KR20190024318A - Pixel and Organic Light Emitting Display Device Using the Same - Google Patents

Abstract

The present invention relates to an organic light emitting display device preventing a change in a threshold voltage due to the capacitance characteristics of an organic light emitting diode itself connected to a driving transistor and preventing color deviation for each region in a structure for compensating for the threshold voltage of the driving transistor to stably maintain brightness.

Description

[0001] The present invention relates to a pixel and an organic light emitting diode (OLED)

In the structure for compensating the threshold voltage of the driving transistor so as to stably maintain the luminance, it is possible to prevent the variation of the threshold voltage due to the capacitance characteristic of the organic light emitting diode itself connected to the driving transistor, To an organic light emitting display device.

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 of miniaturization and light weight. Examples of such flat panel display devices include a liquid crystal display device (LCD), a plasma display panel device, a field emission display (FED), and an organic light emitting display device ).

Among these organic light emitting display devices, the organic light emitting display device has advantages of high response speed, high luminance efficiency, and large viewing angle.

2. Description of the Related Art Generally, an organic light emitting display device 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 a driving transistor to a storage capacitor. The organic light emitting diode emits light by outputting the data voltage charged in the storage capacitor using the emission control signal. That is, the current supplied to the organic light emitting diode can be controlled by the data voltage applied to the gate electrode of the driving transistor.

However, due to the characteristics of the manufacturing process, a variation in the threshold voltage (Vth) occurs in each of the driving transistors formed in the sub-pixels. The current supplied to the organic light emitting diode may be different from the designed value due to the deviation of the threshold voltage of the driving transistor, and accordingly, the luminance to emit light may be different from the desired value. In order to prevent the deviation of the threshold voltage (Vth), generally, in the organic light emitting display device, the potential of the connection portion between the organic light emitting diode and the driving transistor is sensed and compensated.

However, even if compensation is provided by providing a compensation circuit at the connection portion between the driving transistor and the organic light emitting diode for each sub-pixel, the organic light emitting diode functions as a parasitic capacitance rather than the driving transistor in the compensating step due to the instability of the organic light emitting diode itself. Compensation can not be achieved, which may result in a difference in color gamut between regions in the emission region.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide an organic light emitting diode having a structure in which a threshold voltage of a driving transistor is compensated for maintaining a stable luminance, And prevents an unevenness in color tone in each region.

A pixel of the present invention is a pixel including a gate line provided in one direction, a data line crossing the gate line, a power source voltage line, and a scan signal supplied to the gate line, A storage capacitor coupled between the first node and the first storage electrode and having a second storage electrode connected to the second node; and a control circuit coupled to the power supply, A first electrode located between the voltage line and the second node, the first electrode being connected to the driving transistor and the second node, and the second electrode facing the first electrode; and a second electrode between the first electrode and the second electrode, Transporting host having a first content ratio and a hole transporting host having a second content ratio larger than the first content ratio, and a light emitting layer containing a dopant. Lt; / RTI >

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

The LUMO of the hole transporting host is -2.9 eV to -2.0 eV, the LUMO of the electron transporting host is located lower than the LUMO of the hole transporting host, and the hole transporting host has a hole transporting host The HOMO of the electron transporting host may be -5.7 eV to -5.0 eV, and the HOMO of the electron transporting host may be -6.7 eV to -6.0 eV.

The pixel is controlled by a light emission signal and is disposed between the power supply voltage line and the driving transistor. The sensing transistor is controlled by a sensing signal. The sensing transistor is located between the initialization line and the second node. And a compensation capacitor provided between the voltage line and the connection node of the emission control transistor and the second node.

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

Further, the organic light emitting diode display 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 includes a hole transporting layer commonly between the first electrode and the light emitting layer, It is possible to have an electron transporting layer in common between two electrodes.

The pixel and the OLED display of the present invention have the following effects.

Each sub pixel includes a driving thin film transistor and an organic light emitting diode connected to the driving thin film transistor. At least a sub pixel organic light emitting diode includes a phosphorescent dopant, a first hole transporting host and a second electron transporting host, The first host is larger 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 according to the source follower operation of the driving transistor, and the accuracy of compensation can be increased.

In addition, since the compensation accuracy is high, it is possible to prevent the color sense deviation of each screen area, and to improve the life and the efficiency.

1 is a plan view showing an organic light emitting diode display according to the present invention.
2 is an equivalent circuit diagram of each sub-
3 is a timing chart
Fig. 4 is a cross-sectional view showing one embodiment of the organic light emitting diode of Fig. 2
5 is a view showing a white state of the organic light emitting display device when the organic light emitting diode of the comparative example is applied.
6 is a graph showing the CV characteristics of the organic light emitting diode of the comparative example
7 is a graph showing CV characteristics of organic light emitting diodes according to various experimental examples
8 is a band diagram of the light emitting layer and the peripheral layer of the organic light emitting diode of the present invention
9 is a graph showing the left and right color deviations according to the comparative example and the first to third experimental examples
10 is a graph showing the threshold voltage compensation ratio in the comparative example and the third experimental example
11 is a cross-sectional view showing an example of the organic light emitting diode display of the present invention

BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, And is provided to fully illustrate the scope of the invention to those skilled in the art. Accordingly, the invention is defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers and the like disclosed in the drawings for describing various embodiments of the present invention are illustrative, and thus the present invention is not limited to those shown in the drawings. Like reference numerals refer to like elements throughout. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. In the case where the word 'includes', 'having', 'done', etc. are used in this specification, other parts can be added unless '~ only' is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

In interpreting the constituent elements included in the various embodiments of the present invention, the scope of the present invention is interpreted as including an error range without any explicit description.

 In describing the various embodiments of the present invention, when describing the positional relationship, for example, the positional relationship may be expressed in terms of 'on', 'on top', 'under', 'next to' If the positional relationship of the part is described, one or more other parts may be located between the two parts, unless " straight " or " direct "

In describing the various embodiments of the present invention, in describing the time relationship, for example, a temporal posterior relation is set to be 'after', 'after', 'after', 'before' Quot; may be included, it may include cases where " straight " or " direct " is not used and is not continuous.

In describing various embodiments of the present invention, the terms 'first', 'second', etc. may be used to describe various elements, but these terms are also used to distinguish between similar and similar components to be. Therefore, unless otherwise stated, the constituent elements of the present invention may be the same as those of the second constituent element of the present invention.

 It is to be understood that each of the various features of the various embodiments of the present invention may be combined or combined with each other, partially or wholly, and technically various interlocking and driving are possible, and that each of the various embodiments may be practiced independently of each other, It is possible.

In the present specification, the organic light emitting diode is provided as a single stack, but may also be formed as a plurality of stacks with a charge generation layer interposed therebetween. Each stack means a unit structure including a hole transporting layer, an organic layer including an electron transporting layer, and an organic light emitting layer disposed between the hole transporting layer and the electron transporting layer, unless the present invention is limited to a specific structure. The organic layer may further include a hole injection layer, an electron blocking layer, a hole blocking layer, and an electron injection layer. Other organic layers may be further included depending on the structure and design of the organic light emitting device.

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

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

Referring to FIG. 1, the OLED display 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 region 100A in which subpixels are formed and a non-display region 100B in which various signal lines, pads, and the like are formed outside the display region 100A. The display region 100A includes a plurality of sub-pixels P, and displays an image based on the gray levels displayed by the sub-pixels P. A plurality of sub-pixels P are arranged in each of the horizontal lines and arranged in a matrix form. Each sub-pixel P is connected to the data line portion DL and the gate line portion GL which are orthogonal to each other. 2, the data line portion DL connected to each sub-pixel P includes an initialization line 14a and a data line 14b, and the gate line portion GL includes a gate line GL (n-1), the current terminal gate line GL (n), and the emission line 15c. Each of the subpixels P includes an organic light emitting diode OLED, a driving transistor DT and first through 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 a thin film transistor (TFT) including an oxide semiconductor layer or polysilicon as a semiconductor layer.

 The timing controller 110 receives timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a dot clock DLCK through an LVDS or MIPI interface receiving circuit connected to an image board, .

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

The data driver 120 includes a plurality of source drive ICs (Integrated Circuits). The source drive ICs are supplied with digital video data (RGB) and source timing control signal (DDC) from the timing controller 110. The source driver ICs convert the digital video data RGB into gamma voltages in response to the source timing control signal DDC to generate the data voltages and apply the data voltages to the data lines 14b of the display panel 100 through the data lines 14b Supply.

The scan drivers 130 and 140 include a level shifter 130 and a shift register 140. The scan driver 130 includes a level shifter 130 and a shift register 140. The shift register 140 is connected to a gate-in panel (not shown) formed in the non-display area 100B of the display panel 100, Panel (hereinafter referred to as GIP) method.

The level shifter 130 is formed on a printed circuit board (not shown) connected to the display panel 100 in an IC form. The level shifter 130 level-shifts the clock signals (CLK) and the start signal (VST) under the control of the timing controller 11, and supplies the level shift signals to the shift register 140. The shift register 140 is formed by a combination of a plurality of thin film transistors (hereinafter referred to as TFT) in the non-display area 100B of the display panel 100 by the GIP method. The shift register 140 consists of stages for shifting and outputting a scan signal in response to the clock signals CLK and the start signal VST. The 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 multilayer 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 EIL). An electron blocking layer (EBL) may be further provided between the hole transporting layer and the light emitting layer, and a hole blocking layer (HBL) may be further provided between the light emitting layer and the electron transporting layer. In some cases, the hole injection layer and the electron injection layer may be omitted. The first electrode (anode electrode) of the organic light emitting diode OLED is connected to the source electrode of the driving transistor DT and the second electrode (cathode electrode) is connected to the low voltage terminal or the ground terminal VSS.

 The driving transistor DT controls the driving current applied to the organic light emitting diode OLED with the gate-source voltage Vgs of its own. The gate electrode of the driving transistor DT is connected to the data line 14b for supplying the data voltage Vdata through the third transistor T3 and the drain electrode of the driving transistor DT is connected to the input terminal of the power supply voltage line VDL And the source electrode is connected to the low voltage terminal or the ground terminal (Vss) via the organic light emitting diode (OLED).

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

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

 The second transistor T2 provides the initialization voltage Vini provided 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 stage gate line GL (n-1), the drain electrode thereof is connected to the initialization line 14a, and the source electrode thereof is connected to the second node n2.

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

 The storage capacitor Cst holds the data voltage Vdata supplied 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 in the second node n2 to control the efficiency of the voltage supplied to the first node n1 of the driving transistor acting as a source follower Increase.

In some cases, the first transistor T1 (emission control transistor) and the second transistor T2 (sensing transistor) and the compensation capacitor Csub among the circuit configurations of the sub-pixel may be omitted, but the first node n2 ) And the second node (n3) are stabilized, and compensation can be performed in the initial state. The timing charts below describe driving in the form of having the first and second transistors T1 and T2 and the compensation capacitor Csub described above.

Hereinafter, the operation of the sub-pixel P during the video display period in the organic light emitting diode display device will be described.

3 is a timing diagram of Fig.

The signals applied to the subpixel P are the emission scan signal SCAN, the emission control signal EM, the power supply voltage VDD, the reference voltage Vref or the data voltage signal Vdata, The potential at the first node n1 corresponding to the gate electrode of the driving transistor DT and the potential at the second node n2 corresponding to the source electrode are changed according to the change of the potential at the source electrode.

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, The driving current applied to the organic light emitting diode OLED is set to a threshold value by using a sampling period Ts for detecting and storing a voltage, a lighting period Tw for applying a data voltage Vdata, a threshold voltage and a data voltage Vdata, And a light emission period Te that emits light by compensating regardless of the voltage.

During the initialization period Ti, the second transistor T2 supplies the initialization voltage Vini provided from the initialization line 14a in response to the previous scan signal Scan [n-1] or the sense signal SENSE to the second And supplies it to the node n2. Thus, the second node n2 corresponds to the source electrode of the driving transistor DT, and the second node n2 has the potential of the initializing voltage Vini. The third transistor T3 responds to the current scan signal Scan [n] and supplies the reference voltage Vref supplied from the data line 14b to the first node n1 of the gate electrode of the driving transistor DT. . Thus, the first node n1 has the potential of the reference voltage Vref.

The initialization voltage Vini supplied to the second node n2 in the initialization period Ti is for initializing the subpixel P to a certain level. The initialization voltage Vini at this time is the same as that of 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 can be set to a voltage having a magnitude of -1 V to +1 (V), more preferably 0 V or less. However, as described later, the organic light emitting diode (OLED) is a kind of capacitor itself, and can induce an initial parasitic capacitance by an organic component included between the electrodes.

During the sampling period Ts, the third transistor T3 supplies the reference voltage Vref supplied from the data line 14b to the first node n1 in response to the current scan signal Scan [n] Supply. The first transistor T1 is turned on in response to the emission control signal EM to supply the power source voltage VDD to the driving transistor DT. At this time, the first node n1, which is the gate electrode of the driving transistor, maintains the reference voltage Vref. As the second node n2 is in a floating state, the potential of the second node n2 flows in the power supply voltage line VDL through the first transistor T1 and the driving transistor DT Current is accumulated and sensed. The second node n2 has a magnitude corresponding to the difference (Vref-Vth) between the reference voltage Vref and the threshold voltage Vth of the driving transistor DT through the sampling period Ts And is saturated with a voltage. That is, 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 magnitude of the threshold voltage Vth through the sampling period Ts , And the saturated voltage is stored in the storage capacitor Cst.

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

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

In the case of the NMOS transistor according to the source follower method, in addition to the storage capacitor Cst provided between the gate and the source of the driving transistor, in the initial compensation period (sampling and lighting period) before the emission, the organic light emitting diode OLED acts as a parasitic capacitor at the second node n2 due to the instability of the organic light emitting diode OLED connected to the source electrode n2, The voltage value at the second node n2 can be varied. This means that the gate source voltage (Vgs) of the driving transistor changes to a parasitic capacitor other than the storage capacitor. Particularly, fluctuation of the gate-source voltage of the driving transistor can cause a deviation in the compensation value for each region in the initial compensation period. Further, in a structure in which internal compensation or external compensation method for sensing the voltage value on the source node side of the driving transistor sequentially in each pixel line is applied, as the sensing progresses progressively, one end of the same pixel line of the compensation value and the other end There is a problem in that the deviation of the output voltage is further increased. Accordingly, in the compensation structure having the deviation of the compensation value for each sub-pixel in one pixel line, even if the compensated driving current is supplied to the organic light emitting diode by performing the compensation, . Further, due to the parasitic capacitance at the second node (n2), erroneous compensation can not be accurately performed in the entire panel, and compensation of the required threshold voltage and mobility of the driving transistor is not appropriate, It is also a cause.

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

4 is a cross-sectional view showing one embodiment of the organic light emitting diode of FIG.

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 disposed therebetween.

The organic material stack has a basic structure of a light emitting layer 40 in which electrons and holes are recombined to substantially emit light for each subpixel P and a common electrode is provided between the first electrode 10 and the light emitting layer 40 And a common electron-related layer common to the light-emitting layer 40 and the second electrode 70 are included.

The hole-transporting layer 30 and the hole injecting layer 20 are sequentially formed on the first electrode 10 as the hole-transporting layer. In order to adjust the resonance condition of the color wavelength of the corresponding emission layer in each sub-pixel, the hole transport layer 30 may have a different thickness to adjust the distance from the first electrode 10, or may further include an additional hole transport layer .

An electron blocking layer (EBL) is further interposed between the hole transport layer 30 and the light emitting layer 40 to prevent electrons or excitons from falling from the light emitting layer 40 to the hole transport layer 30 .

On the other hand, the electron-transporting layer 50 and the electron-injecting layer 60 may be provided in order from the light-emitting layer 40 as the electron-related common layer. In some cases, the electron injection layer 60 may be formed only of an inorganic material. In this case, the electron injection layer 60 may be formed continuously in the process of forming the second electrode 70.

A hole blocking layer (not shown) may be provided between the light emitting layer 40 and the electron transporting layer 50 to prevent the holes of the light emitting layer 40 from falling over to the electron transporting layer 50.

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

In the light emitting layer 40, the first and second hosts h1 and h2 are made of materials having HOMO and LUMO values, respectively, so as to include the band gap of the dopant (d). The reason why the different first and second hosts h1 and h2 are used in the light emitting layer 40 is that the phosphorescent dopant having a wide bandgap is used as the dopant d.

Generally, in the case of using a phosphorescent dopant or a phosphorescent dopant having a narrow bandgap even when the phosphorescent dopant is used, the host of the emitting layer includes a single electron transporting host. This is because the organic light emitting diode is driven by current and is driven by a hole carrier between the first and second electrodes. Therefore, the organic light emitting diode includes an electron transporting host in order to compensate for a relatively short electron mobility in the light emitting layer.

Here, the hole mobility (hm1) of the hole transporting first host (h1) is 10 times or more larger than the electron mobility (em1), and the hole mobility And the second host (h2) of the electron transporting property is named because the electron mobility (em2) has a property that is 10 times larger than the hole mobility (hm2). When comparing the first and second hosts h1 and h2, the hole mobility hm1 of the first host h1 is determined by the hole mobility of the second host h2, ) hm2, and the electron mobility (em2) of the second host (h2) is greater than the electron mobility (em1) of the first host by 100 times or more.

Particularly, when the light emitting layer 40 is formed with the heterogeneous hosts h1 and h2, the LUMO value is sufficiently large (small as an absolute value) and the HOMO value is sufficiently large for the hosts mixed to include the bandgap of the dopant (Large in absolute value), which facilitates hole transfer from the adjacent hole transport layer 30, facilitates electron transfer from the adjacent electron transport layer 50, and realizes light emission of the dopant This is possible.

On the other hand, the organic light emitting diode is connected to the source electrode (second node: n2) of the driving transistor DT as described above, and the driving current is supplied. The driving transistor DT is initially compensated by using the source follower driving of the NMOS transistor. In this case, even if only a single electron transporting host is used as the host of the light emitting layer of the organic light emitting diode, The organic light emitting diode OLED functions as a parasitic capacitance even in the initial compensation period (sampling (Ts) and lighting period Tw) before the light emission, so that the potential at the second node n2 is unstable can do.

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

As shown in FIG. 5, the organic light emitting diode of the comparative example has a high ratio of electrons transportable hosts using only electrons transporting host or heterogeneous host, and the sensing transistor T2 connected to the second node Even in the ON state, a weak parasitic capacitance (Coled) is generated due to the electron transporting host of the light emitting layer of the organic light emitting diode, so that compensation is performed in the initial compensation period at the first node n1 with the capacity of 'Cst1 + Coled' A deviation of the threshold voltage Vth required for the driving transistor DT occurs and when a plurality of sub pixels located in one pixel line are sequentially compensated for, Since the threshold voltage deviation to which the compensation is applied is large in the sub-pixel at the other end of the pixel, the compensation efficiency is lowered and the color difference is expressed.

Referring to FIG. 6, in the comparative example (a host having an electron transporting property is high even if only a host having an electron transporting property is used as a host of the light emitting layer or a different host is used), for example, The voltage applied to the first node n1 is changed from -3 V to 7 V and the capacitance charged in the first node n1 is increased. Means that there is an increase in capacitance even without driving the sensing transistor T2 adjacent to the second node n2 connected to the second node n2. It is considered that this is caused by the fact that the organic light emitting diode uses only the electron transporting host having a large electron carrier transporting property in the light emitting layer or the electron transporting host is used relatively more than the hole transporting host. An increase in capacitance when the voltage applied to the first electrode (anode electrode) is 0 V or less is referred to as a negative shift. The pixel of the present invention and the organic light emitting display device are referred to as a negative shift negative shifts.

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

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

7 shows the comparative examples and the first to third experimental examples. In the comparative examples and the first to third experimental examples, the content ratios of the first host and the second host were 1: 1.5, 1: 1, 1.5 : 1, 2: 1. The content ratio represents a mass ratio of each host included in the light emitting layer.

In contrast to the comparative example, it can be confirmed that, when the content of the first host (hole transporting host) is gradually increased, the capacitance is not increased gradually at a negative voltage. Particularly, when the content ratio of the first host (hole transporting host) is greater than 1: 1 or less than or equal to 2: 1 in the content ratio of the second host (electron transporting host), there is no increase in capacitance at least at the negative voltage It can be confirmed through experiments.

Table 1 below compares the driving voltage, the luminance and the lifetime (the time when the luminance falls to 95% of the initial value) of the comparative example in the comparative example and the first to third experimental examples, The lifetime is improved in all of the first to third experimental examples. That is, the driving voltage should have a limitation of applying the first host: second host content ratio of 2: 1 or less to prevent the driving voltage from rising. It can be seen that the luminance is the same level or a partial increase in the application of the first to third experimental examples.

Experimental Example The host content ratio of the light emitting layer
(First host content ratio: second host content ratio) The driving voltage (V) The luminance (Cd / A) Life (comparative example is 100%) Comparative Example 1: 1.5 3.8 132.7 100% Example 1 1: 1 4.1 142.1 120% Example 2 1.5: 1 4.3 142.4 110% Example 3 2: 1 4.7 142.8 120%

The physical properties of a 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 the light emitting layer and the peripheral layer of the organic light emitting diode of the present invention.

8, the LUMO level L1 of the hole transporting first host h1 in the light emitting layer 40 of the organic light emitting diode is -2.9 eV to -2.0 eV and the LUMO level of the electron transporting second host L2 is located below the LUMO (L1) of the first hole transporting host h1 and is -3.4 eV to -2.8 eV. 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 second electron transporting host (h2) is -6.7 eV to -6.0 eV to be.

The HOMO level of the hole transporting layer or the electron blocking layer adjacent to the light emitting layer 40 has a HOMO level H1 of the first host h1 and a difference DELTA H between 0.01 eV and 0.25 eV, Hole injection from the layer to the light emitting layer 40 is easy. The LUMO level of the electron transport layer 50 adjacent to the light emitting layer 40 has a LUMO level L2 of the second host h2 and a difference DELTA L between 0.01 eV and 0.25 eV. Hole injection into the light emitting layer 40 is easy.

For example, the first host h1 may be a material of TCTA or CBP series, and the host h2 may be a material of TpBi, TBFTrz or CzTrz series. However, the present invention is not limited to the materials listed above, but may be changed to other host used in the organic light-emitting layer as long as it has the above-described HOMO level, LUMO level characteristic, and mobility characteristics.

Hereinafter, effects of the left-right color deviation and the compensation ratio of the threshold voltage in the comparative example and the experimental example will be described.

FIG. 9 is a graph showing the lateral color deviation according to the comparative example and the first to third experimental examples, and FIG. 10 is a graph showing the threshold voltage compensation ratio in the comparative example and the third experimental example.

As shown in Figs. 9 and 2, in the comparative example and the first to third experimental examples, there is almost no change in the DELTA X color coordinate at the left and right regions (one and the other end of the pixel line) of the screen, The experimental example has a value of 0.025 or more, whereas the second and third experimental examples have a value of 0.015. In the second and third experimental examples, the color deviation is relatively smaller than the comparative example and the first experimental example can confirm.

Experimental Example Luminescent layer host content ratio
(First host content ratio: second 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 Example 1 1: 1 0.007 0.025 Example 2 1.5: 1 0.007 0.015 Example 3 2: 1 0.008 0.015

10 compares the threshold voltage compensation rates of the driving transistors of the comparative example and the third experimental example. Here, the threshold voltage compensation ratio is calculated as "(1 - DELTA Vgs * DELTA Vth) * 100% ". That is, when the gate-source voltage variation ratio (DELTA Vgs) and the threshold voltage variation rate (DELTA Vth) of the driving transistor are large, the value is small and the gate-source voltage variation ratio DELTA Vgs and the threshold voltage variation rate DELTA Vth are small , Which means that the threshold voltage compensation ratio is large when the gate-source voltage and the threshold voltage vary little by region.

Referring to FIG. 10, this threshold voltage ratio is 67.3% in the comparative example, whereas it increases to 93.7% in the case of the third experimental example of the present invention, which means that the threshold voltage compensation ratio rises to 26.3% . That is, the pixel and the organic light emitting diode display of the present invention can reduce or prevent the factors of capacitance variation at the first and second nodes caused by the light emitting layer by controlling the heterogeneous host component ratio of the light emitting layer in the organic light emitting diode, It will reduce color deviation.

Meanwhile, the above-described comparative examples and the first to third experimental examples were conducted on organic light emitting diodes having an emission peak of 500 nm to 640 nm as a phosphorescent dopant. The reason why the experiment is applied to an organic light emitting diode including a phosphorescent light emitting layer having an emission peak of 500 nm or more and visible light of at least 500 nm is as follows. In the case of a lower wavelength light emitting layer, And there is no need to use a heterogeneous host because the blue light emitting layer is mainly formed as a fluorescent layer. If a phosphorescent material having a high luminous efficiency and high efficiency is supplied, it can be applied to organic light emitting diodes including a light emitting layer using a wavelength of 430 to 490 nm.

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

11, the OLED display of the present invention includes a plurality of sub-pixels R-sub, G-sub, and B-sub on a substrate 300, And an organic light emitting diode connected to the organic light emitting diode.

Although only the red sub-pixel R-sub, the green sub-pixel G-sub and the blue sub-pixel B-sub are illustrated in the example of the sub-pixel, Alternatively, a white color may be realized by combining subpixels of different colors according to the case.

Each of the sub-pixels R-sub, G-sub, and B-sub includes a first electrode 210 connected to the driving transistor DT, a hole transport layer 220, a hole transport layer, 241, 242, and 243, an electron transport layer 250, and a second electrode 260.

The red sub-pixel R-sub and the green sub-pixel G-sub are spaced apart from the surface of the first electrode 210 in order to match resonance conditions of the color wavelengths of the red light emitting layer 241 and the green light emitting layer 242, The auxiliary hole transporting layers 231 and 232 may be further provided to differentiate the distance from the blue light emitting layer 243 and the auxiliary hole transporting layers 231 and 232 of the red light emitting layer 241 and the green light emitting layer 242 may have different thicknesses Lt; / RTI >

The thin film transistor array 2050 including the driving transistor DT includes a semiconductor layer 201 made of amorphous silicon or polysilicon or an oxide semiconductor on the substrate 300, And a driving transistor DT including a drain electrode 205a and a source electrode 205b which are connected to both ends of the semiconductor layer 201 are formed on the gate insulating film 202, . In the same array process, the switching transistor T3 and / or the sensing transistor T2 and the emission control transistor Tl may be provided.

The thin film transistor array 2050 is provided with an interlayer insulating film 204 except for the connecting portion between the semiconductor layer 201 and the drain electrode 205a and the source electrode 205b, And a protective film 206 covering the source electrode 205b and the drain electrode 205a except for a part of the contact hole on the driving transistor DT through the contact hole, The first electrode 210 of the first electrode 210 is connected to the source electrode 205b.

In each of the sub-pixels, a driving thin film transistor and an organic light emitting diode connected to the driving thin film transistor are provided. At least a sub pixel organic light emitting diode has a phosphorescent dopant, a hole transporting first host and an electron transporting Wherein 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, As a result, it is possible to prevent color variation in each region and to improve the lifetime and the efficiency.

When the light emitting layer of the organic light emitting diode does not have a configuration including the first host h1 and the second host h2 and the electron transporting material h2 and d as shown in Fig. 4, Lt; / RTI > may include a single transport host and 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 depending on the nature of the dopant. 11, the green light emitting layer 242 is composed of a first host h1, a second host h2, and a dopant having the above-described content ratios, and the blue light emitting layer 243 and the red light emitting layer 241, May be made of a single transporting host and a dopant emitting each color.

Although the embodiments of the present invention have been described in detail with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments and various changes and modifications may be made without departing from the scope of the present invention. . Accordingly, the various embodiments disclosed in the present invention are not intended to limit the scope of the present invention, but are intended to illustrate and not limit the scope of the present invention. Therefore, it should be understood that the various embodiments described above are illustrative in all aspects and not restrictive. The scope of protection of the present invention should be construed according to the claims, and all technical ideas within the scope of equivalents should be interpreted 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 provided in one direction and a data line crossing the gate line and a power source voltage line;
A switching transistor controlled by a scan signal applied to the gate line and connected between the data line and the first node;
A storage capacitor coupled between the first node and the first storage electrode and having a second storage electrode coupled to the second node;
A driving transistor controlled by a signal supplied to the first node, the driving transistor being located between the power supply voltage line and the second node; And
A first electrode connected to the second node and a second electrode opposed to the first electrode, and an electron transporting host having a first content ratio between the first electrode and the second electrode; A hole transporting host having a second content ratio, and an organic light emitting diode having a light emitting layer including a dopant. The method according to claim 1,
Wherein the voltage of the second node is sensed in a compensating step and the voltage difference between the first node and the second node in the compensating step is defined as a threshold voltage of the driving transistor so that compensation is performed. The method according to claim 1,
Wherein the first and second content ratios are greater than 1: 1 and less than or equal to 1: 2. The method according to claim 1,
The driving transistor is an NMOS transistor,
Wherein the dopant is a phosphorescent dopant. The method according to claim 1,
The LUMO of the hole transporting host is -2.9 eV to -2.0 eV and the LUMO of the electron transporting host is located lower than the LUMO of the hole transporting host and is -3.4 eV to -2.8 eV,
The HOMO of the hole transporting host is -5.9 eV to -5.0 eV, and the HOMO of the electron transporting host is -6.7 eV to -6.0 eV. 3. The method of claim 2,
A light emission control transistor which is controlled by an emission signal and is located between the power supply voltage line and the driving transistor;
A sensing transistor which is controlled by a sensing signal and is located between the initialization line and the second node; And
And a compensation capacitor provided between a connection point of the power supply voltage line and the emission control transistor and the second node. The method according to claim 1,
Wherein the dopant has an emission peak at 500 nm to 640 nm. A plurality of gate lines arranged in one direction and a plurality of data lines crossing the gate lines and defining sub-pixels and a power source voltage line;
Each of the sub-
A switching transistor controlled by a scan signal applied to the gate line and connected between the data line and the first node;
A storage capacitor coupled between the first node and the first storage electrode and having a second storage electrode coupled to the second node;
A driving transistor controlled by a signal supplied to the first node, the driving transistor being located between the power supply voltage line and the second node; And
A first electrode connected to the second node, a second electrode opposing the first electrode, and an organic light emitting diode including a light emitting layer between the first electrode and the second electrode,
Wherein at least one of the sub-pixels includes a hole transporting host having a first content ratio and a hole transporting host having a second content ratio larger than the first content ratio, and an organic light emitting diode . 9. The method of claim 8,
The subpixels and other subpixels including the hole transporting host and the dopant having the light emitting layer of the organic light emitting diode with the first content ratio and the second content ratio having the second content ratio larger than the first content ratio may be formed by a single transport host An organic light emitting display device including a dopant. 9. The method of claim 8,
The organic light emitting diodes of the pixels each include:
Further comprising a hole transporting layer between the first electrode and the light emitting layer,
And an electron transport layer between the light emitting layer and the second electrode.

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