Light-emitting structure

Abstract

The light-emitting structure includes a substrate, a sub-pixel stack on the surface of the substrate, a bank surrounding the sub-pixel stack and forming an internal space above the sub-pixel stack, a first material filling the internal space and having a first refractive index, and a second material above the first material and having a second refractive index substantially higher than the first refractive index. The sub-pixel stack includes an emission layer located between a first transport layer and a second transport layer, a first electrode layer coupled to the first transport layer, and a second electrode layer coupled to the second transport layer. The second electrode layer has a third refractive index substantially matching the first refractive index.

Description

Technical Field

[0001] The present disclosure generally relates to layer and bank structures for emissive devices such as quantum dot light emitting diode (QLED) displays. In particular, the present disclosure aims to improve efficiency, reduce color shift, and increase on-axis brightness of a top-emitting structure that is surrounded by a bank and includes an emissive layer and a transparent cathode having a refractive index less than that of the emissive layer. Background Art

[0002] Organic light emitting diodes (OLEDs) are one of the most common LEDs in display devices, and quantum dots have been proposed as an improvement to OLEDs due to their better spectral emission and higher chemical stability. Quantum dots (QDs) are commonly used as phosphors for blue LEDs and exist as backlights for liquid crystal displays (LCDs).

[0003] In a layer-emitting display device, an emissive material (e.g., an organic dye for an OLED and a quantum dot for a QLED) is sandwiched between a hole transport layer and an electrode transport layer and an electrode. This structure operates as a diode, and when current flows, electroluminescence in the emissive material generates light, and one electrode is made partially transmissive to allow light extraction. For OLEDs (and to a lesser extent QLEDs), the main form of energy loss is when light cannot be extracted from the light-emitting structure. A typical OLED only extracts about 20% of the light generated in air. Two key reasons for this lower light extraction percentage are that the refractive indices of the layers in a layer-emitting display device are typically quite high (e.g., a large amount of loss due to total internal reflection), and a partially reflective electrode reflects most of the light, while the optical thickness of the layer between the electrodes is on the order of the wavelength, so interference is an important factor to control. It should also be noted that interference depending on wavelength and angle produces color shift when viewed at different angles.

[0004] The design of a layer-emitting structure can be optimized, but generally a trade-off is required between maximizing efficiency and optimizing the color gamut range and color shift.

[0005] The cavity in an LED structure and its effect on light have been studied. For example, Kodak (US20060158098) describes a top-emitting structure, and Samsung (US9583727) describes an OLED and QLED structure having multiple light-emitting regions between reflective regions, one of which is partially transmissive.

[0006] Several methods for increasing the brightness of such cavities have been proposed. For example, Samsung (US2015 / 0084012) describes the use of a dispersion layer in an OLED structure, Samsung (US8894243) describes the use of microstructural scattering to improve efficiency, and 3M (WO2017 / 205174) describes enhancing luminescence by using surface plasmon nanoparticles or nanostructures in the transport layer.

[0007] Methods involving modifying the cavity (or cavities) are generally difficult to implement because such methods require extremely small size features or control of the layers. An alternative to modifying the cavity is to use a thick top "filler" layer with a high refractive index, which can reduce Fresnel reflection and increase the transmittance through the top electrode. However, the light in the high refractive index layer may mostly be trapped by total internal reflection (TIR). To extract the trapped light, the TIR-trapped light is output-coupled using reflectors and / or scattering dams around the filler layer.

[0008] TCL (CN106876566) and JOLED (US9029843) describe such a pixel arrangement having multiple dams and a filling material above the organic layer of the cavity and between these dams. Hitachi (US7091658) describes dams that can use an electrode metal material for reflection, Cambridge Display Tech (KR1020150020140) describes dams that can be formed in different structures using different assembly steps, and Sharp (US10090489) describes a formed reflector under the organic layer.

[0009] Another method is to control the filling material. For example, Global OLED (US8207668) describes a controllable filler layer where the filler layer and the organic layer have different thicknesses for different sub-pixels to maximize the output light varying with wavelength.

[0010] Another method is to control the organic layer, which can be achieved by appropriate material selection (e.g., lyophilic / lyophobic). For example, SeikoEpson (US7902750) describes that the cavity layer is curved and the encapsulation is a planarizing layer, and JOLED (US9312519) describes that the organic layer is both convex and concave in the orthogonal direction.

[0011] In another method, Lee et al. ("Three-Dimensional Pixel Configuration for Optical Output Coupling of OLED Displays - Optical Simulation", Proceedings of the Society for Information Display (SID) 2019 Display Week Conference) described the simulation of a pixel dam structure by designing the OLED emission layer. This method simulates the optimal extraction efficiency of the dam structure, thus maximizing the efficiency of the actual dam structure. The optimal solution only involves green light and the ITO electrode, but it is not feasible in such a device because the emission spectrum would be too wide, and thus the color gamut would be poor without considering the on-axis brightness (the apparent brightness for the user).

[0012] The above-described structure with a high refractive index filler is most suitable for a high refractive index emission layer and a high refractive index transparent top electrode (e.g., the cathode). A suitable choice for such a cathode is ITO. However, the processing of such a highly conductive layer is usually aggressive and may damage other layers of the layer-emitting display device. Therefore, obtaining a top electrode with a high refractive index that does not degrade other layers (e.g., the emission layer) can be a considerable challenge. In addition, the use of a low refractive index electrode increases the waveguide loss in the emission layer, and the light extracted from the emission layer is within a narrow angular range and is not affected by total internal reflection on the low refractive index layer. Therefore, this dam is not utilized. As a result, the reflection collimation and mixing of light do not occur, and thus the extraction is significantly reduced and the color shift becomes worse.

[0013] In one or more embodiments of the present disclosure, an alternative structure is described that can utilize a top electrode with a low refractive index and can allow the dam to collimate light and merge with the reflected light emitted from the emission layer, thereby increasing the on-axis brightness while reducing the color shift.

[0014] List of cited references

[0015] U.S. Publication No. US2006 / 0158098A1 (Eastman Kodak Company, published on July 20, 2006).

[0016] U.S. Patent No. US9,583,727B2 (Samsung Display Co Ltd, authorized on February 28, 2017).

[0017] U.S. Publication No. US2015 / 0084012A1 (Samsung Display Co Ltd, published on March 26, 2015).

[0018] U.S. Patent No. US8,894,243B2 (Samsung Corning Precision Materials Co Ltd, authorized on November 25, 2014).

[0019] International Publication No. WO2017 / 205174A1 (published by 3M Innovative Properties Company on November 30, 2017).

[0020] Chinese Publication No. CN106876566A (published by TCL on June 20, 2017).

[0021] U.S. Patent No. US9,029,843B2 (issued to JOLED Inc. on May 12, 2015).

[0022] U.S. Patent No. US7,091,658B2 (issued to Hitachi on August 15, 2006).

[0023] KR1020150020140 (published by Cambridge Display Tech on February 25, 2015).

[0024] U.S. Patent No. US10,090,489B2 (issued to Sharp Kabushiki Kaisha on October 2, 2018).

[0025] U.S. Patent No. US8,207,668B2 (issued to Global OLED Technology LLC on June 26, 2012).

[0026] U.S. Patent No. US7,902,750B2 (issued to Seiko Epson Corporation on March 8, 2011).

[0027] U.S. Patent No. US9,312,519B2 (issued to JOLED Inc. on April 12, 2016).

[0028] Lee et al., ("Three-Dimensional Pixel Configuration for Optical Output Coupling of OLED Displays - Optical Simulation", Proceedings of the Society for Information Display (SID) 2019 Display Week Conference, published in 2019). Summary of the Invention

[0029] The present disclosure relates to an emissive display including a quantum dot electroluminescent material in an LED arrangement.

[0030] According to a first aspect of the present disclosure, a light-emitting structure includes: a substrate; a sub-pixel stack located above a surface of the substrate; a dam surrounding the sub-pixel stack and forming an internal space above the sub-pixel stack; a first material filling the internal space and having a first refractive index; and a second material located above the first material and having a second refractive index substantially higher than the first refractive index. The sub-pixel stack includes: an emission layer located between a first transport layer and a second transport layer; a first electrode layer coupled to the first transport layer; and a second electrode layer coupled to the second transport layer. The second electrode layer has a third refractive index substantially matching the first refractive index.

[0031] In one or more embodiments of the first aspect, the second electrode layer includes any conductive non-metallic material. "Non-metallic" may refer to a real part of a refractive index that is significantly greater than an imaginary part (absolute value) of the refractive index. In an exemplary embodiment, the second electrode layer includes at least one of indium tin oxide (ITO) nanoparticles and silver nanowires.

[0032] In another embodiment of the first aspect, the second material includes a high refractive index transparent material, including at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

[0033] In yet another embodiment of the first aspect, the sub-pixel stack emits a first emission peak toward the first material along an on-axis direction substantially perpendicular to a top surface of the sub-pixel stack; the sub-pixel stack emits a second emission peak toward the first material along an off-axis direction at an angle to the on-axis direction; and the second emission along the off-axis direction is reflected by an interface between the first material and the second material and guided to an inclined sidewall of the dam.

[0034] In yet another embodiment of the first aspect, the second emission peak is reflected by the inclined sidewall of the dam and emitted through the interface along the on-axis direction substantially without total internal reflection.

[0035] In yet another embodiment of the first aspect, an angle between the inclined sidewall of the dam and the top surface of the sub-pixel stack is half of an angle between the on-axis direction of the first emission peak and the off-axis direction of the second emission peak.

[0036] In yet another embodiment of the first aspect, the second material covers an entire top surface of the first material.

[0037] In another embodiment of the first aspect, the light-emitting structure further includes an air gap located between the first material and the second material.

[0038] In yet another embodiment of the first aspect, the emission layer includes a quantum dot emission material, the first transport layer includes a hole transport layer, the second transport layer includes an electron transport layer, the first electrode layer is an anode layer, the anode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is a cathode layer having a non-metallic and substantially transparent material.

[0039] In yet another embodiment of the first aspect, the emission layer includes a quantum dot emission material, the first transport layer includes an electron transport layer, the second transport layer includes a hole transport layer, the first electrode layer is a cathode layer, the cathode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is an anode layer having a non-metallic and substantially transparent material.

[0040] According to a second aspect of the present disclosure, a light-emitting structure includes: a substrate; a plurality of sub-pixel stacks emitting different colors above the surface of the substrate; dams surrounding each of the plurality of sub-pixel stacks and forming an internal space above each sub-pixel stack of the plurality of sub-pixel stacks; a first material filling the internal space and having a first refractive index; and a second material located above the first material and having a second refractive index substantially higher than the first refractive index. At least one of the plurality of sub-pixel stacks includes: an emission layer located between a first transport layer and a second transport layer; a first electrode layer coupled to the first transport layer; and a second electrode layer coupled to the second transport layer. The second electrode layer has a third refractive index substantially matching the first refractive index.

[0041] In an embodiment of the second aspect, the second electrode layer includes at least one of indium tin oxide (ITO) nanoparticles and silver nanowires.

[0042] In another embodiment of the second aspect, the second material includes a high refractive index transparent material including at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

[0043] In yet another embodiment of the second aspect, at least two of the plurality of sub-pixel stacks have different distances between the emission layer and the first electrode layer to maintain a substantially same angular distribution in the first material for emissions of different wavelengths.

[0044] In yet another embodiment of the second aspect, the sub-pixel stack emits a first emission peak towards the first material along an in-axis direction that is substantially perpendicular to the top surface of the sub-pixel stack; the sub-pixel stack emits a second emission peak towards the first material along an off-axis direction that is at an angle to the in-axis direction; and the second emission along the off-axis direction is reflected by the interface between the first material and the second material and guided to the inclined sidewalls of the dam.

[0045] In another embodiment of the second aspect, the second emission peak is reflected by the inclined sidewalls of the dam and emitted through the interface along the in-axis direction substantially without total internal reflection; and the angle between the inclined sidewalls of the dam and the top surface of the sub-pixel stack is half of the angle between the in-axis direction of the first emission peak and the off-axis direction of the second emission peak. In yet another embodiment of the second aspect, the top surface of the first material is coplanar with the top surface of the dam, and the second material covers the top surface of the first material in the internal space and the top surfaces of the dams surrounding each of the plurality of sub-pixel stacks.

[0046] In another embodiment of the second aspect, the light-emitting structure further includes an air gap located between the first material and the second material. In yet another embodiment of the second aspect, the emission layer includes a quantum dot emission material, the first transport layer includes a hole transport layer, the second transport layer includes an electron transport layer, the first electrode layer is an anode layer, the anode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is a cathode layer having a non-metallic and substantially transparent material. In yet another embodiment of the second aspect, the emission layer includes a quantum dot emission material, the first transport layer includes an electron transport layer, the second transport layer includes a hole transport layer, the first electrode layer is a cathode layer, the cathode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is an anode layer having a non-metallic and substantially transparent material. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] When read in conjunction with the drawings, various aspects of the example disclosure can be best understood from the following detailed description. The various features are not drawn to scale. For the sake of clarity of discussion, the dimensions of the various features can be increased or decreased arbitrarily.

[0048] Figure 1A is a schematic cross-sectional view of a part of an exemplary light-emitting structure according to an exemplary embodiment of the present disclosure.

[0049] Figure 1B is according to an exemplary embodiment of the present disclosure Figure 1A schematic cross-sectional view of a part of the sub-pixel stack in the light-emitting structure.

[0050] Figure 2A Shows a part of a conventional sub-pixel stack in a light-emitting structure.

[0051] Figure 2B Shows at Figure 2A The angular distribution diagram of a single emission peak at a wavelength measured in the light-emitting structure of.

[0052] Figure 3A Shows a part of a preferred exemplary light-emitting structure according to an exemplary embodiment of the present disclosure.

[0053] Figure 3B Shows according to an exemplary embodiment of the present disclosure at Figure 3A The exemplary angular distribution of a single emission peak at a wavelength measured in the exemplary light-emitting structure of.

[0054] Figure 4A Is a schematic cross-sectional view of an exemplary light-emitting structure according to an exemplary embodiment of the present disclosure.

[0055] Figure 4B , Figure 4C And Figure 4D Are detailed schematic cross-sectional views of three exemplary structures of three sub-pixel stacks in the light-emitting structure of according to an exemplary embodiment of the present disclosure. Figure 4A Of.

[0056] Figure 5 Is a schematic cross-sectional view of another exemplary light-emitting structure according to an exemplary embodiment of the present disclosure. Detailed Description of the Invention

[0057] The following disclosure contains specific information related to the exemplary embodiments in the present disclosure. The drawings and their accompanying detailed descriptions in the present disclosure only relate to the exemplary embodiments. However, the present disclosure is not limited to these exemplary embodiments. Those skilled in the art will think of other variations and embodiments of the present disclosure.

[0058] Unless otherwise specified, the same or corresponding elements in the drawings may be represented by the same or corresponding reference numerals. Moreover, the drawings and illustrations in the present disclosure are generally not drawn to scale and are not intended to correspond to actual relative sizes.

[0059] For the purpose of consistency and ease of understanding, in the example drawings, the same features may be marked with the same reference numerals (although not shown in some examples). However, the features in different embodiments may be different in other respects and should not be limited to those shown in the drawings.

[0060] The phrases “in one embodiment” or “in some embodiments” as used in the specification can each refer to one or more of the same or different embodiments. The term “comprising” means “including but not necessarily limited to” and specifically denotes an open inclusion or membership in the described combination, group, series, and equivalents. The expression “at least one of A, B, and C” or “at least one of the following: A, B, and C” means “only A, or only B, or only C, or any combination of A, B, and C”.

[0061] The phrase “optical distance” (or “optical thickness”) is used in the specification, which can refer to the product of the reflectivity of a material and the actual physical distance (or the actual physical thickness) in the material.

[0062] In addition, for purposes of explanation and not limitation, specific details such as functional entities, technologies, protocols, standards, etc. are elaborated to provide an understanding of the described technology. In other examples, detailed descriptions of well-known methods, technologies, systems, architectures, etc. are omitted so as not to obscure the description with unnecessary details.

[0063] The present disclosure relates to an emissive display that includes a quantum dot electroluminescent material in a light-emitting diode (LED) arrangement. Although one or more embodiments of the present disclosure are described with reference to a display having QLED pixels, the exemplary embodiments provided herein do not limit the scope of the present disclosure and can also be applied to other displays and structures, such as OLED structures. The LED arrangement generally includes a quantum dot (QD) emissive material layer (e.g., an emissive layer) sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL). These three layers are sandwiched between two conductive layers to form a sub-pixel stack. In one or more embodiments of the present disclosure, a “top” emission (TE) structure is employed. The TE structure involves emitting light from the side of the TE structure opposite the glass substrate, and the TE structure is disposed on the glass substrate.

[0064] In one or more embodiments of the present disclosure, the fabrication of the TE device includes depositing a layer of conductive reflective material, typically made of a metal (e.g., silver or aluminum), on a glass substrate, where an HTL layer is deposited on the conductive reflective layer (e.g., reflective conductor or reflective electrode), an emissive layer is deposited on the HTL layer, an ETL layer is deposited on the emissive layer, and a transparent electrode layer is deposited on the ETL layer. In a preferred embodiment, the thickness of the reflective electrode is greater than 80 nm (i.e., 10^-9 meters). In another preferred embodiment, the reflective electrode includes a layer of silver with a thickness of about 100 nm and a layer of indium tin oxide (ITO) with a thickness of about 10 nm. In a preferred embodiment, the HTL layer is made of a layer of about 40 nm thick PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) and a layer of about 35 - 45 nm thick TFB (poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)diphenylamine)) on the PEDOT:PSS layer. In another preferred embodiment, an emissive layer with a thickness of about 20 nm is disposed on the HTL layer, and an ETL layer is disposed on the emissive layer. In another preferred embodiment, the ETL layer is made of zinc oxide (ZnO) nanoparticles and has a thickness of about 30 - 80 nm. In a preferred embodiment, the transparent electrode layer (e.g., the top electrode layer of the TE device) is a thin metal layer that is thick enough to carry sufficient current but thin enough to be transparent to light and is disposed on the ETL layer. In a preferred embodiment, the transparent electrode layer is typically made of silver nanowires with a thickness of about 10 - 15 nm. In another preferred embodiment, the transparent electrode layer is typically made of ITO nanoparticles or bulk ITO with a thickness of about 80 - 100 nm.

[0065] The present disclosure is not limited to the provided examples, because if the arrangement of the ETL and HTL layers is reversed, the basic principle of the disclosed structure still applies. In a preferred embodiment of the present disclosure, regardless of whether the ETL layer or the HTL layer is disposed on the emission side of the emissive layer away from the glass substrate, the transport layer closer to the glass substrate is thinner than the transport layer farther from the glass substrate.

[0066] In an OLED panel, the use of a semi-transparent thin metal top electrode (e.g., cathode) is very common. The partial reflectivity of such an electrode with a fully reflective bottom electrode (e.g., anode) forms an optical cavity for extraction, which strongly depends on the wavelength and direction of light. The OLED dyes used for the emissive layer have a wide phosphorescent spectrum. However, the color gamut range of red / green / blue dyes is poor. Therefore, it is necessary to design the transport of the cavity to suppress many wavelengths, increasing the color gamut at the cost of lower optical efficiency. In addition, the direction dependence also introduces a change in color with angle, which may be undesirable.

[0067] In previous QLED panels, the quantum dot emissive layer may have a spectrum narrow enough for good color gamut; thus, an optical cavity may not be needed. Accordingly, a completely transparent non-metallic element may be used for the top electrode (e.g., the cathode), which can improve efficiency, but more specifically, can reduce color shift. The top electrode as described above is, for example, a cathode having a refractive index in the same order as the other layers, e.g., greater than about 1.7. However, such a high refractive index transparent cathode, e.g., ITO having a refractive index of 1.89 at 620 nm, is a ceramic that requires a manufacturing process that is detrimental to the emissive layer of the QLED. A more preferred transparent cathode has a lower refractive index, e.g., nanoparticle ITO that can be solution processed, e.g., having a value less than 1.45 at 620 nm. However, due to the refractive index and waveguide mode mismatch, such a refractive index forms a reflective boundary with the emissive layer, thereby introducing reflection, which in turn introduces cavity effects such as efficiency loss and color shift. Additionally, by using a high refractive index layer (e.g., Figure 2A ), a very narrow angular distribution is formed in the high refractive index layer (e.g., Figure 2B ), which may allow very little light to be subject to total internal reflection, thus significantly reducing the effect of light collimation and reducing color shift through the dam.

[0068] In one or more embodiments of the present disclosure, as described above, the conventional structure of a high refractive index filler layer and a low refractive index layer located above the high refractive index filler layer is inverted. Specifically, a high refractive index layer (e.g., ITO or indium zinc oxide (IZO) having a refractive index of about 2.07 at 620 nm) is located above a low refractive index filler having a refractive index similar to that of the cathode (e.g., Figure 3A ). By this embodiment of the present disclosure, a wider angular distribution is created in the low refractive index layer (e.g., Figure 3B ). In other words, light at a higher incident angle will be reflected to the dam for light collimation by Fresnel reflection, thereby reducing color shift. The low refractive index layer or filler may be made of aerogel. The details of the embodiments of the present disclosure are further discussed in the following drawings and related descriptions.

[0069] In the prior art, the QLED sub-pixel structure includes an internal space structure (e.g., a cavity structure), which can be outlined by a sub-pixel stack having an emission layer and a dam structure surrounding the sub-pixel stack. The internal space structure above the emission layer within the dam structure is a filler or encapsulation material that protects the emission layer. Due to its higher refractive index, the filling material can also extract light from the emission layer better than air. The light trapped in the emission layer is quickly absorbed, but the light trapped in the higher refractive index filler layer has a chance to propagate to the dam edge and can be extracted by reflection. The dam is usually opaque, and the surface facing the higher refractive index filler layer can be either diffusely reflective or specularly reflective. The higher refractive index filler layer usually has a relatively high refractive index and can be disposed in the internal space structure above the sub-pixel stack. Above the higher refractive index filler layer is usually air or a lower refractive index layer to prevent light from leaking into adjacent pixels via the upper glass layer disposed above the lower refractive index layer and to prevent crosstalk, and to achieve propagation towards the dam edge through total internal reflection. The lower refractive index layer traps the light into the higher refractive index filler layer where it is more easily absorbed. Thus, light can be extracted from the high refractive index filler layer more effectively without coupling the light into the upper glass layer. Then, the extracted light can propagate to the dam by reflection, and the reflected light improves the collimation with high on-axis brightness and mixes light at different angles, thereby further reducing color shift.

[0070] In one or more embodiments of the present disclosure, the QLED sub-pixel structure differs from the QLED sub-pixel structure of the prior art in that a lower refractive index filler layer (e.g., Figure 1A the first material layer 110 in Figure 1A can be disposed in the internal space structure, and a higher refractive index layer (e.g.,

[0071] the second material layer 112 in

[0071] can be disposed above the lower refractive index filler layer having a refractive index similar (e.g., matching) to that of the cathode in the emission layer. In one or more embodiments of the present disclosure, the dam structure can have a height that is at least equal to or higher than that of the lower refractive index filler layer. In one or more embodiments, the lower refractive index filler layer can be at least one of an air gap, a silicone-based nanocomposite polymer from Inkron having a refractive index as low as 1.15, poly(1,1,1,3,3,3-hexafluoroisopropyl acrylate) having a refractive index of 1.375, and poly(2,2,3,3,4,4,4-heptafluorobutyl acrylate) having a refractive index of 1.377.In one or more embodiments of the present disclosure, the angular emission distribution from the emission layer can be determined by the distance between the emission layer and the reflective electrode layer (e.g., at the bottom of the sub-pixel stack), and this distance directly depends on the total optical thickness of the HTL layer. The distance between the emission layer and the reflective electrode layer can be adjusted such that there are two directions of light emission with constructive interference from the light source. One direction is on-axis emission (e.g., emission perpendicular to the plane or top surface of the sub-pixel stack), and the other direction is off-axis emission (e.g., emission at an angle relative to the on-axis direction).

[0072] In an exemplary embodiment where the reflective electrode is a perfect mirror, the reflective electrode layer is separated from the emission layer by an optical distance of one wavelength (e.g., λ). This optical distance can be 0.5, 1, or any integer multiple of 0.5 wavelengths away from the emission layer. In an exemplary embodiment where the reflective electrode is not a perfect mirror (e.g., in other words, there is a phase shift), the reflection point will not be precisely at the surface of the reflective electrode. In one or more embodiments of the present disclosure, the reflective electrode is, for example, separated from the emission layer by an optical distance of approximately 1 wavelength in order to produce two emissions (e.g., on-axis emission and off-axis emission). However, in order to counteract the effect of the phase shift in the reflective electrode, this distance is adjusted to 0.87 wavelengths (this value is an example, and the actual value depends on the material properties of the bottom reflector). The emission layer can produce constructive on-axis emission perpendicular to the reflective electrode and off-axis emission at an angle of approximately 50° - 55° relative to the on-axis emission, thereby obtaining the optical thickness of the HTL layer.

[0073] The correlations between the distances, thicknesses, angular emissions, and wavelengths described above can be expressed by the following equations:

[0074] 2(d - d')cos(θ P ) = Nλ Equation (1)

[0075] d = T Equation (2)

[0076] where d is the sum of the optical thicknesses of all layers in the HTL layer (e.g., Figure 1B 104b1 and 104b2 in Figure 1B ), d' is the optical distance from the top surface of the reflective electrode to the inside of the reflective electrode where effective reflection occurs to compensate for the true phase shift (e.g., P d' in Figure 1A), where N is an integer greater than zero, λ is the wavelength in free space, T is the total optical thickness of the HTL layer, which may include one or more layers (e.g., TFB layer and PEDOT:PSS layer), and each layer has a different refractive index. Using equations (1) and (2), the thickness T can be adjusted accordingly. In an exemplary embodiment, N can be equal to 1 to give a wide forward emission direction. In a preferred exemplary embodiment, if d is predetermined and θ P equals 0 (e.g., d - d' = λ), then N can be equal to 2. Thus, if cos(θ P ) equals 1 / 2 (e.g., θ P is 60°), a second peak may be generated. Due to the difference in refractive index between various elements of the present disclosure (e.g., HTL layer, filler layer, etc.), in a preferred embodiment, θ P is less than 60°, while in another preferred embodiment, θ P is about 50° - 55°. The term "emission" described in the present disclosure may refer to the distribution of emission wavelengths, but is not limited to a single wavelength. The term "wavelength" in the present disclosure may be used to describe the peak or central wavelength among multiple wavelengths in the context of the above equations, but is not limited to the description provided herein. The optical distance (thickness) is calculated as the product of the refractive index of the material and the actual physical distance (thickness) in the material.

[0077] Exemplary embodiments of the present disclosure may relate to QLED structures. However, the present disclosure is not limited to QLED structures and can be applied to various embodiments related to OLED structures.

[0078] In the present disclosure having an internal space structure and a top transparent electrode, the distance between the emission layer and the reflective electrode is adjusted as described above such that on-axis emission and off-axis emission exist. The off-axis emission will be reflected at least once by total internal reflection (TIR) onto the top surface (e.g., interface) of the filler material and then reflected from the inclined surface of the dam and emitted along the on-axis direction through the filler material. The dam structure at each pixel end is designed such that the inclination angle (e.g., dam angle) of the dam structure is half of the angle of the off-axis emission entering the filler material relative to the on-axis emission.

[0079] In the present disclosure, the emission layer in the sub-pixel stack can emit light, and there is a central wavelength in the wavelength range of the light that is generally regarded as the main emission peak. The central wavelength is the wavelength with the highest spectral brightness in the emission spectrum from the light source. In the present disclosure, for wavelengths that are generally longer than the central wavelength emitted by the emission layer, off-axis emission with a higher intensity than the on-axis emission is generated. For wavelengths shorter than the central wavelength, the intensity of the on-axis emission is higher than that of the off-axis emission.

[0080] According to the present disclosure, even if the total light output efficiency is not maximized, the on-axis brightness and the brightness perceived by the user are maximized. Since the user generally perceives the light emitted on-axis in the central region of the pixel and the light emitted off-axis at the edge of the bank, the distribution of light from these different spectral regions can provide a more balanced color distribution at all angles, thereby minimizing color shift at each angle.

[0081] Figure 1A is a schematic cross-sectional view of a part of an exemplary light-emitting structure according to an exemplary embodiment of the present disclosure. In Figure 1A the exemplary light-emitting structure 100 may include a substrate 102, a sub-pixel stack 104, a bank 106, a first material layer 110, a second material layer 112, and a glass cover 122. In one or more embodiments of the present disclosure, the sub-pixel stack 104 may be disposed on the substrate 102, and the bank 106 surrounds the sub-pixel stack 104 to form an internal space 108 above the sub-pixel stack 104. The first material layer 110 may be a low-refractive-index material filled in the internal space 108, and the second material layer 112 may be a relatively higher-refractive-index material disposed on top of the first material layer 110. In one embodiment, the exemplary light-emitting structure 100 may include a pixel structure. In one embodiment, the second material layer 112 may be continuously disposed on the first material layer 110 and the bank 106. In one embodiment, the second material layer 112 may cover the entire top surface of the first material layer 110. In one embodiment, the top surface of the first material layer 110 is coplanar with the top surface of the bank 106, and the second material layer 112 covers the top surface of the first material layer 110 in the internal space 108 and the top surface of the bank 106 surrounding the sub-pixel stack 104.

[0082] In one or more embodiments, the thickness of the bank 106 may be greater than the thickness of the first material layer 110. In one or more embodiments, the bank 106 is in contact with the substrate 102. In a preferred embodiment, the bank 106 may be in contact with or almost in contact with the second material layer 112. In one or more embodiments, the glass cover 122 may be continuously disposed above the second material layer 112.

[0083] In one or more embodiments, the bank 106 may be opaque. The surface of the bank 106 facing the first material layer 110 may be diffusely reflective or specularly reflective and may be at an angle (e.g., inclined) with respect to the plane of the substrate 102 (e.g., a glass substrate).

[0084] In one or more embodiments, light emissions such as the first emission peak 114 and the second emission peak 118 can be emitted from the sub-pixel stack 104. The first emission peak 114 is emitted from the sub-pixel stack 104 along the in-axis direction through the first material layer 110, the second material layer 112, and the glass cover 122. The second emission peak 118 is emitted from the sub-pixel stack 104 along an off-axis direction (e.g., at an angle) relative to the in-axis direction. The second emission peak 118 emitted in the off-axis direction can be reflected at least once by total internal reflection (TIR) onto the interface 120 (e.g., the top surface of the first material layer 110) before being reflected from the inclined sidewall 107 of the dam 106 and emitted as an in-axis emission 116 along the in-axis direction through the first material layer 110, the second material layer 112, and the glass cover 122.

[0085] Figure 1B is a schematic cross-sectional view of a portion of a sub-pixel stack in a light-emitting structure according to an exemplary embodiment of the present disclosure. As Figure 1A shown, the sub-pixel stack 104 includes a first electrode layer 104a, an HTL layer 104b, an emission layer 104c, an ETL layer 104d, and a second electrode layer 104e. In one or more embodiments of the present disclosure, referring to Figure 1B and Figure 1A and Figure 1B , the first material layer 110 having a lower refractive index than the second material layer 112 can be disposed on the second electrode layer 104e (e.g., the top electrode) of the sub-pixel stack 104, and the refractive index of the second electrode layer 104e can match (e.g., be similar or the same as) the refractive index of the first material layer 110. In this embodiment, the first electrode layer 104a can be a bottom reflective electrode, and the second electrode layer 104e can be a transparent top electrode. The first electrode layer 104a can be disposed on the substrate 102 and can be an anode layer, which is a metal reflector that reflects the light emitted from the emission layer 104c. The second electrode layer 104e can be a non-metallic, substantially transparent cathode layer and is disposed on the ETL layer 104d. In one or more embodiments, the second electrode layer 104e can be a low refractive index conductive material, e.g., ITO nanoparticles or silver nanowires. In one or more embodiments, the second electrode layer 104e (the top electrode of the sub-pixel stack 104) can have a refractive index significantly lower than that of the other layers of the sub-pixel stack 104.

[0086] However, the arrangement of the first electrode layer 104a and the second electrode layer 104e is not limited to the examples provided herein and can be reversed. For example, the first electrode layer 104a can be a non-metallic and substantially transparent top cathode layer, and the second electrode layer 104e can be a bottom anode layer, which is a metal reflector that reflects the light emitted from the emission layer 104c.

[0087] AsFigure 1B As shown, the HTL layer 104b may include a TFB layer 104b1 and a PEDOT:PSS layer 104b2. In another embodiment, the HTL layer 104b may include other layers and is not limited to the example layers provided herein. In another embodiment, depending on the arrangement of the first electrode layer 104a and the second electrode layer 104e, the foregoing arrangement of the HTL layer 104d and the ETL layer 104b may be reversed.

[0088] Reference Figure 1A and Figure 1B , the emission structure of the sub-pixel stack 104 can be used when defined by the dams 106 (e.g., high dams). The internal space 108 between the dams 106 and above the sub-pixel stack 104 is filled with a first material layer 110 having a lower refractive index that matches (e.g., is similar or the same) the refractive index of the second electrode layer 104e (top electrode). In other words, the top surface of the second electrode layer 104e has a refractive index that matches the refractive index of the first material layer 110 filling the internal space 108. Thus, although the thickness of the second electrode layer 104e has no significant effect on the overall performance of the display, it may be important in minimizing resistive losses and variations during processing. In addition, light reflection from the top surface of the second electrode layer 104e is minimized. Therefore, most of the light emitted from the emission layer 104c that can pass through the second electrode layer 104e at the top of the sub-pixel stack 104 will pass through with minimal reflection.

[0089] In one or more embodiments, the second material layer 112 is a continuous high refractive index layer, which can be a high refractive index transparent material such as ITO or IZO, and completely covers the first material layer 110 with a relatively lower refractive index. When the higher refractive index second material layer 112 is located above the lower refractive index first material layer 110, off-axis emission from the sub-pixel stack 104 can be converted into Fresnel reflection (total internal reflection), further directed onto the dams 106, and collimated into on-axis emission, which can be combined or mixed with most of the on-axis emission from the sub-pixel stack 104 in the on-axis direction (e.g., the z direction), thereby increasing the on-axis brightness. Specifically, reference Figure 1A and Figure 1B , at least one single emission peak is generated from the sub-pixel stack 104. Reference Figure 1A , a first emission peak 114 can be generated from the sub-pixel stack 104. The first emission peak 114 can be on-axis emission that is emitted from the emission layer 104c perpendicular to the top surface of the emission layer 104c, passes through the ETL layer 104d, the second electrode layer 104e, and then through the first material layer 110 (e.g., lower refractive index), the second material layer 112 (e.g., higher refractive index), and the glass cover 122, with substantially no total internal reflection.

[0090] In one or more embodiments of the present disclosure, reference is made to Figure 1A and Figure 1B , the second emission peak 118 may be an off-axis emission that is emitted from the emission layer 104c at an angle with respect to the first emission peak 114 and enters the first material layer 110. The off-axis second emission peak 118 may be totally and internally reflected at least once at the interface 120 (e.g., the top surface of the first material layer 110) before reaching the inclined sidewall 107 of the dam 106, as total internal reflection (TIR). The off-axis second emission peak 118 that has undergone total internal reflection may be reflected from the inclined sidewall 107 along the axial direction (e.g., at an angle perpendicular to the top surface of the emission layer 104c) and pass through the interface 120 with substantially no total internal reflection occurring.

[0091] In one or more embodiments, the first emission peak 114 may be emitted through the interface 120 with substantially no total internal reflection. In a preferred embodiment, the dam angle θB of the inclined sidewall 107 or the angle between the inclined sidewall 107 of the inclined sidewall 107 and the top surface of the sub-pixel stack 104 is half of the off-axis second emission angle θ P of the on-axis first emission peak 114. With this arrangement, the reflection slope angle θB of the dam 106 can be adjusted to optimize the high on-axis brightness.

[0092] Figure 2A Shows a portion of a conventional sub-pixel stack in a light-emitting structure. Figure 2B Shows in Figure 2A the angular distribution diagram of a single emission peak at a wavelength measured in the light-emitting structure of

[0093] In Figure 2AIn the prior art, the light-emitting structure 200A may include: a substrate (not explicitly shown), a sub-pixel stack 204, a first material layer 210, a bank 206 having inclined sidewalls 207 surrounding the sub-pixel stack 204 and the first material layer 210 (dashed line), a continuous second material layer 212 covering the entire first material layer 210 and the bank 206, and a glass cover 222 covering the second material layer 212, which may correspond to the substrate 102, the sub-pixel stack 104, the first material layer 110, the bank 106 surrounding the sub-pixel stack 104 and the first material layer 110, a continuous second material layer 112 covering the entire first material layer 110 and the bank 106, and a glass cover 122 covering the second material layer 112 of the exemplary light-emitting structure 100. However, the exemplary light-emitting structure 100 of the present disclosure is different from the light-emitting structure 200A of the prior art in that the light-emitting structure 200A of the prior art may include a first material layer 210 having a refractive index higher than that of the second material layer 212, while the light-emitting structure 100 of the present disclosure may include a first material layer 110 having a lower refractive index than the second material layer 112, and the second electrode layer 104e of the sub-pixel stack 104 has a refractive index that matches (e.g., is similar to) that of the first material layer 110 with a lower refractive index.

[0094] Figure 2A The structure 200A in may include a sub-pixel stack 204 having a first electrode layer (not explicitly shown) that may be a reflective bottom electrode layer, a second electrode layer that may be a transparent top electrode layer (not explicitly shown), and an interface 220 (e.g., the surface of the first material layer 210). As described above, a single main emission peak may be generated by the emission layer of the sub-pixel stack 204. The first emission peak 214 in the axial direction may pass through the first material layer 210 and the second material layer 212, while the second emission peak 218 in the off-axis direction may spread at various angles, resulting in lower axial brightness.

[0095] If the top electrode layer (not explicitly shown) of the sub-pixel stack 204 is an electrode with a low refractive index, the angular range that can propagate from the low refractive index top electrode of the sub-pixel stack 204 to the high refractive index first material layer 210 is limited (e.g., Figure 2A ). For example, in the sub-pixel stack 204, the refractive index of the low refractive index top electrode layer may be represented by n t , the refractive index of the emission layer may be represented by n e , the refractive index of the high refractive index first material layer 210 may be represented by nf, and then the maximum angle θ t with the axis (e.g., the axis perpendicular to the top surface of the low refractive index top electrode layer) that can propagate in the low refractive index top electrode layer may be derived from the following equation (3):

[0096] Sinθ t = n t / n e Equation (3);

[0097] And the maximum angle with respect to the axis (e.g., an axis perpendicular to the top surface of the first material layer 210) that can be propagated in the first material layer 210 (e.g., the filler layer), represented by θ f can be derived from the following Equation (4) according to Snell's law:

[0098] Sinθ f = n t / n f Equation (4).

[0099] For the structure 200A, typical values of n t can be 1.4, n e can be 1.766, n f can be 1.82. Thus, θ f may be approximately 50°. Thus, all light propagates in the high refractive index first material layer 210 at an angle less than 50° with respect to the normal. The low refractive index second material layer typically has a refractive index of 1.26 (n LI ), through which the critical angle for total internal reflection can be calculated to be approximately 43° (e.g., arcsin(n LI / n f )). Thus, light is rarely reflected, and the effect of the embankment on improving performance is also small.

[0100] Referring Figure 2B to the illustration 200B in Figure 2A , the angular distribution in the axial direction of the first emission peak 214 at a wavelength is measured in the high refractive index first material layer 210 (e.g., the filler layer) of the structure 200A in

[0101] Figure 3A shows a part of a preferred exemplary light-emitting structure according to an exemplary embodiment of the present disclosure. Figure 3B shows an exemplary angular distribution of a single emission peak at a wavelength measured in an exemplary light-emitting structure according to an exemplary implementation of the present disclosure in Figure 3A .

[0102] In Figure 3A , the preferred exemplary light-emitting structure 300A can be substantially the same as Figure 1ASimilar to the exemplary light-emitting structure 100. Thus, the exemplary light-emitting structure 300A may include a substrate (not explicitly shown), a sub-pixel stack 304, a first material layer 310, a bank 306 having inclined sidewalls 307 surrounding the sub-pixel stack 304 and the first material layer 310, a continuous second material layer 312 covering the entire first material layer 310 and the bank 306, and a glass cover 322 covering the second material layer 312, which may correspond to the substrate 102, the sub-pixel stack 104, the first material layer 110, the bank 106 surrounding the sub-pixel stack 104 and the first material layer 110, a continuous second material layer 112 covering the entire first material layer 110 and the bank 106, and the glass cover 122 covering the second material layer 112 of the exemplary light-emitting structure 100. Therefore, for the sake of brevity, the details of the exemplary light-emitting structure 300A are omitted.

[0103] Similar to Figure 1A the light-emitting structure in, the present disclosure Figure 3A the exemplary light-emitting structure 300A in is different from Figure 2A the prior art light-emitting structure 200A in that the structure 200A may include a first material layer 210 having a higher refractive index relative to the refractive index of the second material layer 212, while the exemplary light-emitting structure 300A of the present disclosure may include a first material layer 310 having a lower refractive index relative to the second material layer 312, and the top electrode (not explicitly shown) of the sub-pixel stack 304 has a refractive index that matches (e.g., is similar or the same as) the refractive index of the low-refractive-index first material layer 310.

[0104] In the exemplary light-emitting structure 300A, an on-axis first emission peak 314 may be emitted from the sub-pixel stack 304. Off-axis emission 318 may also be emitted from the sub-pixel stack 304. Before being reflected from the inclined sidewalls 307 at an angle perpendicular to the top surface of the sub-pixel stack 304 as light emission in the on-axis direction 316, most of the off-axis emission 318 is totally internally reflected 318a at least once at the interface 320 (e.g., the plane between the low-refractive-index first material layer 310 and the high-refractive-index second material layer 312) by total internal reflection (TIR).

[0105] By such as Figure 3AThe arrangement of the refractive index of the low-refractive-index first material layer 310, the high-refractive-index second material layer 312, and the top electrode of the sub-pixel stack 304 that matches (e.g., is similar or the same as) the refractive index of the low-refractive-index first material layer 310 results in a wider angular range in the low-refractive-index first material layer 310 because the light that can propagate through the low-refractive-index top electrode of the sub-pixel stack 304 is not restricted. Thus, the angular range can be as high as 90°, but more preferably, the angular range can be reduced at larger angles. When the light reaches the high-refractive-index second material layer 312, the light will propagate without total internal reflection. With a refractive index n HI high enough in the second material layer 312, total internal reflection can be represented by the following two Fresnel equations (where S and P are polarization vectors):

[0106] and

[0107]

[0108] where n 1 (n f ) is the refractive index of the first material layer (e.g., the first material layer 210 in Figure 2A or the first material layer 310 in Figure 3A ), n 2 can be the refractive index of the second material layer that is higher relative to the first material layer (e.g., n HI for 312) or can be the refractive index of the second material layer that is lower relative to the first material layer (e.g., n LI for 212), and θi is the angle of incidence on the high-refractive-index material layer (e.g., the second material layer 212 in Figure 2A or the second material layer 312 in Figure 3A ). Total reflection is the average of the above two equations. For the prior art structure 200A in Figure 2A , where, if θi equals 0° and the angle is up to 50°, n t equals 1.4, n LI equals 1.26, n f equals 1.82, and the reflectivity on the axis is less than 3% and is only significant (greater than 8%) for angles greater than 37.5°, the first material layer 210 has a higher refractive index than the second material layer 212. Thus, Fresnel reflection is less obvious and TIR dominates in a small angular range between 43° and 50°, where the light intensity is minimal. Additionally, using such light requires a narrow bank angle of 20°, so, given the provided bank height, the non-emitting bank will require more area in the X-Y plane.

[0109] However, for the present disclosureFigure 3A Exemplary light-emitting structure 300A therein, where the refractive index of the first material layer 310 is lower than that of the second material layer 312, n t equals 1.4, n HL equals 2.07, n f equals 1.4, the Fresnel reflectivity is less than 4% on axis, but there is a large amount of light (>70°) off axis, where the Fresnel reflectivity is greater than 15% and higher at higher angles. The dike angle being half of the 35° angle will collimate through Fresnel reflection at the interface (e.g., 320), thereby improving collimation and reducing chromatic shift. In the present exemplary embodiment, if a given dike height is the same as that employed in the prior art structure 200A, a higher dike angle may result in a smaller area in the X-Y plane required for the dike.

[0110] Reference Figure 3B In the diagram 300B in, the angular distribution in the on-axis direction of the first emission peak 314 at one wavelength is measured in the low refractive index first material layer 310 (e.g., the filler layer). The angular distribution of the first emission peak 314 in the low refractive index first material layer 310 in the on-axis direction is relatively wide, which may allow more light to undergo total internal reflection, and different from Figure 2B the diagram 200B in, thus significantly improving the effect of light collimation and reducing the chromatic shift provided by the dike 306.

[0111] Figure 4A is a schematic cross-sectional view of an exemplary structure 400A of a light-emitting structure according to an exemplary embodiment of the present disclosure. Figure 4A The exemplary structure 400A in includes a glass substrate 402, a sub-pixel stack 404, a dike 406, a first material layer 410, a second material layer 412, and a glass cover 422. The exemplary structure 400A may substantially correspond to Figure 1A the exemplary light-emitting structure 100 described in and Figure 3A the exemplary light-emitting structure 300A described in. Therefore, for the sake of brevity, the details of the exemplary structure 400A are omitted.

[0112] In Figure 4A the exemplary structure 400A is compared with Figure 1A the exemplary light-emitting structure 100 in and Figure 3AThe exemplary light emitting structure 300A in the embodiment of the present disclosure is different in that the exemplary structure 400A may include three light emitting structures 400B, 400C, and 400D (e.g., three sub-pixel stacks) for three different pixels. In one or more embodiments of the present disclosure, the exemplary structure 400A may include an exemplary light emitting structure 400B for a blue pixel, an exemplary light emitting structure 400C for a green pixel, and an exemplary light emitting structure 400D for a red pixel. In another embodiment, the exemplary structure 400A may include more than three exemplary structures for more than three pixels, and is not limited to the examples described herein.

[0113] In one or more embodiments, the first emission peak 414 is emitted in the on-axis direction through the first material layer 410, the second material layer 412, and the glass cover 422 without substantially total internal reflection. Before the second emission peak 418 is reflected from the inclined sidewall 407 of the bank 406 in the on-axis direction without substantially total internal reflection as the on-axis emission 416, the second emission peak 418 can be emitted from the sub-pixel stack 404 in the off-axis direction toward the interface 420 (e.g., the top surface of the first material layer 410) between the first material layer 410 and the second material layer 412, and is totally internally reflected at least once by the interface 420.

[0114] Figure 4B , 4C and 4D are exemplary embodiments according to the present disclosure. Figure 4A Detailed schematic cross-sectional views of three exemplary light emitting structures 400B, 400C, and 400D of three sub-pixel stacks (e.g., three dashed circles) in a light emitting structure of FIG. The exemplary light emitting structures 400B-400D are exemplary sub-pixel stacks 404, each of which includes a first electrode layer 404a, an HTL layer 404b including a TFB layer 404b1 and a PEDOT:PSS layer 404b2, an emission layer 404c, an ETL layer 404d, and a second electrode layer 404e. The exemplary structures 400B-400D may substantially correspond to Figure 1B Therefore, for the sake of brevity, the details of the exemplary structures 400B, 400C and 400D are omitted.

[0115] The three exemplary light emitting structures 400B-400D are sub-pixel stacks 404 for three color pixels (e.g., blue, green, and red pixels, respectively). The distance between the emission layer and the reflective electrode at the bottom of the emission structure or the thickness of the HTL layer can be adjusted to emit a first emission peak 414 on the axis and a second emission peak 418 off the axis that are constructive.

[0116] In one or more embodiments, the TFB layer 404b1 of three exemplary light-emitting structures 400B - 400D (e.g., sub-pixel stacks) has different thicknesses. Thus, by adjusting the thickness t (e.g., tB, tG, and tR) of each TFB layer 404b1, the relative intensities of the first emission peak 414 and the second emission peak 416 in each exemplary light-emitting structure 400B - 400D can be changed. Therefore, the overall brightness is adjusted and the color shift is reduced.

[0117] In one exemplary embodiment, the thickness tB of the TFB layer 104b1 in the exemplary light-emitting structure 400B (emitting a central wavelength of about 435 nm) for blue pixels is about 75 nm, the thickness tG of the TFB layer 104b1 in the exemplary light-emitting structure 400C (emitting a central wavelength of about 530 nm) for green pixels is about 115 nm, and the thickness tR of the TFB layer 104b1 in the exemplary light-emitting structure 400D (emitting a central wavelength of about 620 nm) for red pixels is about 150 nm. In a preferred embodiment, when considering the refractive index, for each of the blue, green, and red pixels, the thickness or distance between the emission layer 404c and the first electrode layer 404a is 0.53 of the wavelength. The reflective electrode used causes a deviation between the distance in the preferred embodiment (where the distance is 0.53) and the distance in the ideal embodiment (where the distance is 0.78). In this exemplary embodiment, for the exemplary light-emitting structures 400B, 400C, and 400D shown in Figure 4B , Figure 4C and Figure 4D respectively, only one layer (e.g., the TFB layer 404b1) in each layer of the HTL layer 404b has different thicknesses. However, in one or more embodiments of the present disclosure, the thicknesses of any or all layers of the HTL layer 404b can be different such that the total optical thickness is the same as that in the case where only one layer of the HTL layer 404b has a different thickness. The actual thicknesses of the HTL layer 404b in each of the three light-emitting structures 400B, 400C, 400D with three different colors are different in order to maintain the same angular distribution in the low-refractive-index first material layer 410 (e.g., the filler layer) for emissions of different wavelengths (e.g., colors).

[0118] Figure 5 is a schematic cross-sectional view of another exemplary structure 500 of a light-emitting structure according to an exemplary embodiment of the present disclosure. The exemplary structure 500 includes a glass substrate 502, a sub-pixel stack 504, a bank 506, a first material layer 510 (e.g., a filler layer), a second material layer 512, and a glass cover 522. The exemplary structure 500 can substantially correspond to Figure 1A the exemplary light-emitting structure 100 described in Figure 3Athe exemplary light-emitting structure 300A described in Figure 4A and the exemplary structure 400A described in

[0119] In one or more embodiments, the exemplary structure 500 differs from Figure 1A the exemplary light-emitting structure 100 in Figure 3A the exemplary light-emitting structure 300A described in Figure 4A and the exemplary structure 400A described in that the exemplary structure 500 has an air gap 524 between a low-refractive-index first material layer 510 and a high-refractive-index second material layer 512 to introduce more total internal reflections into the exemplary structure 500 and maximize the Fresnel reflections generated from the lower surface of the high-refractive-index second material layer 512. Accordingly, the use of the air gap 524 can improve the overall efficiency, reduce the color shift, and increase the on-axis brightness. Specifically, a first emission peak 514 can be emitted in the on-axis direction through the interface 520 and the glass cover 522 from the sub-pixel stack 504 in the central region of the exemplary structure 500. A second emission peak 518 can be emitted from the sub-pixel stack 504 in an off-axis direction and be reflected at least once by the interface 520 through total internal reflection before reaching the inclined sidewall 507 of the embankment 506, and be emitted as an on-axis emission 516 in the on-axis direction through the interface 520 at the peripheral portion of the first material layer 510 adjacent to the inclined sidewall 507. These total internal reflections will improve the efficiency, increase the on-axis brightness, and reduce the off-axis color shift at different angles.

[0120] In one or more embodiments, the second material layer 512 with a higher refractive index may cover the entire air gap 524, and the air gap 524 may cover the entire top surface (e.g., a plane parallel to the X-Y plane) of the first material layer 510 with a lower refractive index, except for the peripheral portion of the first material layer 510 adjacent to the embankment 506.

[0121] In another embodiment, the second material layer 512 may only cover the surface area substantially above the central portion of the first material layer 510. The physical arrangement of the second material layer 512 relative to the first material layer 510 is not limited to the exemplary arrangement. The second material layer 512 may partially cover the first material layer 510 in another way not described.

[0122] As can be seen from the present disclosure, various techniques can be used to implement the concepts described in the present disclosure without departing from the scope of those concepts. Although the concepts have been specifically described with reference to certain embodiments, those skilled in the art will recognize that changes in form and detail can be made without departing from the scope of those concepts. Accordingly, the described embodiments are to be considered in all respects illustrative rather than restrictive. It should also be understood that, while the present disclosure is not limited to the specific embodiments described above, many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure.

Claims

1. A light-emitting structure, which comprises: a substrate; a sub-pixel stack located above the surface of the substrate, the sub-pixel stack comprising: an emission layer located between a first transport layer and a second transport layer; a first electrode layer coupled to the first transport layer; and a second electrode layer coupled to the second transport layer; a dam that surrounds the sub-pixel stack and forms an internal space above the sub-pixel stack; a first material that fills the internal space and has a first refractive index; and a second material located above the first material and having a second refractive index substantially higher than the first refractive index, wherein the second electrode layer has a third refractive index that substantially matches the first refractive index, the top surface of the first material is coplanar with the top surface of the dam, and the second material covers the top surface of the first material in the internal space and the top surface of the dam surrounding the sub-pixel stack.

2. The light-emitting structure according to claim 1, wherein, the second electrode layer comprises at least one of indium tin oxide (ITO) nanoparticles and silver nanowires.

3. The light-emitting structure according to claim 1, wherein, the second material comprises a high-refractive-index transparent material, and the high-refractive-index transparent material comprises at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

4. The light-emitting structure according to claim 1, wherein, the sub-pixel stack emits a first emission peak towards the first material along an in-axis direction substantially perpendicular to the top surface of the sub-pixel stack; the sub-pixel stack emits a second emission peak towards the first material along an off-axis direction at an angle to the in-axis direction; and the second emission peak along the off-axis direction is reflected by the interface between the first material and the second material and is guided to the inclined sidewall of the dam.

5. The light-emitting structure according to claim 4, wherein, the second emission peak is reflected by the inclined sidewall of the dam and is emitted through the interface along the in-axis direction substantially without total internal reflection.

6. The light-emitting structure according to claim 4, wherein, the angle between the inclined sidewall of the dam and the top surface of the sub-pixel stack is half of the angle between the in-axis direction of the first emission peak and the off-axis direction of the second emission peak.

7. The light-emitting structure according to claim 1, wherein, the second material covers the entire top surface of the first material.

8. The light-emitting structure according to claim 1, wherein, further comprises: an air gap located between the first material and the second material, and the second material covers the entire air gap and is disposed on the top surface of the dam.

9. The light-emitting structure according to claim 1, wherein, the emission layer comprises a quantum dot emission material, the first transport layer comprises a hole transport layer, the second transport layer comprises an electron transport layer, the first electrode layer is an anode layer, the anode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is a cathode layer made of a non-metallic and substantially transparent material.

10. The light-emitting structure according to claim 1, characterized in that, the emission layer includes a quantum dot emission material, the first transport layer includes an electron transport layer, the second transport layer includes a hole transport layer, the first electrode layer is a cathode layer, the cathode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is an anode layer made of a non-metallic and substantially transparent material.

11. A light-emitting structure, which comprises: a substrate; a plurality of sub-pixel stacks emitting different colors above the surface of the substrate, at least one of the plurality of sub-pixel stacks comprising: an emission layer located between a first transport layer and a second transport layer; a first electrode layer coupled to the first transport layer; and a second electrode layer coupled to the second transport layer; a dam that surrounds each of the plurality of sub-pixel stacks and forms an internal space above each sub-pixel stack of the plurality of sub-pixel stacks; a first material that fills the internal space and has a first refractive index; and a second material located above the first material and having a second refractive index substantially higher than the first refractive index, wherein the second electrode layer has a third refractive index substantially matching the first refractive index, the top surface of the first material is coplanar with the top surface of the dam, and the second material covers the top surface of the first material in the internal space and the top surface of the dam surrounding each of the plurality of sub-pixel stacks.

12. The light-emitting structure according to claim 11, characterized in that, the second electrode layer includes at least one of indium tin oxide (ITO) nanoparticles and silver nanowires.

13. The light-emitting structure according to claim 11, characterized in that, the second material includes a high refractive index transparent material, and the high refractive index transparent material includes at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

14. The light-emitting structure according to claim 11, characterized in that, at least two sub-pixel stacks among the plurality of sub-pixel stacks have different distances between the emission layer and the first electrode layer to maintain a substantially same angular distribution in the first material for emissions of different wavelengths.

15. The light-emitting structure according to claim 11, characterized in that, the sub-pixel stack emits a first emission peak to the first material along an in-axis direction substantially perpendicular to the top surface of the sub-pixel stack; the sub-pixel stack emits a second emission peak to the first material along an off-axis direction at an angle to the in-axis direction; and the second emission peak along the off-axis direction is reflected by the interface between the first material and the second material and is guided to the inclined sidewall of the dam.

16. The light-emitting structure according to claim 15, characterized in that, the second emission peak is reflected by the inclined sidewall of the dam and is emitted through the interface along the in-axis direction substantially without total internal reflection; and The angle between the inclined sidewall of the dike and the top surface of the sub-pixel stack is half of the angle between the on-axis direction of the first emission peak and the off-axis direction of the second emission peak.

17. The light-emitting structure according to claim 11, wherein, further comprising: an air gap located between the first material and the second material, the second material covering the entire air gap and disposed on the top surface of the dike.

18. The light-emitting structure according to claim 11, wherein, the emission layer comprises a quantum dot emission material, the first transport layer comprises a hole transport layer, the second transport layer comprises an electron transport layer, the first electrode layer is an anode layer, the anode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is a cathode layer having a non-metallic and substantially transparent material.

19. The light-emitting structure according to claim 11, wherein, the emission layer comprises a quantum dot emission material, the first transport layer comprises an electron transport layer, the second transport layer comprises a hole transport layer, the first electrode layer is a cathode layer, the cathode layer has a metal reflector for reflecting light emitted from the emission layer, and the second electrode layer is an anode layer having a non-metallic and substantially transparent material.

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