Organic electroluminescent device with improved light extraction efficiency

Abstract

[0003] Embodiments of the present disclosure generally relate to electroluminescent devices, such as organic light-emitting diodes, and displays including the electroluminescent devices. In one embodiment, an electroluminescent device is provided that includes a pixel-defining layer, an organic light-emitting unit disposed over at least a portion of the pixel-defining layer, and a filler layer disposed over at least a portion of the organic light-emitting unit, wherein the refractive index of the pixel-defining layer is lower than the refractive index of the filler layer, and the refractive index of the pixel-defining layer is lower than the refractive index of one or more layers of the organic light-emitting unit. In another embodiment, a display device is provided that includes a substrate, thin-film transistors formed on the substrate, interconnects electrically coupled to the thin-film transistors, and an electroluminescent device electrically coupled to the interconnects.

Description

[Technical Field]

[0001]

[0001] Embodiments of the present disclosure generally relate to electroluminescent devices and displays including electroluminescent devices. More specifically, embodiments described herein relate to organic light-emitting diode structures and applications thereof. [Background technology]

[0002] Description of related technologies

[0002] Organic light-emitting diodes (OLEDs) are electroluminescent devices that emit light when driven by an electric current. Due to their lightweight, flexibility, wide viewing angle, and fast response speed, OLEDs are becoming increasingly important in display technology. In typical OLED structures, there is a large efficiency loss between the internal quantum efficiency (IQE) and the external quantum efficiency (EQE). Thus, a considerable amount of emitted light is confined within the OLED display, and due to mismatches in the optical parameters of the OLED and the functional layer, the emitted light escapes along the horizontal direction (parallel to the substrate). For example, even with an IQE of 100%, existing device configurations achieve an EQE of less than approximately 25%. In addition to light energy loss, leaked light can be captured into the air around adjacent pixels, potentially reducing the sharpness and contrast of the display.

[0003]

[0003] Structures that improve EQE, such as microlenses, surface textures, scattering, embedded low refractive index grids, embedded gratings / corrugations, embedded photonic crystals, and high refractive index substrates, bring about improvements in EQE, but these structures have problems in many respects. For example, such structures may not be compatible with certain OLED structures, may degrade the resolution and image quality of the display, require difficult and expensive manufacturing, are wavelength-dependent, and / or may only be suitable for bottom-emitting OLEDs. In addition, using such structures can cause crosstalk and image blur, which can degrade display resolution and image quality.

[0004]

[0004] A new and improved OLED structure device is needed that overcomes one or more defects of conventional OLED structures and devices. [Overview of the Initiative]

[0005]

[0005] Embodiments of the present disclosure generally relate to electroluminescent devices and displays including electroluminescent devices. More specifically, embodiments described herein relate to organic light-emitting diode structures and applications thereof.

[0006]

[0006] In one embodiment, an electroluminescent device is provided that includes a pixel definition layer, an organic light-emitting unit disposed above at least a portion of the pixel definition layer, an organic light-emitting unit comprising one or more layers, and a filler layer disposed above at least a portion of the organic light-emitting unit. The refractive index of the pixel definition layer is lower than that of the filler layer and lower than that of one or more layers of the organic light-emitting unit.

[0007]

[0007] In another embodiment, an electroluminescent device is provided, comprising: a pixel-defining layer positioned above at least a portion of a bottom electrode; an organic light-emitting unit positioned above at least a portion of the pixel-defining layer; an upper electrode positioned above at least a portion of the organic light-emitting unit; an organic light-emitting unit comprising one or more layers; and a filler layer positioned above at least a portion of the upper electrode. The refractive index of the pixel-defining layer is lower than that of the filler layer and lower than that of one or more layers of the organic light-emitting unit. The refractive index of the filler layer is greater than or equal to that of one or more layers of the organic light-emitting unit. The upper electrode is made of a transparent conductive oxide material, a translucent conductive oxide material, a metal, a metal alloy, or a combination thereof.

[0008]

[0008] In another embodiment, a display device is provided that includes a substrate, a thin-film transistor formed on the substrate, an interconnection portion electrically coupled to the thin-film transistor, and an electroluminescent device electrically coupled to the interconnection portion. The electroluminescent device includes a pixel definition layer, an organic light-emitting unit disposed above at least a portion of the pixel definition layer, one or more organic light-emitting units, and a filler layer disposed above at least a portion of the organic light-emitting units. The refractive index of the pixel definition layer is lower than the refractive index of the filler layer and lower than the refractive index of one or more layers of the organic light-emitting units.

[0009]

[0009] To enable a detailed understanding of the above-described features of the Disclosure, a more specific description of the Disclosure, which has been briefly summarized above, can be obtained by referring to embodiments. Some of these embodiments are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings show only exemplary embodiments and should not be considered to limit the scope of the Disclosure, as other equally valid embodiments are also permitted. [Brief explanation of the drawing]

[0010] [Figure 1] It has a bottom-emitting OLED structure. [Figure 2] It has a top-emitting OLED structure. [Figure 3A] This is a cross-sectional view of an exemplary OLED structure according to at least one embodiment of the present disclosure. [Figure 3B] This is a cross-sectional view of an exemplary OLED structure according to at least one embodiment of the present disclosure. [Figure 4] This is a cross-sectional view of an exemplary organic light-emitting unit according to at least one embodiment of the present disclosure. [Figure 5] This is a cross-sectional view of an exemplary active-matrix organic light-emitting diode (AMOLED) structure according to at least one embodiment of the present disclosure. [Figure 6A]This is an example of the PDL sidewall reflectivity for S-polarized light and P-polarized light with respect to changes in wavelength and incident angle, in accordance with at least one embodiment of the present disclosure. [Figure 6B] This is an example showing the reflectivity of PDL sidewalls having various fillers with different refractive indices, in accordance with at least one embodiment of the present disclosure. [Figure 7] This is a diagram showing an optical path in an exemplary pixel structure, in accordance with at least one embodiment of the present disclosure. [Figure 8A] This is a graph showing the initial emission angle (θ1) relative to the emission intensity of an exemplary OLED device, in accordance with at least one embodiment of the present disclosure. [Figure 8B] This summarizes exemplary light extraction efficiencies (ηext, unit: %) for different bank angles and different filler refractive indices, in accordance with at least one embodiment of the present disclosure. [Figure 9A] This is an example of pixel dimension parameters, in accordance with at least one embodiment of the present disclosure. [Figure 9B] This is a graph of light extraction efficiency for different heights and widths of an exemplary pixel structure having a fixed bank angle θB=60°, in accordance with at least one embodiment of the present disclosure. [Figure 9C] This is a graph showing the relationship between the exemplary aspect ratio of a pixel at a fixed pixel width W1=3 μm and the light extraction efficiency, in accordance with at least one embodiment of the present disclosure. [Modes for Carrying Out the Invention]

[0011]

[0024] For ease of understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0012]

[0025] Embodiments of this disclosure generally relate to electroluminescent devices and displays including electroluminescent devices. More specifically, embodiments described herein relate to organic light-emitting diode structures and their applications. OLED structures with improved light extraction efficiency and improved external quantum efficiency (EQE) are disclosed herein. Briefly, the novel and improved OLED structures include a pixel-defining layer (PDL), a filler material, organic light-emitting units, and an upper electrode (e.g., cathode) in the upper light-emitting configuration, which includes a transparent conductive oxide material, a translucent conductive oxide material, a metal, a metal alloy, or a combination thereof. The PDL is a material (e.g., an organic material) having a lower refractive index than both the filler material and one or more layers of the organic light-emitting units. The reflection mechanism of the OLEDs described herein is based at least on the total internal reflection (TIR) ​​effect. As will be described in more detail below in this specification, the use of a PDL material having a lower refractive index than the material above it in the OLED stack (e.g., filler material, organic light-emitting unit, and top electrode) enhances and increases the reflection of waveguide light from the PDL-organic light-emitting unit interface toward the extraction surface / interface. The high refractive index contrast between the PDL and the layers above it (e.g., organic light-emitting unit, filler layer, and top electrode) results in total internal reflection of incident light, thereby allowing the incident light to be reflected toward the extraction direction into the organic light-emitting unit. This high refractive index contrast can be further enhanced by adding an additional material (e.g., layer / structure) positioned above at least a portion of the PDL having a higher refractive index than the OLED stack. Alternatively, the additional material (e.g., layer / structure) positioned above at least a portion of the PDL has a lower refractive index than the PDL. Such embodiments can be used, for example, when low refractive index PDL materials are difficult to obtain.

[0013]

[0026] Some conventional OLED structures address waveguide loss mechanisms by employing reflective metal surfaces that act like mirrors, reflecting light traveling obliquely or horizontally, which is inherently unremovable from the OLED. In contrast to such conventional OLED structures, the OLED structures described herein employ low refractive index PDLs without the use of additional reflective mirrors. Eliminating the use of reflective mirrors simplifies manufacturing by eliminating the deposition and patterning processes required to create reflective mirrors during OLED production. Furthermore, even without reflective mirrors, the OLED structures described herein can improve EQE. Therefore, light leakage and efficiency loss are mitigated by the OLED structures and devices described herein. Compared to conventional OLED devices and structures, the OLED devices and structures described herein enable better performance without additional structures and are suitable for all OLED structures (e.g., top-emitting OLEDs and bottom-emitting OLEDs).

[0014]

[0027] In addition, some conventional OLED structures use photonic crystals to improve light extraction. However, the properties of photonic crystals can be highly wavelength-dependent. Therefore, three types of photonic crystals—red, green, and blue—are required. The OLED structures described herein do not have such limitations. Furthermore, some approaches to improving light extraction are only suitable for bottom-emitting OLEDs. In contrast, the OLED structures described herein are suitable for both top-emitting and bottom-emitting OLED structures.

[0015]

[0028] OLEDs are two-terminal thin-film structures having a stack of organic layers containing an organic light-emitting layer sandwiched between two electrodes. At least one of the electrodes is transparent or semi-transparent, allowing emitted light to pass through. In a typical OLED structure, there is a large efficiency loss between the internal quantum efficiency (IQE) and the external quantum efficiency (EQE). As a result, a considerable amount of light is trapped inside the OLED display. In addition, emitted light can escape horizontally (parallel to the substrate) due to, for example, a mismatch in the optical parameters of the OLED and the functional layer. For example, even with an IQE of 100%, existing device configurations achieve an EQE of less than approximately 25%. In addition to light energy loss, leaked light from adjacent pixels can be released into the air, potentially reducing the sharpness and contrast of the display.

[0016]

[0029] The fundamental cause of light loss in conventional OLED devices is that light is generated in a high refractive index material and must be transmitted to air, which has a low refractive index (n=1). If the angle of incidence is greater than the critical angle, the light may undergo total internal reflection, escaping from the edges of the device or being converted into heat. Light loss leads to a decrease in efficiency, which means that the device must be driven harder to obtain the same brightness. As a result, the lifespan and / or reliability of the device decreases. In conventional OLED structures, the light extraction efficiency is not maximized due to the large refractive index mismatch and numerous interfaces. Furthermore, conventional OLED structures are classified into bottom-emitting OLEDs and top-emitting OLEDs depending on the direction of light emission relative to the substrate, and their light loss is explained below.

[0017]

[0030] Figure 1 shows a conventional bottom-emitting OLED structure 100. A bottom-emitting OLED emits light by passing through a transparent or translucent substrate 105. A conventional bottom-emitting OLED structure 100 typically consists of one or more organic material layers 120 stacked between an upper reflective electrode 130 and a transparent or translucent electrode 110. By combining materials for the electrodes, carrier transport layers (such as hole transport layers (HTL) and electron transport layers (ETL)), and light-emitting layers (EML), nearly 100% IQE can be achieved. In a conventional bottom-emitting OLED structure 100, due to the refractive index of the various materials, a considerable portion of the internally generated light with a large angle is confined within the device by total internal reflection at the electrode-substrate interface and does not enter the substrate for extraction into the air. For light incident on the transparent or translucent substrate 105, since the refractive index (n) of the transparent substrate (for example, n is approximately 1.5 for a glass substrate) is higher than that of air, a considerable portion of the light with a large angle will be trapped within the substrate again by total internal reflection at the substrate-air interface and will not be released into the air. Thus, in conventional bottom-emitting OLED structures 100, the light extraction efficiency is generally limited to only 20-25%.

[0018]

[0031] Figure 2 shows a conventional top-emitting OLED structure 200. A top-emitting OLED emits light in the direction opposite to the substrate direction. As shown in Figure 2, the top-emitting OLED structure 200 includes a substrate 205 such as glass or plastic, a bottom reflective electrode 210, an organic layer(s) 220, and a transparent (or translucent) electrode 230 such as indium tin oxide (ITO), a metal alloy (e.g., Mg:Ag), or a thin metal. In some cases, the transparent (or translucent) electrode 230 may be further overcoated with a transparent passivation layer or a capping layer. Because the refractive indices of the organic layer(s) (typically n≧1.7), transparent electrode(s) (typically n≧1.8), and transparent passivation or capping layer are higher than those of air, as shown in Figure 2, most of the internally generated light is trapped within the device by total internal reflection at the interface between the device and air and cannot be extracted into the air. Therefore, the light extraction efficiency is generally limited in typical top-emitting OLED structures. Therefore, in order to realize a highly efficient and power-saving OLED display, it is necessary to increase the light extraction efficiency by extracting the confined OLED light. In response to this, in some embodiments, with reference to Figures 3 to 5, the OLED structures described below in this specification have improved light extraction efficiency compared to conventional OLED structures.

[0019]

[0032] The embodiments described herein overcome the EQE challenges and other issues of conventional OLED structures and devices. The OLED structures and devices described herein may include a high refractive index contrast between the PDL and the layer above the PDL (e.g., an organic light-emitting unit, a filler layer, and an upper electrode). This high contrast leads to total internal reflection of incident light (higher contrast results in a smaller critical angle of TIR), allowing the incident light to be reflected in the extraction direction within the organic light-emitting unit. In some embodiments, the OLED structure includes a low refractive index PDL (e.g., n is approximately 1.6 or less), an organic light-emitting unit having a refractive index greater than that of the PDL, and a filler layer having a refractive index greater than or equal to that of the layer of the organic light-emitting unit.

[0020]

[0033] Although the embodiments described herein are shown for top-emitting OLEDs, bottom-emitting OLEDs are also intended. Similar principles, including high refractive index contrast between layers, are also applicable to bottom-emitting OLED configurations.

[0021]

[0034] Figure 3A shows a cross-section of an exemplary OLED structure 300 according to at least one embodiment of the present disclosure. The exemplary OLED structure 300 is a top-emitting OLED. The exemplary OLED structure 300 includes a substrate 302. The substrate 302 can be any suitable material such as glass (hard or soft), plastic, metal foil such as aluminum foil or copper foil, polymer (such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI)), or a combination thereof. A bottom electrode 304 (e.g., an anode), such as a reflective electrode, is positioned above at least a portion of the substrate 302. The bottom electrode 304 can be a combination of highly transparent (or translucent) materials with good conductivity and high reflectivity. When the bottom electrode functions as an anode, the bottom electrode 304 can have a high work function to facilitate hole injection from the bottom electrode 304 to the hole injection layer of the OLED stack. Non-limiting examples of materials for the bottom electrode 304 include one or more oxides, one or more metals, one or more metal alloys, or combinations thereof, such as Ag, Al, Mo, indium tin oxide (ITO), indium zinc oxide (IZO), fluorine-doped tin oxide (FTO), doped zinc oxide, or combinations thereof. In some examples, a bottom electrode 304 made of ITO / Ag / ITO can be used. In at least one embodiment, the bottom electrode 304 may be a distributed Bragg reflector (DBR) combined with one or more conductive materials. The DBR is composed of a lamination of high-refractive-index and low-refractive-index materials. With a proper design, the DBR can exhibit high reflectivity even when fabricated from two or more transparent dielectric materials. The DBR may be non-conductive. When a non-conductive DBR is used, the DBR can be combined with the specific conductive materials described above to form the bottom electrode.

[0022]

[0035] The OLED structure further includes a PDL 306 positioned above at least a portion of the substrate and / or above at least a portion of the bottom electrode 304. The PDL 306 is a layer of one or more materials that defines the pixel regions of the OLED structure. The PDL 306 provides isolation that allows each pixel to be turned on individually. The PDL 306 is also used to define the OLED light-emitting region and / or for planarization of the topography of the receiving substrate. During manufacturing, the PDL 306 can be blanket-coated over the bottom electrode 304, and an opening can be made in the PDL 306 in a subsequent lithography process, thereby providing the OLED light-emitting area. Alternatively, the PDL 306 can also be blanket-coated over the substrate 302.

[0023]

[0036] In some embodiments, PDL 306 comprises one or more materials having high electrical resistance and / or being electrically insulating. Non-limiting examples of materials that can be used for PDL 306 include any suitable material that can be incorporated into OLED manufacturing, such as polymers, photoresists, resins, acrylics, dielectric materials, or combinations thereof. One suitable material is a fluorinated resin. In some embodiments, PDL 306 has a refractive index of about 1.6 or less, for example, about 1.0 to about 1.4, or about 1.1 to about 1.3, at the wavelength or wavelength range of light emitted from the electroluminescent region (e.g., ultraviolet, near-infrared, and visible light (e.g., about 380 nm to about 780 nm)). In at least one embodiment, the PDL 306 has a refractive index (n) of n1 or n2, or within that range, at a wavelength or wavelength range of light emitted from the electroluminescent region, such that n1 and n2 are independently about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, or about 1.6, as long as n2 > n1. In some embodiments, the refractive index of the PDL 306 layer can be lower than the refractive index of the electroluminescent region.

[0024]

[0037] An exemplary OLED structure 300 further includes an organic light-emitting unit 308. The organic light-emitting unit 308 comprises a first surface (e.g., a bottom surface), a second surface positioned at an angle to the first surface, and a third surface (e.g., a top surface) parallel or substantially parallel to the first surface. Non-limiting examples of materials that can be used for the organic light-emitting unit 308 include any suitable material that can be incorporated into the OLED manufacturing process, such as organic materials. The organic light-emitting unit 308 comprises one or more layers.

[0025]

[0038] In some embodiments, one or more layers of the organic light-emitting unit 308 have a refractive index of about 1.3 or greater, for example, about 1.3 to about 2.4, for example, about 1.5 to about 2.2, for example, about 1.6 to about 1.9, or about 1.8 to about 2.0, at the wavelength or wavelength range of light emitted from the electroluminescent region (e.g., ultraviolet, near-infrared, and visible light (e.g., about 380 nm to about 780 nm)). In at least one embodiment, the organic light-emitting unit 308 has a refractive index of n3 or n4, or within that range, at the wavelength or wavelength range of light emitted from the electroluminescent region, and each of n3 and n4 is independently about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, or about 2.4.

[0026]

[0039] The organic light-emitting unit 308 is positioned above at least a portion of the PDL 306. The organic light-emitting unit 308 is also positioned above at least a portion of the bottom electrode 304. An exemplary OLED structure 300 further includes an upper electrode 310 (e.g., a cathode) positioned above at least a portion of the organic light-emitting unit 308. In some embodiments, the upper electrode 310 has suitable conductivity and transparency. Non-limiting examples of materials for the upper electrode 310 may include one or more metals, one or more metal alloys, one or more oxides, one or more transparent or translucent materials, or combinations thereof. For example, transparent conductive oxides (e.g., indium tin oxide (ITO) or indium zinc oxide (IZO)), Ag, Al, Mo, fluorine-doped tin oxide (FTO), doped zinc oxide, or combinations thereof can be used.

[0027]

[0040] An exemplary OLED structure 300 further includes a filler layer 312 positioned above at least a portion of the upper electrode 310. The filler layer 312 can be a light index-matching layer; that is, the filler layer 312 may have a refractive index greater than or equal to that of the layers of the organic light-emitting unit 308. The filler layer 312 may also have a refractive index greater than that of the PDL 306. The filler layer 312 can avoid total internal reflection and extract light from the OLED. Thus, the filler layer 312 can function as a light transport or waveguide medium for guiding light to or from the reflective interface. In some embodiments, the filler layer 312 comprises one or more materials having low absorption to zero absorption (e.g., an absorption coefficient close to 0, k < 0.1) at the wavelength or wavelength range of light emitted from the electroluminescent region. Non-limiting examples of materials that can be used for the filler layer 312 include any suitable material that can be incorporated into OLED manufacturing, such as organic materials, inorganic materials, resins, or combinations thereof. The filler layer 312 may include composites such as colloidal mixtures in which the colloid is a high refractive index inorganic material such as TiO2. In some embodiments, the filler layer 312 has a refractive index of about 1.6 or greater, for example, about 1.8 to about 2.4, for example, about 1.8 to about 1.9, about 1.9 to about 2.0, or about 2.0 to about 2.2, at the wavelength or wavelength range of light emitted from the electroluminescent region (e.g., ultraviolet, near-infrared, and visible light (e.g., about 380 nm to about 780 nm)). In at least one embodiment, the filler layer 312 has a refractive index of n5 or n6, or within that range, at a wavelength or wavelength range of light emitted from the electroluminescent region, and each of n5 and n6 is independently about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, or about 2.5, as long as n6 > n5.

[0028]

[0041] In general, the exemplary OLED structure 300 can be fabricated by the following method. The bottom electrode 304 can be deposited on the substrate by, for example, lithography. In an active matrix display, there are wire connections that connect the bottom electrode of the OLED and the thin film transistor (TFT) via via holes. After the bottom electrode 304 is formed, the PDL 306 can then be deposited. In the case of a photoresist-type PDL, it can be blanket-coated on the bottom electrode and then patterned by lithography. After the PDL openings are formed by lithography, the organic layers can be sequentially deposited. In general, the organic layers can be deposited under vacuum by thermal evaporation. Furthermore, the organic layers and the top electrode 310 can be deposited over the pixels, with or without patterning, such that the organic layers and the top electrode 310 extend to the upper edge of the bank.

[0029]

[0042] Figure 3B illustrates an exemplary OLED structure 300 having various angles, widths (W1), and heights (H), in accordance with at least one embodiment of the present disclosure. As shown in Figure 3B, W1 is the pixel opening which is the width of the bottom electrode 304 not covered by the PDL, and H represents the height extending from the upper edge of the filler layer 312 to the upper edge of the bottom electrode 304.

[0030]

[0043] In some embodiments, the angle of the PDL (Θ, which is the intersection angle between the PDL and the bottom electrode 304 B ) is about 40° to about 70°, for example, about 45° to about 65°, for example, about 50° to about 55°. In at least one embodiment, the angle of the PDL is Θ B1 or Θ B2 , or in the range of Θ B1 to Θ B2 , and as long as Θ B2 > Θ B1 , Θ B1 , Θ B2Each of them is independently approximately 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, or 70°.

[0031]

[0044] In at least one embodiment, the H / W1 ratio is in the range of about 0.01 to about 5, for example, about 0.1 to about 4, for example, about 0.25 to about 1.

[0032]

[0045] In at least one embodiment, the filler layer 312 has a refractive index of n5 or n6, or within that range, at a wavelength or wavelength range of light emitted from the electroluminescent region, and each of n5 and n6 is independently about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, or about 2.5, as long as n6 > n5.

[0033]

[0046] Figure 4 is a cross-sectional view of an exemplary organic light-emitting unit 308 according to at least one embodiment of the present disclosure. The organic light-emitting unit 308 may be positioned above at least a portion of the bottom electrode 304. A non-limiting description of the bottom electrode is provided above with reference to Figure 3A. When the bottom electrode is the anode, the bottom electrode 304 is positively charged to inject holes (e.g., where electrons do not exist) into the organic light-emitting unit, e.g., the organic light-emitting unit 308. The organic light-emitting unit 308 comprises multiple organic layers, including a hole injection layer (HIL) 405 positioned above at least a portion of the bottom electrode 304 (not shown), a hole transport layer (HTL) 410 positioned above at least a portion of the HIL 405, an emissive layer (EML) 415 positioned above at least a portion of the HTL 410, an electron transport layer (ETL) 420 positioned above at least a portion of the EML 415, and an electron injection layer (EIL) 425 positioned above at least a portion of the ETL 420. The HIL 405 facilitates the injection of holes from the bottom electrode 304 into the organic light-emitting unit 308. The HTL 410 assists in the transport of holes throughout the unit so that holes can reach the EML 415. The HTL 410 can be made of an organic material having good hole mobility. In a top-emitting OLED, the thicknesses of the various organic layers of the organic light-emitting unit 308 can be adjusted to match the cavity parameters. The thickness of the HTL 410 can be adjusted to control the overall thickness of the organic light-emitting unit 308. The EML 415 is where electrical energy is converted into light. The ETL 420 supports electron transport throughout the structure so that electrons can reach the EML 415. The EIL 425 facilitates the injection of electrons from the upper electrode 310 to the organic light-emitting unit 308 when the upper electrode is the cathode.

[0034]

[0047] In some embodiments, the organic light-emitting unit 308 further includes a hole-blocking layer and / or an electron-blocking layer. In such embodiments, the hole-blocking layer may be located between the EML 415 and the ETL 420, the electron-blocking layer between the HTL 410 and the EML 415, and / or the electron-blocking layer between the HIL 405 and the EML 415.

[0035]

[0048] In some embodiments, an additional structure (e.g., one or more high-refractive-index layers) can be placed above at least a portion of the PDL 306 to further enhance the refractive index contrast with respect to the PDL. The organic light-emitting unit 308 would then be placed above the additional structure. The additional high-refractive-index layer(s) may have a higher refractive index than the layer(s) below it, thereby enhancing the refractive index difference between the PDL 306 and the additional structure, resulting in a greater TIR effect. This additional structure may be used, for example, in applications where the materials of the filler layer 312 and the organic light-emitting unit 308 are limited, and / or in applications where the high-refractive-index filler layer 312 may not be suitable for large volume deposition. In such cases, the additional structure on the PDL 306 can then be used to increase the refractive index contrast.

[0036]

[0049] The embodiments described herein are also generally relevant to display devices such as AMOLED devices. In an AMOLED display consisting of multiple display elements, OLED pixels are defined by an array of patterned bottom electrodes, each of which is connected to a pixel driver, which typically includes one or more thin-film transistors (TFTs), metal wiring lines, and capacitors. Examples of pixel drivers in OLED devices may include scan lines, data lines, current regulating transistors (sometimes called power TFTs) connected to the OLED emitter, and storage capacitors connected to the gate of the current regulating transistor and the drain of the switch transistor. By employing more complex pixel drive circuits, display uniformity and operational stability can be improved. As a result, the pixel driver may compete with the light-emitting elements within the pixel area, potentially limiting bottom-emitting displays to a certain pixel pitch size.

[0037]

[0050] Figure 5 shows an exemplary pixel cross-section of an AMOLED structure 500 according to at least one embodiment of the present disclosure. The AMOLED structure can utilize the above-described OLED structure (e.g., exemplary OLED structure 300) which has high light extraction efficiency. The AMOLED structure 500 has at least high luminescence efficiency.

[0038]

[0051] An exemplary pixel of the AMOLED structure 500 includes a substrate 502. Thin-film transistors (TFTs) 510, such as a TFT drive circuit array, are positioned above and / or formed on at least a portion of the substrate 502. An interconnect 505 is positioned between the TFT 510 and at least a portion of the OLED 515 so that the TFT 510 can drive and control the OLED 515. The interconnect 505 is electrically coupled to the organic light-emitting unit 308 by a bottom electrode 304, and the interconnect 505 is also electrically coupled to the TFT 510. Generally, the AMOLED structure 500 can be formed by first performing several lithography operations to create the TFTs. After the TFT 510 is formed, a planar layer can be created on the TFT 510 so that the bottom electrode 304 can be deposited on the planar layer. The OLED 515 can then be formed on the bottom electrode 304 as described above by other approaches such as thermal evaporation in a high vacuum or inkjet printing. The AMOLED structure 500 may include additional elements where applicable, such as a backplane (TFT array), a frontplane (light-emitting structure), a thin film encapsulation (TFE), and a polarizer. The AMOLED may further have scan lines and data lines. The scan lines perform the operation of lighting up the pixels, and the data lines perform the operation of writing values ​​to cause light to be emitted.

[0039] Examples

[0052] The following embodiments are illustrative and not limiting to one or more embodiments of the present disclosure.

[0040] Example 1

[0053] Figure 6A shows S-polarized light (R) for various wavelengths and angles of incidence (AOI). s ) and P-polarization (R p Examples of PDL sidewall reflectance are shown. In these examples, the refractive indices of the filler and PDL are approximately 1.81 and 1.52, respectively. The layer above the filler and pixels is air with a refractive index of 1.0. The cutoff line was found to be between an AOI of approximately 55 and 60 degrees, which is the critical angle of total internal reflection resulting from the difference in refractive index between the filler (high) and the pixel PDL (low). This example shows that TIR can be enhanced by increasing the refractive index difference between the PDL and the filler. Figure 6B shows examples of PDL sidewall reflectance with various fillers with different refractive indices. When a filler with a high refractive index (and therefore a large refractive index difference with the PDL) is used, the cutoff line shifts to a smaller AOI.

[0041] Example 2

[0054] To avoid the loss of light transmitted through the PDL, the pixel structure can be designed to reflect light from the sides, with the help of total internal reflection, to improve the efficiency of light extraction. In addition to the difference in refractive index between the filler and the PDL, the bank angle (θ) of the PDL is also a factor. B Various structural parameters of the pixel, such as the ratio of pixel height to width, can affect extraction. As shown in Figure 7, when light is emitted from the organic light-emitting unit, the initial emission angle θ1 of the incident light (emission angle relative to the normal of the bottom electrode 304) and the bank angle θ of the PDL are related. B The relationship can be divided into two groups. H and W1 are as described above. θ1 is the initial emission angle, θ2 is the incident angle at the filler / PDL interface, and θ3 is the incident angle to the upper filler interface after redirection at the PDL interface.

[0042]

[0055] Path 1 is given by equation θ1 + θ B The condition ≤90° is satisfied, where light is first incident on the horizontal interface between the filler and the layer above it (e.g., air, called the upper filler interface). Path 2 is θ1+θ BThe light is at an angle of >90°, and this light is initially incident on the oblique interface between the filler and the PDL (hereinafter referred to as the filler / PDL interface). For the sake of simplicity, the transition from path 1 to path 2 in the process is not included.

[0043]

[0056] As shown in Figure 7, the light from paths 1 and 2 can be analyzed as follows. Path 1 is the light that first incident on the upper filler interface. Since the bottom electrode should be parallel to the upper filler interface, the light will have the same incident angle at the upper filler interface as the initial emission angle θ1. The upper interface is the critical angle θ of total internal reflection due to the difference in refractive index between the filler and the material above the filler. c,filler Assume that it has θ. c,filler At smaller incident angles θ1, light can be directly coupled to the outside. For the remainder of path 1, light undergoes total internal reflection at the interface and is returned to the filler / PDL interface. From the geometric relationship, we can define θ2, the incident angle of light at the filler / PDL interface. The filler / PDL interface is the critical angle θ for total internal reflection, determined by the difference in refractive indices between the filler and PDL. c,PDL Assume that θ2 is θ c,PDL If the value is smaller, most of the light will pass through the PDL, resulting in a loss of light that passes through the PDL. c,PDL In the above case, light undergoes total internal reflection at the filler / PDL interface, and the light is reflected at the upper filler interface. From this geometric relationship, the angle of incidence θ3 at the upper filler interface after the light has been reflected at the filler / PDL interface is defined. And θ3 is the critical angle θ c,filler If the value is smaller, light can be smoothly extracted from the filler, and the emission / extraction of light is considered successful. c,filler In the above cases, light remains trapped within the pixel structure due to total internal reflection, which is considered a potential loss of light.

[0044]

[0057] Path 2 is the light that first incident on the filler / PDL interface. θ2 is θ c,PDL If θ2 is smaller, most of the light enters the pixel definition layer and is considered a loss of light transmitted to the PDL. c,PDLIn the above cases, the light undergoes total internal reflection and is directed to the upper filler interface. The redirected light is directed at the upper filler interface at θ c,filler When θ3 is smaller, light is smoothly extracted from the filler. c,filler In the above cases, the light remains confined within the pixel structure and is considered a potential loss of light.

[0045] Example 3

[0058] Figure 8A is a graph showing the luminescence intensity versus initial emission angle (θ1) of an exemplary OLED device. S represents S-polarized emission, P represents P-polarized emission, and S+P represents total emission. Total emission (S+P) shows clear peaks at initial emission angles of approximately 0° and 63°. Light emitted at an initial emission angle of 0° does not undergo total internal reflection and can therefore be extracted directly from the filler / pixel. Table 1 shows the incident angle (θ2) at the filler / PDL interface and the incident angle (θ3) at the upper PDL interface for the intensity peak at an initial emission angle of approximately 63° (θ1) (positive values ​​indicate direction, negative values ​​indicate direction). From the incident angles θ2 and θ3, it is possible to determine whether total internal reflection occurs at the interface. TIFF0007933756000001.tif44170

[0046]

[0059] To avoid energy loss and cause total internal reflection at the filler / PDL interface, θ2 should be approximately 57°. c,PDL The above is assumed (assuming the filler has a refractive index of 1.81 and the PDL has a refractive index of 1.52). From Table 1, PDLs with a bank angle less than 60° can satisfy the objective. However, in order to extract light from the filler / pixel while avoiding total internal reflection at the upper filler interface after reflection at the filler / PDL interface, the incident angle θ3 at the upper filler interface must be θ c,filler It needs to be smaller than θ, approximately 34° (assuming the layer above the filler is air with a refractive index of 1.0 and the filler has a refractive index of 1.81). Therefore, from Table 1, θ B It can be seen that tuning of light extraction is possible when the angle falls between approximately 50° and 60°. Figure 8B shows the light extraction efficiency (η) for different bank angles and different filler refractive indices. extThis figure summarizes the results in %). Higher light extraction efficiency was observed when the bank angle was approximately 40° to 70°, for example, approximately 50° to 60°.

[0047] Example 4

[0060] Furthermore, the influence of pixel dimensional parameters such as pixel height and width on light extraction efficiency can be determined by simulation. The ratio of path 1 to path 2 shows a high correlation with the height and width of the pixel structure, and also with the ratio of the height and width of the pixel structure. Figure 9A and Table 2 show the specific parameters used in the simulation, and the simulation results are shown in Figures 9B and 9C. For the parameters labeled in Figure 9A, H is the pixel height. This is the distance from the upper edge of the filler to the bottom electrode layer. W1 is the pixel aperture width, defined by the distance at which the lower PDL edge contacts the bottom electrode layer. W2 is the horizontal distance of the PDL inclined surface. This can be determined by the horizontal distance from the lower PDL edge in contact with the bottom electrode layer to the upper edge of the PDL where the PDL becomes flat. W2 is determined by the height H and the bank angle θ. B It can also be calculated from (W2 = H / tan(θ) B )). n filler and n PDL These are the refractive indices of the filler material and PDL. TIFF0007933756000002.tif44170

[0048]

[0061] As shown in Figure 9B, when the pixel width is different, the light extraction efficiency improves as the height of the pixel structure increases (θ B (Fixed at 60°). It was also confirmed that a smaller pixel width results in higher light extraction efficiency. Therefore, increasing the overall aspect ratio (H / W1) improves light extraction efficiency.

[0049]

[0062] The relationship between extraction efficiency and height-to-width ratio can be further explained in Figure 9C. In Figure 9C, the pixel width is fixed at 3 μm, and the pixel height and bank angle (θ) are fixed. BThe variable is (=50° or 60°). This trend suggests that, given a constant pixel width, better extraction is possible with higher pixel height and a larger H / W1 ratio. A structure with a pixel definition layer having an n refractive index lower than the refractive index of one or more of the filler and organic light-emitting units can lead to improved extraction efficiency. Extraction efficiency can be adjusted by appropriately designing pixel dimensional parameters such as bank angle, pixel width, pixel height, and height-to-width ratio.

[0050]

[0063] Structures and devices having improved light extraction efficiency and improved external quantum efficiency (EQE) are disclosed herein. These structures and devices overcome one or more drawbacks of conventional OLED structures and devices.

[0051]

[0064] All documents described herein, including any priority documents and / or test procedures, are incorporated herein by reference, insofar as they do not conflict with this text. While the forms of this disclosure are illustrated and described as will be obvious from the above summary and specific embodiments, various modifications can be made without departing from the essence and scope of this disclosure. Therefore, this disclosure is not intended to be limited thereto. Similarly, the term “comprising” is to be considered synonymous with the term “including.” Similarly, whenever a composition, element, or group of elements is preceded by the transitional phrase “comprising,” it is understood that the same composition or group of elements may also be assumed to have preceded by the transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is,” and vice versa.

[0052]

[0065] As used herein, the terms “over,” “under,” “between,” “on,” and other similar terms refer to the relative position of one layer to another. Thus, for example, one layer positioned above or below another layer may be in direct contact with the other layer, or it may be connected by one or more layers. Furthermore, one layer positioned between layers may be in direct contact with two layers, or it may be connected by one or more layers. In contrast, a first layer “on” a second layer is in contact with the second layer. The relative position in these terms does not define or restrict the orientation of the layer's vector space. The term “coupled” is used herein to refer to elements that are directly connected or connected through one or more intervening elements.

[0053]

[0066] For the purposes of this disclosure, and unless otherwise specified, all numerical values ​​in the detailed description and claims herein are modified with “about” or “approximately” and take into account experimental errors and variations expected by those skilled in the art. Certain embodiments and features are described using sets of upper and lower numerical limits. Unless otherwise indicated, it should be recognized that ranges are assumed to include any combination of any two values ​​(e.g., any lower and any upper value, any two lower values, and / or any two upper values). Certain lower, upper, and ranges are described in one or more of the following claims.

[0054]

[0067] The above description applies to embodiments of the present disclosure, but other embodiments and further embodiments of the present disclosure may be devised without departing from the basic scope of the present disclosure. The scope of the present disclosure is determined by the following claims.

Claims

1. An electroluminescent device having multiple pixels, wherein each of the multiple pixels is A pixel definition layer including an inclined surface for reflecting emitted light, An additional structure is disposed on the inclined surface of the pixel definition layer, in contact with the inclined surface of the pixel definition layer, An organic light-emitting unit disposed above at least a portion of the aforementioned additional structure, comprising one or more layers, A filler layer disposed above at least a portion of the organic light-emitting unit, wherein the refractive index of the pixel definition layer is lower than the refractive index of the filler layer and lower than the refractive index of one or more layers of the organic light-emitting unit, Equipped with, The refractive index of the pixel definition layer is lower than the refractive index of the additional structure in order to increase refractive index contrast. An electroluminescent device in which each of the plurality of pixels is isolated from the other pixels of the plurality of pixels.

2. The electroluminescent device according to claim 1, wherein the organic light-emitting unit has a first surface, a second surface positioned at an angle to the first surface and located above the inclined surface of the pixel definition layer, and a third surface substantially parallel to the first surface.

3. The electroluminescent device according to claim 1, further comprising an upper electrode, wherein the upper electrode is positioned above at least a portion of the organic light-emitting unit, and the filler layer is positioned above at least a portion of the upper electrode.

4. The electroluminescent device according to claim 3, wherein the upper electrode includes a transparent conductive oxide material, a translucent conductive oxide material, a metal, a metal alloy, or a combination thereof.

5. The electroluminescent device according to claim 1, further comprising a bottom electrode, wherein the pixel definition layer is positioned above at least a portion of the bottom electrode.

6. The electroluminescent device according to claim 1, wherein the refractive index of the pixel defining layer is about 1.0 to about 1.6 in the wavelength or wavelength range of light emitted by the electroluminescent device.

7. The electroluminescent device according to claim 1, wherein the refractive index of one or more layers of the organic light-emitting unit is about 1.3 to about 2.4 in the wavelength or wavelength range of light emitted by the electroluminescent device.

8. The electroluminescent device according to claim 1, wherein the refractive index of the filler layer is greater than about 1.6 in the wavelength or wavelength range of light emitted by the electroluminescent device.

9. The electroluminescent device according to claim 1, wherein the refractive index of the filler layer is equal to or greater than the refractive index of one or more layers of the organic light-emitting unit.

10. Aspect ratio (H / W １ Here, H is the height from the top surface of the bottom electrode to the top surface of the filler layer, and W １ (where is the pixel aperture, which is the width of the bottom electrode not covered by the pixel definition layer) is greater than approximately 0.

01. The electroluminescent device according to claim 5.

11. An electroluminescent device having multiple pixels, wherein each of the multiple pixels is A pixel definition layer including a sloped surface for reflecting emitted light, positioned above at least a portion of the bottom electrode. An additional structure is disposed on the inclined surface of the pixel definition layer, in contact with the inclined surface of the pixel definition layer, An organic light-emitting unit disposed above at least a portion of the aforementioned additional structure, comprising one or more layers, An upper electrode positioned above at least a portion of the organic light-emitting unit, The upper electrode comprises a filler layer positioned above at least a portion thereof, The refractive index of the pixel definition layer is lower than that of the filler layer. The refractive index of the pixel definition layer is lower than the refractive index of one or more layers of the organic light-emitting unit. The refractive index of the pixel definition layer is lower than the refractive index of the additional structure in order to increase refractive index contrast. The refractive index of the filler layer is equal to or greater than the refractive index of one or more layers of the organic light-emitting unit. The upper electrode includes a transparent conductive oxide material, a translucent conductive oxide material, a metal, a metal alloy, or a combination thereof. Each filler layer in each pixel is separated from the filler layers of other pixels. Electroluminescent device.

12. The electroluminescent device according to claim 11, wherein the organic light-emitting unit has a first surface, a second surface positioned at an angle to the first surface and located above the inclined surface of the pixel definition layer, and a third surface substantially parallel to the first surface.

13. The electroluminescent device according to claim 11, wherein the refractive index of the pixel defining layer is about 1.0 to about 1.6 in the wavelength or wavelength range of light emitted by the electroluminescent device.

14. The refractive index of one or more layers of the organic light-emitting unit is about 1.3 to about 2.4 in the wavelength or wavelength range of light emitted by the electroluminescent device. The refractive index of the filler layer is greater than approximately 1.6 in the wavelength or wavelength range of light emitted by the electroluminescent device, or These combinations are, The electroluminescent device according to claim 11.

15. Aspect ratio (H / W １ Here, H is the height from the top surface of the bottom electrode to the top surface of the filler layer, and W １ (where is the pixel aperture, which is the width of the bottom electrode not covered by the pixel definition layer) is greater than approximately 0.

01. The electroluminescent device according to claim 11.

16. circuit board and A thin-film transistor formed on the aforementioned substrate, An interconnection portion electrically coupled to the thin-film transistor, A display device comprising an electroluminescent device electrically coupled to the interconnection portion, wherein the electroluminescent device comprises a plurality of pixels, Each of the aforementioned plurality of pixels is, A pixel definition layer including an inclined surface for reflecting emitted light, An additional structure is disposed on the inclined surface of the pixel definition layer, in contact with the inclined surface of the pixel definition layer, An organic light-emitting unit disposed above at least a portion of the pixel definition layer, comprising one or more layers, A filler layer disposed above at least a portion of the organic light-emitting unit, wherein the refractive index of the pixel definition layer is lower than the refractive index of the filler layer and lower than the refractive index of one or more layers of the organic light-emitting unit, Equipped with, The refractive index of the pixel definition layer is lower than the refractive index of the additional structure in order to increase refractive index contrast. Each filler layer in each pixel is separated from the filler layers of other pixels. Display device.

17. The display device according to claim 16, wherein the electroluminescent device further comprises a bottom electrode electrically coupled to the interconnection portion.

18. The display device according to claim 16, wherein the refractive index of the filler layer is greater than or equal to the refractive index of the organic light-emitting unit.

19. The display device according to claim 16, further comprising an upper electrode, the upper electrode positioned above at least a portion of the organic light-emitting unit, and the filler layer positioned above at least a portion of the upper electrode.

20. The display device according to claim 16, wherein the organic light-emitting unit has a first surface, a second surface positioned at an angle to the first surface and located above the inclined surface of the pixel definition layer, and a third surface substantially parallel to the first surface.

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