JP2011108956A - Electronic display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set the light emission luminance constant with high accuracy, without influencing the configuration of an information display surface. <P>SOLUTION: A light emitted by an organic EL light-emitting layer 30 by itself is transmitted through display electrodes 22a and 22b and received by a luminance detector 50, disposed on the opposite side from the information display surface. The luminance detector 50 measures the luminance thereof, and a control unit 70 controls a current flowing to the organic EL light-emitting layer 30, according to the luminance measured by the luminance detector 50. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electronic display panel that displays information using a light-emitting element that emits light when a current flows, and more particularly, to a technique for making light emission luminance of a light-emitting element constant.

  Conventionally, as a display device for displaying information, a CRT display, a liquid crystal display, a plasma display, and the like are used. These are used in a television receiver to display a television image transmitted from a television station or a personal computer. It is possible to display information stored in a personal computer or information distributed via the Internet. Each of these display devices has advantages and disadvantages. For example, a CRT display has a wide viewing angle but a large depth size, and a liquid crystal display has a thin depth size but a narrow viewing angle, and a plasma display. Has a large viewing angle and a small depth size, but consumes a lot of power.

  In recent years, in addition to the display devices as described above, thin electronic display panels that display digital information on a thin display medium such as paper have begun to spread. In such a thin electronic display panel, an organic EL element that emits light when current flows is disposed between two electrodes facing each other, and a current is applied to the organic EL element by applying a voltage to the electrode. Information is displayed by light emission of the EL element. And since it is as thin as paper, it is easy to carry, consumes little power, and has a wide viewing angle, so it is expected that it will become more popular in the future.

  However, in such an electronic display panel, as the light emission efficiency of the organic EL element decreases with time, the light emission luminance also decreases with time.

  Here, the light emission luminance of the electronic display panel is proportional to a value obtained by multiplying the light emission efficiency of the organic EL element by a current value flowing through the organic EL element per unit area. Therefore, a technique has been considered in which the light emission luminance of the electronic display panel is made constant by measuring the light emission luminance of the electronic display panel and controlling the value of the current flowing through the organic EL element according to the measured value. 1 and 2.

  In the technique disclosed in Patent Document 1, a light receiving measurement unit for measuring the light emission luminance of the electronic display panel is arranged on a part of the display surface side of the electronic display panel, and the light emission measured by the light receiving measurement unit. The drive current or drive voltage of the organic EL element is controlled according to the luminance, and the electrodes on the back side of the electronic display panel among the electrodes for applying a voltage to the organic EL element are formed in stripes, and the electrons A reflective layer is provided in a region facing the electrode on the display surface side of the display panel, and a light receiving measurement unit is disposed in a region facing the electrode on the back surface side of the electronic display panel, and the light is reflected by the reflective layer and received. The light emission luminance of the electronic display panel is made constant by controlling the drive current or drive voltage of the organic EL element according to the luminance of the light received by the measurement unit.

  Further, the technique disclosed in Patent Document 2 receives a semi-transmissive film that reflects light from a side portion of the organic EL element and light reflected by the semi-transmissive film in a region adjacent to the organic EL element. A photoelectric conversion element that converts voltage is arranged, and the drive current of the organic EL element is changed in accordance with the light received by the photoelectric conversion element to make the light emission luminance of the electronic display panel constant.

JP-A-11-109918 JP 2002-311899 A

  However, in the technique disclosed in Patent Document 1, since a light receiving measurement unit and a reflective layer are arranged on the display surface side of the electronic display panel, information display by light emission of the organic EL element is performed in that portion. There is a problem that it cannot be done. In addition, by measuring the brightness of the light reflected by the reflective layer at the light receiving measurement unit by forming the electrodes in a stripe shape, the light reflected by the reflective layer is transmitted only between the stripe electrodes. Therefore, it is difficult to say that the light emission luminance of the electronic display panel can be accurately measured in the light receiving measurement unit.

  Moreover, in what was disclosed by patent document 2, since a semi-transmissive film and a photoelectric conversion element are arrange | positioned in the area | region adjacent to an organic EL element, the information by printing etc. can be displayed on the area | region. In addition, the design of the information display surface is impaired, and there is a problem that a member used as an electronic display panel cannot be placed. The shape of the organic EL element is set according to information displayed on the electronic display panel. If the shape of the organic EL element is the shape of a character displayed on the electronic display panel, the character Depending on the shape, there is a problem that light from the side of the organic EL element cannot be received by the reflective layer.

  The present invention has been made in view of the problems of the conventional techniques as described above, and an electronic display panel that can make the light emission luminance constant accurately without affecting the configuration of the information display surface. The purpose is to provide.

In order to achieve the above object, the present invention provides:
By being sandwiched between the transparent electrode, the display electrode disposed opposite to the transparent electrode, and the transparent electrode and the display electrode, different voltages are applied to the transparent electrode and the display electrode. An electronic display panel that has a light-emitting element layer that emits current and emits light at a luminance corresponding to the magnitude of the current, and displays information by self-light emission of the light-emitting element layer with the transparent electrode side as an information display surface There,
The display electrode is made of a light transmissive material,
A luminance measuring means disposed on the opposite side of the light emitting element layer with respect to the display electrode, receiving light transmitted through the display electrode by self-emission in the light emitting element layer, and measuring the luminance of the light; ,
Control means for controlling a current flowing in the light emitting element layer in accordance with the brightness measured by the brightness measuring means.

  In the present invention configured as described above, when different voltages are applied to the transparent electrode and the display electrode, a current flows through the light emitting element layer and the light emitting element layer self-emits. In addition to being displayed on the information display surface through the transparent electrode, information is displayed and the display electrode is made of a light-transmitting material, so that the display electrode is transmitted and emits light to the display electrode. Light is received by a luminance measuring means arranged on the side opposite to the element layer, and the luminance is measured. Since the luminance of the light-emitting element layer changes according to the magnitude of the flowing current, even if the light emission luminance changes due to a decrease in the light-emitting efficiency of the light-emitting element layer, it is measured by the luminance measuring means in the control means. By controlling the current flowing through the light emitting element layer according to the brightness, the light emitting element layer emits light with the brightness according to the current, and the light emission brightness of the light emitting element layer can be made constant.

  Further, it is conceivable that the display electrode is made of a transparent electrode or a conductive paste having light transmittance.

  As described above, in the present invention, the transparent electrode, the display electrode disposed opposite to the transparent electrode, and the transparent electrode and the display electrode are sandwiched between the transparent electrode and the display electrode. An electron that has a light-emitting element layer that self-emits at a luminance corresponding to the magnitude of the current when applied, and displays information by self-emission of the light-emitting element layer with the transparent electrode side as an information display surface In a display panel, the display electrode is made of a light-transmitting material, and is disposed on the opposite side of the display electrode from the light-emitting element layer. And a control means for controlling the current flowing in the light emitting element layer in accordance with the luminance measured by the luminance measuring means. Self The emitted light is transmitted through the display electrode and received by the luminance measuring unit, the luminance is measured by the luminance measuring unit, and the control unit measures the luminance on the light emitting element layer according to the luminance measured by the luminance measuring unit. Since the current flowing is controlled, even when the light emission brightness changes due to the light emission efficiency of the light emitting element layer being reduced, the luminance measurement is arranged on the opposite side of the light emitting element layer from the display electrode. The current flowing through the light-emitting element layer is controlled according to the luminance measured by the means, and the light-emitting element layer emits light with the luminance according to the current, and the light emission luminance can be reduced without affecting the configuration of the information display surface. It can be made constant with high accuracy.

It is a figure which shows one Embodiment of the electronic display panel of this invention, (a) is a surface figure, (b) is AA 'sectional drawing shown to (a), (c) is a functional block diagram. . It is a figure which shows the relationship between the electric current which flows into the organic electroluminescent light emitting layer in the organic electroluminescent panel shown in FIG. 1, and light emission luminance. It is a figure for demonstrating the control method of the light emission luminance of the organic electroluminescent light emitting layer shown in FIG. 1, (a) is a figure which shows the change of the light emission luminance of an organic electroluminescent light emitting layer, (b) is a figure of an organic electroluminescent light emitting layer. It is a figure which shows the electric current sent through an organic electroluminescent light emitting layer when light emission luminance changes as shown to (a). It is a figure which shows the specific example of the control part shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  1A and 1B are diagrams showing an embodiment of an electronic display panel according to the present invention, in which FIG. 1A is a front view, FIG. 1B is a cross-sectional view along AA ′ shown in FIG. It is a block diagram.

  As shown in FIG. 1, the electronic display panel according to this embodiment has an ITO (Indium Tin Oxide) 21 that is a transparent electrode laminated on a top sheet 10, and an organic EL light emitting layer 30 that is a light emitting element layer on the ITO 21. And the display electrodes 22a and 22b are laminated, and an adhesive 60 is applied to cover the organic EL light emitting layer 30 and the display electrodes 22a and 22b, and the protective film 40 is adhered to the ITO 21 by the adhesive 60. Yes. Thus, the ITO 21 and the display electrodes 22a and 22b are arranged to face each other, and the organic EL light emitting layer 30 is sandwiched between the ITO 21 and the display electrodes 22a and 22b arranged to face each other. Further, a luminance detector 50 which is a luminance measuring means for measuring the luminance of received light is disposed on the surface of the protective film 40 opposite to the display electrodes 22a and 22b. The luminance detector 50, the ITO 21 and the display are displayed. The electrodes 22 a and 22 b are connected to the control unit 70.

  In the surface sheet 10, windows 11 a and 11 b having the same shape as the display electrodes 22 a and 22 b are formed in regions facing the display electrodes 22 a and 22 b and the organic EL light emitting layer 30. The window portions 11a and 11b are formed by forming the topsheet 10 from a transparent material and coloring the regions other than the window portions 11a and 11b.

  ITO21 is laminated | stacked on the whole surface on the surface sheet 10, for example, has thickness of 1000-1500 mm.

  The organic EL light emitting layer 30 is laminated on the ITO 21 laminated on the top sheet 10, has a thickness of, for example, 100 to 1000 nm, and has a shape that is slightly larger than the shapes of the display electrodes 22a and 22b. is doing. Thus, by making the shape of the organic EL light emitting layer 30 slightly larger than the shape of the display electrodes 22a and 22b, between the display electrodes 22a and 22b or between the display electrodes 22a and 22b and the ITO 21. It becomes possible to prevent an electrical short circuit in. The organic EL light emitting layer 30 is made of a solution in which a π-conjugated polymer represented by polyphenylene vinylene or the like, or a dye-containing polymer is dissolved in an organic solvent. Examples of the organic solvent include aromatic solvents such as toluene, xylene, diethylbenzene, and chlorobenzene, and those composed of at least one of aliphatic hydrocarbon solvents such as cyclohexanone. Among them, the organic solvent is preferably chlorobenzene. .

The display electrodes 22a and 22b are stacked on the organic EL light emitting layer 30 stacked on the ITO 21, and each has a shape indicating information to be displayed on the organic EL panel 1, and the display electrode 22a is "T "The display electrode 22b has a shape of" F ". Display electrodes 22a, 22b is, ITO, IZO, and a transparent electrode of SnO ₂ or the like, the conductive particles in a resin binder having a light transmitting property such as a conductive paste containing, and a material having optical transparency. In addition, thickness is 1-5 micrometers, for example.

  The protective film 40 is made of a material such as transparent PEN (polyethylene naphthalate).

  The pressure-sensitive adhesive layer 60 is made of a material that has optical transparency and can block contact between the organic EL light-emitting layer 30 and the outside air. For example, a thermosetting adhesive, an ultraviolet curable adhesive, an electron beam curing, and the like. A mold adhesive or the like is used.

  Below, operation | movement of the organic electroluminescent panel 1 comprised as mentioned above is demonstrated.

  In the organic EL panel 1 configured as described above, when different voltages are applied to the display electrodes 22a and 22b and the ITO 21, current flows in the organic EL light emitting layer 30, and this current causes the organic EL light emitting layer. 30 emits light by itself, and information “TF” is displayed by the self-light emission using the ITO 21 side as an information display surface.

  FIG. 2 is a diagram showing the relationship between the current flowing through the organic EL light emitting layer 30 and the light emission luminance in the organic EL panel 1 shown in FIG. 1, and the rated time is 100%.

  As shown in FIG. 2, the light emission luminance of the organic EL light emitting layer 30 in the organic EL panel 1 shown in FIG. 1 is proportional to the flowing current. Therefore, the light emission luminance of the organic EL light emitting layer 30 can be controlled by changing the current flowing through the organic EL light emitting layer 30.

  3A and 3B are diagrams for explaining a method of controlling the light emission luminance of the organic EL light emitting layer 30 shown in FIG. 1, FIG. 3A is a diagram showing a change in the light emission luminance of the organic EL light emitting layer 30, and FIG. These are figures which show the electric current sent through the organic EL light emitting layer 30 when the light emission luminance of the organic EL light emitting layer 30 changes as shown in FIG. Note that the change in luminance indicated by the solid line in FIG. 3A is obtained when the current flowing through the organic EL light emitting layer 30 is constant as indicated by the broken line in FIG. 3B, and FIG. The current value indicated by the solid line is for making the light emission luminance of the organic EL light emitting layer 30 constant as indicated by the broken line in FIG.

  As described above, the light emission efficiency of the organic EL element decreases with time, so that even if the flowing current is constant, the light emission luminance decreases with time. Also in the organic EL light emitting layer 30 shown in FIG. 1, as shown in FIG. 3A, as the light emission efficiency decreases with time, the light emission luminance also decreases with time. Therefore, when a certain period of time elapses after the organic EL panel 1 is used, the light emission luminance does not reach the desired light emission luminance indicated by the broken line in FIG. There is a possibility that the display of information by the organic EL light emitting layer 30 becomes unclear. Further, in view of the decrease in the light emission luminance of the organic EL light emitting layer 30 in this way, in the initial state, the light emission luminance of the organic EL light emitting layer 30 is desired as indicated by a broken line in FIG. The current flowing through the organic EL light emitting layer 30 is set so as to be higher than the light emission luminance of the organic EL light emitting layer 30, thereby shortening the life of the organic EL light emitting layer 30.

  In order to avoid such an event, as shown in FIG. 3B, the current flowing through the organic EL light emitting layer 30 is changed in accordance with the change in the light emission luminance of the organic EL light emitting layer 30. It is conceivable to suppress a decrease in light emission luminance of the light emitting layer 30. As described above, the light emission luminance of the organic EL light emitting layer 30 is lowered even when a constant current is passed along with a decrease in light emission efficiency. Therefore, in the initial state, as shown by the broken line in FIG. 3B, a current smaller than a constant current flowing in the organic EL light emitting layer 30 is passed through the organic EL light emitting layer 30, and then this current is changed over time. To increase. Thereby, the fall of the light emission luminance of the organic EL light emitting layer 30 can be suppressed.

  However, when such control is performed, it is necessary to set a change in the current flowing through the organic EL light emitting layer 30 based on the rate of decrease in the light emission efficiency of the organic EL light emitting layer 30, and initial setting and control for that purpose are complicated. Become.

  Therefore, in the organic EL panel 1 shown in FIG. 1, light emitted by the organic EL light emitting layer 30 is received by the luminance detector 50, and the current flowing through the organic EL light emitting layer 30 is controlled according to the luminance of the light. It is the composition to do.

  In the organic EL panel 1 shown in FIG. 1, when different voltages are applied to the ITO 21 and the display electrodes 22a and 22b, a current flows through the organic EL light emitting layer 30 and the organic EL light emitting layer 30 self-emits. The self-emitted light is visually recognized through the ITO 21 and the top sheet 10 to display information, and is transmitted through the display electrodes 22a and 22b and received by the luminance detector 50, and the luminance is measured. The controller 70 controls the voltage applied to the display electrodes 22a and 22b in accordance with the luminance measured by the luminance detector 50, thereby controlling the current flowing through the organic EL light emitting layer 30. In the control unit 70, feedback control is performed so that the luminance of the light received by the luminance detector 50 is constant at a predetermined value, whereby the luminance of the organic EL light emitting layer 30 is constant.

  Thus, in the present embodiment, the current flowing through the organic EL light emitting layer 30 is controlled so that the light emission luminance of the organic EL light emitting layer 30 is constant, but the light emission luminance of the organic EL light emitting layer 30 is Since it is measured by the luminance detector 50 disposed on the opposite side of the organic EL light emitting layer 30 with respect to the display electrodes 22a and 22b, the light emission luminance of the organic EL panel 1 can be accurately adjusted without affecting the configuration of the information display surface. It can be well constant.

  In this embodiment, the luminance detector 50 is arranged on the surface of the protective film 40 opposite to the display electrodes 22a and 22b. However, the luminance detector 50 is an organic EL light emitting layer with respect to the display electrodes 22a and 22b. If it is the opposite side to 30, it may be arranged on the display electrodes 22 a, 22 b side of the protective film 40.

  Below, the specific example of the control part 70 shown in FIG. 1 is demonstrated.

  The control unit 70 shown in FIG. 1 can be realized by a computer program for executing the above-described procedure, but can also be realized by an electronic circuit using a general circuit element.

  FIG. 4 is a diagram illustrating a specific example of the control unit 70 illustrated in FIG. 1.

  The control unit 70 shown in FIG. 1 can be realized by an electronic circuit using two operational amplifiers 71 and 72, a transistor 73, and two resistors 74a and 74b, for example, as shown in FIG. . In the control unit 70 shown in FIG. 4, the operational amplifier 71, the transistor 73, and the resistor 74b constitute a constant current circuit, and the operational amplifier 72 operates as a comparator.

  The operation of the control unit 70 shown in FIG. 4 will be described below. In the following description, the light emission luminance of the EL element 31 constituting the organic EL light emitting layer 30 is C0, light is emitted from the organic EL light emitting layer 30, and is received by the luminance detector 50 via the display electrodes 22a and 22b. C1 is the luminance of the light to be received, k1 is the attenuation ratio of the luminance of the light received by the luminance detector 50 with respect to the luminance of the EL element 31, k2 is the luminous efficiency of the EL element 31, and the current conversion rate of the luminance detector 50 is k3, the resistance value of the resistor 74a is Ra, the resistance value of the resistor 74b is Rb, and the luminance setting voltage is Vc.

The light emission luminance C0 of the EL element 31 constituting the organic EL light emitting layer 30 is
C0 = C1 / k1 = k2 × Iel (1)
It is represented by

The luminance response current Icd is
Icd = k3 × C1 (2)
It is represented by

By substituting equation (1) into equation (2), the luminance response current Icd is
Icd = k1 × k3 × C0 (3)
It is represented by

The luminance response voltage Va is
Va = Icd × Ra (4)
It is represented by

The operational amplifier 72 is
Va = Vc (5)
Operates to meet.

From the above formulas (3) to (5), the drive current Iel of the EL element 31 is
Iel = Vb / Rb = Vc / Rb = (Icd × Ra) / Rb = (Ra / Rb) × (k1 × k3 × C0) (6)
Thus, it corresponds to the light emission luminance C0 of the EL element 31.

  Further, by adjusting the value of (Ra / Rb) × (k1 × k3) so that the light emission luminance of the EL element 31 becomes a desired value, the light emission luminance of the EL element 31 may be increased more than necessary. As a result, the lifetime of the EL element 31 can be extended.

DESCRIPTION OF SYMBOLS 1 Organic electroluminescent panel 10 Top sheet 11a, 11b Window part 21 ITO
22a, 22b Display electrode 30 Organic EL light emitting layer 31 EL element 40 Protective film 50 Luminance detector 60 Adhesive 70 Controller 71, 72 Operational amplifier 73 Transistor 74a, 74b Resistance

Claims (2)

By being sandwiched between the transparent electrode, the display electrode disposed opposite to the transparent electrode, and the transparent electrode and the display electrode, different voltages are applied to the transparent electrode and the display electrode. An electronic display panel that has a light-emitting element layer that emits current and emits light at a luminance corresponding to the magnitude of the current, and displays information by self-light emission of the light-emitting element layer with the transparent electrode side as an information display surface There,
The display electrode is made of a light transmissive material,
A luminance measuring means disposed on the opposite side of the light emitting element layer with respect to the display electrode, receiving light transmitted through the display electrode by self-emission in the light emitting element layer, and measuring the luminance of the light; ,
An electronic display panel comprising: control means for controlling a current flowing in the light emitting element layer according to the brightness measured by the brightness measuring means. The electronic display panel according to claim 1,
The display electrode is an electronic display panel composed of a transparent electrode or a light-transmitting conductive paste.

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