JP2016134464A - Organic thin film solar cell and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic thin film solar cell which includes a photoelectric conversion layer capable of effectively increasing parallel resistance, and a manufacturing method thereof.SOLUTION: An organic thin film solar cell 10 includes a photoelectric conversion layer 16 between a positive electrode 12 and a negative electrode 14. The photoelectric conversion layer 16 includes a positive electrode side site 22 facing a positive electrode 12 side and a negative electrode side site 24 facing a negative electrode 14 side. The positive electrode side site 22 has a higher content ratio of electron donors than electron acceptors, while the negative electrode side site 24 has a higher content ratio of the electron acceptors than the electron receptors. The electron donors and electron acceptors included in the positive electrode side site 22 and the negative electrode side site 24 do not form domains divided in phases to each other, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an organic thin film solar cell including a photoelectric conversion layer between a positive electrode and a negative electrode, and a method for producing the same.

  For example, as described in Patent Document 1, attention is paid to an organic thin film solar cell including a photoelectric conversion layer using an organic material between a positive electrode and a negative electrode (hereinafter collectively referred to as an electrode). . The photoelectric conversion layer includes a donor that acts as an electron donor and an acceptor that acts as an electron acceptor, and generates excitons when sunlight enters. The excitons dissociate into electrons and holes at the donor / acceptor interface. When each of these electrons and holes reaches the negative electrode and the positive electrode, electric energy converted from solar energy is obtained.

  As this type of photoelectric conversion layer, for example, one having a bulk heterojunction (BHJ) structure is known. In the BHJ structure, the donor and acceptor each form a phase-separated domain, and these domains are mixed in the photoelectric conversion layer. For this reason, in the BHJ structure, for example, compared with a planar heterojunction structure in which a layer consisting only of a donor and a layer consisting only of an acceptor are stacked, the interface between the donor and the acceptor is increased to generate electrons and holes. It is preferable at the point which can improve efficiency.

JP 2013-213190 A

  In general, the output characteristics of an organic thin-film solar cell are the relationship between current density and output voltage, specifically, a curve (hereinafter also referred to as an IV curve) illustrated with the current density as the vertical axis and the output voltage as the horizontal axis. Be evaluated. Here, the current density is a value obtained by dividing the output current by the surface area of the power generation portion of the organic thin film solar cell.

One of the factors affecting the output characteristics is a parallel resistance (R _sh ) when a thin film solar cell is shown as an equivalent circuit. This parallel resistance is a resistance component resulting from the leakage current, and tends to decrease when the leakage current in the photoelectric conversion layer is large. Therefore, in the organic thin film solar cell, it is preferable that the parallel resistance is large in order to improve the output characteristics.

  Here, in the photoelectric conversion layer having the BHJ structure, among the electrons and holes generated at the interface, the electrons move in the acceptor domain and reach the negative electrode, and the holes move in the donor domain and are positive. It is desirable to reach

  However, since the donor and acceptor domains are mixed in the entire photoelectric conversion layer, there is a site where the acceptor domain is in direct contact with the positive electrode or indirectly through the transport layer or the like. Similarly, there is a site where the donor domain directly or indirectly contacts the negative electrode. Therefore, the electrons moving in the acceptor domain may reach the positive electrode through these contact sites, or the holes moving in the donor domain may reach the negative electrode. In this case, since the leakage current increases, there is a concern that it is difficult to sufficiently increase the parallel resistance in the organic thin film solar cell including the photoelectric conversion layer having the BHJ structure.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an organic thin-film solar cell including a photoelectric conversion layer capable of effectively increasing parallel resistance and a method for manufacturing the same.

ただし、式（１）〜（４）中のＲ１〜Ｒ６の少なくとも一つはアルコキシ基であり、Ｒ７〜Ｒ１０はそれぞれ独立に、水素、アルキル基及びアルコキシ基の何れかである。 In order to achieve the above object, the present invention is an organic thin-film solar cell having a photoelectric conversion layer between a positive electrode and a negative electrode, and the photoelectric conversion layer is represented by formulas (1) to (4). An electron donor containing at least one of the nanographene polymers; and an electron acceptor that accepts electrons donated from the electron donor; in the photoelectric conversion layer, at a positive electrode side portion facing the positive electrode side The ratio of containing the electron donor is larger than that of the electron acceptor, and the ratio of containing the electron acceptor is larger than that of the electron donor in the negative electrode side portion facing the negative electrode side. Each of the electron donor and the electron acceptor contained in the portion and the negative electrode side portion does not form a domain that separates from each other.

However, at least one of R1 to R6 in formulas (1) to (4) is an alkoxy group, and R7 to R10 are each independently any one of hydrogen, an alkyl group, and an alkoxy group.

  In the organic thin-film solar cell according to the present invention, as described above, in the photoelectric conversion layer disposed between the positive electrode and the negative electrode, the portion facing the positive electrode side is the positive electrode side portion, and the portion facing the negative electrode side is the negative electrode side portion. Yes. Each of the positive electrode side portion and the negative electrode side portion includes both a donor and an acceptor. And the ratio which contains a donor is large compared with an acceptor in the positive electrode side site | part, and the ratio which contains an acceptor compared with a donor in the negative electrode side site | part is set large.

  Moreover, the donor and acceptor contained in the positive electrode side part and the negative electrode side part do not form a domain (bulk) that separates each other. That is, the acceptor is dispersed in the donor at the positive electrode site, and the donor is contained in the acceptor at the negative electrode site.

  As described above, in the photoelectric conversion layer of the present invention, each of the positive electrode side portion and the negative electrode side portion includes both a donor and an acceptor. Therefore, excitons can be easily dissociated as compared to a photoelectric conversion layer formed by stacking layers formed only from donors or acceptors. That is, the generation efficiency of electrons and holes can be improved.

  Further, the photoelectric conversion layer of the present invention does not include a donor domain and an acceptor domain that cause a leakage current. That is, at the positive electrode side portion, directly contact the positive electrode or indirectly through the intervening layer when a positive hole transport layer or the like is interposed between the positive electrode and the photoelectric conversion layer, The formation of acceptor domains is suppressed. Similarly, the formation of a donor domain that directly or indirectly contacts the negative electrode is suppressed at the negative electrode side portion.

  Therefore, in the photoelectric conversion layer of the present invention, for example, leakage current can be suppressed as compared with a bulk heterojunction (BHJ) structure in which donor and acceptor domains phase-separated from each other are mixed in the photoelectric conversion layer. That is, the parallel resistance can be effectively increased.

  Furthermore, the donor of this invention is comprised including at least any one of the nano graphene polymer represented by Formula (1)-(4). These nano graphene polymers are composed of a π-conjugated polymer having a condensed aromatic ring in which a π electron cloud spreads as a whole as a structural unit, and the π electron cloud spreads along the main chain. Moreover, the energy level difference (band gap Eg) between HOMO and LUMO is small.

  Therefore, in the photoelectric conversion layer of the present invention, the above-described nano graphene polymer is included as a donor, so that the extinction coefficient is increased and excitons are actively generated. Moreover, since the maximum absorption wavelength is shifted to the long wavelength side and light of the long wavelength (near infrared side) is favorably absorbed, the utilization efficiency of sunlight is improved. That is, the conversion efficiency of the organic thin film solar cell can be improved.

  From the above, in the organic thin film solar cell according to the present invention, it is possible to effectively increase the parallel resistance by reducing the leakage current while suppressing the generation efficiency of electrons and holes from being excessively reduced, and Conversion efficiency can be improved.

ただし、式（１）〜（４）中のＲ１〜Ｒ６の少なくとも一つはアルコキシ基であり、Ｒ７〜Ｒ１０はそれぞれ独立に、水素、アルキル基及びアルコキシ基の何れかである。 Moreover, this invention is a manufacturing method of the organic thin film solar cell which has a photoelectric converting layer between a positive electrode and a negative electrode, Comprising: At least any one of the nano graphene polymers represented by Formula (1)-(4) is included. An electron donor, an electron acceptor that accepts electrons donated from the electron donor, a first solvent that is a good solvent for each of the electron donor and the electron acceptor, and the first solvent A step of mixing a second solvent having a high boiling point and a poor solvent for the electron donor and a good solvent for the electron acceptor to obtain a mixed solution, and above the positive electrode, Supplying the mixed liquid to form a mixed liquid film, and preferentially evaporating the first solvent and the second solvent in the mixed liquid film from the first solvent having a low boiling point, Electron donation than the electron acceptor on the positive electrode side Forming a positive electrode side portion having a large ratio of containing, then forming a negative electrode side portion having a larger ratio of containing the electron acceptor than the electron donor on the negative electrode side to obtain the photoelectric conversion layer; And the electron donor and the electron acceptor included in each of the positive electrode side part and the negative electrode side part form the photoelectric conversion layer in which a domain for phase separation from each other is not formed. And

However, at least one of R1 to R6 in formulas (1) to (4) is an alkoxy group, and R7 to R10 are each independently any one of hydrogen, an alkyl group, and an alkoxy group.

  According to the method for producing an organic thin-film solar cell according to the present invention, the photoelectric conversion layer having the positive electrode side portion and the negative electrode side portion can be easily formed. That is, first, a donor, an acceptor, a first solvent, and a second solvent are mixed to prepare a mixed solution. At this time, a solvent that has a lower boiling point than the second solvent and that serves as a good solvent for each of the donor and the acceptor is selected as the first solvent. The second solvent is selected to be a poor solvent for the donor and a good solvent for the acceptor.

  Then, the obtained mixed liquid is supplied above the positive electrode to form a mixed liquid film. Specifically, when a photoelectric conversion layer is provided directly on the positive electrode, a mixed liquid film is formed on the surface of the positive electrode, and an intervening layer such as a hole transport layer is provided between the positive electrode and the photoelectric conversion layer. Forms a mixed liquid film on the surface of the intervening layer.

  At this stage, since the donor contained in the mixed liquid film is mainly well dissolved in the first solvent and the acceptor is well dissolved in the first solvent and the second solvent, both the donor and the acceptor are mixed liquid film. It is in a state of being distributed almost evenly inside. The photoelectric conversion layer is formed by evaporating the first solvent and the second solvent from the mixed liquid film. At this time, since the boiling point of the second solvent is higher than the boiling point of the first solvent as described above, the first solvent evaporates more easily than the second solvent under the same conditions. That is, first, the first solvent evaporates preferentially from the mixed liquid film.

  Thus, as the first solvent evaporates, the relative concentration of the second solvent in the mixed liquid film increases. As described above, the second solvent is a poor solvent for the donor and a good solvent for the acceptor. For this reason, as the relative concentration of the second solvent increases, most of the donor that cannot be dissolved in the mixed liquid film and part of the acceptor are deposited above the positive electrode. As a result, first, a positive electrode-side portion is formed above the positive electrode, in which the proportion containing the donor is larger than the proportion containing the acceptor, and the acceptor is dispersed in the donor.

  The remaining donor and acceptor are present in the mixed liquid film in a state dissolved in the second solvent. When the second solvent evaporates from this state, the proportion containing the acceptor on the positive electrode side portion is larger than the proportion containing the donor, and the negative electrode side portion contained in a state where the donor is dispersed in the acceptor is formed. The

  As a result, it is possible to obtain a photoelectric conversion layer having a positive electrode side portion and a negative electrode side portion, in which each of the donor and the acceptor does not form a phase-separated domain. That is, in the manufacturing method of the organic thin film solar cell of this invention, the organic thin film solar cell containing said photoelectric conversion layer can be obtained. As a result, it is possible to effectively increase the parallel resistance by reducing the leakage current while suppressing the generation efficiency of electrons and holes from being excessively lowered. Moreover, since the photoelectric conversion layer contains the nano graphene polymer represented by Formula (1)-(4) as a donor, it becomes possible to improve the conversion efficiency of an organic thin film solar cell.

  In the method for producing an organic thin film solar cell, the mixed solution is prepared so that a mass ratio of the first solvent to the second solvent is 94.5: 5.5 to 86.5: 13.5. It is preferable. In this case, it is possible to effectively suppress the formation of donor and acceptor domains that cause a leakage current by directly or indirectly contacting the electrode at the positive electrode side portion and the negative electrode side portion. That is, it is possible to obtain an organic thin-film solar cell having a further increased parallel resistance.

  The organic thin film solar cell according to the present invention includes a photoelectric conversion layer having a positive electrode side portion in which an acceptor is dispersed in a donor and a negative electrode side portion in which the donor is dispersed in the acceptor. In the positive electrode side part and the negative electrode side part, the acceptor and the donor do not form domains that cause leakage current. For this reason, in the photoelectric converting layer of this invention, a leakage current can be reduced compared with the photoelectric converting layer of a BHJ structure. This makes it possible to effectively increase the parallel resistance of the organic thin film solar cell.

  Moreover, since the photoelectric conversion layer of this invention contains the nano graphene polymer which consists of (pi) conjugated polymer with a large spread of (pi) electron cloud as a donor, the conversion efficiency of an organic thin-film solar cell can be improved.

It is a principal part schematic longitudinal cross-sectional view of the organic thin-film solar cell concerning this embodiment. It is the bright-field image observed using the scanning transmission electron microscope (STEM) about the longitudinal cross-section of the organic thin-film solar cell which concerns on Example 1. FIG.

  Hereinafter, preferred embodiments of the organic thin film solar cell and the manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic vertical sectional view of a main part of an organic thin film solar cell 10 according to the present embodiment. This organic thin film solar cell 10 has a photoelectric conversion layer 16 between the positive electrode 12 and the negative electrode 14. Further, a hole transport layer 18 is interposed between the positive electrode 12 and the photoelectric conversion layer 16, and an electron transport layer 20 is interposed between the photoelectric conversion layer 16 and the negative electrode 14. That is, the organic thin film solar cell 10 has a configuration in which a hole transport layer 18, a photoelectric conversion layer 16, an electron transport layer 20, and a negative electrode 14 are superimposed on the positive electrode 12 in this order.

  As the positive electrode 12, one that sufficiently transmits light such as sunlight is selected. For example, indium-tin composite oxide (ITO) deposited on a transparent substrate such as a glass substrate can be employed.

  The hole transport layer 18 is a layer that supports the movement of holes generated in the photoelectric conversion layer 16 to the positive electrode 12. As a material of the hole transport layer 18, for example, poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, that is, so-called PEDOT: PSS or the like can be employed.

  The photoelectric conversion layer 16 includes a donor that functions as an electron donor and an acceptor that functions as an electron acceptor. Among these, a donor contains at least any one of the nano graphene polymers shown to Formula (1)-(4). The nano graphene polymer is a π-conjugated polymer having nanometer-scale graphene (condensed aromatic ring in which a π electron cloud spreads) as one constituent unit.

  However, at least one of R1 to R6 in formulas (1) to (4) is an alkoxy group, and R7 to R10 are each independently any one of hydrogen, an alkyl group, and an alkoxy group.

Thus, for example, in the formulas (1) to (4), when R1, R3, R4, and R6 are OC ₁₀ H ₂₁ , R 7 and R 8 are C ₁₂ H ₂₅ , and R 9 and R 10 are CH ₃ , the donor is And at least one of the nanographene polymers represented by the formulas (5) to (8).

In addition, the nano graphene polymer contained in a donor is not limited to what is shown to Formula (5)-(8). For example, it can be suitably used as donors obtained by introducing the OC ₁₀ H ₂₁ to all R1~R6 nano graphene polymer shown in the above equation (5) to (8). In addition, the donor may be configured by, for example, any two or more of the nanographene polymers represented by the formulas (1) to (4) bonded at random.

On the other hand, the acceptor only needs to be made of a material that accepts electrons donated from the above donor. For example, phenyl C ₆₁ butyric acid methyl ester and phenyl C ₇₁ methyl butyrate shown in formulas (9) to (15), respectively. ester, phenyl C ₆₁ acid butyl ester, phenyl C ₆₁ butyric acid octyl ester, indene C ₆₀ bis adduct, indene C ₆₀ mono-adduct can be suitably adopted indene C ₆₀ tri adducts.

  Specifically, the photoelectric conversion layer 16 containing the above donor and acceptor as a photoelectric conversion material has a positive electrode side portion 22 and a negative electrode side portion 24. The positive electrode side portion 22 is formed on the positive electrode 12 side in the photoelectric conversion layer 16, and the proportion of containing a donor is larger than that of the acceptor. Here, the positive electrode 12 side is a part including at least the vicinity of the contact surface with the hole transport layer 18. In the organic thin-film solar cell that does not include an intervening layer such as the hole transport layer 18, the portion includes the vicinity of the contact surface with the positive electrode.

  Moreover, the negative electrode side part 24 is formed in the negative electrode 14 side among the photoelectric converting layers 16, and the ratio containing an acceptor is large compared with a donor. Here, the negative electrode 14 side is a part including at least the vicinity of the contact surface with the electron transport layer 20. In addition, in the organic thin film solar cell which does not have interposition layers, such as the electron carrying layer 20, it is a site | part containing the contact surface vicinity with a negative electrode.

  The donor and acceptor contained in any of the positive electrode side portion 22 and the negative electrode side portion 24 do not form a domain (bulk) that separates each other. That is, in the positive electrode side part 22, the acceptor is contained in a dispersed state in the donor, and in the negative electrode side part 24, the donor is contained in a dispersed state.

  Further, the positive electrode side portion 22 and the negative electrode side portion 24 are continuously formed so that the content ratios of the acceptor and the donor are continuously changed. In the photoelectric conversion layer 16, the positive electrode 12 and the negative electrode 14, such as a portion excluding the positive electrode side portion 22 and the negative electrode side portion 24, that is, a portion between the positive electrode side portion 22 and the negative electrode side portion 24, etc. The above-described bulk may be formed at a site that does not come into contact.

  The electron transport layer 20 is a layer that supports the movement of electrons generated in the photoelectric conversion layer 16 to the negative electrode 14. As a material for the electron transport layer 20, for example, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, that is, so-called bactoproin (BCP) can be employed.

  The negative electrode 14 can be formed from, for example, silver (Ag) deposited on the electron transport layer 20.

  The organic thin film solar cell 10 according to the present embodiment is basically configured as described above. Next, an example is given and demonstrated about the manufacturing method of the organic thin film solar cell 10. FIG.

  First, for example, a transparent electrode substrate on which the positive electrode 12 is formed is obtained by depositing ITO on a glass substrate. Next, a PEDOT: PSS aqueous solution is dropped on the positive electrode 12, and the hole transport layer 18 is formed by spin coating. At this time, for example, when the spin coating speed is 1000 to 2000 rpm and the PEDOT: PSS aqueous solution is prepared so that the PEDOT: PSS concentration is 1 to 3% by mass, the hole transport layer has a thickness of about 30 to 40 nm. 18 can be obtained.

  Next, the photoelectric conversion layer 16 is formed on the hole transport layer 18. For this purpose, first, a donor and an acceptor each composed of the above-described photoelectric conversion material, a first solvent, and a second solvent are mixed to prepare a mixed solution. As the first solvent, a solvent that is a good solvent for each of the donor and the acceptor is selected. As such a 1st solvent, ortho- dichlorobenzene, chlorobenzene, chloroform etc. are employable, for example.

  The second solvent is selected to have a boiling point higher than that of the first solvent and a poor solvent for the donor and a good solvent for the acceptor. As such a second solvent, for example, diiodooctane, octanediol, dichlorooctane or the like can be employed.

  Here, in order to satisfactorily form the positive electrode side portion 22 and the negative electrode side portion 24 to obtain the photoelectric conversion layer 16, the mass ratio of the first solvent to the second solvent in the mixed solution is 94.5: 5. It is preferable to set it as 5-86.5: 13.5. Further, the donor: acceptor mass ratio in the mixed solution may be adjusted to about 1: 2 to 1: 4, and the total concentration of the donor and acceptor in the mixed solution may be adjusted to about 1 to 3% by mass.

  Next, the mixed liquid is supplied above the positive electrode 12, that is, on the hole transport layer 18 to form a mixed liquid film. For example, a liquid mixture film can be formed by dropping an appropriate amount of the liquid mixture on the hole transport layer 18. At this stage, the donor contained in the mixed liquid film is mainly well dissolved in the first solvent, and the acceptor is well dissolved in both the first solvent and the second solvent. Is in a state of being dispersed substantially uniformly in the mixed liquid film.

  Next, the first solvent and the second solvent in the mixed liquid film are preferentially evaporated from the first solvent having a low boiling point. In this case, for example, spin coating may be performed on the transparent electrode substrate in which the mixed liquid film is formed on the hole transport layer 18 as described above. As described above, since the first solvent has a lower boiling point than the second solvent, the first solvent evaporates more easily than the second solvent under the same conditions. That is, the first solvent can be preferentially evaporated from the mixed liquid film.

  As a result, the relative concentration of the second solvent in the mixed liquid film increases as the first solvent decreases. As described above, the second solvent is a poor solvent for the donor and a good solvent for the acceptor. Therefore, as the relative concentration of the second solvent increases, most of the donors and some of the acceptors that can no longer dissolve in the mixed liquid film are deposited on the hole transport layer 18. As a result, first, the positive electrode side portion 22 is formed on the hole transport layer 18 in which the proportion containing the donor is larger than the proportion containing the acceptor and the acceptor is dispersed in the donor.

  When the evaporation of the second solvent proceeds after the first solvent evaporates preferentially as described above, the remaining donor and acceptor that existed in the mixed solution in the state of being dissolved in the second solvent are converted into the positive electrode. It is deposited on the side portion 22. As a result, the proportion containing the acceptor is larger than the proportion containing the donor, and the negative electrode side portion 24 included in a state where the donor is dispersed in the acceptor is formed on the positive electrode side portion 22.

  That is, the positive electrode side part 22 and the negative electrode side part 24 can be formed in this order on the hole transport layer 18 to obtain the photoelectric conversion layer 16. In the photoelectric conversion layer 16 thus obtained, each of the positive electrode side portion 22 and the negative electrode side portion 24 includes both a donor and an acceptor, and the donor and the acceptor do not form a domain that separates from each other. .

  When the first solvent: second solvent mass ratio, donor: acceptor mass ratio, and donor and acceptor total concentration in the mixed solution are prepared as described above, the spin coat rotation speed is, for example, 1000 to 2000 rpm. And it is sufficient. In this case, the photoelectric conversion layer 16 in which the thickness of the positive electrode side portion 22 is about 10 to 15 nm and the thickness of the negative electrode side portion 24 is about 30 to 35 nm can be obtained.

Next, the electron transport layer 20 is formed on the photoelectric conversion layer 16 so as to have a film thickness of about 10 nm at a rate of 10 Å / s at a vacuum degree of 1 × 10 ⁻⁴ Pa or less by a vacuum vapor deposition apparatus. A bactoproin layer is formed.

Further, an Ag layer as the negative electrode 14 is formed on the electron transport layer 20 so as to have a film thickness of 300 to 350 nm at a rate of 10 Å / s at a vacuum degree of 1 × 10 ⁻⁴ Pa or less by a vacuum deposition apparatus, for example. Form.

  Basically, the organic thin-film solar cell 10 can be obtained through the above steps. When the organic thin film solar cell 10 is irradiated with light such as sunlight from the positive electrode 12 side, the light passes through the hole transport layer 18 and reaches the photoelectric conversion layer 16. , Excitons are generated.

  The excitons are separated into electrons and holes in the positive electrode side portion 22 in which the acceptor is dispersed in the donor and the negative electrode side portion 24 in which the donor is dispersed in the acceptor. That is, the photoelectric conversion layer 16 has a large dissociation surface where excitons dissociate as compared to, for example, a photoelectric conversion layer having a planar heterojunction structure in which a layer composed only of a donor and a layer composed only of an acceptor. Therefore, exciton dissociation can be easily generated, and the generation efficiency of electrons and holes can be improved.

  Of the electrons and holes obtained as described above, the electrons move in the negative electrode side portion 24 having a larger acceptor content than the positive electrode side portion 22 having a large ratio of containing donors, and electrons It is easy to reach the transport layer 20 and the negative electrode 14. On the other hand, the holes move more easily in the positive electrode side portion 22 than in the negative electrode side portion 24 and move to the hole transport layer 18 and the positive electrode 12.

  Further, as described above, the donor and acceptor contained in any of the positive electrode side portion 22 and the negative electrode side portion 24 do not form a domain (bulk) that separates each other. That is, the photoelectric conversion layer 16 of this embodiment does not have an acceptor domain that contacts the hole transport layer 18 or a donor domain that contacts the electron transport layer 20. For this reason, it can be avoided that electrons reach the positive electrode via the acceptor domain and holes reach the negative electrode via the donor domain. Thereby, compared with a bulk heterojunction (BHJ) structure, a leakage current can be reduced.

  Therefore, in the organic thin film solar cell 10 according to the present embodiment, the parallel resistance can be effectively increased as compared with the organic thin film solar cell including the photoelectric conversion layer having the BHJ structure.

  Furthermore, as above-mentioned, the donor of the photoelectric converting layer 16 is comprised including at least any one of the nano graphene polymers represented by Formula (1)-(4). These nano graphene polymers are composed of a π-conjugated polymer having a condensed aromatic ring in which a π electron cloud spreads as a whole as a structural unit, and the π electron cloud spreads along the main chain. Moreover, the energy level difference (band gap Eg) between HOMO and LUMO is small.

  Therefore, in the photoelectric conversion layer 16, by containing the nano graphene polymer as a donor, an absorption coefficient is increased, and excitons are actively generated. Moreover, since the maximum absorption wavelength is shifted to the long wavelength side and light of the long wavelength (near infrared side) is favorably absorbed, the utilization efficiency of sunlight is improved. That is, the conversion efficiency of the organic thin film solar cell 10 can be improved.

  In addition, this invention is not specifically limited to above-described embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary.

[Preparation of donor]
In order to produce the nano graphene polymer represented by the above formulas (5) to (8) as a donor, first, the reaction represented by the formula (16) was performed.

Specifically, first, Compound 1 (60.00 g, 361 mmol) represented by Reaction Formula (16) was dissolved in N, N-dimethylformamide (DMF) (300 ml) under a nitrogen atmosphere. To this solution, potassium carbonate (K ₂ CO ₃ ) (69.80 g, 505 mmol) and 1-bromodecane (95.77 g, 433 mmol) were added and reacted at 80 ° C. for 2 hours. Cooled. To this solution, ethyl acetate and water were further added to extract the product, followed by washing with water and saturated brine. Then, after concentration under reduced pressure, column purification (silica, hexane / ethyl acetate = 100/0 to 90/10) yielded Compound 2 shown in Reaction Formula (16) in a yield of 88%.

  Next, the reaction shown in Formula (17) was performed.

Specifically, first, a solution obtained by dissolving diisopropylamine (i-PR ₂ NH) (35.42 g, 350 mmol) in tetrahydrofuran (THF) (200 ml) was cooled to −50 ° C. in a nitrogen atmosphere. Then, a 1.65M n-butyllithium hexane solution (202 ml, 334 mmol) was dropped into this solution and reacted for 30 minutes, and then a dropping solution was dropped, and the temperature was naturally raised to room temperature for 16 hours. Reaction was performed. Here, the dropping solution was obtained by dissolving Compound 2 (97.35 g, 318 mmol) in THF (200 ml).

  Subsequently, a hydrochloric acid aqueous solution obtained by mixing concentrated hydrochloric acid (20 ml), saturated brine (400 ml) and water (400 ml) and ethyl acetate were added to extract the product, and then a 1M hydrochloric acid aqueous solution, water, Washing with saturated saline was performed. Then, after concentration under reduced pressure, column purification (silica, hexane / ethyl acetate = 100/0 to 90/10) yielded Compound 3a and Compound 3b shown in Reaction Formula (17) at a yield of 93%.

  Next, the reaction shown in Formula (18) was performed.

  Specifically, first, under a nitrogen atmosphere, compounds 3a, 3b (85.89 g, 148 mmol) were dissolved in ethanol (610 ml) and THF (490 ml) to obtain a solution. Concentrated hydrochloric acid (200 ml) was added to this solution, refluxed at 100 ° C. for 17 hours, and then allowed to cool to 55 ° C. Further, water (610 ml) was added and cooled to 10 ° C. Thus, the precipitated solid was filtered and washed with water and cold ethanol to obtain Compound 4 represented by the reaction formula (18) at a yield of 90%.

  Next, the reaction shown in Formula (19) was performed.

  Specifically, first, under a nitrogen atmosphere, Compound 4 (44.86 g, 85.8 mmol) and Compound 5 (14.69 g, 42.9 mmol) represented by Formula (19) were combined with n-butanol (647 ml). And heated to 80 ° C. Subsequently, 40% benzyltrimethylammonium hydroxide / methanol solution (1.80 g, 4.3 mmol) was added dropwise and allowed to react for 1 hour. Thereafter, a 40% benzyltrimethylammonium hydroxide / methanol solution (3.60 g, 8.6 mmol) was further added dropwise and reacted for 30 minutes. And after cooling to 10 degreeC, the obtained solid was filtered and wash | cleaned with n-butanol, cold ethanol, and acetone. This solid was recrystallized with THF (240 ml) / acetone (520 ml) to obtain a compound 6 represented by the formula (19) in a yield of 61%.

  Next, the reaction shown in Formula (20) was performed.

  Specifically, first, Compound 6 (3.00 g) and Compound 7 (1.178 g) represented by Formula (20) were dispersed in diphenyl ether (30 ml), and then freeze degassing was performed. The dispersion thus obtained was heated to reflux at 200 ° C. for 5 days, cooled to room temperature, and then poured into acetone for reprecipitation purification. The precipitated solid was filtered and washed with acetone to obtain Compound 8 shown in Formula (20).

  Next, the reaction shown in Formula (21) was performed.

Specifically, first, under a nitrogen atmosphere, a solution obtained by dissolving Compound 8 (200 mg) in anhydrous dichloromethane (CH ₂ Cl ₂ ) ( ₂ L) was cooled to 0 ° C. To this solution, a FeCl ₃ (770 mg) / CH ₃ NO ₂ (4.7 ml) solution was added dropwise over 30 hours using a syringe pump, reacted at 0 ° C. for 3 days, and then reacted at room temperature for 1 day. I let you. Further, ortho-dichlorobenzene (1 L) was added, and then dichloromethane was distilled off under reduced pressure. The solution thus obtained was washed with water, and ortho-dichlorobenzene was further concentrated under reduced pressure and then poured into acetone for reprecipitation purification. The precipitated solid was filtered and washed with acetone to obtain compounds 9a, 9b, 9c and 9d represented by the formula (21). The compounds 9a to 9d correspond to the nano graphene polymers represented by the above formulas (5) to (8), respectively.

The nanographene polymer thus obtained was employed as a donor, and phenyl _C71 butyric acid methyl ester represented by formula (10) was employed as an acceptor. As shown below, in Examples 1 and 2 and Comparative Examples 1 and 2, The organic thin film solar cell which concerns is produced.

[Example 1]
“703192-10PAK” (trade name) manufactured by Sigma-Aldrich was used as a transparent electrode substrate on which a positive electrode was formed by evaporating ITO on a glass substrate.

  As a PEDOT: PSS aqueous solution, H.P. C. “Clevios P VP AI4083” (trade name) manufactured by Stark Clevios GmbH was added dropwise and spin coated at a rotational speed of 2500 rpm for 60 seconds. Thus, a PEDOT: PSS thin film having a thickness of 30 to 40 nm was formed to form a hole transport layer.

  Next, ortho-dichlorobenzene (o-DCB) was employed as the first solvent, and diiodooctane (DIO) was employed as the second solvent to prepare a mixed solution. Specifically, the mixed solution was prepared in a glove box (oxygen concentration 0.1 ppm or less, moisture concentration 0.1 ppm or less, room temperature). That is, the donor (4 mg) and the acceptor (16 mg) were dissolved so that the concentration with respect to the solvent obtained by mixing o-DCB (0.94 g) and DIO (0.055 g) was 20 mg / ml. Eventually, in Example 1, a liquid mixture in which the mass ratio of o-DCB (first solvent): DIO (second solvent) was 94.5: 5.5 was obtained.

  This mixed liquid was dropped on the hole transport layer in the above glove box to form a mixed liquid film. Then, spin coating was performed for 60 seconds at a rotation speed of 1000 rpm. Thus, first, the first solvent was preferentially evaporated from the mixed liquid film, thereby forming the positive electrode side portion on the hole transport layer. Then, the 2nd solvent was evaporated and the negative electrode side site | part was formed on the positive electrode side site | part. As a result, a photoelectric conversion layer having a positive electrode side part and a negative electrode side part was obtained.

Next, an electron transport layer made of batocuproine was formed on the photoelectric conversion layer so as to have a film thickness of 10 nm at a rate of 1 Å / s with a vacuum degree of 1 × 10 ⁻⁴ Pa or less using a vacuum deposition apparatus. Furthermore, a negative electrode made of Ag was formed on the electron transport layer by a vacuum vapor deposition apparatus so as to have a film thickness of 300 nm at a rate of 10 Å / s at a degree of vacuum of 1 × 10 ⁻⁴ Pa or less.

  FIG. 2 shows a bright-field image of the organic thin-film solar cell 10A according to Example 1 manufactured as described above, observed using a scanning transmission electron microscope (STEM). For convenience of explanation, among the components of the organic thin film solar cell 10A shown in FIG. 2, the same components as those of the organic thin film solar cell 10 shown in FIG. .

  In general, the light-colored region in the bright field image by STEM reflects the state in which there are few electrons scattered by the sample material when the electron beam is transmitted through the sample material, and there are many electrons that are transmitted through the sample material. It is. On the other hand, the area shown in dark color reflects the state where many electrons are scattered by the sample material when the electron beam is transmitted through the sample material, and few electrons are transmitted through the sample material, contrary to the light color. is there. For this reason, in the bright field image by STEM, it turns out that the density of the sample substance which exists in the area | region shown with a relatively light color is smaller than the density of the sample substance which exists in the area | region shown with a dark color.

  From the bright field image of FIG. 2, it was confirmed that the photoelectric conversion layer 16 has a positive electrode side portion 22 indicated by a substantially uniform light color and a negative electrode side portion 24 indicated by a substantially uniform dark color. . Further, in each region of the positive electrode side portion 22 and the negative electrode side portion 24, no remarkable color shading is recognized. Therefore, it turns out that the donor and acceptor contained in any of the positive electrode side portion 22 and the negative electrode side portion 24 do not form a domain (bulk) that separates each other.

  Further, from FIG. 2, it can be confirmed that one surface of the positive electrode side portion 22 is in contact with the hole transport layer 18 on the positive electrode 12 side and the other side is continuous with one side of the negative electrode side portion 24. Furthermore, it can be confirmed that the other surface of the negative electrode side portion 24 is in contact with the electron transport layer 20 on the negative electrode 14 side.

  Here, apart from Examples 1 and 2 and Comparative Examples 1 and 2, Sample 1 in which a layer consisting only of the above donor was formed on a hole transporting layer, and a layer consisting only of the above acceptor was formed as a hole transporting layer Sample 2 formed in the above was prepared. And the bright field image by STEM was obtained similarly about each longitudinal section of samples 1 and 2, and the shade of these colors was compared. As a result, it was confirmed that the layer consisting only of the donor of sample 1 was light and the layer consisting only of the acceptor of sample 2 was dark. Therefore, it can be said that the density of the layer consisting only of the donor is smaller than that of the layer consisting only of the acceptor.

  Further, the shades of the respective colors of the positive electrode side portion 22 and the negative electrode side portion 24 in the bright field image of FIG. 2 and the layer of the sample 1 and the layer of the sample 2 were compared. As a result, the color of the positive electrode side portion 22 is slightly darker than that of the sample 1 donor-only layer, and the color of the negative electrode side portion 24 is slightly darker than that of the sample 2 acceptor only layer. Slightly faint was confirmed.

  From the above observation, of the positive electrode side portion 22 and the negative electrode side portion 24 in the bright field image of FIG. 2, the ratio of the lighter positive side portion 22 containing a donor having a lower density than the acceptor. It can be seen that is larger. On the other hand, it can be seen that the relatively dark negative electrode side portion 24 has a larger proportion of acceptors having a higher density than the donor. In addition, the ratio to contain may be either a mass ratio or a volume ratio.

  Further, since the bright field image of the positive electrode side portion 22 is darker than the bright field image of the layer consisting only of the donor of the sample 1, the positive electrode side portion 22 includes acceptors dispersed in the donor. It can be said that. Similarly, since the bright field image of the negative electrode side portion 24 is lighter than the bright field image of the layer consisting only of the acceptor of the sample 2, the negative electrode side portion 24 includes donors dispersed in the acceptor. It can be said that.

  Therefore, in the photoelectric conversion layer 16, the acceptor or the donor is dispersed in the positive electrode side portion 22 and the negative electrode side portion 24, and accordingly, a photoelectric layer having a planar heterojunction structure in which a layer composed only of a donor and a layer composed only of an acceptor are stacked. Compared to the conversion layer or the like, the dissociation surface from which excitons dissociate can be increased. Thereby, the generation efficiency of electrons and holes can be improved.

  In addition, the raised part formed in the substantially center part in the electron carrying layer 20 represents the state of nucleation at the time of vapor deposition, and the local aggregation at the time of growth, and has a big influence on the performance of this organic thin film solar cell 10A. is not.

[Example 2]
Implementation was carried out except that a mixed solution was prepared by mixing o-DCB and DIO so that the mass ratio of o-DCB (first solvent): DIO (second solvent) was 86.5: 13.5. The organic thin film solar cell of Example 2 was obtained in the same manner as Example 1.

  Also for the vertical cross section of the organic thin film solar cell of Example 2, bright field images were obtained by STEM, and the shades of these colors were compared. As a result, similar to the organic thin film solar cell 10A of Example 1, the donor and acceptor contained in any of the positive electrode side portion and the negative electrode side portion did not form a domain (bulk) that separated each other. In addition, it was found that the positive electrode side portion has a larger proportion of the donor contained than the acceptor, and the acceptor is dispersed in the donor. On the other hand, it was found that the proportion of the negative electrode side portion containing the acceptor was larger than that of the donor, and the donor was contained in the acceptor in a dispersed state.

[Comparative Example 1]
Example except that o-DCB and DIO were mixed to prepare a mixed solution so that the mass ratio of o-DCB (first solvent): DIO (second solvent) was 98.6: 1.4. In the same manner as in Example 1, an organic thin film solar cell of Comparative Example 1 was obtained.

  With respect to the longitudinal section of the organic thin-film solar cell of Comparative Example 1, a bright field image was obtained by STEM, and the shades of these colors were compared. As a result, in the photoelectric conversion layer of Comparative Example 1, it was confirmed that remarkable color shading was mixed. That is, this photoelectric conversion layer has a BHJ structure in which each of the donor and acceptor forms a phase-separated domain, and these domains are mixed in the photoelectric conversion layer.

[Comparative Example 2]
A comparative example was prepared in the same manner as in Example 1 except that the liquid mixture was prepared without using DIO, that is, the mass ratio of o-DCB (first solvent): DIO (second solvent) was 100: 0. 2 organic thin film solar cells were obtained.

  As for the longitudinal section of the organic thin-film solar cell of Comparative Example 2, a bright field image obtained by STEM was obtained, and as a result of comparing the shades of these colors, it was confirmed that it had a BHJ structure like the photoelectric conversion layer of Comparative Example 1. It was.

For each of the organic thin film solar cells of Examples 1 and 2 and Comparative Examples 1 and 2, the parallel resistance (R _sh ) was evaluated. Specifically, a solar solar simulator (manufactured by Eiko Seiki Co., Ltd., product number “YSS-150”) is used, the irradiance is 1 sun (100 mW / cm ² , 25 ° C.), and the measurement voltage is −0.3 to 1. The current corresponding to the voltage was measured as a range of 5V. And the current density was computed from the obtained electric current value and the surface area of the electric power generation part of each organic thin film solar cell, and the curve (IV curve) which shows the relationship between a current density and a voltage was calculated | required.

  Here, the theoretical relationship between the current and voltage of the solar cell is expressed by the following equation.

_{Incidentally, I, I ph, I o} , q, n, R s, R sh, k, T , respectively current, the photocurrent, reverse saturation current, electric charge, the diode factor, series resistance, parallel resistance, Boltzmann Coefficient, measured temperature.

By fitting this equation and the above IV curve, the parallel resistances (R _sh ) of the organic thin film solar cells of Examples 1 and 2 and Comparative Examples 1 and 2 were obtained, respectively, and the results are shown in Table 1.

  From Table 1, it can be seen that the parallel resistance of Examples 1 and 2 is three times or more larger than the parallel resistance of Comparative Examples 1 and 2. Therefore, in the organic thin film solar cell according to the present invention, compared with the organic thin film solar cell having the photoelectric conversion layer having the BHJ structure, the leakage current in the photoelectric conversion layer can be effectively suppressed, and the parallel resistance is remarkably increased. It is clear that it is possible.

DESCRIPTION OF SYMBOLS 10, 10A ... Organic thin-film solar cell 12 ... Positive electrode 14 ... Negative electrode 16 ... Photoelectric conversion layer 18 ... Hole transport layer 20 ... Electron transport layer 22 ... Positive electrode side part 24 ... Negative electrode side part

Claims (3)

An organic thin film solar cell having a photoelectric conversion layer between a positive electrode and a negative electrode,
The photoelectric conversion layer includes an electron donor containing at least one of the nanographene polymers represented by formulas (1) to (4), and an electron acceptor that accepts electrons donated from the electron donor. Including
In the photoelectric conversion layer, the ratio of containing the electron donor is larger in the positive electrode side portion facing the positive electrode side than in the electron acceptor, and the negative electrode side portion facing the negative electrode side is larger than that in the electron donor. And the ratio of containing the electron acceptor is large,
The organic thin-film solar cell, wherein each of the electron donor and the electron acceptor contained in the positive electrode side portion and the negative electrode side portion does not form a domain that separates phases from each other.

However, at least one of R1 to R6 in formulas (1) to (4) is an alkoxy group, and R7 to R10 are each independently any one of hydrogen, an alkyl group, and an alkoxy group. A method for producing an organic thin-film solar cell having a photoelectric conversion layer between a positive electrode and a negative electrode,
An electron donor containing at least one of the nanographene polymers represented by formulas (1) to (4), an electron acceptor that accepts electrons donated from the electron donor, the electron donor, and the electron donor A first solvent that is a good solvent for each of the electron acceptors, a boiling point higher than that of the first solvent, a poor solvent for the electron donor, and a good solvent for the electron acceptor A step of mixing a second solvent to obtain a mixed solution;
Supplying the mixed liquid above the positive electrode to form a mixed liquid film;
By preferentially evaporating the first solvent and the second solvent in the mixed liquid film from the first solvent having a low boiling point, the positive electrode side contains the electron donor rather than the electron acceptor. Forming a positive electrode side portion having a large ratio and then forming a negative electrode side portion having a larger ratio of containing the electron acceptor than the electron donor on the negative electrode side to obtain the photoelectric conversion layer. ,
The organic thin film characterized in that the electron donor and the electron acceptor included in each of the positive electrode side part and the negative electrode side part form the photoelectric conversion layer in which a domain for phase separation is not formed. A method for manufacturing a solar cell.

However, at least one of R1 to R6 in formulas (1) to (4) is an alkoxy group, and R7 to R10 are each independently any one of hydrogen, an alkyl group, and an alkoxy group. In the manufacturing method of the organic thin-film solar cell of Claim 2,
The mixed liquid is prepared so that the mass ratio of the first solvent to the second solvent is 94.5: 5.5 to 86.5: 13.5. Method.

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