JP2011141412A - Organic el display device, driving method of the same, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL display device which suppresses color misregistration in a low grayscale region while securing an expected light emitting life. <P>SOLUTION: The display device 100 has a drive switching section 51 that switches between pulse drive and constant-current drive according to gray levels of display. The drive switching section performs pulse drive in a region having a gray level lower than a predetermined gray level, and performs constant-current drive in a middle high grayscale region having a gray level higher than the predetermined gray level. In the low grayscale region, a drive current whose amplitude of a pulse is higher than a reference current and which is greater than a value obtained by multiplying an inverse of a duty ratio of the pulse drive by the reference current is supplied to an organic EL layer. As this drive current overcomes an energy gap between a plurality of light emitting layers, expected white light can be obtained even in the low grayscale region. Further, in the middle high grayscale region, the constant-current drive is selected, load on the organic EL layer is reduced, thereby ensuring a light emitting life. Therefore, expected color in the low grayscale region and the expected light emitting life are satisfied. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic EL display device, a driving method thereof, and an electronic apparatus including the display device.

As a configuration (production method) of a display device using a low molecular organic EL (Electro Luminescence) element, two methods are known. One is a so-called “RGB coating method” in which red, green, and blue color elements are separately painted for each pixel using a vapor deposition mask to form red, green, and blue color pixels. The other is that without forming a vapor deposition mask, a white element is formed on the entire surface, and each color filter of red, green, and blue is arranged thereon, thereby forming each color pixel of RGB. It is.
For example, when manufacturing a large-screen display device such as a large television, the “white light emission + color filter method” is said to be more suitable. This is because when a large display device is manufactured by the “RGB color separation method”, the dimensional accuracy deteriorates, thermal expansion, deflection due to the weight of the mask, etc. occurs as the deposition mask becomes larger. This is because it is difficult to ensure.

Patent Document 1 discloses an example of a display device adopting “white light emission + color filter system”. In the display device, in order to obtain white light, a plurality of light-emitting layers each emitting different color light are stacked, and the color light emitted from each light-emitting layer is synthesized into substantially white light. As the plurality of light emitting layers, three light emitting layers each emitting green, blue green, yellow orange light are laminated.
In addition, as the plurality of light emitting layers for obtaining substantially white light, for example, a structure in which three light emitting layers of RGB corresponding to the three primary colors of light are stacked, or two of orange (orange) and blue are used. A configuration in which a light emitting layer is laminated is known.

JP-A-1-315988

However, in the case of a laminated structure including a plurality of light emitting layers, there is a problem that desired color development cannot be obtained in a low gradation region. This is because, in the low luminance region, the driving current becomes small, the carrier balance between electrons and holes is lost, and a specific light emitting layer in the stacked structure emits light intensively, so the color tone of the synthesized color light is reduced. This is because there is a bias.
As a result of repeated ingenuity, the inventors have achieved a carrier balance between electrons and holes by pulse driving that supplies a higher driving current than in constant current driving, It has been found that the desired color can be obtained even in the low gradation region.
In other words, it has been found that by adopting pulse driving, a desired substantially white light can be obtained even in a low gradation region.

However, in the course of further evaluation, when this pulse driving is adopted, the problem that the luminance life is shortened as compared with the conventional constant current driving has also become apparent.
FIG. 18 is a graph showing the luminance life for each driving method, with the vertical axis representing luminance and the horizontal axis representing elapsed time. As shown in the figure, it can be seen that the luminance is always lower in the graph 91 showing the luminance transition of the pulse drive than the graph 90 showing the luminance transition of the constant current drive, and the light emission life is shorter. Note that the driving conditions for pulse driving are conditions in which a high current capable of obtaining luminance substantially equal to the luminance in constant current driving is supplied at 1/100 duty.
That is, there is a problem that it is difficult to achieve both the desired color development in the low gradation region and the desired light emission lifetime. In other words, there is a problem that it is difficult to suppress color misregistration in a low gradation region while ensuring a desired light emission lifetime.
In addition, there is a problem that the color misregistration is more conspicuous when the display device is dark than when the surrounding environment of the display device is bright. For this reason, in particular, when the ambient illuminance is low, a display device capable of desired color development has been expected.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples or forms.

(Application example)
It has at least a substrate, a plurality of light emitting layers that emit different color lights, and a color filter in which a plurality of color filters including red, green, and blue are arranged, and each of the light emitting layers emits a plurality of color lights. An organic EL display device that emits substantially white light through a color filter, and a reference current corresponding to a display gradation defined in an image signal is applied to one layer of a laminated structure including a plurality of light emitting layers. A drive switching unit that switches between constant current driving for continuous display and display and pulse driving for displaying by supplying a current higher than a reference current in a predetermined period within one frame, and a drive switching unit The organic EL display device is characterized in that pulse driving is performed when the gradation is equal to or lower than a predetermined gradation, and constant current driving is performed when the gradation is higher than the predetermined gradation.

This organic EL display device includes a drive switching unit that switches between constant current driving and pulse driving according to display gradation. The drive switching unit performs pulse driving in a low gradation region below a predetermined gradation, and performs constant current driving in a medium / high gradation region higher than that.
In particular, since the carrier balance between electrons and holes in the stacked structure can be obtained by applying a pulse-like current higher than the reference current by pulse driving in the low gradation region, the expected result can be obtained even in the low gradation region. Substantially white light can be obtained. In other words, by applying a current higher than the reference current in a pulsed manner, the energy gap between the plurality of light emitting layers in the stacked structure can be exceeded, so that the intended substantially white light can be obtained even in the low gradation region. it can.
Further, in the middle / high gradation region higher than the predetermined gradation, since the switching to the constant current driving is performed, the load on the stacked structure including the light emitting layer is reduced, and the light emission lifetime can be secured.
Therefore, the desired color can be obtained by pulse driving in the low gradation region, and the light emission life can be secured by constant current driving in the middle and high gradation region.
Therefore, it is possible to provide an organic EL display device that achieves both desired color development and desired light emission lifetime in a low gradation region.
In other words, it is possible to provide an organic EL display device that suppresses color misregistration in a low gradation region while ensuring a desired light emission lifetime.

Further, the predetermined gradation is the average luminance per screen in the image signal, and the average luminance corresponds to the range of 3 to ²⁰ cd / cm ² when expressed by the average luminance on the display surface of the organic EL display device. A gradation is preferable.

  It has at least a substrate, a plurality of light emitting layers that emit different color lights, and a color filter in which a plurality of color filters including red, green, and blue are arranged, and each of the light emitting layers emits a plurality of color lights. An organic EL display device that emits substantially white light through a color filter, and a reference current corresponding to a display gradation defined in an image signal is applied to one layer of a laminated structure including a plurality of light emitting layers. A drive switching unit that switches between constant current driving for continuously supplying and displaying in the frame, and pulse driving for supplying and displaying a current higher than the reference current for a predetermined period in one frame, and an organic EL display device And an illuminance detection unit that detects illuminance in the surrounding environment where the illuminance is disposed, and the drive switching unit performs pulse driving when the illuminance detected by the illuminance detection unit is less than or equal to a predetermined illuminance, The organic EL display device when higher than the constant illuminance and performing constant current driving.

The predetermined illuminance is preferably illuminance of 200 lux or less.
Moreover, it is preferable that the duty ratio of the pulse drive in 1 frame exists in the range of 1/3-1/50.
Further, the current higher than the reference current in the pulse drive is preferably larger than a value obtained by multiplying the reference current and the reciprocal of the duty ratio.
In addition, the pulse drive is performed by subfield drive in which scanning of all the scanning lines is sequentially performed in a period length of one frame, which is performed twice in the first subfield and the second subfield. The period length of the second subfield is set in accordance with the duty ratio. In the first subfield, a current higher than the reference current is supplied to the stacked structure, and in the second subfield, the stacked structure is set. It is preferable not to supply current.
In addition, the laminated structure includes a light emitting layer corresponding to each color of red, green, and blue, and a top emission type structure in which the laminated structure and the color filter are formed in this order on the substrate. It is preferable to adopt.

  An electronic apparatus comprising the organic EL display device described above.

  It has at least a substrate, a plurality of light emitting layers that emit different color lights, and a color filter in which a plurality of color filters including red, green, and blue are arranged, and each of the light emitting layers emits a plurality of color lights. A method of driving an organic EL display device that emits substantially white light through a color filter, and when a display gradation specified in an image signal is higher than a predetermined gradation, a reference current corresponding to the gradation Is continuously supplied within one frame to perform constant current driving, and when the gradation is equal to or lower than a predetermined gradation, pulse driving is performed to supply a current higher than the reference current for a predetermined period within one frame. A driving method of an organic EL display device.

FIG. 6 is a perspective view illustrating one embodiment of a display device according to Embodiment 1; The circuit block block diagram. FIG. The sectional side view in the ii cross section of FIG. Detailed sectional drawing of an organic electroluminescent layer. (A) Current waveform diagram of constant current drive, (b) Current waveform diagram of pulse drive. FIG. 4 is a timing chart for vertical scanning driving. FIG. 6 is a timing chart of pulse driving. The flowchart figure which showed the flow of the drive method. FIG. 6 is a circuit block configuration diagram of a display device according to a second embodiment. The flowchart figure which showed the flow of the drive method. The top view which shows the vehicle-mounted meter as an electronic device carrying a display apparatus. Sectional drawing of the organic electroluminescent layer which concerns on the modification 1. FIG. FIG. 10 is a timing chart of a driving method according to Modification 2. The evaluation result table of Example A. FIG. 6 is a chromaticity diagram according to Example A. The evaluation result table of Example B. The graph which showed the brightness | luminance lifetime for every drive method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each part is different from the actual scale so that each layer and each part can be recognized on the drawing.

(Embodiment 1)
"Overview of display device"
FIG. 1 is a perspective view showing an aspect of the display device according to the present embodiment.
First, the outline | summary of the display apparatus 100 as an organic electroluminescent display apparatus which concerns on Embodiment 1 of this invention is demonstrated.

The display device 100 is an organic EL display device, and includes a display panel 18, a flexible substrate 20, and the like. The display panel 18 is a top emission type organic EL display panel in which a functional layer including a light emitting layer is sandwiched between the element substrate 1 and the counter substrate 17, and emits display light from the counter substrate 17 side.
The display panel 18 includes a display region V composed of a plurality of pixels arranged in a matrix. As enlarged and shown in the upper right of FIG. 1, red (R), green (G), and blue (B) color pixels are periodically arranged in the display area V, and each pixel emits display. A full color image is displayed by light. Each pixel is a light-emitting pixel, but is called a pixel.
The display area V has a vertically long rectangle. In each figure including FIG. 1, the vertical direction is defined as the Y-axis direction, and the horizontal direction shorter than the vertical direction is defined as the X-axis direction. The thickness direction of the display panel 18 is the Z-axis direction. Further, the Y-axis (+) and (−) directions are defined as the vertical direction, and the X-axis (+) and (−) directions are defined as the horizontal direction.

As will be described in detail later, the display device 100 includes a plurality of pixels that emit light of substantially white light by laminating each color light emitting layer emitting each color light of RGB on the element substrate 1 side and combining each color light emitted from each color light emitting layer. And a top emission type organic EL display panel by “white light emission + color filter system” in which each color pixel of RGB is formed by disposing color filters of red, green and blue on the counter substrate 17 side.
Conventionally, when such a laminated light emitting layer in which a plurality of light emitting layers are laminated is used, there has been a problem that desired color development cannot be obtained in a low gradation region. In addition, when pulse driving is performed to solve this problem, there is a problem that the luminance life is shortened, and it is difficult to achieve both the color shift in the low gradation region and the luminance life.
On the other hand, according to the display device 100, as will be described later, there is provided a configuration in which pulse driving and constant current driving are switched according to display luminance and environmental illuminance, or a driving method for switching both driving methods. By adopting it, it is possible to suppress color misregistration in the low gradation region while ensuring the desired light emission lifetime.

In the display panel 18, a flexible substrate 20 is connected to an extended region where the element substrate 1 extends from the counter substrate 17. The flexible board is an abbreviation for a flexible printed circuit board having flexibility in which an iron foil wiring or the like is formed on a polyimide film base. In addition, a driving IC (Integrated Circuit) 21 for controlling the driving method described above is mounted on the flexible substrate 20, and an end thereof is connected to a dedicated controller or an external device (both not shown). A plurality of terminals are formed.
The display panel 18 displays images, characters, and the like in the display area V by receiving control signals including power and image signals from an external device via the flexible substrate 20.

"Circuit block configuration of display device"
FIG. 2 is a circuit block diagram of the display device.
Next, a circuit block configuration of the display device 100 will be described with reference to FIG.

Circuit blocks for driving the display panel 18 are disposed in the driving IC 21 and the display panel 18. The driving IC 21 and the display panel 18 are electrically connected via the flexible substrate 20 as described above.
In the driving IC 21, a control circuit 50, a drive switching unit 51, and the like are formed.
The control circuit 50 is a CPU (Central Processing Unit) and controls the operation of each unit. Further, the control circuit 50 is accompanied by a storage circuit 56 constituted by a nonvolatile memory such as a flash memory.
The memory circuit 56 stores various programs and accompanying data for controlling the operation of the display device 100, including a program that defines the order and contents for performing pulse driving and constant current driving. The program also includes a drive control program for switching between pulse driving and constant current driving in accordance with display luminance and environmental illuminance.
In addition, the accompanying data includes a predetermined gradation value, a predetermined illuminance, a reference current value, and a pulse for each duty ratio in pulse driving, which are threshold values (boundary values) when switching between pulse driving and constant current driving. A correlation table that defines the correlation with the current is included.

The drive switching unit 51 includes a timing signal generation circuit 52, a display data processing circuit 53, a drive current generation circuit 54, a drive current output circuit 55, and the like.
The timing signal generating circuit 52 performs various timings for controlling the display panel 18 in synchronization with the vertical synchronizing signal Vs, horizontal synchronizing signal Hs, and dot clock signal Dclk of the image signal Video supplied from an external device (not shown). Generate a signal.
The timing signal generation circuit 52 is accompanied by a clock generation circuit 57 made of an oscillation circuit including a crystal resonator, for example. The clock generation circuit 57 generates a clock signal that serves as a reference for the control operation of each unit and outputs the clock signal to the timing signal generation circuit 52.

The display data processing circuit 53 is an image processor, and a frame memory 58 is attached. The display data processing circuit 53 stores the image signal Video supplied from the external device in the frame memory 58 according to the control of the control circuit 50, and then reads and drives the gradation data in accordance with the aspect ratio and resolution of the display panel. Image processing such as so-called scaling processing for generating data (digital data) is performed.
Further, the control circuit 50 reads (measures) the gradation data per screen of the image signal Video written in the frame memory 58, and calculates the average gradation of display as a predetermined gradation.
The drive current generation circuit 54 has a plurality of DC power supply circuits such as current mirror circuits, for example, and is formed so as to be able to supply a plurality of currents having different weights.
The drive current output circuit 55 has a built-in D / A converter, and the gradation represented by the digital drive data from the display data processing circuit 53 is selected or combined from a plurality of currents of the drive current generation circuit 54. It is converted into a drive current IL that is an analog current corresponding to the gradation and supplied to the display panel 18.

  A scanning line driving circuit 60 and a data line driving circuit 61 are formed at the peripheral edge (frame portion) of the display area V of the display panel 18. Note that the circuit elements constituting these circuits are formed on a substrate using low-temperature polysilicon or amorphous silicon as an active layer, as in the pixel circuit described later.

"Pixel circuit"
FIG. 3 is a diagram illustrating one mode of the pixel circuit.
Here, the outline of the pixel circuit of the pixel of the display panel 18 and the scanning drive of a plurality of pixels will be described with reference to FIGS.
In each of the pixels arranged in a matrix in the display area V in FIG. 1, a pixel circuit as shown in FIG. 3 is formed.
The pixel circuit includes a switching transistor (Thin Film Transistor) Tr1 for selecting a pixel, a driving transistor Tr2 for flowing a current to the organic EL layer 8 having a laminated structure including a plurality of light emitting layers, and a holding circuit. It is composed of a capacitor C and the like.
The scanning line SL from the scanning line driving circuit 60 is connected to the gate terminal of the transistor Tr1, and the data line DL from the data line driving circuit 61 is connected to the source terminal.
The drain terminal of the transistor Tr1 is connected to the gate terminal of the transistor Tr2 and one end of the storage capacitor C.
The source terminal of the transistor Tr2 and the other end of the storage capacitor C are connected to the supply line of the drive current IL from the drive current output circuit 55. The drain terminal of the transistor Tr2 is connected to the pixel electrode 6 (anode).
An organic EL layer 8 is disposed between the pixel electrode 6 and the common electrode 9. The common electrode 9 is connected to an earth line (cathode).

2 includes a shift register and an output buffer (both not shown). Based on the timing signal from the timing signal generation circuit 52, the scanning line driving circuit 60 sequentially applies scanning signals to the plurality of scanning lines SL. Supply.
The data line driving circuit 61 includes a shift register and a latch circuit (both not shown). Based on the timing signal from the timing signal generating circuit 52 and the data signal, the data line driving circuit 61 sends data signals to the plurality of data lines DL. Supply.
In FIG. 3, the transistor Tr1 selected by the scanning signal is turned on, and the data signal is supplied to the transistor Tr2. As a result, the transistor Tr2 is turned on, and the drive current IL flows through the organic EL layer 8 to emit light. In parallel with the turning on of the transistor Tr2, the data signal is held in the holding capacitor C, so that light emission is maintained for a time corresponding to the capacitance (period length corresponding to one frame).
Note that the pixel circuit is not limited to the pixel circuit illustrated in FIG. 3, and may be any pixel circuit that can drive the organic EL layer 8 with the drive current IL.

"Detailed configuration of the display panel"
FIG. 4 is a side sectional view taken along the line ii of FIG.
Next, a detailed configuration of the display panel 18 will be described.
The display panel 18 includes an element substrate 1, an element layer 2, a planarizing layer 4, a reflective layer 5, a pixel electrode 6, a partition wall 7, an organic EL layer 8, a common electrode 9, an electrode protective layer 10, a buffer layer 11, and a gas barrier layer 12. , Filler 13, CF layer 14, counter substrate 17, and the like. A portion sandwiched between the element substrate 1 and the counter substrate 17 is referred to as a functional layer 16. In other words, the laminated structure from the element layer 2 to the CF layer 14 is referred to as a functional layer 16.
The element substrate 1 is made of inorganic glass. In this embodiment, alkali-free glass is used as a suitable example. In addition, it is not limited to this structure, You may use a resin substrate. Further, since it is a top emission type, a material having low light transmittance may be used, and for example, a configuration using a metal substrate may be used.
In the element layer 2, the pixel circuit described with reference to FIG. 3 is formed for each pixel. In the cross section of FIG. 4, only the transistor Tr2 is shown. The pixel circuit uses low-temperature polysilicon as the active layer as a preferred example, but may have a configuration using amorphous silicon as the active layer.

In the upper layer (Z-axis (−) direction) of the element layer 2, for example, a planarization layer 4 that is an insulating layer made of an acrylic resin or the like is formed.
The reflective layer 5 and the pixel electrode 6 are laminated in this order on the flattening layer 4 so as to be divided for each pixel.
The reflection layer 5 is a reflection layer made of, for example, aluminum, and reflects light traveling from the organic EL layer 8 toward the element substrate 1 to make light that contributes to display.
The pixel electrode 6 is composed of a transparent electrode such as ITO (Indium Tin Oxide) or ZnO, and is connected to a drain terminal of the transistor Tr2 of the element layer 2 and a contact hole penetrating the planarization layer 4 for each pixel. Yes. In the present embodiment, as a preferred example, an insulating layer made of a transparent inorganic material such as SiO ₂ is interposed between the reflective layer 5 and the pixel electrode 6, but the present invention is not limited to this configuration. Any structure that functions as a reflective electrode may be used. For example, the reflective layer 5 may be omitted, and only the pixel electrode 6 may be formed of a reflective material such as aluminum. Alternatively, the pixel electrode 6 may be formed directly on the reflective layer 5 without interposing an inorganic insulating layer.

The partition wall 7 is made of a photocurable black resin or the like, and partitions each pixel in a lattice shape in a plane. Note that the pixel circuit including the transistor Tr2 in the element layer 2 is disposed so as to overlap the partition in a planar manner in order to prevent malfunction due to light.
The organic EL layer 8 is formed on one surface so as to cover the pixel electrode 6 and the partition wall 7. In FIG. 4, the organic EL layer 8 is shown as a single layer, but in actuality, it has a laminated structure including light emitting layers for each color of RGB. The laminated structure includes a hole injection layer and an intermediate layer. And an electron injection layer. Details of the laminated structure will be described later.

The common electrode 9 as a common cathode is a metal thin film layer in which a metal such as MgAg is formed very thin so as to transmit light, and is formed so as to cover the organic EL layer 8 across all pixels. Further, since light is emitted through the layer, the thickness thereof is extremely thin, for example, 10 to 20 nm in order to improve light transmittance.
The electrode protective layer 10 is made of a high-density and highly transparent material such as SiO ₂ , Si ₃ N ₄ , or SiOxNy, and the organic EL layer 8 is formed by covering the common electrode 9. Prevents moisture from entering the water.
The buffer layer 11 is a transparent organic buffer layer such as a thermosetting epoxy resin.
The gas barrier layer 12 is a gas barrier layer made of the same material as the electrode protective layer 10, and is formed so as to further cover the buffer layer 11, so that moisture and the like enter the internal laminated structure including the organic EL layer 8. Is preventing.
The filler 13 is a transparent adhesive layer made of, for example, a thermosetting epoxy resin, and fills the uneven surface between the gas barrier layer 12 and the CF layer 14 and bonds them together. The display panel 18 also functions to prevent moisture and the like from entering the internal laminated structure including the organic EL layer 8 from the peripheral edge of the display panel 18.

The counter substrate 17 is made of transparent inorganic glass, and non-alkali glass is used as a suitable example. Further, the CF layer 14 is formed on the organic EL layer 8 side (Z-axis (+) side) of the counter substrate 17.
In the CF layer 14, a red color filter 14r, a green color filter 14g, and a blue color filter 14b are arranged similarly to the pixel arrangement. Specifically, the color filters of each color are arranged so as to overlap with the corresponding pixel electrodes 6, and light shielding portions indicated by hatching are formed between the color filters. The light shielding portion is formed in a lattice shape so as to overlap the partition wall 7 in a plan view, and optically functions as a black matrix.
The counter substrate 17 and the element substrate 1 are bonded and sealed with a sealant 15 formed on the peripheral edge of the counter substrate 17. As the sealant 15, an epoxy adhesive, an ultraviolet curable resin, or the like is used.

From each pixel configured in this manner, display light corresponding to the color tone of the color filter is emitted. For example, in the case of a red pixel, first, in the organic EL layer 8, the RGB color lights emitted from the respective color light emitting layers are combined to become substantially white light and enter the red color filter 14r. Then, red light is selected by the red color filter 14r and emitted from the counter substrate 17 as red display light. The same applies to green and blue pixels.
Thereby, in the display area V, a full-color image is displayed by display light from the plurality of color pixels emitted from the counter substrate 17.

"Details of organic EL layer (laminated structure)"
FIG. 5 is a detailed cross-sectional view of the organic EL layer. Note that the cross section shows a cross section on the pixel electrode 6.
The organic EL layer 8 includes a hole injection layer 81, a hole transport layer 82, a red light emitting layer 83, an intermediate layer 84, a blue light emitting layer 85, a green light emitting layer 86, an electron transport layer 87, and an electron injection on the pixel electrode 6. The layer 88 has a stacked structure in which layers are stacked in this order. A common electrode 9 is formed on the electron injection layer 88.
As a preferable example, the hole injection layer 81 is formed by depositing N, N′-bis- (4-diphenylamino-phenyl) -N, N′-diphenyl-biphenyl-4-4′-diamine by a vacuum deposition method, It is formed with an average thickness of about 20 nm.
The hole transport layer 82 is preferably made of N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4′-diamine (α-NPD). Vapor deposition is performed to form an average thickness of about 10 nm.

As a suitable example, the red light emitting layer 83 is formed by depositing the constituent material of the red light emitting layer by a vacuum vapor deposition method and having an average thickness of about 10 nm. As a constituent material of the red light emitting layer, it is preferable to use a tetraaryldiindenoperylene derivative (RD-1) as a red light emitting material (guest material) and a rubrene derivative (RB) as a host material. Moreover, it is preferable that content (dope density | concentration) of the luminescent material (dopant) in a red light emitting layer shall be about 2.0 wt%.
As a preferred example, the intermediate layer 84 is formed to have an average thickness of about 10 nm by using a vacuum deposition method. As the constituent material of the intermediate layer, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4′-diamine (α-NPD) and an anthracene derivative And the use ratio of the material in the intermediate layer is preferably α-NPD: anthracene derivative = 1: 1 by weight.

As a suitable example, the blue light emitting layer 85 is vapor-deposited by a vacuum vapor deposition method and formed to have an average thickness of about 20 nm. It is preferable to use a distyryldiamine compound as a constituent material of the blue light emitting layer and an anthracene derivative as a host material. Further, the content (dope concentration) of the blue light emitting material (dopant) in the blue light emitting layer is preferably about 10.0 wt%.
As a suitable example, the green light emitting layer 86 is formed by depositing a constituent material of the green light emitting layer by a vacuum vapor deposition method and having an average thickness of about 10 nm. As a constituent material of the green light emitting layer, it is preferable to use a quinacridone derivative as a green light emitting material (guest material) and an anthracene derivative as a host material. Moreover, it is preferable that content (dope density | concentration) of the green light emitting material (dopant) in a green light emitting layer shall be about 10.0 wt%.

As a suitable example, the electron transport layer 87 is formed by depositing tris (8-quinolinolato) aluminum (Alq3) by a vacuum deposition method to an average thickness of about 10 nm.
As a preferred example, the electron injection layer 88 is formed by depositing lithium fluoride (LiF) by a vacuum deposition method to an average thickness of about 1 nm.
It should be noted that the present invention is not limited to the configuration (material, thickness, etc.) of the above-described preferred examples, but may be any material and thickness that can form a laminated structure including a plurality of light emitting layers capable of synthesizing substantially white light. It ’s fine.

"Overview of drive method"
FIGS. 6A and 6B are waveform diagrams showing an outline of the driving method. FIG. 6A shows a current waveform of constant current driving, and FIG. 6B shows a current waveform of pulse driving. The vertical axis represents drive current and the horizontal axis represents time.
Here, an outline of the driving method in the present embodiment will be described.

In the display device 100, when the display gradation is equal to or lower than the predetermined gradation, the “pulse driving” shown in FIG. 6B is performed. When the display gradation is higher than the predetermined gradation, FIG. “Constant current drive” shown in FIG.
Here, the display gradation indicates an average gradation per screen defined in the image signal. The predetermined gradation is a threshold value determined according to the specification of the display panel 18 and is an average gradation (luminance) value per screen in the low luminance area. For example, in the case of the display panel 18 including the organic EL layer 8 of the above-described preferred example, the gradation value for driving the panel in the range of average luminance of 3 to 20 cd / cm ² is obtained. In other words, it refers to gradation data for driving the display panel 18 to display at a predetermined luminance within an average luminance of 3 to 20 cd / cm ² .

“Constant current driving” shown in FIG. 6A is a driving method that continuously supplies a reference current Ik corresponding to a display gradation defined in an image signal during a period of one frame.
In addition, as shown in FIG. 6B, the “pulse drive” supplies a drive current Ip higher than the reference current Ik in a pulse shape for a predetermined duty ratio at the start of one frame, and the remaining period is as follows. This is a driving method in which no current flows.
Here, the duty ratio of the pulse drive in one frame is preferably in the range of 1/3 to 1/50 in order to ensure the color developability and the luminance life in the low luminance region, and 1/10 to 1 More preferably within the range of / 50. The drive current Ip is preferably larger than a value obtained by multiplying the reference current Ik by the reciprocal of the duty ratio.
The numerical values such as the average luminance and the duty ratio described above are obtained by analyzing and analyzing experimental data obtained from the results of many experiments conducted by the inventors, etc. is there.

"Details of driving method"
FIG. 7 is a timing chart of vertical scanning driving.
First, the details of the “constant current drive” will be described with reference to FIG.
The scanning line driving circuit 60 (FIG. 2) sequentially supplies the scanning signals G1 to Gm based on the start signal Dy supplied from the timing signal generation circuit 52 and used as a trigger for sequentially selecting the scanning lines and the clock signal Cly. And sequentially output to the scanning lines. The start signal Dy is a start pulse that defines the start timing of vertical scanning, and is supplied once at the beginning of one frame period in constant current driving, and one scanning line is selected once in one frame period. Will be.
A frame refers to a period during which one image in the image signal is displayed on the display panel 18. For example, when the frequency of the vertical synchronization signal Vs is 60 Hz, the period length of one frame is about 16.7 mm. Second.

The scanning signal G1 supplied to the uppermost scanning line is output at a timing delayed by a half cycle after the clock signal Cly first rises after the start signal Dy is supplied. Subsequently to the scanning signal G1, the sequential scanning signals G2 to Gm sequentially become H level in a period corresponding to a half cycle of the clock signal every time the logic level of the clock signal Cly changes.
In this manner, all the scanning lines are sequentially selected in response to the supply of the start signal Dy, and one vertical scanning drive is performed.
Further, the data line driving circuit 61 (FIG. 2) supplies a data signal to each corresponding data line at a timing synchronized with the scanning signals G1 to Gm, and during the period of one frame in which the signal level is held. The drive current is supplied from the drive current output circuit 55 to the organic EL layer 8.
The supplied drive current is a reference current Ik corresponding to the gradation of the image signal for each pixel. For example, in the case of the laminated structure of the organic EL layer 8 in the above-described preferred example, the reference current Ik is set to 400 mA / cm ² when the gradation data of the image signal is equivalent to 400 cd / m ² .

FIG. 8 is a timing chart of pulse driving.
Next, details of the “pulse drive” will be described with reference to FIG.
In this embodiment, as a preferred example, as shown in FIG. 8, one frame is divided into two subfields in time, and pulse driving is performed by subfield driving in which vertical scanning driving is performed twice in one frame period. Is realized.
Specifically, within one frame, the start pulse is supplied twice in time series, and one scanning line is selected twice in one frame period.
The scanning line driving circuit 60 (FIG. 2) generates and outputs the scanning signals G1 to Gm in order from the timing t1 to the timing t2 using the start signal Dya at the timing t1 as a trigger, and sequentially selects the scanning lines. (First field).
Further, the data signal is supplied from the data line driving circuit 61 (FIG. 2) to each corresponding data line at a timing synchronized with the scanning signals G1 to Gm, and is driven from the driving current output circuit 55 to the organic EL layer 8. Current is supplied.
Here, the driving current Ip higher than the reference current Ik corresponding to the gradation of the image signal is supplied for each pixel. Specifically, the drive current Ip is a current larger than a value obtained by multiplying the reciprocal of the duty ratio of the pulse drive and the reference current Ik.
For example, in the laminated structure of the organic EL layer 8 in the above-described preferred example, when the reference current Ik is 400 mA / cm ² and the duty ratio is 1/5, the driving current Ip is 400 mA / cm ² × 5 = It is set to 2,400 mA / cm ² which is larger than 2,000 mA / cm ² .

Subsequently, similarly to the first field, with the start signal Dyb at the timing t2 as a trigger, the scanning signals G1 to Gm are sequentially generated and output from the timing t2 to the timing t3, and the scanning lines are sequentially selected ( Second field). Note that the timing t2 is a timing at which the duty ratio of the pulse driving in the period length of one frame has elapsed.
For example, when the period length of one frame is about 16.7 milliseconds and the duty ratio is 1/5, the timing t2 is output about 3.34 milliseconds after the timing t1.
Also in the second field, the data signal is supplied to each data line and the drive current is supplied to the organic EL layer 8 at the timing synchronized with the scanning signals G1 to Gm, but the drive current is set to zero. In other words, in the second field, the drive current is not supplied to the organic EL layers 8 of all the pixels, and the light is forcibly turned off.
Similarly, in each successive frame, subfield driving including the first and second fields is performed.
In this way, the “pulse drive” shown in FIG. 6B is realized.

"Flow of driving method"
FIG. 9 is a flowchart showing the flow of the driving method.
Here, the flow of the driving method including the switching between “constant current driving” and “pulse driving” will be described with reference to FIG. The following flow is executed by the control circuit 50 controlling each unit including the drive switching unit 51 based on the drive control program of the storage circuit 56.

In step S1, gradation data per screen of the input image signal is measured (read). Specifically, the gradation data per screen of the image signal written in the frame memory 58 is measured.
In step S2, an average gradation value of display as a display gradation is calculated and derived from the measured gradation data.
In step S <b> 3, it is determined whether the derived average gradation value (display gradation) is equal to or less than a predetermined gradation value stored in the storage circuit 56. If it is less than the predetermined gradation value, the process proceeds to step S4. If it is larger than the predetermined gradation value, the process proceeds to step S5.
In step S4, "pulse driving" is performed. Specifically, as described with reference to FIG. 8, the start pulse is supplied twice from the drive switching unit 51 in time series, and subfield driving is performed in which one scanning line is selected twice in one frame period.
In step S5, “constant current drive” is performed. Specifically, as described with reference to FIG. 7, a start pulse is supplied once from the drive switching unit 51 at the beginning of one frame period, and a constant drive current (reference current) is supplied over one frame period. The
This flow is always executed while the display panel 18 is driven to display. In other words, the drive control program of the storage circuit 56 is resident and always switches between “constant current drive” and “pulse drive” according to the average gradation value.

As described above, according to the display device 100 and the driving method according to the present embodiment, the following effects can be obtained.
The display device 100 includes a drive switching unit 51 that switches between pulse driving and constant current driving according to display gradation. The drive switching unit 51 performs pulse driving in a low gradation region below a predetermined gradation, and performs constant current driving in a medium / high gradation region higher than that. In other words, impulse-type driving is performed in the low gradation region, and hold-type driving is performed in the medium-high gradation region higher than that.
In particular, in the low gradation region, due to pulse driving, the amplitude of the pulse is higher than the reference current Ik, and the driving current Ip larger than the value obtained by multiplying the reciprocal of the duty ratio of pulse driving and the reference current Ik is the organic EL layer 8. To be supplied.
Since this drive current Ip can exceed the energy gap between the plurality of light emitting layers in the organic EL layer 8, the desired substantially white light can be obtained even in the low gradation region. In other words, by adopting impulse type driving, the carrier balance between electrons and holes in the stacked structure can be achieved, so that the desired substantially white light can be obtained even in the low gradation region. Further, the human eye feels the brightness of the display gradation defined by the pixel signal due to the afterimage (integration) effect of the retina.
Therefore, substantially white light can be obtained in the low gradation region, and the desired color can be obtained through the color filter.

Further, in the middle / high gradation region larger than the predetermined gradation, since switching to the constant current driving is performed, the load on the organic EL layer 8 is reduced, and the light emission life can be ensured.
Therefore, it is possible to provide the display device 100 that achieves both desired color development and desired light emission lifetime in the low gradation region. In other words, it is possible to provide the display device 100 that suppresses color misregistration in a low gradation region while ensuring an expected light emission lifetime.

Further, according to the driving method of the present embodiment, the duty ratio of pulse driving in one frame is in the range of 1/3 to 1/50, more preferably in the range of 1/10 to 1/50. .
As a result, as is clear from examples (FIGS. 15 and 16) described later, it is possible to ensure a good balance between the color developability in the low luminance region and the luminance life.
Accordingly, it is possible to provide a method for driving a display device that achieves both desired color development and desired light emission lifetime in a low gradation region. In other words, it is possible to provide a method for driving a display device that suppresses color misregistration in a low gradation region while ensuring a desired light emission lifetime.

Further, the display device 100 employs a “white light emission + color filter system” that is easy to increase in size and a top emission type configuration.
Therefore, the pixel aperture ratio can be increased as compared with the bottom emission type in which light is extracted from the element substrate 1 side on which the element layer 2 including the pixel circuit is formed.
Therefore, it is possible to provide the display device 100 that is highly versatile and can display a bright display.

(Embodiment 2)
FIG. 10 is a circuit block configuration diagram of the display device according to the second embodiment, and corresponds to FIG.
Hereinafter, the display device 110 according to Embodiment 2 of the present invention will be described. In addition, about the component same as Embodiment 1, the same number is attached | subjected and the overlapping description is abbreviate | omitted.

The display device 110 according to the second embodiment detects the illuminance in the surrounding environment where the display panel 18 is disposed, and performs “pulse driving” when the environmental illuminance is equal to or lower than the predetermined illuminance. “Constant current drive”.
For this reason, the display device 110 includes an illuminance detection unit 70 in addition to the configuration of the display device of the first embodiment. Specifically, the illuminance detection unit 70 is connected to the control circuit 50.
The illuminance detection unit 70 is a detection circuit incorporating an A / D converter, and an optical sensor 71 is attached. The optical sensor 71 is a photodiode, and although not shown in the drawing, the optical sensor 71 is arranged on the peripheral portion (frame portion) of the display area V of the display panel 18 so that external light can be detected. The optical sensor 71 may be any sensor that can detect the brightness of the environment, and may be, for example, a phototransistor or a Cds cell.
The illuminance detection unit 70 transmits the analog detection data detected by the optical sensor 71 to the control circuit 50 as encoded luminance data.

Here, as a preferred example, the predetermined illuminance serving as a threshold for switching between “pulse driving” and “constant current driving” is set to an illuminance of 200 lux or less. More preferably, it is set to 150 lux or less.
This is because the “color shift” phenomenon is more conspicuous when the surrounding environment is darker than when the surrounding environment is bright, so that “pulse drive” is performed when the ambient illuminance is lower than 200 lux to suppress the color shift. It is.

"Flow of driving method"
FIG. 11 is a flowchart showing the flow of the driving method according to the present embodiment.
Here, the flow of a driving method for switching between “constant current driving” and “pulse driving” in accordance with the ambient illuminance will be described with reference to FIG. The following flow is executed by the control circuit 50 controlling each unit including the drive switching unit 51 based on the drive control program of the storage circuit 56.

In step S11, the illuminance of the surrounding environment where the display panel 18 is disposed is detected. Specifically, the illuminance detection unit 70 is used to detect the illuminance of the surrounding environment of the optical sensor 71.
In step S <b> 12, it is determined whether the detected illuminance is equal to or less than a predetermined illuminance value stored in the storage circuit 56. If it is less than the predetermined illuminance value, the process proceeds to step S13. If it is greater than the predetermined illuminance value, the process proceeds to step S14. The predetermined illuminance is 150 lux.
In step S13, "pulse driving" is performed. Specifically, as described with reference to FIG. 8, the start pulse is supplied twice from the drive switching unit 51 in time series, and subfield driving is performed in which one scanning line is selected twice in one frame period.
In step S14, “constant current driving” is performed. Specifically, as described with reference to FIG. 7, a start pulse is supplied once from the drive switching unit 51 at the beginning of one frame period, and a constant drive current (reference current) is supplied over one frame period. The
This flow is always executed while the display panel 18 is driven to display. In other words, the drive control program of the storage circuit 56 is resident and always switches between “constant current drive” and “pulse drive” according to the ambient illuminance.

As described above, according to the present embodiment, in addition to the effects in the first embodiment, the following effects can be obtained.
According to the display device 110, the illuminance detection unit 70 and the drive switching unit 51 perform “pulse drive” when the environmental illuminance is equal to or lower than the predetermined illuminance, and perform “constant current drive” when the environmental illuminance is higher than the predetermined illuminance. In other words, when the ambient illuminance is dark (below the predetermined illuminance), the impulse type drive is performed, and when the ambient illuminance is brighter than that, the hold type drive is performed.
Therefore, color misregistration can be suppressed by performing “pulse driving” in a dark environment where the “color misregistration” phenomenon is easily noticeable when the ambient illuminance is equal to or lower than a predetermined illuminance. In other words, substantially white light can be obtained even in a dark environment, and the desired color can be obtained through the color filter.

Further, when the ambient illuminance is brighter than the predetermined illuminance, switching to the constant current drive is performed, so the load on the organic EL layer 8 is reduced and the light emission life can be ensured.
Therefore, it is possible to provide the display device 110 that achieves both the desired color development and the light emission lifetime when the ambient illuminance is low. In other words, it is possible to provide the display device 110 that suppresses the color misregistration when the ambient illuminance is low while ensuring the expected light emission lifetime.

(Electronics)
FIG. 12 is a plan view showing an on-vehicle meter equipped with the display device.
The display device 110 according to the second embodiment described above can be used by being mounted on, for example, an in-vehicle meter 200 for an automobile as an electronic device.
The on-vehicle meter 200 includes three display devices 110 arranged side by side. Specifically, the display device 211, the display device 212, and the display device 213 are arranged in this order from the left. Note that the outline of the display device is indicated by a dotted line.
The display device 212 located in the middle has a panel size that is slightly larger than the left and right display devices 211 and 213. With these three display devices, one on-vehicle meter exposed from the opening 215 of the dashboard is displayed. It is composed. In other words, one in-vehicle meter exposed from a horizontally long and elliptical opening 215 with the base cut in a straight line is configured by arranging three display devices 211, 212, and 213 in the horizontal direction.

For example, a fuel gauge, a water temperature gauge, and the like are displayed on the left display device 211.
For example, a speedometer, a direction indicator, or the like is displayed on the central display device 212.
For example, a tachometer or the like is displayed on the right display device 213. Although FIG. 12 shows a state in which analog display is performed, digital display can be performed by operating a switch (not shown). Further, the present invention is not limited to the three-panel configuration, and may be configured by a single display panel formed of a rectangle that is long in the horizontal direction (X-axis direction).
Since each of the display devices 211, 212, and 213 includes the illuminance detection unit 70 and the drive switching unit 51, the in-vehicle meter 200 suppresses color misregistration when the environmental illuminance is low while ensuring the desired light emission life. can do. In particular, since there is often no light source other than the meter in a car at night, the “color shift” tends to be more conspicuous. However, according to the in-vehicle meter 200, the low-luminance region is in a dark environment. Even the display of the desired color can be displayed.
Therefore, it is possible to provide the vehicle-mounted meter 200 that achieves both the desired color development and the light emission lifetime when the ambient illuminance is low.

Moreover, you may link the vehicle-mounted meter 200 and the electric system of a motor vehicle.
Specifically, on / off of the headlight of an automobile is linked with “constant current drive” / “pulse drive”. In this case, the output signal of the operation switch of the automobile headlight is input to the control circuit 50 of FIG. 10, and “constant current driving” is performed when the signal is on, and “pulse driving” is performed when the signal is off. To control.
Normally, a headlight of an automobile is turned on at night or when it is dark, so that the function similar to the function of the illuminance detection unit 70 can be obtained also by an output signal of an operation switch of the headlight.
Therefore, it is possible to provide the vehicle-mounted meter 200 that achieves both the desired color development and the light emission lifetime when the ambient illuminance is low.
Note that the display device 100 may be used instead of the display device 110. Moreover, you may use combining these. Even if it is this structure, the same effect can be acquired.

Further, the present invention is not limited to the vehicle-mounted meter 200, and any electronic device including a display unit may be used. For example, the present invention may be applied to a monitor or a notebook computer. Further, it can be used for various electronic devices such as mobile phones, display devices for car navigation systems, PDAs (Personal Digital Assistants), mobile computers, digital cameras, digital video cameras, in-vehicle devices, and audio devices.
Even with these electronic devices, similar effects can be obtained.

  Note that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be added to the above-described embodiment. A modification will be described below.

(Modification 1)
FIG. 13 is a cross-sectional view of an organic EL layer according to Modification 1, and corresponds to FIG.
In each of the above embodiments, the laminated structure constituting the organic EL layer has been described as including three light emitting layers corresponding to RGB. However, the present invention is not limited to this structure, and substantially white light can be synthesized. Any stacked structure including a plurality of light emitting layers may be used.
For example, a laminated structure including two light emitting layers like the organic EL layer 98 shown in FIG. 13 may be used. In addition, about the component same as Embodiment 1, the same number is attached | subjected and the overlapping description is abbreviate | omitted.

In the organic EL layer 98, a hole injection layer 81, a hole transport layer 82, an orange light emitting layer 91, a blue light emitting layer 92, an electron transport layer 87, and an electron injection layer 88 are laminated on the pixel electrode 6 in this order. It has a laminated structure. A common electrode 9 is formed on the electron injection layer 88.
As a preferred example, the orange light emitting layer 91 is formed by depositing the constituent material of the orange light emitting layer by a vacuum evaporation method. As a constituent material of the orange light emitting layer, a tetraaryldiindenoperylene derivative (RD-1) is used as an orange light emitting material (guest material), and N, N′-bis (1-naphthyl) is used as a host material. It is preferable to use —N, N′-diphenyl [1,1′-biphenyl] -4,4′-diamine (α-NPD). Further, it is preferable to use BH-140 (registered trademark) as an assist dopant.
As a suitable example, the blue light emitting layer 92 is formed by depositing a constituent material of the blue light emitting layer by a vacuum evaporation method. As a constituent material of the blue light emitting layer, it is preferable to use BD-102 (registered trademark) as a guest material and EK-109 (registered trademark) as a host material. Further, α-NPD (registered trademark) is preferably an assist dopant.

Even in this laminated structure, the configuration and driving method of each of the above embodiments can be applied, and similar effects can be obtained.
Accordingly, it is possible to provide a display device that achieves both desired color development and desired light emission lifetime in a low gradation region. In addition, it is possible to provide a display device that achieves both desired color development and a light emission lifetime when the ambient illuminance is low.
It should be noted that the present invention is not limited to the configuration and material of the preferred examples described above, and any configuration and material may be used as long as it can form a laminated structure including a plurality of light emitting layers capable of synthesizing substantially white light. For example, a configuration in which an intermediate charge generation layer is interposed between the light emitting layers, that is, a so-called tandem organic EL layer configuration may be used.

(Modification 2)
FIG. 14 is a timing chart of the driving method according to the second modification, and corresponds to FIG. 6A and FIG.
In each of the above embodiments, the constant current drive is described as being performed by one vertical scanning drive in one frame. However, the present invention is not limited to this method, and constant current drive may be performed by subfield drive. In addition, about the description same as Embodiment 1, the same symbol is attached | subjected and the overlapping description is abbreviate | omitted.
For example, as shown in FIG. 14, constant current driving may be realized by subfield driving in which one frame is divided into two subfields in time and vertical scanning driving is performed twice within one frame period. .
Specifically, the reference current Ik is supplied as a drive current in both the first field triggered by the start signal Dya at the timing t1 and the second field triggered by the start signal Dyb at the timing t2.

Also by this driving method, since the reference current Ik is supplied over a period of one frame, the “constant current driving” of FIG. 6A can be realized.
Accordingly, it is possible to provide a method for driving a display device that achieves both desired color development and desired light emission lifetime in a low gradation region. Furthermore, “constant current drive” in addition to “pulse drive” can be performed by subfield drive controlled at the same timing, so that drive control is simplified and the frequency of malfunctions can be suppressed.

(Modification 3)
This will be described with reference to FIG.
In each of the above embodiments, the configuration of the display device has been described as being a top emission type, but is not limited to this configuration, and may be a bottom emission type configuration.
In this case, the reflective layer 5 is deleted and the common electrode 9 is used as a reflective electrode. Further, the CF layer 14 is formed on the Z-axis (+) side of the element substrate 1. Accordingly, a bottom emission type display device that extracts light from the element substrate 1 side can be configured.
Even in this configuration, since the display device is a “white light emission + color filter type” display device having a stacked structure including a plurality of light emitting layers, it is possible to apply the configurations and driving methods of the above embodiments. Yes, similar effects can be obtained.

(Example A)
“Results of Driving with Laminated Structure of Embodiment 1”
FIG. 15 shows a list of changes in chromaticity when constant current driving and pulse driving with a plurality of duty ratios are performed for each of a plurality of gradations using the display panel 18 having the laminated structure of the first embodiment. It is a table.
First, the display panel 18 used in the experiment has a laminated structure including the three light-emitting layers of RGB described in the preferred example of Embodiment 1 as the configuration of the organic EL layer 8. Further, a display panel (evaluation panel) in a state in which light emitted from the organic EL layer 8 from the counter substrate 17 can be directly measured without forming a color filter was used.

As Comparative Example 1, chromaticity data was measured when the evaluation panel was driven with constant current at each gradation corresponding to the display gradation.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, the luminance when the driving current of 400 mA / cm ² is supplied and DC driving is performed as the reference current Ik. The chromaticity data is shown in the upper left of FIG.
The luminance (gradation) at this time was 415 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
Similarly, in order to obtain a luminance equivalent to 40 cd / m ^{2 on} the display surface of the display panel, the luminance and chromaticity data when DC driving is performed by supplying a necessary reference current are data on the right side. . The luminance at this time was 38 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.34, 0.34). You can see that it is changing.

Similarly, in order to obtain a luminance equivalent to 4 cd / m ^{2 on} the display surface of the display panel, the luminance and chromaticity data when DC driving is performed by supplying a necessary reference current are data on the right side. The luminance at this time is 3.58 cd / m ² on the display surface, and the chromaticity is (x, y) = (0.42, 0.37). .
Similarly, in order to obtain a luminance equivalent to 0.3 cd / m ^{2 on} the display surface of the display panel, the luminance and chromaticity data when DC driving is performed by supplying a necessary reference current are data on the right side. . The luminance at this time is 0.23 cd / m ² on the display surface, and the chromaticity is further reddish as (x, y) = (0.50, 0.41).
Finally, in order to obtain a luminance equivalent to 0.01 cd / m ^{2 on} the display surface of the display panel, the luminance and chromaticity data when the required reference current is supplied and DC driving is the data on the right side. . The luminance at this time was 0.01 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.53, 0.41).

FIG. 16 is a chromaticity diagram.
In FIG. 16, a graph 95 (distribution of x) shows the change in chromaticity of Comparative Example 1 described above. When the display surface has a low luminance area of 38 cd / m ² or less, the emission color of the organic EL layer 8 is changed. It can be seen that “color shift” occurs, resulting in reddish colored light.

Returning to FIG.
Further, in the upper right of FIG. 15, the luminance life when a DC current drive is performed by supplying a drive current of 400 mA / cm ² as the reference current Ik is shown. Specifically, the luminance life is shown by the time until the luminance reaches 80% of the initial luminance, and is about 400 hours in the DC drive.

As Comparative Example 2, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/2 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 800 mA / cm ² is supplied as a driving current Ip for a period of ½ frame and pulsed. Luminance and chromaticity data when driven are shown in the lower part of Comparative Example 1. The luminance (gradation) at this time was 414 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
Hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the change is almost the same as in Comparative Example 1, and in the low-luminance region, a “color shift” occurs in the emission color, and redness appears. It turns out that it becomes a colored light.
Further, the luminance life when pulse driving with a duty ratio of 1/2 was about 400 hours, and no difference from constant current driving was recognized.

As Example 1, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/3 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 1,600 mA / cm ² is supplied as a drive current Ip for a period of 1/3 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of Comparative Example 2. The luminance (gradation) at this time was 417 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1, but the degree of color misregistration at each gradation is smaller than that of Comparative Example 2, and the lowest chromaticity at 0.01 cd / m ² is It can be seen that (x, y) = (0.37, 0.35), and substantially predetermined white light is obtained.
Further, the luminance life when pulse driving with a duty ratio of 1/3 is about 400 hours, and no difference from constant current driving was recognized.

As Example 2, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/5 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 2,400 mA / cm ² is supplied as a driving current Ip for a period of 1/5 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the first embodiment. The luminance (gradation) at this time was 416 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the degree of color misregistration at each gradation is equal to or less than that of Example 1, and particularly the lowest 0.01 cd / m. The chromaticity in ² is (x, y) = (0.34, 0.33), which indicates that the whiteness is higher than that in Example 1.
Further, the luminance life when pulse driving with a duty ratio of 1/5 is about 395 hours, and a difference from constant current driving was hardly recognized.

Returning to FIG.
In FIG. 16, a graph 96 (circle distribution) shows the change in chromaticity of Example 2 described above, and it can be seen that color misregistration is suppressed even in the low luminance region.

As Example 3, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/10 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 4,400 mA / cm ² is supplied as a drive current Ip for a period of 1/10 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the second embodiment. The luminance (gradation) at this time was 418 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the degree of color misregistration at each gradation is equal to or less than that of Example 1, and particularly the lowest 0.01 cd / m. The chromaticity in ² is (x, y) = (0.32, 0.31), which indicates that the whiteness is higher than those in the first and second embodiments.
In addition, the luminance life in the case of pulse driving with a duty ratio of 1/10 is about 390 hours, and the difference from the constant current driving was not recognized so much.

As Example 4, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/50 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 20,400 mA / cm ² is supplied as a drive current Ip for a period of 1/50 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the third embodiment. The luminance (gradation) at this time was 417 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.31).
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is the same as (x, y) = (0.31, 0.31), and there is no color shift. Occurrence was not observed.
In addition, the luminance life when pulse driving with a duty ratio of 1/50 was about 390 hours, and a difference from constant current driving was not recognized so much.

As Comparative Example 3, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/100 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 40,400 mA / cm ² is supplied as a drive current Ip for a period of 1/100 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the fourth embodiment. The luminance (gradation) at this time was 414 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.32).
In addition, hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is substantially the same, and no color misregistration was observed.
However, it can be seen that the luminance life when pulse driving with a duty ratio of 1/100 is about 220 hours, which is about half that of constant current driving.

As Comparative Example 4, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/500 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 410 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 200,400 mA / cm ² is supplied as a driving current Ip for a period of 1/500 frames. Luminance and chromaticity data when pulse driving is shown at the bottom. The luminance (gradation) at this time was 418 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.31, 0.32).
In addition, hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is substantially the same, and no color misregistration was observed.
However, it can be seen that the luminance life in the case of pulse driving with a duty ratio of 1/500 is about 100 hours, which is about 1/4 of the constant current driving.

(Example B)
“Driving result of laminated structure of modification 1”
FIG. 17 shows a list of changes in chromaticity when constant current driving and pulse driving with a plurality of duty ratios are performed for each of a plurality of gradations using the display panel 18 having the laminated structure of the first modification. This table corresponds to FIG. In addition, the description which overlaps with Example A is abbreviate | omitted.
First, the display panel 18 used in the experiment has a laminated structure including two light emitting layers of orange and blue, the configuration of the organic EL layer 8 described in the preferred example of the first modification. Further, a display panel (evaluation panel) in a state in which light emitted from the organic EL layer 8 from the counter substrate 17 can be directly measured without forming a color filter was used.

As Comparative Example 1, chromaticity data was measured when the evaluation panel was driven with constant current at each gradation corresponding to the display gradation.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, the luminance when the driving current of 400 mA / cm ² is supplied as the reference current Ik and DC driving is performed, The chromaticity data is shown in the upper left of FIG.
The luminance (gradation) at this time was 470 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.32).
Similarly, in order to obtain a luminance equivalent to 45 cd / m ^{2 on} the display surface of the display panel, the luminance and chromaticity data when DC driving is performed by supplying a necessary reference current are data on the right side. . The luminance at this time is 45 cd / m ² on the display surface, and the chromaticity is slightly changed as (x, y) = (0.36, 0.35).
Also, Similarly, 4.2 cd / m ² at the display surface, 0.3 cd / m ^2, but measures the chromaticity at the point where the 0.01cd / m ² equivalent brightness, the more becomes the low luminance, It can be seen that the chromaticity change increases and the color light becomes reddish.
The luminance life until the luminance reaches 80% of the initial luminance was about 350 hours in the case of constant current driving.

As Comparative Example 2, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/2 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 800 mA / cm ² is supplied as a driving current Ip for a period of ½ frame and pulsed. Luminance and chromaticity data when driven are shown in the lower part of Comparative Example 1. The luminance (gradation) at this time was 475 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.32), and the expected white light was obtained.
Hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the change is almost the same as in Comparative Example 1, and in the low-luminance region, a “color shift” occurs in the emission color, and redness appears. It turns out that it becomes a colored light.
Further, the luminance life when pulse driving with a duty ratio of 1/2 was about 350 hours, and no difference from constant current driving was recognized.

As Example 1, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/3 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 1,600 mA / cm ² is supplied as a driving current Ip for a period of 1/3 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of Comparative Example 2. The luminance (gradation) at this time was 477 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.33), and a substantially expected white light was obtained.
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1, but the degree of color misregistration at each gradation is smaller than that of Comparative Example 2, and the lowest chromaticity at 0.01 cd / m ² is It can be seen that (x, y) = (0.35, 0.36), and substantially predetermined white light is obtained.
In addition, the luminance life when pulse driving with a duty ratio of 1/3 was about 350 hours, and no difference from constant current driving was recognized.

As Example 2, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/5 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 2,400 mA / cm ² is supplied as a driving current Ip for a period of 1/5 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the first embodiment. The luminance (gradation) at this time was 476 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.33), and a substantially expected white light was obtained.
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the degree of color misregistration at each gradation is equal to or less than that of Example 1, and particularly the lowest 0.01 cd / m. It can be seen that the chromaticity in ² is (x, y) = (0.33, 0.33), which is higher in whiteness than in Example 1.
Further, the luminance life when pulse driving with a duty ratio of 1/5 is about 350 hours, and no difference from constant current driving was recognized.

As Example 3, chromaticity data was measured when the evaluation panel was pulse-driven with a duty ratio of 1/10 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 4,400 mA / cm ² is supplied as a drive current Ip for a period of 1/10 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the second embodiment. The luminance (gradation) at this time was 478 cd / m ² on the display surface, and the desired white light was obtained with the chromaticity of (x, y) = (0.29, 0.33).
In the following, chromaticity data is measured at the same gradation as in Comparative Example 1. However, the degree of color misregistration at each gradation is equal to or less than that of Example 1, and particularly the lowest 0.01 cd / m. The chromaticity in ² is (x, y) = (0.29, 0.33), which indicates that the whiteness is higher than that in Example 1.
Further, the luminance life when pulse driving with a duty ratio of 1/10 was about 340 hours, and there was almost no difference from constant current driving.

As Example 4, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/50 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 20,400 mA / cm ² is supplied as a drive current Ip for a period of 1/50 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the third embodiment. The luminance (gradation) at this time was 476 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.34), which was a substantially desired white light.
In addition, hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is substantially the same, and no color misregistration was observed.
In addition, the luminance life when pulse driving with a duty ratio of 1/50 is about 340 hours, and almost no difference from constant current driving was recognized.

As Comparative Example 3, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/100 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a drive current of 40,400 mA / cm ² is supplied as a drive current Ip for a period of 1/100 frame. Luminance and chromaticity data when pulse driving is performed are shown in the lower part of the fourth embodiment. The luminance (gradation) at this time was 476 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.34), which was a substantially desired white light.
In addition, hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is substantially the same, and no color misregistration was observed.
However, it can be seen that the luminance life when pulse driving with a duty ratio of 1/100 is about 180 hours, which is about half that of constant current driving.

As Comparative Example 4, chromaticity data was measured when the evaluation panel was pulse-driven at a duty ratio of 1/500 at the same gradation as in Comparative Example 1.
Specifically, in order to obtain a luminance equivalent to 470 cd / m ^{2 on} the display surface of the display panel as a display gradation, a driving current of 200,400 mA / cm ² is supplied as a driving current Ip for a period of 1/500 frames. Luminance and chromaticity data when pulse driving is shown at the bottom. The luminance (gradation) at this time was 474 cd / m ² on the display surface, and the chromaticity was (x, y) = (0.29, 0.34), and the expected white light was obtained.
In addition, hereinafter, chromaticity data is measured at the same gradation as in Comparative Example 1, but the chromaticity at all gradations is substantially the same, and no color misregistration was observed.
However, it can be seen that the luminance life in the case of pulse driving at a duty ratio of 1/500 is about 80 hours, which is about ¼ of the constant current driving.

  DESCRIPTION OF SYMBOLS 1 ... Element substrate, 6 ... Pixel electrode, 8 ... Organic EL layer as laminated structure, 9 ... Common electrode, 14 ... CF layer as a color filter, 17 ... Opposite substrate, 18 ... Display panel, 20 ... Flexible substrate, 21 DESCRIPTION OF SYMBOLS ... IC for drive, 50 ... Control circuit, 51 ... Drive switching part, 70 ... Illuminance detection part, 81 ... Hole injection layer, 82 ... Hole transport layer, 83, 85, 86, 91, 92 ... Light emitting layer, 84 DESCRIPTION OF SYMBOLS ... Intermediate | middle layer, 87 ... Electron transport layer, 88 ... Electron injection layer, 100,110 ... Display apparatus as an organic EL display apparatus, 200 ... Car-mounted meter as electronic equipment, V ... Display area as a display surface.

Claims (10)

A substrate,
A plurality of light emitting layers each emitting different colored light,
A color filter in which a plurality of color filters including red, green, and blue are arranged, and
An organic EL display device that emits substantially white light, which is a combination of a plurality of color lights emitted from each of the light emitting layers, through the color filter,
Constant current driving for performing display by continuously supplying a reference current corresponding to a display gradation defined in an image signal within one frame to the stacked structure including the plurality of light emitting layers;
A drive switching unit that switches between pulse driving for supplying the current higher than the reference current during a predetermined period in the one frame and performing the display;
The drive switching unit performs the pulse driving when the gradation is equal to or lower than a predetermined gradation, and performs the constant current driving when the gradation is higher than the predetermined gradation. . The predetermined gradation is an average luminance per screen in the image signal,
2. The organic EL display according to claim 1, wherein the average luminance is a gradation corresponding to a range of 3 to ²⁰ cd / cm ² when expressed by an average luminance on a display surface of the organic EL display device. apparatus. A substrate,
A plurality of light emitting layers each emitting different colored light,
A color filter in which a plurality of color filters including red, green, and blue are arranged, and
An organic EL display device that emits substantially white light, which is a combination of a plurality of color lights emitted from each of the light emitting layers, through the color filter,
Constant current driving for performing display by continuously supplying a reference current corresponding to a display gradation defined in an image signal within one frame to the stacked structure including the plurality of light emitting layers;
A drive switching unit for switching between pulse drive for supplying a current higher than the reference current for a predetermined period in the one frame and performing display;
An illuminance detection unit that detects illuminance in the surrounding environment where the organic EL display device is disposed;
The drive switching unit performs the pulse drive when the illuminance detected by the illuminance detection unit is equal to or lower than a predetermined illuminance, and performs the constant current drive when the illuminance is higher than the predetermined illuminance. EL display device.   The organic EL display device according to claim 3, wherein the predetermined illuminance is 200 lux or less.   5. The organic EL display device according to claim 1, wherein a duty ratio of the pulse drive in the one frame is in a range of 1/3 to 1/50. 6.   The current higher than the reference current in the pulse drive is larger than a value obtained by multiplying the reference current and the reciprocal of the duty ratio. Organic EL display device. The pulse driving is performed by subfield driving in which scanning driving for sequentially scanning all the scanning lines in the period length of the one frame is performed twice in the first subfield and the second subfield,
The period lengths of the first subfield and the second subfield are set according to the duty ratio,
In the first subfield, a current higher than the reference current is supplied to the stacked structure,
The organic EL display device according to claim 1, wherein no current is supplied to the stacked structure in the second subfield. The laminated structure includes the light emitting layer corresponding to each color of red, green, and blue,
8. The top emission type configuration in which the stacked structure and the color filter are formed in this order on the substrate is employed. 8. Organic EL display device.   An electronic apparatus comprising the organic EL display device according to claim 1. A substrate,
A plurality of light emitting layers each emitting different colored light,
A color filter in which a plurality of color filters including red, green, and blue are arranged, and
A method of driving an organic EL display device that emits substantially white light, which is a combination of a plurality of color lights emitted from each of the light emitting layers, through the color filter,
When the gradation of display specified in the image signal is higher than a predetermined gradation, a constant current drive is performed by continuously supplying a reference current corresponding to the gradation within one frame,
A driving method of an organic EL display device, wherein pulse driving is performed to supply a current higher than the reference current for a predetermined period in the one frame when the gradation is equal to or lower than a predetermined gradation.

Images