Patent Publication Number: US-2022231252-A1

Title: Organic light-emitting device and display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation to international patent application PCT/CN2021/084011, filed on Mar. 30, 2021, which claims priority to Chinese Patent Application No. 202010462196.1, filed on May 27, 2020, the contents of both applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technology. 
     BACKGROUND 
     The organic light-emitting diode (OLED) has been commercially used in the field of display technology due to its advantages of high response speed, high color purity, wide view angle, foldability, and low energy consumption, etc. 
     SUMMARY 
     The present disclosure provides for an organic light-emitting device and a display device. 
     In an aspect of the present disclosure, an organic light-emitting device is provided. The organic light-emitting device includes an anode, a cathode, and a plurality of layers that are stacked between the anode and the cathode. The plurality of layers includes a first hole transport layer, a first light-emitting layer, a first electron transport layer, an n-type charge generation layer, and a p-type charge generation layer stacked in sequence. The n-type charge generation layer includes a matrix, a first dopant, and a second dopant. The matrix is a first electron transport organic material, the first dopant is a metal quinoline complex, and the second dopant is selected from the group consisting of a rare earth metal, an alkali metal, an alkaline-earth metal, and any combination thereof; or the matrix is a first electron transport organic material, the first dopant is a metal quinoline complex, and the second dopant is an n-type organic material. 
     In another aspect of the present disclosure, a display panel including the above-described organic light-emitting device is provided. 
     In the present disclosure, by doping the metal quinoline complex in the n-type charge generation layer, the driving voltage of the organic light-emitting device is decreased, the lifetime of the organic light-emitting device is prolonged, and the stability of the organic light-emitting device is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional structural view of an organic light-emitting device according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic sectional structural view, showing an embodiment of an n-type charge generation layer of the organic light-emitting device shown in  FIG. 1 . 
         FIG. 3  is a schematic sectional structural view showing another embodiment of the n-type charge generation layer, in which a first electron transport organic material, a metal quinoline complex, and a rare earth metal are distributed non-uniformly, of the organic light-emitting device shown in  FIG. 1 . 
         FIG. 4  is a schematic sectional structural view, showing yet another embodiment of the n-type charge generation layer, in which the first electron transport organic material, the metal quinoline complex, and the rare earth metal are distributed non-uniformly, of the organic light-emitting device shown in  FIG. 1 . 
         FIG. 5  is a schematic sectional structural view, showing an embodiment of a first electron transport layer, in which a second electron transport organic material and the metal quinoline complex are distributed non-uniformly, of the organic light-emitting device having the n-type charge generation layer shown in  FIG. 3 . 
         FIG. 6  is a schematic sectional structural view, showing another embodiment of the first electron transport layer, in which a second electron transport organic material and the metal quinoline complex are distributed non-uniformly, of the organic light-emitting device having the n-type charge generation layer shown in  FIG. 4 . 
         FIG. 7A  shows curves of current varying with voltage of the organic light-emitting devices in Comparative Example and Example 1. 
         FIG. 7B  shows curves of efficiency varying with luminance of the organic light-emitting devices in Comparative Example and Example 1. 
         FIG. 7C  shows curves of luminance varying with time of the organic light-emitting devices in Comparative Example and Example 1. 
         FIG. 7D  shows curves of voltage change varying with time of the organic light-emitting devices in Comparative Example and Example 1. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in detail below with reference to the accompanying drawings and the embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present disclosure rather than to limit the present disclosure. In addition, for convenience of description, only part but not all structures related to the present disclosure are shown in the accompanying drawings. 
     The lifetime of the organic light-emitting device is one of the most important factors in determining the performance of the device in use. The lifetime of the device can be significantly increased by adopting a layer stack structure. However, the increase in operating voltage of the organic light-emitting device is accelerated and the lifetime of the organic light-emitting device is reduced as the number of the stacked layers increases. In addition, the instability of the metal doped charge generation layer can also lead to the accelerated increase in the operating voltage of the device, which will adversely affect the performance of the device in use. An n-type charge generation layer of an organic light-emitting device includes an electron transport of organic material and a dopant doped in the electron transport of organic material. The dopant is one or more of rare earth metals, alkali metals, and alkaline-earth metals. The stability of the organic light-emitting device may be adjusted by material selection, which is limited. The doped n-type charge generation layer is not sufficiently stable, which accelerates the increase in the operating voltage of the organic light-emitting device, which reduces the lifetime of the organic light-emitting device, and thus adversely affects the performance of the organic light-emitting device in use. 
     In the present disclosure, to address the above-described problem, an n-type charge generation layer is formed by blending a metal quinoline complex, a first electron transport of organic material, and a rare earth metal, or by blending a metal quinoline complex, a first electron transport organic material, and an n-type organic material, which reduces the energy level difference at an interface between the n-type charge generation layer and the light-emitting layer, thereby decreasing the driving voltage of the organic light-emitting device, prolonging the lifetime of the organic light-emitting device, and improving the stability of the organic light-emitting device. 
     Referring to  FIGS. 1 to 4 , an organic light-emitting device includes a plurality of layers stacked with each other between an anode  110  and a cathode  120 . The plurality of layers includes a first hole transport layer  131  (HTL 1 ), a first light-emitting layer  132  (EML 1 ), a first electron transport layer  133  (ETL 1 ), an n-type charge generation layer  134  (N-CGL), and a p-type charge generation layer  135  (P-CGL) stacked in sequence. The n-type charge generation layer  134  includes a matrix, a first dopant, and a second dopant. In an embodiment, the matrix is a first electron transport organic material N 1 , the first dopant is a metal quinoline complex N 2 , and the second dopant is selected from the group consisting of a rare earth metal D, an alkali metal, an alkaline-earth metal, and any combination thereof. In another embodiment, the matrix includes the first electron transport organic material N 1 , the first dopant includes the metal quinoline complex N 2 , and the second dopant includes an n-type organic material. 
     As shown in  FIG. 1 , the anode  110  can be a transparent electrode, a semi-transparent electrode, and the like. The transparent electrode is made of a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO). The semi-transparent electrode is made of a mixture of a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO), and a non-transparent conductive material, such as aluminum (Al), gold (Au), molybdenum (Mo), chromium (Cr), copper (Cu), or LiF. The cathode  120  can be a light-reflective electrode made of a light-reflective metal material, such as aluminum (Al), gold (Au), molybdenum (Mo), chromium (Cr), copper (Cu), LiF, and any combination thereof. The light-reflective electrode can be a multi-layer structure with the characteristics of the above materials. In the case where the anode  110  is a semi-transparent electrode and the cathode  120  is a light-reflective electrode, the organic light-emitting device is a bottom-emitting structure, in which lights are emitted from the bottom of the device in  FIG. 1  as an example. In the case where the cathode  120  is a semi-transparent electrode and the anode  110  is a light-reflective electrode, the organic light-emitting device is a top-emitting structure, in which lights are emitted from the top of the device in  FIG. 1  as an example. Optionally, both the cathode  120  and the anode  110  are transparent electrodes, so that the organic light-emitting device is a bilaterally emitting structure, in which lights are emitted from both sides. 
     In an embodiment, the first light-emitting layer  132  includes a fluorescent or phosphorescent blue dopant and a matrix, and is configured to emit blue lights. In another embodiment, the first light-emitting layer  132  includes a fluorescent or phosphorescent green dopant and a matrix, and is configured to emit green lights. In yet another embodiment, the first light-emitting layer  132  includes a fluorescent or phosphorescent red dopant and a matrix, and is configured to emit red lights. 
     The alkali metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), and any combination thereof. The alkali-earth metal is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), and any combination thereof. The rare earth metal is selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and any combination thereof. In an embodiment of the present disclosure, the dopant is ytterbium (Yb). The dopant can also be one or a combination of the alkali metal, the alkali-earth metal, and the rare earth metal. 
     The metal quinoline complex is not specifically limited in the present disclosure, as long as it can be used to achieve the concept of the present disclosure. In an embodiment, the metal quinoline complex N 2  is 8-hydroxyquinolinato lithium or 8-hydroxyquinolinato aluminum. 
     The first electron transport organic material N 1  can be selected from the group consisting of 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), and any combination thereof. 
     The n-type organic material can be selected from the group consisting of 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), and any combination thereof. The n-type organic material is different from the first electron transport organic material N 1  in the present disclosure. 
     In an embodiment, the mass percent of the metal quinoline complex doped in the n-type charge generation layer  134  is 10% to 30%, and the mass percent of the second dopant doped in the n-type charge generation layer  134  is 1% to 5%. In an embodiment, the mass percent of the metal quinoline complex doped in the n-type charge generation layer  134  can be 20%, and the mass percent of the second dopant doped in the n-type charge generation layer  134  can be 3%. 
     In an embodiment, the lowest unoccupied molecule orbital (LUMO) energy level difference between the n-type charge generation layer  134  and the first electron transport layer  133  is smaller than or equal to 0.3 eV. The lowest unoccupied molecule orbital (LUMO) energy level difference between the n-type charge generation layer  134  and the first electron transport layer  133  is actually determined by the energy level difference between the materials of the two layers. With the lowest unoccupied molecule orbital (LUMO) energy level difference smaller than or equal to 0.3 eV, the energy barrier in the electron transport process can be reduced, thereby reducing the driving voltage. 
     As shown in  FIGS. 2 to 4 , the first electron transport organic material N 1 , the metal quinoline complex N 2 , and the rare earth metal D are arranged irregularly in the n-type charge generation layer  134  (N-CGL), although the first electron transport organic material N 1 , the metal quinoline complex N 2 , and the rare earth metal D are to be blended uniformly in theory. The doping with the metal quinoline complex N 2  can decrease the lowest unoccupied molecule orbital (LUMO) energy level difference between the n-type charge generation layer  134  and the first electron transport layer  133 . Therefore, less energy is required for the electrons to be transported from the n-type charge generation layer  134  to the first electron transport layer  133  (ETL 1 ). As a result, the transmission rate is increased, the driving voltage of the organic light-emitting device is decreased, the lifetime of the organic light-emitting device is prolonged, and the stability of the organic light-emitting device is improved. 
     In an embodiment, the organic light-emitting device further includes a second hole transport layer  136  (HTL 2 ), a second light-emitting layer  137  (EML 2 ), and a second electron transport layer  138  (ETL 2 ) stacked in sequence. The second hole transport layer  136  is disposed at a side of the p-type charge generation layer  135  away from the first electron transport layer  133 . By stacking the plurality of layers, the transportation of electrons and holes can be achieved and the luminance of the light-emitting layer can be regulated to meet the requirement for the performance of the product. 
     In an embodiment, the thickness of the n-type charge generation layer  134  is 10 nm to 30 nm. In an embodiment, the thickness of the n-type charge generation layer  134  can be 15 nm, 20 nm, or 25 nm. The purpose of controlling the thickness of the n-type charge generation layer  134  is to prevent an acceleration of the operating voltage increase of the organic light-emitting device with the increase of the layer thickness, which will reduce the lifetime of the organic light-emitting device. 
     In an embodiment, the p-type charge generation layer  135  includes a hole transport organic material as a matrix and a p-type organic material as a dopant. In an embodiment, a small amount of material used for the hole transport layer can be doped in the p-type charge generation layer  135  to partially decrease the barrier gap at an interface between the p-type charge generation layer  135  and the second hole transport layer  136 , cause effective charge separation, decrease the driving voltage of the device, and prolong the lifetime of the device. 
     In the present disclosure, the n-type charge generation layer  134  is formed by blending the metal quinoline complex, the first electron transport organic material, and the rare earth metal, or by blending the metal quinoline complex, the first electron transport organic material, and the n-type organic material, which reduces the energy level difference at an interface between the n-type charge generation layer and the light-emitting layer, decreases the driving voltage of the organic light-emitting device, prolongs the lifetime of the organic light-emitting device, and improves the stability of the organic light-emitting device. 
     Referring to  FIGS. 5 to 6 , an organic light-emitting device includes a plurality of layers stacked with each other between an anode  110  and a cathode  120 . The plurality of layers includes a first hole transport layer  131  (HTL 1 ), a first light-emitting layer  132  (EML 1 ), a first electron transport layer  133  (ETL 1 ), an n-type charge generation layer  134  (N-CGL), and a p-type charge generation layer  135  (P-CGL) stacked in sequence. The n-type charge generation layer  134  includes a matrix, a first dopant, and a second dopant. In an embodiment, the matrix is a first electron transport organic material N 1 , the first dopant is a metal quinoline complex N 2 , and the second dopant is selected from the group consisting of a rare earth metal D, an alkali metal, an alkaline-earth metal, and any combination thereof. In another embodiment, the matrix is the first electron transport organic material N 1 , the first dopant is the metal quinoline complex N 2 , and the second dopant is an n-type organic material. The first electron transport layer  133  includes a second electron transport organic material N 3  as a matrix and the metal quinoline complex N 2  as a dopant. 
     The second electron transport organic material is selected from the group consisting of 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), 1,3,5-tri(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), and any combination thereof. The first electron transport organic material and the second electron transport organic material can be the same material or different materials, which can be selected according to the need of the organic light-emitting device. The materials of the first electron transport organic material and the second electron transport organic material are not specifically limited herein. 
     In an embodiment, the lowest unoccupied molecule orbital (LUMO) energy level difference between the first electron transport organic material and the second electron transport organic material is smaller than or equal to 0.3 V, which can meet the need of the organic light-emitting device. 
     In an embodiment, the mass percent of the metal quinoline complex doped in the first electron transport layer  133  is 30% to 50%, for example, 35%, 40%, 45%, or 50%. Generally, the mass percent of a dopant should not be more than 50%, while the increase in doping ratio is beneficial to reduce the energy level difference between layers, increase the contact force at the interface between layers, and increase the electron transmission rate. 
     Referring to  FIGS. 5 to 6 , the first electron transport organic material N 1 , the metal quinoline complex N 2 , and the rare earth metal D are arranged irregularly, i.e., distributed non-uniformly, in the n-type charge generation layer  134  (N-CGL), although the first electron transport organic material N 1 , the metal quinoline complex N 2 , and the rare earth metal D are to be blended uniformly in theory. The second electron transport organic material N 3  and the metal quinoline complex N 2  can also be arranged irregularly, i.e., distributed non-uniformly, in the first electron transport layer  133 . More specifically, the metal quinoline complexes N 2  in both the n-type charge generation layer  134  and the first electron transport layer  133  are arranged close to the interface between the n-type charge generation layer  134  and the first electron transport layer  133 . Both the n-type charge generation layer  134  and the first electron transport layer  133  are doped with a small amount of metal quinoline complex N 2 , so that the barrier gap at the interface between the n-type charge generation layer  134  and the first electron transport layer  133  are partially decreased, an effective charge separation is obtained, and the contact force at the interface between the n-type charge generation layer  134  and the first electron transport layer  133  is increased, thereby enhancing the electron transport capacity and decreasing the driving voltage of the organic light-emitting device, which is beneficial to prolong the lifetime of the organic light-emitting device and keep the stability of the organic light-emitting device. 
     In the present disclosure, by doping the metal quinoline complex N 2  in both the n-type charge generation layer  134  and the first electron transport layer  133 , the interface contact between the n-type charge generation layer  134  and the first electron transport layer  133  is improved, the electron transport capacity is increased, the energy level difference at the interface between the n-type charge generation layer  134  and the first electron transport layer  133  is reduced, and so that the driving voltage of the organic light-emitting device is decreased, the lifetime of the organic light-emitting device is prolonged, and the stability of the organic light-emitting device is improved. 
     Table 1 shows data obtained in related tests for the organic light-emitting devices in Comparative Example, Example 1, and Example 2, wherein all the first electron transport layers  133  are doped with 50% (mass percent) of 8-hydroxyquinolinato lithium. N 2  in Table 1 is 8-hydroxyquinolinato lithium. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 L 
                 V d   
                 Eff. 
                 LT (20 h) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 IVL ID 
                 N-CGL 
                 nits 
                 (V) 
                 (cd/A) 
                 LT 
                 ΔV 
               
               
                   
               
               
                 Comparative 
                 N2 = 0% 
                 750 
                 8.19 
                 8.9 
                 98.6% 
                 0.287 
               
               
                 Example 
               
               
                 Example 1 
                 N2 = 20% 
                   
                 8.03 
                 8.8 
                 99.4% 
                 0.197 
               
               
                 Example 2 
                 N2 = 50% 
                   
                 8.25 
                 8.1 
                 99.3% 
                 0.209 
               
               
                   
               
            
           
         
       
     
     The n-type charge generation layers  134  (N-CGL) of the organic light-emitting devices in Comparative Example, Example 1, and Example 2 are respectively doped with 0%, 20%, and 50% (mass percent) of the metal quinoline complex N 2  in the same environment. Then the performance of the devices is tested at the luminance of 750 nits. It can be seen from Table 1 that the initial voltages of the organic light-emitting devices with the n-type charge generation layers  134  respectively doped with 0%, 20%, and 50% (mass percent) of the metal quinoline complex N 2  are respectively 8.19V, 8.03 V, and 8.25 V. The smaller the initial voltage of the organic light-emitting device, the smaller the power consumption of the organic light-emitting device, and the better the performance of the organic light-emitting device. The efficiencies (Eff for short) of the organic light-emitting devices with the n-type charge generation layers  134  respectively doped with 0%, 20%, and 50% (mass percent) of the metal quinoline complex N 2  are respectively 8.9 cd/A, 8.8 cd/A, and 8.1 cd/A. The larger the efficiency of the organic light-emitting device, the smaller the voltage of the organic light-emitting device, and the smaller the current of the organic light-emitting device. The smaller the current of the organic light-emitting device, the smaller the power consumption of the organic light-emitting device, and the better the performance of the organic light-emitting device. In the lifetime (LT for short) attenuation test, with other conditions being the same, after 20 hours of attenuation, the lifetimes of the organic light-emitting devices with the n-type charge generation layers  134  respectively doped with 0%, 20%, and 50% (mass percent) of the metal quinoline complex N 2  are respectively attenuated to 98.6%, 99.4%, and 99.3%. The larger the LT, the smaller the attenuation degree of the organic light-emitting device, and the longer the service time of the organic light-emitting device. The voltage difference (ΔV) is the difference between the initial voltage V and the voltage V 1  after 20 hours of attenuation. The smaller the voltage difference, the longer the lifetime of the organic light-emitting device, and the longer the service time of the organic light-emitting device. In summary, from Table 1, it is obvious that the organic light-emitting device with the first electron transport layer  133  (ETL 1 ) doped with 50% (mass percent) of 8-hydroxyquinolinato lithium (LiQ) and the n-type charge generation layers  134  (N-CGL) doped with 20% (mass percent) of 8-hydroxyquinolinato lithium (LiQ) has a better performance than that of the organic light-emitting device in the comparative example. 
       FIG. 7A  shows curves of current varying with voltage of the organic light-emitting devices in Comparative Example and Example 1, obtained in combination with Table 1, on the condition that the luminance is 750 nits and the first electron transport layer  133  (ETL 1 ) is doped with 50% (mass percent) of 8-hydroxyquinolinato lithium (LiQ). It can be seen from  FIG. 7A  that the current gradually increases with the increase of the voltage. At the same current, the voltage in Example 1 is significantly smaller than the voltage in Comparative Example, which suggests that Example 1 has smaller voltage when other conditions are the same. Therefore, compared with Comparative Example, the power consumption of the organic light-emitting device in Example 1 is smaller and the performance of the organic light-emitting device in Example 1 is better. 
       FIG. 7B  shows curves of efficiency varying with luminance of the organic light-emitting devices in Comparative Example and Example 1, obtained in combination with Table 1, on the condition that the luminance is 750 nits and the first electron transport layer  133  (ETL 1 ) is doped with 50% (mass percent) of 8-hydroxyquinolinato lithium (LiQ). It can be seen from  FIG. 7B  that the efficiency variations in Comparative Example and Example 1 are substantially consistent with each other, suggesting that the efficiency in Example 1 can meet the production requirement. 
       FIG. 7C  shows curves of luminance varying with time of the organic light-emitting devices in Comparative Example and Example 1, obtained in combination with Table 1, on the condition that the luminance (initial) is 750 nits and the first electron transport layer  133  (ETL 1 ) is doped with 50% (mass percent) of 8-hydroxyquinolinato lithium (LiQ). It can be seen from  FIG. 7C  that at the same illumination time, the luminance in Example 1 is significantly larger than the luminance in Comparative Example 1. The larger the luminance at the same illumination time, the longer the lifetime and the service time of the organic light-emitting device. 
       FIG. 7D  shows curves of voltage change varying with time of the organic light-emitting devices in Comparative Example and Example 1, obtained in combination with Table 1, on the condition that the luminance is 750 nits and the first electron transport layer  133  (ETL 1 ) is doped with 50% (mass percent) of 8-hydroxyquinolinato lithium (LiQ). It can be seen from  FIG. 7D  that as the illumination time increases, the curve of Example 1 is more flat than the curve of Comparative Example. Therefore, at the same illumination time, the voltage change in Example 1 is significantly smaller than the voltage change in Comparative Example. The smaller the voltage change, the longer the lifetime and the service time of the organic light-emitting device. 
     The present disclosure further provides a display panel. The display panel includes the organic light-emitting device of any one of embodiments as described above. The display panel can be used in a display apparatus such as mobile phone and tablet computer. 
     The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features are described in the embodiments. However, as long as there is no contradiction in the combination of these technical features, the combinations should be considered as in the scope of the present disclosure.