KR102408903B1 - Pixel and Organic Light Emitting Display Device Using the Same - Google Patents

Abstract

The present invention prevents a change in threshold voltage due to the capacitance characteristic of an organic light emitting diode connected to the driving transistor itself in a structure that compensates the threshold voltage of the driving transistor to stably maintain luminance, and prevents color deviation by region The present invention relates to an organic light emitting display device.

Description

Pixel and Organic Light Emitting Display Device Using the Same

The present invention prevents a change in threshold voltage due to the capacitance characteristic of an organic light emitting diode connected to the driving transistor itself in a structure that compensates the threshold voltage of the driving transistor to stably maintain luminance, and prevents color deviation by region The present invention relates to an organic light emitting display device.

BACKGROUND ART Flat panel displays are widely used not only for monitors of desktop computers, but also for portable computers such as notebook computers, PDAs, and mobile phone terminals due to their advantages in miniaturization and weight reduction. Examples of the flat panel display include a liquid crystal display device (LCD), a plasma display panel device (FED), a field emission display device (FED), and an organic light emitting display device (OLED). ), etc.

Among them, the organic light emitting diode display has advantages of fast response speed, high luminance efficiency, and a large viewing angle.

In general, an organic light emitting diode display applies a data voltage to a gate electrode of a driving transistor using a transistor turned on by a scan signal, and charges a data voltage supplied to the driving transistor to a storage capacitor. Then, the organic light emitting diode emits light by outputting the data voltage charged to the storage capacitor using the light emission control signal. That is, the current supplied to the organic light emitting diode may be adjusted by the data voltage applied to the gate electrode of the driving transistor.

However, the threshold voltage Vth of each driving transistor formed in the sub-pixels varies due to the characteristics of the manufacturing process. The current supplied to the organic light emitting diode may have a different value than the designed value due to the deviation of the threshold voltage of the driving transistor, and accordingly, the luminance of light emission may be different from the desired value. In order to prevent the deviation of the threshold voltage Vth, in general, the organic light emitting diode display senses the potential of the connection portion between the organic light emitting diode and the driving transistor and applies a compensation method.

However, even when compensation is applied by providing a compensation circuit at the connection between the driving transistor and the organic light emitting diode for each sub-pixel, the organic light emitting diode acts as a parasitic capacitance in the compensation step due to the instability of the organic light emitting diode itself other than the driving transistor. Compensation cannot be made, and as a result, it may become a factor inducing a color difference for each region in the light emitting section.

The present invention has been devised to solve the above problems, and in a structure for compensating for the threshold voltage of a driving transistor to stably maintain luminance, The present invention relates to an organic light emitting display device that prevents change and prevents color deviation for each area.

The pixel of the present invention is controlled by a gate line provided in one direction on a substrate, a data line and a power voltage line intersecting the gate line, and a scan signal supplied to the gate line, the data line and the first A switching transistor connected between nodes, a storage capacitor connected to the first node and a first storage electrode, and a storage capacitor having a second storage electrode connected to a second node, and a signal supplied to the first node, the power supply a first electrode positioned between a voltage line and the second node, a driving transistor, a first electrode connected to the second node, a second electrode opposite to the first electrode, and a first electrode between the first electrode and the second electrode An organic light emitting diode having an electron transporting host having a content ratio, a hole transporting host having a second content ratio greater than the first content ratio, and a light emitting layer including a dopant.

Here, a voltage value of the second node is sensed in the compensation step, and a voltage difference between the first node and the second node is defined as a threshold voltage of the driving transistor in the compensation step, so that compensation may be performed.

The first content ratio and the second content ratio may be greater than 1:1 and less than or equal to 1:2.

The driving transistor is an NMOS transistor, and the dopant of the organic light emitting diode is a phosphorescent dopant.

Here, the LUMO of the hole transporting host is -2.9eV to -2.0eV, the LUMO of the electron transporting host is located below the LUMO of the hole transporting host, -3.4eV to -2.8eV, and the hole transporting host The HOMO of -5.9eV to -5.0eV, and the HOMO of the electron transporting host may be -6.7eV to -6.0eV.

The pixel is controlled by a light emitting signal, a light emission control transistor positioned between the power supply voltage line and the driving transistor, a sensing signal controlled by a sensing signal, and a sensing transistor positioned between an initialization line and the second node, and the power source A compensation capacitor may be further included between the voltage line and the connection portion of the light emission control transistor and the second node.

In addition, the dopant may have an emission peak at 500 nm to 640 nm.

In addition, the organic light emitting display device of the present invention has a substrate including a plurality of the above-described pixels, and the organic light emitting diode of each pixel further has a hole transport layer in common between the first electrode and the light emitting layer, and the light emitting layer and the second light emitting layer It may further have an electron transport layer in common between the two electrodes.

The pixel and organic light emitting display device of the present invention have the following effects.

Each sub-pixel includes a driving thin film transistor and an organic light emitting diode connected thereto, and the light emitting layer in the organic light emitting diode of at least one sub pixel includes a phosphorescent dopant, a first host for hole transport, and a second host for transporting electrons, Since the content ratio of the first host is greater than that of the second host, the organic light emitting diode does not act as a parasitic capacitor in the compensation step according to the source-follower operation of the driving transistor, thereby increasing the accuracy of compensation.

In addition, since the compensation accuracy is high, color deviation for each area of the screen can be prevented, and lifespan and efficiency can be improved.

1 is a plan view illustrating an organic light emitting diode display according to the present invention;
FIG. 2 is an equivalent circuit diagram of each sub-pixel of FIG. 1 ;
3 is a timing diagram of FIG. 2
4 is a cross-sectional view illustrating one form of the organic light emitting diode of FIG. 2 ;
5 is a view showing a white realization state of an organic light emitting diode display when an organic light emitting diode of a comparative example is applied;
6 is a graph showing CV characteristics when the organic light emitting diode of Comparative Example is applied;
7 is a graph showing CV characteristics of organic light emitting diodes according to various experimental examples;
8 is a band diagram of a light emitting layer and a peripheral layer of an organic light emitting diode of the present invention;
9 is a graph showing left and right color deviations according to Comparative Examples and Experimental Examples 1 to 3;
10 is a graph showing the threshold voltage compensation rate of Comparative Example and Experimental Example 3
11 is a cross-sectional view illustrating an example of an organic light emitting diode display according to the present invention;

Advantages and features of the invention, and methods of achieving them, will become apparent with reference to the various embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the various embodiments disclosed below, but will be implemented in various different forms, and only the various embodiments of the present invention make the disclosure of the present invention complete, and in the technical field to which the present invention pertains It is provided to fully inform those of ordinary skill in the scope of the invention. Accordingly, the invention is defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining various embodiments of the present invention are exemplary, and thus the present invention is not limited to the matters shown in the drawings. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components included in various embodiments of the present invention, it is interpreted as including an error range even if there is no separate explicit description.

In describing various embodiments of the present invention, in the case of describing the positional relationship, for example, two When the positional relationship of parts is described, one or more other parts may be positioned between the two parts unless 'directly' or 'directly' is used.

In describing various embodiments of the present invention, in the case of describing a temporal relationship, for example, a temporal precedence relationship such as 'after', 'next to', 'after', 'before', etc. When is described, a case that is not continuous may be included unless 'directly' or 'directly' is used.

In describing various embodiments of the present invention, 'first ~', 'second ~', etc. may be used to describe various components, but these terms are only used to distinguish between the same and similar components. to be. Accordingly, in the present specification, elements modified by 'first to' may be the same as elements modified by 'second to' within the technical spirit of the present invention, unless otherwise specified.

Each feature of the various embodiments of the present invention may be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the various embodiments may be implemented independently of each other or may be implemented together in a related relationship. may be

Meanwhile, although the organic light emitting diode is provided as a single stack in the present specification, it may also be formed in the form of a plurality of stacks having a charge generating layer therebetween. Each stack means a unit structure including a hole transport layer, an organic layer including an electron transport layer, and an organic light emitting layer disposed between the hole transport layer and the electron transport layer, unless limited to a specific structure in Examples. The organic layer may further include a hole injection layer, an electron blocking layer, a hole blocking layer, and an electron injection layer, and in addition, other organic layers may be further included according to the structure or design of the organic light emitting device.

First, circuit operations of the organic light emitting diode display of the present invention and sub-pixels included therein will be described.

1 is a plan view of an element illustrating an organic light emitting diode display according to the present invention, and FIG. 2 is an equivalent circuit diagram of each sub-pixel of FIG. 1 .

Referring to FIG. 1 , an organic light emitting diode display according to the present invention includes a display panel 100 , a timing controller 110 , a data driver 120 , and scan drivers 130 and 140 .

The display panel 100 includes a display area 100A in which sub-pixels are formed and a non-display area 100B in which various signal lines or pads are formed outside the display area 100A. The display area 100A includes a plurality of sub-pixels P, and displays an image based on a gradation displayed by each of the sub-pixels P. In addition, a plurality of sub-pixels P are arranged on each of the horizontal lines to form a matrix. Each of the sub-pixels P is connected to the data line part DL and the gate line part GL orthogonal to each other. Referring to FIG. 2 , the data line part DL connected to each sub-pixel P includes an initialization line 14a and a data line 14b, and the gate line part GL is the previous gate line GL. (n-1)), a current stage gate line GL(n), and an emission line 15c. Each of the sub-pixels P includes an organic light emitting diode OLED, a driving transistor DT, first to third transistors T1 , T2 , and T3 , a storage capacitor Cst, and an auxiliary capacitor Csub. The driving transistor DT and the first to third transistors T1 , T2 , and T3 may be implemented as thin film transistors (hereinafter, TFTs) including an oxide semiconductor layer or polysilicon as a semiconductor layer.

The timing controller 110 provides timing signals such as a vertical sync signal (Vsync), a horizontal sync signal (Hsync), a data enable signal (DE), and a dot clock (DLCK) through an LVDS or MIPI interface receiving circuit connected to the image board. is input.

The timing controller 110 includes a data control signal DDC for controlling the operation timing of the data driver 120 based on the input timing signal and a gate control signal for controlling the operation timing of the scan drivers 130 and 140 ( GDC) is created.

The data driver 120 includes a plurality of source drive integrated circuits (ICs). The source drive ICs receive digital video data RGB and a source timing control signal DDC from the timing controller 110 . The source drive ICs generate a data voltage by converting the digital video data RGB into a gamma voltage in response to the source timing control signal DDC, and transmit the data voltage through the data lines 14b of the display panel 100 . supply

The scan drivers 130 and 140 include a level shifter 130 and a shift register 140 . In the scan driver 130 , the level shifter 130 and the shift register 140 are separated, and the shift register 140 is formed in the non-display area 100B of the display panel 100 . Panel; hereinafter GIP) is formed.

The level shifter 130 is formed on a printed circuit board (not shown) connected to the display panel 100 in the form of an IC. The level shifter 130 level-shifts the clock signals CLK and the start signal VST under the control of the timing controller 11 , and then supplies them to the shift register 140 . The shift register 140 is formed by a combination of a plurality of thin film transistors (hereinafter, TFTs) in the non-display area 100B of the display panel 100 by the GIP method. The shift register 140 includes stages that shift and output the scan signal in response to the clock signals CLK and the start signal VST. Stages included in the shift register 140 sequentially output the scan signal Scan and the emission control signal EM through output terminals.

The organic light emitting diode OLED emits light by the driving current Ioled supplied from the driving transistor DT. A multi-layered organic compound layer is formed between the anode electrode and the cathode electrode of the organic light emitting diode (OLED). The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (Electron Injection layer, EIL). An electron blocking layer (EBL) may be further provided between the hole transport layer and the light emitting layer, and a hole blocking layer (HBL) may be further provided between the light emitting layer and the electron transport layer. In some cases, the hole injection layer and the electron injection layer may be omitted. A first electrode (anode electrode) of the organic light emitting diode (OLED) is connected to a source electrode of the driving transistor DT, and a second electrode (cathode electrode) is connected to a low voltage terminal or a ground terminal (VSS).

The driving transistor DT controls a driving current applied to the organic light emitting diode OLED by its gate-source voltage Vgs. To this end, the gate electrode of the driving transistor DT is connected to the data line 14b supplying the data voltage Vdata via the third transistor T3, and the drain electrode is connected to the input terminal of the power supply voltage line VDL. 1 is connected through the transistor T1, and the source electrode is connected with the low voltage terminal or the ground terminal Vss and the organic light emitting diode (OLED) interposed therebetween.

The initialization line 14a is a line related to compensation, and is a second transistor between the initialization line 14a and a second node n2 that is a connection node between the source of the driving transistor DT and the organic light emitting diode OLED. T2 (sensing transistor) is provided, and the gate electrode of the second transistor T2 is connected to the previous gate line GL(n-1). In some cases, the gate electrode of the second transistor T2 may receive a separate sensing signal SENSE.

The first transistor T1 (light emission control transistor) controls a current path between the driving voltage VDD input terminal and the driving transistor DT in response to the emission control signal EM. To this end, the gate electrode of the first transistor ST1 is connected to the light emitting line EL, the drain electrode is connected to the driving voltage VDD input terminal, and the source electrode is connected to the driving transistor DT.

The second transistor T2 provides the initialization voltage Vini received from the initialization line 14a to the second node n2 in response to the previous stage scan signal Scan(n-1). To this end, the gate electrode of the second transistor T2 is connected to the previous gate line GL(n-1), the drain electrode is connected to the initialization line 14a, and the source electrode is connected to the second node n2.

The third transistor T3 (switching transistor) drives the reference voltage Vref or the data voltage Vdata provided from the data line 14b in response to the current stage scan signal Scan(n) to the driving transistor DT. provided to To this end, the gate electrode of the third transistor T3 is connected to the current gate line GLn, the drain electrode is connected to the data line 14b, and the source electrode is connected to the driving transistor DT.

The storage capacitor Cst maintains the data voltage Vdata received from the data line 14b for one frame so that the driving transistor DT maintains a constant voltage. To this end, the storage capacitor Cst is connected to the gate electrode and the source electrode of the driving transistor DT. The auxiliary capacitor Csub is connected in parallel with the storage capacitor Cst at the second node n2 to increase the efficiency of the voltage supplied to the first node n1 of the driving transistor operating as a source-follower. raises it

In some cases, the first transistor T1 (emission control transistor), the second transistor T2 (sensing transistor), and the compensation capacitor Csub may be omitted from the circuit configuration of the sub-pixel, but the first node n2 ) and the level of the second node n3 are stabilized, and a structure including these transistors is preferable so that compensation can be performed in the initialization state. The following timing diagram describes driving in a form including the above-described first to second transistors T1 and T2 and the compensation capacitor Csub.

The operation of the sub-pixel P during the image display period in such an organic light emitting diode display device is as follows.

3 is a timing diagram of FIG. 2 .

Signals applied to the sub-pixel P include an emission scan signal SCAN, an emission control signal EM, a power supply voltage VDD, a reference voltage Vref, or a data voltage signal Vdata, and FIG. 3 shows these signals. In accordance with the change of , a potential change is indicated at the first node n1 corresponding to the gate electrode of the driving transistor DT and the second node n2 corresponding to the source electrode.

Referring to FIG. 3 , the operation of the sub-pixel P according to the present invention includes an initialization period Ti for initializing the gate-source potential Vgs of the driving transistor DT to a specific voltage, and the threshold of the driving transistor DT. The sampling period (Ts) for detecting and storing the voltage, the writing period (Tw) for applying the data voltage (Vdata), and the threshold voltage and the data voltage (Vdata) are used to limit the driving current applied to the organic light emitting diode (OLED). It includes a light-emitting period Te in which light is emitted by compensating regardless of the voltage.

During the initialization period Ti, the second transistor T2 applies the initialization voltage Vini received from the initialization line 14a in response to the previous stage scan signal Scan[n-1] or the sensing signal SENSE to the second stage. It is supplied to the node n2. Accordingly, the second node n2 corresponds to the source electrode of the driving transistor DT, and the second node n2 has a potential of the initialization voltage Vini. In addition, the third transistor T3 applies the reference voltage Vref received from the data line 14b in response to the current stage scan signal Scan[n] to the first node n1 of the gate electrode of the driving transistor DT. supply to Accordingly, the first node n1 has a potential of the reference voltage Vref.

In the initialization period Ti, the initialization voltage Vini supplied to the second node n2 is to initialize the sub-pixel P to a certain level, and in this case, the magnitude of the initialization voltage Vini is the organic light emitting diode (OLED). is set to a voltage value smaller than the operating voltage of the organic light emitting diode (OLED) so as not to emit light. For example, the initialization voltage Vini may be set to a voltage having a magnitude of -1V to +1 (V), more preferably 0V or less. However, as will be described later, the organic light emitting diode (OLED) itself is a kind of capacitor, and may induce an initial parasitic capacitance by an organic material included between both electrodes.

Thereafter, during the sampling period Ts, the third transistor T3 transfers the reference voltage Vref provided from the data line 14b to the first node n1 in response to the current stage scan signal Scan[n]. supply In addition, the first transistor T1 is turned on in response to the emission control signal EM to supply the power supply voltage VDD to the driving transistor DT. In this case, the first node n1 serving as the gate electrode of the driving transistor maintains the reference voltage Vref. And, as the second node n2 is in a floating state, the potential of the second node n2 flows from the power supply voltage line VDL through the first transistor T1 and the driving transistor DT. Current is accumulated and sensed. In the second node n2 through the sampling period Ts, the potential rises to have a magnitude corresponding to the difference (Vref-Vth) between the reference voltage Vref and the threshold voltage Vth of the driving transistor DT. It is saturated with voltage. That is, through the sampling period Ts, the potential difference between the gate and the source of the driving transistor DT, that is, the voltage difference between the first node n2 and the second node n2, becomes the threshold voltage Vth. , the saturated voltage is stored in the storage capacitor Cst.

During the writing period Tw, the first and second transistors T1 and T2 are turned off. In addition, the third transistor T3 is turned on and supplies the data voltage Vdata received from the data line 14b to the first node n1. At this time, the second transistor is turned on and in a floating state, and the voltage of the second node n2 is coupled by the ratio of the storage capacitor Cst and the auxiliary capacitor Csub to rise or fall. do.

During the light emission period Te, the second transistor T2 is turned off, the third transistor T3 is turned off, and the first transistor T1 is turned on. During the light emission period, the data voltage Vdata stored in the storage capacitor Cst is supplied to the organic light emitting diode OLED, and accordingly, the organic light emitting diode OLED emits light with a brightness proportional to the data voltage Vdata. At this time, a current flows in the driving transistor DT by the voltages of the first node n1 and the second node n2 determined in the writing period Tw, and a desired current is supplied to the organic light emitting diode OLED, Accordingly, the brightness of the organic light emitting diode OLED can be controlled by the data voltage Vdata.

That is, in the sub-pixel P of the present invention, the driving transistor DT controls the driving current Ioled applied to the organic light emitting diode OLED with the gate source voltage Vgs.

However, in the case of the NMOS transistor following the source follower method, in the initial compensation period (sampling and writing period) before light emission, in addition to the storage capacitor (Cst) provided between the gate and the source of the driving transistor, the second node serving as the source electrode of the driving transistor Due to the instability of the organic light emitting diode (OLED) connected to the (n2) side, the organic light emitting diode (OLED) acts as a parasitic capacitor at the second node (n2), so that the source electrode of the driving transistor, that is, the first The voltage value at the second node n2 may be changed. This means that the gate-source voltage (Vgs) of the driving transistor is changed to a parasitic capacitor other than the storage capacitor. In particular, in the initial compensation period, a deviation may be caused in the compensation value for each region due to a change in the voltage between the gate and source of the driving transistor. Also, in a structure in which an internal compensation or an external compensation method of sequentially sensing the voltage value of the source node of the driving transistor is applied in each pixel line, one end and the other end of the same pixel line of the compensation value as the sensing progresses sequentially There is a problem that the deviation of the is further increased. Accordingly, in a compensation structure having a deviation in the compensation value for each sub-pixel in one pixel line, even when the compensation is performed and the compensated driving current is supplied to the organic light emitting diode, the deviation of the compensation value for each region may cause color deviation for each region. can In addition, due to incorrect compensation applied by the parasitic capacitance at the second node n2 , accurate compensation is not made in the entire panel, so that the required threshold voltage or mobility of the driving transistor is not properly compensated, resulting in reduced efficiency and lifespan. It can also be a cause

Hereinafter, a detailed configuration of the organic light emitting diode will be described.

4 is a cross-sectional view illustrating one form of the organic light emitting diode of FIG. 2 .

As shown in FIG. 4 , the organic light emitting diode includes a first electrode 10 and a second electrode 70 facing each other, and an organic material stack provided therebetween.

In the organic material stack, a light emitting layer 40 in which light is emitted by recombination of electrons and holes for substantially each sub-pixel P is a basic configuration, and the first electrode 10 and the light emitting layer 40 are common to the sub-pixels. A hole-related common layer and an electron-related common layer common between the light emitting layer 40 and the second electrode 70 are included.

The hole-related common layer may include a hole injection layer 20 and a hole transport layer 30 that are sequentially formed in the first electrode 10 . In each sub-pixel, the hole transport layer 30 may be provided with a different thickness, or an additional hole transport layer may be further provided to adjust the distance from the first electrode 10 in order to match the resonance condition of the color wavelength of the corresponding light emitting layer. .

In addition, between the hole transport layer 30 and the light emitting layer 40 , an electron blocking layer (EBL) is further provided to prevent electrons or excitons from passing from the light emitting layer 40 to the hole transport layer 30 . can be provided.

Meanwhile, as the electron-related common layer, the electron transport layer 50 and the electron injection layer 60 may be sequentially provided from the emission layer 40 . In some cases, the electron injection layer 60 may be formed of only an inorganic material. In this case, the electron injection layer 60 may be continuously formed together in the process of forming the second electrode 70 .

In addition, a hole blocking layer (not shown) may be provided between the light emitting layer 40 and the electron transport layer 50 to prevent holes in the light emitting layer 40 from passing into the electron transport layer 50 .

On the other hand, in the light emitting layer 40 of the organic light emitting diode (OLED) shown in FIG. 4, a dopant (d) is included in a mixed host of the hole transporting first host (h1) and the electron transporting second host (h2). have.

In the emission layer 40 , the first and second hosts h1 and h2 are made of materials having HOMO and LUMO values to include the band gap of the dopant d, respectively. Here, the reason why the first and second hosts h1 and h2 different from each other are used in the emission layer 40 is because a phosphorescent dopant having a wide bandgap is used as the dopant d.

In general, when a light emitting layer using a fluorescent dopant or a phosphorescent dopant having a narrow band gap is used, the host of the light emitting layer includes a single electron transporting host. This is because the organic light emitting diode is a current-driven type, and is mainly formed by hole carriers between the first and second electrodes, and thus includes an electron transporting host in the light emitting layer to compensate for the relatively insufficient electron mobility.

Here, the hole mobility (hm1) of the first host (h1) having the hole transport property is 10 times or more greater than the electron mobility (em1), and the hole mobility in the material is relatively higher than that of the electrons. It is named because it is larger than the figure, and the second host (h2) having the electron transport property is named because the electron mobility (em2) is 10 times greater than the hole mobility (hm2). And, when comparing the first and second hosts h1 and h2, the hole mobility hm1 of the first host h1 is the hole mobility hm1 of the second host h2. ) (hm2), the second host (h2) electron mobility (em2) is greater than 100 times greater than the electron mobility (em1) of the first host.

In particular, when the light emitting layer 40 is formed with the heterogeneous hosts h1 and h2 as described above, the LUMO values of the hosts mixed to include the band gap of the dopant are sufficiently large (small in absolute values), and the HOMO values are It can have a wide energy bandgap that becomes small (large in absolute value), and through this, hole transport from the adjacent hole transport layer 30 is easy, electron transport from the adjacent electron transport layer 50 is easy, and the dopant emits light because it is possible

Meanwhile, as described above, the organic light emitting diode is connected to the source electrode (second node: n2) of the driving transistor DT, and a driving current is supplied thereto. In addition, initial compensation is applied to the driving transistor DT by using the source-follower driving of the NMOS transistor. When the ratio of the transporting host is high, even in the initial compensation period (sampling (Ts) and lighting period (Tw)) before light emission, the organic light emitting diode (OLED) acts as a parasitic capacitance to make the potential unstable at the second node (n2). can do.

5 is a diagram illustrating a white realization state of an organic light emitting diode display when the organic light emitting diode of the comparative example is applied, and FIG. 6 is a graph showing the CV characteristics when the organic light emitting diode of the comparative example is applied.

As shown in FIG. 5 , the organic light emitting diode of the comparative example uses only an electron transport host as a host of the light emitting layer or uses a heterogeneous host, with a high ratio of electron transport hosts, and the sensing transistor T2 connected to the second node turns Even in the on-off state, a weak parasitic capacitance (Coled) occurs due to the electron transporting host of the light emitting layer of the organic light emitting diode, and due to this, compensation is performed in the initial compensation section, at the first node (n1), with the capacity of 'Cst1 + Coled' As a result, a deviation of the threshold voltage Vth required for the driving transistor DT occurs, and when compensation is sequentially performed on a plurality of sub-pixels positioned in one pixel line, the sub-pixel at one end of one pixel line Since the difference in the threshold voltage to which compensation is applied is large in the sub-pixel at the other end compared to the pixel, the compensation efficiency is lowered and a color difference is expressed.

Referring to FIG. 6 , in a comparative example (a thing with a high ratio of an electron-transporting host even if only an electron-transporting host is used as the host of the light-emitting layer or a heterogeneous host is used), for example, the first electrode (anode) of the organic light emitting diode Looking at the capacitance value charged in the first node n1 by changing the voltage value applied to the electrode) from -3V to 7V, it can be seen that there is an increase in the capacitance even at 0V or less, which is the first electrode (anode) electrode) means that the capacitance is increased even without driving the sensing transistor T2 adjacent to the second node n2 connected to the second node n2 . And, this is interpreted as occurring because the organic light emitting diode uses only an electron transporting host having a high electron carrier transporting property in the light emitting layer or uses a relatively large amount of an electron transporting host compared to a hole transporting host. In addition, when the voltage value applied to the first electrode (anode electrode) is 0V or less, the point in which the capacitance increases is referred to as a negative shift, and the pixel and the organic light emitting display of the present invention are subjected to such a negative shift ( negative shift) is to be removed.

In the pixel of the present invention, the above-mentioned problem is solved by adjusting the ratio of the mixed host of the emission layer of the organic light emitting diode.

7 is a graph illustrating CV characteristics of a first node of a driving transistor according to various experimental examples.

7 shows Comparative Examples and Experimental Examples 1 to 3, Comparative Examples and Experimental Examples 1 to 3 have a content ratio of the first host and the second host of 1:1.5, 1:1, 1.5, respectively. :1, 2:1. The content ratio represents a mass ratio (wt ratio) of each host included in the light emitting layer.

Compared to the comparative example, when the content of the first host (hole-transporting host) is gradually increased, it can be seen that the capacitance does not gradually increase at a negative voltage. In particular, when the content ratio of the first host (hole-transporting host) is greater than 1:1 or less than or equal to 2:1 of the second host (electron-transporting host), there is no increase in capacitance at least at a negative voltage. This can be verified through experimentation.

Table 1 below compares the driving voltage, luminance, and lifespan (time when the luminance of 95% compared to the initial stage) of the comparative example in Comparative Examples and Experimental Examples 1 to 3 is compared, and the driving voltage is the content of the first host It can be seen that the increase occurs as the number increases, but the lifespan is improved in all of the first to third experimental examples. That is, the driving voltage must have a limit in which the content ratio of the first host to the second host is 2:1 or less to prevent an increase in the driving voltage. It can be seen that the luminance is at the same level as in the comparative example or has a partial increase when the first to third experimental examples are applied.

Experimental example Host content ratio of light emitting layer
(1st host content ratio: 2nd host content ratio) Driving voltage (V) Luminance (Cd/A) Lifespan (Comparative example is 100%) comparative example 1:1.5 3.8 132.7 100% Experiment 1 1:1 4.1 142.1 120% 2nd Experimental Example 1.5:1 4.3 142.4 110% 3rd Experimental Example 2:1 4.7 142.8 120%

The physical properties of the host applied to the light emitting layer of the organic light emitting diode of the present invention are as follows.

8 is a band diagram of a light emitting layer and a peripheral layer of an organic light emitting diode of the present invention.

As shown in Figure 8, the LUMO level (L1) of the first host (h1) of the hole transporting property in the light emitting layer 40 of the organic light emitting diode is -2.9eV to -2.0eV, and the LUMO level of the electron transporting second host ( L2) is located below the LUMO (L1) of the hole transporting first host (h1), and is -3.4 eV to -2.8 eV. In addition, the HOMO level (H1) of the hole transporting first host (h1) is -5.9 eV to -5.0 eV, and the HOMO level (H2) of the electron transporting second host (h2) is -6.7 eV to -6.0 eV to be.

The HOMO level of the hole transport layer or electron blocking layer adjacent to the light emitting layer 40 has a difference (ΔH) between the HOMO level (H1) of the first host (h1) and 0.01 eV to 0.25 eV, and the hole transport layer or the battery blocking layer Hole injection from the layer into the light emitting layer 40 is easy. In addition, the LUMO level of the electron transport layer 50 adjacent to the light emitting layer 40 has a difference (ΔL) between the LUMO level (L2) of the second host h2 and 0.01 eV to 0.25 eV, from the electron transport layer 50 Hole injection into the light emitting layer 40 is easy.

For example, the first host h1 may be a TCTA or CBP-based material, and the second host h2 may be a TpBi, TBFTrz, or CzTrz-based material. However, it is not limited to the materials listed as above, and by changing the substituent, if it has the above-described HOMO level, LUMO level characteristics and mobility characteristics, it may be changed to other hosts used in the organic light emitting layer.

Hereinafter, effects of the left and right color deviation and the threshold voltage compensation rate in Comparative Examples and Experimental Examples will be examined.

9 is a graph showing left and right color deviations according to Comparative Examples and Experimental Examples 1 to 3, and FIG. 10 is a graph illustrating threshold voltage compensation rates of Comparative Examples and Experimental Examples 3 and 3. Referring to FIG.

9 and Table 2, in the comparative example and the first to third experimental examples, there is little change in ΔX color coordinates in the left and right regions of the screen (one end and the other end of the pixel line), but the ΔY color coordinates are the comparative examples, first Experimental example has a value of 0.025 or more, in contrast, the second and third experimental examples have a value of 0.015. can confirm.

Experimental example Light emitting layer host content ratio
(1st host content ratio: 2nd host content ratio) Left and right ΔX color coordinate deviation Left and right ΔY color coordinate deviation comparative example 1:1.5 0.008 0.028 Experiment 1 1:1 0.007 0.025 2nd Experimental Example 1.5:1 0.007 0.015 3rd Experimental Example 2:1 0.008 0.015

10 is a comparison of the threshold voltage compensation ratios of the driving transistors of the comparative example and the third experimental example, where the threshold voltage compensation ratio is calculated as "(1-ΔVgs*ΔVth)*100%". That is, when the gate-source voltage change rate (ΔVgs ) and the threshold voltage change rate (ΔVth ) of the driving transistor are large, the values are small, and the gate-source voltage change rate (ΔVgs ) and the threshold voltage change rate (ΔVth ) are small. When the value is large, it means that the threshold voltage compensation rate is large when the gate-source voltage and the threshold voltage vary little by region.

Referring to FIG. 10 , in the comparative example, this threshold voltage rate is 67.3%, whereas when the third experimental example of the present invention is applied, it rises to 93.7%, meaning that the threshold voltage compensation rate is increased to 26.3% compared to the comparative example. . That is, the pixel and the organic light emitting display device of the present invention control the heterogeneous host component ratio of the light emitting layer in the organic light emitting diode to reduce or prevent capacitance fluctuation factors at the first and second nodes caused by the light emitting layer, thereby reducing or preventing each area of the screen. This will reduce the color variation.

On the other hand, the above-described Comparative Examples and the first to third experimental examples are experiments on the organic light emitting diode having an emission peak of 500 nm to 640 nm as a phosphorescent dopant. As such, the reason for applying the experiment to the organic light emitting diode including the phosphorescent light emitting layer having an emission peak of visible light of 500 nm or more is as follows. This is because there is no need to use a heterogeneous host because the research on the blue wavelength light emitting layer is mainly implemented as a fluorescent layer. If a long-life, high-efficiency blue phosphorescent material is supplied, it will be applicable to an organic light emitting diode including a light emitting layer applying a wavelength of 430 nm to 490 nm.

11 is a cross-sectional view illustrating an example of an organic light emitting diode display according to the present invention.

11 , the organic light emitting diode display according to the present invention includes a plurality of sub-pixels R-sub, G-sub, and B-sub on a substrate 300 , and in each sub-pixel, a driving transistor DT It may include an organic light emitting diode connected to.

In the illustrated sub-pixel example, only the red sub-pixel R-sub, the green sub-pixel G-sub, and the blue sub-pixel B-sub are illustrated, but the present invention is not limited thereto. It may be provided, or white may be realized by combining sub-pixels of different colors according to the case.

In addition, each of the sub-pixels R-sub, G-sub, and B-sub includes a first electrode 210 connected to the driving transistor DT, followed by a hole transport layer 220, a hole transport layer, and a light emitting layer ( 241 , 242 , and 243 , an electron transport layer 250 , and a second electrode 260 may be provided.

The red sub-pixel R-sub and the green sub-pixel G-sub are spaced apart from the surface of the first electrode 210 to meet the resonance condition of the color wavelengths of the red light emitting layer 241 and the green light emitting layer 242, respectively. Auxiliary hole transport layers 231 and 232 may be further provided to make the distance from the blue light emitting layer 243 different, and the auxiliary hole transport layers 231 and 232 of the red light emitting layer 241 and the green light emitting layer 242 have different thicknesses. can be

On the other hand, looking at the cross-sectional configuration of the thin film transistor array 2050 including the driving transistor DT, it is a semiconductor layer 201 made of amorphous silicon or polysilicon or oxide semiconductor on the substrate 300, and the semiconductor layer ( A driving transistor DT including a gate electrode 203 formed on 201 with a gate insulating layer 202 interposed therebetween, and a drain electrode 205a and a source electrode 205b connected to both ends of the semiconductor layer 201, made including In the same array process, the switching transistor T3 and/or the sensing transistor T2 and the emission control transistor T1 may be provided.

In addition, the thin film transistor array 2050 includes an interlayer insulating film 204 excluding a connection portion between the semiconductor layer 201 and the drain electrode 205a and the source electrode 205b, and An organic light emitting diode provided in each sub-pixel on the driving transistor DT through the contact hole, further comprising a passivation layer 206 covering the source electrode 205b and the drain electrode 205a except for a part of the contact hole thereon. The first electrode 210 of the is connected to the source electrode 205b.

In the above-described organic light emitting display device, each sub-pixel includes a driving thin film transistor and an organic light emitting diode connected thereto, and the light emitting layer in the organic light emitting diode of at least one sub pixel includes a phosphorescent dopant, a hole transporting first host and electron transporting properties. of a second host, wherein the content ratio of the first host is greater than the content ratio of the second host, so that the organic light emitting diode does not act as a parasitic capacitor in the compensation step in the source follower operation of the driving transistor, thereby increasing the accuracy of compensation; Accordingly, color deviation for each region can be prevented, and lifespan and efficiency can be improved.

And, when the light emitting layer of the organic light emitting diode does not have a configuration including the hole transporting first host (h1), the electron transporting second host (h2) and the dopant (d) as in FIG. 4, the light emitting layer may contain a single transportable host and a dopant. In this case, the single-transporting host may be an electron-transporting host or a hole-transporting host, and the mobility may be changed according to the properties of the dopant provided. For example, in FIG. 11 , the green light emitting layer 242 includes the first host h1 and the second host h2 and a dopant having the above-described content ratio, and includes a blue light emitting layer 243 and a red light emitting layer 241 . Silver may consist of a single transporting host and a dopant emitting each color.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made within the scope without departing from the technical spirit of the present invention. . Therefore, the various embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the various embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

10: first electrode 20: hole injection layer
30: hole transport layer 40: light emitting layer
50: electron transport layer 60: electron injection layer
70: second electrode

Claims (10)

a gate line disposed in one direction on a substrate, a data line and a power voltage line intersecting the gate line;
a switching transistor controlled by a scan signal applied to the gate line and connected between the data line and a first node;
a storage capacitor connected to the first node and a first storage electrode, and a second storage electrode connected to a second node;
a driving transistor controlled by a signal supplied to the first node and positioned between the power supply voltage line and the second node;
A first electrode connected to the second node, a second electrode facing the first electrode, and an electron transporting host having a first content ratio between the first electrode and the second electrode, wherein the first content ratio is greater than the first content ratio an organic light emitting diode having a light emitting layer including a hole transporting host having a second content ratio and a dopant;
a light emission control transistor controlled by a light emission signal and positioned between the power supply voltage line and the driving transistor;
a sensing transistor controlled by a sensing signal and positioned between an initialization line and the second node; and
and a compensation capacitor provided between a connection portion between the power supply voltage line and the emission control transistor and the second node. The method of claim 1,
A pixel in which a voltage value of the second node is sensed in a compensation step, and a voltage difference between the first node and the second node is defined as a threshold voltage of the driving transistor in the compensation step and compensation is performed. The method of claim 1,
A pixel wherein the first content ratio and the second content ratio are greater than 1:1 and less than or equal to 1:2. The method of claim 1,
The driving transistor is an NMOS transistor,
The dopant is a phosphorescent dopant. The method of claim 1,
The LUMO of the hole transporting host is -2.9eV to -2.0eV, the LUMO of the electron transporting host is located below the LUMO of the hole transporting host, and -3.4eV to -2.8eV,
The HOMO of the hole transporting host is -5.9eV to -5.0eV, and the HOMO of the electron transporting host is -6.7eV to -6.0eV. delete The method of claim 1,
The dopant is a pixel having an emission peak at 500 nm to 640 nm. a plurality of gate lines disposed in one direction and a plurality of data lines and power supply voltage lines intersecting the gate lines to define sub-pixels on a substrate;
Each of the sub-pixels is
a switching transistor controlled by a scan signal applied to the gate line and connected between the data line and a first node;
a storage capacitor connected to the first node and a first storage electrode, and a second storage electrode connected to a second node;
a driving transistor controlled by a signal supplied to the first node and positioned between the power supply voltage line and the second node;
an organic light emitting diode including a first electrode connected to the second node, a second electrode facing the first electrode, and a light emitting layer between the first electrode and the second electrode;
a light emission control transistor controlled by a light emission signal and positioned between the power supply voltage line and the driving transistor;
a sensing transistor controlled by a sensing signal and positioned between an initialization line and the second node; and
and a compensation capacitor provided between a connection part of the power supply voltage line and the light emission control transistor and the second node,
In at least one of the sub-pixels, an organic light emitting layer of the organic light emitting diode includes an electron transporting host having a first content ratio, a hole transporting host having a second content ratio greater than the first content ratio, and a dopant . 9. The method of claim 8,
The sub-pixels different from the sub-pixels in which the emission layer of the organic light emitting diode includes an electron transporting host having a first content ratio, a hole transporting host having a second content ratio greater than the first content ratio, and a dopant, a single transporting host and An organic light emitting diode display including a dopant. 9. The method of claim 8,
The organic light emitting diode of each sub-pixel,
Further comprising a hole transport layer between the first electrode and the light emitting layer,
The organic light emitting display device of claim 1, further comprising an electron transport layer between the light emitting layer and the second electrode.

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