Electro-optical device and electronic apparatus

Abstract

The invention provides an electro-optical device and an electronic apparatus, which restrain a driving voltage to be low while ensuring high brightness. The electro-optical device includes a light-emitting element in which are laminated in this order: a first electrode having reflectivity; a first light emitting layer emitting light of a first wavelength region including a first wavelength; a donor layer; an acceptor layer in contact with the donor layer; a second light emitting layer emitting light of a second wavelength region including a second wavelength; and a second electrode having reflectivity and translucency, the first wavelength region and the second wavelength region partially or entirely overlapping each other.

Description

Technical Field

[0001] This invention relates to electro-optical devices and electronic devices. Background Technology

[0002] An electro-optical device using, for example, an OLED (Organic Light Emitting Diode) as the light-emitting element is known. In such an electro-optical device using an OLED, a technique is known to ensure high brightness by using a so-called series element (see, for example, Patent Document 1) that connects two or more light-emitting units in series. In such a series element, compared to a structure with a single light-emitting unit, twice the brightness can be obtained with the same amount of current.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2006-302506

[0004] However, the series element described in Patent Document 1 has a technical problem where the driving voltage needs to be more than twice that required. In particular, since the pixel pitch is only a few μm, and in a microdisplay where the driving circuit and pixel unit are constructed on a semiconductor substrate, the driving voltage cannot be increased due to the limitation imposed by the size of the transistors that form the components. Summary of the Invention

[0005] One aspect of the electro-optical device disclosed herein includes a light-emitting element comprising, in sequence: a first electrode having reflectivity; a first light-emitting layer emitting light in a first wavelength region including a first wavelength; a donor layer; a acceptor layer in contact with the donor layer; a second light-emitting layer emitting light in a second wavelength region including a second wavelength; and a second electrode having reflectivity and transmittance, wherein the first wavelength region partially or completely overlaps with the second wavelength region. Attached Figure Description

[0006] Figure 1 This is a diagram showing the structure of the electro-optical device according to the first embodiment.

[0007] Figure 2 This is a block diagram showing the electrical structure of the electro-optical device.

[0008] Figure 3 This is a circuit diagram showing the pixel section of an electro-optical device.

[0009] Figure 4 It is a timing diagram showing the operation of the electro-optical device.

[0010] Figure 5 This is a top view showing the pixel section of the electro-optical device.

[0011] Figure 6This diagram shows organic layers, etc., stacked on pixel electrodes in an electro-optic device.

[0012] Figure 7 This is a diagram showing an example of the thickness of organic layers, etc., in an electro-optical device.

[0013] Figure 8 This is a diagram showing the organic layer, etc., stacked on the pixel electrode in the comparative example.

[0014] Figure 9 This is a diagram showing an example of the thickness of the organic layer, etc., in a comparative example.

[0015] Figure 10 This is a graph showing the characteristics of the driving voltage-current density in the first embodiment and the comparative example.

[0016] Figure 11 This is a graph showing the emission spectra in the first embodiment and the comparative example.

[0017] Figure 12 This is a diagram showing the brightness and chromaticity in the first embodiment and the comparative example.

[0018] Figure 13 This is a diagram showing the luminescence location in the comparative example.

[0019] Figure 14 This is a diagram showing the light-emitting position in the first embodiment.

[0020] Figure 15 This is a perspective view showing a head-mounted display using an electro-optical device as described in the embodiments, etc.

[0021] Figure 16 This is a diagram showing the optical structure of a head-mounted display.

[0022] Explanation of reference numerals in the attached figures

[0023] 10: Electro-optic device; 12: Scan line; 14: Data line; 100: Display area; 62: Reflective electrode; 131: Pixel electrode; 130: OLED; 132: Organic layer; 133: Common electrode. Detailed Implementation

[0024] Hereinafter, the electro-optical device according to embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the dimensions and scales of each part in the drawings are appropriately different from the actual dimensions and scales. Furthermore, the embodiments described below are preferred examples, and therefore various technically preferred limitations have been added. However, unless the scope of the present invention is specifically limited in the following description, the scope of the present invention is not limited to these embodiments.

[0025] Figure 1This is a perspective view showing the electro-optical device 10 according to the first embodiment. Figure 2 This is a block diagram showing the electrical structure of the electro-optical device 10.

[0026] The electro-optical device 10 is, for example, a miniature display panel that displays color images in a head-mounted display or similar device. The electro-optical device 10 includes multiple pixel units, driving circuitry for driving the pixel units, etc. The pixel units and the driving circuitry are integrated onto a semiconductor substrate. The semiconductor substrate is typically a silicon substrate, but other semiconductor substrates may also be used.

[0027] The electro-optical device 10 is housed in a frame-shaped housing 192 with an opening in the display area 100. An FPC substrate 194 is connected to one end of the electro-optical device 10. It should be noted that FPC is short for Flexible Printed Circuits. Multiple terminals 196 for connecting a main device (not shown) are provided at the other end of the FPC substrate 194. When the multiple terminals 196 are connected to the main device, image data, synchronization signals, etc., are supplied from the main device to the electro-optical device 10 via the FPC substrate 194.

[0028] It should be noted that in the figure, the X direction is the extension direction of the scan line in the electro-optic device 10, which represents the horizontal direction in the display screen. The Y direction is the extension direction of the data line, which represents the vertical direction in the display screen. The two-dimensional plane defined by the X and Y directions is the substrate surface of the semiconductor substrate. The Z direction is the emission direction of light emitted from the light-emitting element, which is perpendicular to the substrate surface of the semiconductor substrate. In addition, in this description, top view means observing the semiconductor substrate from the direction opposite to the Z direction, and cross-sectional view means observing the semiconductor substrate by cutting it in the direction perpendicular to the substrate surface.

[0029] like Figure 2 As shown, the electro-optical device 10 is roughly divided into a control circuit 30, a data signal output circuit 50, a display area 100, and a scan line drive circuit 120.

[0030] In the display area 100, the scan lines 12 of m rows are arranged along the X direction, and the data lines 14 of (3n) columns are arranged along the Y direction and in a manner that keeps them electrically insulated from each scan line 12. It should be noted that m and n are integers greater than 2.

[0031] In the display area 100, the pixel units 110 are arranged corresponding to the intersections of the m-row scan lines 12 and the (3n)-column data lines 14. Therefore, the pixel units 110 are arranged in a matrix of m rows × (3n) columns. In the matrix arrangement, in order to distinguish the rows, they are sometimes referred to as rows 1, 2, 3, ..., (m-1), m from top to bottom in the diagram. Similarly, in order to distinguish the columns of the matrix, they are sometimes referred to as columns 1, 2, 3, ..., (3n-2), (3n-1), (3n) from left to right in the diagram.

[0032] It should be noted that, for the general description of scan line 12, an integer i of 1 or higher and less than m is used. Similarly, for the general description of data line 14, an integer j of 1 or higher and less than (3n) is used.

[0033] The control circuit 30 controls each component based on the image data Vid and the synchronization signal Sync supplied from the host device (not shown in the figure). Specifically, the control circuit 30 generates various control signals to control each component.

[0034] Image data Vid, for example, uses 8 bits to specify the grayscale level of the pixels in the image to be displayed. The synchronization signal Sync includes a vertical synchronization signal indicating the start of vertical scanning of image data Vid, a horizontal synchronization signal indicating the start of horizontal scanning, and a dot clock signal indicating the amount of image data in one pixel.

[0035] In this embodiment, the pixels of the image to be displayed correspond one-to-one with the pixel portions 110 in the display area 100.

[0036] The brightness characteristics of the grayscale levels shown in the image data Vid supplied from the main device may not be consistent with the brightness characteristics of the OLED included in the pixel unit 110. Therefore, in order to make the OLED emit light with a brightness corresponding to the grayscale levels shown in the image data Vid, the control circuit 30 upconverts, for example, the 8 bits of the image data Vid to 10 bits and outputs it as image data Vdata. Thus, the 10-bit image data Vdata becomes data corresponding to the grayscale levels specified by the image data Vid.

[0037] It should be noted that in the upconversion process, a lookup table is used that pre-stores the correspondence between the 8 bits of the input image data Vid and the 10 bits of the output image data Vdata.

[0038] The scan line drive circuit 120 is a circuit used to drive the pixel section 110 arranged in m rows (3n columns) one row at a time, according to the control of the control circuit 30. For example, the scan line drive circuit 120 supplies scan signals / Gwr(1), / Gwr(2), ..., / Gwr(m-1), / Gwr(m) sequentially to the scan lines 12 in rows 1, 2, 3, ..., (m-1), and m. Generally, the scan signal supplied to the scan line 12 in row i is denoted as / Gwr(i).

[0039] The data signal output circuit 50 is a circuit that outputs data signals to the pixel portions 110 located in the row selected by the scan line drive circuit 120 via the data line 14 under the control of the control circuit 30. The data signal is a voltage signal obtained by converting 10-bit image data Vdata into an analog signal. That is, the data signal output circuit 50 converts the amount of image data Vdata corresponding to one row of pixel portions 110 in columns 1 to (3n) of the selected row into an analog signal and outputs it to the data line 14 of columns 1 to (3n) in that order.

[0040] In the diagram, the data signals output to data lines 14 in columns 1, 2, 3, ..., (3n-2), (3n-1), and (3n) are denoted as Vd(1), Vd(2), Vd(3), ..., Vd(3n-2), Vd(3n-1), and Vd(3n) respectively. Generally, the potential of data line 14 in column j is denoted as Vd(j).

[0041] In display area 100, such as Figure 2 As shown, at the electrical level, the pixel units 110 are arranged along the X direction in the order of R pixel units 110, B pixel units 110, and G pixel units 110, and the pixel units 110 of the same color are arranged along the Y direction. Therefore, if we focus on any one column of data lines 14, there are corresponding pixel units 110 of the same color.

[0042] It should be noted that color is represented by a single point through additive color mixing of adjacent RBG pixel portions 110 in the X direction. Therefore, in the first embodiment, color display of m rows × n columns can be achieved using a single point. Strictly speaking, pixel portion 110 should be called a sub-pixel portion, but for ease of explanation, it is referred to as pixel portion.

[0043] Figure 3 This diagram shows the electrical structure of the pixel unit 110 in the electro-optic device 10. The pixel units 110 arranged in m rows (3n columns) are electrically identical to each other. Therefore, for each pixel unit 110, we will describe one pixel unit 110 corresponding to the i-th row and j-th column.

[0044] As shown in the figure, from an electrical perspective, the pixel unit 110 includes P-channel MOS transistors 121 and 122, an OLED 130, and a capacitor element 140.

[0045] It should be noted that in the description of the pixel unit 110, "from an electrical point of view" is used to describe the multiple elements constituting the pixel unit 110 and the connection relationship between these multiple elements. The pixel unit 110 includes elements that do not contribute to the electrical connection relationship from a mechanical or physical point of view, hence this expression is used.

[0046] OLED 130 is an example of a light-emitting element, consisting of an organic layer 132 containing the light-emitting layer sandwiched between a pixel electrode 131 and a common electrode 133. As described above, the pixel electrode 131 functions as the anode of the OLED 130, and the common electrode 133 functions as the cathode of the OLED 130. It should be noted that details regarding the OLED 130 will be described later. When current flows from the anode to the cathode, holes injected from the anode and electrons injected from the cathode recombine in the light-emitting layer to generate excitons, producing light.

[0047] A portion of the wavelength range of the produced light is in Figure 3 The light emitted from the OLED 130 resonates in the common electrode 133 formed by the reflective electrode and the semi-reflective / semi-transmissive layer. The wavelength of the light is amplified by this resonator before being emitted, while light from other wavelength regions is emitted without resonating in the resonator. In this embodiment, some of the light is blue light, and the rest is yellow light. Therefore, the emitted light from the OLED 130 becomes white light, a mixture of blue and yellow light. It should be noted that the emitted light from the OLED 130 passes through a color layer corresponding to the color of the pixel 110, and is visually perceived by the observer as the color of this color layer.

[0048] In row i and column j, in the transistor 121 of pixel section 110, the gate node g is connected to the drain node of transistor 122, the source node s is connected to the power supply line 116 of voltage Vel, and the drain node is connected to the pixel electrode 131, which serves as the anode of OLED 130.

[0049] In transistor 122, the gate node is connected to the scan line 12 in the i-th row, and the source node is connected to the data line 14 in the j-th column. The common electrode 133, which functions as the cathode of OLED 130, is connected to the power supply line 118 with voltage Vct. Furthermore, since the electro-optic device 10 is formed on a silicon substrate, the substrate potential of transistors 121 and 122 is, for example, a potential equivalent to voltage Vel.

[0050] It should be noted that the voltage (Vel-Vct) is the driving voltage of the OLED 130.

[0051] From an electrical perspective, Figure 3 The pixel unit 110 shown is identical for each red, green, and blue color, so it has been described generally without specifying the color. However, from a structural perspective, it differs for each color. Therefore, when described by color, it is designated as pixel unit 110R, 110G, and 110B. Similarly, regarding OLED 130 and pixel electrode 131, when described by color, they are also designated as OLED 130R, 130G, and 130B, and pixel electrode 131R, 131G, and 131B.

[0052] Figure 4 This is a timing diagram used to illustrate the operation of the electro-optical device 10.

[0053] In the electro-optical device 10, the m-line scan lines 12 scan one line at a time during the frame (V) in the order of line 1, 2, 3, ..., m. Specifically, as shown in the figure, the scan signals / Gwr(1), / Gwr(2), ..., / Gwr(m-1), / Gwr(m) are sequentially and exclusively at the L level during each horizontal scan period (H) via the scan line drive circuit 120.

[0054] It should be noted that in this embodiment, the periods during which adjacent scan signals / Gwr(1) to / Gwr(m) are at the L level are time-isolated. Specifically, after the scan signal / Gwr(i-1) changes from the L level to the H level, it becomes the L level again after the interval of the next scan signal / Gwr(i). This period corresponds to the horizontal retrace period.

[0055] In this description, the duration of 1 frame (V) refers to the period required to display 1 frame of the image specified by the image data Vid. If the length of the duration of 1 frame (V) is the same as the vertical synchronization period, specifically, if the frequency of the vertical synchronization signal included in the synchronization signal Sync is 60Hz, then it is 16.7 milliseconds, which is equivalent to one cycle of that vertical synchronization signal. In addition, the horizontal scan period (H) is the interval between the scan signals / Gwr(1) to / Gwr(m) successively reaching the L level, but for convenience in the figure, the start timing of the horizontal scan period (H) is set to approximately the center of the horizontal retrace period.

[0056] When one of the scan signals / Gwr(1) to / Gwr(m) is supplied to the scan signal / Gwr(i) of the scan line 12 in the i-th row and becomes L level, in the pixel section 110 of the i-th row and j-th column, the transistor 122 becomes on. Therefore, the gate node g of the transistor 121 in the pixel section 110 becomes electrically connected to the data line 14 of the j-th column.

[0057] It should be noted that, in this explanation, the "on state" of a transistor refers to the low-impedance state where the source and drain nodes are electrically closed. Conversely, the "off state" of a transistor refers to the high-impedance state where the source and drain nodes are electrically disconnected.

[0058] In addition, in this description, "electrical connection" or simply "connection" refers to a state in which two or more elements are directly or indirectly connected or combined. "Non-electrical connection" or simply "non-connection" refers to a state in which two or more elements are not directly or indirectly connected or combined.

[0059] During the horizontal scan (H) when the scan signal / Gwr(i) is at level L, the data signal output circuit 50 converts the gray levels of the pixels in row i, column 1 to row i (3n) represented by image data Vdata into analog potentials Vd(1) to Vd(3n), and outputs them as data signals to the data lines 14 of columns 1 to (3n). For the j-th column, the data signal output circuit 50 converts the gray level d(i,j) of the pixel in row i, column j into the analog potential Vd(j), and outputs it as a data signal to the data line 14 of column j.

[0060] It should be noted that during the horizontal scanning period (H) when the scanning signal / Gwr(i-1) in the row preceding the scanning signal / Gwr(i) becomes L level, the data signal output circuit 50 converts the gray level d(i-1,j) of the pixel in row (i-1) and column j into the potential Vd(j) of the analog signal, and outputs it as a data signal to the data line 14 of column j.

[0061] The data signal at potential Vd(j) is applied to the gate node g of transistor 121 in pixel portion 110 of row i and column j via data line 14 of column j, and the potential Vd(j) is held by capacitor element 140. Therefore, transistor 121 causes current corresponding to the voltage between gate node and source node to flow through OLED 130.

[0062] Even when the scan signal Gwr(i) reaches a high level and transistor 122 is in the off state, the potential Vd(j) is maintained by capacitor element 140, thus current continues to flow in OLED 130. Therefore, in the pixel section 110 of row i and column j, before transistor 122 turns on again and applies the voltage of the data signal again after one frame (V), OLED 130 continuously emits light with a brightness corresponding to the voltage maintained by capacitor element 140, i.e., the grayscale level.

[0063] It should be noted that the pixel unit 110 in row i and column j has been described here, but the OLED 130 in the pixel unit 110 outside the row i and column j also emits light with a brightness represented by image data Vdata.

[0064] In addition, for the OLED 130 of the pixel section 110 other than the i-th row, the scanning signals / Gwr(1) to / Gwr(m) are sequentially changed to L level to emit light with the brightness represented by the image data Vdata.

[0065] Therefore, in the electro-optical device 10, during one frame (V), the OLEDs 130 in all pixel units 110 from row 1 column to m rows (3n) columns emit light at the brightness shown by the image data Vdata, displaying an image of one frame.

[0066] Figure 5 This diagram simply illustrates the structure of the pixel portion 110 in the display area 100 when viewed from above. In the display area 100, the color of a point is represented by additive color mixing of the colored light emitted from the three regions enclosed by the frame Dp. Specifically, in the frame Dp, regions R, G, and B are arranged in this order along the X direction. White light emitted from region R is colored red after passing through a coloring layer near the front of the paper (omitted in diagram 5) and emitted. Similarly, white light emitted from regions G and B is colored green and blue respectively after passing through the coloring layers and emitted.

[0067] In the pixel section 110R, a reflective electrode 62R and a pixel electrode 131R are stacked sequentially. It should be noted that the reflective electrode 62R is electrically connected to the drain node d of the transistor 121 via a contact hole that opens into the insulating layer.

[0068] The diagram omits the insulating layer disposed between the drain node d and the reflective electrode 62R in transistor 121 and the contact hole for the opening in the insulating layer.

[0069] The reflective electrode 62R corresponds to the pixel unit 110R, such as Figure 5 The rectangular light-reflective conductive electrode, as shown, reflects light incident from the opposite direction of the Z direction back to the Z direction. For example, a conductive layer of an alloy (AlCu) film of aluminum and copper is used as the reflective electrode 62R.

[0070] The pixel electrode 131R is a rectangular conductive electrode that is patterned by overlapping a light-transmitting material, such as ITO (Indium Tin Oxide), with the reflective electrode 62R.

[0071] Pixel electrode 131R is an electrode formed by patterning the same ITO film as pixel electrodes 131G and 131B corresponding to other colors. With a thickness of 15nm for pixel electrodes 131R, 131G, and 131B and a refractive index of 1.98 for ITO, the optical distance, which is the product of the thickness and refractive index, in pixel electrodes 131R, 131G, and 131B is 29.7nm.

[0072] The same applies to pixel units 110G and 110B. Specifically, in pixel unit 110G, a reflective electrode 62G and a pixel electrode 131G are stacked sequentially, and in pixel unit 110B, a reflective electrode 62B and a pixel electrode 131B are stacked sequentially.

[0073] The openings Ap_R, Ap_G, and Ap_B are the frame ends of the openings covering the insulating layer of pixel electrodes 131R, 131G, and 131B. In other words, the pixel electrodes 131R, 131B, and 131G sequentially expose the insulating layer defined by the openings Ap_R, Ap_G, and Ap_B at their openings.

[0074] In the exposed areas of pixel electrodes 131R, 131B, and 131G, organic layers, etc., which will be described below, are stacked. It should be noted that the stacking of organic layers, etc., is the same for pixel portions 110R, 110G, and 110B. Therefore, the reference numerals from the pixel electrodes to the common electrodes will be omitted in the following description.

[0075] In the electro-optical device 10 of this embodiment, a series element consisting of three light-emitting units connected in series is used to obtain high brightness. However, in a simple series element, a high driving voltage is required as described above. Therefore, in this embodiment, the light-emitting unit closest to the reflective electrode among the three light-emitting units constituting the series element is configured to use an up-conversion type derived from an excimer compound.

[0076] Figure 6 This diagram illustrates the layer structure of electrodes, organic layers, etc., stacked on the exposed area of ​​the pixel electrode in the pixel section. It should be noted that in the diagram, the left column shows a general outline of the layer structure, while the right column shows a detailed representation. Additionally, Figure 7 This is a diagram showing an example of the thickness of the organic layer, electrode layer, etc.

[0077] like Figure 6 As shown in the left column, in the exposed area of ​​the pixel electrode in the pixel part, a first light-emitting unit, a charge-generating layer, a second light-emitting unit, a charge-generating layer, a third light-emitting unit, and a common electrode are stacked in sequence.

[0078] It should be noted that, although omitted in the figure, a sealing layer, a coloring layer, and a cover glass are stacked sequentially on the common electrode.

[0079] like Figure 6 As shown in the right column, the first light-emitting unit is a structure in which a first donor layer, a first light-emitting layer, a second donor layer, and a acceptor layer are stacked sequentially on the pixel electrode.

[0080] The first donor layer is a material with a LUMO (lowest unoccupied molecular orbital) of about 3.0 eV and a HOMO (highest occupied molecular orbital) of about 6.0 eV, such as an anthracene derivative.

[0081] It should be noted that the thickness of the first donor layer is, for example, 10 nm. If the refractive index of the first donor layer is 1.90, then the optical distance of the first donor layer is 19.0 nm.

[0082] The first light-emitting layer has a matrix formed of the same material as the first donor layer, and is doped with a dopant that emits blue light. In other words, the first light-emitting layer is a layer in which a portion of the donor layer is doped with a blue light-emitting dopant.

[0083] It should be noted that the thickness of the first light-emitting layer is, for example, 20 nm. If the refractive index of the first light-emitting layer is 1.90, then the optical distance of the first light-emitting layer is 38.0 nm. Furthermore, the wavelength region of blue light is above 400 nm and below 500 nm.

[0084] The second donor layer is made of the same material as the first donor layer. It should be noted that the thickness of the second donor layer is, for example, 10 nm. If the refractive index of the second donor layer is the same as that of the first donor layer, then the optical distance of the second donor layer is 19.0 nm.

[0085] The acceptor layer is made of a material with a LUMO of approximately 3.8 eV, such as a naphthalimide (NTCDI) derivative. The thickness of the acceptor layer is, for example, 45 nm. If the refractive index of the acceptor layer is 1.84, then the optical distance of the acceptor layer is 82.8 nm.

[0086] The charge generation layer (CGL) is a pn junction of an n-type charge generation layer (nCGL) and a hole generation layer (pCGL). The nCGL located on the n-side of the pn junction generates electrons and injects these electrons into the layer adjacent to the anode side. The pCGL located on the p-side of the pn junction generates holes and injects the generated holes into the layer adjacent to the cathode side.

[0087] That is, the nCGL of the charge generation layer in the light-emitting unit of the series element supplies electrons to the first light-emitting unit on the anode side, and the pCGL supplies holes to the second light-emitting unit on the cathode side.

[0088] It should be noted that the thickness of nCGL is, for example, 10 nm. If the refractive index of nCGL is 1.93, then the optical distance of nCGL is 19.3 nm. Similarly, the thickness of pCGL is, for example, 10 nm. If the refractive index of pCGL is 2.09, then the optical distance of pCGL is 20.9 nm.

[0089] The second light-emitting unit is a structure consisting of a hole injection layer (HIL), a hole transporting layer (HTL), an electron blocking layer (EBL), a second light-emitting layer, a hole blocking layer (HBL), and an electron transporting layer (ETL), stacked sequentially.

[0090] HIL is the layer in which holes are injected from the anode side into the second light-emitting layer.

[0091] The HTL is a layer that reduces the difference between the ionization energy of the second light-emitting layer and the work function of the anode. The thickness of the HTL is, for example, 43 nm. In the second light-emitting unit, if the refractive index of the HTL is 2.09, then the optical distance of the HTL is 89.9 nm.

[0092] EBL is a layer that prevents electrons from leaking out to the anode side.

[0093] Similar to the first light-emitting layer, the second light-emitting layer is a single-layer structure of a blue light-emitting layer that emits blue light in a wavelength region of 400 nm or more but less than 500 nm. Therefore, in this embodiment, the wavelength region of the light emitted by the first light-emitting layer overlaps with the wavelength region of the light emitted by the second light-emitting layer.

[0094] It should be noted that in this embodiment, the wavelength regions of the light emitted in the first light-emitting layer and the second light-emitting layer are the same, but it is sufficient that the wavelength regions partially overlap.

[0095] It should be noted that the thickness of the second light-emitting layer is, for example, 20 nm.

[0096] HBL is a layer on the cathode side that prevents holes from overflowing. The thickness of HBL is, for example, 10 nm.

[0097] An ETL is a layer that reduces the difference between the electron affinity of the second emitting layer and the work function of the cathode. The thickness of an ETL is, for example, 20 nm.

[0098] A charge generation layer is disposed between the second and third light-emitting units, similar to that between the first and second light-emitting units. Specifically, nCGL and pCGL are sequentially disposed from the second light-emitting unit, with the same thickness of 10 nm.

[0099] The third light-emitting unit, like the second light-emitting unit, has a structure in which HTL, EBL, the third light-emitting layer, HBL, ETL, and EIL are stacked sequentially from the charge generation layer.

[0100] However, in the third light-emitting unit, the third light-emitting layer differs from the first and second light-emitting layers. It consists of a green light-emitting layer that emits green light and a red light-emitting layer that emits red light, stacked sequentially. The wavelength region of green light is above 500 nm and below 580 nm, while the wavelength region of red light is above 580 nm and below 700 nm. Therefore, the second light-emitting layer emits yellow light in the wavelength region above 500 nm and below 700 nm by mixing green and red light.

[0101] Therefore, in this embodiment, the wavelength regions of blue light based on the first and second light-emitting layers do not overlap with the wavelength regions of yellow light based on the third light-emitting layer, and white light is emitted through the mixing of blue and yellow light.

[0102] In addition, EIL is a layer from which electrons are injected from the cathode, using materials such as alkali metals and transparent amorphous oxides.

[0103] It should be noted that in the third light-emitting unit, the thicknesses of HTL, green light-emitting layer, red light-emitting layer, HBL and ETL are 30nm, 15nm, 10nm, 10nm and 20nm respectively.

[0104] The common electrode of the semi-reflective and semi-transmissive layer, which serves as the cathode, is the same for all pixels and is connected to the power supply line 118 for voltage Vct as described above. For example, an alloy of magnesium and silver is used as the common electrode. Furthermore, the thickness of the common electrode is, for example, 20 nm.

[0105] exist Figure 6 The details are omitted, but a sealing layer, a coloring layer, and a cover glass are provided to cover the common electrode. The sealing layer is a layer that is both transparent and insulating, protecting the common electrode and the layer below it from moisture. Figure 7 As shown, the thickness of the sealing layer is, for example, 1 μm.

[0106] The color layer is a color filter that allows light of the color corresponding to the color of the pixel to pass through. Specifically, the color layer corresponding to pixel 110R transmits red light, the color layer corresponding to pixel 110G transmits green light, and the color layer corresponding to pixel 110B transmits blue light. It should be noted that the thickness of the color layer is, for example, 1 μm.

[0107] Cover glass is a transparent protective material used to protect surfaces. The thickness of cover glass is, for example, 1 mm.

[0108] In this embodiment, in the first light-emitting unit, the contact surface between the donor layer and the acceptor layer becomes the excitocomplex interface, and the energy is up-converted through triplet-triplet annihilation (TTA). This up-conversion enables the generation of blue light with a driving voltage lower than the wavelength energy.

[0109] In this embodiment, blue light is emitted from both the first and second light-emitting units. Here, the wavelength of the blue light is set to 460 nm. In order to extract the blue light in the optical resonator and improve efficiency, the following optical distance can be used.

[0110] As the first optical distance L1, in Figure 6 and Figure 7 In this context, the value is represented by the cumulative product of the distance from the interface between the reflective electrode and the pixel electrode to the interface between the second donor layer and the acceptor layer, multiplied by the refractive index of each layer.

[0111] As the second optical distance L2, in Figure 6 as well as Figure 7 In this context, the value is represented by the cumulative product of the distance from the interface between the donor and acceptor layers to the EBL and the second luminescent layer in the second luminescent unit, multiplied by the refractive index of each layer.

[0112] To extract blue light with a wavelength of 460nm and improve efficiency, it is sufficient to make the first optical distance L1 106nm and the second optical distance L2 213nm. Specifically, the thickness of each layer is as follows: Figure 7 Adjust as shown.

[0113] In order to illustrate the advantages of the electro-optical device 10 according to this embodiment, the electro-optical device according to the comparative example will be described.

[0114] Figure 8 This diagram illustrates the layer structure of electrodes, organic layers, etc., stacked in the exposed area of ​​the pixel electrode in the pixel section of the electro-optic device involved in the comparative example. It should be noted that in the diagram, the left column shows a schematic representation of the layer structure, while the right column shows a detailed representation. Furthermore, Figure 9This is a diagram showing an example of the thickness of the organic layer, electrode layer, etc.

[0115] In the comparative example, the first light-emitting unit has a structure that does not use an excimer complex interface. Specifically, the first light-emitting unit has the same structure as the second and third light-emitting units, except that the first light-emitting layer is a single-layer structure of a blue light-emitting layer. That is, in the comparative example, it is a series element in which three light-emitting units with substantially the same structure are connected in series.

[0116] One of the advantages of the electro-optical device 10 according to this embodiment is that the driving voltage is relatively low.

[0117] Figure 10 This is a graph showing the characteristics of the driving voltage-current density in this embodiment and the comparative example.

[0118] In the comparative example, since it is a series element that connects only three light-emitting units in series, the driving voltage is high. In contrast, in this embodiment, since the excitocomplex interface between the donor layer and the acceptor layer is used in the first light-emitting unit to upconvert the energy and generate blue light, the driving voltage can be reduced compared to the wavelength energy.

[0119] For example, when the electro-optical device 10 has a high-resolution pixel portion of, for example, more than 3000 dpi, the voltage that can be applied to the light-emitting element in the semiconductor substrate of the electro-optical device 10 is at most about 10 to 12 V. In the comparative example, the voltage exceeded the above-mentioned voltage in order to obtain the desired brightness; in contrast, in this embodiment, the voltage can be converged within the above-mentioned range.

[0120] Next, the advantage of the electro-optic device 10 according to this embodiment, which is that it can shorten the distance from the first light-emitting layer to the reflective electrode, will be explained.

[0121] In the comparative example, if blue light with a wavelength of 460 nm is to be extracted efficiently, the first optical distance L1 needs to be adjusted to the same value as in this embodiment.

[0122] However, in the comparative example, in order to efficiently inject holes from the anode side into the first light-emitting layer of the blue light-emitting layer, or to block electrons, multiple organic layers are required to hold the first light-emitting layer. These organic layers cannot perform the desired function when their thickness is around a few nm. Therefore, as a result, in the comparative example, it is difficult to efficiently extract the color at a wavelength of 460 nm at the same optical distance as in this embodiment. In the comparative example, the thickness of the organic layers holding the first light-emitting layer is set as follows: Figure 9 The values ​​shown require increasing the resonance order in the optical resonance compared to this embodiment. Different resonance orders will affect the half-width of the resonance-based peak waveform.

[0123] Figure 11 This is a graph comparing and showing the emission spectra observed through a 1 μm thick blue coloring layer in this embodiment and comparative examples. Additionally, Figure 12 This is a graph showing a comparison of the brightness and chromaticity observed after passing through the above-described coloring layer in this embodiment and comparative example.

[0124] like Figure 11 As shown, in this embodiment, the full width at half maximum (FWHM) at the peak wavelength of 460 nm is wider compared to the comparative example with a higher resonance order. Therefore, in this embodiment, as... Figure 12 As shown, a relatively high brightness can be obtained compared to the comparative example.

[0125] It should be noted that, in Figure 12 In this embodiment, the brightness is normalized to 100, while the brightness in the comparative example is shown as a relative value. Furthermore, chromaticity is represented by the x and y coordinate values ​​in the chromaticity diagram. Additionally, there is no significant difference between the x and y coordinate values ​​in this embodiment and the comparative example.

[0126] In the comparative example, the luminescence position in the luminescent layer varies according to the balance of holes and electrons, i.e., the carrier balance. Specifically, if the hole transport layer deteriorates due to prolonged driving, i.e., the hole transport capacity decreases, then... Figure 13 As shown, the light-emitting position in the light-emitting layer moves towards the pixel electrode, which serves as the anode (opposite to the Z direction). If the light-emitting position moves from its optimal design position, the distance from the light-emitting position to the reflective layer changes, resulting in a decrease in the light extraction efficiency of the optical resonator.

[0127] In contrast, in this embodiment, holes and electrons recombine at the excimer interface, which serves as the carrier. Therefore, even if the carrier balance changes, the recombination position of the carrier remains unchanged. The first luminescent layer emits light through energy movement from the excimer interface, thus, as... Figure 14 As shown, the luminescent position is always the part of the first luminescent layer closest to the receptor layer.

[0128] Therefore, in this embodiment, even if the carrier balance changes, the light emission position is not easily changed. Thus, the distance from the light emission position to the reflective layer does not change, and there is no adverse situation such as a decrease in the light extraction efficiency in the optical resonator.

[0129] Next, an electronic device using the electro-optical device 10 according to this embodiment will be described. The electro-optical device 10 is suitable for display applications with small pixel size and high resolution. Therefore, as an electronic device, a head-mounted display will be used as an example for description.

[0130] Figure 15 This is a diagram showing the appearance of a head-mounted display. Figure 16 This is a diagram showing its optical structure.

[0131] First, such as Figure 15 As shown, the head-mounted display 300 resembles ordinary eyeglasses in appearance, featuring temples 310, a bridge 320, and lenses 301L and 301R. Additionally, as... Figure 16 As shown, the head-mounted display 300 has an electro-optical device 10L for the left eye and an electro-optical device 10R for the right eye located near the bridge of the nose 320 and inside the lenses 301L and 301R (lower side in the figure).

[0132] The image display surface of the electro-optical device 10L is used to display images on the screen. Figure 16 The display surface of the electro-optical device 10R is arranged to the left. Therefore, the display image of the electro-optical device 10L is emitted towards the direction of point 9 in the figure via the optical lens 302L. The semi-reflective mirror 303L reflects the display image of the electro-optical device 10L towards the direction of point 6, while allowing light incident from the direction of point 12 to pass through. The image display surface of the electro-optical device 10R is arranged to the right, opposite to the electro-optical device 10L. Therefore, the display image of the electro-optical device 10R is emitted towards the direction of point 3 in the figure via the optical lens 302R. The semi-reflective mirror 303R reflects the display image of the electro-optical device 10R towards the direction of point 6, while allowing light incident from the direction of point 12 to pass through.

[0133] In this structure, the wearer of the head-mounted display 300 can observe the displayed images of the electro-optical devices 10L and 10R in a perspective state that overlaps with the external environment.

[0134] Furthermore, in this head-mounted display 300, if the electro-optical device 10L displays the left-eye image in the binocular images accompanied by parallax, and the electro-optical device 10R displays the right-eye image, the wearer can perceive that the displayed image has depth and a three-dimensional feel.

[0135] It should be noted that, in addition to the head-mounted display 300, electronic devices including the electro-optical device 10 can also be applied to electronic viewfinders in cameras or digital cameras with interchangeable lenses, portable information terminals, watch displays, light valves in projection projectors, etc.

[0136] Based on the above description, the preferred manner of this disclosure can be grasped, for example, as follows.

[0137] The electro-optical device according to Embodiment 1 of this disclosure includes a light-emitting element, which comprises, in sequence: a first electrode having reflectivity; a first light-emitting layer emitting light in a first wavelength region including a first wavelength; a donor layer; a acceptor layer in contact with the donor layer; a second light-emitting layer emitting light in a second wavelength region including a second wavelength; and a second electrode having reflectivity and transmittance; wherein the first wavelength region and the second wavelength region partially or completely overlap.

[0138] According to the electro-optical device of Method 1, since it is a series element in which the first light-emitting layer and the second light-emitting layer are connected in series, high brightness can be ensured. In the series element, the first light-emitting layer can be driven at a low voltage through the excitocomplex of the donor layer and the acceptor layer, and therefore, from the perspective of the series element, it can also be driven at a low voltage.

[0139] It should be noted that the reflective electrode and pixel electrode are examples of the "first electrode", and the common electrode is an example of the "second electrode".

[0140] In the electro-optical device involved in the specific method 2 of method 1, the light-emitting element further includes a third light-emitting layer between the second light-emitting layer and the second electrode, and the third light-emitting layer emits light including a third wavelength region that is different from the first wavelength.

[0141] According to the electro-optical device involved in Method 2, the third light-emitting layer emits light including a third wavelength that is different from the first wavelength.

[0142] In the electro-optical device involved in the specific method three of method two, the third wavelength region does not overlap with the first wavelength region, and the third wavelength is longer than the first wavelength.

[0143] According to the electro-optical device involved in Method 3, the emitted light from the light-emitting element can be easily whitened.

[0144] The electronic device involved in Method 4 includes the electro-optical device involved in any one of Methods 1 to 3.

Claims

1. An electro-optical device, characterized in that, The electro-optical device includes a light-emitting element. The light-emitting elements are stacked in sequence as follows: The first electrode is reflective; The first light-emitting layer emits light in a first wavelength region, including a first wavelength. Donor layer; The acceptor layer is in contact with the donor layer; The second light-emitting layer emits light in the second wavelength region, including the second wavelength. as well as The second electrode is both reflective and transparent. The first wavelength region partially or completely overlaps with the second wavelength region.

2. The electro-optical device according to claim 1, characterized in that, The light-emitting element further includes a third light-emitting layer between the second light-emitting layer and the second electrode. The third light-emitting layer emits light in a third wavelength region that is different from the first wavelength.

3. The electro-optical device according to claim 2, characterized in that, The third wavelength region does not overlap with the first wavelength region. The third wavelength is longer than the first wavelength.

4. An electronic device, characterized in that, An electro-optical device having any one of claims 1 to 3.

Images