Organic electroluminescent device

Abstract

An organic electroluminescent device includes at least two light-emissive units provided between a cathode electrode and an anode electrode opposed to the cathode electrode, each of the light-emissive units including at least one light-emissive layer. The light-emissive units are partitioned from each other by at least one charge generation layer, the charge generation layer being an electrically insulating layer having a resistivity of not less than 1.0×10 2 Ωcm.

What is claimed is:  
     
         1 . An organic electroluminescent device comprising: 
 at least two light-emissive units provided between a cathode electrode and an anode electrode opposed to said cathode electrode, each of said light-emissive units including at least one light-emissive layer;    wherein said light-emissive units are partitioned from each other by at least one charge generation layer, said charge generation layer constituting an electrically insulating layer having a resistivity of not less than 1.0×10 2  Ωcm.    
     
     
         2 . The organic electroluminescent device according to  claim 1 , wherein the charge generation layer constitutes an electrically insulating layer having a resistivity of not less than 1.0×10 5  Ωcm.  
     
     
         3 . The organic electroluminescent device according to  claim 1  or  2 , wherein said charge generation layer comprises at least one of a laminated and mixed layer formed from two different materials; 
 wherein a charge transfer complex including a radical cation and a radical anion is formed upon an oxidation-reduction reaction between said two materials, and a radical cation state and a radical anion state in said charge transfer complex is transferred to a direction of the cathode and a direction of the anode, respectively, when a voltage is applied to said device, so that a hole is injected into the light-emissive unit which is located on a cathode side of the charge generation layer and is adjacent thereto, and an electron is injected into the light-emissive unit which is located on an anode side of the charge generation layer and is adjacent thereto.  
 
     
     
         4 . The organic electroluminescent device according to  claim 1 , wherein said charge generation layer comprises one of a laminated and a mixed layer comprising: 
 an organic compound having an ionization potential of less than 5.7 eV and a hole transporting property or electron donating property; and    one of an inorganic and organic material capable of forming a charge transfer complex through the oxidation-reduction reaction thereof with said organic compound; wherein 
 said charge generation layer contains a charge transfer complex formed upon the oxidation-reduction reaction between said organic compound and one of an inorganic and organic material.  
   
     
     
         5 . The organic electroluminescent device according to  claim 4 , wherein said organic compound comprises an arylamine compound, wherein said arylamine compound is represented by the following formula (I):  
       
         
           
           
               
               
           
         
         wherein Ar1, Ar2 and Ar3 each independently represents an aromatic hydrocarbon group which may have substituents.  
       
     
     
         6 . The organic electroluminescent device according to  claim 5 , wherein said organic compound comprises an arylamine compound having a glass transition temperature of not lower than 90° C.  
     
     
         7 . The organic electroluminescent device according to  claim 6 , wherein said arylamine comprises one of α-NPD, 2-TNATA, spiro-TAD, and spiro-NPB.  
     
     
         8 . The organic electroluminescent device according to  claim 4 , wherein said inorganic material comprises a metal oxide.  
     
     
         9 . The organic electroluminescent device according to  claim 4 , wherein said inorganic material comprises a metal halide.  
     
     
         10 . The organic electroluminescent device according to  claim 8 , wherein said metal oxide comprises one of vanadium pentaoxide and rhenium heptaoxide.  
     
     
         11 . The organic electroluminescent device according to  claim 4 , wherein said inorganic material is deposited by one of a resistive heating vapor deposition method, an electron beam vapor deposition method and a laser beam vapor deposition method.  
     
     
         12 . The organic electroluminescent device according to  claim 4 , wherein said inorganic material is deposited by a sputtering method; 
 wherein a sputtering apparatus used in the sputtering method is a facing target sputtering system which comprises a pair of opposed targets provided at a certain distance, a reflection electrode capable of reflecting electrons towards a front peripheral area of each target, and a magnetic field generation device capable of forming a parallel magnetic field in the vicinity of the peripheral portion of each target, said magnetic field having a portion parallel to the peripheral portion of the target.    
     
     
         13 . The organic electroluminescent device according to  claim 4 , wherein said organic material-comprises at least one fluorine as a substituent group, and possesses at least one of an electron injection property and an electron accepting property.  
     
     
         14 . The organic electroluminescent device according to  claim 4 , wherein said organic material comprises at least one cyano group as a substituent group, and possesses at least one of an electron injection property and an electron accepting property.  
     
     
         15 . The organic electroluminescent device according to  claim 13 , wherein said organic material comprises tetrafluoro-tetracyanoquinodimethane (4F-TCNQ).  
     
     
         16 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive unit comprises, as a layer located on an anode side of said charge generation layer and being adjacent thereto, an electron injection layer having a mixture including an organic compound and a metal functioning as an electron donating dopant.  
     
     
         17 . The organic electroluminescent device according to  claim 16 , wherein said electron donating dopant comprises at least one metal selected from a group including an alkaline metal, an alkaline earth metal and a rare earth metal.  
     
     
         18 . The organic electroluminescent device according to  claim 17 , wherein said metal of the electron donating dopant is provided in a molar ratio of 0.1 to 10 with respect to said organic compound in said electron injection layer.  
     
     
         19 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive unit comprises, as a layer located on an anode side of said charge generation layer and being adjacent thereto, a metal layer having a thickness of not more than 5 nm formed from a metal selected from an alkaline metal, an alkaline earth metal and a rare earth metal; 
 wherein said metal constituting the layer diffuses in the adjacent electron transporting layer to react with electron transporting organic material; and  
 wherein, as a result of said diffusion, an electron injection layer is composed of a mixture including said electron transporting organic material and a metal functioning as an electron donating dopant is formed.  
 
     
     
         20 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive unit comprises, as a layer located on an anode side of said charge generation layer and being adjacent thereto, a layer including an organic metal complex compound including at least one metal ion selected from an alkaline metal ion, an alkaline earth metal ion and a rare earth metal ion, and a reaction generating layer which is formed by an in-situ reduction reaction when a thermally reducible metal, which can reduce a metal ion in said organic metal complex to a metal in a vacuum is deposited on the organic metal complex constituting the layer.  
     
     
         21 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive unit comprises, as a layer located on an anode side of said charge generation layer and being adjacent thereto, a layer including an inorganic compound including at least one metal ion selected from an alkaline metal ion, an alkaline earth metal ion and a rare earth metal ion, and a reaction generating layer which is formed by an in-situ reduction reaction when a thermally reducible metal, which can reduce a metal ion in the inorganic compound to a metal in a vacuum is deposited on the inorganic compound constituting the layer.  
     
     
         22 . The organic electroluminescent device according to  claim 20  or  21 , wherein the thermally reducible metal includes at least one selected from Aluminum, Zirconium, Silicon, Titanium and Tungsten.  
     
     
         23 . The organic electroluminescent device according to  claim 1 , wherein said light-emissive unit comprises a structure, as a layer located on an anode side of said charge generation layer and being adjacent thereto, in which a layer of a mixture including an organic compound and an electron donating dopant is formed, thereafter, a reaction generating layer is generated by an in-situ reduction reaction when a thermally reducible metal, which can reduce an alkaline metal ion, an alkaline earth metal ion or a rare earth metal ion to a metal in a vacuum, is deposited on an organic metal complex compound containing at least one metal ion selected from an alkaline metal ion, an alkaline earth metal ion and a rare earth metal ion.  
     
     
         24 . The organic electroluminescent device according to  claim 1 , wherein said light-emissive unit comprises a structure, as a layer located on an anode side of said charge generation layer and being adjacent thereto, in which a layer of a mixture including an organic compound and an electron donating dopant is formed, thereafter, a reaction generating layer is generated by an in-situ reduction reaction when a thermally reducible metal, which can reduce an alkaline metal ion, an alkaline earth metal ion or a rare earth metal ion to a metal in a vacuum, is deposited on an inorganic compound containing at least one metal ion selected from an alkaline metal ion, an alkaline earth metal ion and a rare earth metal ion.  
     
     
         25 . The organic electroluminescent device according to  claim 1  or  2 , in which said light-emissive unit comprises, as a layer located on a cathode side of said charge generation layer and being adjacent thereto, a hole injection layer comprising a mixture of an organic compound and an electron accepting compound having a property capable of oxidizing said organic compound in terms of Lewis acid chemistry.  
     
     
         26 . The organic electroluminescent device according to  claim 25 , wherein the electron accepting compound having a property capable of oxidizing the organic compound in said hole injection layer in terms of Lewis acid chemistry is provided in a molar ratio of 0.01 to 10 with respect to the organic compound.  
     
     
         27 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive unit comprises, as a layer located on a cathode side of said charge generation layer and being adjacent thereto, a hole injection layer including an electron accepting compound and having a thickness of not more than 30 nm.  
     
     
         28 . The organic electroluminescent device according to  claim 1  or  2 , wherein said light-emissive units each have different emission spectrums.  
     
     
         29 . The organic electroluminescent device according to  claim 1  or  2 , wherein said organic electroluminescent device emits white light due to superimposing of different lights from each light-emissive unit.  
     
     
         30 . The organic electroluminescent device according to  claim 1  or  2 , wherein at least one of said light-emissive units includes a light-emissive layer containing a phosphorescent material.  
     
     
         31 . The organic electroluminescent device according to  claim 1  or  2 , wherein, in each of said light-emissive units, an optical path length from a light-emissive site to a light-reflective metal electrode is an odd-numbered times a quarter wavelength of light.  
     
     
         32 . The organic electroluminescent device according to  claim 1  or  2 , wherein all the layers including said light-emissive units, said charge generation layer, and an electrode layer are formed on a substrate by heating a vaporizable material in a vacuum to deposit one of a vaporized and sublimed material on the substrate; 
 wherein upon depositing said one of vaporized and sublimed material on the substrate, a substrate is transported in a direction of a planar surface thereof, a deposition area being open in a lower surface of the substrate; a container is provided, in a lower position of the transporting substrate, including a vaporizable material having a deposition width which can cover the deposition area extending in a direction perpendicular to the transportation direction of the substrate; and said container is heated to thereby one of vaporize and sublime so as to deposit the vaporizable material provided in the container.  
 
     
     
         33 . The organic electroluminescent device according to  claim 1  or  2 , wherein a combined thickness of said light-emissive units and said charge generation layers, sandwiched between the cathode and the anode, is greater than 1,000 nm (1 μm).  
     
     
         34 . The organic electroluminescent device according to  claim 1  or  2 , wherein said organic electroluminescent device is operated at a driving voltage of more than 25 volts.  
     
     
         35 . The organic electroluminescent device according to  claim 1  or  2 , wherein light can be passed in only one direction which is one of an anode electrode direction and a cathode electrode direction, from a light generation site in the organic electroluminescent device, wherein light advancing in a direction opposite to said only one direction is absorbed by a light-absorbing medium, and wherein, in each of said light-emissive units, a light interference effect is removed so that an adjustment of an optical path length from a light-emissive site of said light-emissive layers to a light-reflective metal electrode is substantially not necessary.  
     
     
         36 . The organic electroluminescent device according to  claim 1  or  2 , wherein a light advancing in one direction which is one of an anode electrode direction and a cathode electrode direction, from a light generation site in the organic electroluminescent device is reflected diffusely by a diffused reflection medium, and wherein, in each of said light-emissive units, a light interference effect is removed, so that an adjustment of an optical path length from a light-emissive site of said light-emissive layers to a light-reflective metal electrode is substantially not necessary.