METHOD OF IMPRINTING A TEXTURE ON A SUBSTRATE FIELD OF INVENTION
[0001] The invention disclosed herein relates, in general, to light emitting devices. More specifically, the present invention relates to light emitting devices having improved light extraction.
BACKGROUND
[0002] During working of lighting devices like the Organic Light Emitting Devices (OLEDs) light management is a very critical aspect that determines the efficiency and effectiveness and visual appearance of the OLED.
[0003] The OLEDs have many different layers having different refractive indices, and because of the difference in refractive indices of these layers light emitted by the light emitting layers of the OLED often gets trapped within the layers itself
[0004] In order to solve this problem, usually light extraction designs, such as layers of scatter materials or layers with structured surfaces, are provided in between the various layers of the OLED and other lighting devices. These structured surface designs often require complex structures and/or difficult manufacturing methods like lithography, laser ablation, ion beam etching etc. Moreover, these designs are typically expensive to make and difficult to scale up to larger areas.
[0005] Further, structured surface designs made using such processes are that they are periodic in nature and they have been known to cause an inhomogeneous intensity distribution upon illumination. This is generally avoided by using scattering materials. However, use of scattering material leads to less light gain and/or is expensive.
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[0006] In light of the above discussion, there is a need for a lighting device that can enable easier light extraction and overcome one or more drawbacks associated with the prior art.
BRIEF DESCRIPTION OF FIGURES
[0007] The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention may best be understood by reference to the following description, taken in conjunction with the accompanying drawings. These drawings and the associated description are provided to illustrate some embodiments of the invention, and not to limit the scope of the invention.
[0008] FIG. 1 is a diagrammatic illustration of various components of an exemplary light emitting device, in accordance with an embodiment of the present invention;
[0009] FIG. 2a is a diagrammatic illustration of an exemplary light emitting device having a first light extraction texture, in accordance with an embodiment of the present invention;
[0010] FIG. 2b is a diagrammatic illustration of an exemplary light emitting device having a second light extraction texture, in accordance with an embodiment of the present invention;
[0011] FIG. 2c is a diagrammatic illustration of an exemplary light emitting device having both a first light extraction texture and a second light extraction texture, in accordance with an embodiment of the present invention;
[0012] FIGs. 3a and 3b are diagrammatic illustrations of a light extraction texture, in accordance with two exemplary embodiments of the present invention;
[0013] FIGs. 4a and 4b are SEM images of a light extraction master texture, in accordance with two exemplary embodiments of the present invention;
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[0014] FIG. 5 is a diagrammatic illustration of formation of a texture on a substrate using a master texture and nano-imprint process, in accordance with an exemplary embodiment of the present invention;
[0015] FIG. 6 is a flowchart representing an exemplary method of forming a light extraction texture on a substrate, in accordance with an exemplary embodiment of the present invention;
[0016] FIG. 7 is a graph representing an experimental test conducted to compare the light gain obtained on using random light extraction texture of the present invention;
[0017] FIG. 8 is a graph representing an experimental test conducted to compare the reduction in color shift as function of viewing angle obtained on using random light extraction texture of the present invention;
]0018] FIGs. 9a, 9b and 9c are comparative graphs representing an experimental test conducted to compare the light intensity patterns upon illumination when the light extraction textures are illuminated with a parallel beam which is perpendicular to the surface.
[0019] Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, in order to improve the understanding of the present invention.
[0020] There may be additional structures described in the foregoing application that are not depicted on one of the described drawings. In the event such a structure is described, but not depicted in a drawing, the absence of such a drawing should not be considered as an omission of such design from the specification.
SUMMARY
[0021] The instant exemplary embodiments provide a lighting device that provides improved light extraction.
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[0022] The instant exemplary embodiments provide a lighting device that is easy and cheap to manufacture.
[0023] The instant exemplary embodiments provide a lighting device with application specific quality aspects like reduced color shift, uniform intensity distribution and an improved visual appearance.
[0024] Some exemplary embodiments of the invention provide a method of manufacturing a lighting device. The method of manufacturing the lighting device including providing a substrate having a first surface and a substantially parallel second surface and coating the first surface with a lacquer layer. Thereafter, the method includes imprinting an internal light extraction texture on the lacquer layer, such that the internal light extraction texture facilitates light extraction out of the lighting device. Further the step of imprinting includes providing a first replication substrate and chemically etching the first replication substrate to develop a texture profile on its surface, such that the texture profile corresponds to a plurality of pyramids which are randomly distributed over the surface of the first replication substrate and are also randomly sized. Thereafter the first replication substrate is pressurized over the lacquer layer to imprint the internal light extraction texture on the lacquer layer. The method also includes depositing a first electrode layer on the lacquer layer having the internal light extraction texture, followed by depositing one or more light emitting layers on the first electrode layer and depositing a second electrode layer on the one or more light emitting layers.
[0025] Some embodiments of the invention provide a method of manufacturing a stamper for creating a light extraction texture in a lighting device. The stamper is created by wet etching a stamper substrate to form a randomly distributed and randomly sized texture in the form of a plurality of pyramids on a surface of the stamper. Thereafter the stamper or a copy of the stamper is used to imprint the texture on a lacquer layer deposited on a substrate, which finds use in lighting devices. The texture thus formed on the lacquer layer enables light extraction in the lighting devices.
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DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0026] Before describing the present invention in detail, it should be observed that the present invention utilizes apparatus components related to a light emitting device such as an organic light emitting device. Accordingly the apparatus components have been represented where appropriate by conventional symbols in the drawings, showing only specific details that are pertinent for an understanding of the present invention so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art having the benefit of the description herein.
[0027] While the specification concludes with the claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawings, in which like reference numerals are carried forward.
[0028] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.
[0029] The terms "a" or "an", as used herein, are defined as one or more than one. The term "another", as used herein, is defined as at least a second or more. The terms "including" and/or "having" as used herein, are defined as comprising (i.e. open transition). The term "coupled" or
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"operatively coupled" as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
[0030] Referring now to the drawings, there is shown in FIG. 1, an exemplary lighting device 100, in accordance with an embodiment of the present invention. Examples of the lighting device 100 include light emitting device (LEDs), Organic Light Emitting Devices (OLEDs), liquid crystalline displays, and other organic displays.
[0031] Some real life examples of an OLED can include, but are not limited to. White Organic Light Emitting Diode (W-OLED), Active-matrix Organic Light Emitting Diodes (AMOLED), Passive-matrix Organic Light Emitting Diodes (PMOLED), Flexible Organic Light Emitting Diodes (FOLED), Stacked Organic Light Emitting Diodes (SOLED), Tandem Organic Light Emitting Diode, Transparent Organic Light Emitting Diodes (TOLED), Top Emitting Organic Light Emitting Diode, Bottom Emitting Organic Light Emitting Diode, Fluorescence doped Organic Light Emitting Diode (F-OLED) and Phosphorescent Organic Light Emitting Diode (PHOLED).
[0032] For the purpose of the description, the light emitting device 100 illustrated here will be described with reference to an OLED 100. However, it should be appreciated that this description is also applicable for other lighting devices, without deviating from the scope of the invention. Further, the OLED 100 has been shown to include only those layers that are pertinent to the description of the invention. However, it should be understood that the invention is not limited to the layers listed in the description here. In some cases, the OLED 100 may include additional layers to enhance efficiency or to improve reliability, without deviating from the scope of the invention.
[0033] The OLED 100 is shown to include a substrate 102, a first light extraction layer 104, a second light extraction layer 106, a functional layer stack 108, electrical contacts 120 and a cover substrate 118 The functional layer stack 108 is configured to have one or more functional layers therein. The one or more functional layers include a first electrode layer 110, one or more organic layers 112 and 114, and a second electrode layer 116.
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[0034] The substrate 102 functions to provide strength to the OLED 100, and also acts as the emissive surface of the OLED 100 when in use in case of a bottom side emitting device. Examples of material useful as the substrate include, but are not limited to, glass, flexible glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC) and other transparent or translucent material. The substrate 102 is defined by a first surface and a substantially parallel second surface. Further, the substrate 102 is configured to receive the first light extraction layer 104 on the first surface and the second light extraction layer 106 on the second surface. In an embodiment, the substrate may only include one of the first light extraction layer 104 and the second light extraction layer 106.
[0035] The first light extraction layer 104 and the second light extraction layer 106 are generally made up of a curable material and are provided over the substrate 102. It should be appreciated that, the first light extraction layer 104 may be interchangeably referred to as an internal light extraction layer 104 or a lacquer layer 104 and the second light extraction layer 106 may be interchangeably referred to as an external light extraction layer 106, for the purpose of the description.
[0036] The internal light extraction layer 104 and the external light extraction layer 106 can be provided on the substrate 102 at the beginning of the deposition process, or the external light extraction layer 106 can be provided layer once the OLED 100 has been finished. This can be done using a brush or roller, dispensing, screen printing, slot dye coating, spin-coating, spray coating, diverse replication techniques, or printing. A lacquer layer made of a curable material having a property to retain light extraction texture embossed on it when it is cured by using mediums such as heat or light. The curable material can include, but is not limited to, a ultra¬violet curable material, a photo-polymer lacquer, an acrylate, and silica or silica-titania based sol-gel materials.
[0037] The texture facilitates light extraction in the OLED 100. For example, in the OLED 100, light emitted by organic layers of the OLED 100, needs to pass through the substrate 102. However, when light is incident from a high refractive index material onto an interface with a
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lower refractive index material or medium, the light undergoes total internal reflection (TIR) for all incidence angles greater than the critical angle 9c, defined by 6c = arcsin (n2/ni), where ni and T\2 are the refractive indices of the high refractive index material and low refractive index material, respectively. In this way the light can get trapped inside the lighting device. Due to the same reason, when the light emitted by the one or more organic layers 112 and 114 reaches an interface between the substrate 102 and an ambient medium, a substantial amount of light is reflected back into the OLED. Further, details of the structure and shape of the light extraction texture has been provided with reference to FIGs. 3a and 3b. In an embodiment, the internal light extraction texture may be planarized using a material that has a refractive index comparable to that of the first electrode layer 110. In another embodiment, the substrate 102 may be replaced by an injection molded plastic substrate that may receive light extraction texture on one or both surfaces. In yet another embodiment, the light extraction texture may undergo further processing, for example UV-Ozone treatment, to further modify the shape and structure of the light extraction texture.
[0038] The first electrode layer 110 and the second electrode layer 116 are used to apply a voltage across the one or more organic layers 112 and 114. In an embodiment, the first electrode layer 106 can be implemented with, for example, transparent conductive oxide (TCO), such as indium tin oxide (ITO). Other examples of TCOs include, but are not limited to. Zinc Oxide, Tin Oxide, Aluminum-doped Zinc Oxide (AZO), Boron doped Zinc Oxide (BZO), Gallium doped Zinc Oxide (GZO), Fluorine doped Tin Oxide (FTO), and Indium Zinc Oxide. In another embodiment, the first electrode layer 110 can be in the form of soluble anodes. Examples of material for soluble anodes include, but are not limited to, Ag-nanowires and PedotrPSS. Further, in an embodiment, the second electrode layer 116 can be implemented with metals having appropriate work function to make injection of charge carriers, such as calcium, aluminum, gold, lithium, lithium fluoride, magnesium, silver and stacked layers of combination thereof.
[0039] The first electrode layer 110 is deposited by Plasma Vapor Deposition (PVD) and the second electrode layer 116 is deposited by Thermal evaporation. In other embodiments, of the invention, the first electrode layer 110 and the second electrode layer 116 can be deposited by
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using any one of a brush or roller, dispensing, slot dye coating, spin-coating, spray coating, diverse replication techniques, plasma vapor deposition, by evaporation or printing.
[0040] In an arrangement when the first electrode layer 110 is made of a transparent conductive oxide and the second electrode layer 116 is made of a metal for example aluminum, the OLED 100 usually functions as a bottom emitting OLED, i.e. the light emitted by the OLED 100 goes through the substrate 102. Usually, for the bottom emitting device, an external light extraction layer may also be provided to the stack of layers in the bottom emitting OLED. This is an additional layer provided on the substrate 102 on the outside. In the case of a top emitting OLED or dual-side emitting OLED, external light extraction layer can also be placed on a transparant cover layer 118.
[0041] Moving on to the next set of layers, the one or more organic layers 112 and 114. Generally, the one or more organic layers 112 and 114 are deposited using methods such as evaporation, dip coating, spin coating, doctored blade, spray coating, printing techniques, sputtering, glass mastering, photoresist mastering, all kinds of CVD and electroforming. In an embodiment, the one or more organic layers 112 and 114 can be implemented with any organic electroluminescent material such as a light-emitting polymer, evaporated small molecule materials, light-emitting dendrimers or molecularly doped polymers. For the purpose of this description, the organic layers are shown to include only two layers, however, it will be readily apparent to those skilled in the art that the OLED device 100 can include or exclude one or more organic layers without deviating from the scope of the invention. Further, in cases of other lighting devices the one or more organic layers may be replaced by one or more light emitting layers made of some other material. In another example, the OLED 100 may also include additional layers for functional improvement of the OLED 100, like a hole transport layer, hole injection layer, hole blocking layer, or an electron transport layer, electron injection layer, electron blocking layer.
[0042] Following the one or more organic layers 112 and 114, the second electrode layer 116 is deposited. However, in accordance with another embodiment of the present invention, the second electrode layer 116 can also be implemented using two layers, a first layer of a thin metal
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layer as silver, gold or a transition metal oxide, with on top a transparent highly conductive layer as a ITO or PedotrPSS in order to make the OLED 100 to function as a top emitting or fully transparent OLED 100 where the light can be emitted through the second electrode layer 114 itself because of the transparency provided by the TCO layer as the TCOs have more than 80% transmittance of incident light and have conductivities higher than 103 S/cm for efficient carrier transport. In an embodiment, the first electrode layer 110 acts as an anode and the second electrode layer 116 acts as a cathode.
[0043] In an embodiment, the OLED 100 may also include the electrical contacts 120 that are used to make contact between the two electrodes when voltage is applied across the one or more organic layers 110 and 112 respectively. The electrical contacts 120 are deposited by Physical Vapor Deposition (PVD), but they can be deposited also by other processes such as Plasma Enhanced Chemical Vapor Deposition (PECVD) or printing.
[0044] Thereafter, all the above mentioned layers are encapsulated using a cover substrate 118, between the substrate 102 and the cover substrate 118. In an embodiment, a gas barrier layer 117 may also be present between the functional layers 108 and the cover substrate 118.
[0045] Moving on there is shown in FIGs. 2a, 2b and 2c three exemplary embodiments of the lighting device 100 in accordance with the present invention. In Fig. 2a, for example, the lighting device 100 is shown to include only the first light extraction layer 104 and does not include the second light extraction layer 106. Similarly, in FIG. 2b, the lighting device 100 is shown to include only the second light extraction layer 106 and does not include the first light extraction layer 104. In an embodiment, such a configuration can also be used in a conventional lighting fixture, which can have an external light extraction layer provided as per the scope of the present invention.
[0046] Moving on, FIG. 2c illustrates the lighting device 100 including both the first light extraction layer 104 and the second light extraction layer 106. A real life application of such a configuration can be an OLED having both the internal light extraction layer and the external
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light extraction layer provided as per the scope of the present invention. In such a case, one of the two light extraction layers can be of another type of light extraction than is described here.
[0047] Moving on there is shown in FIGs. 3a and 3b, light extraction textures 302 and 304 provided on the substrate 102 of the lighting device 100, in accordance with embodiments of the present invention. As illustrated the light extraction texture 302 and 304 are shaped in the form of a plurality of pyramids that are randomly distributed over the substrate 102 and the plurality of pyramids are also randomly sized. The light extraction texture 304 is a master texture formed after the etching process and the light extraction texture 302 is a negative impression of the light extraction texture 304. According to an embodiment of the present invention, a height of the light extraction textures 302 and 304 or the plurality of pyramids 302 and 304 ranges between 0.2 to 10 nm. Further, in an embodiment, a wall angle of the plurality of pyramids 302 and 304 range between 20° to 75°.
[0048] Similarly, another illustration of the light extraction texture formed on the master, in accordance with the embodiments of the present invention, has been illustrated in FIGs. 4a and 4b. FIG. 4a is a representative SEM image of the master texture having a favorable light scattering property. Fig 4b is a representative SEM image of the inverse texture.
[0049] Moving on, there is illustrated in FIG.5 the various stages in the formation of a texture on a substrate using a replication substrate, in accordance with an exemplary embodiment of the present invention. To start off a replication substrate 502 is provided. The replication substrate is usually made of a material selected from the group comprising silicon, nickel or other similar crystalline materials. Further, since the replication substrate 502 is usually made of silicon, it is easy to scale up the size of the replication substrate 502 to sizes ranging from 1mm to above 250 mm, till up to 2000 mm, preferably from about 250 to 400 mm.
[0050] Thereafter the replication substrate 502 undergoes a wet etching process, in which the replication substrate 502 is treated with suitable chemicals to etch and remove material from the replication substrate 502 and form a first replication substrate 504 having a texture profile
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thereon. Examples of suitable chemicals include, but are not limited to, alkaline anisotropic etchant solution like KOH, EDP (an aqueous solution of ethylene diamine and pyrocatechol) etc.
[0051] The texture profile created is random in shape and size and corresponds to the light extraction texture needed to be formed on the substrate 102 of the lighting device. However, it should be appreciated that the profile illustrated in the figure is only for representative purpose and not limiting to the scope of the invention. Thereafter, the first replication substrate 504 is pressurized over the lacquer layer 104 on the substrate 102 to imprint the light extraction texture on the lacquer layer 104 and subsequently the first replication substrate is removed.
[0052] In another embodiment, an intermediate second replication substrate may be used for transferring the texture profile onto the substrate 102. This may involve transferring the texture profile of the first replication substrate 504 onto a surface of the second replication substrate and using the second replication substrate for imprinting the light extraction texture on the lacquer layer 104. This enables keeping the first replication substrate 504 as a master stamper and preparing multiple intermediate replication substrates for use thereafter. In another embodiment, a third replication substrate may also be used for transferring the texture profile depending upon whether an upright texture profile or an inverted texture profile is required as the light extraction texture. Further, the second replication substrate and the third replication substrate can be made of less expensive material than the first replication substrate 504 to further reduce the cost associated with the process.
[0053] Moving on, there is shown a flowchart depicfing a method 600 of forming a light extraction texture on substrate for use in a lighting device, for example the OLED 100, in accordance with an embodiment of the present invention. To describe the method 600, reference will be made to FIGs. 1, 2, 3, 4 and 5, although it is understood that the method 600 can be implemented to manufacture any other suitable lighting device. Moreover, the invenfion is not limited to the order of in which the steps are listed in the method 600. In addition, the method 600 can contain a greater or fewer numbers of steps than those shown in FIG. 6.
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[0054] Further, for the purpose of description, the method 600 has been explained in reference to light extraction in an OLED; however, it will be readily apparent to those ordinarily skilled in the art that the present invention can be implemented in any other lighting device as well for light extraction purposes.
[0055] The method 600 is initiated at step 602. At step 606, a first replication substrate, for example the replication substrate 504 is developed by treating a replication substrate, for example the replication substrate 502, with suitable chemicals to etch and remove material from the first replication substrate 502 and form a first replication substrate 504 having a texture profile thereon.
[0056] Thereafter, at step 606, the substrate, for example the substrate 102 is coated with a lacquer layer, for example the lacquer layer 104. The lacquer layer 104 may be applied on the substrate by using a brush or roller, dispensing, screen printing, slot dye coating, spin-coating, spray coating, diverse replication techniques, or printing.
[0057] Thereafter at step 608, a texture, for example the light extraction texture 302 or 304 is formed by imprinting or replicating impressions of the texture profile on the first replication substrate 504 into the lacquer layer 104. This step is then followed by a curing process at step 610 to affix the light extraction texture 302 or 304 on the lacquer layer 104.
[0058] Thereafter, at step 612, the first replication substrate 504 is removed and the method 600 is terminated at step 614.
[0059] Various embodiments, as described above, provide a lighting device that has several advantages. The substrate having the random texture, according to the present invention, can be used for lighting applications, for example it can find application as a diffuser plate for any kind of lighting or display application. Further, the random texture can also be used as both internal and external light extraction textures.
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[0060] Furthermore, upon experimental investigations it can be deduced that both upright and inverted pyramids type of texture used as external light extraction layer behave equally to in cases even better than other external light extraction structures, gaining up to 50% more light for a typical green OLED device. A representative graph comparing the light gain offered on using the light extraction textures according to the present invention has been provided in FIG. 7. The comparison has been shown with respect to commercially available light extraction foils based on microlenses or scattering materials and a periodic array of pyramidic texture.
[0061] Similarly, upon experimental investigations it can be deduced that both upright and inverted pyramids type of texture reduce color shift when compared to lighting device not having extraction textures. For example, a representative graph comparing the reduction in color shift offered on using the light extraction textures in OLEDs, according to the present invention, as compared to a bare OLED has been provided in FIG. 8. As can be seen there is a reduction of almost 50% in color shift on using the external light extraction textures of the present invention in the OLEDs. It should be appreciated that the light extraction textures (upright and inverted pyramids) were provided to the bare OLED being used as a reference sample during the experiment. Using the texture as internal light extraction has similar behavior.
[0062] Further, the uniform distribution of light provided on using the random light extraction texture of the present invention is more than that obtained on using periodic light extraction texture. For example, as is known LED light are typically point sources which are not very useful to illuminate a large area. However, on combining LED light with a diffuser plate having a random pyramidal texture as per the present invention causes the light to scatter creating a uniform light source. Graphical representation of such an experiment has been illustrated in FIGs. 9a, 9b and 9c, where the structures have been illuminated with a parallel light beam perpendicular to the sample surface. As can be seen, compared to a regular pyramid array (periodic) in FIG. 9c, the upright pyramids and inverted pyramids in FIGs. 9a and 9b respectively have a much more smoothed image upon illumination.
[0063] While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon
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will become readily apparent to those ordinarily skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense allowable by law.
[0064] All documents referenced herein are hereby incorporated by reference.
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CLAIMS What is claimed is:
1. A method of manufacturing a lighting device, said method comprising:
forming a textured replication substrate, said forming comprising:
providing a first replication substrate;
chemically etching said first replication substrate to develop a texture profile on a surface of said first replication substrate, said texture profile corresponding to a plurality of pyramids, wherein said plurality of pyramids being randomly distributed over the surface of said first replication substrate, further wherein said plurality of pyramids are randomly sized;
imprinting said texture profile on a substrate to form a light extraction texture on said substrate, wherein said light extraction texture facilitates light extraction in said lighting device, said imprinting comprising:
providing a substrate having a first surface and a substantially parallel second surface;
coating said first surface with a lacquer layer;
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pressurizing said first replication substrate over said lacquer layer to imprint said light extraction texture on said lacquer layer;
curing said lacquer layer to affix said internal light extraction texture on said substrate;
removing said first replication substrate;
depositing a first electrode layer on said lacquer layer having said light extraction texture;
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depositing one or more light emitting layers on said first electrode layer; and depositing a second electrode layer on said one or more light emitting layers.
2. The method according to claim 1, wherein a material of said first replication substrate is selected from the group comprising silicon, nickel, and other crystalline material that yields pyramidal shapes upon chemical etching.
3. The method according to claim 1 further comprising:
transferring said texture profile of said first replication substrate onto a surface of a second replication substrate, thereby creating a plurality of pyramid shaped recesses being randomly distributed over the surface of said second replication substrate, further wherein said plurality of pyramid recesses are randomly sized; and
imprinting said light extraction texture on said lacquer layer using said second replication substrate.
4. The method according to claim 1 further comprising:
coating said second surface with a lacquer layer; and
imprinting a light extraction texture on said lacquer layer on said second surface using said first replication substrate.
5. The method according to claim 1, wherein height of said pyramids ranges between 0.2 to 10 ^m.
6. The method according to claim 1, wherein a wall angle of said pyramids of said light extraction texture range between 20° to 75°.
7. The method according to claim I, wherein a dimension of said first replication substrate ranges from 1mm to 2000 mm, preferably from about 250 to 400 mm.
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8. The method according to claim 1, wherein said lighting device can be selected from the group comprising a light emitting device, an organic light emitting device, a liquid crystalline display, any other organic displays, and any other lighting and display devises in which a part of the light gets trapped within the device.
9. The method according to claim 1, wherein said chemical etching is carried out using an alkaline anisotropic etchant solution.
10. The method according to claim 1, wherein said substrate with said internal light extraction texture is replaced by a molded textured plastic substrate, wherein said light extraction texture is applied on one or both surfaces of said plastic substrate.
IS