Patent Publication Number: US-2023157040-A1

Title: Photoelectric conversion element and imaging device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a photoelectric conversion element using an organic semiconductor material and an imaging device including the photoelectric conversion element. 
     BACKGROUND ART 
     For example, PTL 1 discloses a photoelectric conversion element with improved external quantum efficiency and response speed, which is achieved by providing an organic photoelectric conversion layer having, in the layer, a percolation structure that traverses vertically in a film thickness direction and having a domain of which a domain length in a planar direction is smaller than a domain length in the film thickness direction. 
     CITATION LIST 
     Patent Literature 
     PTL 1: International Publication No. WO2019/098315 
     SUMMARY OF THE INVENTION 
     Thus, a photoelectric conversion element using an organic semiconductor material is required to have improved response characteristics. 
     It is desirable to provide a photoelectric conversion element and an imaging device that make it possible to improve response characteristics. 
     A photoelectric conversion element of an embodiment of the present disclosure includes: a first electrode; a second electrode disposed to be opposed to the first electrode; and an organic photoelectric conversion layer provided between the first electrode and the second electrode, the organic photoelectric conversion layer having, in the layer, a domain being larger than 1 nm and smaller than 10 nm and including one organic semiconductor material in a predetermined cross-section between the first electrode and the second electrode. 
     An imaging device of an embodiment of the present disclosure includes pixels, each of which includes one or multiple organic photoelectric conversion sections, and includes the photoelectric conversion element of an embodiment of the present disclosure as the one or the multiple organic photoelectric conversion sections. 
     In the photoelectric conversion element of an embodiment of the present disclosure and the imaging device of an embodiment of the present disclosure, the organic photoelectric conversion layer is provided that has a domain being larger than 1 nm and smaller than 10 nm and including one organic semiconductor material in a predetermined cross-section between the first electrode and the second electrode. This improves movement of electric charges having undergone charge separation in the organic photoelectric conversion layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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 planar view of a configuration of a unit pixel of the photoelectric conversion element illustrated in  FIG.  1   . 
         FIG.  3    is a model diagram of a crystal of one organic semiconductor material as viewed in a direction of [301]. 
         FIG.  4    is a model diagram of the crystal of the one organic semiconductor material as viewed in in a direction of [20-1]. 
         FIG.  5    is a schematic cross-sectional view of another example of the configuration of the photoelectric conversion element according to an embodiment of the present disclosure. 
         FIG.  6    is an explanatory schematic cross-sectional view of a method of manufacturing the photoelectric conversion element illustrated in  FIG.  1   . 
         FIG.  7    is a schematic cross-sectional view of 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 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 view of arrangement of transistors constituting a control section of the photoelectric conversion element and a lower electrode of an organic photoelectric conversion section illustrated in  FIG.  8   . 
         FIG.  11    is a timing diagram illustrating an operation example of the photoelectric conversion element illustrated in  FIG.  8   . 
         FIG.  12    is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to Modification Example 2 of the present disclosure. 
         FIG.  13 A  is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to Modification Example 3 of the present disclosure. 
         FIG.  13 B  is a schematic planar view of an example of a pixel configuration of an imaging device including the photoelectric conversion element illustrated in  FIG.  13 A . 
         FIG.  14 A  is a schematic cross-sectional view of an example of a configuration of a photoelectric conversion element according to Modification Example 4 of the present disclosure. 
         FIG.  14 B  is a schematic planar view of an example of a pixel configuration of an imaging device including the photoelectric conversion element illustrated in  FIG.  14 A . 
         FIG.  15    is a block diagram illustrating an overall configuration of an imaging device including the photoelectric conversion element illustrated in  FIG.  1   , etc. 
         FIG.  16    is a functional block diagram illustrating an example of an electronic apparatus using the imaging device illustrated in  FIG.  15   . 
         FIG.  17    is a block diagram depicting an example of a schematic configuration of an in-vivo information acquisition system. 
         FIG.  18    is a view depicting an example of a schematic configuration of an endoscopic surgery system. 
         FIG.  19    is a block diagram depicting an example of a functional configuration of a camera head and a camera control unit (CCU). 
         FIG.  20    is a block diagram depicting an example of schematic configuration of a vehicle control system. 
         FIG.  21    is a diagram of assistance in explaining an example of installation positions of an outside-vehicle information detecting section and an imaging section. 
         FIG.  22    is a schematic cross-sectional view of a configuration of a device sample used in Experimental Examples 1 to 3. 
         FIG.  23    is a schematic cross-sectional view of a configuration of a domain confirmation sample used in Experimental Examples 1 to 3. 
         FIG.  24 A  is an explanatory schematic view of a manufacturing step of a planar observation sample by means of FIB. 
         FIG.  24 B  is a schematic view of a step subsequent to  FIG.  24 A . 
         FIG.  24 C  is a schematic view of a step subsequent to  FIG.  24 B . 
         FIG.  25    is a schematic view of a step subsequent to  FIG.  24 C . 
         FIG.  26    is an explanatory schematic view of a working method for the domain confirmation sample. 
         FIG.  27    is a schematic view of a step subsequent to  FIG.  26   . 
         FIG.  28    is a schematic view of a TEM image of Experimental Example 1. 
         FIG.  29    is a schematic view of a TEM image of Experimental Example 2. 
         FIG.  30    is a schematic view of a TEM image of Experimental Example 3. 
         FIG.  31    is a diagram illustrating results of X-ray diffraction of Experimental Examples 1 to 3. 
         FIG.  32    is a diagram illustrating a distance between crystal domains of Experimental Example 1. 
         FIG.  33    is a diagram illustrating a distance between crystal domains of Experimental Example 2. 
         FIG.  34    is a diagram illustrating a distance between crystal domains of Experimental Example 3. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, description is given of embodiments of the present disclosure in detail with reference to the drawings. The following description is merely a specific example of the present disclosure, and the present disclosure should not be limited to the following aspects. Moreover, the present disclosure is not limited to arrangements, dimensions, dimensional ratios, and the like of each component illustrated in the drawings. It is to be noted that the description is given in the following order. 
     1. Embodiment (An example of providing an organic photoelectric conversion layer having a domain of 1 nm or more and 10 nm or less in a predetermined 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 in which a lower electrode includes multiple electrodes)   2-2. Modification Example 2 (An example of a photoelectric conversion element in which multiple organic photoelectric conversion sections are stacked)   2-3. Modification Example 3 (An example of a photoelectric conversion element that performs dispersion for an inorganic photoelectric conversion section using a color filter)   2-4. Modification Example 4 (An example of a photoelectric conversion element that performs dispersion for an inorganic photoelectric conversion section using a color filter)   
   3. Application Examples   4. Practical Application Examples   5. 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  constitutes one pixel (a unit pixel P) in an imaging device (an imaging device  100 ) such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor to be used, for example, in an electronic apparatus such as a digital still camera or a video camera (see  FIG.  15   ). The photoelectric conversion element  1  includes, for example, an organic photoelectric conversion section  10  in which a lower electrode  11 , an organic photoelectric conversion layer  12 , and an upper electrode  13  are stacked in this order. The photoelectric conversion element  1  of the present embodiment has a configuration in which the organic photoelectric conversion layer  12  constituting the organic photoelectric conversion section  10  has, in a predetermined cross-section, a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material. 
     1-1. Configuration of Photoelectric Conversion Element 
     The photoelectric conversion element  1  is a so-called vertical spectroscopic photoelectric conversion element in which one organic photoelectric conversion section  10  and two inorganic photoelectric conversion sections  32 B and  32 R are stacked in a vertical direction, for each unit pixel P. The organic photoelectric conversion section  10  is provided on a side of a back surface (a first surface  30 S 1 ) of a semiconductor substrate  30 . The inorganic photoelectric conversion sections  32 B and  32 R are each formed to be embedded in the semiconductor substrate  30 , and are stacked in a thickness direction of the semiconductor substrate  30 . 
     The organic photoelectric conversion section  10  and the inorganic photoelectric conversion sections  32 B and  32 R selectively detect light beams of different wavelength bands and perform photoelectric conversion. For example, the organic photoelectric conversion section  10  acquires a color signal of green (G). The inorganic photoelectric conversion sections  32 B and  32 R acquire color signals of blue (B) and red (R), respectively, depending on differences in absorption coefficients. This enables the photoelectric conversion element  1  to acquire multiple types of color signals in one pixel without using a color filter. 
     It is to be noted that description is given, for the photoelectric conversion element  1 , of a case of reading holes, among electron-hole pairs generated by photoelectric conversion, as signal charges (a case of adopting a p-type semiconductor region as a photoelectric conversion layer). In addition, in the diagram, “+ (plus)” attached to “p” and “n” indicates that p-type or n-type impurity concentration is high. 
     The semiconductor substrate  30  is configured by, for example, an n-type silicon (Si) substrate, and includes a p-well  31  in a predetermined region. A second surface (a front surface of the semiconductor substrate  30 )  30 S 2  of the p-well  31  is provided with, for example, various floating diffusions (floating diffusion layers) FD (e.g., FD 1 , FD 2 , and FD 3 ), various transistors Tr (e.g., a vertical transistor (transfer transistor) T r   2 , a transfer transistor T r   3 , an amplifier transistor (modulation element) AMP, and a reset transistor RST), and a multilayer wiring layer  40 . The multilayer wiring layer  40  has a configuration in which, for example, wiring layers  41 ,  42 , and  43  are stacked in an insulating layer  44 . In addition, a peripheral part of the semiconductor substrate  30  is provided with a peripheral circuit (unillustrated) including a logic circuit or the like. 
     It is to be noted that, in  FIG.  1   , the side of the first surface  30 S 1  of the semiconductor substrate  30  is denoted by a light incident side S 1 , and a side of the second surface  30 S 2  thereof is denoted by a wiring layer side S 2 . 
     The organic photoelectric conversion section  10  has a configuration in which the lower electrode  11 , the organic photoelectric conversion layer  12 , and the upper electrode  13  are stacked in this order, and the organic photoelectric conversion layer  12  has, in the layer, a bulk hetero junction structure. The bulk hetero junction structure is a p/n junction surface formed by mixing a p-type semiconductor and a n-type semiconductor together. 
     The inorganic photoelectric conversion sections  32 B and  32 R are configured by, for example, a PIN (Positive Intrinsic Negative) type photodiode, and each thereof has a p-n junction in a predetermined region of the semiconductor substrate  30 . The inorganic photoelectric conversion sections  32 B and  32 R enable light to be dispersed in the vertical direction by utilizing a difference in wavelength bands to be absorbed depending on incidence depth of light in the silicon substrate. 
     The inorganic photoelectric conversion section  32 B selectively detects blue light and accumulates signal charges corresponding to a blue color; the inorganic photoelectric conversion section  32 B is installed at a depth at which the blue light is able to be efficiently subjected to photoelectric conversion. The inorganic photoelectric conversion section  32 R selectively detects red light and accumulates signal charges corresponding to a red color; the inorganic photoelectric conversion section  32 R is installed at a depth at which the red light is able to be efficiently subjected to photoelectric conversion. It is to be noted that blue (B) is a color corresponding to a wavelength band of 450 nm or more and less than 495 nm, for example, and red (R) is a color corresponding to a wavelength band of 620 nm or more and less than 750 nm, for example. It is sufficient for each of the inorganic photoelectric conversion sections  32 B and  32 R to be able to detect light of a portion or all of each wavelength band. 
     Specifically, as illustrated in  FIG.  1   , each of the inorganic photoelectric conversion section  32 B and the inorganic photoelectric conversion section  32 R includes, for example, a p+ region serving as a hole accumulation layer and an n region serving as an electron accumulation layer (having a p-n-p stacked structure). The n region of the inorganic photoelectric conversion section  32 B is coupled to the vertical transistor T r   2 . The p+ region of the inorganic photoelectric conversion section  32 B bends along the vertical transistor T r   2 , and is linked to the p+ region of the inorganic photoelectric conversion section  32 R. 
     The vertical transistor T r   2  is a transfer transistor that transfers, to a floating diffusion FD 2 , the signal charges corresponding to the blue color generated and accumulated in the inorganic photoelectric conversion section  32 B. 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 thus the transfer transistor of the inorganic photoelectric conversion section  32 B is preferably configured by the vertical transistor T r   2 . 
     The transfer transistor T r   3  transfers, to a floating diffusion FD 3 , the signal charges corresponding to the red color generated and accumulated in the inorganic photoelectric conversion section  32 R, and is configured by, for example, a MOS transistor. 
     The amplifier transistor AMP is, for example, a modulation element that modulates an amount of electric charges generated in the organic photoelectric conversion section  10 , and is configured by, for example, a MOS transistor. 
     The reset transistor RST resets, for example, electric charges transferred from the organic photoelectric conversion section  10  to a floating diffusion FD 1 , and is configured by, for example, a MOS transistor. 
     Interlayer insulating layers  14  and  15  are stacked in this order, for example, from a side of the semiconductor substrate  30  between the first surface  30 S 1  of the semiconductor substrate  30  and the lower electrode  11 . The interlayer insulating layer  14  has a configuration in which, for example, a layer having a fixed charge (fixed charge layer)  14 A and a dielectric layer  14 B having an insulating property are stacked. A protective layer  51  is provided on the upper electrode  13 . An on-chip lens layer  52 , which configures an on-chip lens  52 L and serves also as a planarization layer, is disposed above the protective layer  51 . 
     A through-electrode  34  is provided 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 1  via the through-electrode  34 . This makes it possible for the photoelectric conversion element  1  to favorably transfer electric charges (holes) generated in the organic photoelectric conversion section  10  on the side of the first surface  30 S 1  of the semiconductor substrate  30  to the side of the second surface  30 S 2  of the semiconductor substrate  30  via the through-electrode  34 , and thus to enhance the characteristics. 
     The through-electrode  34  is provided for each unit pixel P, for example. The through-electrode  34  functions as a connector between the organic photoelectric conversion section  10  and the gate Gamp of the amplifier transistor AMP as well as the floating diffusion FD 1 , and serves as a transmission path for electric charges generated in the organic photoelectric conversion section  10 . 
     The lower end of the through-electrode  34  is coupled to, for example, 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 to each other via a lower first contact  45 . The coupling section  41 A and the floating diffusion FD 1  are coupled to the lower electrode  11  via a lower second contact  46 . It is to be noted that, in  FIG.  1   , the through-electrode  34  is illustrated to have a cylindrical shape, but this is not limitative; the through-electrode  34  may also have a tapered shape, for example. 
     As illustrated in  FIG.  1   , a reset gate Grst of the reset transistor RST is preferably disposed next to the floating diffusion FD 1 . This makes it possible to reset electric charges accumulated in the floating diffusion FD 1  by the reset transistor RST. 
     In the photoelectric conversion element  1  of the present embodiment, light incident on the organic photoelectric conversion section  10  from the light incident side S 1  is absorbed by the organic photoelectric conversion layer  12 . Excitons thus generated move to an interface between an electron donor and an electron acceptor constituting the organic photoelectric conversion layer  12 , and undergo exciton separation, i.e., dissociate into electrons and holes. The electric charges (electrons and holes) generated here are transported to different electrodes by diffusion due to a difference in carrier concentrations or by an internal electric field due to a difference in work functions between an anode (here, the lower electrode  11 ) and a cathode (here, the upper electrode  13 ), and are detected as a photocurrent. In addition, application of a potential between the lower electrode  11  and the upper electrode  13  makes it possible to control directions in which electrons and holes are transported. 
     In the following, description is given of configurations, materials, and the like of the respective sections constituting the photoelectric conversion element  1 . 
     The organic photoelectric conversion section  10  is an organic photoelectric conversion element that absorbs green light corresponding to a portion or all of a selective wavelength band (e.g., 495 nm or more and less than 620 nm) to generate excitons (electron-hole pairs). In the imaging device  100  described later, for example, holes, among the electron-hole pairs generated by photoelectric conversion, are read as signal charges from a side of the lower electrode  11 . In the photoelectric conversion element  1 , the lower electrode  11  is formed separately for each unit pixel P, for example. The organic photoelectric conversion layer  12  and the upper electrode  13  are provided as successive layers common to multiple unit pixels P (e.g., a pixel section  100 A illustrated in  FIG.  11   ). 
     The lower electrode  11  is provided in a region opposed to and covering light-receiving surfaces of the inorganic photoelectric conversion sections  32 B and  32 R formed in the semiconductor substrate  30 . The lower electrode  11  is configured by an electrically-conductive film having light transmissivity. Examples of a constituent material of the lower electrode  11  include ITO (indium tin oxide), In 2 O 3  doped with tin (Sn) as a dopant, indium tin oxides including crystalline ITO and amorphous ITO. As a constituent material of the lower electrode  11 , a tin oxide (SnO 2 )-based material doped with a dopant or a zinc oxide-based material doped with a dopant may be used. Examples of the zinc oxide-based material include aluminum zinc oxide (AZO) doped with aluminum (Al) as a dopant, gallium zinc oxide (GZO) doped with gallium (Ga), boron zinc oxide doped with boron (B), and indium zinc oxide (IZO) doped with indium (In). In addition, CuIs, InSbO 4 , ZnMgO, CuInO 2 , MgIN 2 O 4 , CdO, ZnSnO 3 , TiO 2 , or the like may be used as a constituent material of the lower electrode  11 . Further, a spinel-type oxide or an oxide having a YbFe 2 O 4  structure may be used. It is to be noted that the lower electrode  11  formed using the material as described above typically has a high work function, and functions as an anode electrode. 
     The organic photoelectric conversion layer  12  converts optical energy into electric energy. The organic photoelectric conversion layer  12  absorbs light of a portion or all of wavelengths in a visible light region of 495 nm or more and less than 620 nm, for example. The organic photoelectric conversion layer  12  includes, for example, organic materials of at least two types of a p-type semiconductor and an n-type semiconductor. The n-type semiconductor is an electron-transporting material that functions relatively as an electron acceptor (acceptor), and the p-type semiconductor is a hole-transporting material that functions relatively as an electron donor (donor). The organic photoelectric conversion layer  12  provides a field in which excitons generated upon light absorption are separated into electrons and holes; specifically, excitons are separated into electrons and holes at an interface (p/n junction plane) between the electron donor and the electron acceptor. 
     In a case where the organic photoelectric conversion layer  12  is formed using two types of organic materials of the p-type semiconductor and the n-type semiconductor, for example, one of the p-type semiconductor or the n-type semiconductor is preferably a material having light transmissivity to visible light, and the other one thereof is preferably a material that performs photoelectric conversion of light of a selective wavelength band of a visible light region. Alternatively, the organic photoelectric conversion layer  12  may be formed using, for example, three types of organic materials of a pigment material having a local maximum absorption wavelength in a selective wavelength band (e.g., 495 nm or more and less than 620 nm in the present embodiment) of the visible light region, and the n-type semiconductor and the p-type semiconductor, which have light transmissivity to visible light. The organic photoelectric conversion layer  12  has, in the layer, a bulk hetero structure in which the multiple kinds of organic materials are randomly mixed. 
     In the layer of the organic photoelectric conversion layer  12  of the present embodiment, as described above, a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material is formed in a predetermined cross-section between the lower electrode  11  and the upper electrode  13 . It is to be noted that the domain refers to a region in which organic materials of one kind of multiple organic materials constituting the organic photoelectric conversion layer  12  are arranged in succession. In the organic photoelectric conversion layer  12 , one of the p-type semiconductor (hole-transporting material) or the n-type semiconductor (electron-transporting material) described above may form a domain, or each of the p-type semiconductor and the n-type semiconductor may form a domain. 
     For example, it is preferable for the domain to at least partially have a crystal property, and specifically the domain preferably includes a crystal. The domain configured by a crystal enables reduction in trapping of electric charges in the domain. Further, the component ratio of the one organic material forming a crystal in this domain is preferably 20% or more and 70% or less. Setting the component ratio of the one organic material to the above-described range allows the domains of a size larger than 1 nm and smaller than 10 nm to be dispersed in the organic photoelectric conversion layer  12 . 
     The full width at half maximum (Full width at half maximum; FWHM) of a crystallization peak by means of X-ray diffraction (XRD) of the domain including the one organic semiconductor material is preferably 0.015 rad or more and 0.15 rad or less. The FWHM of the crystallization peak is inversely proportional to a crystal size. That is, a microcrystal has a larger FWHM. Meanwhile, also in the case of amorphous, the half-power band width becomes large because of a broad peak. Accordingly, it is difficult to determine whether it is microcrystal or amorphous only from the half-power band width. It is to be noted that “crystallization peak by means of XRD” means that a crystallization peak obtained by a single molecular crystal is broad in the present embodiment, or a case where a lattice fringe indicating the presence of a microcrystal is confirmed by a transmission electron microscope. In observation by the transmission electron microscope (Transmission Electron Microscope), observation of a smaller size requires higher observation magnification, which results in a narrower field of view for observation. This involves a disadvantage in that only spatially localized information is obtained. Obtaining information on a wider region by shooting while gradually moving the field of view for observation is not theoretically impossible. However, it is impractical to move the field of view in nm order, for example, to grasp even the extent of nm order. Meanwhile, the XRD enables obtainment of information on an average of entire samples by irradiation of the entire samples with an X-ray. Therefore, using the TEM and the XRD in combination in a complementary manner enables understanding of a local structure and an entire structure. That is, the FWHM of the crystallization peak being 0.015 rad or more means existence of the microcrystal in the entire samples. 
     It is to be noted that the numerical range of the FWHM of the crystallization peak described above is the one in a case of using a Cu-Kα ray as the X-ray. As for measurement of a domain size by means of the XRD, a domain observation sample is prepared to enable measurement of the domain size by means of a thin-film method using a Cu-Kα ray and a divergence slit of 1 mm, although detailed description thereof is given in Example. 
     Multiple domains are formed in a layer of the organic photoelectric conversion layer  12 . An average cycle obtained from autocorrelation of a two-dimensional distribution of the multiple domains is preferably 3 nm or more and 5 nm or less. The autocorrelation refers to an index indicating how far away from a domain there are domains of equivalent shapes and sizes. Typically, in the case of amorphous, there is no long-range regularity as compared with an interatomic distance; meanwhile the amorphous state is no such complete chaotic state as a gas. Examples of a method for quantitatively representing the regularity of such a single range include a scale of a radial distribution function, which is typically measured by scattering of an X-ray or a neutron ray. However, the radial distribution function should be regarded as a one-dimensional distribution, and is not necessarily appropriate as a method for representing a difference between the organic photoelectric conversion layer  12  of the present embodiment and a common organic photoelectric conversion layer. Therefore, in the present embodiment, a domain distribution existing in a cross-section between the lower electrode  11  and the upper electrode  13  is grasped two-dimensionally, and an average cycle of the domains is obtained from the autocorrelation of the two-dimensional distribution to define the average cycle as 5 nm or less. 
     Examples of a specific material constituting the organic photoelectric conversion layer  12  include the following organic materials. Examples of the electron-transporting material include C 60  fullerene, C 70  fullerene, and derivatives thereof. It is preferable to use, as the hole-transporting material, an organic material having an ionization potential of 6 eV or less in a case of using it as an image sensor, from the viewpoint of reduction in a dark current as well as external quantum efficiency. Examples of such a hole-transporting material include a compound (BDT3) represented by the following formula (1). This BDT3 is an example of the one organic semiconductor material forming the domain described above  
     
       
         
         
             
             
         
       
     
       FIG.  3    is a model diagram of a crystal of the BDT3 as viewed in a direction of [301]. A stacking cycle (C) in a short axis direction of the crystal of the BDT3 molecules stacked in a herringbone structure is about 0.75 nm. In a case where crystal growth is finished at that cycle (smallest unit of the crystal), the crystal size (L1) in the short axis direction is about 1.2 nm. This value is not considered to differ significantly regardless of whether a benzene ring of the main skeleton is one or two. This crystal size in the short axis direction is defined as “larger than 1 nm” as the smallest unit of the domain.  FIG.  4    is a model diagram of a crystal of the BDT3 as viewed in a direction of [20-1]. For example, in a case where two molecules are aligned in a long axis direction of molecules of the BDT3 to form a crystal, a length (L2) of the long axis (direction a) is about 6.5 nm. This direction a becomes longer as the benzene ring of the main skeleton is increased. For this reason, it is presumed that, in the organic photoelectric conversion layer  12  of the present embodiment, the one organic semiconductor material does not undergo crystal growth in the long axis direction, and molecules are stacked only in the short axis direction. 
     From those described above, examples of the hole-transporting material available as the one organic semiconductor material include an organic material including carbon atoms (C), hydrogen atoms (H), nitrogen atoms (N), oxygen atoms (O), and sulfur atoms (S), and including 9 or more and 13 or less aromatic rings in the entire molecules. Further, such an organic material preferably includes 5 or less aromatic rings forming the largest condensed ring, and the number of single bonds linking the aromatic rings is preferably 5 or more and 9 or less. Further, a length of the short side of the entire molecules is preferably 15% or more and 30% or less of the long side. Examples of an organic material satisfying these include compounds represented by the following formulae (2) to (7).  
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     The layer of the organic photoelectric conversion layer  12  has a configuration in which domains (crystal domains) each including a crystal of the above-described hole-transporting material are dispersed in the amorphous domain including C 60  fullerene, for example. 
     It is to be noted that the domains in the organic photoelectric conversion layer  12  are confirmable using a transmission electron microscope (TEM). The TEM is an apparatus that projects a three-dimensional object into two-dimensional image to capture a so-called TEM image, thus making it possible to grasp a crystal form in nm-meter order. 
     The crystal generally refer to a three-dimensional structure in which atoms or molecules are regularly arranged. Electrons scatter during transmission through the crystal, and interfere by wave nature of the electrons. As a result, the electrons strengthen or weaken in a specific direction. In a case where a direction of transmitted electrons relative to a cyclic structure called a crystal plane is substantially parallel, an interference fringe is observed in the TEM image. The interference fringe is generally called a lattice fringe, and a TEM image thereof is referred to here as a lattice image. 
     A condition in which the lattice image is observed depends on the apparatus, and an amount of focus shift (defocus amount) is observed in the vicinity of so-called Scherzer focus, in many cases, and is calculated, for example, by the following Expression (1). In the Scherzer focus, an image of a diffracted wave is formed about ¼ wavelength shifted from a transmitted wave, and a contrast is formed that is suitable for associating the lattice image with atomic arrangement. In addition, an interval (cycle) of the lattice fringe corresponds to a cycle of the crystal plane. When the focus is further shifted, the black and white of the lattice image is reversed, and moreover, the phase of the image changes variously in such a manner that a peripheral contour of the crystal becomes remarkable. In addition, the phase differs depending on an accelerating voltage of the TEM (wavelength of electrons), an aberration of a lens, the size of the crystal, and the like. 
     Expression 1 
     
       
         
           
             Scherzer 
               
             focus 
             = 
             1.2 
             √ 
             
               
                 Cs 
                 ⋅ 
                 λ 
               
             
           
         
       
     
      (Cs: spherical aberration coefficient, λ: wavelength of electrons) 
     Even in a case where the crystal plane is not parallel to an electron transmission direction, shifting a focus allows for formation of a fringe (so-called fringe contrasts) in the vicinity of the contour of a scattering body (e.g., crystal) having a different density in the sample. In general, the interference fringe in the order of atomic rows or molecular rows is likely to be observed in the Scherzer focus; when the defocus amount is in the µm order, the fringe contrast tends to be relatively strong. 
     For the purpose of observing the scattering body difficult to be contrasted by positively utilizing this phenomenon, the defocus amount may be shifted to the µm order in some cases. This may be referred to as a defocus image in some cases; however, the Scherzer focus is also strictly the defocus image (having different order of the defocus amount). 
     The sample to be analyzed by the TEM generally has a thickness of about several tens of nm in the electron transmission direction. One reason for this is that electrons and materials interact strongly with each other, and thus electrons are not able to be transmitted through a sample unless the sample is thin. However, there are also examples in which the thickness is several nm for a nano carbon and in which the thickness is several hundred nm to µm in the case of observation using an ultra-high voltage electron microscope. In general, determination is made that the defocus amount is zero in a case where the contrast is the weakest, and defocusing is performed by the Scherzer focus to capture the lattice image. However, the defocus amount differs depending on the position of the sample in the electron transmission direction, and thus only a portion of the sample satisfies the Scherzer focus condition. 
     Meanwhile, in a case where the defocus amount is in the µm order, the defocus amount is much larger than the thickness of the sample. As a result, the contour of the scattering body such as the crystal is observed as a substantially similar fringe contrast regardless of a difference in the position in the electron transmission direction. 
     In the present embodiment, from those described above, in a case where a cyclic stripe pattern is observed partially in a domain in an image (TEM image) in which the domain is captured in a defocusing condition in which the focus of the TEM is shifted by 1 µm or more, the domain is defined as a crystal. Here, one reason for using the phrase “partially in a domain” results from a theoretical reason that the stripe pattern is observed only partially in the crystal due to the crystal plane being not necessarily parallel to the electron transmission direction. 
     Further, as for the distribution of the domains in the organic photoelectric conversion layer  12 , distribution within an amorphous region is confirmable by using amorphous staining by means of osmium tetraoxide (OsO 4 ) and by using high-angle annular dark-field scanning transmission electron microscope (High-angle annular dark-field scanning transmission electron microscopy; HAADF-STEM). 
     For example, when staining is performed using a vacuum electron staining apparatus manufactured by Filgen, Inc., the amorphous region is stained, whereas a crystal portion forming the domain is not stained because a molecular spacing thereof is narrower than osmium tetraoxide. When confirming results of observations of the same field of view of the TEM image and a HAADF-STEM image, it is appreciated that a region reflected in black contrast in the HAADF-STEM image indicates the crystal domain, whereas a region reflected in white contrast indicates a stained amorphous domain. 
     The upper electrode  13  is configured by an electrically-conductive film having light transmissivity similar to that of the lower electrode  11 . In the imaging device  100  using the photoelectric conversion element  1  as one pixel (unit pixel P), the upper electrode  13  may be separated for each of the pixels, or may be formed as an electrode common to the pixels. 
     It is to be noted that another layer may be provided 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 either 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 ; or alternatively, the buffer layers  17 A and  17 B may be provided both therebetween. In addition thereto, for example, an underlying layer, a hole transport layer, an electron blocking layer, and the like may be provided in this order from the side of the lower electrode  11 . A hole blocking layer, a work function adjusting layer, an electron transport layer, and the like may be provided between the organic photoelectric conversion layer  12  and the upper electrode  13 . 
     The fixed charge layer  14 A may be a film having a positive fixed charge or a film having a negative fixed charge. Examples of a material of the film having a negative fixed charge include hafnium oxide (HfO 2 ), aluminum oxide (AI 2 O 3 ), zirconium oxide (ZrO 2 ), tantalum oxide (Ta 2 O 5 ), and titanium oxide (TiO 2 ). In addition, as a material other than those mentioned above, there may be used 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. 
     The fixed charge layer  14 A may have a configuration in which two or more types of films are stacked. This makes it possible to further enhance a function as the hole accumulation layer, for example, in a case of the film having a negative fixed charge. 
     A material of the dielectric layer  14 B is not particularly limited, and the dielectric layer  14 B is formed by, for example, silicon oxide (SiO x ), TEOS, silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), or the like. 
     For example, the interlayer insulating layer  15  is configured by a monolayer film of one of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), or the like, or alternatively is configured by a stacked film of two or more thereof. 
     A pad section  16 A, an upper contact  16 B, a pad section  16 C, a lower first contact  45 , and a lower second contact  46  are each configured by 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), for example. 
     The protective layer  51  is configured by a material having light transmissivity, and, for example, is configured by a monolayer film of one of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), or the like, or alternatively is configured by a stacked film of two or more thereof. 
     The on-chip lens layer  52  is formed on the protective layer  51  to cover the entire surface thereof. Multiple on-chip lenses (microlenses)  52 L are provided on a front surface of the on-chip lens layer  52 . The on-chip lens  52 L condenses light incident from above on 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 layer  40  is formed on the side of the second surface  30 S 2  of the semiconductor substrate  30 . This enables 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 arranged close to each other, thus making it possible to reduce variations in sensitivities between colors generated depending on a F-value of the on-chip lens  52 L. 
       FIG.  2    is a plan view of a configuration example of the photoelectric conversion element  1  in which multiple photoelectric conversion sections (e.g., organic photoelectric conversion section  10  and inorganic photoelectric conversion sections  32 B and  32 R) are stacked to which the technology according to the present disclosure is applicable. That is,  FIG.  2    illustrates an example of a planar configuration of the unit pixel P constituting the pixel section  100 A of the imaging device  100  illustrated in  FIG.  15   , for example. 
     The unit pixel P includes a photoelectric conversion region  1100  in which a red photoelectric conversion section (inorganic photoelectric conversion section  32 R in  FIG.  1   ), a blue photoelectric conversion section (inorganic photoelectric conversion section  32 B in  FIG.  1   ), and a green photoelectric conversion section (organic photoelectric conversion section  10  in  FIG.  1   ) (neither of which is illustrated in  FIG.  2   ) that perform photoelectric conversion of light beams of respective 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 a side of the light-receiving surface (light incident side S 1  in  FIG.  1   ). Further, the unit pixel P includes a Tr group  1110 , a Tr group  1120 , and a Tr group  1130  as charge readout sections that read charges corresponding to light beams of the respective wavelengths of R, G, and B from the red photoelectric conversion section, the green photoelectric conversion section, and the blue photoelectric conversion section. The organic photoelectric conversion section  10  performs, in one unit pixel P, spectroscopy in the vertical direction, i.e., spectroscopy of light beams of R, G, and B in respective layers 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, a signal charge corresponding to light of R generated and accumulated in the red photoelectric conversion section. The Tr group  1110  is configured by 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, a signal charge corresponding to light of B generated and accumulated in the blue photoelectric conversion section. The Tr group  1120  is configured by 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, a signal charge corresponding to 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  is configured by a gate G, a source/drain region S/D, and an FD (floating diffusion)  1115  (constituting source/drain region). The transfer Tr  1121  is configured by a gate G, a source/drain region S/D, and an FD  1125 . The transfer Tr  1131  is configured by a gate G, (a source/drain region S/D coupled to) the green photoelectric conversion section of the photoelectric conversion region  1100 , and an 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 that 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 . 
     Each of the reset Trs  1112 ,  1122 , and  1132 , the amplification Trs  1113 ,  1123 , and  1133 , and the selection Trs  1114 ,  1124 , and  1134  is configured by a gate G and a pair of source/drain regions S/D arranged to interpose the gate G therebetween. 
     The FDs  1115 ,  1125 , and  1135  are coupled to the source/drain regions S/D serving as sources of the reset Trs  1112 ,  1122 , and  1132 , respectively, and are coupled to the gates G of the amplification Trs  1113 ,  1123 , and  1133 , respectively. A power supply Vdd is coupled to the common source/drain regions 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 . A VSL (vertical signal line) is coupled to each of the source/drain regions S/D serving as the sources of the selection Trs  1114 ,  1124 , and  1134 . 
     1-2. Method of Manufacturing Photoelectric Conversion Element 
     The photoelectric conversion element  1  illustrated in  FIG.  1    may be manufactured, for example, as follows. 
       FIGS.  6  and  7    illustrate the method of manufacturing the photoelectric conversion element  1  in the order of steps. First, as illustrated in  FIG.  6   , the p-well  31 , for example, is formed as a well of a first electrically-conductivity type in the semiconductor substrate  30 , and the inorganic photoelectric conversion sections  32 B and  32 R of a second electrically-conductivity type (e.g., n-type) is formed in the p-well  31 . The p+ region is formed in the vicinity of the first surface  30 S 1  of the semiconductor substrate  30 . 
     As illustrated in  FIG.  6    as well, on the second surface  30 S 2  of the semiconductor substrate  30 , n + regions serving as the floating diffusions FD 1  to FD 3  are formed, and then, a gate insulating layer  33  and a gate wiring layer  47  including respective gates of the vertical transistor T r   2 , the transfer transistor T r   3 , the amplifier transistor AMP, and the reset transistor RST are formed. This allows for formation of the vertical transistor T r   2 , the transfer transistor T r   3 , the amplifier transistor AMP, and the reset transistor RST. Further, the multilayer wiring layer  40  that includes the lower first contact  45 , the lower second contact  46 , the wiring layers  41  to  43  including the coupling section  41 A, and the insulating layer  44  is formed on the second surface  30 S 2  of the semiconductor substrate  30 . 
     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 (unillustrated), and a holding substrate (unillustrated) are stacked. Although not illustrated in  FIG.  6   , the embedded oxide film and the holding substrate are joined to the first surface  30 S 1  of the semiconductor substrate  30 . 
     Next, a supporting substrate (unillustrated) or another semiconductor substrate, etc. is joined to the side of the second surface  30 S 2  (side of the multilayer wiring layer  40 ) of the semiconductor substrate  30 , and the substrate is turned upside down. 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 . The above steps may be performed by techniques used in common CMOS processes such as ion implantation and CVD (Chemical Vapor Deposition). 
     Next, as illustrated in  FIG.  7   , the semiconductor substrate  30  is worked from the side of the first surface  30 S 1  by dry-etching, for example, to form a ring-shaped through-hole  30 H. As illustrated in  FIG.  7   , as for the depth, the through-hole  30 H  penetrates from the first surface  30 S 1  to the second surface  30 S 2  of the semiconductor substrate  30 , and reaches, for example, the coupling section  41 A. 
     Subsequently, as illustrated in  FIG.  7   , for example, the fixed charge layer  14 A is formed on the first surface  30 S 1  of the semiconductor substrate  30  and a side surface of the through-hole  30 H. Two or more types of films may be stacked as the fixed charge layer  14 A. This makes it possible to further enhance the function as the hole accumulation layer. After the fixed charge layer  14 A is formed, the dielectric layer  14 B is formed. 
     Next, an electric conductor is buried in the through-hole  30 H to form the through-electrode  34 . It may be possible to use, as the electric conductor, for example, a metal material such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (Hf), and tantalum (Ta), in addition to a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon). 
     Subsequently, after formation of the pad section  16 A on the through-electrode  34 , there is formed on the dielectric layer  14 B and the pad section  16 A, the interlayer insulating layer  15  in which the upper contact  16 B and the pad section  16 C that electrically couple the lower electrode  11  and the through-electrode  34  (specifically, the pad section  16 A on the through-electrode  34 ) are provided on the pad section  16 A. 
     Thereafter, 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 interlayer insulating layer  15 . The organic photoelectric conversion layer  12  is formed, for example, by the above-described two or three types of organic materials by means of a vapor deposition method (resistive heating method), for example. At this time, allowing a substrate stage to have a predetermined temperature makes it possible to control a surface density of the domain in the organic photoelectric conversion layer  12 . Finally, the on-chip lens layer  52 , which includes the multiple on-chip lenses  52 L, is disposed on the surface thereof. Thus, the photoelectric conversion element  1  illustrated in  FIG.  1    is completed. 
     It is to be noted that, in a case of forming another organic layer (e.g., an electron blocking layer, etc.) 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 deposition method; another method, for example, a spin-coating technique, a printing technique, or the like may be used. 
     In the photoelectric conversion element  1 , when light is incident on the organic photoelectric conversion section  10  via the on-chip lens  52 L, the light passes through the organic photoelectric conversion section  10 , the inorganic photoelectric conversion sections  32 B and the  32 R in this order, and is subjected to photoelectric conversion for each color light beam of green (G), blue (B), and red (R) in the passing process. Hereinafter, description is given of a signal acquisition operation of each color. 
     Acquisition of Green Signal by Organic Photoelectric Conversion Section  10   
     Green light, of the light incident on the photoelectric conversion element  1 , is first selectively detected (absorbed) by the organic photoelectric conversion section  10  and is subjected to photoelectric conversion. 
     The organic photoelectric conversion section  10  is coupled to the gate Gamp of the amplifier transistor AMP and the floating diffusion FD 1  via the through-electrode  34 . Accordingly, holes of the electron-hole pairs generated in the organic photoelectric conversion section  10  are extracted from the side of the lower electrode  11 , transferred to the side of the second surface  30 S 2  of the semiconductor substrate  30  via the through-electrode  34 , and accumulated in the floating diffusion FD 1 . At the same time, a charge amount generated in the organic photoelectric conversion section  10  is modulated into a voltage by the amplifier transistor AMP. 
     In addition, the reset gate Grst of the reset transistor RST is disposed next to the floating diffusion FD 1 . As a result, the electric charges accumulated in the floating diffusion FD 1  are reset by the reset transistor RST. 
     Here, the organic photoelectric conversion section  10  is coupled not only to the amplifier transistor AMP but also to the floating diffusion FD 1  via the through-electrode  34 , thus making it possible to easily reset the electric charges accumulated in the floating diffusion FD 1  by the reset transistor RST. 
     On the other hand, in a case where the through-electrode  34  and the floating diffusion FD 1  are not coupled to each other, it is difficult to reset the electric charges accumulated in the floating diffusion FD 1 , thus resulting in application of a large voltage to pull out the electric charges to the side of the upper electrode  13 . Accordingly, there is a possibility that the organic photoelectric conversion layer  12  may be damaged. In addition, the structure that enables resetting in a short period of time leads to an increase in dark noises, resulting in a trade-off, which structure is thus difficult. 
     Acquisition of Blue Signal and Red Signal by Inorganic Photoelectric Conversion Sections  32 B and  32 R 
     Subsequently, of the light transmitted through the organic photoelectric conversion section  10 , blue light and red light are sequentially absorbed by the inorganic photoelectric conversion section  32 B and the inorganic photoelectric conversion section  32 R, respectively, and are subjected to photoelectric conversion. In the inorganic photoelectric conversion section  32 B, electrons corresponding to the incident blue light are accumulated in an n region of the inorganic photoelectric conversion section  32 B, and the accumulated electrons are transferred to the floating diffusion FD 2  by the vertical transistor T r   2 . Similarly, in the inorganic photoelectric conversion section  32 R, electrons corresponding to the incident red light are accumulated in an n region of the inorganic photoelectric conversion section  32 R, and the accumulated electrons are transferred to the floating diffusion FD 3  by the transfer transistor T r   3 . 
     1-3. Workings and Effects 
     In the photoelectric conversion element  1  of the present embodiment, the organic photoelectric conversion layer  12  having a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material is provided in a predetermined cross-section between the lower electrode  11  and the upper electrode  13 . This improves movement of electric charges having undergone charge separation in the organic photoelectric conversion layer. This is described below. 
     The organic photoelectric conversion layer constituting the organic photoelectric conversion element to be used in an organic thin film solar cell, an organic imaging element, or the like is typically implemented by mixing different organic semiconductors together. This organic photoelectric conversion element has a mechanism in which light absorption causes electric charge pairs (excitons) including positive electric charges (holes) and negative electric charges (electrons) to be generated, and the excitons reach (diffuse to) a semiconductor interface and then move (are transported), as free electric charges, to the electrode after charge separation, thus allowing a current to flow. 
     An organic semiconductor typically has a dielectric constant lower than an inorganic semiconductor. As a result, the electrostatic attractive force of excitons is strong, thus making electric charges unlikely to be separated. In addition, the movement distance of excitons generated by light absorption is as short as nm order, and thus the probability is high that excitons undergo recombination (deactivation) before the excitons move to the interface and undergo charge separation. In contrast, as described above, a photoelectric conversion element with improved external quantum efficiency and response speed is reported, which is achieved by providing an organic photoelectric conversion layer having, in the layer, a percolation structure that traverses vertically in a film thickness direction and having a domain of which a domain length in a planar direction is smaller than a domain length in the film thickness direction. 
     Incidentally, in a case of using an organic photoelectric conversion element as an imaging element constituting an image sensor, an afterimage for a long period of time (signal delay) becomes an issue after having shot an object that emits light at low illuminance. An organic semiconductor varies greatly in its form depending on a composition thereof, a film formation condition, thermal processing after the film formation, and the like. For example, from the viewpoint of electric charge mobility, the organic semiconductor having a crystal form is more advantageous than having an amorphous form. In addition, the anisotropy of the crystal form also changes photoelectric conversion characteristics. Meanwhile, crystal fault, a grain boundary, or the like cause electric charge trapping, and the trapped electric charges are discharged over a period of time of about 10 ms to 1 s. It is considered that this deteriorates response characteristics. 
     As a method for solving this issue, it is conceivable to increase a drive voltage. In this case, however, an electrode to be consumed is increased, and characteristics are deteriorated due to dielectric breakdown, temperature rise, or the like, giving rise to issues such as safety and reliability to be impaired as well as manufacturing costs to be increased due to measures therefor. 
     In contrast, in the present embodiment, the organic photoelectric conversion layer  12  having a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material is provided in a predetermined cross-section between the lower electrode  11  and the upper electrode  13 . This increases the probability that excitons generated by light absorption move to an interface between a p-type semiconductor and an n-type semiconductor and undergo charge separation. 
     As described above, in the photoelectric conversion element  1  of the present embodiment, excitons generated by light absorption move to the interface between the p-type semiconductor and the n-type semiconductor and undergo charge separation, and movement of free electric charges to the lower electrode  11  and the upper electrode  13  is improved. This makes it possible to improve the response characteristic including a long range of time equal to or more than 10 ms, for example. That is, in the imaging device  100  using the photoelectric conversion element  1  of the present embodiment as well as in a thermography, a ranging sensor, or the like, for example, including the imaging device  100 , an afterimage for a long period of time is improved, thus enabling favorable use thereof at night. 
     In addition, the photoelectric conversion element  1  of the present embodiment has no need to increase the drive voltage as described above, and thus is superior also in aspects of safety, reliability, power consumption, and manufacturing costs. 
     Next, description is given of Modification Examples 1 to  4  of the present disclosure. It is to be noted that components corresponding to those of the photoelectric conversion element  1  of the foregoing embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. 
     2. Modification Examples 
     2-1. Modification Example 1 
       FIG.  8    illustrates an example of a cross-sectional configuration of a photoelectric conversion element (a photoelectric conversion element  2 ) according to 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 arrangement of transistors constituting a control section of the photoelectric conversion element  2  and a lower electrode  21  constituting an organic photoelectric conversion section  20 . The photoelectric conversion element  2  of the present modification example differs from the foregoing embodiment in that the lower electrode  21  constituting the organic photoelectric conversion section  20  includes multiple electrodes (e.g., a readout electrode  21 A and an accumulation electrode  21 B) independent of each other, with an insulating layer  22  interposed therebetween. 
     It is to be noted that description is given, in the present modification example, of a case of reading electrons, among the electron-hole pairs generated by photoelectric conversion, as signal charges (a case of setting an n-type semiconductor region as the photoelectric conversion layer). 
     Similarly to the foregoing first embodiment, the organic photoelectric conversion section  20  and the inorganic photoelectric conversion sections  32 B and  32 R selectively detect wavelengths (light) of wavelength bands different from each other and perform photoelectric conversion. 
     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 side of the first surface  30 S 1  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 formed separately for each photoelectric conversion element  2 , for example, and is configured by the readout electrode  21 A and the accumulation electrode  21 B separated from each other with the insulating layer  22  interposed therebetween, as described above. The readout electrode  21 A is electrically coupled to the semiconductor layer  23  via an opening  22 H provided in the insulating layer  22 . The readout electrode  21 A is provided to transfer electric charge generated in the organic photoelectric conversion layer  24  to the floating diffusion FD 1 , and is coupled to the floating diffusion FD  1  via an upper second contact  29 B, a pad section  39 A, an upper first contact  29 A, the through-electrode  34 , the coupling section  41 A, and the lower second contact  46 , for example. The accumulation electrode  21 B is provided to accumulate, in the semiconductor layer  23 , electrons, among electric charges generated in the organic photoelectric conversion layer  24 , as signal charges. The accumulation electrode  21 B is provided in a region opposed to and covering the light receiving surface of the inorganic photoelectric conversion sections  32 B and  32 R formed in the semiconductor substrate  30 . The accumulation electrode  21 B is preferably larger than the readout electrode  21 A, which makes it possible to accumulate a number of electric charges. As illustrated in  FIG.  10   , a voltage application circuit  60  is coupled to the accumulation electrode  21 B via a wiring line, and a voltage (e.g., Vo A ) is independently applied thereto. 
     The insulating layer  22  is provided to electrically separate the accumulation electrode  21 B and the semiconductor layer  23  from each other. The insulating layer  22  is provided on an interlayer insulating layer  28 , for example, to cover the lower electrode  21 . The insulating layer  22  is provided with the opening  22 H on the readout electrode  21 A, and the readout electrode  21 A and the semiconductor layer  23  are electrically coupled to each other via the opening  22 H. For example, the insulating layer  22  is configured by a monolayer film of one of silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), or the like, or alternatively is configured by a stacked film of two or more thereof. 
     The semiconductor layer  23  is provided under the organic photoelectric conversion layer  24 , specifically, between the insulating layer  22  and the organic photoelectric conversion layer  24 , and is provided to accumulate signal charges generated in the organic photoelectric conversion layer  24 . It is preferable for the semiconductor layer  23  to have electric charge mobility higher than and to be formed by using a material having a band gap larger than those of the organic photoelectric conversion layer  24 . For example, the band gap of a constituent material of the semiconductor layer  23  is preferably 3.0 eV or more. Examples of such a material include an oxide semiconductor material such as IGZO and an organic semiconductor material. Examples of the organic semiconductor material include transition metal dichalcogenide, silicon carbide, diamond, graphene, a carbon nanotube, a condensed polycyclic hydrocarbon compound, and a condensed heterocyclic compound. Providing the semiconductor layer  23  configured by the above-mentioned material under the organic photoelectric conversion layer  24  makes it possible to prevent recombination of electric charges at the time of accumulation of electric charges and thus to improve transmission efficiency. 
     It is to be noted that, as in photoelectric conversion elements  4  and  5  described later, for example, the semiconductor layer  23  may have, for example, a stacked structure of a layer (a layer  23 A) and a layer (a layer  23 B). The layer  23 A is provided to prevent electric charges accumulated in the semiconductor layer  23  from being trapped at an interface with the insulating layer  22  and transfer the electric charges efficiently to a readout electrode  11 A. The layer  23 B is provided to prevent oxygen desorption on a front surface of the layer  23 A and prevent electric charges generated in the organic photoelectric conversion layer  24  from being trapped at an interface with the semiconductor layer  23 . 
     The organic photoelectric conversion layer  24  converts optical energy into electric energy, and has a configuration similar to that of the organic photoelectric conversion layer  12  in the foregoing embodiment. 
     Similarly to the upper electrode  13  in the foregoing embodiment, the upper electrode  25  is configured by an electrically-conductive film having light transmissivity. 
     It is to be noted that, although  FIG.  8    illustrates the example in which the semiconductor layer  23 , the organic photoelectric conversion layer  24 , and the upper electrode  25  are provided as successive layers common to multiple photoelectric conversion elements  2 , these layers may be formed separately for each of the photoelectric conversion elements  2 , for example. In addition, another layer may be provided 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, similarly to the photoelectric conversion element  1  illustrated in  FIG.  5   , the buffer layers  17 A and  17 B may be provided 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 , for example. 
     For example, a dielectric layer  26 , an insulating layer  27 , and the interlayer insulating layer  28  are provided between the first surface  30 S 1  of the semiconductor substrate  30  and the lower electrode  21 . The dielectric layer  26 , the insulating layer  27 , and the interlayer insulating layer  28  have configurations similar to those of the fixed charge layer  14 A, the dielectric layer  14 B, and the interlayer insulating layer  15 , respectively, in the foregoing embodiment. 
     A second surface  30 B of the semiconductor substrate  30  is provided with a readout circuit constituting a control section in each of the organic photoelectric conversion section  20  and the inorganic photoelectric conversion sections  32 B and  32 R. Specifically, there are provided: a reset transistor TR 1   rst , an amplifier transistor TR 1   amp , and a selection transistor TR 1   sel  constituting a readout circuit of the organic photoelectric conversion section  20 ; a transfer transistor TR 2   trs  (TR 2 ), a reset transistor TR 2   rst , an amplifier transistor TR 2   amp , and a selection transistor TR 2   sel  constituting a readout circuit of the inorganic photoelectric conversion section  32 B; and a transfer transistor TR 3   trs  (TR 3 ), a reset transistor TR 3   rst , an amplifier transistor TR 3   amp , and a selection transistor TR 3   sel  constituting a readout circuit of the inorganic photoelectric conversion section  32 R. 
     The reset transistor TR 1   rst  resets electric charges transferred from the organic photoelectric conversion section  20  to the floating diffusion FD 1 , and is configured by, for example, a MOS transistor. Specifically, the reset transistor T r   1   rst  is configured by the reset gate Grst, a channel formation region  36 A, and source/drain regions  36 B and  36 C. The reset gate Grst is coupled to a reset line RST 1 , and one source/drain region  36 B of the reset transistor T r   1   rst  also serves as the floating diffusion FD 1 . Another source/drain region  36 C constituting the reset transistor T r   1   rst  is coupled to a power source VDD. 
     The amplifier transistor TR 1   amp  is a modulation element that modulates an amount of electric charges generated in the organic photoelectric conversion section  20  into a voltage, and is configured by, for example, a MOS transistor. Specifically, the amplifier transistor TR 1   amp  is configured by the gate Gamp, a channel formation region  35 A, and 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 (floating diffusion FD 1 ) of the reset transistor T r   1   rst  via the lower first contact  45 , the coupling section  41 A, the lower second contact  46 , the through-electrode  34 , and the like. In addition, one source/drain region  35 B shares a region with the other source/drain region  36 C constituting the reset transistor T r   1   rst , and is coupled to the power source VDD. 
     The selection transistor TR 1   se   1  is configured by a gate G se   1 , a channel formation region  34 A, and source/drain regions  34 B and  34 C. The gate G se   1  is coupled to a selection line SEL 1 . In addition, one source/drain region  34 B shares a region with another source/drain region  35 C constituting the amplifier transistor AMP, and another source/drain region  34 C is coupled to the signal line (data output line) VSL 1 . 
     The transfer transistor TR 2   trs  (TR 2 ) is provided to transfer, to the floating diffusion FD 2 , signal charges corresponding to a blue color generated and accumulated in an inorganic photoelectric conversion section  32 G. The inorganic photoelectric conversion section  32 G is formed at a deep position from the second surface  30 S 2  of the semiconductor substrate  30 , and thus the transfer transistor TR 2   trs  of the inorganic photoelectric conversion section  32 G is preferably configured by 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 in the vicinity of the gate G trs   2  of the transfer transistor TR 2   trs . The electric charges accumulated in the inorganic photoelectric conversion section  32 G is read by the floating diffusion FD 2  via a transfer channel formed along the gate G trs   2 . 
     The reset transistor TR 2   rst  is configured by a gate, a channel formation region, and source/drain regions. A gate of the reset transistor TR 2   rst  is coupled to a reset line RST 2 , and one of the source/drain regions of the reset transistor TR 2   rst  is coupled to the power source VDD. Another of the source/drain regions of the reset transistor TR 2   rst  also serves as the floating diffusion FD 2 . 
     The amplifier transistor TR 2   amp  is configured by a gate, a channel formation region, and source/drain regions. The gate is coupled to the other source/drain region (floating diffusion FD 2 ) of the reset transistor TR 2   rst . In addition, one of the source/drain regions constituting the amplifier transistor TR 2   amp  shares a region with the one of the source/drain regions constituting the reset transistor TR 2   rst , and is coupled to the power source VDD. 
     The selection transistor TR 2   sel  is configured by a gate, a channel formation region, and source/drain regions. The gate is coupled to a selection line SEL 2 . In addition, one of the source/drain regions constituting the selection transistor TR 2   sel  shares a region with another of the source/drain regions constituting the amplifier transistor TR 2   amp . Another of the source/drain regions constituting the selection transistor TR 2   sel  is coupled to a signal line (data output line) VSL 2 . 
     The transfer transistor TR 3   trs  (TR 3 ) transfers, to the floating diffusion FD 3 , signal charges corresponding to a red color generated and accumulated in the inorganic photoelectric conversion section  32 R, and is configured by, 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 in the vicinity of a gate G trs   3  of the transfer transistor TR 3   trs . The electric charges accumulated in the inorganic photoelectric conversion section  32 R is read by the floating diffusion FD 3  via a transfer channel formed along the gate G trs   3 . 
     The reset transistor TR 3   rst  is configured by a gate, a channel formation region, and source/drain regions. A gate of the reset transistor TR 3   rst  is coupled to a reset line RST 3 , and one of the source/drain regions constituting the reset transistor TR 3   rst  is coupled to the power source VDD. Another of the source/drain regions constituting the reset transistor TR 3   rst  also serves as the floating diffusion FD 3 . 
     The amplifier transistor TR 3   amp  is configured by a gate, a channel formation region, and source/drain regions. The gate is coupled to the other source/drain region (floating diffusion FD 3 ) of the reset transistor TR 3   rst . In addition, one of the source/drain regions constituting the amplifier transistor TR 3   amp  shares a region with the one of the source/drain regions constituting the reset transistor TR 3   rst , and is coupled to the power source VDD. 
     The selection transistor TR 3   sel  is configured by a gate, a channel formation region, and source/drain regions. The gate is coupled to a selection line SEL 3 . In addition, one of the source/drain regions constituting the selection transistor TR 3   sel  shares a region with another of the source/drain regions constituting the amplifier transistor TR 3   amp . Another of the source/drain regions constituting the selection transistor TR 3   sel  is coupled to a signal line (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  111  constituting a drive circuit. The signal lines (data output lines) VSL 1 , VSL 2 , and VSL 3  are coupled to a column signal processing circuit  112  constituting the drive circuit. 
     The protective layer  51  is provided on the upper electrode  25 . In the protective layer  51 , for example, a light blocking film  53  is provided at a position corresponding to the readout electrode  21 A. This light blocking film  53  may be provided to cover at least a region of the readout electrode  21 A in direct contact with the semiconductor layer  23 , without being engaged with at least the accumulation electrode  21 B. 
       FIG.  11    illustrates an operational example of the photoelectric conversion element  2 . (A) indicates a potential in the accumulation electrode  21 B, (B) indicates a potential in the floating diffusion FD 1  (readout electrode  21 A), and (C) indicates a potential in the gate (G se   1 ) of the reset transistor TR 1   rst . In the photoelectric conversion element  2 , voltages are applied individually to the readout electrode  21 A and the accumulation electrode  21 B. 
     In the photoelectric conversion element  2 , during an accumulation period, a potential V 1  is applied from the drive circuit to the readout electrode  21 A, and a potential V 2  is applied to the accumulation electrode  21 B. Here, as for the potentials V 1  and V 2 , V 2  &gt; V 1  holds true. This allows electric charges (signal charges; electrons) generated by photoelectric conversion to be attracted to the accumulation electrode  21 B and accumulated in a region, of the semiconductor layer  23 , opposed to the accumulation electrode  21 B (accumulation period). Incidentally, a potential in the region, of the semiconductor layer  23 , opposed to the accumulation electrode  21 B has a value on a more negative side as time of photoelectric conversion elapses. It is to be noted that holes are sent from the upper electrode  13  to the drive circuit. 
     In the photoelectric conversion element  2 , a reset operation is performed at a later stage in the accumulation period. Specifically, at timing t1, a scanning section changes a voltage of a reset signal RST from a low level to a high level. This brings, in the unit pixel P, the reset transistor TR 1   rst  into an ON state; as a result, a voltage of the floating diffusion FD 1  is set to a power source voltage, and the voltage of the floating diffusion FD 1  is reset (reset period). 
     After completion of the reset operation, electric charges are read. Specifically, at timing t2, a potential V 3  is applied to the readout electrode  21 A from the drive circuit, and a potential V 4  is applied to the accumulation electrode  21 B. Here, as for the potentials V3 and V4, V3 &lt; V4 holds true. This allows electric charges accumulated in a region corresponding to the accumulation electrode  21 B to be read from the readout electrode  21 A to the floating diffusion FD 1 . That is, the electric charges accumulated in the semiconductor layer  23  are read by the control section (transfer period). 
     After completion of the reading operation, the potential V1 is applied again to the readout electrode  21 A from the drive circuit, and the potential V2 is applied to the accumulation electrode  21 B. This allows electric charges generated by photoelectric conversion to be attracted to the accumulation electrode  21 B and accumulated in a region, of the organic photoelectric conversion layer  24 , opposed to the accumulation electrode  21 B (accumulation period). 
     As described above, the present technology is applicable to the photoelectric conversion element (photoelectric conversion element  2 ) in which the lower electrode  21  includes the multiple electrodes (readout electrode  21 A and accumulation electrode  21 B). That is, in the photoelectric conversion element  2  of the present modification example, the organic photoelectric conversion layer  24  is formed to have a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material in a predetermined cross-section between the lower electrode  21  and the upper electrode  25 , thereby making it easier for electric charges (electrons and holes) generated in the organic photoelectric conversion layer  24  to move to the lower electrode  21  and the upper electrode  25 . Thus, it is possible to obtain effects similar to those of the foregoing embodiment. 
     2-2. Modification Example 2 
       FIG.  12    schematically illustrates an example of a cross-sectional configuration of a photoelectric conversion element (a photoelectric conversion element  3 ) according to Modification Example 2 of the present disclosure. Similarly to the above-described photoelectric conversion element  1 , for example, the photoelectric conversion element  3  constitutes one unit pixel P in the imaging device  100  such as a CMOS image sensor that is able to capture an image obtained from visible light, for example, without using a color filter. The photoelectric conversion element  3  of 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 an insulating layer  76  interposed therebetween. 
     The red photoelectric conversion section  70 R, the green photoelectric conversion section  70 G, and the blue photoelectric conversion section  70 B include, respectively, organic photoelectric conversion layers  72 R,  72 G, and  72 B between respective pairs of electrodes, specifically, between a lower electrode  71 R and an upper electrode  73 R, between a lower electrode  71 G and an upper electrode  73 G, and between a lower electrode  71 B and an upper electrode  73 B, respectively. 
     The on-chip lens layer  52  including the on-chip lens  52 L is provided over the blue photoelectric conversion section  70 B with the protective layer  51  interposed therebetween. A red electricity storage layer  310 R, a green electricity storage layer  310 G, and a blue electricity storage layer  310 B are provided in the semiconductor substrate  30 . Light incident on the on-chip lens  52 L is 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, and respective signal charges are sent, 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. The signal charges may be either electrons or holes generated by photoelectric conversion; however, in the following, description is given by exemplifying a case where electrons are read as the signal charges. 
     The semiconductor substrate  30  is configured by, 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 the semiconductor substrate  30  each include the n-type semiconductor region, and the signal charges (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 are accumulated in the n-type semiconductor region. The n-type semiconductor region of the red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B is 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 (unillustrated) including glass or the like. 
     The semiconductor substrate  30  is provided with a pixel transistor for reading electrons from each of the red electricity storage layer  310 R, the green electricity storage layer  310 G, and the blue electricity storage layer  310 B and transferring them, for example, to a vertical signal line (a vertical signal line Lsig in  FIG.  15   ). 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 is configured by the n-type semiconductor region. 
     The insulating layer  76  is configured by, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiON), hafnium oxide (HfO x ), or the like. Multiple types of insulating films may be stacked to configure the insulating layer  76 . The insulating layer  76  may be configured by an organic insulating material. The insulating layer  76  is provided with respective plugs and electrodes for coupling the red electricity storage layer  310 R and the red photoelectric conversion section  70 R together, the green electricity storage layer  310 G and the green photoelectric conversion section  70 G together, and the blue electricity storage layer  310 B and the blue photoelectric conversion section  70 B together. 
     The red photoelectric conversion section  70 R includes the lower electrode  71 R, the organic photoelectric conversion layer  72 R, and the upper electrode  73 R in this order from a position close to the semiconductor substrate  30 . The green photoelectric conversion section  70 G includes the lower electrode  71 G, the organic photoelectric conversion layer  72 G, and the upper electrode  73 G in this order from a position close to the red photoelectric conversion section  70 R. The blue photoelectric conversion section  70 B includes the lower electrode  71 B, the organic photoelectric conversion layer  72 B, and the upper electrode  73 B in this order from a position close to the green photoelectric conversion section  70 G. The insulating layer  44  is provided between the red photoelectric conversion section  70 R and the green photoelectric conversion section  70 G, and an insulating layer  75  is provided between the green photoelectric conversion section  70 G and the blue photoelectric conversion section  70 B. The red photoelectric conversion section  70 R selectively absorbs red light (e.g., a wavelength of 620 nm or more and 750 nm or less); the green photoelectric conversion section  70 G selectively absorbs green light (e.g., a wavelength of 495 nm or more and 620 nm or less); and the blue photoelectric conversion section  70 B selectively absorbs blue light (e.g., a wavelength of 450 nm or more and 495 nm or less) to generate electron-hole pairs. 
     The lower electrode  71 R extracts signal charges generated in the organic photoelectric conversion layer  72 R; the lower electrode  71 G extracts signal charges generated in the organic photoelectric conversion layer  72 G; and the lower electrode  71 B extracts signal charges generated in the organic photoelectric conversion layer  72 B. The lower electrodes  71 R,  71 G, and  71 B are provided for each pixel, for example. The lower electrodes  71 R,  71 G, and  71 B are each configured by, for example, a light-transmissive electrically-conductive material, specifically, ITO. The lower electrodes  71 R,  71 G, and  71 B may be configured by, for example, a tin oxide-based material or a zinc oxide-based material. The tin oxide-based material is a material in which tin oxide is doped with a dopant. The zinc oxide-based material is, for example, an aluminum zinc oxide in which zinc oxide is doped with aluminum as a dopant, a gallium zinc oxide in which zinc oxide is doped with gallium as a dopant, an indium zinc oxide in which zinc oxide is doped with indium as a dopant, or the like. Alternatively, it may also be possible to use IGZO, CuI, InSbO 4 , ZnMgO, CuInO 2 , MgIn 2 O 4 , CdOs, ZnSnO 3 , and the like. 
     For example, an electron transport layer or the like may be provided between the lower electrode  71 R and the organic photoelectric conversion layer  72 R, between the lower electrode  71 G and the organic photoelectric conversion layer  72 G, and between the lower electrode  71 B and the organic photoelectric conversion layer  72 B. The electron transport layer is provided to facilitate the supply of electrons generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to the lower electrodes  71 R,  71 G, and  71 B, and is configured by, for example, titanium oxide, zinc oxide, or the like. Titanium oxide and zinc oxide may be stacked to configure the electron transport layer. 
     Each of the organic photoelectric conversion layers  72 R,  72 G, and  72 B absorbs and photoelectrically converts light of a selective wavelength region, and transmits light of another wavelength region. Here, the light of a selective wavelength region is: for example, light of a wavelength region having a wavelength of 620 nm or more and less than 770 nm for the organic photoelectric conversion layer  72 R; for example, light of a wavelength region having a wavelength of 495 nm or more and less than 620 nm for the organic photoelectric conversion layer  72 G; and, for example, light of a wavelength region having a wavelength of 450 nm or more and less than 495 nm for the organic photoelectric conversion layer  72 B. 
     The organic photoelectric conversion layers  72 R,  72 G, and  72 B each have a configuration similar to that of the organic photoelectric conversion layer  12  in the foregoing embodiment. 
     For example, a hole transport layer or the like may be provided between the organic photoelectric conversion layer  72 R and the upper electrode  73 R, between the organic photoelectric conversion layer  72 G and the upper electrode and  73 G, and between the organic photoelectric conversion layer  72 B and the upper electrode  73 B. The hole transport layer is provided to facilitate the supply of holes generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to the upper electrodes  73 R,  73 G, and  73 B, and is configured by, for example, molybdenum oxide, nickel oxide, vanadium oxide, or the like. Alternatively, an organic material such as PEDOT (Poly(3,4-ethylenedioxythiophene)) and TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine) may be used to form the hole transport layer. 
     The upper electrode  73 R is provided to extract holes generated in the organic photoelectric conversion layer  72 R. The upper electrode  73 G is provided to extract holes generated in the organic photoelectric conversion layer  72 G. The upper electrode  73 B is provided to extract holes generated in the organic photoelectric conversion layer  72 G. Holes extracted from the upper electrodes  73 R,  73 G, and  73 B are discharged, via respective transmission paths (unillustrated), to a p-type semiconductor region (unillustrated) in the semiconductor substrate  30 , for example. The upper electrodes  73 R,  73 G, and  73 B are each configured by, for example, an electrically-conductive material such as gold (Au), silver (Ag), copper (Cu), and aluminum (Al). Similarly to the lower electrodes  71 R,  71 G, and  71 B, the upper electrodes  73 R,  73 G, and  73 B may be each configured by a transparent electrically-conductive material. In the photoelectric conversion element  3 , holes extracted from the upper electrodes  73 R,  73 G, and  73 B are discharged. Thus, for example, when multiple photoelectric conversion elements  3  are disposed in the imaging device  100  described later, the upper electrodes  73 R,  73 G, and  73 B may be provided in common to the photoelectric conversion elements  3  (unit pixels P). 
     An insulating layer  74  is provided to insulate the upper electrode  73 R and the lower electrode  71 G from each other, and an insulating layer  75  is provided to insulate the upper electrode  73 G and the lower electrode  71 B from each other. The insulating layers  74  and  75  are each configured by, for example, a metal oxide, a metal sulfide, or an organic matter. Examples of the metal oxide include silicon oxide (SiO x ), aluminum oxide (A1O x ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), zinc oxide (ZnO X ), tungsten oxide (WO x ), magnesium oxide (MgO x ), niobium oxide (NbO x ), tin oxide (SnO x ), and gallium oxide (GaO X ). Examples of the metal sulfide include zinc sulfide (ZnS), and magnesium sulfide (MgS). For example, the band gap of a constituent material of each of the insulating layers  74  and  75  is preferably 3.0 eV or more. 
     As described above, the present technology is also applicable to the photoelectric conversion element (organic 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, which include the respective photoelectric conversion layers (photoelectric conversion layers  72 R,  72 G, and  72 B) configured using organic semiconductor materials. That is, in the photoelectric conversion element  3  of the present modification example, the organic photoelectric conversion layers  72 R,  72 G, and  72 B are formed to have respective domains larger than 1 nm and smaller than 10 nm including one organic semiconductor material in respective predetermined cross-sections between the lower electrodes  71 R,  71 G, and  71 B and the upper electrodes  73 R,  73 G, and  73 B, thereby making it easier for electric charges (electrons and holes) generated in the organic photoelectric conversion layers  72 R,  72 G, and  72 B to move to the lower electrodes  71 R,  71 G, and  71 B and the upper electrodes  73 R,  73 G, and  73 B, respectively. Thus, it is possible to obtain effects similar to those of the foregoing embodiment. 
     2-3. Modification Example 3 
       FIG.  13 A  schematically illustrates a cross-sectional configuration of a photoelectric conversion element  4  of Modification Example 3 of the present disclosure.  FIG.  13 B  schematically illustrates an example of a planar configuration of the photoelectric conversion element  4  illustrated in  FIG.  13 A .  FIG.  13 A  illustrates a cross-section along a line I-I illustrated in  FIG.  13 B . The photoelectric conversion element  4  is, for example, a stacked photoelectric conversion element in which an inorganic photoelectric conversion section  32  and the organic photoelectric conversion section  20  are stacked. In the pixel section  100 A of the imaging device (e.g., imaging device  100 ) including the photoelectric conversion element  4 , a pixel unit  1   a  including four pixels arranged in two rows × two columns is a repeating unit, for example, as illustrated in  FIG.  13 B , and the pixel units  1   a  are repeatedly arranged in array in a row direction and a column direction. 
     The photoelectric conversion element  4  of the present modification example is provided with color filters  54  above the organic photoelectric conversion section  20  (light incident side S 1 ) for the respective unit pixels P. The respective color filters  54  selectively transmit red light (R), green light (G), and blue light (B). Specifically, in the pixel unit  1   a  including the four pixels arranged in two rows × two columns, two color filters each of which selectively transmits green light (G) are disposed on a diagonal line, and color filters that selectively transmit red light (R) and blue light (B) are arranged one by one on the orthogonal diagonal line. Unit pixels (Pr, Pg, and Pb) provided with the respective color filters each detect the corresponding color light, for example, in the organic photoelectric conversion section  20 . That is, the respective pixels (Pr, Pg, and Pb) that detect red light (R), green light (G), and blue light (B) have a Bayer arrangement in the pixel section  100 A. 
     The organic photoelectric conversion section  20  includes, for example, the lower electrode  21 , the insulating layer  22 , the semiconductor layer  23 , the organic photoelectric conversion layer  24 , and the upper electrode  25 . The lower electrode  21 , the insulating layer  22 , the semiconductor layer  23 , and the upper electrode  25  each have a configuration similar to that of the organic photoelectric conversion section  20  in the foregoing Modification Example 1. For example, similarly to the foregoing embodiment, the organic photoelectric conversion layer  24  is formed to have a domain larger than 1 nm and smaller than 10 nm including one organic semiconductor material in a predetermined cross-section between the lower electrode  21  and the upper electrode  25 , and to have absorption between visible light and near infrared light. The inorganic photoelectric conversion section  32  detects light of a wavelength region (e.g., light of an infrared light region (infrared light (IR)) of 700 nm or more and 1000 nm or less) different from that of the organic photoelectric conversion section  20 . 
     In the photoelectric conversion element  4 , light beams (red light (R), green light (G), and blue light (B)) of the visible light region, among the light beams transmitted through the color filters  54 , are absorbed by the organic photoelectric conversion sections  20  of the unit pixels (Pr, Pg, and Pb) provided with the respective color filters. The other light, e.g., infrared light (IR) is transmitted through the organic photoelectric conversion section  20 . This infrared light (IR) transmitted through the organic photoelectric conversion section  20  is detected by the inorganic photoelectric conversion section  32  of each of the unit pixels Pr, Pg, and Pb. Each of the unit pixels Pr, Pg, and Pb generates signal charges corresponding to the infrared light (IR). That is, the imaging device  100   including the photoelectric conversion element  4  is able to simultaneously generate both a visible light image and an infrared light image. 
     2-4. Modification Example 4 
       FIG.  14 A  schematically illustrates a cross-sectional configuration of a photoelectric conversion element  5  of Modification Example 4 of the present disclosure.  FIG.  14 B  schematically illustrates an example of a planar configuration of the photoelectric conversion element  5  illustrated in  FIG.  14 A .  FIG.  14 A  illustrates a cross-section along a line II-II illustrated in  FIG.  14 B . In the foregoing Modification Example 3, the example has been described in which the color filters  54  that selectively transmit red light (R), green light (G), and blue light (B) are provided above the organic photoelectric conversion section  20  (light incident side S 1 ), but the color filter  54  may be provided between the inorganic photoelectric conversion section  32  and the organic photoelectric conversion section  20 , for example, as illustrated in  FIG.  14 A . 
     For example, the color filters  54  in the photoelectric conversion element  5  have a configuration in which color filters (color filters  54 R) each of which selectively transmits at least red light (R) and color filters (color filters  54 B) each of which selectively transmits at least blue light (B) are arranged on the respective diagonal lines in the pixel unit  1   a . Similarly to Modification Example 1, for example, the organic photoelectric conversion section  20  (organic photoelectric conversion layer  24 ) is configured to selectively absorb a wavelength corresponding to green light. This allows the organic photoelectric conversion sections  20  and the respective inorganic photoelectric conversion sections  32  (inorganic photoelectric conversion sections  32 R and  32 G) arranged below the color filters  54 R and  55 B to acquire signals corresponding to blue light (B) or red light (R). The photoelectric conversion element  5  according to the present modification example allows the respective photoelectric conversion sections of R, G, and B to each have larger area than that of a photoelectric conversion element having a typical Bayer arrangement. This makes it possible to improve the S/N ratio. 
     It is to be noted that, in the foregoing Modification Examples 3 and 4, the example has been described in which the lower electrode  21  constituting the organic photoelectric conversion section  20  includes the multiple electrodes (readout electrode  21 A and accumulation electrode  21 B); however, as in the photoelectric conversion element  1  in the foregoing embodiment, the present modification example is also applicable to the case where the lower electrode includes one electrode for each unit pixel P, thus making it possible to obtain effects similar to those of the present modification example. 
     3. Application Examples 
     Application Example 1 
       FIG.  15    illustrates an example of an overall configuration of the imaging device (imaging device  100 ) including the photoelectric conversion element (e.g., photoelectric conversion element  1 ) illustrated in  FIG.  1   , for example. 
     The imaging device  100  is, for example, a CMOS image sensor. The imaging device  100  takes in incident light (image light) from a subject via an optical lens system (unillustrated), and converts the amount of incident light formed on an imaging surface as an image into electric signals in units of pixels to output the electric signals as pixel signals. The imaging device  100  includes the pixel section  100 A as an imaging area on the semiconductor substrate  30 . In addition, the imaging device  100  includes, for example, the vertical drive circuit  111 , the column signal processing circuit  112 , a horizontal drive circuit  113 , an output circuit  114 , a control circuit  115 , and an input/output terminal  116  in a peripheral region of this pixel section  100 A. 
     The pixel section  100 A includes, for example, the multiple unit pixels P that are two-dimensionally arranged in matrix. The unit pixels P are provided, for example, with a pixel drive line Lread (specifically, a row selection line and a reset control line) for each of pixel rows and provided with the vertical signal line Lsig for each of pixel columns. The pixel drive line Lread transmits drive signals for reading signals from the pixels. One end of the pixel drive line Lread is coupled to an output terminal of the vertical drive circuit  111  corresponding to each of the rows. 
     The vertical drive circuit  111  is a pixel drive section that is configured by a shift register, an address decoder, and the like and drives the unit pixels P of the pixel section  100 A on a row-by-row basis, for example. Signals outputted from the respective unit pixels P in the pixel rows selectively scanned by the vertical drive circuit  111  are supplied to the column signal processing circuit  112  through the respective vertical signal lines Lsig. The column signal processing circuit  112  is configured by an amplifier, a horizontal selection switch, and the like provided for each of the vertical signal lines Lsig. 
     The horizontal drive circuit  113  is configured by a shift register, an address decoder, and the like. The horizontal drive circuit  113  drives horizontal selection switches of the column signal processing circuit  112  in order while scanning the horizontal selection switches. The selective scanning by this horizontal drive circuit  113  causes signals of the respective pixels transmitted through the respective vertical signal lines Lsig to be outputted to a horizontal signal line  121  in order and causes the signals to be transmitted to the outside of the semiconductor substrate  30  through the horizontal signal line  121 . 
     The output circuit  114  performs signal processing on signals sequentially supplied from the respective column signal processing circuits  112  via the horizontal signal line  121 , and outputs the signals. The output circuit  114  performs, for example, only buffering in some cases, and performs black level adjustment, column variation correction, various kinds of digital signal processing, and the like in other cases. 
     The circuit portion including the vertical drive circuit  111 , the column signal processing circuit  112 , the horizontal drive circuit  113 , the horizontal signal line  121 , and the output circuit  114  may be formed directly on the semiconductor substrate  30 , or may be provided on an external control IC. In addition, the circuit portion may be formed in another substrate coupled by a cable or the like. 
     The control circuit  115  receives a clock supplied from the outside of the semiconductor substrate  30 , data for an instruction about an operation mode, and the like and also outputs data such as internal information on the imaging device  100 . The control circuit  115  further includes a timing generator that generates a variety of timing signals, and controls driving of the peripheral circuits including the vertical drive circuit  111 , the column signal processing circuit  112 , the horizontal drive circuit  113 , and the like on the basis of the variety of timing signals generated by the timing generator. 
     The input/output terminal  116  exchanges signals with the outside. 
     Application Example 2 
     The above-described imaging device  100  or the like is applicable, for example, to any type of electronic apparatus with an imaging function including a camera system such as a digital still camera and a video camera, a mobile phone having an imaging function, and the like.  FIG.  16    illustrates an outline configuration of an electronic apparatus  1000 . 
     The electronic apparatus  1000  includes, for example, a lens group  1001 , the imaging device  100 , a DSP (Digital Signal Processor) circuit  1002 , a frame memory  1003 , a display unit  1004 , a recording unit  1005 , an operation unit  1006 , and a power source unit  1007 . They are coupled to each other via a bus line  1008 . 
     The lens group  1001  takes in incident light (image light) from a subject, and forms an image on an imaging surface of the imaging device  100 . The imaging device  100  converts the amount of incident light formed as an image on the imaging surface by the lens group  1001  into electric signals in units of pixels, and supplies the DSP circuit  1002  with the electric signals as pixel signals. 
     The DSP circuit  1002  is a signal processing circuit that processes a signal supplied from the imaging device  100 . The DSP circuit  1002  outputs image data obtained by processing the signal from the imaging device  100 . The frame memory  1003  temporarily holds the image data processed by the DSP circuit  1002  in units of frames. 
     The display unit  1004  includes, for example, a panel-type display device such as a liquid crystal panel or an organic EL (Electro Luminescence) panel, and records image data of a moving image or a still image captured by the imaging device  100  in a recording medium such as a semiconductor memory or a hard disk. 
     The operation unit  1006  outputs an operation signal for a variety of functions of the electronic apparatus  1000  in accordance with an operation by a user. The power source unit  1007  appropriately supplies the DSP circuit  1002 , the frame memory  1003 , the display unit  1004 , the recording unit  1005 , and the operation unit  1006  with various kinds of power for operations of these supply targets. 
     4. Practical Application Examples 
     Example of Practical Application to In-Vivo Information Acquisition System 
     Further, the technology according to an embodiment of the present disclosure (present technology) is applicable to various products. For example, the technology according to an embodiment of the present disclosure may be applied to an endoscopic surgery system. 
       FIG.  17    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.  17   , 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 description has been given above of one example of the in-vivo information acquisition system, to which the technology according to an embodiment of the present disclosure is applicable. The technology according to an embodiment of the present disclosure is applicable to, for example, the image pickup unit  10112  of the configurations described above. This makes it possible to improve detection accuracy. 
     Example of Practical Application to Endoscopic Surgery System 
     The technology according to an embodiment of the present disclosure (present technology) is applicable to various products. For example, the technology according to an embodiment of the present disclosure may be applied to an endoscopic surgery system. 
       FIG.  18    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.  18   , 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.  19    is a block diagram depicting an example of a functional configuration of the camera head  11102  and the CCU  11201  depicted in  FIG.  18   . 
     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 description has been given above of one example of the endoscopic surgery system, to which the technology according to an embodiment of the present disclosure is applicable. The technology according to an embodiment of the present disclosure is applicable to, for example, the image pickup unit  11402  of the configurations described above. Applying the technology according to an embodiment of the present disclosure to the image pickup unit  11402  makes it possible to improve detection accuracy. 
     It is to be noted that although the endoscopic surgery system has been described as an example here, the technology according to an embodiment of the present disclosure may also be applied to, for example, a microscopic surgery system, and the like. 
     Example of Practical Application to Mobile Body 
     The technology according to an embodiment of the present disclosure (present technology) is applicable to various products. For example, the technology according to an embodiment of the present disclosure may be achieved in the form of an apparatus to be mounted to a mobile body of any kind. Non-limiting examples of the mobile body may include an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, any personal mobility device, an airplane, an unmanned aerial vehicle (drone), a vessel, a robot, a construction machine, and an agricultural machine (tractor). 
       FIG.  20    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.  20   , 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 automated driving, which makes the vehicle to travel automatedly 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.  20   , 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.  21    is a diagram depicting an example of the installation position of the imaging section  12031 . 
     In  FIG.  21   , 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.  21    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’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 automated driving that makes the vehicle travel automatedly 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. Examples 
     Next, description is given in detail of Examples of the present disclosure. In the present Example, a device sample having a cross-sectional configuration illustrated in  FIG.  22    and a domain confirmation sample having a cross-sectional configuration illustrated in  FIG.  23    were prepared to evaluate a domain size, a domain cycle, and response characteristics. 
     Experimental Example 1 
     First, an Si substrate  81  provided with an ITO electrode (lower electrode  11 ) having a thickness of 50 nm was cleaned using UV/ozone treatment. Thereafter, a resistive heating method was used while rotating a substrate holder at a substrate stage temperature of 25° C. under a vacuum of 1 × 10 -5  Pa or less to form a buffer layer  17 A having a thickness of 5 nm, the organic photoelectric conversion layer  12  having a thickness of 150 nm, and a buffer layer  18 B having a thickness of 5 nm in this order. Subsequently, ITO was formed as the upper electrode  13  to have a thickness of 100 nm by sputtering, and then subjected to heating treatment at 120° C. It is to be noted that the composition ratio between the hole-transporting material and the electron-transporting material constituting the organic photoelectric conversion layer  12  was set to 2:1. As described above, the device samples having a photoelectric conversion region of 1 mm × 1 mm was prepared. 
     In addition, a similar method was used to form an amorphous carbon  82  having a thickness of 5 nm, the buffer layer  17 A having a thickness of 5 nm, and the organic photoelectric conversion layer  12  having a thickness of 10 nm in this order, which were then subjected to heating treatment at 120° C. to prepare a domain observation sample. 
     Experimental Example 2 
     In Experimental Example 2, a device sample and a domain observation sample were prepared using a method similar to that in Experimental Example 1 except that the substrate stage temperature was set to 35° C. 
     Experimental Example 3 
     In Experimental Example 3, a device sample and a domain observation sample were prepared using a method similar to that in Experimental Example 1, except that the substrate stage temperature was set to 45° C., the composition ratio between the hole-transporting material and the electron-transporting material constituting the organic photoelectric conversion layer  12  was set to 2:3, and the heating treatment temperature was set to 150° C. 
     Comparison Between Device Sample and Domain Observation Sample 
     Comparison in a domain distribution between the device sample and the domain observation sample was confirmed as follows. 
     As for the device sample, as illustrated in  FIG.  24 A , first, film formation was performed up to the lower electrode  11 , the buffer layer  17 A, and the organic photoelectric conversion layer  12  on the Si substrate  81 , and then osmium tetraoxide staining was performed. Thereafter, as illustrated in  FIG.  24 B , a protective film  83  for preventing damage upon sampling was formed on the organic photoelectric conversion layer  12 . After sampling, as illustrated in  FIG.  24 C , the sample was rotated by 90°, and supported on a TEM observation grid. Thereafter, focused ion beam (Focused Ion Beam; FIB, HELIOS NANOLAB  400 S manufactured by FEI Company) was used to work and remove regions A 1  and A 2  illustrated in  FIG.  25   .  FIGS.  26  and  27    illustrate the working procedures. First, the samples were rotated by about 52°, and the protective film  83  was worked using the FIB in an arrow (solid line) direction. Subsequently, the lower electrode  11  and buffer layer  17 A were worked using the FIB in an arrow (broken line) direction to allow a region B to be a thin film of only the organic photoelectric conversion layer  12  as illustrated in  FIG.  27   , and the thin film was set as a flake sample  1 . Further, a layer damaged by the FIB working was removed by an argon ion beam. 
     As for the domain observation sample, film formation was performed up to the organic photoelectric conversion layer  12  illustrated in  FIG.  23   , and then osmium tetraoxide staining was performed to obtain a flake sample  2 . 
     HAADF-STEM images of the flake samples 1 and 2 obtained by the above-described steps were observed. A region reflected in black contrast in the HAADF-STEM image is a crystal domain, and a region reflected in white contrast is a stained amorphous domain. In the flake samples 1 and 2, the numbers of crystal domains confirmed in a square region with each side being 100 nm were  33  and  34 , respectively, and were confirmed to be substantially equal to each other. 
     Evaluation of Domain Size and Domain Cycle 
     Domain size was measured using XRD as follows. First, the domain observation sample was used to perform measurement by means of a thin-film method using a Cu-Kα ray and a divergence slit of 1 mm. No light-receiving slit was used because of weak diffraction intensity of the organic photoelectric conversion layer  12 . Under such a condition, the full width at half maximum FWHM of a diffraction peak derived from a measured organic crystal was measured; in a case where the FWHM thereof was 0.015 rad or more, favorable response characteristics were obtained. The value of the FWHM also varies depending on diffraction angles and on presence or absence of the light-receiving slit; converted crystallite size at 0.015 rad was about 10 nm. 
     As for the domain cycle, analysis software attached to an electron microscope was used to determine autocorrelation of the HAADF-STEM image, and a distance to be the local maximum value was defined as an average cycle of the domain. 
     Evaluation of Response Characteristics 
     Response characteristics of Experimental Examples 1 to 3 were evaluated. The response characteristics were evaluated by measuring a rate at which a bright current value observed at the time of light irradiation fell after the light irradiation was stopped using a semiconductor parameter analyzer. Specifically, the amount of light to be irradiated from a light source to the photoelectric conversion element via a filter was set to 1.62 µW/cm 2 , and a bias voltage to be applied between the electrodes was set to -2.6 V. After a steady current was observed in this state, the light irradiation was stopped and the current was observed to decay. Subsequently, an area surrounded by a current-time curve and the dark current was set to 100%, and time until the area corresponds to 3% was used as an index of responsiveness. All the evaluations were made at room temperature. 
     Table 1 summarizes a composition ratio between the hole-transporting material and the electron-transporting material constituting each of the organic photoelectric conversion layers  12  formed as Experimental Examples 1 to 3, a film-forming substrate temperature, a heating treatment temperature, a domain size, a domain cycle, relative time at which a current value after light irradiation OFF is reduced to 1/25, and a relative current at 10 ms after the irradiation OFF.  FIGS.  28  to  30    schematically illustrate TEM images of Experimental Examples 1 to 3.  FIG.  31    illustrates results of X-ray diffraction of Experimental Examples 1 to 3.  FIGS.  32  to  34    illustrate average distances (average cycles) between crystal domains in Experimental Examples 1 to 3.  
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
               
             
               
                   
                 Crystal: Amorphous 
                 Film-Forming Substrate Temperature (°C) 
                 Heating Treatment Temperature (°C) 
                 Domain Size (nm) 
                 Domain Cycle (nm) 
                 Relative Time at which Current Value after Light Irradiation OFF Is Reduced to 1/25 
                 Relative Current at 10 ms after Light Irradiation OFF 
               
             
            
               
                 Experimental Example 1 
                 2:1 
                 25 
                 120 
                 3 
                 4 
                 0.05 
                 0.1 
               
               
                 Experimental Example 2 
                 2:1 
                 35 
                 120 
                 6 
                 8 
                 0.1 
                 0.2 
               
               
                 Experimental Example 3 
                 2:3 
                 45 
                 150 
                 8 
                 10 
                 1 
                 1 
               
            
           
         
       
     
     It is appreciated from Table 1 that a smaller domain size and a smaller domain cycle allow the response characteristics to be improved. 
     Description has been given hereinabove referring to the embodiment, Modification Examples 1 to 4, and Examples; however, the content of the present disclosure is not limited to the foregoing embodiment and the like, and may be modified in a wide variety of ways. For example, in the foregoing embodiment, 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 detect, respectively, blue light and red light are stacked. However, the content of the present disclosure is not limited to such a structure. That is, no limitation is made to visible light; red light or blue light may be detected in the organic photoelectric conversion section, or green light may be detected in the inorganic photoelectric conversion section. 
     In addition, the numbers of the organic photoelectric conversion section and the inorganic photoelectric conversion section, and the ratio therebetween are not limitative. Two or more organic photoelectric conversion sections may be provided, or color signals of multiple colors may be obtained only by the organic photoelectric conversion sections. Further, no limitation is made to the structure in which the organic photoelectric conversion section and the inorganic photoelectric conversion section are stacked in the vertical direction; they may be arranged side by side along the substrate surface. 
     Moreover, the foregoing embodiment, and the like exemplify the configuration of the back-illuminated imaging device; however, the content of the present disclosure is also applicable to a front-illuminated imaging device. In addition, the photoelectric conversion element of the present disclosure does not necessarily include all of the components described in the foregoing embodiment, and may include any other layer, conversely. 
     It is to be noted that the effects described herein are merely exemplary and are not limitative, and may further include other effects. 
     It is to be noted that the present technology may also have the following configurations. According to the present technology having the following configurations, an organic photoelectric conversion layer having a domain of 1 nm or more and 10 nm or less including one organic semiconductor material is provided in a predetermined cross-section between a first electrode and a second electrode. This improves movement of electric charges having undergone charge separation in the organic photoelectric conversion layer, thus making it possible to improve the response characteristics. 
     (1) A photoelectric conversion element including:
   a first electrode;   a second electrode disposed to be opposed to the first electrode; and   an organic photoelectric conversion layer provided between the first electrode and the second electrode, the organic photoelectric conversion layer having, in the layer, a domain being larger than 1 nm and smaller than 10 nm and including one organic semiconductor material in a predetermined cross-section between the first electrode and the second electrode.   
   (2) The photoelectric conversion element according to (1), in which 
   the domain at least partially has a crystal property, and   a ratio of the one organic semiconductor material having a crystal structure in the organic photoelectric conversion layer is 20% or more and 70% or less.   
   (3) The photoelectric conversion element according to (1) or (2), in which a full width at half maximum of a crystal peak of the one organic semiconductor material by X-ray diffraction is 0.015 rad or more and 0.15 rad or less.   (4) The photoelectric conversion element according to any one of (1) to (3), in which an average cycle of the domain determined from autocorrelation of a two-dimensional distribution in the organic photoelectric conversion layer is 3 nm or more and 5 nm or less.   (5) The photoelectric conversion element according to any one of (1) to (4), in which the organic photoelectric conversion layer includes a hole-transporting material and an electron-transporting material.   (6) The photoelectric conversion element according to (5), in which 
   the one organic semiconductor material includes the hole-transporting material or the electron-transporting material, or   the one organic semiconductor material includes both of the hole-transporting material and the electron-transporting material.   
   (7) The photoelectric conversion element according to (5) or (6), in which the organic photoelectric conversion layer includes, as the hole-transporting material, an organic material having an ionization potential of 6 eV or less.   (8) The photoelectric conversion element according to (7), in which 
   the organic material includes carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, and sulfur atoms, and includes 9 or more and 13 or less aromatic rings in an entire molecule,   the number of the aromatic rings forming a largest condensed ring is 5 or less,   the number of single bonds linking the aromatic rings is 5 or more and 9 or less, and   a length of a short side in the entire molecule is 15% or more and 30% or less of a long side.   
   (9) The photoelectric conversion element according to any one of (5) to (8), in which the organic photoelectric conversion layer includes, as the electron-transporting material, fullerene or a derivative thereof.   (10) The photoelectric conversion element according to any one of (5) to (9), in which the organic photoelectric conversion layer further includes a pigment material having a local maximum absorption wavelength in a visible region (450 nm or more and 750 nm or less).   (11) An imaging device including pixels, the pixels each including one or multiple organic photoelectric conversion sections, 
   the one or the multiple organic photoelectric conversion sections including 
   a first electrode,   a second electrode disposed to be opposed to the first electrode, and   an organic photoelectric conversion layer provided between the first electrode and the second electrode, the organic photoelectric conversion layer having, in the layer, a domain being larger than 1 nm and smaller than 10 nm and including one organic semiconductor material in a predetermined cross-section between the first electrode and the second electrode.   
   
   (12) The imaging device according to (11), in which, in each of the pixels, the one or the multiple organic photoelectric conversion sections and one or multiple inorganic photoelectric conversion sections are stacked, the one or the multiple inorganic photoelectric conversion sections performing photoelectric conversion of a wavelength region different from the organic photoelectric conversion section.   (13) The imaging device according to (12), in which 
   the inorganic photoelectric conversion section is formed to be embedded in a semiconductor substrate, and   the organic photoelectric conversion section is formed on a side of a first surface of the semiconductor substrate.   
   (14) The imaging device according to (13), in which a multilayer wiring layer is formed on a side of a second surface, of the semiconductor substrate, opposite to the side of the first surface.   (15) The imaging device according to (14), in which 
   the organic photoelectric conversion section performs photoelectric conversion of green light, and   the inorganic photoelectric conversion section that performs photoelectric conversion of blue light and the inorganic photoelectric conversion section that performs photoelectric conversion of red light are stacked in the semiconductor substrate.   
   (16) The imaging device according to any one of (11) to (15), in which, in each of the pixels, the multiple organic photoelectric conversion sections are stacked, the multiple organic photoelectric conversion sections performing photoelectric conversion of wavelength regions different from one another.   

     This application claims the benefit of Japanese Priority Patent Application JP2020-106510 filed with the Japan Patent Office on Jun. 19, 2020, the entire contents of which are incorporated herein 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.