Organic electroluminescent device

Abstract

An organic electroluminescent device comprises a pair of electrodes and a layer structure provided between the paired electrodes and including, at least, an emission layer comprising a specific type of oligomer. The layer structure may further comprise an electron injection layer and an electron transport layer, one of which comprises a specific type of oligomer. Alternatively, the layer structure may be of the type which comprises an organic layer having a charge transport interference layer in the inside thereof along with an emission layer.

What is claimed is:  
     
         1 . An organic electroluminescent device, which comprises a pair of electrodes, and a layer structure provided between the paired electrodes and including, at least, an emission layer comprising up to 10 mole % of a thiophene oligomer of the following formula  
       
         
           
           
               
               
           
         
       
       wherein R and R′ independently represent H, an alkyl group having from 1 to 10 carbon atoms, an amino group, an aryl group and n is an integer of 2 to 10.  
     
     
         2 . An organic electroluminescent device according to  claim 1 , wherein n is 2 to 7.  
     
     
         3 . An organic electroluminescent device according to  claim 1 , wherein the content of said thiophene oligomer ranges from 0.1 to 5 mole %, based on a composition for said emission layer.  
     
     
         4 . An organic electroluminescent device according to  claim 1 , wherein said layer structure includes a hole injection layer, a hole transport layer and the emission layer formed on one of the electrodes serving as an anode in this order.  
     
     
         5 . An organic electroluminescent device, which comprises a pair of electrodes, and a layer structure provided between the paired electrodes and including an emission layer, a hole injection layer and a hole transport layer wherein at least one of the hole injection layer and the hole transport layer comprises an oligomer selected from the group consisting of a triphenylamine oligomer of the following formula,  
       
         
           
           
               
               
           
         
       
       wherein m is an integer of 2 to 6, a thiophene oligomer define din  claim 1  and mixtures thereof  
       
         
           
           
               
               
           
         
       
       wherein R and R′ independently represent H, an alkyl group having from 1 to 10 carbon atoms, an amino group, an aryl group and n is an integer of 2 to 10.  
     
     
         6 . An organic electroluminescent device according to  claim 5 , wherein said oligomer is present in an amount of 10 to 90 mole % in the at least one layer.  
     
     
         7 . An organic electroluminescent device according to  claim 5 , wherein said electron injection layer and said electron transport layer are combined into one layer made of a mixture of an electron injection material and an electron transport material.  
     
     
         8 . An organic electroluminescent device according to  claim 5 , wherein said oligomer consists of said triphenylamine oligomer.  
     
     
         9 . An organic electroluminescent device according to  claim 5 , wherein said oligomer consists of the thiophene oligomer.  
     
     
         10 . An organic electroluminescent device according to  claim 5 , wherein said oligomer consists of the mixture.  
     
     
         11 . An organic electroluminescent device, which comprises a pair of electrodes and a layer structure provided between the paired electrodes and including an emission layer and at least one organic layer in contact with the emission layer wherein the organic layer comprises a fluorescent material having an absorption peak wavelength shorter than a peak wavelength of luminescence emitted from the emission layer.  
     
     
         12 . An organic electroluminescent device according to  claim 11 , wherein said at least one organic layer includes two organic sub-layers wherein said fluorescent material is present in one of the sub-layers not in contact with the emission layer.  
     
     
         13 . An organic electroluminescent device, which comprises a pair of electrodes, and a layer structure sandwiched between the paired electrodes and including an organic layer capable of transporting electrons or holes and an emission layer wherein the organic layer has a charge transport interference sub-layer therein when the organic layer consists of a hole transport layer made of a hole transport material so that the sub-layer is made of an organic material having an ionization potential greater than the hole transport material of the organic layer, or wherein the organic layer has a charge transport interference sub-layer therein when the organic layer consists of an electron transport layer made of an electron transport material so that the sub-layer is made of an organic material having an electron affinity smaller than the electron transport material of the organic layer.  
     
     
         14 . An organic electroluminescent device comprising a pair of electrodes, and a layer structure sandwiched between the paired electrodes and including a charge transport layer and an emission layer wherein the charge transport layer has a charge transport interference sub-layer therein, and the sub-layer is made of a mixture of both a hole transport material and an electron transport material, an inorganic compound or a metal.  
     
     
         15 . An organic electroluminescent device according to  claim 14 , wherein said sub-layer is made of the mixture.  
     
     
         16 . An organic electroluminescent device according to  claim 15 , wherein said mixture consists of a hole transport material and an electron transport material at a ratio by mole of 1:99 to 99:1.  
     
     
         17 . An organic electroluminescent device according to  claim 14 , wherein said sub-layer is made of an inorganic compound selected from the group consisting of oxides, halides, nitrides, sulfides, hydroxides and mixtures thereof.  
     
     
         18 . An organic electroluminescent device according to  claim 14 , wherein said sub-layer is made of a metal.