Hole-transporting polymers, photoelectric conversion elements using the same, and organic thin-film solar cells

Abstract

To provide: hole transport polymers with excellent high-temperature and high-humidity durability and excellent photoelectric conversion properties even with weak light such as room light; and photoelectric conversion elements and organic thin-film solar cells employing the polymers.SOLUTION: The invention provides a hole transport polymer represented by the general formula (1) in the figure. In the formula (1), R1 to R5 each represent a hydrogen atom or an at most C4 alkyl or alkoxy group, excluding the case where all of R1 to R5 are hydrogen atoms; Ar1 is represented by a prescribed formula defined separately. The use of the polymer compound represented by the formula (1) as a material for a hole transport layer of photoelectric conversion elements and solar cells can improve high-temperature and high-humidity durability and charge (hole) mobility, improving the energy conversion efficiency of the photoelectric conversion elements and solar cells.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a hole-transporting polymer used as a material for a hole transport layer, and to a photoelectric conversion element and an organic thin-film solar cell using the same. [Background technology]

[0002] In recent years, the driving power required for electronic circuits has become extremely low, allowing various electronic components such as sensors to be driven even with very little power. Furthermore, there is growing expectation for the application of self-sustaining power sources (energy harvesting elements) that can generate and consume electricity on the spot when using sensors, and among these, solar cells are attracting attention as elements that can generate electricity anywhere there is light.

[0003] Inorganic and organic solar cells are known types of solar cells. However, inorganic solar cells use inorganic semiconductor materials such as silicon as the p-type and n-type semiconductors, which limits their range of application due to high manufacturing costs and difficulty in scaling them up. Therefore, development is currently underway on organic solar cells, which are manufactured using organic semiconductors instead of inorganic semiconductors. Organic solar cells are classified into types such as dye-sensitized solar cells, organic thin-film solar cells, and organic-inorganic hybrid solar cells.

[0004] Organic solar cells contain p-type and n-type semiconductors, and often have a hole transport layer between the photoelectric conversion layer, which absorbs light and generates positive and negative charges, and the anode. The hole transport layer plays a role in improving the photoelectric conversion efficiency of the solar cell by enabling the positive charges (holes) and negative charges (electrons) generated by photoexcitation to move efficiently without rejoining.

[0005] Among organic solar cells, solar cells equipped with a photoelectric conversion layer containing a perovskite compound, as described in Patent Document 1, Non-Patent Documents 1 and 2 (hereinafter also referred to as perovskite solar cells), have been reported to exhibit higher photoelectric conversion efficiency than amorphous silicon solar cells in weak indoor light environments, and reports on further improvements in photoelectric conversion efficiency have been successively published. The basic structure of a perovskite solar cell is generally a laminate in which a transparent electrode (cathode), electron transport layer, photoelectric conversion layer (perovskite layer), hole transport layer, and metal electrode (anode) are stacked in this order. In some cases, a mesoporous titania layer is included between the electron transport layer and the perovskite layer, and the photoelectric conversion layer is composed of the perovskite layer and the mesoporous titania layer. Of these layers, the hole transport layer is generally composed of a material containing an organic semiconductor.

[0006] Non-patent document 2 describes the use of poly[bis(4-phenyl)(2,4,6-triphenylmethyl)amine] (hereinafter also referred to as PTAA), a hole-transporting polymer having an arylamine structure, as a hole transporter, and PTAA is also commonly used in the aforementioned perovskite solar cells. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 2016-539914 [Non-patent literature]

[0008] [Non-Patent Document 1] Michael M. Lee et al., “Efficient Hybrid Solar Cells Based on Meso-Super structured Organometal Halide Perovskites”, Science (2012) 338, P643-647 [Non-Patent Document 2] Nam Joong Jeon et al., “Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells”, Nature Materials (2014) 13, P897-903 [Non-Patent Document 3] Nature volume (1998) 395, P583-585 [Summary of the Invention] [Problems to be Solved by the Invention]

[0009] However, when PTAA is used as the material for the hole transport layer, it cannot be said that sufficiently good photovoltaic conversion performance is exhibited. Therefore, generally when using this material, it is necessary to add a large amount of dopants such as lithium bis(trifluoromethanesulfonyl)imide (hereinafter also referred to as LiTFSI salt) in order to improve the photovoltaic conversion performance. Due to the doping of the大量添加された LiTFSI salt, there is a problem that the solar cell is inferior in high temperature and high humidity durability.

[0010] In view of the above problems, an object of the present invention is to provide a hole transporting polymer having excellent high temperature and high humidity durability and excellent photovoltaic conversion properties even in weak light such as indoor light, a photovoltaic conversion device using the same, and an organic thin film solar cell. [Means for Solving the Problems]

[0011] In order to achieve the above object, a first configuration of the present invention is a hole transporting polymer represented by the following general formula (1). [Chemical formula] (In formula (1), R1 to R5 represent a hydrogen atom, an alkyl group or an alkoxy group having 4 or less carbon atoms, except when all of R1 to R5 are hydrogen atoms. Ar1 is any one of the following chemical formulas (2) to (4).) [Chemical formula]

Chem.

Chem.

Advantages of the Invention

[0012] According to the first configuration of the present invention, by using the polymer compound represented by the above formula (1) as a material for the hole transport layer of the photoelectric conversion element and the solar cell, the high-temperature and high-humidity durability and the mobility of charges (holes) can be improved, and the energy conversion efficiency of the photoelectric conversion element and the solar cell is improved.

Brief Description of the Drawings

[0013] [Figure 1] Partial cross-sectional view of an organic thin-film solar cell 100 according to an embodiment of the present invention [Figure 2] Schematic diagram showing a measuring device 20 for the hole mobility of the hole transport layer by the MIS-CELIV method [Figure 3] Explanatory diagram showing the measurement result of the hole mobility by the MIS-CELIV method, which is a graph showing the time transition of the reverse voltage increasing linearly [Figure 4] Explanatory diagram showing the measurement result of the hole mobility by the MIS-CELIV method, which is a graph showing the time transition of the transmission current generated by the application of the reverse voltage <( [Figure 5] Graph showing the transmission current waveform observed when the reverse voltage application acceleration A = 150 kV / s and the forward voltage VFB is changed from 0 V to -10 V [Figure 6] Graph showing the electric field dependence of the hole mobility predicted from the transient current observed under the conditions of the reverse voltage application acceleration A = 100 to 350 kV / s and the forward voltage VFB = -10 V

Modes for Carrying Out the Invention

[0014] [1. Configuration of Organic Thin-Film Solar Cell] First, the solar cell using the hole-transporting polymer of the present invention will be described. Figure 1 is a partial cross-sectional view of an organic thin-film solar cell 100 according to one embodiment of the present invention. The organic thin-film solar cell 100 (hereinafter simply referred to as solar cell 100) comprises a substrate 1, a first electrode 2, a hole transport layer 3, a photoelectric conversion layer 4, an electron transport layer 5, and a second electrode 6. The first electrode 2 is provided on the substrate 1. The photoelectric conversion layer 4 is laminated on the first electrode 2 via the hole transport layer 3. The second electrode 6 is laminated on the photoelectric conversion layer 4 via the electron transport layer 5. The second electrode 6 may also be provided directly on the photoelectric conversion layer 4. In this case, the electron transport layer 5 shown in Figure 1 is omitted. When the solar cell 100 is used, for example, light L (for example, sunlight or indoor light) is irradiated onto the substrate 1 side of the solar cell 100. When the solar cell 100 is used, light L may also be irradiated onto the second electrode 6 side of the solar cell 100.

[0015] (substrate) The substrate 1 is not particularly limited as long as it can be used for the solar cell 100. The substrate 1 may be transparent or opaque. However, if the surface of the solar cell 100 facing the substrate 1 is the light-receiving surface, it is preferable that the substrate 1 be transparent. Examples of transparent substrates include transparent rigid substrates such as glass like quartz glass or synthetic quartz plates, and transparent flexible substrates such as transparent resin films or optical resin plates. Transparent flexible substrates have advantages such as ease of processing, reduced manufacturing costs, lighter weight, resistance to breakage, and applicability to curved surfaces.

[0016] <1st electrode> The first electrode 2 is, for example, a hole injection electrode. The first electrode 2 is not particularly limited as long as it is made of a conductive material. The material of the first electrode 2 is appropriately selected considering the work function of the material of the second electrode 6. If the material of the second electrode 6 is a material with a low work function, it is preferable that the material of the first electrode 2 is a material with a high work function. Examples of high work function materials that can be used as the material of the first electrode 2 include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide, and zinc oxide (ZnO).

[0017] Furthermore, the material of the first electrode 2 is appropriately selected considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 side or the surface on the second electrode 6 side. When the light-receiving surface is the surface on the substrate 1 side, it is preferable that the first electrode 2 is a transparent electrode. Examples of materials used when the first electrode 2 is a transparent electrode include indium zinc oxide (IZO), ITO, ZnO-Al, and Zn-Sn-O.

[0018] The total light transmittance of the first electrode 2 is preferably 85% or more, more preferably 90% or more, and particularly preferably 92% or more. When the total light transmittance of the first electrode 2 is 85% or more, when the light-receiving surface of the solar cell 100 is the surface facing the substrate 1, light can be sufficiently transmitted through the first electrode 2 on the substrate 1, and the photoelectric conversion layer 4 can efficiently absorb the light.

[0019] The sheet resistance of the first electrode 2 is preferably 20 [Ω / sq] or less, and more preferably 15 [Ω / sq] or less. When the sheet resistance of the first electrode 2 is 20 [Ω / sq] or less, the charge generated in the photoelectric conversion layer 4 is sufficiently transmitted to the external circuit. The sheet resistance can be measured, for example, using a resistivity meter (Loresta AXMCP-T370, manufactured by Mitsubishi Chemical Analytec, 4-probe type) in accordance with JIS (Japanese Industrial Standards) R1637 (Test method for resistivity of fine ceramic thin films - Measurement method by 4-probe method).

[0020] The film thickness of the first electrode 2 is preferably 0.1 nm or more and 500 nm or less, and more preferably 1 nm or more and 300 nm or less. When the film thickness of the first electrode 2 is 0.1 nm or more, the sheet resistance of the first electrode 2 does not become too large, and the charge (holes) generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit. On the other hand, when the film thickness of the first electrode 2 is 500 nm or less, the total light transmittance of the first electrode 2 is high.

[0021] The first electrode 2 may be a single layer. Alternatively, the first electrode 2 may be composed of multiple layers having different work functions. If the first electrode 2 consists of multiple layers, the film thickness of the first electrode 2 as described above refers to the total film thickness of the multiple layers.

[0022] The first electrode 2 may be formed in a sheet shape over the entire surface of the substrate 1, or it may be formed in a pattern shape on the substrate 1. The shape of the first electrode 2 may be flat or uneven. Examples of uneven shapes include a textured structure, a pyramidal structure, a wave-shaped structure, a comb-shaped structure, and a nanopillow structure. When the first electrode 2 is uneven, the incident light is scattered by the unevenness of the first electrode 2, so that more light is taken up by the photoelectric conversion layer 4, and the energy conversion efficiency of the solar cell 100 is improved.

[0023] <Hole transport layer> The hole transport layer 3 is laminated between the first electrode 2 and the photoelectric conversion layer 4. The hole transport layer 3 is provided to facilitate the injection (movement) of holes from the photoelectric conversion layer 4 to the first electrode 2 (hole injection electrode). By laminating the hole transport layer 3, the hole injection efficiency from the photoelectric conversion layer 4 to the first electrode 2 is increased, improving the energy conversion efficiency of the solar cell 100. The photoelectric conversion layer 3 contains a hole-transporting polymer represented by the following general formula (1). The hole transport layer 3 may contain only the hole-transporting polymer represented by general formula (1), or it may further contain additives. Conventional known additives such as interface treatment agents can be used as additives.

[0024] [ka]

[0025] In formula (1), R1 to R5 represent hydrogen atoms or alkyl or alkoxy groups having 4 or fewer carbon atoms, except in the case where all of R1 to R5 are hydrogen atoms. Ar1 is one of the following chemical formulas (2) to (4). [ka] [ka] [ka]

[0026] Specific examples of hole-transporting polymers represented by general formula (1) include compounds HTM-1 to HTM-5, represented by the following chemical formulas.

[0027] [ka]

[0028] [ka]

[0029] [ka]

[0030] [ka]

[0031] [ka]

[0032] By using the polymer compound represented by formula (1) above as the hole-transport polymer constituting the hole transport layer 3, the mobility of charge (holes) can be improved, thereby increasing the energy conversion efficiency of the solar cell 100. The mobility of charge (holes) will be discussed later.

[0033] <Photoelectric conversion layer> The photoelectric conversion layer 4 contains a donor (electron donor) and an acceptor (electron acceptor). The donor is not particularly limited as long as it functions as a donor, but it is preferably a conductive polymer (electron-donating organic material) that has electron-donating properties. An electron-donating organic material is defined as the organic compound with the lower electron affinity when two organic compounds are brought into contact. In other words, any organic compound that has electron-donating properties can be used as a donor. The donor is preferably a compound that can be formed into a thin film using a solution in which the donor is dissolved in an organic solvent (for example, a coating method such as casting or spin coating). The photoelectric conversion layer 4 may contain only a donor and an acceptor, or it may contain other compounds.

[0034] Examples of electron-donating conductive polymers that can be used as donors include polyphenylene, polyphenylene vinylene, polysilane, polythiophene, polybenzodithiophene, polycarbazole, polyvinylcarbazole, porphyrin, polyacetylene, polypyrrole, polyaniline, polyfluorene, polyvinylpyrene, polyvinylanthracene, and derivatives thereof. The donor may be a copolymer obtained by copolymerizing at least two of these electron-donating conductive polymers. Other examples of electron-donating conductive polymers include phthalocyanine-containing polymers, carbazole-containing polymers, and organometallic polymers.

[0035] As an electron-donating conductive polymer that can be used as a donor, a polymer having at least one of the following structures—thiophene, benzothiophene, and benzodithiophene (polythiophene polymer)—is preferred. The polythiophene polymer is preferably capable of absorbing visible light. Furthermore, the polythiophene polymer is preferably of the donor-acceptor (DA) type.

[0036] The acceptor is not particularly limited as long as it functions as an acceptor, but it is preferably a conductive polymer (electron-accepting organic material) that has electron-accepting properties. Electron-accepting organic materials are mainly represented by electron-transporting organic compounds and refer to organic compounds that have a property of readily accepting electrons. More specifically, it refers to the organic compound with the greater electron affinity when two organic compounds are used in contact. In other words, any organic compound that has electron-accepting properties can be used as an acceptor.

[0037] Examples of electron-accepting organic materials include fullerenes and their derivatives (such as PCBM), carbon nanotubes and their derivatives, perylenes and their derivatives (such as PTCDA and PTCDI), naphthalene derivatives (such as NTCDA and NTCDI), oligomers and polymers having pyridine and its derivatives as a backbone, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and their derivatives, tris(8-hydroxyquinolinate)aluminum complexes, bis(4-methyl-8-quinolinate)aluminum complexes, distylyl arylene derivatives, and silole compounds. Fullerene derivatives (such as PCBM) are particularly preferred, but the material is not limited thereto.

[0038] In the photoelectric conversion layer 4, the ratio of the acceptor mass (MA) to the donor mass (MD) (MA / MD) is preferably 0.1 or more and 2.0 or less, and more preferably 1.0 or more and 2.0 or less. When the ratio (MA / MD) is within this range, the balance between the acceptor and donor of the solar cell 100 is good, and the energy conversion efficiency of the solar cell 100 is improved.

[0039] The thickness of the photoelectric conversion layer 4 is not particularly limited, as long as the desired energy conversion efficiency can be obtained. The thickness of the photoelectric conversion layer 4 is preferably 0.2 nm or more and 3000 nm or less, and more preferably 10 nm or more and 600 nm or less. When the thickness of the photoelectric conversion layer 4 is 3000 nm or less, the sheet resistance of the photoelectric conversion layer 4 is more likely to be the desired value. On the other hand, when the thickness of the photoelectric conversion layer 4 is 0.2 nm or more, a short circuit between the first electrode 2 and the second electrode 6 is less likely to occur.

[0040] <Electron transport layer> The electron transport layer 5 is laminated between the photoelectric conversion layer 4 and the second electrode 6. The electron transport layer 5 is provided to facilitate the injection (movement) of electrons from the photoelectric conversion layer 4 to the second electrode 6 (electron injection electrode). By laminating the electron transport layer 5, the electron injection efficiency from the photoelectric conversion layer 4 to the second electrode 6 is increased, and the energy conversion efficiency of the solar cell 100 is improved.

[0041] The material contained in the electron transport layer 5 (electron transport layer material) is not particularly limited as long as it is a material that can stably inject electrons from the photoelectric conversion layer to the second electrode. Examples of electron transport layer materials include conductive organic compounds, charge transfer complexes, alkali metals, alkaline earth metals, and organic compounds doped with alkali metals or alkaline earth metals.

[0042] Examples of alkali metals that can be used as electron transport layer materials include lithium, sodium, potassium, rubidium, and cesium. Examples of alkaline earth metals that can be used as electron transport layer materials include beryllium, magnesium, calcium, strontium, and barium. Examples of alkali metal or alkaline earth metal-doped organic compounds that can be used as electron transport layer materials include alkali metal or alkaline earth metal-doped bathocuproin (BCP) and batphenanthroline (Bphen). Preferred alkali metals and alkaline earth metals used for doping are lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, or barium, with lithium, cesium, barium, or strontium being more preferred.

[0043] When the electron transport layer material is a conductive organic compound or a charge transfer complex, the thickness of the electron transport layer is preferably 10 nm to 200 nm. When the electron transport layer material is an alkali metal, an alkaline earth metal, or an organic compound doped with an alkali metal or alkaline earth metal, the thickness of the electron transport layer is preferably 0.1 nm to 50 nm.

[0044] <Second electrode> The second electrode 6 is, for example, an electron injection electrode. The second electrode 6 is provided opposite the first electrode 2. The second electrode 6 is not particularly limited as long as it is conductive. The material of the second electrode 6 is appropriately selected, for example, taking into consideration the work function of the material of the first electrode 2. If the material of the first electrode 2 is a material with a high work function, it is preferable that the material of the second electrode 6 is a material with a low work function.

[0045] Examples of materials with low work functions that can be used as the material for the second electrode 6 include calcium (Ca), lithium (Li), indium (In), aluminum (Al), magnesium (Mg), samarium (Sm), terbium (Tb), ytterbium (Yb), zirconium (Zr), and lithium fluoride (LiF).

[0046] Furthermore, the material of the second electrode 6 is appropriately selected, for example, by considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 side or the surface on the second electrode 6 side. If the light-receiving surface is the surface on the substrate 1 side, the first electrode 2 is preferably a transparent electrode, but the second electrode 6 does not have to be a transparent electrode.

[0047] The film thickness of the second electrode 6 is preferably 0.1 nm or more and 500 nm or less, and more preferably 1 nm or more and 300 nm or less. When the film thickness of the second electrode 6 is 0.1 nm or more, the sheet resistance of the second electrode 6 does not become too large, and the charge generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit. On the other hand, when the film thickness of the second electrode 6 is 500 nm or less, the total light transmittance of the second electrode 6 is high.

[0048] The second electrode 6 may be a single layer. Alternatively, the second electrode 6 may be composed of multiple layers having different work functions. If the second electrode 6 consists of multiple layers, the film thickness of the second electrode 6 as described above refers to the total film thickness of the multiple layers.

[0049] The second electrode 6 may be formed in a sheet shape over the entire surface of the electron transport layer 5, or it may be formed in a pattern shape on the electron transport layer 5.

[0050] <Other components> The solar cell 100 may further include other components in addition to the substrate 1, first electrode 2, hole transport layer 3, photoelectric conversion layer 4, electron transport layer 5, and second electrode 6 described above, as needed. Examples of other components include a protective sheet layer, filler layer, barrier layer, protective hard coat layer, strength support layer, anti-fouling layer, high light reflectivity layer, light containment layer, ultraviolet blocking layer, infrared blocking layer, and encapsulating layer. Furthermore, adhesive layers may be laminated between each layer of the solar cell 100, as needed.

[0051] [2. Measurement of hole mobility of hole-transporting polymers] Next, we will explain the charge (hole) mobility of the hole transport material constituting the hole transport layer 3. Mobility is the speed at which carriers diffuse. The greater the mobility of the hole transport material, the greater the distance that carriers can diffuse, which is thought to contribute to high photoelectric conversion efficiency in perovskite solar cells, for example. Methods for measuring this mobility include the time-of-flight (TOF) method, the evaluation method using a fabricated field-effect transistor (FET method), the Photo-CELIV method, and the MIS-CELIV method as described in AIP ADVANCES 8, 105001 (2018).

[0052] Each of the above measurement methods has its advantages and disadvantages. For example, the time-of-flight method requires the formation of a thick film of about 1 μm, making it difficult to produce films using coating methods. From the standpoint of being able to measure relatively accurately and easily with coated films of 1 μm or less, it is preferable to evaluate using the Photo-CELIV method or the MIS-CELIV (injection-charge extraction by linearly increasing voltage in metal-insulator-semiconductor structures) method.

[0053] The MIS-CELIV method is a technique that accumulates injected charge at the insulating layer interface and determines electron or hole mobility from the transient current waveform resulting from the extraction of this accumulated charge. It is expected to be a new measurement technique that enables the analysis of organic semiconductor thin films. The following describes how to evaluate hole mobility using the MIS-CELIV method.

[0054] Figure 2 is a schematic diagram of a measurement apparatus 20 for measuring the hole mobility of a hole transport layer using the MIS-CELIV method. A highly n-doped silicon wafer was used as the measurement substrate 21, in which a thermal silicon oxide (SiO2) layer 21b was laminated on the surface of a Si layer 21a. A hole transport layer 3 was formed on the surface of this measurement substrate 21 by spin coating. Subsequently, a molybdenum trioxide (MoO3) hole injection layer 22 and an Al electrode 23 were sequentially deposited on the surface of the hole transport layer 3. Then, a circuit including a waveform generator 25, an oscilloscope 27, and a resistor 29 was connected to the Si layer 21a and the Al electrode 23.

[0055] The film thicknesses of each layer are as follows: SiO2 layer 21b is 30 nm, hole transport layer 3 is approximately 100 nm, hole injection layer 22 (MoO3) is 5 nm, and Al electrode 23 is 100 nm. Film thickness was measured using a stylus-type film thickness step meter (Dektak XT, Bruker).

[0056] Figures 3 and 4 are explanatory diagrams showing the measurement results of hole mobility by the MIS-CELIV method, and are graphs showing the time evolution of reverse voltage and transmitted current, respectively. A negative forward voltage V is applied to the negative measurement substrate 21. FB When applied, holes h are transferred from the Al electrode 23 to the hole transport layer 3 via the hole injection layer 22. + As shown in Figure 2, holes h are injected into the interface between the SiO2 layer (insulating layer) 21b and the hole transport layer (semiconductor) 3. + It accumulates.

[0057] In this state, by applying a reverse voltage that rises linearly with a voltage rise rate A = dV / dt as shown in Figure 3, the accumulated holes h + This can be extracted. The transient phenomena of the MIS-CELIV method are the displacement current j0 due to the sum of the geometric capacitances of the insulating layer and the semiconductor, and the accumulated holes h. + The saturation current j is drawn out as a result of this process. sat It consists of a current peak Δj due to the accumulated holes h. + Saturation current j by extraction sat The current peak Δj is determined by the following equation (5). The mobility μ is determined by the following equation (5).

[0058] JPEG0007841269000014.jpg2392

[0059] In Equation (5), εs is the dielectric constant of the semiconductor, εi is the dielectric constant of the insulating layer, ds is the film thickness of the semiconductor, di is the film thickness of the insulating layer, and A is the reverse voltage application acceleration. The carrier transport time t tr is the characteristic time t until the value of j0 doubles 2j0 and is related to it.

[0060] When the capacitance Ci of the insulating layer is sufficiently larger than the capacitance Cs of the semiconductor (Ci / Cs ≥ 1), t tr is defined by the following Equation (6) by the method of Appl. Phys. Lett. 110, 153504 (2017), considering the applied voltage drop due to the finite insulator layer.

[0061] JPEG0007841269000015.jpg1567

[0062] Figure 5 is a graph showing the transmission current waveform observed when the forward voltage V FB is changed from 0 V to -10 V under the condition of a reverse voltage application acceleration A = 150 kV / s for an element in which NPB (naphthylphenylbiphenyldiamine, film thickness 290 nm) is laminated as the hole transport layer 3 on the SiO2 layer 21b. As shown in Figure 5, at V FB = 0 [V], the transmission current is composed of a rectangular wave consisting only of the displacement current j0, which is derived from the total capacitance of the SiO2 layer 21b and the hole transport layer 3. This flat response indicates that there are no holes h + accumulated in the hole transport layer 3.

[0063] V FB When -2 to -10 [V] is applied, holes h + are injected from the Al electrode 23 through the hole injection layer 22 into the hole transport layer 3 and accumulate at the interface between the SiO2 layer 21b and the hole transport layer 3, resulting in a current peak Δj due to hole extraction. As V FB increases, Δj increases, and further j sat = 172 [A / m 2It saturated at [ ]. The transient current of MIS-CELIV is ultimately limited by the displacement current of the insulating layer (SiO2 layer 21b).

[0064] That is, sufficient holes h from the interface between the SiO2 layer 21b and the hole transport layer 3 + V before it is supplied FB In regions where V is low, FB Δj increases linearly with respect to V, and eventually V FB Even if we increase V, Δj will saturate to a state where it does not change. FB When the voltage is -10[V], there are enough holes h at the interface between the SiO2 layer 20b and the hole transport layer 3. + It can be seen that it is accumulating.

[0065] Figure 6 shows the reverse voltage application rate A = 100~350 kV / s and the forward voltage V FB This graph shows the electric field dependence of hole mobility predicted from transient current observed under the condition of -10V. The charge dependence of hole mobility shown in Figure 6 can be analyzed using the following equation (7) to calculate the hole mobility μ0 at an electric field of 0.

[0066] JPEG0007841269000016.jpg1892

[0067] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiments, an example was described in which the hole-transporting polymer of the present invention was used in the hole transport layer 3 of a solar cell 100, but it is not limited to the solar cell 100, and can also be used, for example, as a hole transport layer of a photoelectric conversion element.

[0068] As an example of a photoelectric conversion element, for instance, a semiconductor electrode (first electrode) is fabricated by laminating a hole-blocking layer and a porous electron transport layer on a glass substrate, and further supporting a photosensitizing material. A hole transport layer is formed on this semiconductor electrode (first electrode) by spin coating using a solution of the hole-transporting polymer of the present invention dissolved in an organic solvent, and a second electrode is formed by laminating silver on the formed hole transport layer using a vacuum deposition method. The effects of the present invention will be further explained in detail below with reference to examples. [Examples]

[0069] [Example of hole-transport polymer (HMT-1) synthesis] (Polymerization process) A 1000 mL two-necked flask equipped with a reflux condenser was charged with the dibromo starting material (compound B in the synthesis scheme), Pd2(dba)3, Amphos, sodium tert-butoxide, and a stirring bar. The system was then stirred at room temperature using a magnetic stirrer while purging the atmosphere with nitrogen. Subsequently, xylene and the diamine starting material (compound A in the synthesis scheme) were added, and the oil bath was heated to 135-140°C (liquid temperature in the flask 130°C) while stirring, and the reaction was carried out for 2 hours.

[0070] (Terminal stop step 1) A mixture of xylene and bromobenzene was added dropwise to the reaction solution, and the mixture was allowed to react for 2 hours, for a total of 4 hours. This stopped the reaction of the terminal amino groups of the polymer.

[0071] (Terminal stop process 2) A xylene solution of diphenylamine was added dropwise to the reaction mixture, and the reaction was allowed to continue for 2 hours for a total of 6 hours. This stopped the reaction of the terminal bromo groups of the polymer.

[0072] (Primary purification process) A poor solvent mixture of 1350 mL of acetone and 150 mL of water was stirred, and the reaction mixture was slowly added to precipitate the solid. After stirring for 1 hour, the solid was separated by filtration. 1000 mL of methanol was added to the separated solid and stirred for 30 minutes. The solid was again separated by filtration, and the mixture was vacuum-dried (100°C, 8 hours) to obtain the primary solid.

[0073] (Final purification process) The primary solid was heated and dissolved in 1200 mL of toluene, and then washed twice with 400 mL of water using a separatory funnel. Anhydrous sodium sulfate was added to the organic layer and stirred at room temperature for 5 minutes. The reaction mixture was then filtered and the filtrate was collected. Subsequently, as a clay adsorption treatment, 66.6 g of activated clay was added to the filtrate, and the mixture was heated to 100°C and stirred for 50 minutes. The reaction mixture was then filtered by hot filtration and the filtrate was collected. This clay adsorption treatment was performed a total of six times.

[0074] After six rounds of clay adsorption treatment, the filtrate was concentrated to 400 mL using an evaporator. The concentrated solution was then added dropwise to a poor solvent of 1350 mL of acetone and 150 mL of water, and the precipitated solid was separated by filtration. 1000 mL of methanol was added to the separated solid and stirred. The solid was again separated by filtration, and the mixture was vacuum-dried (100°C, 8 hours) to obtain the final solid. The synthesis scheme is shown below. Table 1 shows the molecular weight (MW), weight, moles, and mole ratios of the compounds used in the synthesis.

[0075] [ka]

[0076] [Table 1]

[0077] [Measurement of charge mobility of hole-transport polymers using the MIS-CELIV method] Using the measuring apparatus 20 shown in Figure 2, the hole mobility of the hole-transporting polymers HTM-1 to HTM-5, HTM-R1, HTM-R2, and the following comparative examples, HTM-R1 to HTM-R4, was measured by the MIS-CELIV method.

[0078] [ka]

[0079] [ka]

[0080] [ka]

[0081] [ka]

[0082] The hole mobility was measured by cleaning a highly n-doped silicon wafer substrate with a 30 nm thick thermal silicon oxide (SiO2) layer using ultrasonic cleaning in the following order: ultrasonic cleaning in a solution of ultrapure water mixed with 20% Shikaclean (20 minutes), ultrasonic cleaning in ultrapure water (10 minutes), ultrasonic cleaning in acetone (10 minutes), ultrasonic cleaning in IPA (isopropyl alcohol) (10 minutes), and UV ozone cleaning (20 minutes).

[0083] A 300 μL drop of a 3% chloroform solution of a hole-transporting polymer was added to a cleaned substrate under atmospheric pressure. A hole-transporting layer (with a thickness of approximately 200 nm) was then deposited by spin coating using a spin coater at 500 rpm for 60 seconds.

[0084] A hole implantation layer of molybdenum trioxide (MoO3) and an Al electrode are placed on a hole transport layer, with a MoO3 deposition rate of 0.1 Å / s, an Al deposition rate of 10-15 Å / s, and a vacuum of 1 × 10⁻¹⁰. -3The measurement element was fabricated by deposition using Pa. The element structure was Si / SiO2 (30 nm) / hole transport layer (200 nm) / MoO3 (5 nm) / Al (100 nm).

[0085] The fabricated measuring element is set in the measuring device 20 shown in Figure 2, and under the condition of reverse voltage application rate A = 150kV, V FB The transient current waveform obtained when a forward voltage of -10[V] was applied was t 2j0 The hole mobility was estimated and calculated from equations (5) and (6) mentioned above. The transient phenomena of MIS-CELIV were measured under medium vacuum (<10 Pa) using a waveform generator (33511B, Agilent) and an oscilloscope (DSO-X 2004A, Agilent).

[0086] Furthermore, the solubility in chlorobenzene and toluene was compared. For chlorobenzene, a score of ○ was used if the substance dissolved at a concentration of 9.09% by mass, and a score of × was used if it did not dissolve. Similarly, for toluene, a score of ○ was used if the substance dissolved at a concentration of 4.76% by mass, and a score of × was used if it did not dissolve. The results, along with the ionization potential (IP), weight-average molecular weight (Mw), and number-average molecular weight (Mn), are shown in Table 2.

[0087] [Table 2]

[0088] As shown in Table 1, the hole-transporting polymers of the present invention, compounds HTM-1 to HTM-5, all have a hole mobility of 1.7 × 10⁻⁶. -4 The above results demonstrate excellent hole mobility. In particular, HTM-3 to HTM-5 showed a hole mobility of 8.5 × 10⁻⁶. -4 The above results demonstrate extremely high hole mobility. This is thought to be due to the fact that the bond structure between the amino groups of HTM-3 to HTM-5 (Ar1 in general formula (1)) is either a diphenylethylene structure represented by chemical formula (2) (HTM-3, HTM-4) or a diphenylbutadiene structure represented by chemical formula (4) (HTM-5), which contributes to the hole mobility.

[0089] Furthermore, all of HTM-1 to HTM-5 showed good solubility in chlorobenzene. In particular, HTM-1 to HTM-3 and HTM-5 also showed good solubility in toluene, and since halogen-free solvents can be used, the environmental impact can be reduced.

[0090] In contrast, the comparative examples HTM-R1 and HTM-R2 showed a hole mobility of 1.0 × 10⁻⁶. -4 The results were as follows and were insufficient. Furthermore, since HTM-R3 and HTM-R4 are insoluble in toluene and chlorobenzene, purification during synthesis was not possible, and hole mobility measurement was also impossible.

[0091] Based on these results, it was confirmed that using compounds HTM-1 to HTM-5 as hole-transporting polymers can effectively improve the energy conversion efficiency of solar cells. [Industrial applicability]

[0092] The present invention relates to a hole-transporting polymer used as a material for a hole transport layer, and can be used in photoelectric conversion elements and organic thin-film solar cells using the same. By utilizing the present invention, it is possible to provide a hole-transporting material that has excellent high temperature and high humidity resistance and excellent photoelectric conversion performance even in weak light such as indoor light, as well as a photoelectric conversion element and an organic thin-film solar cell using the same. [Explanation of Symbols]

[0093] 1 circuit board 2 1st electrode 3. Hole transport layer 4. Photoelectric conversion layer 5 Electron transport layer 6 Second electrode 20 Measuring devices 21 Measurement board 21a Si layer 21b SiO2 layer 22 Hole injection layer 23 Al electrode 25 Waveform Generator 27 Oscilloscope 29 Resistors 100 solar cells

Claims

1. A hole-transporting polymer represented by the following general formula (1), 【Chemistry 1】 (In formula (1), R1 to R5 represent hydrogen atoms or alkyl or alkoxy groups having 4 or fewer carbon atoms, except when all of R1 to R5 are hydrogen atoms. Ar1 is one of the following chemical formulas (2) to (4).) At least one of R1, R2, R4, and R5 in the general formula (1) is an alkyl group having 4 or fewer carbon atoms. A hole-transporting polymer characterized in that Ar1 in the general formula (1) is the following chemical formula (2) or (4). 【Chemistry 2】 【Chemistry 4】

2. A hole-transporting polymer characterized by having any of the following chemical formulas: (HTM-1), (HTM-2), (HTM-3), (HTM-4), (HTM-5). 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】

3. The hole-transport polymer according to claim 2, characterized in that it is any one of the chemical formulas (HTM-3), (HTM-4), or (HTM-5).

4. A substrate and A first electrode stacked on the substrate, A hole transport layer is stacked on the first electrode, A photoelectric conversion layer is laminated on the hole transport layer, A second electrode is laminated directly on the photoelectric conversion layer or via an electron injection layer, Equipped with, The hole transport layer comprises a hole-transporting polymer according to any one of claims 1 to 3, wherein the hole transport layer is an organic thin-film solar cell.

5. A substrate and A hole-blocking layer and a porous electron transport layer are laminated on the aforementioned substrate, and a first electrode supporting a photosensitizing material is provided. A hole transport layer is stacked on the first electrode, A second electrode stacked on the hole transport layer, Equipped with, The hole transport layer comprises a hole-transporting polymer according to any one of claims 1 to 3, in a photoelectric conversion element.

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