Electro-optical devices and electronic equipment

Abstract

It ensures high brightness while keeping the drive voltage low. [Solution] The device includes a light-emitting element in which a first electrode having reflectivity, a first light-emitting layer emitting light in a first wavelength range including a first wavelength, a donor layer, an acceptor layer in contact with the donor layer, a second light-emitting layer emitting light in a second wavelength range including a second wavelength, and a second electrode having reflectivity and light transmission are stacked in that order, with the first wavelength range and the second wavelength range overlapping in part or in whole.

Description

Technical Field

[0001] The present invention relates to an electro-optical device and an electronic device.

Background Art

[0002] An electro-optical device using, for example, an OLED (Organic Light Emitting Diode) as a light-emitting element is known. In such an electro-optical device using an OLED, in order to ensure high luminance, a technique using a so-called tandem element in which two or more light-emitting units are connected in series is known (see, for example, Patent Document 1). In such a tandem element, compared with a configuration having one light-emitting unit, twice the luminance can be obtained with the same current amount.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the tandem element described in Patent Document 1, there is a problem that a driving voltage of two or more times is required. In particular, in a microdisplay in which the pixel pitch is about several μm and the driving circuit and pixel portion are formed on a semiconductor substrate, there is a situation where the driving voltage cannot be increased because the size of the transistor, which is a constituent element, is restricted.

Means for Solving the Problems

[0005] An electro-optical device according to one aspect of the present disclosure includes a light-emitting element in which a first electrode having reflectivity, a first light-emitting layer emitting light in a first wavelength range including a first wavelength, a donor layer, an acceptor layer in contact with the donor layer, a second light-emitting layer emitting light in a second wavelength range including a second wavelength, and a second electrode having reflectivity and light transmission are stacked in that order, wherein the first wavelength range and the second wavelength range overlap in part or in whole. [Brief explanation of the drawing]

[0006] [Figure 1] This figure shows the configuration of the electro-optical device according to the first embodiment. [Figure 2] This is a block diagram showing the electrical configuration of an electro-optical device. [Figure 3] This is a circuit diagram showing the pixel section of an electro-optical device. [Figure 4] This is a timing chart showing the operation of an electro-optical device. [Figure 5] This is a plan view showing the pixel section of an electro-optical device. [Figure 6] This figure shows organic layers, etc., that are stacked on pixel electrodes in an electro-optical device. [Figure 7] This figure shows examples of the thickness of organic layers, etc., in electro-optical devices. [Figure 8] This figure shows the organic layer and the like that are stacked on the pixel electrode in the comparative example. [Figure 9] This figure shows examples of the thickness of the organic layer, etc., in comparative examples. [Figure 10] This figure shows the characteristics of the drive voltage-current density in the first embodiment and the comparative example. [Figure 11] This figure shows the emission spectrum in the first embodiment and the comparative example. [Figure 12] This figure shows the luminance and chromaticity in the first embodiment and comparative example. [Figure 13] This figure shows the position of light emission in the comparative example. [Figure 14] This figure shows the light emission position in the first embodiment. [Figure 15]This is a perspective view showing a head-mounted display using an electro-optical device according to an embodiment, etc. [Figure 16] This figure shows the optical configuration of a head-mounted display. [Modes for carrying out the invention]

[0007] Hereinafter, an electro-optical apparatus according to an embodiment of the present invention will be described with reference to the drawings. Note that the dimensions and scale of each part in each drawing have been appropriately changed from those of the actual parts. Furthermore, the embodiments described below are preferred examples and are subject to various technically preferred limitations, but the scope of the present invention is not limited to these forms unless otherwise stated in the following description.

[0008] Figure 1 is a perspective view showing an electro-optical device 10 according to the first embodiment, and Figure 2 is a block diagram showing the electrical configuration of the electro-optical device 10. This electro-optical device 10 is a microdisplay panel that displays color images, for example, in a head-mounted display. The electro-optical device 10 includes a plurality of pixel units and a drive circuit that drives the pixel units. The pixel units and the drive circuit are integrated on a semiconductor substrate. The semiconductor substrate is typically a silicon substrate, but other semiconductor substrates may also be used.

[0009] The electro-optical device 10 is housed in a frame-shaped case 192 that opens in the display area 100. One end of an FPC board 194 is connected to the electro-optical device 10. FPC stands for Flexible Printed Circuits. The other end of the FPC board 194 is provided with a plurality of terminals 196 for connecting a host device (not shown). When the plurality of terminals 196 are connected to the host device, the electro-optical device 10 is supplied with video data, synchronization signals, etc., from the host device via the FPC board 194.

[0010] In the figure, the X direction is the extending direction of the scanning lines in the electro-optical device 10, which indicates the horizontal direction on the display screen. The Y direction is the extending direction of the data lines, which indicates the vertical direction on the display screen. The two-dimensional plane defined by the X direction and the Y direction is the substrate surface of the semiconductor substrate. The Z direction is perpendicular to the substrate surface in the semiconductor direction and is the light emission direction of the light emitted from the light-emitting element. In this description, a plan view means looking at the semiconductor substrate from the opposite direction of the Z direction, and a cross-sectional view means looking at the semiconductor substrate after breaking it in the direction perpendicular to the substrate surface.

[0011] As shown in FIG. 2, the electro-optical device 10 is roughly classified into a control circuit 30, a data signal output circuit 50, a display area 100, and a scanning line driving circuit 120. In the display area 100, m rows of scanning lines 12 are provided along the X direction, and (3n) columns of data lines 14 are provided along the Y direction and are electrically insulated from each scanning line 12. Here, m and n are integers of 2 or more.

[0012] In the display area 100, pixel portions 110 are provided corresponding to the intersections of the m rows of scanning lines 12 and the (3n) columns of data lines 14. For this reason, the pixel portions 110 are arranged in a matrix of m rows in the vertical direction and (3n) columns in the horizontal direction. In the matrix arrangement, in order to distinguish the rows, they may be called the 1st, 2nd, 3rd,..., (m - 1)th, and mth rows in order from the top in the figure. Similarly, in order to distinguish the columns of the matrix, they may be called the 1st, 2nd, 3rd,..., (3n - 2)th, (3n - 1)th, and (3n)th columns in order from the left in the figure. In order to explain the scanning line 12 in a generalized manner, an integer i from 1 to m is used. Similarly, in order to explain the data line 14 in a generalized manner, an integer j from 1 to (3n) is used.

[0013] The control circuit 30 controls each part based on video data Vid and a synchronization signal Sync supplied from an upper host device (not shown). Specifically, the control circuit 30 generates various control signals to control each part. The video data Vid specifies the gradation level of pixels in the image to be displayed, for example, in 8 bits. The synchronization signal Sync includes a vertical synchronization signal for instructing the start of vertical scanning of the video data Vid, a horizontal synchronization signal for instructing the start of horizontal scanning, and a dot clock signal indicating the timing for one pixel of the video data.

[0014] 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. The luminance characteristics at the gradation level indicated by the video data Vid supplied from the host device do not necessarily match the luminance characteristics of the OLEDs included in the pixel portion 110. Therefore, in order to cause the OLEDs to emit light with a luminance corresponding to the gradation level indicated by the video data Vid, the control circuit 30 up-converts the 8 bits of the video data Vid to, for example, 10 bits and outputs it as the video data Vdata. For this reason, the 10-bit video data Vdata becomes data corresponding to the gradation level specified by the video data Vid. Note that for up-conversion, a look-up table that stores in advance the correspondence between the 8 bits of the input video data Vid and the 10 bits of the output video data Vdata is used.

[0015] The scanning line driving circuit 120 is a circuit for driving the pixel portions 110 arranged in m rows (3n columns) one row at a time according to the control by the control circuit 30. For example, the scanning line driving circuit 120 sequentially supplies the scanning signals / Gwr(1), / Gwr(2),..., / Gwr(m - 1), / Gwr(m) to the scanning lines 12 of the first, second, third,..., (m - 1)th, and mth rows. Generally, the scanning signal supplied to the scanning line 12 of the ith row is denoted as / Gwr(i).

[0016] The data signal output circuit 50 is a circuit that outputs a data signal via the data line 14 to the pixel section 110 located in the row selected by the scan line drive circuit 120, in accordance with the control of the control circuit 30. The data signal is a voltage signal obtained by converting 10-bit video data Vdata into an analog. That is, the data signal output circuit 50 converts the video data Vdata for one row corresponding to the pixel section 110 of columns 1 to (3n) in the selected row into an analog and outputs it in this order to the data line 14 of columns 1 to (3n).

[0017] In the diagram, the data signals output to data line 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).

[0018] In the display area 100, as shown in Figure 2, the pixel sections 110 are electrically arranged such that R pixel sections 110, B pixel sections 110, and G pixel sections 110 are arranged in the X direction in order, and the same color pixel sections 110 are arranged in the Y direction. Therefore, if one row of data lines 14 is considered, it will correspond to the same color pixel section 110. In addition, a single dot represents color through additive color mixing of adjacent RGB pixel portions 110 in the X direction. Therefore, in the first embodiment, a color display of m rows x n columns is possible using dots. Strictly speaking, the pixel portions 110 should be called sub-pixel portions, but for the sake of explanation, they are referred to as pixel portions.

[0019] Figure 3 shows the electrical configuration of the pixel section 110 in the electro-optical device 10. The pixel sections 110, arranged in m rows (3n) columns, are electrically identical to each other. Therefore, the pixel section 110 will be described using one pixel section 110, which is in the i-th row and corresponds to the j-th column, as a representative example.

[0020] As shown in the figure, the pixel section 110 electrically includes P-channel MOS type transistors 121 and 122, an OLED 130, and a capacitive element 140. In the description of the pixel section 110, the phrase "electrically speaking" is used to refer to the multiple elements that constitute the pixel section 110 and the connection relationships between those multiple elements. This expression is used because, from a mechanical or physical perspective, the pixel section 110 includes elements that do not contribute to the electrical connection relationships.

[0021] OLED130 is an example of a light-emitting element, in which an organic layer 132 containing a light-emitting layer is sandwiched between a pixel electrode 131 and a common electrode 133. As described above, the pixel electrode 131 functions as the anode of OLED130, and the common electrode 133 functions as the cathode of OLED130. Details of OLED130 will be described later, but when an electric 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 and produce light.

[0022] Of the generated light, some wavelengths resonate in an optical resonator composed of a reflective electrode and a common electrode 133 of a semi-reflective, semi-transparent layer (omitted in Figure 3), and are amplified by wavelength and emitted, while light in other wavelengths is emitted without resonating in the optical resonator. In this embodiment, some of the light is blue light, and the other light is yellow light. Therefore, the light emitted from the OLED 130 is white due to the mixing of blue and yellow light. The light emitted from the OLED 130 passes through a colored layer corresponding to the pixel portion 110, and is visible to the observer as colored light from that colored layer.

[0023] In row i and column j, for transistor 121 of pixel unit 110, the gate node g is connected to the drain node of transistor 122, the source node s is connected to the voltage Vel power supply line 116, and the drain node d is connected to the pixel electrode 131, which is the anode of OLED 130. In transistor 122, the gate node is connected to the i-th row scan line 12, and the source node is connected to the j-th column data line 14. The common electrode 133, which functions as the cathode of the OLED 130, is connected to the voltage Vct power supply line 118. Furthermore, since the electro-optical device 10 is formed on a silicon substrate, the substrate potential of transistors 121 and 122 is set to a potential equivalent to, for example, the voltage Vel. Note that the voltage (Vel-Vct) is the driving voltage for the OLED130.

[0024] The pixel portion 110 shown in Figure 3 is electrically common to all red, green, and blue colors, and has therefore been described generally without specifying the color. However, structurally, it differs for each color. For this reason, when describing them by color, they will be denoted as pixel portion 110R, 110G, and 110B. Similarly, when describing the OLED 130 and pixel electrode 131 by color, they will be denoted as OLED130R, 130G, and 130B, and as pixel electrode 131R, 131G, and 131B.

[0025] Figure 4 is a timing chart illustrating the operation of the electro-optical device 10. In the electro-optical device 10, the m-row scan lines 12 are scanned one line at a time in the order of the 1st, 2nd, 3rd, ..., mth line during the frame (V) period. More specifically, as shown in the figure, the scan signals / Gwr(1), / Gwr(2), ..., / Gwr(m-1), and / Gwr(m) are sequentially and exclusively set to L level by the scan line drive circuit 120 for each horizontal scanning period (H). In this embodiment, among the scan signals / Gwr(1) to / Gwr(m), the periods during which adjacent scan signals are at an L level are temporally separated. Specifically, after the scan signal / Gwr(i-1) changes from an L level to an H level, the next scan signal / Gwr(i) becomes L level after a period of time. This period corresponds to the horizontal retrace period.

[0026] In this explanation, the duration of one frame (V) refers to the period required to display one frame of the image specified by the video data Vid. If the length of one 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 60 Hz, then it is 16.7 milliseconds, which corresponds to one cycle of the vertical synchronization signal. The horizontal scanning period (H) is the time interval between the scan signals / Gwr(1) to / Gwr(m) sequentially becoming L levels. For convenience, in the diagram, the start timing of the horizontal scanning period (H) is set to approximately the center of the horizontal retrace period.

[0027] When one of the scan signals / Gwr(1) to / Gwr(m), for example, the scan signal / Gwr(i) supplied to the i-th row scan line 12, reaches a low level, the transistor 122 in the i-th row, j-th column pixel 110 turns on. As a result, the gate node g of the transistor 121 in that pixel 110 becomes electrically connected to the j-th column data line 14.

[0028] In this explanation, the "on state" of a transistor refers to a state where the source node and drain node are electrically closed, resulting in a low impedance state. Conversely, the "off state" of a transistor refers to a state where the source node and drain node are electrically open, resulting in a high impedance state. Furthermore, in this explanation, "electrically connected" or simply "connected" means a state in which two or more elements are directly or indirectly connected or coupled. "Electrically disconnected" or simply "disconnected" means a state in which two or more elements are not directly or indirectly connected or coupled.

[0029] During the horizontal scanning period (H) when the scanning signal / Gwr(i) is at the L level, the data signal output circuit 50 converts the gradation levels of the pixels in row i, column 1 to row i, column (3n), indicated by the video data Vdata, into analog potentials Vd(1) to Vd(3n), and outputs them as data signals to the data lines 14 in columns 1 to (3n). In the case of column j, the data signal output circuit 50 converts the gradation level d(i,j) of the pixel in row i, column j, into an analog potential Vd(j), and outputs it as a data signal to the data line 14 in column j. Furthermore, during the horizontal scanning period (H) when the scan signal / Gwr(i-1) one row prior to the scan signal / Gwr(i) is at a low level, the data signal output circuit 50 converts the grayscale level d(i-1,j) of the pixel in row (i-1) and column j into an analog signal potential Vd(j) and outputs it as a data signal to the data line 14 in column j.

[0030] The data signal of the potential Vd(j) is applied to the gate node g of the transistor 121 in the i-row, j-column pixel section 110 via the j-column data line 14, and the potential Vd(j) is held by the capacitive element 140. As a result, the transistor 121 supplies a current to the OLED 130 corresponding to the voltage between the gate node and source node. Even when the scanning signal Gwr(i) reaches a high level and transistor 122 turns off, the potential Vd(j) is maintained by the capacitive element 140, so current continues to flow through the OLED 130. Therefore, in the i-row, j-column pixel section 110, the OLED 130 continues to emit light at a brightness corresponding to the voltage maintained by the capacitive element 140, i.e., the grayscale level, until a frame (V) has elapsed, transistor 122 turns on again, and the voltage of the data signal is reapplied.

[0031] Although the pixel portion 110 in row i and column j has been described here, the OLED 130 of the pixel portion 110 other than column j in row i also emits light at the brightness indicated by the video data Vdata. Furthermore, the OLED 130 of the pixel section 110 in rows other than row i also emits light at the brightness indicated by the video data Vdata as the scanning signals / Gwr(1) to / Gwr(m) sequentially become L levels. Therefore, in the electro-optical device 10, during the period of one frame (V), the OLED 130 in all pixel sections 110 from row 1 to column m (3n) emits light with a brightness indicated by the video data Vdata, and one frame of image is displayed.

[0032] Figure 5 is a simplified plan view diagram showing the configuration of the pixel section 110 in the display area 100. In the display area 100, the color of one dot is represented by additive color mixing of colored light emitted from three areas enclosed by the frame Dp in the figure. Specifically, in frame Dp, areas R, G, and B are arranged in this order along the X direction. White light emitted from area R is colored red by passing through the colored layer on the near side of the paper (not shown in Figure 5) and then emitted. Similarly, white light emitted from areas G and B is colored green and blue, respectively, by passing through the colored layers and then emitted.

[0033] In the pixel section 110R, the reflective electrode 62R and the pixel electrode 131R are stacked in that order. The reflective electrode 62R is electrically connected to the drain node d of the transistor 121 via a contact hole that opens in the insulating layer. The insulating layer provided between the drain node d and the reflective electrode 62R in transistor 121, and the contact holes opening in the insulating layer, are not shown in the illustration.

[0034] The reflective electrode 62R corresponds to the pixel portion 110R and is a light-reflective conductive electrode patterned in a rectangle as shown in Figure 5, which reflects light incident from the opposite direction of the Z direction in the Z direction. For the reflective electrode 62R, for example, a conductive layer is used in which an aluminum and copper alloy (AlCu) film is laminated on a titanium (Ti) film. The pixel electrode 131R is a conductive electrode made of a light-transmitting material, such as ITO (Indium Tin Oxide), which is patterned in a rectangle so as to overlap the reflective electrode 62R. Pixel electrode 131R is patterned with the same ITO film as pixel electrodes 131G and 131B corresponding to other colors. When the thickness of pixel electrodes 131R, 131G, and 131B is 15 μm and the refractive index of ITO is 1.98, the optical distance, which is the product of thickness and refractive index, is 29.7 nm for pixel electrodes 131R, 131G, and 131B.

[0035] The same applies to pixel sections 110G and 110B. More specifically, in pixel section 110G, the reflective electrode 62G and the pixel electrode 131G are stacked in that order, and in pixel section 110B, the reflective electrode 62B and the pixel electrode 131B are stacked in that order. The opening ends Ap_R, Ap_G, and Ap_B are the frame edges of the opening, with the insulating layer covering the pixel electrodes 131R, 131G, and 131B. In other words, the pixel electrodes 131R, 131G, and 131G, respectively, expose the insulating layer defined by the opening ends Ap_R, Ap_G, and Ap_B at the opening.

[0036] The regions where the pixel electrodes 131R, 131G, and 131G are exposed are laminated with organic layers, as described below. Note that the lamination of organic layers is common to the pixel portions 110R, 110G, and 110B. Therefore, in the following explanation, the reference numerals from the pixel electrodes to the common electrodes will be omitted.

[0037] In the electro-optical device 10 according to this embodiment, a tandem element is employed in which three light-emitting units are connected in series in order to obtain high brightness. However, as mentioned above, a simple tandem element requires a high driving voltage. Therefore, in this embodiment, of the three light-emitting units constituting the tandem element, the one closest to the reflective electrode is of a type that uses upconversion from an excyplex.

[0038] Figure 6 shows the layer structure of electrodes and organic layers stacked on the exposed region of the pixel electrode in the pixel area. In the figure, the left column shows a general overview of the layer structure, and the right column shows a detailed overview of the layer structure. Figure 7 shows an example of the thickness of the organic layer and electrode layer.

[0039] As shown in the left column of Figure 6, in the pixel section, the exposed area of ​​the pixel electrode is stacked in the following order: first light-emitting unit, charge generation layer, second light-emitting unit, charge generation layer, third light-emitting unit, and common electrode. Although not shown in the diagram, the common electrode is laminated with a sealing layer, a colored layer, and a cover glass in that order.

[0040] As shown in the right column of Figure 6, the first light-emitting unit has a structure in which a first donor layer, a first light-emitting layer, a second donor layer, and an acceptor layer are stacked in order on the pixel electrode. The first donor layer is a material with a LUMO (Lowest Unoccupied Molecular Orbital) of approximately 3.0 eV and a HOMO (Highest Occupied Molecular Orbital) of approximately 6.0 eV, such as anthracene derivatives. 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 will be 19.0 nm.

[0041] The first luminescent layer is formed from the same material as the first donor layer, and is doped with a dopant that emits blue light. In other words, the first luminescent layer is a layer in which a portion of the donor layer is doped with a blue luminescent dopant. 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, the optical distance of the first light-emitting layer will be 38.0 nm. Also, the wavelength range for blue light is between 400 nm and 500 nm.

[0042] The second donor layer is composed of the same material as the first donor layer. 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, the optical distance of the second donor layer will be 19.0 nm.

[0043] The acceptor layer is made of a material with a LUMO of approximately 3.8 eV, such as a naphthalenediimide (NTCDI) derivative. The thickness of the acceptor layer is, for example, 45 nm. If the refractive index of the acceptor layer is 1.84, the optical distance of the acceptor layer will be 82.8 nm.

[0044] The charge generation layer (CGL) is a pn junction consisting of an n-type charge generation layer (nCGL) and a hole generation layer (pCGL). The nCGL on the n side of the pn junction generates electrons and injects these electrons into the adjacent layer on the anode side, while the pCGL on the p side of the pn junction generates holes and injects these holes into the adjacent layer on the cathode side. In other words, in the light-emitting units of the tandem element, the nCGL field transport layer 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. For example, the thickness of nCGL is 10 nm. If the refractive index of nCGL is 1.93, the optical distance of nCGL will be 19.3 nm. Similarly, for example, the thickness of pCGL is 10 nm. If the refractive index of pCGL is 2.09, the optical distance of pCGL will be 20.9 nm.

[0045] The second light-emitting unit has a structure in which 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) are stacked in that order.

[0046] HIL is a layer that injects holes into the second light-emitting layer from the anode side. The High-Level Layer (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, the optical distance of the HTL will be 89.9 nm. EBL is a layer that prevents electrons from overflowing into the anode layer.

[0047] The second light-emitting layer, like the first light-emitting layer, is a single-layer structure of a blue light-emitting layer that emits blue light in the wavelength range of 400 nm to less than 500 nm. Therefore, in this embodiment, the wavelength range of the light emitted by the first light-emitting layer and the wavelength range of the light emitted by the second light-emitting layer overlap. In this embodiment, the wavelength ranges of the light emitted by the first light-emitting layer and the second light-emitting layer are the same, but it is sufficient if a portion of the wavelength ranges overlap. The thickness of the second light-emitting layer is, for example, 20 nm.

[0048] HBL is a layer that prevents holes from spilling out onto the cathode layer. The thickness of HBL is, for example, 10 nm. The ETL is a layer that reduces the difference between the electron affinity of the second light-emitting layer and the work function of the cathode. The thickness of the ETL is, for example, 20 nm.

[0049] A charge generation layer is provided between the second and third light-emitting units, similar to the layer between the first and second light-emitting units. Specifically, nCGL and pCGL are provided sequentially starting from the second light-emitting unit, and their thickness is also 10 nm.

[0050] The third light-emitting unit, like the second light-emitting unit, has a structure in which the HTL, EBL, third light-emitting layer, HBL, ETL, and EIL are stacked in order from the charge transport layer. However, in the third light-emitting unit, the third light-emitting layer differs from the first and second light-emitting layers in that it has a structure in which a green light-emitting layer that emits green light and a red light-emitting layer that emits red light are stacked in sequence. The wavelength range for green light is 500 nm to less than 580 nm, and the wavelength range for red light is 580 nm to less than 700 nm. Therefore, the second light-emitting layer emits yellow light in the wavelength range of 500 nm to less than 700 nm by mixing the green light and the red light.

[0051] Therefore, in this embodiment, the wavelength range of the blue light emitted by the first and second light-emitting layers does not overlap with the wavelength range of the yellow light emitted by the third light-emitting layer, and white light is emitted by mixing the blue and yellow light. Furthermore, the EIL (Electron Injection Layer) is a layer into which electrons are injected from the cathode, and materials such as alkali metals or transparent amorphous oxides are used. In the third light-emitting unit, the thicknesses of the HTL, green light-emitting layer, red light-emitting layer, HBL, and ETL are 30 nm, 15 nm, 10 nm, 10 nm, and 20 nm, respectively.

[0052] The common electrode of the semi-reflective, semi-transparent cathode is common to all pixel regions and is connected to the voltage Vct feed line 118 as described above. For example, a magnesium-silver alloy can be used as the common electrode. The thickness of the common electrode is, for example, 20 nm.

[0053] Although not shown in Figure 6, a sealing layer, a colored layer, and a cover glass are provided to cover the common electrode. The sealing layer is light-transmitting and insulating, and protects the common electrode and the layer below it from moisture. The thickness of the sealing layer is, for example, 1 μm, as shown in Figure 7. The colored layer is a color filter that transmits colored light corresponding to the color of the pixel. Specifically, the colored layer corresponding to pixel 110R transmits red light, the colored layer corresponding to pixel 110G transmits green light, and the colored layer corresponding to pixel 110B transmits blue light. The thickness of the colored layer is, for example, 1 μm. A cover glass is a light-transmitting protective material used to protect the surface. The thickness of the cover glass is, for example, 1 mm.

[0054] In this embodiment, in the first light-emitting unit, the contact surface between the donor layer and the acceptor layer becomes an excyplex interface, and the energy is upconverted by triplet-triplet annihilation (TTA). This upconversion makes it possible to generate blue colored light with a driving voltage lower than the wavelength energy.

[0055] In this embodiment, blue light is emitted from both the first light-emitting unit and the second light-emitting unit. Here, assuming a wavelength of 460 nm for the blue light, the optical distance should be set as follows to improve the efficiency of extracting the blue light in the optical resonator. As the first optical distance L1, in Figures 6 and 7, it will be expressed as 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. As the second optical distance L2, in Figures 6 and 7, it will be expressed as the cumulative product of the distance from the interface between the donor layer and the acceptor layer to the EBL and the second light-emitting layer in the second light-emitting unit, multiplied by the refractive index of each layer. To extract blue light with a wavelength of 460 nm and improve efficiency, the first optical distance L1 should be set to 106 nm and the second optical distance L2 to 213 nm. Specifically, the thickness of each layer is adjusted as shown in Figure 7.

[0056] To explain the advantages of the electro-optical apparatus 10 according to this embodiment, a comparative example of an electro-optical apparatus will be described.

[0057] Figure 8 shows the layer structure of electrodes, organic layers, etc., stacked in the exposed region of the pixel electrode in the pixel section of an electro-optical apparatus according to a comparative example. In the figure, the left column shows a schematic of the layer structure, and the right column shows the detailed layer structure. Figure 9 shows an example of the thickness of the organic layer, electrode layer, etc.

[0058] In the comparative example, the first light-emitting unit does not use an exciplex interface. More specifically, the first light-emitting unit has the same configuration 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. In other words, the comparative example is a tandem element in which three light-emitting units with almost identical configurations are connected in series.

[0059] One of the advantages of the electro-optical device 10 according to this embodiment is that it requires a low driving voltage.

[0060] Figure 10 shows the characteristics of the drive voltage-current density in this embodiment and in a comparative example. In the comparative example, since it is simply a tandem element with three light-emitting units connected in series, the driving voltage is high. In contrast, in this embodiment, the first light-emitting unit uses the exciplex interface between the donor layer and the acceptor layer to upconvert energy and generate blue light, so the driving voltage can be lower compared to the wavelength energy. For example, if the electro-optical device 10 has high-resolution pixels, such as those exceeding 3000 dpi, the maximum voltage that can be applied to the light-emitting element on the semiconductor substrate of the electro-optical device 10 is approximately 10 to 12 V. In the comparative example, the voltage would have to be exceeded to obtain the required brightness, whereas in this embodiment, it is possible to keep the voltage within the above range.

[0061] Next, we will explain one of the advantages of the electro-optical device 10 according to this embodiment: the ability to shorten the distance from the first light-emitting layer to the reflective electrode. In the comparative example, if blue light with a wavelength of 460 nm is to be efficiently extracted, the first optical distance L1 needs to be adjusted to a value similar to that of the first embodiment.

[0062] However, in the comparative example, in order to give the first light-emitting layer of the blue light-emitting layer the function of efficiently injecting holes from the anode side or blocking electrons, the first light-emitting layer needs to be sandwiched between multiple organic layers. These organic layers cannot perform the expected functions if their thickness is only a few nanometers. As a result, in the comparative example, it is difficult to efficiently extract the color with a wavelength of 460 nm at the same optical distance as in the embodiment. In the comparative example, the thickness of the organic layer sandwiching the first light-emitting layer needs to be set to the value shown in Figure 9, and the resonance order in optical resonance needs to be increased compared to the embodiment. The difference in resonance order affects the full width at half maximum of the peak waveform due to resonance.

[0063] Figure 11 shows a comparison of the emission spectra observed through a 1 μm thick blue colored layer in this embodiment and in a comparative example. Figure 12 shows a comparison of the luminance and chromaticity observed through the above colored layer in this embodiment and in a comparative example. As shown in Figure 11, the full width at half maximum at the peak wavelength of 460 nm is wider in this embodiment compared to the comparative example with a higher resonance order. Therefore, as shown in Figure 12, a relatively higher brightness can be obtained in this embodiment compared to the comparative example. In Figure 12, the luminance in this embodiment is normalized to 100, and the luminance in the comparative example is shown as a relative value. Chromaticity is shown by the x and y coordinate values ​​in the chromaticity diagram. Furthermore, there is no significant difference in the x and y coordinate values ​​between this embodiment and the comparative example.

[0064] In the comparative example, the emission position in the light-emitting layer changes depending on the carrier balance, which is the balance between holes and electrons. More specifically, when the hole transport layer deteriorates due to prolonged operation, that is, when the hole transportability decreases, the emission position in the light-emitting layer moves in the direction of the anode pixel electrode (opposite direction to the Z direction), as shown in Figure 13. When the emission position moves from the optimal position at the time of design, the distance from the emission position to the reflective layer changes, and the light extraction efficiency in the optical resonator decreases.

[0065] In contrast, in this embodiment, holes and electrons, which are carriers, recombine at the excyplex interface. Therefore, even if the carrier balance changes, the carrier recombination position does not change. Since the first light-emitting layer emits light through energy transfer from the excyplex interface, as shown in Figure 14, the light emission position is always in the part of the first light-emitting layer that is close to the acceptor layer. Therefore, in this embodiment, even if the carrier balance changes, the light emission position does not change easily, so the distance from the light emission position to the reflective layer does not change, and the problem of reduced light extraction efficiency in the optical resonator does not occur.

[0066] Next, we will describe an electronic device to which the electro-optical device 10 according to this embodiment is applied. The electro-optical device 10 is suitable for applications requiring small-sized pixels and high-resolution display. Therefore, we will use a head-mounted display as an example of such an electronic device.

[0067] Figure 15 shows the external appearance of the head-mounted display, and Figure 16 shows its optical configuration. First, as shown in Figure 15, the head-mounted display 300 has, externally, the same features as ordinary eyeglasses, including temples 310, a bridge 320, and lenses 301L and 301R. Furthermore, as shown in Figure 16, the head-mounted display 300 is equipped with an electro-optical device 10L for the left eye and an electro-optical device 10R for the right eye near the bridge 320, behind (below in the figure) the lenses 301L and 301R. The image display surface of the electro-optical device 10L is positioned to the left in Figure 16. As a result, the image displayed by the electro-optical device 10L is emitted in the 9 o'clock direction in the figure via the optical lens 302L. The half mirror 303L reflects the image displayed by the electro-optical device 10L in the 6 o'clock direction while transmitting light incident from the 12 o'clock direction. The image display surface of the electro-optical device 10R is positioned to the right, opposite to the electro-optical device 10L. As a result, the image displayed by the electro-optical device 10R is emitted in the 3 o'clock direction in the figure via the optical lens 302R. The half mirror 303R reflects the image displayed by the electro-optical device 10R in the 6 o'clock direction while transmitting light incident from the 12 o'clock direction.

[0068] In this configuration, the wearer of the head-mounted display 300 can observe the images displayed by the electro-optical devices 10L and 10R in a see-through state, superimposed on the outside environment. Furthermore, in this head-mounted display 300, if the left-eye image is displayed by the electro-optical device 10L and the right-eye image is displayed by the electro-optical device 10R, the wearer can perceive the displayed images as if they had depth and three-dimensionality.

[0069] Furthermore, the electronic device including the electro-optical device 10 can be applied not only to the head-mounted display 300, but also to electronic viewfinders in video cameras and interchangeable-lens digital cameras, personal digital assistants, watch displays, and light bulbs in projection projectors.

[0070] From the above description, preferred embodiments of this disclosure can be understood, for example, as follows:

[0071] An electro-optical device according to Embodiment 1 of the present disclosure includes a light-emitting element in which a first electrode having reflectivity, a first light-emitting layer emitting light in a first wavelength range including a first wavelength, a donor layer, an acceptor layer in contact with the donor layer, a second light-emitting layer emitting light in a second wavelength range including a second wavelength, and a second electrode having reflectivity and light transmission are stacked in that order, wherein the first wavelength range and the second wavelength range overlap in part or in whole.

[0072] According to the electro-optic apparatus of Embodiment 1, a tandem element is formed by connecting a first light-emitting layer and a second light-emitting layer in series, thus ensuring high brightness. Of the tandem elements, the first light-emitting layer can be driven at a low voltage by the exciplex between the donor layer and the acceptor layer, so the tandem element can also be driven at a low voltage. Note that the reflective electrode and pixel electrode are examples of "first electrodes," and the common electrode is an example of "second electrodes."

[0073] In an electro-optical apparatus according to a specific embodiment 2 of embodiment 1, the light-emitting element further includes a third light-emitting layer between the second light-emitting layer and the second electrode, which emits light in a third wavelength range including a third wavelength different from the first wavelength. According to the electro-optical apparatus of embodiment 2, the third light-emitting layer emits light of a third wavelength that includes a wavelength different from the first wavelength.

[0074] In the electro-optic apparatus according to specific embodiment 3 of embodiment 2, the third wavelength range does not overlap with the first wavelength range, and the third wavelength is longer than the first wavelength. According to the electro-optical apparatus of embodiment 3, it becomes easier to whiten the light emitted from the light-emitting element.

[0075] The electronic device according to Embodiment 4 includes an electro-optical device according to any one of Embodiments 1 to 3. [Explanation of Symbols]

[0076] 10... Electro-optical device, 12... Scan line, 14... Data line, 100... Display area, 62... Reflective electrode, 131... Pixel electrode, 130... OLED, 132... Organic layer, 133... Common electrode.

Claims

1. A first electrode having reflective properties, A first light-emitting layer that emits light in a first wavelength range including the first wavelength, Donor population, An acceptor layer in contact with the donor layer, A second light-emitting layer that emits light in the second wavelength range, including the second wavelength, A second electrode having reflectivity and light transmission, It includes a light-emitting element in which these elements are stacked in order, The first wavelength range and the second wavelength range overlap in part or in whole. Electro-optical device.

2. The light-emitting element is Between the second light-emitting layer and the second electrode The present invention further includes a third light-emitting layer that emits light in a third wavelength range, which includes a third wavelength different from the first wavelength. The electro-optical apparatus according to claim 1.

3. The third wavelength range does not overlap with the first wavelength range. The third wavelength is longer than the first wavelength. The electro-optical apparatus according to claim 2.

4. An electronic device having an electro-optical device according to any one of claims 1 to 3.

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