Light-emitting device, material selection method and display panel

Abstract

This application discloses a light-emitting element, a material selection method, and a display panel. The light-emitting element has a light-emitting layer containing a host material and a guest material, and when carriers are injected into the light-emitting layer, there is a defect energy between the host material and the guest material, and the absolute value of the defect energy is 0.03 eV or more. The light-emitting element has improved luminous efficiency in a highlight display state, reducing the operating voltage of the light-emitting element, ensuring the display quality of the display panel in a highlight state while reducing the overall power consumption of the display panel.

Description

[Technical field]

[0001] This application claims priority to Chinese Patent Application No. 202011476865.7, entitled "Light-emitting device, material selection method and display panel," filed on December 15, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of display technology, and more particularly to a light-emitting element, a material selection method, and a display panel. [Background technology]

[0003] Currently, organic light-emitting diode (OLED) display panels are tending to develop toward highlight display, and therefore it is necessary to improve the luminous efficiency of the light-emitting element in the highlight display state. In general, in order to improve the luminous efficiency by increasing the aperture area of ​​the light-emitting element, the pixel density must be sacrificed, and the power consumption of the display panel increases accordingly, thereby affecting the performance of the display panel and increasing the usage cost. Summary of the Invention [Problem to be solved by the invention]

[0004] The present application provides a light-emitting device, the light-emitting device having an emitting layer including a host material and a guest material, wherein when carriers are injected into the emitting layer, there is a defect energy Et between the host material and the guest material, and the absolute value of the defect energy Et is 0.03 eV or more.

[0005] The light-emitting element according to the present application has improved light-emitting efficiency in a highlighted display state while reducing the operating voltage of the light-emitting element, thereby ensuring the display quality of the display panel in the highlighted state while reducing the overall power consumption of the display panel. [Means for solving the problem]

[0006] The material selection method according to the present application is used for selecting a light-emitting layer material of a green or red light-emitting element, and the material selection method includes the steps of: arranging a plurality of light-emitting material sets, each of which includes a host material and a guest material, and at least one of the host material and the guest material included in each of the two light-emitting material sets is different from each other; fabricating a plurality of single-carrier elements, each of which has a light-emitting layer, using each of the light-emitting material sets as a light-emitting layer material; obtaining a defect energy Eti between the host material and the guest material in the single-carrier element corresponding to each of the light-emitting material sets; and selecting a target light-emitting material set from the plurality of light-emitting material sets based on the defect energy Eti corresponding to each of the light-emitting material sets to be used as a light-emitting layer material of the light-emitting element.

[0007] The light-emitting layer material selected by the material selection method of the present application can improve the light-emitting efficiency of the light-emitting element in the highlighted display state and reduce the power consumption, thereby ensuring the display quality and display effect of the display panel in the highlighted display state and at the same time reducing the overall power consumption of the display panel. [Brief description of the drawings]

[0008] [Figure 1] 4 is a diagram showing the relationship between the energy levels of the activation energies of the functional layers on the hole injection side of the light emitting layer of the light emitting element in one embodiment of the present application. FIG. [Diagram 2] FIG. 13 is a diagram showing the relationship between the energy levels of the activation energies of the functional layers on the electron injection side of the light-emitting layer of the light-emitting element in another embodiment of the present application. [Diagram 3] 1 is a graph showing the relationship between luminous efficiency and luminance of a light-emitting element in one set of comparative experiments of the present application. [Figure 4] 1 is a graph showing the relationship between the operating voltage and the luminous efficiency of a light-emitting element in a set of comparative experiments of the present application. [Diagram 5] 1 is a step flowchart of a material sorting method in one embodiment of the present application. [Figure 6] 1 is a step flowchart of a material selection method according to another embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In order to better understand the present application, the light emitting device, the material selection method and the display panel provided by the embodiments of the present application will be described in detail below with reference to FIGS.

[0010] The inventors have found through extensive research that, in a situation where display panels are developed toward highlight display, the roll-off situation of the light emitting device becomes serious in the highlight display state. The general roll-off situation refers to a phenomenon in which the light emitting efficiency of the light emitting device gradually increases to a maximum value and then decreases in the process of a continuous increase in current density. In the stage where the light emitting efficiency decreases, the faster the rate of decrease in the light emitting efficiency, the more serious the roll-off situation becomes. The seriousness of the roll-off situation not only affects the highlight display quality of the display panel, but also increases the power consumption of the display panel due to low light emitting efficiency, affecting the usage performance and lifespan of the display panel.

[0011] Generally, the actual brightness of the light-emitting element is reduced by increasing the pixel aperture area of ​​the light-emitting element to improve the brightness of the display panel. This method sacrifices the high pixel density of the display panel, making it difficult to effectively improve the overall performance of the light-emitting element.

[0012] Therefore, one aspect of the present application provides a light-emitting element, the light-emitting element having an emission layer including a host material and a guest material, wherein when carriers are injected into the emission layer, there is a defect energy Et between the host material and the guest material, and the absolute value of the defect energy Et is 0.03 eV or more.

[0013] The light-emitting element of the present application can improve the light-emitting efficiency in a highlight display state, while at the same time lowering the operating voltage of the light-emitting element, and further reducing the power consumption of the light-emitting element itself, thereby realizing a reduction in the power consumption of the entire display panel.

[0014] In one embodiment, the light-emitting layer of the light-emitting device is a phosphorescent light-emitting layer, where the guest material is a phosphorescent material. In these embodiments, the emission color of the light-emitting layer can be blue, red, green, or the like.

[0015] In another embodiment, the light-emitting layer of the light-emitting device is a phosphorescent light-emitting layer, the guest material is a phosphorescent light-emitting material, the host material is a phosphorescent light-emitting host material, and the emission color of the light-emitting layer is any of the primary colors red or green.

[0016] The inventors have studied green and red light emitting devices and found that the light emitting layer of the light emitting device includes a host material and a guest material. Generally, the guest material is doped into the host material, and in the process of the light emitting device being energized to emit light, the electrons and holes are injected into the light emitting layer from the electron injection direction and the hole injection direction, respectively, and the guest material forms a carrier trap for the host material, so that the electrons and holes are less likely to be injected into the host material first and more likely to be injected directly into the guest material, and the carriers are bound to the guest material to form exciton emission. The above carrier trap has the ability to trap carriers, i.e., to trap holes and electrons, so that when the carriers are injected into the host material, the energy required to overcome the carrier trap is the defect energy Et. When it is understood that the carriers are injected into the light emitting layer, there is a defect energy Et between the host material and the guest material. The inventors have studied and found that by controlling the defect energy Et within a certain predetermined range, the light emitting efficiency of the light emitting device can be improved and the overall performance of the light emitting device can be guaranteed.

[0017] In some alternative embodiments, the absolute value of the defect energy Et is in the range of 0.03 eV to 0.08 eV.

[0018] In the present embodiment, the first reference defect state energy Et a Obtaining the absolute value range of can take the following steps.

[0019] S01, preparing a plurality of test monochromatic light-emitting devices, each of which has a monochromatic light-emitting layer, the test monochromatic light-emitting devices have different light-emitting layer materials, and the remaining functional layers have the same structure and functional layer materials.

[0020] The light-emitting layer materials of each test single-color light-emitting device include a host material and a guest material.

[0021] S02, obtaining test parameters for each test single-color light-emitting device, and selecting a plurality of target test single-color light-emitting devices using first reference test parameters.

[0022] In some embodiments, the first reference test parameter is a luminous efficacy parameter of the light-emitting element.

[0023] S03, for each target test single-color light-emitting device, when carriers are injected into the light-emitting layer of each target test single-color light-emitting device, the defect energy Et j where j≧1 and j is an integer.

[0024] First reference defect state energy Et a The absolute value range of Et j is determined based on:

[0025] The defect energy Et between the host material and the guest material can be calculated based on the following formula: Et=mkT Equation (1) m=logJ / logV Equation (2)

[0026] In equations (1) and (2), Et is the defect energy, J is the current density, V is the preset voltage, k is the Boltzmann constant, and T is the preset temperature.

[0027] In some examples, a single carrier device is prepared, which includes a light-emitting layer of a light-emitting device, and the light-emitting layer includes a host material and a guest material. Then, a current test is performed on the single carrier device to obtain an IV curve, i.e., a current-voltage curve, of the single carrier device at a preset temperature. Based on the current-voltage curve, the defect energy Et between the host material and the guest material is calculated using the above formula (1) and formula (2).

[0028] In some optional embodiments, the light-emitting device further includes a hole transport layer disposed on the hole injection side of the light-emitting layer, and a first activation energy difference ΔEa 1 and a first activation energy difference ΔEa 1 The absolute value of is in the range of 0.1 eV to 0.3 eV.

[0029] Referring to FIG. 1, a first activation energy difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer 1 and the first activation energy difference is ΔEa 1 >0 eV. That is, the activation energy of the host material is greater than the activation energy of the hole transport layer in the hole injection direction of the light emitting layer. In some examples, the first activation energy difference ΔEa 1 The numerical range of is 0.1 eV to 0.3 eV. In these examples, ΔEa 1 If the value of is within the above reasonable range, ΔEa 1 If the value of ΔEa is small, a large amount of holes will accumulate in the light-emitting layer, which will affect the light-emitting performance of the light-emitting device. 1 A large value of θ2 prevents the hole transport from being affected.

[0030] In these alternative embodiments, the light-emitting device further includes a compensation layer disposed between the hole transport layer and the light-emitting layer. In the hole injection direction of the light-emitting layer, the activation energy of the compensation layer is between the activation energy of the hole transport layer and the activation energy of the host material. The activation energy of the compensation layer is between the activation energy of the hole transport layer and the activation energy of the host material.

[0031] In another embodiment, in the hole injection direction of the light emitting layer, the activation energy of the compensation layer is the same as that of the hole transport layer, and both of the activation energies of the compensation layer and the hole transport layer are lower than that of the host material; or in the hole injection direction of the light emitting layer, the activation energy of the compensation layer is higher than that of the hole transport layer and lower than that of the host material; or in the hole injection direction of the light emitting layer, the activation energy of the compensation layer is higher than that of the hole transport layer and the same as that of the host material.

[0032] In some alternative embodiments, the light-emitting device further comprises an electron transport layer disposed on the electron injection side of the light-emitting layer. A second activation energy difference ΔEa between the activation energies of the host material and the electron transport layer. 2 and a second activation energy difference value ΔEa 2 The absolute value of ΔEa is in the range of 0.1 eV to 0.3 eV. 2 If the value of is within the above reasonable range, ΔEa 2 If the value of ΔEa is small, a large amount of electrons will be accumulated in the light-emitting layer, which will prevent the light-emitting performance of the light-emitting device from being affected. 2 A large value of avoids affecting the electron transfer.

[0033] In some embodiments, in the electron injection direction of the light-emitting layer, the activation energy of the host material is higher than the activation energy of the electron transport layer, and a second activation energy difference ΔEa 2 The numerical range of is 0.1 eV to 0.3 eV.

[0034] 2, the light-emitting device further includes a hole-blocking layer disposed between the electron-transporting layer and the light-emitting layer, and in the electron injection direction of the light-emitting layer, the activation energy of the hole-blocking layer is between the activation energy of the electron-transporting layer and the activation energy of the host material.

[0035] The activation energy of the hole blocking layer is between the activation energy of the electron transport layer and the activation energy of the host material. In the electron injection direction of the light emitting layer, the activation energy of the hole blocking layer is the same as the activation energy of the electron transport layer, and the activation energy of the hole blocking layer and the activation energy of the electron transport layer are both lower than the activation energy of the host material. Alternatively, in the electron injection direction of the light emitting layer, the activation energy of the hole blocking layer is higher than the activation energy of the electron transport layer and lower than the activation energy of the host material. Alternatively, in the electron injection direction of the light emitting layer, the activation energy of the hole blocking layer is higher than the activation energy of the electron transport layer and the same as the activation energy of the host material.

[0036] In the present application, the activation energy is a barrier that electrons or holes must overcome when they are transferred between different functional layers of a light-emitting device. In the present application, the activation energy of a single-layer or multi-layer functional layer can be understood as a barrier that electrons (or holes) must overcome when they flow from the cathode side (or anode side) through a single-layer or multi-layer functional layer. The above-mentioned functional layer means a carrier layer and a light-emitting layer in a light-emitting device. The carrier layer in a light-emitting device includes an electron transport layer, a hole blocking layer, a compensation layer, a hole transport layer, and a hole injection layer. Alternatively, the activation energy in the present application can be understood as the energy required for electrons to flow from the cathode side through the functional layer of an electron carrier, and the energy required for holes to flow from the anode side through the functional layer of a hole carrier. The activation energy difference can be understood as the energy required for carriers to flow from one functional layer to the other functional layer in a certain carrier flow direction (for example, the electron injection direction or the hole injection direction).

[0037] When the functional layer is composed of a single material, the activation energy Ea of the material is the activation energy Ea corresponding to the functional layer. When the functional layer is composed of two or more materials, the calculation method of the activation energy of the functional layer is as follows: First, obtain the multiplication value of the activation energy of each material and the molar mass fraction corresponding to each material, and then add the above multiplication values ​​to obtain the overall activation energy of the functional layer, which can also be called the weighted average activation energy. When the light-emitting layer includes a host material and a guest material, the activation energy of the host material refers to the activation energy of the host material in the light-emitting layer.

[0038] The activation energy is given by the Arrhenius equation: Ea = E 0 +mRT, where Ea is the activation energy and E 0 and m are constants independent of temperature, T is temperature, and R is the molar gas constant. In other words, as can be seen from the above formula, activation energy is related to temperature. Also, the unit of activation energy obtained from the calculation formula is joule J, and the above unit of activation energy can be converted to electron volts eV using a simple conversion formula. Here, the conversion formula is 1 eV = 1.602176565 x 10 -19 J. As will be understood, the present application provides a basic formula for calculating Ea, and a person skilled in the art can calculate Ea using the basic Arrhenius formula provided by the present application or various modifications of the Arrhenius formula.

[0039] In some examples, the activation energy of the carrier layer located on the hole injection side of the light emitting layer and the light emitting layer, the activation energy difference between the carrier layer on the hole injection side, and the activation energy difference between the light emitting layer and the carrier layer on the hole injection side can all be calculated by preparing a hole-only element and performing a current test on the hole-only element. The current test is performed on the hole-only element to obtain an IV curve (i.e., a current-voltage curve) of the hole-only element, and the activation energy is obtained by employing the Arrhenius equation or various modifications of the Arrhenius equation based on the IV curve of the hole-only element.

[0040] As a specific example, when calculating the activation energy difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer in the light-emitting device, a first hole-only device and a second hole-only device are prepared. The first hole-only device having a hole transport layer is prepared, a current test is performed on the first hole-only device to obtain a first IV curve, and the Ea of the hole transport layer is calculated using the Arrhenius equation. 1 A second hole-only device having a hole transport layer and an emitting layer (having a host material) is prepared, and a current test is performed on the second hole-only device, so that holes flow from the hole transport layer to the emitting layer, and a second IV curve is obtained, and the Ea 2 The difference calculation method can be used, i.e. ΔEa = Ea 2 -Ea 1 Based on this, the difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer in the light-emitting device is calculated.

[0041] In some examples, the hole-only element allows only holes to pass through. The first hole-only element may include an anode, a first hole transport layer, an electron blocking layer, and a cathode, which are stacked together. The second hole-only element may include an anode, a second hole transport layer, an emitting layer (containing only a host material), an electron blocking layer, and a cathode, which are stacked together. The first hole transport layer and the second hole transport layer are the same, and the first hole-only element and the second hole-only element are subjected to a current test with only the emitting layer (containing only a host material) as a single variable. In addition, the electron blocking layer can block the electrons generated by the cathode from being transferred through the hole-only element, thereby achieving the purpose that the hole-only element only allows hole transport.

[0042] In some embodiments, the activation energy of the carrier layer located on the electron injection side of the light-emitting layer in the light-emitting device and the light-emitting layer, the activation energy difference between the carrier layer on the electron injection side, and the activation energy difference between the light-emitting layer and the carrier layer on the electron injection side can all be calculated by preparing an electron-only device and performing a current test on the electron-only device. The current test is performed on the electron-only device to obtain an IV curve (i.e., a current-voltage curve) of the electron-only device, and the activation energy is calculated based on the obtained IV curve of the electron-only device using the Arrhenius equation or various modifications of the Arrhenius equation.

[0043] As a specific example, when calculating the difference ΔEa' between the activation energy of the host material and the electron transport layer in the light-emitting device, a first electron-only device and a second electron device are prepared. A first electron-only device having an electron transport layer is prepared, and a current test is performed on the first electron-only device to obtain a first IV curve, and the Ea1' of the electron transport layer is calculated using the Arrhenius equation. A second electron-only device having an electron transport layer and a light-emitting layer (having only a host material) is prepared, and a current test is performed on the second electron-only device, electrons flow from the electron transport layer to the light-emitting layer, and a second IV curve is obtained, and the Ea2' of the electron transport layer and the light-emitting layer (having only a host material) is calculated using the Arrhenius equation. Using the difference calculation method, that is, ΔEa'=Ea 2 '-Ea 1 Based on this, the difference ΔEa′ between the activation energy of the host material and the activation energy of the electron-transporting layer in the light-emitting device can be calculated.

[0044] In some examples, the electron-only element allows only electrons to pass through. The first electron-only element may include an anode, a hole blocking layer, a first electron transport layer, and a cathode, which are stacked together. The second electronic element may include an anode, a hole blocking layer, an emitting layer (having only a host material), a second electron transport layer, and a cathode, which are stacked together. The first electron transport layer is the same as the second electron transport layer, and the first electron-only element and the second electron-only element are subjected to a current test with only the emitting layer (having only a host material) as a single variable. The hole blocking layer can block the holes generated by the anode from being transferred in the single-electron element, achieving the purpose that the electron-only element only allows electron transfer.

[0045] In another embodiment, the activation energy of the functional layer can be obtained by using a thermogravimetric analysis method. For example, the first carrier layer and the single-color light-emitting layer are subjected to a thermogravimetric analysis as a whole, and the activation energy of each of the functional layers is directly calculated based on the thermogravimetric analysis results. Thermogravimetric analysis refers to a method of obtaining the change relationship of the mass of a substance with temperature (or time) at a program-controlled temperature. After obtaining a thermogravimetric curve using a thermogravimetric analysis technique, the average activation energy is calculated by a differential subtraction (Freeman-Carroll) method or an integral (OWAZa) method, etc.

[0046] Generally, the highest occupied energy level orbital HOMO and the lowest occupied energy level orbital LUMO are used to judge the energy level matching status of each functional layer in a light emitting device. However, the HOMO level and the LUMO level only consider the carrier injection efficiency, and do not consider the interface factor between the functional layers and the temperature and other factors. When each functional layer in a light emitting device is designed and matched only by the HOMO level and the LUMO level, the performance parameters of the finished light emitting device and the designed light emitting device have a large error from the expected performance.

[0047] In some optional embodiments of the present application, it is found that when designing a red or green light-emitting device, the defect energy Et between the host material and the guest material in the light-emitting layer affects the light-emitting efficiency of the light-emitting device in the highlighted state. The defect energy Et between the host material and the guest material in the light-emitting layer can be used to determine the matching relationship between the host material and the guest material in the light-emitting device, so as to more effectively improve the light-emitting efficiency of the light-emitting device.

[0048] On the other hand, the activation energy Ea is considered after considering the defect energy Et between the host material and the guest material of the light-emitting layer, and the level matching relationship of the activation energy Ea of each functional layer in the light-emitting device is considered. By starting from the activation energy, the effects of various factors such as carrier injection between the functional layers, carrier transport between the functional layers, and temperature during the actual use of the light-emitting device on the overall performance of the light-emitting device can be comprehensively considered.

[0049] In some embodiments, the light-emitting device has a defect energy Et between the host material and the guest material when carriers are injected into the light-emitting layer, and the absolute value of the defect energy Et is 0.03 eV or more. And, a first activation energy difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer. 1 and a first activation energy difference value ΔEa 1 The absolute value of is in the range of 0.1 eV to 0.3 eV.

[0050] The light-emitting device further includes an electron transport layer disposed on the electron injection side of the light-emitting layer. A second activation energy difference ΔEa between the activation energy of the host material and the activation energy of the electron transport layer is 2 and a second activation energy difference ΔEa 2 The absolute value of Et is in the range of 0.1 eV to 0.3 eV. In these examples, the light-emitting element taking into consideration both the defect energy Et and the activation energy Ea has an increased luminous efficiency of 0% to 15% and an extended luminous life of 0% to 40% compared to a light-emitting element that only satisfies the requirement that the absolute value of the defect energy Et between the host material and the guest material is 0.03 eV or more.

[0051] In order to demonstrate the effect of the light-emitting device according to the present application in improving the light-emitting efficiency in a highlight display state, the following set of comparative experiments is designed. The comparative experiments include Comparative Example 1 and Experimental Example 1. Comparative Example 1 is a first red light-emitting device, in which the absolute value of the defect energy Et1 between the host material and the guest material in the light-emitting layer of the first red light-emitting device is less than 0.03 eV. Experimental Example 1 is a second red light-emitting device, in which the absolute value of the defect energy Et2 between the host material and the guest material in the light-emitting layer of the second red light-emitting device is greater than 0.03 eV and less than 0.08 eV. In the comparative experiments, only the defect energy Et between the host material and the guest material in the light-emitting layer of the red light-emitting device is used as a variable.

[0052] [Table 1]

[0053] In Table 1, CIEx is the color coordinate and refers to the red light emitted by the red light emitting element. L is the light emitting luminance of the first red light emitting element and the second red light emitting element. Nits is the unit of light emitting luminance. In the experimental test, the first red light emitting element and the second red light emitting element are both in the highlighted display state, and the luminance is 6000 nits. Vd represents the operating voltage of the light emitting element. The operating voltage of the first red light emitting element in Comparative Example 1 is the reference voltage value Vd 0 The operating voltage of the second red light emitting element in Experimental Example 1 is lower than that of the first red light emitting element in Comparative Example 1, and the operating voltage of the second red light emitting element in Experimental Example 1 is 0.03V lower, so that the second red light emitting element consumes less power than the first red light emitting element. Eff. shows the luminous efficiency of the light emitting elements. As can be seen from Table 1, the luminous efficiency of the second red light emitting element is 10.2% higher than that of the first red light emitting element.

[0054] Based on the comparative experimental results shown in Table 1, the light-emitting element of the embodiment of the present application has a defect energy Et between the host material and the guest material when carriers are injected into the light-emitting layer, and the defect energy Et>0.03 eV. This can improve the luminous efficiency of the light-emitting element in the highlighted display state and reduce the operating voltage of the light-emitting element, thereby reducing the power consumption of the light-emitting element and further reducing the overall power consumption of the display panel.

[0055] Fig. 3 shows the relationship curves between the luminous efficiency and the luminous brightness in the test process of the first and second red light emitting devices in the comparative experiment. As can be seen from Fig. 3, with the increase in the luminous brightness of the light emitting devices, the luminous efficiency of the second red light emitting device is always higher than that of the first red light emitting device.

[0056] 4 shows the relationship between the operating voltage and the luminous efficiency in the test process of the first and second red light emitting devices in the comparative experiment. As can be seen from FIG. 4, at the same luminance, the operating voltage of the first red light emitting device is higher than that of the second red light emitting device.

[0057] The light-emitting element has a defect energy Et between the host material and the guest material having an absolute value of 0.03 eV or more when carriers are injected into the light-emitting layer, and a first activation energy difference ΔEa 1 The absolute value of the numerical range of 0.1 eV to 0.3 eV, and / or the second activation energy difference ΔEa 2 In order to further demonstrate that a better luminescence effect can be obtained when the absolute value of satisfies the numerical range of 0.1 eV to 0.3 eV, another set of comparative experiments is carried out. The comparative experiments include Comparative Example 2, Experimental Example 2, Experimental Example 3 and Experimental Example 4.

[0058] [Table 2]

[0059] As can be seen from the color coordinate values ​​in Table 2, Comparative Example 2, Experimental Example 2, Experimental Example 3, and Experimental Example 4 are all red light emitting devices that emit red light. LT97@6000nits is the time elapsed until the emission luminance of the red light emitting device attenuates to 97% of the initial emission luminance when the initial emission luminance is 6000nits, and LT97@6000nits indicates the emission life of the light emitting device.

[0060] The luminous life of the light-emitting element in Comparative Example 2 is taken as a reference value, the luminous life of Experimental Example 2 is increased by 23% compared to the luminous life of Comparative Example 2, the luminous life of Experimental Example 3 is increased by 20% compared to the luminous life of Comparative Example 2, and the luminous life of Experimental Example 4 is increased by 40% compared to the luminous life of Comparative Example 2. Vd is an operating voltage, and the operating voltage in Comparative Example 2 is taken as a reference value, the operating voltage of Experimental Example 2 is reduced by 0.11V compared to the operating voltage of Comparative Example 2, the operating voltage of Experimental Example 3 is reduced by 0.10V compared to the operating voltage of Comparative Example 2, and the operating voltage of Experimental Example 4 is reduced by 0.32V compared to the operating voltage of Comparative Example 2. The reduction in the operating voltage reduces the power consumption while the light-emitting element is emitting light, and the display power consumption of the entire display panel can be reduced. However, at the same time as the power consumption of the light-emitting element is reduced, the luminous efficiency of Experimental Example 2 is increased by 5% compared to Comparative Example 2, the luminous efficiency of Experimental Example 3 is increased by 4% compared to Comparative Example 2, and the luminous efficiency of Experimental Example 4 is increased by 12.2% compared to Comparative Example 2.

[0061] The above data shows that the light-emitting element satisfies the requirement that the defect energy Et between the host material and the guest material has an absolute value of 0.03 eV or more, and the first activation energy difference ΔEa 1 The absolute value of the numerical range of 0.1 eV to 0.3 eV, and / or the second activation energy difference ΔEa 2 It has been explained that when the absolute value of is in the range of 0.1 eV to 0.3 eV, the light emitting lifetime of the light emitting device is longer, the operating voltage is reduced, the power consumption is reduced, and the light emitting efficiency of the light emitting device is further improved.

[0062] The present embodiment further provides a material selection method, which is used to select materials for the light-emitting layer of a green or red light-emitting device, as shown in FIG. S10: disposing a plurality of sets of light-emitting materials, each set of light-emitting materials including a host material and a guest material, and at least one of the host material and the guest material included in each of the two sets of light-emitting materials is different from each other; S20, using each set of luminescent materials as a luminescent layer material to prepare a plurality of single carrier devices each having a luminescent layer; S30, in a single-carrier element corresponding to each set of light-emitting materials, obtain a defect energy Eti between the host material and the guest material; S40, selecting a target luminescent material set from the plurality of luminescent material sets according to the defect energy Eti corresponding to each set of luminescent materials as a luminescent layer material of a light-emitting device; Includes.

[0063] In some alternative embodiments, in step S30, the single-carrier element is a hole-only element, and the single-carrier element further includes a hole transport layer stacked on the light-emitting layer and located on the hole injection side of the light-emitting layer, and the hole transport layers of each single-carrier element are the same. In some embodiments, the hole transport layer of the light-emitting element is the same as the hole transport layer of each single-carrier element.

[0064] In other alternative embodiments, the single-carrier element is an electron-only element, and the single-carrier element further comprises an electron transport layer disposed over the light-emitting layer and located on the electron injection side of the light-emitting layer, and the electron transport layer of each single-carrier element is the same. In some embodiments, the electron transport layer of the light-emitting element is the same as the electron transport layer of each single-carrier element.

[0065] In some cases, the hole transport layer in the hole-only device is the same as the hole transport layer in the light-emitting device. Generally, the hole transport layer is formed by deposition on the entire display panel, and is required to match the operating performance of the three light-emitting devices of red, green and blue. Therefore, when selecting the light-emitting layer material, by providing the same hole transport layer as the light-emitting device in the hole-only device, the effect of the hole transport layer on the defect energy Et between the host material and the guest material of the light-emitting layer in the light-emitting device during the hole transport process can be taken into consideration, and the light-emitting layer material that improves the efficiency of the light-emitting device can be more accurately selected and obtained.

[0066] In some other examples, the electron transport layer in the electron-only device is the same as the electron transport layer in the light-emitting device. Generally, the electron transport layer is formed by deposition on the entire display panel, and is required to match the operating performance of red, green and blue light-emitting devices. Therefore, when selecting the light-emitting layer material, by providing the same electron transport layer as the light-emitting device in the electron-only device, the effect of the electron transport layer on the defect energy Et between the host material and the guest material of the light-emitting layer in the light-emitting device during the electron transport process can be taken into consideration, and the light-emitting layer material that improves the efficiency of the light-emitting device can be more accurately selected.

[0067] Referring to FIG. 6, step S40 includes step S41.

[0068] Step S41, the first reference defect state energy Et a A target luminescent material set is selected based on the above.

[0069] In some embodiments, the first reference defect state energy Et a The absolute value of is in the range of 0.03 eV to 0.08 eV.

[0070] The light-emitting layer material selected by the material selection method of the present application can improve the light-emitting efficiency of the light-emitting element in a highlighted display state and reduce power consumption, thereby ensuring the display quality and display effect of the display panel in a highlighted display state and at the same time reducing the overall power consumption of the display panel.

[0071] A display panel according to the present application includes the light-emitting element, and in a highlight display state, the display panel has improved display quality and reduced power consumption.

Claims

1. The light-emitting layer includes a host material and a guest material. When carriers are injected into the light-emitting layer, there is a defect energy Et between the host material and the guest material, and the absolute value of the defect energy Et is 0.03 eV or more; The absolute value of the defect energy Et has a numerical range of 0.03 eV to 0.08 eV, The light-emitting device further includes a hole transport layer disposed on the hole injection side of the light-emitting layer, A first activation energy difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer. １ The first activation energy difference ΔEa １ Absolute value of The numerical range of is 0.1 eV to 0.3 eV, The light-emitting device further includes a compensation layer disposed between the hole transport layer and the light-emitting layer, In the hole injection direction of the light emitting layer, the activation energy of the compensation layer is between the activation energy of the hole transport layer and the activation energy of the host material. Light emitting element.

2. the light-emitting layer is a phosphorescent light-emitting layer, and the guest material is a phosphorescent light-emitting material; The emission color of the light-emitting layer is either a primary color of red or green light. The light-emitting device according to claim 1 .

3. The light-emitting device further includes an electron transport layer disposed on the electron injection side of the light-emitting layer, A second activation energy difference ΔEa between the activation energy of the host material and the activation energy of the electron transport layer. ２ The second activation energy difference ΔEa ２ The absolute value of the numerical range is 0.1 eV to 0.3 eV, The light-emitting device further includes a hole-blocking layer disposed between the electron transport layer and the light-emitting layer, In the electron injection direction of the light-emitting layer, the activation energy of the hole blocking layer is between the activation energy of the electron transport layer and the activation energy of the host material. The light-emitting device according to claim 1 .

4. A material selection method for selecting a light-emitting layer material for a green or red light-emitting element, comprising the steps of: Arranging a plurality of sets of luminescent materials, each of the luminescent material sets including a host material and a guest material, and at least one of the host material and the guest material included in each of the two sets of luminescent materials is different from each other; A step of fabricating a plurality of single carrier devices each having a light emitting layer, using each of the light emitting material sets as a light emitting layer material; In the single carrier element corresponding to each set of the light emitting materials, the defect energy Et ｉ and obtaining The defect energy Et corresponding to each set of the luminescent materials ｉ and selecting a target set of luminescent materials from the plurality of sets of luminescent materials based on the result as a luminescent layer material of the light-emitting element; The defect energy Et corresponding to each set of the luminescent materials ｉ The step of selecting a target light-emitting material set from the plurality of light-emitting material sets based on the above to use the target light-emitting material set as a light-emitting layer material of the light-emitting element includes: First reference defect state energy Et ａ and selecting the target set of luminescent materials based on The first reference defect state energy Et ａ The absolute value of the numerical range is 0.03 eV to 0.08 eV, the single-carrier element is a hole-only element, the single-carrier element further includes a hole transport layer disposed on the light-emitting layer and located on a hole injection side of the light-emitting layer, the hole transport layer of each of the single-carrier elements being the same; the hole transport layer of the light-emitting device is the same as the hole transport layer of each of the single-carrier devices; A first activation energy difference ΔEa between the activation energy of the host material and the activation energy of the hole transport layer. １ The first activation energy difference ΔEa １ The absolute value of the numerical range is 0.1 eV to 0.3 eV, The light-emitting device further includes a compensation layer disposed between the hole transport layer and the light-emitting layer, In the hole injection direction of the light emitting layer, the activation energy of the compensation layer is between the activation energy of the hole transport layer and the activation energy of the host material. Material selection methods.

5. A light-emitting device comprising the light-emitting device according to any one of claims 1 to 3. Display panel.

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