Patent Publication Number: US-9899633-B2

Title: OLED display and display module having gradient change of reflectivities

Description:
FIELD OF THE INVENTION 
     The present invention relates to a technology field of an OLED display, and more particularly to an OLED display and a display module thereof. 
     BACKGROUND OF THE INVENTION 
     The organic electroluminesence diode (OLED) element is composed of a cathode, an anode and a luminance layer. The cathode is made of Al etc. metal material and the anode is made of ITO etc. material. Electrons and holes are respectively injected to the cathode and the anode to form excitons in the organic luminance layer to excite the luminance layer to luminesce. The present product in the laboratory mainly employs a transparent ITO anode. The element structure presents a condition of a top emission. However, in a production line, the ITO is always formed on a bottom, since an ITO deposition damages the organic material. Thus, a structure of a bottom emission is employed and lights are emitted from the cathode. 
     Currently, most of OLED employ an anode-luminance structure and the cathode is used as a reflection layer, so the cathode reflects environment lights and inside stray lights. In particular, the cathode made of the metal material has high reflectivity to decrease the contrast and sharpness of the OLED. A general solution is to add a ¼ wavelength plate and a polarizer on a light-emitting face of the OLED to improve the reflection problem, but it causes a high cost. 
     SUMMARY OF THE INVENTION 
     The embodiment of the present invention provides an OLED display and display module thereof to solve the technical problem of decreasing the contrast and sharpness of the OLED display caused by the cathode plate with the high reflectivity. 
     To solve the above-mentioned problem, the embodiment of the present invention provides the OLED display module. The OLED display module comprises: a cathode plate, an anode plate and a luminance function layer sandwiched in between the cathode plate and the anode plate. Multiple reflectivities among multiple layers of the luminance function layer are satisfied with a following relationship, which is a reflectivity of the material of the luminance function layer near to the cathode plate is greatly higher than a reflectivity of another material of the luminance function layer distant from the cathode plate. 
     According to a preferred embodiment, the luminance function layer comprises sequentially along a direction from the cathode plate to the anode plate: an electron ejection layer, an electron transport layer, a light emitting layer, a hole transport layer and a hole ejection layer. 
     According to a preferred embodiment, one-layer or multi-layer reflectivity-change layer(s) are formed among the layers of the luminance function layer. 
     According to a preferred embodiment, the reflectivity-change layer is made of inorganic material. 
     According to a preferred embodiment, a thickness of the reflectivity-change layer is less than 50 nm. 
     According to a preferred embodiment, a visible light with 500 nm±25 nm luminance wavelength range generated by the luminance function layer. 
     According to a preferred embodiment, a material of the hole ejection layer comprises one or more of CuPc, TCNQ, PPDN and TiOPC. 
     According to a preferred embodiment, a material of the hole transport layer comprises one or more of TCTA, F4TCNQ, TCNQ, PPDN, CuPc and TiOPC; and the hole transport layer is a multi-layer structure. 
     According to a preferred embodiment, the light emitting layer is made of a combination of phosphorescence material, TCTA and TAZ; a material of the electron transport layer comprises one or more of Alq3, BCP, Bphen, TPBi, Liq and Nbphen; and a material of the electron injection layer is one or more of LiF, LiBq4 and Alq3:Li3N. 
     To solve the above-mentioned problem, the present invention also provides the OLED display. The OLED display comprises any one of the above-mentioned OLED modules. 
     In comparison with the prior art, the OLED display and the display module thereof provided by the present invention, the reflectivities among the layers of the luminance function are satisfied with a following relationship, which is the reflectivity of the material of the luminance function layer near to the cathode plate is greatly higher than the reflectivity of another material of the luminance function layer distant from the cathode plate. It solves the technical problem of decreasing the contrast and sharpness of the OLED display caused by the cathode plate with the high reflectivity. In addition, to satisfy that the reflectivity of the material of the luminance function layer is greatly higher than the reflectivity of another material of the luminance function layer distant from the cathode plate, the present invention solution forms one-layer or multi-layer reflectivity-change layer(s) among the layers of the luminance function layer. The luminance function layer is used to obtain the gradient change of the reflectivities and to make the luminance function layer satisfy with the requirement of the gradient change. It further improves the technical problem of decreasing the contrast and sharpness of the OLED display caused by the cathode plate with the high reflectivity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate the embodiments of the present invention or prior art, the following figures will be described in the embodiments are briefly introduced. It is obvious that the drawings are merely some embodiments of the present invention, those of ordinary skill in this field can obtain other figures according to these figures without paying the premise. 
         FIG. 1  is a structural schematic drawing of an OLED display module of a preferred embodiment of the present invention; 
         FIG. 2  is a structural schematic drawing of another OLED display module of a preferred embodiment of the present invention; and 
         FIG. 3  is a simplified structural drawing of an OLED display of a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention are described in detail with the technical matters, structural features, achieved objects, and effects with reference to the accompanying drawings as follows. It is clear that the described embodiments are part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments to those of ordinary skill in the premise of no creative efforts obtained, should be considered within the scope of protection of the present invention. 
     Please refer to  FIG. 1 .  FIG. 1  is structural schematic drawing of an OLED display module of a preferred embodiment of the present invention. The OLED display module comprises: a cathode plate  100 , an anode plate  200  and a luminance function layer  300  sandwiched in between the cathode plate  100  and the anode plate  200 . Multiple reflectivities among multiple layers of the luminance function layer  300  are satisfied with a following relationship, which is a reflectivity of a material of the luminance function layer  300  near to the cathode plate  100  is greatly higher than a reflectivity of another material of the luminance function layer  300  distant from the cathode plate  100 . Specifically, the luminance function layer  300  generates a visible light with 500 nm±25 nm luminance wavelength range. 
     Particularly, the luminance function layer  300  comprises sequentially along a direction from the cathode plate  100  to the anode plate  200  but is not limited to following functional layers: an electron ejection layer  310 , an electron transport layer  320 , a light emitting layer  330 , a hole transport layer  340 , a hole ejection layer  350 , etc. 
     The solution of the present invention is to change a structure of the OLED and to propose a new structure of decreasing the reflection of the cathode plate  100 . According to the Fresnel equation of a penetrating optics theory, we can deduce that intensities of lights on a vertical polarization direction and a horizontal polarization direction satisfy with two following equations: 
     
       
         
           
             
               
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     Wherein, Rs represents the intensity of lights on the vertical polarization direction, Rp represents the intensity of lights on the horizontal polarization direction, and θ is a light incidence and departure angle. n represents a reflectivity of lights passing through a medium material. 
     If the reflectivities of the functional layers arranged along the direction from the cathode plate  100  to the anode plate  200  are respectively and sequentially represented as n1, n2, n3, n4, n5, n6, n7 . . . , the reflectivities are satisfied with relationships of n1&gt;&gt;n2, n2&gt;&gt;n3, n3&gt;&gt;n4, n4&gt;&gt;n5, . . . . Since the luminance function layer  300  of the OLED has a N-layer structure, at least N−2 of the satisfied inequalities are required. The meaning of the inequality is that the reflectivity of the material of the luminance function layer  300  near to the cathode plate  100  is greatly higher than the reflectivity of the another material of the luminance function layer  300  distant from the cathode plate  100 . More inequalities are satisfied and an effect is better. 
     Specifically, the anode plate is an Indium Tin Oxide (ITO) layer. The hole ejection layer  350  may be made of copper phthalocyanine (CuPc) having an excellent hole injection ability, or may be made of 2,3,5,6-tetrafluoro-7,7,8,-tetracyanoquinodimethane (F4TCNQ), tetracyanoquinodimethane (TCNQ), phenanthroline-23-dinitrile (PPDN), or titanyl-phthalocyanine (TiOPC). 
     The hole transport layer  340  may be made of 4,4′,4″-tri(carbazole-9-yl)triphenylamine (TCTA) having an excellent hole transport ability, or may be made of 2,3,5,6-tetrafluoro-7,7,8,-tetracyanoquinodimethane (F4TCNQ), tetracyanoquinodimethane (TCNQ), phenanthroline-23-dinitrile (PPDN), copper phthalocyanine (CuPc), or titanyl-phthalocyanine (TiOPC). 
     Specifically, the hole transport layer  340  may be a multi-layer structure and 2 to 4 layers are preferred. A thickness of each layer may be different. The light emitting layer  330  may use a mixed-type main light emitting layer including a green phosphorescent material of fac-tris(2-phenylpyridine)iridium (Ir(ppy)3) and a red phosphorescent material of bis(2,4-diphenyl-quinoline)iridium(III) acetylanetonate (Ir(pq)2acac) co-doped with TCTA and 1,2,4-triazole derivative (3,5-diphenyl-4-naphthalene-1-yl-1,2,4-triazole, TAZ), and also uses an auxiliary light emitting layer including a blue phosphorescent material of FCNIr doped with mCP at the same time. According to the principle of colorimetry, one light emitting layer doped with red, green and blue light emitting materials generates white lights by color mixing. 
     The electron transport layer  320  may be made of quinoline aluminum (Alq3) having an excellent electron transport ability, or may be made of BCP (Bathocuproine), 4,7-diphenyl-1,10-phenanthroline (Bphen), 1,3,5-tri(N-phenyl-benzimidazol-2-yl)benzene (TPBi), hydroxyquinolinolate-lithium (Liq), 2,9-bis(2-naphthyl)-4,7-diphenyl-1,10-phenanthroline (Nbphen), or 1,2,4-triazole derivative (TAZ). 
     The electron injection layer  310  may be made of a low working function material such as LiF, which has an excellent electron injection ability, or may be made of lithiumtetra-(8-hydroxy-quinolinato)boron (LiBq4) or Alq3:Li3N (in which Li3N is an n-type doping agent, and Alq3 is the doped material). 
     Specifically, the cathode plate  100  is made of aluminum or silver to increase a conductivity thereof and a display effect of the display is better accordingly. 
     In comparison with the prior art, in the OLED display module provided by the present embodiment, the reflectivities among the layers of the luminance function are satisfied with the following relationship, which is the reflectivity of the material of the luminance function layer near to the cathode plate is greatly higher than the reflectivity of another material of the luminance function layer distant from the cathode plate. 
     Please refer to  FIG. 2 ,  FIG. 2  is a structural schematic drawing of another OLED display module of a preferred embodiment of the present invention. The OLED display module of the present embodiment also comprises: a cathode plate  100 , an anode plate  200  and a luminance function layer  300  sandwiched in between the cathode plate  100  and the anode plate  200 . Multiple reflectivities among multiple layers of the luminance function layer  300  are satisfied with a following relationship, which is a reflectivity of the material of the luminance function layer  300  near to the cathode plate  100  is greatly higher than a reflectivity of another material of the luminance function layer  300  distant from the cathode plate  100 . The luminance function layer  300  comprises sequentially along the direction from the cathode plate  100  to the anode plate  200  but is not limited to following functional layers: an electron ejection layer  310 , an electron transport layer  320 , a light emitting layer  330 , a hole transport layer  340 , a hole ejection layer  350 , etc. 
     According to the previous embodiment, it can understand that more inequalities are satisfied and the effect is better. Thus, a downward gradient change of the reflectivities of n1 to n5, or more like n6, n7, n8 is increasingly large and the reflective effect of the cathode plate is improved better.  FIG. 2  only discloses an arrangement of one type of a reflectivity-change layer  399 , but another embodiment is not limited in this type as shown in the drawing. According to particular requirements of design, people who is skilled in the art can add different numbers of the reflectivity-change layers  399 , so no more details thereof are described here. 
     Specifically, the reflectivity-change layer  399  is made of inorganic material. A thickness of the reflectivity-change layer  399  is less than 50 nm. Adding more reflectivity-change layers  399  is to improve the gradient change of the reflectivities. If the reflectivities of the material of the functional layers arranged along the direction from the cathode plate  100  to the anode plate  200  are respectively and sequentially represented as n1, n2, n3, n4, n5, n6, n7 . . . , and the reflectivities of the added reflectivity-change layers  399  arranged along the direction from the cathode plate  100  to the anode plate  200  are respectively and sequentially represented as n2′, n3′, n4′, n5′ . . . . The reflectivities are satisfied with relationships of n1&gt;&gt;n2′, n2′&gt;&gt;n2, n2&gt;&gt;n3′, n3′&gt;&gt;n3, n3&gt;&gt;n4′, . . . . Similarly, if the N-layer structure is composed of the luminance function layer  300  and the reflectivity-change layers  399 , the at least N−2 of the satisfied inequalities are required. 
     In the structure of the present embodiment, the visible light with 500 nm±25 nm luminance wavelength range generated by the luminance function layer  300  is employed. In addition, the nature, composition etc. features of the material of each of the anode plate  200 , the cathode plate  100  and the luminance function layer  300  are the same as these of the previous embodiment, so the details thereof are not further described here. 
     In comparison with the prior art, the OLED display and the display module thereof provided by the present invention, the reflectivities among the layers of the luminance function are satisfied with a following relationship, which is the reflectivity of the material of the luminance function layer near to the cathode plate is greatly higher than the reflectivity of another material of the luminance function layer distant from the cathode plate. It solves the technical problem of decreasing the contrast and sharpness of the OLED display caused by the cathode plate with the high reflectivity. In addition, to satisfy that the reflectivity of the material of the luminance function layer is greatly higher than the reflectivity of another material of the luminance function layer distant from the cathode plate, the present invention solution forms one-layer or multi-layer reflectivity-change layer(s) among the layers of the luminance function layer. The luminance function layer is used to obtain the gradient change of the reflectivities and to make the luminance function layer satisfy with the requirement of the gradient change. It further improves the technical problem of decreasing the contrast and sharpness of the OLED display caused by the cathode plate with the high reflectivity. 
     In addition, the embodiment of the present invention also provides an OLED display and please refer to  FIG. 3 .  FIG. 3  is simplified structural drawing of the OLED display of a preferred embodiment of the present invention. Wherein, the OLED display comprises a shell  800  and the above-mentioned OLED display module mounted inside the shell  800 . Regarding the technological features of the OLED display module, please refer to the detail description of the above-mentioned embodiments. People who is skilled in the art can understand other technological features of other partial structures of the OLED display so the details thereof are not further described here. 
     Above are embodiments of the present invention, which does not limit the scope of the present invention. Any modifications, equivalent replacements or improvements within the spirit and principles of the embodiment described above should be covered by the protected scope of the disclosure.