Electroluminescent flat panel displays and methods for manufacture thereof

Abstract

An electroluminescent (EL) device used, for example, in a flat panel display (FPD) comprises a top electrode, a plurality of bottom electrodes connected to a substrate, and a plurality of layers of EL materials interposed between the top electrode and the bottom electrodes. In some examples, a first EL layer comprises a first EL material capable of emitting a first colour of light, and a second layer comprises a second EL material capable of emitting a second colour of light, where a selected region of the first layer is coated in a metal capable of reducing EL properties of the first EL material in the selected region. In some examples, the first EL material and / or the second EL material comprise one or more of colloidal quantum dots, perovskites, and organic pi-conjugated molecules.

Description

ELECTROLUMINESCENT FLAT PANEL DISPLAYS AND METHODS FOR MANUFACTURE THEREOFCROSS REFERENCE TO PRIOR APPLICATIONS

[0001] This application claims priority from US 63 / 731 ,902 filed June 20, 2024, which is incorporated herein by reference in its entirety.FIELD OF THE DESCRIPTION

[0002] The present invention pertains to the field of electroluminescent (EL) devices, and in particular to flat panel displays (FPDs) comprising EL devices.BACKGROUND

[0001] RGB patterning, the process by which red (R), green (G) and blue (B) light emitting devices (LEDs) are formed side by side on a substrate of a flat panel display (FPD) to form pixels or subpixels, is a key step in the manufacturing process of full colour FPDs.

[0002] There has been a recent emergence of organic and hybrid (organic-inorganic) electroluminescent (EL) materials, such as colloidal quantum dot and perovskite. As a result, organic light emitting devices (OLEDs) are now widely used in the FPDs of many commercial products, such as screens of mobile phones, TVs, and the like. Quantum dot light emitting devices (QLEDs), as well as perovskite light emitting devices (PvLEDs), are expected to follow suit in the near future.

[0003] Compared to LCDs or inorganic LEDs, these new generations of LEDs may provide several advantages, including better colour purity and easier processing. The easier processing arises from the amenability of these EL materials to a) processing at temperatures close to room temperatures, b) ease of fabrication in large areas without undermining EL properties, and c) the ability to use low cost wet-coating processes in forming the EL materials into thin films for making these LEDs (e.g. the OLEDs, QLEDs, PvLEDs).SUMMARY OF THE DESCRIPTION

[0003] According to a broad aspect, there is provided a method for manufacturing an electroluminescent (EL) flat panel display (FPD) comprising a substrate and a plurality of electrodes connected thereto. The method comprises depositing, onto the substrate and theplurality of electrodes, a first layer comprising a first EL material capable of emitting a first colour of light. The method further comprises depositing, onto a selected region of the first layer, a first metal capable of reducing EL properties of the first EL material in the selected region of the first layer. The further comprises depositing, onto the first layer, a second layer comprising a second EL material capable of emitting a second colour of light.

[0004] According to some examples, the method comprises depositing, onto a selected region of the second layer, a second metal capable of reducing EL properties of the second EL material in the selected region of the second layer.

[0005] According to some examples, the method comprises depositing, onto the second layer, a third layer comprising a third EL material capable of emitting a third colour of light.

[0006] According to some examples, the method comprises depositing, onto a selected region of the third layer, a third metal capable of reducing EL properties of the third EL material in the selected region of the third layer.

[0007] According to some examples, the method comprises depositing, onto at least a portion of the selected region of the second layer, a charge injection material capable of facilitating injection of electrons or holes.

[0008] According to some examples, the method comprises, prior to depositing the second layer onto the first layer, depositing, onto at least a portion of the selected region of the first layer, a charge injection material capable of facilitating injection of electrons or holes.

[0009] According to some examples, the first layer and the second layer are deposited using wet-coating processes.

[0010] According to some examples, the selected region of the first layer is defined by a first shadow mask, and the method comprises depositing the first metal through the first shadow mask.

[0011] According to some examples, the third layer is deposited using a vacuum deposition process.

[0012] According to some examples, the first EL material and / or the second EL material comprise one or more of colloidal quantum dots, perovskites, and organic pi-conjugated molecules.

[0013] According to another broad aspect, there is provided an EL device comprising a top electrode, a plurality of bottom electrodes connected to a substrate, and, interposed between the top electrode and the plurality of bottom electrodes, a first layer comprising a first EL material capable of emitting a first colour of light, and a second layer comprising a second EL material capable of emitting a second colour of light, where a selected region of the first layer is coated in a metal capable of reducing EL properties of the first EL material in the selected region.

[0014] According to some examples, the metal causes a photoluminescence quantum yield (PLQY) of the EL materials in the selected region of the first layer to decrease by at least 50%.

[0015] According to some examples, the first EL material or the second EL material or both comprise one or more of colloidal quantum dots, perovskites, and organic pi-conjugated molecules

[0016] According to some examples, the first EL material differs from the second EL material.

[0017] According to some examples, the EL device comprises a third layer interposed between the top electrode and the plurality of bottom electrodes, the third layer comprising a third EL material capable of emitting a third colour of light.

[0018] According to some examples, each of the first colour, the second colour, and the third colour is uniquely selected from the group consisting of blue light with luminescence peak in a range of 400-500 nm, green light with a luminescence peak in a range of 500- 600 nm, and red light with a luminescence peak in a range of 600-700 nm.

[0019] According to some examples, the first EL material comprises organic pi- conjugated materials capable of emitting the blue light, wherein the second EL material comprises colloidal quantum dot materials capable of emitting green light, and wherein the third EL material comprises colloidal quantum dot materials capable of emitting red light

[0020] According to some examples, the metal comprises silver, gold, platinum, or aluminum, or compounds thereof.

[0021] According to some examples, the metal is coated with a layer comprising a charge injection material capable of facilitating injection of electrons or holes.

[0022] According to some examples, the charge injection material comprises magnesium.BRIEF DESCRIPTION OF THE FIGURES

[0023] The features of certain examples will become more apparent in the following detailed description in which reference is made to the appended figures wherein:

[0024] FIGs. 1-9 are schematic illustrations of a first example process for manufacturing an electroluminescent (EL) flat panel display (FPD), each illustration showing a cross- sectional view of a single EL device in the EL FPD at a different stage in the first example process.

[0025] FIG. 10 is a cross-sectional view of an EL device manufactured according to the first example process.

[0026] FIGs. 11-18 are schematic illustrations of a second example process for manufacturing an EL FPD, each illustration showing a cross-sectional view of a single EL device in the EL FPD at a different stage in the second example process.

[0027] FIG. 19 is a cross-sectional view of an EL device manufactured according to the second example process.

[0028] FIG. 20 illustrates an example method for manufacturing an EL FPD.DETAILED DESCRIPTION

[0029] The following description provides examples of the present subject matter. Although the examples illustrated herein may be described with reference to one or more specific features, it will be understood that, unless otherwise specified, all features described herein may be used interchangeably or in any combination with one or more other examples. Thus, any description of features relating one example is not intended to limit the incorporation of such features to only that example.

[0030] Flat panel displays (FPDs) may be manufactured by coating multiple layers of electroluminescent (EL) materials onto a substrate. Substantial reductions in manufacturing costs and product costs may be achieved through the use of wet-coating processes in forming organic and hybrid EL materials into the thin films used for fabricating light emitting devices (LEDs), referred to herein as EL devices. Examples of wet-coating processes include blade coating, web-coating, spin-coating, inkjet printing, and the like. However, these processes, in general, may only provide films that cover the entire substrate on which they are coated, or at least large regions of that substrate. Only a small subset of these processes, such as inkjet printing [1 ,2], may allow covering small enough regions to enable fabrication of multiple devices that comprise different materials or compositions side-by-side on the same substrate.

[0031] The feature size (e.g., line width or areal dimensions) of red (R), green (G), and blue (B) EL devices may limit the resolution achievable on a FPD comprising the EL devices. For example, in order to achieve a resolution of greater than 100 pixels per inch (ppi), it may be necessary to fabricate EL devices having a minimum feature size below 100 pm. Even with the use of inkjet printing, it may be difficult to fabricate EL devices of this size.

[0032] Challenges in fabricating small EL devices may arise from limitations in RGB patterning accuracy, resolution, and uniformity [3-9] that are inherent in wet-coating processes. These limitations may not only prevent the use of low-cost fabrication processes in making high-resolution FPDs (also known as high definition or HD FPDs), but may also hamper the use of novel materials that can only be processed through wet-coating processes, such as colloidal quantum dot. This may limit the commercial adoption of quantum dot light emitting devices (QLEDs) in FPDs.

[0033] Alternative approaches, including contact / transfer printing [10,11] and photolithography

[0012] , have therefore been pursued. These approaches, however, may add significant complexities that may inherently limit production yields and / or limit the minimum feature size to well above 10 pm, making them non-viable options for fabricating high- resolution FPDs, where a pixel density of greater than 500 ppi may be required.

[0034] It is of interest to provide a method for manufacturing EL FPDs that uses wetcoating processes in fabricating R, G, and B EL devices side-by-side on the same substrate, where the EL devices comprise organic, colloidal quantum dot and / or perovskite EL materials. It is also of interest to form the EL devices in sizes small enough to meet thedemands of high-resolution FPDs. For example, it is of interest to fabricate EL devices that have a minimum feature size of less than 100 pm, and more particularly less than 10 pm. EL devices having these feature sizes may achieve resolutions, for example, of greater than 500 ppi.

[0035] It will be understood that the features, elements, structures, or characteristics of a given example of the description are not necessarily limited to such example. In other words, any of the features described herein with respect to one example may be used with, incorporated into, or combined with any of the described examples as would be understood by persons skilled in the art.

[0036] The terms “comprise”, “comprises”, “comprised” or “comprising” may be used in the present description. As used herein (including the specification and / or the claims), and unless stated otherwise, these terms are to be interpreted as open-ended terms and as specifying the presence of the stated features, integers, steps or components, but not as precluding the presence of one or more other feature, integer, step, component or a group thereof as would be apparent to persons having ordinary skill in the relevant art. Thus, the term "comprising" as used in this specification means "consisting at least in part of’. When interpreting statements in this specification that include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0037] For the purposes of the present description and / or claims, and unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present invention, inclusive of the stated value and has the meaning including the degree of error associated with measurement of the particular quantity. The term “about” generally refers to a range of numbers that one of ordinary skill in the art would consider as a reasonable amount of deviation to the recited numeric values (i.e., having the equivalent function or result). For example, this term “about” can be construed as including a deviation of ±10 percent of the given numeric valueprovided such a deviation does not alter the end function or result of the value. Therefore, a value of about 1% can be construed to be a range from 0.9% to 1.1%.

[0038] The term "and / or" can mean "and" or "or".

[0039] Unless stated otherwise herein, the articles “a” and “the”, when used to identify an element, are not intended to constitute a limitation of just one and will, instead, be understood to mean “at least one” or “one or more”.

[0040] In accordance with examples of the technology, an EL FPD comprises a plurality of EL devices positioned side by side on a substrate, where each EL device is capable of emitting light characterized by some combination of different colours. For example, the colours may be selected from red (R), green (G), and blue (B), where red light has a luminescence peak in a range of 600-700 nm, where green EL has a luminescence peak in a range of 500-600 nm, and where blue EL has a luminescence peak in a range of 400- 500 nm. A given one of the plurality of EL devices may comprise a stack of layers of EL materials (herein referred to as “EL layers”) interposed between a set of electrodes, where the stack covers at least a portion of the substrate. The set of electrodes may comprise, for example, a plurality of bottom electrodes connected to the substrate and a top electrode connected to charge transport layers of the EL FPD, where the stack is interposed between the top electrode and the plurality of bottom electrodes. The substrate may comprise any suitable materials, for example, silicon or glass polymers, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). In some examples, the substrate may include electronic devices or components such as thin-film transistors (TFTs). For example, the substrate may include TFT circuits to individually switch on and off a voltage applied to each of the bottom electrodes.

[0041] In some examples, the stack of EL layers may comprise a first layer comprising a first EL material capable of emitting a first colour of light, and a second layer comprising a second EL material capable of emitting a second colour of light. In some examples, the stack may further comprise a third layer comprising a third EL material capable of emitting a third colour of light. In some examples, each layer has a thickness of less than 100 nm. For example, each layer may have a thickness of less than 50 nm. The EL materials may comprise, for example, any materials capable of electroluminescence under bias (e.g., voltage). They may, for example, comprise electroluminescent quantum dot (e.g. colloidalquantum dot) materials, perovskite materials, organic materials, and metal-organic materials, and the like.

[0042] In some examples, the EL layers may be coated by any thin film coating process, including wet-coating techniques (such as blade-coating, web-coating, dipping, spin-coating, inkjet printing, spray-coating, etc.) and dry-coating processes (such as vacuum deposition). In particular, since the stack of EL layers may cover the entire substrate (or optionally a certain region of it), thin film coating processes that produce continuous layers with no specific lateral selectivity or resolution constraints may be used in creating the EL layers comprised in the stacks. For example, wet-coating, blade-coating, spin-coating and spray coating may be used in fabricating the EL layers.

[0043] In some examples, a metal capable of quenching the electroluminescence (referred to here as a “quenching metal”) may be deposited or coated on selected area(s) or region(s) of one or more of the EL layers following the coating of that respective layer. The quenching metal may act to substantially quench (or degrade or reduce) the EL properties of the respective EL layer in the selected area(s) to which it is applied, while leaving the EL properties in other non-selected areas unchanged. The quenching metal may comprise, for example, any metal that is capable of reducing a photoluminescence quantum yield (PLQY) of the EL layer by at least 50% in the area(s) or region(s) where the quenching metal is deposited. In some examples, the quenching metal is capable of reducing the PLQY by at least 75% in those regions where the quenching metal is deposited. Examples of quenching metals include Ag, Au and Al. Certain metals from the group of metals with work function exceeding 3.8 eV, such as Pt and Cu, may also be used as quenching metals. Other metals may also be used. In some examples, the quenching metal may be any metal-containing compound. For example, the quenching metal may be an electrically-conductive metalcontaining compound, such as a conductive metal oxide (e.g. Ag2O).

[0044] The quenching metal may be deposited, for example, by any process that allows the metal to be deposited or retained only on desired area(s) or region(s) of the preceding EL layer. For example, the quenching metal may be deposited by thermal evaporation or other physical vapor deposition (PVD) processes through a shadow mask. Alternatively, the quenching metal may be coated using wet-coating processes that allow deposition in only certain areas such as ink-jet printing. Photolithographic processes, and especially lift-off photolithographic processes, may also be used in the deposition and fabrication of thequenching metal. The metal may also be deposited on a precoated layer that comprises regions comprising nucleation-inhibiting materials and other regions comprising nucleationpromoting materials. Examples of these two types of materials and their use in the selective deposition of metals on certain regions of a layer may, for example, be found in US Patent Application Publication Nos. 2018 / 0226581 and 2023 / 0165124.

[0045] When the set of electrodes are used to apply an external bias or voltage across the stack of EL layers, the quenching metal may change a peak wavelength (or colour) that is produced by the stack in the areas where the quenching metal has been deposited.

[0046] In some examples, a charge injection material may be deposited on at least part of one or more of the EL layers. The charge injection material may comprise either a metal or a metal compound. In one example, the charge injection material is magnesium (Mg). For cases when the bottom electrodes are biased at a more negative potential relative to the top electrode, the charge injection material may facilitate the injection of electrons. For cases when the bottom electrodes are biased at a more positive potential relative to the top electrode, the charge injection material may facilitate the injection of holes. The charge injection material may be deposited, for example, using the shadow mask.

[0047] FIGs. 1-9 illustrate a first example process for manufacturing an EL FPD, where each one of FIGs. 1-9 depicts a cross-sectional view of a single EL device of the EL FPD (i.e., a single pixel) at a different stage of the first example process.

[0048] FIG. 1 illustrates a first EL layer 104 being formed on a set of bottom electrodes 102, in this case, three bottom electrodes 102-1 , 102-2, and 102-3. The bottom electrodes 102 are, in turn, affixed or connected to a substrate 100. The first EL layer 104 may be formed, for example, by a wet-coating process, and may be designed to emit a blue (B) colour.

[0049] FIG. 2 illustrates a quenching metal 106 being deposited on a selected region105 of the first EL layer 104. The region 105 may be defined, for example, by depositing the quenching metal 106 through a shadow mask 108. The deposition of the quenching metal106 may cause a PLQY of the EL material to be reduced in a first portion 104-1 of the first EL layer 104, while leaving a second portion 104-2 of the first EL layer 104 unaffected (i.e., no reduction in PLQY). In this example, the shadow mask 108 is designed such that the firstportion 104-1 is opposite the bottom electrodes 102-1 and 102-2, while the second portion 104-2 is opposite the bottom electrode 102-3.

[0050] FIG. 3 illustrates a charge injection material 110 being deposited on the region 105 of the first EL layer 104, in accordance with some examples. The charge injection material 110 may be deposited, for example, using the shadow mask 108.

[0051] FIG. 4 illustrates a second EL layer 112 being formed on the first EL layer 104 (which includes the portions 104-1 and 104-2, where the portion 104-1 optionally includes a layer of the charge injection material 110). The second EL layer 112 may be formed, for example, by a wet-coating process, and may be designed to emit a green (G) colour.

[0052] FIG. 5 illustrates a quenching metal 114 being deposited on a selected region 113 of the second EL layer 112. The region 113 may be defined, for example, by depositing the quenching metal 114 through a shadow mask 116. The deposition of the quenching metal 114 may cause a PLQY of the second EL material to be reduced in a portion 112-2 of the second EL layer 112, while leaving another portion 112-1 of the second EL layer 112 unaffected (i.e., no reduction in PLQY). In this example, the shadow mask 116 is designed such that the portion 112-1 is opposite the bottom electrode 102-1 , while the portion 112-2 is opposite the bottom electrodes 102-2 and 102-3.

[0053] FIG. 6 illustrates a charge injection material 118 being deposited on a selected region 115 of the second EL layer 112, in accordance with some examples. The region 115 may be defined, for example, by depositing the charge injection material 118 through a shadow mask 120. The shadow mask 120 may be designed such that the charge injection material 118 is deposited only on the part of the portion 112-2 that is opposite the bottom electrode 102-2.

[0054] FIG. 7 illustrates a third EL layer 122 being deposited on the second EL layer 112 (which includes the portions 112-1 and 112-2, where the portion 112-2 optionally includes a layer of the charge injection material 118). The third EL layer 122 may be formed, for example, by a wet-coating process, and may be designed to emit a red (R) colour.

[0055] FIG. 8 illustrates a quenching metal 124 being deposited on a selected region 123 of the third EL layer 122, where the region 123 comprises two non-contiguous subregions 123-1 and 123-2. The region 123 may be defined, for example, by depositing the quenching metal 124 through a shadow mask 126. The deposition of the quenching metal124 may cause a PLQY of the third EL material to be reduced in portions 122-1 and 122-2 of the third EL layer 122 (corresponding to the respective subregions 123-1 and 123-2), while leaving another portion 122-3 of the third EL layer 122 unaffected (i.e., no reduction in PLQY). As shown in FIG. 8, the shadow mask 126 may be designed such that the portion 122-1 of the third EL layer 122 is opposite from the portion 112-1 of the second EL layer 112, and the portion 122-2 of the third EL layer 122 is opposite from the portion 104-2 of the first EL layer 102.

[0056] FIG. 9 illustrates the deposition of charge transport layers and top electrode (together denoted by 128) on the third EL layer 122 (including the portions 122-1 , 122-2, and 122-3). The charge transport layers and top electrode 128 may be deposited in a selected region 127 defined by a shadow mask 130. The shadow mask 130 may be designed such that the region 127 is opposite all three bottom electrodes 102-1 , 102-2, and 102-3. The charge transport layers and top electrode 128 may be deposited, for example, via a wetcoating process and / or a vacuum deposition process.

[0057] FIG. 10 illustrates a cross-sectional view of an EL device 140 manufactured according to the first example process illustrated in FIGs. 1-9. A voltage from a voltage source 132 may be applied across the top electrode 128 and each of the bottom electrodes 102-1 , 102-2, and 102-3, thereby resulting in the emission of G, R, and B electroluminescence 134 from the different areas or regions of the stack of EL layers 104, 112, and 122, as illustrated in FIG. 10.

[0058] The deposition of quenching metals, such as the quenching metals 106, 114, and 124, enables the PLQY from any regions of the EL layers to be quenched, as desired. Consequently, a wide range of coating processes, including wet-coating and vacuum deposition processes, may be used for forming the EL layers without constraints imposed by meeting certain lateral resolution requirements. More specifically, the ability to use wetcoating processes in forming the EL layers makes the manufacturing process highly suitable for EL materials that are normally prepared suspended or dissolved in solvents, such as colloidal quantum dot EL materials.

[0059] It is contemplated that different types of EL materials may be used in the different layers of the same stack. For example, some layers may comprise quantum dot EL materials, whereas other layers may comprise perovskite, organic EL materials and / or polymeric EL materials in any desired combination. Similarly, different coating processesmay be used in coating the different EL layers in a stack. For example, the first EL layer and second EL layer may be formed using wet-coating processes, whereas the third (or additional) EL layer may be formed by vacuum deposition. In this case, for example, the first and second EL layers may comprise quantum dot EL materials whereas the additional EL layer may comprise organic EL material or perovskite EL material. FIGs. 11-19 depict an example of this.

[0060] FIGs. 11-18 illustrate a second example process for manufacturing an EL device, where each one of FIGs. 11-18 depicts a cross-sectional view of the EL device at a different stage of the second example process.

[0061] FIG. 11 illustrates a first EL layer 204 being formed on a set of bottom electrodes 202, in this case, three bottom electrodes 202-1 , 202-2, and 202-3. The bottom electrodes 202 are in turn affixed or connected to a substrate 200. The first EL layer 204 may be formed, for example, by a wet-coating process, and may be designed to emit a green (G) colour.

[0062] FIG. 12 illustrates a quenching metal 206 being deposited on a selected region 205 of the first EL layer 204. The region 205 may be defined, for example, by depositing the quenching metal 206 through a shadow mask 208. The deposition of the quenching metal 106 may cause a PLQY of the EL material to be reduced in a portion 204-1 of the first EL layer 204, while leaving another portion 204-2 of the first EL layer 204 unaffected (i.e., no reduction in PLQY). In this example, the shadow mask 208 is designed such that the portion 204-1 is opposite the bottom electrodes 202-1 and 202-2, while the portion 204-2 is opposite the bottom electrode 202-3.

[0063] FIG. 13 illustrates a charge injection material 210 being deposited on the region 205 of the first EL layer 204, in accordance with some examples. The charge injection material 210 may be deposited, for example, using the shadow mask 208.

[0064] FIG. 14 illustrates a second EL layer 212 being formed on the first EL layer 204 (which includes the portions 204-1 and 204-2, where the portion 204-1 optionally includes a layer of the charge injection material 210). The second EL layer 212 may be formed, for example, by a wet-coating process, and may be designed to emit a red (R) colour.

[0065] FIG. 15 illustrates a quenching metal 214 being deposited on a selected region 213 of the second EL layer 212. The region 213 may be defined, for example, by depositingthe quenching metal 214 through a shadow mask 216. The deposition of the quenching metal 214 may cause a PLQY of the second EL material to be reduced in a portion 212-2 of the second EL layer 212, while leaving another portion 212-1 of the second EL layer 212 unaffected (i.e., no reduction in PLQY). In this example, the shadow mask 216 is designed such that the portion 212-1 is opposite the bottom electrode 202-1 , while the portion 212-2 is opposite the bottom electrodes 202-2 and 202-3.

[0066] FIG. 16 illustrates a charge injection material 218 being deposited on a selected region 215 of the second EL layer 212, in accordance with some examples. The region 215 may be defined, for example, by depositing the charge injection material 218 through a shadow mask 220. The shadow mask 220 may be designed such that the charge injection material 218 is deposited only on the part of the portion 212-2 that is opposite the bottom electrode 202-2.

[0067] FIG. 17 illustrates a third EL layer 222 being deposited on the second EL layer 212 (which includes the portions 212-1 and 212-2, wherein the portion 212-2 optionally includes a layer of the charge injection material 218). The third EL layer 222 may be formed, for example, by a vacuum deposition process through a shadow mask 224 that allows deposition within a selected region 226. In this example, the third EL layer 222 is located opposite the bottom electrode 202-2, while leaving portions of the second EL layer 212 uncoated or exposed, namely those portions of the second EL layer 212 that are opposite the bottom electrodes 202-1 and 202-3. According to some examples, the shadow mask 224 may be identical to the shadow mask 220, such that the selected region 226 is identical to the region 215. The third EL layer 222 may be designed to emit a blue (B) colour.

[0068] FIG. 18 illustrates the deposition of charge transport layers and top electrode (together denoted by 228) on the third EL layer 222 and the exposed portions of the second EL layer 212. The charge transport layers and top electrode 228 may be deposited in a selected region 227 defined by a shadow mask 230. The charge transport layers and top electrode 228 may be deposited, for example, via a wet-coating process and / or vacuum deposition.

[0069] FIG. 19 illustrates a cross-sectional view of an EL device 240 manufactured according to the second example process illustrated in FIGs. 11-18. A voltage from a voltage source 232 may be applied across the top electrode 228 and each of the bottom electrodes 202-1 , 202-2, and 202-3, thereby resulting in the emission of R, B, and Gelectroluminescence 234 from the different areas or regions of the stack of EL layers 204, 212, and 222, as illustrated in FIG. 19.

[0070] FIG. 20 illustrates an example method 300 for manufacturing an EL device, such as the EL device 140 or the EL device 240. As described previously, the EL device may comprise a substrate and a plurality of electrodes connected thereto, such as the substrate 100 or 200 and the bottom electrodes 102 or 202.

[0071] At 302, a first layer is deposited onto the substrate and the plurality of electrodes connected thereto, where the first layer comprises a first EL material capable of emitting a first colour of light under bias. The first EL material may comprise, for example, colloidal quantum dots, perovskites, or organic pi-conjugated molecules. The first layer may be deposited, for example, using a wet-coating process or a dry-coating process. Examples of the first layer include the EL layers 104 and 204.

[0072] At 304, a first metal is deposited onto a selected region of the first layer, where the first metal is capable of reducing EL properties of the first EL material in the selected region of the first layer. The first metal may comprise, for example, Ag, Au, or Al, or certain metals from the group of metals with work function exceeding 3.8 eV, such as Pt and Cu, or an electrically-conductive metal-containing compound, such as a conductive metal oxide like Ag2O. The first metal may be deposited, for example, using thermal evaporation or other PVD processes through a shadow mask, or using wet-coating processes that allow deposition in only certain areas, or photolithographic processes. The first metal may alternatively be deposited on a precoated layer that comprises regions comprising nucleation-inhibiting materials and other regions comprising nucleation-promoting materials. Examples of the first metal include the quenching metals 106 and 206.

[0073] Optionally, at 306, a charge injection material may be deposited onto a part of the first layer, where the charge injection material is capable of facilitating injection of electrons or holes. The charge injection material may be deposited, for example, on at least a portion of the selected region on which the first metal was deposited at 304. The charge injection material may comprise, for example, a metal such as Mg or a metal compound. The charge injection material may be deposited, for example, using similar techniques to those for depositing the first metal at 304, such as through a shadow mask. Examples of the charge injection material include the charge injection materials 110 and 210.

[0074] At 308, a second layer is deposited onto the first layer, where the second layer comprises a second EL material capable of emitting a second colour of light under bias. The second EL material may comprise, for example, colloidal quantum dots, perovskites, or organic pi-conjugated molecules. The second layer may be deposited, for example, using a wet-coating process or a dry-coating process. Examples of the second layer include the layers 112 and 212.

[0075] Optionally, at 310, a second metal is deposited onto a selected region of the second layer, where the second metal is capable of reducing EL properties of the second EL material in the selected region of the second layer. The second metal may comprise, for example, Ag, Au, or Al, or certain metals from the group of metals with work function exceeding 3.8 eV, such as Pt and Cu, or an electrically-conductive metal-containing compound, such as a conductive metal oxide like Ag2O. The second metal may be deposited, for example, using thermal evaporation or other PVD processes through a shadow mask, or using wet-coating processes that allow deposition in only certain areas, or photolithographic processes. The second metal may alternatively be deposited on a precoated layer that comprises regions comprising nucleation-inhibiting materials and other regions comprising nucleation-promoting materials. Examples of the second metal include the quenching metals 114 and 214.

[0076] Optionally, at 312, a charge injection material may be deposited onto a part of the second layer, where the charge injection material is capable of facilitating injection of electrons or holes. The charge injection material may be deposited, for example, on at least a portion of the selected region on which the second metal was deposited at 310. The charge injection material may comprise, for example, a metal such as Mg or a metal compound. The charge injection material may be deposited, for example, using similar techniques to those for depositing the charge injection material at 306. Examples of the charge injection material include the charge injection materials 118 and 218.

[0077] Optionally, at 314, a third layer is deposited onto the second layer, where the third layer comprises a third EL material capable of emitting a third colour of light under bias. The third EL material may comprise, for example, colloidal quantum dots, perovskites, or organic pi-conjugated molecules. The third layer may be deposited, for example, using a wet-coating process or a dry-coating process. Examples of the third layer include the layers 122 and 222.

[0078] Optionally, at 316, a third metal is deposited onto a selected region of the third layer, where the third metal is capable of reducing EL properties of the third EL material in the selected region of the third layer. The third metal may comprise, for example, Ag, Au, or Al, or certain metals from the group of metals with work function exceeding 3.8 eV, such as Pt and Cu, or an electrically-conductive metal-containing compound, such as a conductive metal oxide like Ag2O. The third metal may be deposited, for example, using thermal evaporation or other PVD processes through a shadow mask, or using wet-coating processes that allow deposition in only certain areas, or photolithographic processes. The third metal may alternatively be deposited on a precoated layer that comprises regions comprising nucleation-inhibiting materials and other regions comprising nucleationpromoting materials. An example of the third metal is the quenching metal 124.

[0079] Optionally, at 318, the charge transport layers and top electrode are deposited onto the third layer. The charge transport layers and top electrode may be deposited, for example, using a wet-coating process and / or vacuum deposition. Examples of the charge transport layers and top electrode include the charge transport layers and top electrode 128 and 228.

[0080] According to some examples, a stack may have the same composition and sequence of EL layers over an entire substrate (or a part of the substrate, if the substrate does not need to be entirely coated). The entire substrate may, for example, be coated with a stack of layers of EL materials that each produce blue (B), green (G) and / or red (R) electroluminescence, and may have these layers in the same sequence.

[0081] In some examples, the quenching metal may be made more effective in reducing the PLQY of an EL layer in a selected area or region by coating the quenching metal directly on the selected area or region of the EL layer, such that the quenching metal is in direct physical contact with the EL layer.

[0082] In some examples, deposition of a quenching metal on the selected area(s) or region(s) of an EL layer may increase electrical conductivity of the EL layer. Consequently, the ohmic resistance for electrical current flow across the EL layer may be reduced in the selected area(s) or region(s) by at least 2 times, or in some examples, by at least 5 times, as compared to the ohmic resistance of the same area(s) and region(s) of the EL layer when measured before deposition of the quenching metal.

[0083] In the preceding examples, the term “first layer” or “first EL layer” generally refers to the layer that is in direct contact with the bottom electrodes, the term “third layer” or “third EL layer” refers to the layer that is in direct contact with the top electrode, and the term “second layer” or “second EL layer” refers to the layer that interposed between the first layer and the third layer. However, the terms “first”, “second”, and “third” should be broadly understood as mere identifiers for the different EL layers. Use of the terms “first”, “second”, and “third” should not be understood as limiting in terms of the relative positions of the layers in a given stack. In other words, unless explicitly stated, the position of a “first” layer need not be limited to one of direct contact with the bottom electrodes and the position of a “third” layer need not be limited to one of direct contact with the top electrode. Similarly, the position of a “second” layer need not be limited one that is interposed between a “first” layer and a “third” layer.

[0084] Although the above description includes reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art. Any examples provided herein are included solely for the purpose of illustration and are not intended to be limiting in any way. Any drawings provided herein are solely for the purpose of illustrating the subject matter described herein and are not intended to be drawn to scale or to be limiting in any way. The scope of the claims appended hereto should not be limited by the preferred embodiments set forth in the above description but should be given the broadest interpretation consistent with the present specification as a whole. The disclosures of all references in the present description herein are incorporated herein by reference in their entirety.References

[0001] C. Xiang et al. , "High efficiency and stability of ink-jet printed quantum dot light emitting diodes," Nature Communications, vol. 11 , no. 1 , p. 1646, 2020.[2] H. Roh et al., "Enhanced performance of pixelated quantum dot light-emitting diodes by inkjet printing of quantum dot-polymer composites," Advanced Optical Materials, vol. 9, no. 11 , p. 2002129, 2021.[3] X. Xiong et al., "Realizing 17.0% external quantum efficiency in red quantum dot lightemitting diodes by pursuing the ideal inkjet-printed film and interface," Organic Electronics, vol. 73, pp. 247-254, 2019.[4] W. Sun, L. Xie, X. Guo, W. Su, and Q. Zhang, "Photocross-linkable hole transport materials for inkjet-printed high-efficient quantum dot light-emitting diodes," ACS Applied Materials & Interfaces, vol. 12, no. 52, pp. 58369-58377, 2020.[5] M. Chen et al., "High performance inkjet-printed QLEDs with 18.3% EQE: improving interfacial contact by novel halogen-free binary solvent system," Nano Research, pp. 1-7, 2021.[6] Y. Liu et al., "Efficient all-solution processed quantum dot light emitting diodes based on inkjet printing technique," ACS applied materials & interfaces, vol. 9, no. 30, pp. 25506- 25512, 2017.[7] T.-H. Kim et al., "Full-colour quantum dot displays fabricated by transfer printing," Nature photonics, vol. 5, no. 3, pp. 176-182, 2011.[8] P. Yang, L. Zhang, D. J. Kang, R. Strahl, and T. Kraus, "High-resolution inkjet printing of quantum dot light-emitting microdiode arrays," Advanced Optical Materials, vol. 8, no. 1 , p. 1901429, 2020.[9] V. Wood et al., "Inkjet-printed quantum dot-polymer composites for full-color ac-driven displays," Advanced Materials, vol. 21 , no. 21 , pp. 2151-2155, 2009.

[0010] L. Kim, P. O. Anikeeva, S. A. Coe-Sullivan, J. S. Steckel, M. G. Bawendi, and V. Bulovic, "Contact printing of quantum dot light-emitting devices," Nano letters, vol. 8, no. 12, pp. 4513- 4517, 2008.

[0011] H. Cho et al., "Soft contact transplanted nanocrystal quantum dots for light-emittingdiodes: effect of surface energy on device performance," ACS applied materials & interfaces, vol. 7, no. 20, pp. 10828-10833, 2015.

[0012] W. Mei et al., "High-resolution, full-color quantum dot light-emitting diode display fabricated via photolithography approach," Nano research, vol. 13, pp. 2485-2491 , 2020.

Claims

WE CLAIM:1 . A method for manufacturing an electroluminescent (EL) flat panel display (FPD) comprising a substrate and a plurality of electrodes connected thereto, the method comprising: depositing, onto the substrate and the plurality of electrodes, a first layer comprising a first EL material capable of emitting a first colour of light; depositing, onto a selected region of the first layer, a first metal capable of reducing EL properties of the first EL material in the selected region of the first layer; and depositing, onto the first layer, a second layer comprising a second EL material capable of emitting a second colour of light.

2. The method as claimed in claim 1 , further comprising: depositing, onto a selected region of the second layer, a second metal capable of reducing EL properties of the second EL material in the selected region of the second layer.

3. The method as claimed in claim 2, further comprising: depositing, onto the second layer, a third layer comprising a third EL material capable of emitting a third colour of light.

4. The method as claimed in claim 3, further comprising: depositing, onto a selected region of the third layer, a third metal capable of reducing EL properties of the third EL material in the selected region of the third layer.

5. The method as claimed in claim 2, further comprising depositing, onto at least a portion of the selected region of the second layer, a charge injection material capable of facilitating injection of electrons or holes.

6. The method as claimed in claim 1 , wherein, prior to depositing the second layer onto the first layer, the method further comprises: depositing, onto at least a portion of the selected region of the first layer, a charge injection material capable of facilitating injection of electrons or holes.

7. The method as claimed in claim 1 , wherein the first layer and the second layer are deposited using wet-coating processes.

8. The method as claimed in claim 1 , wherein the selected region of the first layer is defined by a first shadow mask, the method further comprising: depositing the first metal through the first shadow mask.

9. The method as claimed in claim 3, wherein the third layer is deposited using a vacuum deposition process.

10. The method as claimed in claim 1 , wherein the first EL material and / or the second EL material comprise one or more of colloidal quantum dots, perovskites, and organic pi- conjugated molecules.

11. An electroluminescent (EL) device comprising: a top electrode; a plurality of bottom electrodes connected to a substrate; and interposed between the top electrode and the plurality of bottom electrodes, a first layer comprising a first EL material capable of emitting a first colour of light, and a second layer comprising a second EL material capable of emitting a second colour of light, wherein a selected region of the first layer is coated in a metal capable of reducing EL properties of the first EL material in the selected region.

12. The EL device as claimed in claim 11 , wherein the metal causes a photoluminescence quantum yield (PLQY) of the EL materials in the selected region of the first layer to decrease by at least 50%.

13. The EL device as claimed in claim 11 , wherein the first EL material and / or the second EL material comprise one or more of colloidal quantum dots, perovskites, and organic pi- conjugated molecules.

14. The EL device as claimed in claim 11 , wherein the first EL material differs from the second EL material.

15. The EL device as claimed in claim 11 , further comprising: a third layer interposed between the top electrode and the plurality of bottom electrodes, the third layer comprising a third EL material capable of emitting a third colour of light.

16. The EL device as claimed in claim 15, wherein each of the first colour, the second colour, and the third colour is uniquely selected from the group consisting of blue light with luminescence peak in a range of 400-500 nm, green light with a luminescence peak in a range of 500-600 nm, and red light with a luminescence peak in a range of 600-700 nm.

17. The EL device as claimed in claim 16, wherein the first EL material comprises organic pi-conjugated materials capable of emitting the blue light, wherein the second EL material comprises colloidal quantum dot materials capable of emitting green light, and wherein the third EL material comprises colloidal quantum dot materials capable of emitting red light.

18. The EL device as claimed in claim 11 , wherein the metal comprises silver, gold, platinum, or aluminum, or compounds thereof.

19. The EL device as claimed in claim 11 , wherein the metal is coated with a layer comprising a charge injection material capable of facilitating injection of electrons or holes.

20. The EL device as claimed in claim 19, wherein the charge injection material comprises magnesium.

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