CN108987609B

CN108987609B - White light OLED device and display device

Info

Publication number: CN108987609B
Application number: CN201810845020.7A
Authority: CN
Inventors: 周青超; 杨盛际; 王青; 周卢阳; 陈小川
Original assignee: BOE Technology Group Co Ltd
Current assignee: BOE Technology Group Co Ltd
Priority date: 2018-07-27
Filing date: 2018-07-27
Publication date: 2020-05-01
Anticipated expiration: 2038-07-27
Also published as: CN108987609A

Abstract

The invention provides a white OLED device and a display device. The white OLED device includes: a reflective electrode and a transparent electrode which are oppositely arranged; an organic light emitting layer disposed between the reflective electrode and the transparent electrode; a distributed Bragg reflector disposed on a surface of the transparent electrode distal from the reflective electrode. Therefore, the reflectivity of the distributed Bragg reflector in the white-light OLED device in the full-wave band has the designable and adjustable properties, the full utilization of the microcavity effect of the OLED device can be realized flexibly through the design of the DBR reflector, and the brightness and the luminous efficiency of the OLED device are increased.

Description

White light OLED device and display device

Technical Field

The invention relates to the technical field of display, in particular to a white light OLED device and a display device.

Background

In recent years, silicon-based OLED (organic light emitting diode) microdisplays are being applied in the VR/AR field as near-eye displays, because the silicon-based semiconductor CMOS (complementary metal oxide semiconductor) process is mature, ultra-high PPI (number of pixels per inch) display can be realized, and in addition, OLED displays can be used in a wider temperature range, the silicon-based OLED microdisplays are showing great application prospects. However, the brightness of the silicon-based OLED display currently limits its application in the AR field, and thus the development of a silicon-based OLED display with high brightness is a major current problem.

The application of the strong microcavity effect is an effective means for improving the brightness of the silicon-based OLED device, but in the white-light OLED device, designers often do not want the device to have the strong microcavity effect, because the strong microcavity effect can enhance light of a certain waveband, but correspondingly, due to the resonance periodicity, the strong microcavity effect can also weaken light of the corresponding waveband. Therefore, how to avoid or utilize the microcavity effect of a good OLED device is the key to design a high performance OLED device.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide an OLED device having high luminous efficiency and a simple structure, which can enhance light of a certain wavelength band without weakening light of other wavelength bands or can sufficiently utilize a microcavity effect, and another object of the present invention is to provide a display device.

In one aspect of the invention, the invention provides a white OLED device. According to an embodiment of the present invention, the white OLED device includes: a reflective electrode and a transparent electrode which are oppositely arranged; an organic light emitting layer disposed between the reflective electrode and the transparent electrode; a distributed Bragg reflector disposed on a surface of the transparent electrode distal from the reflective electrode. Therefore, the reflectivity of the distributed Bragg reflector (DBR reflector) in the white light OLED device has designable and adjustable properties in all bands, the full utilization of the microcavity effect of the OLED device can be realized flexibly through the design of the DBR reflector, the brightness and the luminous efficiency of the OLED device are increased, and light in a certain band is enhanced while light in other bands is not weakened.

According to an embodiment of the present invention, the distributed bragg reflector includes a plurality of periodic structures sequentially stacked, each of the periodic structures including a titanium dioxide layer and a silicon dioxide layer, the silicon dioxide layer being disposed on an upper surface of the titanium dioxide layer.

According to an embodiment of the present invention, the dbr comprises a plurality of periodic structures, each of the periodic structures comprising a silicon dioxide layer and hafnium oxide, the hafnium oxide layer being disposed on an upper surface of the silicon dioxide layer.

According to an embodiment of the invention, said distributed bragg reflector comprises 2-6 of said periodic structures.

According to an embodiment of the invention, the microcavity length of the OLED device is adapted for resonance enhancement of red and blue light, and the reflectivity of the distributed bragg mirror for green light is not more than 35%.

According to the embodiment of the invention, the microcavity length of the OLED device is integral multiple of half wavelength of blue light, the distributed Bragg reflector comprises 3 periodic structures, the thickness of the titanium dioxide layer is 40 +/-5 nanometers, and the thickness of the silicon dioxide layer is 70 +/-5 nanometers.

According to the embodiment of the invention, the reflectivity of the distributed Bragg reflector to red light, green light or blue light is more than or equal to 85%.

According to an embodiment of the present invention, the reflectivity of the dbr is greater than 85% for the blue light and less than 30% for the red light and the green light.

According to an embodiment of the present invention, the dbr includes at least 3 periodic structures, the thickness of the silicon dioxide layer is 80 ± 5 nm, and the thickness of the hafnium dioxide layer is 60 ± 5 nm.

In another aspect of the present invention, a display device is provided. According to an embodiment of the present invention, the display apparatus is the aforementioned white OLED device. The display device includes all the structures and features of the white OLED device described above, and will not be described in detail herein.

Drawings

Fig. 1 is a schematic structural diagram of a white OLED device according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Fig. 5 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Fig. 6 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Fig. 7 is a schematic structural diagram of a white OLED device according to another embodiment of the present invention.

Figure 8 is a graph of reflectivity of a DBR mirror according to one embodiment of the invention.

Fig. 9 is a graph of reflectivity of a DBR mirror according to another embodiment of the invention.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

In one aspect of the invention, the invention provides a white OLED device. According to an embodiment of the present invention, referring to fig. 1, the white OLED device includes: a reflective electrode 10 and a transparent electrode 20 disposed opposite to each other; an organic light emitting layer 30, the organic light emitting layer 30 being disposed between the reflective electrode 10 and the transparent electrode 20; a distributed bragg reflector (DBR mirror) 40, the DBR mirror 40 being disposed on a surface of the transparent electrode 20 remote from the reflective electrode 10. In the white light OLED device, the reflecting electrodes and the DBR reflector are two reflecting surfaces of the white light OLED device microcavity, wherein the reflectivity of the distributed Bragg reflector in a full wave band has designable and adjustable properties, the DBR reflector can be flexibly designed, the microcavity effect of the white light OLED device is fully utilized, the brightness and the luminous efficiency of the OLED device are increased, light in a certain wave band is enhanced, and light in other wave bands is not weakened.

It should be noted that, in the above-mentioned white OLED device, due to the reflection effect of the reflective electrode and the DBR mirror on light, light can be reflected back and forth inside the device, and only light with a specific wavelength can be emitted to the outside of the device, which is a microcavity effect.

According to the embodiment of the present invention, the OLED device is generally formed on a substrate, and therefore, referring to fig. 2, the white OLED device according to the embodiment of the present invention may further include a substrate 50, where the substrate 50 is located on a surface of the reflective electrode 10 away from the transparent electrode 20. According to an embodiment of the present invention, the specific material of the substrate 50 is not particularly limited, and for example, a silicon substrate, a glass substrate, a polymer substrate, or the like may be used. Therefore, the material source is wide, and the application range is wide.

According to the embodiment of the present invention, the material forming the reflective electrode may be a metal, a transparent conductive oxide, or the like, and may have a single-layer structure or a multi-layer structure. In some embodiments of the present invention, referring to fig. 3, the reflective electrode 10 has a three-layer structure, for example, a structure including a first transparent oxide layer 11, a metal layer 12, and a second transparent oxide layer 13, which are sequentially stacked, specifically, indium tin oxide is used as a material forming the first transparent oxide layer and the second transparent conductive oxide layer, and silver is used as a material forming the metal layer. Therefore, the reflecting electrode has good conductive performance and good reflectivity, and is beneficial to improving the luminous efficiency of the white light OLED device.

According to an embodiment of the present invention, a material forming the transparent electrode may be a transparent conductive oxide, such as indium zinc oxide. Therefore, the transparent electrode has higher transmittance, so that the microcavity effect of the white OLED device can be effectively and fully adjusted by using the DBR reflector, and the white OLED device can effectively enhance light with a preset color or enhance light with a certain waveband without excessively weakening light with other wavebands.

According to the embodiment of the present invention, the method for forming the reflective electrode and the transparent electrode includes, but is not limited to, chemical vapor deposition and vacuum sputtering methods, and the thicknesses of the reflective electrode and the transparent electrode can be selected according to the requirement, for example, the thickness of the transparent electrode can be 80-200 nm, and the surface flatness and transmittance of the transparent electrode can be ensured in the thickness range; the thickness of the reflecting electrode can be selected according to the requirement on the premise of ensuring the smoothness and the conductivity of the reflecting electrode, so that the microcavity effect of the OLED device is fully utilized, and a better using effect is achieved.

According to an embodiment of the present invention, the light emitting layer may be electroluminescent by the reflective electrode and the transparent electrode. In some embodiments of the invention, the light emitting layer may comprise only a layer of electroluminescent material; in other embodiments of the present invention, the light emitting layer may include a hole injection layer, a hole transport layer, an electroluminescent material layer, an electron transport layer, or an electron injection layer; in some embodiments of the present invention, the light emitting layer between the two reflective surfaces may be a single unit light emitting diode structure (e.g., 2tandem or 3tandem) or a stacked light emitting diode structure (e.g., 2tandem or 3tandem) according to the structure of the white OLED device, and in particular, referring to fig. 4, the single unit structure may be HIL (hole injection layer) 31/HTL (hole transport layer) 32/B-EML (blue electroluminescent material layer) 33/RG-EML (red green mixed electroluminescent material layer) 34/ETL (electron transport layer) 35, referring to fig. 5, the structure of 2tandem may be HIL 31/HTL 32/B-EML 33/n-ETL (n-type doped electron transport layer) 36/HIL 31/HTL 32/R-EML (red electroluminescent material layer) 37/G-EML (green electroluminescent material layer) 38/ETL 35. Therefore, the luminous effect is better, the service life is longer, and the current efficiency and the brightness can be effectively improved.

According to the embodiment of the invention, the forming method of the light-emitting layer comprises but is not limited to vacuum evaporation and the like, so that the process is mature, the precision is high, the operation is convenient, and the method is suitable for industrial production. According to the embodiment of the invention, the thickness of the light-emitting layer can be properly adjusted according to the use requirement, and as the refractive index and the thickness of the light-emitting layer are one of the main factors influencing the microcavity effect, under the condition of ensuring the light-emitting function of the light-emitting layer, a person skilled in the art can adjust the refractive index and the thickness of each layer in the light-emitting layer according to the use requirement of the OLED device, so as to fully utilize the microcavity effect and achieve a better use effect.

According to an embodiment of the present invention, the DBR mirror is a periodic structure composed of two materials of different refractive indices alternating in an ABAB fashion, with fresnel reflections occurring at each interface of the two materials. At the operating wavelength, the optical path difference of the reflected light at two adjacent interfaces is half a wavelength, and in addition, the sign of the reflection coefficient at the interfaces is also changed. Thus, all reflected light at the interface undergoes destructive interference, resulting in a strong reflection. The reflectivity is determined by the number of layers of material and the difference in refractive index between the materials. The reflection bandwidth is mainly determined by the refractive index difference, so that the target reflectivity for different wave bands of light can be obtained according to requirements by changing the refractive index and the thickness of the material.

In some embodiments of the present invention, referring to fig. 6, the dbr includes a plurality of periodic structures sequentially stacked, each of the periodic structures includes a titanium dioxide layer 41 and a silicon dioxide layer 42, and the silicon dioxide layer 42 is disposed on an upper surface of the titanium dioxide layer 41. In other embodiments of the present invention, referring to fig. 7, the dbr comprises a plurality of periodic structures, each of the periodic structures comprising a silicon dioxide layer 42 and a hafnium dioxide layer 43, the hafnium dioxide layer 43 being disposed on an upper surface of the silicon dioxide layer 42. According to the embodiments of the present invention, the number of the periodic structures in the dbr is not particularly limited, and may be selected by those skilled in the art according to actual needs, and in some embodiments of the present invention, the dbr includes 2 to 6 periodic structures. Therefore, the reflectivity of the DBR reflector can be adjusted within a visible light range, the use requirement can be well met, the use requirement of a display device is particularly met, the white light OLED device can enhance the brightness and the luminous efficiency, meanwhile, the luminous effect cannot be influenced by weakening light in a certain wave band, and a good display effect is achieved.

According to the embodiment of the invention, in order to improve the using effect of the white OLED device, particularly the display effect when the white OLED device is used as a display device, the microcavity length of the white OLED device is suitable for resonantly enhancing red light and blue light, and the reflectivity of the distributed Bragg reflector to green light is not more than 35%. Therefore, the white light OLED device can enhance red light and blue light simultaneously through the microcavity effect, the DBR reflector has very low reflectivity in a green light wave band and cannot form a microcavity resonance effect with a reflecting surface formed by a reflecting electrode at the bottom of the OLED device, the microcavity effect of a green light wave band in the white light OLED device is very weak, high green light-emitting rate is guaranteed, and the high-efficiency white light OLED device is obtained.

According to the embodiment of the invention, the resonant mode of the microcavity effect of the white OLED device satisfies the F-P equation, which specifically comprises: the microcavity length is the sum of the product of refractive index and thickness of each layer structure between the effective reflective surface (i.e., the layer structure that mainly plays a role in reflection, such as a metal layer) in the reflective electrode and the DBR mirror and the absolute value of the displacement of the light beam from the vertical direction, as shown in the following formula:

where L is the length of the microcavity,

is the phase shift at the reflective surface (e.g., metal layer in reflective electrode) formed by the light-emitting layer and the reflective electrode, ni and di are the refractive index and thickness of the layer structure (e.g., including the light-emitting layer and the transparent electrode, and including the second transparent oxide layer when the reflective electrode is formed by the first transparent oxide layer, the metal layer, and the second oxide layer, etc.) between the effective reflective surface in the reflective electrode and the DBR mirror, respectively; m is the number of stages of the transmit mode. According to this formula, in the white OLED device, the microcavity length of the microcavity effect can be adjusted to meet the use requirement by adjusting the film thickness of each layer structure between the effective reflective surface in the reflective electrode and the DBR mirror (e.g., the film thickness of the reflective electrode (e.g., the second transparent oxide layer) and the film thickness of the light-emitting layer (e.g., the hole transport layer)).

According to the embodiment of the invention, in order to obtain better intensity and light emitting effect, the microcavity length of the white OLED device can be made to be an integral multiple of half-wavelength of blue light according to the above formula and a method for adjusting the cavity length, and the distributed bragg reflector includes 3 periodic structures, the thickness of the titanium dioxide layer is 40 ± 5 nm, and the thickness of the silicon dioxide layer is 70 ± 5 nm. Therefore, the microcavity length of the white OLED device is adjusted to be an integral multiple of the half-wavelength of the blue light emission wavelength, specifically, an integral multiple of the half-wavelength of 450nm, that is, 225m (m is 1, 2), which also approximately satisfies an integral multiple of the half-wavelength of the red light emission wavelength, that is, an integral multiple of the half-wavelength of 620nm, that is, 310m (m is 1, 2), and both the red light and the blue light can be effectively located at a resonance enhancement position, where there is a weakening effect on the green light in general, however, the DBR mirror (the reflectivity curve is shown in fig. 8) of the above structure has a very low reflectivity in the green light band, and cannot form a microcavity resonance effect with the reflective surface of the reflective electrode, and in the white OLED device, the microcavity effect of the green light band is very weak, and a high light extraction rate is ensured, thereby obtaining a high-efficiency white OLED device.

According to the embodiment of the invention, the DBR mirror can be designed and adjusted to enhance light of a certain predetermined color according to different white OLED device structures or different use requirements. In some embodiments of the present invention, the reflectivity of the dbr to red, green, or blue light is greater than or equal to 85%. Therefore, red light, green light or blue light can be enhanced, and the luminous efficiency is improved.

According to the embodiment of the invention, when the OLED device is used for display, the light emitting efficiency of the blue light is generally low, and in order to obtain a better display effect, the reflectivity of the distributed bragg reflector to the blue light is greater than 85%, and the reflectivity to the red light and the green light is less than 30%. Therefore, the OLED device with the microcavity effect for enhancing the blue light can be obtained, the luminous efficiency of the blue light is effectively improved, and the problem of low blue light luminous efficiency in the OLED device is solved.

According to the embodiment of the invention, in order to better improve the light emitting efficiency of blue light, the distributed bragg reflector comprises at least 3 periodic structures, the thickness of the silicon dioxide layer is 80 +/-5 nanometers, and the thickness of the hafnium dioxide layer is 60 +/-5 nanometers. The DBR reflector has high reflectivity at a blue light waveband, so that an OLED device with a microcavity effect for enhancing blue light can be obtained, the problem of low blue light luminous efficiency in the OLED device is effectively solved, and in practical application, SiO₂/HfO₂The number of the periodic structures can be adjusted according to the requirements of the OLED device, and when the number of the periodic structures is less than the number of the periodic structures>3, a better reflection effect can be achieved, and the reflectivity curve of the DBR mirror with 6 periodic structures is shown in fig. 9.

In another aspect of the present invention, a display device is provided. According to an embodiment of the present invention, the display apparatus is the aforementioned white OLED device. Therefore, the display device has better brightness and luminous efficiency, can achieve better display effect, and comprises all the structures and characteristics of the white OLED device, so that redundant description is omitted.

According to an embodiment of the present invention, the specific type of the display device is not particularly limited, and may be a display panel, a mobile phone, a tablet computer, a notebook computer, a desktop computer display, a game machine, a wearable device, a television, a painted screen, or the like having a display function. Moreover, it can be understood by those skilled in the art that, in addition to the white OLED device, the display device further includes structures and components necessary for a conventional display device, for example, a mobile phone, which may further include structures and components of a housing, a camera module, a fingerprint identification module, a CPU, a sound processing system, and the like, which are provided for a conventional mobile phone, and thus, the description thereof is omitted.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A white OLED device comprising:

a reflective electrode and a transparent electrode which are oppositely arranged;

an organic light emitting layer disposed between the reflective electrode and the transparent electrode;

the distributed Bragg reflector is arranged on the surface of the transparent electrode far away from the reflecting electrode;

the microcavity length of the OLED device is suitable for resonantly enhancing red light and blue light, and the reflectivity of the distributed Bragg reflector to the green light is not more than 35%; or

The reflectivity of the distributed Bragg reflector to the blue light is more than 85%, and the reflectivity to the red light and the green light is less than 30%.

2. The white OLED device according to claim 1, wherein the DBR comprises a plurality of periodic structures stacked in sequence, each periodic structure comprising a titanium dioxide layer and a silicon dioxide layer, the silicon dioxide layer being disposed on an upper surface of the titanium dioxide layer.

3. The white OLED device of claim 1 wherein the dbr includes a plurality of periodic structures, each periodic structure including a silicon dioxide layer and hafnium oxide, the hafnium oxide layer being disposed on an upper surface of the silicon dioxide layer.

4. The white OLED device of claim 2 or 3, wherein the dbr includes 2-6 periodic structures.

5. The OLED device of claim 2 wherein the microcavity length of the OLED device is an integer multiple of half the wavelength of blue light and the dbr includes 3 periodic structures, the titanium dioxide layer has a thickness of 40 ± 5 nanometers and the silicon dioxide layer has a thickness of 70 ± 5 nanometers.

6. The OLED device of claim 3, wherein the dbr includes at least 3 of the periodic structures, the silicon dioxide layer has a thickness of 80 ± 5 nanometers, and the hafnium dioxide layer has a thickness of 60 ± 5 nanometers.

7. A display device comprising a white OLED device according to any one of claims 1 to 6.