Patent Publication Number: US-2004058193-A1

Title: White organic light-emitting devices with improved performance

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] Reference is made to commonly assigned U.S. patent application Ser. No. 09/651,624 filed Aug. 30, 2000 by Tukaram K. Hatwar, entitled “White Organic Electroluminescent Devices with Improved Stability and Efficiency”; Ser. No. 09/930,050 filed Aug. 15, 2001 by Tukaram K. Hatwar, entitled “White Organic Electroluminescent Devices with Improved Efficiency”; Ser. No. 10/191,251 filed July, 2002 by Tukaram K. Hatwar, entitled “White Organic Light-Emitting Devices Using Rubrene Layer”; Ser. No. 10/183,242 filed Jun. 27, 2002 by Benjamin P. Hoag et al., entitled “Organic Element for Electroluminescent Devices”; Ser. No. 10/086,067 filed Feb. 28, 2002 by Benjamin P. Hoag et al., entitled “Organic Element for Electroluminescent Devices”; and Ser. No. 10/184,356 filed Jun. 27, 2002 by Lelia Cosimbescu, entitled “Device Containing Green Organic Light-Emitting Diode”, the disclosures of which are incorporated herein. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates to organic light-emitting OLED devices, which produce white light.  
       BACKGROUND OF THE INVENTION  
       [0003] An OLED device includes a substrate, an anode, a hole-transporting layer made of an organic compound, an organic luminescent layer with suitable dopants, an organic electron-transporting layer, and a cathode. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing and capability for full-color flat emission displays. Tang et al. described this multilayer OLED device in their U.S. Pat. Nos. 4,769,292 and 4,885,211.  
       [0004] Efficient white light producing OLED devices are considered as low cost alternative for several applications such as paper-thin light sources, backlights in LCD displays, automotive dome lights, and office lighting. White light producing OLED devices should be bright, efficient, and generally have Commission International d&#39;Eclairage (CIE) chromaticity coordinates of about (0.33, 0.33). In any event, in accordance with this disclosure, white light is that light which is perceived by a user as having a white color.  
       [0005] The following patents and publications disclose the preparation of organic OLED devices capable of emitting white light, comprising a hole-transporting layer and an organic luminescent layer, and interposed between a pair of electrodes.  
       [0006] White light producing OLED devices have been reported before by J. Shi (U.S. Pat. No. 5,683,823) wherein the luminescent layer includes red and blue light-emitting materials uniformly dispersed in a host emitting material. This device has good electroluminescent characteristics, but the concentration of the red and blue dopants are very small, such as 0.12% and 0.25% of the host material. These concentrations are difficult to control during large-scale manufacturing. Sato et al. in JP 07,142,169 discloses an OLED device, capable of emitting white light, made by sticking a blue light-emitting layer next to the hole-transporting layer and followed by a green light-emitting layer having a region containing a red fluorescent layer.  
       [0007] Kido et al., in Science, Vol. 267, p. 1332 (1995) and in APL Vol. 64, p. 815 (1994), report a white light producing OLED device. In this device three emitter layers with different carrier transport properties, each emitting blue, green or red light, are used to generate white light. Littman et al. in U.S. Pat. No. 5,405,709 disclose another white emitting device, which is capable of emitting white light in response to hole-electron recombination, and comprises a fluorescent in a visible light range from bluish green to red. Recently, Deshpande et al., in Applied Physics Letters, Vol. 75, p. 888 (1999), published white OLED device using red, blue, and green luminescent layers separated by a hole blocking layer.  
       [0008] However, these OLED devices require a very small amount of dopant concentrations, making the process difficult to control for large-scale manufacturing. Also, emission color varies due to small changes in the dopant concentration. White OLEDS are used making full-color devices using the color filters. However, the color filter transmits only about 30% of the original light. Therefore, high luminance efficiency and stability are required for the white OLEDs.  
       SUMMARY OF THE INVENTION  
       [0009] It is an object of the present invention to produce an effective white light-emitting organic device.  
       [0010] It is another object of this invention to provide an efficient and stable white light producing OLED device with simple structure and which can be reproduced in manufacturing environment.  
       [0011] It has been found quite unexpectedly that white light producing OLED devices with high luminance efficiency and operational stability can be obtained by doping yellow super rubrene derivative dopants 6,11-diphenyl-5,12-bis(4-(6-methyl-benzothiazol-2-yl)phenyl)naphthacene (DBzR), or 5,6,11,12-tetra(2-naphthyl)naphthacene (NR) in the NPB hole-transporting layer and distyrylamine derivatives blue dopant in the TBADN host light-emitting layer.  
       [0012] The object is achieved by an organic light-emitting diode (OLED) device which produces substantially white light, comprising:  
       [0013] a) an anode;  
       [0014] b) a hole-transporting layer disposed over the anode;  
       [0015] c) a blue light-emitting layer doped with a blue light-emitting compound disposed directly on the hole-transporting layer;  
       [0016] d) an electron-transporting layer disposed over the blue light-emitting layer;  
       [0017] e) a cathode disposed over the electron-transporting layer; and  
       [0018] f) the hole-transporting layer or electron-transporting layer, or both the hole-transporting layer and electron-transporting layer, being selectively doped with the following compound or derivatives thereof which emits light in the yellow region of the spectrum which corresponds to an entire layer or a partial portion of a layer in contact with the blue light-emitting layer:  
                 
 
       [0019]  wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6  represent one or more substituents on each ring where each substituent is individually selected from the following groups:  
       [0020] Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;  
       [0021] Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;  
       [0022] Group 3: carbon atoms from 4 to 24 necessary to complete a fused aromatic ring of naphthyl, anthracenyl, phenanthryl, pyrenyl, or perylenyl;  
       [0023] Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbon atoms such as thiazolyl, furyl, thienyl, pyridyl, quinolinyl or other heterocyclic systems, which may be bonded via a single bond, or may complete a fused heteroaromatic ring system;  
       [0024] Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbon atoms; or  
       [0025] Group 6: fluorine, chlorine, bromine or cyano,  
       [0026] except R 5  and R 6  do not form a fused ring, and at least one of the substituents R 1 , R 2 , R 3 , and R 4  are substituted with a group other than hydrogen.  
       ADVANTAGES  
       [0027] The following are features and advantages of the present invention.  
       [0028] A simplified OLED device for producing white light by having a yellow emitting super rubrene or derivatives thereof dopant 6,11-diphenyl-5,12-bis(4-(6-methyl-benzothiazol-2-yl)phenyl)naphthacene (DBzR), or 5,6,11,12-tetra(2-naphthyl)naphthacene (NR) in the hole-transporting layer, or the electron-transporting layer, or both.  
       [0029] High efficiency white OLEDs can be used to fabricate full-color devices using the substrate with the on chip color filters and integrated thin film transistors.  
       [0030] OLED devices made in accordance with the present invention eliminate the need for using shadow mask for making light-emitting layers in full-color OLED devices.  
       [0031] OLED devices made in accordance with the present invention can be produced with high reproducibility and consistently to provide high light efficiency.  
       [0032] These devices have high operational stability and also require low drive voltage. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0033]FIG. 1 depicts a prior art organic light-emitting device;  
     [0034]FIG. 2 depicts another prior art organic light-emitting device;  
     [0035]FIG. 3 depicts a white light producing OLED device wherein the hole-transporting layer is doped with the super rubrene yellow dopant;  
     [0036]FIG. 4 depicts another structure of white light producing OLED device wherein hole-transporting layer is doped with super rubrene yellow dopant and has two sub layers;  
     [0037]FIG. 5 depicts a white light producing OLED device wherein the electron-transporting layer is doped with DBzR yellow dopant;  
     [0038]FIG. 6 depicts another structure of white light producing OLED device wherein both the hole-transporting layer and the electron-transporting layer are doped with super rubrene yellow dopant;  
     [0039]FIG. 7 depicts another structure of white light producing OLED device wherein both the hole-transporting layer and the electron-transporting layer are doped with super rubrene yellow dopant and has two sub layers;  
     [0040]FIG. 8 depicts a white light producing OLED device wherein the hole-transporting layer is doped with the super rubrene yellow dopant and has additional green-emitting layer;  
     [0041]FIG. 9 depicts another structure of white light producing OLED device wherein hole-transporting layer is doped with super rubrene yellow dopant and has two sub layers and has additional green-emitting layer;  
     [0042]FIG. 10 depicts a white light producing OLED device wherein the electron-transporting layer is doped with DBzR yellow dopant and has additional green-emitting layer;  
     [0043]FIG. 11 depicts another structure of white light producing OLED device wherein both the hole-transporting layer and the electron-transporting layer are doped with super rubrene yellow dopant and has additional green-emitting layer;  
     [0044]FIG. 12 depicts another structure of white light producing OLED device wherein both the hole-transporting layer and the electron-transporting layer are doped with super rubrene yellow dopant and has two sub layers. and has additional green-emitting layer;  
     [0045]FIG. 13 shows relative luminance change as a function of operation time for the three devices of Table 7; and  
     [0046]FIG. 14 shows relative luminance as a function of current density for four devices with several different combinations of the blue dopant and the yellow dopants I) rubrene with TBP II) NR with TBP, III) DBzR with TBP, IV) rubrene with B-1 V) NR with B-1, III) DBzR with B-1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0047] A conventional light-emitting layer of the organic OLED device comprises a luminescent or fluorescent material where electroluminescence is produced as a result of electron-hole pair recombination in this region. In the simplest construction, the device  100  as shown in FIG. 1 has a substrate  110  and a light-emitting layer  140  sandwiched between anode  120  and cathode  170 . The light-emitting layer  140  is a pure material with a high luminescent efficiency. A well known material is tris(8-quinolinato) aluminum (Alq) which produces excellent green electroluminescence.  
     [0048] The simple structure can be modified to a three-layer structure (device  200 ) as shown in FIG. 2, in which an additional electroluminescent layer is introduced between the hole and electron-transporting layers to function primarily as the site for hole-electron recombination and thus electro-luminescence. In this respect, the functions of the individual organic layers are distinct and can therefore be optimized independently. Thus, the electroluminescent or recombination layer can be chosen to have a desirable OLED color as well as high luminance efficiency. Likewise, the electron and hole-transporting layers can be optimized primarily for the carrier transport property. It will be understood to those skilled in the art that the electron-transporting layer and the cathode can be made to be transparent thus facilitating illumination of the device through its top layer and not through the substrate.  
     [0049] Turning to FIG. 2, an organic light-emitting device  200  has a light-transmissive substrate  210  on which is disposed a light-transmissive anode  220 . An organic light-emitting structure is formed between the anode  220  and a cathode  270 . The organic light-emitting structure is comprised of, in sequence, an organic hole-transporting layer  240 , an organic light-emitting layer  250 , and an organic electron-transporting layer  260 . Layer  230  is a hole-injecting layer. When an electrical potential difference (not shown) is applied between the anode  220  and the cathode  270 , the cathode will inject electrons into the electron-transporting layer  240 , and the electrons will migrate across layer  260  to the light-emitting layer  250 . At the same time, holes will be injected from the anode  220  into the hole-transporting layer  240 . The holes will migrate across layer  240  and recombine with electrons at or near a junction formed between the hole-transporting layer  240  and the light-emitting layer  250 . When a migrating electron drops from its conduction band to a valance band in filling a hole, energy is released as light, and which is emitted through the light-transmissive anode  220  and substrate  210 .  
     [0050] The organic OLED devices can be viewed as a diode, which is forward biased when the anode is at a higher potential than the cathode. The anode and cathode of the organic OLED device can each take any convenient conventional form, such as any of the various forms disclosed by Tang et al. in U.S. Pat. No. 4,885,211. Operating voltage can be substantially reduced when using a low-work function cathode and a high-work function anode. The preferred cathodes are those constructed of a combination of a metal having a work function less than 4.0 eV and one other metal, preferably a metal having a work function greater than 4.0 eV. The Mg:Ag of Tang et al. U.S. Pat. No. 4,885,211 constitutes one preferred cathode construction. The Al:Mg cathodes of Van Slyke et al. U.S. Pat. No. 5,059,062 is another preferred cathode construction. Hung et al. in U.S. Pat. No. 5,776,622 has disclosed the use of a LiF/Al bilayer to enhanced electron injection in organic OLED devices. Cathodes made of either Mg:Ag, Al:Mg or LiF/Al are opaque and displays cannot be viewed through the cathode. Recently, series of publications Gu et al. in APL 68, 2606 (1996); Burrows et al., J. Appl. Phys. 87, 3080 (2000); Parthasarathy et al. APL 72, 2138 9198); Parthasarathy et al. APL 76, 2128 (2000), and Hung et al. APL, 3209 (1999) have disclosed transparent cathode. Cathode based on the combination of thin semitransparent metal (˜100 A) and indium-tin-oxide (ITO) on top of the metal. An organic layer of copper phthalocyanine (CuPc) also replaced thin metal.  
     [0051] Conventionally, anodes  220  is formed of a conductive and transparent oxide. Indium tin oxide has been widely used as the anode contact because of its transparency, good conductivity, and high-work function.  
     [0052] In a preferred embodiment, an anode  220  can be modified with a hole-injecting layer  230 . The hole-injecting material can serve to improve the film formation property of subsequent organic layers and to facilitate injection of holes into the hole-transporting layer. Suitable materials for use in the hole-injecting layer include, but are not limited to, porphyrinic compounds such as CuPC as described in U.S. Pat. No. 4,720,432, and plasma-deposited fluorocarbon polymers as described in U.S. Pat. No. 6,208,075. and some aromatic amines, for example, m-MTDATA (4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine). Alternative hole-injecting materials reportedly useful in organic EL devices are described in EP 0 891 121 A1 and EP 1 029 909 A1. An example of material in such a hole-injecting layer are the fluorocarbons disclosed by Hung U.S. patent application Ser. No. 09/186,829 filed Nov. 5, 1998, the disclosure of which is incorporated herein by reference.  
     [0053] The OLED device of this invention is typically provided over a supporting substrate  210  where either the cathode or anode can be in contact with the substrate. The electrode in contact with the substrate is conveniently referred to as the bottom electrode. Conventionally, the bottom electrode is the anode, but this invention is not limited to that configuration. The substrate can either be light-transmissive or opaque, depending on the intended direction of light emission. The light-transmissive property is desirable for viewing the EL emission through the substrate. Transparent glass or plastic is commonly employed in such cases. For applications where the EL emission is viewed through the top electrode, the transmissive characteristic of the bottom support is immaterial, and therefore can be light-transmissive, light absorbing or light reflective. Substrates for use in this case include, but are not limited to, glass, plastic, semiconductor materials, silicon, ceramics, circuit board materials, and polished metal surface. Of course, it is necessary to provide in these device configurations a light-transparent top electrode.  
     [0054] The white OLED emission can be used to prepare a full-color device using red, green, and blue (RGB) color filters. The RGB filters may be deposited on the substrate (when light transmission is through the substrate), incorporated into the substrate, or deposited over the top electrode (when light transmission is through the top electrode). When depositing a RGB filter array over the top electrode, a buffer layer may be used to protect the top electrode. The buffer layer may comprise inorganic materials, for example, silicon oxides and nitrides, or organic materials, for example, polymers, or multiple layers of inorganic and organic materials. Methods for providing RGB filter arrays are well known in the art. Lithographic means, inkjet printing, and laser thermal transfer are just a few of the methods RGB filters may be provided.  
     [0055] This technique of producing of full-color display using white light plus RGB filters has several advantages over the precision shadow masking technology used for producing the full-colors. This technique does not require precision alignment, is low cost and easy to manufacture. The substrate itself contains thin film transistors to address the individual pixels. U.S. Pat. Nos. 5,550,066 and 5,684,365 to Ching and Hseih describe the addressing methods of the TFT substrates.  
     [0056] The hole-transporting layer contains at least one hole-transporting compound such as an aromatic tertiary amine, where the latter is understood to be a compound containing at least one trivalent nitrogen atom that is bonded only to carbon atoms, at least one of which is a member of an aromatic ring. In one form the aromatic tertiary amine can be an arylamine, such as a monoarylamine, diarylamine, triarylamine, or a polymeric arylamine. Exemplary monomeric triarylamines are illustrated by Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable triarylamines substituted with one or more vinyl radicals and/or comprising at least one active hydrogen containing group are disclosed by Brantley et al. U.S. Pat. Nos. 3,567,450 and 3,658,520.  
     [0057] A more preferred class of aromatic tertiary amines are those which include at least two aromatic tertiary amine moieties as described in U.S. Pat. Nos. 4,720,432 and 5,061,569. The hole-transporting layer can be formed of a single or a mixture of aromatic tertiary amine compounds. Illustrative of useful aromatic tertiary amines is the following:  
     [0058] 1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane  
     [0059] 1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane  
     [0060] 4,4′-Bis(diphenylamino)quadriphenyl  
     [0061] Bis(4-dimethylamino-2-methylphenyl)-phenylmethane N,N,N-Tri(p-tolyl)amine  
     [0062] 4-(di-p-tolylamino)-4′-[4(di-p-tolylamino)-styryl]stilbene  
     [0063] N,N,N′,N′-Tetra-p-tolyl-4-4′-diaminobiphenyl  
     [0064] N,N,N′,N′-Tetraphenyl-4,4′-diaminobiphenyl  
     [0065] N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl  
     [0066] N,N,N′,N ′-tetra-2-naphthyl-4,4′-diaminobiphenyl  
     [0067] N-Phenylcarbazole  
     [0068] 4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)  
     [0069] 4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB)  
     [0070] 4,4″-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl  
     [0071] 4,4′-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl  
     [0072] 4,4′-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl  
     [0073] 1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene  
     [0074] 4,4′-Bis[N-(9-anthryl)-N-phenylamino]biphenyl  
     [0075] 4,4″-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl  
     [0076] 4,4′-Bis[N-(2-phenantheryl)-N-phenylamino]biphenyl  
     [0077] 4,4′-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl  
     [0078] 4,4′-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl  
     [0079] 4,4′-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl  
     [0080] 4,4′-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl  
     [0081] 4,4′-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl  
     [0082] 2,6-Bis(di-p-tolylamino)naphthalene  
     [0083] 2,6-Bis[di-(1-naphthyl)amino]naphthalene  
     [0084] 2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene  
     [0085] N,N,N′,N′-Tetra(2-naphthyl)-4,4″-diamino-p-terphenyl  
     [0086] 4,4′-Bis {N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl  
     [0087] 4,4′-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl  
     [0088] 2,6-Bis[N,N-di(2-naphthyl)amine]fluorene  
     [0089] 1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene  
     [0090] 4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA)  
     [0091] 4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD)  
     [0092] Another class of useful hole-transporting materials includes polycyclic aromatic compounds as described in EP 1 009 041. Tertiary aromatic amines with more than two amine groups may be used including oligomeric materials. In addition, polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also called PEDOT/PSS.  
     [0093] Preferred materials for use in forming the electron-transporting layer of the organic OLED devices of this invention are metal chelated oxinoid compounds, including chelates of oxine itself (also commonly referred to as 8-quinolinol or 8-hydroxyquinoline) as disclosed in U.S. Pat. No. 4,885,211. Such compounds exhibit both high levels of performance and are readily fabricated in the form of thin layers. Some examples of useful electron-transporting materials are:  
     [0094] CO-1: Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III)] 
     [0095] CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)] 
     [0096] CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)  
     [0097] CO-4: Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato) aluminum(III)  
     [0098] CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium] 
     [0099] CO-6: Aluminum tris(5-methyloxine) [alias, tris(5-methyl-8-quinolinolato) aluminum(III)] 
     [0100] CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)] 
     [0101] CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)] 
     [0102] CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)] 
     [0103] Other electron-transporting materials include various butadiene derivatives as disclosed in U.S. Pat. No. 4,356,429 and various heterocyclic optical brighteners as described in U.S. Pat. No. 4,539,507. Benzazoles and triazines are also useful electron-transporting materials.  
     [0104] A preferred embodiment of the luminescent layer consists of a host material doped with fluorescent dyes. Using this method, highly efficient EL devices can be constructed. Simultaneously, the color of the EL devices can be tuned by using fluorescent dyes of different emission wavelengths in a common host material. Tang et al. in commonly assigned U.S. Pat. No. 4,769,292 has described this dopant scheme in considerable details for EL devices using Alq as the host material.  
     [0105] Shi et al. in commonly assigned U.S. Pat. No. 5,935,721 has described this dopant scheme in considerable details for the blue emitting OLED devices using 9,10-di-(2-naphthyl)anthracene (ADN) derivatives as the host material.  
     [0106] Derivatives of 9,10-di-(2-naphthyl)anthracene (Formula 1) constitute one class of useful hosts capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 400 nm, e.g., blue, green, yellow, orange, or red.  
                 
 
     [0107] wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6  represent one or more substituents on each ring where each substituent is individually selected from the following groups:  
     [0108] Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;  
     [0109] Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;  
     [0110] Group 3: carbon atoms from 4 to 24 necessary to complete a fused aromatic ring of naphthyl, anthracenyl; phenanthryl, pyrenyl, or perylenyl;  
     [0111] Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbon atoms such as thiazolyl, furyl, thienyl, pyridyl, quinolinyl or other heterocyclic systems, which may be bonded via a single bond, or may complete a fused heteroaromatic ring system;  
     [0112] Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbon atoms; or  
     [0113] Group 6: fluorine, chlorine, bromine or cyano,  
     [0114] except R 5  and R 6  do not form a fused ring; and at least one of the substituents R 1 , R 2 , R 3 , and R 4  are substituted with a group other than hydrogen.  
     [0115] It is desirable that these substitutions should yield a shift to lower emission energy relative to rubrene. Preferred groups for substitution on R 1 -R 4  are Groups 3 and 4.  
     [0116] Illustrative examples include 9,10-di-(2-naphthyl)anthracene (ADN) and 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN). Other anthracene derivatives can be useful as a host in the LEL, such as diphenylanthracene and its derivatives, as described in U.S. Pat. No. 5,927,247. Styrylarylene derivatives as described in U.S. Pat. No. 5,121,029 and JP 08333569 are also useful hosts for blue emission. For example, 9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene and 4,4′-Bis(2,2-diphenylethenyl)-1,1′-biphenyl (DPVBi) are useful hosts for blue emission.  
     [0117] Many blue fluorescent dopants are known in the art, and are contemplated for use in the practice of this invention. Particularly useful classes of blue-emitting dopants include perylene and its derivatives such as 2,5,8,11-tetra-tert-butyl perylene (TBP), and distyrylamine derivatives as described in U.S. Pat. No. 5,121,029, such as B 1 (structure shown below)  
                 
 
     [0118] Another useful class of blue-emitting dopants is represented by Formula 2 and is described in commonly assigned U.S. patent application Ser. No. 10/183,242 filed Jun. 27, 2002 by Benjamin P. Hoag et al., entitled “Organic Element for Electroluminescent Devices”; the disclosure of which is incorporated herein.  
                 
 
     [0119] Formula 2  
     [0120] wherein:  
     [0121] A and A′ represent independent azine ring systems corresponding to 6-membered aromatic ring systems containing at least one nitrogen;  
     [0122] each X a  and X b  is an independently selected substituent, two of which may join to form a fused ring to A or A′;  
     [0123] m and n are independently 0 to 4;  
     [0124] Z a  and Z b  are independently selected substituents; and  
     [0125] 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are independently selected as either carbon or nitrogen atoms.  
     [0126] Desirably, the azine rings are either quinolinyl or isoquinolinyl rings such that 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are all carbon; m and n are equal to or greater than 2; and X a  and X b  represent at least two carbon substituents which join to form an aromatic ring. Desirably, Z a  and Z b  are fluorine atoms.  
     [0127] Preferred embodiments further include devices where the two fused ring systems are quinoline or isoquinoline systems; the aryl or heteroaryl substituent is a phenyl group; there are present at least two X a  groups and two X b  groups which join to form a 6-6 fused ring, the fused ring systems are fused at the 1-2, 3-4, 1′-2′, or 3′-4′ positions, respectively; one or both of the fused rings is substituted by a phenyl group; and where the dopant is depicted in Formula 3, 4, or 5.  
                 
 
     [0128] wherein each X c , X d , X e , X f , X g , and X h  is hydrogen or an independently selected substituent, one of which must be an aryl or heteroaryl group.  
     [0129] Desirably, the azine rings are either quinolinyl or isoquinolinyl rings such that 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are all carbon; m and n are equal to or greater than 2; and X a  and X b  represent at least two carbon substituents which join to form an aromatic ring, and one is an aryl or substituted aryl group. Desirably, Z a  and Z b  are fluorine atoms.  
     [0130] Illustrative, non-limiting examples of boron compounds complexed by two ring nitrogens of a deprotonated bis(azinyl)amine ligand, wherein the two ring nitrogens are members of different 6,6 fused ring systems in which at least one of the systems contains an aryl or heteroaryl substituent, useful in the present invention are the following:  
                 

                 
 
     [0131] Preferred materials for uses as a yellow-emitting dopant in the hole-transporting or electron-transporting layers are those represented by Formula 6.  
                 
 
     [0132] wherein R 1 , R 2 , R 3 , and R 4  represent one or more substituents on each ring where each substituent is individually selected from the following groups:  
     [0133] Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;  
     [0134] Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;  
     [0135] Group 3: carbon atoms from 4 to 24 necessary to complete a fused aromatic ring of naphthyl, anthracenyl; phenanthryl, pyrenyl, or perylenyl;  
     [0136] Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbon atoms such as thiazolyl, furyl, thienyl, pyridyl, quinolinyl or other heterocyclic systems, which may be bonded via a single bond, or may complete a fused heteroaromatic ring system;  
     [0137] Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbon atoms; or  
     [0138] Group 6: fluorine, chlorine, bromine or cyano.  
     [0139] R 5  and R 6  are defined in the same way as R 1 -R 4  except that they do not form a fused ring.  
     [0140] Further, at least one of R 1 -R 4  must be substituted with a group other than hydrogen. It is desirable that these substitutions should yield a shift to lower emission energy relative to rubrene. Preferred groups for substitution on R 1 -R 4  are Groups 3 and 4.  
     [0141] In order to facilitate an understanding of the present invention and to simplify the following discussion, all of the yellow light-emitting dopant compounds defined above will sometimes be referred to as “super rubrene”.  
     [0142] Examples of particularly useful super rubrene dopants include include 6,11-diphenyl-5,12-bis(4-(6-methyl-benzothiazol-2-yl)phenyl)naphthacene (DBzR) and 5,6,11,12-tetra(2-naphthyl)naphthacene (NR), the formulas of which are shown below:  
                 
 
     [0143] Coumarins represent a useful class of green-emitting dopants as described by Tang et al. in U.S. Pat. Nos. 4,769,292 and 6,020,078. Examples of useful green-emitting coumarins include C545T and C545TB. Quinacridones represent another useful class of green-emitting dopants. Useful quinacridones are described in U.S. Pat. No. 5,593,788, publication JP 09-13026A, and commonly assigned U.S. patent application Ser. No. 10/184,356 filed Jun. 27, 2002 by Lelia Cosimbescu, entitled “Device Containing Green Organic Light-Emitting Diode”, the disclosure of which is incorporated herein.  
     [0144] Examples of particularly useful green-emitting quinacridones are shown below:  
                 
 
     [0145] Another useful class of green-emitting dopants is represented by Formula 7 below.  
     [0146] Compounds useful in the invention are suitably represented by Formula 7.  
                 
 
     [0147] wherein:  
     [0148] A and A′ represent independent azine ring systems corresponding to 6-membered aromatic ring systems containing at least one nitrogen;  
     [0149] each X a  and X b  is an independently selected substituent, two of which may join to form a fused ring to A or A′;  
     [0150] m and n are independently 0 to 4;  
     [0151] Y is H or a substituent;  
     [0152] Z a  and Z b  are independently selected substituents; and  
     [0153] 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are independently selected as either carbon or nitrogen atoms.  
     [0154] In the device, 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are conveniently all carbon atoms. The device may desirably contain at least one or both of ring A or A′ that contains substituents joined to form a fused ring. In one useful embodiment, there is present at least one X a  or X b  group selected from the group consisting of halide and alkyl, aryl, alkoxy, and aryloxy groups. In another embodiment, there is present a Z a  and Z b  group independently selected from the group consisting of fluorine and alkyl, aryl, alkoxy and aryloxy groups. A desirable embodiment is where Z a  and Z b  are F. Y is suitably hydrogen or a substituent such as an alkyl, aryl, or heterocyclic group.  
     [0155] The emission wavelength of these compounds may be adjusted to some extent by appropriate substitution around the central bis(azinyl)methene boron group to meet a color aim, namely green. Some examples of useful formulas follow:  
                 
 
     [0156] The invention and its advantages are further illustrated by the specific examples that follow. The term “percentage” indicates the volume percentage (or a thickness ration as measured on the thin film thickness monitor) of a particular dopant with respect to the host material.  
     [0157] FIGS.  3 - 14  shows schematics of the white light producing OLED device structure prepared of the present invention and graphs of various parameters of their operations. The invention and its advantages are further illustrated by the specific examples that follow.  
     [0158] Turning to FIG. 3, an organic white light-emitting device  300  has a light-transmissive substrate  310  on which is disposed a light-transmissive anode  320 . An organic white light-emitting structure  300  is formed between the anode  320  and a cathode  370 . The organic light-emitting structure is comprised of, in sequence, a hole-injecting layer  330 , and an organic hole-transporting layer  340 , which is doped with super rubrene yellow dopants. An organic light-emitting layer  350  is blue light-emitting layer comprising TBADN host and B-1 dopant. An organic electron-transporting layer  360  is made of Alq.  
     [0159]FIG. 4 depicts an organic white light-emitting device  400  which is similar to that shown in FIG. 3, except that the organic hole-transporting layer comprises two sub layers, layers  441  and layer  442 . Layer  442  is made of undoped NPB and the layer  441 , which is adjacent to the blue light-emitting layer  450 , is doped with super rubrene yellow dopant. Other layers of the structure  400  are substrate  410 , anode  420 , hole-injecting layer  430 , electron-transporting layer  460 , and cathode  470 .  
     [0160]FIG. 5 depicts an organic white light-emitting device  500 . The electron-transporting layer comprises two sub layers,  561  and  562 . Electron-transporting sub layer  561  is doped with the super rubrene yellow dopant. Electron-transporting sub layer  562  is not doped with a light-emitting dopant. The blue light-emitting layer  550  comprises TBADN host and B-1 blue dopant. Other layers of the structure  500  are substrate  510 , anode  520 , hole-injecting layer  530 , and cathode  570 .  
     [0161]FIG. 6 depicts an organic white light-emitting device  600 , which is a combination of the structure  300  and structure  500 . The hole-transporting layer  640  is doped with a super rubrene yellow dopant. The electron-transporting layer comprises two electron-transporting sub layers,  661  and  662 , and sub layer  661  is doped with a super rubrene yellow dopant. The blue light-emitting layer  650  is made of TBADN host with B-1 blue dopant. This device shows very high stability and high luminance efficiency. Other layers of the structure  600  are substrate  610 , anode  620 , hole-injecting layer  630 , electron-transporting layer  662 , and cathode  670 .  
     [0162]FIG. 7 depicts an organic white light-emitting device  700  which is similar to that shown in FIG. 6, except that the organic hole-transporting layer consists of two sub layers, sub layers  741  and layer  742 . Layer  742  is made of undoped NPB, and the layer  741  adjacent to the blue light-emitting layer  750  is doped with a super rubrene yellow dopant. The electron-transporting layer comprises two sub layers, sub layers  761  and  762 . Electron-transporting sub layer  761  is adjacent to the blue light-emitting layer  750 , and is also doped with super rubrene. Electron-transporting sub layer  762  is not doped with a light-emitting dopant. Other layers of the structure  700  are substrate  710 , anode  720 , hole-injecting layer  730 , and cathode  770 .  
     [0163]FIG. 8 depicts an organic white light-emitting device  800  that is similar to that shown in FIG. 3, except that the electron-transporting layer comprises two sub layers,  861  and  862 . Electron-transporting sub layer  861  comprises a green-emitting dopant such as C545T, CFDMQA and DPQA, and layer  861  is adjacent to the blue light-emitting layer  850 . Electron-transporting sub layer  862  is not doped with a light-emitting dopant. The blue light-emitting layer is  850  and consists of TBADN host and B-1 blue dopant. The hole-transporting layer  840  is doped with super rubrene yellow dopant. Other layers of the structure  800  are substrate  810 , anode  820 , hole-injecting layer  830 , and cathode  870 .  
     [0164]FIG. 9 depicts an organic white light-emitting device  900  which is similar to that shown in FIG. 8, except that the organic hole-transporting layer comprises two sub layers,  941  and  942 . Hole-transporting sub layer  942  is made of undoped NPB, and the layer  941  adjacent to the blue light-emitting layer  950  is doped with super rubrene yellow dopant. The electron-transporting layer comprises two sub layers,  961  and  962 . The electron-transporting sub layer  961  is adjacent to the blue light-emitting layer  950 , and comprises Alq doped with green dopants such as C545T, CFDMQA and DPQA dopants. Electron-transporting sub layer  962  is not doped with a light-emitting dopant. The blue light-emitting layer is  950  and consists of TBADN host and B-1 blue dopant. Other layers of the structure  900  are substrate  910 , anode  920 , hole-injecting layer  930 , and cathode  970 .  
     [0165]FIG. 10 depicts an organic white light-emitting device  1000 . Here, the electron-transporting layer comprises three sub layers,  1061 ,  1062 , and  1063 . The electron-transporting sub layer  1061  is doped with the super rubrene yellow dopant, and this layer is adjacent to the blue light-emitting layer  1050 . Electron-transporting sub layer  1062  comprises a green-emitting dopant such as C545T, CFDMQA or DPQA. Electron-transporting sub layer  1063  is not doped with a light-emitting dopant. The blue light-emitting layer  1050  can comprise TBADN host and B-1 blue dopant. Other layers of the structure  1000  are substrate  1010 , anode  1020 , hole-injecting layer  1030 , hole-transporting layer  1040 , and cathode  1070 .  
     [0166]FIG. 11 depicts an organic white light-emitting device  1100 . Here, the electron-transporting layer comprises three sub layers,  1161 ,  1162 , and  1163 . The electron-transporting sub layer  1161  is doped with the super rubrene yellow dopant, and this layer is adjacent to the blue light-emitting layer  1150 . Electron-transporting sub layer  1162  comprises a green-emitting dopant such as C545T, CFDMQA or DPQA. Electron-transporting sub layer  1163  is not doped with a light-emitting dopant. The blue light-emitting layer  1150  can comprise TBADN host and B-1 blue dopant. The hole-transporting layer  1140  is both doped with a super rubrene yellow dopant. This device shows very high stability, high luminance efficiency, and good spectral radiance for all colors after the R, G, B color filters. Other layers of the structure  1100  are substrate  1110 , anode  1120 , hole-injecting layer  1130 , and cathode  1170 .  
     [0167]FIG. 12 depicts an organic white light-emitting device  1200 . Here, the electron-transporting layer comprises three sub layers,  1261 ,  1262 , and  1263 . The electron-transporting sub layer  1261  is doped with the super rubrene yellow dopant, and this layer is adjacent to the blue light-emitting layer  1250 . Electron-transporting sub layer  1262  comprises a green-emitting dopant such as C545T, CFDMQA or DPQA. Electron-transporting sub layer  1263  is not doped with a light-emitting dopant. The blue light-emitting layer  1250  can comprise TBADN host and B-1 blue dopant. The hole-transporting layer comprises two sub layers,  1241  and  1242 . Hole-transporting sub layer  1241  is undoped NPB. Hole-transporting sub layer 1242 is adjacent to blue light-emitting layer  1250 , and is doped with a super rubrene yellow dopant. Other layers of the structure  1200  are substrate  1210 , anode  1220 , hole-injecting layer  1230 , and cathode  1170 .  
     [0168] The invention and its advantages are further illustrated by the specific following examples.  
     DEVICES EXAMPLES 1 TO 6  
     Table 1  
     [0169] An OLED device was constructed in the following manner.  
     [0170] Substrates coated with 80 nm ITO were sequentially ultrasonicated in a commercial detergent, rinsed in deionized water, and degreased in toluene vapor. These substrates were treated with an oxygen plasma for about one minute and coated with one nm fluorocarbon layer by plasma assisted deposition of CHF 3 . The same procedure was used for preparing all other devices described in this invention.  
     [0171] These substrates were loaded into a deposition chamber for organic layers and cathode depositions.  
     [0172] Device of Example 1 was prepared by sequential deposition of 150 nm NPB hole-transporting layer (HTL), 20 nm blue light-emitting layer (LEL) comprising TBADN host with 2% TBP blue dopant, 37.5 nm Alq electron-transporting layer (ETL), and then 0.5 nm LiF and 200 nm Al as a part of cathode. The above sequence completed the deposition of the OLED device.  
     [0173] The OLED device was then hermetically packaged in a dry glove box filled with nitrogen for protection against ambient environment. The ITO patterned substrates used for preparing these OLED devices contained several test patterns. Each of the devices was tested for current voltage characteristics and the electroluminescence yield.  
     [0174] Devices of Examples 2 to 6 were prepared following structure of OLED  300  as shown in FIG. 3. NPB hole-transporting layer of 150 nm thickness was doped with varying amount of rubrene concentrations varying from 1% to 5%. It was found that the device of Example 1 has emission in the blue region of the electromagnetic spectrum, while the emission from devices of Examples 2 to 6 is either white or bluish white or yellowish-white. Table 1 shows luminance, color coordinates, and drive voltage for devices 1 to 6 prepared using rubrene yellow dopant in the hole-transporting layer, and TBP dopant in the TBADN blue light-emitting layer. The maximum luminance efficiency obtained from the devices of Examples 2 to 6 was about 3.9 cd/A.  
               TABLE 1                          White devices characteristics using Rubrene doping into HTL with TBADN + TBP as a Blue LEL                                                                     HTL layer   Rubrene doping               Drive       EL peak               Device   Example   thickness   into 150 nm   Blue Light-emitting           Volt.   Luminance   pos       Example #   type   (nm)   HTL layer   layer   ETL layer   Cathode   (V)   Yield (cd/A)   (nm)   ClEx   ClEy               1   Comparison   150 nm   0   20 nm TBADN + 2%   35 nm Alq   200 nm   7.4   3.1   464   0.15   0.25                       TBP       MgAg       2   Comparison   150 nm   1%   20 nm TBADN + 2%   35 nm Alq   200 nm   7.0   3.3   464   0.24   0.31                       TBP       MgAg       3   Comparison   150 nm   2%   20 nm TBADN + 2%   35 nm Alq   200 nm   7.0   3.9   464   0.31   0.36                       TBP       MgAg       4   Comparison   150 nm   3%   20 nm TBADN + 2%   35 nm Alq   200 nm   7.1   3.9   464   0.34   0.38                       TBP       MgAg       5   Comparison   150 nm   4%   20 nm TBADN + 2%   35 nm Alq   200 nm   7.0   3.8   464   0.36   0.40                       TBP       MgAg       6   Comparison   150 nm   5%   20 nm TBADN + 2%   35 nm Alq   200 nm   7.1   3.8   464   0.38   0.41                       TBP       MgAg                  
 
     DEVICE EXAMPLES 7 TO 12  
     Table 2  
     [0175] Devices of Examples 7 to 12 were prepared following structure of OLED  300  as shown in FIG. 3. NPB hole-transporting layer of 150 nm thickness was doped with varying amount of super rubrene NR compound with concentrations varying from 0% to 5%. It was found that the device of Example 7 has emission in the blue region of the electromagnetic spectrum, while the emission from devices of Example 8 to 12 is either white or bluish white or yellowish-white. Table 2 shows luminance, color coordinates, and drive voltage for devices 1 to 6 prepared using super rubrene NR as yellow dopant in the hole-transporting layer and TBP dopant in the TBADN blue light-emitting layer. The maximum luminance efficiency obtained from the devices of Examples 7 to 12 was about 4.6 cd/A. Table 1 shows that the devices using super rubrene NR generally have higher luminance yield.  
               TABLE 2                          White device characteristics using NR doping into HTL with TBADN + TBP as a Blue EML                                                                     NR doping into                                   Device   Example   HTL layer   150 nm HTL   Blue Light-           Drive Volt.   Luminance   EL peak pos       Example #   type   thickness (nm)   layer   emitting layer   ETL layer   Cathode   (V)   Yield (cd/A)   (nm)   ClEx                7   Comparison   150 nm   0   20 nm TBADN +   35 nm Alq   200 nm   7.18   2.94   464   0.156                       2% TBP       MgAg        8   Inventive   150 nm   1%   20 nm TBADN +   35 nm Alq   200 nm   7.67   3.28   464   0.227                       2% TBP       MgAg        9   Inventive   150 nm   2%   20 nm TBADN +   35 nm Alq   200 nm   7.01   3.82   464   0.287                       2% TBP       MgAg       10   Inventive   150 nm   3%   20 nm TBADN +   35 nm Alq   200 nm   7.04   4.22   464   0.329                       2% TBP       MgAg       11   Inventive   150 nm   4%   20 nm TBADN +   35 nm Alq   200 nm   7.05   4.38   464   0.355                       2% TBP       MgAg       12   Inventive   150 nm   5%   20 nm TBADN +   35 nm Alq   200 nm   6.98   4.61   464   0.386                       2% TBP       MgAg                  
 
     DEVICE EXAMPLES 13 TO 18  
     Table 3  
     [0176] Devices of Examples 13 to 18 were prepared following structure of OLED  300  as shown in FIG. 3. NPB hole-transporting layer of 150 nm thickness was doped with varying amount of super rubrene DBzR compound with concentrations varying from 0% to 5%. It was found that the device of Example 13 has emission in the blue region of the electromagnetic spectrum, while the emission from devices of Example 14 to 18 is either white or bluish white or yellowish-white. Table 3 shows luminance, color coordinates, and drive voltage for devices 1 to 6 prepared using super rubrene DBzR as yellow dopant in the hole-transporting layer and TBP dopant in the TBADN blue light-emitting layer. The maximum luminance efficiency obtained from the devices of Examples 13 to 18 was about 5.9 cd/A. Table 1 shows that the devices using super rubrene DBzR have significantly higher luminance yield.  
               TABLE 3                          White device characteristics using DBzR doping into HTL with TBADN + TBP as a Blue EML                                                             Device       HTL layer   DBzR doping                       EL               Example   Example   thickness   into 150 nm   Blue Light-           Drive Volt.   Luminance   peak pos       #   type   (nm)   HTL layer   emitting layer   ETL layer   Cathode   (V)   Yield (cd/A)   (nm)   ClEx   ClEy               13   Comparitive   150 nm   0   20 nm TBADN +   35 nm Alq   200 nm   7.8   3.1   468   0.16   0.25                       2% TBP       MgAg       14   Inventive   150 nm   1%   20 nm TBADN +   35 nm Alq   200 nm   7.4   5.6   572   0.39   0.40                       2% TBP       MgAg       15   Inventive   150 nm   2%   20 nm TBADN +   35 nm Alq   200 nm   7.5   5.9   576   0.43   0.41                       2% TBP       MgAg       16   Inventive   150 nm   3%   20 nm TBADN +   35 nm Alq   200 nm   7.6   5.9   580   0.45   0.42                       2% TBP       MgAg       17   Inventive   150 nm   4%   20 nm TBADN +   35 nm Alq   200 nm   7.5   5.9   464   0.46   0.42                       2% TBP       MgAg       18   Inventive   150 nm   5%   20 nm TBADN +   35 nm Alq   200 nm   7.1   5.7   464   0.49   0.42                       2% TBP       MgAg                  
 
     DEVICE EXAMPLES 19 TO 24  
     Table 4  
     [0177] Devices of Examples 19 to 24 were prepared following structure of OLED  300  as shown in FIG. 3. NPB hole-transporting layer of 150 nm thickness was doped with varying amounts of rubrene with concentrations varying from 0% to 5%. It was found that the device of Example 19 has emission in the blue region of the electromagnetic spectrum, while the emission from devices of Example 20 to 24 is either white or bluish white or yellowish-white. Table 4 shows luminance, color coordinates, and drive voltage for devices 19 to 24 prepared using rubrene as yellow dopant in the hole-transporting layer and B-1 as blue dopant in the TBADN blue light-emitting layer. The maximum luminance efficiency obtained from the devices of Examples 19 to 24 was about 6.6 cd/A.  
               TABLE 4                          White device characteristics using Rubrene doping into HTL with TBADN + B-1 dopant as a Blue EML                                                                         Rubrene                   Yield (cd/A)                           HTL layer   doping into               Drive   @20 mA/cm2       Device   Example   thickness   150 nm HTL   Blue Light-emitting           Volt.   (TK011216-   EL peak       Example #   type   (nm)   layer   layer   ETL layer   Cathode   (V)   2_Rub)   pos (nm)   ClEx   ClEy               19   Comparison   150 nm   0   20 nm TBADN + 1.5%   35 nm Alq   200 nm   7.8   6.3   472   0.18   0.33                       B-1       MgAg       20   Comparison   150 nm   1%   20 nm TBADN + 1.5%   35 nm Alq   200 nm   6.4   2.2   472   0.24   0.39                       B-1       MgAg       21   Comparison   150 nm   2%   20 nm TBADN + 1.5%   35 nm Alq   200 nm   7.7   6.6   560   0.37   0.44                       B-1       MgAg       22   Comparison   150 nm   3%   20 nm TBADN + 1.5%   35 nm Alq   200 nm   7.8   6.6   560   0.36   0.44                       B-1       MgAg       23   Comparison   150 nm   4%   20 nm TBADN + 1.5%   35 nm Alq   200 nm   7.7   6.2   560   0.38   0.44                       B-1       MgAg       24   Comparison   150 nm   5%   20 nm TBADN + 1.5%   35 nm Alq   200 nm   7.5   6.2   560   0.38   0.44                       B-1       MgAg                  
 
     DEVICE EXAMPLES 25 TO 30  
     Table 5  
     [0178] Devices of Examples 25 to 30 were prepared following structure of OLED  300  as shown in FIG. 3. NPB hole-transporting layer of 150 nm thickness was doped with varying amounts of super rubrene DBzR compound with concentrations varying from 0% to 5%. It was found that the device of Example 25 has emission in the blue region of the electromagnetic spectrum, while the emission from devices of Example 26 to 30 is either white or bluish white or yellowish-white. Table 5 shows luminance, color coordinates, and drive voltage for devices 25 to 30 prepared using rubrene as yellow dopant in the hole-transporting layer and B-1 as blue dopant in the TBADN blue light-emitting layer. The maximum luminance efficiency obtained from the devices of Examples 25 to 30 was about 8.5 cd/A. One can see that, relative to the devices in Table 4, the devices using super rubrene DBzR have significantly higher luminance yield.  
     [0179] This is an important feature of this invention that doping super rubrene DBzR in the NPB hole-transporting layer adjacent to a blue light light-emitting layer consisting of TBADN host with B-1 dopant produce white light OLED with very efficiency. The efficiency from the device of Example 28 has the highest efficiency among the various combinations of yellow and blue dopants.  
               TABLE 5                          White device characteristics using DBzR doping into HTL with TBADN + B-1 dopant as a Blue EML                                                                         DBzR                                               HTL layer   doping into               Drive       Device   Example   thickness   150 nm   Blue Light-   ETL       Volt.(V)   Luminance   EL peak       Example #   type   (nm)   HTL layer   emitting layer   layer   Cathode   @J = 20   Yield (cd/A)   pos (nm)   ClEx   ClEy               25   Comparison   150 nm   0   20 nm TBADN +   35 nm   200 nm MgAg   7.0   6.8   472   0.18   0.35                       1.5% B-1   Alq       26   Inventive   150 nm   1%   20 nm TBADN +   35 nm   200 nm MgAg   7.0   8.0   472   0.26   0.40                       1.5% B-1   Alq       27   Inventive   150 nm   2%   20 nm TBADN +   35 nm   200 nm MgAg   7.2   8.5   560   0.32   0.42                       1.5% B-1   Alq       28   Inventive   150 nm   3%   20 nm TBADN +   35 nm   200 nm MgAg   7.2   8.3   472   0.34   0.41                       1.5% B-1   Alq       29   Inventive   150 nm   4%   20 nm TBADN +   35 nm   200 nm MgAg   7.1   8.0   572   0.36   0.42                       1.5% B-1   Alq       30   Inventive   150 nm   5%   20 nm TBADN +   35 nm   200 nm MgAg   7.2   8.0   572   0.37   0.42                       1.5% B-1   Alq                  
 
     DEVICE EXAMPLES 31 TO 33  
     Table 6  
     [0180] Another important feature of this invention is that white light can be produced by an OLED by doping super rubrene both in the NPB hole-transporting layer  640  and in the Alq electron-transporting layer  661  as shown in FIG. 6. The blue light-emitting layer the OLED device of FIG. 6 consists of TBADN host and the B-1 dopant. These devices have high luminance yield and higher operational stability as compared to those obtained by super rubrene doping in either the hole-transporting layer or the electron-transporting layer.  
               TABLE 6                          White device characteristics using DBzR doping into HTL and Alq ETL layer with TBADN host &amp; B-1 as dopant in the Blue LEL                                                                                 DBzR                                                           doping       Blue dopant           Total   Drive   Yield   EL       Device       HTL   into 150 nm   TBADN   B-1 in the   DBzR into   AlQ   DBzR into   Volt.   (cd/A)   peak       Exam-   Example   layer   NPB HTL   thickness   TBADN   20 nm Alq   undoped   HTL +   (V)@   @20   pos       ple #   type   (NPB)   layer   (nm)   layer (%)   ETL layer   ETL layer   ETL   J = 20   mA/cm2   (nm)   ClEx   ClEy               31   Inventive   150 nm   3.50%   20 nm   2%   0.00%   15 nm   3.50%   7.5   9.25   472   0.33   0.43       32   Inventive   150 nm   0.00%   20 nm   2%   2.50%   15 nm   2.50%   8.4   5.46   472   0.28   0.41       33   Inventive   150 nm   2.00%   20 nm   2%   1.50%   15 nm   3.50%   8.3   6.61   472   0.32   0.43                  
 
     [0181] The operational stability of the encapsulated OLED devices in ambient environments was found by measuring the changes in the drive voltage and the luminance as a function of time when OLED devices were operated at a constant current density of 20 mA/cm 2 . White OLED devices prepared by following the different structures of this invention have high operational stability. FIG. 13 shows the operational luminance stability for the devices of Examples  31  to  33 .  
     [0182]FIG. 14 shows relative luminance as a function of current density for devices with several different combinations of the blue dopant and the yellow dopants:  
     [0183] I) Rubrene with TBP;  
     [0184] II) DBzR with TBP;  
     [0185] III) Rubrene with B-1; and  
     [0186] IV) DBzR with B-1.  
     [0187] It is clear that the DBzR yield superior device performance relative to rubrene. Also, the combination of DBzR super rubrene yellow emitting dopant into NPB HTL layer and B-1 blue emitting dopant into TBADN host give the best efficiency. It also gives the highest stability and white emitting light.  
     [0188] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, multiple dopants can be used in any of the hole-transporting, electron-transporting or light-emitting layers.  
     Parts List  
     [0189] 100  OLED with a simple structure  
     [0190] 110  substrate  
     [0191] 120  anode  
     [0192] 140  light-emitting layer  
     [0193] 170  cathode  
     [0194] 200  OLED with a multilayer structure  
     [0195] 210  substrate  
     [0196] 220  light-transmissive anode  
     [0197] 230  hole-injecting layer (HIL)  
     [0198] 240  hole-transporting layer (HTL)  
     [0199] 250  light-emitting layer (LEL)  
     [0200] 260  electron-transporting layer (ETL)  
     [0201] 270  cathode  
     [0202] 300  OLED  
     [0203] 310  substrate  
     [0204] 320  anode  
     [0205] 330  hole-injecting layer  
     [0206] 340  hole-transporting layer  
     [0207] 350  light-emitting layer  
     [0208] 360  electron-transporting layer  
     [0209] 370  cathode  
     [0210] 400  OLED  
     [0211] 410  substrate  
     [0212] 420  anode  
     [0213] 430  hole-injecting layer  
     [0214] 441  hole-transporting sub layer  
     [0215] 442  hole-transporting sub layer  
     [0216] 450  light-emitting layer  
     [0217] 460  electron-transporting layer  
     [0218] 470  cathode  
     [0219] 500  OLED  
     [0220] 510  substrate  
     [0221] 520  anode  
     [0222] 530  hole-injecting layer  
     [0223] 540  hole-transporting layer  
     [0224] 550  blue light-emitting layer  
     [0225] 561  electron-transport sub layer  
     [0226] 562  electron-transport sub layer  
     [0227] 570  cathode  
     [0228] 600  OLED  
     [0229] 610  substrate  
     [0230] 620  anode  
     [0231] 630  hole-injecting layer  
     [0232] 640  hole-transporting layer  
     [0233] 650  blue light-emitting layer  
     [0234] 661  electron-transporting sub layer  
     [0235] 662  electron-transporting sub layer  
     [0236] 670  cathode  
     [0237] 700  OLED  
     [0238] 710  substrate  
     [0239] 720  anode  
     [0240] 730  hole-injecting layer  
     [0241] 741  hole-transporting layer sub layer  
     [0242] 742  hole-transporting layer sub layer  
     [0243] 750  blue light-emitting layer  
     [0244] 761  electron-transport sub layer  
     [0245] 762  electron-transport sub layer  
     [0246] 770  cathode  
     [0247] 800  OLED  
     [0248] 810  substrate  
     [0249] 820  anode  
     [0250] 830  hole-injecting layer  
     [0251] 840  hole-transporting layer  
     [0252] 850  light-emitting layer  
     [0253] 861  electron-transport sub layer  
     [0254] 862  electron-transport sub layer  
     [0255] 870  cathode  
     [0256] 900  OLED  
     [0257] 910  substrate  
     [0258] 920  anode  
     [0259] 930  hole-injecting layer  
     [0260] 941  hole-transport sub layer  
     [0261] 942  hole-transport sub layer  
     [0262] 950  blue light-emitting layer  
     [0263] 961  electron-transport sub layer  
     [0264] 962  electron-transport sub layer  
     [0265] 970  cathode  
     [0266] 1000  OLED  
     [0267] 1010  substrate  
     [0268] 1020  anode  
     [0269] 1030  hole-injecting layer  
     [0270] 1040  hole-transporting layer  
     [0271] 1050  blue light-emitting layer  
     [0272] 1061  electron-transporting sub layer  
     [0273] 1062  electron-transporting sub layer  
     [0274] 1063  electron-transporting sub layer  
     [0275] 1070  cathode  
     [0276] 1100  OLED  
     [0277] 1110  substrate  
     [0278] 1120  anode  
     [0279] 1130  hole-injecting layer  
     [0280] 1140  hole-transporting layer  
     [0281] 1150  blue light-emitting layer  
     [0282] 1161  electron-transport sub layer  
     [0283] 1162  electron-transport sub layer  
     [0284] 1163  electron-transport sub layer  
     [0285] 1170  cathode  
     [0286] 1200  OLED  
     [0287] 1210  substrate  
     [0288] 1220  anode  
     [0289] 1230  hole-injecting layer  
     [0290] 1241  hole-transporting layer sub layer  
     [0291] 1242  hole-transporting layer sub layer  
     [0292] 1250  light-emitting layer  
     [0293] 1261  electron-transport sub layer 1  
     [0294] 1262  electron-transport sub layer 2  
     [0295] 1263  electron-transport sub layer 3