KR20060111643A - Flexible electroluminescent devices - Google Patents

Abstract

An organic light emitting diode (OLED) formed on an opaque flexible substrate is disclosed. The opaque flexible substrate is composed of one of the following: (i) a plastic layer laminated to or coated with a metal layer, (ii) a metal layer sandwiched between two plastic layers, or (iii) a metal foil. When the OLED is formed on a metal surface of the flexible substrate, the metal surface may be coated with an isolation layer. The isolation layer may be a spin- coated polymer layer or a dielectric layer. The metal in the flexible substrate serves as a barrier to minimize the permeation of oxygen and moisture to the OLED. In addition, the OLED is provided with a transparent or semi-transparent upper electrode so that light can emit through the upper electrode.

Description

Flexible electroluminescent device {FLEXIBLE ELECTROLUMINESCENT DEVICES}

The present invention generally relates to organic electroluminescent devices, and more particularly to flexible organic light emitting devices (OLEDs).

Recently, organic light emitting diodes (OLEDs) can produce high visibility by self-luminescence, and thus can replace liquid crystal displays (LCDs) because they do not require the necessary back-lighting in LCDs. It is attracting attention as a display element. Typical OLEDs are made by placing an organic light emitting material between a cathode layer capable of injecting electrons and an anode layer capable of injecting holes. When a voltage of the appropriate polarity is applied between the cathode and the anode, holes injected from the anode and electrons injected from the cathode combine to release the light energy, producing electroluminescence. Polymer electroluminescent materials have been used in OLEDs and these devices are called PLEDs.

One common structure of an OLED is a bottom-emitting structure, where light can be emitted from the bottom of the structure, including a metal or metal alloy cathode and a transparent anode on a transparent substrate. OLEDs can also have a top-emitting structure formed on an opaque substrate or a transparent substrate. The top-emitting OLED has a relatively transparent top electrode so that light can be emitted from the top electrode side. Top-emitting OLEDs have two typical structures. If the OLED structure has a transparent anode on top of the organic layer, that structure is called inverted OLED. In addition, the top-emitting OLED can be made of a transparent cathode on top of the organic layer. OLEDs having a transparent anode and a transparent cathode formed on a transparent substrate are called transparent OLEDs. Top-emitting OLED structures increase flexibility in device integration and processing. Top-emitting OLEDs are also desirable for high resolution displays.

Typically, OLEDs have been fabricated on rigid glass substrates. The glass has low permeability to oxygen and water vapor. In the past years, ultrathin glass sheets and transparent plastic substrates have been considered as selectable substrates for flexible OLEDs and PLEDs. However, cottage glass sheets are very fragile, and OLEDs formed on ultrathin glass sheets have limited potential as flexible OLED displays. Plastic substrates such as polyethylene terephthalate (PET) and polyethylene naphthalene (PEN) have been used for flexible OLEDs to produce lighter, thinner, rugged, and highly flexible OLEDs. However, these devices have a very short lifespan because plastics exhibit low resistance to water and oxygen. Thus, efforts have been made to protect OLEDs formed on plastic substrates from exposure to oxygen and water vapor in order to minimize degradation of the device.

Various approaches have been proposed to form protective barriers on plastic substrates. See, eg, WO 02/065558, WO 02/091064, US Pat. No. 5,757,126, US Patent Publication No. 2002/0022156. U.S. Patent 5,757,126 discloses a multilayer barrier coating made of organic and inorganic materials. US Patent Publication No. 2002/0022156 proposes a multilayer barrier composite formed on a plastic substrate, wherein the composite consists of a thin transparent metal oxide or metal nitride, and a thin transparent metal film, an organic polymer, a thin transparent dielectric and a thin transparent conductive oxide. At least one additional layer selected from the group. WO 02/065558 discloses a transparent organosilicon protective layer polymerized on a transparent polymer substrate. WO 02/091064 discloses a multilayer barrier comprising an organic layer and an inorganic layer. However, these approaches require many deposition steps and have the potential to adversely affect the optical and mechanical performance of OLEDs. Therefore, these approaches cannot solve the transmission problem in a cost effective way.

Summary of the Invention

The present invention relates to a flexible organic light emitting diode (OLED), more specifically a polymer light emitting diode (PLED), formed on an opaque flexible substrate. An opaque flexible substrate consists of one of (i) a plastic layer laminated or coated with a metal layer, (ii) a metal layer sandwiched between two plastic layers, and (iii) a metal foil. When the OLED is formed on the metal surface of the flexible substrate, the metal surface may be coated with an isolation layer. The isolation layer can be a spin-coated polymer layer or a dielectric layer. The metal in the flexible substrate serves as a barrier to minimize the transmission of oxygen and moisture into the OLED. In addition, the OLED of the present invention is provided with a transparent or translucent top electrode to allow light to be emitted through the top electrode. The novel design of the present invention yields OLEDs that can be easily manufactured by mass production while having excellent barrier properties and high flexibility.

Advantages and novel features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings.

1 shows a cross-sectional view of a representative OLED formed on a plastic / metal substrate, in accordance with the present invention.

2 shows a cross-sectional view of an OLED formed on a metal / plastic substrate having an isolation layer, in accordance with the present invention.

3 shows a cross-sectional view of an OLED formed on a plastic / metal / plastic substrate, in accordance with the present invention.

4 shows a cross-sectional view of an OLED formed on a metal foil, according to the present invention.

5 shows an example of an OLED having a transparent multilayer cathode, according to the present invention.

Referring to FIG. 1, a representative OLED of the present invention is a flexible opaque substrate 1, a lower electrode 2 on top of the substrate, an organic stack 3 on top of the lower electrode and a top of the organic stack. Translucent or transparent top electrode 4. In one embodiment, the flexible opaque substrate 1 consists of a plastic layer 1a laminated to or coated with a metal layer 1b as shown in FIG. 1. Alternatively, as shown in FIG. 2, the OLED may be formed on the metal surface of the substrate 1. In this case, it may be desirable to form the isolation layer 5 between the metal layer 1b and the lower electrode 2. In another embodiment shown in FIG. 3, the flexible substrate 1 consists of a metal layer 1d sandwiched between two plastic layers 1c and 1e. Metallic materials used in the substrate 1 include aluminum and other highly reflective metals. Aluminum is preferred because it is an excellent barrier to water and oxygen. The plastic materials used for the flexible substrate 1 may be selected from polyethylene terephthalate (PET), polyethylene naphthalene (PEN), polyether sulfone (PES) and other plastics known in the art to provide properties suitable for flexible OLEDs. Include. The isolation layer 5 may be a spin-coated polymer layer or a dielectric layer, such as an inorganic oxide or spin-on-glass (SOG). This isolation layer 5 also functions as a polarizing layer.

In another embodiment shown in FIG. 4, the flexible substrate 1 is a metal foil coated with an isolation layer 5. The metal foil can be made of aluminum, copper or stainless steel. The isolation layer 5 is as described above with respect to FIG. 2. The metal foil in this case reflects the emitted light back to the relatively transparent upper electrode 4 and functions as a mirror-like surface and a barrier layer.

The upper electrode 4 may be a cathode or an anode. If the upper electrode 4 is an anode, the lower electrode 2 acts as a cathode, the OLED of which is called an inverted OLED. The lower electrode 2 may be transparent or opaque, and may be reflective or light absorbing. The upper electrode 4 should be translucent or transparent (hereinafter referred to as "relatively transparent"). Suitable materials for the upper electrode 4 and the lower electrode 2 include a conductive polymer material, a conductive organic material, a transparent conductive oxide (TCO), a metal or a metal alloy. Examples of TCO are indium-tin-oxide (ITO), zinc-indium-oxide (ZIO), aluminum-doped ZnO, Ga-In-Sn-O (GITO), SnO ₂ , Zn-In-Sn-O ( ZITO) and Ga-In-O (GIO). Suitable metals include gold (Au), silver (Ag), aluminum (Al), iridium (Ir), nickel (Ni) and chromium (Cr). The lower electrode 2 or the upper electrode 4 may be a single layer structure made of one of the aforementioned materials or a combination of these materials or a multilayer structure made of a combination of these materials. If metal is used as the electrode material, the interface of the metal electrode (ie, the interface between the metal electrode and the organic stack 3) can be modified to promote electron carrier injection in the OLED. TCO (eg ITO) has been found to be effective for modifying metal surfaces. The material used to modify the metal surface of the electrode is not limited to the TCO, but other inorganic materials as well as organic materials may be used for the same purpose. When the metal electrode is modified, the interface modification layer is located between the organic stack 3 and the metal electrode.

The relatively transparent upper electrode 4 may consist of a relatively transparent conductive monolayer, or a multilayer structure containing one or more relatively transparent conductive layers. The multilayer top electrode may comprise a relatively transparent conductive layer covered with an index-matching layer to enhance light output. The index-matching layer is made of an organic or inorganic material having a refractive index effective to enhance light output. Examples of materials for the index-matching layer include tris- (8-hydroxyquinoline) aluminum (Alq3), N, N'-di (naphthalen-1-yl) -N, N'-diphenylbenzidine (NPB), MgF ₂ , SiO ₂ , MgO, ITO, ZnO, TiO ₂ . In some cases, the TCO layer (such as ITO) serves as both a relatively transparent top electrode and an index-matching layer to promote light output. The index-matching layer also serves as a barrier or encapsulation layer. The index-matching layer may have a thickness of 1 to 500 nm, depending on the refractive index of the material used. The multilayer top electrode may further comprise one or more thin charge carrier injection layers formed between the relatively transparent conductive layer and the organic stack 3. When the multilayer upper electrode is the cathode, the charge carrier injection layer is an electron injection layer. Suitable materials for the electron injection layer include low work function metals, such as rare earth metals. When the multilayer upper electrode is an anode, the charge carrier injection layer is a hole injection layer. The hole injection layer may be made of high work function metal (eg Au or Ag) or TCO. Various inorganic materials, organic materials or combinations of inorganic and organic materials are also possible as materials for the hole injection layer, so long as they are effective for hole injection. The charge carrier injection layer may have a thickness of 50 nm or less. The thickness of the relatively transparent conductive monolayer can be 1 to 150 nm. The total thickness of the multilayer electrode structure may be at least 30 nm thick.

Those skilled in the art will appreciate that various materials and multilayer structures can be used in the upper electrode 4 and the lower electrode 2 as long as they can provide the interfacial properties necessary for lateral conductivity and effective charge carrier injection.

The organic stack 3 may be a single layer or multilayer stack comprising a plurality of organic sub-layers suitable for emitting light. Organic materials for the organic stack 3 include electroluminescent and phosphorescent organic materials conventional in the art for light emitting devices. More specifically, the organic stack 3 may be made of electroluminescent and / or phosphorescent polymer materials commonly used in PLEDs. The organic stack can be a single layer of luminescent material or two layers consisting of a hole transport layer and a luminescent layer. Another possibility is a three layer organic stack comprising a hole transport layer, an electron transport layer, and a light emitting layer between the hole transport layer and the electron transport layer. Devices with such three-layer organic stacks are called double heterostructures. Because holes are injected from the anode, the hole transport layer must be adjacent to the anode. If an electron transport layer is used, it must be adjacent to the cathode. The total thickness of the organic stack 3 may range from 50 to 1000 nm.

One example of a top emitting PLED according to the invention is shown in FIG. 5. The flexible substrate 1 consisted of a 125 micron thick PET sheet 1a laminated on a 25 micron thick Al foil 1b. A 120 nm thick transparent ITO anode 2 was formed on the plastic side of the flexible substrate 1. Two-layer organic stack (3) consisting of an 80 nm thick light emitting layer (3a) made of polyphenylene vinylene (Ph-PPV) and a 30 nm thick hole transport layer (3b) made of polyethylene dioxythiophene (PEDOT) Was formed on the ITO anode 2. The comparatively transparent cathode (4) is a 52 nm thick Tris- (8-hydroxyquinoline) aluminum (Alq3) layer (4a), a 15 nm thick translucent Ag layer (4b), 1.0 nm thick calcium in order from above (Ca) is a multilayer structure consisting of a layer 4c and a lithium fluoride (LiF) layer 4d having a thickness of 0.6 nm. In this case, Alq 3 serves as an index-matching layer, Ag serves as a conducting layer for lateral conductivity, and the combination of LiF / Ca serves as an electron injector. The multilayer cathode can be formed by thermal evaporation to prevent the damaging effects of the sputter deposition process. Al foil 1b serves as an excellent barrier to PET substrates, improving device lifetime. This embodiment of the present invention can be considered as a convenient and cost-effective method of manufacturing a top-emitting PLED.

The present invention provides a flexible OLED on an opaque flexible substrate that can be bent to a substantial extent without breaking. Thus, the flexible OLEDs of the present invention have the ability to conform, bend, or curl into any shape. This flexibility will enable the fabrication of display elements by a continuous roll process to provide a cost-effective mass production method. In addition, the flexible substrates disclosed herein may be organic photo-detectors, organic thin film transistors, organic photovoltaic cells, organic memories, organic integrated circuits, and other organic or inorganic optoelectronics that require flexible substrates with good barrier properties and mechanical flexibility. It can be used in the device.

The OLED of the present invention has a variety of uses, including cell phones, PDAs and other portable devices, computer monitors, digital audio devices, video cameras, lighting devices, decoration devices and advertising devices.

While the present invention has been described with respect to preferred embodiments, it will be understood that modifications may be made to the invention without departing from the spirit and scope of the appended claims.

Claims (28)

Flexible substrates; A lower electrode layer on the flexible substrate; An upper electrode layer that is at least translucent; Including an organic region between the lower electrode layer and the upper electrode layer, Electroluminescence may occur when a voltage is applied between the lower electrode layer and the upper electrode layer, Wherein said flexible substrate is comprised of one of (i) a plastic layer laminated or coated with a metal layer, (ii) a metal layer sandwiched between two plastic layers, and (iii) a metal foil. The method of claim 1, And the flexible substrate is formed of a plastic layer laminated on or coated with an aluminum layer, and the plastic layer is positioned between the lower electrode layer and the aluminum layer. The method of claim 1, The flexible organic light emitting device of which the flexible substrate is made of steel foil. The method of claim 1, The flexible organic light emitting device further comprises an isolation layer between the flexible substrate and the lower electrode layer. The method of claim 4, wherein Flexible organic light emitting device wherein the isolation layer is a spin-coated polymer layer or a dielectric layer. The method of claim 3, wherein Flexible organic light-emitting device further comprises an isolation layer between the steel foil and the lower electrode layer. The method of claim 1, The flexible organic light emitting device of which the upper electrode layer is transparent. The method of claim 1, The flexible organic light emitting device of which the upper electrode layer is a translucent or transparent anode. The method of claim 1, The flexible organic light emitting device of which the upper electrode layer is a translucent or transparent cathode. The method of claim 1, The flexible organic light emitting device of claim 1, wherein the upper electrode layer is a multilayer structure including at least one translucent or transparent conductive film. The method of claim 10, And the multilayer structure comprises an index-matching layer and a charge carrier injection layer. The method of claim 11, And the index-matching layer comprises an organic or inorganic material having an index of refraction effective to enhance light output. The method of claim 11, Wherein the index-matching layer comprises a combination of organic and inorganic materials having a refractive index effective to enhance light output. The method of claim 11, And the multilayer structure is an anode, and the charge carrier layer is a hole injection layer. The method of claim 14, The flexible organic light emitting device of which the hole injection layer includes a high work function metal or a transparent conductive oxide (TCO). The method of claim 15, The flexible organic light emitting device of which the high work function metal is gold or silver. The method of claim 15, A flexible organic light emitting device, wherein the TCO is a metal oxide. The method of claim 15, The TCO is indium-tin-oxide (ITO), zinc-indium-oxide, aluminum-doped zinc oxide, Ga-In-Sn-O, SnO ₂ , Zn-In-Sn-O and Ga-In-O Flexible organic light emitting device selected from the group consisting of. The method of claim 14, And the hole injection layer includes an organic material effective for hole injection or a combination of an inorganic material and an organic material effective for hole injection. The method of claim 14, And the hole injection layer comprises an inorganic material effective for hole injection or a combination of inorganic and organic materials effective for hole injection. The method of claim 11, And the multilayer structure is a cathode, and the charge carrier injection layer is an electron injection layer. The method of claim 21, The flexible organic light emitting device of claim 1, wherein the electron injection layer comprises a low work function metal. The method of claim 22, A flexible organic light emitting device, wherein the low work function metal is a rare earth metal. The method of claim 21, The index-matching layer comprises tris- (8-hydroxyquinoline) aluminum (Alq ₃ ) or N, N'-di (naphthalen-1-yl) -N, N'-diphenylbenzidine (NPB) Organic light emitting device. The method of claim 21, Wherein said cathode comprises a silver layer and said electron injection layer is comprised of a calcium sublayer on a lithium fluoride sub-layer, said silver layer being formed on a calcium layer. The method of claim 1, At least one of the lower electrode layer and the upper electrode layer is modified to promote charge carrier injection. The method of claim 1, And the organic region comprises (i) a hole transporting layer and (ii) a light emitting layer or an electron transporting layer. The method of claim 1, And the organic region comprises (i) a hole transport layer, (ii) a light emitting layer, and (iii) an electron transport layer.

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