CN113611808A - Light emitting unit, preparation method thereof, display panel and display device - Google Patents
Light emitting unit, preparation method thereof, display panel and display device Download PDFInfo
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- H—ELECTRICITY
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K2101/00—Properties of the organic materials covered by group H10K85/00
- H10K2101/40—Interrelation of parameters between multiple constituent active layers or sublayers, e.g. HOMO values in adjacent layers
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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]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
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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]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
- H10K50/12—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising dopants
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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]
- H10K50/18—Carrier blocking layers
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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
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- H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
- H10K85/60—Organic compounds having low molecular weight
- H10K85/649—Aromatic compounds comprising a hetero atom
- H10K85/657—Polycyclic condensed heteroaromatic hydrocarbons
- H10K85/6572—Polycyclic condensed heteroaromatic hydrocarbons comprising only nitrogen in the heteroaromatic polycondensed ring system, e.g. phenanthroline or carbazole
Abstract
The embodiment of the application provides a light-emitting unit, a preparation method thereof, a display panel and display equipment. The light emitting unit comprises an electron blocking layer and a light emitting layer which are sequentially laminated; the difference between the absolute values of the highest occupied orbital level of the host material and the absolute value of the highest occupied orbital level of the doping material in the light-emitting layer is not larger than a first design value, and the highest occupied orbital level of the electron blocking layer is within a first design energy level range; or the difference between the absolute values of the host material and the doping material at the highest occupied orbital level is not less than a first design value and not more than a second design value, the highest occupied orbital level of the electron blocking layer is within the range of the second design level, the triplet state level is not less than a third design value, and the material of the electron blocking layer comprises a carbazole structure. According to the embodiment of the application, the disorder degree of an electron barrier layer material system is adjusted by matching the main material, the doping material and the electron barrier layer, so that the light-emitting unit with higher light-emitting layer efficiency or longer service life is obtained.
Description
Technical Field
The application relates to the technical field of display, in particular to a light-emitting unit, a preparation method of the light-emitting unit, a display panel and display equipment.
Background
With the development of Organic Light-Emitting Diode (OLED) display technology, OLED display devices are widely used. The OLED (organic light emitting diode) screen has the characteristics of self luminescence, high contrast, lightness and thinness, high response speed, wide visual angle, low power consumption, large applicable temperature range, low cost, simple manufacturing process and the like, is more and more widely applied in the fields of vehicle-mounted displays, computer displays, television screens, mobile phone screens and the like in recent years, and has wide application prospect.
However, the current blue OLEDs have less efficient or shorter lifetimes in the emissive layer.
Disclosure of Invention
The application provides a light-emitting unit, a preparation method thereof, a display panel and display equipment aiming at the defects of the existing mode, and aims to solve the technical problems that the light-emitting layer of a blue OLED is low in efficiency or short in service life in the prior art.
In a first aspect, an embodiment of the present application provides a light emitting unit, including: an electron blocking layer and a light emitting layer laminated in sequence; the light-emitting layer comprises a host material and a doping material; a difference between an absolute value of a highest occupied orbital level of the host material and an absolute value of a highest occupied orbital level of the dopant material is not greater than a first design value, the highest occupied orbital level of the electron blocking layer being within a first design energy level range; or the difference between the absolute value of the highest occupied orbital level of the host material and the absolute value of the highest occupied orbital level of the doping material is greater than the first design value and not greater than a second design value, the highest occupied orbital level of the electron blocking layer is within the second design level range, the triplet state level of the electron blocking layer is not less than a third design value, and the material of the electron blocking layer comprises a carbazole structure.
Optionally, the light emitting unit comprises at least one of: the highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts; the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 electron volts; the first design energy level range is no less than-5.5 electron volts and no greater than-5.2 electron volts.
Optionally, the light emitting unit comprises at least one of: the highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts; the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 electron volts; the second design value is 0.8 electron volts; the third design value is 2.5 electron volts; the second designed energy level range is no less than-5.3 electron volts and no greater than-5.7 electron volts.
Optionally, the triplet energy level of the electron blocking layer is no greater than 2.9 electron volts.
Optionally, the mass ratio of the host material to the dopant material is 9: 1-119: 1.
alternatively, the carbazole structure has the following general structural formula:
wherein, R1, R2, R3, Ar1 and Ar2 all comprise one of hydrogen, alkyl with the carbon number of 2-30, aryl with the carbon number of 6-30 and heteroaryl with the carbon number of 5-30.
In a second aspect, an embodiment of the present application provides a display panel including the light emitting unit provided in the first aspect of the embodiment of the present application.
In a third aspect, the present application provides a display device including the light emitting unit provided in the second aspect of the present application.
In a fourth aspect, an embodiment of the present application provides a method for manufacturing a light emitting unit, including: preparing an electron blocking layer with the highest occupied orbital energy level within a first design energy level range; and simultaneously preparing a host material and a doping material with the difference of the absolute value of the highest occupied orbital level not greater than a first design value on one side of the electron blocking layer to obtain the light-emitting layer.
In a fifth aspect, embodiments of the present application provide a method for manufacturing a light emitting unit, including: preparing an electron blocking layer with the highest occupied orbital level in a second design level range, the triplet state level not less than a third design value and including a carbazole structure; and simultaneously preparing a host material and a doping material, of which the difference of the absolute values of the highest occupied orbital levels is not less than the first design value and not more than the second design value, on one side of the electron blocking layer to obtain the light emitting layer.
The beneficial technical effects brought by the technical scheme provided by the embodiment of the application comprise:
according to the range of the difference value of the absolute value of the highest occupied orbital level of the host material and the doping material of the light-emitting layer, the host material and the doping material are matched with the resistance blocking layer with different highest occupied orbital levels or different highest occupied orbital levels, triplet state levels and material structures, so that the disorder degree of an electron blocking layer material system is in a design range, holes and electron mobility of the light-emitting layer are maintained at a relatively close level, electrons in an exciton recombination region are uniformly distributed in the light-emitting layer, the transmission performance of a blue light-emitting layer is changed, and the efficiency of the light-emitting layer is improved or the service life of the light-emitting layer is prolonged.
Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.
Drawings
The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is an energy level diagram of a host material, a dopant material, and an electron blocking layer of a light emitting device according to an embodiment of the present disclosure;
fig. 2 is an energy level diagram of a host material, a dopant material, and an electron blocking layer of a light emitting device according to another embodiment of the present disclosure;
fig. 3 is a schematic structural diagram of a light emitting unit according to an embodiment of the present disclosure;
FIG. 4 is a graph of the logarithm of the mobility versus the inverse of the square of the temperature for a first single hole carrier light-emitting unit provided in the examples of the present application, a device of the examples of the present application, and a light-emitting unit of the examples of the present application as a comparative example;
FIG. 5 is a graph of current density versus voltage for a first hole carrier light emitting cell provided in an embodiment of the present application, a device of an embodiment of the present application, and a light emitting cell of an embodiment of the present application as a comparative example;
FIG. 6 provides a schematic representation of a carbazole structure included in an electron blocking layer material in a second embodiment of the present application;
FIG. 7 is a graph of the logarithm of the mobility of a second hole carrier light-emitting cell provided in an embodiment of the present application, a device of another embodiment of the present application, and a light-emitting cell of another embodiment of the present application as a comparative example, plotted against the inverse of the square of the temperature;
FIG. 8 is a graph of current density versus voltage for a second hole carrier light emitting cell provided in an embodiment of the present application, a device of another embodiment of the present application, and a light emitting cell of another embodiment of the present application as a comparative example;
fig. 9 is a schematic flowchart of a method for manufacturing a light emitting unit according to an embodiment of the present disclosure;
fig. 10 is a schematic flow chart of a method for manufacturing a light-emitting unit according to another embodiment of the present disclosure.
Description of reference numerals:
10-a light emitting layer;
20-an electron blocking layer; 21-a host material; 22-a doping material;
l1-log of the mobility of the first single hole carrier light-emitting unit versus the inverse of the square of the temperature;
l2 — log of mobility of light-emitting unit of the present embodiment versus reciprocal of square of temperature;
l3-log of mobility versus reciprocal of square of temperature for luminescent cells of examples of the present application as comparative examples;
l4-current density versus voltage curve for the first single hole carrier light emitting cell;
l5-current density versus voltage curve of the light emitting cell of the present embodiment;
l6-current density vs. voltage curve of the light emitting cell of the present example as a comparative example;
l7-log of the mobility of the second single hole carrier light-emitting unit versus the inverse of the square of the temperature;
l8-log of mobility versus inverse of square of temperature for a light-emitting cell of another embodiment of the present application;
l9-log of mobility versus inverse of square of temperature for the luminescent cell of another example of the present application as a comparative example;
l10-current density vs. voltage curve for the second hole carrier light-emitting cell;
l11-current density versus voltage curve of a light emitting cell of another embodiment of the present application;
l12-current density versus voltage curve of a light emitting cell of another example of the present application as a comparative example.
Detailed Description
Reference will now be made in detail to the present application, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar parts or parts having the same or similar functions throughout. In addition, if a detailed description of the known art is not necessary for illustrating the features of the present application, it is omitted. The embodiments described below with reference to the drawings are exemplary only for the purpose of explaining the present application and are not to be construed as limiting the present application.
It will be understood by those within the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. As used herein, the term "and/or" includes all or any element and all combinations of one or more of the associated listed items.
The inventors of the present application have conducted studies to find that the electron mobility of the host material itself of the blue light emitting layer is higher than the hole mobility, electrons in the exciton recombination region approach the electron blocking layer and attack the electron blocking layer, and holes are accumulated at the interface of the electron blocking layer and the light emitting layer, which may reduce the efficiency of the blue light emitting layer or shorten the service life.
The application provides a light-emitting unit, a preparation method thereof, a display panel and display equipment, and aims to solve the technical problems that in the prior art, a light-emitting layer is low in efficiency or short in service life.
The following describes the technical solutions of the present application and how to solve the above technical problems with specific embodiments.
The embodiment of the application provides a light-emitting unit, and the structure of the light-emitting unit is as shown in fig. 1-3, and mainly comprises an electron blocking layer and a light-emitting layer which are sequentially laminated. The light-emitting layer comprises a host material and a doping material; the difference between the absolute value of the Highest Occupied Orbital (HOMO) level of the host material and the absolute value of the Highest Occupied Orbital level of the doping material is not greater than a first design value, and the Highest Occupied Orbital level of the electron blocking layer is within the first design level range; or the difference value between the absolute value of the highest occupied orbital level of the host material and the absolute value of the highest occupied orbital level of the doping material is greater than a first design value and not greater than a second design value, the highest occupied orbital level of the electron blocking layer is within the range of the second design level, the triplet state level of the electron blocking layer is not less than a third design value, and the material of the electron blocking layer comprises a carbazole structure.
Specifically, the difference between the absolute value of the highest occupied orbital level of the host material and the absolute value of the highest occupied orbital level of the doping material is matched with the electron blocking layer, so that the added disorder degree of the luminescent layer doped with the doping material is in a certain range.
In this embodiment, the host material and the dopant material of the light-emitting layer are matched with the resistance blocking layer having different highest occupied orbital energy levels or having different highest occupied orbital energy levels, triplet state energy levels, and a material structure according to the range of the difference between the absolute values of the highest occupied orbital energy levels, so that the disorder degree of the material system of the electron blocking layer is within the design range, the hole mobility and the electron mobility of the light-emitting layer are maintained at relatively close levels, electrons in the exciton recombination region are uniformly distributed in the light-emitting layer, the transportability of the blue light-emitting layer is changed, and the efficiency of the light-emitting layer is improved or the service life of the light-emitting layer is prolonged.
In some embodiments, the light emitting unit includes at least one of: a highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts; the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 electron volts; the first design energy level range is no less than-5.5 electron volts and no greater than-5.2 electron volts.
Specifically, the host material has a highest occupied orbital level between-5.6 electron volts and-6.2 electron volts, and the dopant material has a highest occupied orbital level between-5.2 electron volts and-5.8 electron volts. When the highest occupied orbital energy level difference between the host material and the doping material is not more than 0.3 electron volt, in order to ensure that the doping material in the light-emitting layer does not obviously cause the reduction of hole mobility and simultaneously ensure that excitons are uniformly distributed in the whole light-emitting layer, the increase of disorder degree caused by the host material and the doping material system is not more than 0.3 electron volt compared with the host material, and the highest occupied orbital energy level of the electron blocking layer material which needs to be matched is not less than-5.5 electron volt and not more than-5.2 electron volt. All range values in the examples of this application may be taken to be the endpoints of the range values.
In some embodiments, at least one of: a highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts; the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 electron volts; the second design value is 0.8 electron volts; the third design value is 2.5 electron volts; the second designed energy level range is no less than-5.3 electron volts and no greater than-5.7 electron volts.
Specifically, when the highest occupied orbital energy level difference between the host material and the doping material is not less than 0.3 electron volt and not more than 0.8 electron volt, in order to prevent the doping material in the light emitting layer from causing larger hole traps, excitons are distributed near one side of the electron blocking layer, the disorder degree caused by the system of the host material and the doping material is increased to be between 0.3 electron volt and 0.6 electron volt, the highest occupied orbital energy level of the matched electron blocking layer material is not less than-5.3 electron volt and not more than-5.7 electron volt, the triplet energy level of the electron blocking layer is not less than 2.5 electron volt, and the core structure of the electron blocking layer material comprises a carbazole structure which can simultaneously improve the triplet energy level and the stability of electrons.
In some embodiments, the triplet energy level of the electron blocking layer is no greater than 2.9 electron volts.
Specifically, the triplet level of the electron blocking layer is not less than 2.5 electron volts, and not more than 2.9 electron volts. Optionally, the triplet energy level of the electron blocking layer is 2.6 electron volts.
In some embodiments, the mass ratio of host material to dopant material is 9: 1-119: 1.
specifically, the proportion of the weight ratio of the doping material is not less than 0.5% and not more than 10%. Optionally, the mass ratio of host material to dopant material is 10: 1.
In some embodiments, the general structural formula of the carbazole structure includes:
wherein, R1, R2, R3, Ar1 and Ar2 all comprise one of hydrogen, alkyl with the carbon number of 2-30, aryl with the carbon number of 6-30 and heteroaryl with the carbon number of 5-30.
Specifically, the electron blocking layer comprises a carbazole-arylamine compound, and the carbazole-arylamine compound comprises the structural general formula. Carbazole-arylamine compounds are directly available from commercial sources. The nitrogen element which is not connected with R3 and R1 is aryl with 6-30 carbon atoms or heteroaryl with 5-30 carbon atoms through a single bond. The arrangement can improve the stability of the material of the electron barrier layer so as to prolong the service life of the light-emitting unit.
In some embodiments, the host material comprises a blue-light host material; the dopant material includes a blue dopant.
Specifically, a blue light emitting layer, a display panel including the blue light emitting layer, and a display device including the blue light emitting layer may be prepared by a blue light host material and a blue light dopant.
In a first specific embodiment, one selective blue host material and two different blue dopants are used, the two blue dopants including a first blue dopant and a second blue dopant.
The highest occupied orbital level of the blue host material is-5.93 electron volts, the highest occupied orbital level of the first blue dopant is-5.72 electron volts, and the difference between the highest occupied orbital levels of the blue host material and the blue dopant is 0.21 electron volts. The highest occupied orbital energy level difference of the second blue dopant is-5.34 electron volts and the highest occupied orbital energy level difference of the blue host material and the blue dopant is 0.59 electron volts.
Three single-hole carrier light-emitting units are prepared, and the disorder degree and the hole mobility of the light-emitting layer are obtained by preparing the single-hole carrier light-emitting units.
The step of preparing a first single hole carrier light emitting cell comprises: cleaning and drying the conductive glass substrate; and sequentially evaporating and plating a hole injection layer, a hole transmission layer, an electron blocking layer, a light emitting layer comprising a blue light main body material and a cathode on one side of the conductive glass substrate. In this example, the highest occupied orbital level of the electron blocking layer is-5.3 electron volts.
The preparation steps of the light-emitting unit of the embodiment of the application are different from the preparation of the first single-hole carrier light-emitting unit: an emissive layer including a blue host material and a first blue dopant is prepared. The mass ratio of the blue host material to the first blue dopant is 97: 3.
the preparation steps of the luminescent unit as a comparative example in the examples of the present application are different from those of the first singlet hole carrier luminescent unit: a light emitting layer including a blue host material and a second blue dopant is prepared. The mass ratio of the blue host material to the second blue dopant is 97: 3.
the three single-hole carrier light-emitting units are subjected to IV test at the temperature of 25 ℃, 35 ℃, 55 ℃ and 85 ℃ respectively to obtain the IV characteristics of the three single-hole carrier light-emitting units at different temperatures, and the mobility of the three single-hole carrier light-emitting units at different temperatures is obtained by calculating the current density and voltage curve through a space charge limited current method.
As shown in fig. 4, the relationship between the mobility under the electric field of 0 and the temperature is obtained by using the calculation formula of the gaussian disorder model, and logarithmic plotting is performed to obtain the linear relationship between the mobility and the temperature. In the figure, L1 represents a plot of the logarithm of the mobility of the first hole carrier light-emitting unit against the reciprocal of the square of the temperature, L2 represents a plot of the logarithm of the mobility of the light-emitting unit of the example of the present application against the reciprocal of the square of the temperature, L3 represents a plot of the logarithm of the mobility of the light-emitting unit of the example of the present application as a comparative example against the reciprocal of the square of the temperature, HOD represents the hole carrier light-emitting unit, μ is the mobility, E ═ 0 represents that the electric field is 0, the ordinate means the logarithm of the mobility under the electric field is 0, and the abscissa represents the reciprocal of the square of the temperature. The slope of the curve is a numerical value related to the disorder degree, the disorder degree is obtained according to the slope of the fitted curve, and the greater the slope is, the greater the disorder degree is. As can be seen from the figures, the proximity of L1 and L2 indicates that the disorder degrees of the first single-hole-carrier light-emitting unit and the light-emitting unit of the embodiment of the present application are close, and the inclination of L3 is greater than the inclination of L1 and the inclination of L2, indicating that the disorder degree of the light-emitting unit of the embodiment of the present application as a comparative example is higher than the disorder degrees of the first single-hole-carrier light-emitting unit and the light-emitting unit of the embodiment of the present application.
The current density versus voltage versus current density plots for the first single hole carrier light emitting cell, the device of the example of the present application, and the light emitting cell of the example of the present application as a comparative example are shown in fig. 5, where L4 represents the current density versus voltage plot for the first single hole carrier light emitting cell, and L5 represents the current density versus voltage plot for the light emitting cell of the example of the present application; l6 shows a current density versus voltage curve of the light emitting cell of the example of the present application as a comparative example. As can be seen from the figures, the mobility of the first single hole carrier light emitting unit and the light emitting unit of the example of the present application are close, and the mobility of the light emitting unit of the example of the present application as a comparative example is lower than that of the light emitting unit.
According to the embodiment, the disorder degree is increased, the mobility is reduced, the first blue light dopant has little influence on the disorder degree of the system, the hole mobility has no obvious change, and the second blue light dopant can obviously increase the disorder degree.
In a second specific embodiment, the blue host material and the blue dopant of the first specific embodiment are used.
Preparing three blue OLED light-emitting units, wherein the process for preparing the first blue OLED light-emitting unit comprises the following steps: cleaning and drying the conductive glass substrate; and sequentially evaporating and plating an anode, a hole injection layer, an electron blocking layer, a luminescent layer comprising a blue light main body material, the hole blocking layer, the electron injection layer and a cathode on one side of the conductive glass substrate. In this example, the highest occupied orbital level of the electron blocking layer is-5.45 electron volts.
The preparation process of the second blue light OLED light-emitting unit is different from that of the first blue light OLED light-emitting unit in that: a light emitting layer including a host material and a first blue dopant is prepared. The mass ratio of the blue host material to the first blue dopant is 97: 3.
the blue OLED light-emitting unit 3 is prepared by a different process from the first blue OLED light-emitting unit: after the electron blocking layer material is evaporated, the host material and the second blue light dopant are co-evaporated. The mass ratio of the blue host material to the second blue dopant is 97: 3.
and performing IV test on the three blue light OLED light-emitting units, and obtaining the percentage data of the voltage, the efficiency and the service life of the blue light OLED light-emitting units when the current density is 15 milliampere/square centimeter.
TABLE 1 percent Voltage, efficiency and lifetime obtained at a current density of 15 mA/cm
As can be seen from table 1, the efficiency of the first blue OLED light emitting unit is the lowest due to the low fluorescence quantum yield of the host material, which results in the low efficiency of the first blue OLED light emitting unit. The efficiency is significantly improved after the blue dopant material. Comparing the data of the second blue light OLED light-emitting unit and the third blue light OLED light-emitting unit, the second blue light OLED light-emitting unit has the longest service life, and the reasons include that after the first blue light dopant material is doped, the disorder degree is almost unchanged, and the hole mobility is close to that of the intrinsic material of the host material, so that hole electrons in the light-emitting layer are more balanced, and the light-emitting unit does not fail due to the fact that the light-emitting layer is matched with the electron blocking layer material which occupies the shallower orbital energy level to the highest degree. The third blue OLED light emitting unit has a very short lifetime because the doped second blue dopant, which is doped in, increases disorder, resulting in a decrease in hole mobility. The electron mobility is unchanged, so that the electron hole transport ratio in the light-emitting layer is increased, and the exciton recombination region is deviated to one side of the electron blocking layer. If the electron blocking layer with the shallow highest occupied orbital level is matched at this time, holes and excitons are concentrated on the interface of the electron blocking layer and the light emitting layer, so that the interface is damaged, and the service life of the light emitting unit is reduced.
In a third specific embodiment, one selective blue host material and two different blue dopants are used, the two blue dopants including a third blue dopant and a fourth blue dopant.
The highest occupied orbital level of the blue host material is-5.93 electron volts, the highest occupied orbital level of the third blue dopant is-5.37 electron volts, and the difference between the highest occupied orbital levels of the blue host material and the blue dopant is 0.56 electron volts. The highest occupied orbital energy level difference of the fourth blue dopant is-5.78 electron volts, and the highest occupied orbital energy level difference of the blue host material and the blue dopant is 0.15 electron volts.
Three single-hole carrier light-emitting units are prepared, and the disorder degree and the hole mobility of the light-emitting layer are obtained by preparing the single-hole carrier light-emitting units.
The step of preparing a second single hole carrier light emitting cell comprises: cleaning and drying the conductive glass substrate; and sequentially evaporating and plating a hole injection layer, a hole transmission layer, an electron blocking layer, a light emitting layer comprising a blue light main body material and a cathode on one side of the conductive glass substrate.
In this embodiment, as shown in fig. 6, the electron blocking layer material includes a carbazole structure, and the highest occupied orbital level of the electron blocking layer is-5.45 ev and the triplet level is 2.63 ev.
The preparation steps of the light-emitting unit according to another embodiment of the present application are different from those of the second single-hole carrier light-emitting unit, in which a blue light host material and a third blue light dopant are evaporated on a side of the hole transport layer away from the hole injection layer to obtain a light-emitting layer. The mass ratio of the blue host material to the third blue dopant is 97: 3.
the difference between the preparation steps of the light-emitting unit as a comparative example and the preparation of the second single-hole carrier light-emitting unit is that a blue light host material and a fourth blue light dopant are evaporated on the side, far away from a hole injection layer, of a hole transport layer to obtain a light-emitting layer. The mass ratio of the blue host material to the fourth blue dopant is 97: 3.
the three single-hole carrier light-emitting units are subjected to IV test at the temperature of 25 ℃, 35 ℃, 55 ℃ and 85 ℃ respectively to obtain the IV characteristics of the three single-hole carrier light-emitting units at different temperatures, and the mobility of the three single-hole carrier light-emitting units at different temperatures is obtained by calculating the current density and voltage curve through a space charge limited current method.
As shown in fig. 7, the relationship between the mobility under the 0 electric field and the temperature is obtained by using the calculation formula of the gaussian disorder model, and logarithmic plotting is performed to obtain that the mobility and the temperature are in a linear relationship. In the figure, L7 represents a log of mobility of the second hole carrier light emitting cell with respect to an inverse of a square of temperature, L8 represents a log of mobility of the light emitting cell of another embodiment of the present application with respect to an inverse of a square of temperature, L9 represents a log of mobility of the light emitting cell of another embodiment of the present application as a comparative example with respect to an inverse of a square of temperature, μ represents mobility, Ln represents a base logarithm (i.e., a natural logarithm), E ═ 0 represents an electric field of 0, ordinate means a log of mobility under an electric field of 0, and abscissa represents an inverse of a square of temperature. The slope of the curve is a numerical value related to the disorder degree, the disorder degree is obtained according to the slope of the fitted curve, and the greater the slope is, the greater the disorder degree is. As can be seen from the graph, L7 is close to L8, indicating that the disorder degrees of the second single-hole carrier light-emitting unit and the light-emitting unit of the present example as a comparative example are close, and the inclination of L9 is greater than the inclination of L7 and the inclination of L8, indicating that the disorder degree of the light-emitting unit of the present example is higher than the disorder degrees of the second single-hole carrier light-emitting unit and the light-emitting unit of the present example as a comparative example.
Current density versus voltage plots for the second hole carrier light-emitting cell, a device of another embodiment of the present application, and a light-emitting cell of another embodiment of the present application as a comparative example, as shown in fig. 8, where L10 represents the current density versus voltage plot for the second hole carrier light-emitting cell, L11 represents the current density versus voltage plot for the light-emitting cell of another embodiment of the present application, and L12 represents the current density versus voltage plot for the light-emitting cell of another embodiment of the present application as a comparative example. As can be seen from the graph, the mobility of the second single hole carrier light emitting unit and the light emitting unit of the other embodiment of the present application as a comparative example are close, and the mobility of the light emitting unit of the other embodiment of the present application is lower than that of the light emitting unit.
In a fourth specific embodiment, the blue host material and the blue dopant of the third specific embodiment are used.
Three blue light OLED light-emitting units are prepared, and the process for preparing the fourth blue light OLED light-emitting unit comprises the following steps: cleaning and drying the conductive glass substrate; and sequentially evaporating an anode material, a hole injection layer material, an electron blocking layer material, a blue light main body material, a hole blocking layer material, an electron injection layer material and a cathode material on one side of the conductive glass substrate. In this example, the highest occupied orbital level of the electron blocking layer is-5.45 electron volts.
The preparation process of the fifth blue light OLED light-emitting unit is different from that of the fourth blue light OLED light-emitting unit in that: after the electron blocking layer material is evaporated, the host material and the third blue light dopant are co-evaporated. The mass ratio of the blue host material to the third blue dopant is 97: 3.
the preparation process of the sixth blue light OLED light-emitting unit is different from that of the fourth blue light OLED light-emitting unit in that: after the electron blocking layer material is evaporated, the host material and the fourth blue light dopant are co-evaporated. The mass ratio of the blue host material to the fourth blue dopant is 97: 3.
IVL testing was performed on three light emitting cells and the percent voltage, efficiency and lifetime data were obtained at a current density of 15 milliamps/square centimeter.
TABLE 2 percent Voltage, efficiency and lifetime obtained at a current density of 15 mA/cm
As can be seen from table 2, the efficiency of the fourth blue OLED light emitting unit is the lowest, and the efficiency life of the fifth blue OLED light emitting unit is the best, because after the third blue dopant material is doped, although the hole mobility is reduced, the hole injection from the electron blocking layer to the host material is smooth by the deeper electron blocking layer material, so that the reduction of the mobility is compensated. Meanwhile, the matched electron blocking layer material uses a high triplet state energy level, so that excitons can be limited in the light emitting layer, and the efficiency is improved. Meanwhile, the carbazole structure is beneficial to improving the electron stability of the electron barrier layer material, so that the service life of the light-emitting unit is prolonged. However, in the sixth blue OLED light-emitting unit, the hole mobility of the light-emitting layer is not reduced, and meanwhile, the electron blocking layer material with the highest occupied rail energy level is used, so that holes injected into the light-emitting layer are smooth, the holes in the light-emitting layer are excessive, and the efficiency is reduced. The sixth blue OLED light emitting unit has a long lifetime but low efficiency.
In some embodiments, the disorder is tested by a method including, but not limited to, temperature swing mobility testing.
The disorder degree change of the host material and the doping material system in this embodiment is an increased value of the disorder degree relative to the pure host material itself.
Based on the same inventive concept, embodiments of the present application provide a display panel including the light emitting unit provided in the first aspect of the embodiments of the present application.
In a possible embodiment, the display panel comprises a blue light generating unit.
Based on the same inventive concept, embodiments of the present application provide a display device including a light emitting unit provided in the second aspect of the embodiments of the present application.
In a possible embodiment, the display panel of the display device comprises a blue light generating unit.
Based on the same inventive concept, the present application provides a method for manufacturing a light emitting unit, as shown in fig. 9, which mainly includes steps S1 and S2:
step S1: an electron blocking layer is prepared having a highest occupied orbital level within a first designed energy level range.
Step S2: and simultaneously preparing a host material and a doping material with the difference of the absolute value of the highest occupied orbital level not greater than a first design value on one side of the electron blocking layer to obtain the light-emitting layer.
Based on the same inventive concept, the present embodiment provides a method for manufacturing a light emitting unit, as shown in fig. 10, which mainly includes steps S3 and S4:
step S3: preparing an electron blocking layer having a maximum occupied orbital level within a second design level range and not less than a third design value, and including a carbazole structure;
step S4: and simultaneously preparing the host material and the doping material with the difference value of the absolute value of the highest occupied orbital level not less than the first design value and not more than the second design value on one side of the electron blocking layer to obtain the light emitting layer.
By applying the embodiment of the application, at least the following beneficial effects can be realized:
according to the range of the difference value of the absolute value of the highest occupied orbital level of the host material and the doping material of the light-emitting layer, the host material and the doping material are matched with the resistance blocking layer with different highest occupied orbital levels or different highest occupied orbital levels, triplet state levels and material structures, so that the disorder degree of an electron blocking layer material system is in a design range, holes and electron mobility of the light-emitting layer are maintained at a relatively close level, electrons in an exciton recombination region are uniformly distributed in the light-emitting layer, the transmission performance of a blue light-emitting layer is changed, and the efficiency of the light-emitting layer is improved or the service life of the light-emitting layer is prolonged.
Those of skill in the art will appreciate that the various operations, methods, steps in the processes, acts, or solutions discussed in this application can be interchanged, modified, combined, or eliminated. Further, other steps, measures, or schemes in various operations, methods, or flows that have been discussed in this application can be alternated, altered, rearranged, broken down, combined, or deleted. Further, steps, measures, schemes in the prior art having various operations, methods, procedures disclosed in the present application may also be alternated, modified, rearranged, decomposed, combined, or deleted.
In the description of the present application, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the present application.
The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless otherwise specified.
In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.
In the description herein, particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
It should be understood that, although the steps in the flowcharts of the figures are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and may be performed in other orders unless explicitly stated herein. Moreover, at least a portion of the steps in the flow chart of the figure may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed alternately or alternately with other steps or at least a portion of the sub-steps or stages of other steps.
The foregoing is only a partial embodiment of the present application, and it should be noted that, for those skilled in the art, several modifications and decorations can be made without departing from the principle of the present application, and these modifications and decorations should also be regarded as the protection scope of the present application.
Claims (10)
1. A light-emitting unit, comprising: an electron blocking layer and a light emitting layer laminated in sequence;
the light-emitting layer comprises a host material and a doping material;
a difference between an absolute value of a highest occupied orbital level of the host material and an absolute value of a highest occupied orbital level of the dopant material is not greater than a first design value, the highest occupied orbital level of the electron blocking layer being within a first design energy level range;
or the difference between the absolute value of the highest occupied orbital level of the host material and the absolute value of the highest occupied orbital level of the doping material is greater than the first design value and not greater than a second design value, the highest occupied orbital level of the electron blocking layer is within the second design level range, the triplet state level of the electron blocking layer is not less than a third design value, and the material of the electron blocking layer comprises a carbazole structure.
2. The lighting unit of claim 1, comprising at least one of:
the highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts;
the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 electron volts;
the first design energy level range is no less than-5.5 electron volts and no greater than-5.2 electron volts.
3. The lighting unit of claim 1, comprising at least one of:
the highest occupied orbital level of the host material is not less than-6.2 electron volts and not more than-5.6 electron volts;
the highest occupied orbital level of the doping material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 electron volts;
the second design value is 0.8 electron volts;
the third design value is 2.5 electron volts;
the second designed energy level range is no less than-5.3 electron volts and no greater than-5.7 electron volts.
4. The lighting unit according to claim 3,
the triplet energy level of the electron blocking layer is not greater than 2.9 electron volts.
5. The lighting unit according to claim 1,
the mass ratio of the host material to the doping material is 9: 1-119: 1.
6. the light-emitting unit according to claim 1, wherein the carbazole structure has a general structural formula:
wherein, R1, R2, R3, Ar1 and Ar2 all comprise one of hydrogen, alkyl with the carbon number of 2-30, aryl with the carbon number of 6-30 and heteroaryl with the carbon number of 5-30.
7. A display panel, comprising: the light-emitting unit according to any one of claims 1 to 6.
8. A display device, comprising: the display panel of claim 7.
9. A method of making a light-emitting unit, comprising:
preparing an electron blocking layer with the highest occupied orbital energy level within a first design energy level range;
and simultaneously preparing a host material and a doping material with the difference of the absolute value of the highest occupied orbital level not greater than a first design value on one side of the electron blocking layer to obtain the light-emitting layer.
10. A method of making a light-emitting unit, comprising:
preparing an electron blocking layer with the highest occupied orbital level in a second design level range, the triplet state level not less than a third design value and including a carbazole structure;
and simultaneously preparing a host material and a doping material, of which the difference of the absolute values of the highest occupied orbital levels is not less than the first design value and not more than the second design value, on one side of the electron blocking layer to obtain the light emitting layer.
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