JP2001117525A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescence element which does not cause significant fluctuation in the emission luminance by the changes of the ambient temperature and which can improve the display quality. SOLUTION: The element has at least an anode 12, an organic layer consisting of one or more layers and a cathode 14 on a transparent substrate. In the anode 12, a plurality of segments Seg1 to Seg7 which act as a display part are separately connected to a driving circuit 40 through the respective adjusting resistors 30. The adjusting resistor is connected to a temperature sensing element 50 in parallel or in series, and the temperature sensing element 50 compensates the changes in the forward voltage Vf of the organic electroluminescence element 10 according to the changes of the ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device.

[0002]

2. Description of the Related Art As shown in FIG. 3, an anode 12 made of a transparent conductive material such as indium tin oxide (ITO) and an organic layer comprising at least one layer (at least a single organic light emitting layer) are provided on a transparent substrate 11. A layer structure or a multilayer structure in which any one of a hole injection layer, a hole transport layer, an electron transport layer, etc. is laminated with an organic light emitting layer from the anode side) 13 and a metal conductive material such as aluminum (Al). Cathode 14
EL device 1 having at least
0 is disclosed, for example, in Japanese Patent Publication No. 6-32307.

[0003] Such an organic electroluminescent device 1
Numeral 0 indicates that light can be emitted in a predetermined pattern depending on the shapes of the anode 12 and the cathode 14. By applying a DC voltage Vd of several volts to several tens of volts between the anode 12 and the cathode 14, the organic layer The light emission corresponding to the pattern from No. 13 can be seen through the transparent substrate 11, and has an advantage that a low voltage driving by a DC power supply is possible as compared with a thin film type or dispersion type electroluminescence element.

One of the anode 12 and the cathode 14 is divided and formed as a plurality of display pixel electrodes (segments) corresponding to a display shape, and the other is used as a common electrode (common) by connecting a power supply between the two electrodes. A so-called segment type organic electroluminescent element for selectively emitting light is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-106888.
There is an advantage that a desired display shape is easily obtained. In FIG. 4, the anode 12 has segments Seg1 to Seg7, and the cathode 14 has common Com.

FIG. 5 shows a circuit configuration of such an organic electroluminescent element 10, wherein Vcc is a DC power supply for supplying a current I, 20 is a DC power supply Vcc with a predetermined constant applied voltage Vd, and each segment Seg1 A constant current circuit 21 for supplying a current I 'to the Seg7, a switch circuit 21 for supplying or stopping (on or off) the current I' from the constant current circuit 20 to each of the segments Seg1 to Seg7. Sets the applied voltage Vd individually such that the difference between the current densities in the segments Seg1 to Seg7 falls within a certain range according to the area of the segments Seg1 to Seg7 and the light emission luminance in each of the segments Seg1 to Seg7 becomes substantially equal. Constant current section 2
0a to 20g, and the display selection switch circuit 21 includes constant current units 20a to 20g and segments Seg1 to Seg7.
And switches 21a to 21g located between the switches 21a to 21g.

In the organic electroluminescence element 10, the common Com is connected to the external DC power supply Vcc by one wire.
A book and wiring electrodes are prepared by the number of segments Seg1 to Seg7, and the switch 2 provided in each segment Seg1 to Seg7.
A desired display can be realized by power supply control by 1a to 21g, that is, by static driving.

[0007]

In such an organic electroluminescence device 10, when the ambient temperature changes,
Since the forward voltage Vf of the organic electroluminescence element 10 changes and the current I ′ changes accordingly, the light emission luminance depending on the current density also changes according to the temperature change.

That is, as shown in FIG.
Applied voltage Vd, forward voltage Vf, each segment Seg1 to Seg7
The resistance value R of the entire circuit in units is I′∝ (Vd−Vf) / R
Since the forward voltage Vf increases in accordance with a decrease in the ambient temperature (in FIG. 6, a relationship of T1>T2> T3 in FIG. 6), the forward voltage Vf decreases as the ambient temperature decreases. The current I ′ decreases, and the light emission luminance decreases.

The present invention has been made in view of such problems, and provides an organic electroluminescence element capable of suppressing a change in light emission luminance due to a change in ambient temperature and improving display quality. Aim.

[0010]

According to a first aspect of the present invention, there is provided an organic electroluminescence device comprising an anode made of a transparent conductive material on a transparent substrate, an organic layer comprising at least one layer, and An organic electroluminescent element capable of emitting light in a predetermined pattern by having at least a cathode made of a metal conductive material so as to face the anode, and a plurality of the organic electroluminescent elements corresponding to a shape displaying one of the anode and the cathode. A display unit comprising a segment, the other of the anode or the cathode being a common, for adjusting a current density in the segment between the segment and a drive circuit that drives by applying a voltage to the segment and the common. It is characterized in that an adjustment resistor is connected.

According to a second aspect of the present invention, at least an anode made of a transparent conductive material on a transparent substrate, an organic layer composed of one or more layers, and a cathode made of a metal conductive material opposed to the anode are provided. An organic electroluminescence element capable of emitting light in a predetermined pattern by having a display portion including a plurality of segments according to a shape displaying one of the anode or the cathode, and the other of the anode or the cathode Is connected to a common, and an adjustment resistor for adjusting a current density in the segment is connected between the segment and a drive circuit that applies a voltage to the segment and drives the voltage, and connected in series or in parallel with the adjustment resistor. Connecting a temperature-sensitive element for canceling a change in a forward voltage of the organic electroluminescent element according to a change in ambient temperature; And it features.

According to a third aspect of the present invention, in the first or second aspect, the driving circuit outputs a PWM pulse voltage.

According to a fourth aspect of the present invention, in the third aspect, the driving circuit outputs a PWM pulse voltage commonly to all of the segments.

According to a fifth aspect of the present invention, in the first or second aspect, the driving circuit adjusts the effective value of the voltage applied to the segment at the same ratio by an external signal.

According to a sixth aspect of the present invention, in the third aspect, the driving circuit adjusts an effective value of a voltage applied to the segment at the same ratio by an external signal.
A duty and / or a drive voltage value of the PWM pulse voltage is changed.

According to a seventh aspect of the present invention, in the third aspect, the drive circuit changes the waveform for each segment while keeping the effective value of the PWM pulse voltage the same.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the invention described in claim 1,
A predetermined pattern can be emitted by having at least an anode 12 made of a transparent conductive material, an organic layer 13 composed of one or more layers, and a cathode 14 made of a metal conductive material facing the anode 12 on a transparent substrate 11. The organic electroluminescent element 10 is a display unit including a plurality of segments Seg1 to Seg7 corresponding to a shape to display the anode 12, the cathode 14 is a common Com, and the voltage Vd is applied to the segments Seg1 to Seg7 and the common Com. By connecting the adjusting resistor 30 for adjusting the current density in the segments Seg1 to Seg7 between the driving circuit 40 for driving by applying the driving voltage and the segments Seg1 to Seg7, a remarkable variation occurs in the emission intensity of the display unit. Therefore, display quality can be improved.

According to the second aspect of the present invention, an anode 12 made of a transparent conductive material, an organic layer 13 composed of one or more layers, and a metal conductive material are formed on a transparent substrate 11 so as to face the anode 12. An organic electroluminescent element 10 capable of emitting light in a predetermined pattern by having at least a cathode 14 comprising a plurality of segments Seg1 to Seg7 corresponding to a shape for displaying an anode 12; Common Seg, segment Seg1
A segment Se is provided between the drive circuit 40 that drives the Seg 7 and the common Com by applying the voltage Vd to the segments Seg 1 to Seg 7.
An adjusting resistor 30 for adjusting the current density in g1 to Seg7 is connected, and the organic electroluminescent element 1 is connected in series or in parallel with the adjusting resistor 30 according to a change in ambient temperature.
By connecting the temperature sensing element 50 for canceling the change of the forward voltage Vf of 0, the forward voltage is changed according to the ambient temperature change.
Even if Vf changes, the resistance value r50 of the temperature sensing element 50 changes so that the resistance value R 'also changes so that the current I does not greatly change. , The change of the light emission luminance can be suppressed.

According to the invention of claim 3, according to claim 1,
Alternatively, the driving circuit 40 outputs a PWM pulse voltage to suppress the polarization generated in the organic electroluminescent element 10 when the current I always flows, thereby extending the life of the organic electroluminescent element 10. be able to.

According to the fourth aspect of the present invention, the third aspect is provided.
In, the drive circuit 40 outputs the PWM pulse voltage commonly to all of the segments Seg1 to Seg7, so that the effective value can be uniformly and easily changed by an external instruction.

According to the invention described in claim 5, according to claim 1,
Alternatively, in the second embodiment, the driving circuit 40 includes the segment Seg
By adjusting the effective value of the voltage Vd applied to each of the segments Seg1 to Seg7 at the same ratio by an external signal,
The light emission luminance in eg7 can be changed uniformly at a constant rate.

According to the invention of claim 6, according to claim 3,
In order to adjust the effective value of the voltage Vd applied to the segments Seg1 to Seg7 at the same ratio by an external signal, the drive circuit 40 changes the duty of the PWM pulse voltage and / or the drive voltage value, thereby changing each segment Seg.
The light emission luminance in 1 to Seg 7 can be changed uniformly at a constant rate.

According to the invention of claim 7, according to claim 3,
The drive circuit 40 changes the waveform for each of the segments Seg1 to Seg7 while making the effective value of the PWM pulse voltage the same, thereby preventing the flicker phenomenon that occurs at the time of low duty when driven at the same time by the human eye. It can be suppressed by utilizing the characteristics.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the embodiments shown in the accompanying drawings, in which the same or corresponding parts as those in the prior art are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows the shape and positional relationship of the electrodes 12 and 14 of the organic electroluminescence element 10 for segment display according to the present invention. The cathode 14 forming the common Com is the same as that of the above-mentioned prior art. There is a segment Se
The anodes 12 constituting g1 to Seg7 are connected to a DC power supply via a display selection switch circuit 21 (switches 21a to 21g).
An adjusting resistor 30 is connected between each of the segments Seg1 to Seg7 and each of the switches 21a to 21g, and is controlled by static driving. Reference numeral 40 denotes a DC power supply Vcc which is a predetermined constant applied voltage Vcc.
This is a constant current circuit that supplies the current I ′ to each of the segments Seg1 to Seg7 as d, and corresponds to the constant current circuit 20 of the related art. However, instead of controlling each of the segments Seg1 to Seg7 independently, one Each segment Se in the constant current circuit 40
This is a drive circuit that determines an applied voltage Vd to be applied to g1 to Seg7.

The adjustment resistor 30 is formed of the same material as that of the anode 12 in the same manufacturing process. Alternatively, the adjustment resistor 30 is formed by using another material such as a trimming resistor or a chip resistor before the anode 12 is formed.
Alternatively, they are formed after the formation, and are all formed on the substrate 11. Then, the resistance value r30 of the adjustment resistor 30 is determined so that the resistance value R of the entire circuit in each segment Seg1 to Seg7 unit, which becomes a different value in each segment Seg1 to Seg7 unit, falls within a predetermined range.

That is, each segment constituting the display unit
The emission intensities of Seg1 to Seg7 are calculated for each segment Seg1 to Seg7.
, Ie, each segment Seg1 to Seg7
The voltage is almost proportional to the voltage difference between the common Com and the common Com, and since the metal material having a relatively low resistance is used for the cathode 14 serving as the common Com, there is almost no difference in voltage over the entire region. It is affected by the voltage at the anode 12 constituting Seg1 to Seg7.

For this reason, each segment Seg1 to Seg7 is controlled so that the variation of the light emission intensity in the display unit is not visually recognized.
The resistance value r30 of the adjustment resistor 30 is set to adjust the current density at Specifically, all segments Se
Experiments have confirmed that if the difference between the minimum value and the maximum value of the voltage in g1 to Seg7 falls within a range corresponding to 20% of the maximum value, no significant difference is observed in the light emission intensity of the display unit. . That is, the difference between the minimum value and the maximum value of the voltage in all the segments Seg1 to Seg7 is the maximum value of 20.
The resistance value r30 of the adjustment resistor 30 is set so as to fall within the range corresponding to%.

As a result, there is no noticeable variation in the luminous intensity of the display section, so that the display quality can be improved.
The constant current circuit 40 of this embodiment includes a constant current section 20a for individually controlling the segments Seg1 to Seg7 used in the conventional technique.
The driving circuit can be simplified as compared with the constant current circuit 20 having 20 to 20 g.

Then, the adjusting resistor 30 is connected in series (FIG. 2).
(See FIG. 2A) or in parallel (see FIG. 2B), a temperature sensing element 50 such as a thermistor is connected.

The temperature-sensitive element 50 is connected to the forward voltage of the organic electroluminescence element 10 in accordance with a change in ambient temperature.
Even if Vf changes, the change of the forward voltage Vf is controlled so as to suppress the change in the current I 'flowing through each of the segments Seg1 to Seg7, that is, so that the current I' becomes substantially constant irrespective of the ambient temperature change. It is desirable that the resistance value r50 be changed so as to cancel out.

Accordingly, the resistance value R ′ in this embodiment is a value obtained by combining the conventional resistance value R, the resistance value r30 of the adjustment resistor 30 and the resistance value r50 of the temperature sensing element 50, and the current I ′, Applied voltage Vd, forward voltage Vf, each segment Seg
The resistance value R ′ of the entire circuit in units of 1 to Seg7 is I′∝ (V
d−Vf) / R ′, so that even if the forward voltage Vf changes in accordance with a change in ambient temperature, the resistance value r50 of the temperature-sensitive element 50 changes so as to cancel the change. Since R ′ also changes, the current I ′ does not change significantly.
Therefore, it is possible to suppress a change in light emission luminance with respect to a change in ambient temperature.

By using a trimming resistor as the adjusting resistor 30, while measuring the light emission intensity at the segments Seg1 to Seg7 in an actual energized state, the adjusting resistor 30 is damaged by a laser to easily reduce the resistance value r. In addition, it can be adjusted accurately, which contributes to improvement of workability.

The constant current circuit 40 includes a segment Seg
Since the current I ′ flowing through each of the segments Seg1 to Seg7 can be made substantially constant by the adjusting resistor 30 connected to each of the 1 to Seg7, a power supply circuit having a single voltage waveform can be obtained. As described above, the circuit configuration can be simplified. Specifically, by using a power supply circuit that outputs a PWM pulse voltage, the organic electroluminescent element 10 Life can be extended. That is, in the organic electroluminescent element 10, when the current I 'flows in the same direction for a long time, polarization occurs due to capacitive factors such as the element capacity and the wiring capacity of the organic electroluminescent element 10. It is known that the light emission luminance is reduced and the life is shortened due to the fact that the current is not eliminated. However, by using the PWM pulse voltage, a time period during which the current I ′ does not flow occurs, thereby suppressing the polarization. It is thought to be due to.

The constant current circuit 40 is connected to the segment Seg
By making it possible to adjust the effective value of the voltage applied to 1 to Seg7 at the same ratio by an external signal, the effective value can be uniformly and easily changed by an external instruction. By making the effective value higher in the former case and lower in the latter case in the bright case and the dark case, the light emission luminance in each segment Seg1 to Seg7 can be uniformly changed at a constant rate. When the organic electroluminescent element 10 is used as a display device for a vehicle, a signal from a light switch is input to a constant current circuit 40, and when the light switch is off, the effective value is increased. When the light switch is on (small light or headlight is on), the effective value is changed to a lower value to ensure visibility when the surroundings are bright. And it makes it possible to glare suppression of a dark environment. As a means for changing the effective value, when the output of the constant current circuit 40 is a PWM pulse voltage, a method of changing a duty, a method of changing a drive voltage value (peak value), or a combination thereof is used. it can.

The waveform of the PWM pulse voltage is as follows:
It is not necessary for each segment Seg1 to Seg7 to have the same waveform, and the duty is determined by the effective value. However, the waveform may be changed for each segment Seg1 to Seg7. This allows
It is possible to suppress the flicker phenomenon that occurs at the time of low duty when the segments Seg1 to Seg7 are simultaneously driven with the same waveform by using the visual characteristics of humans.

In the above embodiment, the anode 12 is connected to the segment Se.
g1 to Seg7 and the cathode 14 were set to common Com.
The anode 12 may be configured as a common and the cathode 14 may be configured as a segment. However, the anode 12 is easier to form a pattern and is preferable for forming a segment serving as a display portion.

Further, in the above-described embodiment, the display unit having the segments Seg1 to Seg7 is shown, but it is needless to say that the shape and the number of the display units are not limited to the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a driving circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory view of a main part of the above driving circuit.

FIG. 3 is a cross-sectional view of a principal part explaining a structure of an organic electroluminescence element.

FIG. 4 is a plan view illustrating an electrode shape according to a conventional technique.

FIG. 5 is an explanatory diagram of a drive circuit according to a conventional technique.

FIG. 6 is a characteristic diagram illustrating characteristics of an organic electroluminescence element according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Organic electroluminescent element 11 Substrate 12 Anode 13 Organic layer 14 Cathode 30 Adjusting resistance 40 Constant current circuit (drive circuit) 50 Temperature sensitive element Seg1-Seg7 Segment (display part) Com common

Claims (7)

[Claims] 1. A light emitting device having a predetermined pattern by having at least an anode made of a transparent conductive material on a transparent substrate, an organic layer composed of one or more layers, and a cathode made of a metal conductive material facing the anode. A possible organic electroluminescent element, and a display unit consisting of a plurality of segments according to a shape displaying one of the anode or the cathode, the other of the anode or the cathode as a common, the segment and the An organic electroluminescent element, wherein an adjusting resistor for adjusting a current density in the segment is connected between a drive circuit that drives a common by applying a voltage to the common and the segment. 2. A light emission in a predetermined pattern by having at least an anode made of a transparent conductive material on a transparent substrate, an organic layer composed of one or more layers, and a cathode made of a metal conductive material facing the anode. A possible organic electroluminescent element, and a display unit consisting of a plurality of segments according to a shape displaying one of the anode or the cathode, the other of the anode or the cathode as a common, the segment and the An adjustment resistor for adjusting the current density in the segment is connected between the drive circuit that drives by applying a voltage to the common and the segment. Organic electroluminescence characterized by connecting a temperature sensitive element for canceling a change in forward voltage of the organic electroluminescent element. Luminescence element. 3. The organic electroluminescence device according to claim 1, wherein the driving circuit outputs a PWM pulse voltage. 4. The organic electroluminescence device according to claim 3, wherein the driving circuit outputs a PWM pulse voltage to all of the segments in common. 5. The organic electroluminescence device according to claim 1, wherein the drive circuit adjusts an effective value of a voltage applied to the segment at an equal ratio by an external signal. 6. The driving circuit changes a duty and / or a driving voltage value of the PWM pulse voltage in order to adjust an effective value of a voltage applied to the segment by an external signal at the same ratio. The organic electroluminescence device according to claim 3, wherein 7. The organic electroluminescence device according to claim 3, wherein the drive circuit changes the waveform for each of the segments while making the effective value of the PWM pulse voltage the same.