Patent Application
20230037057
The present disclosure generally relates to quantum-dot light-emitting diodes (QLEDs), and in particular relates to patterning of one or more layers of a QLED (e.g., such that the QLED provides improved electrical characteristics).
QLEDs represent an emerging emissive display technology with the potential to outperform organic light-emitting diodes (OLEDs) while being less expensive to fabricate due to the ability to solution-process the different layers of the QLED. QLED structures may be carefully designed to optimize light extraction to render the QLEDs as efficient as possible. The most efficient designs are typically top-emitting QLEDs having transparent top electrodes. No “perfect” solution for a transparent top electrode currently exists, but several attempts at such a solution have been made using graphene, conductive nanowires, and conductive nanoparticles. However, many of these approaches are associated with one or more poor performance characteristics, including, but not limited to, reduced transparency and low refractive index. Further, at least some of these solutions provide reduced protection for, or result in increased damage to, lower QLED layers during the manufacturing process.
For example, typical top-emitting QLED devices may employ a transparent electrode fabricated from indium tin oxide (ITO). ITO is also typically used as a transparent electrode in liquid-crystal display (LCD) and bottom-emitting OLED technology. However, deposition of ITO usually involves high-energy processing that may be destructive to the underlying QLED layers. ITO may be sputtered atop an electron transport layer (ETL) of a QLED under particular conditions. However, without a high-temperature bake operation, which is not possible with QLED structures, the sputtered ITO layer may possess undesirably low transparency.
The present disclosure is directed to QLEDs in which one or more layers thereof are patterned (e.g., to provide improved electrical characteristics).
In accordance with one aspect of the present disclosure, a top-emitting pixel device may include a reflective bottom electrode disposed over a substrate, a first charge transport layer disposed over the reflective bottom electrode, an emissive layer disposed over the first charge transport layer, and a second charge transport layer disposed over the emissive layer. Further, the pixel device may include a patterned transparent polymer electrode disposed over the second charge transport layer and extending laterally to cover an emissive area of the top-emitting pixel device, and a patterned auxiliary electrode disposed at least partially over the patterned transparent polymer electrode outside of the emissive area of the top-emitting pixel device to make direct electrical contact with the patterned transparent polymer electrode.
In an implementation of the first aspect, the patterned transparent polymer electrode may include a conductive polymer that is crosslinked by an ultraviolet-activated (UV-activated) crosslinking agent.
In another implementation of the first aspect, the patterned transparent polymer electrode may include a conductive polymer within a crosslinked matrix. In an example, the crosslinked matrix may be formed using a crosslinking agent, a photoinitiator, and a monomer. In another example, the crosslinked matrix may be formed using a UV-activated crosslinking agent and a monomer. In another example, the crosslinked matrix may be formed using a UV-activated crosslinking agent.
In another implementation of the first aspect, the top-emitting pixel device may further include a pixel-defining structure at least partially surrounding the emissive layer, the patterned transparent polymer electrode may extend partially over the pixel-defining structure, and the patterned auxiliary electrode may extend over a portion of the patterned transparent polymer electrode and the pixel-defining structure. In an example, the pixel-defining structure may include a bank structure separating at least the emissive layer of the top-emitting pixel device from an emissive layer of a second pixel device.
In another implementation of the first aspect, the reflective bottom electrode may include an anode, the first charge transport layer may include a hole transport layer, the second charge transport layer may include an electron transport layer, and a combination of the patterned transparent polymer electrode and the patterned auxiliary electrode may include a cathode. In an example, the patterned transparent polymer electrode of the cathode may have an energy level in a range of −3.8 electron-volts (eV) to −4.7 eV.
In another implementation of the first aspect, the reflective bottom electrode may include a cathode, the first charge transport layer may include an electron transport layer, the second charge transport layer may include a hole transport layer, and a combination of the patterned transparent polymer electrode and the patterned auxiliary electrode may include an anode. In an example, the patterned transparent polymer electrode of the anode may have an energy level in a range of −4.7 eV to −5.6 eV.
In accordance with a second aspect of the present disclosure, a display device may include a substrate, a pixel-defining structure defining a plurality of pixel regions over the substrate, and an array of top-emitting pixel devices positioned over the substrate. Each of the top-emitting pixel devices may be located within a corresponding one of the plurality of pixel regions. Also, each of the top-emitting pixel devices may include a reflective bottom electrode disposed over the substrate, a first charge transport layer disposed over the reflective bottom electrode, an emissive layer disposed over the first charge transport layer, and a second charge transport layer disposed over the emissive layer. Each of the top-emitting pixel devices may further include a patterned transparent polymer electrode disposed over the second charge transport layer and extending laterally to cover an emissive area of the top-emitting pixel device, and a patterned auxiliary electrode disposed at least partially over the patterned transparent polymer electrode outside of the emissive area of the top-emitting pixel device to make direct electrical contact with the patterned transparent polymer electrode. The patterned transparent polymer electrodes and the patterned auxiliary electrodes of the display device may form a plurality of electrically separated conductive regions, where each of the electrically separated conductive regions forms an electrode for at least one of the top-emitting pixel devices.
In an implementation of the second aspect, at least one of the electrically separated conductive regions may form an electrode for more than one of the top-emitting pixel devices.
In another implementation of the second aspect, at least two of the electrically separated conductive regions may operate as in-cell touch panel electrodes.
In another implementation of the second aspect, the in-cell touch panel electrodes may include a first portion of the electrically separated conductive regions operating as in-cell touch panel signal electrodes, and a second portion of the electrically separated conductive regions operating as in-cell touch panel sensing electrodes.
In accordance with a third aspect of the present disclosure, a top-emitting pixel device may include a reflective bottom anode disposed over a substrate, a hole injection layer disposed over the reflective bottom anode, a hole transport layer disposed over the hole injection layer, an emissive layer disposed over the hole transport layer, an electron transport layer disposed over the emissive layer and a pixel-defining structure at least partially surrounding the top-emitting pixel device, and a transparent cathode disposed over the electron transport layer. The hole injection layer may include a patterned transparent conductive polymer that is electrically separated from the electron transport layer.
In an implementation of the third aspect, the patterned transparent conductive polymer may be crosslinked via an ultraviolet-activated crosslinking agent.
In another implementation of the third aspect, the hole injection layer, the hole transport layer, and the emissive layer may be patterned to prevent covering the pixel-defining structure.
Aspects of the example disclosure are best understood from the following detailed description when read with the accompanying figures. Various features are not drawn to scale. Dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.
The following description contains specific information pertaining to exemplary implementations in the present disclosure. The drawings and their accompanying detailed description are directed to exemplary implementations. However, the present disclosure is not limited to these exemplary implementations. Other variations and implementations of the present disclosure will occur to those skilled in the art. Unless noted otherwise, like or corresponding elements in the figures may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations are generally not to scale and are not intended to correspond to actual relative dimensions.
For consistency and ease of understanding, like features are identified (although, in some examples, not shown) by numerals in the exemplary figures. However, the features in different implementations may be different in other respects, and therefore will not be narrowly confined to what is shown in the figures.
The phrases “in one implementation” and “in some implementations” may each refer to one or more of the same or different implementations. The term “coupled” is defined as connected, whether directly or indirectly via intervening components, and is not necessarily limited to physical connections. The term “comprising” means “including, but not necessarily limited to” and specifically indicates open-ended inclusion or membership in the described combination, group, series, and equivalent.
Additionally, any two or more of the following paragraphs, (sub-)bullets, points, actions, behaviors, terms, alternatives, examples, or claims described in the following disclosure may be combined logically, reasonably, and properly to form a specific method. Any sentence, paragraph, (sub-)bullet, point, action, behavior, term, or claim described in the following disclosure may be implemented independently and separately to form a specific method. Dependency, e.g., “according to”, “more specifically”, “preferably”, “in one embodiment”, “in one implementation”, “in one alternative”, etc., in the following disclosure refers to just one possible example which would not restrict the specific method.
For explanation and non-limitation, specific details, such as functional entities, techniques, protocols, and standards, are set forth for providing an understanding of the described technology. In other examples, detailed description of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the description with unnecessary details.
Also, while certain directional references (e.g., top, bottom, up, down, height, width, and so on) are employed in the description below and appended claims, such references are utilized to provide guidance regarding the positioning and dimensions of various elements relative to each other and are not intended to limit the orientation of the various embodiments to those explicitly discussed herein.
Various embodiments of QLED structures, as described in greater detail below, may include one or more patterned layers (e.g., a patterned transparent top electrode, a patterned auxiliary electrode, a patterned hole injection layer, etc.) to provide enhanced electrical properties, and thus increased display performance. Further, in some embodiments, use of these patterned layers may be extended to efficiently incorporate touch input functionality into the associated display.
In some embodiments, patterned transparent polymer electrode 107 may be deposited and patterned on top of second CTL 106. As illustrated in
More particularly, in some implementations of pixel structure 100, transparent polymer electrode 107 may be an ultraviolet-patterned (UV-patterned) conductive polymer, and auxiliary electrode 108 may be a UV-patterned metal. Patterned transparent polymer electrode 107 (e.g., crosslinked with a UV-activated crosslinking agent) may span to at least cover the emissive area of pixel structure 100, but may be patterned so that it is not continuous over bank 102 that surrounds and defines the emissive area. Auxiliary electrode 108 may be patterned such that auxiliary electrode 108 may only be present in the non-emissive region on bank 102. In some examples, auxiliary electrode 108 may extend over bank 102 to the edge of the emissive area or may be non-continuous over bank 102. In some implementations, at least one region may exist where patterned transparent polymer electrode 107 overlaps with auxiliary electrode 108, thus forming a direct electrical contact therebetween that allows electrical current to spread from auxiliary electrode 108 through polymer electrode 107 and across pixel structure 100.
The choice of which conductive polymer to employ for a given pixel structure may be affected by the energy level (or, alternatively, work function) of the particular material to be used. In many cases, the energy level may vary considerably with small changes to a conductive polymer, such as poly(3,4-ethylenedioxythiophene) (PEDOT) (e.g., PEDOT complexed with polystyrene sulfonate, or PEDOT:PSS). For example, different types of PEDOT dispersions may result in polymer films with different energy levels. Moreover, additives used in the dispersions, such as to help with solubility or conductivity, may have a large effect on the energy level. Therefore, a given conductive polymer may be more suitable for an inverted pixel structure 100 or a standard pixel structure 100.
Polymer dispersion 307 may include a conductive polymer (e.g., PEDOT) dissolved in a solvent. In some implementations, polymer dispersion may include PEDOT:PSS dissolved in water. In other implementations, PEDOT may be employed with other complexing agents aside from PSS to facilitate dispersion of the PEDOT in other solvents. Other combinations of a conductive polymer and a solvent are also possible. Based on how the conductive polymer is prepared and dispersed in polymer dispersion 307, the resulting transparent polymer electrode may possess any of a range of different conductivities and work functions, or energy levels. Further, in some implementations, the solvent within which the conductive polymer is dispersed may affect which materials may reside adjacent thereto within pixel structure 100.
In some implementations, a crosslinking agent may be mixed with polymer dispersion 307 prior to processing onto substrate 301. The crosslinking agent may include a UV-activated crosslinking agent that forms links directly between polymer chains of the conductive polymer. In some implementations, the UV-activated crosslinking agent may include UV-sensitive compounds that form highly reactive species that insert into carbon-hydrogen (C—H) bonds of the conductive polymer. Examples of such compounds may include the families of bis-azide or poly-azide molecules.
In other embodiments, the crosslinking agent may form a crosslinked matrix around individual components of the conductive polymer. In some implementations, the crosslinked matrix may be formed from one or more of a crosslinking agent, a monomer, a photoinitiator, or a UV-activated crosslinking agent. For example, the crosslinked matrix may be formed from a crosslinking agent, a monomer, and a photoinitiator. In yet another example, the crosslinked matrix may be formed from a UV-activated crosslinking agent and a monomer, or may be formed from a UV-activated crosslinker without a monomer.
At operation 352 of method 300, the solvent of polymer dispersion 307 may evaporate, leaving a dried, continuous polymer film 310 atop substrate 301. At operation 354, a photomask 311 may be configured and positioned over polymer film 310 such that selected areas of polymer film 310 may exposed to UV light 312 through photomask 311. In the regions exposed to UV light 312, the crosslinking agent may form bonds with the polymer chains of the conductive polymer, or may form a crosslinked matrix, such that the exposed regions of polymer film 310 may become a patterned crosslinked polymer film 313. Consequently, patterned crosslinked polymer film 313 may become less soluble than those regions of polymer film 310 that were not exposed to UV light 312. At operation 356, the structure may be washed with a compatible solvent 309, thus washing away the more soluble regions of polymer film 310. Consequently, at operation 358, removing solvent 309 may leave patterned crosslinked polymer film 313 atop substrate 301 to serve as patterned transparent polymer electrode 107 (as shown in
At operations 360 through 370, a metal wet-etch process may be employed to pattern an auxiliary electrode atop patterned crosslinked polymer film 313, which may be resilient to aqueous processing. Specifically, at operation 360, for example, metal 314 may be deposited (e.g., via thermal evaporation, sputtering, or the like) atop patterned crosslinked polymer film 313. Continuing with
In some QLED manufacturing processes, some conductive polymers are dispersed in solvents which are not compatible with underlying QLED structures, which are often fabricated using “orthogonal” solvent solution processing (e.g., each solvent used in one layer does not re-dissolve and/or re-disperse the layer below). For example, PEDOT:PSS dispersions are typically dispersed in water, and PEDOT dispersions are typically dispersed in other solvents such as methoxybenzene, both of which may cause defects in underlying layers when deposited on a QLED stack.
Thus, to enable flexibility with respect to which solvents may be used for depositing conductive polymers (e.g., PEDOT or PEDOT:PSS) on QLED structures, one or more, or potentially all, of the underlying layers (e.g., substrate 301, which may include one or more layers of pixel structure 100) located below the conductive polymer layer (e.g., patterned crosslinked polymer film 313 or patterned transparent polymer electrode 107) may be made more robust via crosslinking of some form. In some implementations, several crosslinking techniques may be used for those layers, such as forming a crosslinked matrix around an active layer, using bifunctional crosslinkers that crosslink to specific functional groups (e.g., amine groups or carbonyl groups) of an active layer, and nonselective (or photoreactive) crosslinkers that insert randomly into sites on organic chains of an active layer.
For example, the ETL (e.g., serving as first CTL 104 or second CTL 106), which may include magnesium zinc oxide (MgZnO), may be mixed with a polymer (e.g., polyvinylpyrrolidone (PVP)) to improve QLED performance. In some implementations, this polymer may be crosslinked with the addition of a crosslinking agent to form a polymer matrix around the ETL.
Regarding EML 105, by adding a crosslinker, the ligands of adjacent quantum dots may become linked together, making the resulting QD film insoluble. Alternatively, the QDs may be mixed with a crosslinkable HTL that may fix the QDs in place when crosslinked. Crosslinkable HTLs may include OTPD (e.g., N4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4′-diphenylbiphenyl-4,4′-diamine) and TFB (e.g., poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine).
Moreover, in addition to the layers discussed above, top-emitting QLED pixel structure 100 of
By crosslinking one or more layers of top-emitting QLED pixel structure 100 underlying patterned transparent polymer electrode 107, pixel structure 100 may be made more stable to processing in various solvents. In some implementations, the crosslinking process for each layer may be employed to pattern that layer in a similar way as described for patterned transparent polymer electrode 107, as described above. Alternatively, with the exception of EML 105 and patterned transparent polymer electrode 107, all remaining crosslinked layers may be common (e.g., continuous across pixels).
As is discussed in greater detail below, multiple patterned transparent polymer electrodes 107 and patterned auxiliary electrodes 108 of a QLED display may be configured in various ways, such as to support additional functionality integrated with the display. For example,
Partially covering patterned transparent polymer electrodes 402 are two auxiliary electrodes 403A and 403B that may be patterned such that they do not cover the emissive regions of subpixels 401A-401C. A first auxiliary electrode 403A may cover, and thus may be directly connected to, portions of each patterned transparent polymer electrode 402 corresponding to the top-left, top-right, and bottom-left pixels 405. A second auxiliary electrode 403B may cover and be directly connected to portions of patterned transparent polymer electrode 402 corresponding to the bottom-right pixel 405. Auxiliary electrodes 403A and 403B may be electrically isolated from each other, as shown by way of a boundary 404 in
In some implementations, patterning the top electrodes of a QLED display in such a manner, as depicted in
Depending on the design, the in-cell touch top electrode may be used to enable self-capacitance touch sensing, mutual capacitance touch sensing, haptic feedback touch, and/or force sensitive touch. The conductive regions may act as sensing electrodes, signal electrodes, and/or floating electrodes. In some implementations, conductive bridging structures may be included where two separate conductive regions cross. Also, in some examples, an additional electrode may be applied in a plane separate from a plane containing the in-cell top electrodes to enable additional non-display functionality.
While the above discussion focusses on the use of direct UV-patterning of conductive polymers, such as PEDOT, for a top electrode of a pixel structure, other layers of the pixel structure may benefit from such a technology. For example, a conventional top-emitting QLED device may include a semi-transparent thin metal top electrode. Large-area, solution-based deposition techniques such as spin coating, blade coating, slot-die coating, or spray coating are generally unable to pattern underlying QLED layers without additional, and sometimes complex, processing. Ink-jet printing may be used to pattern layers at low resolutions, but such patterning technology currently faces challenges at high resolution. In general, QLED layers are deposited across an entirety of the display such that each layer is continuous. The exception to this general rule is the emissive layer, which is patterned to form the individual subpixels of the QLED display.
In some conventional QLED displays, an HIL may not be patterned (e.g., due to typical patterning processes possibly inflicting damage on conventional HIL materials), and thus may lie continuously across both the bottom electrodes and banks of a display device. Oppositely, a combined HTL/EML of conventional displays may be patterned (e.g., using a patternable HTL matrix or a photolithography-based lift-off process) so that they are restricted primarily within the emissive area. Consequently, in regions (e.g., on the banks) where no combined EML layer in the structure is present, the ETL (lying atop the combined HTL/EML) and the HIL may make direct electrical contact. Accordingly, if the HIL possesses reasonable conductivity, then this contact may create a path for undesirable current leakage between the top and bottom electrodes of the conventional QLED. Consequently, by patterning HIL 604 in pixel structure 600, as illustrated in
In some implementations, to render HIL 604 of pixel structure 600 patternable, HIL 604 may include a UV-patterned conductive polymer, such as a PEDOT based-material mixed with a crosslinking agent. In some implementations, the PEDOT material may have a deep energy level. Examples of such a PEDOT material may include PH1000 or AI4083 (e.g., another member of the Clevios™ PEDOT:PSS product line by Heraeus of Hanau, Germany), either of which may be dispersed in water as a solution. Accordingly, a water-soluble crosslinking agent may be included in the dispersion to facilitate use of water as a solvent. An example of such a crosslinking agent is a bis-azide salt, such as disodium 4,4′-Diazidostilbene-2,2′-disulfonate. Constructing HIL 604 in such a manner may facilitate patterning of HIL 604, and well as render HIL 604 more resilient to harsh processing (e.g., EML patterning processes), thus minimizing damage to HIL 604 during manufacturing of the display.
Embodiments of the present disclosure are applicable to many display devices to permit display devices of high resolution with effective threshold voltage compensation and true black performance. Examples of such devices include televisions, mobile phones, personal digital assistants (PDAs), tablet and laptop computers, desktop monitors, digital cameras, and like devices for which a high-resolution display is desirable.
From the above discussion, it is evident that various techniques can be utilized for implementing the concepts of the present disclosure without departing from the scope of those concepts. Moreover, while the concepts have been described with specific reference to certain implementations, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the scope of those concepts. As such, the disclosure is to be considered in all respects as illustrative and not restrictive. It should also be understood that the present disclosure is not limited to the particular described implementations, but that many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure.
