer 24a and the 1st electron carrying layer 28a like FIG.3 and 4, a conductive polymer and a self-dispersion type | mold are used. It is preferable to form the metal grid 25 before forming the transparent conductive layer 26 containing a polymer. Since the metal fine line pattern of the metal grid has a gap between the patterns, it is preferable to have an element configuration in which a transparent conductive layer 26 containing a conductive polymer and a self-dispersing polymer is filled between the patterns. .

  The material of the metal grid is a metal or a metal oxide, but a metal is preferable from the viewpoint of conductivity. Examples of the metal include gold, silver, copper, iron, nickel, and chromium. From the viewpoint of conductivity, gold, silver, and copper are preferable, and silver is most preferable. An alloy containing these metals may be used, and the metal pattern may be a single layer or a plurality of layers laminated. Although there is no restriction | limiting in particular in the shape of a thin wire | line pattern, For example, stripe shape or mesh shape etc. are mentioned, It can determine from a viewpoint of the electroconductivity and transparency of an electrode.

  The metal grid may be formed using metal or metal oxide nanoparticles (hereinafter also referred to as “metal nanoparticles” and “metal oxide nanoparticles”, respectively). In this specification, a metal nanoparticle or a metal oxide nanoparticle means a metal or metal oxide in the form of fine particles having a particle diameter of from atomic scale to nm size. The average particle size of the metal nanoparticles or metal oxide nanoparticles is preferably 10 to 300 nm, and more preferably 30 to 200 nm. The metal used for the metal nanoparticles is preferably silver or copper from the viewpoint of conductivity, may be silver or copper alone, or may be a combination of them, an alloy of silver and copper, or silver plated with copper. Alternatively, copper plated with silver may be used.

  The metal nanoparticles or metal oxide nanoparticles may have a particle shape, a rod shape, or a wire shape as long as the minor axis of the particle diameter is nm size. In general, a nanowire refers to a linear structure having a diameter from the atomic scale to the nm size, which contains a metal element as a main component.

  When using metal nanowires or metal oxide nanowires for the metal grid, in order to form a long conductive path with one nanowire, the average length is preferably 3 μm or more, more preferably 3 to 500 μm. More preferably, it is -300 micrometers. The relative standard deviation of the length is preferably 40% or less. Moreover, there is no restriction | limiting in particular in an average minor axis, Although it is preferable that it is small from a viewpoint of transparency, the one where it is somewhat large is preferable from a viewpoint of electroconductivity. Therefore, the average minor axis of the metal nanowire or metal oxide nanowire is preferably 10 to 300 nm, and more preferably 30 to 200 nm. The relative standard deviation of the minor axis is preferably 20% or less. The metal nanowires or metal oxide nanowires of the metal grid are preferably in contact with each other, and more preferably in mesh form. A metal grid in which metal nanowires or metal oxide nanowires are brought into contact with each other or meshed can be easily obtained by using the above liquid phase film forming method.

  In the present invention, the means for producing the metal nanowire or metal oxide nanowire is not particularly limited, and for example, a known means such as a liquid phase method or a gas phase method can be used. Moreover, there is no restriction | limiting in particular in a specific manufacturing method, A well-known manufacturing method can be used. For example, as a method for producing silver nanowires, Adv. Mater. , 2002, 14, 833-837; Chem. Mater. 2002, 14, 4736-4745, and Japanese Patent Application Laid-Open No. 2002-266007 as a method for producing copper nanowires. According to the method for producing silver nanowires, it is preferable to apply the production because silver nanowires can be produced easily in an aqueous solution.

  As a method for forming an intermediate layer including a metal grid, first, a fine line pattern made of metal or metal oxide is formed as a metal grid 25 on a functional layer located immediately below the intermediate layer. The fine line pattern can be formed by applying a dispersion liquid composed of metal or metal oxide particles and a binder and drying to form a film, followed by patterning by etching or the like. Alternatively, a silver halide dispersion may be applied and dried to form a film by a silver salt method, followed by exposure and development to form a pattern. These film forming methods are not particularly limited as long as they are liquid phase film forming methods. Specifically, roll coating method, bar coating method, dip coating method, spin coating method, casting method, die coating method, blade coating method, bar coating method, gravure coating method, curtain coating method, spray coating method, doctor coating method A coating method such as an ink jet method can be used. Further, a pattern may be formed directly using a dispersion of metal or metal oxide nanoparticles by a spray coating method, an inkjet method, a gravure coating method, a flexographic printing method, or using a mask. The fine line shape can be adjusted by changing the concentration and viscosity of the dispersion of the metal nanoparticles or metal oxide nanoparticles used and the cross-sectional shape of the plate.

  After forming the metal grid 25, a transparent conductive layer 26 is formed by applying and drying a dispersion containing a conductive polymer and a self-dispersing polymer so as to cover the patterned thin metal wire layer. As a specific method in this case, the above-described liquid phase film forming method can be used.

  By making the intermediate layer of this embodiment a laminated structure composed of such a metal grid and a transparent conductive layer, high conductivity that cannot be obtained by the metal grid or the transparent conductive layer alone can be obtained uniformly in the electrode plane. Can do.

  Although the distance (line | wire width W) of the thin wires in a metal grid is 20-200 micrometers normally, Preferably it is 40-120 micrometers, More preferably, it is 40-80 micrometers. When the line width of the fine line is 20 μm or more, desired conductivity can be obtained. On the other hand, when the line width is 200 μm or less, desired transparency can be obtained. Moreover, although the height H of a thin wire | line is 0.1-2.0 micrometers normally, Preferably it is 0.2-1.5 micrometers, More preferably, it is 0.3-1.0 micrometer. When the height of the fine wire is 0.1 μm or more, desired conductivity can be obtained. On the other hand, when the height H of the thin wire is 2 μm or less, problems such as current leakage and poor film thickness distribution of each functional layer are unlikely to occur during device manufacture. Further, the aspect ratio H / W of the fine wire is usually 0.001 to 0.1, preferably 0.01 to 0.03. When the aspect ratio of the fine line is 0.001 or more, desired conductivity can be obtained. On the other hand, when the aspect ratio of the thin line is 0.1 or less, the performance of the element is hardly deteriorated. Furthermore, the cross-sectional area of the cross section of the fine wire in the direction perpendicular to the substrate is S, and the cross-sectional shape factor represented by S / (W × H) is usually 0.6 to 0.9, preferably 0.7. ~ 0.8. If the cross-sectional shape factor is smaller than 0.6, the cross-sectional shape of the fine line is close to a cone, and if it is larger than 0.9, it is close to a rectangle, but if it is in the range of 0.6 to 0.9, Current leakage is less likely to occur, and device defects are less likely to occur.

  After forming the metal grid, drying and heat treatment can be appropriately performed. The conditions for the drying treatment are not particularly limited, but the drying treatment is preferably performed at a temperature that does not damage the substrate and the metal grid. For example, a drying process can be performed at 80 to 120 ° C. for 10 seconds to 10 minutes. In this invention, after completion | finish of drying, by further heat-processing, the electroconductivity of a metal grid can be improved significantly and element performance improves. Furthermore, the scratch resistance and water resistance of the metal grid, and the adhesion between adjacent layers can be improved. The heat treatment is preferably performed at a temperature of 50 ° C. or more for 5 minutes or more, and if it is less than 50 ° C., the conductivity improvement effect can be reduced. Moreover, even if it is the temperature over 120 degreeC, you may perform the process for 0.001 second to several seconds, for example in the range which does not damage a board | substrate and a metal grid. The heat treatment may be performed on-line or off-line after forming the metal grid, but is preferably performed immediately after coating and drying from the viewpoint of improving conductivity.

The intermediate layer of this embodiment may include a metal grid having high conductivity and a transparent conductive layer having relatively low conductivity but higher transparency than the metal grid, but the surface ratio of the thin line portion of the metal grid at this time resistance is preferably not more than 100Ω ^/ cm 2 square, more preferably 10Ω ^/ cm 2 square or less, and more preferably not more than 5Ω ^/ cm 2 square. On the other hand, the surface resistivity of the transparent conductive layer is preferably not more than 10 ⁵ Ω ^/ cm 2 square, more preferably not more than 10 ⁴ Ω ^/ cm 2 square, or less 10 ³ Ω ^/ cm 2 square More preferably. These surface specific resistances can be measured according to, for example, JIS K6911, ASTM D257, etc., and can be easily measured using a commercially available surface resistivity meter.

  When the transparent conductive layer contains a hydroxyl group-containing non-conductive polymer, the ratio of the conductive polymer to the hydroxyl group-containing non-conductive polymer is as follows. The conductive polymer is preferably 30 to 900 parts by mass, and from the viewpoints of preventing current leakage, enhancing the conductivity of the hydroxyl group-containing nonconductive polymer, and transparency, the hydroxyl group-containing nonconductive polymer is 100 parts by mass. More preferably.

  The dry film thickness of the transparent conductive layer is preferably 30 nm to 2000 nm. From the viewpoint of conductivity, it is more preferably 100 nm or more, and from the viewpoint of surface smoothness of the intermediate layer, it is more preferably 200 nm or more. Moreover, it is more preferable that it is 1000 nm or less from the point of transparency.

  After applying the transparent conductive layer, a drying treatment can be appropriately performed. Although there is no restriction | limiting in particular as conditions of a drying process, It is preferable to dry-process at the temperature of the range which does not damage a board | substrate and a transparent conductive layer. For example, the drying treatment can be performed at 80 to 120 ° C. for 10 seconds to 10 minutes. In the present invention, after the drying is completed, the crosslinking reaction of the hydroxyl group-containing nonconductive polymer can be promoted and completed by further heat treatment. Thereby, the cleaning resistance and solvent resistance of the intermediate layer are remarkably improved, and the device performance is further improved.

  The heat treatment is preferably performed at a temperature of 50 to 120 ° C. for 30 minutes or more. If it is less than 50 ° C., the reaction promoting effect is small, and if it exceeds 120 ° C., the effect is small because thermal damage to the material increases. The treatment temperature is more preferably 80 to 120 ° C., and the treatment time is more preferably 1 hour or more. The upper limit of the treatment time is not particularly limited, but is preferably 24 hours or less from the viewpoint of productivity. The heat treatment may be performed on-line or off-line after applying and drying the metal grid. In the case of off-line, it is preferable to further perform under reduced pressure because it leads to accelerated drying of moisture.

  Moreover, the intermediate | middle layer of this form has high transparency. Specifically, the value of total light transmittance measured according to JIS K 7361-1: 1997 is preferably 75% or more, and more preferably 80% or more.

[Charge transport layer]
In the tandem organic photoelectric conversion element of this embodiment, the photoelectric conversion layer can be formed on the transport layer. In this transport layer, it is determined whether the top cell (cell on the light incident side) is a normal layer type or a reverse layer type, and which layer carries carriers of any polarity.

  In this embodiment, the transport layer may be either a hole transport layer or an electron transport layer. Hereinafter, materials for forming each layer will be described.

(Hole transport layer / electron block layer)
The organic photoelectric conversion element preferably has a hole transport layer between the photoelectric conversion layer and the anode. By disposing the hole transport layer, charges generated in the photoelectric conversion layer can be taken out more efficiently.

  As a material constituting the hole transport layer, for example, PEDOT-PSS made by Stark Vitec Co., Ltd., trade name BaytronP, polyaniline and its doped material, cyan compounds described in International Publication No. 2006/019270, etc. Can be used. Note that the hole transport layer having a LUMO level shallower than the LUMO level of the n-type organic semiconductor used for the photoelectric conversion layer has a rectifying effect that prevents electrons generated in the photoelectric conversion layer from flowing to the anode side. It has an electronic block function. Such a hole transport layer is also called an electron block layer, and it is preferable to use a hole transport layer having such a function. As such a material, a triarylamine compound described in JP-A-5-271166 or a metal oxide such as molybdenum oxide, nickel oxide, or tungsten oxide can be used. Moreover, the layer which consists only of p-type organic semiconductor used for the photoelectric converting layer can also be used. The means for forming these layers may be either a vacuum deposition method or a solution coating method, but is preferably a solution coating method. Forming a coating film in the lower layer before forming the photoelectric conversion layer is preferable because it has the effect of leveling the coating surface and reduces the influence of leakage and the like.

  As described above, when the hole transport layer is located in the lower layer of the metal grid, the hole transport layer is preferably crosslinked. In this case, a triarylamine compound having a crosslinking group having a crosslinking group, MoOx prepared by a sol-gel method, manufactured by Stark Vitec Co., Ltd. with a crosslinking agent added, PEDOT-PSS such as trade name BaytronP, polyaniline and its dope Materials, cyan compounds described in International Publication No. 2006/019270 pamphlet and the like can be preferably used.

(Electron transport layer / hole blocking layer)
The organic photoelectric conversion element of this embodiment preferably forms an electron transport layer in the photoelectric conversion layer and the cathode. By providing the electron transport layer, the charge generated in the photoelectric conversion layer can be taken out more efficiently.

  As a material constituting the electron transport layer, for example, octaazaporphyrin, a perfluoro body of a p-type organic semiconductor (perfluoropentacene, perfluorophthalocyanine, or the like) can be used. Note that the electron transport layer having a HOMO level deeper than the HOMO level of the p-type organic semiconductor used in the photoelectric conversion layer has a rectifying effect that prevents holes generated in the photoelectric conversion layer from flowing to the cathode side. It has a hole blocking function. Such an electron transport layer is also called a hole blocking layer, and it is preferable to use an electron transport layer having such a function. Examples of such materials include phenanthrene compounds such as bathocuproine, n-type organic semiconductors such as naphthalene tetracarboxylic acid anhydride, naphthalene tetracarboxylic acid diimide, perylene tetracarboxylic acid anhydride, perylene tetracarboxylic acid diimide, and titanium oxide. N-type inorganic oxides such as zinc oxide and gallium oxide, and alkali metal compounds such as lithium fluoride, sodium fluoride, and cesium fluoride can be used. Moreover, the layer which consists of a n-type organic semiconductor single-piece | unit used for the photoelectric converting layer can also be used. The means for forming these layers may be either a vacuum deposition method or a solution coating method, but is preferably a solution coating method.

  As described above, when the electron transport layer is located in the lower layer of the metal grid, the electron transport layer is preferably crosslinked. In this case, phenanthrene compounds such as bathocuproin having a cross-linking group as a material constituting the electron transport layer, naphthalene tetracarboxylic acid anhydride, naphthalene tetracarboxylic acid diimide, perylene tetracarboxylic acid anhydride, perylene tetracarboxylic acid diimide, etc. An n-type organic semiconductor, titanium oxide, zinc oxide and the like produced by a sol-gel method are preferably used.

  As described above, in the case of an inverted layer type element that is advantageous from the viewpoint of durability, the photoelectric conversion layer is formed after the electron transport layer is formed on the first electrode. A compound that is insoluble in the coating liquid to be contained is preferred as the electron transport material. From such a viewpoint, the electron transport material is preferably an inorganic substance such as titanium oxide or zinc oxide and a crosslinkable organic substance such as polyethyleneimine or an aminosilane coupling agent described in International Publication No. 2008-134492. Of these, aminosilane coupling agents (3- (2-aminoethyl) -aminopropyltrimethoxysilane, for example) are preferably used. That's right. In addition, APPLIED PHYSICS LETTERS 95 (2009), p043301, Adv. Funct. Mat. 2010, p. 1977, Adv. Mater. , 2011, 23, 3086, J.A. Am. Chem. Soc. , 2011, p. 8416, Advanced Materials, 2011 (Vol 23, no. 40), p4636-4643, and the following compounds, etc., which are soluble in alcohol solvents but not in aromatic solvents that dissolve the power generation layer Can also be preferably used.

[Photoelectric conversion layer]
The tandem photoelectric conversion element of this embodiment includes two or more photoelectric conversion layers, and these photoelectric conversion layers preferably have a bulk heterojunction structure including a p-type organic semiconductor and an n-type organic semiconductor. Hereinafter, the p-type organic semiconductor and the n-type organic semiconductor will be described.

(P-type organic semiconductor)
Examples of the p-type organic semiconductor used in the photoelectric conversion layer include various condensed polycyclic aromatic low-molecular compounds and conjugated polymers. The tandem organic photoelectric conversion element of this embodiment includes two or more photoelectric conversion layers. Therefore, it is preferable to use a p-type organic semiconductor suitable for each layer.

  Examples of the condensed polycyclic aromatic low molecular weight compound include anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, thacumanthracene, bisanthene, zeslene. , Heptazethrene, pyranthrene, violanthene, isoviolanthene, cacobiphenyl, anthradithiophene, etc., porphyrin, copper phthalocyanine, tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene ( BEDTTTTF) -perchloric acid complexes, and derivatives and precursors thereof.

  Examples of the derivative having the above-mentioned condensed polycycle include WO 03/16599 pamphlet, WO 03/28125 pamphlet, US Pat. No. 6,690,029, JP 2004-107216 A. A pentacene derivative having a substituent described in JP-A No. 2003-136964, a pentacene precursor described in US Patent Application Publication No. 2003/136964, and the like; Amer. Chem. Soc. , Vol127. No. 14.4986, J. MoI. Amer. Chem. Soc. , Vol. 123, p9482; Amer. Chem. Soc. , Vol. 130 (2008), no. 9, acene-based compounds substituted with a trialkylsilylethynyl group described in 2706 and the like.

  Examples of the conjugated polymer include a polythiophene such as poly-3-hexylthiophene (P3HT) and an oligomer thereof, or a technical group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007, P1225. Polythiophene, Nature Material, (2006) vol. 5, p328, polythiophene-thienothiophene copolymer, polythiophene-diketopyrrolopyrrole copolymer described in International Publication No. 2008/000664 pamphlet, Adv. Mater, 2007, p4160, polythiophene-thiazolothiazole copolymer, Adv. Mater. , Vol. 19 (2007) p2295, polythiophene-carbazole-benzothiadiazole copolymer (PCDTBT), Nature Mat. vol. 6 (2007), p497 described in PCPDTBT, etc., polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, Examples thereof include polymer materials such as σ-conjugated polymers such as polysilane and polygermane.

  In addition, oligomeric materials instead of polymer materials include thiophene hexamer α-sexual thiophene α, ω-dihexyl-α-sexual thiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3 Oligomers such as -butoxypropyl) -α-sexithiophene can be preferably used.

  The first photoelectric conversion layer (the light incident side, that is, the photoelectric conversion layer of the top cell is preferably a layer that absorbs a short wave region as compared with the second photoelectric conversion layer, specifically about 350 to 900 nm. Therefore, the absorption region of the p-type organic semiconductor used for the first photoelectric conversion layer is preferably about 350 to 900 nm, and light having a wavelength shorter than 350 nm. Is harmful to the substrate film, etc., and often provides an ultraviolet absorption function to the substrate itself, and it is substantially unnecessary to absorb light having a shorter wavelength than this. When the light of 900 nm or more is absorbed, the band of light that can be used by the second photoelectric conversion layer is reduced, so that the power generation current of the second photoelectric conversion layer is decreased, and as a result, the power generation of the entire tandem element is performed. Therefore, it is preferable to use a p-type organic semiconductor that absorbs light of 380 to 750 nm for the first photoelectric conversion layer. Any one having an absorption spectrum in such a range is suitable for the first photoelectric conversion layer, but preferably polythiophene such as poly-3-hexylthiophene (P3HT) and its oligomer, polyphenylene vinylene and its oligomer, polythieny. Lembinylene and its oligomer, Polythiophene-thienothiophene copolymer described in Nature Material, (2006) vol.5, p328, Polythiophene-thiazolothiazole copolymer described in Adv.Matter, 2007, p4160, Adv.Matter , Vol.19 (2007) Polythiophene-carbazole-benzothiadiazole copolymer (PCDTBT) described in p2295, pentacene or a derivative thereof, anthradithiophene and a derivative thereof, porphyrin, a benzoporphyrin or a derivative thereof, or a phthalocyanine derivative.

  On the other hand, the second photoelectric conversion layer is preferably a layer that can also absorb light in a long wave region as compared with the first photoelectric conversion layer, and specifically, light in a region of about 350 to 2000 nm. It is preferable that it is a layer which absorbs. Therefore, the absorption region of the p-type organic semiconductor used for the second photoelectric conversion layer is preferably about 350 to 2000 nm. Since light having a wavelength shorter than 350 nm is harmful to the substrate film or the like, the substrate itself is often provided with an ultraviolet absorbing function, and it is substantially unnecessary to absorb light having a wavelength shorter than this. In addition, a p-type organic semiconductor that absorbs light of 2000 nm or more is not preferable because the band gap becomes too small, the electromotive force is lowered, and improvement in power generation efficiency when tandemized cannot be expected. More preferably, it is a p-type organic semiconductor that absorbs light of 380 to 1200 nm. Specifically, the polythiophene-diketopyrrolopyrrole copolymer described in International Publication No. 2008/000664 pamphlet, Nature Mat. vol. 6 (2007), p497 described in PCPDTBT described in p497, APFO-Green1 described in APL2004v85p5081, porphyrin, benzoporphyrin or a derivative thereof, and a phthalocyanine derivative.

[N-type organic semiconductor]
The n-type organic semiconductor used in the tandem-type organic photoelectric conversion element of this embodiment is not particularly limited. For example, perfluoro compounds in which hydrogen atoms of the above-described p-type organic semiconductor such as fullerene and octaazaporphyrin are substituted with fluorine atoms. (Skeletons such as perfluoropentacene and perfluorophthalocyanine), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide, etc. The polymer compound etc. which are contained as can be mentioned.

  Among these, as the n-type organic semiconductor, it is preferable to use a fullerene derivative that can perform charge separation efficiently with various p-type organic semiconductors at high speed (up to 50 femtoseconds).

Fullerene derivatives include fullerene C ₆₀ , fullerene C ₇₀ , fullerene C ₇₆ , fullerene C ₇₈ , fullerene C ₈₄ , fullerene C ₂₄₀ , fullerene C ₅₄₀ , mixed fullerene, fullerene nanotube, multi-wall nanotube, single-wall nanotube, nanohorn (cone Type), etc., and some of these are hydrogen atoms, halogen atoms, substituted or unsubstituted alkyl groups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, cycloalkyl groups, silyl groups, ether groups, thioether groups, The fullerene derivative substituted by the amino group, the silyl group, etc. can be mentioned.

Among them, N-methylfullylpyrrolidine, [6,6] -phenyl C ₆₁ -butyric acid methyl ester (abbreviation PCBM) represented by the following formula, [6,6] -phenyl C ₆₁ -butyric acid-n-butyl ester (PCBnB) ), [6,6] - phenyl _{C 61} - butyric acid - isobutyl ester (PCBiB), [6,6] - phenyl _{C 61} - butyric acid -n- hexyl ester (PCBH), Adv. Mater. , Vol. 20 (2008), p2116, etc., aminated fullerenes such as JP-A 2006-199674, metallocene fullerenes such as JP-A 2008-130889, US Pat. No. 7,329,709, etc. Fullerene having a cyclic ether group such as Amer. Chem. Soc. , (2009) vol. 130, p15429, SIMEF, Appl. Phys. Lett. , Vol. 87 (2005), C ₆₀ MC12 described in p203504, and the like. It is preferable to use a fullerene derivative having a substituent and having improved solubility.

[Method for forming photoelectric conversion layer]
The method for forming the photoelectric conversion layer in this embodiment is not particularly limited, but as a method for forming the photoelectric conversion layer having a bulk heterojunction structure in which the above-described p-type organic semiconductor and n-type organic semiconductor are mixed, an evaporation method, Examples thereof include a coating method (including a casting method and a spin coating method). Among these, in order to increase the area of the interface where charges are separated from holes and electrons and to produce a device having high photoelectric conversion efficiency, it is preferable to employ a coating method. The coating method is also excellent in improving the production rate.

  After applying a coating solution containing a p-type organic semiconductor and an n-type organic semiconductor, heating may be performed to remove residual solvent, moisture, and gas, and improve mobility and increase absorption longwave by crystallization of the semiconductor. preferable. When annealing is performed at a predetermined temperature during the manufacturing process, a part of the particles is microscopically aggregated or crystallized, and the bulk heterojunction structure of the photoelectric conversion layer can be made into an appropriate phase separation structure. As a result, carrier mobility in the photoelectric conversion layer is improved, and high photoelectric conversion efficiency can be obtained.

  The photoelectric conversion layer may be a single layer in which a p-type organic semiconductor and an n-type organic semiconductor are uniformly mixed, but a plurality of layers having different mixing ratios with the p-type organic semiconductor and the n-type organic semiconductor are stacked. You may have the structure which consists of.

[electrode]
The organic photoelectric conversion element of this embodiment essentially includes a first electrode and a second electrode. Therefore, the first electrode may function as an anode and the second electrode may function as a cathode. Conversely, the first electrode may function as a cathode and the second electrode may function as an anode. is there. Carriers (holes / electrons) generated in the photoelectric conversion layer 14 move between the electrodes, and the holes reach the anode 12 and the electrons reach the cathode 16. In the present invention, an electrode through which holes mainly flow is called an anode, and an electrode through which electrons mainly flow is called a cathode. Furthermore, from the functional aspect of whether or not the electrode has translucency, the translucent electrode is sometimes referred to as a transparent electrode, and the non-translucent electrode is sometimes referred to as a counter electrode. In the normal layer type of FIG. 1, the anode is usually a transparent electrode having a light transmitting property, and the cathode is a counter electrode having no light transmitting property.

  The material used for the electrode of this embodiment is not particularly limited as long as it is driven as a photoelectric conversion element, and an electrode material that can be used in this technical field can be appropriately employed. In particular, the anode is preferably composed of a material having a relatively large work function compared to the cathode, and conversely, the cathode is preferably composed of a material having a relatively small work function compared to the anode. Note that in the case where a charge transport layer (a hole transport layer or an electron transport layer) is present, it functions sufficiently as a photoelectric conversion element even in a form other than the above.

  In the organic photoelectric conversion element 10 shown in FIG. 1 described above, the anode 11 has a relatively large work function and is transparent (preferably has a transmittance of 80% or more for visible light of 380 to 800 nm). It is preferable that it is comprised from a material. On the other hand, the cathode 12 has a relatively small work function (for example, 4 eV or less), and can usually be composed of an electrode material having low translucency.

In the organic photoelectric conversion element 10 shown in FIG. 1, examples of electrode materials used for the anode (transparent electrode) include metals such as gold, silver, and platinum; indium tin oxide (ITO), SnO _2. Transparent conductive metal oxides such as ZnO; carbon materials such as metal nanowires and carbon nanotubes. It is also possible to use a conductive polymer as the anode electrode material. Examples of the conductive polymer that can be used for the anode include PEDOT-PSS, polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polyphenyl. Examples include acetylene, polydiacetylene, polynaphthalene, and derivatives thereof. These electrode materials may be used alone or as a mixture of two or more materials. Also, the shape of these materials is not particularly limited, and can be used in the form of nanoparticles, nanowires, ultrathin films and the like. Furthermore, it is also possible to constitute an electrode by laminating two or more layers made of each material. In the present invention, a crude product composed of a self-dispersing polymer and a conductive polymer, which is described as an intermediate layer, and a transparent conductive film in which a metal grid is combined with these are also the first and second in the present invention. It can be used as an electrode.

On the other hand, in the organic photoelectric conversion element of FIG. 1, an alloy, an electron conductive compound, and a mixture thereof can be used as an electrode material used for the cathode (counter electrode). Specifically, sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, indium, Examples include lithium / aluminum mixtures and rare earth metals. Of these, a mixture of a first metal having a low work function and a second metal, which is a metal having a larger work function and more stable than the first metal, from the viewpoint of electron extraction performance and durability against oxidation, etc. For example, it is preferable to use a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, a lithium / aluminum mixture, aluminum which is a stable metal, or the like. In addition, it is also preferable to use a metal among these materials, so that light that is incident from the first electrode side and transmitted without being absorbed by the photoelectric conversion layer is reflected by the second electrode and is regenerated for photoelectric conversion. The photoelectric conversion efficiency can be improved. Also, the shape of these materials is not particularly limited, and can be used in the form of nanoparticles, nanowires, ultrathin films and the like. Furthermore, it is also possible to constitute an electrode by laminating two or more layers made of each material.

  In the organic photoelectric conversion element shown in FIG. 2, the cathode 12 is located on the substrate 25 side where light enters, and the anode 11 is located on the opposite side. Therefore, the anode 11 shown in FIG. 2 is preferably composed of an electrode material having a relatively large work function and usually low translucency. On the other hand, the cathode 12 has a relatively small work function and is made of a transparent electrode material.

In the organic photoelectric conversion element of FIG. 2, examples of the electrode material used for the cathode (transparent electrode) include metals such as gold, silver, copper, platinum, rhodium, ruthenium, aluminum, magnesium, indium, tin, and zinc, Metal compounds and alloys (specifically, indium tin oxide (ITO), SnO ₂ , ZnO, IDIXO (In ₂ O ₃ —ZnO)); carbon nanoparticles, carbon nanowires, carbon nanostructures, etc. And carbon materials. These electrode materials may be used alone or as a mixture of two or more materials. Also, the shape of these materials is not particularly limited, and can be used in the form of nanoparticles, nanowires, ultrathin films and the like. Furthermore, it is also possible to constitute an electrode by laminating two or more layers made of each material. Among these, it is preferable to use carbon nanowires because a transparent and highly conductive cathode can be formed by a coating method. Moreover, when using a metal-type material, gold | metal | money, silver, copper, iron, nickel, chromium, aluminum, or these alloys (aluminum alloy), metal compound (on the side facing an anode (counter electrode), for example After preparing an auxiliary electrode (also referred to as a grid electrode or a bus line electrode) using a silver compound) or the like, the conductive polymer exemplified as the anode (transparent electrode) material of the organic photoelectric conversion element in FIG. By providing this film, a cathode (transparent electrode) can be obtained. By providing the auxiliary electrode in this way, it is possible to suppress the reduction of the fill factor (FF) that occurs when the element has a large area.

  On the other hand, in the organic photoelectric conversion element of FIG. 2, examples of the electrode material used for the anode (counter electrode) include silver, nickel, molybdenum, gold, platinum, tungsten, and copper.

The sheet resistance of the first electrode and the second electrode is not particularly limited, is preferably from several hundred Ω ^/ cm 2 square, more preferably less 50Ω ^/ cm 2 square, more preferably less 15Ω ^/ cm 2 square . In addition, the lower limit of the sheet resistance of the first electrode and the second electrode is not particularly limited, but it is generally preferable that the sheet resistance is as low as possible within a range showing 80% or more transmittance with respect to visible light having a wavelength of 380 to 800 nm. . Normally 0.01 Ohm ^/ cm 2 square or more, preferably it is possible to obtain the effect of the present invention as long as 0.1Ω ^/ cm 2 square or more. Here, the sheet resistance of the first electrode and the second electrode may be the same or different. Further, the film thicknesses of the first electrode and the second electrode are not particularly limited and vary depending on the material, but are usually 10 to 1000 nm, preferably 100 to 200 nm, from the viewpoint of light transmittance or resistance. It can be set appropriately by those skilled in the art. Here, the film thicknesses of the first electrode and the second electrode may be the same or different.

Further, the sheet resistance when having an auxiliary electrode, is preferably not more than 10Ω ^/ cm 2 square, and more preferably 0.01~8Ω ^/ cm 2 square. In this case, the sheet resistance is determined by the shape (line width, height, pitch, shape) of the auxiliary electrode, and even if a material having higher resistance than the auxiliary electrode is used, the resistance of the window portion is hardly affected.

(substrate)
The organic photoelectric conversion element of the present invention may include a substrate as necessary. The substrate has a role as a member to be coated with a coating solution when the electrode is formed by a coating method.

  When light that is photoelectrically converted enters from the substrate side, the substrate is preferably a member that can transmit the light that is photoelectrically converted, that is, a member that is transparent to the wavelength of the light to be photoelectrically converted. As the substrate, for example, a glass substrate, a resin substrate and the like are preferably mentioned, but it is desirable to use a transparent resin film from the viewpoint of light weight and flexibility.

  There is no restriction | limiting in particular in the transparent resin film which can be preferably used as a transparent substrate by this invention, The material, a shape, a structure, thickness, etc. can be suitably selected from well-known things. For example, polyolefins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester resin film such as modified polyester, polyethylene (PE) resin film, polypropylene (PP) resin film, polystyrene resin film, cyclic olefin resin, etc. Resin films, vinyl resin films such as polyvinyl chloride and polyvinylidene chloride, polyether ether ketone (PEEK) resin films, polysulfone (PSF) resin films, polyether sulfone (PES) resin films, polycarbonate (PC) resin films , Polyamide resin film, polyimide resin film, acrylic resin film, triacetyl cellulose (TAC) resin film, and the like. If the resin film transmittance of 80% or more in from zero to eight hundred nanomolar), can be preferably applied to a transparent resin film according to the present invention. Among these, from the viewpoint of transparency, heat resistance, ease of handling, strength and cost, it is preferably a biaxially stretched polyethylene terephthalate film, a biaxially stretched polyethylene naphthalate film, a polyethersulfone film, or a polycarbonate film, and biaxially stretched. More preferred are polyethylene terephthalate films and biaxially stretched polyethylene naphthalate films.

  The transparent substrate used in the present invention can be subjected to a surface treatment or an easy adhesion layer in order to ensure the wettability and adhesiveness of the coating solution. A conventionally well-known technique can be used about a surface treatment or an easily bonding layer. For example, the surface treatment includes surface activation treatment such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and laser treatment. Examples of the easy adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer.

  In order to suppress permeation of oxygen and water vapor, a barrier coat layer may be formed in advance on the transparent substrate.

(Other layers)
The organic photoelectric conversion device of this embodiment may further include other members (other layers) in addition to the above-described members (each layer) in order to improve photoelectric conversion efficiency and improve the lifetime of the device. . Examples of other members include a hole injection layer, an electron injection layer, an exciton block layer, a UV absorption layer, a light reflection layer, and a wavelength conversion layer. Further, a layer such as a silane coupling agent may be provided in order to make the metal oxide fine particles unevenly distributed in the upper layer more stable. Further, a metal oxide layer may be laminated adjacent to the photoelectric conversion layer of the present invention.

  Moreover, the organic photoelectric conversion element of this invention may have various optical function layers for the purpose of more efficient light reception of sunlight. Examples of the optical functional layer include a condensing layer such as an antireflection film and a microlens array, and a light diffusion layer that can scatter the light reflected by the cathode and make it incident on the photoelectric conversion layer again.

  Various known antireflection layers can be provided as the antireflection layer. For example, when the transparent resin film is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy adhesion layer adjacent to the film is 1.57. It is more preferable to set it to ˜1.63 because the interface reflection between the film substrate and the easy adhesion layer can be reduced and the transmittance can be improved. The method for adjusting the refractive index can be carried out by appropriately adjusting the ratio of the oxide sol having a relatively high refractive index such as tin oxide sol or cerium oxide sol and the binder resin. The easy adhesion layer may be a single layer, but may be composed of two or more layers in order to improve adhesion.

  As the condensing layer, for example, it is processed so as to provide a structure on the microlens array on the sunlight receiving side of the support substrate, or the amount of light received from a specific direction is increased by combining with a so-called condensing sheet. Conversely, the incident angle dependency of sunlight can be reduced.

  As an example of the microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are two-dimensionally arranged on the light extraction side of the substrate. One side is preferably 10 to 100 μm. If it becomes smaller than this, the effect of diffraction will generate | occur | produce and color, and if too large, thickness will become thick and is not preferable.

  Examples of the light scattering layer include various antiglare layers, layers in which nanoparticles or nanowires such as metals or various inorganic oxides are dispersed in a colorless and transparent polymer, and the like.

<Method for producing organic photoelectric conversion element>
The manufacturing method of the tandem organic photoelectric conversion element of the above-described embodiment is not particularly limited, and can be manufactured by appropriately referring to conventionally known methods. Hereinafter, a method for manufacturing an element having the reverse layer type will be described. However, it is possible to manufacture an element having a normal layer or a series / parallel structure by appropriately changing the order of the steps.

  The manufacturing method of the tandem organic photoelectric conversion device of this embodiment includes a step of forming a cathode and a step of forming two or more photoelectric conversion layers containing a p-type organic semiconductor material and an n-type organic semiconductor material on the cathode. And a step of forming an anode on the two or more photoelectric conversion layers. Hereinafter, each process of the manufacturing method of the tandem organic photoelectric conversion element of this form is demonstrated in detail.

  In the manufacturing method of this embodiment, first, a cathode is formed. The method of forming the cathode is not particularly limited, but is easy to operate and can be produced by roll-to-roll using a device such as a die coater. Preferably, the method is a method of applying and drying. Besides this, a commercially available thin film electrode material may be used as it is.

  After forming the cathode as described above, an electron transport layer may be formed on the cathode as necessary. The means for forming the electron transport layer may be either vapor deposition or solution coating, but is preferably solution coating. When forming an electron transport layer using a solution coating method, a solution in which the above-described electron transport material is dissolved and dispersed in a suitable solvent is coated on the cathode using a suitable coating method and dried. That's fine. The coating methods used for the solution coating method include cast method, spin coating method, blade coating method, wire bar coating method, gravure coating method, spray coating method, dipping (dipping) coating method, bead coating method, air knife coating method. Ordinary methods such as a curtain coating method, an ink jet method, a screen printing method, a relief printing method, an intaglio printing method, an offset printing method, a flexographic printing method, and a Langmuir-Blodgett (LB) method can be used. Among these, it is particularly preferable to use a spin coating method or a blade coating method. In addition, although the solid content concentration of the solution used for the coating method may vary depending on the coating method and the film thickness, it is preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass. Further, the temperature of the coating solution and / or the coating surface during coating is not particularly limited, but is preferably 30 to 120 ° C. from the viewpoint of preventing precipitation and unevenness due to temperature fluctuations during coating and drying. More preferably, it is 50-120 degreeC. Furthermore, there is no restriction | limiting in particular also about the specific form of drying, A conventionally well-known knowledge can be referred suitably. An example of the drying (heat treatment) condition is exemplified by a condition of about 90 to 120 ° C. and about 5 to 90 minutes. Examples of the apparatus used for drying include a hot plate, hot air drying, an infrared heater, a microwave, and a vacuum dryer. Of course, other drying apparatuses can be used.

  Subsequently, a photoelectric conversion layer including a p-type organic semiconductor and an n-type organic semiconductor is formed on the cathode or the electron transport layer formed as described above. A specific method for forming the photoelectric conversion layer is not particularly limited, but preferably, a solution in which a p-type organic semiconductor and an n-type organic semiconductor are dissolved or dispersed in an appropriate solvent, respectively or collectively. Then, it may be applied on the cathode using an appropriate application method (the specific form is as described above) and dried. After that, it is preferable to perform heating in order to cause removal of residual solvent, moisture and gas, and improvement of mobility and absorption longwave by crystallization of the semiconductor material. When annealing is performed at a predetermined temperature during the manufacturing process, a part of the particles is microscopically aggregated or crystallized, and the photoelectric conversion layer can have an appropriate phase separation structure. As a result, the mobility of holes and electrons (carriers) in the photoelectric conversion layer is improved, and high efficiency can be obtained. In this manner, the p-type organic semiconductor and the n-type organic semiconductor are uniformly mixed, and a bulk heterojunction type organic photoelectric conversion element can be obtained.

  On the other hand, in the case of forming a photoelectric conversion layer (for example, a pin structure) composed of a plurality of layers having different mixing ratios of the p-type organic semiconductor and the n-type organic semiconductor, the first layer is applied and dried sequentially. It is also possible to form by applying with a blade coater.

  In the case of forming a photoelectric conversion layer containing polyalkyleneimine, for example, a solution in which P-type organic semiconductor and / or n-type organic semiconductor, polyalkyleneimine and polyalkyleneimine are dissolved and dispersed in an appropriate solvent is prepared and applied. What is necessary is just to dry.

  The step of forming the photoelectric conversion layer is preferably performed in a glove box under a nitrogen atmosphere so as not to be exposed to oxygen or moisture. Thus, by performing in a nitrogen atmosphere, it is possible to prevent the p-type organic semiconductor from being deteriorated by oxygen or moisture in the air, and to increase the durability of the element.

  Note that this embodiment is characterized by having two or more photoelectric conversion layers, but an intermediate layer is formed between the photoelectric conversion layers by the above-described method.

  Next, an anode is formed on the photoelectric conversion layer formed above. The means for forming the anode is not particularly limited and may be either a vapor deposition method or a solution coating method, but a vapor deposition method (for example, a vacuum vapor deposition method) is preferably used.

  Furthermore, when providing a positive hole transport layer between a photoelectric converting layer and an anode, a positive hole transport layer is formed using the vapor deposition method or the solution coating method, Preferably the solution coating method. In addition, it is preferable to perform the process of forming the said positive hole transport layer within the glove box of nitrogen atmosphere similarly to the process of forming the said photoelectric converting layer. Thus, by performing in nitrogen atmosphere, it can prevent that a photoelectric converting layer deteriorates with the oxygen or water | moisture content in air | atmosphere, and can improve durability of an element.

  Furthermore, when layers other than the various layers described above are included, a step for forming these layers can be appropriately added by using a solution coating method, a vapor deposition method, or the like. Further, if necessary, a charge transport layer (electron transport layer / hole transport layer) is further disposed between the first photoelectric conversion layer and the intermediate layer and between the second photoelectric conversion layer and the intermediate layer. May be.

  The electrodes (cathode / anode), photoelectric conversion layer, hole transport layer, electron transport layer, and the like can be patterned as necessary. The patterning method is not particularly limited, and a known method can be appropriately applied. For example, when patterning soluble materials used in bulk heterojunction type photoelectric conversion layers, hole transport layers, electron transport layers, etc., only unnecessary portions may be wiped after the entire surface of die coating, dip coating, etc. Alternatively, patterning may be performed by ablation using a carbonic acid laser or the like after film formation, by direct scraping with a scriber, or by direct patterning at the time of coating using a method such as an inkjet method or screen printing. . On the other hand, in the case of insoluble materials used in electrodes, etc., vacuum deposition method, vacuum sputtering method, plasma CVD method, screen printing method using ink in which fine particles of electrode material are dispersed, gravure printing method, ink jet method, etc. Various printing methods, and known methods such as etching or lift-off of the deposited film can be used. Alternatively, the pattern may be formed by transferring a pattern formed on another substrate.

  Moreover, the organic photoelectric conversion element of this embodiment can be sealed as necessary in order to prevent deterioration due to oxygen, moisture, and the like in the environment. There is no restriction | limiting in particular in the method of sealing, It can carry out by the well-known method used with an organic photoelectric conversion element, an organic electroluminescent element, etc. For example, (1) a method of sealing a cap made of aluminum or glass by bonding with an adhesive; (2) a plastic film on which a gas barrier layer such as aluminum, silicon oxide or aluminum oxide is formed and organic photoelectric conversion (3) A method of spin-coating an organic polymer material (polyvinyl alcohol, etc.) having a high gas barrier property; (4) An inorganic thin film (silicon oxide, aluminum oxide, etc.) having a high gas barrier property Alternatively, a method of depositing an organic film (parylene or the like) under vacuum; and a method of laminating these in a composite manner can be used.

  Furthermore, the organic photoelectric conversion element of this embodiment may have a configuration in which the entire element is sealed with two substrates with a barrier from the viewpoint of improving energy conversion efficiency and element lifetime, and preferably includes a moisture getter, an oxygen getter, and the like. It is more preferable that the configuration is as described above.

<Uses of organic photoelectric conversion elements>
According to the other form of this invention, the solar cell which has the above-mentioned tandem type | mold organic photoelectric conversion element is provided. Since the tandem organic photoelectric conversion element of this embodiment can achieve excellent durability and photoelectric conversion efficiency, it can be suitably used for a solar cell using this as a power generation element.

  According to still another aspect of the present invention, there is provided an optical sensor array in which the above-described tandem organic photoelectric conversion elements are arranged in an array. That is, the tandem organic photoelectric conversion element of this embodiment can be used as an optical sensor array that converts an image projected on the optical sensor array into an electrical signal by using the photoelectric conversion function.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
<Synthesis of hole blocking layer material / compound 1>

Adv. Mater. Compound B was synthesized with reference to 2007, 19, 2010. Compound B had a weight average molecular weight of 4,400. 1.0 g of Compound B and 9.0 g of 3,3′-iminobis (N, N-dimethylpropylamine) (manufactured by Aldrich) were dissolved in a mixed solvent of 100 ml of tetrahydrofuran and 100 ml of N, N-dimethylformamide, and room temperature ( The reaction was carried out at 48 ° C. for 48 hours. After completion of the reaction, the solvent was distilled off under reduced pressure, and further reprecipitation was performed in water to obtain 1.3 g of Compound 15 (yield 90%). The structure of the obtained compound was identified by ¹ H-NMR. The results are shown below.

  7.6-8.0 ppm (br), 2.88 ppm (br), 2.18 ppm (m), 2.08 ppm (s), 1.50 ppm (m), 1.05 ppm (br).

<Evaluation of tandem organic photoelectric conversion elements with reverse layer and parallel connection>
[Preparation of organic photoelectric conversion device TC-101] (Example)
An organic photoelectric conversion device was prepared with reference to the pamphlet of International Publication No. 2008/134492. On a polyethylene terephthalate (PET) substrate, an indium tin oxide (ITO) transparent conductive film 150 nm deposited as a first electrode (sheet resistance 12 Ω / cm ² square) is subjected to normal photolithography technology and wet etching. The first electrode was formed by patterning to a width of 10 mm. The patterned first electrode was cleaned in the order of ultrasonic cleaning with a surfactant and ultrapure water, followed by ultrasonic cleaning with ultrapure water, dried with nitrogen blow, and finally subjected to ultraviolet ozone cleaning. Thereafter, the substrate was brought into the glove box and operated in a nitrogen atmosphere.

  On this first electrode, 0.05 wt% methoxyethanol solution of 3- (2-aminoethyl) -aminopropyltrimethoxysilane manufactured by Aldrich was used with a blade coater so that the dry film thickness was about 5 nm. The coating was dried. Thereafter, a heat treatment was performed on a hot plate at 120 ° C. for 1 minute to form a first electron transport layer.

  Next, p-type organic semiconductor P3HT (manufactured by BASF: regioregular poly-3-hexylthiophene) is added to o-dichlorobenzene by 1.5 mass%, and n-type organic semiconductor PC61BM (frontier carbon nanom spectra E100H). ) Was mixed at 1.2% by mass, dissolved by stirring overnight while heating to 80 ° C. on a hot plate, and then applied using a blade coater to a dry film thickness of about 200 nm. The film was dried at 80 ° C. for 2 minutes to form a first photoelectric conversion layer.

After the drying of the first photoelectric conversion layer is completed, it is taken out again into the atmosphere, and then, as a hole transport layer, PEDOT-PSS (CLEVIOS (registered trademark) PVP AI 4083, made by Helios Co., Ltd.) composed of a conductive polymer and a polyanion. , Conductivity 1 × 10 ⁻³ S / cm) was prepared by diluting with an equal amount of isopropanol, and applied and dried using a blade coater so that the dry film thickness was about 30 nm. Thereafter, heat treatment was performed with warm air of 90 ° C. for 20 seconds to form a first hole transport layer (organic material layer) made of an organic substance. The atmospheric temperature and relative humidity at the time of application were 23 ° C. and 65%.

  Next, a TEC-PR type manufactured by InkTec Co., Ltd. is used with a gravure plate having a shape with a fine line width of 50 μm, a fine line depth of 15 μm, and a line interval of 1000 μm on the first hole transport layer formed with the above-described series of functional layers Was used as an ink and an Ag metal fine line pattern was printed. Subsequently, it was dried on a hot plate at 120 ° C. for 30 minutes to produce a grid-like fine metal wire pattern (metal grid). The fine line pattern after printing had a height of 0.6 μm and a line width of 60 μm.

  On the metal grid, a coating solution containing the following conductive polymer and self-dispersing polymer was applied to a wet film thickness of 10 μm and dried at 90 ° C. for 1 minute. Thereafter, a heat treatment was performed on a hot plate at 120 ° C. for 30 minutes to form a transparent conductive layer. In addition, the intermediate layer consisting of the metal grid and the transparent conductive layer is formed directly on a part of the PET substrate (portion where there is no photoelectric conversion layer, etc.), and the transparency, conductivity, etc. of the intermediate layer itself are controlled by the method described later. evaluated.

(Coating liquid containing conductive polymer and self-dispersing polymer)
Conductive polymer: PEDOT-PSS CLEVIOS PH510 (solid content concentration 1.89%, manufactured by HC Starck) 1.59 g (0.14 g)
Self-dispersing polymer (binder): Vylonal MD1245 (30% solid content aqueous solution) 0.23 g (0.07 g)
Dimethyl sulfoxide (DMSO) 0.16g
The above components were mixed to prepare a coating solution. The pH of the coating solution was 2.

  Subsequently, while a PEDOT-PSS (Clevios (registered trademark) P4083, manufactured by Heraeus) dispersion was filtered through a 0.45 μm PVDF filter, a blade coater was used so that the film thickness was 30 nm on the intermediate layer. It was applied and dried. Furthermore, it was made to dry at 120 degreeC for 5 minute (s), and the 2nd positive hole transport layer was formed.

Subsequently, to o-dichlorobenzene, J.P. AM. CHEM. SOC. PSBTBT synthesized based on 2008, 130, p16144, and PC ₆₁ BM (manufactured by Frontier Carbon Co., E100H: 6,6-phenyl-C ₆₁ -butyric acid methyl ester) were mixed at 1: 1 (mass ratio). The above second hole transport using a blade coater so that the dry film thickness is about 100 nm while filtering the solution A in which 3.0% by mass is dissolved with a 0.45 μm PTFE filter. A film was formed on the layer to form a second photoelectric conversion layer.

  Subsequently, a solution in which the synthesized hole blocking layer material / compound 1 is dissolved in butanol: hexafluoroisopropanol = 1: 1 so as to be 0.02% by mass is prepared so that the dry film thickness becomes about 5 nm. Then, a second electron transport layer was formed by coating and drying using a blade coater.

Next, the substrate on which the series of functional layers is formed is moved into a vacuum deposition apparatus chamber, the inside of the vacuum deposition apparatus is depressurized to 1 × 10 ⁻⁴ Pa or less, and then Ag is deposited at a deposition rate of 1.0 nm / second. A second electrode (counter electrode; cathode) was formed by laminating 100 nm of metal. The obtained organic photoelectric conversion element was moved to a nitrogen chamber, and sealing was performed using a sealing cavity glass and a UV curable resin (manufactured by Nagase ChemteX Corporation, UV RESIN XNR5570-B1). An organic photoelectric conversion element TC-101 having a size of × 20 mm was completed.

[Production of Organic Photoelectric Conversion Elements TC-102 to TC-106, 110 to 113]
In the preparation of TC-101, the self-dispersing polymer (binder) was changed to the one shown in Table 1 (TC-113 has no binder), and the solid content concentration of the self-dispersing polymer (binder) was 0 after drying. Organic photoelectric conversion elements TC-102 to TC-106, 110 to 113 were produced in the same manner as TC-101 except that the amount was changed to 0.07 g. Nypol LX435 used for TC112 is a non-self-dispersing polymer (including a surfactant) manufactured by Nippon Zeon Seiyaku.

[Production of Organic Photoelectric Conversion Element TC-107]
In the production of TC-101, the organic photoelectric conversion element TC was made in the same manner as TC-101 except that the conductive polymer PH510 was changed to 0.5 g of polyaniline M (solid content concentration 6.0%, T-Chemical). -107 was produced.

[Production of Organic Photoelectric Conversion Element TC-108]
Adv. Mater. , 2002, 14, 833 to 837, by using PVP K30 (molecular weight 50,000; manufactured by ISP), silver nanowires having an average minor axis of 75 nm and an average length of 35 μm were produced. After silver nanowires are filtered and washed using a filtration membrane, hydroxypropylmethylcellulose 60SH-50 (manufactured by Shin-Etsu Chemical Co., Ltd.) is redispersed in an aqueous solution containing 25% by mass of the silver nanowires. Was prepared.

  And in preparation of the said TC-101, formation of the metal fine wire pattern was formed by using the said silver nanowire dispersion liquid instead of a vapor deposition method.

The silver nanowire dispersion is applied using a bar coating method so that the basis weight of the silver nanowire is 0.06 g / m ^2, and dried and heated at 110 ° C. for 5 minutes. A substrate was produced. Then, organic photoelectric conversion element TC-108 was produced like TC-101 except having formed the random network structure of silver nanowire on the 1st positive hole transport layer by heating at 120 ° C for 30 minutes. .

[Production of Organic Photoelectric Conversion Element TC-109]
In the production of TC-101, an organic photoelectric conversion element TC-109 was produced in the same manner as TC-101 except that the forming material of the metal fine line pattern was changed from silver to copper.

[Production of Organic Photoelectric Conversion Element TC-114] (Comparative Example)
In the production of the TC-113 (without self-dispersing polymer), the organic fine wire pattern was formed in the same manner as in the TC-113 except that the material for forming the metal fine line pattern was changed from silver to gold and a 12 nm uniform thin film was used instead of the pattern. A photoelectric conversion element TC-114 was produced.

<Evaluation of tandem organic photoelectric conversion elements connected in series>
[Production of Organic Photoelectric Conversion Element TC-115] (Comparative Example)
It was produced with reference to Patent Document 4 above. After carrying out the formation and cleaning of the transparent conductive film in the same manner as in the production of TC-101, the first electron transport layer was titrated with titania sol (PASOL HPW-10R manufactured by Catalyst Chemical Industry Co., Ltd.) 4 times with water. The diluted solution was applied by blade coating and heated in air at 120 ° C. for 10 minutes to obtain a first electron transport layer (film thickness: about 20 nm).

  Then, the coating liquid for photoelectric conversion layer formation which consists of PSBTBT used by preparation of organic photoelectric conversion element TC-101 was apply | coated by spin coating, and the photoelectric conversion layer (film thickness of about 100 nm) of the top cell of an organic thin film solar cell Got. A solution was prepared by mixing 1.5% by mass of P3HT (manufactured by BASF: regioregular poly-3-hexylthiophene) and 1.2% by mass of PC61BM which is an n-type organic semiconductor (nanom spectra E100H made by Frontier Carbon). Then, the mixture was stirred and dissolved overnight while heating on a hot plate at 80 ° C., then applied using a blade coater so that the dry film thickness was about 200 nm, dried at 80 ° C. for 2 minutes, and the first photoelectric A conversion layer was formed.

  Next, an OC1200 solution (manufactured by Plextronics, trade name Plexcore OC1200, purchased from Sigma-Aldrich) was applied by spin coating to obtain a hole transport layer (film thickness of about 50 nm). When the pH of the OC1200 solution was measured with a pH test paper (manufactured by Advantech Toyo Corporation, product name “Universal”, model number “07011030”), the pH was 7. Thereafter, 2 nm of gold was vapor-deposited as an intermediate layer (charge recombination layer) by a vacuum vapor deposition machine. Thereafter, a solution obtained by diluting titania sol (PASOL HPW-10R manufactured by Catalytic Chemical Industry Co., Ltd.) 4 times with water was applied by spin coating to obtain an electron transport layer (film thickness: about 20 nm). Note that no heat treatment was performed. Then, the said composition 1 was apply | coated by spin coating, and the photoelectric conversion layer (film thickness of about 100 nm) of the bottom cell of an organic thin film solar cell was obtained. An OC1200 solution (manufactured by Plextronics, trade name Plexcore OC1200, purchased from Sigma-Aldrich) was applied by spin coating, and finally, Al was vapor-deposited to a thickness of 100 nm as an anode by a vacuum vapor deposition machine, and the organic photoelectric conversion element TC -114 was produced.

[Production of Organic Photoelectric Conversion Element TC-116] ( Reference Example)
In the production of the organic photoelectric conversion element TC-115, instead of depositing 2 nm of gold as an intermediate layer (charge recombination layer), a charge recombination layer was formed using the coating solution used in TC-105. An organic photoelectric conversion element TC-116 connected in series was created.

<Evaluation of intermediate layer>
When the intermediate layer was formed, an evaluation was performed using a portion in which only a partial intermediate layer was formed on the PET substrate.

(Dispersion particle size)
The average value of the dispersed particles of the coating liquid containing the conductive polymer and the self-dispersing polymer was measured using a dynamic light scattering photometer DLS-8000 manufactured by Otsuka Electronics.

(transparency)
Based on JIS K 7361-1: 1997, total light transmittance was measured using HAZE METER NDH5000 manufactured by Tokyo Denshoku Co., Ltd., and evaluated according to the following criteria. In addition, in order to use as an intermediate | middle layer, it is preferable that it is 75% or more.

◎: 80% or more ○: 75% or more and less than 80% △: 70% or more and less than 75% ×: less than 70% (surface resistance)
The surface resistance was measured using a resistivity meter (Loresta GP (MCP-T610 type): manufactured by Dia Instruments Co., Ltd.) in accordance with JIS K 7194: 1994. The surface resistance is preferably 100 Ω / cm ² square (□) or less, and is preferably 30 Ω / cm ² square or less in order to increase the area of the device.

(Surface roughness (Ra, Ry))
Using an AFM (Seiko Instruments SPI3800N probe station and SPA400 multifunctional unit) and using a sample cut to a size of about 1 cm square, the surface roughness specified in the above method (JIS B601 (1994)). ).

(Membrane strength)
The strength of the conductive layer film was evaluated by a tape peeling method.

  Crimping / peeling was repeated 10 times on the conductive layer using a Scotch tape manufactured by Sumitomo 3M Co., and the dropping of the conductive layer was visually observed and evaluated according to the following criteria.

◎: No change after 5 times of pressure bonding / peeling ○: No change after 3 times of pressure peeling / bonding △: Peeling is observed after 1 time of pressure peeling, but more than 80% pattern remains ×: 1 time of pressure peeling Peeling is observed, and the remaining pattern is less than 80%. <Evaluation of organic photoelectric conversion element>
(Evaluation of photoelectric conversion efficiency)
The organic photoelectric conversion element sealed prepared above, was irradiated with light having an intensity of 100 mW / cm ² solar simulator (AM1.5G filter), a superposed mask in which the effective area 1.0 cm ² to the light receiving portion, the short circuit The current density Jsc (mA / cm ² ), the open circuit voltage Voc (V), and the fill factor (fill factor) FF were measured for each of the four light receiving portions formed on the same element, and the average value was obtained. Further, energy conversion efficiency η (%) was obtained from the measured Jsc, Voc, and FF according to the following formula 1.

  The evaluation results are shown in Table 1 below. It shows that energy conversion efficiency (photoelectric conversion efficiency) is so favorable that the number of an average value is large. In addition, the smaller the difference between the maximum value and the minimum value, the more stable conversion efficiency is obtained.

[Durability (temperature cycle test)]
A temperature cycle test was performed with reference to JIS C8938-1995.

That is, after measuring the initial photoelectric conversion efficiency, 20 cycles of changing the temperature from normal temperature (25 ° C.) → + 90 ± 2 ° C. → −40 ± 3 ° C. → normal temperature (25 ° C.) (reference: JIS C8938- 1995, 200 times), the solar simulator light was again irradiated at an irradiation intensity of 100 mW / cm ² (AM1.5G), voltage-current characteristics were measured, and post-endurance photoelectric conversion efficiency was measured.

◎: Initial photoelectric conversion efficiency of 90% or more remains ○: Initial photoelectric conversion efficiency of 80% or more remains Δ: Initial photoelectric conversion efficiency of 50% or more remains ×: Initial 50 Table 1 shows the results of evaluation in which less than% photoelectric conversion efficiency remains.

  As shown in Table 1, according to the present invention, it is possible to form an intermediate layer that is sufficiently transparent and excellent in electrical conductivity by a low-temperature process that can be applied to formation on a plastic substrate and an organic semiconductor device. It was found that the obtained tandem element was excellent in photoelectric conversion efficiency and temperature cycle durability.

  As can be seen from the results of the elements of TC-116, high photoelectric conversion efficiency and durability are obtained not only in the case of tandem elements connected in parallel but also in the case of tandem elements connected in series (without a metal grid). It was found that can be provided.

10 Forward layer type single type organic photoelectric conversion element,
11, 21 substrate,
12, 22 First electrode,
13, 23 Second electrode,
14 photoelectric conversion layer,
17 hole transport layer,
18 electron transport layer,
20 Reverse layer type single type organic photoelectric conversion element,
24a First photoelectric conversion layer,
24b Second photoelectric conversion layer,
25 metal grid,
26 transparent conductive layer,
27a first hole transport layer,
27b second hole transport layer,
28a a first electron transport layer,
28b a second electron transport layer,
29 middle class,
30 tandem type organic photoelectric conversion element of normal layer / series connection type,
40 Forward-layer / parallel-connected tandem organic photoelectric conversion elements,
200 External circuit.

Claims (4)

The first electrode, the first photoelectric conversion layer, the second photoelectric conversion layer, and the second electrode are laminated in this order,
Between the first photoelectric conversion layer and the second photoelectric conversion layer, having an intermediate layer containing both a conductive polymer and a self-dispersing polymer dispersible in an aqueous solvent,
The first photoelectric conversion layer and the second photoelectric conversion layer are electrically connected in parallel via the intermediate layer,
The intermediate layer functions as an extraction electrode ;
The conductive polymer is polythiophene,
The self-dispersing polymer is a polymer having a polyester skeleton, the glass transition point (Tg) is 25 to 64 ° C., and the average particle size is 19.8 to 80 nm,
The intermediate layer will have a metal grid containing silver formed in a pattern,
Tandem organic photoelectric conversion element with reverse layer and parallel connection. The tandem organic photoelectric conversion device according to claim 1, wherein the self-dispersing polymer has a dissociable group. The tandem organic photoelectric conversion device according to claim 1 or 2 , wherein the self-dispersing polymer has a glass transition point (Tg) of 50 to 64 ° C. The solar cell which has a tandem organic photoelectric conversion element of any one of Claims 1-3 .