Photoelectric conversion element, method for manufacturing a photoelectric conversion element, and composition of a photoelectric conversion layer

Abstract

To provide a photoelectric conversion element with improved power generation characteristics for indoor light sources (visible light) such as an LED and a fluorescent lamp.SOLUTION: A photoelectric conversion device according to the present invention includes a first electrode and a second electrode, and a photoelectric conversion layer located between the first electrode and the second electrode, and the photoelectric conversion layer contains a first compound represented by Formula (1) and a second compound represented by a specific formula.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion element, a method for manufacturing the photoelectric conversion element, and a composition of a photoelectric conversion layer.

Background Art

[0002] In recent years, the development of photoelectric conversion elements such as organic thin-film solar cells, organic-inorganic hybrid thin-film solar cells, and optical sensors has been actively carried out. As a photoelectric conversion element, for example, a photoelectric conversion element has been proposed in which a fullerene derivative is included as an electron acceptor in a photoelectric conversion layer and polythiophene is included as an electron donor in the photoelectric conversion layer (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003] <​​​​​​​​​​​​​​​​​​​​​​​​The present invention was made to solve the above problems, and the photoelectric conversion element of the present invention comprises a first electrode and a second electrode, and a photoelectric conversion layer located between the first electrode and the second electrode, wherein the photoelectric conversion layer contains a first compound represented by the following formula (1) and a second compound represented by the following formula (2). In formula (2), X represents an integer from 6 to 12, Y represents an integer of 2X+1, and n represents an integer from 10 to 300. [ka] [ka]

[0007] Furthermore, in the photoelectric conversion element of the present invention, the second compound is characterized by having a structure represented by the following formula (3). However, in the following formula (3), n represents an integer from 10 to 300. [ka]

[0008] Furthermore, the photoelectric conversion layer composition of the present invention is a composition used in the photoelectric conversion layer of a photoelectric conversion element, and is characterized by comprising a first compound represented by the following formula (1) and a second compound represented by the following formula (2). However, in formula (2), X represents an integer from 6 to 12, Y represents an integer of 2X+1, and n represents an integer from 10 to 300. [ka] [ka]

[0009] Furthermore, in the photoelectric conversion layer composition of the present invention, the second compound is characterized by having a structure represented by the following formula (3). However, in the following formula (3), n represents an integer from 10 to 300. [ka]

[0010] Further, the method for manufacturing a photoelectric conversion element of the present invention is characterized in that a mixed solution containing a first compound represented by the following formula (1) and a second compound represented by the following formula (2) is applied to provide a photoelectric conversion layer. However, in formula (2), X represents an integer of 6 to 12, Y represents an integer of 2X + 1, and n represents an integer of 10 to 300. [Chemical formula] [Chemical formula] [Advantages of the Invention]

[0011] According to the photoelectric conversion element, the method for manufacturing the photoelectric conversion element, and the composition of the photoelectric conversion layer of the present invention, excellent effects can be achieved, such as improving the power generation characteristics in indoor light sources (visible light) such as LEDs and fluorescent lamps. [Brief Description of the Drawings]

[0012] [Figure 1] It is a schematic diagram showing the structure of the photoelectric conversion element in an embodiment of the present invention. [Figure 2] It is a flowchart of the method for manufacturing the photoelectric conversion element in an embodiment of the present invention. [Figure 3] It is a graph showing the power generation characteristics of the photoelectric conversion element as an example of the present invention and the photoelectric conversion element as a comparative example in an LED light source. [Modes for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that FIG. 1 is merely a schematic diagram showing the structure of the photoelectric conversion element 1 in an embodiment of the present invention, and the thickness of each layer of the photoelectric conversion element 1 is not accurate. The photoelectric conversion element of the present invention includes those having various thicknesses of each layer.

[0014] Referring to Figure 1, the photoelectric conversion element 1 in an embodiment of the present invention will be described. As shown in Figure 1, the photoelectric conversion element 1 in this embodiment has a cathode (first electrode) 10, an anode (second electrode) 11, a photoelectric conversion layer 12, and an electron transport layer 13. On a substrate 14, the cathode 10, electron transport layer 13, photoelectric conversion layer 12, and anode 11 are stacked in that order.

[0015] <Electrode> The cathode 10 is preferably made of a material that is conductive and light-transmitting, particularly a conductive transparent material. More specifically, examples of materials that make up the cathode 10 include conductive metal oxides such as tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), antimond-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO). The cathode 10 may be a single layer or a configuration in which multiple materials are stacked.

[0016] The anode 11 only needs to be composed of a material that is at least conductive. Examples of materials that make up the anode 11 include conductive polymer compounds, metals such as platinum, gold, silver, copper, and aluminum, carbon-based compounds such as graphite, fullerene, carbon nanotubes, and graphene, and mixtures thereof. Examples of conductive polymer compounds include PEDOT-PSS, but are not limited to this, and may also include polythiophene, polyaniline, polypyrrole and their derivatives. PEDOT-PSS is a substituted polythiophene containing ions with added polyanions, consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid This is an abbreviation for a composite material consisting of (PSS). The anode 11 may be a single layer or a configuration in which multiple materials are laminated. The anode 11 may also be composed of a material having conductivity and light transmittance.

[0017] <Photoelectric conversion layer> The photoelectric conversion layer 12 generates electrons and holes in response to light incident from the outside. The photoelectric conversion layer 12 is formed between the anode 11 and the cathode 10. When light is incident, excitons are generated in the photoelectric conversion layer 12, generating electrons and holes. The electrons then move towards the cathode 10 side via the electron transport layer 13, and the holes move towards the anode 11 side. As a result, an electric current (photoexcitation current) flows through an external circuit (not shown) connected to the anode 11 and cathode 10.

[0018] In this embodiment, the photoelectric conversion layer 12 comprises a metal alkoxide and a thiophene derivative. That is, the photoelectric conversion layer 12 in this embodiment is composed of a composition comprising a metal alkoxide and a thiophene derivative. The metal alkoxide functions as an electron-donating electron donor and forms an n-type semiconductor in the photoelectric conversion layer 12. As the metal alkoxide, for example, titanium alkoxide is preferred. Incidentally, as a titanium alkoxide, for example, a compound represented by the structure of the following formula (1) (first compound) can be mentioned. [ka]

[0019] Conventional fullerene derivatives used in photoelectric conversion layers are expensive and prone to degradation by oxidation. Therefore, when photoelectric conversion elements (photoelectric conversion layers) are manufactured in the atmosphere using fullerene derivatives, the durability of the photoelectric conversion elements is reduced. On the other hand, metal alkoxides such as titanium alkoxides have the advantage of being less susceptible to degradation by oxidation and being inexpensive.

[0020] Thiophene derivatives function as electron acceptors with electron-accepting properties, constituting a p-type semiconductor in the photoelectric conversion layer 12. Examples of thiophene derivatives include compounds represented by the structure of the following formula (2) (second compound). In formula (2), X represents an integer from 6 to 12, Y represents an integer of 2X+1, and n represents an integer from 10 to 300. [ka]

[0021] Furthermore, the compound of formula (2) and the compound of formula (3), described later, have the characteristic of absorbing a predetermined range of light spectrum in indoor light sources such as fluorescent lamps and LEDs with high sensitivity. Specifically, the compound of formula (2) and the compound of formula (3), described later, have the absorbance-wavelength characteristics described below. In the compound of formula (2) and the compound of formula (3), described later, the absorbance continues to increase from around 350 nm, reaches a peak around 440 nm, decreases from 440 nm to 460 nm, increases from 460 nm to 470 nm, and continues to decrease from 470 nm to 700 nm. When the properties of the compound of formula (2) and the compound of formula (3), described later, are represented by an absorbance-wavelength characteristic graph with wavelength of light on the horizontal axis and absorbance on the vertical axis, the graph shows a gentle curve in which absorbance increases from 300 nm to 320 nm, a curve in which absorbance remains roughly flat between 320 nm and 350 nm, a curve in which absorbance peaks between 440 nm and 470 nm between 350 nm and 520 nm, a convex curve that is generally convex in the positive direction of the vertical axis, and a gentle curve that is concave in the negative direction of the vertical axis beyond 500 nm. In the above characteristic graph, the curve is slightly concave in the negative direction of the vertical axis from 440 nm to 470 nm. The degree of this concavity is about half the absorbance at a wavelength of light of 350 nm, when the absorbance at a wavelength of light of 350 nm is used as a reference. Furthermore, the absorbance peak is approximately eight times greater than the absorbance at a wavelength of 350 nm. Also, the absorbance at a wavelength of 500 nm is approximately 2.3 times greater than the absorbance at a wavelength of 350 nm. Considering these characteristics, the compound of formula (2) and the compound of formula (3), described later, absorb light in the visible light region with wavelengths of 300 nm to 700 nm well among the indoor light sources mentioned above. In particular, they absorb light in the visible light region with wavelengths of 350 nm to 600 nm more well, and even more well in the visible light region with wavelengths of 350 nm to 500 nm.

[0022] In this embodiment, the photoelectric conversion layer 12 has a bulk heterojunction structure composed of a random mixture of a material containing a metal alkoxide and a thiophene derivative. Alternatively, the photoelectric conversion layer 12 may have a planar heterojunction structure in which an n-type semiconductor layer containing a metal alkoxide and a p-type semiconductor layer containing a thiophene derivative are joined. In other words, the photoelectric conversion layer 12 can have any structure as long as it has a junction surface between the metal alkoxide and the thiophene derivative.

[0023] <Electron transport layer> The electron transport layer 13 contains a material with high electron mobility and performs an electron transport function that efficiently and rapidly transports electrons generated in the photoelectric conversion layer 12 to the cathode 10. Furthermore, the electron transport layer 13 acts as an n-type semiconductor, performing a rectifying effect that prevents holes generated in the photoelectric conversion layer 12 from flowing to the cathode 10. As shown in Figure 1, the electron transport layer 13 is formed between the cathode 10 and the photoelectric conversion layer 12, so as to be continuous with both the cathode 10 and the photoelectric conversion layer 12.

[0024] Furthermore, it is preferable that the electron transport layer 13 and the photoelectric conversion layer 12 contain a common electron-accepting material. In this case, the proportion of the same component in contact at the boundary between the electron transport layer 13 and the photoelectric conversion layer 12 increases, thereby reducing the contact resistance between the electron transport layer 13 and the photoelectric conversion layer 12. The higher the content ratio of the common component in the electron transport layer 13 and the photoelectric conversion layer 12, the greater the reduction in contact resistance. In addition, mutual penetration of the common component occurs between the electron transport layer 13 and the photoelectric conversion layer 12, improving the mechanical strength of the photoelectric conversion layer 12 and the electron transport layer 13. As a result, delamination between the photoelectric conversion layer 12 and the electron transport layer 13 becomes less likely.

[0025] From the above viewpoint, the main material constituting the electron transport layer 13 is preferably, for example, a metal alkoxide, particularly titanium alkoxide (a compound represented by the structure of formula (1) (first compound)), but is not limited thereto, and may be composed of other electron-accepting materials.

[0026] Furthermore, if the electron transport layer 13 is made excessively thick, electrons cannot reach the cathode 10 and become inactive. Conversely, if the electron transport layer 13 is made excessively thin, it cannot cover the surface of the cathode 10. For this reason, in order to enable rapid electron arrival at the cathode 10 and obtain a high output current, the thickness of the electron transport layer 13 is preferably approximately 100 nm or less.

[0027] <Manufacturing method for photoelectric conversion elements> Referring to Figure 2, the method for manufacturing the photoelectric conversion element 1 in this embodiment will be described below. When the photoelectric conversion element 1 is formed on the substrate 14, first a material corresponding to the cathode 10 is deposited on the substrate 14 (step S100). The deposition of the material corresponding to the cathode 10 is carried out, for example, by sputtering or vapor deposition. This completes the cathode 10.

[0028] Next, the electron transport layer 13 is formed on the cathode 10 using a coating solution corresponding to the electron transport layer 13, for example, by a spin coating method (step S101). This completes the electron transport layer 13. Preferably, the coating solution corresponding to the electron transport layer 13 contains titanium alkoxide (a compound represented by the structure of formula (1) (first compound)).

[0029] Next, using a coating solution corresponding to the photoelectric conversion layer 12, the photoelectric conversion layer 12 is deposited on the electron transport layer 13 (adjacent layer) by, for example, a spin coating method (step S102). This completes the photoelectric conversion layer 12. The coating solution corresponding to the photoelectric conversion layer 12 contains a metal alkoxide such as titanium alkoxide (a compound represented by the structure of formula (1) (first compound)) and a thiophene derivative represented by the above formula (2). The coating solution corresponding to the photoelectric conversion layer 12 is prepared by adding the above to a solvent and stirring.

[0030] Finally, the material corresponding to the anode 11 is deposited on the photoelectric conversion layer 12 (step S103). This completes the anode 11 and the photoelectric conversion element 1.

[0031] The sputtering, vapor deposition, and spin coating methods described above for each layer are merely examples. The film deposition methods for each layer in this invention include all other film deposition methods, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), immersion, casting, printing methods including screen printing and inkjet printing, spraying, blade coater, rod coater, knife coater, squeeze coater, and reverse roll coater. [Examples]

[0032] Next, the inventors of the present invention conducted experiments on the power generation efficiency of a photoelectric conversion element as an embodiment of the present invention and a photoelectric conversion element as a comparative example.

[0033] <Photoelectric conversion element as an example of this embodiment, photoelectric conversion element as a comparative example> In this embodiment and in the comparative example, the photoelectric conversion element is formed by sequentially depositing an electron transport layer 13, a photoelectric conversion layer 12 having a bulk heterojunction structure, and an organic electrode (anode 11) on a glass substrate coated with ITO (indium-doped tin oxide transparent conductive film). In the ITO-coated glass substrate, the ITO (indium-doped tin oxide transparent conductive film) portion constitutes the cathode 10, and the glass substrate portion constitutes the substrate 14.

[0034] First, to create the electron transport layer 13 on the cathode 10, 2.0 wt% of titanium alkoxide (titanium tetraisopropoxide Ti[OCH(CH3)2]4: manufactured by Sigma-Aldrich), represented by the structure of formula (1) above, was added to the same chlorobenzene (manufactured by Fujifilm Wako Pure Chemical Industries), and the mixture was stirred to prepare the electron transport layer solution. A magnetic stirrer was used to stir the electron transport layer solution. The electron transport layer 13 was then prepared by dropping the above photoelectric conversion solution onto ITO on an ITO-coated glass substrate and depositing the film by spin coating.

[0035] Next, in preparing the photoelectric conversion layer 12 of this embodiment, a photoelectric conversion solution was prepared by adding 2.0 wt% of titanium alkoxide (titanium tetraisopropoxide Ti[OCH(CH3)2]4: manufactured by Sigma-Aldrich) represented by the structure of formula (1) above, and 1.0 wt% of a compound (thiophene derivative: Kmd101) represented by the structure of formula (3) below, to chlorobenzene (manufactured by Fujifilm Wako Pure Chemical Industries), and stirring in air. Here, n represents an integer between 10 and 300. [ka]

[0036] The compound Kmd101, a thiophene derivative, was prepared as follows: First, in a 25 mL Schlenk tube containing a magnetic rotor, palladium acetate (1.1 mg, 0.0050 mmol), 1-adamantanecarboxylic acid (27.1 mg, 0.15 mmol), potassium carbonate (173 mg, 1.3 mmol), 2,7-dibromo-9,9-dioctylfluorene (274 mg, 0.50 mmol), 3,4-ethylenedioxythiophene (53.4 μL, 0.50 mmol), and dimethylacetamide (1.7 mL) were added under a nitrogen atmosphere to prepare a reaction solution. The reaction solution was heated to 100 °C using an oil bath and reacted for 6 hours with stirring. After the reaction was complete, the Schlenk tube was removed from the oil bath and the reaction solution was allowed to cool to room temperature. Subsequently, approximately 20 mL of an aqueous solution of ethylenediaminetetraacetic acid-dipotassium, adjusted to pH 8, was added to the reaction mixture and stirred overnight. The precipitated product in the reaction mixture was filtered off, and the product was sequentially washed with 0.1 M hydrochloric acid, pure water, methanol, and hexane. The product (filtrate) was then dissolved in chloroform. The resulting chloroform solution was filtered using Celite, and the filtrate was concentrated. The concentrated filtrate was poured into methanol, and the solid was reprecipitated to obtain compound Kmd101 as a pale yellow polymer product. The yield of Kmd101 was 88%. The number-average molecular weight of Kmd101 in polystyrene equivalent (M n ) is 39000, and the weight-average molecular weight (M w ) is 98280, and the molecular weight distribution (Mw / M n The value was 2.52.

[0037] On the other hand, in preparing the comparative example photoelectric conversion layer 12, a photoelectric conversion solution was prepared by adding 2.0 wt% titanium alkoxide represented by the structure of formula (1) above and 1.0 wt% poly-3-hexylthiophene (P3HT) (manufactured by Sigma-Aldrich) to the same chlorobenzene as above, and stirring to mix.

[0038] For stirring the photoelectric conversion solution, a magnetic stirrer was used, with the rotation speed set to 800 rpm, and the temperature of the mixed solution was set to 80°C. The mixture was then mixed and stirred in air for 30 minutes. The photoelectric conversion layer 12 was then prepared by dropping the photoelectric conversion solution onto the electron transport layer 13 and depositing the film by spin coating in air.

[0039] Furthermore, PEDOT-PSS (manufactured by Baytron) was used as the material for the organic electrode (anode 11) of the photoelectric conversion element in this embodiment and comparative example. PEDOT-PSS was then applied to the surface of the photoelectric conversion layer 12, and the organic electrode (anode 11) was prepared by heat treatment at a temperature of approximately 130°C for approximately 10 minutes.

[0040] <Measurement of power generation characteristics> In measuring the power generation characteristics of the photoelectric conversion element as this embodiment and the photoelectric conversion element as a comparative example, a 1000 (lux) LED light source was used to irradiate both the photoelectric conversion element as this embodiment and the photoelectric conversion element as a comparative example with LED light. The results are shown in the graph in Figure 3. According to the graph in Figure 3, the short-circuit current density of the photoelectric conversion element as a comparative example was 0.054 (mA / cm²). 2 ) and the short-circuit current density of the photoelectric conversion element in this embodiment is 0.077 (mA / cm²). 2 This confirms that the short-circuit current density of the photoelectric conversion element in this embodiment is approximately 1.43 times higher than that of the photoelectric conversion element used as a comparative example.

[0041] On the other hand, the power generation conversion efficiency η of the comparative photoelectric conversion element was 2.194%, while the power generation conversion efficiency η of the photoelectric conversion element in this embodiment was 2.594%. This confirmed that the power generation conversion efficiency η of the photoelectric conversion element in this embodiment was improved by approximately 1.2 times compared to the power generation efficiency of the comparative photoelectric conversion element. Note that the power generation conversion efficiency η is calculated by current density × open-circuit voltage × FF (resistive component).

[0042] The above experiments confirmed that when the photoelectric conversion layer 12 is fabricated using a titanium alkoxide represented by the structure of formula (1) as the electron acceptor, using a thiophene derivative with the structure of formula (3) as the electron donor improves the short-circuit current density and power generation efficiency when irradiated with an LED (indoor light source) mainly containing visible light (wavelengths within the range of 360 nm to 830 nm) compared to using poly-3-hexylthiophene (P3HT) as the electron donor.

[0043] Conventionally, the aim has been to improve the power generation efficiency of photoelectric conversion elements when irradiated with sunlight, which consists of a wide range of light wavelengths from short to long wavelengths (ultraviolet light, visible light, and infrared light). As in the present invention, by using a thiophene derivative with a structure represented by formulas (2) and (3), which absorbs light in the visible light region particularly well, as an electron donor for the photoelectric conversion element, it is possible to provide a photoelectric conversion element with good power generation efficiency even for LEDs (indoor light sources) that mainly contain light in the visible light region.

[0044] The structure of the photoelectric conversion element 1 described above is merely an example, and a hole transport layer may be interposed between the anode (second electrode) 11 and the photoelectric conversion layer 12. The hole transport layer contains a material with high hole mobility and performs a hole transport function that efficiently and quickly transports holes generated in the photoelectric conversion layer 12 to the anode 11. Furthermore, the present invention also includes configurations where only a hole transport layer is provided without an electron transport layer 13, or where other layers are interposed in the stacking direction of each layer in the photoelectric conversion element 1.

[0045] It should be noted that the photoelectric conversion element 1 of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. [Explanation of Symbols]

[0046] 1. Photoelectric conversion element 10 Cathode (first electrode) 11. Anode (second electrode) 12 Photoelectric conversion layer 13 Electron transport layer 14 circuit boards

Claims

1. The first electrode and the second electrode, A photoelectric conversion layer located between the first electrode and the second electrode, Equipped with, The photoelectric conversion layer comprises a first compound represented by the following formula (1) and a second compound represented by the following formula (2). The second compound is characterized in that, in a characteristic curve with absorbance on the vertical axis and wavelength of light on the horizontal axis, the curve is a convex curve that is convex in the positive direction of the vertical axis between 350 nm and 520 nm in the wavelength range from 300 nm to 700 nm. Photoelectric conversion element. 【Chemistry 1】 【Chemistry 2】 However, in equation (2), X represents an integer between 6 and 12, Y represents an integer between 2X and 1, and n represents an integer between 10 and 300.

2. The second compound is characterized by having a structure represented by the following formula (3): The photoelectric conversion element according to claim 1. 【Transformation 3】 However, n represents an integer between 10 and 300.

3. A composition used in the photoelectric conversion layer of a photoelectric conversion element, The compound comprises a first compound represented by the following formula (1) and a second compound represented by the following formula (2). The second compound is characterized in that, in a characteristic curve with absorbance on the vertical axis and wavelength of light on the horizontal axis, the curve is a convex curve that is convex in the positive direction of the vertical axis between 350 nm and 520 nm in the wavelength range from 300 nm to 700 nm. Composition for the photoelectric conversion layer. 【Chemistry 1】 【Chemistry 2】 However, in equation (2), X represents an integer between 6 and 12, Y represents an integer between 2X and 1, and n represents an integer between 10 and 300.

4. The second compound is characterized by having a structure represented by the following formula (3): The photoelectric conversion layer composition according to claim 3. 【Transformation 3】 However, n represents an integer between 10 and 300.

5. A method for manufacturing a photoelectric conversion element, A photoelectric conversion layer is provided by coating a mixed solution containing a first compound represented by the following formula (1) and a second compound represented by the following formula (2). The second compound is characterized in that, in a characteristic curve with absorbance on the vertical axis and wavelength of light on the horizontal axis, the curve is a convex curve that is convex in the positive direction of the vertical axis between 350 nm and 520 nm in the wavelength range from 300 nm to 700 nm. A method for manufacturing a photoelectric conversion element. 【Chemistry 1】 【Chemistry 2】 However, in equation (2), X represents an integer between 6 and 12, Y represents an integer between 2X and 1, and n represents an integer between 10 and 300.

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