Light-emitting diode devices, display panels and display devices

Abstract

This application discloses a light-emitting diode (LED) device, a display panel, and a display apparatus, comprising an anode layer, a hole transport layer, an emissive layer, an electron transport layer, and a cathode layer stacked sequentially. The emissive layer includes a first emissive layer and a second emissive layer stacked together. The first emissive layer is located on the side of the second emissive layer facing the hole transport layer. The first emissive layer includes a first host material, and the second emissive layer includes a second host material. The first triplet excited state energy level of the first host material of the first emissive layer is greater than the first triplet excited state energy level of the second host material of the second emissive layer. This solution ensures low power consumption of the LED device at high grayscale levels while improving color uniformity at low grayscale levels, thus enhancing the display effect.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to a light-emitting diode device, a display panel, and a display apparatus. Background Technology

[0002] Organic light-emitting diodes (OLEDs) and planar light-emitting diode devices based on light-emitting diode (LED) technology are widely used in various consumer electronics products such as mobile phones, televisions, laptops, and desktop computers due to their advantages such as high image quality, power saving, thin body and wide range of applications, becoming the mainstream of light-emitting diode devices.

[0003] However, current OLED display products are prone to color unevenness at low grayscale levels. Summary of the Invention

[0004] The main technical problem solved by this application is to provide a light-emitting diode device, a display panel, and a display device that ensures low power consumption at high grayscale levels while improving the problem of uneven color at low grayscale levels and enhancing the display effect.

[0005] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a light-emitting diode device, including an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode layer stacked sequentially, wherein the light-emitting layer includes a first light-emitting layer and a second light-emitting layer stacked together, the first light-emitting layer being located on the side of the second light-emitting layer facing the hole transport layer, the first light-emitting layer including a first host material, and the second light-emitting layer including a second host material; wherein, the first triplet excited state energy level of the first host material of the first light-emitting layer is greater than the first triplet excited state energy level of the second host material of the second light-emitting layer.

[0006] Preferably, the energy difference between the first triplet excited state of the first host material and the first triplet excited state of the second host material is greater than 0.2 eV.

[0007] Preferably, the first light-emitting layer further includes a first doped material, and the second light-emitting layer further includes a second doped material, wherein the quantum efficiency of the first doped material is lower than that of the second doped material.

[0008] Preferably, the first doping material includes at least one of a quencher or an organic fluorescent material; and / or, the second doping material includes an organic phosphorescent material.

[0009] Preferably, the ratio of the quantum efficiency of the first doped material to the quantum efficiency of the second doped material is less than or equal to 1 / 4.

[0010] Preferably, the first light-emitting layer further includes a first doped material, and the second light-emitting layer further includes a second doped material, wherein the first doping ratio is less than the second doping ratio, the first doping ratio is the volume ratio of the first doped material to the sum of the first main material and the first doped material, and the second doping ratio is the volume ratio of the second doped material to the sum of the second main material and the second doped material.

[0011] Preferably, the ratio of the first doping ratio to the second doping ratio is less than or equal to 1 / 4.

[0012] Preferably, in the stacking direction, the thickness of the first light-emitting layer is less than the thickness of the second light-emitting layer.

[0013] Preferably, the thickness ratio of the first light-emitting layer to the second light-emitting layer is less than or equal to 1 / 3.

[0014] Preferably, the luminous efficiency of the first light-emitting layer is lower than that of the second light-emitting layer, and as the electric field strength of the electric field where the hole transport layer and the electron transport layer are located increases, the rate of increase of the hole mobility of the hole transport layer is greater than that of the electron mobility of the electron transport layer.

[0015] Preferably, the mobility change is defined as the value at which the electric field is at 1.6 x 10⁻⁶. 5 Mobility at V / cm and electric field at 10 4 The ratio of migration rates at V / cm; the ratio of the change in hole migration rate to the change in electron migration rate is greater than or equal to 10.

[0016] Preferably, the light-emitting diode device emits red or green light.

[0017] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a light-emitting diode device, including an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode layer stacked sequentially, wherein the light-emitting layer includes a first light-emitting layer and a second light-emitting layer stacked, the first light-emitting layer being located on the side of the hole transport layer facing the hole transport layer; wherein, the luminous efficiency of the first light-emitting layer is lower than that of the second light-emitting layer, and as the electric field strength of the electric field where the hole transport layer and the electron transport layer are located increases, the rate of increase of hole mobility of the hole transport layer is greater than the rate of increase of electron mobility of the electron transport layer.

[0018] Preferably, the mobility change is defined as the value at which the electric field is at 1.6 x 10⁻⁶. 5 Mobility at V / cm and electric field at 10 4The ratio of migration rates at V / cm; the ratio of the change in hole migration rate to the change in electron migration rate is greater than or equal to 10.

[0019] Preferably, the electric field is at 10 4 At V / cm, the mobility of holes is less than that of electrons.

[0020] Preferably, the light-emitting diode device emits red or green light.

[0021] To solve the above-mentioned technical problems, another technical solution adopted in this application is to provide a display panel, including the light-emitting diode device in any embodiment.

[0022] The beneficial effects of this application are as follows: Unlike the prior art, the light-emitting layer of the light-emitting diode device provided in this application is configured as a double-layer structure. The energy level of the first light-emitting layer, which is closer to the hole transport layer, is higher than the energy level of the second light-emitting layer, which is closer to the electron transport layer. This creates a potential barrier between the first and second light-emitting layers. The energy generated during exciton recombination can only be transferred from the first light-emitting layer to the second light-emitting layer, but not from the second light-emitting layer to the first light-emitting layer. This avoids the energy generated during exciton recombination in the second light-emitting layer when the voltage is high, which is transferred to the first light-emitting layer with lower luminous efficiency. This ensures that excitons always generate energy in the second light-emitting layer, so that the luminous efficiency of the light-emitting diode device remains at a high level at high gray levels, thereby ensuring that the device has low power consumption.

[0023] This application provides a light-emitting diode (LED) device. Since the mobility of electrons and holes increases with increasing voltage, and the rate of increase in hole mobility in the hole transport layer is greater than that in the electron transport layer, due to the difference in electron and hole mobility, at low voltage, the region where electrons and holes recombine is closer to the hole transport layer, i.e., the exciton recombination region is located in the first light-emitting layer. At this time, the luminous efficiency of the OLED device is low. Furthermore, as the voltage increases, the rate of increase in hole mobility is faster than that of electrons, causing the exciton recombination region to gradually shift towards the electron transport layer, i.e., the exciton recombination region gradually moves from the first light-emitting layer to the second light-emitting layer. Since the luminous efficiency of the second light-emitting layer is higher than that of the first light-emitting layer, the OLED device has higher luminous efficiency at high voltage. The LED device provided in this application exhibits lower luminous efficiency at low voltage levels. Since voltage is positively correlated with display grayscale, the luminous efficiency of the LED device is lower at low grayscale levels, thus increasing the operating current of the device. This ensures that the anode of the device is fully initialized upon startup, allowing all devices on the display panel to light up simultaneously and avoiding color unevenness. On the other hand, the LED device provided in this application has higher luminous efficiency at high grayscale levels, thereby reducing the operating current of the device at high grayscale levels and lowering its power consumption. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of one embodiment of the light-emitting diode device of this application;

[0025] Figure 2 This is a schematic diagram showing the change of carrier mobility as a function of electric field in the light-emitting diode device of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Since the luminous efficiency of OLED devices is inversely proportional to their operating current, related technologies typically aim to reduce power consumption at high grayscale levels by ensuring high luminous efficiency. The inventors discovered that this setup usually results in high luminous efficiency at low grayscale levels as well, leading to a lower operating current. This results in insufficient anode initialization of the OLED device upon startup, causing differences in startup time for OLEDs at different locations on the display panel, and consequently, uneven color display.

[0028] In view of the above-mentioned technical problems, this application provides a light-emitting diode device 10, see reference. Figure 1 , Figure 1 This is a schematic diagram of one embodiment of the light-emitting diode device of this application. Specifically, the light-emitting diode device 10 is an OLED device, comprising an anode layer 11, a hole transport layer 12, a light-emitting layer 13, an electron transport layer 14, and a cathode layer 15 stacked sequentially. The light-emitting layer 13 includes a first light-emitting layer 131 and a second light-emitting layer 132 stacked together. The first light-emitting layer 131 is located on the side of the second light-emitting layer 132 facing the hole transport layer 12, i.e., the first light-emitting layer 131 is disposed between the hole transport layer 12 and the second light-emitting layer 132, and the second light-emitting layer 132 is disposed between the first light-emitting layer 131 and the electron transport layer 14. The first triplet excited state energy level of the first light-emitting layer 131 is greater than the first triplet excited state energy level of the second light-emitting layer 132.

[0029] Specifically, the light-emitting layer 13 typically includes a host material and a dopant material. The first light-emitting layer 131 includes a first host material (Host1) and a first dopant material (Dopant1), and the second light-emitting layer 132 includes a second host material (Host2) and a second dopant material (Dopant2). Typically, a light-emitting material with hole or electron transport capabilities is used as the host material, and a small amount of organic fluorescent or phosphorescent material is used as the dopant material. The doping ratio is adjusted according to different material properties to enhance the lifetime and efficiency of the host light-emitting layer.

[0030] Optionally, in one embodiment, the first triplet excited state energy level of the first host material Host1 is greater than the first triplet excited state energy level of the second host material Host2, i.e., T1(Host1) > T1(Host2). Specifically, the difference between the first triplet excited state energy level of the first host material Host1 and the first triplet excited state energy level of the second host material Host2 is greater than 0.2 eV, i.e., T1(Host1) - T1(Host2) > 0.2 eV. This application sets the light-emitting layer 13 as a double-layer structure. Since the T1 energy level of the first host material Host1 is greater than the T1 energy level of the second host material Host2, a potential barrier is generated between the first light-emitting layer 131 and the second light-emitting layer 132. The energy generated during exciton recombination can only be transferred from the first light-emitting layer 131 to the second light-emitting layer 132, but not from the second light-emitting layer 132 to the first light-emitting layer 131. This avoids the energy generated during exciton recombination in the second light-emitting layer 132 being transferred to the first light-emitting layer 131, which has lower luminous efficiency, when the voltage is high. This ensures that the exciton always generates energy in the second light-emitting layer 132, so that the luminous efficiency of the light-emitting diode device 10 remains at a high level when the voltage is high, i.e., at high gray levels, thus ensuring that the device has low power consumption.

[0031] In an optional embodiment, the quantum efficiency of the first dopant 1 is lower than that of the second dopant 2. For example, the first dopant 1 may include materials with low quantum efficiency such as quenchers or organic fluorescent materials, while the second dopant 2 may be materials with high quantum efficiency such as organic phosphorescent materials, thereby making the quantum efficiency of the first emitting layer 131 lower than that of the second emitting layer 132. Specifically, the ratio of the quantum efficiency of the first dopant 1 to that of the second dopant 2 is less than or equal to 1 / 4. For example, the first dopant 1 may be an organic fluorescent material with a quantum efficiency of 25%, and the second dopant 2 may be an organic phosphorescent material with a quantum efficiency of 100%.

[0032] In another optional embodiment, the luminous efficiency of the light-emitting layer 13 can also be changed by adjusting the doping ratio. For example, the first doping material Dopant1 and the second doping material Dopant2 can be of the same material, and the doping ratio of the first doping material Dopant1 can be set lower than the doping ratio of the second doping material Dopant2, wherein the doping ratio is defined as the volume ratio of the doping material Dopant to the sum of the host material Host and the doping materials Dopant. Specifically, the doping ratio of the first doping material Dopant1, i.e., the first doping ratio, can be 1 / 4 or less of the doping ratio of the second doping material Dopant2, i.e., the second doping ratio.

[0033] This application also provides a light-emitting diode device 10, wherein the luminous efficiency of the first light-emitting layer 131 is lower than that of the second light-emitting layer 132, and as the voltage increases, the hole mobility of the hole transport layer 12 increases at a faster rate than the electron mobility of the electron transport layer 14.

[0034] For details, please refer to [link / reference]. Figure 1 and combined Figure 2 , Figure 2 This is a schematic diagram illustrating the change in carrier mobility as a function of an electric field in the light-emitting diode device of this application. For ease of illustration, Figure 2The horizontal axis represents the electric field strength to the power of 1 / 2, and the vertical axis represents mobility. The solid line represents the mobility of the first charge carrier (hole) as a function of the electric field, and the dashed line represents the mobility of the second charge carrier (electron) as a function of the electric field. Driven by voltage, electrons are injected from the cathode layer 15 into the electron transport layer 14 and migrate through the electron transport layer 14 to the light-emitting layer 13 (as shown by the dashed arrow in the figure). Holes are injected from the anode layer 11 into the hole transport layer 12 and migrate through the hole transport layer 12 to the light-emitting layer 13 (as shown by the solid arrow in the figure). Holes and electrons meet in the light-emitting layer 13, recombine to form excitons, and the excited state energy undergoes radiative transitions, generating photons and releasing energy. In this application, the light-emitting layer 13 is configured as a double-layer structure. Since the mobility of charge carriers (including electrons and holes) increases with the increase of the electric field strength, and as the voltage of the electric field of the hole transport layer 12 and the electron transport layer 14 increases, the rate of increase of the hole mobility of the hole transport layer 12 is greater than the rate of increase of the electron mobility of the electron transport layer 14, that is, the slope of the solid line is greater than the slope of the dashed line. Due to the difference in electron and hole mobility, in the low voltage state, the region of electron and hole recombination is close to the hole transport layer 12, that is, the exciton recombination region is located in the first light-emitting layer 131. At this time, the luminous efficiency of the OLED device is low. Furthermore, as the voltage increases, the hole mobility increases faster than the electron mobility, causing the exciton recombination region to gradually shift towards the electron transport layer 14, that is, the exciton recombination region gradually moves from the first light-emitting layer 131 to the second light-emitting layer 132. Since the luminous efficiency of the second light-emitting layer 132 is higher than that of the first light-emitting layer 131, the luminous efficiency of the OLED device is higher in the high voltage state. The LED device 10 provided in this application has two main advantages. First, its luminous efficiency is low under low voltage conditions. Since voltage is positively correlated with display grayscale, the luminous efficiency of the LED device 10 is low under low grayscale conditions, which increases the operating current of the device under low grayscale conditions. This ensures that the anode of the device can be fully initialized when it is turned on, and all devices on the display panel can be turned on simultaneously, avoiding the problem of uneven color. Second, the LED device 10 provided in this application has high luminous efficiency under high grayscale conditions, which reduces the operating current of the device under high grayscale conditions and lowers the power consumption of the device.

[0035] Further reading Figure 2 The mobility change K is defined as the electric field at 1.6 x 10⁻⁶. 5 Mobility at V / cm (i.e., the half power of the electric field strength in the figure is 400) and the electric field at 10 4The ratio of the mobility at V / cm (i.e., the electric field strength in the figure is 1 / 2 to 100); the ratio of the change in hole mobility K1 to the change in electron mobility K2 is greater than or equal to 10, that is, K1 / K2≥10. As can be seen from the figure, under low electric field conditions, such as when the electric field strength to the power of 1 / 2 is 100, the hole mobility is lower than the electron mobility, causing the recombination position of holes and electrons to be closer to the hole transport layer 12. That is, at this time, the exciton recombination region is located in the first luminescent layer 131 near the hole transport layer 12, resulting in low luminous efficiency. Since the hole mobility change value K1 is 10 times or more than the electron mobility change value K2, the hole mobility increases rapidly with the increase of electric field. Under high electric field conditions, such as when the electric field strength to the power of 1 / 2 is 400, the hole mobility is higher than the electron mobility, causing the recombination position of holes and electrons to be closer to the electron transport layer 14. That is, at this time, the exciton recombination region is located in the second luminescent layer 132 near the electron transport layer 14, resulting in higher luminous efficiency.

[0036] Optionally, in the stacking direction Z, the thickness d1 of the first light-emitting layer 131 is less than the thickness d2 of the second light-emitting layer 132. Specifically, the thickness ratio of the first light-emitting layer 131 to the second light-emitting layer 132 is less than or equal to 1 / 3. Because the first light-emitting layer 131 is thinner, the distance between the first light-emitting layer 131 and the second light-emitting layer 132 in the stacking direction Z is less than the distance between the second light-emitting layer 132 and the first light-emitting layer 131. This results in a shorter time for holes to pass through the first light-emitting layer 131 and enter the second light-emitting layer 132 compared to the time for electrons to pass through the second light-emitting layer 132 and enter the first light-emitting layer 131. Consequently, holes and electrons have a higher probability of recombination in the second light-emitting layer 132 to generate excitons. This further ensures that, except for low grayscale conditions, the exciton recombination region is located in the second light-emitting layer 132, which has higher luminous efficiency, thereby ensuring that the light-emitting diode device 10 has lower power consumption.

[0037] Optionally, the light-emitting diode device 10 emits either red or green light. Since the luminous efficiency of red and green light-emitting materials is typically higher at low grayscale levels, red and green light-emitting diode devices 10 are more prone to color unevenness due to excessively high luminous efficiency at low grayscale levels, especially the red light-emitting diode device 10. Therefore, the structure of the light-emitting diode device 10 in this application can be applied only to the red light-emitting diode device 10, or to both the red and green light-emitting diode devices 10.

[0038] This application also provides a display panel, including a substrate and a light-emitting diode device 10 of any of the above embodiments disposed on the substrate.

[0039] This application also provides a display device, including the aforementioned display panel, which can be a mobile phone, tablet computer, wearable smart device, etc. The display panel and display device provided by this application ensure low power consumption at high grayscale levels while improving the problem of uneven color at low grayscale levels, thus enhancing the display effect.

[0040] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A light-emitting diode device, characterized in that, It includes an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode layer stacked in sequence. The light-emitting layer includes a first light-emitting layer and a second light-emitting layer stacked in sequence. The first light-emitting layer is located on the side of the second light-emitting layer facing the hole transport layer. The first light-emitting layer includes a first main material and the second light-emitting layer includes a second main material. Wherein, the first triplet excited state energy level of the first host material of the first light-emitting layer is greater than the first triplet excited state energy level of the second host material of the second light-emitting layer; The luminous efficiency of the first light-emitting layer is lower than that of the second light-emitting layer, and as the electric field strength of the electric field where the hole transport layer and the electron transport layer are located increases, the rate of increase of hole mobility of the hole transport layer is greater than that of the electron mobility of the electron transport layer.

2. The light-emitting diode device according to claim 1, characterized in that, The energy difference between the first triplet excited state of the first host material and the first triplet excited state of the second host material is greater than 0.2 eV.

3. The light-emitting diode device according to claim 1, characterized in that, The first light-emitting layer further includes a first doped material, and the second light-emitting layer further includes a second doped material, wherein the quantum efficiency of the first doped material is lower than that of the second doped material.

4. The light-emitting diode device according to claim 3, characterized in that, The first doping material includes at least one of a quencher or an organic fluorescent material; and / or, The second doped material includes organic phosphorescent materials.

5. The light-emitting diode device according to claim 4, characterized in that, The ratio of the quantum efficiency of the first doped material to the quantum efficiency of the second doped material is less than or equal to 1 / 4.

6. The light-emitting diode device according to claim 1, characterized in that, The first light-emitting layer further includes a first doped material, and the second light-emitting layer further includes a second doped material, wherein the first doping ratio is less than the second doping ratio, the first doping ratio is the volume ratio of the first doped material to the sum of the first main material and the first doped material, and the second doping ratio is the volume ratio of the second doped material to the sum of the second main material and the second doped material.

7. The light-emitting diode device according to claim 6, characterized in that, The ratio of the first doping ratio to the second doping ratio is less than or equal to 1 / 4.

8. The light-emitting diode device according to claim 1, characterized in that, In the stacking direction, the thickness of the first light-emitting layer is less than the thickness of the second light-emitting layer.

9. The light-emitting diode device according to claim 8, characterized in that, The thickness ratio of the first light-emitting layer to the second light-emitting layer is less than or equal to 1 / 3.

10. The light-emitting diode device according to claim 1, characterized in that, The change in mobility is defined as the electric field at 1.6 x 10⁻⁶. 5 Mobility at V / cm and electric field at 10 4 The ratio of migration rates at V / cm; The ratio of the change in hole mobility to the change in electron mobility is greater than or equal to 10.

11. The light-emitting diode device according to claim 1, characterized in that, The light-emitting diode device emits either red or green light.

12. A light-emitting diode device, characterized in that, It includes an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode layer stacked in sequence. The light-emitting layer includes a first light-emitting layer and a second light-emitting layer stacked in sequence. The first light-emitting layer is located on the side of the second light-emitting layer facing the hole transport layer. The luminous efficiency of the first light-emitting layer is lower than that of the second light-emitting layer, and as the electric field strength of the electric field where the hole transport layer and the electron transport layer are located increases, the rate of increase of hole mobility of the hole transport layer is greater than that of the electron mobility of the electron transport layer. The change in mobility is defined as the electric field at 1.6 x 10⁻⁶. 5 Mobility at V / cm and electric field at 10 4 The ratio of migration rates at V / cm; The ratio of the change in hole mobility to the change in electron mobility is greater than or equal to 10; electric field at 10 4 At V / cm, the mobility of holes is less than that of electrons.

13. The light-emitting diode device according to claim 12, characterized in that, The light-emitting diode device emits either red or green light.

14. A display panel, characterized in that, Includes the light-emitting diode device as described in any one of claims 1 to 13.

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