Patent Publication Number: US-11043181-B2

Title: Display unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Priority Patent Application No. 2018-094851 filed on May 16, 2018, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The disclosure relates to a display unit. 
     A variety of display units have been proposed which include organic electroluminescent elements. Reference is made to Japanese Unexamined Patent Application Publication Nos. 2013-156635 and 2014-072126, for example. 
     SUMMARY 
     It is desired that a display unit display an image based on an image signal in a display region while performing a process of enhancing a display quality in the display region, to achieve novel image-display representation. 
     It is desirable to provide a display unit that makes it possible to achieve image displaying based on an image signal in a display region while enhancing a display quality in the display region to achieve novel image-display representation. 
     A display unit according to one embodiment of the disclosure includes a display panel that includes a plurality of pixels arranged in a matrix. Each of the pixels includes: one of an optical modulator and a self-luminescent element; one of an electrochromic element, an electrophoretic element, and an electrowetting element; and a pixel circuit configured to selectively drive the one of the optical modulator and the self-luminescent element, and the one of the electrochromic element, the electrophoretic element, and the electrowetting element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the technology and are incorporated in and constitute a part of this specification. The drawings illustrate example embodiments and, together with the specification, serve to explain the principles of the technology. 
         FIG. 1  is a schematic diagram of an example configuration of a display unit according to one embodiment of the disclosure. 
         FIG. 2  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 1 . 
         FIG. 3  is an example schematic view of an organic EL panel illustrated in  FIG. 1 . 
         FIG. 4  is an example cross-sectional view of the organic EL panel taken along the line A-A in  FIG. 3 . 
         FIG. 5  is an example cross-sectional view of the organic EL panel taken along the line A-A in  FIG. 3 . 
         FIG. 6  is an example cross-sectional view of the organic EL panel taken along the line A-A in  FIG. 3 . 
         FIG. 7  is a schematic view of the organic EL panel of  FIG. 3  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 8  is a schematic view of the organic EL panel of  FIG. 3  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 9  is a schematic view of the organic EL panel of  FIG. 3  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 10  is a schematic view of the organic EL panel of  FIG. 3  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIGS. 11A to 11D  are diagrams illustrating example manufacturing processes for the organic EL panel of  FIG. 3 . 
         FIGS. 12A to 12C  are diagrams illustrating example manufacturing processes subsequent to the manufacturing process illustrated in  FIG. 11D . 
         FIG. 13  is a diagram illustrating example waves of various voltages applied to the organic EL panel of  FIG. 3  and example waves of various voltages generated in the organic EL panel of  FIG. 3 . 
         FIG. 14  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 1  according to one modification example of the disclosure. 
         FIG. 15  is a diagram illustrating example waves of various voltages applied to an organic EL panel provided with the subpixels illustrated in  FIG. 14  and example waves of various voltages generated in the organic EL panel provided with the subpixels illustrated in  FIG. 14 . 
         FIG. 16  is an example cross-sectional view of the organic EL panel taken along the line A-A in  FIG. 3  according to one modification example of the disclosure. 
         FIG. 17  is a schematic view of the organic EL panel of  FIG. 16  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 18  is a schematic view of the organic EL panel of  FIG. 16  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 19  is a schematic view of the organic EL panel of  FIG. 16  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 20  is a schematic view of the organic EL panel of  FIG. 16  for illustrating example image enhancement according to one embodiment of the disclosure. 
         FIG. 21  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 16 . 
         FIG. 22  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 16 . 
         FIG. 23  is a cross-sectional view of the organic EL panel of  FIG. 3  according to one modification example of the disclosure. 
         FIG. 24  is an example plan view of the organic EL panel of  FIG. 23 . 
         FIG. 25  is a cross-sectional view of the organic EL panel of  FIG. 3  according to one modification example of the disclosure. 
         FIG. 26  is an example plan view of the organic EL panel of  FIG. 25 . 
         FIG. 27  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 3  according to one modification example of the disclosure. 
         FIG. 28  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 14  according to one modification example of the disclosure. 
         FIG. 29  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 27  according to one modification example of the disclosure. 
         FIG. 30  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIG. 28  according to one modification example of the disclosure. 
         FIG. 31  is an example circuit diagram of a subpixel included in each pixel illustrated in  FIGS. 27 to 30  according to one modification example of the disclosure. 
         FIG. 32  is an example schematic diagram of an electrophoretic element used in place of an electrochromic element. 
         FIG. 33  is a diagram illustrating an example state of the electrophoretic element of  FIG. 32  to which a voltage is applied. 
         FIG. 34  is an example schematic diagram of an electrowetting element used in place of the electrochromic element. 
         FIG. 35  is an example diagram illustrating an example state of the electrowetting element of  FIG. 34  to which a voltage is applied. 
         FIG. 36  is an example perspective view of an appearance of an electronic apparatus that includes a display unit according to one embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, some example embodiments of the disclosure are described in detail, in the following order, with reference to the accompanying drawings. Note that the following description is directed to illustrative examples of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiments which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Note that the like elements are denoted with the same reference numerals, and any redundant description thereof will not be described in detail. 
     1. Embodiment 
     Example Configuration 
       FIG. 1  is a schematic diagram of an example configuration of a display unit  1  according to an example embodiment of the disclosure.  FIG. 2  is an example circuit diagram of a subpixel  12  included in each pixel of the display unit  1 . The display unit  1  may include, for example, an organic electroluminescent (EL) panel  10 , a controller  20 , and a driver  30 . The driver  30  may be mounted on an outer edge portion of the organic EL panel  10 , for example. The organic EL panel  10  includes a plurality of pixels  11  arranged in a matrix. The controller  20  and the driver  30  may drive the organic EL panel  10  (i.e., the pixels  11 ) on the basis of an external image signal Din and an external synchronizing signal Tin. The organic EL panel  10  may correspond to a specific but non-limiting example of “display panel” according to one embodiment of the disclosure. 
     [Organic EL Panel  10 ] 
     In response to the active-matrix driving of the pixels  11  performed by the controller  20  and the driver  30 , the organic EL panel  10  may display an image based on the external image signal Din and the external synchronizing signal Tin. Additionally, the organic EL panel  10  may perform an enhancement of the image that is displayed on the basis of the image signal Din and the synchronizing signal Tin, in response to the active-matrix driving. The enhancement of the image is described in detail below. The organic EL panel  10  may include multiple scanning lines WSL 1 , WSL 2 , and WSL 3  that extend in a row direction, multiple signal lines DTL extending in a column direction, and the multiple pixels  11  arranged in matrix. 
     The scanning lines WSL 1  may be used to select the pixels  11 . For example, a selection pulse may be supplied through the scanning lines WSL 1  to the pixels  11  to select the pixels  11  on a predetermined unit basis. The pixels  11  may be selected on a pixel-row basis, for example. The scanning lines WSL 2  and WSL 3  may be used to select electrochromic (EC) elements  15  (described below) in each of the pixels  11 . In other words, the scanning lines WSL 2  and WSL 3  may be used to apply a voltage to the EC elements  15 . The signal lines DTL may be used to supply a signal voltage Vsig based on the image signal Din to the pixels  11 . For example, a data pulse that includes a signal voltage Vsig may be supplied through the signal lines DTL to the pixels  11 . 
     The pixels  11  may each include, for example, a subpixel  12  emitting red light, a subpixel  12  emitting green light, a subpixel emitting blue light, and a subpixel emitting white light. In other words, a predetermined number of the subpixels  12  may be grouped into a color pixel (i.e., the pixel  11 ). Optionally, the pixel  11  may further include a subpixel  12  emitting light of another color, such as yellow. Alternatively, the pixel  11  may include no subpixel  12  emitting white light. Still alternatively, the pixel  11  may include a subpixel  12  emitting yellow light in place of the subpixel  12  emitting white light. 
     Each of the signal lines DTL may be coupled to an output terminal of a horizontal selector  31  described below. Each of the signal lines DTL may be allocated to its corresponding pixel column, for example. The scanning lines WSL 1 , WSL 2 , and WSL 3  may be each coupled to an output terminal of a write scanner  32  described below. Each of the scanning lines WSL 1  may be allocated to its corresponding pixel row, for example. Additionally, each of the scanning lines WSL 2  may be allocated to its corresponding pixel row, for example. Furthermore, each of the scanning lines WSL 3  may be allocated to its corresponding pixel row, for example. 
     Each of the subpixels  12  includes a pixel circuit  13 , an organic EL element  14 , and an electrochromic (EC) element  15 . The configurations of the organic EL element  14  and the EC element  15  are described in detail below. The organic EL element  14  may correspond to a specific but non-limiting example of “self-luminescent element” according to one embodiment of the disclosure. The EC element  15  may correspond to a specific but non-limiting example of “electrochromic element” according to one embodiment of the disclosure. 
     The pixel circuit  13  may control light emission and light extinction of the organic EL element  14 , and a change in state of the EC element  15 . The pixel circuit  13  may hold a voltage written into the subpixel  12  through write scanning described below. The pixel circuit  13  may include, for example, a driving transistor Tr 1 , a writing transistor Tr 2 , switching transistors Tr 3  and Tr 4 , and a storage capacitor Cs. 
     The writing transistor Tr 2  may control application of the signal voltage Vsig to a gate of the driving transistor Tr 1 . The signal voltage Vsig may correspond to the image signal Din. For example, the writing transistor Tr 2  may sample a voltage of the signal line DTL and write the sampled voltage into the gate of the driving transistor Tr 1 . The driving transistor Tr 1  may be coupled in series to the organic EL element  14 . The driving transistor Tr 1  may drive the organic EL element  14 . The driving transistor Tr 1  may control an electric current flowing in the organic EL element  14  on the basis of the magnitude of the voltage sampled at the writing transistor Tr 2 . The storage capacitor Cs may hold a predetermined voltage between the gate and source of the driving transistor Tr 1 . The storage capacitor Cs may hold a gate-source voltage Vgs of the driving transistor Tr 1  at a constant level for a predetermined period of time. 
     The switching transistors Tr 3  and Tr 4  may control application of a signal voltage Vsig 2  to the EC element  15 . The signal voltage Vsig 2  may be irrelevant to the image signal Din. The switching transistors Tr 3  and Tr 4  may be coupled in series to the EC element  15 . The EC element  15  may be coupled in parallel to the organic EL element  14 . An electric current path P 2  of an electric current flowing through the switching transistor Tr 4 , the EC element  15 , and the switching transistor Tr 3  may intersect with an electric current path P 1  of an electric current flowing through the driving transistor Tr 1  and the organic EL element  14 , at a node between the EC element  15  and the organic EL element  14 . This allows the pixel circuit  13  to selectively drive the organic EL element  14  and the EC element  15 . Note that the pixel circuit  13  may have a circuit configuration that includes the 4Tr1C circuit described above and additional capacitors and transistors. Alternatively, the pixel circuit  13  may have a different circuit configuration from the 4Tr1C circuit described above. 
     Each of the signal lines DTL may be coupled to the output terminal of the horizontal selector  31  described below and a source or drain of the writing transistor Tr 2 . Each of the scanning lines WSL 1  may be coupled to the output terminal of the write scanner  32  and a gate of the writing transistor Tr 2 . Each of the scanning lines WSL 2  may be coupled to the output terminal of the write scanner  32  described below and the gate of the switching transistor Tr 3 . Each of the scanning lines WSL 3  may be coupled to the output terminal of the write scanner  32  described below and the gate of the switching transistor Tr 3 . 
     The gate of the writing transistor Tr 2  may be coupled to the scanning line WSL 1 . One of the source and drain of the writing transistor Tr 2  may be coupled to the signal lines DTL. The other of the source and drain of the writing transistor Tr 2  that is uncoupled to the signal lines DTL may be coupled to the gate of the driving transistor Tr 1 . One of source and drain of the driving transistor Tr 1  may be coupled to a wiring line at a voltage Vcc. The other of the source and drain of the driving transistor Tr 1  that is uncoupled to the wiring line at the voltage Vcc may be coupled to an anode (i.e., an electrode  12 A described below) of the organic EL element  14 . One terminal of the storage capacitor Cs may be coupled to the gate of the driving transistor Tr 1 . In an example where the driving transistor Tr 1  is a p-channel transistor, the other terminal of the storage capacitor Cs may be coupled to the wiring line at the voltage Vcc. 
     The gate of the switching transistor Tr 3  may be coupled to the scanning line WSL 2 . One of source and drain of the switching transistor Tr 3  may be coupled to the anode of the organic EL element  14 . The other of the source and drain of the switching transistor Tr 3  that is uncoupled to the anode of the organic EL element  14  may be coupled to the wiring line at the voltage Vss. A gate of the switching transistor Tr 4  may be coupled to the scanning line WSL 3 . One of the source and drain of the switching transistor Tr 4  may be coupled to the EC element  15 . The other of the source and drain of the switching transistor Tr 4  that is uncoupled to the EC element  15  may be coupled to the wiring line at the signal voltage Vsig  2 . The EC element  15  may be coupled to the anode of the organic EL element  14  and the source or drain of the switching transistor Tr 4 . 
     [Driver  30 ] 
     The driver  30  may include, for example, the horizontal selector  31  and the write scanner  32 . The horizontal selector  31  may apply the analog signal voltage Vsig received from the controller  20  to each of the signal lines DTL in response to (in synchronization with) a control signal. The write scanner  32  may scan the subpixels  12  on a predetermined unit basis. 
     [Controller  20 ] 
     The controller  20  will now be described. The controller  20  may perform a predetermined correction on an external digital image signal Din, and generate a signal voltage Vsig on the basis of the corrected image signal, for example. The controller  20  may output the generated signal voltage Vsig to the horizontal selector  31 , and output a control signal to each circuit in the driver  30  in response to (in synchronization with) an external synchronizing signal Tin. 
     The organic EL element  14  and the EC element  15  will now be described with reference to  FIGS. 3 and 4 .  FIG. 3  illustrates an example schematic configuration of the organic EL panel  10 .  FIG. 4  illustrates an example cross-sectional configuration of the organic EL panel  10  taken along the line A-A of  FIG. 3  (i.e., along a row direction of the pixels  11 ). 
     In  FIG. 3 , a region patterned with dots may be provided with a light-emitting layer described below. The subpixel  12  emitting red light may be provided in a region R, the subpixel  12  emitting green light in a region G, the subpixel  12  emitting blue light in a region B, the subpixel  12  emitting white light in a region W. In  FIG. 3 , each of the pixels  11  may include four subpixels  12 . 
     The organic EL panel  10  may include the pixels  11  arranged in a matrix. As described above, each of the pixels  11  may include, for example, the subpixel  12  emitting red light, the subpixel  12  emitting green light, the subpixel  12  emitting blue light, and the subpixel  12  emitting white light. The organic EL panel  10  may also include a plurality of non-luminescent pixels each including a light transmissive region  24 B that transmits visual light. 
     The subpixel  12  emitting red light may include the organic EL element  14  emitting red light. The subpixel  12  emitting green light may include the organic EL element  14  emitting green light. The subpixel  12  emitting blue light may include the organic EL element  14  emitting blue light. The subpixel  12  emitting white light may include the organic EL element  14  emitting white light. 
     The organic EL panel  10  may include a substrate  21 . The substrate  21  may include, for example, a base that supports the organic EL elements  14  and the EC elements  15 , and a wiring layer provided on the base. The base of the substrate  21  may be, for example, a substrate having transmittance for visible light. The base of the substrate  21  may include, for example, non-alkali glass, soda glass, nonfluorescent glass, phosphate glass, borate glass, or quartz. Alternatively, the base of the substrate  21  may include, for example, acrylic resin, styrene resin, polycarbonate resin, epoxy resin, polyethylene, polyester, silicone resin, or alumina. Still alternatively, the base of the substrate  21  may be a substrate having no transmittance for visible light. The wiring layer of the substrate  21  may include, for example, the pixel circuits  13  of the respective pixels  11 . 
     The organic EL panel  10  may include, on the substrate  21 , the organic EL elements  14  each included in the subpixel  12 , and the EC elements  15  each included in the subpixel  12 , for example. The organic EL panel  10  may also include a sealing layer  26  that covers the organic EL elements  14  and the EC elements  15 . The sealing layer  26  may include, for example, a light-transmissive resin. In an alternative example illustrate in  FIG. 3 , for example, the EC element  15  may be shared between the subpixels  12  in each of the pixels  11 . In a still alternative example, the EC element  15  may be shared between the subpixels  12  in the plurality of pixels  11 . 
     The organic EL element  14  may be a display element that performs light emission and light extinction in response to application of the signal voltage Vsig based on the image signal Din. The organic EL element  14  may include, for example, an electrode  14 A, an indium tin oxide (ITO) layer  14 B, an EL layer  14 C, and an ITO layer  14 D, in this order, on the substrate  21 . The electrode  14 A may serve as an anode, and the ITO layer  14 D may serve as a cathode. In place of the ITO layer  14 B, a layer that includes a transparent electrically-conductive material, such as indium zinc oxide (IZO), may be provided. In place of the ITO layer  14 D, a layer that include a transparent electrically-conductive material, such as IZO, may be provided. The EL layer  14 C may include, for example, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer that are stacked in this order from the substrate  21 . 
     In this example embodiment, the hole injection layer may enhance efficiency in injecting holes. The hole transport layer may transfer, to the light-emitting layer, holes injected from the electrode  14 A serving as the anode. The light-emitting layer may emit light of a predetermined color through recombination of an electron and a hole. The electron transport layer may transfer, to the light-emitting layer, electrons injected from the ITO layer  14 D serving as the cathode. The electron injection layer may enhance efficiency in injecting electrons. 
     The electrode  14 A may be provided on the substrate  21 , for example. The electrode  14 A may be a reflective electrode that includes a material having reflectivity, such as aluminum (Al), silver (Ag), an aluminum alloy or a silver alloy. In an example where the electrode  14 A has optical reflectivity and the ITO layer  14 D has optical transparency, the organic EL element  14  may have a top-emission structure that emits light through the ITO layer  14 D. In an alternative example, the ITO layer  14 D may be a portion of an ITO layer  25  extending over the entire display region of the organic EL panel  10 . In this example, the ITO layer  25  may be shared between the organic EL elements  14 . 
     The EC elements  15  may be enhancement elements reversibly change their color in response to application of a voltage, and thereby perform an enhancement of an image on the organic EL panel  10  (i.e., an image generated through light-emission of the organic EL elements  14 ). The signal voltage Vsig 2  irrelevant to the image signal Din may be applied to the EC elements  15 . The term “enhancement” as used herein refers to color display, such as black display and white display, and modulation of transmittance between a transparent state and a reflective state, in a region adjacent to the organic EL element  14  emitting light, without directly changing the image generated through the light emission of the organic EL element  14 . The EC element  15  may perform such an enhancement on the image. 
     The EC element  15  may include, for example, an electrode  15 A, an EC layer  15 B, and an electrode  15 C that are stacked in this order, on the substrate  21 . The electrodes  15 A and  15 C may include, for example, a transparent electrically-conductive material, such as ITO or IZO. The EC layer  15 B may include an electrochromic material. The electrochromic material may exhibit a reversible change in its optical property through an oxidation-reduction reaction of its electrochromic substances, and thereby change its absorption property. 
     In an example, the EC elements  15  may be in a transparent state (i.e., have optical transparency) while receiving no voltage, and may turn into a black or bluish-black state when receiving a voltage. In another example, the EC elements  15  may be in a white or gray state while receiving no voltage, and may turn into the black or bluish-black state when receiving a voltage. In still another example, the EC elements  15  may be in a mirror state (i.e., have optical reflectivity) while receiving a predetermined negative voltage, and may turn into the black or bluish-black state when receiving a predetermined positive voltage. In yet another example, the EC elements  15  may be in the mirror state (i.e., have optical reflectivity) while receiving a predetermined negative voltage, and may turn into the transparent state (i.e., have optical transparency) while receiving no voltage. 
     In an example, the EC element  15  may include a first ITO layer, an IrO 2  layer, a Ta 2 O 5  layer (i.e., a solid-electrolyte layer), a WO 3  layer (i.e., an electrochromic-material layer), and a second ITO layer that are stacked in this order. While no voltage is applied to the EC element  15  having such a configuration, the WO 3  layer may be in the transparent state (i.e., have optical transparency). On the other hand, when a voltage is applied to the EC element  15  to cause the second ITO layer adjacent to the WO 3  layer to be at a negative voltage, the WO 3  layer in the transparent state may be reduced through a reaction of WO 3 +xH + +xe − →HxWO 3  to turn into the black or bluish-black state, causing the EC element  15  to turn into the black or bluish-black state. 
     In another example, the EC element  15  may include a TiO 2  layer, the first ITO, the IrO 2  layer, the Ta 2 O 5  layer (i.e., the solid-electrolyte layer), the WO 3  layer (i.e., the electrochromic-material layer), and the second ITO layer that are stacked in this order. The TiO 2  layer may have a white-scattering property. While no voltage is applied to the EC element  15  having such a configuration, the WO 3  layer may be in the transparent state (i.e., have optical transparency), whereas the EC element  15  may be in the white or gray state due to the white-scattering property of the TiO 2  layer. When a voltage is applied to the EC element  15  to cause the second ITO layer adjacent to the WO 3  layer to be at a negative voltage, the WO 3  layer in the transparent state may be reduced through a reaction of WO 3 +xH + +xe − →HxWO 3  to turn into the black or bluish-black state, causing the EC element  15  to turn into the black or bluish-black state. 
     In still another example, the EC element  15  may include a reflective metal layer, the IrO 2  layer, the Ta 2 O 5  layer (i.e., the solid-electrolyte layer), the WO 3  layer (i.e., the electrochromic-material layer), and the ITO layer that are stacked in this order. While no voltage is applied to the EC element  15  having such a configuration, the WO 3  layer may be in the transparent state (i.e., have optical transparency), and the EC element  15  may thus be in the mirror state (i.e., have optical reflectivity) due to light reflection by the reflective metal layer. On the other hand, when a voltage is applied to the EC element  15  to cause the ITO layer adjacent to the WO 3  layer to be at a negative voltage, the WO 3  layer in the transparent state may be reduced through a reaction of WO 3 +xH + +xe − →HxWO 3  to turn into the black or bluish-black state, causing the EC element  15  to turn into the black or bluish-black state. 
     In yet another example, the EC element  15  may have a configuration described in “Applied physics express”; Volume 6, Issue 2, p: 026503; Feb. 1, 2013 published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics; Onodera, Ryou; Seki, Yoshiyuki; Seki, Shigeyuki; Yamada, Katsumi; Sawada, Yutaka; and Uchida, Takayuki (hereinafter referred to as “Reference 1”). In this example, one of ITO layers may be a smooth ITO layer, and the other ITO layer may be a rough ITO layer. When a predetermined positive voltage is applied to the EC element  15  having such a configuration (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the EC element  15  may become the mirror state (i.e., have optical reflectivity) due to deposition of Ag on the smooth ITO layer. On the other hand, while no voltage is applied to the EC element  15 , the EC element  15  may be in the transparent state (i.e., have optical transparency) due to dissolution of Ag. 
     In this example embodiment, the EC element  15  may be provided on a plane parallel to the substrate  21  so as to surround the organic EL element  14 . In other words, the organic EL element  14  and the EC element  15  may be provided on a plane parallel to the substrate  21 . With reference to  FIG. 4 , for example, the electrode  15 A of the EC element  15  may cover an end portion of the electrode  14 A of a predetermined organic EL element  14 . In this example embodiment, the electrode  15 A of the EC element  15  may be electrically coupled to the electrode  14 A of the predetermined organic EL element  14 . The electrode  15 A of the EC element  15  may be electrically coupled to the electrode  14 A in corresponding one of the subpixels  12  (subpixel  12  that emits red light, for example) in the pixel  11 . The EC element  15  may include an electrode  15 D that is coupled to the switching transistor Tr 4 . The electrode  15 D may be in contact with the electrode  15 C. 
     The organic EL panel  10  may further include a metal layer  22  in contact with the substrate  21 , and an ITO layer  23  in contact with surfaces of the metal layer  22  and the EC layer  15 B, for example. A portion of the metal layer  22  may serve as the electrode  14 A of the organic EL element  14 . Additionally, a portion of the ITO layer  23  may serve as the ITO layer  14 B of the organic EL element  14 , and a portion of the ITO layer  23  may serve as the electrode  15 C of the EC element  15 . In an example where the EC element  15  may be in the white state while receiving no voltage and the EC element  15  may become the mirror state (i.e., have optical reflectivity) when receiving a predetermined negative voltage, an ITO layer  27  may be provided in place of the metal layer  22  and the ITO layer  14 B, as illustrated in  FIG. 5 , for example. In this example, a portion of the ITO layer  27  may serve as the electrode  14 A of the organic EL element  14 , and a portion of the ITO layer  27  may serve as the electrodes  15 A and  15 D of the EC element  15 . In an alternative example, a metal layer  28  may be provided in place of the ITO layer  27 , as illustrated in  FIG. 6 . In this example, a portion of the metal layer  28  may serve as the electrode  14 A of the organic EL element  14 , and a portion of the metal layer  28  may serve as the electrodes  15 A and  15 D of the EC element  15 . 
     The organic EL panel  10  may further include an insulating layer  24  on the substrate  21 . The insulating layer  24  may suppress or prevent electrical short-circuiting between the electrode  15 C of the EC element  15  and the ITO layer  14 D of the organic EL element  14 . The insulating layer  24  may include, for example, SiN, SiON, or SiOx. The organic EL panel  10  may further include a sealing layer  26  on the substrate  21 . The sealing layer  26  may seal each of the organic EL elements  14  and each of the EC elements  15 . The sealing layer  26  may include, for example, an organic material, such as epoxy resin and vinyl resin. 
     [Operations] 
     An example operation of the display unit  1  according to the example embodiment of the disclosure will now be described. 
     Described below is the operation of the display unit  1  according to this example embodiment in which each of the EC elements  15  includes WO 3  as the electrochromic material and no TiO 2  layer having the white scattering property. While no voltage is applied to the EC elements  15 , the EC elements  15  may be in a transparent state, as illustrated on the left of  FIG. 7 , for example. When the signal voltage Vsig 2  is applied to some of the EC elements  15  in the transparent state, the EC elements  15  receiving the signal voltage Vsig 2  may change from the transparent state to the black or bluish-black state, as illustrated on the right of  FIG. 7 . When the application of voltage to some of the EC elements  15  is halted, the EC elements  15  in the black or bluish-black state may turn into the transparent state, as illustrated on the left of  FIG. 7 , for example. 
     Described below is the operation of the display unit  1  according to this example embodiment in which each of the EC elements  15  includes WO 3  as the electrochromic material and a TiO 2  layer having the white scattering property. While no voltage is applied to the EC elements  15 , the EC elements  15  may be in the white or gray state, as illustrated on the left of  FIG. 8 , for example. When the signal voltage Vsig 2  is applied to some of the EC elements  15  in the white or gray state, the EC elements  15  receiving the signal voltage Vsig 2  may change from the white or gray state to the black or bluish-black state, as illustrated on the right of  FIG. 8 , for example. When the application of voltage to some of the EC elements  15  is halted, the EC elements  15  in the black or bluish-black state may turn into the white or gray state, as illustrated on the left of  FIG. 8 , for example. 
     Described below is the operation of the display unit  1  according to this example embodiment in which each of the EC elements  15  includes WO 3  as the electrochromic material and no TiO 2  layer having the white scattering property, and each of the electrodes  15 A includes a metal material having high reflectivity. While no voltage is applied to the EC elements  15 , the EC layers  15 B in the respective EC elements  15  may be in the transparent state, and the EC elements  15  may be in the mirror state (i.e., have optical reflectivity) due to the reflectivity of the electrodes  15 A, as illustrated on the left of  FIG. 9 . When the signal voltage Vsig 2  is applied to some of the EC elements  15  in the mirror state (i.e., the EC elements  15  having optical reflectivity), the EC elements  15  receiving the signal voltage Vsig 2  may change from the mirror or light-reflective state to the black or bluish-black state, as illustrated on the right of  FIG. 9 , for example. When the application of voltage to some of the EC elements  15  is halted, the EC elements in the black or bluish-black state may turn into the mirror or light-reflective state, as illustrated on the left of  FIG. 9 . 
     Described below is the operation of the display unit  1  according to this example embodiment in which each of the EC elements  15  has the configuration described in Reference 1 described above, one of the ITO layers is a smooth ITO layer, and the other ITO layer is a rough ITO layer. When a predetermined positive voltage, which corresponds to the signal voltage Vsig  2 , is applied to the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the EC elements  15  may become the mirror (i.e., have optical reflectivity), as illustrated on the left of  FIG. 9 , for example. When a predetermined negative voltage, which corresponds to the signal voltage Vsig  2 , is applied to the EC elements  15  in the mirror or light-reflective state (i.e., a negative voltage is applied to the rough ITO layer and a positive voltage is applied to the smooth ITO layer), the EC elements  15  in the mirror or light-reflective state may turn into the black or bluish-black state, as illustrated on the right of  FIG. 9 , for example. When a predetermined positive voltage, which corresponds to the signal voltage Vsig  2 , is applied to the EC elements  15  in the black or bluish-black state (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the EC elements  15  in the black or bluish-black state may turn into the mirror (i.e., have optical reflectivity), as illustrated on the left of  FIG. 9 . 
     Described below is the operation of the display unit  1  according to this example embodiment in which each of the EC elements  15  has the configuration described in Reference 1 described above, one of the ITO layers is a smooth ITO layer, and the other ITO layer is a rough ITO layer. When a predetermined positive voltage, which corresponds to the signal voltage Vsig 2 , is applied to the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the EC elements  15  may become the mirror (i.e., have optical reflectivity), as illustrated on the left of  FIG. 10 , for example. When the signal voltage Vsig 2  of 0 volts is applied to the EC elements  15  in the mirror or light-reflective state (i.e., the voltage of 0 volts is applied to both the rough ITO layer and the smooth ITO layer), the EC elements  15  in the mirror or light-reflective state may turn into the transparent state (i.e., have optical transparency), as illustrated on the right of  FIG. 10 , for example. When a predetermined positive voltage, which corresponds to the signal voltage Vsig 2 , is applied to the EC elements  15  in the transparent state (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the EC elements  15  in the transparent state (i.e., the EC elements  15  having optical transparency) may turn into the mirror state (i.e., may have optical reflectivity), as illustrated on the left of  FIG. 10 , for example. 
     [Manufacturing Method] 
     Described below is a method of manufacturing the organic EL panel  10  according to the example embodiment of the disclosure.  FIGS. 11 and 12  illustrate an example procedure for manufacturing the organic EL panel  10 . Note that  FIGS. 11 and 12  each illustrate a cross-sectional configuration of the organic EL panel  10  taken along the line A-A in  FIG. 3 . 
     Firstly, the metal material may be formed into a film on the substrate  21 , and the film may be subjected to patterning, for example, to form the electrodes  14 A and  15 D on the substrate  21 , as illustrated in  FIG. 11A . Thereafter, the ITO layer may be formed over the entire surface of the substrate  21  on which the electrodes  14 A and  15 D are provided, and the ITO layer may be subjected to patterning, for example, to form the electrode  15 A, as illustrated in  FIG. 11A . Thereafter, with reference to  FIG. 11B , the EC layer  15 B may be formed over the entire surface of the substrate  21 , and a resist layer  110  may be formed only on the electrode  15 A. The EC layer  15 B may be selectively etched with the use of the resist layer  110  as a mask. The etching may be performed using an etchant with which the EC layer  15 B is etched at a higher etching rate than the electrode  14 A is. For example, to form a laminate structure of the metal-based electrodes  14 A and  15 D and the ITO layer, the etching may be performed using an etchant with which the EC layer  15 B is etched at a higher etching rate than the ITO layer is. Through these processes, the EC layer  15 B may be formed only on the electrode  15 A, as illustrated in  FIG. 11C . Thereafter, the resist layer  110  may be removed, as illustrated in  FIG. 11D . 
     Thereafter, with reference to  FIG. 12A , the ITO layer  23  may be formed on surfaces of the EC layer  15 B and the electrode  14 A, thereby forming the EC elements  15 . Thereafter, with reference to  FIG. 12B , the insulating layer  24  may be formed to cover each of the EC elements  15 . Thereafter, with reference to  FIG. 12C , the EL layer  14 C may be formed on a surface of the ITO layer  23  on the electrode  14 A. Thereafter, the ITO layer  25  (refer to  FIG. 4 , for example) may be formed over the entire display region that includes the surface of each EL layer  14 C, thereby forming the organic EL elements  14 . Finally, the sealing layer  26  may be formed. The organic EL panel  10  may be manufactured through these processes described above. 
     [Operation of Pixel] 
     The operation of each of the pixels  11  in the organic EL panel  10  according to the example embodiment of the disclosure will now be described.  FIG. 13  illustrates example waves of various voltages applied to the organic EL panel  10 , and example waves of various voltages generated in the organic EL panel  10 . 
     In this embodiment, the switching transistor Tr 3 , the switching transistor Tr 4 , and the writing transistor Tr 2  may be turned on in this order, and the writing transistor Tr 2 , the switching transistor Tr 4 , and the switching transistor Tr 3  may be turned off in this order. This allows for writing of the signal voltage Vsig to a gate of the driving transistor Tr 1 , at the same time as the application of a predetermined voltage to each of the EC elements  15 . The ON-operation in this order suppresses abnormal electric charging to each of the EC elements  15 . Alternatively, the switching transistor Tr 3 , the switching transistor Tr 4 , and the writing transistor Tr 2  may be turned on at the same time. Still alternatively, the switching transistor Tr 3  and the switching transistor Tr 4  may be turned on after the writing transistor Tr 2  is turned on. 
     In this example embodiment, light emission by the organic EL element  14  may be performed after the writing of the signal voltage Vsig and the application of voltage to the EC element  15 . In other words, the EC element  15  and the organic EL element  14  are selectively driven, in this embodiment. 
     Example Effects 
     Some effects of the display unit  1  according to the example embodiment of the disclosure will now be described. 
     In the example embodiment, the organic EL element  14  and the EC element  15  are selectively driven by the pixel circuit  13 . This allows the display unit  1  to display an image using the organic EL elements  14  and at the same time perform the enhancement of the image using the EC elements  15 , as illustrated in  FIGS. 7 to 10 , for example. Accordingly, it is possible to achieve novel image-display representation. 
     In the example embodiment, the organic EL element  14  and the EC element  15  may be coupled in parallel to each other, and the electric current path P 1  of the electric current flowing through the organic EL element  14  may intersect with the electric current path P 2  of the electric current flowing through the EC element  15 , at a node between the organic EL element  14  and the EC element  15 . This allows the display unit  1  to display an image using the organic EL elements  14  and at the same time perform the enhancement of the image using the EC elements  15 , as illustrated in  FIGS. 7 to 10 , for example. Accordingly, it is possible to achieve novel image-display representation. 
     In the example embodiment, the organic EL element  14  and the EC element  15  may be provided on a plane parallel to the substrate  21 . This allows the organic EL element  14  and the EC element  15  to be formed in a common manufacturing process, which results in a reduction in manufacturing costs. 
     In the example embodiment, the EC element  15  may be shared between the subpixels  12  adjacent to each other. This configuration allows the EC element  15  to be driven by a simple way, compared with the configuration in which the EC element  15  is provided for each of the subpixels  12 . Accordingly, it is possible to reduce a cost for the display unit  1 . 
     In the example embodiment, some of the EC elements  15  in the display region of the organic EL panel  10  may change from the transparent state to the black or bluish-black state, as illustrated in  FIG. 7 , for example. This allows an image that is displayed on the transparent organic EL panel  10  using the organic EL elements  14  to be adjusted in contrast. Accordingly, it is possible to achieve novel image-display representation. 
     In the example embodiment, some of the EC elements  15  in the display region of the organic EL panel  10  may change from the white or gray state to the black or bluish-black state, as illustrated in  FIG. 8 , for example. This allows an image that is displayed on the organic EL panel  10  using the organic EL elements  14  to be adjusted in contrast. Accordingly, it is possible to achieve novel image-display representation. In another example embodiment of the disclosure, only the EC elements  15  that have memory functionality may be driven by an extremely low electric power to change a panel color from white to gray. This mitigates an oppressive appearance of a typical black panel that appears when the image disappears. Additionally, image displaying in white and black colors is able to be achieved using only the EC elements  15 . This allows an image such as a wallpaper to be displayed by an extremely low electrical power. 
     In the example embodiment, some of the EC elements  15  in the display region of the organic EL panel  10  may change from the mirror or light-reflective state to the black or bluish-black state, as illustrated in  FIG. 9 , for example. This allows an image that is displayed on the organic EL panel  10  using the EL elements  14  to be adjusted in contrast. Accordingly, it is possible to achieve novel image-display representation. In the example embodiment, some of the EC elements  15  in the display region of the organic EL panel  10  may change from the mirror or light-reflective state to the transparent or light-transmissive state, and from the transparent or light-transmissive state to the mirror or light-reflective state, as illustrated in  FIG. 10 , for example. This allows the organic EL panel  10  to serve as a mirror display or a transparent display. Accordingly, it is possible to achieve novel image-display representation. 
     2. Modification Examples 
     Some modification examples of the organic EL panel  10  according to the foregoing example embodiment will now be described. 
     Modification Example A 
       FIG. 14  illustrates Modification Example A of the circuit configuration of the subpixel  12  included in each of the pixels  11  in the organic EL panel  10  according to the foregoing example embodiment of the disclosure. In Modification Example A, the driving transistor Tr 1  may be an n-channel transistor. The storage capacitor Cs may be coupled to the gate of the driving transistor Tr 1  and the anode of the organic EL element  14 . Also in Modification Example A, the electric current path P 1  may intersect with the electric current path P 2 , at the node between the EC element  15  and the organic EL element  14 . This allows the pixel circuit  13  to selectively drive the organic EL element  14  and the EC element  15 . Accordingly, it is possible for the display unit  1  of Modification Example A to provide a similar or the same effects as those of the foregoing example embodiments. 
     Additionally, in Modification Example A, the controller  20  and the driver  30  may perform a threshold correction of the driving transistor Tr 1  in each of the subpixels  12 , as illustrated in  FIG. 15 , for example. The term “threshold correction” as used herein refers to an operation for correcting the gate-source voltage of the driving transistor Tr 1  close to a threshold voltage of the driving transistor Tr 1 . Referring to driving timings illustrated in  FIG. 15 , the switching transistors Tr 3  and Tr 4  may be turned on before a preparation time for the threshold correction, and voltages Vss and Vsig 2  are thereby applied to respective terminals of the EC element  15 . Thereafter, the threshold correction and signal writing may be performed to cause the organic EL elements  14  to emit light. The voltage application to each of the EC elements  15  before the threshold correction allows each of the EC elements  15  to be supplied with the constant voltage regardless of a fluctuation of the source potential of the driving transistor Tr 1  caused by the threshold correction. 
     In Modification Example A that involves the threshold correction of the driving transistor Tr 1  in each of the subpixels  12 , it is possible to achieve image display representation with higher display quality. 
     Modification Example B 
       FIG. 16  illustrates Modification Example B of the cross-sectional configuration of the organic EL panel  10  according to the foregoing example embodiment of the disclosure. In Modification Example B, the organic EL element  14  and the EC element  15  may be laminated to each other. For example, the organic EL element  14  may be provided on the EC element  15 , as illustrated in  FIG. 16 . The EC element  15  may be provided so as to face the entire light emission region of the organic EL element  14 , when seen from the normal direction of the substrate  21 . In Modification Example B, the EC element  15  may be provided so as to face a portion (e.g., a central portion) of the light emission region of the organic EL element  14 , as illustrated in  FIG. 16 . Additionally, the organic EL element  14  and the EC element  15  may be embedded in the insulating layer  41 , as illustrated in  FIG. 16 , for example. In this example, a common electrode serving as the electrode  15 A of the EC element  15  and the electrode  14 A of the organic EL element  14  may be provided, and a connection  42  serving as a lead-out wiring line may be provided in the insulating layer  41  and electrically coupled to the common electrode serving as the electrode  15 A and the electrode  14 A. This configuration allows the EC element  15  and the organic EL element  14  to be densely provided, compared with a configuration in which the EC element  15  and the organic EL element  14  are provided in a common layer. Accordingly, it is possible to achieve image display representation with higher resolution. 
     [Operations] 
     The operation of the display unit  1  according to Modification Example B will now be described. 
     Described below is the operation of the display unit  1  according to Modification Example B in which each of the EC elements  15  includes WO 3  as the electrochromic material and no TiO 2  layer having the white scattering property, and the electrodes  15 A and  15 D of each of the EC elements  15  may include a transparent electrically-conductive material, such as ITO or IZO. While no voltage is applied to the EC elements  15  and the organic EL elements  14 , the organic EL elements  14  may be in a transparent state and the EC elements  15  immediately below the respective organic EL elements  14  in the transparent state may be in a transparent state, as illustrated on the left of  FIG. 17 , for example. Referring to  FIG. 17 , the organic EL elements  14  without dots are not emitting light and are in the transparent state. When the signal voltage Vsig is applied to some of the organic EL elements  14  and the signal voltage Vsig 2  is applied to some of the EC elements  15 , the organic EL elements  14  receiving the signal voltage Vsig may emit light and the EC elements  15  receiving the signal voltage Vsig 2  may change from the transparent state to the black or bluish-black state, as illustrated on the right of  FIG. 17 , for example. Referring to  FIG. 17 , the organic EL elements  14  with dots are emitting light. When the application of voltage to some of the organic EL elements  14  and some of the EC elements  15  is halted, the organic EL elements  14  emitting light may stop emitting light and turn into the transparent state, and the EC elements  15  in the black or bluish-black state may turn into the transparent state, as illustrated on the left of  FIG. 17 , for example. 
     Described below is the operation of the display unit  1  according to Modification Example B in which each of the EC elements  15  includes WO 3  as the electrochromic material and a TiO 2  layer having the scattering property. While no voltage is applied to the EC elements  15  and the organic EL elements  14 , the organic EL elements  14  may be in a transparent state and the EC elements  15  immediately below the respective organic EL elements  14  may be in a white or gray state, as illustrated on the left of  FIG. 18 , for example. When the signal voltage Vsig is applied to some of the organic EL elements  14  and the signal voltage Vsig 2  is applied to some of the EC elements  15 , the organic EL elements  14  receiving the signal voltage Vsig may emit light, and the EC elements  15  receiving the signal voltage Vsig 2  may change from the white or gray state to the black or bluish-black state, as illustrated on the right of  FIG. 18 , for example. When the application of voltage to some of the organic EL elements  14  and some of the EC elements  15  is halted, the organic EL elements  14  emitting light may stop emitting light and turn into the transparent state, and the EC element  15  in the black or bluish-black state may turn into the white or gray state, as illustrated on the left of  FIG. 18 , for example. 
     Described below is the operation of the display unit  1  according to Modification Example B in which each of the EC elements  15  includes WO 3  as the electrochromic material and no TiO 2  layer having the white scattering property, and each of the electrodes  15 C includes a metal material having high reflectivity. While no voltage is applied to the EC elements  15  and the organic EL elements  14 , the organic EL elements  14  may be in the transparent state, and the EC elements  15  immediately below the respective organic EL element  14  in the transparent state may be in the mirror state (i.e., have optical reflectivity) due to the reflectivity of the electrode  15 C, as illustrated on the left of  FIG. 19 , for example. Referring to  FIG. 19 , the EC elements  15  with stars are in the mirror state. When the signal voltage Vsig is applied to some of the organic EL elements  14  and the signal voltage Vsig 2  is applied to some of the EC elements  15 , the organic EL elements  14  receiving the signal voltage Vsig may emit light and the EC elements  15  receiving the signal voltage Vsig 2  may change from the mirror or light-reflective state to the black or bluish-black state, as illustrated on the right of  FIG. 19 , for example. When the application of voltage to some of the organic EL elements  14  and to some of the EC elements  15  is halted, the organic EL elements  14  emitting light may stop emitting light and turn into the transparent state, and the EC elements  15  in the black or bluish-black state may turn into the mirror state (i.e., have optical reflectivity), as illustrated on the left of  FIG. 19 , for example. 
     Described below is the operation of the display unit  1  according to Modification Example B in which each of the EC elements  15  has the configuration described in Reference 1 described above, one of the ITO layers is a smooth ITO layer, and the other ITO layer is a rough ITO layer. When a predetermined positive voltage, which corresponds to the signal voltage Vsig  2 , is applied to the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), and no voltage is applied to the organic EL elements  14 , the organic EL elements  14  may be in the transparent state, and the EC elements  15  immediately below the respective organic EL elements  14  in the transparent state may be in the mirror state (i.e., have optical reflectivity), as illustrated on the left of  FIG. 19 , for example. When the signal voltage Vsig is applied to some of the organic EL elements  14 , and a predetermined negative voltage, which corresponds to the signal voltage Vsig 2 , is applied to some of the EC elements  15  (i.e., a negative voltage is applied to the rough ITO layer and a positive voltage is applied to the smooth ITO layer), the organic EL elements  14  receiving the signal voltage Vsig may emit light, and the EC elements  15  receiving the signal voltage Vsig 2  may change from the mirror or light-reflective state to the black or bluish-black state, as illustrated on the right of  FIG. 19 , for example. When the application of voltage to some of the organic EL elements  14  is halted and a predetermined positive voltage, which corresponds to the signal voltage Vsig 2 , is applied to some of the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the organic EL elements  14  emitting light may stop emitting light and turn into the transparent state, and the EC elements  15  in the black or bluish-black state may turn into the mirror state (i.e., have optical reflectivity), as illustrated on the left of  FIG. 19 , for example. 
     Described below is the operation of the display unit  1  according to Modification Example B in which each of the EC elements  15  has the configuration described in Reference 1 described above, one of the ITO layers is a smooth ITO layer, and the other ITO layer is a rough ITO layer. When a predetermined positive voltage, which corresponds to the signal voltage Vsig 2 , is applied to the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), and no voltage is applied to the organic EL elements  14 , the organic EL elements  14  may be in the transparent state and the EC elements  15  immediately below the respective organic EL elements  14  in the transparent state may be in the mirror state (i.e., have optical reflectivity), as illustrated on the left of  FIG. 20 , for example. When the signal voltage Vsig is applied to some of the organic EL elements  14  and the signal voltage Vsig 2  of 0 volts is applied to some of the EC elements  15  (i.e., the voltage of 0V is applied to both the rough ITO layer and the smooth ITO layer), the organic EL element  14  receiving the signal voltage Vsig may emit light and the EC elements  15  receiving the signal voltage Vsig 2  may change from the mirror or light-reflective state to the transparent or light-transmissive state, as illustrated on the right of  FIG. 20 , for example. When the application of voltage to some of the organic EL elements  14  is halted and a predetermined positive voltage, which corresponds to the signal voltage Vsig 2 , is applied to some of the EC elements  15  (i.e., a positive voltage is applied to the rough ITO layer and a negative voltage is applied to the smooth ITO layer), the organic EL elements  14  emitting light may stop emitting light and turn into the transparent state, and the EC elements  15  in the transparent (i.e., the EC elements  15  having optical transparency) may turn into the mirror state (i.e., may have optical reflectivity), as illustrated on the left of  FIG. 20 . 
     As described above, it is possible also in Modification Example B to display an image using the organic EL elements  14  and at the same time perform the enhancement of the image using the EC elements  15 , as illustrated in  FIGS. 17 to 20 . Accordingly, it is possible to achieve novel image-display representation. 
     In Modification Example B, the constant-voltage wiring line coupled to the switching transistor Tr 3  and the constant-voltage wiring line coupled to the switching transistor Tr 4  are reversed from those in the foregoing example embodiments and Modification Example A because of the laminated structure of the EC element  15  and the organic EL element  14 , as illustrated in  FIGS. 21 and 22 , for example. Also in Modification Example B of the disclosure, the electric current path P 1  may intersect with the electric current path P 2 , at the node between the EC element  15  and the organic EL element  14 . This allows the pixel circuit  13  to selectively drive the organic EL element  14  and the EC element  15 . Accordingly, it is possible for the display unit  1  of Modification Example B to provide a similar or the same effects as those of the foregoing example embodiments and modification example. 
     Modification Example C 
       FIG. 23  illustrates Modification Example C of the cross-sectional configuration of the organic EL panel  10  according to Modification Example B described above. In Modification Example C, the organic EL panel  10  may include a black matrix  43 . The black matrix  43  may be provided in a gap between each two adjacent organic EL elements  14 , when seen from the normal direction of the organic EL panel  10 . The black matrix  43  may be in contact with an upper surface of the sealing layer  26 , for example. 
       FIG. 24  illustrates an example configuration on an upper surface of the organic EL panel  10  according to Modification Example C. In  FIG. 24 , both the organic EL elements  14  and the EC elements  15  are in the transparent state. As illustrated in  FIG. 24 , the gap between each two adjacent organic EL elements  14  may be in the black state because of the presence of the black matrix  43 , when seen from the normal direction of the organic EL panel  10 . It is possible also in Modification Example C to achieve novel image-display representation, as in the foregoing example embodiments and the modification examples described above. 
     Modification Example D 
       FIG. 25  illustrates Modification Example D of the cross-sectional configuration of the organic EL panel  10  according to Modification Example B described above. In Modification Example D, the organic EL panel  10  may have a mirror layer  44 . The mirror layer  44  may include a metal material having high reflectivity. Specific but non-limiting example of the high-reflective metal material used for the mirror layer  44  may include aluminum (Al), silver (Ag), aluminum alloy, and silver alloy. The mirror layer  44  may be provided in a gap between each two adjacent organic EL elements  14 , when seen from the normal direction of the organic EL panel  10 . The mirror layer  44  may be provided on the upper surface of the substrate  21 , for example. 
       FIG. 26  illustrates an example configuration on the upper surface of the organic panel  10  according to Modification Example D. In  FIG. 26 , both the organic EL elements  14  and the EC elements  15  are in the transparent state. As illustrated in  FIG. 26 , the gap between each two adjacent organic EL elements  14  may be in the mirror state (i.e., have optical reflectivity) because of the presence of the mirror layer  44 , when seen from the normal direction of the organic EL panel  10 . It is possible also in Modification Example D to achieve novel image-display representation, as in the foregoing example embodiments and the modification examples described above. 
     Modification Example E 
     According to Modification Example E illustrated in  FIGS. 27 to 30 , for example, a liquid crystal cell  16  may be provided in place of the organic EL element  14  in the foregoing example embodiments and the modification examples described above. Also in Modification Example E, the electric current path P 1  may intersect with the electric current path P 2 , at the node between the EC element  15  and the liquid crystal cell  16 . This allows the pixel circuit  13  to selectively drive the liquid crystal cell  16  and the EC element  15 . Accordingly, it is possible for the display unit  1  of Modification Example E to provide a similar or the same effects as those of the foregoing example embodiments and the modification examples. It should be noted that the configuration of the pixel circuit  13  is not limited to the example configurations illustrated in  FIGS. 27 to 30 , and may be a simple circuit configuration illustrated in  FIG. 31 , for example. In  FIG. 31 , the pixel circuit  13  may include switching transistors Tr 5  and Tr 6 , and a storage capacitor C 1 . A gate of the switching transistor Tr 5  may be coupled to the scanning line WSL 1 . One of source and drain of the switching transistor Tr 5  may be coupled to the signal line DTL. The other of the source and drain of the switching transistor Tr 5  that is uncoupled to the signal line DTL may be coupled to the EC element  15 . A gate of the switching transistor Tr 6  may be coupled to the scanning line WSL 3 . One of source and drain of the switching transistor Tr 6  may be coupled to the EC element  15 . The other of the source and drain of the switching transistor Tr 6  that is uncoupled to the EC element  15  may be coupled to the wiring line of the signal voltage Vsig 2 . The liquid crystal cell  16  may be coupled to the node between the switching transistor Tr 5  and the EC element  15  and a fixed voltage line Vcom. Likewise, the storage capacitor C 1  may be coupled to the node between the switching transistor Tr 5  and the EC element  15  and to the fixed voltage line Vcom. In other words, the crystal cell  16  and the storage capacitor C 1  may be coupled in parallel to each other. The crystal cell  16  may correspond to a specific but non-limiting example of “optical modulator” according to one embodiment of the disclosure. 
     Modification Example F 
     According to Modification Example F illustrated in  FIGS. 32 and 33 , for example, an electrophoretic (EP) element  17  may be provided in place of the EC element  15  in the foregoing example embodiments and the modification examples described above. The EP element  17  may accommodate a liquid  124  in a space defined by a substrate  121 , a sealing layer  126 , and partition walls  123 . The liquid  124  may contain microparticles  125 . The microparticles  125  may be aggregated in one place or dispersed in the liquid  124  in response to application of a voltage to paired electrodes  122  provided on the respective partition walls  123 , to control light-transmissive and light-blocking properties of the EP element  17 . In  FIG. 32 , the microparticles  125  are dispersed in the liquid  124 . In  FIG. 33 , the microparticles  125  are aggregated in one place. 
     Also in Modification Example F in which the EP element  17  is provided in place of the EC element  15 , it is possible to achieve novel image-display representation, as in the foregoing example embodiments and the modification examples described above. 
     Modification Example G 
     According to Modification Example G illustrated in  FIG. 34 , for example, an electrowetting (EW) element  18  may be provided in place of the EC element  15  in the foregoing example embodiments and the modification examples described above. The EW element  18  may accommodate an electrolyte  134  in a space defined by an insulating layer  132  provided on a substrate  131 , a sealing layer  136 , and a partition wall  133 . The electrolyte  134  may contain a colored oil  135 . The oil  135  may be aggregated in one place or dispersed in the space in response to application of a voltage to an electrode provided on the partition wall  133  and an electrode  137  provided at a predetermined position on the substrate  131 , to control light-transmissive and light-blocking properties of the EW element  18 . In  FIG. 34 , the oil  135  is dispersed in the electrolyte  134 . In  FIG. 35 , the oil  135  is aggregated in one place. 
     Also in Modification Example E in which the EW element  18  are provided in place of the EC element  15 , it is possible to achieve novel image-display representation, as in the foregoing example embodiments and the modification examples described above. 
     3. Application Examples 
     Described below is an application example of the display unit  1  according to any example embodiment or modification example of the disclosure. The display unit  1  according to any example embodiment and modification examples of the disclosure is applicable to a variety of display devices of electronic apparatuses that display images or pictures based on external or internal image signals. Non-limiting examples of the electronic apparatuses may include televisions, digital cameras, notebook personal computers, sheet-like personal computers, portable terminal devices such as mobile phones, and video cameras. 
       FIG. 36  is a perspective view of an electronic apparatus  2  having an example appearance according to an application example. The electronic apparatus  2  may be, for example, a sheet-like personal computer that includes a body  310  having a display surface  320  on a main face. The display unit  1  according to any foregoing example embodiment or modification example of the disclosure may be provided on the display surface  320  of the electronic apparatus  2 . The display unit  1  may be so disposed that the organic EL panel  10  is provided on a front surface of the electronic apparatus  2 . In this application example, the display unit  1  according to any foregoing example embodiment or modification example of the disclosure may be provided on the display surface  320 . This allows the electronic apparatus  2  to achieve high-contrast image displaying. 
     Although the disclosure is described with reference to the example embodiments, modification examples, and application examples hereinabove, these example embodiments, modification examples, and application examples are not to be construed as limiting the scope of the disclosure and may be modification in a wide variety of ways. It should be appreciated that the effects described herein are mere examples. Effects of an example embodiment of the disclosure are not limited to those described herein. The disclosure may further include any effects other than those described herein. Furthermore, the disclosure encompasses any possible combination of some or all of the various example embodiments and the modification examples described herein and incorporated herein. 
     It is possible to achieve at least the following configurations from the foregoing example embodiments of the disclosure. 
     (1) A display unit including 
     a display panel that includes a plurality of pixels arranged in a matrix, each of the pixels including: 
     one of an optical modulator and a self-luminescent element; 
     one of an electrochromic element, an electrophoretic element, and an electrowetting element; and 
     a pixel circuit configured to selectively drive the one of the optical modulator and the self-luminescent element, and selectively drive the one of the electrochromic element, the electrophoretic element, and the electrowetting element. 
     (2) The display unit according to (1), in which 
     the one of the electrochromic element, the electrophoretic element, and the electrowetting element is coupled in parallel to the one of the optical modulator and the self-luminescent element, and 
     the pixel circuit has a first electric current path and a second electric current path that intersect each other at a node between the one of the electrochromic element, the electrophoretic element, and the electrowetting element, and the one of the optical modulator and the self-luminescent element, the first electric current path being a path of an electric current flowing through the one of the optical modulator and the self-luminescent element, the second electric current path being a path of an electric current flowing through the one of the electrochromic element, the electrophoretic element, and the electrowetting element. 
     (3) The display unit according to (1) or (2), in which 
     the display panel further includes a substrate that supports the plurality of pixels, and 
     the one of the electrochromic element, the electrophoretic element, and the electrowetting element, and the one of the optical modulator and the self-luminescent element are provided on a plane parallel to the substrate. 
     (4) The display unit according to (1) or (2), in which the one of the electrochromic element, the electrophoretic element, and the electrowetting element, and the one of the optical modulator and the self-luminescent element are laminated to each other. 
     (5) The display unit according to any one of (1) to (4), in which the one of the electrochromic element, the electrophoretic element, and the electrowetting element is shared between the plurality of pixels. 
     (6) The display unit according to any one of (1) to (5), in which the one of the electrochromic element, the electrophoretic element, and the electrowetting element has optical transparency while receiving no voltage, and turns into a black or bluish-black state when receiving a voltage.
 
(7) The display unit according to any one of (1) to (5), in which the electrochromic element is in a white or gray state while receiving no voltage, and turns into a black or bluish-black state when receiving a voltage.
 
(8) The display unit according to any one of (1) to (5), in which the electrochromic element has optical reflectivity while receiving no voltage, and turns into a black or bluish-black state when receiving a voltage.
 
(9) The display unit according to any one of (1) to (5), in which the electrochromic element has optical reflectivity while receiving a positive voltage, and has optical transparency while receiving no voltage.
 
     In the display unit according to any example embodiment or modification example of the disclosure, the display element (e.g., optical modulator or self-luminescent element) and the enhancement element (e.g., electrochromic element, electrophoretic element, or electrowetting element) are selectively driven by the pixel circuit. Accordingly, it is possible to display an image using the display elements and at the same time perform the enhancement of the image using the enhancement elements. 
     In the display unit according to any example embodiment or modification example of the disclosure, the image displaying using the display elements is performed along with the enhancement of the image using the enhancement elements. Accordingly, it is possible to achieve novel image-display representation. Effects of the example embodiments and modification examples of the disclosure are not limited to those described hereinabove, and may be any effect described herein. 
     Although the disclosure is described hereinabove in terms of example embodiments, it is not limited thereto. It should be appreciated that variations may be made in the described example embodiments by persons skilled in the art without departing from the scope of the disclosure as defined by the following claims. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in this specification or during the prosecution of the application, and the examples are to be construed as non-exclusive. For example, in this disclosure, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. The term “disposed on/provided on/formed on” and its variants as used herein refer to elements disposed directly in contact with each other or indirectly by having intervening structures therebetween. Moreover, no element or component in this disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.