Top-emission laminated organic light-emitting device and display equipment thereof

Abstract

The top-emission laminated organic light-emitting device comprises an anode, a cathode, a first light-emitting unit and a second light-emitting unit, wherein the first light-emitting unit and the second light-emitting unit are sequentially arranged between the anode and the cathode; the chromaticity coordinate CIEx1 of the single-light-emitting-layer top-emission benchmarking device corresponding to the first light-emitting unit and the chromaticity coordinate CIEx2 of the single-light-emitting-layer top-emission benchmarking device corresponding to the second light-emitting unit meet the condition that CIEx2 is smaller than CIEx1, and the brightness attenuation factor sigma 0 of the top-emission laminated organic light-emitting device is larger than or equal to 0.88; wherein the brightness attenuation factor sigma0 is equal to L15 / L0, and L0 and L15 are the corresponding brightness of the brightness attenuation factor sigma0 at the visual angle of 0 degree and the visual angle of 15 degrees respectively. By adjusting the microcavities, the color coordinates and the brightness decay degree of the two light-emitting units, the brightness retention rate of the top-emission laminated organic light-emitting device at the visual angle of 0-15 degrees can reach or exceed 0.88, the visual angle stability is obviously improved, meanwhile, the top-emission laminated organic light-emitting device is also effective at different wave bands, and the display effect can be obviously improved. The invention further discloses a display device comprising the top-emission laminated organic light-emitting device.

Description

TECHNICAL FIELD

[0001] The present invention relates to organic electronic devices, such as organic light emitting devices. More particularly, it relates to an organic electroluminescent device having a top-emission stack structure and a display apparatus comprising the same. BACKGROUND

[0002] Organic electronic devices include, but are not limited to, the following kinds: organic light emitting diodes (OLEDs), organic field effect transistors (O-FETs), organic light emitting transistors (OLETs), organic photovoltaic devices (OPVs), dye-sensitized solar cells (DSSCs), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), light-emitting electrochemical cells (LECs), organic laser diodes and organic electroluminescent devices.

[0003] In 1987, Tang and Van Slyke at Kodak reported a two-layer organic electroluminescent device that included an arylamine hole-transport layer and a tris-8-hydroxyquinoline-aluminum layer as the electron-transport and light-emitting layers (Applied Physics Letters, 1987, 51(12): 913-915). Upon biasing the device, green light emitted from the device. This invention laid the foundation for the development of modern organic light emitting diodes (OLEDs). State-of-the-art OLEDs can include multiple layers, such as charge injection and transport layers, charge and exciton blocking layers, and one or more light emitting layers between the cathode and anode. Since OLEDs are self-emitting solid-state devices, they offer tremendous potential for display and lighting applications. In addition, the intrinsic properties of organic materials, such as their flexibility, can make them well suited for special applications, such as fabrication on flexible substrates.

[0004] OLEDs can be categorized into three different types according to their light emission mechanism. OLED invented by Tang and van Slyke is fluorescent OLED. It only uses singlet emission. The triplet states generated in the device are wasted through a nonradiative decay channel. Therefore, the internal quantum efficiency (IQE) of fluorescent OLED is only 25%. This limitation hinders the commercialization of OLED. In 1997, Forrest and Thompson reported phosphorescent OLED, which uses triplet emission from heavy metals containing complexes as emitters. Therefore, both singlet and triplet states can be harvested, achieving 100% IQE. Due to its high efficiency, the discovery and development of phosphorescent OLEDs have directly contributed to the commercialization of active-matrix OLEDs (AMOLEDs). Recently, Adachi achieved high efficiency through thermally activated delayed fluorescence (TADF) of organic compounds. These emitters have small singlet-triplet gaps, making it possible for excitons to return from triplet to singlet states. In TADF devices, triplet excitons can generate singlet excitons through reverse intersystem crossing, resulting in high IQE.

[0005] OLEDs can also be classified into small molecule and polymer OLEDs according to the form of materials used. Small molecule refers to any organic or organometallic material that is not a polymer. The molecular weight of small molecules can be quite large as long as it has a precise structure. Dendrimers with well-defined structures are considered small molecules. Polymer OLEDs include conjugated polymers and non-conjugated polymers with pendant light-emitting groups. Small molecule OLEDs can become polymer OLEDs if post-polymerization occurs during the manufacturing process.

[0006] There are various OLED manufacturing methods. Small molecule OLEDs are usually manufactured by vacuum thermal evaporation. Polymer OLEDs are manufactured by solution methods, such as spin coating, inkjet printing, and nozzle printing. Small molecule OLEDs can also be manufactured by solution methods if the materials can be dissolved or dispersed in solvents.

[0007] The emission color of OLEDs can be achieved by the design of light-emitting material structure. OLEDs can include one light-emitting layer or multiple light-emitting layers to achieve the desired spectrum. Green, yellow, and red OLEDs, phosphorescent materials have been successfully commercialized. Blue phosphorescent devices still have problems of blue unsaturation, short device lifetime, and high operating voltage. Commercial full-color OLED displays usually use a hybrid strategy, using blue fluorescent and phosphorescent yellow, or red and green. Currently, the rapid decrease in efficiency of phosphorescent OLEDs at high brightness is still a problem. In addition, it is desirable to have more saturated emission spectrum, higher efficiency, and longer device lifetime.

[0008] The patent application CN100505371C solves the problem of the angle of white light emission of OLED, which diffuses light by introducing a TIRF barrier to display monochromatic light with narrow spectrum as white light at all angles. The TIRF barrier of the application is arranged outside the OLED device, i.e. outside the substrate, between the substrate and the anode, or the substrate itself. The patent application CN103887438A also arranges a light compensation layer outside the OLED device, which is composed of a series of composite layers and can change the optical path length of the light emitted at large angles, thereby expanding the viewing angle, but such diffusion also weakens the microcavity effect to some extent, thereby reducing the light intensity emitted from the normal direction of the device. The patent applications CN103928624A and CN111933670A also aim to solve the color deviation problem of white light at large angles in display, the former balances the color deviation at large viewing angles by increasing the blue light intensity at the normal, and the latter balances the color deviation at large viewing angles by increasing the red and green light intensity at the normal, but such methods do not actually solve the problem of brightness decay of each color, and in fact, the brightness decay of each light at large angles is more severe, resulting in overall brightness decay. The patent application CN107546333A arranges an optical multilayer film outside the OLED device to convert the original narrow spectrum into a wide spectrum, thereby improving the color deviation problem, but the optical multilayer film in the application is also a series of inorganic insulating layers arranged above the cathode, and similarly, such method also destroys the microcavity and reduces the light intensity at the normal. The patent application CN108470839A arranges a light output coupling layer outside the OLED device to suppress the microcavity effect, and also uses a high-transmittance electrode and a high-refractive-index hole injection layer to further reduce the microcavity effect, thereby improving color deviation and brightness decay. Although the application introduces special materials inside the OLED device, it essentially reduces the light intensity at the normal. The patent application CN110890478A arranges a composite anode including multiple conductive layers with different optical properties to control the microcavity, thereby improving the color deviation and brightness decay of the display panel. Similarly, the patent application CN115394938A arranges a composite cathode layer to control the microcavity. However, such method also does not perform in the organic layer, and still inevitably brings the problem of suppressed small-angle brightness. The patent application CN115440779A uses the method of hole digging in the color filter to control the light emission, so that the light at small angles passes through the holes and the light at large angles passes through the filter, thereby changing the color deviation. The use of the filter in this method reduces the light efficiency and causes uneven light color, and cannot solve the brightness decay problem. The patent application CN116546856A selects at least one pixel among red, green and blue pixels to be Lambertian emission and at least one pixel to be microcavity emission to balance the color deviation problem. However, the pixel with Lambertian emission also sacrifices the light intensity at the normal, and the brightness decay of the pixel with microcavity emission is greater than that of the pixel with Lambertian emission, which ultimately still causes color deviation.The patent application US11011586B2 discloses a way of using different microcavity lengths for adjacent pixels of the same color to improve color decay, but this way is realized at the expense of the overall panel brightness, and when the microcavities are different, the color of the emitted light will also be different, although the luminescent material is the same, which will pollute the final color purity.

[0009] Therefore, how to effectively improve the viewing angle characteristics of the top-emitting OLED while maintaining high efficiency of the device has become a technical problem that needs to be solved in the field. SUMMARY

[0010] The present application aims to provide a top-emitting stacked organic electroluminescent device to solve at least part of the above problems. The organic electroluminescent device includes two single-layer top-emitting light-emitting units, and by adjusting the microcavity and color coordinates of the light-emitting units, the viewing angle characteristics of the organic electroluminescent device are effectively improved, and the display effect is significantly improved.

[0011] According to one embodiment of the present application, a top-emitting stacked organic electroluminescent device is disclosed, which comprises:

[0012] an anode,

[0013] a cathode,

[0014] a first light-emitting unit and a second light-emitting unit arranged in sequence between the anode and the cathode;

[0015] The single-light-emitting-layer top-emitting reference device corresponding to the first light-emitting unit has a color coordinate CIEx1,

[0016] The single-light-emitting-layer top-emitting reference device corresponding to the second light-emitting unit has a color coordinate CIEx2, and satisfies CIEx2 < CIEx1;

[0017] The luminance decay factor σ0 of the top-emitting stacked organic electroluminescent device is ≥0.88;

[0018] Wherein, the luminance decay factor σ0 = L 15 / L0, L0 and L 15 are the luminances of the top-emitting stacked organic electroluminescent device at 0° and 15° viewing angles, respectively.

[0019] According to one embodiment of the present application, a display device comprising the top-emitting stacked organic electroluminescent device of the aforementioned embodiments is also disclosed.

[0020] The novel top-emitting stacked organic electroluminescent device disclosed in the present application comprises at least two light-emitting units, by adjusting the microcavity, color coordinates and brightness decay degree of the two light-emitting units, the brightness retention rate of the top-emitting stacked organic electroluminescent device under 0-15° viewing angle can reach or exceed 0.88, while maintaining high efficiency of the device, the viewing angle stability has also been significantly improved, and it is also effective under multiple light-emitting wavebands, which can significantly improve the display effect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a cross-sectional schematic diagram of an organic electroluminescent device 100 provided in the specific embodiment of the present application.

[0022] Figure 2 is a cross-sectional schematic diagram of a single-layer organic electroluminescent device 200 used in the present application.

[0023] Figure 3 is a brightness decay-angle relationship curve diagram of an organic electroluminescent device provided in the specific embodiment of the present application.

[0024] Figure 4 is a brightness decay-angle relationship curve diagram of an organic electroluminescent device provided in the specific embodiment of the present application. DETAILED DESCRIPTION

[0025] Top-emitting OLEDs can be fabricated on a variety of substrates, such as glass, plastic and metal. Figure 1 An organic light emitting device 100 is schematically and non-limitingly illustrated. The figures are not necessarily drawn to scale and some layer structures in the figures can be omitted as desired. The device 100 can include a substrate 101, an anode 110, a first light-emitting unit 120, an n-type charge generation layer 130, a p-type charge generation layer 140, a second light-emitting unit 150, a cathode 160, a light extraction layer 170 over the cathode, and an encapsulation layer 180 over that. The first light-emitting unit 120 includes a hole injection layer 121, a hole transport layer 122, an electron blocking layer 123, a light-emitting layer 124, and an electron transport layer 125. The second light-emitting unit 150 includes a hole transport layer 151, an electron blocking layer 152, a light-emitting layer 153, an electron transport layer 154, and an electron injection layer 155. The device 100 can be fabricated by sequentially depositing the described layers. The properties and functions of the layers, as well as exemplary materials, are described in more detail in U.S. Patent No. 7,279,704 B2, columns 6-10, the entire contents of which are incorporated herein by reference.

[0026] As used herein, as Figure 2A single layer organic light emitting device 200 is schematically, non- limitingly illustrated, which can include a substrate 201, an anode 210, a hole injection layer 220, a hole transport layer 230, an electron blocking layer 240, a light emitting layer 250, a hole blocking layer 260, an electron transport layer 270, an electron injection layer 280, and a cathode 290. Device 200 can be fabricated by sequentially depositing the layers described. A encapsulation layer 202 can also be included on top of cathode 190 to protect from harmful materials from the environment, such as moisture and oxygen. Any material that can provide an encapsulation function can be used as the encapsulation layer, such as glass or an organic-inorganic hybrid layer. The encapsulation layer should be placed directly or indirectly on the outside of the OLED device. Multilayer thin film encapsulation is described in U.S. Patent No. 7,968,146 B2, which is incorporated by reference in its entirety.

[0027] There are many more examples of each of these layers. For example, flexible and transparent substrate-anode combinations are disclosed in U.S. Patent No. 5,844,363, incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ in a 50:1 molar ratio, as disclosed in U.S. Patent Application Publication No. 2003 / 0230980, incorporated by reference in its entirety. Examples of host materials are disclosed in U.S. Patent No. 6,303,238 to Thompson et al., incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li in a 1:1 molar ratio, as disclosed in U.S. Patent Application Publication No. 2003 / 0230980, incorporated by reference in its entirety. U.S. Patent Nos. 5,703,436 and 5,707,745, incorporated by reference in their entirety, disclose examples of cathodes, including composite cathodes with a thin layer of a metal such as Mg:Ag overlying a transparent, conductive, sputter-deposited ITO layer. The principles and use of blocking layers are described in more detail in U.S. Patent No. 6,097,147 and U.S. Patent Application Publication No. 2003 / 0230980, incorporated by reference in their entirety. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004 / 0174116, incorporated by reference in its entirety. Descriptions of protective layers can be found in U.S. Patent Application Publication No. 2004 / 0174116, incorporated by reference in its entirety.

[0028] The above-described layered structure is provided by way of non-limiting example. The functionality of an OLED can be achieved by combining various layers described above, or some layers can be omitted entirely. It can also include other layers not explicitly described. Within each layer, a single material or a mixture of materials can be used to achieve optimal performance. Any functional layer can include several sub-layers. For example, an emissive layer can have two layers of different emissive materials to achieve a desired emission spectrum.

[0029] In one embodiment, an OLED can be described as having a "layer" disposed between the anode and the cathode. The layer can comprise one or more layers.

[0030] Devices made according to embodiments of the application can be incorporated into a variety of consumer products with one or more electronic component modules (or units) of the device. Some examples of these consumer products include flat-panel displays, monitors, medical monitors, televisions, billboards, lights for indoor or outdoor illumination and / or signaling, heads-up displays, fully or partially transparent displays, flexible displays, smartphones, tablet computers, phablets, wearable devices, smartwatches, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicle displays and tail-lights.

[0031] The materials and structures described herein can also be used in other organic electronic devices listed previously.

[0032] As used herein, "top" means furthest from the substrate and "bottom" means closest to the substrate. Where a first layer is described as "disposed on" a second layer, the first layer is disposed further from the substrate than the second layer. Unless specified that the first layer is "in contact with" the second layer, there can be intervening layers between the first and second layers. For example, a cathode can be described as "disposed on" an anode even though various organic layers are between the cathode and the anode.

[0033] As used herein, "first emissive unit" means closer to the anode side, closer to the N-type electron generation layer. "Second emissive unit" means closer to the cathode side, closer to the P-type electron generation layer.

[0034] As used herein, "solution processible" means capable of being dissolved, dispersed, or transported in and / or deposited from a liquid medium, either in solution or suspension form.

[0035] As used herein, "brightness decay factor σ" means the brightness of a device in the direction of the substrate normal is L0, and the brightness at an angle θ from the normal is L θ at which time the brightness decay of the device at this angle is σ(θ) = L θL0. The top-emitting stacked organic electroluminescent device of the present application has a luminance decay of σ0(θ) at an angle of θ from the normal direction. When comparing the luminance decay between different devices, the comparison should be made at the same angle from the normal direction.

[0036] As used herein, "σ1>σ2" means that the luminance decay of two light-emitting units are compared at each of the same angles, and σ2<σ1 is satisfied, for example, when the viewing angle θ=5°, σ2(5°)<σ1(5°); when θ=15°, σ2(15°)<σ1(15°); when θ=20°, σ2(20°)<σ1(20°).

[0037] As used herein, "σ0(θ)≥0.18 is satisfied at each of the angles in the range of 15° to 30°" means that the top-emitting stacked organic electroluminescent device of the present application has a luminance decay of σ0(θ)≥0.18 at each of the angles in the range of 15° to 30° from the normal direction.

[0038] As used herein, "horizontal orientation ratio of the light-emitting layer" means the proportion of the light-emitting molecules whose transition dipole moment is parallel or more inclined to be parallel to the substrate plane in the total number of light-emitting molecules in the light-emitting layer, which is usually expressed as a percentage (%) or an order parameter (between 0 and 1), for example, a horizontal orientation ratio of 80% means that 80% of the molecules have their transition dipole moment more inclined to be parallel to the substrate. For molecules without significant horizontal orientation, i.e. the case of isotropic light-emitting molecules, the horizontal orientation ratio of the light-emitting layer is 67%. In general, the preparation process of the organic layer also affects the horizontal orientation ratio of the light-emitting layer.

[0039] In application scenarios with special requirements on viewing angle characteristics, light-emitting layers with a lower horizontal orientation ratio can be adopted. In theory, if the dipole moment orientation of light-emitting molecules in the light-emitting layer is distributed isotropically (i.e., the horizontal orientation ratio is low), the light-emitting characteristics of the light-emitting layer can exhibit higher consistency in different observation directions. This is because the isotropic light-emitting dipole distribution can reduce the light-emitting intensity decay and color coordinate shift caused by the increase in viewing angle, thereby enabling the device to maintain a relatively stable visual performance in a wide viewing angle range. Specifically, the orientation distribution of light-emitting molecules directly affects the angle-dependent light-emitting behavior of the device. A lower horizontal orientation ratio generally means that the distribution of light-emitting dipole moments in three-dimensional space is more uniform. Therefore, when viewed obliquely, the degree of brightness decline of the device with a low horizontal orientation ratio can be more gradual than that of a device with a high horizontal orientation ratio, and the chromaticity change is relatively small. This characteristic is considered to be beneficial to improving the viewing experience of users in some display applications. However, it should be pointed out that the use of a light-emitting layer with a low horizontal orientation ratio will also significantly limit the external quantum efficiency of the device. The reason is that most of the light-emitting energy has a low escape opportunity in the horizontal direction and is easily confined inside the device or converted into waveguide mode and surface plasmon polariton mode loss. Therefore, although a low horizontal orientation ratio can help improve the viewing angle performance, it usually leads to a low overall light-emitting efficiency of the device, and a strict trade-off between advantages and disadvantages needs to be made in actual applications.

[0040] Solution process is a kind of preparation technology that forms a uniform solution by dissolving functional materials (such as organic small molecules, polymers or quantum dots, etc.) in a volatile solvent, and then deposits it on the target substrate through processes such as spin coating, inkjet printing, slot coating, screen printing or blade coating, etc. After the solvent evaporates, it solidifies into a continuous thin film. The core feature of this method is that its film-forming process relies on the fluidity of the solution state and the subsequent drying and curing stage. In this process, the solvent molecules usually present a random arrangement state, and it is difficult to form a highly ordered structure spontaneously, resulting in the prepared light-emitting layer often showing a low horizontal orientation rate, even showing isotropic optical properties. The main reasons for this phenomenon include rapid evaporation of the solvent, lack of directional induction of external fields (such as electric field, magnetic field or mechanical shear force), and random distribution of intermolecular forces in a non-equilibrium state. Solution process is widely concerned in the field of optoelectronic display due to its simple process, low cost, high material utilization rate, and suitability for large-area and flexible substrate preparation. However, its inherent poor controllability of molecular orientation often leads to a gap in luminous efficiency, carrier mobility and stability compared with vacuum evaporation devices, so it is a key challenge that needs to be overcome for the technology to move towards high-performance applications. When using solution processing technology to prepare light-emitting layers, due to the lack of external field induction or effective orientation control means during the film-forming process, the light-emitting molecules in the formed thin film usually present a random arrangement state, showing a low horizontal orientation rate or no significant orientation characteristics. During the solution preparation process, the rapid evaporation of the solvent and the solidification of the thin film often lead to the random distribution of light-emitting molecules in three-dimensional space, and their light-emitting dipole moment tends to be isotropic, with a generally low horizontal orientation rate.

[0041] In summary, solution process has inherent shortcomings in preparing high-performance multilayer optoelectronic devices: the process of spin-coating the upper layer solution is extremely easy to dissolve or damage the lower layer thin film, leading to interface mixing, energy level mismatch, and seriously restricting device efficiency and life; at the same time, this method is strongly dependent on the solubility of materials, and it is difficult to control the uniformity of film formation, and the material waste is serious. The hybrid process combined with vacuum evaporation technology can effectively break through this bottleneck - the main structure such as thick transport layer can be prepared quickly by solution method, and then the light-emitting layer, electron transport layer or metal electrode sensitive to interface can be accurately deposited without damage by evaporation technology. This strategy not only perfectly avoids the problem of solvent erosion and builds a clear and steep ideal heterojunction, but also combines the large-area economy of solution method with the nanoscale precision and material universality of evaporation method, providing a highly competitive technical path for realizing high-performance and high-stability OLED displays and other frontier devices.

[0042] In organic electroluminescent devices (OLED), the top emission structure is widely used due to its high light extraction efficiency and more suitable structure design for high-resolution display panels. However, compared with the bottom emission structure, the top emission OLED often has a more serious viewing angle dependence problem. The main reason is that the top emission structure generally forms a strong microcavity effect, and the emission spectrum will shift with the observation angle, resulting in a significant decrease in brightness and a color coordinate shift at large angles.

[0043] Specifically, at a small angle (for example, 0°), the emission spectrum and brightness of the device can meet the design requirements, but when the observation angle increases (for example, 15°, 30°), the change of the microcavity resonance condition will cause the emission peak to blue shift or red shift, resulting in the shift of the emission color coordinate, and the brightness will also decrease significantly. This phenomenon not only affects the optical performance of the device, but also causes the display panel to have inconsistent colors and uneven brightness at different viewing angles, thereby reducing the display quality.

[0044] According to an embodiment of the present application, a top emission stacked organic electroluminescent device is disclosed, comprising:

[0045] an anode,

[0046] a cathode,

[0047] a first light-emitting unit and a second light-emitting unit arranged in sequence between the anode and the cathode;

[0048] The color coordinates of the single light-emitting layer top emission reference device corresponding to the first light-emitting unit are CIEx1,

[0049] The color coordinates of the single light-emitting layer top emission reference device corresponding to the second light-emitting unit are CIEx2, and CIEx2 < CIEx1 is satisfied;

[0050] The brightness decay factor σ0 of the top emission stacked organic electroluminescent device is ≥0.88;

[0051] Wherein, the brightness decay factor σ0 = L 15 / L0, L0 and L 15 are the brightness of the top emission stacked organic electroluminescent device at 0° and 15° viewing angles, respectively.

[0052] According to an embodiment of the present application, the peak wavelength of the electroluminescent spectrum of the first light-emitting unit is λ1, the peak wavelength of the electroluminescent spectrum of the second light-emitting unit is λ2, and 0nm≤λ1-λ2≤20nm; preferably, 0nm≤λ1-λ2≤7nm.

[0053] According to one embodiment of the present application, wherein the luminance decay factor of the first light emitting unit is σ1, the luminance decay factor of the second light emitting unit is σ2, the color coordinate of the top emission stacked organic electroluminescent device is CIEx0, the thickness of the first light emitting unit and the second light emitting unit is fixed, when CIEx2 < CIEx0 ≤ CIEx1, σ1 > σ2.

[0054] According to one embodiment of the present application, the structure of the single light emitting layer top emission reference device corresponding to the first light emitting unit is the same as that of the top emission stacked organic electroluminescent device, the only difference is that the organic layer of the light emitting layer corresponding to the second light emitting unit in the reference device does not contain light emitting material, that is, the reference device only contains light emitting material in the light emitting layer of the first light emitting unit, and this structure is used to test σ1 and CIEx1.

[0055] According to one embodiment of the present application, the structure of the single light emitting layer top emission reference device corresponding to the second light emitting unit is the same as that of the top emission stacked organic electroluminescent device, the only difference is that the organic layer of the light emitting layer corresponding to the first light emitting unit in the reference device does not contain light emitting material, that is, the reference device only contains light emitting material in the light emitting layer of the second light emitting unit, and this structure is used to test σ2 and CIEx2.

[0056] According to one embodiment of the present application, when the first light emitting unit and the second light emitting unit contain different light emitting materials, λ1 ≥ λ2.

[0057] According to one embodiment of the present application, λ1 ≥ 500 nm.

[0058] According to one embodiment of the present application, λ2 ≥ 500 nm.

[0059] According to one embodiment of the present application, λ1 and λ2 are between 600 nm and 700 nm.

[0060] According to one embodiment of the present application, λ1 and λ2 are between 620 nm and 630 nm.

[0061] According to one embodiment of the present application, λ1 and λ2 are between 500 nm and 600 nm.

[0062] According to one embodiment of the present application, λ1 and λ2 are between 520 nm and 540 nm.

[0063] According to one embodiment of the present application, wherein the color shift ΔCIEx when the viewing angle θ is in the range of 15°-30° is ≤0.010, and the luminance decay factor σ0(θ) ≥0.18 when the viewing angle θ is in the range of 15°-30°.

[0064] According to one embodiment of the present application, the viewing angle θ satisfies the luminance decay factor σ0(θ)≥0.4 in the range of 15°-30°.

[0065] According to one embodiment of the present application, when the same light-emitting material is contained in the first and second light-emitting units, CIEx1>CIEx2is achieved by keeping the optical path of the second light-emitting unit unchanged and increasing the optical path of the first light-emitting unit.

[0066] According to one embodiment of the present application, the thickness of the hole transport layer or the electron blocking layer of the first and second light-emitting units is adjusted to keep the optical path of the second light-emitting unit unchanged and increase the optical path of the first light-emitting unit.

[0067] According to one embodiment of the present application, the horizontal orientation ratio of the second light-emitting unit of the top-emitting stacked organic electroluminescent device is higher than that of the first light-emitting unit, and the horizontal orientation ratio of the light-emitting layer of the second light-emitting unit is greater than or equal to 80%.

[0068] According to one embodiment of the present application, the horizontal orientation ratio of the light-emitting layer of the second light-emitting unit is greater than or equal to 90%.

[0069] According to one embodiment of the present application, the light-emitting layer of the first light-emitting unit is prepared by a solution processing technology, which can include but is not limited to spin coating, inkjet printing, or blade coating, etc. It should be noted that the light-emitting layer prepared by such a solution process usually exhibits random molecular arrangement, and has a low horizontal orientation ratio or no significant orientation characteristics.

[0070] Controlling the horizontal orientation ratio is an effective way to optimize the viewing angle characteristics of a device. In a stacked device with strong microcavity effect, a light-emitting layer with high horizontal orientation ratio can greatly enhance the front brightness, but will lead to a highly concentrated light intensity distribution, resulting in a sharp decay of brightness with increasing viewing angle (the "viewing angle roll-off" effect). On the contrary, a light-emitting body with a lower horizontal orientation ratio has a more uniform spatial light intensity distribution, and such an anisotropic emission makes the brightness curve with viewing angle more flat.

[0071] According to one embodiment of the present application, by combining the lower light-emitting layer with inherently low horizontal orientation ratio prepared by a solution method, and the upper light-emitting layer introduced by evaporation method, fine control of the overall light field distribution of the device is achieved. By balancing the front enhancement advantage of the "high orientation ratio layer" and the viewing angle uniformity advantage of the "low orientation ratio layer", the comprehensive viewing angle performance of the device can be synergistically optimized, maintaining high front efficiency while achieving better viewing angle stability. This broadens the range of material selection and provides an effective viewing angle optimization technology path.

[0072] According to one embodiment of the present application, a display device is disclosed comprising a top-emitting stacked organic electroluminescent device as described in any of the preceding embodiments.

[0073] According to one embodiment of the present application, in order to improve the viewing angle stability, the optical path inside the stacked organic electroluminescent device is precisely designed, and the resonance mode of the microcavity is optimized to optimize the viewing angle. The core is to regulate the device structure, so that a specific red shift occurs from the lower layer, so as to pre-achieve the brightness decay stability of the device within a certain viewing angle range. The regulation of the optical path length is realized by two technical paths: one is the material selection strategy, that is, by regulating the refractive index (n) of different optical functional layer materials to change the propagation phase and equivalent optical path of light waves in the medium; the second is the thickness control strategy, that is, under the premise of keeping the materials of each layer unchanged, by controlling the physical thickness (d) of one or more functional layers, the geometric distance of light propagation is directly changed. The optical path length (OPL) can be approximately characterized by the formula OPL = n x d. Through the above-mentioned coordinated design and combination of material refractive index and layer thickness, the present application can flexibly and accurately "customize" the resonance wavelength of the microcavity, significantly improving the viewing angle dependence of the device, and improving the uniformity of the display picture and the visual experience.

[0074] Combinations with other materials

[0075] The materials described herein for particular layers in an organic light emitting device can be used in combination with a variety of other materials present in the device. Combinations of materials are described in detail in U.S. Patent Application Publication No. US 2016 / 0359122 Al, paragraphs 0132-0161, the entire contents of which are incorporated by reference. The materials described or referenced in those paragraphs are non-limiting examples of materials that can be used in combination with the compounds disclosed herein, and one of skill in the art can readily identify other materials that can be useful in combination with the compounds disclosed herein.

[0076] The materials described herein for particular layers in an organic light emitting device can be used in combination with a variety of other materials present in the device. For example, the compounds disclosed herein can be used in conjunction with a variety of light emitting dopants, hosts, transport layers, blocking layers, injection layers, electrodes, and other layers that can be present. Combinations of materials are described in detail in U.S. Patent Application Publication No. US 2015 / 0349273 Al, paragraphs 0080-0101, the entire contents of which are incorporated by reference. The materials described or referenced in those paragraphs are non-limiting examples of materials that can be used in combination with the compounds disclosed herein, and one of skill in the art can readily identify other materials that can be useful in combination with the compounds disclosed herein.

[0077] In the following, the present application will be described in more detail with reference to the following examples. The compounds used in the following examples are readily available to the person skilled in the art and thus the synthesis methods thereof are not described herein. It is obvious that the following examples are only for illustrative purposes and are not intended to limit the scope of the present application. The person skilled in the art can reasonably modify the preparation methods of the following examples according to the prior art. For example, the ratio of various materials in the light-emitting layer is not particularly limited and the person skilled in the art can reasonably select within a certain range according to the prior art, for example, the host material can account for 80%-99.9% and the light-emitting material can account for 0.1%-20% based on the total weight of the light-emitting layer materials. In addition, the host material can be one or two materials, and the ratio of the two host materials in the host material can be 99:1 to 1:99. In the examples of the device, the characteristics of the device are also tested by using the conventional equipment in the art (including but not limited to the evaporation machine produced by Angstrom Engineering, the optical test system produced by Suzhou Fushida, the ellipsometer produced by Beijing Liangtuo, etc.), and the method well known to the person skilled in the art.

[0078] As described herein, the term "simulation" refers to simulation by optical simulation software only through the refractive index, thickness of each layer of material, and the EL spectrum corresponding to the light-emitting layer, without including electrical simulation, etc. The optical simulation software used in the present application is SETFOS 5.1.1 semiconductor thin film optical simulation software developed by Fluxim AG Company.

[0079] As described herein, the test method of the refractive index of the organic material is to evaporate the material with a thickness of 30 nm on a silicon wafer in an Angstrom Engineering evaporation machine, and to obtain the refractive index curve at a wavelength of 400 nm-800 nm by an ellipsometer of model ES Nano produced by Beijing Liangtuo Technology Co., Ltd. In addition, the refractive index parameters of glass, cathode layer material, anode layer material Ag and ITO, and EIL material Yb are derived from the refractive index library provided with the SETFOS optical simulation software. Specifically as follows:

[0080] Table 1 Refractive index of organic material at part of wavelength

[0081]

[0082] As described herein, the test method of the electroluminescence spectrum (EL spectrum) of the light-emitting layer is to prepare a device as follows in an Angstrom Engineering evaporation machine: Figure 2The devices were tested by optical test system equipment produced by Suzhou Fosdta Co., Ltd. and the electroluminescence spectrum test was carried out. The wavelength range of the test was 400-750 nm. Through the preparation and test of the single-layer device, the maximum emission wavelength λmax of the EL spectrum of the light-emitting layer compound was obtained as shown in Table 2 below, which was used for optical simulation.

[0083] Single-layer device D1: first use 0.7 mm thick glass substrate 201, which has a previously patterned thick indium tin oxide (ITO) as anode 210, and compound HT and compound HI as hole injection layer (HIL, 97:3, ) 220 are simultaneously evaporated on the anode layer, compound HT is evaporated as hole transport layer (HTL, ) 230, compound EB is evaporated as electron blocking layer (EBL, ) 240, RH1:RD1 (97:3, as light-emitting layer (EML) 250, compound H-2 is evaporated as hole blocking layer (HBL, ) 260, compound ET and Liq are co-deposited as electron transport layer (ETL, 40:60, ) 270, compound Liq is evaporated as electron injection layer (EIL, ) 280. Finally, aluminum metal is evaporated as cathode (Cathode, ) 290. Then the device is transferred back to the glove box and packaged with a glass cover sheet 202 to complete the device.

[0084] Single-layer device D2: the preparation method of single-layer device D2 is consistent with D1, and the only difference is that the compound in the EML is replaced by RH1:RD2 (97:3, ).

[0085] Single-layer device D3: the preparation method of single-layer device D3 is consistent with D1, and the only difference is that the compound in the EML is replaced by RH1:RD3 (97:3, ).

[0086] Single-layer device D4: the preparation method of single-layer device D4 is consistent with D1, and the only difference is that the compound in the EBL is replaced by H1 (EBL, ), and the compound in the EML is replaced by H1:GH1:GD1 (37.6:56.4:6, ).

[0087] Single-layer device D5: the preparation method of single-layer device D5 is consistent with D4, and the only difference is that the compound in the EML is replaced by H1:GH1:GD2 (37.6:56.4:6,

[0088] Single layer device D6: The method of preparation of single layer device D6 was identical to D4, except that the compounds in the EML were replaced by H1:GH1:GD3 (37.6:56.4:6,

[0089] Table 2 Partial electroluminescence spectra of organic materials

[0090]

[0091] Example 1:

[0092] First, a 0.7 mm thick glass substrate 101 having a previously patterned thick indium tin oxide-silver-indium tin oxide (IAI, 75:1500:150, ) as anode 110 was used. After washing the substrate with deionized water and detergent water, the ITO surface was treated with oxygen plasma and UV ozone. Subsequently, the substrate was dried in a glove box to remove moisture and loaded into a holder for transfer into a vacuum chamber. The organic layers specified below were sequentially evaporated by vacuum thermal evaporation at a rate of -6 400​​​​​​​​​​​​ )153, re-evaporate compound ET and Liq co-deposited as electron transport layer (ETL, 40:60, )154, re-evaporate Yb as electron injection layer (EIL, ) as second light emitting unit. Simultaneously evaporate metal magnesium and silver as cathode (Cathode, 10:90, )160. Finally, evaporate CPL 54 as light extraction layer (CPL, )170. Then the device is transferred back to the glove box and encapsulated with a glass cover sheet 102 to complete the device.

[0093] CIEx1 test method: prepare a first light emitting unit single light emitting layer top emission reference device, the preparation method is the same as that of example 1 device, the only difference is that the second light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )153. The CIEx1 is obtained by testing the optical test system equipment produced by Suzhou Fosd Company Limited at a current density of 10 mA / cm 2 .

[0094] CIEx2 test method: prepare a second light emitting unit single light emitting layer top emission reference device, the preparation method is the same as that of the above device, the only difference is that the first light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )124. The CIEx2 is obtained by testing the optical test system equipment produced by Suzhou Fosd Company Limited at a current density of 10 mA / cm 2 .

[0095] Example 2: the preparation method is the same as that of example 1, except that the first light emitting unit and the second light emitting unit simultaneously evaporate compound RH1 and RD2 as the light emitting layer (EML, 97:3, ), the thickness of HTL in the first light emitting unit is adjusted to the thickness of HTL in the second light emitting unit is adjusted to

[0096] CIEx1 test method: prepare a first light emitting unit single light emitting layer top emission reference device, the preparation method is the same as that of example 2 device structure, the only difference is that the second light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )153. The CIEx1 is obtained by testing the optical test system equipment produced by Suzhou Fosd Company Limited at a current density of 10 mA / cm 2 .

[0097] CIEx2 test method: prepare the second light emitting unit single light emitting layer top emission reference device, the preparation method is the same as the device structure of example 2, the only difference is that the first light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )124. The optical test system equipment produced by Suzhou Fosda Co., Ltd. is used to test CIEx2 under the current density of 10 mA / cm 2 .

[0098] Comparative example 1: the preparation method is the same as that of example 1, except that the first light emitting unit and the second light emitting unit evaporate compound RH1 and RD2 as the light emitting layer (EML, 97:3, ).

[0099] CIEx1 test method: prepare the first light emitting unit single light emitting layer top emission reference device, the preparation method is the same as the device structure of comparative example 1, the only difference is that the second light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )153. The optical test system equipment produced by Suzhou Fosda Co., Ltd. is used to test CIEx1 under the current density of 10 mA / cm 2 .

[0100] CIEx2 test method: prepare the second light emitting unit single light emitting layer top emission reference device, the preparation method is the same as the device structure of comparative example 1, the only difference is that the first light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )124. The optical test system equipment produced by Suzhou Fosda Co., Ltd. is used to test CIEx2 under the current density of 10 mA / cm 2 .

[0101] Comparative example 2: the preparation method is the same as that of example 1, except that the first light emitting unit and the second light emitting unit evaporate compound RH1 and RD1 as the light emitting layer (EML, 97:3, ).

[0102] CIEx1 test method: prepare the first light emitting unit single light emitting layer top emission reference device, the preparation method is the same as the device structure of comparative example 2, the only difference is that the second light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )153. The optical test system equipment produced by Suzhou Fosda Co., Ltd. is used to test CIEx1 under the current density of 10 mA / cm 2 .

[0103] CIEx2 test method: prepare the second light emitting unit single light emitting layer top emission reference device, the preparation method is the same as the device structure of comparative example 2, the only difference is that the first light emitting unit only evaporates compound RH1 as the light emitting layer (EML, )124. The CIEx2 was obtained by testing the device with an optical testing system produced by Suzhou FASLA Co., Ltd. at a current density of 10 mA / cm 2 .

[0104] Comparative Example 3: The same preparation method as Example 1, except that the first light-emitting unit and the second light-emitting unit were simultaneously evaporated with compounds RH1 and RD3 as the light-emitting layer (EML, 97:3, ).

[0105] CIEx1 test method: a first light-emitting unit single light-emitting layer top emission reference device was prepared, and the preparation method was the same as that of the device structure of Comparative Example 3, except that the second light-emitting unit was evaporated only with compound RH1 as the light-emitting layer (EML, )153. The CIEx1 was obtained by testing the device with an optical testing system produced by Suzhou FASLA Co., Ltd. at a current density of 10 mA / cm 2 .

[0106] CIEx2 test method: a second light-emitting unit single light-emitting layer top emission reference device was prepared, and the preparation method was the same as that of the device structure of Comparative Example 3, except that the first light-emitting unit was evaporated only with compound RH1 as the light-emitting layer (EML, )124. The CIEx2 was obtained by testing the device with an optical testing system produced by Suzhou FASLA Co., Ltd. at a current density of 10 mA / cm 2 .

[0107] Comparative Example 4: The same preparation method as Example 1, except that the first light-emitting unit was evaporated with compounds RH1 and RD2 as the light-emitting layer (EML, 97:3, ), and the second light-emitting unit was evaporated with compounds RH1 and RD1 as the light-emitting layer (EML, 97:3, ).

[0108] CIEx1 test method: a first light-emitting unit single light-emitting layer top emission reference device was prepared, and the preparation method was the same as that of the device structure of Comparative Example 4, except that the second light-emitting unit was evaporated only with compound RH1 as the light-emitting layer (EML, )153. The CIEx1 was obtained by testing the device with an optical testing system produced by Suzhou FASLA Co., Ltd. at a current density of 10 mA / cm 2 .

[0109] CIEx2 test method: a second light-emitting unit single light-emitting layer top emission reference device was prepared, and the preparation method was the same as that of the device structure of Comparative Example 4, except that the first light-emitting unit was evaporated only with compound RH1 as the light-emitting layer (EML, )124. The CIEx2 was tested by optical test system equipment produced by Suzhou Fosd Company Limited at a current density of 10 mA / cm 2 .

[0110] Table 3 Partial device structure of Examples 1-2 and Comparative Examples 1-4

[0111]

[0112]

[0113] Among them, the compound CPL54 is a cover layer material (refractive index n@620nm is 2.06) purchased from Jiangsu San Yue Technology Co., Ltd., and the structures of other compounds used in the device are as follows:

[0114]

[0115] Table 4 lists the partial device performance of Examples 1-2 and Comparative Examples 1-4, wherein the color coordinates CIEx1 of the top-emitting device corresponding to the single light-emitting layer of the first light-emitting unit, the color coordinates CIEx2 of the top-emitting device corresponding to the single light-emitting layer of the second light-emitting unit, the luminance decay factor σ0, the color coordinates CIEx0, and the current efficiency CE of the top-emitting stacked organic electroluminescence device are all measured at a current density of 10 mA / cm 2 .

[0116] Table 4 Device performance of Examples 1-2 and Comparative Examples 1-4

[0117]

[0118]

[0119] Discussion:

[0120] As shown in Tables 3 and 4, in Example 1, the light-emitting layer of the first light-emitting unit uses RD1, and the light-emitting layer of the second light-emitting unit uses RD2. The color coordinates CIEx1 and CIEx2 of the single-emitting top-emitting benchmark devices of the first and second light-emitting units are 0.707 and 0.699, respectively, forming a certain color coordinate difference. Simultaneously, the color coordinates of the lower light-emitting unit are relatively reddish, satisfying CIEx1 > CIEx2. Under this structure, in terms of viewing angle performance, the brightness attenuation factor σ0 of the top-emitting stacked organic light-emitting device in Example 1 reaches 0.90, indicating a significant advantage in viewing angle performance. Compared to Example 1, the light-emitting layers of both the first and second light-emitting units in Comparative Example 1 use RD2, the light-emitting layers of both the first and second light-emitting units in Comparative Example 2 use RD1, and the light-emitting layers of both the first and second light-emitting units in Comparative Example 3 use RD3. The σ0 values ​​of their top-emitting stacked organic light-emitting devices are 0.87, 0.86, and 0.86, respectively, all significantly smaller than those in Example 1. Furthermore, in Comparative Example 4, the first light-emitting unit uses RD2 as its light-emitting layer, and the second light-emitting unit uses RD1. Compared to Example 1, the light-emitting layers of the first and second light-emitting units are swapped, and CIEx1 < CIEx2. In this case, its σ0 is significantly smaller than that of Example 1, indicating that only when CIEx1 > CIEx2 can there be a significant improvement in brightness attenuation. Figure 3 The brightness decay curves from 0° to 30° are shown, with the horizontal axis representing the viewing angle (in degrees), taking values ​​of 5°, 10°, 15°, 20°, 25°, and 30°; the vertical axis represents the relative brightness value. As can be seen from the figure, the solution provided in Example 1 maintains a high brightness level under viewing angle conditions of 0-30°, exhibiting excellent optical performance. Specifically, as the viewing angle increases, the brightness decay of Example 1 is relatively gradual, indicating good viewing angle characteristics. In contrast, Comparative Examples 1 to 4 show significant brightness decay as the viewing angle increases, especially after the viewing angle exceeds a certain range, where the brightness decreases significantly, indicating poor viewing angle performance. The device design in Example 1 effectively suppresses the brightness decay of the device in different angle ranges, demonstrating the importance of this design in improving viewing angle characteristics. Furthermore, the overall device operates at a current density of 10 mA / cm². 2 Under the given conditions, the color coordinate CIEx0 is 0.703, which meets the current requirements for BT.2020 displays. In terms of efficiency, Example 1 achieves 128 cd / A, which is basically equivalent to the efficiency of Comparative Examples 3 and 4, which have similar color coordinate CIEx. Combined with σ0, it can be seen that Example 1 achieves better viewing angle stability while maintaining high efficiency.

[0121] In embodiment 2, the light-emitting layer of the first light-emitting unit uses RD2, and the light-emitting layer of the second light-emitting unit also uses RD2. This is achieved by increasing the HTL thickness of the first light-emitting unit. and the second light emitting unit HTL thickness is reduced (i.e. the total thickness of the device is unchanged), keeping the optical path of the second light emitting unit unchanged and increasing the optical path of the first light emitting unit, the total optical path of the device is unchanged, CIEx1>CIEx2 can also be met. Under this structure, combined with Figure 3 It can be seen that the brightness of Example 2 can also maintain a high level under the condition of 0-30° viewing angle. The brightness of Example 2 attenuates slowly with the increase of viewing angle, showing good viewing angle performance. Compared with Comparative Example 2, the brightness attenuation factor σ0 of Example 2 reaches 0.88, indicating that it has a significant advantage in viewing angle performance. In addition, under the condition of current density 10 mA / cm 2 2, the device efficiency of Example 2 reaches 131 cd / A, which not only has a certain advantage in color gamut, but also has an efficiency greater than 130 cd / A. Combined with σ0, it can be seen that Example 2 not only maintains high efficiency, but also obtains better viewing angle stability.

[0122] In addition, the SETFOS 5.1.1 semiconductor thin film optical simulation software developed by Fluxim AG Company is also used to simulate the viewing angle stability under different light emitting wavebands.

[0123] Example 3: In the device structure, the refractive index (see Table 1) and thickness of each layer material and the λmax of the EL spectrum of each light emitting material (see Table 2) are substituted in the manner known to those skilled in the art. Specifically: a 0.7 mm glass substrate, such as Figure 1 101; followed by I indium tin oxide-silver-indium tin oxide (IAI, 75:1500:150, ) anode 110; followed by the first light emitting unit, which in turn includes: HT-1:HT-2 (97:3) as a hole injection layer (HIL, 97:3, ), 121; HT-1 of Example 1 as a hole transport layer (HTL, ), 122; EB as an electron blocking layer (EBL, ) 123, H1:GH1:GD2 as a light emitting layer EML (37.6:56.4:6, ) 124, the refractive index of H1:GH1 is shown in Table 1, and the λmax of the EL spectrum of GD2 is shown in Table 2, such as Figure 1 124 in Example 1; ET:Liq as an electron transport layer ETL, (40:60, ), 125;

[0124] followed by a charge generation layer, which includes: Yb:ET-1 as n-type layer (n-CGL, 0.7:99.3, )130; HT-1:HT-2 as p-type layer (p-CGL, 97:3, )140;

[0125] followed by a second light-emitting unit, which in turn comprises: HT-1 as hole transport layer HTL, )151; EB as electron blocking layer (EBL, )152; H1:GH1:GD1 as light-emitting layer EML (37.6:56.4:6, ), the refractive index of H1:GH1 see Table 1, the EL spectrum of GD1 see Table 2, as Figure 1 in 153; ET:Liq as electron transport layer ETL, (40:60, )154; Yb as electron injection layer;

[0126] followed by Mg:Ag as cathode (Cathode, 10:90, )160; followed by CPL54 as light extraction layer (CPL, )170.

[0127] CIEx1 simulation method: as the first light-emitting unit single light-emitting layer top-emitting reference device of Example 1, the same parameters are substituted as in Example 3, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1:GH1, and does not substitute the EL spectrum of GD1 max, CIEx1 is simulated.

[0128] CIEx2 simulation method: as the second light-emitting unit single light-emitting layer top-emitting reference device of Example 1, the same parameters are substituted as in Example 3, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1:GH1, and does not substitute the EL spectrum of GD2 max, CIEx2 is simulated.

[0129] The simulated device performance is shown in Table 6.

[0130] Example 4: the simulation method is the same as Example 3, except that the second light-emitting unit brings in the EL spectrum of GD2 and the HTL thickness of the first light-emitting unit is adjusted to and the HTL thickness of the second light-emitting unit is adjusted to

[0131] CIEx1 simulation method: The first light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Example 4, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD2, and CIEx1 is simulated.

[0132] CIEx2 simulation method: The second light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Example 4, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD2, and CIEx2 is simulated.

[0133] Comparative Example 5: The same simulation method as in Example 3, except that the first light-emitting unit and the second light-emitting unit simultaneously substitute the EL spectrum of GD2.

[0134] CIEx1 simulation method: The first light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Comparative Example 5, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD2, and CIEx1 is simulated.

[0135] CIEx2 simulation method: The second light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Comparative Example 5, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD2, and CIEx2 is simulated.

[0136] Comparative Example 6: The same simulation method as in Example 3, except that the first light-emitting unit and the second light-emitting unit simultaneously substitute the EL spectrum of GD1.

[0137] CIEx1 simulation method: The first light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Comparative Example 6, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD1, and CIEx1 is simulated.

[0138] CIEx2 simulation method: The second light-emitting unit single-emitting layer top-emission reference device as in Example 1, the same parameters as in Comparative Example 6, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD1, and CIEx2 is simulated.

[0139] Comparative Example 7: The same simulation method as Example 3, except that the first light-emitting unit and the second light-emitting unit are simultaneously brought into the EL spectrum of GD3.

[0140] CIEx1 simulation method: The first light-emitting unit single light-emitting layer top-emitting reference device as in Example 1, the same parameters are substituted as in Comparative Example 7, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum of GD3, CIEx1 is simulated.

[0141] CIEx2 simulation method: The second light-emitting unit single light-emitting layer top-emitting reference device as in Example 1, the same parameters are substituted as in Comparative Example 7, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum of GD3, CIEx2 is simulated.

[0142] Comparative Example 8: The same simulation method as Example 3, except that the light-emitting layer of the first light-emitting unit substitutes the EL spectrum of GD1, and the light-emitting layer of the second light-emitting unit substitutes the EL spectrum λmax of GD2.

[0143] CIEx1 simulation method: The first light-emitting unit single light-emitting layer top-emitting reference device as in Example 1, the same parameters are substituted as in Comparative Example 8, the only difference is that the light-emitting layer EML of the second light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD2, CIEx1 is simulated.

[0144] CIEx2 simulation method: The second light-emitting unit single light-emitting layer top-emitting reference device as in Example 1, the same parameters are substituted as in Comparative Example 8, the only difference is that the light-emitting layer EML of the first light-emitting unit only substitutes the refractive index of compound H1: GH1, and does not substitute the EL spectrum λmax of GD1, CIEx2 is simulated.

[0145] Table 5 Partial device structure of Examples 3-4 and Comparative Examples 5-8

[0146]

[0147] The structures of the compounds used in the devices are shown below:

[0148]

[0149] Table 6 lists the performance of the simulated devices of Examples 3-4 and Comparative Examples 5-8, the color coordinates CIEx1 corresponding to the bottom-emitting device of the first light-emitting layer, the color coordinates CIEx2 corresponding to the bottom-emitting device of the second light-emitting layer, the luminance decay factor σ0, the color coordinates CIEx0, and the current efficiency CE of the top-emitting stacked organic electroluminescent device.

[0150] Table 6 Performance of simulated devices of Examples 3-4 and Comparative Examples 5-8

[0151]

[0152]

[0153] Discussion:

[0154] As shown in Table 6, in Example 3, the first light-emitting layer uses GD2, and the second light-emitting layer uses GD1. The single light-emitting layer top-emission reference device color coordinates CIEx1 and CIEx2 of the first light-emitting layer and the second light-emitting layer are 0.24 and 0.17, respectively, forming a certain color coordinate difference between them, and the color coordinates of the lower light-emitting unit are relatively reddish, satisfying CIEx1>CIEx2. Under this structure, in terms of viewing angle performance, the brightness decay factor σ0 of Example 3 reaches 0.90, indicating that it has a significant advantage in viewing angle performance. Compared with Example 3, the light-emitting layers of the first light-emitting unit and the second light-emitting unit of Comparative Example 5 both use GD2, the light-emitting layers of the first light-emitting unit and the second light-emitting unit of Comparative Example 6 both use GD1, and the light-emitting layers of the first light-emitting unit and the second light-emitting unit of Comparative Example 7 both use GD3. The σ0 of the stacked devices thereof are 0.86, 0.86 and 0.85, respectively, all of which are significantly less than that of Example 3. In addition, the light-emitting layer of the first light-emitting unit of Comparative Example 8 uses GD1, and the light-emitting layer of the second light-emitting unit uses GD2. Compared with Example 3, the light-emitting layers of the first light-emitting unit and the second light-emitting unit are exchanged, CIEx1<CIEx2, and the σ0 thereof is significantly less than that of Example 3, indicating that only when CIEx1>CIEx2 can there be a significant improvement in brightness decay. In Example 4, the first light-emitting unit and the second light-emitting unit both use GD2, and the thickness of the HTL of the first light-emitting unit is adjusted to 50 nm, which is less than that of the second light-emitting unit. By increasing the thickness of the HTL of the first light-emitting unit and reducing the thickness of the HTL of the second light-emitting unit (i.e. the total thickness of the device remains unchanged), the optical path of the second light-emitting unit is kept unchanged and the optical path of the first light-emitting unit is increased, the total optical path of the device remains unchanged, so that it satisfies CIEx1>CIEx2, and also plays a role in improving the viewing angle

[0155] As shown in the 0-30° brightness decay curve of Figure 4 , the brightness retention rates of Examples 3 and 4 are significantly higher than those of Comparative Examples 5 to 8 under the condition of increased viewing angle. As the viewing angle increases from 0° to 30°, the brightness decay of Examples 3 and 4 is relatively slow, showing good viewing angle stability. Through the device design of Examples 3 and 4, the viewing angle problem of green light can also be improved.

[0156] In summary, the top emission stacked organic electroluminescent device of the present application can achieve the purpose of improving the viewing angle characteristics of the device. The effectiveness of the present application is proved by experimental data. On this basis, we simulated the green light top emission stacked organic electroluminescent device, which can also achieve the effect of improving the viewing angle characteristics of the device, and also proves the effectiveness of the present application under different wavebands.

[0157] It should be understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the application. Therefore, as evident to one of ordinary skill in the art, the claimed application can include variations of the specific embodiments and preferred embodiments described herein. Many of the materials and structures described herein can be substituted with other materials and structures without deviating from the spirit of the application. It is understood that the various theories as to why the application works are not intended to be limiting.

Claims

1. A top emission stacked organic electroluminescent device, comprising: an anode, a cathode, a first light-emitting unit and a second light-emitting unit arranged in sequence between the anode and the cathode; a single light-emitting layer top emission reference device corresponding to the first light-emitting unit, having a color coordinate of CIEx1, a single light-emitting layer top emission reference device corresponding to the second light-emitting unit, having a color coordinate of CIEx2, and satisfying CIEx2 < CIEx1; a luminance decay factor σ0 of the top emission stacked organic electroluminescent device is greater than or equal to 0.88; wherein the luminance decay factor σ0= L 15 L0, L0and L 15 Luminance of the top-emitting stacked organic electroluminescence device at 0° and 15° viewing angle, respectively.

2. The top-emission stacked organic electroluminescent device according to claim 1, wherein a peak wavelength of an electroluminescence spectrum of a light-emitting material of the first light-emitting unit is λ1, a peak wavelength of an electroluminescence spectrum of a light-emitting material of the second light-emitting unit is λ2, and 0 nm ≤ λ1 - λ2 ≤ 20 nm; preferably, 0 nm ≤ λ1 - λ2 ≤ 7 nm.

3. The top-emission stacked organic electroluminescent device according to claim 2, wherein the first light-emitting unit and the second light-emitting unit comprise different light-emitting materials, and λ1 ≥ λ2.

4. The top emission stacked organic electroluminescent device according to claim 2, wherein, λ1 ≥ 500 nm, and λ2 ≥ 500 nm; preferably, the λ1 and λ2 are between 600 nm and 700 nm, or the λ1 and λ2 are between 500 nm and 600 nm; preferably, the λ1 and λ2 are between 620 nm and 630 nm, or the λ1 and λ2 are between 520 nm and 540 nm. 5.The top emission stacked organic electroluminescent device of claim 1, having a color shift ΔCIEx of less than or equal to 0.010 at a viewing angle θ in a range of 15° to 30°, and a luminance decay factor σ0(θ) of greater than or equal to 0.18 at the viewing angle θ in the range of 15° to 30°; preferably, the luminance decay factor σ0(θ) of greater than or equal to 0.4 at the viewing angle θ in the range of 15° to 30°. 6.The top emission stacked organic electroluminescent device of claim 2, when the first light-emitting unit and the second light-emitting unit comprise the same light-emitting material, CIEx1 > CIEx2 is achieved by keeping the optical path of the second light-emitting unit unchanged and increasing the optical path of the first light-emitting unit.

7. The top emission stacked organic electroluminescent device according to claim 1, wherein a luminance decay factor of the first light-emitting unit is σ1, a luminance decay factor of the second light-emitting unit is σ2, and a color coordinate of the top emission stacked organic electroluminescent device is CIEx0, when CIEx2 < CIEx0 ≤ CIEx1, σ1 > σ2. 8.The top emission stacked organic electroluminescent device of claim 6, the optical path of the second light-emitting unit unchanged and the optical path of the first light-emitting unit increased are achieved by adjusting a thickness of a hole transport layer or an electron blocking layer of the first light-emitting unit and the second light-emitting unit. 9.The top emission stacked organic electroluminescent device of claim 1, a horizontal orientation ratio of the second light-emitting unit of the top emission stacked organic electroluminescent device is higher than a horizontal orientation ratio of the first light-emitting unit, and a light-emitting layer horizontal orientation ratio of the second light-emitting unit is greater than or equal to 80%; preferably, the light-emitting layer horizontal orientation ratio of the second light-emitting unit is greater than or equal to 90%. 10.The top emission stacked organic electroluminescent device of claim 1, a light-emitting layer of the first light-emitting unit is prepared by a solution processing technology, the technology comprising spin coating, inkjet printing or blade coating.

11. A display device comprising the top-emission stacked organic electroluminescent device according to any one of claims 1 to 10.

Images