Patent Publication Number: US-2021184183-A1

Title: Manufacturing method of graphene oxide film, organic light-emitting diode, and manufacturing method thereof

Description:
FIELD OF INVENTION 
     The present disclosure relates to the field of display technologies, and more particularly, to a manufacturing method of a graphene oxide film, an organic light-emitting diode (OLED), and a manufacturing method thereof. 
     BACKGROUND OF INVENTION 
     Organic light-emitting diodes (organic light emission diodes, OLEDs) possess advantages of high brightness, a wide range of materials selection, low driving voltages, fully-cured active light emission, etc. Moreover, OLEDs possess advantages of high definition, wide viewing angles, and fast response time. OLEDs are thus display technologies and light sources with great potential. Luminous performance of OLEDs is mainly associate with energy-level matching between functional layers. However, traditional OLEDs have poor luminous efficiency and stability. Affinity between each functional layer is weak, such that the energy level matching between the functional layers is poor. Therefore, the luminous efficiency of the OLEDs is directly affected. 
     In summary, in existing OLEDs and manufacturing methods thereof, the energy level matching between the functional layers is poor because of the weak affinity between each functional layer. Therefore, the luminous efficiency of the OLEDs is directly affected. 
     Technical Problems 
     In existing OLEDs and manufacturing methods thereof, the energy level matching between the functional layers is poor because of the weak affinity between each functional layer. Therefore, the luminous efficiency of the OLEDs is directly affected. 
     SUMMARY OF INVENTION 
     Technical Solutions 
     In a first aspect, an embodiment of the present disclosure provides a manufacturing method of a graphene oxide film, comprising: 
     a step S 10  of providing a graphene oxide aqueous solution in an initial concentration which is a specific concentration, and dispersing the initial concentration to a first concentration by an ultraviolet reduction process to prepare a first graphene oxide solution; 
     a step S 20  of putting the first graphene oxide solution into an ultrasonic cleaning apparatus and subjecting the first graphene oxide solution to a shaking water bath in the ultrasonic cleaning apparatus at a first temperature; and 
     a step S 30  of coating the first graphene oxide solution, after being subjected to the shaking water bath, to form a graphene oxide film by a spin-coating process. 
     In the manufacturing method of the graphene oxide film, in the step S 10 , the first concentration is 0.06-0.2 times as much as the initial concentration. 
     In the manufacturing method of the graphene oxide film, in the step S 20 , the first temperature ranges from 20 to 40° C. and duration of subjecting the first graphene oxide solution to the shaking water bath ranges from 2 to 6 hours. 
     In the second aspect, an embodiment of the present disclosure further provides an organic light-emitting diode (OLED), comprising: a substrate, an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode stacked in sequence, wherein the hole injection layer is a graphene oxide layer, and the hole transport layer is any one of N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine, 1,4-bis(diphenylamino) biphenyl, or N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine. 
     In the OLED, a concentration of a graphene oxide solution used in the graphene oxide layer ranges from 0.3 to 1 mg/ml. 
     In the third aspect, an embodiment of the present disclosure further provides a manufacturing method of an organic light-emitting diode (OLED), comprising: 
     a step S 10  of forming an anode on a cleaned substrate by a magnetron sputtering process to obtain an anode substrate; 
     a step S 20  of adjusting a concentration of a graphene oxide solution by an ultraviolet reduction process, and then coating the graphene oxide solution on the anode substrate by a spin coating process, and performing a drying treatment to form a hole injection layer; and 
     a step S 30  of depositing a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode on the hole injection layer in sequence by evaporation processes. 
     In the manufacturing method of the OLED, the S 20  further comprises: 
     a step S 201  of providing a graphene oxide aqueous solution in an initial concentration which is a specific concentration and adjusting the concentration of the graphene oxide solution by the ultraviolet reduction process to prepare a first graphene oxide solution; and 
     a step S 202  of subjecting the first graphene oxide solution to a shaking water bath via an ultrasonic cleaning instrument for 2-6 hours, wherein an ultrasonic process is controlled at 20-40° C., and then coating the first graphene oxide solution on the anode substrate, and performing the drying treatment to form the hole injection layer. 
     In the manufacturing method of the OLED, in the step S 201 , the first concentration is 0.06 to 0.2 times as much as the initial concentration. 
     In the manufacturing method of the OLED, in the step S 30 , an evaporation rate of the light-emitting layer is between 1-4 Å/s, an evaporation rate of the electron injection layer is between 0.1-0.3 Å/s, and an evaporation rate of the cathode is between 1-5 Å/s. 
     In the manufacturing method of the OLED, in the step S 30 , material of the light-emitting layer is tris(8-hydroxyquinoline) aluminum, material of the electron injection layer is LiF, and material of the cathode is Al. 
     Beneficial Effects 
     Compared with the prior art, the manufacturing method of the graphene oxide film, the OLED, and the manufacturing method thereof provided by the present disclosure employ different concentrations of the graphene oxide solution as a hole injection layers and employ specific types of hole transport layers, which are beneficial to the injection and transport of holes and further increase luminous efficiency of OLED. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart of a manufacturing method of a graphene oxide film according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic structural diagram of an OLED according to an embodiment of the present disclosure. 
         FIG. 3  is a flowchart of a manufacturing method of an OLED according to an embodiment of the present disclosure. 
         FIGS. 3A-3B  are schematic diagrams of the manufacturing method of the OLED shown in  FIG. 3 . 
         FIG. 4  is an electroluminescence spectrum diagram of an OLED using TPD as a hole transport layer and using three different concentrations of graphene oxide as a hole injection layer. 
         FIG. 5  is a voltage-luminance curve diagram of an OLED using TPD as a hole transport layer and using three different concentrations of graphene oxide as a hole injection layer. 
         FIG. 6  is an electroluminescence spectrum diagram of an OLED using 0.5 mg/mL of graphene oxide as a hole injection layer and using three different materials as a hole transport layer. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present disclosure provides a manufacturing method of a graphene oxide film, an OLED, and a manufacturing method thereof. In order to make purposes, technical solutions, and effects of the application to be clearer and more specific, the present disclosure is further described with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are only used to explain the present disclosure, and are not intended to limit the present disclosure. 
     As shown in  FIG. 1 .  FIG. 1  is a flowchart of a manufacturing method of a graphene oxide film according to an embodiment of the present disclosure. The manufacturing method includes the following: 
     a step S 10  of providing a graphene oxide aqueous solution in an initial concentration which is a specific concentration and dispersing the initial concentration to a first concentration by an ultraviolet reduction process to prepare a first graphene oxide solution. 
     Specifically, the step S 10  further includes the following: 
     First, a specific concentration of graphene oxide aqueous solution is obtained from commercial sources. The specific concentration may be 5 mg/ml. Then, the initial concentration of the graphene oxide solution is dispersed to a first concentration by an ultraviolet reduction process to prepare a first graphene oxide solution. The concentration of the first concentration is 0.06 to 0.2 times as much as the initial concentration. Preferably, when the initial concentration is set to 5 mg/ml, the first concentration ranges from 0.3 mg/ml to 1 mg/ml. Preferably, the initial concentration of the graphene oxide solution is dispersed into a graphene oxide solution A having a solution concentration of 0.3 mg/ml, a graphene oxide solution B having a solution concentration of 0.5 mg/ml, and an Graphene solution C having a solution concentration of 1 mg/ml. 
     a step S 20  of putting the first graphene oxide solution into an ultrasonic cleaning apparatus and subjecting the first graphene oxide solution to a shaking water bath in the ultrasonic cleaning apparatus at a first temperature. 
     Specifically, the step S 20  further includes the following: 
     Afterwards, the first graphene oxide solution is put into an ultrasonic cleaning apparatus and is subjected to the shaking water bath at the first temperature. The first temperature ranges from 20 to 40° C. and duration of subjecting the first graphene oxide solution to the shaking water bath ranges from 2 to 6 hours. Preferably, the first graphene oxide solution includes the graphene oxide solution A, the graphene oxide solution B, and the graphene oxide solution C. 
     A step S 30  of coating the first graphene oxide solution after being subjected to the shaking bath to form a graphene oxide film by a spin-coating process. 
     Specifically, the step S 30  further includes the following: 
     Finally, the first graphene oxide solution after being subject to the shaking bath is coated to form a graphene oxide film by the spin-coating process. Preferably, the graphene oxide film includes a film prepared from the graphene oxide solution A, a film prepared from the graphene oxide solution B, and a film prepared from the graphene oxide solution C. 
     As shown in  FIG. 2 .  FIG. 2  is a schematic structural diagram of an OLED according to an embodiment of the present disclosure. The OLED  10  includes a substrate  11 , an anode  12 , a hole injection layer  13 , a hole transport layer  14 , a light-emitting layer  15 , an electron transport layer  16 , an electron injection layer  17 , and a cathode  18  stacked in sequence. The hole injection layer  13  is a graphene oxide layer. The hole transport layer  14  is one of N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine, 1,4-bis(diphenylamino) biphenyl, or N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine. 
     Preferably, the substrate  11  is a glass substrate. 
     Specifically, the anode  12  is preferably indium tin oxide (ITO). 
     Specifically, when the graphene oxide of the graphene oxide layer is in an oxidized state, the sp 2  hybrid conjugation of graphene itself will be destroyed which results in the lack of freely moving  7 E electrons. The graphene oxide is in an insulated state and have a wide energy gap, about 3.5 eV or more. When the graphene oxide of the graphene oxide layer is in a reduced state, freely moving  7 E electrons can be generated in a conjugated region, which is in a conductive state. The use of graphene oxide as a hole injection layer effectively increases an injection rate of holes, thereby increasing a light emission rate of the OLED. 
     Specifically, the concentration of the graphene oxide solution used for the graphene oxide layer ranges from 0.3 mg/ml to 1 mg/ml. Preferably, the concentration of the graphene oxide solution used for the graphene oxide layer is 0.3 mg/ml, or 0.5 mg/ml, or 1 mg/ml. 
     Specifically, material of the light-emitting layer  15  is preferably tris(8-hydroxyquinoline) aluminum (Alq 3 ). 
     Specifically, material of the electron transport layer  16  is preferably tris(8-hydroxyquinoline) aluminum (Alq 3 ). 
     Specifically, material of the electron injection layer is preferably LiF. 
     Specifically, material of the cathode is preferably Al. 
     The OLEDs provided in the embodiments of the present disclosure employ different concentrations of graphene oxide films as hole injection layers and employ specific hole transport layers, which greatly increases conductivity of the OLEDs and further increases light-emitting efficiency of the OLED. 
     As shown in  FIG. 3 .  FIG. 3  is a flowchart of a manufacturing method of an OLED according to an embodiment of the present disclosure. The manufacturing method is as follows: 
     a step S 10  of forming an anode  22  on a cleaned substrate by a magnetron sputtering process to obtain an anode substrate  21 . 
     Specifically, the step S 10  further includes the following: 
     First, a substrate  21  is provided. The substrate  21  is preferably a glass substrate. After being rinsed with distilled water and ethanol, the substrate  21  is immersed in isopropyl alcohol for one night, and is then dried for use. Then, an anode  22  is formed on the substrate  21  by the magnetron sputtering process to obtain an anode substrate. Material of the anode  22  is conductive ITO glass and has a sputtering rate of 0.2 nm/s. Afterwards, the anode substrate is rinsed with deionized water, then the anode substrate is rinsed with warm water for 30-50 min, dried, and is finally washed in an ion cleaner for 6-15 min. The use of plasma treatment here is to increase work function of the ITO surface to 4-8 eV or more, and increase the interface contact between the anode substrate and the subsequent organic functional layer, as shown in  FIG. 3A . 
     A step S 20  of adjusting a concentration of a graphene oxide solution by an ultraviolet reduction process, and then coating the graphene oxide solution on the anode substrate by a spin coating process, and performing a drying treatment to form a hole injection layer  23 . 
     Specifically, the step S 20  further includes the following: 
     First, a specific concentration of graphene oxide aqueous solution is obtained from commercial sources. The specific concentration may be 5 mg/ml. Then, the initial concentration of the graphene oxide solution is dispersed to a first concentration by an ultraviolet reduction process to prepare a first graphene oxide solution. The concentration of the first concentration is 0.06 to 0.2 times as much as the initial concentration. Preferably, when the initial concentration is set to 5 mg/ml, the first concentration ranges from 0.3 mg/ml to 1 mg/ml. Preferably, the initial concentration of the graphene oxide solution is dispersed into a graphene oxide solution A having a solution concentration of 0.3 mg/ml, a graphene oxide solution B having a solution concentration of 0.5 mg/ml, and a graphene oxide solution C having a solution concentration of 1 mg/ml. Afterwards, the first graphene oxide solution is subjected to a shaking water bath via an ultrasonic cleaning instrument for 2-6 hours. The ultrasonic process is controlled at 20-40° C., and then different concentrations of the graphene oxide solutions (equal amounts) are coated on three of the anode substrates via the spin coating process. Three batches of the sample were prepared and dried to obtain the hole injection layer  23 , as shown in the  FIG. 3B . 
     A step S 30  of depositing a hole transport layer  24 , a light-emitting layer  25 , an electron transport layer  26 , an electron injection layer  27 , and a cathode  28  on the hole injection layer  23  in sequence by evaporation processes. 
     Specifically, the step S 30  further includes the following: 
     First, the anode substrate that is spin-coated with graphene oxide is fixed on a mask plate, transferred to a vacuum evaporation chamber, and vacuumed using a molecular pump. Until the degree of vacuum is lower than 4.0×10 −4  Pa to 6.5×10 −4  Pa, a hole transport layer  24  is deposited on the hole injection layer  23 . The hole transport layer  24  is N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (TPD), 1,4-bis(diphenylamino) biphenyl (DDB), and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB). Thereafter, a light-emitting layer  25 , an electron transporting layer  26 , an electron injection layer  27 , and a cathode  28  are deposited on the hole transporting layer  24  in sequence. Finally, OLEDs with different concentrations of graphene oxide and OLEDs that correspond to different hole transport layers are obtained, as shown in  FIG. 3C . 
     An evaporation rate of the light-emitting layer  25  is between 1 to 4 Å/s. Material of the light-emitting layer  25  is preferably tris(8-hydroxyquinoline) aluminum (Alq 3 ). Material of the electron transport layer  26  is preferably tris(8-hydroxyquinoline) aluminum (Alq 3 ). An evaporation rate of the electron injection layer  27  is between 0.1 to 0.3 Å/s. Material of the electron injection layer is preferably LiF. An evaporation rate of the cathode  28  is between 1 to 5 Å/s. Material of the cathode  28  is preferably Al. 
     Preferably, the manufacturing method of an OLED provided in the embodiments of the present disclosure obtains OLEDs of 9 different embodiments. Details are described as follows: 
     The OLED A 1  includes a hole injection layer that is prepared from a 0.3 mg/ml of the graphene oxide solution and a hole transporting layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (TPD). The OLED A 2  includes a hole injection layer that is prepared from a 0.5 mg/ml of the graphene oxide solution and a hole-transporting layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine. The OLED A 3  includes a hole injection layer that is prepared from 1 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (TPD). 
     The OLED B 1  includes a hole injection layer that is prepared from a 0.3 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from 1,4-bis(diphenylamino) biphenyl (DDB). The OLED B 2  includes a hole injection layer that is prepared from a 0.5 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from 1,4-bis(diphenylamino) biphenyl (DDB). The OLED B 3  includes a hole injection layer prepared from 1 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from 1,4-bis(diphenylamino) biphenyl (DDB). 
     The OLED C 1  includes a hole injection layer that is prepared from 0.3 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (NPB). The OLED C 2  includes a hole injection layer that is prepared from 0.5 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (NPB). The OLED C 3  includes a hole injection layer that is prepared from 1 mg/ml of the graphene oxide solution and a hole transport layer that is prepared from N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine. 
     As shown in  FIG. 4 .  FIG. 4  is an electroluminescence spectrum diagram of an OLED using TPD as a hole transport layer and using three different concentrations of graphene oxide as a hole injection layer. The abscissa is wavelength (in nm) and the ordinate is intensity (in absorbance unit, abbreviated as au). It can be seen from  FIG. 4  that the light-emitting layer of the OLED is Alq 3 . Positions of peaks on the electroluminescence spectrum of the OLED having different concentrations of graphene oxide as the hole injection layer are all around 502 nm. Therefore, the concentration of the graphene oxide solution does not have much influence on the electroluminescence peak of Alq 3 . 
     As shown in  FIG. 5 .  FIG. 5  is a voltage-luminance curve diagram of an OLED using TPD as a hole transport layer and using three different concentrations of graphene oxide as a hole injection layer. The abscissa is voltage (in V) and the ordinate is brightness (luminance, in cd/m 2 ). It can be seen from  FIG. 5  that the light-emitting layer of this OLED is Alq 3 . In the case that other functional layers are unchanged, the hole injection ability of OLEDs having different concentrations of graphene oxide as the hole injection layer is different. The voltage is less than or equal to 7V. As the concentration of the graphene oxide solution increases, the luminous ability of the graphene oxide solution increases. When the voltage is greater than about 7V, the hole injection ability of the OLED having a 0.5 mg/ml of the graphene oxide solution as a hole injection layer is greater than the hole injection ability of the OLED having more than 1 mg/ml of the graphene oxide solution. When the graphene oxide solution having a concentration of 5 mg/ml is used as a hole injection layer to prepare the OLED, the brightness starts to decrease after the voltage reaches 5 to 7 V. Because the current density of the device increases rapidly, which may be caused by the enhancement of hole injection ability, but electron injection level is not increased, non-radiative recombination in the OLED increases, and the brightness of the OLED decreases. 
     As shown in  FIG. 6 .  FIG. 6  is an electroluminescence spectrum diagram of an OLED using 0.5 mg/mL of graphene oxide as a hole injection layer and three different materials as a hole transport layer. The abscissa is wavelength (in nm) and the ordinate is intensity (in absorbance unit, abbreviated as au). It can be seen from  FIG. 6  that the light-emitting layer of this OLED is Alq 3 . The graphene oxide solution having a concentration of 0.5 mg/ml is used as a hole injection layer. In the case that other functional layers are unchanged, hole injection ability of different materials of the hole transport layers are different. Charge transport performances of the hole transport layers are: NPB&gt;TPD&gt;DDB. 
     In summary, in combination with the experimental results of  FIGS. 4-6 , it can be concluded that the OLED B 2  has the best luminous efficiency, in which the hole injection layer of is prepared with 0.5 mg/ml graphene oxide solution and the hole transporting layer is prepared with the material of N,N′-diphenyl-N,N′-bis(3-tolyl)-1,1′-biphenyl-4,4′-diamine (NPB). 
     The OLEDs and manufacturing methods provided in the embodiments of the present disclosure comprehensively compare the effects of the graphene oxide solution concentrations and the material choices of the hole transport layer on the light-emitting efficiency of the OLED in the nine embodiments, which is beneficial to the increase of luminous efficiency of the OLED. 
     The manufacturing method of the graphene oxide film, the OLED, and the manufacturing method thereof provided by the present disclosure employ different concentrations of the graphene oxide solution as hole injection layers and employ specific types of hole transport layers, which are beneficial to the injection and transport of holes and further increase luminous efficiency of OLED. 
     It can be understood that one of ordinarily skill in the art can carry out changes and modifications to the described embodiment according to technical solutions and technical concepts of the present application, and all such changes and modifications are considered encompassed in the scope of protection defined by the claims of the present application.