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    • 专利摘要:
    The present invention discloses OLED devices suitable for top and bottom emitters. For top emitting OLEDs, a transparent substrate; A reflective, weakly absorbing and conductive anode layer comprising a metal, a metal alloy, or both formed on the substrate; A hole injection layer; A plurality of organic layers formed on the hole injection layer and including an emission layer having an electroluminescent material and an electron transport layer disposed on the emission layer; And a reflective and conductive cathode comprising a metal, a metal alloy, or both provided on the electron transport layer, wherein the transparency and reflectivity of the anode structure, the reflectivity of the cathode structure, and the thickness of the organic layer between the electrodes, By varying the internal reflection it is chosen to improve emission and to obtain a substrate penetration brightness that is superior to an optimized control device that does not have a reflective, weakly absorbing and conductive anode.
    公开号:KR20040066724A
    申请号:KR1020040003364
    申请日:2004-01-16
    公开日:2004-07-27
    发明作者:레이차우드후리프라납케이；마다틸조셉케이；쇼어조엘디
    申请人:이스트맨 코닥 캄파니；
    IPC主号:
    专利说明:

    ORGANIC LIGHT EMITTING DIODE (OLED) DISPLAY WITH IMPROVED LIGHT EMISSION USING A METALLIC ANODE}
    [7] The present invention relates to an enhanced bottom-emitting and high efficiency top-emitting organic light emitting diode (OLED) device using a metal anode.
    [8] Organic electroluminescent (OEL) devices, also known as organic light emitting diodes (OLEDs), are useful in flat-panel display products. This light emitting device is attractive because it can be designed to produce red, green and blue with high luminance efficiency, it can operate with low drive voltages as low as a few volts and is clearly visible in squares. This unique property derives from the basic OLED structure, which consists of a multi-layer stack of low molecular organic material films located between the anode and the cathode. Tang et al. Disclose such structures in commonly assigned US Pat. Nos. 4,769,292 and 4,885,211. Conventional electroluminescent (EL) media consists of a two-layered structure of a hole transport layer (HTL) and an electron transport layer (ETL), typically each layer being tens of nanometers (nm) thick. When an electrical potential difference is applied to the electrode, the injected carriers-holes at the anode and electrons at the cathode-move in the direction of each other through the EL medium and some of them recombine and emit light. The intensity of electroluminescence depends on the EL medium, drive voltage, and charge injection properties of the electrode. Light visible from the outside of the device is further dependent on the design and optical properties of the organic stack of substrates, anodes and cathodes.
    [9] Typical devices have a bottom emission as the emitted light passes through the bottom support on which all the layers are deposited. The device usually uses a glass substrate having a very transparent indium-tin-oxide (ITO) layer that may act as an anode. Although lithium-containing alloys are also known to provide efficient electron injection, the cathode is typically a reflective MgAg thin film. Light is emitted in all directions. Light emitted towards the substrate passes through the anode and the substrate to the viewer, and light emitted in the opposite direction is reflected at the cathode and passes through the substrate to enhance under-emission. Highly transparent substrates and anodes and highly reflective cathodes are used in high efficiency devices. High efficiency displays are especially needed because of their low power consumption. In addition, such displays can be operated at low drive currents to enhance operating life. Typical bottom-emitting device engineering is near maturity. In general, less than 80% of the generated light cannot be observed in the glass, ITO and organic layers due to the loss in the waveguide method (M.-H. Lu and JC Sturm, J. Appl. Phys. 91 , 595 (2002)). . However, fabricating ultra-high efficiency devices can be very difficult. The device structure can be very complex to recover some light loss for the waveguide scheme.
    [10] In the case of an active matrix bottom emitting device, which is used to switch the elements of the thin film transistor, the transistor is assembled on a glass substrate. As a result, the open area that can be used to emit light is reduced due to the presence of transistors. The ratio of open area to total device area is called the aperture ratio. The display will work dimly due to the reduction in the aspect ratio. To compensate for the reduced average brightness level, the drive current must be increased, increasing the risk of operability degradation in the display. To alleviate this problem, the emitted light is made to exit through the top surface. The contrast ratio will be significantly increased in contrast to the bottom emission device, which is typically about 30%. This type of device is called a top-emitting or surface-emitting device. Surface-emitting devices are of considerable interest in active matrix displays and in products where the substrate needs to be made of an opaque material such as silicon. The top surface needs to be at least translucent to allow light to exit through the top surface.
    [11] Changing the discharge direction in the bottom-emitting device to switch to the top-emitting device is not a trivial problem, especially when efficiency must be preserved. This is due to the lack of highly transparent conductive cathode materials compatible with Alq ETL. Top electrode (cathode) materials that are compatible for Alq-based emission / electron transport layers (EML / ETL) are low work function metals or alloys that are absorbent and reflective. Of the light emitted towards the translucent cathode, only a small portion is emitted through the cathode and most of it is reflected back towards the transparent anode where the light comes from. Reducing the thickness of the cathode cannot significantly increase the top-emission, since the cathode layer needs to be 8 to 10 nm thick to ensure low voltage and contact stability in order to maintain the originality of the contact. Because. At this thickness, the film has low permeability and high interfacial reflectivity. Substrate penetration emission is still dominant at about 70% of the emission from the same device with a thick fully reflective cathode. Top-release is typically weak, about 15-25%.
    [12] The top emission can be substantially increased when a reflector is used in the anode structure to reflect light towards the cathode. In EP 1 154 676 A1 Sony Corporation used a reflector with a buffer / hole injector. Reflective materials were presumably high work function materials Pt, Au, Cr and W. The complete layer is made of m-MTDATA as a layer to prevent leakage, which is also a hole injection layer. Lu et al. (“High-efficiency top-emitting organic light-emitting devices”, M.-H. Lu, MS Weaver, TXZhou, M. Rothman, RCKwong, M.Hack, and JJ Brown, Appl. Phys. Lett. 81, 3921 (2002) discloses a top emitting OLED with Ag / 16 nm ITO anode and Ca (20 nm) / ITO (80 nm) cathode. A 30 nm thick CBP layer doped with 6% by weight of Ir (ppy) 3 as the emission medium is about 20 cd / A about 15% higher than the corresponding bottom emitter with an ITO anode and a fully reflective LiF / Al cathode. The efficiency of was obtained. Both types of devices use CuPc as the hole injector. They used ITO on Ag and probably further used a CuPc hole-injection layer to have good hole injection properties. These layers reduced anode reflectivity.
    [13] Accordingly, it is an object of the present invention to provide a bottom-emitting OLED that is superior in performance to conventional bottom-emitting OLEDs.
    [14] Another object of the present invention is to provide a very efficient top-emitting OLED.
    [15] Another object of the present invention is to use metal instead of ITO as anode material as the metal anode is more conductive and easier to fabricate than ITO anode.
    [16] Another object of the present invention is to use an ultra-thin hole injection layer on a highly reflective anode to preserve anode reflectivity and improve top-emission.
    [17] A further further object of the present invention is to achieve the above objects without incurring process complexity or without major modification of the device structure.
    [18] This purpose,
    [19] (a) a transparent substrate,
    [20] (b) a reflective, weakly absorbing and conductive anode layer comprising a metal, a metal alloy, or both formed on the substrate,
    [21] (c) a hole injection layer deposited on the reflective, weakly absorbing and conductive anode layer,
    [22] (d) a plurality of organic layers formed on the hole injection layer and including an emission layer having an electroluminescent material and an electron transport layer disposed on the emission layer, and
    [23] (e) a reflective and conductive cathode comprising a metal, a metal alloy, or both provided on the electron transport layer,
    [24] (f) an optimized control device in which the transparency and reflectivity of the anode structure, the reflectivity of the cathode structure, and the thickness of the organic layer between the electrodes improve emission by varying the internal reflection of light and have no reflective, weakly absorbing and conductive anode A bottom-emitting OLED device is selected that yields better substrate penetration brightness.
    [25] These targets are
    [26] (a) a transparent or opaque substrate,
    [27] (b) a reflective, substantially opaque, conductive anode layer comprising a metal, a metal alloy, or both formed on the substrate,
    [28] (c) a hole injection layer deposited on the reflective, substantially opaque and conductive anode layer,
    [29] (d) a plurality of organic layers formed on the hole injection layer and including an emission layer having an electroluminescent material and an electron transport layer disposed on the emission layer, and
    [30] (e) a reflective, translucent and conductive cathode comprising a metal, a metal alloy, or both provided on the electron transport layer,
    [31] (f) The reflectivity of the anode structure, the transparency of the cathode and the thickness of the organic layer between the electrodes are further achieved with a top-emitting OLED device, which is selected to improve emission through the top electrode by changing the internal reflection of light.
    [32] According to the present invention, by including a weakly absorptive but reflective metal layer and an ultra-thin hole injection layer in the anode structure and selecting the thickness of the weakly absorptive metal layer and the plurality of organic layers, the efficiency of the bottom-emitting device is substantial compared to conventional devices It was confirmed that it can be improved.
    [33] According to the present invention, it was further confirmed that high efficiency top-emission can be achieved by including a reflective metal and an ultra-thin hole injection layer in the anode structure and selecting the thickness of the cathode layer and the plurality of organic layers.
    [34] An advantage of the present invention is the use of low drive voltages to improve emission.
    [1] 1 schematically illustrates the layer structure of a conventional conventional bottom-emitting OLED device.
    [2] 2 schematically illustrates the layer structure of the bottom-emitting OLED device of the present invention.
    [3] 3 schematically illustrates the layer structure of the bottom-emitting OLED device of the present invention.
    [4] 4 schematically illustrates the layer structure of the bottom-emitting OLED device of the present invention.
    [5] 5 schematically illustrates the layer structure of the top-emitting OLED device of the present invention.
    [6] 6 shows on-axis luminance of a top-emitting OLED device with Ag anode and 11 nm thick MgAg cathode as a function of NPB thickness measured by optical modeling.
    [35] Throughout the following description, the use of bimolecular words indicates the names of the various organic layers and the operating characteristics of the organic light emitting device. Listed in Table 1 below for reference.
    [36]
    [37] Returning now to FIG. 1, the OLED 100 is a transparent substrate 101, a transparent anode 102, a hole injection layer (HIL) 103, a hole transport layer (HTL) 104, an emission layer (EML) 105. , An electron transport layer (ETL) 106 and a reflective cathode 107. Cathode 107 includes a work function metal of less than about 4 eV. In operation, anode 102 and cathode 107 are connected to a voltage source and current passes through the organic layer to generate light emission or electroluminescence from emitting layer 105. The intensity of the generated light depends on the magnitude of the current passing through the OLED 100, which in turn depends on the electrical characteristics and brightness of the organic layer as well as the charge injection properties of the anode 102, hole injection layer 103 and cathode 107. Change accordingly. The visible emission is further dependent on the layer structure of the OLED 100 as well as the transparency of the substrate 101 and the anode 102 and the reflectivity of the cathode 107.
    [38] 2 to 4, the OLED device of the present invention is shown. In OLED 100A (FIG. 2), the anode comprises a translucent metal layer 108, but otherwise similar to the conventional OLED device 100. Through the current, the OLED 100A emits light seen through the substrate 101 like the conventional device OLED 100. On the other hand, the thickness of the anode 108 and the organic layer is chosen to maximize efficiency.
    [39] In OLED 100B (FIG. 3), a transmission enhancement layer (TEL) 109 is positioned between the transparent substrate 101 and the translucent, conductive and reflective anode 108 made of a metal or metal alloy to provide a substrate 101. ) To further enhance release.
    [40] In OLED 100C (FIG. 4), conductive reflector 111 is used regardless of the work function. Conductive reflector 111 is deposited on ultra-thin cathode 110, which is formed on electron transport layer 106. OLED 100C is otherwise similar to OLED 100B.
    [41] In OLED 100D (FIG. 5), light passes through translucent conductive cathode 107x and transmission enhancement layer 109x. Conductive reflective anode 108x is a fully reflective layer deposited on transparent or opaque substrate 101x.
    [42] The composition and function of the various layers constituting the OLED device are as follows.
    [43] The substrate 101 may include glass, ceramic, or plastic. In the case of a device emitting through the substrate 101, the substrate should be as transparent as possible. Since OLED device fabrication does not require a high temperature process, any substrate 101 capable of withstanding a process temperature on the order of 100 ° C. is useful, including most thermal plastics. Substrate 101 may take the form of a rigid plate, a flexible sheet or a curved surface. Substrate 101 includes an active matrix substrate having electron addressing or switching elements as it may comprise a support having an electronic back plate. The active matrix substrate may contain high temperature polysilicon thin film transistors, low temperature polysilicon thin film transistors or amorphous silicon thin film transistors. Those skilled in the art will understand that other circuit elements can be used to address and drive OLED devices.
    [44] The anode 102 (FIG. 1) provides the ability to inject holes into the organic layer when a positive potential is applied to the OLED 100 relative to the cathode 107. For example, commonly assigned US Pat. No. 4,720,432 has been found to form an efficient anode because indium tin oxide (ITO) has a relatively high work function. Since the ITO film itself is transparent and conductive, commercially available ITO-coated glass provides an excellent support for the manufacture of OLED 100 type devices (FIG. 1). The OLED 100A type device (FIG. 2) uses a conductive and translucent metal / alloy layer as the anode 108 deposited on the transparent substrate 101. The anode 108 may be deposited by a typical deposition method and may also be used with the OLED 100 manufacturing method. This anode 108 may or may not require a hole injection layer 103 overlying it.
    [45] The hole injection layer 103 provides the function of increasing the efficiency of hole injection from the anode 102 (FIG. 1) or the anode 108 (FIG. 2) into the hole transport layer. For example, commonly assigned U.S. Pat.No. 4,885,211 shows that porpoline or phthalocyanine compounds are useful as the hole injection layer 103 for the hole transport layer 104 of the conventional type of device (FIG. 1), and have luminance efficiency and operational stability. It has been found to increase. Other preferred hole injection materials include CF x , where x is greater than 0 and less than or equal to 2, which is a fluorinated polymer deposited by plasma-assisted deposition. Processes and properties of CF x have been disclosed in commonly assigned US Pat. No. 6,208,077. Other materials can also be used as the hole injector. These include oxides of Mo, V or Ru. A layer of about 30 nm thick of this material, each on 120 nm thick ITO, has been found to be useful as a hole injector to the TPD, hole transport layer ("Metal oxides as a hole-injecting layer for an organic electroluminescent device", S. Tokito , K. Noda and Y. Taga, J. Phys. D; Appl. Phys. 29, 2750 (1996)). In accordance with the present invention, CF x and MoO x (x <3.0) provide efficient hole injection from the metal anode 108 or anode 108x of FIGS. 2, 3, 4 or 5 to the hole transport layer 104. It was found to provide. The MoO x layer is prepared by vacuum evaporation of MoO 3 , and the deposited film can be non-stoichiometric. Other hole injectors for the metal anode may include ITO, IZO, Pr 2 O 3 , TeO 2 , CuPc or SiO 2 .
    [46] The hole transport layer 104 provides the function of transporting holes to the emissive layer 105. Hole transport materials include various classes of aromatic amines as disclosed in commonly assigned US Pat. No. 4,720,432. Preferred classes of hole transport materials include tetraaryldiamines of the formula
    [47]
    [48] Where
    [49] Ar, Ar1, Ar2 and Ar3 are independently selected from phenyl, biphenyl and naphthyl residues,
    [50] L is a divalent naphthylene residue or d n ,
    [51] d is a phenylene moiety,
    [52] n is an integer from 1 to 4,
    [53] At least one of Ar, Ar1, Ar2 and Ar3 is a naphthyl residue.
    [54] Useful selected (containing fused aromatic rings) aromatic tertiary amines are:
    [55] 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPB),
    [56] 4,4 "-bis [N- (1-naphthyl) -N-phenylamino] -p-terphenyl,
    [57] 4,4'-bis [N- (2-naphthyl) -N-phenylamino] biphenyl,
    [58] 1,5-bis [N- (1-naphthyl) -N-phenylamino] naphthalene,
    [59] 4,4'-bis [N- (2-pyrenyl) -N-phenylamino] bi-phenyl,
    [60] 4,4'-bis [N- (2-perylenyl) -N-phenylamino] biphenyl,
    [61] 2,6-bis (di-p-tolylamino) naphthalene,
    [62] 2,6-bis [di- (1-naphthyl) amino] naphthalene.
    [63] Emissive layer 105 (FIGS. 1-5) provides the function of light emission resulting from the recombination of holes and electrons in this layer. Emissive layer 105 of the preferred embodiment comprises a host material doped with one or more fluorescent dyes. Using this host-dopant combination, it is possible to manufacture high efficiency OLED devices. At the same time, the color of the EL device can be adjusted by using fluorescent dyes of different emission wavelengths in conventional host materials. Tang et al. Describe this dopant outline in considerable detail for OLED devices using Alq as host material in commonly assigned US Pat. No. 4,769,292. As disclosed in commonly assigned US Pat. No. 4,769,292 to Tang et al., The emissive layer may contain a green luminescent doped material, a blue luminescent doped material or a red luminescent doped material.
    [64] Preferred host materials include a class of 8-quinolinol metal chelate compounds, which chelate metals are for example Al, Mg, Li, Zn. Another preferred class of host materials are anthracene derivatives, such as 9,10-dinaphthyl anthracene, 9,10-dianthryl anthracene, and alkyl, as disclosed in commonly assigned US Pat. No. 5,935,721 to Shi et al. Substituted 9,10-dinaphthyl anthracene.
    [65] Dopant materials include most fluorescent and phosphorescent dyes and pigments. Preferred dopant materials include coumarins (e.g., coumarin 6), dicyanomethylenepyranes (e.g., as disclosed in commonly assigned US Pat. No. 4,769,292 to Tang et al. And commonly assigned US Pat. No. 6,020,078 to Chen et al. : 4-dicyanomethylene-4H-pyran).
    [66] The electron transport layer 106 (FIGS. 1-5) provides the function of transferring electrons injected from the cathode into the emission layer 105 (FIGS. 1-5). Useful materials include Alq, benzazole, as disclosed in commonly assigned US Pat. No. 5,645,948 to Shh et al.
    [67] Cathode 107 (FIGS. 1-3) is typically a conductive and fully reflective thin film (i.e. about 50-500 nm thick) and can efficiently inject electrons into electron transport layer 106 (FIGS. 1-3). Consisting of a material containing an alloy. Mg and Li containing alloys are generally used because they have a low work function and make efficient electron injection contacts to the Alq electron transport layer 106. Other materials having a work function of less than 4.0 eV can also be used as the electron injector. These include metals or metal alloys including Mg, alkali metals, alkaline earth metals or alloys of Mn and Ag or Al. The cathode 107x is generally deposited in the electron transport layer 106 (FIGS. 1-3). Cathode 107x (FIG. 5) is also deposited as a translucent film of about 4-50 nm thick, and is characterized by low work function (<4 eV) metals and alloys of Mg, alkali metals, alkaline earth metals or Mn with Ag or Al. Including metal alloys.
    [68] The anode 108 (FIGS. 2-4) is a reflective, weakly absorbing, conductive film and consists of a material comprising an alloy having significant transmission at the emission wavelength. Such materials include Ag, Al, Mg, Zn, Rh, Ru, Ir, Au, Cu, Pd, Ni, Cr, Pt, Co, Te or Mo or alloys or mixtures thereof. Weak absorbency means that the adsorption of the film on the glass is less than 30%. The reflectivity of this layer can be at least about 30%. Depending on the metal, the thickness of the layer should be greater than about 4 nm and less than 50 nm. Anode 108x (FIG. 5) is a conductive and fully reflective layer 50-500 nm thick, including Ag, Al, Mg, Zn, Rh, Ru, Ir, Au, Cu, Pd, Ni, Cr, Pt, Co, Te, Mo, Hf, Fe, Mn, Nb, Ge, Os, Ti, V or W or alloys or mixtures thereof.
    [69] The transmission enhancement layer 109 (FIGS. 3 and 4) is a highly transmissive film inserted between the substrate 101 and the translucent anode 108 to further increase emission through the substrate 101. The transmission enhancement layer 109x (FIG. 5) is also a highly transmissive film deposited on the reflective and conductive cathode 107x to further increase emission through the translucent, reflective and conductive cathode 107x. . The transmission enhancement layers 109 and 109x include ITO, indium zinc oxide (IZO), tin oxide (TO), antimony-doped tin oxide (ATO), fluorine-doped tin oxide (FTO), indium oxide (IO) , Zinc oxide (ZO), cadmium stannate (CTO), cadmium oxide, phosphorus-doped TO, and aluminum-doped ZO, MgO, MoO x , SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 , SiN , Conductive or nonconductive materials, including but not limited to, AlN, TiN, ZrN, SiC or Al 4 C 3 or mixtures thereof. Depending on the optical index of the material, the thickness of the transmission enhancement layer 109 or 109x may range from 20 to 150 nm.
    [70] Ultra-thin cathode 110 (FIG. 4) is effectively a transparent electron injection layer formed on electron transport layer 106. This cathode 110 is made by depositing an ultrathin layer of alkali metal, alkaline earth metal or combinations thereof. Cathode 110 may also be prepared by depositing metals and compounds such as activating metals such as Al, Mg. The two layer structure (each about 1 nm thick), including a thin Al, Mg or MgAg layer on LiF, provides efficient electron injection into the electron transport layer 106. This cathode 110 may use any metal / alloy as the top electrode regardless of the work function.
    [71] Reflector 111 (FIG. 4) is a reflective layer of highly reflective metal, typically but not limited to Au, Ag, Cu, Al or alloys thereof. The reflector reflects the light emitted towards the cathode and directs it back towards the substrate. Although the highly reflective reflector helps significantly enhance substrate penetration emission, other lower reflecting metals such as Mg, Zn, Ni Pd or Pt or alloys or mixtures thereof may be useful. The thickness of the reflector is chosen large enough to provide maximum reflectivity.
    [72] The above-mentioned organic materials are suitably deposited by evaporation at high vacuum. The metal / alloy layer is also deposited even if it is possible to use sputter deposition if the device structure comprises a buffer layer (PK Raychaudhuri and JK Madathil, "Fabrication of Sputtered Cathodes for Organic Light-Emitting Diodes Using Transparent Buffer", Proceedings of the 7th Asian Symposium on Information Display (Sept 2-4, Singapore a) Digest, paper 50; Vol. 32, pp. 55-58, 2001).
    [73] Most OLED devices are sensitive to moisture or oxygen or both, so desiccants such as alumina, bauxite, calcium sulfate, clay, silica gel, zeolites, alkali metal oxides, alkaline earth metal oxides, sulfates, or metal halides It is usually sealed in an inert atmosphere such as nitrogen or argon together with cargo and perchlorate. Encapsulation and desiccation methods include, but are not limited to, those described in US Pat. No. 6,226,890. In addition, barrier layers such as SiO x , Teflon, other inorganic / polymer layers are known in the art for encapsulation.
    [74] The OLED device of the present invention can use a variety of well-known optical effects to enhance their properties according to the purpose. This can be achieved by optimizing the layer thickness to obtain maximum light transmission, replacing the reflective electrode with a light absorbing electrode to enhance the contrast, providing an anti-glare or anti-reflective coating on the display, or providing a polarizing medium on the display, Providing a neutral neutral density, or color conversion filter, on the display.
    [75] Example
    [76] Conventional devices were fabricated using glass substrates with commercial grade 42 nm thick 70 ohm / sq patterned ITO layers. After routine washing, a 1 nm thick CF x HIL layer was deposited on the ITO surface by decomposing the CHF 3 gas in the RF plasma. The substrate for the device of the present invention is a glass plate on which a weak absorbent metal layer was deposited by sputtering in an Ar containing atmosphere. This metalized glass substrate was also coated with the CF x hole injection layer or the deposited MoO x hole injection layer. The substrate was then transferred to a vacuum coater operating at about 1 × 10 −6 Torr where the organic stack consisting of HTL, EML, ETL was deposited in order. A cathode layer of MgAg or a cathode layer of LiF / MgAg was deposited through a rectangular mask (limited to an active area of 0.1 cm 2 for the device). Finally, the device was encapsulated encapsulated in a glove box filled with dry nitrogen. The brightness of the device was measured using a Photo Research PR650 spectrophotometer as a function of current. The drive voltage and brightness given here are obtained when a current corresponding to 20 mA / cm 2 passes through the device, where the brightness is measured in a direction perpendicular to the device surface. The voltage drop caused by a series of resistances of the ITO layer or the translucent anode layer 108 or 108x was subtracted from the measured drive voltage to compare with the device based on the "real" drive voltage.
    [77] Example 1
    [78] Conventional devices were fabricated using ITO as a transparent anode, CF x as HIL, Alq as EML / ETL and LiF / MgAg layers as cathode (top electrode). The upper electrode, which contains 90% Mg and 10% Ag, is 100 nm thick, fully reflective and opaque. Optimize the device for maximization of bottom emission. The device has a layer structure of glass (1.1 mm) / ITO (42 nm) / CF x (1 nm) / NPB (105 nm) / Alq (60 nm) / LiF (0.5 nm) / MgAg (100 nm).
    [79] Light emits through the substrate. At a drive current corresponding to 20 mA / cm 2, the drive voltage was 7.8 V and the emission was 641 cd / m 2. The efficiency of the device is 3.2 cd / A. The peak emission wavelength is 525 nm.
    [80] Example 2
    [81] The device according to the invention was prepared using a translucent Ag anode, MoO x as HIL, Alq as EML / ETL, and LiF / MgAg layer as cathode (top electrode). The MgAg layer is completely reflective and opaque. Optimize the device for maximization of bottom emission. The device has a layer structure of glass (1.1 mm) / Ag (20 nm) / MoO x (2 nm) / NPB (40 nm) / Alq (60 nm) / LiF (0.5 nm) / MgAg (100 nm).
    [82] Light emits through the substrate. At a drive current corresponding to 20 mA / cm 2, the drive voltage was 6.9 V and the bottom emission was 1346 cd / m 2. The efficiency of the device is 6.7 cd / A. The peak emission wavelength is 525 nm.
    [83] Examples 1 and 2 show that the device of the present invention is twice as efficient as the conventional device and the emission wavelength has not changed.
    [84] Example 3 (comparative)
    [85] A conventional device 3F having a 42 nm thick ITO anode, and a series of devices (devices 3A, 3B, 3C, 3D, and 3E) of the present invention, each having a translucent Ag anode layer, were fabricated. The device structure in each case was optimized for maximizing bottom emission by selecting NPB layer thickness. The hole injection layer for each device was a 1 nm thick CF x layer. All devices also used 30 nm thick Alq doped with 1% C545T as emitter, 30 nm thick undoped Alq as electron-transport layer, and 100 nm thick MgAg layer as cathode. The results are shown in Table 2.
    [86]
    [87] The results of Example 3 show that the devices of the present invention (devices 3E, 3D and 3C) having translucent Ag anodes of 10 to 30 nm thickness show greater luminance than the conventional device 3F. The efficiency of a device with a 20 nm Ag anode is about twice as efficient as the conventional device 3F.
    [88] Example 4 (comparative)
    [89] A conventional device 4F having a 42 nm thick ITO anode, and a series of devices (devices 4A, 4B, 4C, 4D and 4E) with translucent Au anode layers respectively, were prepared. The device structure in each case was optimized for maximizing bottom emission by selecting NPB layer thickness. The hole injection layer for each device was a 1 nm thick CF x layer. All devices also used 30 nm thick Alq doped with 1% DCJTB as emitter, 30 nm thick undoped Alq as electron-transport layer, and 100 nm thick MgAg layer as cathode. The results are shown in Table 3.
    [90]
    [91] The results of Example 4 show that the devices of the present invention (devices 4E, 4D, 4C and 4B) with translucent Au anodes of 15 to 40 nm thick exhibit greater emission than conventional devices 4F. The efficiency of the device 4D with the 20 nm Ag anode is about twice as efficient as the conventional device 4F.
    [92] Example 5
    [93] Optical modeling is performed using conventional device structures [device 5A-glass (1.1 mm) / ITO (42 nm) / NPB (105 nm) / Alq (60 nm) / MgAg (100 nm)) and devices of the present invention [device 5B-glass]. (1.1 mm) / Mo (5 nm) / NPB (50 nm) / Alq (60 nm) / MgAg (100 nm)]. For optical modeling, the presence of ultra thin layer stacks of CF x or MoO x was ignored. The output of device 5B was found to be about 92% compared to that of device 5A. However, a transparent TEL with an index of n = 2.7 was inserted between the glass substrate and the Mo anode and the layer structure was glass (1.1 mm) / TEL (49.1 nm) / Mo (5 nm) / NPB (67 nm) / Alq (64.6). When readjusted to have a device 5C having a structure of nm) / MgAg (100 nm), the output of the device 5C is expected to be about 1.5 times that of the conventional device 5A. Since the device 5C has only slightly thicker Alq and NPB, the drive voltage increase will be ignored. The surface resistance of the 5 nm thick Mo layer is estimated to be 11 ohm / sq lower than the ITO layer used to make conventional devices.
    [94] Example 6 (comparative)
    [95] Optical modeling was performed using conventional device structures (Device 6A-Glass (1.1 mm) / ITO (42 nm) / NPB (105 nm) / Alq (60 nm) / MgAg (100 nm)) and Glass (1.1 mm) / Ag (20). Nm) / NPB (variable) / Alq (60 nm) / MgAg (100 nm). For optical modeling, the presence of ultra thin layer stacks of CF x or MoO x was ignored. The results indicate that on-axis maximum brightness occurs at 50 nm (first maximum) and 200 nm (second maximum), as shown in FIG. 6. At the first maximum position, the brightness of the device of the present invention is about 1.7 times that of the optimized bottom-emitting conventional device 6A. This is in considerable agreement with the experimental data presented in the above examples. OLEDs of the present invention having a TEL layer and NPB of 20 to 80 nm or 180 to 230 nm are expected to be superior to the brightness of conventional devices. The total thickness of the organic layer between the electrodes for the high efficiency bottom emitter is 80 to 140 nm or 240 to 290 nm for the first maximum or the second maximum, respectively.
    [96] Example 7
    [97] A series of top emitters (devices 7A, 7B, 7C, 7D, 7E, and 7F) of the present invention were prepared, each having a 60 nm thick Ag anode, translucent cathode, and variable NPB layer thickness. The HIL for each device was 1 nm thick CF x . For all the devices used were 30 nm thick Alq doped with 1% C545T as EML, 30 nm thick undoped Alq as ETL, and 14 nm thick translucent MgAg layer as cathode. The device does not have a TEL but otherwise is similar to the device of FIG. 5. The results are shown in Table 4.
    [98]
    [99] The results of Example 7 show that for devices of the invention with translucent MgAg cathode the luminance is maximized when the NPB layer thickness is 50 nm. A simulation similar to Example 6 predicts that the first maximum in on-axis brightness occurs at an NPB thickness of 45 nm and the second maximum occurs at an NPB thickness of 180 nm. Thus, the ideal thickness of the organic medium for maximizing top emission is 105 or 204 nm. High efficiency devices can be manufactured with NPB thicknesses of 30 to 80 nm or 160 to 230 nm. This results in an overall organic layer thickness of 90 to 140 nm or 220 to 290 nm.
    [100] Example 8
    [101] Several top emitters of the present invention were prepared using several reflective anodes (all of which had a conventional 14 nm MgAg cathode and a conventional organic layer-50 nm NPB hole transport layer and 60 nm Alq EML / ETL). The reflectors used were fully reflective films of Ag, Pd and Mo. The reflectivity of the fully reflective film in air at about 525 nm, extracted from the literature, is also shown in Table 5. The hole injection layer for each device was a 1 nm thick MoO x film. The device does not have a TEL. Device performance is shown in Table 5.
    [102]
    [103] The results of Example 8 show that top emission increases the function of anode reflectivity. However, the output is not simply proportional to the anode reflectivity, but rises significantly faster in the high reflectivity range. Considering the advantages of the top emitter over the bottom emitter in terms of aspect ratio, it is expected that the top emitter with the Mo anode will outperform the bottom emitter with the ITO anode.
    [104] Example 9
    [105] Two inventions each having a 72 nm thick Ag anode, 2.5 nm thick MoO x HIL, 45 nm thick NPB HTL, 60 nm thick Alq EML / ETL and 0.5 nm thick LiF / 14 nm MgAg cathode The top discharge device was made. The device 9A does not have a TEL. An 85 nm Alq layer as TEL was deposited on the cathode of the device 9B. At a drive current corresponding to 20 mA / cm 2, device 9A has a drive voltage of 7.3 V and a brightness of 1260 cd / m 2. Under similar conditions, the device 9B has a driving voltage of 7.1 V and a luminance of 1630 cd / m 2. The 85 nm Alq layer acts as a TEL. The improvement due to TEL is about 29%.
    [106] It will be appreciated from all examples that the OLED penetrating axial emission can be greater than that of a conventional control device with a low reflective, highly transparent ITO anode when the OLED device is fabricated using two reflective electrodes, i.e., by fabricating a microcavity device. Can be. However, the device structure must change. The emission from the microcavity is strongly directed along the optical axis (perpendicular to the emitting plane). In the case of the device of the invention, upon optimization, the light loss of the OLED device 100A, 100B or 100C (FIGS. 2-4) due to absorption at the anode can be further compensated by the gain due to the microcavity effect.
    [107] Optical microcavity OLEDs somewhat similar to those of the present invention have been reported in the literature ("Control of emission characteristics in organic thin-film electro luminescent devices using an optical-microcavity structure" N. Takada, T. Tsutusi, and S. Saito, Appl. Phys. Lett. 63 , 2032 (1993). A microcavity structure was constructed consisting of a reflective and translucent 36 nm thick Ag anode and a reflective 250 nm thick MgAg cathode. In addition, devices without microcavity structures with transparent ITP anodes were prepared for reference. These two devices were fabricated on a support, which had a conventional organic layer and cathode. The microcavity device did not show an improvement in bottom emission compared to the non-microcavity device. The microcavity device characteristically exhibited the emission peak shift along with the angle dependence of the emission and the viewing angle. However, emissions from microcavity devices were weaker than non-microcavity devices. Inefficient devices can be fabricated as a result of the thick anode, the unoptimized device structure, and more importantly the absence of the hole-injection layer. Optimization in these three aspects is the most distinguishing feature included in the present invention.
    [108] The present invention uses metal anodes to provide enhanced bottom-emitting and highly efficient top-emitting organic light emitting diodes (OLEDs) and can also improve emission with low drive voltages.
    权利要求:
    Claims (10)
    [1" claim-type="Currently amended] (a) a transparent substrate,
    (b) a reflective, weakly absorbing and conductive anode layer comprising a metal, a metal alloy, or both formed on the substrate,
    (c) a hole injection layer deposited on the reflective, weakly absorbing and conductive anode layer,
    (d) a plurality of organic layers formed on the hole injection layer and including an emission layer having an electroluminescent material and an electron transport layer disposed on the emission layer, and
    (e) a reflective and conductive cathode comprising a metal, a metal alloy, or both provided on the electron transport layer,
    (f) an optimized control device in which the transparency and reflectivity of the anode structure, the reflectivity of the cathode structure, and the thickness of the organic layer between the electrodes improve emission by varying the internal reflection of light and have no reflective, weakly absorbing and conductive anode Selected to obtain better substrate penetration brightness,
    Bottom-emitting OLED device.
    [2" claim-type="Currently amended] The method of claim 1,
    A bottom-emitting OLED device further comprising a transmission enhancement layer (TEL) between the reflective, weakly absorbing and conductive anode layer and the transparent substrate to further improve the amount of light passing through the anode.
    [3" claim-type="Currently amended] The method of claim 2,
    TEL comprises ITO, MgO, MoO x , SnO 2 , TiO 2 , Al 2 O 3 , SiO 2 , ZnO, ZrO 2 , Alq, NPB, SiN, AlN, TiN, SiC, Al 4 O 3 or mixtures thereof A bottom-emitting OLED device.
    [4" claim-type="Currently amended] The method of claim 3, wherein
    Bottom-emitting OLED device with a TEL thickness of 20-150 nm.
    [5" claim-type="Currently amended] The method of claim 1,
    Bottom-emitting OLED device in which the sum of the thicknesses of all the layers between the anode and the cathode is in the range of 90 to 150 nm or 230 to 330 nm.
    [6" claim-type="Currently amended] (a) a transparent or opaque substrate,
    (b) a reflective, substantially opaque, conductive anode layer comprising a metal, a metal alloy, or both formed on the substrate,
    (c) a hole injection layer deposited on the reflective, substantially opaque and conductive anode layer,
    (d) a plurality of organic layers formed on the hole injection layer and including an emission layer having an electroluminescent material and an electron transport layer disposed on the emission layer, and
    (e) a reflective, translucent and conductive cathode comprising a metal, a metal alloy, or both provided on the electron transport layer,
    (f) the reflectivity of the anode structure, the transparency of the cathode and the thickness of the organic layer between the electrodes are selected to improve emission through the upper electrode by varying the internal reflection of the light,
    Top-emitting OLED device.
    [7" claim-type="Currently amended] The method of claim 6,
    A top-emitting OLED device further comprising a transmission enhancement layer (TEL) on the reflective, translucent and conductive cathode to further improve the amount of light passing through the cathode.
    [8" claim-type="Currently amended] The method of claim 6,
    A top-emitting OLED device comprising a metal or metal alloy having a work function selected such that the reflective, substantially opaque, and conductive anode layer is greater than about 4.0 eV.
    [9" claim-type="Currently amended] The method of claim 6,
    A top-emitting OLED device in which the hole injection layer comprises CF x , ITO, IZO, Pr 2 O 3 , TeO 2 , CuPc, SiO 2 , VO x , MoO x or mixtures thereof.
    [10" claim-type="Currently amended] The method of claim 7, wherein
    TEL comprises ITO, MgO, MoO x , SnO 2 , TiO 2 , Al 2 O 3 , SiO 2 , ZnO, ZrO 2 , Alq, NPB, SiN, AlN, TiN, SiC or Al 4 O 3 or mixtures thereof Top-emitting OLED device.
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    同族专利:
    公开号 | 公开日
    EP1439588A2|2004-07-21|
    US20040140758A1|2004-07-22|
    JP2004228081A|2004-08-12|
    TW200423798A|2004-11-01|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    2003-01-17|Priority to US10/347,013
    2003-01-17|Priority to US10/347,013
    2004-01-16|Application filed by 이스트맨 코닥 캄파니
    2004-07-27|Publication of KR20040066724A
    优先权:
    申请号 | 申请日 | 专利标题
    US10/347,013|2003-01-17|
    US10/347,013|US20040140758A1|2003-01-17|2003-01-17|Organic light emitting devicedisplay with improved light emission using a metallic anode|
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