JP5170746B2 - Stacked organic solar cell - Google Patents

Description

  The present invention relates to a stacked organic solar battery formed by stacking a plurality of organic solar battery single cells that generate light by receiving light.

  Organic solar cells have gained attention as one of the next generation solar cells because of improved conversion efficiency by developing a bulk heterojunction structure that blends donor and acceptor materials and disperses the heterojunction interface throughout the film. Has reached the point. However, the current performance is insufficient for practical use, and further performance improvement is required in the future. One effective means for this is the development of a stacked (tandem) organic solar battery in which a plurality of organic solar battery single cells are stacked (see, for example, Patent Document 1).

  Here, the biggest factor that the efficiency of the organic solar cell is low is lack of light absorption. There are two major problems when the cause of the lack of light absorption is further explained. The first problem is that since the carrier diffusion length is as short as about 100 nm, the film thickness can only be set to about 100 nm, and the light transmission loss is large. The second problem is that the light absorption band of the organic semiconductor is narrow and the unabsorbed loss of sunlight is large. For example, in the case of a polythiophene-based material that is often used at present, only a short wavelength region of 400 nm to 600 nm can be absorbed, and a phthalocyanine-based material known as a material that absorbs a long wavelength region among organic semiconductors is 600 nm. It absorbs only in the long wavelength region of ˜800 nm.

  Therefore, as with the inorganic thin film solar cell, development of a stacked organic solar cell in which a plurality of organic solar cell single cells are stacked is essential for improving the efficiency of the organic solar cell. In particular, when a plurality of organic solar cell single cells having different absorption bands are stacked, power can be generated by absorbing light in a wide band, and improvement in power generation efficiency can be expected.

  FIG. 2 shows an example of a low molecular weight stacked organic solar cell developed so far by vapor deposition (see Non-Patent Document 1). This stacked organic solar cell A ′ is a single organic solar cell having a photoelectric conversion layer 3 formed by stacking a p-type semiconductor layer 14 made of Cu phthalocyanine and an n-type semiconductor layer 15 made of PTCBI by vapor deposition. A cell 1 and another organic solar cell single cell 2 having a photoelectric conversion layer 3 formed by laminating a p-type semiconductor layer 14 made of Cu phthalocyanine and an n-type semiconductor layer 15 made of PTCBI by a vapor deposition method. It is laminated through a recombination layer 16 made of electrodes. 17 is a transparent substrate such as glass, 8 is an anode made of a transparent electrode, and 9 is an electrode such as Ag.

  By laminating the organic solar cell single cells 1 and 2 in this way, light passing through one organic solar cell single cell 1 is absorbed by the other organic solar cell single cell 2 and increases the light absorption as a whole. Conversion efficiency can be increased. In addition, in this organic solar cell, since the organic solar cell single cells 1 and 2 having the same configuration are laminated, each organic solar cell single cell 1 and 2 absorbs light in the same band and generates power. is there.

  In such a stacked organic solar cell A ′, a recombination layer 16 for recombining electrons and holes is required between the organic solar cell single cells 1 and 2 in order to obtain an output of power generation. That is, the electrons generated in one organic solar cell 1 and the holes generated in the other organic solar cell 2 are recombined in the recombination layer 16 and disappeared, and in one organic solar cell 1 The generated holes reach the anode 8 and the electrons generated in the other organic solar cell single cell 2 reach the cathode 9 and can be taken out as an output current.

  Here, the recombination layer 16 has conductivity for recombining holes and electrons, does not form a carrier transport barrier between the organic solar cell single cells 1 and 2 on both sides, It is required to have a high transmittance for transmitting unabsorbed light in the single organic solar cell 1 and transmitting it to the other single organic solar cell 2. In the example of Non-Patent Document 1, an Ag ultrathin layer having a thickness of 5 mm is formed as the recombination layer 16.

  However, the above-mentioned Ag ultrathin layer needs to be thinned to about 10 mm in order to ensure light transmittance, and as a result, Ag nanoclusters are formed to be distributed in islands. , A portion where the n-type semiconductor layer 15 of one organic solar cell single cell 1 and the p-type semiconductor layer 14 of the other organic solar cell single cell 2 are directly joined is formed, and this portion serves as a potential barrier, and holes There is a problem that the recombination of electrons with electrons is not completely performed.

  Next, FIG. 3 shows a conventional example of a stacked organic solar cell A in which polymer-type bulk heterojunction single cells are stacked by a coating method (see Non-Patent Document 2). The bulk heterojunction organic solar cell includes a photoelectric conversion layer 3 in which a donor material 12 and an acceptor material 13 are blended, and the work function difference between the electrodes on both sides of the photoelectric conversion layer 3 affects the open circuit voltage. There is an operational characteristic of giving. In this example, the photoelectric conversion layer 3 of each of the organic solar cell single cells 1 and 2 is formed by coating a film obtained by blending a fullerene derivative as the acceptor material 13 and a conductive polymer as the donor material 12. . Reference numeral 17 denotes a transparent substrate such as glass, 8 denotes a transparent anode, 9 denotes a cathode made of Al, and 10 denotes a hole transport layer. The recombination layer 16 is formed of a transparent electrode.

  Thus, when the recombination layer 16 is formed with a transparent electrode, this recombination layer 16 will be excellent in recombination property and light transmittance. However, since the transparent electrodes 8 and 16 are respectively disposed on both sides of one organic solar cell 1, the work function difference between the electrodes 8 and 16 is reduced, and the open circuit voltage is lowered. is there.

Next, another conventional example of a stacked organic solar battery A ′ in which polymer-type bulk heterojunction single cells are stacked by a coating method will be shown (see Non-Patent Document 3). In this example, the electron transport layer composed of a TiO ₂ thin film in one organic solar cell single cell 1 and the hole transport layer composed of a PEDOT: PSS layer in the other organic solar cell single cell are directly joined. In this case, it is considered that the interface between the electron transport layer and the hole transport layer or the hole transport layer having high conductivity serves as a recombination point between electrons and holes.

  However, in this example, since the work functions of the electron transport layer and the hole transport layer are greatly different, there is a concern that the ohmic property is lowered.

  Next, FIG. 4 shows a conventional example of a stacked organic solar cell A ′ in which two bulk heterojunction organic solar cells 1 and 2 having different absorption bands are stacked (see Non-Patent Document 4). One organic solar cell single cell 1 that absorbs a short wavelength includes a photoelectric conversion layer 3 composed of a P3HT: C60PCBM layer. The photoelectric conversion layer 3 of the other organic solar cell unit cell 2 that absorbs a long wavelength includes a p-type semiconductor layer 14 made of zinc phthalocyanine, an i-type semiconductor layer 18 made of zinc phthalocyanine: fullerene layer, and an n-type made of fullerene. A pin-type photoelectric conversion layer 3 in which a semiconductor layer 15 is stacked is provided. High power generation efficiency can be expected by the combination of such organic solar cell single cells 1 and 2.

  In this stacked organic solar cell A ′, three layers of a fullerene vapor deposition layer 19 / Au ultrathin film 20 / zinc phthalocyanine layer 21 are formed as an intermediate layer 4 between two organic solar cell single cells 1 and 2. The zinc phthalocyanine layer 21 also serves as the p-type semiconductor layer 14 in the photoelectric conversion layer 3 of the organic solar cell single cell 2 that absorbs a long wavelength.

However, also in this intermediate layer 4, since the Au ultrathin film 20 is formed such that Au nanoclusters are distributed in islands, a portion where the fullerene vapor-deposited layer 19 and the zinc phthalocyanine layer 21 are directly joined is formed. The portion becomes a potential barrier, and there is a problem that recombination of holes and electrons is not completely performed.
JP 2006-351721 A Apply Physics Letter Vol80 No.9 March 2002 page 1667 Apply Physics Letter Vol88, 073514, 2006 Science 13 July 2007 vol317 p.222 Apply Physics Letter Vol89, 073502-1, 2006

  The present invention has been made in view of the above points, and achieves higher power generation efficiency by tandemizing a bulk heterojunction type organic solar battery having high characteristics as an organic solar battery, and between organic solar battery single cells The organic solar cell single cells are ohmic-bonded to the intermediate layer interposed between them and the electrons and holes injected from the organic solar cell can be recombined in a well-balanced manner and have an appropriate work function. In addition, it is possible to maintain a high open-circuit voltage of a single organic solar cell, and to give each of the properties of excellent light transmission, and to maximize the performance of individual organic solar cell An object is to provide a type organic solar cell.

  The invention according to claim 1 is a stacked type in which a plurality of organic solar battery single cells 1 and 2 each having a photoelectric conversion layer 3 formed by blending a donor material 12 and an acceptor material 13 are stacked via an intermediate layer 4. An organic solar cell A, in which the intermediate layer 4 has a lithium fluoride layer 5 disposed on the anode 8 side of the stacked organic solar cell A, a molybdenum oxide layer 6 disposed on the cathode 9 side, A metal layer 7 disposed between the lithium fluoride layer 5 and the molybdenum oxide layer 6 is provided.

Furthermore the invention according to claim 1, upper Symbol metal layer 7, characterized in that it is formed of gold or silver.

The invention according to claim 2, comprising Oite to claim 1, the photoelectric conversion layer 3 one organic solar cell unit 1 adjacent to each other through the intermediate layer 4 containing an organic polymer compound as a donor material 12, the other The organic solar battery single cell 2 includes a photoelectric conversion layer 3 containing phthalocyanine as a donor material 12.

  According to the invention of claim 1, the intermediate layer 4 is given sufficient transparency to transmit unabsorbed light in one organic solar cell single cell 1 and send it to the other organic solar cell single cell 2. Among the electrons and holes generated in the photoelectric conversion layer 3 in the organic solar cell single cell 1 adjacent to the intermediate layer 4 on the anode 8 side, the electrons mainly pass through the lithium fluoride layer 5. Of the electrons and holes generated in the photoelectric conversion layer 3 in the organic solar cell unit cell 2 adjacent on the cathode 9 side, the holes are mainly metal via the molybdenum oxide layer 6. Electrons and holes are supplied to the metal layer 7 in a well-balanced manner, and the electrons and holes can be recombined in a well-balanced state in the metal layer 7. Furthermore, it becomes easy to set work functions of the metal layer 7 and the cathode 9 and the anode 8 in the stacked organic solar cell A to appropriate values, and the open circuit voltage can be improved. Thereby, the power generation efficiency of the stacked organic solar cell A can be improved.

According to the invention of claim 1 , the metal layer 7 in the intermediate layer 4 is formed of gold or silver, so that the work of the metal layer 7 and the cathode 9 and the anode 8 in the stacked organic solar cell A is performed. It becomes easier to set the function to an appropriate value, and the improvement of the open circuit voltage becomes more remarkable. This effect is particularly remarkable when the metal layer 7 is made of silver.

Moreover, according to the invention which concerns on Claim 2 , in each organic solar cell single cell 1 and 2 of the both sides of the intermediate | middle layer 4, a long wavelength is absorbed with the photoelectric converting layer containing an organic polymer compound, and the photoelectric conversion containing a phthalocyanine Short wavelengths are absorbed by the layers, and light in different wavelength bands is efficiently absorbed to generate power, thereby further improving power generation efficiency.

  Hereinafter, the best mode for carrying out the present invention will be described.

  As shown in FIG. 1, the stacked organic solar cell A according to the present invention has a structure in which a plurality of organic solar cell single cells 1 and 2 are stacked via an intermediate layer 4. Hereinafter, for convenience, one organic solar cell single cell 1 disposed on the anode 8 (positive electrode) side of the stacked organic solar cell A with respect to the intermediate layer 4 is referred to as a first single cell 1, and the intermediate layer 4 On the other hand, the other organic solar cell single cell 2 disposed on the cathode 9 (negative electrode) side of the stacked organic solar cell A is referred to as a second single cell 2.

  The intermediate layer 4 is composed of a plurality of layers. Of the plurality of layers constituting the intermediate layer 4, the lithium fluoride layer 5 is disposed on the most anode 8 side of the stacked organic solar cell A, and on the most cathode 9 side of the stacked organic solar cell A. A molybdenum oxide layer 6 is disposed. A metal layer 7 is disposed between the lithium fluoride layer 5 and the molybdenum oxide layer 6.

  The lithium fluoride layer 5 is formed of, for example, a vapor deposition film of lithium fluoride (LiF). The lithium fluoride layer 5 is formed with a thickness of, for example, 0.1 nm to 1 nm. The lithium fluoride layer 5 functions as the electron transport layer 11 in the first unit cell 1 adjacent to the intermediate layer 4.

The molybdenum oxide layer 6 is formed of, for example, a vapor deposition film of molybdenum oxide (MoO _x ; X = 2 to 4). The molybdenum oxide layer 6 is formed to have a thickness of 1 nm to 30 nm, for example. The molybdenum oxide layer 6 functions as a hole transport layer 10 in the second unit cell 2 adjacent to the intermediate layer 4.

  In addition, the metal layer 7 is formed of an appropriate metal, but is preferably formed of gold (Au) or silver (Ag). The metal layer 7 may be formed in a structure in which a plurality of metal layers are stacked. For example, the metal layer 7 may be a layer in which a layer made of gold and a layer made of silver are stacked. When the metal layer 7 is a laminate of two kinds of metals, the metal work function of the metal layer 7 on the lithium fluoride side is preferably larger than the metal work function of the metal layer 7 on the molybdenum oxide side. The metal layer 7 becomes a region (recombination layer 16) in which electrons sent from the lithium fluoride layer 5 and holes sent from the molybdenum oxide layer 6 are recombined.

  Even if the metal layer 7 is formed as a layer in which nanoclusters are distributed in an island shape, the metal layer 7 exhibits its function. However, in order to increase the recombination probability of electrons and holes in the metal layer 7 and to function as an electrode having an appropriate work function, the thickness of the metal layer 7 must be 1 nm or more. preferable.

  The lithium fluoride layer 5 functions as the electron transport layer 11 even with a very thin film thickness and forms a good interface. The molybdenum oxide layer 6 has excellent hole transportability and light transmission. And has a characteristic that the organic layer such as the photoelectric conversion layer 3 as a base is hardly damaged and has high stability against sunlight. When the intermediate layer 4 is formed by interposing the metal layer 7 between the lithium fluoride layer 5 and the molybdenum oxide layer 6, the photoelectric conversion layer 3 in the first single cell 1 adjacent to the intermediate layer 4 is formed. Among the generated electrons and holes, mainly electrons are sent to the metal layer 7 through the lithium fluoride layer 5, and among the electrons and holes generated in the photoelectric conversion layer 3 in the second single cell 2. The holes are mainly sent to the metal layer 7 through the molybdenum oxide layer 6. That is, the lithium fluoride layer 5 and the molybdenum oxide layer 6 do not generate carriers upon receiving light by themselves, but exhibit a function of supplying electrons and holes to the metal layer 7 in a balanced manner. In the metal layer 7, recombination of electrons and holes occurs, and at this time, if the carrier generation amount of the single cells 1 and 2 is designed to be equal, any carrier will not be excessive and the balance will be increased. Good recombination takes place. At this time, even if the metal layer 7 is formed as a layer in which the nanoclusters are distributed in an island shape, a part of the lithium fluoride layer 5 and the molybdenum oxide layer 6 are in direct contact with each other, the rectification at the interface between them is No longer occurs. Therefore, the first single cell 1 and the second single cell 2 are joined ohmic via the intermediate layer 4.

  The first unit cell 1 and the second unit cell 2 that are adjacent to each other through the intermediate layer 4 having the above-described configuration can be formed in an appropriate structure that has been applied to conventional organic solar cells. The single cell 1 and the second single cell 2 must have the photoelectric conversion layer 3 formed by blending the donor material 12 and the acceptor material 13. At this time, the photoelectric conversion layer 3 includes a case of a pin junction type including an i layer formed by blending the donor material 12 and the acceptor material 13. Thus, by forming each single cell in a bulk hetero structure, the conversion efficiency of the stacked organic solar cell A is remarkably improved.

  In addition, the photoelectric conversion layer 3 in the first unit cell 1 and the photoelectric conversion layer 3 in the second unit cell 2 can be provided with different absorption wavelength bands. In this case, each of the organic solar cell single cells 1 and 2 can absorb light of different wavelength bands to generate power, thereby improving power generation efficiency.

  In particular, it is preferable that the photoelectric conversion layer 3 in one of the first single cell 1 and the second single cell 2 includes an organic polymer compound as the donor material 12, and the photoelectric conversion layer 3 in the other is The donor material 12 preferably contains phthalocyanine. At this time, contrary to the case where the photoelectric conversion layer 3 in the first single cell 1 contains an organic polymer compound as a donor material, and the photoelectric conversion layer 3 in the second single cell 2 contains phthalocyanine as a donor material. In any case where the photoelectric conversion layer 3 in the first single cell 1 contains phthalocyanine as a donor material, and the photoelectric conversion layer 3 in the second single cell 2 contains an organic polymer compound as a donor material. Similarly, improvement in power generation efficiency is achieved.

  A configuration of the first single cell 1 when the photoelectric conversion layer 3 in the first single cell 1 includes an organic polymer compound as the donor material 12 will be described.

  Although it does not restrict | limit especially as an organic polymer compound which is the donor material 12 contained in the photoelectric converting layer 3, The material which has an absorption wavelength range in the range of 400 nm-600 nm is preferable, and especially poly (3-alkyl Polythiophene derivatives such as thiophene) and poly (p-phenylene) -vinylene derivatives such as (2-methoxy-5- (3 ′, 7′-dimethyloctyloxy) -1,4-phenylene-vinylene) (MDMO-PPV) And the like that are soluble in organic solvents such as toluene.

The acceptor material 13 includes compound semiconductor particles such as III-V group compound semiconductor crystals such as InP, InAs, GaP, and GaAs, III-V group compound semiconductor crystals such as CaSe, CdS, CdTe, and ZnS, fullerene, Examples include fullerene derivatives such as C60PCBM (phenyl C ₆₁ -butyric acid methyl ester).

  By forming the photoelectric conversion layer 3 as a layer in which the donor material 12 and the acceptor material 13 are mixed, the first single cell 1 can be formed in a bulk hetero structure. In forming the photoelectric conversion layer 3, for example, a mixed solution obtained by mixing and dissolving the organic polymer compound and the acceptor material 13 in an appropriate solvent such as chlorobenzene or chloroform solution at a predetermined ratio is spin-coated. However, the method is not particularly limited to such a method.

  Further, the content ratio of the organic polymer compound and the acceptor material 13 in the active layer 4 may be appropriately set so as to exhibit desired photoelectric conversion characteristics according to the types of the organic polymer compound and the acceptor material 13 and the like. The weight ratio of the acceptor material 13 with respect to the weight of the organic polymer compound is preferably 30 to 60%.

  This photoelectric conversion layer 3 can be formed adjacent to the lithium fluoride layer 5 in the intermediate layer 4. At this time, as described above, the lithium fluoride layer 5 is the electron transport layer 11 in the first unit cell 1. Function as.

  Further, an anode 8 (positive electrode) and a substrate 17 can be arranged on the opposite side of the first unit cell 1 from the intermediate layer 4. The substrate 17 has an insulating property and transmits visible light. In addition to being colorless and transparent, the substrate 17 may be slightly colored or ground glass. Specific examples of the material include soda lime glass, alkali-free glass, and various transparent plastics (PE, PP, PS, AS, ABS, PMMA, PVC, PA, POM, PBT, PC, PES, and the like).

  Further, the anode 8 can be formed to have conductivity and transmit visible light. The anode 8 preferably has a good sheet resistance of 20Ω / □ or less. The anode 8 preferably has a high work function in order to collect holes efficiently, and particularly preferably has a work function in the range of 4.9 to 5.1 eV. Specific examples of the material for the anode 8 include conductive transparent materials such as ITO (indium tin oxide), AZO, and GZO. The film thickness of the anode 8 is not particularly limited, but is preferably in the range of 50 to 300 nm in order to ensure good conductivity and light transmittance.

  Such an anode 8 can be formed by, for example, forming an electrode material as described above on the surface of the substrate 17 by physical vapor deposition or coating, and for example, vacuum deposition, sputtering, ion It can be produced by forming a thin film by a method such as a plating method, a spin coating method, or a printing method.

  Further, a hole transport layer 10 may be interposed between the photoelectric conversion layer 3 of the first single cell 1 and the anode 8. Examples of the material for forming the hole transport layer 10 include compounds having the ability to transport holes, further preventing the movement of electrons to the hole transport layer 10, and excellent in thin film formation ability. . Specifically, phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) and 4,4 ′ -Aromatic diamine compounds such as bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, poly Arylalkane, butadiene, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA), and polyvinylcarbazole, polysilane, polyethylenedioxythiophene: polystyrene Phonate (PEDOT It can be given a polymer material such as a conductive polymer PSS), etc., but is not limited thereto.

  Moreover, you may laminate | stack another organic photovoltaic cell on the opposite side to the intermediate | middle layer 4 of this 1st single cell 1 through another intermediate | middle layer.

  Next, the configuration of the second single cell 2 in the case where the photoelectric conversion layer 3 in the second single cell 2 contains phthalocyanine as the donor material 12 will be described.

  The phthalocyanine that is the donor material 12 contained in the photoelectric conversion layer 3 is not particularly limited as long as it has a phthalocyanine skeleton, and the central metal is not particularly limited. For example, the central metal is Cu, Zn, Co, Ni, Pb, Oxygen such as divalent compounds such as Pt, Fe, and Mg, trivalent metal phthalocyanines coordinated with halogen atoms such as metal-free phthalocyanine, aluminum chlorophthalocyanine, indium chlorophthalocyanine, and gallium chlorophthalocyanine, and other vanadyl phthalocyanine and titanyl phthalocyanine And phthalocyanine coordinated with.

  As the acceptor material 13, for example, a material similar to that in the case of the first unit cell 1 or an organic semiconductor material exhibiting n-type such as perylene suitable for vapor deposition can be used.

  By forming the photoelectric conversion layer 3 as a layer in which the donor material 12 and the acceptor material 13 are mixed, the second single cell 2 can be formed in a bulk hetero structure. In forming the photoelectric conversion layer 3, for example, a mixed layer is formed by co-evaporation (simultaneous vapor deposition) of acceptor materials 13 such as phthalocyanine and fullerene.

  The content ratio of the phthalocyanine and the acceptor material 13 in the photoelectric conversion layer 3 may be appropriately set according to the types of the phthalocyanine and the acceptor material 13 so as to exhibit desired photoelectric conversion characteristics. It is preferable to contain so that the volume ratio of the acceptor material 13 with respect to a containing weight may be in the range of 40 to 60%.

  This photoelectric conversion layer 3 can be formed adjacent to the molybdenum oxide layer 6 in the intermediate layer 4. At this time, the molybdenum oxide functions as the hole transport layer 10 in the second single cell 2 as described above. .

  Further, a cathode 9 (negative electrode) can be disposed on the opposite side of the second unit cell 2 from the intermediate layer 4.

  The cathode 9 is formed of a material having good conductivity. The cathode 9 preferably has a small work function in order to collect electrons efficiently, and particularly preferably has a work function in the range of 3 to 4.5 eV. Specific examples of such a cathode 9 include Al, Ca, Mg, Ag, Cu, and Pt.

  Such a cathode 9 can be produced, for example, by forming an electrode material as described above into a thin film by a method such as vacuum deposition, sputtering, ion plating, spin coating, or printing. The film thickness of the cathode 9 is not particularly limited, but is preferably about 100 nm in order to ensure good conductivity.

  Further, an electron transport layer 11 may be interposed between the photoelectric conversion layer 3 of the second single cell 2 and the cathode 9. Examples of the material for forming the electron transport layer 11 include compounds having an ability to transport electrons, further preventing movement of holes to the electron transport layer 11, and excellent in thin film formation ability. For example, a layer made of lithium fluoride similar to the lithium fluoride layer 5 in the intermediate layer 4 can be formed.

  Moreover, you may laminate | stack another photovoltaic cell through another intermediate | middle layer on the opposite side to the intermediate | middle layer 4 of this 2nd single cell 2. FIG.

  This laminated organic solar cell A can be manufactured by sequentially laminating each layer from the substrate 17 side.

  By combining the first single cell 1 and the second single cell 2 as described above, the characteristics of the organic solar cell single cells 1 and 2 are extracted, and a high-efficiency stacked organic solar in which the absorption wavelength band is divided. Battery A can be obtained.

  Moreover, when the metal layer 7 in the intermediate layer 4 is formed of gold or silver, a difference in work function is appropriately set between the metal layer 7 and the positive electrode and the negative electrode of the stacked organic solar cell A. It becomes possible to do. For this reason, the open circuit voltage of each organic solar cell single cell 1 and 2 can be improved, and the open circuit voltage of the stacked organic solar cell A as a whole can be improved.

  That is, when a transparent electrode is disposed as the anode 8, the first unit cell 1 is sandwiched between the anode 8 and the metal layer 7 formed of gold or silver, so that a difference in work function is provided between the two. The open circuit voltage can be increased. In particular, when the metal layer 7 is made of silver and the anode 8 is made of ITO, a remarkable effect can be obtained.

  Similarly, in the case of the second unit cell 2, when the cathode 9 made of the metal having a low work function as described above is provided on the side opposite to the intermediate layer 4 of the second unit cell 2, A work function difference can be provided between the intermediate layer 4 and the metal layer 7, and the open circuit voltage can be increased.

  Hereinafter, the present invention will be described in more detail by giving specific examples.

Example 1
A PEDOT: PSS with a thickness of 30 nm is formed as the hole transport layer 10 of the first single cell 1 on the surface of the glass substrate 17 on which the ITO film with a thickness of 150 nm serving as the anode 8 is formed. A layer was formed. At this time, a PEDOT: PSS solution (manufactured by Bayer, Baytron P AI4083) was applied by a spin coating method (3000 rpm, 60 seconds), and then heated and dried to form a film.

  Next, P3HT is used as the organic polymer compound that is the donor material 12, and a fullerene derivative (C60PCBM) is used as the acceptor material 13, and the weight ratio of P3HT and C60PCBM is 1: 0.7 in a solvent (chlorobenzene). So that it was dissolved. This solution was applied and formed by spin coating to form the photoelectric conversion layer 3 in the first single cell 1 with a thickness of 80 nm.

  Next, an intermediate layer 4 was formed by sequentially forming a lithium fluoride layer 5 having a thickness of 0.1 nm, a metal layer 7 made of gold having a thickness of 1 nm, and a molybdenum oxide layer 6 having a thickness of 5 nm by vacuum deposition.

  Next, zinc phthalocyanine as the phthalocyanine which is the donor material 12 and fullerene as the acceptor material 13 are co-evaporated at a volume ratio of 1: 1, so that the photoelectric conversion layer 3 in the second single cell 2 has a thickness. It was formed to 70 nm.

  Next, a layer made of lithium fluoride having a thickness of 0.1 nm was formed as the electron transport layer 11 in the second single cell 2 by a vacuum deposition method.

Further, an Al layer having a thickness of 100 nm was formed as the cathode 9 by vapor deposition to obtain a stacked organic solar battery A having a cell power generation area of 0.04 cm ² . The layered structure of the stacked organic solar cell A is ITO / PEDOT: PSS / P3HT: C60PCBM / LiF / Au / MoO _x / Zn phthalocyanine: C60 / Al.

This laminated organic solar cell A was irradiated with light of AM 1.5 100 mW / cm ² in a nitrogen atmosphere, and IV characteristics were measured.

In addition, as a comparison object, a non-stacked organic solar battery having a configuration corresponding to the first single cell 1 in the stacked organic solar battery A and a non-stacked type having a configuration corresponding to the second single cell 2 are used. An organic solar cell was prepared. The layer structure of the non-stacked organic solar battery having the structure corresponding to the first single cell 1 is ITO / PEDOT: PSS / P3HT: C60PCBM / LiF / Au, and the cathode 9 is the same as the metal layer 7 in the intermediate layer 4. Similarly, an Au layer is formed. The layer structure of the non-stacked organic solar battery having a structure corresponding to the second unit cell 2 is ITO / Au / MoO _x / Zn phthalocyanine: C60 / Al, and the ITO film serving as the anode 8 Further, an Au layer corresponding to the metal layer 7 in the intermediate layer 4 is laminated.

  The IV characteristics were also measured for these non-stacked organic solar cells in the same manner as described above.

  The results are shown in Table 1 below.

As shown in this result, the open circuit voltage (V _oc ) of the stacked organic solar cell A according to Example 1 corresponds to each of the organic solar cell single cells 1 and 2 constituting the stacked organic solar cell A. It agrees with the sum of the open circuit voltage of each non-stacked organic solar cell. Therefore, in the stacked organic solar cell A according to Example 1, it was confirmed that the series operation of the organic solar cell single cells 1 and 2 was completely performed.

Moreover, regarding the short circuit current (J _SC ), the short circuit current of the stacked organic solar cell A matched the short circuit current having the smaller value among the short circuit currents of the open-circuit voltages of the non-stacked organic solar cell A. Since the band of absorbed light in each organic solar cell single cell 1, 2 is different, the lower current value of the generated current in each organic solar cell single cell 1, 2 does not decrease as it is, and the stacked organic This appears as the current value of the solar cell A. As a result, it was found that the stacked organic solar cell A according to the present invention can perform an ideal tandem operation when the organic solar cell single cells 1 and 2 having different absorption bands are combined.

(Example 2)
A laminated organic solar cell A was produced in the same manner as in Example 1 except that the metal layer 7 in the intermediate layer 4 was formed of silver.

  Also for this stacked organic solar cell A, the same evaluation test as in Example 1 was performed, and the same result as in Example 1 was obtained.

  In particular, in Example 2, the open-circuit voltage in the non-stacked organic solar battery having a configuration corresponding to the first single cell 1 is 0.53 V, and the open-circuit voltage in the stacked organic solar battery A is 1.0 V. As a result, it increased compared to the case of Example 1. Thereby, when the metal layer 7 in the intermediate layer 4 is made of silver, the work function difference between the anode 8 on both sides of the first unit cell 1 and the metal layer 7 is increased, and the open circuit voltage is improved. It was confirmed that it was possible.

(Example 3)
A laminated organic solar cell A was produced in the same manner as in Example 1 except that the metal layer 7 in the intermediate layer 4 was formed of aluminum. However, since aluminum is easily oxidized, the thickness of the metal layer 7 is 5 nm, which is larger than that of Example 1. An evaluation test was performed on the stacked organic solar cell A in the same manner as in Example 1.

As a result, the short-circuit current was 4.5 mA / cm ² , the open circuit voltage was 0.81 V, the fill factor was 0.45, and the conversion efficiency was 1.6%.

  In the third embodiment, in terms of work function, the first single cell 1 is sandwiched between the anode 8 made of ITO and the metal layer 7 made of aluminum, so that the open circuit voltage is high. Since the single cell 2 is sandwiched between the cathode 9 and the metal layer 7 both made of aluminum, the open circuit voltage becomes low, so the open voltage of the stacked organic solar cell A as a whole is superior to that of Example 1. However, it was confirmed that the tandem operation of each organic solar cell single cell 1, 2 was performed.

Example 4
In Example 1, when forming the photoelectric converting layer 3 in the 1st single cell 1, the organic polymer compound which is the donor material 12 was changed into MDMO-PPV. Moreover, when forming the photoelectric converting layer 3 in the 2nd single cell 2, the donor material was changed into copper phthalocyanine. An evaluation test was performed on the stacked organic solar cell A in the same manner as in Example 1.

As a result, the short circuit current was 4.5 mA / cm ² , the open circuit voltage was 1.02 V, the fill factor was 0.47, and the conversion efficiency was 2.16%.

  As a result, in Example 1, the organic polymer compound that is the donor material 12 in the first single cell 1 is changed to another, and the phthalocyanine that is the donor material 12 in the second single cell 2 is changed to another. Even if it changed, it was confirmed that the tandem operation | movement of each organic solar cell single cell 1 and 2 is performed.

  In addition, since the PPV type organic polymer compound such as MDMO-PPV contributes to the improvement of the open voltage of the single cell, the open voltage of the stacked organic solar cell A as a whole is higher than that of Example 1.

(Example 5)
It was confirmed as follows that the intermediate layer 4 according to the present invention operates even in a tandem of three or more layers.

  The photoelectric conversion layer 3 formed by co-evaporation of zinc phthalocyanine (ZnPc) and C60 fullerene by the vapor deposition method as the photoelectric conversion layer 3 is laminated via the intermediate layer 4 according to the present invention, and the two layers, three layers, A four-layer organic solar cell A was produced.

The cell structure of the four-layer tandem is as follows: Glass / ITO (150 nm) / ZnPc: C60 (50 nm) / LiF (0.1 nm) / Au (1 nm) / MoO _x (5 nm) / (hereinafter the same thickness) ZnPc: C60 / _{LiF / Au / MoO X / ZnPc} : C60 / LiF / Au / MoO X / ZnPc: was C60 / LiF / Al (100nm) .

  At this time, the open-circuit voltages of the single-layer, two-layer, three-layer, and four-layer cells are 0.56 V, 1.06 V, 1.47 V, and 2.07 V, respectively, and the voltage increases almost in proportion to the number of layers. It was confirmed. Therefore, it was confirmed that the intermediate layer 4 works effectively even in a tandem cell having three or more layers.

(Comparative Example 1)
In Example 1, a fullerene vapor deposition layer having a thickness of 5 nm, which is an n-type organic semiconductor, was formed in place of the lithium fluoride layer 5 constituting the intermediate layer 4. An evaluation test was performed on the stacked organic solar cell A in the same manner as in Example 1.

  As a result, the short circuit current decreased to 4.6 mA, and the open circuit voltage decreased to 0.7V. Thereby, the effectiveness of the lithium fluoride layer 5 was confirmed.

(Comparative Example 2)
In Example 1, a PEDOT: PSS layer, which is a representative hole transport layer, was formed in place of the molybdenum oxide layer 6 constituting the intermediate layer 4. An evaluation test was performed on the stacked organic solar cell A in the same manner as in Example 1.

  As a result, the form factor decreased to 0.35. This is probably because the PEDOT: PSS layer, which is a water-soluble organic conductive film, has low wettability with the metal layer 7, and the adjacent photoelectric conversion layer 3 was damaged by moisture.

(Comparative Example 3)
In Example 1, a tungsten oxide layer having a thickness of 5 nm was formed in place of the molybdenum oxide layer 6 constituting the intermediate layer 4. An evaluation test was performed on the stacked organic solar cell A in the same manner as in Example 1.

  As a result, the initial characteristics were almost the same as those in Example 1. However, as the light irradiation time was increased, the amount of decrease in the short-circuit current was 30% or more larger than that in Example 1. . This is presumably because tungsten oxide received ultraviolet light and its transmittance was reduced.

(Comparative Example 4)
In Example 1 above, three types of stacked organic solar cells A having a configuration in which any one of the lithium fluoride layer 5, the metal layer 7, and the molybdenum oxide layer 6 constituting the intermediate layer 4 is removed are manufactured. did. For these three types of stacked organic solar cells A, the same evaluation test as in Example 1 was performed.

  As a result, it was found that each of the stacked organic solar cells A can only obtain an open voltage for a single cell and does not perform a sufficient tandem operation.

  Therefore, the provision of the intermediate layer 4 having the lithium fluoride layer 5, the metal layer 7, and the molybdenum oxide layer 6 as in the present invention contributes to the stacked organic solar cell A exhibiting a complete tandem operation. That was confirmed.

It is general | schematic sectional drawing which shows an example of the laminated organic solar cell which concerns on this invention. It is a schematic sectional drawing which shows an example of a prior art. It is a schematic sectional drawing which shows the other example of a prior art. It is a schematic sectional drawing which shows the other example of a prior art.

Explanation of symbols

A Stacked organic solar cell 1 Organic solar cell single cell (first single cell)
2 Organic solar cell (second single cell)
3 Photoelectric conversion layer 4 Intermediate layer 5 Lithium fluoride layer 6 Molybdenum oxide layer 7 Metal layer 8 Anode 9 Cathode 12 Donor material

Claims (2)

A laminated organic solar battery in which a plurality of organic solar battery single cells having a photoelectric conversion layer formed by blending a donor material and an acceptor material are stacked via an intermediate layer,
The intermediate layer is disposed between the lithium fluoride layer disposed on the anode side of the stacked organic solar cell, the molybdenum oxide layer disposed on the cathode side, and the lithium fluoride layer and the molybdenum oxide layer. has been provided with a metal layer are stacked organic solar cell, wherein the metallic layer that you have been formed by gold or silver. One organic solar cell adjacent to the intermediate layer has a photoelectric conversion layer containing an organic polymer compound as a donor material, and the other organic solar cell single cell has a photoelectric conversion layer containing phthalocyanine as a donor material The stacked organic solar cell according to claim 1 , wherein: