Organic Light-Emitting Diode and Display Device Using the Same

Abstract

The present disclosure relates to an organic light emitting diode and a display device using the same. The organic light emitting diode includes: a hole injection layer; a hole transport layer on the hole injection layer; a first light emitting layer configured to generate light in a short wavelength in a visible light band, the first light emitting layer being on the hole transport layer, wherein the organic light emitting diode further includes a light absorption layer, the light absorption layer being included in the hole injection layer and / or the hole transport layer at an interface between the hole injection layer and the hole transport layer, and including a phosphorescent dopant material added to at least one of the hole injection layer and the hole transport layer.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefit of Korean Patent Application No. 10 - 2020 - 0186376, filed on December 29, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The present disclosure relates to an organic light - emitting diode and a display device using the same. Background art

[0004] Electroluminescent display devices are roughly classified into inorganic light - emitting display devices and organic light - emitting display devices according to the material of the light - emitting layer. An active - matrix organic light - emitting display device includes an organic light - emitting diode (hereinafter, referred to as "OLED") that emits light by itself, and has advantages such as a fast response speed, high luminous efficiency, high brightness, and a large viewing angle. In an organic light - emitting display device, a light - emitting diode (organic light - emitting diode, referred to as "OLED") is formed in each pixel. The organic light - emitting display device has a fast response speed, excellent luminous efficiency, brightness, and viewing angle, and has excellent contrast and color reproducibility because it can represent black gradation in pure black.

[0005] The organic light - emitting display device does not require a backlight unit and can be implemented on a plastic substrate, a thin glass substrate, or a metal substrate that is a flexible material.

[0006] When an OLED element is driven for a long time, its driving voltage increases due to the deterioration of the materials constituting the OLED element, which adversely affects the lifespan. Summary of the invention

[0007] The present disclosure aims to solve all of the above - mentioned needs and problems.

[0008] The present disclosure provides an OLED element and a display device using the same, in which the problems of deterioration of the OLED element and increase in its driving voltage are improved.

[0009] It should be noted that the object of the present disclosure is not limited to the above - mentioned object, and other objects of the present disclosure will be apparent to those skilled in the art according to the following description.

[0010] The OLED device of the present disclosure includes: a hole injection layer; a hole transport layer on the hole injection layer; a first light-emitting layer configured to generate light of short wavelengths in the visible light band, the first light-emitting layer being on the hole transport layer, wherein the OLED device further includes a light absorption layer, the light absorption layer being contained in the hole injection layer and / or the hole transport layer at the interface between the hole injection layer and the hole transport layer, and containing a phosphorescent dopant material added to one or more of the hole injection layer and the hole transport layer.

[0011] The display device of the present disclosure includes: a display panel in which pixels for displaying an input image are arranged; and a display panel driver configured to write pixel data of the input image to the pixels of the display panel. Each pixel includes the OLED device.

[0012] The present disclosure can generate triplet excitons at the interface between the hole injection layer and the hole transport layer by adding a material that absorbs light of short wavelengths in the visible light band to at least one of the hole injection layer and the hole transport layer, and can cause the combination of holes and triplet excitons using the material.

[0013] The present disclosure can prevent the deterioration of the interface between the hole injection layer and the hole transport layer when driving an organic light-emitting diode, thereby minimizing an increase in the driving voltage and improving the lifespan and stability of the device when driving the organic light-emitting diode for a long time.

[0014] The effects that can be achieved by the present disclosure are not limited to the above effects. That is, based on the following description, those skilled in the art to which the present disclosure pertains can clearly understand other effects not mentioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By describing in detail exemplary embodiments of the present disclosure with reference to the drawings, the above and other objects, features, and advantages of the present disclosure will become more apparent to those of ordinary skill in the art, wherein:

[0016] Figure 1 is a cross-sectional view showing a cross-sectional structure of an OLED device according to an embodiment of the present disclosure;

[0017] Figure 2 is a view showing Figure 1 triplet-polaron annihilation occurring in the light absorption layer shown;

[0018] Figures 3A to 3C is a view showing Figure 1 the light-emitting layer of the OLED device shown;

[0019] Figures 4A to 4C is a view showing OLED devices used as test target samples in a comparative example and an embodiment;

[0020] Figure 5 It is a graph showing the luminance versus the external quantum efficiency in Comparative Example 1 and Embodiments 1-1 and 1-2;

[0021] Figure 6 It is a graph showing the peak wavelength in Comparative Example 1 and Embodiments 1-1 and 1-2;

[0022] Figure 7 It is a graph showing the change in the driving voltage according to the driving time in Comparative Example 1 and Embodiments 1-1 and 1-2;

[0023] Figures 8A to 8C It is a graph showing the structure of an OLED element having a three-stack structure used as a test target sample;

[0024] Figure 9 It shows Figures 8A to 8C a graph of the peak wavelength of the OLED element shown;

[0025] Figure 10 It is shown as Figures 8A to 8C a graph of the experimental result of the OLED element shown, where the driving voltage increases as the driving time elapses;

[0026] Figure 11 It is a block diagram showing a display device according to an embodiment of the present disclosure;

[0027] Figure 12 It is a block diagram showing an embodiment in which a display device according to an embodiment of the present disclosure is applied to a mobile device;

[0028] Figures 13 to 15 It is a circuit diagram showing various pixel circuits that can be used for the pixel circuit of the present disclosure; and

[0029] Figure 16 It shows the driving Figure 15 a waveform diagram of the method for the pixel circuit shown. Detailed Description

[0030] The advantages, features, and implementation methods of the present disclosure will be clarified by the following embodiments described with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed herein and can be implemented in various different forms. These embodiments are provided to make the disclosure of the present disclosure detailed and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that the scope of the present disclosure is defined by the claims.

[0031] The figures, dimensions, ratios, angles, quantities, etc. disclosed in the drawings used to describe the embodiments of the present disclosure are merely exemplary and are not limited to the matters shown in the present disclosure. Throughout the text, like reference numerals refer to like elements. In addition, when determining that a detailed description of well-known technologies may unnecessarily obscure the gist of the present disclosure, the detailed description of well-known technologies will be omitted.

[0032] Terms such as "comprising / including" and "having" used herein are intended to allow the addition of other elements, unless the term is used together with the term "only". Any reference to the singular may include the plural unless otherwise expressly stated.

[0033] Even if not expressly stated, components are construed to include a normal error range.

[0034] For the description of positional relationships, for example, when the positional relationship between two components is described as "on...", "above...", "below...", "adjacent to...", etc., unless the terms "immediately" or "directly" are used in the expression, one or more components may be inserted therebetween.

[0035] Although terms such as "first", "second", etc. may be used to describe multiple components, such components are not necessarily limited by the above terms. The above terms are only used to distinguish one component from another component.

[0036] For the description of time relationships, for example, when the time relationship is described as "after...", "subsequently", "then", "before...", etc., unless the terms "immediately" or "directly" are used in the expression, non-consecutive cases may be included.

[0037] The features of multiple embodiments of the present disclosure may be combined or combined with each other partially or wholly. These embodiments may cooperate and execute with each other in various ways technically, and may be carried out independently or in association with each other.

[0038] Hereinafter, multiple embodiments of the present disclosure will be described in detail with reference to the drawings.

[0039] Figure 1 is a cross-sectional view showing the cross-sectional structure of an OLED element according to an embodiment of the present disclosure. Figure 2 is shown in Figure 1 a diagram of triplet-polaron annihilation occurring in the light absorption layer shown. Figures 3A to 3C is shown Figure 1 a diagram of the light-emitting layer of the OLED element shown. In Figures 3A to 3C the light absorption layer ADL, the electron injection layer EIL, and the electron transport layer ETL are omitted.

[0040] Reference Figure 1 and Figure 2 , the OLED element includes at least a first stack and a second stack stacked between a cathode electrode CAT and an anode electrode ANO. The OLED element may have a structure of a first stack ST1, a second stack ST2, and a third stack ST3, but is not limited thereto. For example, the OLED element may be implemented with a two-stack structure without the third stack ST3.

[0041] An electron injection layer EIL and an electron transport layer ETL may be stacked between the third stack ST3 and the cathode electrode CAT. When the third stack ST3 does not exist, the electron injection layer EIL and the electron transport layer ETL may be stacked between the second stack ST2 and the cathode electrode CAT.

[0042] The anode electrode ANO may be formed of a transparent electrode material such as indium tin oxide (ITO), but is not limited thereto. As an example, the anode electrode ANO may be formed of a transparent conductive oxide (TCO) such as indium zinc oxide (IZO). The cathode electrode CAT may be formed of aluminum (Al), but is not limited thereto. For example, the cathode electrode CAT may be a semi-transparent electrode formed of magnesium-silver (Mg-Ag).

[0043] A driving voltage of the OLED element is applied to the cathode electrode CAT and the anode electrode ANO. The cathode electrode CAT may be a common electrode formed over the entire substrate of the display device. The anode electrode ANO is divided for each sub-pixel on the substrate of the display device, and different voltages may be applied to each sub-pixel according to the data voltage of the pixel data. When the voltage between the cathode electrode CAT and the anode electrode ANO is greater than or equal to the threshold voltage of the OLED element, the OLED element may emit light. The first stack to the third stack may include light-emitting layers having different peak wavelengths. When a driving voltage is applied to the OLED element, charges are injected into the light-emitting layer, and excitons are formed by the combination of electrons and holes in the light-emitting layer, and then annihilate while emitting light of a wavelength determined by the material of the light-emitting layer.

[0044] The stacking structures of the first stack ST1, the second stack ST2, and the third stack ST3 may include a variety of light-emitting materials having different photoluminescence peaks to emit white light. In order to emit visible light of different wavelengths in the sub-pixels of the display device, a color filter layer or a color conversion layer may be provided above the cathode electrode CAT or below the anode electrode ANO.

[0045] The first stack ST1 is arranged to be closest to the anode electrode ANO. The first stack ST1 includes a hole injection layer HIL, a light absorption layer (absorbing dopant material layer) ADL, a hole transport layer HTL, and a first light-emitting layer (blue light-emitting material layer) B-EML1. The first light-emitting layer B-EML1 contains at least one host material and a dopant material for emitting blue light, and emits blue light when a driving voltage is applied to the OLED element. The peak wavelength of the light emitted from the first stack ST1 may be from 430 nm to 480 nm.

[0046] The light absorption layer ADL is formed by adding a phosphorescent dopant material to at least one of the hole injection layer HIL and the hole transport layer HTL at the interface between the hole injection layer HIL and the hole transport layer HTL. As Figure 2 shown, when driving the OLED element, the light absorption layer ADL absorbs short-wavelength light in the visible light band to generate triplet excitons, and causes triplet-polaron annihilation in which holes and triplet excitons combine. As a result, the light absorption layer ADL prevents deterioration of the interface between the hole injection layer HIL and the hole transport layer HTL caused by hole accumulation, and minimizes an increase in the driving voltage required to drive the OLED element as the driving time of the OLED element elapses, thereby improving the problems of OLED element deterioration and driving voltage increase.

[0047] To realize the light absorption layer ADL, it is desirable that the phosphorescent dopant be a dopant material doped into the hole injection layer HIL or the hole transport layer HTL. When the hole injection layer HIL is made of a compound containing an inorganic material, it is difficult to generate triplet excitons even when a phosphorescent dopant is added. Therefore, when the hole injection layer HIL contains an inorganic material, it is preferable to dope the phosphorescent dopant into the hole transport layer HTL to realize the light absorption layer ADL. In particular, the phosphorescent dopant as a dopant material can be doped into the surface portion of one or more of the hole injection layer HIL and the hole transport layer HTL.

[0048] In the case of a fluorescent dopant, since the singlet exciton lifetime is short, the rate of intersystem crossing is reduced due to immediate light emission after absorption of light, resulting in a small hole annihilation effect. On the other hand, since the phosphorescent dopant contains triplet excitons, triplet-polaron annihilation occurs when it absorbs light. Therefore, when the phosphorescent dopant is included in the light absorption layer ADL, the hole annihilation effect at the interface between the hole injection layer HIL and the hole transport layer HTL can be improved.

[0049] In the case of a thermally activated delayed fluorescence (TADF) dopant, there is no hole annihilation effect. Phosphorescent dopant materials based on Ir or Pt can provide a hole annihilation effect in the light absorption layer ADL. As an example, an Ir-based red phosphorescent dopant material that can be used as the phosphorescent dopant in the light absorption layer ADL may include, but is not limited to, phosphorescent dopant materials such as Ir(piq)2(acac) (bis(1-phenylisoquinoline)acetylacetonatoiridium(III)) or Ir(piq)3 (tris(1-phenylisoquinoline)iridium(III)).

[0050] Although light can be generated when triplet excitons and holes combine in the light absorption layer ADL, experimental results show that there is no problem of image quality degradation caused by the light generated from the light absorption layer ADL by meeting the target values of white light in the color coordinates.

[0051] The hole injection layer HIL is provided on the anode electrode ANO and smoothly supplies holes from the anode electrode ANO to the first light-emitting layer B-EML1. The hole injection layer HIL may be formed of one or more selected from the following: MoO3, copper phthalocyanine (CuPc), poly(3,4)-ethylenedioxythiophene (PEDOT), polyaniline (PANI), and N,N-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine (NPD), but is not limited thereto.

[0052] The hole injection layer HIL may be formed of a composite in which an organic material and an inorganic material are mixed. The organic material may be rubrene, and the inorganic material may be magnesium fluoride (MgF2). In this case, even if a phosphorescent dopant material is doped in the hole injection layer HIL, it is difficult to generate triplet excitons. Therefore, it is preferable to dope the phosphorescent dopant material into the organic material (host material) of the hole transport layer HTL made only of an organic material for realizing the light absorption layer ADL.

[0053] The hole transport layer HTL is provided above the hole injection layer HIL and smoothly transports the holes that move to the first light-emitting layer B-EML1. The hole transport layer HTL may be a single layer having a hybrid structure including two types of materials with different properties (for example, a first material and a second material). A phosphorescent dopant material may be doped into the hole transport layer HTL for realizing the light absorption layer ADL.

[0054] The first material of the hole transport layer HTL can be selected as a material with a hole mobility higher than that of the second material to improve the hole transfer to the first light-emitting layer B-EML1. The first material can include at least any one of the following: N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine (α-NPD), 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine (TPD), tetra-N-phenylbenzidine (TPB), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), m-TPEE, fluorinated triphenyl diamine (FTPD), TRP, p-phenylenediamine (PPD), or OPT1. m-TPEE can be a compound represented by Chemical Formula 1 below. TRP can be a compound represented by Chemical Formula 2. OTP1 can be a compound represented by Chemical Formula 3.

[0055] [Chemical Formula 1]

[0056]

[0057] [Chemical Formula 2]

[0058]

[0059] [Chemical Formula 3]

[0060]

[0061] The second material of the hole transport layer HTL can be a material with a triplet energy level higher than that of the first material to reduce the diffusion of electrons from the first light-emitting layer B-EML1. In addition, the second material of the hole transport layer HTL can be a material with a highest occupied molecular orbital (HOMO) energy level lower than that of the first material to minimize the accumulation of holes at the interface between the hole transport layer HTL and the first light-emitting layer B-EML1. In addition, the second material can be a material with high thermal stability to improve the durability of the hole transport layer. The second material can be an organic compound containing a spirofluorene group.

[0062] When the hole transport layer HTL is configured as a hybrid structure, the transfer of holes from the hole transport layer HTL to the first light-emitting layer B-EML1 can be improved, while the transfer of electrons from the first light-emitting layer B-EML1 to the hole transport layer HTL can be reduced, thereby obtaining the effects of improving the driving voltage, luminous efficiency, and lifetime.

[0063] Referring to Figure 1 and Figures 3A to 3C , the second stack ST2 is disposed between the first stack ST1 and the third stack ST3.

[0064] The first stack ST1 includes a hole injection layer HIL disposed on the anode electrode ANO, a hole transport layer HTL disposed above the hole injection layer HIL, a first light-emitting layer B-EML1 disposed on the hole transport layer HTL and emitting light with a peak wavelength in the range of 430 nm to 480 nm, and a light absorption layer ADL disposed at the interface between the hole injection layer HIL and the hole transport layer HTL and containing a phosphorescent dopant material added to at least one of the hole injection layer HIL and the hole transport layer HTL. The light absorption layer ADL can absorb light from the first light-emitting layer B-EML1 using the phosphorescent dopant to emit light with a wavelength of 550 nm or greater within the visible light band.

[0065] The second stack ST2 is disposed between the cathode electrode CAT and the first stack ST1, and may include at least one second light-emitting layer that emits light with a wavelength longer than the wavelength of the light emitted from the first light-emitting layer B-EML1.

[0066] The third stack ST3 is disposed between the cathode electrode CAT and the second stack ST2, and may include a third light-emitting layer B-EML2 that emits light with a wavelength substantially the same as the wavelength of the light emitted from the first light-emitting layer B-EML1.

[0067] The second light-emitting layer emits light with a wavelength different from the wavelength of the light emitted from the first light-emitting layer B-EML1. The second light-emitting layer may include one or more light-emitting layers, or may include two or more light-emitting layers having different peak wavelengths. For example, as Figure 3A shown, the second light-emitting layer according to one embodiment may have a structure in which a first red light-emitting layer R-EML containing at least one host material and a dopant for emitting red light, and a second yellow-green light-emitting layer YG-EML containing at least one host material and a dopant for emitting yellow-green light are stacked. The peak wavelength of the light emitted from the first red light-emitting layer R-EML may be 600 nm to 650 nm. The peak wavelength of the light emitted from the second yellow-green light-emitting layer YG-EML may be 510 nm to 580 nm.

[0068] As Figure 3B shown, the second light-emitting layer according to another embodiment may have a structure in which a first red light-emitting layer R-EML containing at least one host material and a dopant for emitting red light, and a second green light-emitting layer G-EML containing at least one host material and a dopant for emitting green light are stacked. The peak wavelength of the light emitted from the second green light-emitting layer G-EML may be 500 nm to 570 nm.

[0069] As Figure 3CAs shown, the second light-emitting layer according to yet another embodiment may have a structure in which a first red light-emitting layer R-EML containing at least one host material and a dopant for emitting red light, a second yellow-green light-emitting layer YG-EML containing at least one host material and a dopant for emitting yellow-green light, and a third green light-emitting layer G-EML containing at least one host material and a dopant for emitting green light are stacked.

[0070] The first stack ST1 may further include a second electron transport layer disposed on the first light-emitting layer B-EML1. The second stack ST2 may further include a second hole transport layer disposed below the second light-emitting layer. The second electron transport layer and the second hole transport layer are omitted in the figure.

[0071] A first charge generation layer CGL1 may be disposed between the first stack ST1 and the second stack ST2. The first charge generation layer CGL1 may be divided into an n-type charge generation layer (nCGL) and a p-type charge generation layer (pCGL). The n-type charge generation layer may be disposed on the second electron transport layer. The p-type charge generation layer may be disposed between the n-type charge generation layer and the second hole transport layer.

[0072] The third stack ST3 may include a third light-emitting layer B-EML2. The third light-emitting layer B-EML2 emits blue light by including at least one host material and a dopant material for emitting blue light. The peak wavelength of the light emitted from the third stack ST3 may be 430 nm to 480 nm. The third stack ST3 may improve the efficiency of the blue light-emitting layer having a relatively low efficiency.

[0073] As Figure 1 shown, an electron injection layer EIL and an electron transport layer ETL may be stacked between the third stack ST3 and the cathode electrode CAT. The electron injection layer EIL is disposed between the cathode electrode CAT and the electron transport layer ETL. The electron transport layer ETL is disposed between the electron injection layer EIL and the third stack ST3. In the absence of the third stack ST3, the electron transport layer ETL may be disposed between the electron injection layer EIL and the second stack ST2.

[0074] The second stack ST2 may further include a third electron transport layer disposed on the second light-emitting layer. The third stack ST3 may further include a third hole transport layer disposed below the third light-emitting layer B-EML2. The third electron transport layer and the third hole transport layer are omitted in the figure.

[0075] A second charge generation layer CGL2 may be provided between the second stack ST2 and the third stack ST3. The second charge generation layer CGL2 may be divided into an n-type charge generation layer and a p-type charge generation layer. The n-type charge generation layer may be provided on the third electron transport layer. The p-type charge generation layer may be provided between the n-type charge generation layer and the third hole transport layer.

[0076] As the host material of the light-emitting layer emitting red light, the h-host may be selected as DNTPD, and the e-host may be selected as DCzTrz. The dopant material of the light-emitting layer emitting red light may include one or more phosphorescent materials selected from Ir(piq)2(acac) (bis(1-phenylisoquinoline)acetylacetonatoiridium(III)) and Ir(piq)3 (tris(1-phenylisoquinoline)iridium(III)).

[0077] As the host material of the light-emitting layer emitting green light, the h-host may be selected as CBP, and the e-host may be selected as TPBI (1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene). The dopant material of the light-emitting layer emitting green light may be selected as Ir(ppy)3.

[0078] The host material of the light-emitting layer emitting blue light may be selected as 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN). The dopant material of the light-emitting layer emitting blue light may be selected as a boron-based blue fluorescent dopant, such as 5,9-diphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (DABNA-1).

[0079] The light absorption layer ADL absorbs short-wavelength light in the visible light wavelength band to prevent deterioration of the interface between the hole injection layer HIL and the hole transport layer HTL during long-term driving of the OLED element, thereby minimizing an increase in the driving voltage of the OLED element. The conditions of the light absorption layer ADL capable of obtaining such an effect are as follows.

[0080] The triplet energy level T1 of the light absorption layer ADL may be 2.5 eV ≥ T1 ≥ 2.0 eV, that is, 2.0 eV to 2.5 eV. The highest occupied molecular orbital (HOMO) of the light absorption layer ADL is equal to or less than the highest occupied molecular orbital (HOMO) of the hole transport layer HTL so as not to interfere with the flow of holes. The light absorption spectrum of the light absorption layer ADL is short wavelength in the visible light wavelength band, such as 530 nm or less. The peak spectrum of the light emitted from the light absorption layer ADL is a wavelength of 550 nm or more.

[0081] The thickness of the light absorption layer ADL may be set in to (or 5 nm to 30 nm). If the thickness of the light absorption layer ADL is less than (or 5 nm), since the photoabsorption layer ADL is too thin, the triplet-polaron annihilation effect at the interface between the hole injection layer HIL and the hole transport layer HTL is small. If the thickness of the photoabsorption layer ADL is greater than (or 30 nm), the blue light emitted from the first light-emitting layer B-EML1 may be lost.

[0082] In the photoabsorption layer ADL, the concentration of the phosphorescent dopant material doped into the host material can be 0.1% to 15%. Here, the concentration (%) is the weight percentage (wt%). Hereinafter, the concentration (%) is wt%. If the doping concentration is lower than 0.1%, the amount of the phosphorescent dopant in the photoabsorption layer ADL is insufficient, so that the triplet-polaron annihilation effect is greatly reduced. If the doping concentration is higher than 15%, the holes move to the phosphorescent dopant material instead of the hole transport layer HTL, so that the electrical characteristics of the OLED element may be changed and the triplet-polaron annihilation effect is reduced.

[0083] It should be noted that the present disclosure is not limited to the above OLED structure. For example, a structure in which a blue light-emitting layer B-EML1 is provided in the second stack ST2 and light-emitting layers of different colors are provided in the first stack ST1 is also within the scope of the present disclosure.

[0084] The inventors of the present disclosure conducted various experiments (see Figures 4A to 10 ) to verify the effects of the present disclosure.

[0085] Figures 4A to 4C Samples of simple OLED elements having a single-stack structure including a single light-emitting layer are shown. Figures 8A to 8C Samples of OLED elements having a three-stack structure including a plurality of light-emitting layers are shown. In the OLED element samples used in the experiments, the anode electrode ANO, the hole injection layer HIL, the hole transport layer HTL, the electron (or exciton) blocking layer EBL, the light-emitting layers B-EML, R-EML, and G-EML, the electron transport layer ETL, the charge generation layer CGL, the electron transport layer ETL, the electron injection layer EIL, and the cathode electrode CAT are formed as follows, respectively.

[0086] In Figures 4A to 4C and Figures 8A to 8C In the OLED element shown, the anode electrode ANO is formed of ITO having a thickness of . The hole injection layer HIL provided on the anode electrode ANO is a composite in which NPD and MgF2 are mixed at a composition ratio of 1:1 and has a thickness. The hole transport layer HTL provided on the hole injection layer HIL is formed of m-TPEE and has a Thickness.

[0087] An electron blocking layer EBL is provided between the hole transport layer HTL and the blue emission layer B-EML1. The electron blocking layer EBL is formed of α-NPD and has a thickness. The blue emission layer B-EML1 is formed by doping MADN with 4 wt% of DABNA-1 and has a thickness. The electron transport layer ETL provided on the blue emission layer B-EML1 is formed of 2-[4-(9,10-di-naphthalen-2-yl-anthracen-2-yl)phenyl]-1-phenyl-1H-benzoimidazole (ZADN) and has a thickness.

[0088] In the first charge generation layer CGLl, the nCGL is formed by doping bathophenanthroline (Bphen) with 1 wt% of Li and has a thickness. The pCGL is formed by doping NPD with 10 wt% of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN) and has a thickness.

[0089] The hole transport layer HTL between the first charge generation layer CGL1 and the red emission layer R-EML is formed of m-TPEE and has a thickness.

[0090] The red emission layer R-EML is formed of a composite in which DPTPD and DCzTrz are mixed at a composition ratio of 1:1, doped with 2 wt% of Ir(piq)2acac, and has a thickness. The green emission layer G-EML is formed of a composite in which CBP and TPBI are mixed at a composition ratio of 1:1, doped with 8 wt% of Ir(ppy)3, and has a thickness.

[0091] The electron transport layer ETL between the green emission layer G-EML and the second charge generation layer CGL2 is formed of ZADN and has a thickness.

[0092] In the second charge generation layer CGL2, the nCGL is formed by doping bathophenanthroline (Bphen) with 1 wt% of Li and has a thickness. The pCGL is formed by doping NPD with 10 wt% of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN) and has a thickness. The hole transport layer HTL on the pCGL is formed of m-TPEE and has The thickness of

[0093] An electron blocking layer EBL is provided between the hole transport layer HTL and the blue emitting layer B-EML2. The electron blocking layer EBL is formed of α-NPD and has The thickness of

[0094] The blue emitting layer B-EML2 is formed by doping MADN with 4 wt% of DABNA-1 and has The thickness of

[0095] The cathode electrode CAT is formed of Al with a thickness of The electron transport layer ETL below the cathode electrode CAT is formed of ZADN and has The thickness of. The electron injection layer EIL provided between the cathode electrode CAT and the electron transport layer ETL is formed of LiF and has The thickness of

[0096] Figures 4A to 4C Shows OLED elements used as test target samples in the comparative examples and the embodiments. In Figures 4A to 4C , an OLED element having only the first stack ST1 without the second stack ST2 and the third stack ST3 is realized. Figure 4A Shows the structure of the OLED element without the light absorption layer ADL in Comparative Example 1. Figure 4B The OLED element of Embodiment 1-1 shown includes a light absorption layer ADL in which 5% of a red phosphorescent dopant is doped in the hole transport layer HTL at the interface between the hole injection layer HIL and the hole transport layer HTL. Figure 4C The OLED element of Embodiment 1-2 shown includes a light absorption layer ADL in which 10% of a red phosphorescent dopant is doped in the hole transport layer HTL at the interface between the hole injection layer HIL and the hole transport layer HTL.

[0097] In Figure 4A shown in Comparative Example 1, the hole transport layer HTL is an organic material with a thickness of . In Figure 4B and Figure 4C shown in the embodiments, the hole transport layer HTL is an organic material with a thickness of . In Figure 4B and Figure 4C , a light absorption layer ADL is provided between the hole injection layer HIL and the hole transport layer HTL. The sum of the thickness of the hole transport layer HTL and the thickness of the light absorption layer ADL is which is the same as the thickness of the hole transport layer HTL in Comparative Example 1.

[0098] In Figure 4B Embodiment 1-1 shown, the light absorption layer ADL is formed between the hole injection layer HIL and the hole transport layer HTL, and contains a red phosphorescent dopant added at 5% to the host material of the hole transport layer HTL. In Figure 4C Embodiment 1-2 shown, the light absorption layer ADL is formed between the hole injection layer HIL and the hole transport layer HTL, and contains a red phosphorescent dopant added at 10% to the host material of the hole transport layer HTL. In Figure 4B and Figure 4C the thickness of the light absorption layer ADL is i.e., 15 nm. In this experiment, the driving voltage (V), current efficiency (cd / A), and external quantum efficiency (EQE) in Comparative Example 1 and Embodiments 1-1 and 1-2 were obtained as the results shown in Table 1.

[0099] [Table 1]

[0100]

[0101] In Table 1, "RD" is the red phosphorescent dopant. The lower the driving voltage (V) of the OLED element and the higher the current efficiency (cd / A) and external quantum efficiency (EQE), the higher the brightness can be obtained with less energy.

[0102] Figure 5 show the experimental results of the brightness (Cd / m 2 ) versus the external quantum efficiency (EQE) in Comparative Example 1 and Embodiments 1-1 and 1-2. Figure 6 show the experimental results of the peak wavelength (465 nm) in Comparative Example 1 and Embodiments 1-1 and 1-2. Figure 7 show the experimental results of the change (ΔV) in the driving voltage with the driving time (hours) in Comparative Example 1 and Embodiments 1-1 and 1-2. As can be seen in Figure 6 and Figure 7 in Comparative Example 1 and Embodiments 1-1 and 1-2, the intensity is at the same level at the peak wavelength, and compared with Comparative Example 1, in Embodiments 1-1 and 1-2, the problem of the increase in the driving voltage is improved by reducing the rising amplitude of the driving voltage with the passage of the driving time.

[0103] Figures 8A to 8C is a diagram showing the structure of an OLED element having a triple-stack structure used as a test target sample. Figure 8A shows the structure of the OLED element without the light absorption layer ADL in Comparative Example 2. Figure 8BThe OLED element of Embodiment 2-1 shown includes a light absorption layer ADL in which a red phosphorescent dopant is doped into the hole transport layer HTL at 5% at the interface between the hole injection layer HIL and the hole transport layer HTL. Figure 8C The OLED element of Embodiment 2-2 shown includes a light absorption layer ADL in which a red phosphorescent dopant is doped into the hole transport layer HTL at 10% at the interface between the hole injection layer HIL and the hole transport layer HTL.

[0104] In Figures 8A to 8C , the basic structure of the OLED element used as a test target sample is substantially the same as Figure 3B . In this experiment, the driving voltage (V), current efficiency (cd / A), external quantum efficiency (EQE), and color coordinate values (CIEx, CIEy) in Comparative Example 2 and Embodiments 2-1 and 2-2 were obtained as the results shown in Table 2.

[0105] [Table 2]

[0106]

[0107] As Figure 9 shown, in Comparative Example 2 and Embodiments 2-1 and 2-2, Figures 8A to 8C the peak wavelengths and corresponding intensities in the wavelength spectra of the OLED elements shown are substantially the same. As can be seen from Figure 10 the experimental results, compared with Comparative Example 2, in Embodiments 2-1 and 2-2, the rising amplitude of the driving voltage as the driving time elapses decreases, and thus, the lifetime of the OLED element is improved.

[0108] The OLED element of the present disclosure can be implemented as a pixel of a display device. The pixel circuit includes: an OLED element; a driving element that drives the OLED element by controlling the current flowing through the OLED element according to the gate-source voltage Vgs; one or more switching elements that switch the voltages required to drive the OLED element and the driving element; a storage capacitor that stores the gate voltage of the driving element; and so on. The driving element and the switching element can be implemented as transistors.

[0109] The transistors of the pixel circuit can be implemented as oxide thin film transistors (TFTs) including an oxide semiconductor, LTPS TFTs including low-temperature polycrystalline silicon (LTPS), etc. In addition, each transistor can be implemented as a p-channel TFT or an n-channel TFT. In one embodiment, an example in which the transistors of the pixel circuit are implemented as p-channel TFTs will be mainly described, but the present disclosure is not limited thereto.

[0110] A transistor is a three - electrode device including a gate, a source, and a drain. The source is the electrode that supplies carriers to the transistor. In a transistor, carriers start flowing from the source. The drain is the electrode through which carriers leave the transistor. In a transistor, carriers flow from the source to the drain. In the case of an n - channel transistor, since the carriers are electrons, the source voltage is lower than the drain voltage, enabling electrons to flow from the source to the drain. In an n - channel transistor, current flows from the drain to the source. In the case of a p - channel transistor (PMOS), since the carriers are holes, the source voltage is higher than the drain voltage, enabling holes to flow from the source to the drain. In a p - channel transistor, since holes flow from the source to the drain, current flows from the source to the drain. It should be noted that the source and drain of a transistor are not fixed. For example, the source and drain can be switched according to the applied voltage. Therefore, the present disclosure is not limited by the source and drain of the transistor. In the following description, the source and drain of the transistor will be referred to as the first electrode and the second electrode.

[0111] The gate signal swings between a gate - on voltage and a gate - off voltage. The gate - on voltage is set to be higher than the threshold voltage of the transistor, and the gate - off voltage is set to be lower than the threshold voltage of the transistor. The transistor conducts in response to the gate - on voltage and turns off in response to the gate - off voltage. In the case of an n - channel transistor, the gate - on voltage can be the gate - high voltage VGH, and the gate - off voltage can be the gate - low voltage VGL. In the case of a p - channel transistor, the gate - on voltage can be the gate - low voltage VGL, and the gate - off voltage can be the gate - high voltage VGH.

[0112] The driving elements of a pixel circuit need to have uniform electrical characteristics in all pixels. However, due to element characteristic deviations and process deviations caused during the manufacturing process of the display panel, there may be differences in the electrical characteristics of the driving elements between pixels, and as the driving time of the pixels elapses, these differences may further increase. To compensate for the deviations in the electrical characteristics of the driving elements between pixels, an internal compensation technique or an external compensation technique can be applied to the display device.

[0113] The internal compensation technique uses an internal compensation circuit embedded in each pixel to sense the threshold voltage of the driving element of each sub - pixel and compensates the gate - source voltage Vgs of the driving element through this threshold voltage. The external compensation technique uses an external compensation circuit to sense in real - time the current or voltage of the driving element that varies according to the electrical characteristics of the driving element. In the external compensation technique, the pixel data (digital data) of the input image is modulated by as much as the deviation (or change) in the electrical characteristics of the driving element sensed for each pixel to compensate in real - time for the deviation (or change) in the electrical characteristics of the driving element in each pixel.

[0114] Refer to Figure 11 andFigure 12 , a display device according to an embodiment of the present disclosure includes a display panel 100, a display panel driver for writing pixel data of an input image into pixels P of the display panel 100, a timing controller 130 for controlling the display panel driver, and a power supply unit 150 for generating power required to drive the display panel 100.

[0115] The display panel 100 includes a pixel array AA that displays an input image on the screen. Each pixel P of the pixel array AA includes sub-pixels having different colors for color reproduction. The sub-pixels include a red sub-pixel (hereinafter referred to as "R sub-pixel"), a green sub-pixel (hereinafter referred to as "G sub-pixel"), and a blue sub-pixel (hereinafter referred to as "B sub-pixel"). Although not shown, each pixel P may further include a white sub-pixel (hereinafter referred to as "W sub-pixel"). Hereinafter, a "pixel" or a "dot" may be interpreted as a sub-pixel.

[0116] At least one color of the sub-pixels may include an OLED element having the above-described light absorption layer ADL. In addition, the OLED elements of the sub-pixels may be implemented in at least a two-stack structure or a series structure as shown in Figures 3A to 3C to generate white light. In this case, a color filter layer or a color conversion layer may be provided in the red sub-pixel, the green sub-pixel, and the blue sub-pixel. The pixel circuit of the sub-pixel may be implemented as the pixel circuit shown in Figures 13 to 15 , but is not limited thereto.

[0117] A touch sensor may be provided on the screen of the display panel 100. The touch sensor may be arranged on the screen of the display panel in an on-cell type or an add-on type, or may be implemented as an in-cell type touch sensor embedded in the pixel array.

[0118] The display panel 100 may be implemented as a flexible display panel in which pixels P are provided on a flexible substrate such as a plastic substrate or a metal substrate. In a flexible display, the size and shape of the screen may be changed by winding, folding, or bending the flexible display panel. The flexible display may include a slidable display, a rollable display, a bendable display, a foldable display, etc.

[0119] The display panel driver reproduces an input image on the screen of the display panel 100 by writing pixel data of the input image into pixels P. The display panel driver includes a data driver 110 and a gate driver 120. The display panel driver may further include a demultiplexer 112 provided between the data driver 110 and the data line DL.

[0120] The data driver 110 uses a digital-to-analog converter (hereinafter referred to as "DAC") to convert the pixel data of the input image, which is digital data, into a gamma-compensated voltage to generate a data voltage Vdata. The data driver 110 may include a voltage divider circuit that outputs the gamma-compensated voltage. The voltage divider circuit divides the gamma reference voltage from the power supply unit 150 to generate a gamma-compensated voltage for each gray level and supplies it to the DAC. The DAC may convert the pixel data into a gamma-compensated voltage and output the data voltage. The data voltage output from the channel of the data driver 110 may be supplied to the data line DL of the display panel 100 through the demultiplexer 112.

[0121] The demultiplexer 112 time-division multiplexes and distributes the data voltage Vdata output through the channel of the data driver 110 to multiple data lines DL. Due to the demultiplexer 112, the number of channels of the data driver 110 can be reduced. The demultiplexer 112 may be omitted. In this case, the channels of the data driver 110 are directly connected to the data line DL.

[0122] The gate driver 120 may be implemented as an in-panel gate (GIP) circuit formed directly on the border area BZ of the display panel 100 together with the TFT array of the pixel array AA. The gate driver 120 outputs a gate signal to the gate line GL under the control of the timing controller 130. The gate driver 120 may use a shift register to shift the gate signal to sequentially supply the signal to the gate line GL. The voltage of the gate signal swings between a gate cut-off voltage and a gate on-voltage. The gate signal may include Figure 16 the scan pulse, EM pulse, sense pulse, etc. shown in

[0123] The gate driver 120 may be provided on each of the left and right borders of the display panel 100 to supply the gate signal to the gate line GL by a dual-feed method. In the dual-feed method, the gate drivers 120 on both sides are synchronized so that the gate signal can be applied simultaneously to both ends of a gate line. In another embodiment, the gate driver 120 may be provided on one of the left and right borders of the display panel 100 to supply the gate signal to the gate line GL by a single-feed method.

[0124] The gate driver 120 may include a first gate driver 121 and a second gate driver 122. The first gate driver 121 outputs a scan pulse and a sense pulse and shifts the scan pulse and the sense pulse according to a shift clock. The second gate driver 122 outputs an EM pulse and shifts the EM pulse according to a shift clock. In the case of a model without a border, at least some of the switching elements constituting the first gate driver 121 and the second gate driver 122 may be distributed in the pixel array.

[0125] The timing controller 130 receives pixel data of an input image and a timing signal synchronized with the pixel data from a host system. The timing signal includes a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a clock CLK, a data enable signal DE, etc. One cycle of the vertical synchronization signal Vsync is one frame period. One cycle of the horizontal synchronization signal Hsync and the data enable signal DE is one horizontal period (1H). Pulses of the data enable signal DE are synchronized with a row of data of pixels P to be written to one pixel line. Since the frame period and the horizontal period can be known by counting the data enable signal DE, the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync can be omitted. The timing controller 130 controls the operation timings of the data driver 110, the demultiplexer 112, and the gate driver 120 based on the timing signals Vsync, Hsync, and DE received from the host system.

[0126] The timing controller 130 transmits the pixel data of the input image to the data driver 110 and synchronizes the data driver 110, the demultiplexer 112, and the gate driver 120. The timing controller 130 may include a data operation unit that modulates the pixel data by receiving sensed data obtained from the pixels P in a display panel driver to which an external compensation technique is applied. In this case, the timing controller 130 transmits the pixel data modulated by the data operation unit to the data driver 110.

[0127] The power supply unit 150 may include a charge pump, a regulator, a buck converter, a boost converter, a programmable gamma IC (P-GMA IC), etc. The power supply unit 150 generates the power required to drive the display panel driver and the display panel 100 by regulating the DC input voltage from the host system. The power supply unit 150 may output DC voltages, such as a gamma reference voltage, a gate cut-off voltage VGH / VEH, a gate on voltage VGL / VEL, a pixel driving voltage ELVDD, a low-potential source voltage ELVSS, an initialization voltage Vini, a reference voltage VREF, etc. The programmable gamma IC may change the gamma reference voltage according to register settings. The gamma reference voltage is supplied to the data driver 110. The gate cut-off voltage VGH / VEH and the gate on voltage VGL / VEL are supplied to the level shifter and the gate driver 120. The pixel driving voltage ELVDD, the low-potential source voltage ELVSS, the initialization voltage Vini, and the reference voltage VREF are commonly supplied to the pixel circuit through power lines. The pixel driving voltage ELVDD is set to be higher than the low-potential source voltage ELVSS, the initialization voltage Vini, and the reference voltage VREF.

[0128] The host system can be the main circuit board of a television (TV) system, a set-top box, a navigation system, a personal computer (PC), a vehicle system, a home theater system, a mobile device, or a wearable device. In a mobile device or a wearable device, as Figure 12 shown, the timing controller 130, the data driver 110, and the power supply unit 150 can be integrated into one driving integrated circuit (D-IC). In Figure 12 , the reference numeral “200” represents the host system.

[0129] Figures 13 to 15 is a circuit diagram showing various pixel circuits that can be used in the present disclosure.

[0130] Referring to Figure 13 , the pixel circuit includes an OLED element EL, a driving element DT that supplies current to the OLED element EL, a switching element M01 that connects to a data line DL responsive to a scan pulse SCAN, and a capacitor Cst that connects to the gate of the driving element DT. The driving element DT and the switching element M01 can be implemented with n-channel transistors.

[0131] A pixel driving voltage ELVDD is applied to a first electrode of the driving element DT through a power line PL. The driving element DT drives the OLED element EL by supplying current to the OLED element EL according to a gate-source voltage Vgs. When the forward voltage between the anode electrode and the cathode electrode is greater than or equal to the threshold voltage, the OLED element EL conducts and emits light. The capacitor Cst is connected between the gate electrode and the source electrode of the driving element DT to maintain the gate-source voltage Vgs of the driving element DT.

[0132] Figure 14 is an example of a pixel circuit connected to an external compensation circuit.

[0133] Referring to Figure 14 , the pixel circuit further includes a second switching element M02 connected between a reference voltage line REFL and a second electrode (or source) of the driving element DT. In this pixel circuit, the driving element DT and the switching elements M01 and M02 can be implemented with n-channel transistors.

[0134] The second switching element M02 applies a reference voltage VREF responsive to a scan pulse SCAN or a separate sense pulse SENSE. The reference voltage VREF is applied to the pixel circuit through the reference voltage line REFL.

[0135] In the sensing mode, the current flowing through the channel of the driving element DT or the voltage between the driving element DT and the OLED element EL is sensed through the reference voltage line REFL. The current flowing through the reference voltage line REFL is converted into a voltage by an integrator and then converted into digital data by an analog-to-digital converter (ADC). The digital data is sensing data containing information about the mobility or threshold voltage of the driving element DT. The sensing data is transmitted to the data operation unit of the timing controller 130. The data operation unit may receive the sensing data from the ADC and add or multiply a compensation value selected based on the sensing data to the pixel data to compensate for the driving deviation and degradation of the pixel.

[0136] Figure 15 FIG. is a circuit diagram showing an example of a pixel circuit to which an internal compensation circuit is applied. Figure 16 FIG. shows the driving Figure 15 FIG. is a waveform diagram showing a method of driving the Figure 16 In FIG., "DTG" is the gate voltage of the driving element DT, that is, Figure 15 the voltage of the second node n2 shown in FIG.

[0137] Referring to Figure 15 and Figure 16 FIG., the pixel circuit includes an OLED element EL, a driving element DT that supplies current to the OLED element EL, and a switching circuit that switches the voltages applied to the OLED element EL and the driving element DT.

[0138] The switching circuit is connected to power supply lines PL1, PL2, and PL3 to which a pixel driving voltage ELVDD, an initialization voltage Vini, and a low-potential source voltage ELVSS are applied; a data line DL; and gate lines GL1, GL2, and GL3, and switches the voltages applied to the OLED element EL and the driving element DT in response to scan pulses SCAN(N-1), SCAN(N), and EM pulse EM(N).

[0139] The switching circuit samples the threshold voltage Vth of the driving element DT using a plurality of switching elements M1 to M6 and stores it in the capacitor Cst1. The switching circuit includes an internal compensation circuit that compensates the gate voltage of the driving element DT through the threshold voltage Vth of the driving element DT. Each of the driving element DT and the switching elements M1 to M6 can be implemented by a p-channel TFT.

[0140] As Figure 16 shown in Figure 15 FIG., the driving period of the pixel circuit shown in

[0141] In a sampling period Tsam, the N-th scan pulse SCAN(N) is generated as a gate-on voltage VGL and applied to a first gate line GL1. In an initialization period Tini before the sampling period, the (N-1)-th scan pulse SCAN(N-1) is generated as a gate-on voltage VGL and applied to a second gate line GL2. During the initialization period Tini and the sampling period Tsam, an EM pulse EM(N) is generated as a gate-off voltage VGH and applied to a third gate line GL3.

[0142] During the initialization period Tini, the (N-1)-th scan pulse SCAN(N-1) is generated as a gate-on voltage VGL, and the voltage of each of the N-th scan pulse SCAN(N) and the EM pulse EM(N) is a gate-off voltage VGH. During the sampling period Tsam, the N-th scan pulse SCAN(N) is generated as a pulse of a gate-on voltage VGL, and the voltage of each of the (N-1)-th scan pulse SCAN(N-1) and the EM pulse EM(N) is a gate-off voltage VGH. During at least a part of a light-emitting period Tem, the EM pulse EM(N) is generated as a gate-on voltage VGL, and the voltage of each of the (N-1)-th scan pulse SCAN(N-1) and the N-th scan pulse SCAN(N) is generated as a gate-off voltage VGH.

[0143] During the initialization period Tini, a fifth switching element M5 is turned on according to the gate-on voltage VGL of the (N-1)-th scan pulse SCAN(N-1) to initialize a pixel circuit. During the sampling period Tsam, a first switching element M1 and a second switching element M2 are turned on according to the gate-on voltage VGL of the N-th scan pulse SCAN(N), and a data voltage Vdata compensated by a threshold voltage of a driving element DT is stored in a capacitor Cst1. At the same time, a sixth switching element M6 is turned on during the sampling period Tsam to reduce the voltage of a fourth node n4 to a reference voltage VREF, thereby suppressing light emission of an OLED element EL.

[0144] During the light-emitting period Tem, a third switching element M3 and a fourth switching element M4 are turned on so that the OLED element EL emits light. During the light-emitting period Tem, in order to accurately express the luminance of a low gray level, the voltage level of the EM pulse EM(N) can be inverted between a gate-on voltage VGL and a gate-off voltage VGH at a predetermined duty ratio. In this case, during the light-emitting period Tem, the third switching element M3 and the fourth switching element M4 can be repeatedly turned on and off according to the duty ratio of the EM pulse EM(N).

[0145] The anode electrode of the OLED element EL is connected to the fourth node n4 between the fourth switching element M4 and the sixth switching element M6. The fourth node n4 is connected to the anode electrode of the OLED element EL, the second electrode of the fourth switching element M4, and the second electrode of the sixth switching element M6. The cathode electrode of the OLED element EL is connected to the VSS line PL3 to which a low-potential source voltage ELVSS is applied. The OLED element EL emits light by a current Ids flowing according to the gate-source voltage Vgs of the driving element DT. The current path of the OLED element EL is switched by the third switching element M3 and the fourth switching element M4.

[0146] The capacitor Cst1 is connected between the VDD line PL1 and the second node n2. The first switching element M1 is turned on in response to the gate conduction voltage VGL of the Nth scan pulse SCAN(N) to connect the second node n2 to the third node n3. Since the first switching element M1 is turned on for a very short horizontal period 1H (where the Nth scan pulse SCAN(N) is generated as the gate conduction voltage VGL in one frame period), a leakage current may be generated in the off state. To suppress the leakage current of the first switching element M1, the first switching element M1 can be implemented by a transistor having a double-gate structure in which two transistors are connected in series.

[0147] The second switching element M2 is turned on in response to the gate conduction voltage VGL of the Nth scan pulse SCAN(N) to supply the data voltage Vdata to the first node n1. The gate electrode of the second switching element M2 is connected to the first gate line GL1 to receive the Nth scan pulse SCAN(N). The third switching element M3 is turned on in response to the gate conduction voltage VGL of the EM pulse EM(N) to connect the VDD line PL1 to the first node n1. The gate electrode of the third switching element M3 is connected to the third gate line GL3 to receive the EM pulse EM(N).

[0148] The fourth switching element M4 is turned on in response to the gate conduction voltage VGL of the EM pulse EM(N) to connect the third node n3 to the anode electrode of the OLED element EL. The gate electrode of the fourth switching element M4 is connected to the third gate line GL3 to receive the EM pulse EM(N). The fifth switching element M5 is turned on in response to the gate conduction voltage VGL of the (N - 1)th scan pulse SCAN(N - 1) to connect the second node n2 to the Vini line PL2. The gate electrode of the fifth switching element M5 is connected to the second gate line GL2 to receive the (N - 1)th scan pulse SCAN(N - 1).

[0149] The sixth switching element M6 is turned on in response to the gate-on voltage VGL of the Nth scan pulse SCAN(N) to connect the Vini line PL2 to the fourth node n4. The gate electrode of the sixth switching element M6 is connected to the first gate line GL1 to receive the Nth scan pulse SCAN(N).

[0150] In another embodiment, the gate electrodes of the fifth switching element M5 and the sixth switching element M6 may be commonly connected to the second gate line GL2 to which the (N - 1)th scan pulse SCAN(N - 1) is applied. In this case, the fifth switching element M5 and the sixth switching element M6 may be turned on simultaneously in response to the (N - 1)th scan pulse SCAN(N - 1).

[0151] The driving element DT drives the OLED element EL by controlling the current flowing through the OLED element EL according to the gate-source voltage Vgs. The driving element DT includes a gate connected to the second node n2, a first electrode connected to the first node n1, and a second electrode connected to the third node n3.

[0152] Since the content of the present disclosure described in general terms does not specify the essential features of the claims, the scope of the claims is not limited to the matters described in the content of the present disclosure.

[0153] In particular, the present disclosure relates to the following embodiments:

[0154] 1. An organic light emitting diode, comprising:

[0155] A hole injection layer;

[0156] A hole transport layer on the hole injection layer;

[0157] A first light emitting layer configured to generate light having a short wavelength in the visible light band; and

[0158] A light absorption layer contained in the hole injection layer and / or the hole transport layer at an interface between the hole injection layer and the hole transport layer, and containing a phosphorescent dopant material added to one or more of the hole injection layer and the hole transport layer.

[0159] 2. The organic light emitting diode according to item 1, wherein the first light emitting layer emits blue light, and

[0160] The light absorption layer absorbs the blue light to generate triplet excitons bound to holes.

[0161] 3. The organic light emitting diode according to item 1, wherein the phosphorescent dopant material includes a red phosphorescent dopant material that generates red light.

[0162] 4. The organic light-emitting diode according to item 1, wherein the triplet energy level of the light absorption layer is 2.0 eV to 2.5 eV.

[0163] 5. The organic light-emitting diode according to item 4, wherein the highest occupied molecular orbital (HOMO) of the light absorption layer is equal to or less than the highest occupied molecular orbital (HOMO) of the hole transport layer.

[0164] 6. The organic light-emitting diode according to item 5, wherein the wavelength of the light absorbed by the light absorption layer is 530 nm or less in the visible light band, and

[0165] the peak wavelength of the light emitted from the light absorption layer is 550 nm or greater in the visible light band.

[0166] 7. The organic light-emitting diode according to item 4, wherein the thickness of the light absorption layer is 5 nm to 30 nm.

[0167] 8. The organic light-emitting diode according to item 7, wherein the concentration of the phosphorescent dopant material in the light absorption layer is 0.1 wt% to 15 wt%.

[0168] 9. The organic light-emitting diode according to item 8, wherein when the hole injection layer contains an inorganic material, the phosphorescent dopant material is added to the hole transport layer.

[0169] 10. The organic light-emitting diode according to item 1, further comprising:

[0170] a second stack disposed on the first light-emitting layer and including at least one second light-emitting layer that emits light having a wavelength different from the wavelength of the light emitted from the first light-emitting layer;

[0171] a third stack disposed on the second stack and including a third light-emitting layer that emits light having the same wavelength as the wavelength of the light emitted from the first light-emitting layer;

[0172] an electron injection layer disposed between the third light-emitting layer and the cathode electrode; and

[0173] an electron transport layer disposed between the electron injection layer and the third light-emitting layer.

[0174] 11. The organic light-emitting diode according to item 10, wherein the second light-emitting layer includes:

[0175] a first red light-emitting layer that emits red light; and

[0176] a second yellow-green light-emitting layer that emits yellow-green light.

[0177] 12. The organic light emitting diode according to item 10, wherein the second light emitting layer comprises:

[0178] a first red light emitting layer that emits red light; and

[0179] a second green light emitting layer that emits green light.

[0180] 13. The organic light emitting diode according to item 10, wherein the second light emitting layer comprises:

[0181] a first red light emitting layer that emits red light;

[0182] a second yellow-green light emitting layer that emits yellow-green light; and

[0183] a third green light emitting layer that emits green light.

[0184] 14. An organic light emitting diode, comprising:

[0185] an anode electrode;

[0186] a cathode electrode;

[0187] a first stack including a hole injection layer disposed on the anode electrode, a hole transport layer disposed on the hole injection layer, a first light emitting layer disposed on the hole transport layer and emitting light with a peak wavelength in the range of 430 nm to 480 nm, and a light absorption layer, the light absorption layer being contained in the hole injection layer and / or the hole transport layer at an interface between the hole injection layer and the hole transport layer and containing a phosphorescent dopant material added to at least one of the hole injection layer and the hole transport layer; and

[0188] a second stack disposed between the cathode electrode and the first stack and including at least one second light emitting layer, the at least one second light emitting layer emitting light with a wavelength longer than the wavelength of the light emitted from the first light emitting layer,

[0189] wherein the light absorption layer absorbs light from the first light emitting layer by using the phosphorescent dopant material and emits light with a wavelength of 550 nm or more in the visible light band.

[0190] 15. The organic light emitting diode according to item 14, further comprising:

[0191] a third stack disposed between the cathode electrode and the second stack and including a third light emitting layer, the third light emitting layer emitting light with a wavelength the same as the wavelength of the light emitted from the first light emitting layer.

[0192] 16. The organic light-emitting diode according to item 14, wherein the thickness of the light absorption layer is 5 nm to 30 nm, and

[0193] the concentration of the phosphorescent dopant material in the light absorption layer is 0.1 wt% to 15 wt%.

[0194] 17. A display device, comprising:

[0195] a display panel in which pixels for displaying an input image are arranged; and

[0196] a display panel driver configured to write pixel data of the input image to the pixels of the display panel,

[0197] wherein each of the pixels includes:

[0198] an organic light-emitting diode;

[0199] the organic light-emitting diode includes:

[0200] a hole injection layer, a hole transport layer on the hole injection layer, and a light-emitting layer that generates light in the short wavelength range of the visible light band and is on the hole transport layer; and

[0201] the organic light-emitting diode further includes a light absorption layer, the light absorption layer being included in the hole injection layer and / or the hole transport layer at the interface between the hole injection layer and the hole transport layer and including a phosphorescent dopant material added to at least one of the hole injection layer and the hole transport layer.

[0202] Although the embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to these embodiments, and various changes and modifications can be made without departing from the technical spirit of the present disclosure. Therefore, the embodiments disclosed herein should be considered as illustrative of the technical spirit of the present disclosure rather than limiting the technical spirit of the present disclosure, and the scope of the technical spirit of the present disclosure is not limited by these embodiments. Therefore, it should be understood that the above embodiments are illustrative in all respects and not restrictive. The scope of the present disclosure should be interpreted by the appended claims, and all technical spirits within the scope of their equivalents should be construed as being included within the scope of the present disclosure.

Claims

1. An organic light-emitting diode, comprising: a hole injection layer; a hole transport layer on the hole injection layer; a first light-emitting layer configured to generate light in a short wavelength in the visible light band; and a light absorption layer, the light absorption layer being contained in the hole injection layer and / or the hole transport layer at an interface between the hole injection layer and the hole transport layer, and containing an Ir-based or Pt-based phosphorescent dopant material added to one or more of the hole injection layer and the hole transport layer, wherein the thickness of the light absorption layer is 5 nm to 30 nm, and wherein the concentration of the phosphorescent dopant material in the light absorption layer is 0.1 wt% to 15 wt%.

2. The organic light-emitting diode according to claim 1, wherein the first light-emitting layer emits blue light, and the light absorption layer absorbs the blue light to generate triplet excitons that combine with holes.

3. The organic light-emitting diode according to claim 1, wherein the phosphorescent dopant material includes a red phosphorescent dopant material that generates red light.

4. The organic light-emitting diode according to claim 1, wherein the triplet energy level of the light absorption layer is 2.0 eV to 2.5 eV.

5. The organic light-emitting diode according to claim 4, wherein the highest occupied molecular orbital (HOMO) of the light absorption layer is equal to or less than the highest occupied molecular orbital (HOMO) of the hole transport layer.

6. The organic light-emitting diode according to claim 5, wherein the wavelength of the light absorbed by the light absorption layer is 530 nm or less in the visible light band, and the peak wavelength of the light emitted from the light absorption layer is 550 nm or greater in the visible light band.

7. The organic light-emitting diode according to claim 1, wherein when the hole injection layer contains an inorganic material, the phosphorescent dopant material is added to the hole transport layer.

8. The organic light-emitting diode according to claim 1, further comprising: a second stack disposed on the first light-emitting layer and including at least one second light-emitting layer that emits light having a wavelength different from the wavelength of the light emitted from the first light-emitting layer; a third stack disposed on the second stack and including a third light-emitting layer that emits light having the same wavelength as the wavelength of the light emitted from the first light-emitting layer; an electron injection layer disposed between the third light-emitting layer and the cathode electrode; and an electron transport layer disposed between the electron injection layer and the third light-emitting layer.

9. The organic light-emitting diode according to claim 8, wherein the second light-emitting layer includes: a first red light-emitting layer that emits red light; and a second yellow-green light-emitting layer that emits yellow-green light.

10. The organic light-emitting diode according to claim 8, wherein the second light-emitting layer includes: a first red light-emitting layer that emits red light; and a second green light-emitting layer that emits green light.

11. The organic light-emitting diode according to claim 8, wherein the second light-emitting layer includes: A first red light-emitting layer that emits red light; A second yellow-green light-emitting layer that emits yellow-green light; and A third green light-emitting layer that emits green light.

12. An organic light-emitting diode, comprising: An anode electrode; A cathode electrode; A first stack including a hole injection layer disposed on the anode electrode, a hole transport layer disposed on the hole injection layer, a first light-emitting layer disposed on the hole transport layer and emitting light with a peak wavelength in the range of 430 nm to 480 nm, and a light absorption layer, the light absorption layer being contained in the hole injection layer and / or the hole transport layer at the interface between the hole injection layer and the hole transport layer and containing an Ir-based or Pt-based phosphorescent dopant material added to at least one of the hole injection layer and the hole transport layer; and A second stack disposed between the cathode electrode and the first stack and including at least one second light-emitting layer that emits light with a wavelength longer than the wavelength of the light emitted from the first light-emitting layer, wherein the light absorption layer absorbs the light from the first light-emitting layer using the phosphorescent dopant material and emits light with a wavelength of 550 nm or greater in the visible light band, wherein the thickness of the light absorption layer is 5 nm to 30 nm, and wherein the concentration of the phosphorescent dopant material in the light absorption layer is 0.1 wt% to 15 wt%.

13. The organic light-emitting diode according to claim 12, further comprising: A third stack disposed between the cathode electrode and the second stack and including a third light-emitting layer that emits light with the same wavelength as the light emitted from the first light-emitting layer.

14. A display device, comprising: A display panel in which pixels for displaying an input image are arranged; and A display panel driver configured to write pixel data of the input image into the pixels of the display panel, wherein each of the pixels includes: An organic light-emitting diode; The organic light-emitting diode includes: A hole injection layer, a hole transport layer on the hole injection layer, and a light-emitting layer that generates short-wavelength light in the visible light band and is on the hole transport layer; and The organic light-emitting diode further includes a light absorption layer, the light absorption layer being contained in the hole injection layer and / or the hole transport layer at the interface between the hole injection layer and the hole transport layer and containing an Ir-based or Pt-based phosphorescent dopant material added to at least one of the hole injection layer and the hole transport layer, wherein the thickness of the light absorption layer is 5 nm to 30 nm, and wherein the concentration of the phosphorescent dopant material in the light absorption layer is 0.1 wt% to 15 wt%.

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