CN113611808B - 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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- 238000002360 preparation method Methods 0.000 title abstract description 10
- 239000000463 material Substances 0.000 claims abstract description 173
- 230000000903 blocking effect Effects 0.000 claims abstract description 76
- 238000013461 design Methods 0.000 claims abstract description 70
- 239000002019 doping agent Substances 0.000 claims abstract description 52
- 125000000609 carbazolyl group Chemical group C1(=CC=CC=2C3=CC=CC=C3NC12)* 0.000 claims abstract description 14
- 238000004519 manufacturing process Methods 0.000 claims description 12
- 125000004432 carbon atom Chemical group C* 0.000 claims description 11
- 125000003118 aryl group Chemical group 0.000 claims description 4
- 125000001072 heteroaryl group Chemical group 0.000 claims description 4
- 125000000217 alkyl group Chemical group 0.000 claims description 3
- 229910052739 hydrogen Inorganic materials 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 claims description 3
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims description 3
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- 230000005684 electric field Effects 0.000 description 6
- 238000007740 vapor deposition Methods 0.000 description 6
- 238000005215 recombination Methods 0.000 description 5
- 230000006798 recombination Effects 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- 238000004140 cleaning Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000005525 hole transport Effects 0.000 description 3
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- 230000002035 prolonged effect Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 2
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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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- 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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- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
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- 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
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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 host material and the doping material at the highest occupied track energy level of the light-emitting layer is not more than a first design value, and the highest occupied track energy level of the electron blocking layer is in a first design energy level range; alternatively, the difference between the absolute values of the host material and the dopant material at the highest occupied orbital energy level is not less than the first design value and not greater than the second design value, the highest occupied orbital energy level of the electron blocking layer is within the second design energy level range, the triplet energy level is not less than the third design value, and the material of the electron blocking layer includes a carbazole structure. According to the embodiment of the application, the disorder degree of the electron blocking layer material system is regulated by matching the main material, the doping material and the electron blocking 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 thereof, a display panel and display equipment.
Background
An OLED (Organic Light-Emitting Diode) display technology has been developed, and an OLED display device has been widely used. OLED (organic light emitting diode) screens have the characteristics of self-luminescence, high contrast, light weight, high response speed, wide viewing angle, low power consumption, large applicable temperature range, low cost, simple manufacturing process and the like, and have been widely applied in the fields of vehicle-mounted displays, computer displays, television screens, mobile phone screens and the like in recent years, and have wide application prospects.
However, current blue OLEDs have a low efficiency or a short lifetime of the light emitting layer.
Disclosure of Invention
Aiming at the defects of the prior art, the application provides a light-emitting unit, a preparation method thereof, a display panel and display equipment, which are used for solving the technical problems of low efficiency or short service life of a light-emitting layer of a blue light OLED 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 this order; the light-emitting layer comprises a host material and a doping material; the difference between the absolute value of the highest occupied orbit energy level of the host material and the absolute value of the highest occupied orbit energy level of the doping material is not greater than a first design value, and the highest occupied orbit energy level of the electron blocking layer is in a first design energy level range; alternatively, 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 dopant 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 energy range, the triplet energy level of the electron blocking layer is not less than a third design value, and the material of the electron blocking layer includes a carbazole structure.
Optionally, the light emitting unit comprises at least one of: the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 ev; the first design energy level range is not less than-5.5 electron volts and not greater than-5.2 electron volts.
Optionally, the light emitting unit comprises at least one of: the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 ev; the second design value is 0.8 ev; the third design value is 2.5 ev; the second design energy level range is not less than-5.3 ev and not greater than-5.7 ev.
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 doping material is 9:1 to 119:1.
optionally, the carbazole structure has a general structural formula as follows:
wherein R1, R2, R3, ar1 and Ar2 each comprise one of hydrogen, an alkyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms and a heteroaryl group having 5 to 30 carbon atoms.
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 present application.
In a third aspect, an embodiment of the present application provides a display device, including the light emitting unit provided in the second aspect of the embodiment 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 orbit energy level within a first design energy level range; and preparing a host material and a doping material with the absolute value difference of the highest occupied orbit energy level not larger than a first design value at one side of the electron blocking layer at the same time to obtain the light emitting layer.
In a fifth aspect, an embodiment of the present application provides a method for manufacturing a light emitting unit, including: preparing an electron blocking layer having a highest occupied orbit energy level within the second design energy level range, a triplet energy level not less than a third design value, and a carbazole structure; and preparing a host material and a doping material of which the absolute value difference of the highest occupied orbit energy level is not smaller than the first design value and not larger than the second design value at one side of the electron blocking layer at the same time to obtain the light-emitting layer.
The technical scheme provided by the embodiment of the application has the beneficial technical effects that:
according to the range of the difference value of the absolute values of the main body material and the doping material of the light-emitting layer at the highest occupied orbit energy level, the main body material and the doping material are matched with the resistance barrier layers with different highest occupied orbit energy levels or highest occupied orbit energy levels, triplet state energy levels and material structures, so that the disorder degree of an electron barrier layer material system is in a design range, the hole mobility and the electron mobility of the light-emitting layer are maintained at relatively similar levels, electrons in an exciton recombination area are uniformly distributed in the light-emitting layer, the transmissibility 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.
Additional aspects and advantages of the 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 application.
Drawings
The foregoing and/or additional aspects and advantages of the application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:
fig. 1 is an energy level diagram of a host material, a doping material, and an electron blocking layer of a light emitting unit according to an embodiment of the present application;
fig. 2 is an energy level diagram of a host material, a dopant material, and an electron blocking layer of a light emitting unit according to another embodiment of the present application;
fig. 3 is a schematic structural diagram of a light emitting unit according to an embodiment of the present application;
fig. 4 is a graph showing the relationship between the logarithm of the mobility of the first single hole carrier light emitting unit provided in the embodiment of the present application, the device in the embodiment of the present application, and the reciprocal of the square of the temperature of the light emitting unit in the embodiment of the present application as a comparative example;
fig. 5 is a graph showing the relationship between current density and voltage of a first single hole carrier light emitting cell provided in an embodiment of the present application, an emitter according to an embodiment of the present application, and a light emitting cell according to an embodiment of the present application as a comparative example;
FIG. 6 is a schematic diagram of a carbazole structure included in an electron blocking layer material according to a second embodiment of the present application;
fig. 7 is a graph showing the relationship between the logarithm of the mobility of the second single hole carrier light emitting unit, the device according to another embodiment of the present application, and the reciprocal of the square of the temperature of the light emitting unit according to another embodiment of the present application as a comparative example;
fig. 8 is a graph of current density versus voltage versus current density versus voltage for a second single hole carrier light emitting cell provided by an embodiment of the present application, an emitter 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 flow chart of a method for manufacturing a light emitting unit according to an embodiment of the present application;
fig. 10 is a flow chart of a method for manufacturing a light emitting unit according to another embodiment of the application.
Reference numerals illustrate:
10-a light emitting layer;
20-an electron blocking layer; 21-a host material; 22-doping material;
l1-a plot of the logarithm of the mobility of the first single hole carrier light emitting cell versus the inverse square of the temperature;
l2-a plot of the logarithm of the mobility of the light emitting unit versus the inverse square of the temperature for embodiments of the present application;
l3-inventive example as a comparative example, a relationship curve of the logarithm of the mobility of the light emitting unit to the reciprocal of the square of the temperature;
l4-a current density versus voltage curve for the first single hole carrier light emitting cell;
l5-a relation curve of current density and voltage of the light-emitting unit according to the embodiment of the application;
l6-inventive example as a current density versus voltage curve for the light emitting unit of the comparative example;
l7-a plot of the logarithm of the mobility of the second single hole carrier light emitting cell versus the reciprocal of the square of temperature;
l8-a plot of the logarithm of the mobility of a light emitting cell of another embodiment of the application versus the inverse of the square of temperature;
l9-another embodiment of the present application is a relationship curve of the logarithm of the mobility of the light emitting unit of the comparative example to the reciprocal of the square of the temperature;
l10-a current density versus voltage curve for a second single hole carrier light emitting cell;
l11-a current density versus voltage curve for a light emitting cell according to another embodiment of the present application;
l12-another embodiment of the present application is a current density versus voltage curve of the light emitting unit of the comparative example.
Detailed Description
The present application is described in detail below, examples of embodiments of the application are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar components or components having the same or similar functions throughout. Further, if detailed description of the known technology is not necessary for the illustrated features of the present application, it will be omitted. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the application.
It will be understood by those skilled in the art that 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 unless defined otherwise. 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 expressly stated otherwise, as understood by those skilled in the art. 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. The term "and/or" as used herein includes all or any element and all combination of one or more of the associated listed items.
The inventor of the present application conducted research and found 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 may approach the electron blocking layer and attack the electron blocking layer, and holes may be 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 of low efficiency or short service life of a light-emitting layer in the prior art.
The following describes the technical scheme of the present application and how the technical scheme of the present application solves the above technical problems in detail with specific embodiments.
The embodiment of the application provides a light-emitting unit, and the structure of the light-emitting unit is shown in figures 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, highest Occupied Molecular Orbital) energy level of the host material and the absolute value of the highest occupied orbital energy level of the dopant material is not greater than a first design value, the highest occupied orbital energy level of the electron blocking layer being within a first design energy level range; alternatively, 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 dopant material is greater than the first design value and not greater than the second design value, the highest occupied orbital level of the electron blocking layer is within the second design energy range, the triplet energy level of the electron blocking layer is not less than the third design value, and the material of the electron blocking layer includes a carbazole structure.
Specifically, the light-emitting layer doped by the doping material has increased disorder in a certain range by matching the difference between the absolute value of the highest occupied orbit energy level of the host material and the absolute value of the highest occupied orbit energy level of the doping material with the electron blocking layer.
In this embodiment, according to the range of the difference between the absolute values of the host material and the dopant material of the light-emitting layer at the highest occupied track energy level, the resistive barrier layer having different highest occupied track energy levels or having the highest occupied track energy levels, triplet energy levels, and material structures is matched, so that the disorder degree of the material system of the electron barrier layer is within the design range, so as to maintain the hole mobility and the electron mobility of the light-emitting layer at relatively similar levels, and make the electrons in the exciton recombination region uniformly distributed in the light-emitting layer, so as to change the transmissibility of the blue light-emitting layer, thereby improving the efficiency of the light-emitting layer or prolonging the service life.
In some embodiments, the light emitting unit comprises at least one of: the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 ev; the first design energy level range is not less than-5.5 ev and not more than-5.2 ev.
Specifically, the host material has a highest occupied orbital energy level between-5.6 electron volts and-6.2 electron volts, and the dopant material has a highest occupied orbital energy level between-5.2 electron volts and-5.8 electron volts. When the highest occupied orbit energy level difference between the host material and the doped material is not more than 0.3 ev, in order to ensure that the doped material in the light-emitting layer does not obviously cause the reduction of hole mobility, and meanwhile, the excitons are uniformly distributed in the whole light-emitting layer, the disorder degree increment caused by the system of the host material and the doped material compared with the host material per se should not more than 0.3 ev, and the highest occupied orbit energy level of the electron blocking layer material to be matched should not less than-5.5 ev and not more than-5.2 ev. In the embodiment of the application, all range values can take the end value of the range value.
In some embodiments, at least one of the following is included: the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts; the first design value is 0.3 ev; the second design value is 0.8 ev; the third design value is 2.5 ev; the second design energy level range is not less than-5.3 ev and not more than-5.7 ev.
Specifically, when the highest occupied orbital energy level difference between the host material and the doped material is not less than 0.3 ev and not more than 0.8 ev, in order to prevent the doped 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 doped material is increased to be between 0.3 ev and 0.6 ev, the highest occupied orbital energy level of the matched electron blocking layer material is not less than-5.3 ev and not more than-5.7 ev, the triplet energy level of the electron blocking layer is not less than 2.5 ev, 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 energy level of the electron blocking layer is not less than 2.5 ev and not more than 2.9 ev. Optionally, the triplet energy level of the electron blocking layer is 2.6 ev.
In some embodiments, the mass ratio of host material to dopant material is 9:1 to 119:1.
specifically, the proportion of the weight ratio of the doping materials 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 structural formula of the carbazole structure includes:
wherein R1, R2, R3, ar1 and Ar2 each comprise one of hydrogen, an alkyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms and a heteroaryl group having 5 to 30 carbon atoms.
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 through market procurement. 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. This arrangement can improve the stability of the electron blocking layer material to improve the lifetime of the light emitting unit.
In some embodiments, the host material comprises a blue host material; the doping material includes a blue dopant.
In particular, 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 host material and a blue dopant.
In a first specific embodiment, one selected 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 ev, the highest occupied orbital level of the first blue dopant is-5.72 ev, and the highest occupied orbital level difference between the blue host material and the blue dopant is 0.21 ev. The highest occupied orbital energy level difference of the second blue dopant is-5.34 ev, and the highest occupied orbital energy level difference of the blue host material and the blue dopant is 0.59 ev.
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 includes: cleaning and drying the conductive glass substrate; and forming a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer comprising a blue light main body material and a cathode by vapor deposition on one side of the conductive glass substrate. In this embodiment, the electron blocking layer has a highest occupied orbital energy level of-5.3 ev.
The preparation steps of the light emitting unit according to the embodiment of the present application are different from those of the first single hole carrier light emitting unit: a light emitting layer including a blue host material and a first blue dopant is prepared. The mass ratio of the blue light host material to the first blue light dopant is 97:3.
the steps for preparing the light emitting unit according to the embodiment of the present application as a comparative example are different from those for preparing the coated single hole carrier light emitting unit: a light emitting layer including a blue host material and a second blue dopant is prepared. The mass ratio of the blue light host material to the second blue light dopant is 97:3.
and respectively performing IV tests on the three single hole carrier light-emitting units at the temperature of 25 ℃,35 ℃,55 ℃ and 85 ℃ to obtain IV characteristics of the three single hole carrier light-emitting units at different temperatures, and performing space charge limiting current method calculation on current density and voltage curves to obtain mobility of the three single hole carrier light-emitting units at different temperatures.
As shown in fig. 4, the relationship between the mobility and the temperature in the 0 electric field is obtained by using a calculation formula of the gaussian disorder model, and the relationship between the mobility and the temperature is plotted logarithmically, so that the mobility and the temperature are in a linear relationship. In the figure, L1 represents a plot of the logarithm of the mobility of the first single hole carrier light-emitting unit versus the inverse square of the temperature, L2 represents a plot of the logarithm of the mobility of the light-emitting unit versus the inverse square of the temperature, L3 represents a plot of the logarithm of the mobility of the light-emitting unit versus the inverse square of the temperature as a comparative example, HOD represents a single hole carrier light-emitting unit, μ is the mobility, e=0 represents the electric field is 0, the ordinate represents the logarithm of the mobility under 0 electric field, and the abscissa represents the inverse square of the temperature. The slope of the curve is a numerical value related to the disorder degree, and the disorder degree is obtained according to the slope of the fitted curve, and the larger the slope is, the larger the disorder degree is. As can be seen from the figures, the proximity of L1 and L2 indicates that the disorder degree of the first single hole carrier light emitting unit and the light emitting unit of the embodiment of the present application is close, the inclination of L3 is larger than the inclination of L1 and the inclination of L2, and the disorder degree of the light emitting unit of the embodiment of the present application as a comparative example is higher than the disorder degree 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 curve of the first single hole carrier light emitting cell, the device of the embodiment of the present application, and the light emitting cell of the embodiment of the present application as comparative examples is shown in fig. 5, in which L4 represents the current density versus voltage curve of the first single hole carrier light emitting cell, and L5 represents the current density versus voltage curve of the light emitting cell of the embodiment of the present application; l6 represents a current density versus voltage curve of the light emitting unit as a comparative example of the embodiment of the present application. 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 embodiment of the present application is close, and the mobility of the light emitting unit of the embodiment of the present application as a comparative example is lower than that of the light emitting unit of the first single hole carrier light emitting unit and the light emitting unit of the embodiment of the present application.
As can be seen from the present example, the disorder degree is increased, the mobility is reduced, the disorder degree of the system is not greatly affected by the first blue light dopant, the hole mobility is not significantly changed, and the disorder degree is significantly increased by the second blue light dopant.
In a second specific embodiment, the blue host material and blue dopant of the first specific embodiment are used.
Three blue OLED light emitting units are prepared, and the process for preparing the first blue OLED light emitting unit comprises the following steps: cleaning and drying the conductive glass substrate; an anode, a hole injection layer, an electron blocking layer, a light emitting layer comprising a blue light main body material, a hole blocking layer, an electron injection layer and a cathode are formed on one side of the conductive glass substrate by vapor deposition in sequence. In this embodiment, the electron blocking layer has a highest occupied orbital level of-5.45 ev.
The preparation process of the second blue OLED light-emitting unit is different from that of the first blue OLED light-emitting unit: a light emitting layer including a host material and a first blue dopant is prepared. The mass ratio of the blue light host material to the first blue light dopant is 97:3.
the blue OLED light emitting unit 3 is different from the first blue OLED light emitting unit in the process of manufacturing: after vapor deposition of the electron blocking layer material, the host material and the second blue dopant are co-evaporated. The mass ratio of the blue light host material to the second blue light dopant is 97:3.
and IV testing is carried out on the three blue OLED light-emitting units, and when the current density is 15 milliamperes/square centimeter, the voltage, the efficiency and the service life percentage data of the blue OLED light-emitting units are obtained.
Table 1 percentage of efficiency and lifetime for the voltage obtained at a current density of 15 milliamp/square cm
As can be seen from table 1, the efficiency of the first blue OLED light emitting unit is the lowest, because the fluorescence quantum yield of the host material is low, resulting in the low efficiency of the first blue OLED light emitting unit. After the blue dopant material, the efficiency is significantly improved. Comparing the data of the second blue OLED light-emitting unit and the third blue OLED light-emitting unit, the second blue OLED light-emitting unit has the longest service life, because the disorder degree is almost unchanged after the first blue dopant material is doped, and the hole mobility is close to that of the intrinsic material of the main material, so that electrons in the light-emitting layer are more balanced, and the electron blocking layer material with the highest occupied orbit energy level is matched, so that the light-emitting unit is not in failure. The third blue OLED light emitting cell has a very low lifetime due to the doped second blue dopant, which results in reduced hole mobility due to increased disorder after doping. The electron mobility is unchanged, so that the electron-hole transport ratio in the light-emitting layer is increased, and the exciton recombination zone is biased to the side of the electron blocking layer. If the electron blocking layer with the shallow highest occupied orbit energy level is matched at this time, holes and excitons are concentrated at 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 selected 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 ev, the highest occupied orbital level of the third blue dopant is-5.37 ev, and the highest occupied orbital level difference between the blue host material and the blue dopant is 0.56 ev. The highest occupied orbital energy level difference of the fourth blue dopant is-5.78 ev, and the highest occupied orbital energy level difference of the blue host material and the blue dopant is 0.15 ev.
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 includes: cleaning and drying the conductive glass substrate; and forming a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer comprising a blue light main body material and a cathode by vapor deposition 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 electron blocking layer has a highest occupied orbital energy level of-5.45 ev and a triplet energy level of 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 that a blue host material and a third blue dopant are vapor-deposited 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 light host material to the third blue light dopant is 97:3.
another embodiment of the present application is a light emitting unit of a comparative example, which is different from the second single hole carrier light emitting unit in that a light emitting layer is obtained by vapor-depositing a blue host material and a fourth blue dopant on a side of a hole transporting layer remote from a hole injecting layer. The mass ratio of the blue light host material to the fourth blue light dopant is 97:3.
and respectively performing IV tests on the three single hole carrier light-emitting units at the temperature of 25 ℃,35 ℃,55 ℃ and 85 ℃ to obtain IV characteristics of the three single hole carrier light-emitting units at different temperatures, and performing space charge limiting current method calculation on current density and voltage curves to obtain mobility of the three single hole carrier light-emitting units at different temperatures.
As shown in fig. 7, the relationship between the mobility and the temperature in the 0 electric field is obtained by using a calculation formula of the gaussian disorder model, and the relationship between the mobility and the temperature is plotted logarithmically. In the figure, L7 represents a plot of the logarithm of the mobility of the second single hole carrier light-emitting unit versus the inverse square of the temperature, L8 represents a plot of the logarithm of the mobility of the light-emitting unit versus the inverse square of the temperature, L9 represents a plot of the logarithm of the mobility of the light-emitting unit versus the inverse square of the temperature as a comparative example, μ represents the mobility, ln represents taking the logarithm (i.e., taking the natural logarithm) as the base, e=0 represents the electric field as 0, the ordinate represents the logarithm of the mobility under 0 electric field, and the abscissa represents the inverse square of the temperature. The slope of the curve is a numerical value related to the disorder degree, and the disorder degree is obtained according to the slope of the fitted curve, and the larger the slope is, the larger the disorder degree is. As can be seen from the figure, the approximation of L7 to L8 indicates that the second single hole carrier light emitting unit is approximated to the light emitting unit of the other embodiment of the present application as a comparative example, and the approximation of L9 is larger than the approximation of L7 and the approximation of L8 indicates that the disorder of the light emitting unit of the other embodiment of the present application is higher than the approximation of the disorder of the second single hole carrier light emitting unit and the approximation of the other embodiment of the present application as a comparative example.
The second single hole carrier light emitting cell, the device of another embodiment of the present application, and the light emitting cell of another embodiment of the present application are graphs of current density versus voltage as a comparative example, as shown in fig. 8, in which L10 represents a current density versus voltage curve of the second single hole carrier light emitting cell, L11 represents a current density versus voltage curve of the light emitting cell of another embodiment of the present application, and L12 represents a current density versus voltage curve of the light emitting cell of another embodiment of the present application as a comparative example. As can be seen from the figure, the mobility of the second single hole carrier light emitting unit and the light emitting unit according to the other embodiment of the present application as a comparative example is close, and the mobility of the light emitting unit according to the other embodiment of the present application is lower than that of the light emitting unit second single hole carrier light emitting unit and the light emitting unit according to the other embodiment of the present application as a comparative example.
In a fourth specific embodiment, the blue host material and blue dopant of the third specific embodiment are used.
Preparing three blue OLED light emitting units, and preparing a fourth blue OLED light emitting unit comprises the following steps: cleaning and drying the conductive glass substrate; 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 are sequentially evaporated on one side of the conductive glass substrate. In this embodiment, the electron blocking layer has a highest occupied orbital level of-5.45 ev.
The fifth blue OLED light-emitting unit is different from the fourth blue OLED light-emitting unit in the preparation process: after vapor deposition of the electron blocking layer material, the host material and the third blue dopant are co-evaporated. The mass ratio of the blue light host material to the third blue light dopant is 97:3.
the sixth blue OLED light emitting unit is different from the fourth blue OLED light emitting unit in the process of manufacturing: after vapor deposition of the electron blocking layer material, the host material and the fourth blue dopant are co-evaporated. The mass ratio of the blue light host material to the fourth blue light dopant is 97:3.
the three light emitting units were subjected to IVL testing for percentage data of voltage, efficiency and lifetime at a current density of 15 milliamp/cm.
Table 2 percentage of voltage, efficiency and lifetime obtained at a current density of 15 milliamp/square cm
As can be seen from table 2, the efficiency of the fourth blue OLED light emitting unit is the lowest, and the life of the fifth blue OLED light emitting unit is the best, because the hole mobility is reduced after doping the third blue dopant material, but the hole injection from the electron blocking layer to the host material is smooth due to the deep electron blocking layer material. Meanwhile, the matched electron blocking layer material uses a higher triplet state energy level, so that excitons can be limited in the light emitting layer, and the efficiency is improved. The carbazole structure is beneficial to improving the electronic stability of the electronic barrier layer material, so that the service life of the light-emitting unit is prolonged. However, in the sixth blue OLED light emitting unit, hole mobility of the light emitting layer is not reduced, and meanwhile, an electron blocking layer material having a deep highest occupied orbit energy level is used, so that holes injected into the light emitting layer are smooth, holes in the light emitting layer are excessive, and efficiency is reduced. The sixth blue OLED light emitting unit has a longer lifetime but lower efficiency.
In some embodiments, the method of testing for disorder includes, but is not limited to, temperature swing mobility testing.
The disorder degree change of the host material and the doping material system in the embodiment is an increased value relative to the disorder degree of the pure host material.
Based on the same inventive concept, 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 possible embodiment, the display panel comprises a blue light generating unit.
Based on the same inventive concept, an embodiment of the present application provides a display device including the light emitting unit provided in the second aspect of the embodiment 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 embodiment of the present application provides a method for manufacturing a light emitting unit, as shown in fig. 9, mainly including steps S1 and S2:
step S1: an electron blocking layer having a highest occupied orbital energy level within a first design energy level range is prepared.
Step S2: and preparing a host material and a doping material with the absolute value difference of the highest occupied orbit energy level not larger than a first design value at one side of the electron blocking layer at the same time to obtain the light emitting layer.
Based on the same inventive concept, the embodiment of the present application provides a method for manufacturing a light emitting unit, as shown in fig. 10, mainly including steps S3 and S4:
step S3: preparing an electron blocking layer having a highest occupied orbit energy level within the second design energy level range and not less than a third design value and including a carbazole structure;
step S4: and preparing a host material and a doping material of which the absolute value difference of the highest occupied orbit energy level is not smaller than a first design value and not larger than a second design value at one side of the electron blocking layer at the same time 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 values of the main body material and the doping material of the light-emitting layer at the highest occupied orbit energy level, the main body material and the doping material are matched with the resistance barrier layers with different highest occupied orbit energy levels or highest occupied orbit energy levels, triplet state energy levels and material structures, so that the disorder degree of an electron barrier layer material system is in a design range, the hole mobility and the electron mobility of the light-emitting layer are maintained at relatively similar levels, electrons in an exciton recombination area are uniformly distributed in the light-emitting layer, the transmissibility 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.
Those of skill in the art will appreciate that the various operations, methods, steps in the flow, acts, schemes, and alternatives discussed in the present application may be alternated, altered, combined, or eliminated. Further, other steps, means, or steps in a process having various operations, methods, or procedures discussed herein may be alternated, altered, rearranged, disassembled, combined, or eliminated. Further, steps, measures, schemes in the prior art with various operations, methods, flows disclosed in the present application may also be alternated, altered, rearranged, decomposed, combined, or deleted.
In the description of the present application, it should 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 the orientation or positional relationships shown in the drawings, merely to facilitate describing the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
The terms "first," "second," and the like, 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 defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art.
In the description of the present specification, a particular feature, structure, material, or characteristic may be combined in any suitable manner in 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, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited in order and may be performed in other orders, unless explicitly stated herein. Moreover, at least some of the steps in the flowcharts of the figures may include a plurality of sub-steps or stages that are not necessarily performed at the same time, but may be performed at different times, the order of their execution not necessarily being sequential, but may be performed in turn or alternately with other steps or at least a portion of the other steps or stages.
The foregoing is only a partial embodiment of the present application, and it should be noted that it will be apparent to those skilled in the art that modifications and adaptations can be made without departing from the principles of the present application, and such modifications and adaptations are intended to be comprehended within the scope of the present application.
Claims (7)
1. A light emitting unit, comprising: an electron blocking layer and a light emitting layer laminated in this order;
the light-emitting layer comprises a host material and a doping material;
the difference between the absolute value of the highest occupied orbit energy level of the host material and the absolute value of the highest occupied orbit energy level of the doping material is not greater than a first design value, the highest occupied orbit energy level of the electron blocking layer is in a first design energy level range, and the increased disorder of the light emitting layer after doping of the doping material is in a design range;
the light emitting unit includes at least one of:
the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 ev;
the first design energy level range is not less than-5.5 electron volts and not greater than-5.2 electron volts;
alternatively, 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 dopant 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 energy range, the triplet energy level of the electron blocking layer is not less than a third design value, and the material of the electron blocking layer includes a carbazole structure;
the light emitting unit includes at least one of:
the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 ev;
the second design value is 0.8 ev;
the third design value is 2.5 ev;
the second design energy level range is not less than-5.3 ev and not more than-5.7 ev;
the triplet energy level of the electron blocking layer is no greater than 2.9 electron volts.
2. A light emitting unit as claimed in claim 1, wherein,
the mass ratio of the main material to the doping material is 9:1 to 119:1.
3. the light-emitting unit according to claim 1, wherein the carbazole structure has a general structural formula as follows:
wherein R1, R2, R3, ar1 and Ar2 each comprise one of hydrogen, an alkyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms and a heteroaryl group having 5 to 30 carbon atoms.
4. A display panel, comprising: a light emitting unit according to any one of claims 1-3.
5. A display device, comprising: the display panel of claim 4.
6. A method of manufacturing a light emitting unit, comprising:
preparing an electron blocking layer with the highest occupied orbit energy level within a first design energy level range;
preparing a main material and a doping material at the same time on one side of the electron blocking layer, wherein the difference value between the absolute value of the highest occupied orbit energy level of the main material and the absolute value of the highest occupied orbit energy level of the doping material is not more than a first design value, so as to obtain a light-emitting layer;
the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 ev;
the first design energy level range is not less than-5.5 electron volts and not greater than-5.2 electron volts.
7. A method of manufacturing a light emitting unit, comprising:
preparing an electron blocking layer having a highest occupied orbit energy level within the second design energy level range, a triplet energy level not less than a third design value, and a carbazole structure;
preparing a main material and a doping material at the same time on one side of the electron blocking layer, wherein the difference value between the absolute value of the highest occupied orbit energy level of the main material and the absolute value of the highest occupied orbit energy level of the doping material is not smaller than a first design value and not larger than a second design value, so as to obtain a light-emitting layer;
the highest occupied orbital energy 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 energy level of the doped material is not less than-5.8 electron volts and not more than-5.2 electron volts;
the first design value is 0.3 ev;
the second design value is 0.8 ev;
the third design value is 2.5 ev;
the second design energy level range is not less than-5.3 ev and not more than-5.7 ev;
the triplet energy level of the electron blocking layer is no greater than 2.9 electron volts.
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