The present disclosure relates to a display device and an electronic device including the display device.
In recent years, as an organic electroluminescence (EL) display device (hereinafter simply referred to as a “display device”), a device having an organic layer common to all subpixels has been proposed. However, in the display device having such a configuration, leakage of a drive current is likely to occur between adjacent subpixels. Accordingly, a technology for preventing leakage of a drive current between adjacent subpixels has been proposed (see, for example, Patent Document 1).
As described above, in recent years, in a display device having an organic EL layer common to all subpixels, a technology for preventing leakage of a drive current generated between adjacent subpixels is desired.
An object of the present disclosure is to provide a display device capable of preventing leakage of a drive current generated between adjacent subpixels, and an electronic device including the display device.
In order to achieve the above-described object, a first disclosure is a display device, including:
0≤Ebulk(1)−Einterface(1)≤0.3 eV (1)
A second disclosure is a display device, including:
0≤Ebulk(2b)−Ebulk(2a)≤0.3 eV (2)
A third disclosure is a display device, including:
0≤Ebulk(3)−Einterface(3)≤0.3 eV (3)
A fourth disclosure is a display device, including:
0≤Ebulk(4b)−Ebulk(4a)≤0.3 eV (4)
The embodiments of the present disclosure will be described in the following order.
The subpixel 100R displays red, the subpixel 100G displays green, and the subpixel 100B displays blue. Note that, in the following description, in a case where the subpixels 100R, 100G, and 100B are collectively referred to without being particularly distinguished, they are referred to as subpixels 100. A combination of adjacent subpixels 100R, 100G, and 100B constitutes one pixel (pixel).
In the peripheral region 110B, a signal line drive circuit 111 and a scanning line drive circuit 112, which are drivers for video display, are provided. The signal line drive circuit 111 supplies a signal voltage of a video signal corresponding to luminance information supplied from a signal supply source (not illustrated) to the subpixel 100 selected via the signal line 111A. The scanning line drive circuit 112 includes a shift register or the like that sequentially shifts (transfers) a start pulse in synchronization with an input clock pulse. The scanning line drive circuit 112 scans the subpixels 100 row by row at the time of writing the video signal to each subpixel 100, and sequentially supplies a scanning signal to each scanning line 112A.
The display device 10 may be a microdisplay. The display device 10 may be included in a virtual reality (VR) device, a mixed reality (MR) device, an augmented reality (AR) device, an electronic view finder (EVF), a small projector, or the like.
The display device 10 is an example of a light emitting device. The display device 10 is a top emission type display device. The counter substrate 19 side of the display device 10 is the top side, and the drive substrate 11 side of the display device 10 is the bottom side. In the following description, in each layer constituting the display device 10, a surface on the top side of the display device 10 is referred to as a first surface, and a surface on the bottom side of the display device 10 is referred to as a second surface.
The display device 10 includes a plurality of light emitting elements 20. The plurality of light emitting elements 20 includes the first electrode layer 12, the organic EL layer 14, and the second electrode layer 15. The light emitting element 20 is, for example, a white light emitting element such as a white OLED or a white Micro-OLED (MOLED). As a coloring method in the display device 10, a method using a white light emitting element and the color filter 17 is used.
The drive substrate 11 is what is called a backplane, and drives the plurality of light emitting elements 20. The drive substrate 11 is provided with a drive circuit that drives the plurality of light emitting elements 20, a power supply circuit that supplies power to the plurality of light emitting elements 20, and the like (none of which is illustrated).
The substrate body of the drive substrate 11 may be formed by, for example, a semiconductor easily formed with a transistor or the like, or may be formed by glass or resin having low moisture and oxygen permeability. Specifically, the substrate body may be a semiconductor substrate, a glass substrate, a resin substrate, or the like. The semiconductor substrate includes, for example, amorphous silicon, polycrystalline silicon, monocrystalline silicon, or the like. The glass substrate includes, for example, high strain point glass, soda glass, borosilicate glass, forsterite, lead glass, quartz glass, or the like. The resin substrate includes, for example, at least one selected from a group including polymethyl methacrylate, polyvinyl alcohol, polyvinyl phenol, polyethersulfone, polyimide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and the like.
The first electrode layer 12 is provided on the first surface of the drive substrate 11. The first electrode layer 12 is an anode. When a voltage is applied between the first electrode layer 12 and the second electrode layer 15, holes are injected from the first electrode layer 12 into the organic EL layer 14. The first electrode layer 12 also functions as a reflecting layer, and is preferably formed by a material having the highest reflectance and largest work function possible in order to enhance the light emission efficiency. The first electrode layer 12 includes a plurality of electrodes 12A. The plurality of electrodes 12A is electrically separated between the adjacent light emitting elements 20. The plurality of electrodes 12A shares the organic EL layer 14. The plurality of electrodes 12A is two-dimensionally arranged in a prescribed arrangement pattern such as a matrix shape.
The electrode 12A is formed by at least one of a metal layer or a metal oxide layer. More specifically, the electrode 12A is formed by a single layer film of a metal layer or a metal oxide layer, or a stacked film of a metal layer and a metal oxide layer. In a case where the electrode 12A is formed by the stacked film, the metal oxide layer may be provided on the organic EL layer 14 side, or the metal layer may be provided on the organic EL layer 14 side, but from the viewpoint of including a layer having a high work function adjacent to the organic EL layer 14, the metal oxide layer is preferably provided on the organic EL layer 14 side.
The metal layer includes, for example, at least one metal element selected from a group including chromium (Cr), gold (Au), platinum (Pt), nickel (Ni), copper (Cu), molybdenum (Mo), titanium (Ti), tantalum (Ta), aluminum (Al), magnesium (Mg), iron (Fe), tungsten (W), and silver (Ag). The metal layer may include the at least one metal element described above as a constituent element of an alloy. Specific examples of the alloy include an aluminum alloy and a silver alloy. Specific examples of the aluminum alloy include AlNd and AlCu.
The metal oxide layer includes, for example, a transparent conductive oxide (TCO). The transparent conductive oxide includes, for example, at least one selected from a group including a transparent conductive oxide including indium (hereinafter referred to as “indium-based transparent conductive oxide”), a transparent conductive oxide including tin (hereinafter referred to as a “tin-based transparent conductive oxide”), and a transparent conductive oxide including zinc (hereinafter referred to as a “zinc-based transparent conductive oxide”).
The indium-based transparent conductive oxide includes, for example, indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium oxide (IGO), or indium gallium zinc oxide (IGZO) fluorine-doped indium oxide (IFO). Among these transparent conductive oxides, the indium tin oxide (ITO) is particularly preferable. This is because the indium tin oxide (ITO) has a particularly low hole injection barrier into the organic EL layer 14 as a work function, and thus the drive voltage of the display device 10 can be particularly reduced. The tin-based transparent conductive oxide includes, for example, tin oxide, antimony-doped tin oxide (ATO), or fluorine-doped tin oxide (FTC). The zinc-based transparent conductive oxide includes, for example, zinc oxide, aluminum-doped zinc oxide (AZO), boron-doped zinc oxide, or gallium-doped zinc oxide (GZO).
The second electrode layer 15 is provided to face the first electrode layer 12. The second electrode layer 15 is provided as an electrode common to all the subpixels 100 in the display region 110A. The second electrode layer 15 is a cathode. When a voltage is applied between the first electrode layer 12 and the second electrode layer 15, electrons are injected from the second electrode layer 15 into the organic EL layer 14. The second electrode layer 15 is a transparent electrode having transparency to light generated in the organic EL layer 14. Here, the transparent electrode also includes a semi-transmissive reflecting layer. The second electrode layer 15 is preferably formed by a material having as high permeability as possible and a small work function in order to enhance luminous efficiency.
The second electrode layer 15 is formed by, for example, at least one of a metal layer or a metal oxide layer. More specifically, the second electrode layer 15 is formed by a single layer film of a metal layer or a metal oxide layer, or a stacked film of a metal layer and a metal oxide layer. In a case where the second electrode layer 15 is formed by a stacked film, the metal layer may be provided on the organic EL layer 14 side, or the metal oxide layer may be provided on the organic EL layer 14 side, but from the viewpoint of including a layer having a low work function adjacent to the organic EL layer 14, the metal layer is preferably provided on the organic EL layer 14 side.
The metal layer includes, for example, at least one metal element selected from a group including magnesium (Mg), aluminum (Al), silver (Ag), calcium (Ca), and sodium (Na). The metal layer may include the at least one metal element described above as a constituent element of an alloy. Specific examples of the alloy include an MgAg alloy, an MgAl alloy, an AlLi alloy, and the like. The metal oxide layer includes a transparent conductive oxide. As the transparent conductive oxide, a material similar to the transparent conductive oxide of the electrode 12A described above can be exemplified.
The organic EL layer 14 is provided between the first electrode layer 12 and the second electrode layer 15. The organic EL layer 14 is continuously provided over all the subpixels 100 (that is, the plurality of electrodes 12A) in the display region 110A, and is provided as a layer common to all the subpixels 100 in the display region 110A. The organic EL layer 14 is configured to emit white light.
The hole transport layer 14A is adjacent to the first electrode layer 12 and the insulating layer 13. The hole transport layer 14A is for enhancing hole transport efficiency to each of the light emitting layers 14B, 14D, and 14E. The hole transport layer 14A includes, for example, α-NPD (N,N′-di(1-naphthyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine).
The electron transport layer 14F is for enhancing electron transport efficiency to each of the light emitting layers 14B, 14D, and 14E. The electron transport layer 14F includes, for example, at least one selected from a group including BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Alq3 (aluminum quinolinol complex), Bphen (bathophenanthroline), and the like.
An electron injection layer 17H is for enhancing electron injection from the cathode. The electron injection layer 17H includes, for example, a simple substance of an alkali metal or an alkaline earth metal or a compound including them, specifically, for example, lithium (Li) or lithium fluoride (LiF), or the like.
The light emission separation layer 14C is a layer for adjusting injection of carriers into each of the light emitting layers 14B, 14D, and 14E, and light emission balance of each color is adjusted by injecting electrons or holes into each of the light emitting layers 14B, 14D, and 14E via the light emission separation layer 14C. The light emission separation layer 14C includes, for example, 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl derivative, or the like.
When an electric field is applied to each of the red light emitting layer 14B, the blue light emitting layer 14D, and the green light emitting layer 14E, recombination occurs between holes injected from the electrode 12A and electrons injected from the second electrode layer 15, and red, blue, and green are generated.
The red light emitting layer 14B includes, for example, a red light emitting material. The red light emitting material may be fluorescent or phosphorescent. Specifically, the red light emitting layer 14B includes, for example, a mixture of 4,4-bis(2,2-diphenylvinin) biphenyl (DPVBi) and 2,6-bis[(4′-methoxydiphenylamino)styryl]-1,5-dicyanonaphthalene (BSN).
The blue light emitting layer 14D includes, for example, a blue light emitting material. The blue light emitting material may be fluorescent or phosphorescent. Specifically, the blue light emitting layer 14D includes, for example, a mixture of 4,4′-bis[2-{4-(N,N-diphenylamino)phenyl}vinyl] biphenyl (DPAVBi) with DPVBi.
The green light emitting layer 14E includes, for example, a green light emitting material. The green light emitting material may be fluorescent or phosphorescent. Specifically, the green light emitting layer 14E includes, for example, a mixture of DPVBi and coumarin 6.
The insulating layer 13 is provided on the first surface of the drive substrate 11 and between the adjacent electrodes 12A. The insulating layer 13 insulates the separated electrodes 12A from each other. The insulating layer 13 has a plurality of openings 13A. Each of the plurality of openings 13A is provided corresponding to each subpixel 100. More specifically, each of the plurality of openings 13A is provided on the first surface (the surface facing the second electrode layer 15) of each of the separated electrodes 12A. The electrode 12A and the organic EL layer 14 are in contact with each other through the opening 13A.
The insulating layer 13 may be an organic insulating layer, an inorganic insulating layer, or a stack thereof. The organic insulating layer includes, for example, at least one selected from a group including a polyimide-based resin, an acrylic resin, a novolac-based resin, and the like. The inorganic insulating layer includes, for example, at least one selected from a group including silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiOxNy), and the like.
The protective layer 16 is provided on the first surface of the second electrode layer 15 and covers the plurality of light emitting elements 20. The protective layer 16 shields the light emitting element 20 from the outside air, and prevents moisture infiltration into the light emitting element 20 from the external environment. Furthermore, in a case where the second electrode layer 15 is formed by a metal layer, the protective layer 16 may have a function of preventing oxidation of the metal layer.
The protective layer 16 includes, for example, an inorganic material or a polymer resin having low hygroscopicity. The protective layer 16 may have a single-layer structure or a multilayer structure. In a case where the thickness of the protective layer 16 is increased, it is preferable to have a multilayer structure. This is to alleviate the internal stress in the protective layer 16. The inorganic material includes, for example, at least one selected from a group including silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiOxNy), titanium oxide (TiOx), aluminum oxide (AlOx), and the like. The polymer resin includes, for example, at least one selected from a group including a thermosetting resin, an ultraviolet curable resin, and the like.
The color filter 17 is provided on the first surface of the protective layer 16. The color filter 17 is, for example, an on-chip color filter (OCCF). The color filter 17 includes, for example, a red filter 17R, a green filter 17G, and a blue filter 17B. Each of the red filter 17R, the green filter 17G, and the blue filter 17B is provided to face the light emitting element 20. The red filter 17R and the light emitting element 20 constitute the subpixel 100R, the green filter 17G and the light emitting element 20 constitute the subpixel 100G, and the blue filter 17B and the light emitting element 20 constitute the subpixel 100B.
White light emitted from the light emitting elements 20 in the subpixels 100R, 100G, and 100B is transmitted through the red filter 17R, the green filter 17G, and the blue filter 17B described above, so that red light, green light, and blue light are each emitted from the display surface. Furthermore, a light shielding layer 17BM may be provided between the color filters 17R, 17G, and 17B, that is, in a region between the subpixels 100. Note that the color filter 17 is not limited to the on-chip color filter, and may be provided on the second surface of the counter substrate 19 (the surface facing the organic EL layer 14).
The filling resin layer 18 is provided between the color filter 17 and the counter substrate 19. The filling resin layer 18 has a function as an adhesive layer for bonding the color filter 17 and the counter substrate 19. The filling resin layer 18 includes, for example, at least one selected from a group including a thermosetting resin, an ultraviolet curable resin, and the like.
The counter substrate 19 is provided to face the drive substrate 11. More specifically, the counter substrate 19 is provided such that the second surface of the counter substrate 19 and the first surface of the drive substrate 11 face each other. The counter substrate 19 and the filling resin layer 18 seal the light emitting element 20, the color filter 17, and the like. The counter substrate 19 includes a material such as glass transparent to each color light emitted from the color filter 17.
0≤Ebulk(1)−Einterface(1)≤0.3 eV (1)
In order to control band bending of the hole transport layer 14A so as to satisfy the above Formula (1), it is only required to control the positional relationship of the Fermi level between the insulating layer 13 and the hole transport layer 14A.
The energy level Einterface(1) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 14 is removed. After the removal, the organic EL layer 14 is etched from the interface between the insulating layer 13 and the hole transport layer 14A to a position of 2 nm on the hole transport layer 14A side by ion sputtering. Subsequently, an energy level (highest occupied molecular orbital (HOMO)) of the surface exposed by etching is measured by X-ray photoelectron spectroscopy (XPS), and the measured value is defined as the energy level Einterface(1). The measurement conditions of XPS are as follows.
The energy level Ebulk(1) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 14 is removed. After the removal, the organic EL layer 14 is etched from the interface between the insulating layer 13 and the hole transport layer 14A to a position of 10 nm on the hole transport layer 14A side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(1). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) described above.
Hereinafter, an example of a method of manufacturing the display device 10 according to the first embodiment of the present disclosure will be described.
First, a metal layer and a metal oxide layer are sequentially formed on the first surface of the drive substrate 11 by, for example, a sputtering method, and then the metal layer and the metal oxide layer are patterned using, for example, a photolithography technique and an etching technique. Thus, the first electrode layer 12 having the plurality of electrodes 12A is formed.
Next, the insulating layer 13 is formed on the first surface of the drive substrate 11 so as to cover the plurality of electrodes 12A by, for example, a chemical vapor deposition (CVD) method. At this time, for example, by using two types of gases of SiH4 and NH3 as process gases and adjusting the flow ratio of these two types of process gases, it is possible to set the energy level Einterface(1) and the energy level Ebulk(1) to satisfy the above Formula (1). Next, an opening 13A is formed in a portion of the insulating layer 13 located on the first surface of each electrode 12A by, for example, the photolithography technique and the dry etching technique.
Next, the hole transport layer 14A, the red light emitting layer 14B, the light emission separation layer 14C, the blue light emitting layer 14D, the green light emitting layer 14E, the electron transport layer 14F, and the electron injection layer 14G are stacked in this order on the first surface of the plurality of electrodes 12A and the first surface of the insulating layer 13 by, for example, a vapor deposition method, thereby forming the organic EL layer 14. Next, the second electrode layer 15 is formed on the first surface of the organic EL layer 14 by, for example, the vapor deposition method or the sputtering method. Thus, the plurality of light emitting elements 20 is formed on the first surface of the drive substrate 11.
Next, the protective layer 16 is formed on the first surface of the second electrode layer 15 by, for example, the CVD method or the vapor deposition method, and then the color filter 17 is formed on the first surface of the protective layer 16 by, for example, photolithography. Note that, in order to flatten a level difference of the protective layer 16 and a level difference due to a film thickness difference of the color filter 17 itself, a flattening layer may be formed on an upper side, a lower side, or both the upper and lower sides of the color filter 17. Next, the color filter 17 is covered with the filling resin layer 18 using, for example, a one drop fill (ODF) method, and then the counter substrate 19 is placed on the filling resin layer 18. Next, for example, by applying heat to the filling resin layer 18 or irradiating the filling resin layer 18 with ultraviolet rays to cure the filling resin layer 18, the drive substrate 11 and the counter substrate 19 are bonded via the filling resin layer 18. Thus, the display device 10 is sealed. As described above, the display device 10 illustrated in
As described above, in the display device 10 according to the first embodiment, as illustrated in
The organic EL layer 34 is different from the organic EL layer 14 in the first embodiment in including a hole transport layer 34A having a two-layer structure instead of the hole transport layer 14A having a single-layer structure. The hole transport layer 34A includes a first hole transport layer 34A1 and a second hole transport layer 34A2. The first hole transport layer 34A1 is adjacent to the first electrode layer 12 and the insulating layer 13 (see
0≤Ebulk(2b)−Ebulk(2a)≤0.3 eV (2)
The energy level Ebulk(2a) is measured as follows described above. Each layer formed on the first surface of the organic EL layer 34 is removed. After the removal, the organic EL layer 34 is etched from the interface between the insulating layer 13 and the first hole transport layer 34A1 to a position of 10 nm toward the first hole transport layer 34A1 side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(2a). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) in the first embodiment.
The energy level Ebulk(2b) is measured as follows described above. Each layer formed on the first surface of the organic EL layer 34 is removed. After the removal, the organic EL layer 34 is etched from the interface between the first hole transport layer 34A1 and the second hole transport layer 34A2 to a position of 10 nm toward the second hole transport layer 34A2 side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(2b). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) in the first embodiment.
As described above, in the display device 30 according to the second embodiment, as illustrated in
The organic EL layer 44 is different from the organic EL layer 14 in the first embodiment in further including a hole injection layer 44A. The hole injection layer 44A is provided between the first electrode layer 12 (see
0≤Ebulk(3)−Einterface(3)≤0.3 eV (3)
The energy level Einterface(3) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, the organic EL layer 44 is etched from the interface between the hole injection layer 44A and the hole transport layer 14A to a position of 2 nm toward the hole transport layer 14A side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Einterface(3). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) in the first embodiment.
The energy level Ebulk(3) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, the organic EL layer 44 is etched from the interface between the hole injection layer 44A and the hole transport layer 14A to a position of 10 nm toward the hole transport layer 14A side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(3). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) described above.
In a case where the hole injection layer 44A and the insulating layer 13 include nitrogen, the bond energy EHILN of N1s in the hole injection layer 44A and the bond energy EILN of N1s in the insulating layer 13 preferably satisfy the following Formula (3a).
2.7 eV<EHILN−EILN (3a)
The bond energy EHILN described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, the organic EL layer 44 is etched by ion sputtering to expose the surface (first surface) of the hole injection layer 44A. Subsequently, the exposed surface of the hole injection layer 44A is subjected to XPS measurement to acquire an XPS spectrum. From this XPS spectrum, a bond energy value at the vertex of the peak derived from the N1s orbit of the hole injection layer 44A is obtained and defined as bond energy EHILN.
The bond energy EILN described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, next, the organic EL layer 44 is etched by ion sputtering to expose the surface (first surface) of the insulating layer 13. Next, the exposed surface of the insulating layer 13 is subjected to XPS measurement to acquire an XPS spectrum. From this XPS spectrum, a bond energy value at the vertex of the peak derived from the N1s orbit of the insulating layer 13 is obtained and defined as bond energy EILN. Note that the measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) described above.
As described above, in the display device 40 according to the third embodiment, as illustrated in
The organic EL layer 54 is different from the organic EL layer 44 in the third embodiment in including a hole transport layer 54A having a two-layer structure instead of the hole transport layer 14A having a single-layer structure. The hole transport layer 54A includes a first hole transport layer 54A1 and a second hole transport layer 54A2. The first hole transport layer 54A1 is adjacent to the hole injection layer 44A. The second hole transport layer 54A2 is adjacent to the red light emitting layer 14B.
0≤Ebulk(4b)−Ebulk(4a)≤0.3 eV (4)
The energy level Ebulk(4a) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, the organic EL layer 54 is etched from the interface between the hole injection layer 44A and the first hole transport layer 54A1 to a position of 10 nm toward the first hole transport layer 34A1 side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(4a). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) described above.
The energy level Ebulk(4b) described above is measured as follows. Each layer formed on the first surface of the organic EL layer 44 is removed. After the removal, the organic EL layer 54 is etched from the interface between the first hole transport layer 54A1 and the second hole transport layer 54A2 to a position of 10 nm toward the second hole transport layer 54A2 side by ion sputtering. Subsequently, the energy level (HOMO) of the surface exposed by etching is measured by XPS, and the measured value is defined as the energy level Ebulk(4b). The measurement conditions of XPS are similar to those of the method of measuring the energy level Einterface(1) in the first embodiment.
As described above, in the display device 50 according to the fourth embodiment, as illustrated in
In the first to fourth embodiments, an example in which the organic EL layers 14, 34, 44, and 54 include a single-layer light emitting unit has been described, but the organic EL layers may have a stack structure including a plurality of stacked light emitting units. In this case, a charge generation layer is sandwiched between adjacent light emitting units.
In the second and fourth embodiments, an example has been described in which the hole transport layers 34A and 54A have a stacked structure including two layers, but may have a stacked structure including three or more layers.
In the first to fourth embodiments, an example of adjusting the band bending of the hole transport layers 14A, 34A, and 54A by adjusting the process gas flow ratio at the time of forming the insulating layer 13 has been described, but the method of adjusting the band bending is not limited thereto.
The band bending may be controlled by adjusting film formation conditions of the insulating layer 13 other than the process gas flow ratio. Specifically, for example, the hydrogen content in the insulating layer 13 may be controlled. Alternatively, p-type doping or n-type doping may be performed on the insulating layer 13 to change a donor level or an acceptor level in the insulating layer 13.
Constituent materials of the hole transport layers 14A, 34A, and 54A may be selected to control the band bending. Specifically, for example, a hole transport material having a Fermi level (HOMO, LUMO (Lowest Unoccupied Molecular Orbital)) such that the band bending is 0.3 eV or less may be used. In a case of the hole transport layer 34A having a stacked structure including two layers, as the hole transport material of the first hole transport layer 34A1 and the second hole transport layer 34A2, one having a Fermi level (HOMO, LUMO) such that the HOMO energy difference is 0.3 eV or less in a state where the first hole transport layer 34A1 and the second hole transport layer 34A2 are joined may be used. Also in a case of the hole transport layer 54A having a stacked structure including two layers, the hole transport material of each layer may be selected similarly to a case of the hole transport layer 34A having the stacked structure described above.
In the first to fourth embodiments, an example in which the method using the white light emitting element and the color filter 17 is used as a coloring method in the display device 10 has been described, but the coloring method is not limited thereto. For example, a method of extracting three-color light (red light, green light, and blue light) by a resonator structure may be used, or a method of enhancing color purity by using the color filter 17 and the resonator structure in combination may be used.
The display devices 10, 30, 40, and 50 (hereinafter referred to as a “display devices 10 and so on”) according to the above-described first to fourth embodiments and the modification examples thereof can be used for various electronic devices. The display devices 10 and so on are incorporated in various electronic devices, for example, as a module as illustrated in
A monitor 314 is provided at a position shifted to the left from the center of a rear surface of the camera body 311. An electronic viewfinder (eyepiece window) 315 is provided above the monitor 314. By looking through the electronic viewfinder 315, the photographer can visually confirm a light image of the subject guided from the imaging lens unit 312 and determine a picture composition. As the electronic viewfinder 315, any of the display devices 10 and so on can be used.
Hereinafter, the present disclosure will be specifically described with reference to examples, but the present disclosure is not limited to only these examples.
First, a metal layer (Al alloy layer) and a metal oxide layer (ITO layer) were sequentially formed on the first surface of the drive substrate by the sputtering method, and then the metal layer and the metal oxide layer were patterned using the photolithography technique and an etching technique. Thus, a first electrode layer having a plurality of electrodes was formed.
Next, an insulating layer (SiN layer) having an average thickness of 40 nm was formed on the first surface of the drive substrate by the CVD method. At this time, SiH4 gas and NH3 gas were used as process gases. Furthermore, the flow ratio between the SiH4 gas and the NH3 gas was adjusted so that EHILN EILN had values indicated in Table 1. Thus, a layer having a fixed charge was simultaneously formed on the first surface of the insulating layer. The larger EHILN EILN, the smaller the amount of the fixed charge.
Next, an opening was formed in a portion of the insulating layer located on the first surface of each electrode by the photolithography technique and the dry etching technique. Next, an organic EL layer was formed by stacking a hole injection layer (HATCN), a hole transport layer (α-NPD), a light emitting layer, and an electron transport layer on the electrode and the insulating layer by the vapor deposition method. Next, a second electrode layer (MgAg alloy layer) was formed on the first surface of the organic EL layer. Thus, an intended display device was obtained.
(EHILN−EILN)
EHILN and EILN of the display devices of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described above were measured as in the third embodiment, and EHILN−EILN was obtained. The results are indicated in Table 1.
Leakage currents between subpixels of the display devices of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described above were measured. The results are indicated in Table 1. Furthermore, the relationship between EHILN−EILN and the leakage currents between the subpixels is illustrated in
Table 1 indicates evaluation results of the display devices of Examples 1 and 2 and Comparative Examples 1 and 2.
Table 1 and
The leakage currents between the subpixels depend on the value of EHILN−EILN. Specifically, when leakage is determined with the leakage amount (=1.0) of Comparative Example 1 as a reference value, in a case where 2.7 eV<EHILN−EILN, a leakage current flowing between the subpixels can be prevented. On the other hand, in a case where EHILN−EILN 2.7 eV, it is difficult to prevent the leakage current from flowing between the subpixels.
By device simulation, the relationship between the difference between the HOMO of the hole injection layer and the HOMO of the insulating layer and the hole concentration (leakage amount) between the subpixels was obtained. The results are indicated in
Conditions of the device simulation were set as follows. Note that a state in which the display device is driven was simulated in the device simulation.
From the result of the device simulation described above (see
The band bending amount in which the difference in leakage amount as described above appears is calculated as follows.
I=envS
(I: current, e: charge of one free electron, n: number density of free electrons, and vS: volume corresponding to movement of free electron)
In a case where the above formula is used, the current I can be expressed as follows.
I∝n∝exp(−ΔE/kT)
(ΔE: energy difference, k: Boltzmann constant, and T: absolute temperature)
Using the energy values E0, E1, and E2 defined in
I
1∝exp(−(E0−E1)/kT)
I
2∝exp(−(E0−E2)/kT)
Since there is a difference of 104 times between the current I1 and the current I2, the difference is expressed as follows.
I
1
/I
2=104=exp(−((E0−E1)+(E0−E2))/kT)=exp((E1−E2)/kT)
When the above formula is solved by substituting values for k and T, E1−E2 is expressed as follows.
E
1
−E
2=0.3 eV
In a case where the leakage current is prevented, assuming that Ebulk−Einterface=0 (E0−E1=0), E1−E2 is expressed as follows.
E
1
−E
2
=E
0
−E
2=0.3 eV
Therefore, the band bending amount in a state where 104 times the leakage current flows from the state where the leakage current is prevented is 0.3 eV.
Although the first to fourth embodiments of the present disclosure and modification examples thereof have been specifically described above, the present disclosure is not limited to the first to fourth embodiments described above and their modification examples, and various modifications based on the technical idea of the present disclosure are possible.
For example, the configurations, methods, steps, shapes, materials, numerical values, and the like given in the first to fourth embodiments described above and the modification examples thereof are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, and the like may be used as necessary.
The configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described first to fourth embodiments and the modifications thereof can be combined with each other without departing from the gist of the present disclosure.
The materials exemplified in the above-described first to fourth embodiments and the modification examples thereof can be used alone or in combination of two or more unless otherwise specified.
Further, the present disclosure can also employ the following configurations.
(1)
A display device, including:
0≤Ebulk(1)−Einterface(1)≤0.3 eV (1)
(2)
A display device, including:
0≤Ebulk(2b)−Ebulk(2a)≤0.3 eV (2)
(3)
A display device, including:
0≤Ebulk(3)−Einterface(3)≤0.3 eV (3)
(4)
A display device, including:
0≤Ebulk(4b)−Ebulk(4a)≤0.3 eV (4)
(5)
The display device according to (3) or (4), in which
2.7 eV<EHILN−EILN (3a)
(6)
The display device according to (5), in which
(7)
The display device according to any one of (1) to (6), in which
(8)
An electronic device including the display device according to any one of (1) to (7).
Number | Date | Country | Kind |
---|---|---|---|
2020-212887 | Dec 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2021/047535 | 12/22/2021 | WO |