CN114639790B - Light emitting device, material screening method and display panel - Google Patents
Light emitting device, material screening method and display panel Download PDFInfo
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- 239000000463 material Substances 0.000 title claims abstract description 86
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000012216 screening Methods 0.000 title claims abstract description 35
- 230000004913 activation Effects 0.000 claims abstract description 191
- 238000002347 injection Methods 0.000 claims description 36
- 239000007924 injection Substances 0.000 claims description 36
- 230000000903 blocking effect Effects 0.000 claims description 25
- 230000000694 effects Effects 0.000 abstract description 5
- 239000003086 colorant Substances 0.000 abstract description 3
- 238000009877 rendering Methods 0.000 abstract description 2
- 239000010410 layer Substances 0.000 description 219
- 238000012360 testing method Methods 0.000 description 17
- 239000002346 layers by function Substances 0.000 description 15
- 238000002474 experimental method Methods 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- 238000002411 thermogravimetry Methods 0.000 description 5
- 230000005525 hole transport Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 239000000969 carrier Substances 0.000 description 3
- 230000004888 barrier function Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000004770 highest occupied molecular orbital Methods 0.000 description 2
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- 238000005036 potential barrier Methods 0.000 description 2
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- 239000000126 substance Substances 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 1
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
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- H—ELECTRICITY
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/14—Carrier transporting layers
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/85—Arrangements for extracting light from the devices
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/86—Arrangements for improving contrast, e.g. preventing reflection of ambient light
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
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- H—ELECTRICITY
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
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Abstract
The embodiment of the application discloses a light emitting device, a material screening method and a display panel. A light emitting device provided in a first direction according to an embodiment of the present application includes: the light-emitting layer is provided with a light-emitting material, and the light-emitting color of the light-emitting layer is any one of the primary colors of chromatic light of red or green; the first carrier layer is arranged on the luminescent layer; the light-emitting device is provided with a starting state and an operating state, and a first activation energy difference delta Ea x is arranged between the activation energy of the light-emitting layer and the activation energy of the first carrier layer in the starting state; in the working state, the second activation energy difference delta Ea x 'exists between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, and delta Ea x>ΔEax' >0eV. The light-emitting device has higher starting voltage in the starting state; meanwhile, the light-emitting device has lower working voltage in the working state, so that the problem of color cast of display caused by current crosstalk when the light-emitting device with high starting voltage is started on the display panel is avoided, and the color rendering precision and the display effect of the display panel are improved.
Description
Technical Field
The invention relates to the field of display, in particular to a light emitting device, a material screening method and a display panel.
Background
An Organic Light-Emitting Diode (OLED) display panel has advantages of high image quality, power saving, thin body, and wide application range, and is widely used in various consumer electronic products such as mobile phones, televisions, personal digital assistants, digital cameras, notebook computers, desktop computers, etc., and becomes a mainstream display panel in the display field.
However, a general OLED display panel includes three color light emitting devices of red, green, and blue, and a general blue light emitting device has the highest turn-on voltage. The light emitting device with Gao Qiliang voltage and high operating voltage is turned on and current crosstalk problem is generated during operation, so that the red and/or green light emitting device with relatively low turn-on voltage is also turned on, so that the color shift of the display panel is affected, and the display effect of the display panel is affected.
Therefore, there is an urgent need for a light emitting device, a material screening method, and a display panel.
Disclosure of Invention
The embodiment of the application provides a light emitting device, a material screening method and a display panel. The light-emitting device provided by the embodiment of the application has higher starting voltage and lower working voltage, can avoid the wrong starting of the light-emitting device caused by the problem of current crosstalk, and also can avoid the problem of crosstalk current caused by the overhigh working voltage when the light-emitting device works. The light-emitting device provided by the embodiment of the application improves the color development accuracy of the display panel and the display quality of the display panel.
A first aspect of an embodiment of the present application provides a light emitting device, including:
The light-emitting layer is provided with a light-emitting material, and the light-emitting color of the light-emitting layer is any one of the primary colors of chromatic light of red or green;
the first carrier layer is arranged on the luminescent layer;
The light-emitting device is provided with a starting state and an operating state, and a first activation energy difference delta Ea x is arranged between the activation energy of the light-emitting layer and the activation energy of the first carrier layer in the starting state; in the working state, the second activation energy difference delta Ea x 'exists between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, and delta Ea x>ΔEax' >0eV.
In one possible implementation of the first aspect of the present embodiment,
The first carrier layer is a compensation layer and is positioned on the hole injection side of the light-emitting layer; or alternatively
The first carrier layer is a hole blocking layer and is positioned on the electron injection side of the light emitting layer.
In one possible implementation of the first aspect of the present embodiment,
The first carrier layer is a compensation layer and is positioned on the hole injection side of the light-emitting layer;
the light-emitting device further comprises a hole blocking layer, wherein the hole blocking layer is arranged on the layer of the light-emitting layer and is positioned on the electron injection side of the light-emitting device; in the on-state, a third activation energy difference delta Ea y is arranged between the activation energy of the light-emitting layer and the activation energy of the hole blocking layer; in the operating state, the light-emitting layer and the first carrier layer have a fourth activation energy difference Δea y 'between activation energies, and Δea y>ΔEay' >0eV.
Preferably, the third activation energy difference Δea y >0.2eV;
Preferably, the third activation energy difference Δea y has a value ranging from 0.2eV < Δea y <0.6eV;
Preferably, the fourth activation energy difference Δea 2 'has a value ranging from 0eV < Δea y' <0.1eV.
In a possible implementation manner of the first aspect of the embodiment of the present application, the first activation energy difference Δea x >0.2eV;
Preferably, the first activation energy difference Δea x is in the range of 0.2eV < Δea x <0.6eV.
Preferably, when the first activation energy difference Δea x is provided between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, the value range of the turn-on voltage boost Δv on,ΔVon of the light-emitting device is 0.1V to 0.2V.
In one possible implementation of the first aspect of the present embodiment,
The second activation energy difference Δea x 'has a value ranging from 0eV < Δea x' <0.1eV;
preferably, when the second activation energy difference Δea x' is provided between the activation energy of the light emitting layer and the activation energy of the first carrier layer, the operating voltage of the light emitting device is reduced by Δv d,ΔVd to a value ranging from 0.1V to 0.6V.
In a possible implementation of the first aspect of the embodiments of the present application, the luminescent material comprises a host luminescent material and a guest luminescent material doped to the host luminescent material.
A second aspect of the embodiment of the present application provides a material screening method for screening a light emitting layer material of a light emitting device, the screening method including:
Providing a plurality of first single-carrier devices, wherein each first single-carrier device comprises a single-color light emitting layer and a first carrier layer, the first carrier layers among the plurality of first single-carrier devices are the same, and the materials of the single-color light emitting layers are different;
Providing a second single carrier device, the second single carrier device comprising a second carrier layer, the first carrier layer being the same as the second carrier layer;
Acquiring a first starting activation energy Ea i of each first single-carrier device and a second starting activation energy Ea l of each second single-carrier device under the starting current density, and acquiring a first working activation energy Ea j of each first single-carrier device and a second working activation energy Ea w of each second single-carrier device under the working current density;
And screening according to the first starting activation energy Ea i, the first working activation energy Ea j corresponding to each first single-carrier device and the second starting activation energy Ea l and the second working activation energy Ea w of the second single-carrier device to obtain a plurality of first target luminescent layer materials.
The luminescent layer material screened by the material screening method provided by the embodiment of the application can improve the starting voltage of the luminescent device and reduce the working voltage of the luminescent device, so that the problem of color cast of the display panel caused by the starting of the luminescent device due to current crosstalk is avoided.
In a possible implementation manner of the second aspect of the embodiment of the present application, the step of screening to obtain the plurality of first target light emitting layer materials according to the first activation energy Ea i, the first operation activation energy Ea j corresponding to each first single carrier device, and the second activation energy Ea l and the second operation activation energy Ea w of the second single carrier device includes:
Calculating an activation energy difference delta Ea i between the monochromatic light emitting layer and the first carrier layer in each first single-carrier device by using a first starting activation energy Ea i and a second starting activation energy Ea l corresponding to each first single-carrier device, and calculating an activation energy difference delta Ea j between the monochromatic light emitting layer and the first carrier layer in each first single-carrier device by using a first working activation energy Ea j and a second working activation energy Ea w corresponding to each first single-carrier device;
Screening to obtain a plurality of first target luminescent layer materials by using a first standard activation energy difference value delta Ea a and a second standard activation energy difference value delta Ea b;
Preferably, the monochromatic light emitting layer is a green or red light emitting layer, the value of the first standard activation energy difference Δea a is 0.2eV < Δea a <0.6eV, and the value of the second standard activation energy difference Δea b is 0eV < Δea b <0.1eV;
preferably, the light emitting layer material includes a host light emitting material and a guest light emitting material doped in the host light emitting material.
In a possible implementation manner of the second aspect of the embodiment of the present application, the first single carrier device is a single electron device or a single hole device.
A third aspect of the application provides a display panel comprising the light emitting device of the first aspect of the application.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar features, and in which the figures are not to scale.
FIG. 1 is a schematic diagram of operating voltages and on-luminance voltages of different color light emitting devices;
FIG. 2 is a flow chart of a material screening method according to a second aspect of an embodiment of the present application;
FIG. 3 is a flow chart of another material screening method of the second aspect of the present application;
FIG. 4 is a graph of the energy level of activation of a single electron device in accordance with a second aspect of an embodiment of the present application;
FIG. 5 is another graph of activation energy level relationship for a single electron device in a second aspect of an embodiment of the application;
FIG. 6 is a graph of the energy level of activation of a single hole device in accordance with a second aspect of an embodiment of the present application;
FIG. 7 is a graph of another activation energy level relationship for a single hole device in accordance with a second aspect of an embodiment of the present application;
Fig. 8 is a flow chart of yet another material screening method according to the second aspect of the embodiment of the present application.
In the figure:
a B-blue light emitting device; an R-red light emitting device; a G-green light emitting device;
E-electron injection direction;
F-hole injection direction;
An EML-light emitting layer; HB-hole blocking layer; a prime-compensation layer;
unowns—an energy level region that is not considered.
Detailed Description
Features and exemplary embodiments of various aspects of the present invention will be described in detail below, and in order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and the detailed embodiments. It should be understood that the specific embodiments described herein are merely configured to illustrate the invention and are not configured to limit the invention. It will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by showing examples of the invention.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
It will be understood that when a layer, an area, or a structure is described as being "on" or "over" another layer, another area, it can be referred to as being directly on the other layer, another area, or another layer or area can be included between the layer and the other layer, another area. And if the component is turned over, that layer, one region, will be "under" or "beneath" the other layer, another region.
The inventors found in the study that in an OLED display panel, the on-state voltage of a blue light emitting device is about 2.7V, the on-state voltage of a green light emitting device is about 2.34V, and the on-state voltage of a red light emitting device is about 2.0V in theory. As shown in fig. 1, the turn-on voltage of the blue light emitting device and the operation voltage of the blue light emitting device are higher than those of the green light emitting device and the red light emitting device in a general display panel. Therefore, when the blue light emitting device is turned on and/or works, crosstalk current or leakage current of the thin film transistor is generated, and the crosstalk current or the leakage current generated by the thin film transistor is transversely conducted through the hole injection layer, so that the green light emitting device and the red light emitting device with lower turn-on voltage can be turned on, and color cast of the display panel is caused. Compared with blue and green light-emitting devices, the red light-emitting device has lower starting voltage and working voltage, so that crosstalk current is generated when the green light-emitting device is started and/or works, and the starting and working of the red light-emitting device are influenced.
The present application has been made based on the knowledge and findings of the above-mentioned problems.
A first aspect of an embodiment of the present application provides a light emitting device including a light emitting layer and a first carrier layer. The light-emitting layer is provided with a light-emitting material, and the light-emitting color of the light-emitting layer is any one of red or green color primary color, namely the light-emitting device is a red light-emitting device or a green light-emitting device in the display panel. The first carrier layer is laminated with the light emitting layer.
The light-emitting device has a starting state and a working state, and has a starting voltage in the starting state and is started; the light emitting device has an operating voltage in an operating state, and performs normal operation light emission.
In general, an operating voltage of a light emitting device in a display panel is higher than an on-state voltage.
In the on-state, a first activation energy difference delta Ea x is formed between the activation energies of the light-emitting layer and the first carrier layer; in the working state, the second activation energy difference delta Ea x 'exists between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, and delta Ea x>ΔEax' >0eV.
A first aspect of an embodiment of the present application proposes a light emitting device that emits red light or green light and has a higher on-luminance voltage and a lower operating voltage. The light-emitting device has higher starting voltage, so that the light-emitting device which is not expected to start to emit light when the display panel displays is not started due to crosstalk current, the problem of color cast of the display panel is avoided, and the display effect of the display panel is further improved. Meanwhile, the light-emitting device has lower working voltage, so that the light-emitting device can be prevented from becoming a crosstalk source generating transverse crosstalk current in the working state, the working of other light-emitting devices with low starting voltage is influenced, and the problem of color cast of display panels is further avoided.
The activation energy in the embodiment of the application refers to potential barriers which need to be overcome for transferring electrons or holes between different functional layers of the light-emitting device. The activation energy of a single layer or multiple layers in embodiments of the present application may be understood as the potential barrier that electrons (or holes) need to overcome to flow from the cathode side (or anode side) through the single layer or multiple functional layers, where the functional layers refer to the carrier layer as well as the light emitting layer in the light emitting device. The carrier layer in the light emitting device includes an electron transport layer, a hole blocking layer, a compensation layer, a hole transport layer, a hole injection layer, and the like. Alternatively, the activation energy in the embodiments of the present application may be understood as the energy required for electrons to flow from the cathode side through the functional layer carrying electrons and holes to flow from the anode side through the functional layer carrying holes. The activation energy difference is understood to be the energy required for a carrier to flow from one functional layer to another in a certain carrier flow direction (e.g. electron injection direction or hole injection direction).
When the functional layer is made 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 made of two or more materials, the activation energy of the functional layer may be calculated by: firstly, obtaining the product value of the activation energy of each material and the molar mass fraction corresponding to each material; the individual product values are then summed to obtain the overall activation energy of the functional layer, which may also be referred to as a weighted average activation energy.
The activation energy can be calculated by the following Arrhenius (Arrhenius) formula: ea=e 0 +mrt, where Ea is the activation energy, E 0 and m are constants independent of temperature, T is temperature, R is molar gas constant. I.e. from the above formula, the activation energy is temperature dependent. In addition, the unit of the activation energy obtained by the calculation formula is joule J, and the unit of the activation energy can be converted into electron volt eV by a simple conversion formula, wherein the conversion formula is as follows: 1 ev=1.60217665 x 10 -19 J. It will be appreciated that in the embodiments of the present application, a basic formula for calculating Ea is given, and those skilled in the art may calculate Ea based on the basic Arrhenius (Arrhenius) formula given in the embodiments of the present application or from various variations of the Arrhenius (Arrhenius) formula.
In other embodiments, the activation energy of the functional layer may be obtained using thermogravimetric analysis. For example, the whole of the first carrier layer and the single-color light-emitting layer is subjected to thermogravimetric analysis, and the activation energy of each functional layer is directly calculated according to the thermogravimetric analysis structure. Wherein, the thermogravimetric analysis refers to a method for obtaining the change relation of the mass of a substance with the temperature (or time) under the control of the temperature by a program; when thermogravimetric analysis is used to obtain thermogravimetric curve, average activation energy can be calculated by differential subtraction (Freeman-Carroll) method or integral (OWAZa) method.
The highest occupied energy level orbital HOMO and the lowest occupied energy level orbital LUMO are generally used in the prior art to measure the energy level matching of each functional layer in a light emitting device. However, HOMO and LUMO only consider the injection efficiency of carriers, and in the embodiment of the present application, the energy level matching relationship between the light emitting layer and the activation energy of the first carrier layer stacked on the light emitting layer is adjusted, so as to adjust the on-luminance voltage and the operating voltage of the light emitting device. Starting from the activation energy direction, the influence of various factors such as the injection of carriers, the transmission of carriers, the temperature and the like between actual functional layers on the starting voltage and the working voltage of the light-emitting device can be comprehensively considered. The matching relation between the light-emitting layer of the light-emitting device and the first carrier layer is comprehensively evaluated through the activation energy Ea, so that the starting voltage of the green or red light-emitting device is increased, the working voltage is reduced, the influence of crosstalk current on the light-emitting device is effectively avoided, and the problem of color cast of the display panel is further avoided.
In some alternative embodiments, the first carrier layer is a compensation layer, located on the hole injection side of the light emitting layer; or the first carrier layer is a hole blocking layer and is positioned on the electron injection side of the light emitting layer. The inventors have further found during the course of the study that the cross-talk current generally conducts in the lateral direction of the hole injection layer so that other light emitting devices with lower turn-on voltages are turned on. The difference value of the activation energy between the activation energy of the light-emitting layer and the activation energy of the first carrier layer is a positive value, so that crosstalk current flowing in the hole injection layer can be prevented from easily flowing into the light-emitting layer through the first carrier layer, and the light-emitting device is prevented from being turned on by the crosstalk current.
In some alternative embodiments, the first carrier layer is a compensation layer, located on the hole injection side of the light emitting layer; the light-emitting device further comprises a hole blocking layer, wherein the hole blocking layer is arranged on the layer of the light-emitting layer and is positioned on the electron injection side of the light-emitting device; in the on-state, a third activation energy difference delta Ea y is arranged between the activation energy of the light-emitting layer and the activation energy of the hole blocking layer; in the operating state, the light-emitting layer and the first carrier layer have a fourth activation energy difference Δea y 'between activation energies, and Δea y>ΔEay' >0eV. In these embodiments, the activation energy of the hole blocking layer and the compensation layer, which are respectively disposed on the electron injection side and the hole injection side of the light emitting layer, is lower than that of the light emitting layer. It can also be understood that on the electron injection side, electrons need to overcome a certain energy barrier from the hole blocking layer into the light emitting layer; on the hole injection side, holes flow into the light-emitting layer from the compensation layer to overcome a certain energy barrier, so that the light-emitting device is further ensured to have higher starting voltage, and the operating voltage of the light-emitting device is reduced due to delta Ea y>ΔEay '>0eV and delta Ea x>ΔEax' >0eV.
It should be noted that, the compensation layer has the capability of carrying current holes, which can improve the transmission and injection efficiency of holes at the hole injection side of the light emitting layer, and also plays a role in blocking electrons. The light-emitting layers with different light-emitting colors in the display panel correspond to different compensation layers, and the compensation layers are arranged between the light-emitting layers and the hole transport layers.
In some embodiments, the third activation energy difference Δea y between the activation energies of the light-emitting layer and the hole blocking layer is in the range Δea y >0.2eV.
In some embodiments, the third activation energy difference Δea y is in the range of 0.2eV < Δea y <0.6eV;
In other embodiments, the fourth activation energy difference Δea 2 'is in the range of 0eV < Δea y' <0.1eV.
In some embodiments, the first activation energy difference Δea x >0.2eV;
In other embodiments, the first activation energy difference Δea x is in the range of 0.2eV < Δea x <0.6eV.
In some alternative embodiments, when the first activation energy difference Δea x is between the activation energies of the light-emitting layer and the first carrier layer, the value of the turn-on voltage boost Δv on,ΔVon of the light-emitting device ranges from 0.1V to 0.2V.
In some alternative embodiments, the first activation energy difference ΔEa x >0.2eV. Illustratively, the range of values of the first activation energy difference Δea x is 0.2eV < Δea x <0.6eV. For example, when the first activation energy difference Δea x is provided between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, the value of the turn-on voltage boost Δv on,ΔVon of the light-emitting device ranges from 0.1V to 0.2V. In these alternative embodiments the second activation energy difference Δea x 'is in the range of 0eV < Δea x' <0.1eV.
In some embodiments, when the second activation energy difference Δea x' is provided between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, the operating voltage of the light-emitting device is reduced by Δv d,ΔVd to a value ranging from 0.1V to 0.6V.
In some alternative embodiments, the light emitting material of the light emitting layer in the light emitting device of the first aspect of the present application includes a host light emitting material and a guest light emitting material doped with the host light emitting material. Thus, it is understood that the activation energy of the light emitting layer is the weighted average activation energy of the host light emitting material and the guest light emitting material.
A second aspect of the embodiments of the present application provides a material screening method, referring to fig. 2, for screening a light emitting layer material of a light emitting device, where the screening method includes:
Step S10, providing a plurality of first single-carrier devices, wherein each first single-carrier device comprises a single-color light emitting layer and a first carrier layer, and the first carrier layers among the plurality of first single-carrier devices are the same and the materials of the single-color light emitting layers are different;
step S20, providing a second single-carrier device, wherein the second single-carrier device comprises a second carrier layer, and the first carrier layer is the same as the second carrier layer;
Step S30, obtaining a first starting activation energy Ea i of each first single-carrier device and a second starting activation energy Ea l of each second single-carrier device under the starting current density, and obtaining a first working activation energy Ea j of each first single-carrier device and a second working activation energy Ea w of each second single-carrier device under the working current density;
step S40, screening to obtain a plurality of first target luminescent layer materials according to a first starting activation energy Ea i, a first working activation energy Ea j corresponding to each first single-carrier device and a second starting activation energy Ea l and a second working activation energy Ea w of the second single-carrier device.
In some alternative embodiments, referring to fig. 3, step S31 and step S32 are further included in step S30.
In step S31, the first single-carrier devices are subjected to an energization test to obtain an I-V curve related to the first single-carrier devices, i.e., a current-voltage curve of the first single-carrier devices, where the I-V curve represents a relationship between a turn-on current density and a voltage of the first single-carrier devices and also represents a relationship between an operating current density and a voltage of the first single-carrier devices under an operating current density. The first single-carrier device is a test device, and does not emit light in the power-on test process, and the starting current density of the first single-carrier device is equivalent to the starting current density of the monochromatic light emitting device corresponding to the first single-carrier device in the starting state. Similarly, the operating current density of the first single-carrier device corresponds to the operating current density of the single-color light emitting device corresponding to the first single-carrier device in the operating state. In step S31, according to the I-V curve of the first single-carrier device in the test process, an Arrhenius (Arrhenius) formula can be adopted to calculate and obtain a first start-up activation energy Ea i of each first single-carrier device of the first single-carrier device, I is more than or equal to 1, and I is an integer; and calculating to obtain a first work activation energy Ea j, wherein j is more than or equal to 1, and j is an integer.
The first single carrier device further includes a single color light emitting layer and a first carrier layer, the first single carrier device being a test device, the power-on test not emitting light, and therefore, in these embodiments, the first on-luminance activation energy Ea i is the activation energy of the single color light emitting layer and the first carrier layer in the first single carrier device at the on-luminance current density. The first operating activation energy Ea j is the activation energy of the single color light-emitting layer and the first carrier layer in the first single carrier device at the operating current density.
It is understood that when the first single-carrier device is a single-electron device, the first activation energy Ea i and the first operation activation energy Ea j are energies required for electrons to sequentially flow through the first carrier layer and the single-color light-emitting layer of carrier electrons from the cathode side in the first single-carrier device. As shown in fig. 4, the first luminance activation energy Ea i is the energy required for electrons to flow through the first carrier layer (hole blocking layer) carrying electrons and the single color light emitting layer in order in the electron injection direction at the luminance current density. As shown in fig. 5, the first operation activation energy Ea j is the energy required for electrons to flow through the first carrier layer (hole blocking layer) carrying electrons and the single color light emitting layer in this order in the electron injection direction at the operation current density.
When the first single carrier device is a single hole device, the first activation energy Ea i and the first operation activation energy Ea j are energies required for holes to flow through the first carrier layer and the single color light emitting layer of the current-carrying holes in this first single carrier device from the anode side in order. As shown in fig. 6, the first luminance activation energy Ea i, that is, the energy required for the first carrier layer and the single color light-emitting layer in order of holes to flow in the hole injection direction at the luminance current density. As shown in fig. 7, the first operation activation energy Ea j, that is, the energy required for the first carrier layer and the single color light-emitting layer in order of holes to flow in the hole injection direction at the operation current density.
In step S32, performing an energization test on the second single-carrier device to obtain an I-V curve related to the second single-carrier device, that is, a current-voltage curve of the second single-carrier device, where the second start-up activation energy Ea l of the second single-carrier device and the second work activation energy Ea w of the second single-carrier device may be calculated according to the current-voltage curve of the second single-carrier device in the test process by using an Arrhenius (Arrhenius) formula;
The second single carrier device includes a second carrier layer, and the second single carrier device is a test device, and the power-on test does not emit light, so in these embodiments, the second activation energy Ea l is the activation energy of the second carrier layer in the second single carrier device at the activation current density. The second operating activation energy Ea w is the second carrier layer in the second single-carrier device at the operating current density.
Wherein the first carrier layer and the second carrier layer are the same: the first carrier layer and the second carrier layer have the same physical and chemical parameters, and the activation energy of the first carrier layer and the activation energy of the second carrier layer are the same under the same test experimental conditions. The first single carrier device and the second single carrier device have the same experimental conditions in the power-on test process, and the power-on test is carried out only by using the single-color luminescent layer variable of the first single carrier device and the variable of the activation energy experiment is calculated. In some examples, the material of the single color light emitting layer includes a host light emitting material and a guest light emitting material doped in the host light emitting material.
It will be appreciated that when the second single-carrier device is a single-electron device, the second activation energy Ea l and the second operation activation energy Ea w are the energies required for electrons to flow from the cathode side through the second carrier layer of the current-carrying electrons in the second single-carrier device. When the second single carrier device is a single hole device, the second activation energy Ea l and the second operation activation energy Ea w are energies required for holes to flow through the second carrier layer of the current-carrying holes from the anode side in the second single carrier device.
The first single carrier device and the second single carrier device are both single electron devices or are both single hole devices.
It should be noted that, in the embodiment of the present application, the single-electron device only allows electrons to pass through. When the first carrier device and the second carrier device are the first single electron device and the second single electron device, respectively. In some embodiments, the first single electron device has a cathode, a hole blocking layer, a monochromatic light emitting layer, and an anode in a stacked arrangement, the monochromatic light emitting layer being coupled to the anode, the first hole blocking layer being coupled to the cathode. In some embodiments the single electron device further comprises at least one of an electron transport layer and an electron injection layer.
In some embodiments, the second single electron device has a cathode, a second hole blocking layer, and an anode in a stacked arrangement. The second single electron device in some embodiments further comprises at least one of an electron transport layer and an electron injection layer.
It should be noted that, in the embodiment of the present application, the single hole device only allows holes to pass through. When the first carrier device and the second carrier device are the first single hole device and the second single hole device, respectively. In some embodiments, the first single hole device has a cathode, a monochromatic light emitting layer, a first compensation layer, and an anode in a stacked arrangement, the compensation layer being coupled to the anode, the monochromatic light emitting layer being coupled to the cathode. In some embodiments the single hole device further comprises at least one of a hole transport layer and a hole injection layer.
In some embodiments, the second single hole device has a cathode, a second compensation layer, and an anode in a stacked arrangement. In some embodiments the second single hole device further comprises at least one of a hole transport layer and a hole injection layer.
In some alternative embodiments, please refer to fig. 8, in step S40 further includes:
In step S41, an activation energy difference Δea i between the monochromatic light emitting layer and the first carrier layer in each first single carrier device is calculated by using the first activation energy Ea i and the second activation energy Ea l corresponding to each first single carrier device, and an activation energy difference Δea j between the monochromatic light emitting layer and the first carrier layer in each first single carrier device is calculated by using the first operation activation energy Ea j and the second operation activation energy Ea w corresponding to each first single carrier device.
In step S41, the activation energy difference Δea i between the monochromatic light emitting layer and the first carrier layer in each first single carrier device is calculated according to the formula Δea i＝Eai-Eal. The activation energy difference Δea j between the monochromatic light emitting layer and the first carrier layer in each first single carrier device is calculated according to the formula Δea j＝Eaj-Eaw.
Step S42, screening to obtain a plurality of first target luminescent layer materials by using the first standard activation energy difference DeltaEa a and the second standard activation energy difference DeltaEa b;
In some alternative embodiments, the monochromatic light emitting layer is a green or red light emitting layer, the first standard activation energy difference Δea a ranges from 0.2eV < Δea a <0.6eV, and the second standard activation energy difference Δea b ranges from 0eV < Δea b <0.1eV.
In some alternative embodiments, the emissive layer material comprises a host emissive material and a guest emissive material doped in the host emissive material. That is, in these embodiments, the light emitting layer material selected by the second aspect of the embodiment of the present application is a mixture of a host light emitting material and a guest light emitting material having a certain doping ratio.
In some alternative embodiments the first single carrier device is a single electron device or a single hole device.
In order to embody the technical effects of the luminescent layer material obtained by screening by the material screening method of the second aspect of the application on improving the starting voltage of a red or green luminescent device and simultaneously reducing the working voltage, the following two groups of experiments are designed. The first set of experiments were luminescent layer material screening experiments for red light emitting devices, with comparative example 1 and experimental example 1. The second set of experiments was a light emitting layer material screening experiment of a green light emitting device, having comparative example 2 and experimental example 2. Wherein, the luminescent layer materials comprise a host luminescent material and a guest luminescent material doped in the host luminescent material.
The hole blocking layer of the first red light emitting device in comparative example 1 was the same as that of the second red light emitting device in experimental example 1, and the experimental conditions of the first red light emitting device and the second red light emitting device were the same during the test of the on-luminance voltage and the operating voltage, and the experiment was performed using only the light emitting layer material of the single color light emitting layer in the red light emitting device as a variable.
Table 1: test results of comparative example 1 and experiment 1
In table 1 Von represents the on-voltage, vd represents the operating voltage, CE represents the current efficiency, CIEx, CIEy are the color coordinates.
As can be seen from table 1, the color coordinates CIEx and CIEy of the light emitted from the first red light emitting device and the second red light emitting device are substantially the same, and both emit red light, the current efficiency of the second red light emitting device in experimental example 1 is slightly higher, and the on-luminance voltage of the second red light emitting device in experimental example 1 is 0.10V higher than that of the first red light emitting device in comparative example 1, and the operating voltage is reduced by 0.12V. Therefore, when the luminescent layer material of the red luminescent device screened by the material screening method of the second aspect of the application is applied to the red luminescent device, the starting voltage of the red luminescent device can be obviously improved, the working voltage of the red luminescent device can be reduced, the display accuracy of the display panel can be improved, and the problem of color cast of display caused by current crosstalk can be avoided.
The hole blocking layer of the first green light emitting device in comparative example 2 was the same as that of the second green light emitting device in experimental example 2, and the experimental conditions of the first green light emitting device and the second green light emitting device were the same during the test of the on-luminance voltage and the operating voltage, and experiments were performed using only the light emitting layer material of the single color light emitting layer in the green light emitting device as a variable.
Table 2: test results of comparative example 2 and experiment 2
As can be seen from table 2, the color coordinates CIEx and CIEy of the light emitted from the first and second green light emitting devices are substantially the same, and both emit green light, the current efficiency of the second green light emitting device in experimental example 2 is slightly higher, and the on-luminance voltage of the second green light emitting device in experimental example 2 is 0.17V higher than that of the first green light emitting device in comparative example 2, and the operating voltage is reduced by 0.51V. Therefore, when the luminescent layer material of the green luminescent device screened by the material screening method of the second aspect of the application is applied to the green luminescent device, the starting voltage of the green luminescent device can be obviously improved, the working voltage of the green luminescent device can be reduced, the display accuracy of the display panel can be improved, and the problem of color cast of display caused by current crosstalk can be avoided.
A third aspect of embodiments of the present application provides a display panel having the green and/or red light emitting device provided in the first aspect of the present application. The light emitting device layer of the display panel further includes a blue light emitting device. The display panel of the third aspect of the embodiment of the application has excellent display effect and high color rendering accuracy when displaying, and avoids poor display problems such as color shift or low display brightness and the like caused by current crosstalk.
These embodiments are not exhaustive or to limit the invention to the precise embodiments disclosed, and according to the invention described above. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and the full scope and equivalents thereof.
Claims (13)
1. A light emitting device, comprising:
a light-emitting layer having a light-emitting material, the light-emitting layer emitting light in a primary color of either red or green;
A first carrier layer stacked with the light emitting layer;
The light-emitting device is provided with a starting state and an operating state, and in the starting state, a first activation energy difference delta Ea x is arranged between the activation energy of the light-emitting layer and the activation energy of the first carrier layer; in the operating state, the light-emitting layer and the first carrier layer have a second activation energy difference value delta Ea x 'between activation energies, and delta Ea x>ΔEax' >0eV,
Wherein the value range of the first activation energy difference value Δea x is 0.2eV < Δea x <0.6eV;
The second activation energy difference Δea x 'has a value ranging from 0eV < Δea x' <0.1eV.
2. A light-emitting device according to claim 1, wherein,
The first carrier layer is a compensation layer and is positioned on the hole injection side of the light-emitting layer; or alternatively
The first carrier layer is a hole blocking layer and is positioned on the electron injection side of the light emitting layer.
3. A light-emitting device according to claim 1, wherein,
The first carrier layer is a compensation layer and is positioned on the hole injection side of the light-emitting layer;
The light-emitting device further comprises a hole blocking layer, wherein the hole blocking layer is stacked with the light-emitting layer and is positioned on the electron injection side of the light-emitting device; in the on state, a third activation energy difference Δea y is provided between the activation energies of the light-emitting layer and the hole blocking layer; in the operating state, there is a fourth activation energy difference Δea y 'between the activation energies of the light-emitting layer and the first carrier layer, and Δea y>ΔEay' >0eV.
4. A light-emitting device according to claim 3, wherein the value range of the third activation energy difference Δea y is 0.2eV < Δea y <0.6eV.
5. A light-emitting device according to claim 3, wherein the fourth activation energy difference Δea y 'has a value ranging from 0eV < Δea y' <0.1eV.
6. The light-emitting device according to claim 1, wherein when the first activation energy difference Δea x is provided between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, the turn-on voltage of the light-emitting device is increased by Δv on, and the value of Δv on is in the range of 0.1V to 0.2V.
7. The light-emitting device according to claim 1 or 6, wherein when the second activation energy difference Δea x' is provided between the activation energy of the light-emitting layer and the activation energy of the first carrier layer, the operating voltage of the light-emitting device is reduced by Δv d, and the value of Δv d is in the range of 0.1V to 0.6V.
8. The light-emitting device according to claim 1, wherein the light-emitting material comprises a host light-emitting material and a guest light-emitting material doped to the host light-emitting material.
9. A material screening method for screening a light-emitting layer material of a light-emitting device, characterized by comprising the steps of: the screening method comprises the following steps:
Providing a plurality of first single-carrier devices, wherein each first single-carrier device comprises a single-color light emitting layer and a first carrier layer, the first carrier layers among the plurality of first single-carrier devices are the same, and the materials of the single-color light emitting layers are different;
Providing a second single-carrier device comprising a second carrier layer, the first carrier layer being the same as the second carrier layer;
Acquiring a first on-luminance activation energy Ea i of each first single-carrier device and a second on-luminance activation energy Ea l of each second single-carrier device at an on-luminance current density, and acquiring a first on-luminance activation energy Ea j of each first single-carrier device and a second on-luminance activation energy Ea w of each second single-carrier device at an on-luminance current density;
According to a formula delta Ea i＝Eai-Eal, calculating to obtain an activation energy difference delta Ea i between the monochromatic light emitting layer and the first carrier layer in each first single carrier device in the on state, and according to a formula delta Ea j＝Eaj-Eaw, calculating to obtain an activation energy difference delta Ea j between the monochromatic light emitting layer and the first carrier layer in each first single carrier device in the working state;
and screening to obtain a plurality of first target luminescent layer materials by using the first standard activation energy difference delta Ea a and the second standard activation energy difference delta Ea b, wherein the activation energy difference delta Ea i between the monochromatic luminescent layer and the first carrier layer in each first single carrier device in the starting state is within the range of the first standard activation energy difference delta Ea a, and the activation energy difference delta Ea j between the monochromatic luminescent layer and the first carrier layer in each first single carrier device in the working state is within the range of the second standard activation energy difference delta Ea b.
10. The material screening method according to claim 9, wherein in the step of screening a plurality of the first target light emitting layer materials using the first standard activation energy difference Δea a and the second standard activation energy difference Δea b:
The single-color light-emitting layer is a green or red light-emitting layer, the value range of the first standard activation energy difference delta Ea a is 0.2eV < delta Ea a <0.6eV, and the value range of the second standard activation energy difference delta Ea b is 0eV < delta Ea b <0.1eV.
11. The material screening method according to claim 10, wherein the light-emitting layer material includes a host light-emitting material and a guest light-emitting material doped in the host light-emitting material.
12. The material screening method of claim 9, wherein the first single carrier device is a single electron device or a single hole device.
13. A display panel, characterized in that the display panel comprises a light emitting device according to any one of claims 1 to 8.
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