Patent Publication Number: US-2022231246-A1

Title: Photoelectric conversion element and imaging device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a photoelectric conversion element and an imaging device in which this is used. 
     BACKGROUND ART 
     In recent years, devices in which organic thin films are used have been developed. One of such devices is an organic photoelectric conversion element. There has been proposed an organic thin-film solar cell, an organic imaging element, or the like in which the organic photoelectric conversion element is used. A bulk heterostructure is adopted in the organic photoelectric conversion element to increase external quantum efficiency. In the bulk heterostructure, a p-type organic semiconductor and an n-type organic semiconductor are mixed. However, the organic photoelectric conversion element has a problem that it is not possible to obtain sufficient external quantum efficiency due to a low conductive characteristic of an organic semiconductor. In addition, the organic imaging element has a problem that an electric output signal is easily delayed with respect to incident light. 
     In general, it has been found that molecular orientation is important for the conduction of an organic semiconductor. The same applies to an organic photoelectric conversion element having a bulk heterostructure. For this reason, in an organic photoelectric conversion element in which a conduction direction is perpendicular to a substrate, it is preferable that the organic semiconductor be oriented parallel with the substrate. In contrast, for example, PTL 1 discloses a photoelectric conversion element in which an organic semiconductor compound having horizontal orientation is used. For example, PTL 2 discloses an organic thin-film solar cell in which an orientation control layer is provided in a lower layer of an i-layer. For example, PTL 3 discloses a method of manufacturing an organic photoelectric conversion element that controls the orientation of a photoelectric conversion layer by controlling substrate temperature to form a film. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2009-60053 
     PTL 2: Japanese Unexamined Patent Application Publication No. 2007-59457 
     PTL 3: Japanese Unexamined Patent Application Publication No. 2008-258421 
     SUMMARY OF THE INVENTION 
     Incidentally, a photoelectric conversion element in which an organic semiconductor material is used is requested to have high external quantum efficiency and favorable afterimage characteristics. 
     It is desirable to provide a photoelectric conversion element and an imaging device each of which allows both high external quantum efficiency and favorable afterimage characteristics to be achieved. 
     A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode; a second electrode that is disposed to be opposed to the first electrode; and an organic photoelectric conversion layer that is provided between the first electrode and the second electrode and includes one organic semiconductor material. The organic photoelectric conversion layer includes at least one or more domains in a horizontal cross section. The one or more domains are each formed by using the one organic semiconductor material. 
     An imaging device according to an embodiment of the present disclosure includes pixels each including one or more organic photoelectric conversion sections and includes the photoelectric conversion element according to the embodiment of the present disclosure described above as the organic photoelectric conversion section. 
     In the photoelectric conversion element according to the embodiment of the present disclosure and the imaging device according to the embodiment, the organic photoelectric conversion layer provided between the first electrode and the second electrode includes at least the one or more domains in the horizontal cross section. The one or more domains are each formed by using the one organic semiconductor material. This increases the probability that excitons generated in the organic photoelectric conversion layer irradiated with light move to the first electrode and the second electrode. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic plan view of a configuration of a unit pixel of the photoelectric conversion element illustrated in  FIG. 1 . 
         FIG. 3A  is a schematic diagram illustrating an example of a state of a p-type semiconductor in an organic photoelectric conversion layer illustrated in  FIG. 1 . 
         FIG. 3B  is a schematic plan view of the organic photoelectric conversion layer taken along a I-I′ line illustrated in  FIG. 3A . 
         FIG. 4  is a schematic diagram of a TEM image of the organic photoelectric conversion layer illustrated in  FIG. 1 . 
         FIG. 5  is a schematic cross-sectional view of another example of the configuration of the photoelectric conversion element according to the embodiment of the present disclosure. 
         FIG. 6  is a schematic cross-sectional view for describing a method of manufacturing the photoelectric conversion element illustrated in  FIG. 1 . 
         FIG. 7  is a schematic cross-sectional view illustrating a step subsequent to  FIG. 6 . 
         FIG. 8  is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to a modification example 1 of the present disclosure. 
         FIG. 9  is an equivalent circuit diagram of the photoelectric conversion element illustrated in  FIG. 8 . 
         FIG. 10  is a schematic diagram illustrating disposition of a lower electrode of the photoelectric conversion element illustrated in  FIG. 8  and a transistor included in a controller. 
         FIG. 11  is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to a modification example 2 of the present disclosure. 
         FIG. 12  is a block diagram illustrating an overall configuration of a solid-state imaging element including the photoelectric conversion element illustrated in  FIG. 1 . 
         FIG. 13  is a functional block diagram illustrating an example of a solid-state imaging device (a camera) in which the solid-state imaging element illustrated in  FIG. 12  is used. 
         FIG. 14  is a block diagram depicting an example of a schematic configuration of an in-vivo information acquisition system. 
         FIG. 15  is a view depicting an example of a schematic configuration of an endoscopic surgery system. 
         FIG. 16  is a block diagram depicting an example of a functional configuration of a camera head and a camera control unit (CCU). 
         FIG. 17  is a block diagram depicting an example of schematic configuration of a vehicle control system. 
         FIG. 18  is a diagram of assistance in explaining an example of installation positions of an outside-vehicle information detecting section and an imaging section. 
         FIG. 19  is a schematic cross-sectional view of a configuration of Experiment Example 1. 
         FIG. 20A  is a schematic cross-sectional view describing a fabrication step of a sample for TEM analysis. 
         FIG. 20B  is a schematic diagram illustrating a step subsequent to  FIG. 20A . 
         FIG. 21  is a schematic diagram of a TEM image of Experiment Example 1. 
         FIG. 22  is a schematic diagram of a TEM image of Experiment Example 2. 
         FIG. 23  is a schematic diagram of a TEM image of Experiment Example 3. 
         FIG. 24  is a schematic diagram of a TEM image near a lower electrode of Experiment Example 1. 
         FIG. 25  is a schematic diagram of a TEM image near an upper electrode of Experiment Example 1. 
         FIG. 26A  is a diagram describing a film formation method of a deposited film. 
         FIG. 26B  is a schematic diagram illustrating a configuration of a grid and a support film illustrated in  FIG. 26A . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     The following describes an embodiment of the present disclosure in detail with reference to the drawings. The following description is a specific example of the present disclosure, but the present disclosure is not limited to the following embodiment. In addition, the present disclosure does not limit the disposition, dimensions, dimension ratios, and the like of respective components illustrated in the diagrams thereto. It is to be noted that description is given in the following order. 
     1. Embodiment (An example in which an organic photoelectric conversion layer is provided that includes at least one or more domains of an organic semiconductor material in a horizontal cross section) 
     1-1. Configuration of Photoelectric Conversion Element 
     1-2. Method of Manufacturing Photoelectric Conversion Element 
     1-3. Workings and Effects 
     2. Modification Examples 
     2-1. Modification Example 1 (An example of a photoelectric conversion element in which a lower electrode includes a plurality of electrodes)
 
2-2. Modification Example 2 (An example of a photoelectric conversion element in which a plurality of organic photoelectric conversion sections is stacked)
 
     3. Application Examples 
     4. Practical Application Examples 
     5. Working Examples 
     1. EMBODIMENT 
       FIG. 1  illustrates an example of a cross-sectional configuration of a photoelectric conversion element (a photoelectric conversion element  1 ) according to an embodiment of the present disclosure.  FIG. 2  illustrates an example of a planar configuration of the photoelectric conversion element  1  illustrated in  FIG. 1 . The photoelectric conversion element  1  is included, for example, in one pixel (a unit pixel P) in a solid-state imaging device (an imaging device  100 ) such as a back-illuminated (back light receiving) CCD (Charge Coupled Device) image sensor or CMOS (Complementary Metal Oxide Semiconductor) image sensor (see  FIG. 12 ). The photoelectric conversion element  1  is of a so-called vertical spectroscopic type in which one organic photoelectric conversion section  10  and two inorganic photoelectric conversion sections  32 B and  32 R are stacked in the vertical direction. The organic photoelectric conversion section  10  and the two inorganic photoelectric conversion sections  32 B and  32 R each selectively detect respective pieces of light in different wavelength regions to perform photoelectric conversion. The present embodiment adopts a configuration in which an organic photoelectric conversion layer  12  included in the organic photoelectric conversion section  10  includes one or more domains in a horizontal cross section. Each of the one or more domains is formed by using an organic semiconductor material (one organic semiconductor material). 
     1-1. Configuration of Photoelectric Conversion Element 
     In the photoelectric conversion element  1 , one organic photoelectric conversion section  10 , and two inorganic photoelectric conversion sections  32 B and  32 R are stacked in the vertical direction for each unit pixel P. The organic photoelectric conversion section  10  is provided on a back surface (a first surface  30 S 1 ) side of a semiconductor substrate  30 . The inorganic photoelectric conversion sections  32 B and  32 R are formed to be embedded in the semiconductor substrate  30  and stacked in the thickness direction of the semiconductor substrate  30 . The organic photoelectric conversion section  10  includes the organic photoelectric conversion layer  12  including a p-type semiconductor and an n-type semiconductor and having a bulk hetero junction structure in a layer. The bulk hetero junction structure is a p/n junction surface formed by mixture of a p-type semiconductor and an n-type semiconductor. 
     The organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and  32 R perform photoelectric conversion by selectively detecting respective pieces of light in different wavelength bands. Specifically, the organic photoelectric conversion section  10  acquires a green (G) color signal. The inorganic photoelectric conversion sections  32 B and  32 R respectively acquire a blue (B) color signal and a red (R) color signal by using a difference between absorption coefficients. This allows the photoelectric conversion element  1  to acquire a plurality types of color signals in one pixel without using a color filter. 
     It is to be noted that, in the present embodiment, description is given of a case of reading electron as signal charge (a case where the n-type semiconductor region is used as a photoelectric conversion layer) of a pair of the electrons and holes generated from photoelectric conversion. In addition, in the drawings, “+ (plus)” assigned to “p” and “n” indicates that the concentration of p-type or n-type impurities is high and “++” indicates that the concentration of p-type or n-type impurities is further higher than “+”. 
     The semiconductor substrate  30  includes, for example, an n-type silicon (Si) substrate and has a p-well  31  in a predetermined region. A second surface (the front surface of the semiconductor substrate  30 )  30 S 2  of the p-well  31  is provided, for example, with various floating diffusions (floating diffusion layers) FD (e.g., FD 1 , FD 2 , and FD 3 ), various transistors Tr (e.g., a vertical transistor (a transfer transistor) Tr 1 , a transfer transistor Tr 2 , an amplifier transistor (a modulation element) AMP, and a reset transistor RST), and a multilayer wiring line  40 . The multilayer wiring line  40  has a configuration in which wiring layers  41 ,  42 , and  43 , for example, are stacked in an insulating layer  44 . In addition, a peripheral portion of the semiconductor substrate  30  is provided with a peripheral circuit (not illustrated) including a logic circuit or the like. 
     It is to be noted that  FIG. 1  illustrates the first surface  30 S 1  side of the semiconductor substrate  30  as a light incident surface S 1  and the second surface  30 S 2  side thereof as a wiring layer side S 2 . 
     The inorganic photoelectric conversion sections  32 B and  32 R each include, for example, a PIN (Positive Intrinsic Negative) type photodiode and each have a p-n junction in a predetermined region of the semiconductor substrate  30 . The inorganic photoelectric conversion sections  32 B and  32 R allow light to be dispersed in the vertical direction by using the wavelength bands of absorbed light that are different in accordance with the incidence depth on the silicon substrate. 
     The inorganic photoelectric conversion section  32 B selectively detects the blue light to accumulate the signal charge corresponding to blue and is installed at a depth that allows the blue light to be photoelectrically converted efficiently. The inorganic photoelectric conversion section  32 R selectively detects the red light to accumulate the signal charge corresponding to red and is installed at a depth that allows the red light to be photoelectrically converted efficiently. It is to be noted that blue (B) is a color corresponding to a wavelength band of 450 nm to 495 nm, for example, and red (R) is a color corresponding to a wavelength band of 620 nm to 750 nm, for example. It is sufficient if the inorganic photoelectric conversion sections  32 B and  32 R are able to detect pieces of light of a portion or all of the respective wavelength bands. 
     Specifically, as illustrated in  FIG. 1 , the inorganic photoelectric conversion section  32 B and the inorganic photoelectric conversion section  32 R each include, for example, a p+ region serving as a hole accumulation layer and an n region serving as an electron accumulation layer (they each have a p-n-p stacked structure). Then region of the inorganic photoelectric conversion section  32 B is coupled to the vertical transistor Tr 1 . The p+ region of the inorganic photoelectric conversion section  32 B bends along the vertical transistor Tr  1  and links to the p+ region of the inorganic photoelectric conversion section  32 R. 
     As described above, the second surface  30 S 2  of the semiconductor substrate  30  is provided, for example, with the floating diffusions (floating diffusion layers) FD 1 , FD 2 , and FD 3 , the vertical transistor (the transfer transistor) Tr 1 , the transfer transistor Tr 2 , the amplifier transistor (the modulation element) AMP, and the reset transistor RST. 
     The vertical transistor Tr 1  is a transfer transistor that transfers, to the floating diffusion FD 1 , the signal charge (electrons, here) generated and accumulated in the inorganic photoelectric conversion section  32 B. The signal charge corresponds to blue. The inorganic photoelectric conversion section  32 B is formed at a deep position from the second surface  30 S 2  of the semiconductor substrate  30  and it is thus preferable that the transfer transistor of the inorganic photoelectric conversion section  32 B include the vertical transistor Tr 1 . 
     The transfer transistor Tr 2  transfers, to the floating diffusion FD 2 , the signal charge (electrons, here) generated and accumulated in the inorganic photoelectric conversion section  32 R. The signal charge corresponds to red. The transfer transistor Tr 2  includes, for example, a MOS transistor. 
     The amplifier transistor AMP is a modulation element that modulates, into a voltage, the amount of electric charge generated in the organic photoelectric conversion section  10  and includes, for example, a MOS transistor. 
     The reset transistor RST resets the electric charge transferred from the organic photoelectric conversion section  10  to the floating diffusion FD 3  and includes, for example, a MOS transistor. 
     A lower first contact  45 , a lower second contact  46 , and an upper contact  16 B each include, for example, a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon) or a metal material such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (Hf), or tantalum (Ta). 
     The organic photoelectric conversion section  10  is provided on the first surface  30 S 1  side of the semiconductor substrate  30 . The organic photoelectric conversion section  10  has a configuration in which, for example, a lower electrode  11 , the organic photoelectric conversion layer  12 , and an upper electrode  13  are stacked in this order from the side of the first surface  30 S 1  of the semiconductor substrate  30 . The lower electrode  11  is, for example, separately formed for each of the photoelectric conversion elements  1 . The organic photoelectric conversion layer  12  and the upper electrode  13  are provided as continuous layers common to the plurality of photoelectric conversion elements  1 . 
     Between the first surface  30 S 1  of the semiconductor substrate  30  and the lower electrode  11 , for example, inter-layer insulating layers  14  and  15  are stacked in this order from the semiconductor substrate  30  side. The inter-layer insulating layer  14  has a configuration in which, for example, a layer (a fixed electric charge layer)  14 A having fixed electric charge and a dielectric layer  14 B having insulation properties are stacked. There is provided a protective layer  51  on the upper electrode  13 . An on-chip lens layer  52  included in an on-chip lens  52 L and also serving as a planarization layer is disposed above the protective layer  51 . 
     There is provided a through electrode  34  between the first surface  30 S 1  and the second surface  30 S 2  of the semiconductor substrate  30 . The organic photoelectric conversion section  10  is coupled to a gate Gamp of the amplifier transistor AMP and the floating diffusion FD 3  through this through electrode  34 . This allows the photoelectric conversion element  1  to transfer electric charge generated in the organic photoelectric conversion section  10  on the first surface  30 S 1  side of the semiconductor substrate  30  to the second surface  30 S 2  side of the semiconductor substrate  30  through the through electrode  34  in a favorable manner, thus making it possible to increase the characteristics. 
     The through electrode  34  is provided, for example, for each organic photoelectric conversion section  10  of the photoelectric conversion element  1 . The through electrode  34  has a function of a connector for the organic photoelectric conversion section  10  and the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 3  and serves as a transmission path for electric charge generated in the organic photoelectric conversion section  10 . 
     The lower end of the through electrode  34  is coupled, for example, to a coupling section  41 A in the wiring layer  41  and the coupling section  41 A and the gate Gamp of the amplifier transistor AMP are coupled through the lower first contact  45 . The coupling section  41 A and the floating diffusion FD 3  are coupled to the lower electrode  11  through the lower second contact  46 . It is to be noted that  FIG. 1  illustrates the through electrode  34  in the shape of a cylinder, but this is not limitative. The through electrode  34  may have a tapered shape, for example. 
     As illustrated in  FIG. 1 , it is preferable that a reset gate Grst of the reset transistor RST be disposed next to the floating diffusion FD 3 . This makes it possible to cause the reset transistor RST to reset the electric charge accumulated in the floating diffusion FD 3 . 
     In the photoelectric conversion element  1  according to the present embodiment, light inputted to the organic photoelectric conversion section  10  from the upper electrode  13  side is absorbed by the organic photoelectric conversion layer  12 . Excitons generated by this move to an interface between an electron donor and an electron acceptor included in the organic photoelectric conversion layer  12  and undergo exciton separation, that is, dissociate into electrons and holes. The electric charge (electrons and holes) generated here is transported to different electrodes by diffusion due to a difference in carrier concentration or by an internal electric field due to a difference in work functions between an anode (here, the upper electrode  13 ) and a cathode (here, the lower electrode  11 ) and is detected as a photocurrent. In addition, the application of an electric potential between the lower electrode  11  and the upper electrode  13  makes it possible to control directions in which electrons and holes are transported. 
     The following describes configurations, materials, or the like of respective sections. 
     The organic photoelectric conversion section  10  is an organic photoelectric conversion element that absorbs the green light corresponding to a portion or all of selective wavelength bands (e.g., 400 nm or more and 700 nm or less) to generate an electron-hole pair. 
     The lower electrode  11  is provided in a region that directly faces light receiving surfaces of the inorganic photoelectric conversion sections  32 B and  32 R formed in the semiconductor substrate  30  and covers these light receiving surfaces. The lower electrode  11  includes an electrically conducive layer having light transmissivity and includes, for example, ITO (indium-tin oxide). However, as a material included in the lower electrode  11 , a tin oxide (SnO 2 )-based material obtained by adding a dopant or a zinc oxide-based material formed by adding a dopant to aluminum zinc oxide (ZnO) may be used in addition to this ITO. Examples of the zinc oxide-based materials include aluminum zinc oxide (AZO) obtained by adding aluminum (Al) as the dopant, gallium (Ga)-added gallium zinc oxide (GZO), and indium (In)-added indium zinc oxide (IZO). In addition, CuI, InSbO 4 , ZnMgO, CuInO 2 , MglN 2 O 4 , CdO, ZnSnO 3 , or the like may also be used in addition to these. 
     The organic photoelectric conversion layer  12  converts optical energy to electric energy. The organic photoelectric conversion layer  12  includes, for example, two or more types of organic semiconductor materials and includes, for example, one or both of p-type semiconductors and n-type semiconductors. In a case where the organic photoelectric conversion layer  12  includes the two types of organic semiconductor materials including p-type semiconductors and n-type semiconductors, for example, it is preferable one of the p-type semiconductors and the n-type semiconductors be materials having transmissivity to visible light and the other thereof be materials that photoelectrically convert light in a selective wavelength region (e.g., 450 nm or more and 650 nm or less). Alternatively, the organic photoelectric conversion layer  12  includes, for example, three types of organic semiconductor materials including materials (light absorbers), n-type semiconductors, and p-type semiconductors. The materials (the light absorbers) photoelectrically convert light in a selective wavelength region. The n-type semiconductors and the p-type semiconductors each have light transmissivity to visible light. The organic photoelectric conversion layer  12  has a bulk heterostructure in which the plurality of these organic semiconductor materials is randomly mixed in the layer. 
     In the organic photoelectric conversion layer  12 , two types (p-type semiconductors and n-type semiconductors) or three types (light absorbers, p-type semiconductors, and n-type semiconductors) of organic semiconductor materials each form a plurality of grains and randomly mixed as described above. The present embodiment adopts a configuration in which a portion of at least one type of organic semiconductor materials among the plurality of types of organic semiconductor materials described above forms a plurality of domains in the layer and at least one or more domains are confirmed in a horizontal cross section of the organic photoelectric conversion layer  12 . The following describes this in detail with reference to  FIGS. 3A, 3B, and 4 . It is to be noted that the domain is a region including a continuous arrangement of one type of the organic semiconductor materials described above. Each of the organic semiconductor materials described above may form a domain in the organic photoelectric conversion layer  12 . In addition, a domain may include two or more types of organic semiconductor materials. 
       FIG. 3A  schematically illustrates an example of the state of one organic semiconductor material (e.g., p-type semiconductors) in the organic photoelectric conversion layer  12  according to the present embodiment. In the organic photoelectric conversion layer  12 , as illustrated in  FIG. 3A , a plurality of domains is formed that each includes a p-type semiconductor. It is to be noted that  FIG. 3A  illustrates, as an example, a case where three domains D 1 , D 2 , and D 3  are formed.  FIG. 3B  schematically illustrates a planar structure of the organic photoelectric conversion layer  12  taken along a I-I′ line illustrated in  FIG. 3A . It is preferable that it is possible to confirm substantially the same number of domains in horizontal cross sections of the organic photoelectric conversion layer  12  according to the present embodiment at any positions in the Y axis direction. In other words, it is preferable that the organic photoelectric conversion layer  12  have substantially the same areal density of domains at any positions in the film thickness direction (the Y axis direction). Electric charge (electrons and holes) that has undergone exciton separation in the domains moves to the lower electrode  11  and the upper electrode  13  through the domains. Substantially the same areal density of domains at any positions in the organic photoelectric conversion layer  12  in the film thickness direction (the Y axis direction) as described above therefore increases the probability that electric charge moves to the electrodes and makes it possible to obtain high external quantum efficiency and favorable afterimage characteristics. 
     It is to be noted that it is possible to confirm the areal density of domains in the organic photoelectric conversion layer  12  by using a transmission electron microscope (Transmission Electron Microscope; TEM). This is described in detail below. For example, in a case where the number (N) of domains is measured in an area of 100 nm×100 nm observed by TEM, it is possible to predict that the number of domains is substantially the same in planes taken along any positions as long as the front surface side and the substrate side have the same number of domains within an error of ±√N (the square root of N) that is a so-called statistical error. To increase the collection efficiency of electric charge, it is desirable that the domain density be equal to the number N of domains measured in unit area within the error corresponding to the double of the square root of the number N of domains. It is thus assumed that, in a case where the organic photoelectric conversion layer  12  has substantially the same areal density of domains at any positions in the film thickness direction, the areal density falls within the range of ±√N. 
     In addition, it is preferable that the areal density (the number of domains/unit area parallel with the substrate surface of the semiconductor substrate  30 ) of domains in the organic photoelectric conversion layer  12  be 1500 domains/square micron or more. Further, it is preferable that the areal density (the number of domains/unit area parallel with the substrate surface of the semiconductor substrate  30 ) of domains in the organic photoelectric conversion layer  12  be 2500 domains/square micron or more. 2500 domains/square micron corresponds to a density of one domain in square area having a side of 20 nm. Increasing the areal density of domains in the organic photoelectric conversion layer  12  in this way increases the probability that excitons generated in the organic photoelectric conversion layer  12  irradiated with light reach the domains and makes it possible to further increase the probability that electric charge moves to an electrode. 
     Further, it is preferable that each of a plurality of domains have a percolation structure in which the domain vertically extends through the organic photoelectric conversion layer  12  in the film thickness direction (the Y axis direction), for example, as illustrated in  FIG. 3B . Further, it is preferable that at least some domains among the plurality of domains partially (e.g., ends of domains each having a percolation structure) be in contact with one or both of the lower electrode  11  and the upper electrode  13 . This increases the probability that electric charge (electrons and holes) moves from the domains to the lower electrode  11  or the upper electrode  13 . 
     Still further, it is preferable that at least a portion of a plurality of domains have crystallizability. Specifically, it is preferable that at least a portion of a plurality of domains include a crystal. Each of the plurality of domains includes a crystal. This makes it possible to reduce electric charge trapping in the domains. 
     In addition, in a case of the same areal density of domains in the organic photoelectric conversion layer  12 , it is more advantageous that crystals included in the domains are larger in terms of the movement efficiency of electric charge. In contrast, this may possibly decrease regions that absorb light to generate excitons. It is therefore desirable that the planar projected area ratio, for example, obtained by projecting the organic photoelectric conversion layer  12  in the film thickness direction be 0.5 or less as the size of crystals included in a plurality of domains formed in the organic photoelectric conversion layer  12 . This makes it possible to increase the movement efficiency of electric charge while maintaining the generation of excitons necessary for photoelectric conversion. 
     The internal structure of the organic photoelectric conversion layer  12  is confirmable, for example, by using TEM as described above. The TEM is a device that two-dimensionally projects a three-dimensional object to shoot a so-called TEM image. The TEM allows the shape of a crystal having about several nanometers to be grasped. 
     A crystal generally refers to a three-dimensional structure in which atoms or molecules are regularly arranged. Electrons scatter while passing through crystals and interfere due to the electronic waves. As a result, the electrons are strengthened or weakened in a specific direction. In a case where electrons pass through a periodic structure called crystal planes in substantially parallel directions, interference fringes are observed in a TEM image. The interference fringes are referred to as lattice fringes in general. Here, the TEM image thereof is referred to as lattice image. 
     A condition under which a lattice image is observed depends on a device. A defocus amount (a defocus amount) is, however, observed near so-called Scherzer focus in many cases. For example, it is calculated in accordance with Expression (1) below. At the Scherzer focus, the diffracted waves are shifted with respect to the transmitted waves by about ¼ wavelength to form an image. This forms contrast suitable to associate the lattice image and the atomic arrangement. In addition, the intervals (the period) of lattice fringes correspond to the period of crystal planes. In a case where the lattice image further goes out of focus, the lattice image has black and white inverted therein. Further, the contour around the crystals becomes remarkable, for example. The image exhibits varying aspects. In addition, the aspect depends on the accelerating voltage (the wavelength of electrons) of TEM, the aberration of a lens, the size of the crystals, and the like. 
       (Math. 1) 
       Scherzer focus=1.2√(Cs·λ)  Expression (1)
 
     (Cs represents a spherical aberration coefficient and λ represents the wavelength of electrons) 
     Even in a case where a crystal plane is not parallel with the electron transmission direction, a fringe (so-called fringe contrast) is formed near the contour of a scatterer (e.g., a crystal) different in density in the sample by shifting the focus. In general, interference fringes corresponding to about several atomic columns or molecular columns are frequently observed at the Scherzer focus. A defocus amount of about several μm tends to relatively strengthen fringe contrast. 
     The defocus amount is sometimes shifted by about several μm by proactively using this phenomenon to observe a scatterer that is difficult to contrast. This is sometimes referred to as defocus image, but the Scherzer focus is also a defocus image (a defocus amount different in scale) in strict terms. 
     In general, a sample that is analyzed by TEM has a thickness of about several tens of nm in the electron transmission direction. This is because electrons and a substance have a strong interaction and only a thin sample allows electrons to pass through the sample. However, there are examples of several nm for nano-carbon and several hundreds of nm to μm for observation using an ultra-high voltage electron microscope. In general, it is determined that the defocus amount is zero in a case where the contrast is the weakest. A lattice image is shot by defocusing from that by the Scherzer focus. The defocus amount, however, depends on the position of the sample in the electron transmission direction. It is thus a portion of the sample that satisfies the Scherzer focus condition. 
     Meanwhile, in a case of a defocus amount of about several μm, the defocus amount is much greater than the thickness of the sample. As a result, the contour of the scatterer such as a crystal is observed as substantially similar fringe contrast in spite of different positions in the electron transmission direction. 
     As described above, the present embodiment defines a domain as a crystal in a case where a periodic fringe pattern is observed in a portion of domains in an image (a TEM image) of domains shot under the defocus condition under which the focus of the TEM is shifted by 1 μm or more. Here, the wording “a portion of domains” is used because of the principled reason that a crystal plane is not necessarily parallel with the transmission direction of electrons and a fringe pattern is thus observed in only a portion of the crystals. 
       FIG. 4  schematically illustrates a portion (a square having a side of 100 nm) of a TEM image of the organic photoelectric conversion layer  12  (Experiment Example 1 described below) shot under the defocus condition described above. The organic photoelectric conversion layer  12  is fabricated by using p-type semiconductors that form the domains as described above. In the organic photoelectric conversion layer  12  according to the present embodiment, as illustrated in  FIG. 4 , lattice fringes including two or more lines are confirmable. 
     As described above, it is preferable that the organic photoelectric conversion layer  12  include two types of organic semiconductor materials including n-type semiconductors and p-type semiconductors or three types of organic semiconductor materials including light absorbers, n-type semiconductors, and p-type semiconductors. There is a junction surface (a p/n junction surface) between the p-type semiconductors and the n-type semiconductors in the layer. Each of the light absorbers has the maximal absorption wavelength within a range of, for example, 450 nm or more and 650 nm or less. Examples of the light absorbers include subphthalocyanine or a derivative thereof. Each of the p-type semiconductors relatively functions as an electron donor (a donor) and the use of a material having a hole transporting property is preferable, for example. Examples of such a material include a compound including acene or thienoacene as the mother skeleton and including a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group as the side chain or the substituent thereof in addition to 3,6-BP-BBTN (see Expression 1) used in a working example 1. Each of the n-type semiconductors relatively functions as an electron acceptor (acceptor) and the use of a material having an electron transporting property is preferable, for example. Examples of the n-type semiconductors include fullerene C60 or a derivative thereof. The thickness of the organic photoelectric conversion layer  12  is, for example, 50 nm to 500 nm. It is preferable that the interface between the organic photoelectric conversion layer  12  and the upper electrode  13  have a surface roughness of 10 nm or less. 
     It is to be noted that an example in which p-type semiconductors form a plurality of domains has been described in the present embodiment, but this is not limitative. For example, n-type semiconductors may form a plurality of domains. 
     The upper electrode  13  includes an electrically conductive film having light transmissivity similar to that of the lower electrode  11 . In the imaging device  100  in which the photoelectric conversion element  1  is used as one pixel, this upper electrode  13  may be separated for each of the pixels or may be formed as an electrode common to the respective pixels. The thickness of the upper electrode  13  is, for example, 10 nm to 200 nm. 
     It is to be noted that there may be provided other layers between the organic photoelectric conversion layer  12  and the lower electrode  11  and between the organic photoelectric conversion layer  12  and the upper electrode  13 .  FIG. 5  illustrates another example of the cross-sectional configuration of the photoelectric conversion element  1  according to the present embodiment. Buffer layers  17 A and  17 B may be provided between the organic photoelectric conversion layer  12  and the lower electrode  11  or between the organic photoelectric conversion layer  12  and the upper electrode  13 . Alternatively, the buffer layers  17 A and  17 B may be provided both between the organic photoelectric conversion layer  12  and the lower electrode  11  and between the organic photoelectric conversion layer  12  and the upper electrode  13 . In addition, for example, an underlying film, a hole transport layer, an electron blocking film, the organic photoelectric conversion layer  12 , a hole blocking film, an electron transport layer, a work function adjusting film, and the like may be stacked in order from the lower electrode  11  side. 
     The fixed electric charge layer  14 A may be a film having positive fixed electric charge or a film having negative fixed electric charge. As a material of the film having negative fixed electric charge, hafnium oxide, aluminum oxide, zirconium oxide, tantalum oxide, titanium oxide, and the like are included. In addition, as a material other than the materials described, lanthanum oxide, praseodymium oxide, cerium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, thulium oxide, ytterbium oxide, lutetium oxide, yttrium oxide, an aluminum nitride film, a hafnium oxynitride film, an aluminum oxynitride film, or the like may be used. 
     The fixed electric charge layer  14 A may also have a configuration in which two or more types of films are stacked. This makes it possible to further increase a function of a hole accumulation layer in a case of a film having negative fixed electric charge, for example. 
     Although a material of the dielectric layer  14 B is not limited in particular, the dielectric layer  14 B includes, for example, a silicon oxide film, TEOS, a silicon nitride film, a silicon oxynitride film, or the like. 
     The inter-layer insulating layer  15  includes, for example, a single-layer film including one type of silicon oxide, silicon nitride, silicon oxynitride (SiON), and the like or a stacked film including two or more types thereof. 
     The protective layer  51  includes a material having light transmissivity and includes, for example, a single layer film including any of silicon oxide, silicon nitride, silicon oxynitride, and the like or a stacked film including two or more types thereof. The thickness of the protective layer  51  is, for example, 100 nm to 30000 nm. 
     The on-chip lens layer  52  is formed on the protective layer  51  to cover the whole surface thereof. The plurality of on-chip lenses (the microlenses)  52 L is provided on the front surface of the on-chip lens layer  52 . The on-chip lenses  52 L condense light inputted from above the on-chip lens  52 L on the respective light receiving surfaces of the organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and  32 R. In the present embodiment, the multilayer wiring line  40  is formed on the second surface  30 S 2  side of the semiconductor substrate  30 . This allows the respective light receiving surfaces of the organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and  32 R to be disposed close to each other, thus making it possible to reduce sensitivity variations between the respective colors generated depending on the F-value of the on-chip lens  52 L. 
     It is possible in the photoelectric conversion element  1  according to the present embodiment to configure the organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and  32 R, for example, as illustrated in  FIG. 2 .  FIG. 2  illustrates an example of a planar configuration of each of the unit pixels P included in a pixel section  100 A, for example, illustrated in  FIG. 12 . 
     The unit pixel P includes a photoelectric conversion region  1100  in which a red photoelectric conversion section (the inorganic photoelectric conversion section  32 R in  FIG. 1 ), a blue photoelectric conversion section (the inorganic photoelectric conversion section  32 B in  FIG. 1 ), and a green photoelectric conversion section (the organic photoelectric conversion section  10  in  FIG. 1 ) (neither of which is illustrated in  FIG. 2 ) that photoelectrically convert respective pieces of light in the wavelengths of R (Red), G (Green), and B (Blue) are stacked in three layers in the order of the green photoelectric conversion section, the blue photoelectric conversion section, and the red photoelectric conversion section, for example, from the light receiving surface (the light incident surface Si in  FIG. 1 ) side. Further, the unit pixel P includes a Tr group  1110 , a Tr group  1120 , and a Tr group  1130  as electric charge readout sections that read electric charge corresponding to the respective pieces of light in wavelengths of R, G, and B from the red photoelectric conversion section, the green photoelectric conversion section, and the blue photoelectric conversion section. The imaging device  100  disperses light in the vertical direction in one unit pixel P. In other words, the imaging device  100  disperses the respective pieces of light of R, G, and B in the respective layers serving as the red photoelectric conversion section, the green photoelectric conversion section, and the blue photoelectric conversion section stacked in the photoelectric conversion region  1100 . 
     The Tr group  1110 , the Tr group  1120 , and the Tr group  1130  are formed on the periphery of the photoelectric conversion region  1100 . The Tr group  1110  outputs, as a pixel signal, the signal charge corresponding to the light of R generated and accumulated in the red photoelectric conversion section. The Tr group  1110  includes a transfer Tr (MOS FET)  1111 , a reset Tr  1112 , an amplification Tr  1113 , and a selection Tr  1114 . The Tr group  1120  outputs, as a pixel signal, the signal charge corresponding to the light of B generated and accumulated in the blue photoelectric conversion section. The Tr group  1120  includes a transfer Tr  1121 , a reset Tr  1122 , an amplification Tr  1123 , and a selection Tr  1124 . The Tr group  1130  outputs, as a pixel signal, the signal charge corresponding to the light of G generated and accumulated in the green photoelectric conversion section. The Tr group  1130  includes a transfer Tr  1131 , a reset Tr  1132 , an amplification Tr  1133 , and a selection Tr  1134 . 
     The transfer Tr  1111  includes (a source/drain region serving as) a gate G, a source/drain region S/D, and FD (a floating diffusion)  1115 . The transfer Tr  1121  includes a gate G, a source/drain region S/D, and FD  1125 . The transfer Tr  1131  includes a gate G, (a source/drain region S/D coupled to) the green photoelectric conversion section of the photoelectric conversion region  1100 , and FD  1135 . It is to be noted that the source/drain region of the transfer Tr  1111  is coupled to the red photoelectric conversion section of the photoelectric conversion region  1100  and the source/drain region S/D of the transfer Tr  1121  is coupled to the blue photoelectric conversion section of the photoelectric conversion region  1100 . 
     The reset Trs  1112 ,  1132 , and  1122 , the amplification Trs  1113 ,  1133 , and  1123 , and the selection Trs  1114 ,  1134 , and  1124  each include a gate G and a pair of source/drain regions S/D disposed across the gate G. 
     The FDs  1115 ,  1135 , and  1125  are coupled to the respective source/drain regions S/D serving as sources of the reset Trs  1112 ,  1132 , and  1122 , and are coupled to the respective gates G of the amplification Trs  1113 ,  1133  and  1123 . A power supply Vdd is coupled to the common source/drain region S/D in each of the reset Tr  1112  and the amplification Tr  1113 , the reset Tr  1132  and the amplification Tr  1133 , and the reset Tr  1122  and the amplification Tr  1123 . VSL (a vertical signal line) is coupled to each of the source/drain regions S/D serving as the respective sources of the selection Trs  1114 ,  1134 , and  1124 . 
     The technology according to the present disclosure is applicable to the photoelectric conversion element as described above. 
     1-2. Method of Manufacturing Photoelectric Conversion Element 
     It is possible to manufacture the photoelectric conversion element  1  according to the present embodiment, for example, as follows. 
       FIGS. 6 and 7  illustrate a method of manufacturing the photoelectric conversion element  1  in order of steps. First, as illustrated in  FIG. 6 , the p-well  31 , for example, is formed as a first electrical conduction type of well in the semiconductor substrate  30 . The second electrical conduction type (e.g., n-type) of inorganic photoelectric conversion sections  32 B and  32 R are formed in this p-well  31 . A p+ region is formed near the first surface  30 S 1  of the semiconductor substrate  30 . 
     As also illustrated in  FIG. 6 , on the second surface  30 S 2  of the semiconductor substrate  30 , after n+ regions serving as the floating diffusions FD 1  to FD 3  are formed, a gate insulating layer  62  and a gate wiring layer  47  including the respective gates of the vertical transistor Tr 1 , the transfer transistor Tr 2 , the amplifier transistor AMP, and the reset transistor RST are formed. This forms the vertical transistor Tr 1 , the transfer transistor Tr 2 , the amplifier transistor AMP, and the reset transistor RST. Further, the multilayer wiring line  40  is formed on the second surface  30 S 2  of the semiconductor substrate  30 . The multilayer wiring line  40  includes wiring layers  41  to  73  and the insulating layer  44 . The wiring layers  41  to  73  include the lower first contact  45 , the lower second contact  46 , and the coupling section  41 A. 
     As a base of the semiconductor substrate  30 , for example, an SOI (Silicon on Insulator) substrate is used in which the semiconductor substrate  30 , an embedded oxide film (not illustrated), and a holding substrate (not illustrated) are stacked. Although not illustrated in  FIG. 6 , the embedded oxide film and the holding substrate are joined to the first substrate surface  30 S 1  of the semiconductor substrate  30 . After ion implantation, an annealing process is performed. 
     Then, a support substrate (not illustrated), another semiconductor substrate, or the like is joined to the second surface  30 S 2  side (the multilayer wiring line  40  side) of the semiconductor substrate  30  and flipped vertically. Subsequently, the semiconductor substrate  30  is separated from the embedded oxide film and the holding substrate of the SOI substrate to expose the first surface  30 S 1  of the semiconductor substrate  30 . It is possible to perform these steps with technology used in a normal CMOS process such as ion implantation and CVD (Chemical Vapor Deposition). 
     Subsequently, as illustrated in  FIG. 7 , the semiconductor substrate  30  is processed from the first surface  30 S 1  side by dry etching, for example, to form an annular opening  34 H. The opening  34 H has a depth penetrating from the first surface  30 S 1  to the second surface  30 S 2  of the semiconductor substrate  30  as illustrated in  FIG. 7  and reaching, for example, the coupling section  41 A. 
     Subsequently, as illustrated in  FIG. 7 , for example, the negative fixed electric charge layer  14 A is formed on the first surface  30 S 1  of the semiconductor substrate  30  and the side surface of the opening  34 H. Two or more types of films may be stacked as the negative fixed electric charge layer  14 A. This makes it possible to further increase a function of the hole accumulation layer. The dielectric layer  14 B is formed after the negative fixed electric charge layer  14 A is formed. 
     Next, an electric conductor is embedded in the opening  34 H to form the through electrode  34 . As the electric conductor, for example, a metal material such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (Hf), and tantalum (Ta) is usable in addition to a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon). 
     Subsequently, after a pad section  16 A is formed on the through electrode  34 , the inter-layer insulating layer  15  is formed on the dielectric layer  14 B and the pad section  16 A. In the inter-layer insulating layer  15 , the upper contact  16 B and a pad section  16 C are provided on the pad section  16 A. The upper contact  16 B and the pad section  16 C electrically couple the lower electrode  11  and the through electrode  34  (specifically, the pad section  16 A on the through electrode  34 ). 
     Next, the lower electrode  11 , the organic photoelectric conversion layer  12 , the upper electrode  13 , and the protective layer  51  are formed in this order on the inter-layer insulating layer  15 . As the organic photoelectric conversion layer  12 , for example, films of the three types of organic semiconductor materials described above are formed by using, for example, a deposition method (a resistive heating method). In this case, the substrate stage is set at predetermined temperature. This makes it possible to control the areal density of domains in the organic photoelectric conversion layer  12 . Finally, the on-chip lens layer  52  is disposed that includes the plurality of on-chip lenses  52 L on the front surface thereof. As described above, the photoelectric conversion element  1  illustrated in  FIG. 1  is completed. 
     It is to be noted that, in a case where another organic layer (e.g., an electron blocking layer or the like) is formed on or under the organic photoelectric conversion layer  12  as described above, it is desirable to continuously form the other organic layer (by a vacuum-consistent process) in a vacuum step. In addition, the method of forming the organic photoelectric conversion layer  12  is not necessarily limited to the method using a vacuum deposition method, but another method, for example, a spin-coating technique, a printing technique, or the like may be used. 
     In a case where light enters the organic photoelectric conversion section  10  through the on-chip lens  52 L in the photoelectric conversion element  1 , the light passes through the organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and the  32 R in this order and the respective pieces of light of green, blue, and red are photoelectrically converted in the passing process. The following describes an operation of acquiring signals of the respective colors. 
     Acquisition of Green Color Signal by Organic Photoelectric Conversion Section  10   
     First, the green light of the pieces of light inputted into the photoelectric conversion element  1  is selectively detected (absorbed) and photoelectrically converted by the organic photoelectric conversion section  10 . 
     The organic photoelectric conversion section  10  is coupled to the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 3  through the through electrode  34 . The electron of the electron-hole pair generated in the organic photoelectric conversion section  10  is thus taken out from the lower electrode  11  side, transferred to the second surface  30 S 2  side of the semiconductor substrate  30  through the through electrode  34 , and accumulated in the floating diffusion FD 3 . At the same time as this, the amplifier transistor AMP modulates the amount of electric charge generated in the organic photoelectric conversion section  10  into a voltage. 
     In addition, the reset gate Grst of the reset transistor RST is disposed next to the floating diffusion FD 3 . This causes the reset transistor RST to reset the electric charge accumulated in the floating diffusion FD 3 . 
     Here, the organic photoelectric conversion section  10  is coupled to not only the amplifier transistor AMP, but also the floating diffusion FD 3  through the through electrode  34 , making it possible for the reset transistor RST to easily reset the electric charge accumulated in the floating diffusion FD 3 . 
     In contrast, in a case where the through electrode  34  and the floating diffusion FD 3  are not coupled, it is difficult to reset the electric charge accumulated in the floating diffusion FD 3 , resulting in application of a large voltage to pull out the electric charge to the upper electrode  13  side. Accordingly, there is a possibility that the organic photoelectric conversion layer  12  is damaged. In addition, a structure that allows for resetting in a short period of time leads to increased dark-time noise and results in a trade-off. This structure is thus difficult. 
     Acquisition of Blue Color Signal and Red Color Signal by Inorganic Photoelectric Conversion Sections  32 B and  32 R 
     Subsequently, the blue light and the red light of the pieces of light passing through the organic photoelectric conversion section  10  are respectively absorbed in order and photoelectrically converted in the inorganic photoelectric conversion section  32 B and the inorganic photoelectric conversion section  32 R. In the inorganic photoelectric conversion section  32 B, electrons corresponding to the inputted blue light are accumulated in the n-region of the inorganic photoelectric conversion section  32 B and the accumulated electrons are transferred to the floating diffusion FD 1  by the vertical transistor Tr 1 . Similarly, in the inorganic photoelectric conversion section  32 R, electrons corresponding to the inputted red light are accumulated in the n-region of the inorganic photoelectric conversion section  32 R and the accumulated electrons are transferred to the floating diffusion FD 2  by the transfer transistor Tr 2 . 
     1-3. Workings and Effects 
     As described above, an organic photoelectric conversion element used for an organic thin-film solar cell, an organic imaging element, or the like adopts a bulk heterostructure in which a p-type organic semiconductor and an n-type organic semiconductor are mixed. However, organic semiconductors have low conductive characteristics and the organic photoelectric conversion element is thus unable to obtain sufficient quantum efficiency. Therefore, there is a problem that an electric output signal is easily delayed with respect to the incident light. 
     In general, it has been found that molecular orientation is important for the conduction of organic semiconductors. The same applies to an organic photoelectric conversion element having a bulk heterostructure. It has been known that, in an organic photoelectric conversion element in which a conduction direction is perpendicular to a substrate, it is generally preferable that the organic semiconductor be oriented parallel with the substrate. Therefore, as described above, various measures are taken to increase the horizontal orientation of an organic semiconductor included in an organic photoelectric conversion layer. 
     In addition, the size and dispersion state of domains of the organic semiconductor in the layer are important for the conduction of the organic semiconductor in addition to molecular light distribution. 
     In contrast, in the photoelectric conversion element  1  according to the present embodiment, the organic photoelectric conversion layer  12  includes domains in a horizontal cross section. The domains are formed by using one or more organic semiconductor materials (e.g., p-type semiconductors). This increases the probability that electric charge (electrons and holes) moves to the lower electrode  11  and the upper electrode  13  through the domains. The electric charge (electrons and holes) results from exciton separation in the domains in the organic photoelectric conversion layer  12  irradiated with light. 
     As described above, in the photoelectric conversion element  1  according to the present embodiment, the organic photoelectric conversion layer  12  is formed that includes one or more domains in a horizontal cross section. This facilitates electric charge (electrons and holes) generated in the organic photoelectric conversion layer  12  to move to the lower electrode  11  and the upper electrode  13 . The one or more domains are each formed by using an organic semiconductor material. This allows both high external quantum efficiency and favorable afterimage characteristics to be achieved. 
     In addition, in the present embodiment, the areal density of domains in the organic photoelectric conversion layer  12  is increased and the organic photoelectric conversion layer  12  has substantially the same areal density of domains at any positions in the film thickness direction. Specifically, the areal density (the number of domains/unit area parallel with the substrate surface of the semiconductor substrate  30 ) of domains in the organic photoelectric conversion layer  12  is 1500 domains/square micron or more. More preferably, the areal density (the number of domains/unit area parallel with the substrate surface of the semiconductor substrate  30 ) of domains in the organic photoelectric conversion layer  12  is 2500 domains/square micron or more. This further increases the probability that electric charge moves to the lower electrode  11  and the upper electrode  13  and makes it possible to further increase high external quantum efficiency and favorable afterimage characteristics. 
     Further, in the present embodiment, each of a plurality of domains in the organic photoelectric conversion layer  12  has a percolation structure in which the domain vertically extends through the organic photoelectric conversion layer  12  in the film thickness direction (the Y axis direction) and at least a portion of the domains is in contact with one or both of the lower electrode  11  and the upper electrode  13 . This makes it possible to further increase the probability that electric charge generated in the organic photoelectric conversion layer  12  moves to the lower electrode  11  or the upper electrode  13  through the domains. 
     Still further, in the present embodiment, each of a plurality of domains in the organic photoelectric conversion layer  12  includes a crystal of an organic semiconductor material. The organic photoelectric conversion layer  12  is formed to cause the planar projected area ratio obtained by projecting the organic photoelectric conversion layer  12  in the film thickness direction to be 0.5 or less. This makes it possible to further increase the movement efficiency of electric charge while maintaining the generation of excitons necessary for photoelectric conversion. 
     Next, a modification example of the present disclosure is described. It is to be noted that components corresponding to those of the photoelectric conversion element  1  according to the embodiment described above are denoted by the same reference numerals and description thereof is omitted. 
     2. MODIFICATION EXAMPLES 
     2-1. Modification Example 1 
       FIG. 8  illustrates an example of a cross-sectional configuration of an imaging element (a photoelectric conversion element  2 ) according to a modification example 1 of the present disclosure.  FIG. 9  is an equivalent circuit diagram of the photoelectric conversion element  2  illustrated in  FIG. 8 .  FIG. 10  schematically illustrates the disposition of a lower electrode  21  of the photoelectric conversion element  2  illustrated in  FIG. 8  and a transistor included in a controller. The photoelectric conversion element  2  is included, for example, in one pixel (the unit pixel P) in the solid-state imaging device (the imaging device  100 ) such as a back-illuminated (back light receiving) CCD image sensor or CMOS image sensor as in the embodiment described above. Although described in detail below, the lower electrode  21  of the photoelectric conversion element  2  according to the present modification example includes a readout electrode  21 A and an accumulation electrode  21 B. The photoelectric conversion element  2  according to the present modification example is different from the photoelectric conversion element  1  according to the embodiment described above on this point. The lower electrode  21  is included in an organic photoelectric conversion section  20 . The readout electrode  21 A and the accumulation electrode  21 B are separated from each other with an insulating layer  22  interposed in between. 
     In the organic photoelectric conversion section  20 , the lower electrode  21 , a semiconductor layer  23 , an organic photoelectric conversion layer  24 , and an upper electrode  25  are stacked in this order from the first surface (the surface  30 S 1 ) side of the semiconductor substrate  30 . In addition, the insulating layer  22  is provided between the lower electrode  21  and the semiconductor layer  23 . The lower electrode  21  is separately formed, for example, for each of the photoelectric conversion elements  2  and includes the readout electrode  21 A and the accumulation electrode  21 B that are separated from each other with the insulating layer  22  interposed in between as described above. The readout electrode  21 A of the lower electrode  21  is electrically coupled to the semiconductor layer  23  through an opening  22 H provided in the insulating layer  22 .  FIG. 8  illustrates an example in which the semiconductor layer  23 , the organic photoelectric conversion layer  24 , and the upper electrode  25  are provided as continuous layers common to the plurality of photoelectric conversion elements  2 , but the semiconductor layer  23 , the organic photoelectric conversion layer  24 , and the upper electrode  25  may be separately formed for each of the photoelectric conversion elements  2 . For example, there are provided a dielectric layer  26 , an insulating layer  27 , and an inter-layer insulating layer  28  between the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and the lower electrode  21 . There is provided a protective layer  51  on the upper electrode  25 . There is provided a light shielding film  53 , for example, at the position corresponding to the readout electrode  21 A in the protective layer  51 . It is sufficient if this light shielding film  53  is provided to cover the region of the readout electrode  21 A in direct contact with at least the semiconductor layer  23  without overlapping with at least the accumulation electrode  21 B. There are provided, above the protective layer  51 , a planarization layer (not illustrated) and an optical member such as the on-chip lens  52 L. 
     The through electrode  34  is provided between the first surface (the surface  30 S 1 ) and the second surface (the surface  30 S 2 ) of the semiconductor substrate  30  as in the embodiment described above. This through electrode  34  is electrically coupled to the readout electrode  21  of the organic photoelectric conversion section  20  and the organic photoelectric conversion section  20  is coupled to a gate Gamp of the amplifier transistor AMP and one source/drain region  36 B of the reset transistor RST (a reset transistor Tr 1 rst) through the through electrode  34 . The reset transistor RST (the reset transistor Tr 1 rst) also serves as the floating diffusion FD 1 . This allows the photoelectric conversion element  2  to transfer electric charge generated in the organic photoelectric conversion section  20  on the first surface (the surface  30 S 21 ) side of the semiconductor substrate  30  to the second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  in a favorable manner, thus making it possible to increase the characteristics. 
     The lower end of the through electrode  34  is coupled to the coupling section  41 A in the wiring layer  41  and the coupling section  41 A and the gate Gamp of the amplifier transistor AMP are coupled through the lower first contact  45 . The coupling section  41 A and the floating diffusion FD 1  (the region  36 B) are coupled, for example, through the lower second contact  46 . The upper end of the through electrode  34  is coupled to the readout electrode  21 A, for example, through an upper first contact  29 A, a pad section  39 A, and an upper second contact  29 B. 
     The through electrode  34  is provided, for example, for each organic photoelectric conversion section  20  in the photoelectric conversion element  2 . The through electrode  34  has a function of a connector for the organic photoelectric conversion section  20  and the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 1  and serves as a transmission path for electric charge generated in the organic photoelectric conversion section  20 . 
     The reset gate Grst of the reset transistor RST is disposed next to the floating diffusion FD 1  (the one source/drain region  36 B of the reset transistor RST). This makes it possible to cause the reset transistor RST to reset the electric charge accumulated in the floating diffusion FD 1 . 
     The organic photoelectric conversion section  20  is an organic photoelectric conversion element that absorbs the light corresponding to a portion or all of selective wavelength regions (e.g., 400 nm or more and 700 nm or less) to generate an electron-hole pair. 
     As described above, the lower electrode  21  includes the readout electrode  21 A and the accumulation electrode  21 B that are separately formed. The readout electrode  21 A is for transferring electric charge generated in the organic photoelectric conversion layer  24  to the floating diffusion FD 1 . The readout electrode  21 A is coupled to the floating diffusion FD 1 , for example, through the upper second contact  29 B, the pad section  39 A, the upper first contact  29 A, the through electrode  34 , the coupling section  41 A, and the lower second contact  46 . The accumulation electrode  21 B is for accumulating electrons of the electric charge generated in the organic photoelectric conversion layer  24  in the semiconductor layer  23  as signal charge. The accumulation electrode  21 B is provided in a region that directly faces the light receiving surfaces of inorganic photoelectric conversion sections  32 G and  32 R formed in the semiconductor substrate  30  and covers these light receiving surfaces. It is preferable that the accumulation electrode  21 B be larger than the readout electrode  21 A. This makes it possible to accumulate a large amount of electric charge. As illustrated in  FIG. 10 , a voltage application circuit  60  is coupled to the accumulation electrode  21 B through a wiring line. 
     The lower electrode  21  includes an electrically conductive film having light transmissivity as with that of the lower electrode  11  according to the embodiment described above. 
     The semiconductor layer  23  is provided in a lower layer of the organic photoelectric conversion layer  24 . Specifically, the semiconductor layer  23  is provided between the insulating layer  22  and the organic photoelectric conversion layer  24 . The semiconductor layer  23  is for accumulating signal charge generated in the organic photoelectric conversion layer  24 . It is preferable that the semiconductor layer  23  be formed by using a material having higher electric charge mobility and having a larger band gap than those of the organic photoelectric conversion layer  24 . For example, it is preferable that the band gap of a material included in the semiconductor layer  23  be 3.0 eV or more. Examples of such a material include an oxide semiconductor material such as IGZO, an organic semiconductor material, and the like. Examples of the organic semiconductor material include transition metal dichalcogenide, silicon carbide, diamond, graphene, a carbon nanotube, a fused polycyclic hydrocarbon compound, a fused heterocyclic compound, and the like. The thickness of the semiconductor layer  23  is, for example, 10 nm or more and 300 nm or less. The semiconductor layer  23  including the materials described above is provided in a lower layer of the organic photoelectric conversion layer  24 . This makes it possible to prevent electric charge recombination while the electric charge is accumulated and increase the transfer efficiency. 
     The organic photoelectric conversion layer  24  converts optical energy to electric energy. The organic photoelectric conversion layer  24  includes components similar to those of the organic photoelectric conversion layer  12  according to the embodiment described above. 
     The upper electrode  25  includes an electrically conductive film having light transmissivity as with that of the upper electrode  13  according to the embodiment described above. 
     It is to be noted that there may be provided other layers between the semiconductor layer  23  and the organic photoelectric conversion layer  24  and between the organic photoelectric conversion layer  24  and the upper electrode  25 . For example, as with the photoelectric conversion element  1  illustrated in  FIG. 5 , the buffer layers  17 A and  17 B may be provided, for example, between the organic photoelectric conversion layer  24  and the lower electrode  21  or between the organic photoelectric conversion layer  24  and the upper electrode  25  or the buffer layers  17 A and  17 B may be provided both between the organic photoelectric conversion layer  24  and the lower electrode  21  and between the organic photoelectric conversion layer  24  and the upper electrode  25 . 
     The insulating layer  22  is for electrically separating the accumulation electrode  21 B and the semiconductor layer  23 . The insulating layer  22  is provided, for example, on the inter-layer insulating layer  28  to cover the lower electrode  21 . In addition, the insulating layer  22  is provided with the opening  22 H above the readout electrode  21 A of the lower electrode  21 . The readout electrode  21 A and the semiconductor layer  23  are electrically coupled through this opening  22 H. The insulating layer  22  includes, for example, a single-layer film including one of silicon oxide, silicon nitride, silicon oxynitride, and the like, or a stacked film including two or more thereof. The thickness of the insulating layer  22  is, for example, 20 nm to 500 nm. 
     The dielectric layer  26  is for preventing the reflection of light caused by a refractive index difference between the semiconductor substrate  30  and the insulating layer  27 . It is preferable that a material of the dielectric layer  26  be a material having a refractive index between the refractive index of the semiconductor substrate  30  and the refractive index of the insulating layer  27 . Further, it is preferable that a material allowing a film to be formed having, for example, negative fixed electric charge be used as a material of the dielectric layer  26 . Alternatively, it is preferable that a semiconductor material or an electrically conductive material having a wider band gap than that of the semiconductor substrate  30  be used as a material of the dielectric layer  26 . This makes it possible to suppress the generation of dark currents at the interface of the semiconductor substrate  30 . Such a material includes hafnium oxide, aluminum oxide, zirconium oxide, tantalum oxide, titanium oxide, lanthanum oxide, praseodymium oxide, cerium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, thulium oxide, ytterbium oxide, lutetium oxide, yttrium oxide, hafnium nitride, aluminum nitride, hafnium oxynitride, aluminum oxynitride, and the like. 
     The insulating layer  27  is provided on the dielectric layer  26  that is formed on the first surface (the surface  30 S 1 ) of the semiconductor substrate  30  and the side surface of the through hole  30 H. The insulating layer  27  is for electrically insulating the through electrode  34  and the semiconductor substrate  30  from each other. Examples of a material of the insulating layer  27  include silicon oxide, TEOS, silicon nitride, silicon oxynitride, and the like. 
     The inter-layer insulating layer  28  includes, for example, a single-layer film including one of silicon oxide, TEOS, silicon nitride, silicon oxynitride, and the like or a stacked film including two or more thereof. 
     The semiconductor substrate  30  includes, for example, an n-type silicon substrate and includes the p-well  31  in a predetermined region (e.g., a pixel section  1   a ). The second surface (the surface  30 S 2 ) of the p-well  31  is provided with the transfer transistors Tr 2  and Tr 3  described above, the amplifier transistor AMP, the reset transistor RST, a selection transistor SEL, and the like. 
     The reset transistor RST (the reset transistor Tr 1 rst) resets the electric charge transferred from the organic photoelectric conversion section  20  to the floating diffusion FD 1  and includes, for example, a MOS transistor. Specifically, the reset transistor Tr 1 rst includes the reset gate Grst, a channel formation region  36 A, and the source/drain regions  36 B and  36 C. The reset gate Grst is coupled to a reset line RST 1 . The one source/drain region  36 B of the reset transistor Tr 1 rst also serves as the floating diffusion FD 1 . The other source/drain region  36 C included in the reset transistor Tr 1 rst is coupled to a power supply VDD. 
     The amplifier transistor AMP is a modulation element that modulates, into a voltage, the amount of electric charge generated in the organic photoelectric conversion section  20  and includes, for example, a MOS transistor. Specifically, the amplifier transistor AMP includes the gate Gamp, a channel formation region  35 A, and the source/drain regions  35 B and  35 C. The gate Gamp is coupled to the readout electrode  21 A and the one source/drain region  36 B (the floating diffusion FD 1 ) of the reset transistor Tr 1 rst through the lower first contact  45 , the coupling section  41 A, the lower second contact  46 , the through electrode  34 , and the like. In addition, the one source/drain region  35 B shares a region with the other source/drain region  36 C included in the reset transistor Tr 1 rst and is coupled to the power supply VDD. 
     The selection transistor SEL (a selection transistor TR 1 sel) includes a gate Gsel, a channel formation region  34 A, and source/drain regions  34 B and  34 C. The gate Gsel is coupled to a selection line SEL 1 . In addition, the one source/drain region  34 B shares a region with the other source/drain region  35 C included in the amplifier transistor AMP and the other source/drain region  34 C is coupled to a signal line (a data output line) VSL 1 . 
     The transfer transistor Tr 2  (a transfer transistor TR 2 trs) is for transferring signal charge to the floating diffusion FD 2 . The signal charge is generated and accumulated in the inorganic photoelectric conversion section  32 G and corresponds to blue. The inorganic photoelectric conversion section  32 G is formed at a deep position from the second surface (the surface  30 S 2 ) of the semiconductor substrate  30  and it is thus preferable that the transfer transistor TR 2 trs of the inorganic photoelectric conversion section  32 G include a vertical transistor. In addition, the transfer transistor TR 2 trs is coupled to a transfer gate line TG 2 . Further, the floating diffusion FD 2  is provided in a region  37 C near a gate Gtrs 2  of the transfer transistor TR 2 trs. Electric charge accumulated in the inorganic photoelectric conversion section  32 G is read out by the floating diffusion FD 2  through a transfer channel formed along the gate Gtrs 2 . 
     The transfer transistor Tr 3  (the transfer transistor TR 3 trs) transfers, to the floating diffusion FD 3 , the signal charge generated and accumulated in the inorganic photoelectric conversion section  32 R. The signal charge corresponds to red. The transfer transistor Tr 3  (the transfer transistor TR 3 trs) includes, for example, a MOS transistor. In addition, the transfer transistor TR 3 trs is coupled to a transfer gate line TG 3 . Further, the floating diffusion FD 3  is provided in a region  38 C near a gate Gtrs 3  of the transfer transistor TR 3 trs. Electric charge accumulated in the inorganic photoelectric conversion section  32 R is read out by the floating diffusion FD 3  through a transfer channel formed along the gate Gtrs 3 . 
     The second surface (the surface  30 S 2 ) side of the semiconductor substrate  30  is further provided with a reset transistor TR 2 rst, an amplifier transistor TR 2 amp, and a selection transistor TR 2 sel that are included in a controller of the inorganic photoelectric conversion section  32 G. In addition, there are provided a reset transistor TR 3 rst, an amplifier transistor TR 3 amp, and a selection transistor TR 3 sel that are included in a controller of the inorganic photoelectric conversion section  32 R. 
     The reset transistor TR 2 rst includes a gate, a channel formation region, and a source/drain region. The gate of the reset transistor TR 2 rst is coupled to a reset line RST 2  and the one source/drain region of the reset transistor TR 2 rst is coupled to the power supply VDD. The other source/drain region of the reset transistor TR 2 rst also serves as the floating diffusion FD 2 . 
     The amplifier transistor TR 2 amp includes a gate, a channel formation region, and a source/drain region. The gate is coupled to the other source/drain region (the floating diffusion FD 2 ) of the reset transistor TR 2 rst. In addition, the one source/drain region included in the amplifier transistor TR 2 amp shares a region with the one source/drain region included in the reset transistor Tr 2 rst and is coupled to the power supply VDD. 
     The selection transistor TR 2 sel includes a gate, a channel formation region, and a source/drain region. The gate is coupled to a selection line SEL 2 . In addition, the one source/drain region included in the selection transistor TR 2 sel shares a region with the other source/drain region included in the amplifier transistor TR 2 amp. The other source/drain region included in the selection transistor TR 2 sel is coupled to a signal line (a data output line) VSL 2 . 
     The reset transistor TR 3 rst includes a gate, a channel formation region, and a source/drain region. The gate of the reset transistor TR 3 rst is coupled to a reset line RST 3  and the one source/drain region included in the reset transistor TR 3 rst is coupled to the power supply VDD. The other source/drain region included in the reset transistor TR 3 rst also serves as the floating diffusion FD 3 . 
     The amplifier transistor TR 3 amp includes a gate, a channel formation region, and a source/drain region. The gate is coupled to the other source/drain region (the floating diffusion FD 3 ) included in the reset transistor TR 3 rst. In addition, the one source/drain region included in the amplifier transistor TR 3 amp shares a region with the one source/drain region included in the reset transistor Tr 3 rst and is coupled to the power supply VDD. 
     The selection transistor TR 3 sel includes a gate, a channel formation region, and a source/drain region. The gate is coupled to a selection line SEL 3 . In addition, the one source/drain region included in the selection transistor TR 3 sel shares a region with the other source/drain region included in the amplifier transistor TR 3 amp. The other source/drain region included in the selection transistor TR 3 sel is coupled to a signal line (a data output line) VSL 3 . 
     The reset lines RST 1 , RST 2 , and RST 3 , the selection lines SEL 1 , SEL 2 , and SEL 3 , and the transfer gate lines TG 2  and TG 3  are each coupled to a vertical drive circuit  112  included in a drive circuit. The signal lines (the data output lines) VSL 1 , VSL 2 , and VSL 3  are coupled to a column signal processing circuit  113  included in the drive circuit. 
     As described above, the present technology is also applicable to a photoelectric conversion element (the photoelectric conversion element  2 ) in which the lower electrode  21  includes the readout electrode  21 A and the accumulation electrode  21 B that are separated from each other with the insulating layer  22  interposed in between. In other words, in the photoelectric conversion element  2  according to the present modification example, the organic photoelectric conversion layer  24  is formed to include domains in a horizontal cross section. This facilitates electric charge (electrons and holes) generated in the organic photoelectric conversion layer  24  to move to the lower electrode  21  and the upper electrode  25  and makes it possible to obtain an effect similar to that of the embodiment described above. Each of the domains is formed by using one or more organic semiconductor materials. 
     2-2. Modification Example 2 
       FIG. 11  illustrates a cross-sectional configuration of a photoelectric conversion element (a photoelectric conversion element  3 ) according to a modification example 2 of the present disclosure. The photoelectric conversion element  3  is included, for example, in the one unit pixel Pin the solid-state imaging element (the imaging device  100 ) such as a back-illuminated CCD image sensor or CMOS image sensor as with the photoelectric conversion element  1  according to the embodiment or the like described above. The photoelectric conversion element  3  according to the present modification example has a configuration in which a red photoelectric conversion section  70 R, a green photoelectric conversion section  70 G, and a blue photoelectric conversion section  70 B are stacked in this order on the semiconductor substrate  30  with the insulating layer  76  interposed in between. 
     The red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B respectively include organic photoelectric conversion layers  72 R,  72 G, and  72 B between the respective pairs of electrodes. Specifically, the red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B respectively include the organic photoelectric conversion layers  72 R,  72 G, and  72 B between a first electrode  71 R and a second electrode  73 R, between a first electrode  71 G and a second electrode  73 G, and between a first electrode  71 B and a second electrode  73 B. 
     The on-chip lens  52 L is provided on the blue photoelectric conversion section  70 B with the protective layer  51  and the on-chip lens layer  51  interposed in between. There are provided a red electricity storage layer  310 R, a green electricity storage layer  310 G, and a blue electricity storage layer  310 B in the semiconductor substrate  30 . The pieces of light inputted to the on-chip lens  52 L are photoelectrically converted by the red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B. The signal charge is transmitted from the red photoelectric conversion section  70 R to the red electricity storage layer  310 R, from the green photoelectric conversion section  70 G to the green electricity storage layer  310 G, and from the blue photoelectric conversion section  70 B to the blue electricity storage layer  310 B. Although the signal charge may be either electrons or holes generated by photoelectric conversion, the following gives description by exemplifying a case where electrons are read as signal charge. 
     The semiconductor substrate  30  includes, for example, a p-type silicon substrate. The red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B provided in this semiconductor substrate  30  each include an n-type semiconductor region. The signal charge (electrons) supplied from the red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B is accumulated in the n-type semiconductor regions. The n-type semiconductor regions of the red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B are formed, for example, by doping the semiconductor substrate  30  with n-type impurities such as phosphorus (P) or arsenic (As). It is to be noted that the semiconductor substrate  30  may be provided on a support substrate (not illustrated) including glass or the like. 
     The semiconductor substrate  30  includes a pixel transistor for reading out the respective electrons from the red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B and transferring the read electrons to, for example, a vertical signal line (a vertical signal line Lsig in  FIG. 12  described below). A floating diffusion of this pixel transistor is provided in the semiconductor substrate  30  and this floating diffusion is coupled to the red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B. The floating diffusion includes an n-type semiconductor region. 
     The insulating layer  76  includes, for example, silicon oxide, silicon nitride, silicon oxynitride, hafnium oxide, or the like. The insulating layer  76  may include a plurality of types of insulating films that is stacked. The insulating layer  76  may include an organic insulating material. This insulating layer  76  is provided with respective plugs and respective electrodes for coupling the red electricity storage layer  310 R and the red photoelectric conversion section  70 R, the green electricity storage layer  310 G and the green photoelectric conversion section  70 G, and the blue electricity storage layer  310 B and the blue photoelectric conversion section  70 B. 
     The red photoelectric conversion section  70 R includes the first electrode  71 R, an organic photoelectric conversion layer  72 R, and the second electrode  73 R in this order from positions close to the semiconductor substrate  30 . The green photoelectric conversion section  70 G includes the first electrode  71 G, an organic photoelectric conversion layer  72 G, and the second electrode  73 G in this order from positions close to the red photoelectric conversion section  70 R. The blue photoelectric conversion section  70 B includes the first electrode  71 B, an organic photoelectric conversion layer  72 B, and the second electrode  73 B in this order from positions close to the green photoelectric conversion section  70 G. There is provided an insulating layer  44  between the red photoelectric conversion section  70 R and the green photoelectric conversion section  70 G and there is provided an insulating layer  75  between the green photoelectric conversion section  70 G and the blue photoelectric conversion section  70 B. Light of red (e.g., a wavelength of 600 nm or more and less than 700 nm) is selectively absorbed in the red photoelectric conversion section  70 R; light of green (e.g., a wavelength of 480 nm or more and less than 600 nm) is selectively absorbed in the green photoelectric conversion section  70 G; and light of blue (e.g., a wavelength of 400 nm or more and less than 480 nm) is selectively absorbed in the blue photoelectric conversion section  70 B, generating electron-hole pairs. 
     The first electrode  71 R extracts signal charge generated in the organic photoelectric conversion layer  72 R; the first electrode  71 G extracts signal charge generated in the organic photoelectric conversion layer  72 G; and the first electrode  71 B extracts signal charge generated in the organic photoelectric conversion layer  72 B. The first electrodes  71 R,  71 G, and  71 B are each provided for each pixel, for example. These first electrodes  71 R,  71 G, and  71 B each include, for example, a light transmissive electrically conductive material, specifically, ITO. The first electrodes  71 R,  71 G, and  71 B may each include, for example, a tin oxide-based material or a zinc oxide-based material. The tin oxide-based material is obtained by doping tin oxide with a dopant. Examples of the zinc oxide-based material include aluminum zinc oxide in which aluminum is added to zinc oxide as a dopant, gallium zinc oxide in which gallium is added to zinc oxide as a dopant, indium zinc oxide in which indium is added to zinc oxide as a dopant, and the like. In addition, it is also possible to use IGZO, CuI, InSbO 4 , ZnMgO, CuInO 2 , MgIn 2 O 4 , CdO, ZnSnO 3 , and the like. The thickness of each of the first electrodes  71 R,  71 G, and  71 B is, for example, 50 nm to 500 nm. 
     For example, respective electron transport layers may be provided between the first electrode  71 R and the organic photoelectric conversion layer  72 R, between the first electrode  71 G and the organic photoelectric conversion layer  72 G, and between the first electrode  71 B and the organic photoelectric conversion layer  72 B. The electron transport layers serve to facilitate electrons generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to be supplied to the first electrodes  71 R,  71 G, and  71 B and each include, for example, titanium oxide, zinc oxide, or the like. The electron transport layers may each include titanium oxide and zinc oxide that are stacked. The thickness of each of the electron transport layers is, for example, 0.1 nm to 1000 nm. It is preferable that the thickness of each of the electron transport layers be 0.5 nm to 300 nm. 
     The organic photoelectric conversion layers  72 R,  72 G, and  72 B each absorb light in a selective wavelength region for photoelectric conversion and transmit light in another wavelength region. Here, the light in the selective wavelength region is, for example, light in a wavelength region of a wavelength of 600 nm or more and less than 700 nm in the organic photoelectric conversion layer  72 R, light in a wavelength region of a wavelength of 480 nm or more and less than 600 nm, for example, in the organic photoelectric conversion layer  72 G, and light in a wavelength region of a wavelength of 400 nm or more and less than 480 nm, for example, in the organic photoelectric conversion layer  72 B. The thickness of each of the organic photoelectric conversion layers  72 R,  72 G, and  72 B is, for example, 50 nm or more and less than 500 nm. 
     Each of the organic photoelectric conversion layers  72 R,  72 G, and  72 B has a configuration similar to that of the organic photoelectric conversion layer  12  according to the embodiment described above. 
     For example, respective hole transport layers may be provided between the organic photoelectric conversion layer  72 R and the second electrode  73 R, between the organic photoelectric conversion layer  72 G and the second electrode  73 G, and between the organic photoelectric conversion layer  72 B and the second electrode  73 B. The hole transport layers serve to facilitate holes generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to be supplied to the second electrodes  73 R,  73 G, and  73 B and each include, for example, molybdenum oxide, nickel oxide, vanadium oxide, or the like. The hole transport layers may each include an organic material such as PEDOT (Poly(3,4-ethylenedioxythiophene) and TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine). The thickness of each of the hole transport layers is, for example, 0.5 nm or more and 100 nm or less. 
     The second electrode  73 R serves to extract holes generated in the organic photoelectric conversion layer  72 R; the second electrode  73 G serves to extract holes generated in the organic photoelectric conversion layer  72 G; and the second electrode  73 B serves to extract holes generated in the organic photoelectric conversion layer  72 G. The holes extracted from the second electrodes  73 R,  73 G, and  73 B are, for example, discharged to a p-type semiconductor region (not illustrated) in the semiconductor substrate  30  through respective transmission paths (not illustrated). The second electrodes  73 R,  73 G, and  73 B each include, for example, an electrically conductive material such as gold, silver, copper, and aluminum. As with the first electrodes  71 R,  71 G, and  71 B, the second electrodes  73 R,  73 G, and  73 B may each include a transparent electrically conductive material. In the photoelectric conversion element  3 , holes extracted from these second electrodes  73 R,  73 G, and  73 B are discharged. Therefore, for example, in a case where the plurality of photoelectric conversion elements  3  is disposed in the imaging device  100  described below, the second electrodes  73 R,  73 G, and  73 B may be provided in common for each of the photoelectric conversion elements  3  (the unit pixel P). The thickness of each of the second electrodes  73 R,  73 G, and  73 B is, for example, 0.5 nm or more and 100 nm or less. 
     The insulating layer  74  serves to insulate the second electrode  73 R and the first electrode  71 G from each other, and the insulating layer  75  serves to insulate the second electrode  73 G and the first electrode  71 B from each other. The insulating layers  74  and  75  each include, for example, metal oxide, metal sulfide, or an organic material. Examples of the metal oxide include silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, tungsten oxide, magnesium oxide, niobium oxide, tin oxide, gallium oxide, and the like. Examples of the metal sulfide include zinc sulfide, magnesium sulfide, and the like. It is preferable that the band gap of a material included in each of the insulating layers  74  and  75  be 3.0 eV or more. The thickness of each of the insulating layers  74  and  75  is, for example, 2 nm or more and 100 nm or less. 
     As described above, the present technology is also applicable to a photoelectric conversion element (the photoelectric conversion element  3 ) in which the red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B are stacked in this order. The red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B include the respective photoelectric conversion layers (the organic photoelectric conversion layers  72 R,  72 G, and  72 B). Each of the photoelectric conversion layers (the organic photoelectric conversion layers  72 R,  72 G, and  72 B) includes an organic semiconductor material. In other words, in the photoelectric conversion element  3  according to the present modification example, each of the organic photoelectric conversion layers  72 R,  72 G, and  72 B is formed to include domains in a horizontal cross section. This facilitates electric charge (electrons and holes) generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to respectively move to the first electrodes  71 R,  71 G, and  71 B and the second electrodes  73 R,  73 G, and  73 B and makes it possible to obtain an effect similar to that of the embodiment described above. Each of the domains is formed by using one or more organic semiconductor materials. 
     3. APPLICATION EXAMPLES 
     Application Example 1 
       FIG. 12  illustrates, for example, an overall configuration of the imaging device  100  in which a photoelectric conversion element (the photoelectric conversion element  1 ) described in the embodiment or the like described above is used for each of the pixels. This imaging device  100  is a CMOS image sensor. The imaging device  100  includes, on the semiconductor substrate  30 , the pixel section  1   a  as an imaging area and a peripheral circuit unit  130  in a peripheral region of this pixel section  1   a.  The peripheral circuit unit  130  includes, for example, a row scanning section  131 , a horizontal selection section  133 , a column scanning section  134 , and a system control section  132 . 
     The pixel section  1   a  includes, for example, the plurality of unit pixels P (corresponding, for example, to the photoelectric conversion elements  1 ) that is two-dimensionally disposed in a matrix. In these unit pixels P, pixel drive lines Lread (specifically, row selection lines and reset control lines) are disposed for each of pixel rows, for example, and vertical signal lines Lsig are disposed for each of pixel columns. The pixel drive lines Lread are each used to transmit drive signals for reading out signals from pixels. One end of each of the pixel drive lines Lread is coupled to the output end of the row scanning section  131  corresponding to each row. 
     The row scanning section  131  is a pixel drive section that includes a shift register, an address decoder, and the like and drives each of the unit pixels P of the pixel section  1   a  on a row basis, for example. A signal outputted from each of the unit pixels P of the pixel rows selected and scanned by the row scanning section  131  is supplied to the horizontal selection section  133  through each of the vertical signal lines Lsig. The horizontal selection section  133  includes an amplifier, a horizontal selection switch, and the like provided for each of the vertical signal lines Lsig. 
     The column scanning section  134  includes a shift register, an address decoder, and the like and drives each of the horizontal selection switches of the horizontal selection section  133  in order while scanning the horizontal selection switches. The selective scanning by this column scanning section  134  causes signals of the respective pixels transmitted through each of the vertical signal lines Lsig to be outputted to a horizontal signal line  135  in order and causes the signals to be transmitted to the outside of the semiconductor substrate  30  through the horizontal signal line  135 . 
     Circuit portions including the row scanning section  131 , the horizontal selection section  133 , the column scanning section  134 , and the horizontal signal line  135  may be formed directly on the semiconductor substrate  30  or may be disposed on external control IC. In addition, those circuit portions may be formed on another substrate coupled by a cable or the like. 
     The system control section  132  receives, for example, a clock, data for an instruction about an operation mode, and the like. The clock and the data are supplied from the outside of the semiconductor substrate  30 . In addition, the system control section  132  outputs data such as internal information of the imaging device  100 . The system control section  132  further includes a timing generator that generates various timing signals and controls the driving of the peripheral circuit such as the row scanning section  131 , the horizontal selection section  133 , and the column scanning section  134  on the basis of the various timing signals generated by the timing generator. 
     Application Example 2 
     The imaging device  100  described above is applicable, for example, to any type of electronic apparatus (imaging device) having an imaging function. The electronic apparatus (the imaging device) includes a camera system such as a digital still camera and a video camera, a mobile phone having the imaging function, and the like.  FIG. 13  illustrates a schematic configuration of a camera  200  as an example thereof. This camera  200  is, for example, a video camera that is able to shoot a still image or a moving image. The camera  200  includes the imaging device  100 , an optical system (an optical lens)  210 , a shutter device  211 , a drive section  213  that drives the imaging device  100  and the shutter device  211 , and a signal processing section  212 . 
     The optical system  210  guides image light (incident light) from an object to the pixel section  1   a  of the imaging device  100 . This optical system  210  may include a plurality of optical lenses. The shutter device  211  controls a period of time in which the imaging device  100  is irradiated with light and a period of time in which light is blocked. The drive section  213  controls a transfer operation of the imaging device  100  and a shutter operation of the shutter device  211 . The signal processing section  212  performs various types of signal processing on signals outputted from the imaging device  100 . An image signal Dout subjected to the signal processing is stored in a storage medium such as a memory or outputted to a monitor or the like. 
     4. PRACTICAL APPLICATION EXAMPLES 
     Example of Practical Application to In-Vivo Information Acquisition System 
     Further, the technology (the present technology) according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 14  is a block diagram depicting an example of a schematic configuration of an in-vivo information acquisition system of a patient using a capsule type endoscope, to which the technology according to an embodiment of the present disclosure (present technology) can be applied. 
     The in-vivo information acquisition system  10001  includes a capsule type endoscope  10100  and an external controlling apparatus  10200 . 
     The capsule type endoscope  10100  is swallowed by a patient at the time of inspection. The capsule type endoscope  10100  has an image pickup function and a wireless communication function and successively picks up an image of the inside of an organ such as the stomach or an intestine (hereinafter referred to as in-vivo image) at predetermined intervals while it moves inside of the organ by peristaltic motion for a period of time until it is naturally discharged from the patient. Then, the capsule type endoscope  10100  successively transmits information of the in-vivo image to the external controlling apparatus  10200  outside the body by wireless transmission. 
     The external controlling apparatus  10200  integrally controls operation of the in-vivo information acquisition system  10001 . Further, the external controlling apparatus  10200  receives information of an in-vivo image transmitted thereto from the capsule type endoscope  10100  and generates image data for displaying the in-vivo image on a display apparatus (not depicted) on the basis of the received information of the in-vivo image. 
     In the in-vivo information acquisition system  10001 , an in-vivo image imaged a state of the inside of the body of a patient can be acquired at any time in this manner for a period of time until the capsule type endoscope  10100  is discharged after it is swallowed. 
     A configuration and functions of the capsule type endoscope  10100  and the external controlling apparatus  10200  are described in more detail below. 
     The capsule type endoscope  10100  includes a housing  10101  of the capsule type, in which a light source unit  10111 , an image pickup unit  10112 , an image processing unit  10113 , a wireless communication unit  10114 , a power feeding unit  10115 , a power supply unit  10116  and a control unit  10117  are accommodated. 
     The light source unit  10111  includes a light source such as, for example, a light emitting diode (LED) and irradiates light on an image pickup field-of-view of the image pickup unit  10112 . 
     The image pickup unit  10112  includes an image pickup element and an optical system including a plurality of lenses provided at a preceding stage to the image pickup element. Reflected light (hereinafter referred to as observation light) of light irradiated on a body tissue which is an observation target is condensed by the optical system and introduced into the image pickup element. In the image pickup unit  10112 , the incident observation light is photoelectrically converted by the image pickup element, by which an image signal corresponding to the observation light is generated. The image signal generated by the image pickup unit  10112  is provided to the image processing unit  10113 . 
     The image processing unit  10113  includes a processor such as a central processing unit (CPU) or a graphics processing unit (GPU) and performs various signal processes for an image signal generated by the image pickup unit  10112 . The image processing unit  10113  provides the image signal for which the signal processes have been performed thereby as RAW data to the wireless communication unit  10114 . 
     The wireless communication unit  10114  performs a predetermined process such as a modulation process for the image signal for which the signal processes have been performed by the image processing unit  10113  and transmits the resulting image signal to the external controlling apparatus  10200  through an antenna  10114 A. Further, the wireless communication unit  10114  receives a control signal relating to driving control of the capsule type endoscope  10100  from the external controlling apparatus  10200  through the antenna  10114 A. The wireless communication unit  10114  provides the control signal received from the external controlling apparatus  10200  to the control unit  10117 . 
     The power feeding unit  10115  includes an antenna coil for power reception, a power regeneration circuit for regenerating electric power from current generated in the antenna coil, a voltage booster circuit and so forth. The power feeding unit  10115  generates electric power using the principle of non-contact charging. 
     The power supply unit  10116  includes a secondary battery and stores electric power generated by the power feeding unit  10115 . In  FIG. 14 , in order to avoid complicated illustration, an arrow mark indicative of a supply destination of electric power from the power supply unit  10116  and so forth are omitted. However, electric power stored in the power supply unit  10116  is supplied to and can be used to drive the light source unit  10111 , the image pickup unit  10112 , the image processing unit  10113 , the wireless communication unit  10114  and the control unit  10117 . 
     The control unit  10117  includes a processor such as a CPU and suitably controls driving of the light source unit  10111 , the image pickup unit  10112 , the image processing unit  10113 , the wireless communication unit  10114  and the power feeding unit  10115  in accordance with a control signal transmitted thereto from the external controlling apparatus  10200 . 
     The external controlling apparatus  10200  includes a processor such as a CPU or a GPU, a microcomputer, a control board or the like in which a processor and a storage element such as a memory are mixedly incorporated. The external controlling apparatus  10200  transmits a control signal to the control unit  10117  of the capsule type endoscope  10100  through an antenna  10200 A to control operation of the capsule type endoscope  10100 . In the capsule type endoscope  10100 , an irradiation condition of light upon an observation target of the light source unit  10111  can be changed, for example, in accordance with a control signal from the external controlling apparatus  10200 . Further, an image pickup condition (for example, a frame rate, an exposure value or the like of the image pickup unit  10112 ) can be changed in accordance with a control signal from the external controlling apparatus  10200 . Further, the substance of processing by the image processing unit  10113  or a condition for transmitting an image signal from the wireless communication unit  10114  (for example, a transmission interval, a transmission image number or the like) may be changed in accordance with a control signal from the external controlling apparatus  10200 . 
     Further, the external controlling apparatus  10200  performs various image processes for an image signal transmitted thereto from the capsule type endoscope  10100  to generate image data for displaying a picked up in-vivo image on the display apparatus. As the image processes, various signal processes can be performed such as, for example, a development process (demosaic process), an image quality improving process (bandwidth enhancement process, a super-resolution process, a noise reduction (NR) process and/or image stabilization process) and/or an enlargement process (electronic zooming process). The external controlling apparatus  10200  controls driving of the display apparatus to cause the display apparatus to display a picked up in-vivo image on the basis of generated image data. Alternatively, the external controlling apparatus  10200  may also control a recording apparatus (not depicted) to record generated image data or control a printing apparatus (not depicted) to output generated image data by printing. 
     The example of the in-vivo information acquisition system to which the technology according to the present disclosure may be applied has been described above. The technology according to the present disclosure may be applied, for example, to the image pickup unit  10112  among the components described above. This makes it possible to increase the detection accuracy. 
     Example of Practical Application to Endoscopic Surgery System 
     The technology (present technology) according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 15  is a view depicting an example of a schematic configuration of an endoscopic surgery system to which the technology according to an embodiment of the present disclosure (present technology) can be applied. 
     In  FIG. 15 , a state is illustrated in which a surgeon (medical doctor)  11131  is using an endoscopic surgery system  11000  to perform surgery for a patient  11132  on a patient bed  11133 . As depicted, the endoscopic surgery system  11000  includes an endoscope  11100 , other surgical tools  11110  such as a pneumoperitoneum tube  11111  and an energy device  11112 , a supporting arm apparatus  11120  which supports the endoscope  11100  thereon, and a cart  11200  on which various apparatus for endoscopic surgery are mounted. 
     The endoscope  11100  includes a lens barrel  11101  having a region of a predetermined length from a distal end thereof to be inserted into a body cavity of the patient  11132 , and a camera head  11102  connected to a proximal end of the lens barrel  11101 . In the example depicted, the endoscope  11100  is depicted which includes as a rigid endoscope having the lens barrel  11101  of the hard type. However, the endoscope  11100  may otherwise be included as a flexible endoscope having the lens barrel  11101  of the flexible type. 
     The lens barrel  11101  has, at a distal end thereof, an opening in which an objective lens is fitted. A light source apparatus  11203  is connected to the endoscope  11100  such that light generated by the light source apparatus  11203  is introduced to a distal end of the lens barrel  11101  by a light guide extending in the inside of the lens barrel  11101  and is irradiated toward an observation target in a body cavity of the patient  11132  through the objective lens. It is to be noted that the endoscope  11100  may be a forward-viewing endoscope or may be an oblique-viewing endoscope or a side-viewing endoscope. 
     An optical system and an image pickup element are provided in the inside of the camera head  11102  such that reflected light (observation light) from the observation target is condensed on the image pickup element by the optical system. The observation light is photo-electrically converted by the image pickup element to generate an electric signal corresponding to the observation light, namely, an image signal corresponding to an observation image. The image signal is transmitted as RAW data to a CCU  11201 . 
     The CCU  11201  includes a central processing unit (CPU), a graphics processing unit (GPU) or the like and integrally controls operation of the endoscope  11100  and a display apparatus  11202 . Further, the CCU  11201  receives an image signal from the camera head  11102  and performs, for the image signal, various image processes for displaying an image based on the image signal such as, for example, a development process (demosaic process). 
     The display apparatus  11202  displays thereon an image based on an image signal, for which the image processes have been performed by the CCU  11201 , under the control of the CCU  11201 . 
     The light source apparatus  11203  includes a light source such as, for example, a light emitting diode (LED) and supplies irradiation light upon imaging of a surgical region to the endoscope  11100 . 
     An inputting apparatus  11204  is an input interface for the endoscopic surgery system  11000 . A user can perform inputting of various kinds of information or instruction inputting to the endoscopic surgery system  11000  through the inputting apparatus  11204 . For example, the user would input an instruction or a like to change an image pickup condition (type of irradiation light, magnification, focal distance or the like) by the endoscope  11100 . 
     A treatment tool controlling apparatus  11205  controls driving of the energy device  11112  for cautery or incision of a tissue, sealing of a blood vessel or the like. A pneumoperitoneum apparatus  11206  feeds gas into a body cavity of the patient  11132  through the pneumoperitoneum tube  11111  to inflate the body cavity in order to secure the field of view of the endoscope  11100  and secure the working space for the surgeon. A recorder  11207  is an apparatus capable of recording various kinds of information relating to surgery. A printer  11208  is an apparatus capable of printing various kinds of information relating to surgery in various forms such as a text, an image or a graph. 
     It is to be noted that the light source apparatus  11203  which supplies irradiation light when a surgical region is to be imaged to the endoscope  11100  may include a white light source which includes, for example, an LED, a laser light source or a combination of them. Where a white light source includes a combination of red, green, and blue (RGB) laser light sources, since the output intensity and the output timing can be controlled with a high degree of accuracy for each color (each wavelength), adjustment of the white balance of a picked up image can be performed by the light source apparatus  11203 . Further, in this case, if laser beams from the respective RGB laser light sources are irradiated time-divisionally on an observation target and driving of the image pickup elements of the camera head  11102  are controlled in synchronism with the irradiation timings. Then images individually corresponding to the R, G and B colors can be also picked up time-divisionally. According to this method, a color image can be obtained even if color filters are not provided for the image pickup element. 
     Further, the light source apparatus  11203  may be controlled such that the intensity of light to be outputted is changed for each predetermined time. By controlling driving of the image pickup element of the camera head  11102  in synchronism with the timing of the change of the intensity of light to acquire images time-divisionally and synthesizing the images, an image of a high dynamic range free from underexposed blocked up shadows and overexposed highlights can be created. 
     Further, the light source apparatus  11203  may be configured to supply light of a predetermined wavelength band ready for special light observation. In special light observation, for example, by utilizing the wavelength dependency of absorption of light in a body tissue to irradiate light of a narrow band in comparison with irradiation light upon ordinary observation (namely, white light), narrow band observation (narrow band imaging) of imaging a predetermined tissue such as a blood vessel of a superficial portion of the mucous membrane or the like in a high contrast is performed. Alternatively, in special light observation, fluorescent observation for obtaining an image from fluorescent light generated by irradiation of excitation light may be performed. In fluorescent observation, it is possible to perform observation of fluorescent light from a body tissue by irradiating excitation light on the body tissue (autofluorescence observation) or to obtain a fluorescent light image by locally injecting a reagent such as indocyanine green (ICG) into a body tissue and irradiating excitation light corresponding to a fluorescent light wavelength of the reagent upon the body tissue. The light source apparatus  11203  can be configured to supply such narrow-band light and/or excitation light suitable for special light observation as described above. 
       FIG. 16  is a block diagram depicting an example of a functional configuration of the camera head  11102  and the CCU  11201  depicted in  FIG. 15 . 
     The camera head  11102  includes a lens unit  11401 , an image pickup unit  11402 , a driving unit  11403 , a communication unit  11404  and a camera head controlling unit  11405 . The CCU  11201  includes a communication unit  11411 , an image processing unit  11412  and a control unit  11413 . The camera head  11102  and the CCU  11201  are connected for communication to each other by a transmission cable  11400 . 
     The lens unit  11401  is an optical system, provided at a connecting location to the lens barrel  11101 . Observation light taken in from a distal end of the lens barrel  11101  is guided to the camera head  11102  and introduced into the lens unit  11401 . The lens unit  11401  includes a combination of a plurality of lenses including a zoom lens and a focusing lens. 
     The number of image pickup elements which is included by the image pickup unit  11402  may be one (single-plate type) or a plural number (multi-plate type). Where the image pickup unit  11402  is configured as that of the multi-plate type, for example, image signals corresponding to respective R, G and B are generated by the image pickup elements, and the image signals may be synthesized to obtain a color image. The image pickup unit  11402  may also be configured so as to have a pair of image pickup elements for acquiring respective image signals for the right eye and the left eye ready for three dimensional (3D) display. If 3D display is performed, then the depth of a living body tissue in a surgical region can be comprehended more accurately by the surgeon  11131 . It is to be noted that, where the image pickup unit  11402  is configured as that of stereoscopic type, a plurality of systems of lens units  11401  are provided corresponding to the individual image pickup elements. 
     Further, the image pickup unit  11402  may not necessarily be provided on the camera head  11102 . For example, the image pickup unit  11402  may be provided immediately behind the objective lens in the inside of the lens barrel  11101 . 
     The driving unit  11403  includes an actuator and moves the zoom lens and the focusing lens of the lens unit  11401  by a predetermined distance along an optical axis under the control of the camera head controlling unit  11405 . Consequently, the magnification and the focal point of a picked up image by the image pickup unit  11402  can be adjusted suitably. 
     The communication unit  11404  includes a communication apparatus for transmitting and receiving various kinds of information to and from the CCU  11201 . The communication unit  11404  transmits an image signal acquired from the image pickup unit  11402  as RAW data to the CCU  11201  through the transmission cable  11400 . 
     In addition, the communication unit  11404  receives a control signal for controlling driving of the camera head  11102  from the CCU  11201  and supplies the control signal to the camera head controlling unit  11405 . The control signal includes information relating to image pickup conditions such as, for example, information that a frame rate of a picked up image is designated, information that an exposure value upon image picking up is designated and/or information that a magnification and a focal point of a picked up image are designated. 
     It is to be noted that the image pickup conditions such as the frame rate, exposure value, magnification or focal point may be designated by the user or may be set automatically by the control unit  11413  of the CCU  11201  on the basis of an acquired image signal. In the latter case, an auto exposure (AE) function, an auto focus (AF) function and an auto white balance (AWB) function are incorporated in the endoscope  11100 . 
     The camera head controlling unit  11405  controls driving of the camera head  11102  on the basis of a control signal from the CCU  11201  received through the communication unit  11404 . 
     The communication unit  11411  includes a communication apparatus for transmitting and receiving various kinds of information to and from the camera head  11102 . The communication unit  11411  receives an image signal transmitted thereto from the camera head  11102  through the transmission cable  11400 . 
     Further, the communication unit  11411  transmits a control signal for controlling driving of the camera head  11102  to the camera head  11102 . The image signal and the control signal can be transmitted by electrical communication, optical communication or the like. 
     The image processing unit  11412  performs various image processes for an image signal in the form of RAW data transmitted thereto from the camera head  11102 . 
     The control unit  11413  performs various kinds of control relating to image picking up of a surgical region or the like by the endoscope  11100  and display of a picked up image obtained by image picking up of the surgical region or the like. For example, the control unit  11413  creates a control signal for controlling driving of the camera head  11102 . 
     Further, the control unit  11413  controls, on the basis of an image signal for which image processes have been performed by the image processing unit  11412 , the display apparatus  11202  to display a picked up image in which the surgical region or the like is imaged. Thereupon, the control unit  11413  may recognize various objects in the picked up image using various image recognition technologies. For example, the control unit  11413  can recognize a surgical tool such as forceps, a particular living body region, bleeding, mist when the energy device  11112  is used and so forth by detecting the shape, color and so forth of edges of objects included in a picked up image. The control unit  11413  may cause, when it controls the display apparatus  11202  to display a picked up image, various kinds of surgery supporting information to be displayed in an overlapping manner with an image of the surgical region using a result of the recognition. Where surgery supporting information is displayed in an overlapping manner and presented to the surgeon  11131 , the burden on the surgeon  11131  can be reduced and the surgeon  11131  can proceed with the surgery with certainty. 
     The transmission cable  11400  which connects the camera head  11102  and the CCU  11201  to each other is an electric signal cable ready for communication of an electric signal, an optical fiber ready for optical communication or a composite cable ready for both of electrical and optical communications. 
     Here, while, in the example depicted, communication is performed by wired communication using the transmission cable  11400 , the communication between the camera head  11102  and the CCU  11201  may be performed by wireless communication. 
     The example of the endoscopic surgery system to which the technology according to the present disclosure may be applied has been described above. The technology according to the present disclosure may be applied to the image pickup unit  11402  among the components described above. Applying the technology according to an embodiment of the present disclosure to the image pickup unit  11402  increases the detection accuracy. 
     It is to be noted that the endoscopic surgery system has been described here as an example, but the technology according to the present disclosure may be additionally applied to, for example, a microscopic surgery system or the like. 
     Example of Practical Application to Mobile Body 
     The technology according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure may be achieved as a device mounted on any type of mobile body such as a vehicle, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a vessel, a robot, a construction machine, or an agricultural machine (tractor). 
       FIG. 17  is a block diagram depicting an example of schematic configuration of a vehicle control system as an example of a mobile body control system to which the technology according to an embodiment of the present disclosure can be applied. 
     The vehicle control system  12000  includes a plurality of electronic control units connected to each other via a communication network  12001 . In the example depicted in  FIG. 17 , the vehicle control system  12000  includes a driving system control unit  12010 , a body system control unit  12020 , an outside-vehicle information detecting unit  12030 , an in-vehicle information detecting unit  12040 , and an integrated control unit  12050 . In addition, a microcomputer  12051 , a sound/image output section  12052 , and a vehicle-mounted network interface (I/F)  12053  are illustrated as a functional configuration of the integrated control unit  12050 . 
     The driving system control unit  12010  controls the operation of devices related to the driving system of the vehicle in accordance with various kinds of programs. For example, the driving system control unit  12010  functions as a control device for a driving force generating device for generating the driving force of the vehicle, such as an internal combustion engine, a driving motor, or the like, a driving force transmitting mechanism for transmitting the driving force to wheels, a steering mechanism for adjusting the steering angle of the vehicle, a braking device for generating the braking force of the vehicle, and the like. 
     The body system control unit  12020  controls the operation of various kinds of devices provided to a vehicle body in accordance with various kinds of programs. For example, the body system control unit  12020  functions as a control device for a keyless entry system, a smart key system, a power window device, or various kinds of lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or the like. In this case, radio waves transmitted from a mobile device as an alternative to a key or signals of various kinds of switches can be input to the body system control unit  12020 . The body system control unit  12020  receives these input radio waves or signals, and controls a door lock device, the power window device, the lamps, or the like of the vehicle. 
     The outside-vehicle information detecting unit  12030  detects information about the outside of the vehicle including the vehicle control system  12000 . For example, the outside-vehicle information detecting unit  12030  is connected with an imaging section  12031 . The outside-vehicle information detecting unit  12030  makes the imaging section  12031  image an image of the outside of the vehicle, and receives the imaged image. On the basis of the received image, the outside-vehicle information detecting unit  12030  may perform processing of detecting an object such as a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance thereto. 
     The imaging section  12031  is an optical sensor that receives light, and which outputs an electric signal corresponding to a received light amount of the light. The imaging section  12031  can output the electric signal as an image, or can output the electric signal as information about a measured distance. In addition, the light received by the imaging section  12031  may be visible light, or may be invisible light such as infrared rays or the like. 
     The in-vehicle information detecting unit  12040  detects information about the inside of the vehicle. The in-vehicle information detecting unit  12040  is, for example, connected with a driver state detecting section  12041  that detects the state of a driver. The driver state detecting section  12041 , for example, includes a camera that images the driver. On the basis of detection information input from the driver state detecting section  12041 , the in-vehicle information detecting unit  12040  may calculate a degree of fatigue of the driver or a degree of concentration of the driver, or may determine whether the driver is dozing. 
     The microcomputer  12051  can calculate a control target value for the driving force generating device, the steering mechanism, or the braking device on the basis of the information about the inside or outside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030  or the in-vehicle information detecting unit  12040 , and output a control command to the driving system control unit  12010 . For example, the microcomputer  12051  can perform cooperative control intended to implement functions of an advanced driver assistance system (ADAS) which functions include collision avoidance or shock mitigation for the vehicle, following driving based on a following distance, vehicle speed maintaining driving, a warning of collision of the vehicle, a warning of deviation of the vehicle from a lane, or the like. 
     In addition, the microcomputer  12051  can perform cooperative control intended for automatic driving, which makes the vehicle to travel autonomously without depending on the operation of the driver, or the like, by controlling the driving force generating device, the steering mechanism, the braking device, or the like on the basis of the information about the outside or inside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030  or the in-vehicle information detecting unit  12040 . 
     In addition, the microcomputer  12051  can output a control command to the body system control unit  12020  on the basis of the information about the outside of the vehicle which information is obtained by the outside-vehicle information detecting unit  12030 . For example, the microcomputer  12051  can perform cooperative control intended to prevent a glare by controlling the headlamp so as to change from a high beam to a low beam, for example, in accordance with the position of a preceding vehicle or an oncoming vehicle detected by the outside-vehicle information detecting unit  12030 . 
     The sound/image output section  12052  transmits an output signal of at least one of a sound and an image to an output device capable of visually or auditorily notifying information to an occupant of the vehicle or the outside of the vehicle. In the example of  FIG. 17 , an audio speaker  12061 , a display section  12062 , and an instrument panel  12063  are illustrated as the output device. The display section  12062  may, for example, include at least one of an on-board display and a head-up display. 
       FIG. 18  is a diagram depicting an example of the installation position of the imaging section  12031 . 
     In  FIG. 18 , the imaging section  12031  includes imaging sections  12101 ,  12102 ,  12103 ,  12104 , and  12105 . 
     The imaging sections  12101 ,  12102 ,  12103 ,  12104 , and  12105  are, for example, disposed at positions on a front nose, sideview mirrors, a rear bumper, and a back door of the vehicle  12100  as well as a position on an upper portion of a windshield within the interior of the vehicle. The imaging section  12101  provided to the front nose and the imaging section  12105  provided to the upper portion of the windshield within the interior of the vehicle obtain mainly an image of the front of the vehicle  12100 . The imaging sections  12102  and  12103  provided to the sideview mirrors obtain mainly an image of the sides of the vehicle  12100 . The imaging section  12104  provided to the rear bumper or the back door obtains mainly an image of the rear of the vehicle  12100 . The imaging section  12105  provided to the upper portion of the windshield within the interior of the vehicle is used mainly to detect a preceding vehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, or the like. 
     Incidentally,  FIG. 18  depicts an example of photographing ranges of the imaging sections  12101  to  12104 . An imaging range  12111  represents the imaging range of the imaging section  12101  provided to the front nose. Imaging ranges  12112  and  12113  respectively represent the imaging ranges of the imaging sections  12102  and  12103  provided to the sideview mirrors. An imaging range  12114  represents the imaging range of the imaging section  12104  provided to the rear bumper or the back door. A bird&#39;s-eye image of the vehicle  12100  as viewed from above is obtained by superimposing image data imaged by the imaging sections  12101  to  12104 , for example. 
     At least one of the imaging sections  12101  to  12104  may have a function of obtaining distance information. For example, at least one of the imaging sections  12101  to  12104  may be a stereo camera constituted of a plurality of imaging elements, or may be an imaging element having pixels for phase difference detection. 
     For example, the microcomputer  12051  can determine a distance to each three-dimensional object within the imaging ranges  12111  to  12114  and a temporal change in the distance (relative speed with respect to the vehicle  12100 ) on the basis of the distance information obtained from the imaging sections  12101  to  12104 , and thereby extract, as a preceding vehicle, a nearest three-dimensional object in particular that is present on a traveling path of the vehicle  12100  and which travels in substantially the same direction as the vehicle  12100  at a predetermined speed (for example, equal to or more than 0 km/hour). Further, the microcomputer  12051  can set a following distance to be maintained in front of a preceding vehicle in advance, and perform automatic brake control (including following stop control), automatic acceleration control (including following start control), or the like. It is thus possible to perform cooperative control intended for automatic driving that makes the vehicle travel autonomously without depending on the operation of the driver or the like. 
     For example, the microcomputer  12051  can classify three-dimensional object data on three-dimensional objects into three-dimensional object data of a two-wheeled vehicle, a standard-sized vehicle, a large-sized vehicle, a pedestrian, a utility pole, and other three-dimensional objects on the basis of the distance information obtained from the imaging sections  12101  to  12104 , extract the classified three-dimensional object data, and use the extracted three-dimensional object data for automatic avoidance of an obstacle. For example, the microcomputer  12051  identifies obstacles around the vehicle  12100  as obstacles that the driver of the vehicle  12100  can recognize visually and obstacles that are difficult for the driver of the vehicle  12100  to recognize visually. Then, the microcomputer  12051  determines a collision risk indicating a risk of collision with each obstacle. In a situation in which the collision risk is equal to or higher than a set value and there is thus a possibility of collision, the microcomputer  12051  outputs a warning to the driver via the audio speaker  12061  or the display section  12062 , and performs forced deceleration or avoidance steering via the driving system control unit  12010 . The microcomputer  12051  can thereby assist in driving to avoid collision. 
     At least one of the imaging sections  12101  to  12104  may be an infrared camera that detects infrared rays. The microcomputer  12051  can, for example, recognize a pedestrian by determining whether or not there is a pedestrian in imaged images of the imaging sections  12101  to  12104 . Such recognition of a pedestrian is, for example, performed by a procedure of extracting characteristic points in the imaged images of the imaging sections  12101  to  12104  as infrared cameras and a procedure of determining whether or not it is the pedestrian by performing pattern matching processing on a series of characteristic points representing the contour of the object. When the microcomputer  12051  determines that there is a pedestrian in the imaged images of the imaging sections  12101  to  12104 , and thus recognizes the pedestrian, the sound/image output section  12052  controls the display section  12062  so that a square contour line for emphasis is displayed so as to be superimposed on the recognized pedestrian. The sound/image output section  12052  may also control the display section  12062  so that an icon or the like representing the pedestrian is displayed at a desired position. 
     5. WORKING EXAMPLES 
     Next, working examples of the present disclosure are described. 
     Evaluation of Electric Characteristics 
       FIG. 19  schematically illustrates a cross-sectional configuration of a photoelectric conversion element fabricated in the present working example. First, after a Si substrate  81  provided with an ITO electrode (the lower electrode  11 ) having a thickness of 50 nm was cleaned in a UV/ozone process, the organic photoelectric conversion layer  12  was formed at a substrate stage temperature of 27° C. in a resistive heating method while rotating a substrate holder in vacuum of 1×10 −5  Pa or less. For a material of the organic photoelectric conversion layer  12 , 3, 6BP-BBTN indicated in Expression (1) below was used as a hole transporting material (a P material), a subphthalocyanine derivative (F6-SubPc-OPh26F2) was used as a light absorber, and fullerene C60 was used as an electron transporting material (an N material). These were concurrently deposited. The ratio of deposition speed was 3, 6BP-BBTN:F6-SubPc-OPh26F2:C60=4:4:2. Film formation was performed to cause the total film thickness to be 230 nm. Subsequently, B4PyPMP was deposited to have a thickness of 5 nm in a vacuum deposition method at a substrate temperature of 0° C. as the buffer layer  17 B on the organic photoelectric conversion layer  12 . Next, as the upper electrode  13 , a film of ITO was formed by sputtering to have a thickness of 100 nm and then subjected to heating treatment at 160° C. As described above, a photoelectric conversion element (Experiment Example 1) including a photoelectric conversion region of 1 mm×1 mm was fabricated. 
     Additionally, photoelectric conversion elements serving as Experiment Examples 2 and 3 were fabricated. In Experiment Examples 2 and 3, photoelectric conversion elements were fabricated by using a method similar to that of Experiment Example 1 except that the organic photoelectric conversion layers were formed at a substrate temperature of 42° C. (Experiment Example 2) and a substrate temperature of 0° C. (Experiment Example 3). 
     
       
         
         
             
             
         
       
     
     The responsiveness (the afterimage characteristics) of Experiment Examples 1 to 3 were evaluated. The afterimage characteristics were evaluated by measuring the speed at which the bright current value observed at the time of light irradiation fell after the light irradiation was stopped by using a semiconductor parameter analyzer. Specifically, the amount of light with which the photoelectric conversion element was irradiated from the light source through the filter was set at 1.62 μW/cm2 and the bias voltage to be applied between the electrodes was set at −2.6 V. After a steady current was observed in this state, the light irradiation was stopped and the current was observed decaying. Thereafter, the area surrounded by a current-time curve and the dark current was set as 100% and the time elapsed before the area becomes 3% was considered as an index of the responsiveness. All of these evaluations were made at the room temperature. 
     In addition, the quantum efficiency (external quantum efficiency; EQE) of Experiment Examples 1 to 3 was evaluated by using a semiconductor parameter analyzer. Specifically, the external photoelectric conversion efficiency was calculated from a bright current value and a dark current value in a case where the amount of light (LED light having a wavelength of 560 nm) with which the photoelectric conversion element was irradiated from the light source through the filter was set at 1.62 μW/cm 2  and the bias voltage to be applied between the electrodes was set to −2.6 V. 
     Transmission Electron Microscope (TEM) Analysis 
     In addition, TEM observation samples of the organic photoelectric conversion layers corresponding to Experiment Examples 1 to 3 were fabricated and domains of a P material (an organic semiconductor material having a hole transporting property) in each of the layers were observed from the planar direction of the organic photoelectric conversion layers. The domains of the P materials were confirmed by observing transmission images with a transmission electron microscope. 
     First, a thin sample was fabricated from the region of the organic photoelectric conversion layer of the sample of Experiment Example 1 above by using a focused ion beam (Focused Ion Beam; FIB, HELIOS NANOLAB 400S manufactured by FEI) and a damaged layer of an FIB-processed end surface was then removed by an ion milling machine (Model 1040 manufactured by Fischione). TEM (JEM-300F manufactured by JEOL) observed a transmission image at an accelerating voltage of 300 kV in the state of low irradiation electron beams. The transmission image was observed with the transmission image out of focus, that is, shifted by approximately 1500 nm from the just focus position onto the underside as a defocus condition for observing a domain. Additionally, similar methods were used to perform the transmission microscope analyses of Experiment Examples 2 and 3 above. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 film 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 formation 
                   
                 electric characteristics 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 substrate 
                 heating 
                 afterimage 
                   
               
               
                   
                   
                 temperature 
                 treatment 
                 characteristics 
               
               
                   
                 P material 
                 (° C.) 
                 condition 
                 (ms) 
                 EQE (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Experiment 
                 3, 6BP-BBTN 
                 40 
                 ANL 160° C. 
                 1.3 
                 80.4 
               
               
                 Example 1 
               
               
                 Experiment 
                 3, 6BP-BBTN 
                 26 
                 ANL 160° C. 
                 3.5 
                 79.8 
               
               
                 Example 2 
               
               
                 Experiment 
                 3, 6BP-BBTN 
                 0 
                 ANL 160° C. 
                 7.8 
                 62.3 
               
               
                 Example 3 
               
               
                   
               
            
           
         
       
     
       FIGS. 21 to 23  schematically illustrate TEM images obtained by enlarging the interference fringe portions of Experiment Examples 1 to 3. The interference fringes (the lattice fringes) of a TEM image each appear as a peak of high points or low points of the signal intensity in accordance with the strength of the contrast thereof. As described above, paired adjacent lines included in an interference fringe correspond to the molecular period of the P material in the long axis direction. 
     In Experiment Example 2 in which the substrate stage temperature (the film formation substrate temperature) in a case where an organic photoelectric conversion layer was formed was 26° C., fifteen lattice fringes were confirmed in a square plane of the organic photoelectric conversion layer having a side of 100 nm as illustrated in  FIG. 22 . The domain density (ρ) of the plane of the organic photoelectric conversion layer in Experiment Example 2 was about 1500 (domains/square μm). In addition, Experiment Example 2 offered a favorable result: an afterimage characteristic of 3.4 ms and an EQE of 79.8%. In contrast, in Experiment Example 1 in which the film formation substrate temperature in a case where an organic photoelectric conversion layer was formed was 40° C., 25 lattice fringes were confirmed in a square plane of the organic photoelectric conversion layer having a side of 100 nm as illustrated in  FIG. 21 . The domain density (ρ) of the plane of the organic photoelectric conversion layer in Experiment Example 1 was about 2500 (domains/square μm). In addition, Experiment Example 1 offered an afterimage characteristic of 1.2 ms and an EQE of 80.6%. This was a more favorable result than that of Experiment Example 2. In contrast, in Experiment Example 3 in which the film formation substrate temperature in a case where an organic photoelectric conversion layer was formed was 0° C., one lattice fringe was confirmed in a square plane of the organic photoelectric conversion layer having a side of 100 nm as illustrated in  FIG. 23 . The domain density (ρ) of the plane of the organic photoelectric conversion layer in Experiment Example 1 was 100 (domains/square μm) or less. In addition, Experiment Example 3 offered an afterimage characteristic of 7.8 ms and an EQE of 62.3%. Both the afterimage characteristics and the EQE were more unfavorable than those of Experiment Example 2. 
     In addition, TEM analysis was carried out on a sample of Experiment Example 1 by forming a carbon protective film  82  on the upper electrode  13  as illustrated in  FIG. 20A , then rotating it by 90° C. as illustrated in  FIG. 20B , and fabricating a thin sample of the organic photoelectric conversion layer  12  near the lower electrode  11  side and the upper electrode  13  side as in the TEM analysis described above. 
       FIG. 24  schematically illustrates a TEM image of the organic photoelectric conversion layer  12  in Experiment Example 1 near the lower electrode  11  side in the planar direction.  FIG. 25  schematically illustrates a TEM image of the organic photoelectric conversion layer  12  in Experiment Example 1 near the upper electrode  13  side in the planar direction. 28 domains were confirmable near the lower electrode  11  side and 25 domains were confirmable near the upper electrode  13  side. The difference falls within the range (±√N) of the statistical error described above. It can be said that the organic photoelectric conversion layer  12  has substantially the same areal density of domains at any positions in the film thickness direction. 
     It is to be noted that a deposited film A also offers a similar effect under the same film formation condition as the internal structure of the organic photoelectric conversion layer  12 . The deposited film A is formed by co-deposition on a hole  93 H section of a grid  93 . The grid  93  is fixed onto a quartz substrate  91  by Kapton tapes  92 A and  92 B, for example, as illustrated in  FIG. 26A . This seems to be because the speed is limited by molecule diffusion on the surface before the deposition of the next molecules during deposition. As illustrated in  FIG. 26B , the plurality of holes  93 H is formed on the surface of a copper plate, for example, in the shape of a lattice as the grid  93 . The copper plate has, for example, a circular shape. The bottom surface of the grid  93  is provided, for example, with a carbon film and a support film as a support film  94 . A deposited film (the organic photoelectric conversion layer  12 ) is formed on this support film  94 . The carbon film has a minute hole. The support film covers the minute hole of the carbon film. 
     As described above, it has been found that it is possible to obtain favorable afterimage characteristics and EQE by forming domains in a horizontal cross section of an organic photoelectric conversion layer and causing the areal density of domains to be substantially the same at any positions in the film thickness direction. Further, it has been found that it is possible to obtain more favorable afterimage characteristics and EQE by increasing the areal density of domains in the organic photoelectric conversion layer. 
     Description has been given above with reference to the embodiment, the modification examples 1 and 2, and the working examples, but the content of the present disclosure is not limited to the embodiment or the like described above. Various modifications are possible. For example, in the embodiment described above, the photoelectric conversion element has a configuration in which the organic photoelectric conversion section  10  that detects green light and the inorganic photoelectric conversion section  32 B and the inorganic photoelectric conversion section  32 R that respectively detect blue light and red light are stacked. However, the content of the present disclosure is not limited to such a structure. In other words, the content of the present disclosure is not limited to the visible light, but the organic photoelectric conversion section may detect the red light or the blue light or the inorganic photoelectric conversion sections may detect the green light. 
     In addition, the number of these organic photoelectric conversion sections and inorganic photoelectric conversion sections or the proportion thereof is not limited. The two or more organic photoelectric conversion sections may be provided or color signals of a plurality of colors may be obtained with the organic photoelectric conversion section alone. Further, a structure is not limited to the structure in which the organic photoelectric conversion section and the inorganic photoelectric conversion sections are stacked in the vertical direction, but the organic photoelectric conversion section and the inorganic photoelectric conversion sections may be placed side by side along a substrate surface. 
     Moreover, the embodiment or the like described above exemplifies the configuration of the back-illuminated imaging device, but the content of the present disclosure is also applicable to a front-illuminated imaging device. In addition, the photoelectric conversion element according to the present disclosure does not necessarily have to include all of the components described in the embodiment above and may include another layer on the contrary. 
     It is to be noted that the effects described herein are merely examples, but not limitative. In addition, there may be other effects. 
     It is to be noted that the present technology may also have configurations as follows. The present technology having the following configurations forms an organic photoelectric conversion layer including at least one or more domains in a horizontal cross section. Each of the one or more domains is formed by using one organic semiconductor material. This increases the probability that excitons generated in the organic photoelectric conversion layer irradiated with light move to the first electrode and the second electrode. This allows both high external quantum efficiency and favorable afterimage characteristics to be achieved. 
     (1) 
     A photoelectric conversion element including: 
     a first electrode; 
     a second electrode that is disposed to be opposed to the first electrode; and 
     an organic photoelectric conversion layer that is provided between the first electrode and the second electrode and includes one organic semiconductor material, the organic photoelectric conversion layer including at least one or more domains in a horizontal cross section, the one or more domains being each formed by using the one organic semiconductor material. 
     (2) 
     The photoelectric conversion element according to (1), in which the organic photoelectric conversion layer has substantially same areal density of the domains at any positions in a film thickness direction. 
     (3) 
     The photoelectric conversion element according to (1) or (2), in which the one organic semiconductor material forms domains at least a portion of which has a percolation structure in the organic photoelectric conversion layer, the organic photoelectric conversion layer having an areal density of 1500 domains/square micron or more. 
     (4) 
     The photoelectric conversion element according to any one of (1) to (3), in which each of the domains is partially in contact with the first electrode or the second electrode. 
     (5) 
     The photoelectric conversion element according to any one of (1) to (4), in which each of the domains is partially in contact with the first electrode and the second electrode. 
     (6) 
     The photoelectric conversion element according to any one of (1) to (5), further including a buffer layer between at least one of the first electrode or the second electrode and the organic photoelectric conversion layer. 
     (7) 
     The photoelectric conversion element according to any one of (1) to (6), in which at least a portion of the domains has crystallizability. 
     (8) 
     The photoelectric conversion element according to any one of (1) to (7), in which each of the domains includes a crystal of the one organic semiconductor material. 
     (9) 
     The photoelectric conversion element according to (8), in which a planar projected area ratio of the crystal is 0.5 or less, the planar projected area ratio being obtained by projecting the organic photoelectric conversion layer in a film thickness direction. 
     (10) 
     The photoelectric conversion element according to any one of (1) to (9), in which the organic photoelectric conversion layer includes the one organic semiconductor material and another organic semiconductor material having a different electrical conduction type from an electrical conduction type of the one organic semiconductor material, the organic photoelectric conversion layer having a bulk hetero structure in a portion of a layer. 
     (11) 
     An imaging device including 
     pixels each including one or more organic photoelectric conversion sections, in which 
     the organic photoelectric conversion sections each include
         a first electrode,   a second electrode that is disposed to be opposed to the first electrode, and   an organic photoelectric conversion layer that is provided between the first electrode and the second electrode and includes one organic semiconductor material, the organic photoelectric conversion layer including at least one or more domains in a horizontal cross section, the one or more domains being each formed by using the one organic semiconductor material.
 
(12)
       

     The imaging device according to (11), in which the one or more organic photoelectric conversion sections and one or more inorganic photoelectric conversion sections are stacked in each of the pixels, the one or more inorganic photoelectric conversion sections each performing photoelectric conversion in a wavelength region different from wavelength regions of the organic photoelectric conversion sections. 
     (13) 
     The imaging device according to (12), in which 
     each of the inorganic photoelectric conversion sections is formed to be embedded in a semiconductor substrate, and 
     each of the organic photoelectric conversion sections is formed on a first surface side of the semiconductor substrate. 
     (14) 
     The imaging device according to (13), in which a multilayer wiring layer is formed on a second surface side of the semiconductor substrate. 
     (15) 
     The imaging device according to (13) or (14), in which 
     each of the organic photoelectric conversion sections photoelectrically converts green light, and 
     an inorganic photoelectric conversion section that photoelectrically converts blue light and an inorganic photoelectric conversion section that photoelectrically converts red light are stacked in the semiconductor substrate. 
     (16) 
     The imaging device according to any one of (11) to (15), in which a plurality of the organic photoelectric conversion sections is stacked in each of the pixels, the plurality of the organic photoelectric conversion sections performing photoelectric conversion in respective wavelength regions different from each other. 
     This application claims the priority on the basis of Japanese Patent Application No. 2019-093702 filed with Japan Patent Office on May 17, 2019, the entire contents of which are incorporated in this application by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.