Abstract:
An OLED electronic device contains a fullerene chemically bonded to a hole transport layer. The bonding of the fullerene to the hole transport layer improves device lifetime and prevents migration of the fullerene to adjacent layers where deleterious effects may result.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119(e) from Provisional Application No. 61/140,352 filed on Dec. 23, 2008 which is incorporated by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    This disclosure relates in general to electronic devices, and more specifically to carbon structures bonded to organic light-emitting diode (OLED) transport layers as part of the electronic device. 
       BACKGROUND 
       [0003]    Organic electronic devices define a category of products that include an active layer. Such devices convert electrical energy into radiation, detect signals through electronic processes, convert radiation into electrical energy, or include one or more organic semiconductor layers. 
         [0004]    Organic light-emitting diodes (OLEDs) are an organic electronic device comprising an organic layer capable of electroluminescence (“EL”). OLEDs containing conducting polymers can have the following configuration:
       anode/EL material/cathode       
 
         [0006]    The anode is typically any material that is transparent and has the ability to inject holes into the EL material, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. EL materials include fluorescent compounds, fluorescent and phosphorescent metal complexes, conjugated polymers, and mixtures thereof. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the EL material. 
         [0007]    One or more layers may be present between the EL material and the anode and/or cathode. These layers are present primarily for the purpose of charge transport, although they may serve other functions as well. An issue with present OLED devices involves lifetime values of the components used in the OLED device. As the device lifetime is dependent upon the first component to fall outside the required device specifications. A hole transport layer in conjunction with the EL layers, may be one such layer which can strongly influence device lifetime. There is a need, therefore, for hole transport layer(s) exhibiting improved lifetime for the overall electronic device, specifically the OLED device. 
       SUMMARY 
       [0008]    There is provided a hole transport material containing chemically bonded fullerene. Improvements in OLED lifetime of the organic materials is observed when hole transport materials are reacted with fullerenes. 
         [0009]    In one embodiment the electronic device comprises a fullerene and a first layer comprising hole transport material, wherein the fullerene is chemically bonded to the hole transport material. In one embodiment the fullerene is selected from the group consisting of C60, C70 and C84, and combinations thereof. In one embodiment the hole transport material is selected from crosslinked organic compounds and the fullerene is present at 0.1-10% by weight, in another embodiment the hole transport material is selected from non-crosslinked organic compounds and the fullerene is present at 0.01-5% by weight. In one embodiment the crosslinked organic compound contains vinyl functionality as the active bonding site of the fullerene. 
         [0010]    The present disclosure also includes a method of making an electronic device comprising fullerene, hole transport material, and reacting the fullerene with the hole transport material to produce a carbon bonded material. The carbon bonded material is deposited to produce a layer of the electronic device. 
         [0011]    The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Embodiments are illustrated in the accompanying figures to improve understanding of concepts as presented in this disclosure. 
           [0013]      FIG. 1  is a schematic diagram of an organic electronic device. 
           [0014]      FIG. 2  is a summary of lifetime improvement for two hole transport materials when containing fullerene. 
       
    
    
       [0015]    Skilled artisans will appreciate that objects in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the objects in the figures may be exaggerated relative to other objects to help to improve understanding of embodiments. 
       DETAILED DESCRIPTION 
       [0016]    Many aspects and embodiments have been described above and are merely exemplary and not limiting. After reading this specification, skilled artisans will appreciate that other aspects and embodiments are possible without departing from the scope of the invention. 
         [0017]    Other features and benefits of any one or more of the embodiments will be apparent from the following detailed description, and from the claims. The detailed description first addresses Definitions and Clarification of Terms followed by Electronic Devices, and finally Examples. 
       Definitions and Clarification of Terms 
       [0018]    Before addressing details of embodiments described below, some terms are defined or clarified. 
         [0019]    The term “charge transport” is intended to mean when referring to a layer, material, member or structure, such a layer, material, member or structure that promotes or facilitates migration of charges through such a layer, material, member or structure into another layer, material, member or structure. Although some photoactive or electroactive materials may also have charge transport properties, the term “charge transport” is not intended to include materials whose primary function is light emission or light absorption. 
         [0020]    The term “electron transport” refers to charge transport with respect to negative charges. 
         [0021]    The term “hole transport” refers to charge transport with respect to positive charges. 
         [0022]    The term “fullerene” refers to cage-like, hollow molecules composed of hexagonal and pentagonal groups of carbon atoms. In some embodiments, there are at least 60 carbon atoms present in the molecule. 
         [0023]    The term “layer” is used interchangeably with the term “film” and refers to a coating covering a desired area. The term is not limited by size. The area can be as large as an entire device or as small as a specific functional area such as the actual visual display, or as small as a single sub-pixel. 
         [0024]    The term “electroactive” when referring to a layer or material is intended to mean a layer or material that exhibits electronic or electro-radiative properties. An electroactive layer material may emit radiation or exhibit a change in concentration of electron-hole pairs when receiving radiation. 
         [0025]    The term “photoactive” refers to a material that emits light when activated by an applied voltage (such as in an OLED or chemical cell) or responds to radiant energy and generates a signal with or without an applied bias voltage (such as in a photodetector). 
         [0026]    As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
         [0027]    Also, use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
         [0028]    Group numbers corresponding to columns within the Periodic Table of the elements use the “New Notation” convention as seen in the  CRC Handbook of Chemistry and Physics,  81 st  Edition (2000-2001). 
         [0029]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety, unless a particular passage is cited. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
         [0030]    To the extent not described herein, many details regarding specific materials, processing acts, and circuits are conventional and may be found in textbooks and other sources within the organic light-emitting diode display, photodetector, photovoltaic, and semiconductive member arts. 
       Electronic Devices 
       [0031]    Organic electronic devices that may benefit from hole transport layers bonded with a fullerene include, but are not limited to, (1) devices that convert electrical energy into radiation (e.g., a light-emitting diode, light emitting diode display, or diode laser), (2) devices that detect signals through electronics processes (e.g., photodetectors, photoconductive cells, photoresistors, photoswitches, phototransistors, phototubes, IR detectors, biosensors), (3) devices that convert radiation into electrical energy, (e.g., a photovoltaic device or solar cell), and (4) devices that include one or more electronic components that include one or more organic semi-conductor layers (e.g., a transistor or diode). 
         [0032]    One illustration of an organic electronic device structure is shown in  FIG. 1 . The device  100  has a first electrical contact layer, an anode layer  110  and a second electrical contact layer, a cathode layer  160 , and a photoactive layer  140  between them. Additional layers may optionally be present. Adjacent to the anode may be a buffer layer  120 . Adjacent to the buffer layer may be a hole transport layer  130 , comprising hole transport material. Adjacent to the cathode may be an electron transport layer  150 , comprising an electron transport material. As an option, devices may use one or more additional hole injection or hole transport layers (not shown) next to the anode  110  and/or one or more additional electron injection or electron transport layers (not shown) next to the cathode  160 . Layers  120  through  150  are individually and collectively referred to as the active layers. 
         [0033]    In one embodiment, the different layers have the following range of thicknesses: anode 110, 500-5000 Å, in one embodiment 1000-2000 Å; buffer layer 120, 50-2000 Å, in one embodiment 200-1000 Å; hole transport layer 120, 50-2000 Å, in one embodiment 200-1000 Å; photoactive layer 130, 10-2000 Å, in one embodiment 100-1000 Å; layer 140, 50-2000 Å, in one embodiment 100-1000 Å; cathode 150, 200-10000 Å, in one embodiment 300-5000 Å. The desired ratio of layer thicknesses will depend on the exact nature of the materials used. 
         [0034]    The anode  110  is an electrode that is particularly efficient for injecting positive charge carriers. It can be made of, for example materials containing a metal, mixed metal, alloy, metal oxide or mixed-metal oxide, or it can be a conducting polymer, and mixtures thereof. Suitable metals include the Group 11 metals, the metals in Groups 4, 5, and 6, and the Group 8-10 transition metals. If the anode is to be light-transmitting, mixed-metal oxides of Groups 12, 13 and 14 metals, such as indium-tin-oxide, are generally used. The anode may also comprise an organic material such as polyaniline as described in “Flexible light-emitting diodes made from soluble conducting polymer,” Nature vol. 357, pp 477 479 (11 Jun. 1992). At least one of the anode and cathode should be at least partially transparent to allow the generated light to be observed. 
         [0035]    Optional buffer layer  120  comprises buffer materials. The term “buffer layer” or “buffer material” is intended to mean electrically conductive or semiconductive materials and may have one or more functions in an organic electronic device, including but not limited to, planarization of the underlying layer, charge transport and/or charge injection properties, scavenging of impurities such as oxygen or metal ions, and other aspects to facilitate or to improve the performance of the organic electronic device. Buffer materials may be polymers, oligomers, or small molecules, and may be in the form of solutions, dispersions, suspensions, emulsions, colloidal mixtures, or other compositions. 
         [0036]    The buffer layer can be formed with polymeric materials, such as polyaniline (PANI) or polyethylenedioxythiophene (PEDOT), which are often doped with protonic acids. The protonic acids can be, for example, poly(styrenesulfonic acid), poly(2-acrylamido-2-methyl-1-propanesulfonic acid), and the like. The buffer layer  120  can comprise charge transfer compounds, and the like, such as copper phthalocyanine and the tetrathiafulvalene-tetracyanoquinodimethane system (TTF-TCNQ). In one embodiment, the buffer layer  120  is made from a dispersion of a conducting polymer and a colloid-forming polymeric acid. Such materials have been described in, for example, published U.S. patent applications 2004-0102577, 2004-0127637, and 2005/205860. 
         [0037]    Layer  130  comprises hole transport material. Examples of hole transport materials for the hole transport layer have been summarized for example, in Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Vol. 18, p. 837-860, 1996, by Y. Wang. Both hole transporting small molecules and polymers can be used. Commonly used hole transporting molecules include, but are not limited to: 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (TDATA); 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine (MTDATA); N,N′-diphenyl-N,N′-bis(3-methylphenyly[1,1′-biphenyl]-4,4′-diamine (TPD); 4,4′-bis(carbazol-9-yl)biphenyl (CBP); 1,3-bis(carbazol-9-yl)benzene (mCP); 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC); N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine (ETPD); tetrakis-(3-methylphenyl)-N,N,N′,N′-2,5-phenylenediamine (PDA); α-phenyl-4-N,N-diphenylaminostyrene (TPS); p-(diethylamino)benzaldehyde diphenylhydrazone (DEH); triphenylamine (TPA); bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP); 1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline (PPR or DEASP); 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB); N,N,N′,N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TTB); N,N′-bis(naphthalen-1-yl)-N,N′-bis-(phenyl)benzidine (α-NPB); and porphyrinic compounds, such as copper phthalocyanine. Commonly used hole transporting polymers include, but are not limited to, polyvinylcarbazole, (phenylmethyl)polysilane, poly(dioxythiophenes), polyanilines, and polypyrroles. It is also possible to obtain hole transporting polymers by doping hole transporting molecules such as those mentioned above into polymers such as polystyrene and polycarbonate. 
         [0038]    In some embodiments, the hole transport layer comprises a hole transport polymer. In some embodiments, the hole transport polymer is a distyrylaryl compound. In some embodiments, the aryl group is has two or more fused aromatic rings. In some embodiments, the aryl group is an acene. The term “acene” as used herein refers to a hydrocarbon parent component that contains two or more ortho-fused benzene rings in a straight linear arrangement. 
         [0039]    In some embodiments, the hole transport polymer is an arylamine polymer. In some embodiments, it is a copolymer of fluorene and arylamine monomers. 
         [0040]    In some embodiments, the polymer has crosslinkable groups. In some embodiments, crosslinking can be accomplished by a heat treatment and/or exposure to UV or visible radiation. Examples of crosslinkable groups include, but are not limited to vinyl, acrylate, perfluorovinylether, 1-benzo-3,4-cyclobutane, siloxane, and methyl esters. Crosslinkable polymers can have advantages in the fabrication of solution-process OLEDs. The application of a soluble polymeric material to form a layer which can be converted into an insoluble film subsequent to deposition, can allow for the fabrication of multilayer solution-processed OLED devices free of layer dissolution problems. 
         [0041]    Examples of crosslinkable polymers can be found in, for example, published US patent application 2005-0184287 and published PCT application WO 2005/052027. 
         [0042]    In some embodiments, the hole transport layer comprises a polymer which is a copolymer of 9,9-dialkylfluorene and triphenylamine. In some embodiments, the polymer is a copolymer of 9,9-dialkylfluorene and 4,4′-bis(diphenylamino)biphenyl. In some embodiments, the polymer is a copolymer of 9,9-dialkylfluorene and TPB. In some embodiments, the polymer is a copolymer of 9,9-dialkylfluorene and NPB. In some embodiments, the copolymer is made from a third comonomer selected from (vinylphenyl)diphenylamine and 9,9-distyrylfluorene or 9,9-di(vinylbenzyl)fluorene. 
         [0043]    Depending upon the application of the device, the photoactive layer  140  can be a light-emitting layer that is activated by an applied voltage (such as in a light-emitting diode or light-emitting electrochemical cell), a layer of material that responds to radiant energy and generates a signal with or without an applied bias voltage (such as in a photodetector). In one embodiment, the photoactive material is an organic electroluminescent (“EL”) material. Any EL material can be used in the devices, including, but not limited to, small molecule organic fluorescent compounds, fluorescent and phosphorescent metal complexes, conjugated polymers, and mixtures thereof. Examples of fluorescent compounds include, but are not limited to, pyrene, perylene, rubrene, coumarin, derivatives thereof, and mixtures thereof. Examples of metal complexes include, but are not limited to, metal chelated oxinoid compounds, such as tris(8-hydroxyquinolato)aluminum (Alq3); cyclometalated iridium and platinum electroluminescent compounds, such as complexes of iridium with phenylpyridine, phenylquinoline, or phenylpyrimidine ligands as disclosed in Petrov et al., U.S. Pat. No. 6,670,645 and Published PCT Applications WO 03/063555 and WO 2004/016710, and organometallic complexes described in, for example, Published PCT Applications WO 03/008424, WO 03/091688, and WO 03/040257, and mixtures thereof. Electroluminescent emissive layers comprising a charge carrying host material and a metal complex have been described by Thompson et al., in U.S. Pat. No. 6,303,238, and by Burrows and Thompson in published PCT applications WO 00/70655 and WO 01/41512. Examples of conjugated polymers include, but are not limited to poly(phenylenevinylenes), polyfluorenes, poly(spirobifluorenes), polythiophenes, poly(p-phenylenes), copolymers thereof, and mixtures thereof. 
         [0044]    Optional layer  150  can function both to facilitate electron transport, and also serve as a buffer layer or confinement layer to prevent quenching of the exciton at layer interfaces. Preferably, this layer promotes electron mobility and reduces exciton quenching. Examples of electron transport materials which can be used in the optional electron transport layer  150 , include metal chelated oxinoid compounds, including metal quinolate derivatives such as tris(8-hydroxyquinolato)aluminum (AlQ), bis(2-methyl-8-quinolinolato)(p-phenylphenolato) aluminum (BAlq), tetrakis-(8-hydroxyquinolato)hafnium (HfQ) and tetrakis-(8-hydroxyquinolato)zirconium (ZrQ); and azole compounds such as 2- (4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ), and 1,3,5-tri(phenyl-2-benzimidazole)benzene (TPBI); quinoxaline derivatives such as 2,3-bis(4-fluorophenyl)quinoxaline; phenanthrolines such as 4,7-diphenyl-1,10-phenanthroline (DPA) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA); and mixtures thereof. 
         [0045]    The cathode  160 , is an electrode that is particularly efficient for injecting electrons or negative charge carriers. The cathode can be any metal or nonmetal having a lower work function than the anode. Materials for the cathode can be selected from alkali metals of Group 1 (e.g., Li, Cs), the Group 2 (alkaline earth) metals, the Group 12 metals, including the rare earth elements and lanthanides, and the actinides. Materials such as aluminum, indium, calcium, barium, samarium and magnesium, as well as combinations, can be used. Li-containing organometallic compounds, LiF, and Li 2 O can also be deposited between the organic layer and the cathode layer to lower the operating voltage. This layer may be referred to as an electron injection layer. 
         [0046]    It is known to have other layers in organic electronic devices. For example, there can be a layer (not shown) between the anode  110  and buffer layer  120  to control the amount of positive charge injected and/or to provide band-gap matching of the layers, or to function as a protective layer. Layers that are known in the art can be used, such as copper phthalocyanine, silicon oxy-nitride, fluorocarbons, silanes, or an ultra-thin layer of a metal, such as Pt. Alternatively, some or all of anode layer  110 , active layers  120 ,  130 ,  140 , and  150 , or cathode layer  160 , can be surface-treated to increase charge carrier transport efficiency. The choice of materials for each of the component layers is preferably determined by balancing the positive and negative charges in the emitter layer to provide a device with high electroluminescence efficiency. 
         [0047]    It is understood that each functional layer can be made up of more than one layer. 
         [0048]    The device layers can be formed by any deposition technique, or combinations of techniques, including vapor deposition, liquid deposition, and thermal transfer. Substrates such as glass, plastics, and metals can be used. Conventional vapor deposition techniques can be used, such as thermal evaporation, chemical vapor deposition, and the like. The organic layers can be applied from solutions or dispersions in suitable solvents, using conventional coating or printing techniques, including but not limited to spin-coating, dip-coating, roll-to-roll techniques, ink-jet printing, continuous nozzle printing, screen-printing, gravure printing and the like. 
         [0049]    In some embodiments, the device is fabricated by liquid deposition of the buffer layer, the hole transport layer, and the photoactive layer, and by vapor deposition of the anode, the electron transport layer, an electron injection layer and the cathode. 
       Fullerenes 
       [0050]    The hole transport material is bonded to a carbon structure comprising a fullerene. Fullerenes are an allotrope of carbon characterized by a closed-cage structure consisting of an even number of three-coordinate carbon atoms devoid of hydrogen atoms. The fullerenes are well known and have been extensively studied. 
         [0051]    Examples of fullerenes include C60, C60-PCMB, and C70, shown below, 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    as well as C84 and higher fullerenes. Any of the fullerenes may be derivatized with a (3-methoxycarbonyl)-propyl-1-phenyl group (“PCBM”), such as C70-PCBM, C84-PCBM, and higher analogs. Combinations of fullerenes can be used. 
         [0052]    In some embodiments, the fullerene is selected from the group consisting of C60, C60-PCMB, C70, C70-PCMB, and combinations thereof. 
       Examples 
       [0053]    The concepts described herein will be further described in the following examples, which do not limit the scope of the invention described in the claims. 
         [0000]    Reaction of Fullerene with Hole Transport Material 
         [0054]    A polymeric hole transfer material, designated H956, is reacted with a C60 fullerene to produce carbon bonded material. 200 mg of H956 in conjunction with 1.0 mg of C60 is added to 12.0 ml of toluene to produce a light reddish-purple mixture at room temperature. This mixture is exposed to a heating cycle of 1 hour at 85° C., followed by 1 hour at 90° C., followed by 4 hours at 95° C. The resulting mixture was removed from the heating bath and stirred until reaching room temperature. Mixture was precipitated using a 10 fold volume of methanol accompanied by stirring. Precipitate was collected by filtration, washed with additional methanol, and exposed to a vacuum and allowed to dry overnight. 
         [0055]      FIG. 2  illustrates the increase in lifetime for hole transport materials H1431 and H1412 when bonded with C60. Lifetime increases from 8100 and 9100, to 19,500 and 15,000 hours, respectively, are indicative of the substantial advantages in lifetime when fullerenes are bonded to hole transport materials as applied to OLED devices. 
         [0056]    In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. 
         [0057]    Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. 
         [0058]    It is to be appreciated that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. The use of numerical values in the various ranges specified herein is stated as approximations as though the minimum and maximum values within the stated ranges were both being preceded by the word “about.” In this manner slight variations above and below the stated ranges can be used to achieve substantially the same results as values within the ranges. Also, the disclosure of these ranges is intended as a continuous range including every value between the minimum and maximum average values including fractional values that can result when some of components of one value are mixed with those of different value. Moreover, when broader and narrower ranges are disclosed, it is within the contemplation of this invention to match a minimum value from one range with a maximum value from another range and vice versa. 
         [0059]    It is to be appreciated that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.