TWI524815B - Saturated color organic light emitting devices - Google Patents

Description

Saturated color organic light emitting device

The present invention relates to an organic light-emitting device (OLED). More specifically, the present invention relates to an OLED having a reinforcing layer.

This application is related to U.S. Patent Application Serial No. 60/986,711, filed on Nov. 9, 2007, which is incorporated herein by reference in its entirety, the entire entire entire entire entire entire entire entire entire disclosure This is incorporated herein by reference.

The claimed invention was invented by, on behalf of, and/or in conjunction with one or more of the following parties to a joint university collaborative research agreement: the University of Michigan Board of Trustees, Princeton University, the University of Southern California, and Universal Display. The agreement is effective at the time of the date on which the claimed invention is made and the claimed invention is made as a result of the activities taken within the scope of the agreement.

Optoelectronic devices using organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, and thus organic optoelectronic devices have the potential to outperform the cost advantages of inorganic devices. In addition, the inherent properties of organic materials (eg, their flexibility) make them extremely suitable for specific applications, such as fabrication on a flexible substrate. Examples of organic optoelectronic devices include organic light-emitting devices (OLEDs), organic photovoltaic cells, organic photovoltaic cells, and organic photodetectors. For OLEDs, organic materials can have superior performance advantages over conventional materials. For example, the wavelength of light emitted by an organic emissive layer is generally readily tunable with appropriate dopants.

OLEDs use a thin organic film that emits light when a voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for applications such as flat panel displays, lighting and backlighting. Several OLED materials and configurations are described in U.S. Patent Nos. 5,844,363, 6, 303, 238, and 5, 707, 745, the entireties of each of

One application of phosphorescent emissive molecules is a full color display. The industry standard for this display requires that the pixels be adapted to emit a particular color (referred to as a "saturated" color). In particular, these standards require saturated red, green, and blue pixels. Color can be measured using CIE coordinates, which are well known in the art.

An example of a green emitting molecule is tris(2-phenylpyridinium)anthracene (denoted as Ir(ppy) ₃ ) having the structure of formula I:

In this and subsequent figures herein, we describe the coordination bonds from nitrogen to metal (here Ir) as a straight line.

As used herein, the term "organic" encompasses polymeric materials and small molecule organic materials that can be used in the fabrication of organic optoelectronic devices. "Small molecule" means any organic material that is not a polymer, and the "small molecule" can actually be quite large. In some cases, small molecules can contain repeating units. For example, the use of a long chain alkyl group as a substituent does not exclude molecules from the "small molecule" category. Small molecules can also be incorporated into the polymer, for example as a pendant group on a polymer backbone or as part of a backbone. The small molecule can also serve as a core portion of a dendrimer composed of a series of chemical shells constructed on the core portion. The core portion of a dendrimer can be a fluorescent or phosphorescent small molecule emitter. A dendrimer can be a "small molecule" and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, "top" means the farthest from the substrate, and "bottom" means the closest to the substrate. In the case where a first layer is described as being "positioned" above a second layer, the first layer is placed further away from the substrate. Other layers may be present between the first layer and the second layer unless it is indicated that the first layer is "in contact" with the second layer. For example, a cathode can be described as being "placed" above an anode, even if various organic layers are present between them.

As used herein, "processable solution" means capable of being dissolved, dispersed or delivered in a liquid medium and/or deposited from a liquid medium in the form of a solution or suspension.

A ligand is said to have "photoactivity" when it is believed that the ligand contributes to the photoactive nature of the emissive material.

Further details regarding OLEDs and the above definitions can be found in U.S. Patent No. 7,279,704, which is incorporated herein in its entirety by reference.

An organic light emitting device is provided. The device has a first electrode, a second electrode and an emissive layer disposed between the first electrode and the second electrode. The emissive layer comprises an emissive material having an intrinsic emission spectrum having a peak emission wavelength of less than 500 nm in the visible spectrum. The device includes a color saturation enhancement layer in direct contact with the first electrode. The color saturation enhancement layer consists essentially of one or more metals or conductively doped inorganic semiconductors and has a refractive index that differs from the refractive indices of the organic layers by at least 0.2. The color saturation enhancement layer has a thickness of from 1 nm to 10 nm. The reflectance of the color saturation enhancement layer is in the range of 5% to 30% with respect to the peak wavelength of the intrinsic emission spectrum of the emissive material. Preferably, the color saturation enhancement layer is disposed between the first electrode and the second electrode.

In general, an OLED includes at least one organic layer disposed between an anode and a cathode and electrically connected thereto. When a current is applied, the anode injects a hole into the organic layer, and the cathode injects electrons into the organic layer. The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and a hole are confined to the same molecule, an "exciter" is formed which is a local electron-hole pair having an excited state. Light is emitted when the exciter relaxes via a photoemission mechanism. In some cases, the exciton can be limited to a quasi molecule or an exciplex. Non-radiative mechanisms (eg, thermal relaxation) may also occur, but are generally considered undesirable.

The initial OLED uses an emissive molecule that emits light from its singlet ("fluorescent") as disclosed in, for example, U.S. Patent No. 4,769,292, the disclosure of which is incorporated herein in its entirety by reference. Fluorescent emissions generally occur in a time frame of less than 10 nanoseconds.

More recently, OLEDs having an emissive material that emits light from a triplet ("phosphor") have been demonstrated. Baldo et al., "Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices" (Nature, Vol. 395, 151-154, 1998; ("Baldo-I")) and Baldo et al. "Very high-efficiency green organic light-emitting" Devices based on electrophosphorescence" (Appl. Phys. Lett., Vol. 75, No. 3, 4-6 (1999) ("Baldo-II")), which is incorporated by reference in its entirety. Phosphorescence is described in more detail at lines 5-6 in US Patent No. 7,279,704, which is incorporated herein by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily to scale. The device 100 can include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emission layer 135, a hole blocking layer 140, and an electron transport layer 145. An electron injection layer 150, a protective layer 155 and a cathode 160. The cathode 160 is a composite cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 can be fabricated by depositing the described layers in sequence. The nature and function of the various layers, as well as example materials, are described in more detail in U.S. Patent No. 7,279,704, the disclosure of which is incorporated herein by reference.

More examples of each of these layers are available. A flexible and transparent substrate-anode combination is disclosed, for example, in U.S. Patent No. 5,844,363, the disclosure of which is incorporated herein by reference. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a 50:1 molar ratio, as described in U.S. Patent Application Publication No. 2003/0230980 The disclosure is hereby incorporated by reference in its entirety. An example of an emissive and host material is disclosed in U.S. Patent No. 6,303,238, the entire disclosure of which is incorporated herein by reference. An example of an n-doped electron transport layer is a Bphen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, the entire disclosure of which is hereby Incorporated by reference. An example of a cathode comprising a thin metal layer with a transparent, electrically conductive, sputter-deposited ITO layer (eg, Mg) is disclosed in U.S. Patent Nos. 5,703,436 and 5,707,745 each incorporated by reference inco : Ag) composite cathode. The theory and use of barrier layers are described in more detail in U.S. Patent No. 6,097,147, and U.S. Patent Application Publication No. 2003/0230980, the disclosure of which is incorporated herein in its entirety. An example of an injection layer is provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated herein in its entirety by reference. A description of the protective layer can be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated herein in its entirety by reference.

FIG. 2 shows an inverted OLED 200. The device comprises a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225 and an anode 230. Device 200 can be fabricated by depositing the described layers in sequence. Since the most common OLED configuration has a cathode disposed above the anode and the device 200 has a cathode 215 disposed below the anode 230, the device 200 can be referred to as an "inverted" OLED. Materials similar to those described with respect to device 100 can also be used in corresponding layers of device 200. Figure 2 provides an example of how certain layers may be omitted from the structure of device 100.

The simple layered structure illustrated in Figures 1 and 2 is provided in a non-limiting example, and it should be understood that embodiments of the invention may be utilized in connection with a variety of other structures. The particular materials and structures described are actually illustrative and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways based on design, performance, and cost factors, or multiple layers may be omitted altogether. Other layers not specifically described may also be included. Materials other than those specifically described may be used. While many of the examples provided herein describe various layers as including a single material, it should be understood that a combination of materials (e.g., a mixture of host material and dopant) or, more generally, a mixture may also be used. Also, the layers can have various sub-layers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED can be described as having an "organic layer" disposed between a cathode and an anode. The organic layer may comprise a single layer or may further comprise, for example, a plurality of different organic material layers as described with reference to Figures 1 and 2.

OLEDs (PLEDs) of polymeric materials such as those disclosed in U.S. Patent No. 5,247,190, issued to s. By way of further example, an OLED having a single organic layer can be used. The OLEDs can be stacked, for example, as described in U.S. Patent No. 5,707,745, the entire disclosure of which is incorporated herein by reference. The OLED structure can be deviated from the simple layered structure illustrated in Figures 1 and 2. For example, the substrate can include an angled reflective surface to improve the output coupling, such as one of the mesa structures described in U.S. Patent No. 6,091,195 to the name of the disclosure of U.S. Pat. One of the pit structures described in U.S. Patent No. 5,834,893, the entireties of each of which is incorporated herein by reference.

Any of the various embodiments may be deposited by any suitable method unless otherwise stated. The preferred method for the organic layer comprises thermal evaporation, ink jet (for example, as described in U.S. Patent Nos. 6,013,982 and 6,087,196, the entireties of each of OVPD) (for example, as described in US Pat. This application is hereby incorporated by reference in its entirety in its entirety by reference in its entirety in its entirety in its entirety. Other suitable deposition methods include spin coating and other solution based processes. The solution based process is preferably carried out in nitrogen or an inert atmosphere. For other layers, the preferred method involves thermal evaporation. The preferred method of patterning comprises depositing through a mask, cold soldering (for example, as described in U.S. Patent Nos. 6,294,398 and 6,468,819, the entireties of each of For example, inkjet and OVJD) are associated with patterning. Other methods can also be used. The material to be deposited can be modified to be compatible with a particular deposition method. For example, substituents such as alkyl or aryl groups having a branched or unbranched group and preferably containing at least 3 carbons can be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons may be used in a preferred range. Materials having an asymmetric structure may have better solution handling capabilities than materials having symmetric structures, as asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents can be used to enhance the ability of small molecules to undergo solution processing.

Devices made in accordance with embodiments of the present invention can be incorporated into a variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, interior or exterior lights and/or signal lights, heads up displays, fully transparent displays, scratch Display, laser printer, telephone, cellular phone, personal digital assistant (PDA), laptop, digital camera, camcorder, viewfinder, microdisplay, vehicle, large wall, theater or Open-air large stadium screen or signboard. Various control mechanisms can be used to control the device made in accordance with the present invention, including a passive matrix and an active matrix. Many devices are intended to be used in a temperature range that is comfortable for people, such as 18 degrees Celsius to 30 degrees Celsius, and more preferably at room temperature (20-25 degrees Celsius).

The materials and structures described herein can be applied to devices other than OLEDs. For example, other optoelectronic devices (eg, organic solar cells and organic photodetectors) may employ such materials and structures. More generally, organic materials (eg, organic transistors) can employ such materials and structures.

The terms halo, halo, alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic, aryl, aromatic, and heteroaryl are known to the art and are This is defined in U.S. Patent No. 7,279,704, the disclosure of which is incorporated herein by reference.

FIG. 3 shows an organic light emitting device 300 including a color saturation enhancement layer 330. The device 300 includes a substrate 310, a first electrode 320, a color saturation enhancement layer 330, an emission layer 340, and a second electrode 350. The device 300 can be a top emitting device that emits light from the emissive layer 340 through the substrate 310, the anode 320, and the color saturation enhancement layer 330 to a viewer. A color saturation enhancement layer can be used with devices comprising layers other than the layers shown in device 300, many of which have been described in the preceding paragraphs. Although FIG. 3 shows that the color saturation enhancement layer is between the first electrode and the second electrode and is in direct contact with the first electrode, it may also be at other locations in the device as long as it is adjacent to a light. Its electrode can be. Transparent metal oxides are commonly used in OLED devices as electrodes through which light can pass. The color saturation layer can be in direct contact with the first electrode (such as the "bottom emission" device illustrated in Figure 3) or in direct contact with the second electrode (such as the "top emission" device illustrated in Figure 3) And the color saturation enhancement layer can be between the electrodes or not between the electrodes. The particularity of the position of the "first" and "second" electrodes in the device as described in this paragraph is not intended to limit the terms used in the claims, unless specifically recited.

Figure 4 illustrates a preferred configuration. The device 400 includes a substrate 410, a first electrode 420, a color saturation enhancement layer 430, a hole injection layer 440, an emission layer 450, a hole barrier layer 460, an electron transfer layer 470, and a second electrode 480. . The first electrode 420 is an anode and the second electrode 480 is a cathode.

Figure 4 shows a color saturation enhancement layer added to a conventional OLED configuration (i.e., a device in which the anode is closer to the substrate than the cathode and typically emits light through the substrate). However, the use of a color saturation enhancement layer can be applied to various OLED configurations that can emit light through the anode or cathode and/or through the bottom electrode (i.e., the electrode disposed on the substrate) or the top electrode.

Alternatively, the color saturation enhancement layers of Figures 3 and 4 can be sufficiently conductive to act as an electrode. In this case, a first electrode that is separate from the color saturation enhancement layer may not be needed, but it may still be present. The layer illustrated as the first electrode 320 in FIG. 3 or the first electrode 420 in FIG. 4 may be a transparent metal oxide that may or may not be electrically conductive. Examples of suitable transparent non-conductive metal oxides of cerium oxide and tungsten oxide. Indium tin oxide is an example of a suitable conductive metal oxide.

Figure 5 shows a CIE diagram. This is from a specific pattern of 1931. The shaded area contains all CIE coordinates that describe the visible light. The emission from a "single" wavelength source has a CIE coordinate on the horseshoe track. An example of the number of CIEs at a particular wavelength is displayed. It can be said that the emission having a CIE coordinate close to the horseshoe-shaped trajectory is more saturated than the emission having a CIE away from the horseshoe-shaped trajectory. A particular emission spectrum can be made more saturated by reducing the width of the spectrum. A color saturation metric is the full width at half maximum (FWHM) of the emission spectrum. There are specific colors required for various industry standards, such as red, green, and blue for a full color display. Red, green, and blue are the vertices of the triangle in this pattern, with blue on the left, red on the right, and green on the top. A full color display using materials capable of emitting specific red, green, and blue colors at the vertices of the triangle can display any color within the triangle by combining red, green, and blue emissions. Different industry standards require different specific red, green, blue or other colors. One problem is that many materials have an emission spectrum that is not saturated with the red, green, and blue colors desired for a full color display. Blue is especially a problem. By using a color saturation enhancement layer, the emission from a device can be made more saturated with respect to the inherent emission shift of the emissive material used in the device and moved toward the blue desired by the industry.

The color saturation enhancement layer is disposed between the first electrode and the second electrode and is in direct contact with the first electrode. The color saturation enhancement layer is selected to provide a "weak" reflection of light emitted by the emissive material of the emissive layer. It is believed that substantially consists of one or more metals or highly conductive semiconductors (e.g., p or n-type germanium, i.e., a conductively doped inorganic semiconductor) and has a color thickness of from 1 nm to 10 nm. The saturation enhancement layer will generally provide the desired weak reflection. Those skilled in the art can readily determine the amount of reflectance provided by a particular layer in a device. There are also kits that can be used to calculate the optical properties of the device, for example, ETFOS from Switzerland, Fluxim AG. Dorfstrasse 7 8835 Feusisberg.

By a "weak" reflection, this means that the color saturation enhancement layer has a reflectance of less than 30% for the peak wavelength of the intrinsic emission spectrum of the emissive material. The color saturation enhancement layer should have a reflectivity of at least 5% reflectivity to affect the CIE coordinates of the emitted light.

The "reflectance" of a layer is caused by the difference in refractive index between the other layer and the adjacent layer. Most of the light reflection occurs at the interface between the layers, and the amount of light emitted at a particular interface depends on the difference in refractive index. In order to provide sufficient reflectivity, the refractive index of the color saturation enhancement layer should differ from the refractive index of the adjacent organic layer by at least 0.2. In a particular device fabricated and modeled as described herein, the refractive index of the color saturation enhancement layer is modeled to be less than the refractive index of the organic layers. However, it is also desirable that a color saturation enhancement layer having a refractive index higher than the refractive index of the adjacent organic layers causes some reflectivity and may also be used. The difference in refractive index of these materials can be quite large, up to 4.0. However, the combination of the refractive index and thickness of the layer should be such that the color saturation enhancement layer provides a weak reflection. Most organic materials currently used in OLEDs have a refractive index in the range of 1.5 to 2.3. The interface between the color saturation enhancement layer and the underlying metal oxide layer also causes reflectance that should be considered. In the case where a color saturation enhancement layer is not between the electrodes, that is, the color saturation enhancement layer is not in contact with the organic layers, the refractive index of the color saturation enhancement layer should be different from the refractive index of the adjacent electrode. At least 0.2.

Since reflection occurs at the interface, a correlation comparison occurs in comparison to a device having a single interface between an organic layer and a metal oxide layer and appearing in an additional layer having an additional color saturation enhancement layer. The reflection of different devices (having an interface between the organic layer and the color saturation enhancement layer and having another interface between the color saturation enhancement layer and the metal oxide layer). The "weak" reflection provided by the color saturation enhancement layer means that the color saturation enhancement layer is responsible for no more than 30% light reflection. Thus, the additional light reflection in a device having a color saturation enhancement layer is no more than 30% relative to the reflection that would occur in a different device that does not have a color saturation enhancement layer. In a conventional device structure having an organic layer disposed directly over an ITO anode, it is desirable to have about 5-10% reflection at the ITO organic interface. The color saturation enhancement layer complements this reflectivity by adding an additional 5-30% reflectivity.

The reflectivity of one layer can be wavelength dependent. The relevant wavelength for the reflectance of the color saturation enhancement layer is the peak wavelength of the intrinsic emission spectrum of the emissive material. The "inherent" emission spectroscopy is an emission spectrum of a material that does not undergo any optical confinement (eg, the presence of a microcavity). One way to observe the intrinsic emission spectrum of a material is to photoexcite the material in a suitable solvent. The emission spectrum observed from a device can be significantly different from the intrinsic emission spectrum due to the presence of optical microcavities, different absorptions at different wavelengths, or other optical considerations. One purpose of the color saturation enhancement layer is to modify the emission spectrum to obtain a more saturated emission from the device than the intrinsic spectrum of the emissive material, without the undesirably high angular dependence associated with the microcavity.

One way to measure the beneficial effects of a color saturation enhancement layer is to compare the emission spectrum of a device having a color saturation enhancement layer with a different device that does not have a color saturation enhancement layer. By providing additional reflectivity, the color saturation enhancement layer is capable of narrowing the emission spectrum of the light emitted by the device. The full width at half maximum (FWHM) of the emission spectrum is a related parameter. Preferably, the emission spectrum of a device having a color saturation enhancement layer is at least 5 nm narrower than the emission spectrum of a different device having no color saturation enhancement layer, more preferably at least 10 nm narrower than Jiabi is at least 12 nanometers narrow. Referring to FIG. 11, for example, the second device and the seventh device in the illustrated embodiment are different devices, wherein the second device has a 5 nm thick Ag color saturation enhancement layer, and the seventh device does not have a 5 Nano thick Ag color saturation enhancement layer. The FWHM of the emission spectrum of the second device is 44 nm, and the FWHM of the seventh device is 57 nm. Both emission spectra are plotted in Figure 11, and the emission spectrum of the seventh device is clearly wider (i.e., less "saturated") than the emission spectrum of the second device.

It is believed that, in general, it is considered undesirable to use certain metals (e.g., aluminum and chromium) in an organic light-emitting device between the anode and the organic layer. See "Efficient organic light-emitting diode using semitransparent silver as anode" by Peng et al. (Applied Physics Letters 87, 173505, p. 1 (2005)), which teaches that a high work function metal is desired to reduce the barrier of hole injection; Conversely, low work function metals are not desired. Surprisingly, it has been found that these metals can be used as a thin layer between the anode and the organic layer of an organic light-emitting device as a color saturation enhancing layer. A hole injection layer made of a material such as LG101 or NPD doped with F4TCNQ can be used to alleviate the problems caused by the lower work function of the metals. It is believed that the band offset in the hole injection layer can be achieved when the hole injection layer is highly conductive, resulting in a good hole that overcomes the problems associated with low work functions of metals such as aluminum and chromium. injection. Silver is also a preferred material for use as a color saturation enhancement layer. More generally, the color saturation enhancing layer can be a metal having a thickness of from 1 nanometer to 10 nanometers.

The microcavity can be used to adjust the emission spectrum of an OLED. However, the use of microcavities has an undesirable effect at eccentric viewing angles. In general, when the viewing angle is increased from zero (i.e., the normal direction to the substrate) to sixty degrees, the light intensity in a device having a microcavity is more significant than in a device having no microcavity. Reduced. Additionally, the CIE coordinates of the light observed at a non-zero viewing angle can be significantly shifted relative to the CIE coordinates at a zero viewing angle.

Surprisingly, the use of a weak microcavity (i.e., a reflection from a layer between the viewer and the emissive layer that is less than the microcavity typically used for reflection of the microcavity) provides a number of color shifting benefits of a microcavity, At the same time, the intensity associated with the microcavity and the undesired angular dependence of the CIE coordinates are maintained.

Unexpectedly, a color saturation enhancement layer does not produce a strong angular dependence on the CIE coordinates and peak wavelengths typically associated with the use of a microcavity. For example, a color saturation enhancement layer can be used to reduce the FWHM of the emission spectrum of a device to be different from the FWHM of a different device that does not have a color saturation enhancement layer, with zero and sixty degrees by the device. The peak wavelength of the light emitted at all angles is not more than 1.5%, preferably not more than 1.0%, and more preferably not more than 0.5%, with respect to the peak wavelength emitted at an angle of zero. For example, the results are illustrated in Figures 14 and 27. In Fig. 14, a device having a color saturation enhancement layer has a peak wavelength of 462 nm and is not measurably shifted when the viewing angle changes from zero to 60 degrees (i.e., any shift is less than 2 nm). Meter, this is the resolution of the device used to measure the wavelength). In Fig. 27, when the viewing angle is changed from zero to 60 degrees, the peak wavelength of a device having a microcavity is shifted from 464 nm to 456 nm, that is, a displacement of 1.75%.

For a device having a color saturation enhancement layer, as illustrated in FIG. 14, the x coordinate of the CIE may vary less than 0.01 between the normal direction of the substrate and the viewing angle of the substrate at sixty degrees from the normal direction. And the y coordinate of CIE can vary less than 0.03. It is expected that the magnitude of the CIE shift in the case of the viewing angle of Figure 14 will generally be applicable to the color saturation enhancement layer.

Similarly, in the case of using a weak microcavity, the light intensity at various viewing angles is not drastically reduced as it would be when using a strong microcavity. Figures 16A and 16B illustrate this point. Fig. 16B shows that for a weak cavity corresponding to the device of Fig. 15A, the intensity deviation from Lambertian does not exceed 13% for a viewing angle of 60 degrees or less. Thus, by virtue of the benefit of this disclosure, those skilled in the art can make devices having weak microcavities that do not change the light intensity at various viewing angles by more than 20%, and more preferably less than 15%. . For a Lambertian launch that remains close to various viewing angles, a device having a weak microcavity has performance comparable to a standard device (i.e., the device of Figure 15B). Thus, the color shifting properties of the weak microcavities can be achieved without significantly detrimentally affecting the light intensity at various viewing angles.

While a color saturation enhancement layer can be used with beneficial effects in various color OLEDs, it is particularly desirable to use a color saturation enhancement layer in a blue light device. By "blue light", this means that the intrinsic emission spectrum of the emissive material has a peak wavelength of less than 500 nm. Obtaining an OLED device that emits saturated blue light (although having many other desirable properties, such as high efficiency and long device life) has caused considerable challenges. The use of a color saturation enhancement layer allows adjustment of other parameters (eg, the chemical composition of the emissive material) and can compensate for any resulting shift in the CIE coordinates of the light emitted by the device. Looking at the particular emissive material used, it is desirable to use an additional saturated color saturation enhancement layer that results in a particular amount. For example, for a device that has emitted near saturated blue, it may be desirable to use a color saturation enhancement layer to narrow the FWHM of the emission spectrum of the device by only 5 nanometers. For a device that is slightly further away from the saturated blue emission but perhaps as part of a trade-off that results in higher device stability or lifetime, it is desirable to use a color saturation enhancement layer to narrow the FWHM of the emission spectrum of the device. Larger amounts, such as 10 or 12 nm.

A color saturation enhancement layer can also have a conductivity that is significantly greater than the conductivity of a transparent semiconductor that is typically used as a transparent electrode in an OLED. Thus, the use of a color saturation enhancement layer can increase the lateral conductivity in the device and result in higher brightness uniformity.

6, 8, 12, 15, 17, 21 and 26 show schematic cross-sectional views of an OLED. The device of Figure 17 is not actually made. Instead, the parameters of the device are used to calculate the data shown in Figures 18 and 19.

The apparatus illustrated in Figures 6, 8, 12, 15, 21 and 26 was fabricated and measured. Unless otherwise indicated, each device was fabricated as follows: A substrate coated with ITO was purchased from Nippon Sheet Glass Co., Ltd., Kanagawa Prefecture, Japan. All layers after the ITO were deposited by vacuum thermal evaporation (VTE).

In these figures, Complex A or "A" refers to the following complex:

Complex B or "B" refers to the following complex:

Complex C or "C" refers to the following complex:

LG101 ^TM is a product purchased from LG Korea.

Other compounds are described using terms well known in the art.

Figure 6 shows a schematic cross-sectional view of a device that does not include a color saturation enhancement layer. The device of Figure 6 comprises a 80 nm thick ITO anode, a 10 nm thick Ir(ppy) ₃ hole injection layer, a 70 nm thick mCBP emissive layer doped with 15% of composite B, and a 10 nm. The mCBP hole barrier layer, a 20 nm thick Alq electron transfer layer and a LiF/Al cathode. The device of Fig. 6 is also the seventh device in the legend of Fig. 11, that is, the device of Fig. 8 which does not have a color saturation enhancement layer, X = 20 nm and Y = 10 nm.

Figure 7 shows the photoluminescence spectrum measured by the apparatus of Figure 6 at various viewing angles as it passes through the apparatus at a current of 10 mA/cm ² . As can be seen in Figure 7, the CIE coordinates of the emitted light shift as the viewing angle increases from zero to 60 degrees.

Figure 8 shows a cross-sectional view of a device comprising a 5 nm thick Ag color saturation enhancement layer and variable electron transfer and barrier thickness. The device of Figure 8 comprises a 80 nm thick ITO anode, a 5 nm thick Ag color saturation enhancement layer, a 10 nm thick Ir(ppy) ₃ hole injection layer, and a 70 nm thick doping 15%. The mCBP emissive layer of composite B, an mCBP hole blocking layer having a variable thickness Y of from 5 to 15 nm as shown in FIG. 11, an Alq having a variable thickness X as shown in FIG. Electron transfer layer and a LiF/Al cathode. "Variable thickness" means a device having a plurality of hole blocking and electron transfer layers having specific thicknesses X and Y as shown in FIG. One of the devices does not have a color saturation enhancement layer, again as indicated in FIG.

Figure 9 shows a graph of the measured external quantum efficiency versus the brightness of the device of Figure 8. The legend is in Figure 11. Figure 9 shows that at a brightness of 10 cd/m ² , the device without a color saturation enhancement layer has the highest efficiency. However, at higher brightness, the efficiency of a device having a color saturation enhancement layer is improved relative to devices without this layer.

Figure 10 shows a graph of the measured brightness vs. voltage device of Figure 8. The legend is in Figure 11. Figure 10 shows that a device having a color saturation enhancement layer has a lower operating voltage than a device without this layer. It is believed that the lower operating voltage is the result of the more efficient hole injection and recombination of the Ag color saturation enhancement layer towards the cathode.

Figure 11 shows a graph of the measured electroluminescence intensity versus the wavelength of the device of Figure 8. The CIE coordinates of each device are also shown in the legend. Comparison device 2 and device 7, both having X = 20 and Y = 10, and differing in that device 2 has an Ag color saturation enhancement layer and device 7 does not have it. It can be seen that the presence of a color saturation enhancement layer has a significant effect on the emission spectrum. In particular, the device 2 is significantly blue shifted relative to the device 7.

From the legend of Figure 11, the second device is almost identical to the seventh device except that the second device has a 5 nm thick Ag color saturation enhancement layer and the seventh device does not. Both devices have the structure shown in Figure 8, where X = 20 nm and Y = 10 nm. The device having the color saturation enhancement layer has the following characteristics at 1000 cd/m ² : CIE (0.1402, 0.1790), operating voltage 10.9 V, and efficiency = 6%. A different device without a color saturation enhancement layer has the following characteristics at 1000 cd/m ² : CIE (0.1613, 0.2671), operating voltage 13.7 V, and efficiency = 6.5%. Based on the measured values of the slightly different devices of FIG. 14, it is desirable that the x coordinate change of the CIE is less than 0.01 between the substrate and the viewing angle of the substrate at a distance of sixty degrees from the substrate of the second device of FIG. 11 in the normal direction. The y coordinate change of CIE is less than 0.03. For the seventh device of FIG. 11, there is no color saturation enhancement layer, and the x coordinate of the CIE varies by about 0.0045 and CIE in the normal direction between the substrate and the viewing angle of the substrate at sixty degrees from the normal direction. The y coordinate changes by about 0.0059. As illustrated in Figure 7, the apparatus of Figure 6 is the apparatus of Figure 8, where X = 20, Y = 10 and no Ag layer. This increases the CIE coordinate change in the case where the viewing angle in a device having a color saturation enhancement layer is not significant relative to a device layer that does not have this layer.

Figure 12 shows a schematic cross-sectional view of a device comprising a 5 nm thick Ag color saturation enhancement layer. The device of Figure 12 comprises a 80 nm thick ITO anode, a 5 nm thick Ag color saturation enhancement layer, a 10 nm thick Ir(ppy) ₃ hole injection layer, and a 70 nm thick doping with 15%. The mCBP emissive layer of the composite B, a 5 nm thick mCBP hole blocking layer, a 10 nm thick Alq electron transfer layer and a LiF/Al cathode.

Figure 13 is a graph showing the measured normalized photoluminescence intensity versus the wavelength of the device of Figure 12 at various operating currents. A red shift was observed at the higher operating current as indicated by the CIE coordinate in the legend of Figure 13. The optical model shown in Figures 17-19 shows the red shift when the recombination is positioned away from the cathode. Thus, it is believed that the recombined positioning in the apparatus of Figure 12 is shifted away from the cathode when a high current is applied, as illustrated in Figure 13.

Figure 14 is a graph showing the measured photoluminescence intensity versus the wavelength of the device of Figure 12. The peak wavelength remains constant with increasing viewing angle. The peak wavelength difference between zero and sixty degrees is lower than the resolution of the measuring device used, which is 2 nm. It is less than 0.5%. This results in surprisingly different results from the typical results of a device having a microcavity, where the peak wavelength is generally shifted significantly with viewing angle, as seen in Figure 26. The CIE coordinates are also generally changed in a device having a microcavity as the viewing angle increases.

Figure 15 shows a cross-sectional schematic view of other similar devices having various thicknesses of silver over the anode. Figure 15A shows a cross-sectional view of one of the devices without a 5 nm thick Ag color saturation enhancement layer. The device of Fig. 15A comprises a 80 nm thick ITO anode, a 10 nm thick Ir(ppy) ₃ hole injection layer, a 70 nm thick mCBP emissive layer doped with 15% of composite B, and a 10 nm. The mCBP hole barrier layer, a 20 nm thick Alq electron transfer layer and a LiF/Al cathode. The device of Figure 15B is similar to the device of Figure 15A but with an additional layer (a 5 nm thick Ag color saturation enhancement layer between the anode and the hole injection layer). The device of Figure 15C is similar to the device of Figure 15B, but the Ag layer is 25 nanometers thick rather than 5 nanometers thick; too thick for a color saturation enhancement layer. The device of Fig. 15C also uses LG101 instead of Ir(ppy) ₃ for the hole injection layer, and composite C as the emission molecule. Although the use of different hole injection layers can affect certain device properties, the particular substitutions made herein are not expected to affect the angular normalization of the light emitted by the device. The device performs the measurement because LG101 and Ir(ppy) ₃ have similar refractive indices at the wavelengths of interest in the figures.

Figure 16 shows a graph of the measured emission intensity curve and the deviation from the Lambertian emission versus the viewing angle of the device of Figure 15. Figure 16A shows the measured emission intensity curve. Figure 16B shows a plot of the deviation from the Lambertian emission versus the viewing angle. The graph of the Lambertian emission in Figure 16A is calculated and corresponds to the X-axis in Figure 16B (zero deviation from Lambertian). The apparatus of Fig. 15A is described as "standard" in the graphs of Figs. 16A and 16B. The device of Fig. 15B having a color saturation enhancement layer is described as "weak cavity" in Figs. 16A and 16B. Figure 15C shows a device having a thick Ag layer as "microcavity" in Figure 16A.

Figure 17 shows a schematic cross-sectional view of a device comprising a 10 nm thick Ag color saturation enhancement layer. The device of Figure 12 comprises a 80 nm thick ITO anode, a 10 nm thick Ag color saturation enhancement layer, a 10 nm thick Ir(ppy) ₃ hole injection layer, a 75 nm thick mCBP emission layer, and a 10 Nano thick Alq electron transfer layer and an Al cathode. The device of Figure 17 is not actually made. Rather, the results shown in Figures 18 through 20 are modeled using the optical properties of the various materials and the thickness of the layers. Optical modeling using the EFTOS program. Modeling was performed using the emission spectrum of Complex A.

Figure 18 shows a graph of the measured CIE X coordinates versus the dipole distance (nano) of the device of Figure 17 from the Alq/mCBP interface.

Figure 19 is a graph showing the measured dipole moment of the CIE Y coordinate versus the Alq/mCBP interface (nano) of the device of Figure 17. Figures 18 and 19 show that the CIE coordinates of the light emitted from the device increase as the radiation dipole (i.e., recombination position) moves away from the Al cathode. Figures 18 and 19 show one of the blue shifts when recombining toward the cathode. Thus, an enhanced hole injection color saturation enhancement layer can be used to shift and recombine the blue shift of the emission spectrum towards the cathode and the device.

Figure 20 shows a graph of the measured light field intensity versus the positioning of the device of Figure 17 for different wavelengths in the device. In the device corresponding to the location of the emissive layer (ie, at 100 nm to 175 nm), the intensity of the optical field at a wavelength of 460 nm (blue) is greater than some higher wavelengths (eg, The optical field strength of 550 nm) enhances the radiation transition of blue photons. A typical blue emitter has a spectrum with a tail that extends to 550 nm, so the intensity of the square in the range of 460 nm to 550 nm is quite significant.

Figure 21 shows a schematic cross-sectional view of a device comprising a 6 nm thick Al color saturation enhancement layer. The device of Figure 21 comprises a 80 nm thick ITO anode, a 6 nm thick Al color saturation enhancement layer, a LG101 hole injection layer having a variable thickness X, and a doping having a variable thickness Y. % of the composite B's mCBP emissive layer, a 25 nm thick mCBP hole blocking layer, a 20 nm thick Alq electron transfer layer, and a LiF/Al cathode. The variable thickness of the device shown in Figure 21 is provided in the legend of Figure 25. Three devices were made which had a constant total thickness. The first device has X = 30 nm and Y = 30 nm, the second device has X = 20 nm and Y = 40 nm, and the third device has X = 10 nm and Y = 50 nm.

Figure 22 shows a graph of the measured external quantum efficiency versus the brightness of the device of Figure 21 (having various thicknesses for certain layers in the device). Figure 22 shows that a device having a thicker hole injection layer and a thinner emissive layer has a higher external quantum efficiency for a given brightness.

Figure 23 shows a graph of the measured power efficacy versus the brightness of the device of Figure 21 (having various thicknesses for certain layers in the device). Figure 23 shows a device having a thicker hole injection layer and a thinner emissive layer having a higher power efficiency brightness for a given brightness.

Figure 24 shows a graph of the measured brightness versus the voltage of the device of Figure 21 (having various thicknesses for certain layers in the device). Figure 24 shows that a device having a thicker hole injection layer and a thinner emissive layer has a higher brightness for a given voltage.

Figure 25 shows a graph of the measured photoluminescence intensity versus the wavelength (emission spectrum) of the device of Figure 21 (having various thicknesses for certain layers in the device). The CIE coordinates of the three devices are also provided in the legend. The photoluminescence spectrum in Figure 25 shows that the CIE y coordinate changes at the position of the recombination zone as it shifts within the device structure having the same total thickness. A better blue CIE is obtained as the distance of the cathode from the recombination zone is reduced. In a configuration in which the color saturation enhancement layer is disposed on an anode, the color saturation enhancement layer enhances hole injection and causes the recombination zone to shift toward the cathode. In addition to the blue shift of the reflectance of the color saturation enhancement layer, this also causes a blue shift in the light emitted by the device.

Figure 26 shows a schematic cross-sectional view of a device comprising a 25 nm thick layer of Ag (which therefore has a microcavity). The device of Figure 26 comprises a 25 nm thick Ag anode, a 10 nm thick LG101 hole injection layer, a 25 nm thick NPD hole transfer layer, and a mCBP emission layer doped with 12% of composite C. A 37.5 nm thick Alq electron transfer layer and a LiF/Al cathode.

Figure 26 is a graph showing the measured photoluminescence intensity versus the wavelength measured by the device of Figure 26 at various viewing angles. Figure 26 shows that the peak wavelength shifts from 464 nm at a viewing angle of zero to 456 nm at a viewing angle of 50 degrees.

It is to be understood that the various embodiments described herein are merely illustrative and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted by other materials and structures without departing from the spirit of the invention. Thus, it will be apparent to those skilled in the <RTIgt;the</RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; It should be understood that the various theories as to why the invention may be practiced are not intended to be limiting.

100. . . Device

110. . . Substrate

115. . . anode

120. . . Hole injection layer

125. . . Hole transport layer

130. . . Electronic barrier

135. . . Emissive layer

140. . . Hole barrier

145. . . Electronic transport layer

150. . . Electron injection layer

155. . . The protective layer

160. . . cathode

162. . . First conductive layer

164. . . Second conductive layer

200. . . Inverted OLED

210. . . Substrate

215. . . cathode

220. . . Emissive layer

225. . . Hole transport layer

230. . . anode

300. . . Device

310. . . Substrate

320. . . First electrode

330. . . Color saturation enhancement layer

340. . . Emissive layer

350. . . Second electrode

400. . . Device

410. . . Substrate

420. . . First electrode

430. . . Color saturation enhancement layer

440. . . Hole injection layer

450. . . Emissive layer

460. . . Hole barrier

470. . . Electron transfer layer

480. . . Second electrode

Figure 1 shows an organic light emitting device.

Figure 2 shows an inverted organic light-emitting device that does not have a separate electron transport layer.

Figure 3 shows an organic light-emitting device having a color saturation enhancement layer.

Figure 4 shows an organic light-emitting device having a color saturation enhancement layer.

Figure 5 shows a CIE diagram.

Figure 6 shows a schematic cross-sectional view of a device that does not include a color saturation enhancement layer.

Figure 7 shows the photoluminescence spectrum measured by the apparatus of Figure 6 at various viewing angles.

Figure 8 shows a cross-sectional view of a device comprising a 5 nm thick Ag color saturation enhancement layer and variable electron transfer and barrier thickness.

Figure 9 shows a graph of the measured external quantum efficiency versus the brightness of the device of Figure 8. The legend is in Figure 11.

Figure 10 shows a graph of the measured brightness versus the voltage of the device of Figure 8. The legend is in Figure 11.

Figure 11 shows a graph of the measured electroluminescence intensity versus the wavelength of the device of Figure 8.

Figure 12 shows a schematic cross-sectional view of a device comprising a 5 nm thick Ag color saturation enhancement layer.

Figure 13 is a graph showing the measured normalized photoluminescence intensity versus the wavelength of the device of Figure 12 at various operating currents.

Figure 14 is a graph showing the measured photoluminescence intensity versus the wavelength of the device of Figure 12.

Figure 15 shows a cross-sectional schematic view of other similar devices having various thicknesses of silver over the anode. Figure 15A shows a cross-sectional view of one of the devices without a 5 nm thick Ag color saturation enhancement layer. Figure 15B shows a cross-sectional view of one of the devices having a 5 nm thick Ag color saturation enhancement layer. Figure 15C shows a schematic cross-sectional view of a device having a 25 nm thick layer of Ag to create a microcavity.

Figure 16 shows a graph of the measured emission intensity curve and the deviation from the Lambertian emission versus the viewing angle of the device of Figure 15. Figure 16A shows the measured emission intensity curve. Figure 16B shows a plot of the deviation from the Lambertian emission versus the viewing angle. The graph of the Lambertian emission in Figure 16A is calculated and corresponds to the X-axis in Figure 16B (zero deviation from Lambertian).

Figure 17 shows a schematic cross-sectional view of a device comprising a 10 nm thick Ag color saturation enhancement layer.

Figure 18 is a graph showing the measured dipole distance of the CIE X coordinate versus the Alq/mCBP interface (nano) of the device of Figure 17.

Figure 19 is a graph showing the measured dipole moment of the CIE Y coordinate versus the Alq/mCBP interface (nano) of the device of Figure 17.

Figure 20 shows a graph of the measured light field intensity versus the positioning of the device of Figure 17 for different wavelengths in the device.

Figure 21 shows a schematic cross-sectional view of a device comprising a 6 nm thick Al color saturation enhancement layer.

Figure 22 shows a graph of the measured external quantum efficiency versus the brightness of the device of Figure 21 (having various thicknesses for certain layers in the device).

Figure 23 shows a graph of the measured power efficacy versus the brightness of the device of Figure 21 (having various thicknesses for certain layers in the device).

Figure 24 shows a graph of the measured brightness versus the voltage of the device of Figure 21 (having various thicknesses for certain layers in the device).

Figure 25 shows a graph of the measured photoluminescence intensity versus the wavelength (emission spectrum) of the device of Figure 21 (having various thicknesses for certain layers in the device).

Figure 26 shows a schematic cross-sectional view of a device comprising a 25 nm thick layer of Ag (which therefore has a microcavity).

Figure 27 is a graph showing the measured photoluminescence intensity versus the wavelength measured by the device of Figure 26 at various viewing angles.

300. . . Device

310. . . Substrate

320. . . First electrode

330. . . Color saturation enhancement layer

340. . . Emissive layer

350. . . Second electrode

Claims (15)

An organic light-emitting device comprising: a first electrode comprising a transparent metal oxide; a second electrode; at least one organic layer disposed between the first electrode and the second electrode, the at least one organic The layer includes an emissive layer, wherein the emissive layer comprises an emissive material having an intrinsic emission spectrum having a peak emission wavelength of less than 500 nm in the visible spectrum; and a color saturation enhancement layer disposed on Between the first electrode and the second electrode and in direct contact with the first electrode, wherein the color saturation enhancement layer is substantially composed of one or more metals or conductive doped inorganic semiconductors; wherein the color saturation enhancement layer has a The refractive index of the at least one organic layer differs by at least 0.2 and is in direct contact with the at least one organic layer; wherein the color saturation enhancing layer has a thickness of from 1 nm to 10 nm; wherein the intrinsic The peak wavelength of the emission spectrum, the reflectance of the color saturation enhancement layer is in the range of 5% to 30%; wherein the color saturation enhancement layer is substantially composed of silver and chromium Aluminum and cobalt, wherein one composition. The device of claim 1, wherein the first electrode is an anode and the second electrode is a cathode. The device of claim 1, wherein the second electrode comprises a transparent conductive oxide. The device of claim 3, wherein the second electrode comprises an indium tin oxide. The device of claim 1, wherein the device has an emission spectrum having a full width at least one-half of a height of at least 5 nanometers less than a full width at half maximum of the device having one of the different color saturation enhancement layers. The device of claim 1, wherein the device has an emission spectrum having a full width at least one-half of a height of at least 10 nm less than a full width at half maximum of the device having one of the different color saturation enhancement layers. The device of claim 1, wherein the device has an emission spectrum having a full width at least half of a height of at least 12 nm that is less than a full width at half maximum of the device having one of the different color saturation enhancement layers. A device as claimed in claim 1, wherein the device has a peak wavelength of light emitted at all angles between zero and sixty degrees and a deviation from a peak wavelength emitted at an angle of zero degrees of no more than 1.5%. The apparatus of claim 1, wherein the peak wavelength of the light emitted by the apparatus at all angles between zero and sixty degrees is not more than 1.0% of the peak wavelength emitted at an angle of one degree. A device according to claim 1, wherein the device has a peak wavelength of light emitted at all angles between zero and sixty degrees and a deviation from a peak wavelength emitted at an angle of zero degrees of not more than 0.5%. A device according to claim 5, wherein the device has a peak wavelength of light emitted at all angles between zero and sixty degrees and a deviation from a peak wavelength emitted at an angle of zero degrees of not more than 1.5%. The device of claim 1, wherein the emission layer is observed at a zero angle The CIE coordinates of the emitted light differ from the CIE coordinates of the light emitted at an angle of 60 degrees by no more than 0.01 and 0.03. A device as claimed in claim 1, wherein the intensity of the light emitted by the device differs from the Lambertian emission by less than 20% at all angles from zero to sixty degrees. A device as claimed in claim 1, wherein the intensity of the light emitted by the device differs from the Lambertian emission by less than 15% at all angles from zero to sixty degrees. An organic light-emitting device comprising: a first electrode comprising a transparent metal oxide; a second electrode; an emissive layer disposed between the first electrode and the second electrode, wherein the emissive layer comprises An emissive material having an intrinsic emission spectrum having a peak emission wavelength of less than 500 nm in the visible spectrum; and a color saturation enhancement layer in direct contact with the first electrode, wherein the color saturation is enhanced The layer consists essentially of one or more metal or conductive doped inorganic semiconductors; wherein the color saturation enhancement layer has a refractive index that differs from the first electrode by a refractive index of at least 0.2 and is disposed at the first electrode and the second electrode Directly in contact with the emissive layer; wherein the color saturation enhancing layer has a thickness of from 1 nm to 10 nm; wherein the peak wavelength of the intrinsic emission spectrum of the emissive material, The color saturation enhancement layer has a reflectance in the range of 5% to 30%; wherein the color saturation enhancement layer consists essentially of one of silver, chromium, aluminum, and cobalt.