Semiconductor composition, ink composition, film, photoelectric conversion element, and imaging device

Abstract

This semiconductor composition contains an electron-donating first semiconductor material, an electron-accepting second semiconductor material, and an additive. The relationships Ra1 < Ra2 and Ra1 < Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

Description

Semiconductor composition, ink composition, film, photoelectric conversion element and imaging device

[0001] The present disclosure relates to a semiconductor composition, an ink composition, a film, a photoelectric conversion element, and an imaging device.

[0002] Research has been conducted into the realization of photoelectric conversion elements by forming semiconductor materials such as organic semiconductor materials into thin films and using them as photoelectric conversion materials. Photoelectric conversion elements using such thin films can be used as solid-state imaging devices by extracting charges generated by light as electrical signals (see, for example, Patent Document 1).

[0003] Furthermore, fullerene derivatives, such as

[60] PCBM (phenyl C61 butyric acid methyl ester), are widely used as semiconductor materials for photoelectric conversion elements as electron-accepting semiconductor materials. Fullerene derivatives tend to aggregate, and are known to crystallize when exposed to energy such as heat (see, for example, Non-Patent Document 1).

[0004] Patent No. 5969843

[0005] Samuele Lilliu et. al. , “Dynamics of Crystallization and Disorder during Annealing of P3HT / PCBM Bulk Heterojunctions”, Macromolecules, American Chemical Society, 2011, Vol. 44, p. 2725-2734Charles M. Hansen, “THE THREE DIMENSIONAL SOLUBILITY PARAMETER AND SOLVENT DIFFUSION COEFFICIENT Their Importance In Surface Coating Formulation”, COPENHAGEN DANISH TECHNICAL PRESS, 1967

[0006] When semiconductor materials are thinned and used as photoelectric conversion elements, improvement in film quality is desirable. Examples of film quality include heat resistance, weather resistance, strength, coating ability, and adhesion, and improvement in at least one of these is desirable. For example, as mentioned above, fullerene derivatives are known to undergo crystallization due to energy such as heat, which poses a challenge when used in photoelectric conversion elements. For example, if crystals form in the photoelectric conversion layer, the mechanical properties of the thin film change. This can lead to the formation of minute voids at the interface between the thin film and other layers above and below it, and can also lead to cracks in the thin film itself. This can affect device characteristics, particularly in the images captured by imaging devices such as image capture devices.

[0007] To improve the film quality, it is conceivable to form a thin film using a semiconductor composition in which an additive is added to a semiconductor material, but there is a concern that this may result in a decrease in photoelectric conversion efficiency.

[0008] Therefore, the present disclosure provides a semiconductor composition and the like that can achieve both improved film quality and suppression of a decrease in photoelectric conversion efficiency.

[0009] A semiconductor composition according to one embodiment of the present disclosure includes a first electron-donating semiconductor material, a second electron-accepting semiconductor material, and an additive, wherein Ra1<Ra2 and Ra1<Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

[0010] An ink composition according to one embodiment of the present disclosure includes the semiconductor composition and a solvent.

[0011] A film according to one embodiment of the present disclosure is a film formed using the ink composition.

[0012] A photoelectric conversion element according to one aspect of the present disclosure includes a first electrode, a second electrode facing the first electrode, and the above-described film located between the first electrode and the second electrode.

[0013] An imaging device according to an aspect of the present disclosure includes the above-described photoelectric conversion element.

[0014] A photoelectric conversion element according to one embodiment of the present disclosure includes a first electrode, a second electrode facing the first electrode, and a photoelectric conversion layer located between the first electrode and the second electrode. The photoelectric conversion layer includes a first semiconductor material having electron donating properties, a second semiconductor material having electron accepting properties, and an additive. Ra1<Ra2 and Ra1<Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

[0015] An imaging device according to an aspect of the present disclosure includes the above-described photoelectric conversion element.

[0016] According to the present disclosure, it is possible to achieve both improvement in film quality and suppression of a decrease in photoelectric conversion efficiency.

[0017] FIG. 1 is a schematic cross-sectional view showing a photoelectric conversion element according to a second embodiment. FIG. 2 is a flowchart showing a method for manufacturing a photoelectric conversion layer in a photoelectric conversion element according to the second embodiment. FIG. 3 is an exemplary energy band diagram of a photoelectric conversion element according to the second embodiment. FIG. 4 is a diagram showing an example of a circuit configuration of an imaging device according to the second embodiment. FIG. 5 is a schematic cross-sectional view showing an example of a device structure of a pixel in an imaging device according to the second embodiment. FIG. 6 is a diagram showing an example of a schematic current-voltage characteristic of a photoelectric conversion layer according to the second embodiment. FIG. 7 is a diagram showing a part of a schematic circuit configuration of a pixel according to the second embodiment. FIG. 8 is a timing chart showing an example of a voltage applied to a second electrode of a photoelectric conversion unit according to the second embodiment and an example of the timing of operation in each row of a pixel array of an imaging device.

[0018] (Findings that led to the realization of one aspect of the present disclosure) When semiconductor materials are thinned and used as photoelectric conversion elements, improvement of film quality is desired. For example, organic semiconductor materials are less durable to light and heat than inorganic Si, and many of them undergo reactions and / or aggregation in response to some kind of energy. For example, as disclosed in Non-Patent Document 1, it is known that

[60] PCBM, a fullerene derivative that has been widely investigated as a semiconductor material for use in photoelectric conversion elements, undergoes aggregation and crystallization in response to heat.

[0019] In view of the above-mentioned problems, the present inventors have investigated the addition of additives to semiconductor materials in semiconductor compositions in order to improve film quality. In the course of investigating the addition of additives to semiconductor materials, the present inventors have discovered a new problem that the photoelectric conversion efficiency of thin films formed from the semiconductor compositions is reduced by a greater amount than the theoretical reduction due to the addition of additives.

[0020] Therefore, the present disclosure provides a semiconductor composition and the like that can achieve both improved film quality and suppression of a decrease in photoelectric conversion efficiency by suppressing a decrease in photoelectric conversion efficiency caused by additives.

[0021] (Summary of the Present Disclosure) As an overview of one embodiment of the present disclosure, examples of a semiconductor composition, an ink composition, a film, a photoelectric conversion element, and an imaging device according to the present disclosure are shown below.

[0022] (First Aspect) For example, a semiconductor composition according to a first aspect of the present disclosure includes a first electron-donating semiconductor material, a second electron-accepting semiconductor material, and an additive, wherein Ra1<Ra2 and Ra1<Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

[0023] As a result, when a thin film is formed from the semiconductor composition, the additive can improve film quality, such as heat resistance, weather resistance, strength, coverage, and adhesion, depending on the additive. Therefore, for example, when the thin film is used in a photoelectric conversion element, the reliability of the photoelectric conversion element can be improved. Furthermore, even when the semiconductor composition contains an additive, the electron-donating first semiconductor material and the electron-accepting second semiconductor material are more likely to approach each other than the additive, making it less likely that the additive will inhibit the interaction between the first semiconductor material and the second semiconductor material. Therefore, when the semiconductor composition is used as a photoelectric conversion material, the exchange of carriers between the first semiconductor material and the second semiconductor material is less likely to be inhibited, and a decrease in photoelectric conversion efficiency can be suppressed. From the above, the semiconductor composition according to this embodiment can achieve both improved film quality and suppression of a decrease in photoelectric conversion efficiency.

[0024] (Second Aspect) Furthermore, for example, in the semiconductor composition according to the first aspect, the first semiconductor material and the second semiconductor material may be organic semiconductor materials.

[0025] As a result, in organic semiconductor materials, changing the molecular structure of the organic compound used can change the energy level. Therefore, it is easy to give them properties different from those of inorganic semiconductor materials. For example, when organic semiconductor materials are used as photoelectric conversion materials, it is possible to control the absorption wavelength, and they can be given spectral sensitivity even in the near-infrared light region where silicon (Si) has no spectral sensitivity. On the other hand, organic semiconductor materials have inferior durability to light and heat compared to inorganic materials, and semiconductor compositions containing organic semiconductor materials are prone to deterioration in film quality, but the film quality can be improved by adding additives.

[0026] (Third Aspect) Furthermore, for example, in the semiconductor composition according to the second aspect, the first semiconductor material may be a low molecular weight compound.

[0027] This will broaden the options for electron-donating organic semiconductor materials, making it easier to achieve high photoelectric conversion efficiency.

[0028] (Fourth Aspect) Furthermore, for example, in the semiconductor composition according to the second or third aspect, the second semiconductor material may be a low molecular weight compound.

[0029] This will broaden the options for electron-accepting organic semiconductor materials, making it easier to achieve high photoelectric conversion efficiency.

[0030] (Fifth Aspect) Furthermore, for example, in the semiconductor composition according to any one of the first to fourth aspects, the additive may be a polymer compound.

[0031] This improves the heat resistance, adhesion and strength of the thin film formed from the semiconductor composition.

[0032] (Sixth Aspect) Furthermore, for example, an ink composition according to a sixth aspect of the present disclosure contains the semiconductor composition according to any one of the first to fifth aspects and a solvent.

[0033] This allows the composition to be used in a coating method for forming a thin film of a semiconductor composition that can achieve both improved film quality and suppressed reduction in photoelectric conversion efficiency.

[0034] (Seventh Aspect) Furthermore, for example, an ink composition according to a seventh aspect of the present disclosure is the ink composition according to the sixth aspect, wherein the solvent includes an aromatic compound.

[0035] This makes it easier for the solvent to dissolve the semiconductor composition, widening the range in which the concentration of the ink composition can be adjusted, and making it easier to adjust the concentration of the ink composition to suit the process and design.

[0036] (Eighth Aspect) Furthermore, for example, a film according to an eighth aspect of the present disclosure is a film formed using the ink composition according to the sixth or seventh aspect.

[0037] This makes it possible to easily realize a film that achieves both improved film quality and suppression of a decrease in photoelectric conversion efficiency.

[0038] (Ninth Aspect) Furthermore, for example, a photoelectric conversion element according to a ninth aspect of the present disclosure includes a first electrode, a second electrode facing the first electrode, and a film according to the eighth aspect located between the first electrode and the second electrode.

[0039] (Tenth Aspect) Furthermore, for example, an imaging device according to a tenth aspect of the present disclosure includes the photoelectric conversion element according to the ninth aspect.

[0040] As a result, it is possible to realize a photoelectric conversion element and an imaging device that use, as a photoelectric conversion film, a film that achieves both improved film quality and suppression of a decrease in photoelectric conversion efficiency.

[0041] (Eleventh Aspect) Also, for example, a photoelectric conversion element according to an eleventh aspect of the present disclosure includes a first electrode, a second electrode facing the first electrode, and a photoelectric conversion layer located between the first electrode and the second electrode. The photoelectric conversion layer includes a first semiconductor material having electron donating properties, a second semiconductor material having electron accepting properties, and an additive. Ra1<Ra2 and Ra1<Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

[0042] (Twelfth Aspect) Furthermore, for example, an imaging device according to a twelfth aspect of the present disclosure includes the photoelectric conversion element according to the eleventh aspect.

[0043] As a result, a photoelectric conversion element and an imaging device can be realized that have a photoelectric conversion layer that can achieve both improved film quality and suppressed decline in photoelectric conversion efficiency due to the same effects as those of the semiconductor composition according to the first aspect.

[0044] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0045] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, component placement and connection configurations, steps, and step sequences shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims are described as optional components, and the drawings are not necessarily strict illustrations. In the drawings, substantially identical components are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0046] Furthermore, in this specification, terms indicating the relationship between elements, terms indicating the shape of elements, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0047] Furthermore, in this specification, the terms "above" and "below" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in the stacked configuration. Terms such as "above" and "below" are used solely to specify the relative arrangement of components, and are not intended to limit the orientation of the photoelectric conversion element and imaging device during use. Furthermore, the terms "above" and "below" are used not only when two components are arranged with a gap between them and another component is present between them, but also when two components are arranged closely together and the two components are in contact with each other.

[0048] First Embodiment Hereinafter, a semiconductor composition according to this embodiment and an ink composition containing the semiconductor composition will be described.

[0049] [Material Composition of Semiconductor Composition] The semiconductor composition according to this embodiment includes a first electron-donating semiconductor material, a second electron-accepting semiconductor material, and an additive.

[0050] The semiconductor composition includes, for example, a first semiconductor material and a second semiconductor material as main components. Here, "main components" means a content of more than 50 wt %. In other words, in this case, the total content of the first semiconductor material and the second semiconductor material in the semiconductor composition is more than 50 wt %.

[0051] In addition, in the semiconductor composition, the content of the additive is, for example, lower than the content of the first semiconductor material and lower than the content of the second semiconductor material. The semiconductor composition may further contain materials other than the first semiconductor material, the second semiconductor material, and the additive.

[0052] The first semiconductor material, the second semiconductor material, and the additive will be described in detail below.

[0053] [First Semiconductor Material] The first semiconductor material is a donor semiconductor material having electron donating properties, such as an organic semiconductor material.

[0054] Examples of organic semiconductor materials that can be used as the first semiconductor material include triarylamine compounds, benzidine compounds, pyrazoline compounds, styrylamine compounds, hydrazone compounds, triphenylmethane compounds, carbazole compounds, polysilane compounds, thiophene compounds, phthalocyanine compounds, naphthalocyanine compounds, subphthalocyanine compounds, cyanine compounds, merocyanine compounds, oxonol compounds, polyamine compounds, indole compounds, pyrrole compounds, pyrazole compounds, polyarylene compounds, fused aromatic carbocyclic compounds (e.g., naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, and fluoranthene derivatives), and metal complexes having a nitrogen-containing heterocyclic compound as a ligand.

[0055] The first semiconductor material is, for example, a low molecular weight compound among the compounds exemplified above as organic semiconductor materials. A low molecular weight compound is an organic compound that does not have a repeating structure of a monomer formed by polymerizing a monomer. This makes it easier to achieve high photoelectric conversion efficiency. This also broadens the range of materials available, making it easier to realize industrial applications.

[0056] The first semiconductor material is not limited to the above examples and may be, for example, quantum dots, perovskite materials, carbon nanotubes, etc. The first semiconductor material may also be a polymer compound. Any material having a smaller electron affinity than the second semiconductor material may be used as the first semiconductor material.

[0057] [Second Semiconductor Material] The second semiconductor material is an acceptor semiconductor material having electron-accepting properties, such as an organic semiconductor material.

[0058] The organic semiconductor material used as the second semiconductor material is, for example,

[60] PCBM (phenyl C ６１butyric acid methyl ester), and

[70] PCBM (phenyl C ７１ Examples of such fullerene derivatives include fullerene derivatives such as butyric acid methyl ester.

[0059] The second semiconductor material may be, for example, a low-molecular-weight compound such as those exemplified above as organic semiconductor materials. This makes it easier to achieve high photoelectric conversion efficiency. This also broadens the range of materials available, making it easier to implement industrially.

[0060] The second semiconductor material is not limited to the above examples and may be, for example, quantum dots, perovskite materials, carbon nanotubes, etc. The second semiconductor material may also be a polymer compound. Any material having a larger electron affinity than the first semiconductor material may be used as the second semiconductor material.

[0061] [Additives] The additives are additives for improving the film quality of a thin film formed using the semiconductor composition. The additives improve at least one of heat resistance, weather resistance, strength, coating properties, and adhesion of the thin film formed using the semiconductor composition.

[0062] The additive is, for example, a polymer compound. This improves the heat resistance, coating properties, and adhesion of the thin film formed from the semiconductor composition, making it possible to obtain a high-quality thin film of the semiconductor composition with few defects. The polymer compound is an organic compound obtained by polymerizing one or more types of monomers.

[0063] Examples of polymer compounds used as additives include polyethylene, polypropylene, polyester, polystyrene, styrene-ethylene-butylene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, poly(triarylamine), polyvinylcarbazole, polyfluorene, polythiophene, acrylic acrylate, epoxy resin, silicone, and derivatives thereof.

[0064] The weight-average molecular weight of the polymer compound is, for example, 10,000 or more. This increases the viscosity of the ink composition when used as an ink composition containing the semiconductor composition, making it easier to adjust the film thickness when forming a thin film of the semiconductor composition. The weight-average molecular weight of the polymer compound may be 50,000 or more. Alternatively, the weight-average molecular weight of the polymer compound is, for example, 1,000,000 or less. Alternatively, the polymer compound may be thermoplastic.

[0065] The additive may also have insulating properties, which makes it less likely that the additive will inhibit the interaction between the first semiconductor material and the second semiconductor material.

[0066] Furthermore, the additive is transparent to, for example, at least a portion of the light absorption wavelength of the first semiconductor material, for example, wavelengths including the absorption peak wavelength of the first semiconductor material. The additive is transparent to, for example, at least a portion of the wavelength range from visible light to infrared light. This prevents the additive from absorbing light and inhibiting the light absorption of the first semiconductor material. For example, the additive has a smaller absorption coefficient than the first semiconductor material at the absorption peak wavelength of the first semiconductor material.

[0067] [Hansen Distance] Next, the Hansen distance between materials contained in the semiconductor composition will be described.

[0068] The Hansen distance represents the distance between the Hansen solubility parameters of two materials.

[0069] The Hansen solubility parameter is known as an index of the solubility of substances with each other, and is described, for example, in Non-Patent Document 2. The Hansen solubility parameter is composed of three values: a dispersion force term (δD), a polar term (δP), and a hydrogen bonding term (δH). These three parameters are expressed as the coordinates of a point in a three-dimensional space called the Hansen space.

[0070] In this case, the Hansen solubility parameters for the two materials are as follows: for the first material, the dispersion term is δD1, the polar term is δP1, and the hydrogen bond term is δH1; for the second material, the dispersion term is δD2, the polar term is δP2, and the hydrogen bond term is δH2. In this case, the Hansen distance Ra between the first and second materials is: Ra = (4 x (δD1 - δD2) ２ + (δP1-δP2) ２ + (δH1-δH2) ２ ) ０．５ It can be calculated as follows.

[0071] The Hansen solubility parameter may be a value published in a literature or may be determined experimentally. When determining the Hansen solubility parameter experimentally, it can be determined, for example, using the known Hansen sphere method. In the Hansen sphere method, a material is mixed with a solvent with a known Hansen solubility parameter to determine whether the material dissolves, and the Hansen solubility parameter of the solvent is plotted in Hansen space. A sphere is then determined in Hansen space that includes the coordinates of the solvent in which the material has dissolved but does not include the coordinates of the solvent in which the material has not dissolved, and the central coordinates of the sphere are used as the Hansen solubility parameter of the material. When determining the Hansen solubility parameter of a material that is insoluble in a solvent, the Hansen solubility parameter can be determined by determining whether swelling, softening, cracking, dispersion, etc. occur, instead of determining whether the material has dissolved.

[0072] In the semiconductor composition according to this embodiment, when the Hansen distance between the first semiconductor material and the second semiconductor material is Ra1, the Hansen distance between the first semiconductor material and the additive is Ra2, and the Hansen distance between the second semiconductor material and the additive is Ra3, Ra1<Ra2 and Ra1<Ra3 are satisfied.

[0073] By satisfying this Hansen distance relationship, in the semiconductor composition, the electron-donating first semiconductor material and the electron-accepting second semiconductor material are more likely to approach each other than the additive, and the additive is less likely to inhibit the interaction between the first semiconductor material and the second semiconductor material. Therefore, when the semiconductor composition is used as a photoelectric conversion material, the exchange of carriers between the first semiconductor material and the second semiconductor material is less likely to be inhibited, and a decrease in the external quantum efficiency (EQE), which represents the photoelectric conversion efficiency, can be suppressed. Therefore, the additive can improve the film quality of the thin film formed from the semiconductor composition while suppressing a decrease in the photoelectric conversion efficiency.

[0074] [Ink Composition] The semiconductor composition according to this embodiment may be used in an ink composition. The ink composition according to this embodiment includes a semiconductor composition containing the first semiconductor material, the second semiconductor material, and an additive, and a solvent. The ink composition is a mixed solution containing the first semiconductor material, the second semiconductor material, and the additive. In the ink composition, for example, the first semiconductor material, the second semiconductor material, and the additive are dissolved in the solvent. In the ink composition, some materials may be dispersed in the solvent. The ink composition according to this embodiment is used, for example, to form a thin film. A thin film formed using an ink composition containing the above-mentioned semiconductor composition can be used, for example, as a photoelectric conversion layer of a photoelectric conversion element.

[0075] The solvent is not particularly limited as long as it dissolves or disperses the first semiconductor material, the second semiconductor material, and the additive, and includes, for example, at least one of benzene, toluene, xylene, anisole, chlorobenzene, chloronaphthalene, chlorophenol, tetralin, and chloroform.

[0076] The solvent may also contain an aromatic compound. This facilitates dissolution of the semiconductor composition, broadening the range in which the concentration of the ink composition can be adjusted. Since the viscosity of an ink composition varies depending on the thin film manufacturing method, such as a spin coater or inkjet printer, broadening the range in which the concentration can be adjusted is industrially useful. The solvent may be mainly composed of an aromatic compound.

[0077] [Method of Producing Semiconductor Composition and Ink Composition] The semiconductor composition and ink composition are produced, for example, as follows.

[0078] First, the first semiconductor material, the second semiconductor material, and the additive are weighed and placed in a container. Furthermore, an amount of solvent necessary to obtain a predetermined concentration of the semiconductor composition is placed in the container. Next, the container is sealed, and the mixture in the container is stirred at an appropriate temperature. This results in an ink composition containing the semiconductor composition. Alternatively, an ink composition containing the semiconductor composition may be obtained by separately preparing solutions of each material of the semiconductor composition and then mixing these solutions. Furthermore, the semiconductor composition may be used to form a thin film while contained in the ink composition, or the solvent may be removed from the ink composition and the semiconductor composition alone may be used to form a thin film.

[0079] When forming a thin film using the prepared ink composition, the ink composition is first coated on a substrate. The substrate may be made of glass, silicon, resin, or the like. The coating method may be spin coating, inkjet coating, dip coating, or the like. The ink composition coated on the substrate is then dried to obtain a thin film made of the semiconductor composition on the substrate. Heat may be applied during drying.

[0080] (Embodiment 2) Next, a description will be given of embodiment 2. In embodiment 2, a photoelectric conversion element having a thin film containing the semiconductor composition according to embodiment 1 as a photoelectric conversion layer, and an imaging device using the photoelectric conversion element will be described.

[0081] [Photoelectric Conversion Element] First, a photoelectric conversion element according to the present embodiment will be described. The photoelectric conversion element according to the present embodiment is, for example, a charge readout type photoelectric conversion element. Fig. 1 is a schematic cross-sectional view showing a photoelectric conversion element 10 according to the present embodiment.

[0082] As shown in FIG. 1 , the photoelectric conversion element 10 is supported on a support substrate 1. The photoelectric conversion element 10 includes a pair of electrodes, a first electrode 2 and a second electrode 6 disposed opposite the first electrode 2, and a photoelectric conversion layer 4 located between the first electrode 2 and the second electrode 6. The photoelectric conversion element 10 further includes a charge blocking layer 3 located between the first electrode 2 and the photoelectric conversion layer 4, and a charge blocking layer 5 located between the second electrode 6 and the photoelectric conversion layer 4. One of the charge blocking layer 3 and the charge blocking layer 5 is an electron blocking layer, and the other is a hole blocking layer. Note that the photoelectric conversion element 10 is only required to include at least the first electrode 2, the second electrode 6, and the photoelectric conversion layer 4, and may not include at least one of the charge blocking layer 3 and the charge blocking layer 5.

[0083] The photoelectric conversion element 10 is used, for example, in an imaging device. For example, an imaging device using the photoelectric conversion element 10 has a photoelectric conversion unit in each of a plurality of pixels included in the imaging device, the photoelectric conversion element 10 being configured as the photoelectric conversion element 10. The use of the photoelectric conversion element 10 is not particularly limited, and the photoelectric conversion element 10 may be used in an optical sensor or a solar cell.

[0084] Hereinafter, each component of the photoelectric conversion element 10 according to this embodiment will be described.

[0085] The support substrate 1 may be any substrate that is commonly used in photoelectric conversion elements, such as a glass substrate, a semiconductor substrate, or a plastic substrate.

[0086] The first electrode 2 and the second electrode 6 are film-like electrodes arranged opposite to each other.

[0087] The first electrode 2 is formed from a metal, a metal nitride, a metal oxide, or polysilicon that has been made conductive. Examples of metals include aluminum, copper, titanium, and tungsten. An example of a method for making polysilicon conductive is to dope it with impurities.

[0088] The second electrode 6 is a transparent electrode formed of, for example, a transparent conductive material such as a transparent conductive oxide (TCO), indium tin oxide (ITO), indium zinc oxide (IZO), aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO), or SnO. ２ and TiO ２ and the like. The second electrode 6 may be made of a TCO and a metal material such as aluminum (Al) or gold (Au), either singly or in combination, depending on the desired transmittance. In the photoelectric conversion element 10, for example, light transmitted through the second electrode 6 is incident on the photoelectric conversion layer 4. In this specification, the term "transparent" means that the photoelectric conversion layer 4 transmits at least a portion of light of a wavelength that can be absorbed, and does not necessarily transmit light over the entire wavelength range. In this specification, for convenience, electromagnetic waves in general, including visible light, infrared light, and ultraviolet light, are referred to as "light."

[0089] The materials of the first electrode 2 and the second electrode 6 are not limited to the above-mentioned conductive materials, and other materials may be used. For example, the first electrode 2 may be a transparent electrode. In this case, light transmitted through the first electrode 2 may be incident on the photoelectric conversion layer 4.

[0090] Various methods are used to fabricate the first electrode 2 and the second electrode 6 depending on the materials used. For example, when ITO is used, methods such as an electron beam method, a sputtering method, a resistance heating vapor deposition method, a chemical reaction method such as a sol-gel method, or a method of applying a dispersion of indium tin oxide may be used. In this case, to fabricate the first electrode 2 and the second electrode 6, after forming the ITO film, UV-ozone treatment, plasma treatment, or the like may be further performed.

[0091] A bias voltage is applied to the first electrode 2 and the second electrode 6, for example, via wiring (not shown). For example, the polarity of the bias voltage is determined so that, of the charges generated in the photoelectric conversion layer 4, electrons move to the second electrode 6 and holes move to the first electrode 2. An example in which electrons move to the second electrode 6 and holes move to the first electrode 2 will be described below. Note that the bias voltage may also be set so that, of the charges generated in the photoelectric conversion layer 4, holes move to the second electrode 6 and electrons move to the first electrode 2.

[0092] The photoelectric conversion layer 4 is formed from the semiconductor composition according to the first embodiment and contains the first semiconductor material, the second semiconductor material, and the additive. The photoelectric conversion layer 4 can be formed by a wet method such as a coating method using spin coating, for example. The photoelectric conversion layer 4 may be formed by a vacuum deposition method or the like instead of a wet method such as a coating method. The charge blocking layer 3 and the charge blocking layer 5 can also be formed by the same method as the photoelectric conversion layer 4.

[0093] The photoelectric conversion layer 4 is, for example, a thin film formed using the ink composition according to embodiment 1. Fig. 2 is a flowchart showing an example of a method for manufacturing the photoelectric conversion layer 4 in the photoelectric conversion element 10 according to this embodiment.

[0094] 2 , in the method for producing the photoelectric conversion layer 4, first, an ink composition containing the semiconductor composition according to embodiment 1 is prepared (step S11). The method for producing the ink composition is as described in embodiment 1.

[0095] Next, the prepared ink composition is used to form a thin film as the photoelectric conversion layer 4 (step S12). For example, the ink composition is applied to the region where the photoelectric conversion layer 4 is to be formed by a coating method such as spin coating or inkjet printing to form a thin film, and the thin film is dried to form the photoelectric conversion layer 4.

[0096] Fig. 3 is an exemplary energy band diagram of the photoelectric conversion element 10 shown in Fig. 1. In Fig. 3, the energy band of each layer is indicated by a rectangle.

[0097] The photoelectric conversion layer 4 generates electron-hole pairs therein when irradiated with light. The generated electron-hole pairs are separated into electrons and holes by an electric field applied to the photoelectric conversion layer 4, and each migrates to the first electrode 2 side or the second electrode 6 side according to the electric field. Here, of the electron-hole pairs generated by absorbing light, the material that donates the electrons to the other material is an electron-donating first semiconductor material 4A, and the material that accepts the electrons is an electron-accepting second semiconductor material 4B. Here, a case will be described in which organic semiconductor materials are used as the first semiconductor material 4A and the second semiconductor material 4B. When two different types of organic semiconductor materials are used, which one is the electron-donating material and which one is the electron-accepting material is generally determined by the relative positions of the HOMO (Highest-Occupied-Molecular-Orbital) and LUMO (Lowest-Unoccupied-Molecular-Orbital) energy levels of each of the two types of organic semiconductor materials at their contact interface. Specifically, the material with a shallower LUMO energy level that accepts electrons is the electron-donating first semiconductor material 4A, and the material with a deeper LUMO energy level is the electron-accepting second semiconductor material 4B.

[0098] 3 , the upper end of the rectangle representing the energy band is the LUMO energy level, and the lower end is the HOMO energy level. In this way, since the photoelectric conversion layer 4 includes the first semiconductor material 4A and the second semiconductor material 4B, electrons and holes generated in the photoelectric conversion layer 4 are separated into the first semiconductor material 4A and the second semiconductor material 4B by charge transfer between the first semiconductor material 4A and the second semiconductor material 4B. Therefore, the electrons and holes are less likely to recombine, and the photoelectric conversion efficiency of the photoelectric conversion element 10 can be improved.

[0099] The charge blocking layers 3 and 5 suppress the injection of charges from the electrodes into the photoelectric conversion layer 4. By providing the charge blocking layers 3 and 5, it is possible to suppress the injection of charges from the electrodes into the photoelectric conversion layer 4, and to reduce noise signals that adversely affect the signal-to-noise ratio (SN ratio).

[0100] Specifically, the charge blocking layer 3 is an electron blocking layer provided to reduce dark current caused by electrons injected from the first electrode 2. The charge blocking layer 3 suppresses electrons from being injected from the first electrode 2 into the photoelectric conversion layer 4. The charge blocking layer 3 also has the function of transporting holes generated in the photoelectric conversion layer 4 to the first electrode 2.

[0101] The charge blocking layer 5 is a hole blocking layer provided to reduce dark current caused by holes injected from the second electrode 6. The charge blocking layer 5 suppresses holes from being injected from the second electrode 6 into the photoelectric conversion layer 4. The charge blocking layer 5 also has the function of transporting electrons generated in the photoelectric conversion layer 4 to the second electrode 6.

[0102] The charge blocking layer 3 and the charge blocking layer 5 are formed of, for example, an organic semiconductor material having HOMO and LUMO energy levels that act as a barrier to the movement of charges from the electrodes to the photoelectric conversion layer 4 .

[0103] The materials of charge blocking layer 3 and charge blocking layer 5 are not limited to organic semiconductor materials, but may be inorganic semiconductor materials such as oxide semiconductors and nitride semiconductors, or composite materials thereof.

[0104] In the photoelectric conversion element 10, when holes of the charges generated in the photoelectric conversion layer 4 move to the second electrode 6 and electrons move to the first electrode 2, the charge blocking layer 3 becomes a hole blocking layer and the charge blocking layer 5 becomes an electron blocking layer.

[0105] As shown in FIG. 3, the first electrode 2 is electrically connected to a charge storage node when used in an imaging device, for example.

[0106] [Imaging Device] An imaging device according to this embodiment will now be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a diagram showing an example of the circuit configuration of an imaging device 100 that implements a photoelectric conversion unit 10A using the photoelectric conversion element 10 shown in Fig. 1. Fig. 5 is a schematic cross-sectional view showing an example of the device structure of a pixel 24 in the imaging device 100 according to this embodiment.

[0107] 4 and 5 , the imaging device 100 according to the present embodiment includes a semiconductor substrate 40, a charge detection circuit 35 provided on the semiconductor substrate 40, a photoelectric conversion unit 10A provided on the semiconductor substrate 40, and pixels 24 including a charge storage node 34 electrically connected to the charge detection circuit 35 and the photoelectric conversion unit 10A. The photoelectric conversion unit 10A of each pixel 24 includes the photoelectric conversion element 10. The charge storage node 34 stores the charge obtained by the photoelectric conversion unit 10A. The charge detection circuit 35 is connected to the photoelectric conversion unit 10A via the charge storage node 34 and detects the charge stored in the charge storage node 34. The charge detection circuit 35 provided on the semiconductor substrate 40 may be provided on the semiconductor substrate 40 or directly in the semiconductor substrate 40.

[0108] 4, the imaging device 100 includes a plurality of pixels 24 and peripheral circuits. The imaging device 100 is, for example, an image sensor realized by a one-chip integrated circuit, and has a pixel array PA including a plurality of pixels 24 arranged two-dimensionally.

[0109] A plurality of pixels 24 are arranged two-dimensionally, i.e., in row and column directions, on the semiconductor substrate 40 to form a photosensitive region, which is a pixel region. FIG. 4 illustrates an example in which the pixels 24 are arranged in a two-row, two-column matrix. For convenience of illustration, FIG. 4 omits the illustration of a circuit (e.g., a pixel electrode control circuit) for individually setting the sensitivity of the pixels 24. The imaging device 100 may also be a line sensor. In this case, the plurality of pixels 24 may be arranged one-dimensionally. In this specification, the row direction and the column direction refer to the directions in which the rows and columns extend, respectively. In other words, in FIG. 4 , the vertical direction on the paper surface is the column direction, and the horizontal direction is the row direction.

[0110] 4 and 5, each pixel 24 includes a photoelectric conversion unit 10A and a charge storage node 34 electrically connected to a charge detection circuit 35. The charge detection circuit 35 includes an amplification transistor 21, a reset transistor 22, and an address transistor 23.

[0111] The photoelectric conversion unit 10A includes a first electrode 2 provided as a pixel electrode and a second electrode 6 provided as a counter electrode. A predetermined bias voltage is applied to the second electrode 6 via a counter electrode signal line 26.

[0112] The first electrode 2 is connected to the gate electrode 21G of the amplifier transistor 21, and the signal charges collected by the first electrode 2 are stored in a charge storage node 34 located between the first electrode 2 and the gate electrode 21G of the amplifier transistor 21. In this embodiment, the signal charges are holes.

[0113] The signal charge accumulated in the charge accumulation node 34 is applied as a voltage corresponding to the amount of signal charge to the gate electrode 21G of the amplifier transistor 21. The amplifier transistor 21 amplifies this voltage, and the amplified voltage is selectively read out as a signal voltage by the address transistor 23. The reset transistor 22 has its source / drain electrodes connected to the first electrode 2, and resets the signal charge accumulated in the charge accumulation node 34. In other words, the reset transistor 22 resets the potentials of the gate electrode 21G and the first electrode 2 of the amplifier transistor 21.

[0114] In order to selectively perform the above-described operations in the plurality of pixels 24, the imaging device 100 has a power supply wiring 31, a vertical signal line 27, an address signal line 36, and a reset signal line 37, which are connected to each pixel 24. Specifically, the power supply wiring 31 is connected to the source / drain electrode of the amplification transistor 21, and the vertical signal line 27 is connected to the source / drain electrode of the address transistor 23. The address signal line 36 is connected to the gate electrode 23G of the address transistor 23. The reset signal line 37 is connected to the gate electrode 22G of the reset transistor 22.

[0115] The peripheral circuits include a vertical scanning circuit 25 , a horizontal signal readout circuit 20 , a plurality of column signal processing circuits 29 , a plurality of load circuits 28 , and a plurality of differential amplifiers 32 .

[0116] The vertical scanning circuit 25 is connected to address signal lines 36 and reset signal lines 37, selects the multiple pixels 24 arranged in each row on a row-by-row basis, reads out the signal voltage, and resets the potential of the first electrode 2. A power supply wiring 31, which is a source follower power supply, supplies a predetermined power supply voltage to each pixel 24. The horizontal signal readout circuit 20 is electrically connected to multiple column signal processing circuits 29. The column signal processing circuits 29 are electrically connected to the pixels 24 arranged in each column via vertical signal lines 27 corresponding to each column. A load circuit 28 is electrically connected to each vertical signal line 27. The load circuit 28 and the amplification transistor 21 form a source follower circuit.

[0117] A plurality of differential amplifiers 32 are provided corresponding to each column. The negative input terminals of the differential amplifiers 32 are connected to the corresponding vertical signal lines 27. The output terminals of the differential amplifiers 32 are connected to the pixels 24 via feedback lines 33 corresponding to each column.

[0118] The vertical scanning circuit 25 applies a row selection signal, which controls the on / off of the address transistor 23, to the gate electrode 23G of the address transistor 23 via the address signal line 36. This scans and selects the row to be read out. A signal voltage is read out from the pixels 24 in the selected row to the vertical signal line 27. The vertical scanning circuit 25 also applies a reset signal, which controls the on / off of the reset transistor 22, to the gate electrode 22G of the reset transistor 22 via the reset signal line 37. This selects the row of pixels 24 to be subjected to the reset operation. The vertical signal line 27 transmits the signal voltage read out from the pixel 24 selected by the vertical scanning circuit 25 to the column signal processing circuit 29.

[0119] The column signal processing circuit 29 performs noise suppression signal processing, such as correlated double sampling, and analog-to-digital conversion (AD conversion).

[0120] The horizontal signal readout circuit 20 sequentially reads out signals from the plurality of column signal processing circuits 29 to a horizontal common signal line.

[0121] The differential amplifier 32 is connected to the source electrode of the reset transistor 22 via a feedback line 33. Therefore, the differential amplifier 32 receives the output value of the address transistor 23 at its negative terminal. The differential amplifier 32 performs a feedback operation so that the gate potential of the amplifying transistor 21 becomes a predetermined feedback voltage. At this time, the output voltage value of the differential amplifier 32 is 0 V or a positive voltage close to 0 V. The feedback voltage means the output voltage of the differential amplifier 32.

[0122] As shown in FIG. 5, the pixel 24 includes a semiconductor substrate 40, a charge detection circuit 35, a photoelectric conversion unit 10A, and a charge storage node 34 (see FIG. 4).

[0123] The semiconductor substrate 40 may be an insulating substrate having a semiconductor layer formed on the surface on which the photosensitive region is formed, such as a p-type silicon substrate. The semiconductor substrate 40 has impurity regions 21D, 21S, 22D, 22S, and 23S and an element isolation region 41 for electrical isolation between the pixels 24. The impurity regions 21D, 21S, 22D, 22S, and 23S are, for example, n-type regions. Here, the element isolation region 41 is provided between the impurity region 21D and the impurity region 22D. This suppresses leakage of signal charge accumulated in the charge storage node 34. The element isolation region 41 is formed, for example, by implanting acceptor ions under predetermined implantation conditions.

[0124] The impurity regions 21D, 21S, 22D, 22S, and 23S are, for example, diffusion regions formed in the semiconductor substrate 40. As shown in FIG. 5 , the amplifier transistor 21 includes the impurity region 21S, the impurity region 21D, and the gate electrode 21G. The impurity region 21S and the impurity region 21D function as, for example, a source region and a drain region, respectively, of the amplifier transistor 21. A channel region of the amplifier transistor 21 is formed between the impurity region 21S and the impurity region 21D.

[0125] Similarly, the address transistor 23 includes an impurity region 23S, an impurity region 21S, and a gate electrode 23G connected to an address signal line 36. In this example, the amplifier transistor 21 and the address transistor 23 are electrically connected to each other by sharing the impurity region 21S. The impurity region 23S functions as, for example, a source region of the address transistor 23. The impurity region 23S is connected to the vertical signal line 27 shown in FIG. 4 .

[0126] The reset transistor 22 includes impurity regions 22D and 22S and a gate electrode 22G connected to a reset signal line 37. The impurity region 22S functions as, for example, a source region of the reset transistor 22. The impurity region 22S is connected to a feedback line 33 shown in FIG.

[0127] An interlayer insulating layer 50 is laminated on the semiconductor substrate 40 so as to cover the amplifying transistor 21 , the address transistor 23 and the reset transistor 22 .

[0128] Furthermore, a wiring layer (not shown) may be disposed in the interlayer insulating layer 50. The wiring layer may be formed of a metal such as copper, and may include, as a part thereof, wiring such as the above-mentioned vertical signal line 27. The number of insulating layers in the interlayer insulating layer 50 and the number of wiring layers included in the wiring layer disposed in the interlayer insulating layer 50 may be set arbitrarily.

[0129] 5 , the contact plugs 51, 53, 54, 53 connected to the first electrode 2, the gate electrode 21G of the amplifier transistor 21, and the wiring 52 connecting the contact plug 51, the contact plug 54, and the contact plug 53 are arranged in the interlayer insulating layer 50. This electrically connects the impurity region 22D of the reset transistor 22 to the gate electrode 21G of the amplifier transistor 21. In the configuration illustrated in FIG. 5 , the contact plugs 51, 53, and 54, the wiring 52, the gate electrode 21G of the amplifier transistor 21, and the impurity region 22D of the reset transistor 22 form at least a part of the charge storage node 34.

[0130] The charge detection circuit 35 detects the signal charge captured by the first electrode 2 and outputs a signal voltage. That is, the charge detection circuit 35 reads out a signal corresponding to the charge generated by the photoelectric conversion unit 10A. The charge detection circuit 35 includes an amplification transistor 21, a reset transistor 22, and an address transistor 23, and is formed on a semiconductor substrate 40.

[0131] The amplification transistor 21 is formed in a semiconductor substrate 40 and includes an impurity region 21D and an impurity region 21S that function as a drain electrode and a source electrode, respectively, a gate insulating layer 21X formed on the semiconductor substrate 40, and a gate electrode 21G formed on the gate insulating layer 21X.

[0132] The reset transistor 22 is formed in a semiconductor substrate 40 and includes an impurity region 22D and an impurity region 22S that function as a drain electrode and a source electrode, respectively, a gate insulating layer 22X formed on the semiconductor substrate 40, and a gate electrode 22G formed on the gate insulating layer 22X.

[0133] Address transistor 23 is formed in semiconductor substrate 40 and includes impurity regions 21S and 23S functioning as a drain electrode and a source electrode, respectively, a gate insulating layer 23X formed on semiconductor substrate 40, and a gate electrode 23G formed on gate insulating layer 23X. Amplification transistor 21 and address transistor 23 are connected in series to impurity region 21S.

[0134] The above-described photoelectric conversion unit 10A is disposed on the interlayer insulating layer 50. In other words, in this embodiment, a plurality of pixels 24 constituting the pixel array PA are formed on a semiconductor substrate 40. The plurality of pixels 24 arranged two-dimensionally on the semiconductor substrate 40 form a photosensitive region. The distance between two connected pixels 24 (i.e., pixel pitch) may be, for example, approximately 2 μm.

[0135] The photoelectric conversion unit 10A has the structure of the photoelectric conversion element 10 described above.

[0136] A color filter 60 is formed above the photoelectric conversion unit 10A, and a microlens 61 is formed above that. The color filter 60 is formed, for example, as an on-chip color filter by patterning. The color filter 60 is made of a material such as a photosensitive resin in which a dye or pigment is dispersed. The process temperature when forming the color filter 60 is, for example, 170 degrees or higher.

[0137] The microlens 61 is formed as, for example, an on-chip microlens, and is made of a material such as an ultraviolet-sensitive material.

[0138] A general semiconductor manufacturing process can be used to manufacture the imaging device 100. In particular, when a silicon substrate is used as the semiconductor substrate 40, the imaging device 100 can be manufactured by utilizing various silicon semiconductor processes.

[0139] As described above, the charge blocking layer 3 may be used as a hole blocking layer, the charge blocking layer 5 may be used as an electron blocking layer, and electrons may be stored as signal charges in the charge storage node 34 and read out.

[0140] FIG. 6 is a diagram showing an example of a schematic current-voltage (IV) characteristic of the photoelectric conversion layer 4. In the diagram, the thick solid line graph shows an exemplary IV characteristic of the photoelectric conversion layer 4 when a voltage is applied between the first electrode 2 and the second electrode 6 in a state where light is irradiated. In addition, FIG. 6 also shows an example of the IV characteristic of the photoelectric conversion layer 4 when a voltage is applied between the first electrode 2 and the second electrode 6 in a state where light is not irradiated, using a thick dashed line. In the following description, the voltage when a positive voltage is applied to the second electrode 6 is a reverse bias voltage, and the voltage when a negative voltage is applied is a forward bias voltage.

[0141] As shown in FIG. 6 , the photocurrent characteristics of the photoelectric conversion layer 4 according to this embodiment are generally characterized by a first voltage range, a second voltage range, and a third voltage range. In the first voltage range, the dependency of the current change in the photoelectric conversion layer 4 on the voltage applied between the first electrode 2 and the second electrode 6 and the amount of light incident on the photoelectric conversion layer 4 is small. That is, in the first voltage range, the difference between the current value flowing when light is incident on the photoelectric conversion layer 4 and the current value flowing when no light is incident can be considered small. In the first voltage range, even if electron-hole pairs are generated by the incidence of light on the photoelectric conversion layer 4, the absolute value of the voltage applied between the first electrode 2 and the second electrode 6 is not large, so that the electrons and holes recombine before they separate. Furthermore, even if the electrons and holes separate, they recombine via trap levels or the like while being transported through the photoelectric conversion layer 4. Therefore, the number of holes and electrons flowing to the electrodes is expected to be small.

[0142] 6 is a reverse bias voltage range, where the absolute value of the output current density increases as the reverse bias voltage increases. That is, the second voltage range is a range where the current value increases as the amount of light incident on the photoelectric conversion layer 4 and the bias voltage applied between the first electrode 2 and the second electrode 6 increase.

[0143] The third voltage range is a forward bias voltage range in which the output current density increases as the forward bias voltage increases, i.e., the third voltage range is a range in which the current increases as the bias voltage applied between the first electrode 2 and the second electrode 6 increases, even if no light is incident on the photoelectric conversion layer 4.

[0144] The photoelectric conversion unit 10A of the imaging device 100 according to this embodiment is provided with a photoelectric conversion layer 4 having a first voltage range in which the difference between the current value that flows when light is incident on the photoelectric conversion layer 4 and the current value that flows when no light is incident is small, thereby enabling the imaging device 100 to realize a global shutter function while reducing parasitic sensitivity.

[0145] [Operation of the Imaging Device] Next, the operation of the imaging device 100 will be described with reference to Fig. 7 and Fig. 8. Here, a case where holes are used as signal charges will be described.

[0146] 7 is a diagram showing a part of a schematic circuit configuration of a pixel 24. For ease of explanation, one end of the charge storage node 34 is grounded and the potential is zero. This state corresponds to, for example, the case where the feedback line 33 shown in FIG. 4 is set to 0 V. In this state, if the voltage of the charge storage node 34 is Vc, Vc is zero.

[0147] A voltage supply circuit (not shown) supplies different voltages to the second electrode 6 via the counter electrode signal line 26 during the exposure period and the non-exposure period. In this specification, the term "exposure period" refers to a period during which one of electrons and holes generated by photoelectric conversion is accumulated as signal charge in the charge accumulation node 34. In other words, the "exposure period" may also be referred to as the "charge accumulation period." In this specification, a period other than the exposure period during operation of the imaging device is referred to as the "non-exposure period." The "non-exposure period" may be a period during which light is blocked from entering the photoelectric conversion unit 10A, or a period during which light is irradiated onto the photoelectric conversion unit 10A but charge is not substantially accumulated in the charge accumulation node 34.

[0148] In the initial state, the potential difference between the first electrode 2 and the second electrode 6 of the photoelectric conversion unit 10A, i.e., the bias voltage applied to the photoelectric conversion layer 4, charge blocking layer 3, and charge blocking layer 5, is set to a value within a first voltage range. For example, the voltage supply circuit applies a voltage equal to the voltage of the first electrode 2 to the second electrode 6 using the counter electrode signal line 26. Here, let V2 be the voltage applied to the second electrode 6, and let V2 be the reference voltage Vref. In this case, let Vo be the bias voltage applied to the photoelectric conversion unit 10A, and therefore Vo = V2 - Vc, and therefore Vo = 0.

[0149] Next, the operation during the exposure period will be described. At the start of the exposure period, the voltage supply circuit applies a voltage V2 to the second electrode 6 using the counter electrode signal line 26 so that a voltage within the second voltage range, i.e., a reverse bias voltage, is applied to the photoelectric conversion unit 10A. For example, if the photoelectric conversion layer 4 is made of an organic semiconductor material, V2 is a voltage of several volts to a maximum of about 10 volts. As a result, holes are accumulated as signal charges in the charge storage node 34 of each pixel 24, in an amount corresponding to the amount of light incident on the photoelectric conversion layer 4.

[0150] Next, the operation during the non-exposure period will be described. After the exposure period ends, the voltage supply circuit applies a voltage V2 to the second electrode 6 via the counter electrode signal line 26 so that a voltage within the first voltage range is applied to the photoelectric conversion unit 10A. For example, the voltage V2 applied to the second electrode 6 is set to a reference voltage Vref. Holes corresponding to the amount of light incident on the photoelectric conversion layer 4 during the exposure period are accumulated in the charge storage node 34 of each pixel 24, and the value of Vc varies depending on the pixel 24. Since Vo = V2 - Vc, Vo also becomes zero in pixels 24 that are not exposed and whose Vc remains unchanged. However, Vo does not become zero in pixels 24 whose Vc has changed. If the width of the first voltage range is ensured to be a sufficiently wide voltage range, the voltage V2 can be set so that the voltage Vo applied to the photoelectric conversion unit 10A in each pixel 24 falls within the first voltage range, even if the value of Vc differs for each pixel 24. The variation in the value of the voltage Vc falling within the first voltage range corresponds to the width of the dynamic range. For example, if the width of the first voltage range is 0.5 V or more, the conversion gain is 50 μV / e － In this imaging device, a dynamic range of 80 dB or more, which corresponds to the human eye, can be ensured.

[0151] When the voltage V2 that causes the voltage Vo to fall within the first voltage range is applied to the second electrode 6, holes are less likely to move to the charge storage node 34 even when light is incident on the pixel 24. In addition, holes stored in the charge storage node 34 are less likely to be discharged to the first electrode 2, and charges supplied from the voltage supply circuit via the second electrode 6 are less likely to flow into the charge storage node 34.

[0152] Therefore, the holes accumulated in the charge storage node 34 of each pixel 24 are maintained at an amount corresponding to the amount of light incident on the photoelectric conversion layer 4. In other words, the holes accumulated in the charge storage node 34 of each pixel 24 can be maintained even if light is again incident on the photoelectric conversion layer 4, as long as the holes in the charge storage node 34 are not reset. Therefore, even when a readout operation is performed sequentially for each row during a non-exposure period, new holes are unlikely to accumulate during the readout operation. Therefore, for example, rolling distortion, as occurs in a rolling shutter, does not occur. Therefore, for example, a global shutter function can be realized with a simple pixel circuit such as the pixel 24, without requiring a transfer transistor and an additional storage capacitor. Because the pixel circuit is simple, miniaturization of the pixels 24 in the imaging device 100 is advantageous.

[0153] FIG. 8 is a timing chart showing an example of the voltage V2 applied to the second electrode 6 of the photoelectric conversion unit 10A and the timing of operation in each row of the pixel array PA of the imaging device 100. For ease of understanding, FIG. 8 only shows the change in voltage V2 and the timing of exposure and signal readout for each row of the pixel array PA indicated by R0 to R7. As shown in FIG. 8 , in the imaging device 100, during the non-exposure period N, a voltage Vb is applied to the second electrode 6 as the voltage V2 such that the voltage Vo falls within a first voltage range, and during the exposure period E, a voltage Va is applied to the second electrode 6 such that the voltage Vo falls within a second voltage range. As shown in FIG. 8 , during the non-exposure period N, signal readout R is performed sequentially for each row R0 to R7. Furthermore, the start and end timings of the exposure period E are the same for all rows R0 to R7. That is, the imaging device 100 realizes a global shutter function in which all rows of the pixel array PA are exposed simultaneously while sequentially reading out the signals of the pixels 24 in each row.

[0154] The imaging device 100 may be driven by a rolling shutter system.

[0155] The semiconductor composition and photoelectric conversion element according to the present disclosure will be specifically described below in examples, but the present disclosure is not limited to the following examples. Specifically, a photoelectric conversion element formed using the semiconductor composition according to the present disclosure and a photoelectric conversion element for comparing characteristics were fabricated and evaluated.

[0156] (Fabrication of Photoelectric Conversion Element) Photoelectric conversion elements having a thin film made of the semiconductor composition of each of the examples and comparative examples as a photoelectric conversion layer were fabricated by the following steps.

[0157] Example 1 A 0.7 mm thick glass substrate was prepared, having a 150 nm thick ITO film on one major surface as a first electrode. In a nitrogen atmosphere glove box, an electron-blocking layer was formed by spin-coating a 10 mg / ml o-xylene solution of VNPB (N4,N4'-di(Naphthalen-1-yl)-N4,N4'-bis(4-vinylphenyl)biphenyl-4,4'-diamine, manufactured by LUMTEC Corporation) onto the first electrode. After film formation, the substrate was heated at 200°C for 50 minutes on a hot plate to crosslink the VNPB and insolubilize the electron-blocking layer.

[0158] Thereafter, a thin film that would become a photoelectric conversion layer was formed by spin coating using an ink composition prepared by dissolving a naphthalocyanine derivative represented by the following structural formula (1) as the first semiconductor material,

[60] PCBM as the second semiconductor material, and SEBS (styrene-ethylene-butylene-styrene block copolymer) as an additive in toluene. The thickness of the thin film obtained, which was made of a semiconductor composition containing the first semiconductor material, the second semiconductor material, and the additive, was approximately 250 nm. The weight ratio of the first semiconductor material to the second semiconductor material to the additive in the ink composition (semiconductor composition) was 6:24:2.

[0159]

[0160] Furthermore, a film of ClAlPc (chloroaluminum phthalocyanine) was formed to a thickness of 30 nm as a hole blocking layer by vacuum deposition through a metal shadow mask.

[0161] Thereafter, an ITO film was formed as a second electrode on the hole-blocking layer by sputtering to a thickness of 30 nm, thereby obtaining a photoelectric conversion element having a thin film made of the semiconductor composition of Example 1 as a photoelectric conversion layer.

[0162] [Example 2] The same steps as in Example 1 were carried out, except that the weight ratio of the first semiconductor material, the second semiconductor material, and the additive in the ink composition (semiconductor composition) was set to 6:24:5, thereby obtaining a photoelectric conversion element having a thin film made of the semiconductor composition in Example 2 as a photoelectric conversion layer.

[0163] [Comparative Example 1] A photoelectric conversion element having a thin film made of the semiconductor composition of Comparative Example 1 as a photoelectric conversion layer was obtained by carrying out the same steps as in Example 1, except that an ink composition containing no additives was used and the weight ratio of the first semiconductor material to the second semiconductor material in the ink composition (semiconductor composition) was set to 6:24.

[0164] [Comparative Example 2] A photoelectric conversion element having a thin film made of the semiconductor composition of Comparative Example 2 as a photoelectric conversion layer was obtained by carrying out the same steps as in Example 1, except that PVK (polyvinylcarbazole) was used instead of SEBS as the additive.

[0165] [Comparative Example 3] The same steps as in Example 1 were carried out, except that PVK was used instead of SEBS as the additive, and the weight ratio of the first semiconductor material, the second semiconductor material, and the additive in the ink composition (semiconductor composition) was set to 6:24:5, thereby obtaining a photoelectric conversion element having a thin film made of the semiconductor composition in Comparative Example 3 as a photoelectric conversion layer.

[0166] Comparative Example 4 A photoelectric conversion element having a thin film made of the semiconductor composition of Comparative Example 4 as a photoelectric conversion layer was obtained by carrying out the same steps as in Example 1, except that PS (polystyrene) was used instead of SEBS as the additive and the weight ratio of the first semiconductor material, the second semiconductor material, and the additive in the ink composition (semiconductor composition) was set to 6:24:5.

[0167] (Calculation of Hansen distance) The Hansen distance Ra1 between the first semiconductor material and the second semiconductor material, the Hansen distance Ra2 between the first semiconductor material and the additive, and the Hansen distance Ra3 between the second semiconductor material and the additive were calculated for the semiconductor compositions used in the photoelectric conversion layers in Examples 1 and 2 and Comparative Examples 2, 3, and 4. The calculation results are shown in Table 1.

[0168]

[0169] Table 1 shows the results of calculating the Hansen distance from the experimentally determined Hansen solubility parameters. The Hansen solubility parameters of the semiconductor composition materials used in the photoelectric conversion layer were determined using the Hansen sphere method. In the Hansen sphere method, the solvents used to determine the solubility of the materials were acetone, anisole, bromoform, chloroform, cyclohexane, cyclohexanone, ethanol, n-methyl-2-pyrrolidone, 2-propanol, propylene glycol monomethyl ether acetate, tetrahydrofuran, toluene, and o-xylene.

[0170] As shown in Table 1, the semiconductor compositions in Examples 1 and 2 satisfy the relationships Ra1<Ra2 and Ra1<Ra3. On the other hand, the semiconductor compositions in Comparative Examples 2, 3, and 4 satisfy the relationships Ra1>Ra2 and Ra1>Ra3, and do not satisfy the relationships Ra1<Ra2 and Ra1<Ra3.

[0171] (Evaluation of Photoelectric Conversion Element) To evaluate the obtained photoelectric conversion layer, the film quality of the photoelectric conversion layer in the photoelectric conversion element and the photoelectric conversion efficiency were evaluated by the following methods.

[0172] [Evaluation of the film quality of the photoelectric conversion layer] The obtained photoelectric conversion element was heated at 200°C for 50 minutes using a hot plate in a glove box, and the appearance of the photoelectric conversion layer after heating was observed under a microscope. Specifically, it was observed whether or not cracks had occurred in the photoelectric conversion layer. The observation results are shown in Table 2.

[0173] [Measurement of Photoelectric Conversion Efficiency] The photoelectric conversion efficiency of the obtained photoelectric conversion element was measured. Specifically, the photoelectric conversion element was placed in a measurement jig that could be sealed in a glove box under a nitrogen atmosphere, and the external quantum efficiency was measured using a long-wavelength spectral response measurement device (CEP-25RR, manufactured by Bunkoukeiki Co., Ltd.) at a voltage of 10 V. Table 2 shows the measurement results of the external quantum efficiency at a wavelength of 940 nm. Table 2 also shows the theoretical value for the external quantum efficiency, taking into account the decrease in external quantum efficiency due to the decrease in the content of the first semiconductor material and the second semiconductor material in the photoelectric conversion layer caused by the additive, and the difference between the measured value and the theoretical value. Specifically, the theoretical value is calculated by multiplying the measured value of the photoelectric conversion element in Comparative Example 1, which has a photoelectric conversion layer containing no additive, by the reference measured value and the total volumetric content of the first semiconductor material and the second semiconductor material in the photoelectric conversion layer. The volumetric content was calculated from the weight ratio of the first semiconductor material, the second semiconductor material, and the additive, and the specific gravity of each material.

[0174]

[0175] Table 2 also shows the weights of the first semiconductor material, the second semiconductor material, and the additives used to form the photoelectric conversion layer, as well as the types of the additives.

[0176] As shown in Table 2, in the photoelectric conversion element of Comparative Example 1, which did not use an additive, cracks occurred in the photoelectric conversion layer after heating at 200° C. This was caused by thermal stress, and a photoelectric conversion element in which cracks occurred in the photoelectric conversion layer cannot be used industrially in a heated environment.

[0177] Furthermore, in the photoelectric conversion elements of Comparative Examples 2 and 3, in which PVK was used as an additive, cracking of the photoelectric conversion layer was suppressed after heating at 200°C, but the external quantum efficiency was significantly lower than the theoretical value. In other words, although the addition of the additive improved film quality, the photoelectric conversion efficiency was significantly reduced. This is because, as shown in Table 1, in Comparative Examples 2 and 3, the Hansen distance relationships Ra1 < Ra2 and Ra1 < Ra3 were not satisfied. Specifically, the Hansen distance Ra2 between the electron-donating first semiconductor material and the additive, and the Hansen distance Ra3 between the electron-accepting second semiconductor material and the additive were smaller than the Hansen distance Ra1 between the first semiconductor material and the second semiconductor material. This made it easier for the additive PVK to be present around the first semiconductor material and the second semiconductor material, preventing charge transfer between the first semiconductor material and the second semiconductor material during photoelectric conversion.

[0178] Furthermore, in the photoelectric conversion element of Comparative Example 4, which used PS as an additive, the occurrence of cracks in the photoelectric conversion layer after heating at 200° C. was suppressed, as in Comparative Examples 2 and 3, but the external quantum efficiency was significantly reduced compared to the theoretical value. This is also because, as shown in Table 1, in Comparative Example 4, the Hansen distance relationship of Ra1<Ra2 and Ra1<Ra3 was not satisfied.

[0179] On the other hand, in Examples 1 and 2, in which SEBS was used as the additive, not only was cracking of the photoelectric conversion layer suppressed after heating at 200°C, but external quantum efficiency was also able to be obtained that was equivalent to the theoretical value. As shown in Table 1, in Examples 1 and 2, Ra1 < Ra2 and Ra1 < Ra3 were satisfied, and among the Hansen distances between the materials of the photoelectric conversion layer, the Hansen distance Ra1 between the first semiconductor material and the second semiconductor material was the smallest. Therefore, in the photoelectric conversion elements in Examples 1 and 2, the additive did not interfere with the transfer of charge between the first semiconductor material and the second semiconductor material during photoelectric conversion, and the additive was able to improve film quality by suppressing cracking due to heating.

[0180] As described above, by using a semiconductor composition that contains the first semiconductor material, the second semiconductor material, and an additive and that satisfies Ra1<Ra2 and Ra1<Ra3, it is possible to achieve both improvement in film quality and suppression of a decrease in photoelectric conversion efficiency.

[0181] The semiconductor composition, ink composition, film, photoelectric conversion element, and imaging device according to the present disclosure have been described above based on embodiments and examples, but the present disclosure is not limited to these embodiments and examples. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art may make to the embodiments and examples, as well as other forms constructed by combining some of the components of the embodiments and examples, are also included in the scope of the present disclosure.

[0182] The semiconductor composition, ink composition, film, and photoelectric conversion element according to the present disclosure can be used, for example, in an imaging device. The imaging device according to the present disclosure can be applied to various camera systems and sensor systems, such as medical cameras, surveillance cameras, vehicle-mounted cameras, distance measuring cameras, microscope cameras, drone cameras, and robot cameras.

[0183] REFERENCE SIGNS LIST 1 Support substrate 2 First electrode 3, 5 Charge blocking layer 4 Photoelectric conversion layer 4A First semiconductor material 4B Second semiconductor material 6 Second electrode 10 Photoelectric conversion element 10A Photoelectric conversion section 20 Horizontal signal readout circuit 21 Amplifying transistor 22 Reset transistor 23 Address transistor 21D, 21S, 22D, 22S, 23S Impurity region 21G, 22G, 23G Gate electrode 21X, 22X, 23X Gate insulating layer 24 Pixel 25 Vertical scanning circuit 26 Counter electrode signal line 27 Vertical signal line 28 Load circuit 29 Column signal processing circuit 31 Power supply wiring 32 Differential amplifier 33 Feedback line 34 Charge storage node 35 Charge detection circuit 36 ​​Address signal line 37 Reset signal line 40 Semiconductor substrate 41 Element isolation region 50 Interlayer insulating layer 51, 53, 54 Contact plug 52 Wiring 60 Color filter 61 Microlens 100 Imaging device

Claims

1. A semiconductor composition comprising: a first electron-donating semiconductor material; a second electron-accepting semiconductor material; and an additive, wherein Ra1<Ra2 and Ra1<Ra3 are satisfied, where Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material; Ra2 represents the Hansen distance between the first semiconductor material and the additive; and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

2. The semiconductor composition according to claim 1, wherein the first semiconductor material and the second semiconductor material are organic semiconductor materials.

3. The semiconductor composition according to claim 2, wherein the first semiconductor material is a low molecular weight compound.

4. The semiconductor composition according to claim 2, wherein the second semiconductor material is a low molecular weight compound.

5. The semiconductor composition according to claim 1, wherein the additive is a polymer compound.

6. An ink composition comprising the semiconductor composition according to any one of claims 1 to 5 and a solvent.

7. The ink composition according to claim 6, wherein the solvent comprises an aromatic compound.

8. A film formed using the ink composition according to claim 6.

9. A photoelectric conversion element comprising: a first electrode; a second electrode facing the first electrode; and the film according to claim 8 located between the first electrode and the second electrode.

10. An imaging device comprising the photoelectric conversion element according to claim 9.

11. A photoelectric conversion element comprising: a first electrode; a second electrode facing the first electrode; and a photoelectric conversion layer located between the first electrode and the second electrode, wherein the photoelectric conversion layer includes: a first semiconductor material having electron donating properties; a second semiconductor material having electron accepting properties; and an additive, wherein Ra1<Ra2 and Ra1<Ra3 are satisfied, wherein Ra1 represents the Hansen distance between the first semiconductor material and the second semiconductor material, Ra2 represents the Hansen distance between the first semiconductor material and the additive, and Ra3 represents the Hansen distance between the second semiconductor material and the additive.

12. An imaging device comprising the photoelectric conversion element according to claim 11.

Images