Patent Publication Number: US-2022238834-A1

Title: Light-emitting component and method for manufacturing the same, display substrate and display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202110090322.X, filed in China on Jan. 22, 2021, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present application relates to the fields of display technology, and in particular to a light-emitting component and a method for manufacturing the same, a display substrate and a display device. 
     BACKGROUND 
     Organic light-emitting Diodes (OLEDs) are widely considered to be the most promising next-generation display and illumination technology due to their unique advantages of low driving voltage, fast response, wide color gamut and self-luminescence. Depending on the luminescent material, fluorescent OLEDs and phosphorescent OLEDs can be classified. Phosphorescent materials have a wide range of applications due to their ability to realize singlet and triplet excitons to participate in light emission, which can theoretically achieve 100% internal quantum efficiency. 
     However, most high efficiency phosphorescent devices face a common problem: the external quantum efficiency decreases sharply with increasing brightness, i.e. the efficiency rolls off. Phosphorescent device efficiency roll-off is primarily due to exciton Annihilation, including Triplet-Triplet Annihilation (TTA), and Exciton-Polaron quenching (TPA). 
     Therefore, in order to further advance the commercial implementation of OLEDs, there is a need to invent efficient, universally applicable new components to suppress the efficiency roll-off of phosphorescent OLED devices. 
     SUMMARY 
     In view of the shortcomings of the prior art, the present application proposes a light-emitting component and a method for manufacturing the same, a display substrate and a display device, so as to solve the technical problem of efficiency roll-off existing in the prior phosphorescent light-emitting device at a high current density. 
     According to one embodiment of the present application, there is provided a light-emitting component including: an anode layer stacked on one side of a base, a first functional layer group including a plurality of functional layers, an organic light-emitting layer, a second functional layer group including a plurality of functional layers, and a cathode layer ; 
     the first functional layer group comprises a hole injection retarding layer close to the organic light-emitting layer, and the hole injection retarding layer is used for reducing a hole transport rate; and/or, 
     the second functional layer group comprises an electron injection retarding layer close to the organic light-emitting layer, and the electron injection retarding layer is used for reducing an electron transport rate. 
     In one example, in a direction away from the anode layer, the first functional layer group comprises a hole transport layer and the hole injection retarding layer which are sequentially stacked; or 
     the first functional layer group comprises a hole transport layer, wherein doping particles for reducing the hole transport rate are distributed in the hole transport layer, and the hole transport layer is reused as the hole injection retarding layer. 
     In one example, a HOMO level of the hole injection retarding layer is a first ionization energy, and a HOMO level of the hole transport layer is a second ionization energy; and an absolute value of the first ionization energy is greater than an absolute value of the second ionization energy. 
     In one example, a difference between the absolute value of the first ionization energy and the absolute value of the second ionization energy is 0.19 eV to 0.29 eV. 
     In one example, the material of the dopant particles comprises a planar aromatic compound having a conjugated structure. 
     In one example, the first functional layer group further comprises: an electron blocking layer located between the hole transport layer and the hole injection retarding layer for blocking electrons from entering the hole transport layer; and 
     a HOMO energy level of the electron blocking layer is a third ionization energy, and the absolute value of the first ionization energy is greater than an absolute value of the third ionization energy. 
     In one example, a difference between the absolute value of the first ionization energy and the absolute value of the third ionization energy is 0.07 eV to 0.2 eV. 
     In one example, a ratio of a hole mobility of the electron blocking layer to a hole mobility of the hole injection retarding layer ranges from 10 to 100. 
     In one example, the hole injection retarding layer comprises a plurality of hole retarding sub-film layers which are stacked, and absolute values of HOMO levels corresponding to respective hole retarding sub-film layers in the hole injection retarding layer sequentially increase in a direction from the anode layer to the cathode layer. 
     In one example, the material of the hole injection retarding layer comprises a planar aromatic compound having a conjugated structure. 
     In one example, the material of the dopant particles comprises a planar aromatic compound having a conjugated structure. 
     In one example, in a direction away from the cathode layer, the second functional layer group comprises an electron transport layer and the electron injection retarding layer which are sequentially stacked; or 
     the second functional layer group comprises an electron transport layer, wherein doping particles for reducing the electron transport rate are distributed in the electron transport layer, and the electron transport layer is reused as the electron injection retarding layer. 
     In one example, a LUMO level of the electron injection retarding layer is a fourth ionization energy, and a LUMO level of the electron transport layer is a fifth ionization energy; and an absolute value of the fourth ionization energy is greater than an absolute value of the fifth ionization energy. 
     In one example, a difference between the absolute value of the fourth ionization energy and the absolute value of the fifth ionization energy is 0.19 eV to 0.29 eV. 
     In one example, the second functional layer group further comprises: a hole blocking layer located between the electron transport layer and the electron injection retarding layer for blocking electrons from entering the electron transport layer; and 
     a LUMO level of the hole blocking layer is a sixth ionization energy, and the absolute value of the fourth ionization energy is greater than an absolute value of the sixth ionization energy. 
     In one example, a difference between the absolute value of the fourth ionization energy and the absolute value of the sixth ionization energy is 0.07 eV to 0.2 eV. 
     In one example, a ratio of an electron mobility of the hole blocking layer to an electron mobility of the electron injection retarding layer ranges from 10 to 100. 
     In one example, the electron injection retarding layer comprises a plurality of electron retarding sub-film layers which are stacked, and absolute values of LUMO levels corresponding to respective electron retarding sub-film layers in the electron injection retarding layer sequentially increase in a direction from the cathode layer to the anode layer. 
     In one example, the material of the electron injection retarding layer comprises triazines or pyridine. 
     In one example, the first functional layer group further comprises a hole injection layer between the anode layer and the hole transport layer; the second functional layer group further comprises an electron injection layer located between the cathode layer and the electron transport layer; and/or the material of the organic light-emitting layer is a phosphorescent material. 
     According to one embodiment of the present application, there is provided a display substrate, including: a base, a switching device layer, and the above-mentioned light-emitting component; the switching device layer is provided for driving the light-emitting component to emit light. 
     According to one embodiment of the present application, there is provided a display device including the above-mentioned display substrate. 
     According to one embodiment of the present application, there is provided a method for making a light-emitting component, including the following steps: 
     forming an anode layer on one side of a substrate, the substrate including a base and a switching device layer on the base, the anode layer being formed on one side of the switching device layer facing away from the base; 
     forming a first functional layer group on one side of the anode layer facing away from the substrate; 
     sequentially forming an organic light-emitting layer, a second functional layer group and a cathode layer on one side of the first functional layer facing away from the substrate; 
     wherein the first functional layer group comprises a hole injection retarding layer for reducing a hole transport rate; and/or the second functional layer group comprises an electron injection retarding layer for reducing an electron transport rate. 
     The advantageous technical effects brought by the technical solutions provided in the embodiments of the present application at least include: 
     The light-emitting component or the manufacturing method provided in the embodiments of the present application can reduce the hole transport rate by providing a hole injection retarding layer, thereby being able to retard the injection of holes into the organic light-emitting layer at a high voltage (corresponding to a high current density), thereby reducing the exciton concentration between the hole transport layer and the organic light-emitting layer, and reducing exciton quenching, and/or can reduce the electron transport rate by providing a electron injection retarding layer, thereby being able to retard the injection of electrons into the organic light-emitting layer at a high voltage (corresponding to a high current density), thereby reducing the exciton concentration between the electron transport layer and the organic light-emitting layer, by reducing exciton quenching, the light emission efficiency of the device is improved, and the phenomenon of efficiency roll-off at high brightness is avoided, thereby improving the uneven display effect. 
     The light-emitting component or manufacturing method provided in the embodiments of the present application can further retard the injection of holes into the light-emitting layer at a high voltage (corresponding to a high current density) by providing a doped particle for reducing the hole transport rate in the hole transport layer, thereby reducing the exciton concentration at the interface of the hole transport layer and the organic light-emitting layer, reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off of the device at a high brightness, thereby improving the problem of uneven display effect. And/or by providing doping particles for reducing the electron transport rate in the electron transport layer, the injection of electrons into the organic light-emitting layer at a high voltage (corresponding to a high current density) can be retarded, thereby reducing the exciton concentration at the interface between the electron transport layer and the organic light-emitting layer, reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off of the device at a high brightness, thereby the problem of uneven display effects can be overcome. 
     Additional aspects and advantages of the invention 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 invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and/or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic structural diagram of a light-emitting component provided in the related art; 
         FIG. 2  is a schematic structural diagram of a light-emitting component provided in an embodiment of the present application; 
         FIG. 3  is a schematic structural diagram of another light-emitting component provided in an embodiment of the present application; 
         FIG. 4  is a schematic structural diagram of another light-emitting component provided in an embodiment of the present application; 
         FIG. 5  is a schematic diagram showing carrier transition of a light-emitting component according to an embodiment of the present application; 
         FIG. 6  is a schematic structural diagram of another light-emitting component provided in an embodiment of the present application; 
         FIG. 7  is a schematic structural diagram of yet another light-emitting component provided in an embodiment of the present application; 
         FIG. 8  is a schematic structural diagram of still another light-emitting component provided in an embodiment of the present application; 
         FIG. 9  is a schematic structural diagram of another light-emitting component provided in an embodiment of the present application; 
         FIG. 10  is a schematic structural diagram of another light-emitting component provided in an embodiment of the present application; 
         FIG. 11  is a graph showing comparison between current density-voltage relationships of a light-emitting component according to an embodiment of the present application with that a light-emitting component of the related art; 
         FIG. 12  is a graph showing comparison between luminance-luminous efficiency relationships of a light-emitting component according to an embodiment of the present application and a light-emitting component of the related art; 
         FIG. 13  is a graph showing comparison between impedance spectrums of a light-emitting component according to an embodiment of the present application and a light-emitting component of the related art; and 
         FIG. 14  is a flow chart showing a method for making a display substrate according to an embodiment of the present application. 
     
    
    
     In the figures: 
       100 -anode layer; 
       200 -first functional layer; 
       210 -hole injection layer; 
       220 -hole transport layer; 
       230 -hole injection retarding layer;  231 -hole retarding sub-film layer; 
       240 -electron blocking layer; 
       300 -organic light-emitting layer; 
       400 -second functional layer; 
       410 -electron transport layer; 
       420 -electron injection layer; 
       430 -hole blocking layer; 
       440 -electron injection retarding layer,  441 -electron retarding sub-film layer; 
       500 -cathode layer. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present application, examples of embodiments of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. Further, if a detailed description of known technology is not necessary to illustrate the features of the present application, it is omitted. The embodiments described below by referring to the figures are exemplary only and should not be construed as limiting the present application. 
     It will be understood by those skilled in 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 expressly stated 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. As used herein, the term “and/or” includes all or any unit and all combinations of one or more of the associated listed items. 
     The light emission principle of OLEDs is based on the injection of electrons from the cathode into the lowest unoccupied molecular orbital (LUMO) of the organic species and the injection of holes from the anode into the highest occupied molecular orbital (HOMO) of the organic species under the influence of an applied electric field. Electrons and holes meet and recombine in the organic light-emitting layer to form excitons. The excitons release energy in two ways: one is radiative transition, i.e., luminescence; two are non-radiative transitions, i.e., exotherms. 
     In the structure shown in  FIG. 1 , in most cases, the injection and transport of electrons and holes are unbalanced, and when too many electrons or holes pass through the organic light-emitting layer  300  to reach the hole transport layer  220  or the electron transport layer  410 , they combine with holes or electrons to form excitons. The inventors of the present application have found that the light-emitting component shown in  FIG. 1  (a phosphorescent device structure) has a serious efficiency roll-off at a high current density, because the exciton emission center of the light-emitting component is at the interface of the hole transport layer  220  (shown as an HTL in the figure) and the organic light-emitting layer  300  (shown as an EML in the figure). Alternatively, the exciton emission center of the light-emitting component is at the interface of the electron transport layer  410  (shown schematically as an ETL) and the organic light emitting layer  300  (shown schematically as an EML). 
     When the exciton emission center of the light-emitting component is at the interface between the hole transport layer  220  and the organic light-emitting layer  300 , at a low current density, when holes and electrons are injected into the organic light-emitting layer  300 , a small amount of excitons are generated at the interface between the hole transport layer  220  and the organic light-emitting layer  300 , so that the excitons can both radiatively transition and emit light with high efficiency. However, when the current density increases, holes and electrons are largely injected into the interior of the organic light-emitting layer  300 , and at this time, the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300  sharply increases, a reaction occurs between a plurality of excitons, and between holes and excitons, resulting in exciton quenching, and non-radiative transitions of excitons increase due to triplet-triplet quenching and exciton-polaron (hole) quenching effects, resulting in a decrease in efficiency of the phosphorescent device, thereby causing a problem of uneven display. 
     When the exciton emission center of the light-emitting component is at the interface between the electron transport layer  410  and the organic light-emitting layer  300 , at a low current density, when holes and electrons are injected into the organic light-emitting layer  300 , a small amount of excitons are generated at the interface between the electron transport layer  410  and the organic light-emitting layer  300 , so that the excitons can both radiatively transition and emit light with high efficiency. However, when the current density increases, holes and electrons are largely injected into the interior of the organic light-emitting layer  300 , the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300  sharply increases, a reaction occurs between a plurality of excitons, and between electrons and excitons, resulting in exciton quenching, non-radiative transitions of excitons increase due to triplet-triplet quenching and exciton-polaron (hole) quenching effects, resulting in a decrease in efficiency of the phosphorescent device, and thus a problem of uneven display occurs. 
     The embodiments of the present application provide a light-emitting component and a manufacturing method thereof, a display substrate and a display device, aiming to solve the above-mentioned technical problem. 
     The technical solutions of the present application and how the technical solutions of the present application solve the above-mentioned technical problems are described in detail in the following specific embodiments. 
     With reference to  FIGS. 2-4 , in view of the above-mentioned technical problem, embodiments of the present application provide a light-emitting component, including: an anode layer  100 , a first functional layer group  200  including a plurality of functional layers, an organic light-emitting layer  300 , a second functional layer group  400  including a plurality of functional layers and a cathode layer  500  which are arranged on one side of a substrate in a laminated manner; 
     the first functional layer group  200  comprises a hole injection retarding layer  230  close to the organic light-emitting layer  300 , and the hole injection retarding layer  230  is used for reducing the hole transport rate; and/or, 
     the second functional layer group  400  includes an electron injection retarding layer  440  disposed close to the organic light emitting layer  300 , and the electron injection retarding layer  440  serves to reduce a transfer rate of electrons. 
     Referring to  FIG. 2 , when the exciton emission center of the light-emitting component is at the interface of the hole transport layer  220  and the organic light emitting layer  300 , in some embodiments of this embodiment, the first functional layer group  200  includes a hole injection retarding layer  230  disposed adjacent to the organic light emitting layer  300 , the hole injection retarding layer  230  serving to reduce the transport rate of holes. 
     By providing the hole injection retarding layer  230  between the hole transport layer  220  and the organic light-emitting layer  300 , the hole transport rate can be reduced, and then the injection of holes into the organic light-emitting layer  300  can be retarded under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface between the hole transport layer  220  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off at a high brightness of the device, and thus improving the problem of uneven display effect. 
     Referring to  FIG. 3 , when the exciton emission center of the light-emitting component is at the interface of the electron transport layer  410  and the organic light emitting layer  300 , in some embodiments of this embodiment, the second functional layer group  400  includes a electron injection retarding layer  440  disposed adjacent to the organic light emitting layer  300 , the electron injection retarding layer  440  serving to reduce the transfer rate of electrons. 
     By providing the electron injection retarding layer  440  between the electron transport layer  410  and the organic light-emitting layer  300 , the electron transport rate can be reduced, and then electron injection into the organic light-emitting layer  300  can be retarded at a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off at a high brightness of the device, and thus improving the problem of uneven display effect. 
     Referring to  FIG. 4 , when the exciton emission center of the light-emitting component is at the interface of the hole transport layer  220  and the organic light-emitting layer  300 , or when the exciton emission center of the light-emitting component is at the interface of the electron transport layer  410  and the organic light-emitting layer  300 , in some embodiments of this embodiment, the first functional layer group  200  includes a hole injection retarding layer  230  disposed near the organic light-emitting layer  300 , the hole injection retarding layer  230  is used to reduce the transport rate of holes. And the second functional layer group  400  comprises a electron injection retarding layer  440  close to the organic light-emitting layer  300 , and the electron injection retarding layer  440  is used for reducing the electron transport rate. 
     Retarding the arrangement of the hole injection layer  230  can reduce the hole transport rate, and thus can retard the injection of holes into the organic light-emitting layer  300  under a high voltage (corresponding to a high current density); retarding the arrangement of the electron injection layer  440  can reduce the electron transport rate, and thus can retard the injection of electrons into the organic light-emitting layer  300  under a high voltage (corresponding to a high current density), thereby more effectively reducing the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300 , or more effectively reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300 ; by reducing exciton quenching, the light emission efficiency of the device is improved, and the phenomenon of efficiency roll-off at high brightness is avoided, thereby improving the uneven display effect. 
     As an alternative embodiment, the first functional layer group  200  includes a hole injection layer  210  (illustrated as an HIL in the figure), a hole transport layer  220  (illustrated as an HTL in the figure), and a hole injection retarding layer  230  for reducing the hole transport rate, which are sequentially stacked on the anode layer  100  (Anode). 
     In other embodiments, the first functional layer group  200  may include a hole injection layer  210  (shown schematically as an HIL) and a hole transport layer  220  (shown schematically as an HTL) sequentially stacked on the anode layer  100  (Anode). Wherein dopant particles for reducing the hole transport rate are distributed in the hole transport layer  220  to be reused as the hole injection retarding layer. 
     Optionally, the material of the anode layer  100  is indium tin oxide (ITO) to enhance electrical conductivity. 
     In this embodiment, by providing a hole injection retarding layer  230  between the hole transport layer  220  and the organic light-emitting layer  300  or mixing a dopant particle into the hole transport layer  220 , the hole transport rate can be reduced, and then the injection of holes into the light-emitting layer can be retarded under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface between the hole transport layer  220  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off at a high brightness of the device, and thus improving the problem of uneven display effect. 
     In some embodiments, with continued reference to  FIG. 2 , the second functional layer group  400  includes an electron transport layer  410  (shown schematically as an ETL) and an electron injection layer  420  (shown schematically as an EIL) sequentially stacked on the organic light emitting layer  300 . 
     In some embodiments, the material of the organic light emitting layer  300  is a phosphorescent material. 
       FIG. 5  schematically shows a hole and electron transition diagram of a light-emitting component in an example of the present application. For convenience of description, the HOMO (highest occupied orbital) energy level of the hole injection retarding layer  230  is set as a first ionization energy, and the HOMO energy level of the hole transport layer  220  is set as a second ionization energy. Considering that the HOMO level is a negative value, in order to reduce the transport rate of holes at a high current density, the absolute value of the first ionization energy is greater than the absolute value of the second ionization energy, i.e., the HOMO level of the hole injection retarding layer  230  is deeper than the HOMO level of the hole transport layer  220 . 
     Alternatively, the difference between the absolute value of the first ionization energy and the absolute value of the second ionization energy is 0.19 eV to 0.29 eV (inclusive), making transition of holes from the hole transport layer  220  to the hole injection retarding layer  230  more difficult, thereby reducing the transport rate of holes at high current densities, further reducing the exciton concentration at the interface of the hole transport layer  220  and the organic light emitting layer  300 , improving the efficiency roll-off problem at high current densities. 
     In addition, the hole injection retarding layer  230  also has a shallow LUMO (lowest unoccupied molecular orbital) energy level, which can block the diffusion of electrons in the organic light emitting layer  300  to the hole transport layer  220 . 
     In this embodiment, by defining the HOMO level parameter between the hole injection layer  230  and the hole transport layer  220 , it is advantageous to reduce the hole transport rate, thereby reducing the efficiency roll-off and improving the display uniformity. 
     In some embodiments, the material of the retardation hole injection layer  230  may be a planar aromatic compound having a conjugated structure in consideration of the setting requirement of the HOMO level of the retardation hole injection layer  230 . 
     Alternatively, the planar aromatic compound having a conjugated structure may be one or a mixture of both of a polyaryl-substituted triphenylamine derivative or a carbazole derivative. 
     In this embodiment, a planar aromatic compound having a conjugated structure is used as the material of the hole injection retarding layer  230 , so that the HOMO level requirement of the hole injection retarding layer  230  can be satisfied, thereby achieving the purpose of reducing the hole transport rate at a high current density. 
     In some embodiments, as shown in  FIG. 6 , an electron blocking layer  240  (shown schematically as Prime) is further provided between the hole transport layer  220  and the hole injection retarding layer  230  in the first functional layer  200 . The electron blocking layer  240  can further inhibit electrons from entering the hole transport layer  220 , thereby improving the light emitting efficiency of the device. 
     Specifically, the HOMO level of the electron blocking layer  240  is set to a third ionization energy, and the absolute value of the first ionization energy is greater than the absolute value of the third ionization energy. 
     Alternatively, the difference between the absolute value of the first ionization energy and the absolute value of the third ionization energy is 0.07ev-0.2ev, namely, the absolute value of the second ionization energy, the absolute value of the third ionization energy and the absolute value of the first ionization energy successively increase along the direction from the anode layer  100  to the cathode layer  500 , facilitating the migration of holes, while reasonably controlling the hole transport rate at a high current density. 
     In this embodiment, providing an electron blocking layer  240  between the hole transport layer  220  and the hole injection retarding layer  230  can further inhibit electrons from entering the hole transport layer  220 , so that the electrons remain in the organic light-emitting layer  300  as much as possible, thereby improving the light-emitting efficiency of the device; the definition of the HOMO energy level parameter of the electron blocking layer  240  is beneficial to the enhancement of the electron blocking effect, and the reasonable control of the hole transition rate can further enhance the light emitting efficiency of the device. 
     In some embodiments, in order to control the migration rate of holes to the organic light-emitting layer  300 , the mobility of holes in the electron-blocking layer  240  is greater than the mobility of holes in the hole-retarding injection layer  230 , i.e., the mobility of holes decreases the closer to the organic light-emitting layer  300 . 
     Alternatively, the ratio of the hole mobility of the electron blocking layer  240  to the hole mobility of the hole injection retarding layer  230  ranges from 10 to 100, inclusive. 
     Alternatively, the ratio of the hole mobility of the electron blocking layer  240  to the hole mobility of the hole injection retarding layer  230  is 50. 
     In some embodiments, as shown in  FIG. 7 , the retarding hole injection layer  230  comprises a plurality of retarding hole sub-film layers  231  which are stacked. Wherein the absolute value of the HOMO energy levels corresponding to each of the hole retarding sub-film layers  231  in the hole injection retarding layer  230  increases successively in the direction from the anode layer  100  to the cathode layer  500 . 
     It should be noted that the material for forming each of the hole-retarding sub-film layers  231  may be the same, and this may be achieved by setting different thicknesses, adjusting the concentration and ratio of the material for forming the hole-retarding injection layer  230 , etc. In addition, the material of each of the retardation hole sub-film layers  231  may be different as long as the HOMO level of each retardation hole sub-film layer can satisfy the corresponding change trend. 
     In some embodiments, the doping concentration of the dopant particles in the hole transport layer  220  may be set according to the HOMO level requirements of the hole transport layer  220  to be prepared, and the doping concentration of the dopant particles is not particularly limited in this embodiment. The material of the doped particles may likewise comprise a planar aromatic compound having a conjugated structure. 
     Alternatively, the planar aromatic compound having a conjugated structure may be one or a mixture of both of a polyaryl-substituted triphenylamine derivative or a carbazole derivative. 
     In this embodiment, a planar aromatic compound having a conjugated structure is used as the material of the dopant particles distributed in the hole transport layer  220 , so that the HOMO level requirement of the hole transport layer can be satisfied, thereby achieving the purpose of reducing the hole transport rate at a high current density. 
     In some embodiments, as shown in  FIG. 8 , a hole blocking layer  430  (illustrated as HBL) is provided between the electron transport layer  410  and the organic light emitting layer  300 , and the hole blocking layer  430  serves to block holes from entering the electron transport layer  410  so that holes remain in the organic light emitting layer  300  as much as possible, further improving the light emitting efficiency of the device. 
     Referring to  FIG. 3 , as an alternative embodiment, the second functional layer group  400  includes an electron injection layer  420  (illustrated as an EIL), an electron transport layer  410  (illustrated as an ETL), and a electron injection retarding layer  440  sequentially stacked on the cathode layer  500  (Cathode), the electron injection retarding layer  230  serving to reduce the electron transfer rate. 
     In other embodiments, the second functional layer group  400  may include an electron injection layer  420 , a hole transport layer  410 , sequentially stacked on the cathode layer  500 . Wherein doped particles for reducing the electron transport rate are distributed in the electron transport layer  410  so as to be reused as the electron injection retarding layer, namely, the electron transport layer  410  and the electron injection retarding layer  440  are provided integrally. 
     In this embodiment, by providing a electron injection retarding layer  440  between the electron transport layer  410  and the organic light-emitting layer  300  or mixing a dopant particle into the electron transport layer  410 , the electron transport rate can be reduced, and then electron injection into the light-emitting layer can be retarded at a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface between the electron transport layer  410  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off at a high brightness of the device, and thus improving the problem of uneven display effect. 
     In some embodiments, with continued reference to  FIG. 3 , the first functional layer group  200  includes a hole transport layer  220  (shown schematically as an HTL) and a hole injection layer  210  (shown schematically as an HIL) sequentially stacked on the organic light emitting layer  300 . 
     In some embodiments, the material of the organic light emitting layer  300  is a phosphorescent material. 
       FIG. 5  schematically shows a hole and electron transition diagram of a light-emitting component in an example of the present application. For convenience of description, the LUMO (lowest unoccupied molecular orbital) energy level of the electron injection retarding layer  440  is set to the fourth ionization energy, and the LUMO energy level of the electron transport layer  410  is set to the fifth ionization energy. Considering that the LUMO level is a negative value, in order to reduce the electron transport rate at a high current density, the absolute value of the fourth ionization energy is greater than the absolute value of the fifth ionization energy, i.e. the LUMO level of the electron injection retarding layer  440  is deeper than the LUMO level of the electron transport layer  410 . 
     Alternatively, the difference between the absolute value of the fourth ionization energy and the absolute value of the fifth ionization energy is 0.19 eV to 0.29 eV (inclusive), making it more difficult for electrons to transition from the electron transport layer  410  to the electron injection retarding layer  440 , thereby reducing the electron transport rate at high current densities, further reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light emitting layer  300 , improving the efficiency roll-off problem at high current densities. 
     In addition, the electron injection retarding layer  440  also has a shallow HOMO (highest occupied orbital) energy level, which can block holes in the organic light emitting layer  300  from diffusing to the electron transport layer  410 . 
     In this embodiment, by defining the LUMO level parameter between the electron injection retarding layer  440  and the electron transport layer  410 , it is advantageous to reduce the electron transport rate, thereby reducing the efficiency roll-off and improving the display uniformity. 
     In some embodiments, the material of the retardation electron injection layer  440  may be triazine or pyridine in consideration of the setting requirement of the LUMO level of the retardation electron injection layer  440 . 
     In this embodiment, the use of triazines or pyridine as the material of the electron injection retarding layer  440  can satisfy the requirement of the LUMO level of the electron injection retarding layer  440 , thereby achieving the purpose of reducing the electron transport rate at a high current density. 
     In some embodiments, as shown in  FIG. 9 , a hole blocking layer  430  (illustrated as HBL) is further provided between the electron transport layer  410  and the electron injection retarding layer  440  in the second functional layer group  400 . The hole blocking layer  430  can further inhibit holes from entering the electron transport layer  410 , thereby improving the light emitting efficiency of the device. 
     Specifically, the LUMO level of the hole blocking layer  430  is set to the sixth ionization energy, and the absolute value of the fourth ionization energy is greater than the absolute value of the sixth ionization energy. 
     Alternatively, the difference between the absolute value of the fourth ionization energy and the absolute value of the sixth ionization energy is 0.07ev-0.2ev, namely, the absolute value of the fifth ionization energy, the absolute value of the sixth ionization energy and the absolute value of the fourth ionization energy successively increase along the direction from the cathode layer  500  to the anode layer  100 , facilitating the migration of electrons, and at the same time, reasonably controlling the electron transport rate at a high current density. 
     In this embodiment, providing a hole blocking layer  430  between the electron transport layer  410  and the electron injection retarding layer  440  can further inhibit holes from entering the electron transport layer  410 , so that holes remain in the organic light-emitting layer  300  as much as possible, thereby improving the light-emitting efficiency of the device; the definition of the LUMO energy level parameter of the hole blocking layer  430  is beneficial to the enhancement of the hole blocking effect, and the reasonable control of the electron transition rate can further enhance the light emitting efficiency of the device. 
     In some embodiments, in order to control the rate of electron migration to the organic light-emitting layer  300 , the electron mobility in the hole-blocking layer  430  is greater than the electron mobility in the electron-injecting layer  440  is retarded, i.e. the closer to the organic light-emitting layer  300 , the electron mobility decreases. 
     Alternatively, the ratio of the electron mobility of the hole blocking layer  430  to the electron mobility of the electron injection retarding layer  440  ranges from 10 to 100, inclusive. 
     Alternatively, the ratio of the electron mobility of the hole blocking layer  430  to the electron mobility of the electron injection retarding layer  440  is 50. 
     In some embodiments, as shown in  FIG. 10 , the electron injection retarding layer  440  comprises a plurality of retarding electron sub-film layers  441  which are stacked. The absolute value of the LUMO energy level corresponding to each of the electron retardation film layers  441  in the electron retardation injection layer  440  increases successively from the cathode layer  500  to the anode layer  100 . 
     It should be noted that each of the retardation electron film layers  441  may be made of the same material, by setting different thicknesses, adjusting the concentration and ratio of the material for making the retardation electron injection layer  440 , etc. In addition, the material of each of the retardation electron film layers  441  may be different as long as the LUMO level of each of the retardation electron film layers can satisfy the corresponding change trend. 
     In some embodiments, the doping concentration of the dopant particles in the electron transport layer  410  may be set according to the LUMO level requirements of the electron transport layer  410  to be prepared, and the doping concentration of the dopant particles is not particularly limited in this embodiment. The material of the doping particles may likewise comprise triazines or pyridine. 
     In this embodiment, triazine or pyridine is used as the material of the dopant particles distributed in the electron transport layer  410 , so that the requirements of the electron transport layer  410  for the LUMO level can be satisfied, thereby reducing the electron transport rate at a high current density. 
     In some embodiments, as shown in  FIG. 8 , an electron blocking layer  240  (shown schematically as Prime) is provided between the hole transport layer  220  and the organic light emitting layer  300 , and the electron blocking layer  240  serves to block electrons from entering the hole transport layer  220  so that electrons remain in the organic light emitting layer  300  as much as possible, further improving the light emitting efficiency of the device. 
     In order to explain the effect of the addition of the hole injection retarding layer  230  and/or the addition of the electron injection retarding layer  440  on the efficiency roll-off in the light-emitting component, the comparative analysis results as described in  FIGS. 11 to 13  are obtained by specifically analyzing the data of the comparative structure (as shown in  FIG. 1 ) and the retarded hole injection structure (as shown in  FIG. 2  or  FIG. 6 ) in the embodiments of the present application. 
     As shown in  FIG. 11  and  FIG. 12 , the solid lines in  FIG. 11  and  FIG. 12  both correspond to the comparative structure shown in  FIG. 1 , and the dotted lines both correspond to the retarded hole injection structure shown in  FIG. 2  or  FIG. 6 . The comparative structure (shown in  FIG. 1 ) is an OLED (organic electroluminescent diode) device with more severe efficiency roll-off, and the hole injection retarding layer  230  is not evaporated, resulting in a device with a faster hole transport rate at a voltage of 2.4 V, thus producing a more significant efficiency roll-off at high gray levels. This is because holes are rapidly injected into the organic light-emitting layer  300  at a high current density, resulting in generation of a large amount of excitons at the interface of the hole transport layer  220  and the organic light-emitting layer  300 , and exciton quenching occurs, so that the exciton transition light-emitting efficiency decreases. The light-emitting component provided in this embodiment can significantly reduce the hole transport rate at high voltage of the device, reduce the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300  by adding the retardation hole injection layer  230 , thereby reducing exciton quenching, improving the light-emitting efficiency and improving the efficiency roll-off phenomenon at high luminance of the device. 
     To further illustrate the effect of retarding hole injection layer  230  to block hole injection, we tested the impedance spectra of the comparative structure and the retarding hole injection structure at a frequency of 1-1000000 Hz, a DC voltage of 2.4 V, and an AC signal voltage of 100 mV. The test results are shown in  FIG. 13 . In  FIG. 13 , graph  1000  corresponds to the comparative structure shown in  FIG. 1 , and graph  2000  corresponds to the retarded hole injection structure shown in  FIG. 2 . The impedance spectrum of the retarded hole injection structure is two semi-circles (refer to graph  2000 ). The light-emitting component in the embodiment of the present application can be equivalent to two RC circuits, and there is an obvious interface between interfaces in the device (the arrangement of the hole injection retarding layer  230  reduces the hole transport rate, so that charges accumulate at the interface of the hole injection retarding layer  230  and the hole transport layer  22 ). The impedance spectrum of the comparative structure is a complete semicircle (reference pattern  1000 ), demonstrating a faster hole transport rate within the device. 
     Based on the same inventive concept, embodiments of the present application also provide a display substrate, including: a base, a switching device layer, and the above-mentioned light-emitting component in the embodiments of the present application, wherein the switching device layer is used for driving the light-emitting component to emit light. 
     A display substrate provided in an embodiment of the present application comprises the light-emitting component in each of the preceding embodiments, wherein the light-emitting component can retard hole injection into the organic light-emitting layer under a high voltage (corresponding to a high current density) by adding a retarding hole injection layer  230 , thereby reducing the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300 ; and/or adding the electron injection retarding layer  440  can retard the injection of electrons into the organic light-emitting layer under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off of the device under a high brightness, thereby improving the problem of uneven display effects. 
     Based on the same inventive concept, embodiments of the present application also provide a display device including the display substrate as described above in the embodiments of the present application. 
     A display device provided in this embodiment comprises the display substrate in the preceding embodiment, wherein a light-emitting component in the display substrate is provided with a hole injection retarding layer  230  between the hole transport layer  220  and the organic light-emitting layer  300 , and hole injection into the organic light-emitting layer can be retarded under a high voltage (corresponding to a high current density) so as to reduce the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300 ; and/or adding a electron injection retarding layer  440 , which can retard the injection of electrons into the organic light-emitting layer under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300 , reducing exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off of the device under a high brightness, and thereby improving the problem of uneven display effect 
     Based on the same inventive concept, the embodiments of the present application also provide a method for making a light-emitting component, as shown in  FIG. 10 , including the following steps S 100 -S 300 : 
     S 100 , an anode layer is formed on one side of a substrate, the substrate including a base and a switching device layer located on the base, the anode layer being formed on the side of the switching device layer facing away from the base. 
     Alternatively, the substrate is typically a glass substrate. The switching device layer comprises a thin film transistor device arranged in an array, and the switching device layer and the anode layer can generally be formed by a combination of overall film-forming and patterning processes. In addition, an anode layer of a material similar to ITO can also be formed by sputtering. 
     S 200 , a first functional layer group is formed on the side of the anode layer facing away from the substrate; the first functional layer group comprises a hole injection layer, a hole transport layer and a hole injection retarding layer which are sequentially stacked on the anode layer, wherein the hole injection retarding layer is used for reducing the hole transport rate; alternatively, the first functional layer group comprises a hole injection layer and a hole transport layer laminated successively on the anode layer, wherein the hole transport layer is distributed with dopant particles for reducing the hole transport rate, and the hole transport layer is reused as a hole injection retarding layer. 
     Alternatively, after the cleaning of the anode layer is completed, a first functional layer group including a hole injection layer, a hole transport layer, and a hole injection retarding layer is formed on the anode layer using an evaporation process. The material of the hole injection retarding layer may be a planar aromatic compound having a conjugated structure to satisfy the setting requirement of the HOMO level of the hole injection retarding layer, further improving the effect. 
     Alternatively, after the cleaning of the anode layer is completed, a first functional layer group including a hole injection layer and a hole transport layer having dopant particles distributed thereon is formed on the anode layer using an evaporation process, and the dopant particles may be mixed with a material for forming the hole transport layer in advance. The material doped with particles can also adopt a planar aromatic compound having a conjugated structure (doped in the form of particles in the material for forming the hole transport layer) so as to satisfy the setting requirement of the HOMO level of the hole injection retarding layer and further improve the effect. 
     S 300 , an organic light-emitting layer, a second functional layer and a cathode layer are successively formed on one side of the first functional layer group facing away from the substrate. 
     Alternatively, after the cleaning of the anode layer is completed, the organic light-emitting layer, the second functional layer group and the cathode layer may be formed using an evaporation process. Wherein the second functional layer group may comprise a electron injection retarding layer, an electron transport layer and an electron injection layer which are laminated on the organic light-emitting layer, or the second functional layer group may comprise an electron transport layer and an electron injection layer which are laminated on the organic light-emitting layer, wherein the electron transport layer is distributed with dopant particles for reducing the electron transport rate, i.e. the electron transport layer is reused as a electron injection retarding layer. 
     Alternatively, the second functional layer group including the electron transport layer and the electron injection layer in which the dopant particles are distributed is formed on the organic light emitting layer by an evaporation process, and the dopant particles may be mixed with the material for forming the electron transport layer in advance. The material doped with particles can also adopt triazines or pyridine (doped in the form of particles in the material for forming the electron transport layer) so as to satisfy the setting requirement of the LUMO energy level of the electron injection retarding layer and further improve the effect 
     In some embodiments, preparation of a film layer structure, such as an encapsulating layer, is also performed after preparation of the cathode layer. 
     In this embodiment, by providing a hole injection retarding layer  230  between the hole transport layer  220  and the organic light-emitting layer  300  or mixing a doped particle in the hole transport layer, hole injection into the light-emitting layer can be retarded under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the hole transport layer  220  and the organic light-emitting layer  300 ; and/or by providing a electron injection retarding layer  440  between the electron transport layer  410  and the organic light-emitting layer  300  or mixing a doping particle in the electron transport layer, electron injection into the light-emitting layer can be retarded under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer  410  and the organic light-emitting layer  300 ; by reducing exciton quenching, the light emission efficiency of the device is improved, and the phenomenon of efficiency roll-off at high brightness is avoided, thereby improving the uneven display effect. 
     The embodiments of the present application have at least the following technical effects: 
     1, by providing a hole injection retarding layer between the hole transport layer and the organic light-emitting layer, the hole injection retarding layer can retard hole injection into the light-emitting layer under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the hole transport layer and the organic light-emitting layer; by providing a electron injection retarding layer between the electron transport layer and the organic light-emitting layer, electron injection into the light-emitting layer can be retarded under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer and the organic light-emitting layer; by reducing exciton quenching, the light emission efficiency of the device is improved, and the phenomenon of efficiency roll-off at high brightness is avoided, thereby improving the uneven display effect. 
     2, by providing the doped particles in the hole transport layer, since the doped particles can retard hole injection into the light-emitting layer under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the hole transport layer and the organic light-emitting layer; and/or by providing doping particles in the electron transport layer, since the doping particles can retard the injection of electrons into the light-emitting layer under a high voltage (corresponding to a high current density), thereby reducing the exciton concentration at the interface of the electron transport layer and the organic light-emitting layer to reduce exciton quenching, improving the light-emitting efficiency of the device, avoiding the phenomenon of efficiency roll-off of the device under a high brightness, and thereby improving the problem of uneven display effects. 
     3, by defining the HOMO energy level parameter between the hole injection layer and the hole transport layer, the transport rate of holes can be reduced, thereby reducing the efficiency roll-off and improving the display uniformity. 
     4, by defining the LUMO level parameter between the electron injection layer and the electron transport layer, the electron transport rate is reduced, thereby reducing the efficiency roll-off and improving the display uniformity. 
     5, the use of a planar aromatic compound having a conjugated structure in the material of the hole injection retarding layer can satisfy the requirement of the 
     HOMO level of the hole injection retarding layer, thereby achieving the purpose of retarding the hole transport rate at a high current density. 
     6, the use of triazines or pyridine as the material of the electron injection retarding layer can satisfy the requirement of the LUMO energy level of the electron injection retarding layer, thereby achieving the purpose of retarding the electron transport rate at a high current density. 
     7, providing an electron blocking layer between the hole transport layer and the hole injection retarding layer, so as to further inhibit electrons from entering the hole transport layer, so that the electrons remain in the organic light-emitting layer as much as possible, thereby improving the light-emitting efficiency of the device; limiting the HOMO energy level parameter of the electron blocking layer is helpful to improve the blocking effect of electrons, and can also control the transition rate of holes reasonably, further improving the light emitting efficiency of the device. 
     8, A hole blocking layer is provided between the electron transport layer and the organic light-emitting layer, and the hole blocking layer serves to block holes from entering the electron transport layer, so that holes remain in the organic light-emitting layer as much as possible, further improving the light-emitting efficiency of the device. 
     In the description of the present application, it is to be understood that the directional or positional relationships indicated by the terms “center”, “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, and the like, are those based on the orientation or positional relationships shown in the drawings, merely to facilitate and simplify the description of the present application, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present application. 
     The terms “first” and “second” are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or as implicitly designating the number of technical features indicated. Thus, a feature defined as “first” or “second” may explicitly or implicitly comprise one or more of the feature. In the description of the present application, the meaning of “a plurality” is two or more unless otherwise specified. 
     In the description of the present application, it should be noted that, unless expressly stated or limited otherwise, the terms “mounted”, “connected”, and “connected” are to be interpreted broadly, and may, for example, be fixedly connected, detachably connected, or integrally connected; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication between two elements. For a person skilled in the art, the specific meaning of the above terms in the present application can be understood in detail. 
     In the description of the specification, particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.