CN114792759A - Material screening method, light-emitting device, and display panel - Google Patents

Abstract

Embodiments of the present application provide a material screening method, a light-emitting device, and a display panel. The material screening method provided in the first aspect of the present application is used for screening the material of a carrier layer in a light-emitting device. The material screening method includes: configuring a plurality of groups of carrier material groups for forming the carrier layer; The first energy level parameter of the current-carrying material group, the second energy level parameter of at least part of the other film layers other than the carrier layer in each film layer constituting the light-emitting device, and the electrochemical stability parameter of each current-carrying material group, ranging from multiple The target current-carrying material group is obtained by screening from the current-carrying material group, which is used as the material of the carrier layer of the light-emitting device. In order to improve the luminous life of the light-emitting device and avoid the color shift of the display panel.

Description

Material screening method, light-emitting device, and display panel

technical field

The present invention relates to the field of display technology, in particular to a material screening method, a light-emitting device and a display panel.

Background technique

Display modules with organic light-emitting diode (Organic Light-Emitting Diode, OLED) display panels are widely used in mobile phones, TVs, personal digital Assistants, digital cameras, laptops, desktop computers and other consumer electronics.

However, light-emitting devices with different light-emitting colors in a general display panel have different light-emitting lifespans. During the long-term use of the display panel, the light-emitting devices with short light-emitting lifespans fail to emit light, resulting in color shift of the display panel and affecting the display effect.

Therefore, a new material screening method, light-emitting device and display panel are urgently needed.

SUMMARY OF THE INVENTION

The first aspect of the embodiments of the present application provides a material screening method. The material of the carrier layer in the light-emitting device is obtained by the material screening method in the first aspect of the present application, so as to improve the light-emitting life of the light-emitting device and prevent the display panel from displaying during long-term use. The panel color cast improves the display quality of the display panel.

The material screening method of the first aspect of the present application is used for screening the material of the carrier layer in the light-emitting device, and the material screening method includes:

Configuring multiple groups of current-carrying material groups for forming the carrier layer, and obtaining the first energy level parameters of each current-carrying material group;

obtaining the second energy level parameters of each film layer other than the carrier layer in each film layer constituting the light-emitting device;

Provide a plurality of monochromatic light-emitting devices, use each group of current-carrying material groups as the material of the test carrier layer in the monochromatic light-emitting device, and manufacture a plurality of monochromatic light-emitting devices with the test carrier layer respectively, each monochromatic light-emitting device. The light-emitting layer, the cathode layer and the anode layer are all the same;

Perform multiple cyclic voltammetry tests on each monochromatic light-emitting device under the same test conditions to obtain the electrochemical stability parameters of the current-carrying material group corresponding to each monochromatic light-emitting device under the same number of cyclic tests;

According to each first energy level parameter, the second energy level parameter of at least part of other film layers, and the electrochemical stability parameter of each current-carrying material group, a target current-carrying material group is obtained by screening from multiple groups of current-carrying material groups, as material of the carrier layer.

In a possible implementation of the first aspect of the present application, according to each first energy level parameter, the second energy level parameter of at least some other film layers, and the electrochemical stability parameter of each current-carrying material group, the carrier material is selected from multiple groups of carrier materials. In the step of selecting a target current carrier material group from the current material group to be used as the material of the carrier layer, the first energy level parameter includes the LUMO energy level and the second energy level parameter also includes the LUMO energy level, and includes the following steps:

When the carrier layer is arranged on the hole injection side of the light-emitting layer of the light-emitting device, the standard LUMO energy level relationship between the carrier layer, other film layers on the hole injection side and the light-emitting layer is used, and the carrier is used at the same time. The standard electrochemical stability parameters of the material of the layer are screened to obtain the target current-carrying material group;

Preferably, the electrochemical stability parameter is the change in current density of the current-carrying material group corresponding to each monochromatic light-emitting device after multiple cyclic voltammetry tests under the same voltage range.

In a possible implementation manner of the first aspect of the present application, when the carrier layer is arranged on the hole injection side of the light emitting layer of the light emitting device, the carrier material group, other film layers on the hole injection side and the light emitting layer are used to communicate with each other. The standard LUMO energy level relationship between the two, and at the same time using the standard electrochemical stability parameters of the material of the carrier layer, the steps of screening to obtain the target carrier material group include:

When the carrier layer is a compensation layer stacked with the light-emitting layer, the standard LUMO energy level relationship is that the LUMO energy level of the carrier layer is greater than the LUMO energy level of the host material in the light-emitting layer, and the value of the standard electrochemical stability parameter The range is less than or equal to 25%.

In a possible implementation of the first aspect of the present application, according to each first energy level parameter, the second energy level parameter of at least some other film layers, and the electrochemical stability parameter of each current-carrying material group, the carrier material is selected from multiple groups of carrier materials. In the step of selecting the target current carrier material group from the current material group as the material of the carrier layer, the first energy level parameter includes the HOMO energy level and the second energy level parameter also includes the HOMO energy level, and includes the following steps:

When the carrier layer is arranged on the electron injection side of the light-emitting layer of the light-emitting device, the standard HOMO energy level relationship between the carrier layer, other film layers on the electron injection side and the light-emitting layer is used, and at the same time the carrier layer is used. The standard electrochemical stability parameters of the material are screened to obtain the target current-carrying material group.

In a possible implementation of the first aspect of the present application, when the carrier layer is arranged on the electron injection side of the light-emitting layer of the light-emitting device, the carrier layer, other film layers on the electron injection side and the light-emitting layer are used to communicate with each other. The standard HOMO energy level relationship, and at the same time using the standard electrochemical stability parameters of the material of the carrier layer, the steps of screening to obtain the target carrier material group include:

When the carrier layer is a hole blocking layer, the standard HOMO energy level relationship is that the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the carrier layer is greater than the HOMO energy level of the carrier layer The absolute value of the difference with the HOMO energy level of the electron transport layer, and the value range of the standard electrochemical stability parameter is less than or equal to 30%.

In a possible implementation of the first aspect of the present application, when the carrier layer is arranged on the electron injection side of the light-emitting layer of the light-emitting device, the carrier layer, other film layers on the electron injection side and the light-emitting layer are used to communicate with each other. The standard HOMO energy level relationship, and at the same time using the standard electrochemical stability parameters of the material of the carrier layer, the steps of screening to obtain the target carrier material group include:

When the carrier layer is the electron transport layer, the standard HOMO energy level relationship is that the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the hole blocking layer is less than the HOMO energy level of the hole blocking layer and the The absolute value of the difference between the HOMO energy levels of the electron transport layer, and the value range of the standard electrochemical stability parameter is less than or equal to 35%.

A second aspect of the present application provides a light-emitting device, which has a light-emitting layer, and the light-emitting layer includes a host material and a guest material, including:

a first carrier region, located on the electron injection side of the light-emitting layer and having a first carrier layer;

The second carrier region is located on the hole injection side of the light-emitting layer and has a second carrier layer;

Wherein, the electrochemical stability parameter of the material of the first carrier layer is less than or equal to 35%, and/or the electrochemical stability parameter of the material of the second carrier layer is less than or equal to 30%.

A second aspect of the present application provides a light-emitting device. In the light-emitting device of the second aspect of the present application, the accumulation of carriers is prevented from causing damage to a contact interface formed between different film layers, and the light-emitting life of the light-emitting device is improved.

In a possible implementation manner of the second aspect of the present application, the second carrier layer includes a compensation layer stacked with the light-emitting layer, the LUMO energy level of the compensation layer is greater than the LUMO energy level of the host material in the light-emitting layer, and the compensation layer The electrochemical stability parameter of the material is less than or equal to 25%;

Preferably, the light-emitting device is a blue light-emitting device.

In a possible implementation manner of the second aspect of the present application, the first carrier layer includes an electron transport layer and a hole blocking layer stacked along the direction of electron injection into the light-emitting layer,

The absolute value of the difference between the HOMO energy level of the host material and the HOMO energy level of the hole blocking layer is greater than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer, and the material of the hole blocking layer is The value range of the electrochemical stability parameter is less than or equal to 30%; or,

The absolute value of the difference between the HOMO energy level of the host material and the HOMO energy level of the hole blocking layer is smaller than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer. The value range of the chemical stability parameter is less than or equal to 35%.

A third aspect of the present application provides a display panel. The display panel of the third aspect of the present application has the light-emitting device of the second aspect of the present application.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings, wherein the same or similar reference numerals denote the same or similar features, and Figures are not drawn to actual scale.

1 is a schematic flowchart of a material screening method in the first aspect of the embodiment of the present application;

Fig. 2 is the cyclic voltammogram in a kind of voltammetry cycle test in the first aspect of the embodiment of the present application;

3 is a schematic flowchart of another material screening method in the first aspect of the embodiment of the present application;

4 is a schematic flowchart of another material screening method in the first aspect of the embodiment of the present application;

5 is an energy level relationship diagram of each film layer in a light-emitting device in the first aspect of the embodiment of the present application;

6 is a schematic flowchart of another material screening method in the first aspect of the embodiment of the present application;

7 is a schematic flow chart of yet another material screening method in the first aspect of the embodiment of the present application;

8 is a schematic flowchart of yet another material screening method in the first aspect of the embodiment of the present application;

9 is an energy level relationship diagram of each film layer in another light-emitting device in the first aspect of the embodiment of the present application;

In the picture:

B'-compensation layer; host material in BH light-emitting layer; HB-hole blocking layer; ET-electron transport layer.

Detailed ways

The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention, and are not configured to limit the present invention. It will be apparent to those skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by illustrating examples of the invention.

It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element defined by the phrase "comprises" does not preclude the presence of additional identical elements in a process, method, article, or device that includes the element.

During long-term research, the inventor found that due to the inconsistent light-emitting lifespan of light-emitting devices of different colors in the display panel, during the long-term use of the display panel, due to the failure of light-emitting devices of some light-emitting devices, the display panel has display color shift and other undesirable display phenomena. affect the user experience. Therefore, improving the luminous life of light-emitting devices of different colors, especially the light-emitting devices that are prone to luminescence failure, can improve the luminous life of the display panel as a whole, which is beneficial to the long-term use of the display panel and enhances the user experience.

In further research, the inventor found that the electrochemical stability of the material forming each film layer in the light-emitting device is positively correlated with the life of the light-emitting device. The better the electrochemical stability of the material of the film layer, the longer the light-emitting life of the light-emitting device. Further, the inventors found that when the light-emitting device performs light-emitting work, the accumulation of carriers at the interface formed between the film layers will cause damage to the interface formed between the film layers, and also affect the carrier flow between the film layers. The migration and injection processes have a negative impact on the luminous lifetime of the light-emitting device, so that the luminous lifetime of the light-emitting device is reduced. In order to avoid damage caused by carriers at the interface formed between the film layers and affect the light-emitting life of the light-emitting device, it is necessary to improve the electrochemical stability of the film layer to improve the light-emitting life of the light-emitting device. The electrochemical stability of the film layer in the light-emitting device can be improved by defining the electrochemical stability parameters of the material forming the film layer.

The present invention has been made in view of the discovery and analysis of the above-mentioned problems.

A first aspect of the embodiments of the present application provides a material screening method. As shown in FIG. 1 , the first aspect of the present application provides a material screening method for screening the material of a carrier layer in a light-emitting device. The material screening method includes:

S10, multiple groups of current-carrying material groups for forming the carrier layer are configured, and first energy level parameters of each current-carrying material group are acquired.

S20 , acquiring second energy level parameters of each film layer other than the carrier layer in each film layer constituting the light-emitting device.

S30, providing a plurality of monochromatic light-emitting devices, using each group of current-carrying material groups as the material of the test carrier layer in the monochromatic light-emitting device, respectively fabricating a plurality of monochromatic light-emitting devices with the test carrier layer, each monochromatic light-emitting device The light-emitting layer, the cathode layer, and the anode layer in the light-emitting device are all the same.

S40, perform multiple cyclic voltammetry tests on each monochromatic light-emitting device under the same test conditions to obtain electrochemical stability parameters of the current-carrying material group corresponding to each monochromatic light-emitting device under the same number of cyclic tests.

S50, according to each first energy level parameter, the second energy level parameter of at least part of the other film layers, and the electrochemical stability parameter of each current-carrying material group, select a target current-carrying material group from multiple groups of current-carrying material groups, as the material of the carrier layer.

In some embodiments, the first energy level parameter includes the LUMO energy level and/or the HOMO energy level, and the second energy level parameter includes the LUMO energy level and/or the HOMO energy level.

It should be noted that the LUMO energy level of each film layer in the light emitting device can be understood as the energy level of the lowest unoccupied molecular orbital (Lowest Unoccupied Molecular Orbit) of the material forming each film layer in the light emitting device. The LUMO energy level of each carrier material group used to form the carrier layer is the same as the LUMO energy level of the corresponding test carrier layer in the corresponding monochromatic light-emitting device. Similarly, the HOMO energy level of each film layer in the light-emitting device can be understood as the energy level of the highest occupied molecular orbital (Highest Occupied Molecular Orbit) of the material forming each film layer in the light-emitting device. The HOMO energy level of each carrier material group used to form the carrier layer is the same as the HOMO energy level of the corresponding test carrier layer in the corresponding monochromatic light-emitting device. The HOMO energy level of the target carrier material group obtained by screening is the HOMO energy level of the carrier layer in the light-emitting device, and the LUMO energy level of the target carrier material group is the LUMO energy level of the carrier layer in the light-emitting device.

In some optional embodiments, the first energy level parameters of each current-carrying material group (including the HOMO energy level and the LUMO energy level of each current-carrying material group) and the parameters other than the carrier layer in each film layer constituting the light-emitting device The second energy level parameters of each other film layer (including the HOMO energy level and LUMO energy level of each other film layer) can be obtained by theoretical calculation, and can also be obtained by cyclic voltammetry measurement. obtained by other methods.

Understandably, Cyclic Voltammetry is a commonly used method for electrochemical studies. In the examples of the present application, cyclic voltammetry controls the potential (voltage) applied to the monochromatic light-emitting device to perform one or more repeated scans with a triangular waveform at different rates over time, and the potential range (voltage range) makes the monochromatic light emitting The material of the test carrier layer in the device can alternately undergo different reduction and oxidation reactions, and the current-potential curve (which can be a current density-voltage curve) is recorded. When the material of the test carrier layer is used as the single variable of the experiment for multiple monochromatic light-emitting devices tested in the experiment, the material reduction of the test carrier layer in the monochromatic light-emitting device can be judged according to the curve shape of the current density-voltage curve. and the reversibility of the oxidation reaction, and the change in current density of the monochromatic light-emitting device after multiple cyclic voltammetry tests is the current density of the material of the test carrier layer corresponding to the monochromatic light-emitting device. amount of change.

A triangular pulse voltage is applied to the monochromatic light-emitting device, and the obtained current density-voltage curve includes two branches. If the potential of the first half is scanned toward the cathode direction, the material of the test carrier layer of the monochromatic light-emitting device undergoes a reduction reaction, When a reduction wave is generated, when the potential of the second half is scanned in the direction of the anode, the reduction product in the material of the test carrier layer will be re-oxidized again, resulting in an oxidation wave. Therefore, a triangular wave scan completes a cycle of reduction and oxidation process, so it is called cyclic voltammetry, and the current density-voltage curve obtained by cyclic voltammetry is called cyclic voltammogram.

In some optional embodiments, in step S30, each monochromatic light-emitting device includes an anode layer, a light-emitting layer, a test carrier layer, and a cathode layer that are stacked. In order to obtain the electrochemical stability parameters of the material of the test carrier layer, the anode layer, the cathode layer and the light-emitting layer of each monochromatic light-emitting device are all the same.

In some optional embodiments, in step S40, voltages with the same value range are applied to each single-color light-emitting device during multiple cyclic voltammetry tests, so as to obtain the The electrochemical stability parameters of the current-carrying material group corresponding to the light-emitting device. In some examples, the voltage ranges from 0V to 1V. In some embodiments, the electrochemical stability parameter is the change in current density of the current-carrying material group corresponding to each monochromatic light-emitting device after multiple cyclic voltammetry tests are performed under the same voltage range.

In a specific example, it is required to obtain the electrochemical stability parameters of the set of current-carrying materials used to form the electron transport layer, and the electrochemical stability parameters of different sets of current-carrying materials used to form the electron transport layer need to be obtained on the luminescence influence on device lifetime.

In this example, there are five groups of current-carrying material groups for forming the electron transport layer, and five monochromatic light-emitting devices corresponding to the five groups of current-carrying material groups in one-to-one correspondence are provided, and each monochromatic light-emitting device includes a stacked arrangement of Anode layer, light-emitting layer, electron transport layer and cathode layer. The electron transport layer in each monochromatic light-emitting device is formed of the corresponding current-carrying material group. The cathode layer, the light-emitting layer and the anode layer of the five monochromatic light-emitting devices are all the same.

As shown in Figure 2, the initial cyclic voltammetry test was performed on each monochromatic light-emitting device under the condition that the voltage value ranged from 0V to 1V, and the first time the current density corresponding to each monochromatic light-emitting device changed with the voltage was obtained. Current-voltage cycling curves. Perform the same number of cyclic voltammetry tests (for example, 50, 100 or 200 cyclic voltammetry tests) under the condition of voltage ranging from 0V to 1V for each monochromatic light-emitting device, and obtain each The final sub-current-voltage cycling curve of the current density versus voltage of the monochromatic light-emitting device in the final sub-cyclic voltammetry test. The electrochemical stability parameters of the current-carrying material group corresponding to each monochromatic light-emitting device under the same cycle test times (that is, in Under the same voltage range, after multiple cyclic voltammetry tests, the current density variation of the current-carrying material group corresponding to each monochromatic light-emitting device).

In some examples, under the same voltage range, after performing multiple cyclic voltammetry tests, the current density variation of the current-carrying material group corresponding to each monochromatic light-emitting device is based on the maximum test voltage value in cyclic voltammetry The corresponding current density is calculated. As shown in Figure 2, the initial current-voltage cycle curve and the final current-voltage cycle curve in Figure 2 correspond to the places marked by the same circle: in the initial cyclic voltammetry test, the current-carrying material group corresponding to the monochromatic light-emitting device The initial current density value under the maximum test voltage value; and the final current density value of the current-carrying material group corresponding to the monochromatic light-emitting device under the maximum test voltage value in the final cyclic voltammetry test. Under the same voltage range and after multiple cyclic voltammetry tests, the calculation formula of the current density variation of the current-carrying material group corresponding to each monochromatic light-emitting device is as follows (Equation 1):

Current density variation = (initial current density value - final secondary current density value)/initial current density value × 100% (Formula 1)

In Table 1, the current-carrying material group corresponding to each monochromatic light-emitting device has The current density variation of , and the luminous lifetime value of each monochromatic light-emitting device.

Table 1

Monochromatic light-emitting device Current-carrying material group Current density change Luminous life value LT95% first monochromatic light-emitting device ETL-1 25% 100% Second Monochromatic Light Emitting Device ETL-2 30% 97% The third monochromatic light-emitting device ETL-3 35% 94% Fourth Monochromatic Light Emitting Device ETL-4 45% 80% Fifth Monochromatic Light Emitting Device ETL-5 50% 60%

The luminous lifetime value LT95% in Table 1 refers to the time period for a monochromatic light-emitting device to decay from 100% luminous brightness to 95% luminous brightness under the same initial luminous brightness. The longer the elapsed time, the longer the luminous lifetime of the light-emitting device is proved. In this example, the luminous lifetime values of the remaining monochromatic light emitting devices are shown based on the luminous lifetime value of the first monochromatic light emitting device. It can be seen from Table 1 that under the same test conditions and after the same number of cyclic voltammetry tests, the smaller the change in the current density of the current-carrying material corresponding to the monochromatic light-emitting device, the electrochemical stability of the monochromatic light-emitting device. The better the performance, the greater the luminous lifetime value of the monochromatic light-emitting device, and the longer the luminous lifetime of the monochromatic light-emitting device.

In some optional embodiments, referring to FIG. 3 , in step S50, the first energy level parameter includes LUMO energy level and the second energy level parameter also includes LUMO energy level, and step S50 includes the following steps:

Step S51, the carrier layer is arranged on the hole injection side of the light-emitting layer of the light-emitting device, and the standard LUMO energy level relationship between the carrier layer, other film layers on the hole injection side and the light-emitting layer is used, and at the same time, the carrier layer is used. The standard electrochemical stability parameters of the material of the current carrier layer are screened to obtain the target current-carrying material group.

In some embodiments, the carrier layer and the light-emitting layer are stacked and disposed, and there is no film layer between the carrier layer and the light-emitting layer. In this case, the standard LUMO energy level relationship is a preset value between the carrier layer and the light-emitting layer. LUMO energy level relationship.

In other embodiments, there are other film layers on the hole injection side between the carrier layer and the light emitting layer, and the standard LUMO energy level relationship is a preset carrier layer, other layers on the hole injection side The LUMO energy level relationship between the film layer and the light-emitting layer.

In some optional embodiments, referring to FIG. 4 , step S51 further includes the following steps:

Step S511, when the carrier layer is a compensation layer stacked with the light-emitting layer, the standard LUMO energy level relationship is that the LUMO energy level of the carrier layer is greater than the LUMO energy level of the host material in the light-emitting layer, and the material of the carrier layer is The value range of the standard electrochemical stability parameter is less than or equal to 25%.

In these embodiments, as shown in FIG. 5, the LUMO energy level of the compensation layer B' is greater than the LUMO energy level of the host material BH in the light-emitting layer, the standard electrochemical stability parameter of the material of the compensation layer (ie the material of the compensation layer The value range of the current density variation) is less than or equal to 25%, which can avoid the interface damage caused by the accumulation of electrons at the interface formed between the host material and the compensation layer in the light-emitting layer during the operation of the light-emitting device. The overall light-emitting life of the light-emitting device is improved, and the display color shift caused by the long-term use of the display panel is avoided, thereby improving the overall display quality and display life of the display panel.

In some optional embodiments, referring to FIG. 6 , in step S50 the first energy level parameter includes the HOMO energy level and the second energy level parameter also includes the HOMO energy level, and the step S50 includes the following steps:

Step S51 ′, when the carrier layer is arranged on the electron injection side of the light-emitting layer of the light-emitting device, the standard HOMO energy level relationship between the carrier layer, other film layers on the electron injection side and the light-emitting layer is used, and at the same time, the carrier layer is used. The standard electrochemical stability parameters of the material of the current carrier layer are screened to obtain the target current-carrying material group.

In some optional embodiments, referring to Fig. 7, the following steps are also included in step S51':

Step S511', when the carrier layer is a hole blocking layer, the standard HOMO energy level relationship is that the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the carrier layer is greater than that of the carrier layer. The absolute value of the difference between the HOMO energy level of the electron transport layer and the HOMO energy level of the electron transport layer, and the value range of the standard electrochemical stability parameter of the material of the carrier layer is less than or equal to 30%.

Please also refer to FIG. 5 , the hole blocking layer HB has a strong blocking effect on the holes migrated from the host material BH in the light-emitting layer, and the holes are easily blocked by the hole blocking layer HB between the host material BH and the holes in the light-emitting layer. At the interface formed between the barrier layers HB. In these embodiments, holes can be prevented from accumulating at the interface formed between the host material and the hole blocking layer in the light-emitting layer during the operation of the light-emitting device, which may cause interface damage, improve the overall light-emitting life of the light-emitting device, and avoid the display panel. Display color shift occurs in long-term use, thereby improving the overall display quality and display life of the display panel.

In some optional embodiments, referring to Fig. 8, the following steps are also included in step S51':

Step S512', when the carrier layer is the electron transport layer, the standard HOMO energy level relationship is that the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the hole blocking layer is smaller than the hole blocking layer. The absolute value of the difference between the HOMO energy level and the HOMO energy level of the electron transport layer, and the value range of the standard electrochemical stability parameter of the material of the carrier layer is less than or equal to 35%.

Referring to FIG. 9 , in these embodiments, damage to the interface formed between the hole blocking layer HB and the electron transport layer ET is avoided when more holes are blocked at the interface formed between the hole blocking layer HB and the electron transport layer ET during the operation of the light-emitting device, improving the The overall light-emitting life of the light-emitting device can avoid display color shift in the long-term use of the display panel, thereby improving the overall display quality and display life of the display panel.

It can be understood that in some embodiments of the present application, the material screening method is used to screen the material of the carrier layer in the light-emitting device. When the carrier layer is located on the hole injection side of the light-emitting layer of the light-emitting device, the carrier is For the current-carrying holes, it is necessary to obtain the first energy level parameter including the LUMO energy level of each of the current-carrying material groups, and the second energy level including the LUMO energy level of the other film layers on the hole injection side of the light-emitting layer. level parameters and a second energy level parameter of the light-emitting layer (host material in the light-emitting layer) including the LUMO level. When the carrier layer is a compensation layer, since the compensation layer and the light-emitting layer are generally stacked, the compensation layer is close to the light-emitting layer, and the compensation layer has the function of blocking the electron injection of the host material in the light-emitting layer into the hole-carrying region of the light-emitting device and the It also has the function of improving the hole-carrying region of the light-emitting device to inject holes into the host material in the light-emitting layer. Therefore, when electrons accumulate in the interface formed between the compensation layer and the light-emitting layer and cause damage to the interface, the ability of the light-emitting device to inject holes into the light-emitting layer and the ability to block electron injection into the hole-carrying region of the light-emitting device during operation of the light-emitting device It is difficult for electrons and holes to form exciton emission in the light-emitting layer, which seriously affects the light-emitting quality and light-emitting life of the light-emitting device. Therefore, it is necessary to improve the electrochemical stability requirements of the compensation layer and reduce the current density change of the compensation layer. amount to improve the overall light-emitting life of the light-emitting device.

In the electron current-carrying region of the light-emitting device, the hole-blocking layer and the light-emitting layer are generally stacked and disposed, and the hole-blocking layer is disposed close to the light-emitting layer. When the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the carrier layer is greater than the absolute value of the difference between the HOMO energy level of the carrier layer and the HOMO energy level of the electron transport layer, the hole The probability of crossing the hole blocking layer into the electron transport layer is low, so the holes are mostly accumulated at the interface formed between the host material and the hole blocking layer in the light-emitting layer. The electron-carrying ability of the hole-blocking layer is impaired, so it is necessary to improve the electrochemical stability of the hole-blocking layer. When the absolute value of the difference between the HOMO energy level of the host material in the light-emitting layer and the HOMO energy level of the carrier layer is smaller than the absolute value of the difference between the HOMO energy level of the carrier layer and the HOMO energy level of the electron transport layer, the electrons The probability of crossing the hole blocking layer into the electron transport layer is high, then the electrons migrated from the host material in the light-emitting layer are mostly accumulated at the interface formed between the hole blocking layer and the electron transport layer, and the holes are blocked by the electron transport layer. , hole accumulation damages the electron-carrying capacity of the electron transport layer, so it is necessary to improve the electrochemical stability of the electron transport layer. In addition, the hole transport layer is closer to the light-emitting layer than the electron transport layer, and the hole transport layer has a greater impact on the formation of excitons in the light-emitting layer than the electron transport layer. Therefore, the electrochemical stability of the hole transport layer is required. Above the electrochemical stability requirements of the electron transport layer.

Therefore, in some embodiments, the position of the carrier layer relative to the light-emitting device (ie, the number of film layers spaced between the carrier layer and the light-emitting layer), and/or the function of the carrier layer in the light-emitting device may be determined. The electrochemical stability parameters that the carrier layer needs to meet are preset.

A second aspect of the present application provides a light-emitting device, which has a light-emitting layer, the light-emitting layer includes a host material and a guest material, and includes: a first current-carrying region and a second current-carrying region. The first carrier region is located on the electron injection side of the light-emitting layer and has a first carrier layer. The second carrier region is located on the hole injection side of the light-emitting layer and has a second carrier layer. The electrochemical stability parameter of the material of the first carrier layer (that is, under the same test conditions, after multiple cyclic voltammetry tests, the current density change of the material of the first carrier layer) is less than or equal to 35%, and/or the electrochemical stability parameter of the material of the second carrier layer (that is, under the same test conditions, after multiple cyclic voltammetry tests, the material of the second carrier layer is Current density variation) is less than or equal to 30%.

In some embodiments, the current density variation of the material of the first carrier layer and the current density variation of the material of the first carrier layer are obtained under the same test conditions and the same number of cyclic voltammetry tests.

It will be appreciated that, in some embodiments, the first carrier layer includes one or more electron-carrying film layers. The first carrier layer includes one or more film layers that carry holes.

In the light-emitting device of the second aspect of the present application, the electrochemical stability of the first carrier layer and the second carrier layer is improved, which avoids the accumulation of carriers from causing contact interfaces formed between different film layers. damage, the light-emitting life of the light-emitting device is improved.

In some optional embodiments, the second carrier layer includes a compensation layer stacked with the light-emitting layer, the LUMO energy level of the compensation layer is greater than the LUMO energy level of the host material in the light-emitting layer, and the electrochemical properties of the material of the compensation layer are The stability parameter is less than or equal to 25%.

In some optional embodiments, the light emitting device is a blue light emitting device. In further research, the inventor found that the luminous lifetime of the blue light-emitting device in the display panel is often shorter than that of the green and red light-emitting devices, and the display panel is prone to failure due to the luminescence failure of the blue light-emitting device during long-term use. Problems such as display color cast occur. Therefore, increasing the light-emitting life of the blue light-emitting device is beneficial to increase the light-emitting life of the overall display panel, avoid display color shift, and improve the overall display effect of the display panel during long-term use.

In some optional embodiments, the first carrier layer includes an electron transport layer and a hole blocking layer stacked along the direction of electron injection into the light emitting layer, and the difference between the HOMO energy level of the host material and the HOMO energy level of the hole blocking layer is The absolute value of the difference is greater than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer, and the value range of the electrochemical stability parameter of the material of the hole blocking layer is less than or equal to 30% . Alternatively, the absolute value of the difference between the HOMO energy level of the host material and the HOMO energy level of the hole blocking layer is smaller than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer, and the material of the electron transport layer The value range of the electrochemical stability parameter is less than or equal to 35%.

In order to further prove the life-span improvement of the light-emitting device in the second aspect of the embodiment of the present application compared with the common light-emitting device, five sets of comparative experiments were conducted by taking the light-emitting life-span improvement of the blue light-emitting device as an example. Experimental example and a comparative example. In each group of experiments, the comparative example corresponds to the first blue light-emitting device, and the experimental example corresponds to the second blue light-emitting device. Only the carrier layers shown in Table 2 below are experimental variables corresponding to the comparative examples in each group of experiments. The first blue light-emitting device is subjected to a light-emitting life test experiment, and the second blue light-emitting device corresponding to the experimental example is subjected to a light-emitting life test experiment. At the same time, it is also necessary to obtain the current density variation of the material of the carrier layer in the comparative examples of each group of experiments and the variation of the current density of the material of the carrier layer in the experimental example. Table 2 shows the experimental conditions and experimental results of five groups of control experiments.

Table 2

As shown in Table 2, in each of the five groups of experimental examples, control experiments were performed with the carrier layers shown in Table 2 as variables. The change in current density in Table 2 reflects the change in current density of the material of the carrier layer obtained under the same test conditions and the same number of cyclic voltammetry tests. From the first group of experiments to the third group of experiments, it can be concluded that reducing the current density variation of the compensation layer, hole blocking layer or electron transport layer in the blue light-emitting device is beneficial to the improvement of the light-emitting life of the light-emitting device. From the fourth set of experiments, it is concluded that reducing the current density variation of the compensation layer and the hole blocking layer at the same time can have a strong coordinated effect on the improvement of the luminous lifetime of the light-emitting device. From the fifth set of experiments, it is concluded that reducing the current density variation of the compensation layer and the electron transport layer at the same time is beneficial to further improve the luminous lifetime of the light-emitting device. Simultaneously reducing the current density variation of the compensation layer and the hole blocking layer can improve the luminescence lifetime of the light-emitting device, which is stronger than simultaneously reducing the current density variation of the compensation layer and the electron transport layer.

A third aspect of the present application provides a display panel. The display panel of the third aspect of the present application has the light-emitting device of the second aspect of the present application.

In accordance with the embodiments of the present invention as described above, these embodiments do not exhaustively describe all the details and do not limit the invention to only the specific embodiments described. Obviously, many modifications and variations are possible in light of the above description. This specification selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can make good use of the present invention and modifications based on the present invention. The present invention is to be limited only by the claims and their full scope and equivalents.

Claims (10)

1. A material screening method for screening a material of a carrier layer in a light emitting device, the material screening method comprising:

configuring a plurality of current carrying material groups for forming the current carrying layer, and acquiring a first energy level parameter of each current carrying material group;

acquiring second energy level parameters of other film layers except the current carrier layer in the film layers of the light-emitting device;

providing a plurality of monochromatic light emitting devices, taking each current carrying material group as a material of a test current carrying layer in the monochromatic light emitting devices, and respectively manufacturing a plurality of monochromatic light emitting devices with the test current carrying layers, wherein a light emitting layer, a cathode layer and an anode layer in each monochromatic light emitting device are the same;

performing cyclic voltammetry tests on the single-color light-emitting devices for multiple times under the same test condition to obtain electrochemical stability parameters of the current-carrying material group corresponding to the single-color light-emitting devices under the same cyclic test times;

and screening a target current carrying material group from the multiple current carrying material groups according to the first energy level parameters, the second energy level parameters of at least part of other film layers and the electrochemical stability parameters of the current carrying material groups to obtain the target current carrying material group as the material of the current carrying sub-layer.

2. The method of claim 1, wherein the step of screening a target set of charge carrying materials from a plurality of sets of charge carrying materials as the material for the charge carrying layer based on each of the first energy level parameter, the second energy level parameter for at least a portion of the other film layer, and the electrochemical stability parameter for each of the sets of charge carrying materials comprises the steps of:

when the current carrier layer is arranged at the hole injection side of the light emitting layer of the light emitting device, the target current carrier material group is obtained by screening according to the standard LUMO energy level relation among the current carrier layer, the other film layers positioned at the hole injection side and the light emitting layer and the standard electrochemical stability parameters of the material of the current carrier layer;

preferably, the electrochemical stability parameter is a current density variation of the current-carrying material group corresponding to each of the monochromatic light emitting devices after the multiple cyclic voltammetry tests are performed in the same voltage range.

3. The method according to claim 2, wherein the step of screening the target set of the charge carrier material using a standard LUMO energy level relationship among the set of the charge carrier material, the other film layer located on the hole injection side, and the light-emitting layer when the charge carrier layer is disposed on the hole injection side of the light-emitting device, and using a standard electrochemical stability parameter of a material of the charge carrier layer at the same time comprises:

when the charge carrier layer is a compensation layer stacked with the light-emitting layer, the standard LUMO energy level relationship is that the LUMO energy level of the charge carrier layer is greater than the LUMO energy level of a host material in the light-emitting layer, and the value range of the standard electrochemical stability parameter is less than or equal to 25%.

4. The method of claim 1, wherein the step of screening the plurality of sets of current-carrying materials for the material of the current-carrying layer according to the first energy level parameter, the second energy level parameter of at least a portion of the other film layer, and the electrochemical stability parameter of each of the sets of current-carrying materials comprises the steps of:

when the current carrier layer is arranged on the electron injection side of the light emitting layer of the light emitting device, the target current carrier material group is obtained by screening according to the standard HOMO energy level relation among the current carrier layer, the other film layers positioned on the electron injection side and the light emitting layer and the standard electrochemical stability parameters of the material of the current carrier layer.

5. The method according to claim 4, wherein, when the charge carrier layer is disposed on an electron injection side of a light emitting layer of the light emitting device, the step of screening the target charge carrier material group by using a standard HOMO energy level relationship among the charge carrier layer, the other film layer on the electron injection side, and the light emitting layer and by using a standard electrochemical stability parameter of a material of the charge carrier layer comprises:

when the current carrier layer is a hole blocking layer, the standard HOMO level relationship is that the absolute value of the difference between the HOMO level of the host material in the light emitting layer and the HOMO level of the current carrier layer is greater than the absolute value of the difference between the HOMO level of the current carrier layer and the HOMO level of the electron transport layer, and the value range of the standard electrochemical stability parameter is less than or equal to 30%.

6. The method according to claim 4, wherein when the charge carrier layer is disposed on an electron injection side of a light emitting layer of the light emitting device, the step of screening the target charge carrier material group by using a standard HOMO energy level relationship among the charge carrier layer, the other film layer on the electron injection side, and the light emitting layer and using a standard electrochemical stability parameter of a material of the charge carrier layer comprises:

the current carrier layer is an electron transport layer, the standard HOMO energy level relation is that the absolute value of the difference between the HOMO energy level of the host material in the light emitting layer and the HOMO energy level of the hole blocking layer is smaller than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer, and the value range of the standard electrochemical stability parameter is less than or equal to 35%.

7. A light emitting device having a light emitting layer including a host material and a guest material, comprising:

a first current carrier region located at an electron injection side of the light emitting layer and having a first current carrier layer;

a second current carrier region located at the hole injection side of the light emitting layer and having a second current carrier layer;

wherein the electrochemical stability parameter of the material of the first charge carrier layer is less than or equal to 35%, and/or the electrochemical stability parameter of the material of the second charge carrier layer is less than or equal to 30%.

8. The light-emitting device according to claim 7, wherein the second carrier layer includes a compensation layer provided in a layer with the light-emitting layer, a LUMO level of the compensation layer is larger than a LUMO level of the host material in the light-emitting layer, and an electrochemical stability parameter of a material of the compensation layer is less than or equal to 25%;

preferably, the light emitting device is a blue light emitting device.

9. The light-emitting device according to claim 8, wherein the first carrier layer includes an electron transport layer and a hole blocking layer which are stacked in a direction in which electrons are injected into the light-emitting layer,

the absolute value of the difference between the HOMO level of the host material and the HOMO level of the hole blocking layer is greater than the absolute value of the difference between the HOMO level of the hole blocking layer and the HOMO level of the electron transport layer, and the value range of the electrochemical stability parameter of the material of the hole blocking layer is less than or equal to 30%; or,

the absolute value of the difference between the HOMO energy level of the host material and the HOMO energy level of the hole blocking layer is smaller than the absolute value of the difference between the HOMO energy level of the hole blocking layer and the HOMO energy level of the electron transport layer, and the value range of the electrochemical stability parameter of the material of the electron transport layer is less than or equal to 35%.

10. A display panel comprising the light-emitting device according to any one of claims 7 to 9.

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