Nanocrystal electroluminescence device and fabrication method thereof

Abstract

A nanocrystal electroluminescence device comprising a polymer hole transport layer, a nanocrystal light-emitting layer and an organic electron transport layer wherein the nanocrystal light-emitting layer is independently and separately formed between the polymer hole transport layer and the organic electron transport layer. According to the nanocrystal electroluminescence device, since the hole transport layer, the nanocrystal light-emitting layer and the electron transport layer are completely separated from one another, the electroluminescence device provides a pure nanocrystal luminescence spectrum having limited luminescence from other organic layers and substantially no influence by operational conditions, such as voltage. Further, a method for fabricating the nanocrystal electroluminescence device.

1 . An electroluminescence device comprising a polymer hole transport layer, a nanocrystal light-emitting layer and an organic electron transport layer, 
 wherein the nanocrystal light-emitting layer in contact with the polymer hole transport layer is independently formed between the polymer hole transport layer and the organic electron transport layer.    
     
     
         2 . The electroluminescence device according to  claim 1 , wherein the electroluminescence device has a structure consisting of an anode, a polymer hole transport layer, a nanocrystal light-emitting layer, an organic electron transport layer, and a cathode layered in this order on a transparent substrate.  
     
     
         3 . The electroluminescence device according to  claim 2 , further comprising a hole injection layer, an electron blocking layer, a hole blocking layer or an electron/hole blocking layer interposed between the polymer hole transport layer and the anode, or between the organic electron transport layer and the nanocrystal light-emitting layer.  
     
     
         4 . The electroluminescence device according to  claim 1 , wherein the nanocrystal light-emitting layer is made of at least one material selected from the group consisting of metal nanocrystals, Group II-VI compound semiconductor nanocrystals, and Group III-V compound semiconductor nanocrystals and PbS, PbSe and PbTe, wherein the metal nanocrystals include Au, Ag, Pt, Pd, Co, Cu and Mo, the Group II-IV compound semiconductor nanocrystals include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe and HgTe, the Group III-V compound semiconductor nanocrystals include GaN, GaP, GaAs, InP and InAs; and when the nanocrystal light-emitting layer is made of a mixture of two or more nanocrystals, the nanocrystals exist in the state of a simple mixture, fused crystals in which the nanocrystals are partially present in the same crystal structure, or an alloy.  
     
     
         5 . The electroluminescence device according to  claim 1 , wherein the polymer hole transport layer is made of a material selected from the group consisting of poly(3,4-ethylenedioxythiophene) (PEDOT)/polystyrene para-sulfonate (PSS), poly-N-vinylcarbazole derivatives, polyphenylenevinylene derivatives, polyparaphenylene derivatives, polymethacrylate derivatives, poly(9,9-octylfluorene) derivatives, and poly(spiro-fluorene) derivatives.  
     
     
         6 . The electroluminescence device according to  claim 1 , wherein the nanocrystal light-emitting layer has a thickness of 3 nm˜30 nm.  
     
     
         7 . The electroluminescence device according to  claim 1 , wherein the electron transport layer is made of a material selected from the group consisting of oxazoles, isooxazoles, triazoles, isothiazoles, oxydiazoles, thiadiazoles, perylenes, tris(8-hydroxyquinoline)-aluminum (Alq3), Balq, Salq and Almq3; and has a thickness of 10 nm˜100 nm.  
     
     
         8 . The electroluminescence device according to  claim 3 , wherein the electron blocking layer, the hole blocking layer or the electron/hole blocking layer is formed of a material selected from the group consisting of 3-phenyl-4-(1-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), phenanthrolines, imidazoles, triazoles, oxadiazoles, and aluminum complexes; and has a thickness of 5 nm˜50 nm.  
     
     
         9 . A method for fabricating an electroluminescence device, comprising the steps of: 
 patterning a hole-injecting anode on a substrate and forming a polymer hole transport layer thereon;    coating a nanocrystal dispersion on the polymer hole transport layer to form a nanocrystal light-emitting layer;    forming an organic electron transport layer on the nanocrystal light-emitting layer; and    forming an electron-injecting cathode on the organic electron transport layer.    
     
     
         10 . The method according to  claim 9 , wherein the nanocrystal light-emitting layer is formed by dispersing nanocrystals surface-bound by a photosensitive compound in a solvent which does not damage the polymer hole transport layer to obtain a nanocrystal dispersion, and coating the nanocrystal dispersion on the polymer hole transport layer; or dispersing nanocrystals surface-bound by a material containing no photosensitive functional group and a photosensitive compound in a solvent which does not damage the polymer hole transport layer to obtain a nanocrystal dispersion, and coating the nanocrystal dispersion on the polymer hole transport layer.  
     
     
         11 . The method according to  claim 9 , wherein the nanocrystal light-emitting layer is made of at least one material selected from the group consisting of metal nanocrystals, Group II-VI compound semiconductor nanocrystals, Group III-V compound semiconductor nanocrystals, PbS, PbSe and PbTe, the metal nanocrystals including Au, Ag, Pt, Pd, Co, Cu and Mo, the Group II-IV compound semiconductor nanocrystals including CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe and HgTe, the Group III-V compound semiconductor nanocrystals including GaN, GaP, GaAs, InP and InAs; and when the nanocrystal light-emitting layer is made of a mixture of two or more nanocrystals, the nanocrystals exist in the state of a simple mixture, fused crystals in which the nanocrystals are partially present in the same crystal structure, or an alloy.  
     
     
         12 . The method according to  claim 10 , wherein the solvent which does not damage the hole transport layer and disperses the nanocrystals is selected from the group consisting of water, pyridine, ethanol, propanol, butanol, pentanol, hexanol, toluene, chloroform, chlorobenzene, THF, cyclohexane, cyclohexene, methylene chloride, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and mixtures thereof.  
     
     
         13 . The method according to  claim 9 , wherein the electron transport layer is formed by spin coating, dip coating, spray coating, or blade coating.  
     
     
         14 . The method according to  claim 10 , wherein the nanocrystal dispersion has a concentration of 0.01 wt %˜10 wt %.  
     
     
         15 . The method according to  claim 9 , wherein the nanocrystal light-emitting layer has a thickness of 3 nm˜30 nm.  
     
     
         16 . The method according to  claim 9 , wherein the polymer hole transport layer is made of a material selected from the group consisting of poly(3,4-ethylenedioxythiophene) (PEDOT)/polystyrene para-sulfonate (PSS), poly-N-vinylcarbazole derivatives, polyphenylenevinylene derivatives, polyparaphenylene derivatives, polymethacrylate derivatives, poly(9,9-octylfluorene) derivatives, and poly(spiro-fluorene) derivatives.  
     
     
         17 . The method according to  claim 9 , wherein the electron transport layer is formed on the nanocrystal light-emitting layer by thermal deposition, molecular deposition or chemical deposition.  
     
     
         18 . The method according to  claim 9 , further comprising the step of exposing the nanocrystal light-emitting layer to UV light to crosslink it, prior to coating the organic electron transporting material on the nanocrystal light-emitting layer.  
     
     
         19 . The method according to  claim 10 , wherein the photosensitive compound surface-bound to the nanocrystals contains a double bond, a carboxyl group, an amide group, a phenyl group, a biphenyl group, a peroxide group, an amine group, or an acryl group.  
     
     
         20 . The method according to  claim 9 , further comprising the step of inserting a hole injection layer between the anode and the hole transport layer; inserting an electron blocking layer between the nanocrystal light-emitting layer and the hole transport layer; or inserting a hole blocking layer between the nanocrystal light-emitting layer and the electron transport layer.