WO2010132613A2

WO2010132613A2 - High resolution light emitting devices

Info

Publication number: WO2010132613A2
Application number: PCT/US2010/034614
Authority: WO
Inventors: Sayantani Ghosh; Michelle Khine
Original assignee: The Regents Of The University Of California
Priority date: 2009-05-13
Filing date: 2010-05-12
Publication date: 2010-11-18
Also published as: WO2010132613A3

Abstract

Light emitting devices are provided. The light emitting devices include a substrate, a first array of light emitting lines disposed over the substrate, and a second array of light emitting lines disposed over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 µm². The light emitting lines may include quantum dots and the substrate may be formed of a thermoplastic material, such as polystyrene. Also provided are methods of making the light emitting devices using a stamp comprising a heat-shrunk thermoplastic substrate and a film of metal disposed over the surface of the heat-shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features.

Description

HIGH RESOLUTION LIGHT EMITTING DEVICES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U.S. C. § 119(e) of U.S. Provisional Serial No. 61/177,990, filed May 13, 2009, the content of which is hereby incorporated by reference into the present disclosure.

BACKGROUND

[0002] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document were specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0003] Due to the exceptional luminescent properties of colloidal quantum dots (QDs), such as the narrow emission spectra tunable throughout the entire visible spectrum and high photoluminescence efficiencies, QDs find use in a variety of light emitting devices (LEDs), including pixilated full-color displays. However, very few techniques have been developed for generating laterally patterned QD films, which are needed for pixilated full-color displays. One technique involves contact printing using a molded poly(dimethylsiloxane) (PDMS) stamp. See Kim et al, "Contact Printing of Quantum Dot Light-Emitting Devices," Nano Lett. 2008, 8, 4513-4517. In this method, the PDMS stamp is inked via spin-casting with a solution of colloidal QDs suspended in an organic solvent. The QD monolayer is transferred to a substrate by contact printing. However, this method suffers from a number of drawbacks. First, the organic solvents used in QD processing are often not chemically compatible with the PDMS stamp, which critically influences the QD film morphology, and consequently, the QD-LED performance. Second, the size of the patterned QD monolayers, and consequently, the pixel size of the resulting LEDs, is limited by the dimensions of the molded PDMS stamp. Currently, such contact printing methods are only able to achieve pixel sizes of about 20 μm (i.e., 400 μm²). Therefore, a need exists for higher resolution light emitting devices and methods of making such devices. SUMMARY OF THE INVENTION

[0004] Light emitting devices and methods for making the devices are provided herein. The light emitting devices include a substrate, a first array of light emitting lines disposed over the substrate, and a second array of light emitting lines disposed over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel. The light emitting devices may be formed using a stamp coated with a light emitting solution. The stamps comprise a heat-shrunk thermoplastic substrate and a film of metal disposed over the surface of the heat- shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features. The dimensions and orientations of the wrinkle-like features, which ultimately determine the dimensions and orientations of the light emitting lines, may be readily controlled during the process of forming the stamps. The widths of the wrinkles, and thus, the widths of the light emitting lines may be quite small, even 1 μm. Thus, the disclosed stamps are capable of providing light emitting devices having much smaller pixel areas (even 1 μm²) than conventional light emitting devices. Consequently, the disclosed light emitting devices have far greater resolution and can be made to be much smaller than conventional light emitting devices. Finally, not only are the disclosed light emitting devices and stamps used for making the devices formed using ultra-rapid processes and low cost, readily available materials, but also the metallic wrinkled films are compatible with a wide range of light emitting solutions.

[0005] In one aspect, light emitting devices are provided. The light emitting devices include a substrate, a first array of light emitting lines disposed over the substrate, and a second array of light emitting lines disposed over the first array. One or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel. The dimensions and shapes of the pixels may vary. In some embodiments, the areas of the pixels are not more than about 100 μm². The dimensions, orientations, and spacing of the light emitting lines, which affect the characteristics of the pixels, may also vary. Exemplary dimensions, orientations, and spacings are described herein. The composition of the light emitting lines may vary. Light emitting lines may comprise light emitting polymers, light emitting quantum dots, or the like. Similarly, the composition of the substrate may vary. The substrate may comprise a transparent glass or a transparent plastic, such as a thermoplastic material. Polystyrene is a possible substrate material. The disclosed light emitting devices may include other material layers, metallic contacts, and may be coupled to other components. These material layers, metallic contacts, and other components are described below. [0006] In another aspect, methods for making any of the disclosed light emitting devices are provided. The methods involve forming a first array of light emitting lines over a substrate and forming a second array of light emitting lines over the first array. The first array and the second array may be formed by a process comprising coating a stamp with a light emitting solution and contacting the substrate with the coated stamp to provide the first array and the second array. In such a process, the stamp may include a heat shrunk thermoplastic substrate and a film of metal disposed over the surface of the heat- shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features. These stamps and the methods for making the stamps are fully described below. [0007] Thus, in one aspect this invention provides a method of making a light emitting device comprising, or alternatively consisting essentially of, or yet further consisting of, forming a first array of light emitting lines over a substrate; and forming a second array of light emitting lines over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 μm , and further wherein, the first array and the second array are formed by a process comprising coating a stamp with a light emitting solution; and contacting the substrate with the coated stamp to provide the first array and the second array, wherein the stamp comprise a heat shrunk thermoplastic substrate, and a film of metal disposed over the surface of the heat-shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features. Methods for forming the heat shrunk thermoplastic material are described herein.

[0008] In one aspect, the first and second arrays are deposited such that the area is no more than about 50 μm , or alternatively no more than about 10 μm or alternatively no more than about 1 μm². [0009] In a further aspect, the arrays are deposited such that the light emitting lines of the first array are substantially parallel to one another, each of the light emitting lines of the second array are substantially parallel to one another, or both.

[0010] In another aspect, the light emitting lines of the first array are deposited such that they are separated by a distance of no more than about 2 μm, each of the light emitting lines of the second array are separated by a distance of no more than about 2 μm, or both.

[0011] In another embodiment, the light emitting lines of the first array are deposited such that the oriented substantially perpendicular to the light emitting lines of the second array.

[0012] Various materials can be used in the method. For example, the light emitting lines of the first array, the light emitting lines of the second array, or both can comprise a light emitting polymer. In another aspect, the light emitting lines of the first array, the light emitting lines of the second array, or both comprise quantum dots. Non-limiting examples of the quantum dots comprise CdSe, ZnS, ZnSe, CdTe quantum dots, or combinations thereof. [0013] The methods can comprise use of material such that the light emitting lines of the first array that emit light of a first color and the light emitting lines of the second array emit light of a second color.

[0014] In another aspect, the method of this invention further comprises, or alternatively consists essentially of, or yet further consists of depositing one or more metallic contacts electrically coupled to one or more light emitting lines of the first array, one or more light emitting lines of the second array, or both. In another embodiment, the device further comprises, or alternatively consists essentially of, or yet further consists of, depositing any one or more of a hole injecting layer, a hole transport layer, a hole blocking layer, an electron transporting layer, or combinations thereof. [0015] Various substrates can be used in the methods as described herein. Non-limiting examples include a transparent plastic, a transparent glass or a a thermoplastic material such as polystyrene.

[0016] Also provided by this invention is a light emitting device obtainable by or produced by any one or more of the aspects or embodiments described herein and their use for emitting light. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is an illustration of an exemplary high resolution light emitting devices prepared according to the methods described herein.

[0018] FIGs. 2A and 2B are images of exemplary stamps that may be used to form the disclosed light emitting devices. The stamps are made from heat-shrunk thermoplastic substrates coated with a wrinkled metallic surface.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0019] As used herein, the term "comprising" is intended to mean that the compositions and methods include the recited elements, but do not exclude others. "Consisting essentially of when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination when used for the intended purpose. Thus, a composition consisting essentially of the elements as defined herein would not exclude trace contaminants or inert carriers. "Consisting of shall mean excluding more than trace elements of other ingredients and substantial method steps for preparing the micro fluidic device. Embodiments defined by each of these transition terms are within the scope of this invention.

[0020] All numerical designations, e.g., pH, temperature, time, concentration, and molecular weight, including ranges, are approximations which are varied ( + ) or ( - ) by increments of 0.1. It is to be understood, although not always explicitly stated that all numerical designations are preceded by the term "about". It also is to be understood, although not always explicitly stated, that the reagents described herein are merely exemplary and that equivalents of such are known in the art.

[0021] As used in the specification and claims, the singular form "a," "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a micro fluidic channel" includes a plurality of micro fluidic channels.

[0022] A "thermoplastic material" is intended to mean a plastic material which shrinks upon heating. In one aspect, the thermoplastic materials are those which shrink uniformly without distortion. A "Shrinky-Dink" is a commercial thermoplastic which is used a childrens toy. The shrinking can be either bi-axially (isotropic) or uni-axial (anisotropic) and can be un-iaxially or bi-axially stressed prior to further shrinkage. Suitable thermoplastic materials for inclusion in the methods of this invention include, for example, one or more high molecular weight polymers such as acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

[0023] A "metal" for use in this invention includes but is not limited to platinum, gold, titanium, silver, copper, a dielectric substance, a paste or any other suitable metal or combination thereof. Examples of suitable dielectric substances include metal oxides, such as aluminum oxide, titanium dioxide and silicon dioxide. Examples of suitable pastes include conductive pastes such as silver pastes.

[0024] The metal can be applied to the thermoplastic material by a variety of methods known to one skilled in the art, such as printing, sputtering and evaporating. The term "evaporating" is intended to mean thermal evaporation, which is a physical vapor deposition method to deposit a thin film of metal on the surface of a substrate. By heating a metal in a vacuum chamber to a hot enough temperature, the vapor pressure of the metal becomes significant and the metal evaporated. It recondenses on the target substrate. As used herein, the term "sputtering" is intended to mean a physical vapor deposition method where atoms in the target material are ejected into the gas phase by high-energy ions and then land on the substrate to create the thin film of metal. Such methods are well known in the art (Bowden et al. (1998) Nature (London) 393: 146-149; Bowden et al. (1999) Appl. Phys. Lett. 75: 2557-2559; Yoo et al. (2002) Adv. Mater. 14: 1383-1387; Huck et al. (2000) Langmuir 16: 3497-3501; Watanabe et al. (2004) J. Polym. Sci. Part B: Polym. Phys. 42: 2460-2466; Volynskii et al. (2000) J. Mater. Sci. 35: 547-554; Stafford et al. (2004) Nature Mater. 3: 545-550; Watanabe et al. (2005) J. Polym. Sci. Part B: Polym. Phys. 43: 1532-1537; Lacour, et al. (2003) Appl. Phys. Lett. 82: 2404-2406.)

[0025] In addition, the metal can be applied to the thermoplastic material using "pattern transfer." The term "pattern transfer" refers to the process of contacting an image-forming device, such as a mold or stamp, containing the desired pattern with an image-forming material to the thermoplastic material. After releasing the mold, the pattern is transferred to the thermoplastic material. In general, high aspect ratio pattern and sub-nanometer patterns have been demonstrated. Such methods are well known in the art (Sakurai, et al., US Patent 7,412,926; Peterman, et al., US Patent 7,382,449; Nakamura, et al., US Patent 7,362,524; Tamada, US Patent 6,869,735).

[0026] Another method for applying the image forming material includes, for example "micro-contact printing". The term "micro -contact printing" refers to the use of the relief patterns on a PDMS stamp (also referred to as the thermoplastic material) to form patterns of self-assembled monolayers (SAMs) of an image-forming material on the surface of a thermoplastic material through conformal contact. Micro-contact printing differs from other printing methods, like inkjet printing or 3D printing, in the use of self-assembly (especially, the use of SAMs) to form micro patterns and microstructures of various image-forming materials. Such methods are well known in the art (Cracauer, et al., US Patent 6,981,445; Fujihira, et al., US Patent 6,868,786; Hall, et al., US Patent 6,792,856; Maracas, et al., US Patent 5,937,758).

[0027] A "patterning device" is intended to be broadly interpreted as referring to a device that can be used to convey a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate.

[0028] A "pattern" is intended to mean a mark or design.

[0029] Light emitting devices and methods for making the devices are provided herein.

Light emitting devices [0030] The light emitting devices include a substrate, a first array of light emitting lines disposed over the substrate, and a second array of light emitting lines disposed over the first array. In the disclosed LEDs, one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel. Thus, a "pixel" is defined as a region where a light emitting line of the first array overlaps with a light emitting line of the second array. The dimensions of the pixel are determined by the widths of the light emitting lines of the first and second arrays. The widths of the light emitting lines of each array may independently vary. In some embodiments, the widths are no more than about 10 μm. In other embodiments, the widths are no more than about 5 μm, about 2 μm, about 1 μm, or even less. However, other widths are possible. [0031] The shapes of the pixels are determined by the orientation of the light emitting lines of the first and second arrays across the substrate and the manner in which the light emitting lines cross. Exemplary orientations are further described below. However, by way of example only, when one light emitting line crosses another light emitting line at 90°, the resulting pixel is a square. Other shapes are possible. The areas of the pixels may vary. In some embodiments, the area of a pixel is no more than about 100 μm². In other

0 0 0 embodiments, the widths are no more than about 50 μm , about 10 μm , or about 1 μm . However, other areas are possible.

[0032] The orientation of the light emitting lines of the first array and the second array may independently vary. In some embodiments, each of the light emitting lines of the first array are substantially parallel to one another, each of the light emitting lines of the second array are substantially parallel to one another, or both. By "substantially parallel," it is meant that two light emitting lines are parallel, but not necessarily perfectly parallel. For example, the light emitting lines themselves may not be perfectly straight so that two such lines would not be perfectly parallel to one another. In other embodiments, the light emitting lines of the first array are oriented substantially perpendicular to the light emitting lines of the second array. As described above with respect to the phrase substantially parallel, by "substantially perpendicular," it is meant that two lines are perpendicular to each other, but not necessarily perfectly perpendicular. In other embodiments, the light emitting lines of the first array may be oriented at other angles (e.g., less than 90° or more than 90°) with respect to the light emitting lines of the second array.

[0033] The spacing between the light emitting lines of each array may also independently vary. In some embodiments, the light emitting lines of the first array are separated by a distance of no more than about 2 μm, each of the light emitting lines of the second array are separated by a distance of no more than about 2 μm, or both. In other embodiments, the spacing may be no more than about 5 μm, about 10 μm, about 15 μm, or about 20 μm. However, other spacings are possible.

[0034] It is emphasized that the widths, spacing, and orientation of the light emitting lines of both arrays may independently vary so that each array may include light emitting lines, each line having different widths, spacing, and orientation. In other embodiments, the widths, spacing, and orientation of each of the light emitting lines of an array are about the same. In yet other embodiments, the widths, spacing, and orientation of each of the light emitting lines of the first array are about the same as the widths, spacing, and orientation of each of the light emitting lines of the second array. As a result of these possibilities, the dimensions and shapes of each of the pixels of the disclosed LEDs may be about the same, or different from one another. [0035] The composition of the light emitting lines may vary, provided the light emitting lines are capable of emitting light. In some embodiments, the light emitting lines comprise a light emitting polymer. Light emitting polymers are known. Non-limiting examples include P3HT (poly(3-hexylthiophene)) and PEDOT:PSS (poly(3,4- ethylenedioxythiophene): poly(styrenesulfonate)). In other embodiments, the light emitting lines comprise quantum dots. Quantum dots are known. A variety of types of quantum dots may be used, including, but not limited to CdSe, ZnS, ZnSe, CdTe quantum dots, or combinations thereof. The wavelengths of light emitted by the light emitting lines may vary, depending upon the composition of the lines. In some embodiments, the light is visible light. However, other wavelengths of light are also possible. The composition of the light emitting lines of the first array may be the same or different from the composition of the light emitting lines of the second array. In some embodiments, the light emitting lines of the first array comprise a light emitting polymer or a quantum dot of a first color and the light emitting lines of the second array comprise a light emitting polymer or a quantum dot of a second color. [0036] The light emitting devices may include other arrays of light emitting lines and other material layers. In some embodiments, the light emitting devices further include a third array of light emitting lines disposed over the second array. A fourth, fifth, sixth, etc. array is also possible. The characteristics and composition of these other arrays of light emitting lines may vary as described above.

[0037] In other embodiments, the light emitting devices may include other material layers in the device, including, but not limited to a hole injecting layer, a hole transport layer, a hole blocking layer, an electron transporting layer, or combinations thereof. These types of material layers, as well as the composition of such layers are known. By way of example only, any of the hole injecting layers, hole transport layers, hole blocking layers, or electron transporting layers disclosed in Kim et al, "Contact Printing of Quantum Dot Light- Emitting Devices," Nano Lett. 2008, 8, 4513-4517, which is hereby incorporated by reference in its entirety, may be used.

[0038] In yet other embodiments, the light emitting devices further include one or more metallic contacts electrically coupled to one or more light emitting lines of the first array, one or more light emitting lines of the second array, or both. Any kind of conductive metal is suitable for such contacts. In some embodiments, each light emitting line is electrically coupled to an individual metallic contact. When voltage is applied to these and other metallic contacts, the light emitting lines coupled to the contacts will emit light via electroluminescence. The use of individual metallic contacts enables one light emitting line to emit light independently of the other light emitting lines. [0039] The composition of the substrate may vary. In some embodiments, the substrate comprises a transparent glass or transparent plastic. Such substrates are known. In some embodiments, the substrate comprises a thermoplastic material transparent glass or a transparent plastic, such as a thermoplastic material as described herein. In some embodiments, the thermoplastic material is polystyrene. Polystyrene, as well as a number of other thermoplastic materials, is flexible, durable, lightweight, and inexpensive, each of which is a desirable characteristic for a light emitting device. Polystyrene is also useful since metallic contacts adhere well to such a material.

[0040] An exemplary light emitting device is shown in FIG. 1. The LED includes a polystyrene (PS) substrate, a first array of light emitting lines comprising quantum dots that emit blue light disposed over the substrate, and a second array of light emitting lines comprising quantum dots that emit red light disposed over the first array. Each light emitting line of each array is coupled to a metallic contact. The light emitting lines of each array are very narrow, about 1 μm. The spacing between the light emitting lines is also quite narrow, about 10 μm for the first array and about 20 μm for the second array. The light emitting lines of the first array are oriented at about 90° with respect to the light emitting lines of the second array. Thus, the light emitting lines of the arrays cross, forming pixels that are about 1 μm² in area.

[0041] The disclosed light emitting devices may be coupled to a variety of other components. Such components include, but are not limited to, a voltage source. Other components commonly used with light emitting devices, and known means for coupling such components to light emitting devices, are possible.

[0042] Also disclosed are methods of using the light emitting devices. The methods involve inducing the emission of light from one or more light emitting lines of the first array, one or more light emitting lines of the second array, or both. Inducing the emission of light may be accomplished by applying a voltage to one or more light emitting lines of each array, e.g., via one or more metallic contacts coupled to the one or more light emitting lines. Voltage may be applied to individual light emitting lines of a particular array so that one, a few, several, but less than all, of the light emitting lines emit light. Alternatively, voltage may be applied to all light emitting lines of one or both arrays so that all the light emitting lines of one or both arrays emit light at the same time. Methods for making the light emitting devices

[0043] The methods for making the disclosed light emitting devices involve forming a first array of light emitting lines over a substrate and forming a second array of light emitting lines over the first array. The composition and characteristics of the light emitting lines, the substrate, and the resulting light emitting devices may be any of those described above. The first array and the second array may be formed by a process comprising coating a stamp with a light emitting solution and contacting the substrate with the coated stamp to provide the first array and the second array. In such a process, the stamp may include a heat shrunk thermoplastic substrate and a film of metal disposed over the surface of the heat- shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features. These stamps are further described below. [0044] As noted above, the disclosed stamps include metallic films comprising a microstructure characterized by wrinkle-like features. By "microstructure" it is meant a structure comprising features on the micrometer scale. However, the microstructure may also include features on the nanometer scale. FIGs. 2A and 2B show images of a heat- shrunk thermoplastic substrates coated with wrinkled metallic surfaces. As shown in these images, the wrinkle-like features are further characterized as folds in the metallic film, each fold having substantially rounded, smooth edges. Thus, the types of wrinkled metallic films shown in FIG. 2 may be referred to as a metallic films having folded, wrinkle-like features. As shown in FIG. 2, the wrinkles are oriented substantially parallel to one another across the surface of the substrate. Although each of the wrinkles are approximately aligned with one another, many of the wrinkles are not perfectly straight so that the wrinkles are not perfectly parallel to one another.

[0045] The dimensions of the wrinkle-like features of the metallic film may vary. In some embodiments, the average height of the wrinkle-like features ranges from about 2 nm to about 100 nm. This includes average heights of about 10 nm, 25 nm, 50 nm, 75 nm, etc. By height, it is meant the distance between a low point on the top surface of the metallic film (i.e., a valley in the wrinkled metallic film or a flat region on the metallic film) to a high point on the top surface of the metallic film (i.e., the peak of a folded wrinkle). An average height may be obtained by averaging the heights of a plurality of wrinkles of the wrinkled metallic surface. In other embodiments, the average width of a wrinkle ranges from about 100 nm to about 10 μm. This includes average widths of about 500 nm, about 1 μm, about 2 μm, and about 5 μm. Other average widths are possible. An average width may be obtained similar to the average height described above. In other embodiments, the average spacing of the wrinkle-like features ranges from about to 100 nm to about 3 μm. This includes average spacings of about 300 nm, 600 nm, 1 μm, 2 μm, etc. By spacing, it is meant the distance between the high point on one wrinkle (i.e., the peak of a folded wrinkle) and the high point on another wrinkle. An average spacing may be obtained similar to the average height described above.

[0046] The base of the stamp is made from a thermoplastic material. The term "thermoplastic material" encompasses those plastic materials that shrink upon heating. The shrinking can be uniform, without distortion or non-uniform, as further discussed below. A "Shrinky-Dink" is a commercial thermoplastic which is used a children's toy. Suitable thermoplastic materials include, but are not limited to one or more high molecular weight polymers such as acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon. In some embodiments, the substrate comprises polystyrene. Polystyrene, as well as a number of other thermoplastic materials, is flexible, durable, lightweight, and inexpensive, each of which is a desirable characteristic for a stamp.

[0047] In addition, the directionality of the wrinkles is controlled by grooving the substrate prior to metal deposition. Alternatively, the directionality of the wrinkles can be controlled by monodirectional shrinking using a uni-axially or bi-axially biasing thermoplastic receptive material. In one embodiment, the method to prepare a textured metal surface further comprises first heating a heat sensitive thermoplastic receptive material under conditions that reduce the size of the thermoplastic receptive material bi- axially by at least about 60%, followed by uni-axially biasing the thermoplastic receptive material to shrink along one axis or dimension prior to depositing a metal onto a heat sensitive thermoplastic receptive material, and reducing the material by at least about 60%, thereby preparing a textured metal surface.

[0048] In the disclosed stamps, the thermoplastic substrates are heat shrunk. By "heat shrunk" it is meant that the thermoplastic substrate has been exposed to heat, which reduces the size of the substrate as compared to the size of the substrate prior to exposure to heat. The size of the heat shrunk substrate may be reduced by a variety of amounts as compared to the size of the substrate prior to exposure to heat. In some embodiments, the size of the heat shrunk substrate is about 60%, 70%, 80%, or 90% the size of the substrate prior to exposure to heat. Heat shrinking is further described below. [0049] The composition of the metallic film may vary. A variety of metals may be used, including, but not limited to gold, titanium, silver, copper, a dielectric substance, a paste or any other suitable metal or combination thereof. Examples of suitable dielectric substances include metal oxides, such as aluminum oxide, titanium dioxide and silicon dioxide. Examples of suitable pastes include conductive pastes such as silver pastes. In some embodiments, the metallic film includes a single layer of any of these metals or combinations of these metals. In other embodiments, the metallic film may include two or more adjacent layers of metal. By way of example only, a multi-layer metallic film may include a first layer of metal disposed over the substrate and a second layer of metal disposed over the first layer of metal. Other layers of metal may disposed over each previous layer of metal. The composition of the first layer of metal may be the same or different from the composition of the second layer of metal.

[0050] Similarly, the thickness of the metallic film may vary. By "thickness of the metallic film," it is meant the thickness of the film prior to the heating of the substrate which leads to the formation of the wrinkle-like features, as further described below. The thickness of the metallic film may vary from about 1 nm to about 100 nm. This includes embodiments in which the thickness is about 10 nm, 25 nm, 50 nm, 75 nm, etc. For multilayer films, the thickness of each layer of metal may be the same or different.

[0051] As described above, the disclosed stamps have raised features in the form of wrinkles. Light emitting solutions (which may comprise any of the light emitting polymers or light emitting quantum dots described above) are inked onto these features by dipping (or via another method, e.g., spin casting) the stamp into the light emitting solution. Contacting the substrate of the light emitting device with the inked stamp provides the array of light emitting lines. The characteristics (i.e., the dimensions and orientations) of the light emitting lines may be controlled by the adjusting the characteristics of the wrinkles on the stamp, as further described below.

Methods for making the stamps [0052] The methods for making the disclosed stamps involve depositing a film of metal over the surface of a thermoplastic substrate and shrinking the coated substrate. Wrinkles form in the metallic film due to the stiffness incompatibility between the metallic film and the thermoplastic substrate. As further described below, the characteristics of the wrinkles may be controlled by the various parameters of the heating process and thickness of the deposited metal film.

[0053] Methods for depositing films of metal over substrates are known. By way of example only, physical vapor deposition (PVD) techniques or chemical vapor deposition (CVD) techniques may be used to deposit metal films of varying thicknesses on substrates. These techniques may also be used to form patterned metallic films, in which metal is deposited in specific regions on a substrate.

[0054] Shrinking of the coated thermoplastic substrates may be accomplished by exposing the coated thermoplastic substrates to heat. A variety of heat sources may be used, including, but not limited to an oven, such as a conventional oven or toaster oven. The temperature of the heating process may vary. In some embodiments, the temperature ranges from about 100⁰C to about 200⁰C. This includes a temperature of about 16O⁰C, although other temperatures are possible. The length of heating may also vary. In some embodiments, the length of heating may be from about 1 minute, 5 minutes, 10 minutes, or even more. Longer heating times increase the amount of shrinkage of the thermoplastic substrate. The ability to achieve wrinkled metallic surfaces using inexpensive substrates (e.g., polystyrene) and heating sources (e.g., toaster ovens) in a matter of minutes provides an ultra-rapid, ultra- low cost method of making stamps. The coated thermoplastic substrates may be uniaxially shrunk. By "uniaxially" shrunk, it is meant that the shrinking of the thermoplastic material is anisotropic. Uniaxially shrinking may be accomplished by constraining a thermoplastic substrate at two edges during the heating process, resulting in shrinking along only one axis of the material.

[0055] Various parameters of the heating process may be adjusted to control the characteristics of the metallic wrinkles. By way of example only, the length of heating, which determines the degree of shrinkage, affects the wrinkle height and wrinkle spacing. As another example, the orientation of the wrinkles may be controlled through uniaxial shrinking. As shown in FIGs. 2A and 2B, uniaxially shrinking leads to the formation of wrinkles that are oriented substantially parallel across the surface of the substrate. Similarly, the thickness of the metallic film affects the characteristics of the metallic wrinkles. The thickness of the metallic film affects the wrinkle spacing and the wrinkle height. [0056] Certain of the wrinkled metallic films and methods of making the films have been described in International Application No. PCT/US2008/083283, which is hereby incorporated by reference in its entirety. The following method is disclosed.

[0057] Metals are deposited onto the shrinkable thermoplastic by either thermal evaporation or sputtering. Pieces of unshrunk plastic are placed in either the sputter coater or evaporator and vacuumed down. Target metal is deposited onto the plastic. The thickness, or height of the deposited metal is dependent on length of processing time. The plastic substrate should be far enough from the source such that the plastic does not heat up during deposition. A wide range of thicknesses, or heights, of deposited metal are accomplished, from about 5 nanometers to about 90 nanometers. [0058] After the metal is deposited on the thermoplastic, it is placed in the oven to shrink by heating (3-5 minutes at 163° Celsius). Upon heating, because of the stiffness incompatibility between the metal and the shrinking thermoplastic, wrinkles form (see Fig. 6A to 6D of PCT/US2008/083283). The spacing between the wrinkles can be controlled by the amount of heating, and hence shrinkage. In addition, the directionality of the wrinkles can be controlled by grooving the substrate prior to metal deposition. Finally, the periodicity of the wrinkle as the wavelength of the wrinkles scale according to the thickness to the 3/4th power. Therefore, tighter wrinkles are achieved by changing the thickness, or height of the metal layer.

Kits [0059] This invention further provides a kit comprising, or alternatively consisting essentially of, or yet further consisting of the materials necessary to perform the methods described above. In one aspect, the kit comprises, or alternatively consists essentially of, or yet further consists of a substrate material (e.g., transparent plastic or transparent glass) and instructions for making the device. In one aspect the kit comprises, or alternatively consists essentially of, or yet further consists of, a thermoplastic material and instructions for carrying out the method. In one aspect, the thermoplastic material is polystyrene. The kit may further comprise metal for forming wrinkles and/or material for creating the first and/or second array(s) of light emitting lines. In a further aspect, the kit contains materials and instructions for making metallic contacts electrically coupled to the one or more light emitting lines of the arrays. In a yet further aspect, the kit comprises methods and instructions to create any one or more of a hole injecting layer, a hole transport layer, a hole blocking layer, an electron transporting layer, or combinations of the above in the device. The kit provides instructions for making and using the apparatus described above and incorporated herein by reference.

[0060] In another aspect, this invention provides a method for assaying or screening for new materials and methods having the same function of the inventions as described herein. In this aspect, the new materials and/or methods are used in the methods as described herein and compared to the performance of the devices of this invention.

[0061] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above.

[0062] It is to be understood that while the invention has been described in conjunction with the above embodiments, that the foregoing description and examples are intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

Claims

WHAT IS CLAIMED IS:

1. A method of making a light emitting device comprising: forming a first array of light emitting lines over a substrate; and forming a second array of light emitting lines over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 μm , and further wherein, the first array and the second array are formed by a process comprising coating a stamp with a light emitting solution; and contacting the substrate with the coated stamp to provide the first array and the second array, wherein the stamp comprises a heat shrunk thermoplastic substrate, and a film of metal disposed over the surface of the heat- shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle-like features.

2. The method of claim 1 , wherein the area is no more than about 50 μm .

3. The method of claim 1, wherein the area is no more than about 10 μm .

4. The method of claim 1 , wherein the area is no more than about 1 μm².

5. The method of any of claims 1 to 4, wherein each of the light emitting lines of the first array are substantially parallel to one another, each of the light emitting lines of the second array are substantially parallel to one another, or both.

6. The method of any of claims 1 to 5, wherein each of the light emitting lines of the first array are separated by a distance of no more than about 2 μm, each of the light emitting lines of the second array are separated by a distance of no more than about 2 μm, or both.

7. The method of any of claims 1 to 6, wherein the light emitting lines of the first array are oriented substantially perpendicular to the light emitting lines of the second array.

8. The method of any of claims 1 to 7, wherein the light emitting lines of the first array, the light emitting lines of the second array, or both comprise a light emitting polymer.

9. The method of any of claims 1 to 8, wherein the light emitting lines of the first array, the light emitting lines of the second array, or both comprise quantum dots.

10. The method of any of claims 1 to 9, wherein the quantum dots comprise CdSe, ZnS, ZnSe, CdTe quantum dots, or combinations thereof.

11. The method of any of claims 1 to 10, wherein the light emitting lines of the first array emit light of a first color and the light emitting lines of the second array emit light of a second color.

12. The method of any of claims 1 to 11, further comprising depositing one or more metallic contacts electrically coupled to one or more light emitting lines of the first array, one or more light emitting lines of the second array, or both.

13. The method of any of claims 1 to 12, wherein the device further comprising depositing any one or more of a hole injecting layer, a hole transport layer, a hole blocking layer, an electron transporting layer, or combinations thereof.

14. The method of any of claims 1 to 13, wherein the substrate comprises transparent plastic or transparent glass.

15. The method of any of claims 1 to 13, wherein the substrate comprises a thermoplastic material.

16. The method of claim 15, wherein the thermoplastic material is one or more of a high molecular weight polymer selected from the group of acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

17. A light emitting device obtainable by the method of any one of claims 1 to 16.

18. A light emitting device comprising: a substrate; a first array of light emitting lines disposed over the substrate; and a second array of light emitting lines disposed over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 μm .

19. The light emitting device of claim 18, wherein the area is no more than about 50 μm².

20. The light emitting device of claim 18, wherein the area is no more than about 10 μm².

21. The light emitting device 18, wherein the area is no more than about 1 μm .

22. The light emitting device of any of claims 18 to 21, wherein each of the light emitting lines of the first array are substantially parallel to one another, each of the light emitting lines of the second array are substantially parallel to one another, or both.

23. The light emitting device of any of claims 18 to 22, wherein each of the light emitting lines of the first array are separated by a distance of no more than about 2 μm, each of the light emitting lines of the second array are separated by a distance of no more than about 2 μm, or both.

24. The light emitting device of any of claims 18 to 23, wherein the light emitting lines of the first array are oriented substantially perpendicular to the light emitting lines of the second array.

25. The light emitting device of any of claims 18 to 24, wherein the light emitting lines of the first array, the light emitting lines of the second array, or both comprise a light emitting polymer.

26. The light emitting device of any of claims 18 to 25, wherein the light emitting lines of the first array, the light emitting lines of the second array, or both comprise quantum dots.

27. The light emitting device of any of claims 18 to 26, wherein the quantum dots comprise CdSe, ZnS, ZnSe, CdTe quantum dots, or combinations thereof.

28. The light emitting device of any of claims 18 to 27, wherein the light emitting lines of the first array emit light of a first color and the light emitting lines of the second array emit light of a second color.

29. The light emitting device of any of claims 18 to 28, further comprising one or more metallic contacts electrically coupled to one or more light emitting lines of the first array, one or more light emitting lines of the second array, or both.

30. The light emitting device of any of claims 18 to 29, wherein the device further comprises a hole injecting layer, a hole transport layer, a hole blocking layer, an electron transporting layer, or combinations thereof.

31. The light emitting device of any of claims 18 to 30, wherein the substrate comprises transparent plastic or transparent glass.

32. The light emitting device of any of claims 18 to 31 , wherein the substrate comprises a thermoplastic material.

33. The light emitting device of claim 32, wherein the thermoplastic material is one or more of a high molecular weight polymer selected from the group of acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal

(POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

34. A light emitting device comprising: a thermoplastic substrate; a first array of light emitting lines disposed over the thermoplastic substrate; and a second array of light emitting lines disposed over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 μm , and further wherein the light emitting lines of the first array and the light emitting lines of the second array each comprise quantum dots.

35. A method of making a light emitting device comprising: forming a first array of light emitting lines over a substrate; and forming a second array of light emitting lines over the first array, wherein one or more light emitting lines of the first array cross one or more light emitting lines of the second array to provide a pixel having an area of no more than 100 μm .

36. The method of claim 35, wherein the wherein the area is no more than about 50 μm .

37. The method of claim 35, wherein the area is no more than about 10 μm².

38. The method of claim 35, wherein the area is no more than about 1 μm .

39. The method of any of claims 35 to 38, wherein the light emitting lines of the first array, the light emitting lines of the second array, or both comprise quantum dots.

40. The method of any of claims 35 to 39, wherein the substrate comprises one or more of a transparent glass, a transparent plastic and a high molecular weight polymers from the group acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene- vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

41. The method of any of claims 35 to 40, wherein the first array and the second array are formed by a process comprising: coating a stamp with a light emitting solution; and contacting the substrate with the coated stamp to provide the first array and the second array, wherein the stamp comprises a heat shrunk thermoplastic substrate, and a film of metal disposed over the surface of the heat-shrunk thermoplastic substrate, wherein the film of metal comprises a microstructure characterized by wrinkle- like features.

42. The method of claim 41 , wherein the wrinkle-like features are folded wrinkle-like features.

43. The method of claim 41 or 42, wherein the wrinkle-like features are oriented substantially parallel across the surface of the heat shrunk thermoplastic substrate.

44. The method of any of claims 41 to 43, wherein the thermoplastic substrate is one or more of a transparent glass, a transparent plastic or a high molecular weight polymers selected from the group of acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

45. The method of any of claims 41 to 44, wherein the film of metal comprises platinum, gold, silver, copper, titanium, a metal oxide, a metal paste or combinations thereof.