Source: https://patents.com/us-20180019427.html
Timestamp: 2019-11-15 22:47:13
Document Index: 682870163

Matched Legal Cases: ['Application No. 61', 'Application No. 60', 'Application No. 60', 'Application No. 61', 'Application No. 60', 'Application No. 60']

Application # 2018/0019427. DEVICE INCLUDING QUANTUM DOTS - Patents.com
United States Patent Application 20180019427
KAZLAS; PETER T. ; et al. January 18, 2018
Inventors: KAZLAS; PETER T.; (SUDBURY, MA) ; ZHOU; ZHAOQUN; (BRIDGEWATER, NJ) ; NIU; YUHUA; (SOUTHBOROUGH, MA) ; KIM; SANG-JIN; (SANTA CLARA, CA) ; MASHFORD; BENJAMIN S.; (ESSENDON, AU)
Family ID: 1000002900524
Appl. No.: 15/667314
15356563 Nov 19, 2016 9755172
13441394 Apr 6, 2012 9525148
12896856 Oct 2, 2010 9793505
PCT/US2010/051867
Current CPC Class: H01L 2251/303 20130101; H01L 2251/556 20130101; H01L 51/502 20130101; H01L 51/5004 20130101; H01L 51/5221 20130101; H01L 2251/552 20130101; H01L 51/5056 20130101; H01L 51/5072 20130101; H01L 51/5088 20130101; H01L 51/5092 20130101; H01L 2251/301 20130101; H01L 51/56 20130101
International Class: H01L 51/50 20060101 H01L051/50; H01L 51/56 20060101 H01L051/56; H01L 51/52 20060101 H01L051/52
[0003] This invention was made with Government support under Advanced Technology Program Award No. 70NANB7H7056 awarded by NIST and with Government support under Contract No. 2004*H838109*000 awarded by the Central Intelligence Agency. The United States has certain rights in the invention.
1. A device including a first electrode and a second electrode, a layer comprising, quantum dots disposed between the first electrode and the second electrode, a first layer disposed between the first electrode and the layer comprising quantum dots, and a first interfacial layer disposed at the interface between a surface of the layer comprising quantum dots and the first layer, wherein the first interfacial layer is a distinct layer, wherein the first interfacial layer comprises a material non-quenching to quantum dot emission.
2. A device in accordance with claim 1 wherein the first layer comprises a material capable of injecting and transporting charge.
3. A device in accordance with claim 2 further comprising a second layer comprising a material capable of transporting charge disposed over the layer comprising quantum dots.
4. A device in accordance with claim 3 further comprising a second interfacial layer disposed between the layer comprising quantum dots and the second layer.
5. A device in accordance with claim 3 wherein the second layer comprises a material capable of injecting and transporting charge.
6. A device in accordance with claim 3 wherein the first layer comprises one or more inorganic materials.
7. A device in accordance with claim 3 wherein the second layer comprises one or more organic materials.
26. A device in accordance with claim 1 wherein be first interfacial layer comprises an inorganic material.
27. A device in accordance with claim 1 wherein the first interfacial layer comprises an organic material.
28. A device in accordance with claim 1 wherein the first interfacial layer fills voids that may exist between quantum dots.
29. A device in accordance with claim 1 wherein the first interfacial layer protects quantum dots from charge quenching sites in a contiguous device layer.
30. A device in accordance with claim 1 wherein the first interfacial layer comprises a surfactant.
31. A device in accordance with claim 1 wherein the first interfacial layer comprises a silicon-containing coupling agent.
32. A device in accordance with claim 1 wherein the first interfacial layer comprises a metal oxide.
33. A device in accordance with claim 1 wherein the first interfacial layer comprises a metal oxide including an alkali metal or alkaline earth metal dopant.
34. A device in accordance with claim 1 wherein the first interfacial layer comprises an organic small molecule material.
36. A device in accordance with claim 1 wherein the first interfacial layer comprises a material that is non-crystallizing.
37. A device in accordance with claim 1 wherein the first interfacial layer comprises material with a glass transition temperature (Tg) greater than 150.degree. C.
38. A device in accordance with claim 1 wherein the first interfacial layer composes a spiro compound.
39. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting nanoparticles having a bandgap that is the same or similar to the bandgap of quantum dots included in the layer comprising quantum dots.
40. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting nanoparticles having a bandgap that is higher than the bandgap of quantum dots included in the layer comprising quantum dots.
41. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting semiconductor nanoparticles that have been chemically treated to give them intrinsic semiconductor properties.
42. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting semiconductor nanoparticles that have been chemically treated to give them n-type (electron transporting) semiconductor properties.
43. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting semiconductor nanoparticles that have been chemically treated to give them p-type (hole transporting) semiconductor properties.
44. A device in accordance with claim 1 wherein the first interfacial layer comprises non-light-emitting nanoparticles that have been chemically treated to include a chemical linker capable of attaching to the layer comprising quantum dots.
45. A device in accordance with claim 1 wherein the first interfacial layer comprises organic small molecules having a dipole moment that modifies the work function of the first layer.
46. A device in accordance with claim 1 wherein the first interfacial layer comprises organic small molecules that chemically stabilizes the surface of the first layer.
47. A device in accordance with claim 1 wherein the first interfacial layer comprises an inorganic material that chemically stabilizes the surface of the first layer.
48. A device in accordance with claim 1 wherein the first interfacial layer comprises an adhesion promoting moiety.
49. A device in accordance with claim 1 wherein the first interfacial layer comprises a bipolar transport material.
50-100. (canceled)
[0001] This application is a continuation of U.S. patent application Ser. No. 15/356,563 filed 19 Nov. 2016, which is a continuation of U.S. patent application Ser. No. 13/441,394 filed 6 Apr. 2012 (now U.S. Pat. No. 9,525,148), which is a continuation of commonly owned International Application No. PCT/US2010/051867 filed 7 Oct. 2010, which was published in the English language as PCT Publication No. WO 2011/044391 A1 on 14 Apr. 2011, which International Application claims priority to U.S. Application No. 61/249,588 filed 7 Oct. 2009. Each of the foregoing is hereby incorporated herein by reference in its entirety.
[0028] One example of a technique for forming an interfacial layer comprising a surfactant is a spin-coating technique. In certain of such embodiments, for example, the surfactant can be diluted with a volatilizable solvent (typically organic (e.g., hexane, etc.), spun onto the surface to be coated, and dried (e.g., baking in air at 100-150.degree. C.). In embodiments that may include an interfacial layer comprising a surfactant, it may be desirable to apply the surfactant in the thinnest possible thickness to minimize interference of electrical conductivity between the electron transport layer and the quantum dots.
[0036] In certain embodiments, an interfacial layer comprises a solution processable material. Solution processable materials are desirable and can be preferred for use in fabricating devices.
[0038] An interfacial layer can comprise a material that is non-crystallizing. For example, crystallizing of the material in the interfacial layer during device fabrication and device operation can be undesirable.
[0039] An interfacial layer can comprise a material with a glass transition temperature (Tg) greater than 150.degree. C.
[0109] In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and the Work function of the Cathode is less than 0.5 eV. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and the Work function of the Cathode is less than 0.3 eV. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and the Work function of the Cathode is less than 0.2 eV.
[0110] In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and E.sub.conduction band edge of the material capable of transporting & injecting electrons is less than 0.5 eV. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and E.sub.conduction band edge of material capable of transporting & injecting electrons is less than 0.3 eV. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and E.sub.conduction band edge of material capable of transporting & injecting electrons is less than 0.2 eV.
[0111] In certain embodiments, the absolute value of the difference between E.sub.HOMO of the quantum dots and the E.sub.VALENCE band edge of the material capable of transporting and injecting electrons is greater than about 1 eV. In certain embodiments, the absolute value of the difference between E.sub.HOMO of the quantum dots and the E.sub.VALENCE band edge of the material capable of transporting and injecting electrons is greater than about 0.5 eV. In certain embodiments, the absolute value of the difference between E.sub.HOMO of the quantum dots and the E.sub.VALENCE band edge of the material capable of transporting and injecting electrons is greater than about 0.3 eV.
[0113] In certain embodiments, the device can have an initial turn-on voltage that is not greater than 1240/.lamda., wherein .lamda. represents the wavelength (nm) of light emitted by the emissive layer.
[0127] In certain embodiments of the light emitting devices taught herein, the device has an initial turn-on voltage that is not greater than 1240/.lamda., wherein .lamda. represents the wavelength (nm) of light emitted by the emissive layer.
[0179] The cathode 6 can be formed on the substrate (not shown). In certain embodiments, a cathode can comprise, ITO, aluminum, silver, gold, etc. The cathode preferably comprises a material with a work function chosen with regard to the quantum dots included in the device. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and the work function of the cathode is less than about 0.5 eV. In certain embodiments the absolute value of the difference between E.sub.LUMO of the quantum dots and the work function of the cathode is less than about 0.3 eV, and preferably less than about 0.2 eV. E.sub.LUMO of the quantum dots represents the energy level of the lowest unoccupied molecular orbital (LUMO) of the quantum dot. For example, a cathode comprising indium tin oxide (ITO) can be preferred for use with an emissive material including quantum dots comprising a CdSe core/CdZnSe shell.
[0181] The layer comprising a material capable of transporting electrons 5 preferably comprises an inorganic material. Preferably the material capable of transporting electrons also is capable of injecting electrons. In certain embodiments, the inorganic material included in the layer capable or transporting and injection electrons comprises an inorganic semiconductor material. Preferred inorganic semiconductor materials include those having a band gap that is greater than the emission energy of the emissive material. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and E.sub.conduction band edge of material capable of transporting and injecting electrons, is less than about 0.5 eV. In certain embodiments, the absolute value of the difference between E.sub.LUMO of the quantum dots and E.sub.conduction band edge of the material capable of transporting and injecting electrons, is less than about 0.3 eV, and preferably less than about 0.2 eV E.sub.LUMO of the quantum dots represents the energy level of the lowest unoccupied molecular orbital (LUMO) of the quantum dots; E.sub.of the conduction band edge of the material capable of transporting and injecting electrons represents the energy level of the conduction band edge of the material capable of transporting and injecting electrons.
[0205] In certain embodiments in which an interfacial layer comprising a surfactant is included between an electron transport material and a layer including quantum dots, the surfactant is applied with the thinnest possible thickness to minimize interference of electrical conductivity between the electron transport layer and the quantum dots.
[0206] One example of a technique for forming an interfacial layer comprising a surfactant is a spin-coating technique. In certain of such embodiments, for example, the surfactant can be diluted with a volatilizable solvent (typically organic (e.g., hexane, etc.), spun onto the surface to be coated, and dried (e.g., baking in air at 100-150.degree. C.).
[0209] In certain embodiments, an interfacial layer comprises an organic small molecule material (e.g., but not limited to, OXD-7, LG101, S-2NPB, and other small molecule materials typically used in organic light emitting devices and/or quantum dot light emitting devices that include small molecule charge transport materials).
[0214] In certain embodiments, the interfacial layer comprises a solution processable material. Solution processable materials are desirable and can be preferred for use in fabricating devices.
[0217] In certain embodiments, an interfacial layer comprises material with a glass transition temperature (Tg) greater than 150.degree. C.
[0221] An interfacial layer included in light emitting devices taught herein can preferably comprise non-light-emitting nanoparticles having a bandgap that is higher than the bandgap of quantum dots included in the emissive layer. Examples of such nanoparticles include, but are not limited to, nanoparticles comprising ZnO, TiO.sub.2, ZnS, CuAlO.sub.2, WO.sub.3, ZrO.sub.2, or associated alloys.
[0247] Preferably, the quantum dots include one or more ligands attached to the surface thereof. In certain embodiments, a ligand can include an alkyl (e.g., C.sub.1-C.sub.20) species. In certain embodiments, an alkyl species can be straight-chain, branched, or cyclic. In certain embodiments, an alkyl species can be substituted or unsubstituted. In certain embodiments, an alkyl species can include a hetero-atom in the chain or cyclic species. In certain embodiments, a ligand can include an aromatic species. In certain embodiments, an aromatic species can be substituted or unsubstituted. In certain embodiments, an aromatic species can include a hetero-atom. Additional information concerning ligands is provided herein and in various of the below-listed documents which are incorporated herein by reference.
[0252] The particle size distribution of quantum dots can be further refined by size selective precipitation with a poor solvent for the quantum dots, such as methanol/butanol as described in U.S. Pat. No. 6,322,901. For example, semiconductor nanocrystals can be dispersed in a solution of 10% butanol in hexane. Methanol can be added dropwise to this stirring solution until opalescence persists. Separation of supernatant and flocculate by centrifugation produces a precipitate enriched with the largest crystallites in the sample. This procedure can be repeated until no further sharpening of the optical absorption spectrum is noted. Size-selective precipitation can be carried out in a variety of solvent/nonsolvent pairs, including pyridine/hexane and chloroform/methanol. The size-selected quantum dot population preferably has no more than a 15% rms deviation from mean diameter, more preferably 10% rms deviation or less, and most preferably 5% rms deviation or less.
(Y--).sub.k-n--(X)-(-L).sub.n
wherein k is 2, 3 4, or 5, and n is 1, 2, 3, 4 or 5 such that k-n is not less than zero; X is O, O--S, O--Se, O--N, O--P, O--As, S, S.dbd.O, SO.sub.2, Se, Se.dbd.O, N, N.dbd.O, P, P.dbd.O, C.dbd.OAs, or As.dbd.O; each of Y and L, independently, is H, OH, aryl, heteroaryl, or a straight or branched C2-18 hydrocarbon chain optionally containing at least one double bond, at least one triple bond, or at least one double bond and one triple bond. The hydrocarbon chain can be optionally substituted with one or more C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, hydroxyl, halo, amino, nitro, cyano, C3-5 cycloalkyl, 3-5 membered heterocycloalkyl, aryl, heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4 alkylcarbonyl, or formyl. The hydrocarbon chain can also be optionally interrupted by --O--, --S--, --N(Ra)--, --N(Ra)--C(O)--O--, --O--C(O)--N(Ra)--, --N(Ra)--C(O)--N(Rb)--, --O--C(O)--O--, --P(Ra)--, or --P(O)(Ra)--. Each of Ra and Rb, independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy, hydroxylalkyl, hydroxyl, or haloalkyl. An aryl group is a substituted or unsubstituted cyclic aromatic group. Examples include phenyl, benzyl, naphthyl, tolyl, anthracyl, nitrophenyl, or halophenyl. A heteroaryl group is an aryl group with one or more heteroatoms in the ring, for instance furyl, pyridyl, pyrrolyl, phenanthryl.
[0264] The narrow FWHM of semiconductor nanocrystals can result in saturated color emission. The broadly tunable, saturated color emission over the entire visible spectrum of a single material system is unmatched by any class of organic chromophores (see, for example, Dabbousi et al., J. Phys. Chem. 101, 9463 (1997), which is incorporated by reference in its entirety). A monodisperse population of semiconductor nanocrystals will emit light spanning a narrow range of wavelengths. A pattern including more than one size of semiconductor nanocrystal can emit light in more than one narrow range of wavelengths. The color of emitted light perceived by a viewer can be controlled by selecting appropriate combinations of semiconductor nanocrystal sizes and materials. The degeneracy of the band edge energy levels of semiconductor nanocrystals facilitates capture and radiative recombination of all possible excitons.
[0265] Transmission electron microscopy (TEM) can provide information about the size, shape, and distribution of the semiconductor nanocrystal population. Powder X-ray diffraction (XRD) patterns can provide the most complete information regarding the type and quality of the crystal structure of the semiconductor nanocrystals. Estimates of size are also possible since particle diameter is inversely related, via the X-ray coherence length, to the peak width. For example, the diameter of the semiconductor nanocrystal can be measured directly by transmission electron microscopy or estimated from X-ray diffraction data using, for example, the Scherrer equation. It also can be estimated from the UV/Vis absorption spectrum.
[0266] An emissive material can be deposited by spin-casting, screen-printing, inkjet printing, gravure printing, roll coating, drop-casting, Langmuir-Blodgett techniques, contact printing or other techniques known or readily identified by one skilled in the relevant art.
[0268] In certain preferred embodiments, after the emissive material is deposited, it is exposed to small molecules and/or light prior to forming another device layer thereover. Examples of small molecules include a molecule with a molecular weight of less than 100 a.m.u., e.g., water. Small polar molecules can be preferred. A small molecule can be in the form of a gas, a liquid dispersed in carrier gas (e.g., a mist, vapor, spray, etc.), a liquid, and/or a mixture thereof. Mixtures including small molecules having different compositions can also be used. A small molecule can include a lone electron pair. Such exposure to small molecules and/or light can be carried out in air or in the absence or substantial absence of oxygen. Exposure to small molecules and/or light can be carried out at a temperature in a range from about 20.degree. to about 80.degree. C. When carried out in light, the light can include a peak emission wavelength that can excite at least a portion of the quantum dots. For example, light can include a peak emission wavelength in a range from about 365 nm to about 480 nm. Light can be provided by a light source with peak wavelength at a desired wavelength. Light flux can be in a range from about 10 to about 100 mW/cm.sup.2. See also, for example, U.S. Application Nos. 61/377,242 of Peter T. Kazlas, et al., entitled "Device Including Quantum Dots", filed 26 Aug. 2010, and 61/377,148 of Peter T. Kazlas, et al., entitled "Quantum Dot Light Emitting Device", filed 26 Aug. 2010, each of the foregoing being hereby incorporated herein by reference in its entirety.
[0269] Examples of hole transport materials include organic material and inorganic materials. An example of an organic material that can be included in a hole transport layer includes an organic chromophore. The organic chromophore can include a phenyl amine, such as, for example, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD). Other hole transport layer can include (N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-spiro (spiro-TPD), 4-4'-N,N'-dicarbazolyl-biphenyl (CBP), 4,4-. bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD), etc., a polyaniline, a polypyrrole, a poly(phenylene vinylene), copper phthalocyanine, an aromatic tertiary amine or polynuclear aromatic tertiary amine, a 4,4'-bis(p-carbazolyl)-1,1'-biphenyl compound, N,N,N',N'-tetraarylbenzidine, poly(3,4-ethylenedioxythiophene) (PEDOT)/polystyrene para-sulfonate (PSS) derivatives, poly-N-vinylcarbazole derivatives, polyphenylenevinylene derivatives, polyparaphenylene derivatives, polymethacrylate derivatives, poly(9,9-octylfluorene) derivatives, poly(spiro-fluorene) derivatives, N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB), tris(3-methylphenylphenylamino)-triphenylamine (m-MTDATA), and poly(9,9'-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine (TFB), and spiro-NPB.
[0271] In certain embodiments of the inventions described herein, a hole transport layer can comprise an inorganic material. Examples of inorganic materials include, for example, inorganic semiconductor materials capable of transporting holes. The inorganic material can be amorphous or polycrystalline Examples of such inorganic materials and other information related to fabrication of inorganic hole transport materials that may be helpful are disclosed in International Application No. PCT/US2006/005184, filed 15 Feb. 2006, for "Light Emitting Device Including Semiconductor Nanocrystals, which published as WO 2006/088877 on 26 Aug. 2006, the disclosure of which is hereby incorporated herein by reference in its entirety.
[0273] Organic hole transport materials may be deposited by known methods such as a vacuum vapor deposition method, a sputtering method, a dip-coating method, a spin-coating method, a casting method, a bar-coating method, a roll-coating method, and other film deposition methods. Preferably, organic layers are deposited under ultra-high vacuum (e.g., .ltoreq.10.sup.-8 torr), high vacuum (e.g., from about 10.sup.-8 torr to about 10.sup.-5 torr), or low vacuum conditions (e.g., from about 10.sup.-5 torr to about 10.sup.-3 torr).
[0276] Device 10 can further include a hole-injection material. The hole-injection material may comprise a separate hole injection material or may comprise an upper portion of the hole transport layer that has been doped, preferably p-type doped. The hole-injection material can be inorganic or organic. Examples of organic hole injection materials include, but are not limited to, LG-101 (see, for example, paragraph (0024) of EP 1 843 411 A1) and other HIL materials available from LG Chem, LTD. Other organic hole injection materials can be used. Examples of p-type dopants include, but are not limited to, stable, acceptor-type organic molecular material, which can lead to an increased hole conductivity in the doped layer, in comparison with a non-doped layer. In certain embodiments, a dopant comprising an organic molecular material can have a high molecular mass, such as, for example, at least 300 amu. Examples of dopants include, without limitation, F.sub.4-TCNQ, FeCl.sub.3, etc. Examples of doped organic materials for use as a hole injection material include, but are not limited to, an evaporated hole transport material comprising, e.g., 4, 4', 4''-tris (diphenylamino)triphenylamine (TDATA) that is doped with tetrafluoro-tetracyano-quinodimethane (F.sub.4-TCNQ); p-doped phthalocyanine (e.g., zinc-phthalocyanine (ZnPc) doped with F.sub.4-TCNQ (at, for instance, a molar doping ratio of approximately 1:30); N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'biphenyl-4,4''diamine (alpha-NPD) doped with F.sub.4-TCNQ. See J. Blochwitz, et al., "Interface Electronic Structure Of Organic Semiconductors With Controlled Doping Levels", Organic Electronics 2 (2001) 97-104; R. Schmechel, 48, Internationales Wissenschaftliches Kolloquium, Technische Universtaat Ilmenau, 22-25 Sep. 2003; C. Chan et al., "Contact Potential Difference Measurements Of Doped Organic Molecular Thin Films", J. Vac. Sci. Technol. A 22(4), July/August 2004. The disclosures of the foregoing papers are hereby incorporated herein by reference in their entireties. See also, Examples of p-type doped inorganic hole transport materials are described in U.S. Patent Application No. 60/653,094 entitled "Light Emitting Device Including Semiconductor Nanocrystals, filed 16 Feb. 2005, which is hereby incorporated herein by reference in its entirety. Examples of p-type doped organic hole transport materials are described in U.S. Provisional Patent Application No. 60/795,420 of Beatty et al, for "Device Including Semiconductor Nanocrystals And A Layer Including A Doped Organic Material And Methods", filed 27 Apr. 2006, which is hereby incorporated herein by reference in its entirety.
[0283] In certain embodiments, a device can further include a passivation or other protective layer that can be used to protect the device from the environment. For example, a protective glass layer can be included to encapsulate the device. Optionally a desiccant or other moisture absorptive material can be included in the device before it is sealed, e.g., with an epoxy, such as a UV curable epoxy. Other desiccants or moisture absorptive materials can be used.
[0292] Quantum dots included in the emissive layer can include those described elsewhere herein.
[0293] Examples of interfacial layers include those described elsewhere herein. Optionally, a second interfacial layer can be included on the side of the emissive layer opposite the first interfacial layer. Preferably, the first and second interfacial layer are distinct layers.
[0294] In certain embodiments, different conductivities can be accomplished, for example, by changing the carrier mobility and/or charge density of the material.
[0295] In certain embodiments including an inorganic material comprising a metal oxide, for example, conduction properties of layers comprising a metal oxide are highly dependent on the concentration of oxygen in the layer structure since vacancies are the main mode of carrier conduction. For example, in certain embodiments, to control the oxygen concentration in sputter deposited layers (e.g., made by magnetron RF sputter deposition) two properties of the deposition can be altered. The power of deposition can be varied, increasing and decreasing the amount of oxygen that is incorporated in the layer. The powers and resulting conductivities are highly dependent on the material and the sputter system used. More oxygen can also be incorporated into the layer by adding oxygen to the sputter chamber gas environment which is often dominated by noble gases like Argon. Both the power and oxygen partial pressure can be used or customized to produce the desired layered metal oxide structure. Lowering the RF power during deposition can increase the conductivity of the layer, reducing the parasitic resistance of the layer. To deposit a low conductivity layer, oxygen is incorporated into the deposition ambient to place a thin insulating surface on the layer formed.
[0296] Other information and techniques described herein and incorporated by reference can also be useful with this aspect of the present invention.
[0297] In certain embodiments of the present invention, there is provided a light emitting device taught herein, wherein light emission from the light emissive material occurs at a bias voltage across the device that is less than the energy in electron-Volts of the bandgap of the emissive material. In certain embodiments, the light emitting device includes an emissive material comprising quantum dots.
[0298] In certain embodiments of the present invention, there is provided a light emitting device taught herein, wherein the device has an initial turn-on voltage that is not greater than 1240/.lamda., wherein .lamda. represents the wavelength (nm) of light emitted by the emissive layer.
[0299] A light-emitting device in accordance with the invention can be used to make a light-emitting device including red-emitting, green-emitting, and/or blue-emitting quantum dots. Other color light-emitting quantum dots can be included, alone or in combination with one or more other different quantum dots. In certain embodiments, separate layers of one or more different quantum dots may be desirable. In certain embodiments, a layer can include a mixture of two or more different quantum dots.
[0300] Light-emitting devices in accordance with various embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, a sign, lamps and various solid state lighting devices.
[0301] In certain embodiments, a device taught herein can comprise a photodetector device including a layer comprising quantum dots selected based upon absorption properties. The layer comprising quantum dots is included between a pair of electrodes and an interfacial layer is disposed on at least one surface of the quantum dot containing layer. When included in a photodetector, quantum dots are engineered to produce a predetermined electrical response upon absorption of a particular wavelength, typically in the IR or MIR region of the spectrum. Examples of photodetector devices including quantum dots (e.g., semiconductor nanocrystals) are described in "A Quantum Dot Heterojunction Photodetector" by Alexi Cosmos Arango, Submitted to the Department of Electrical Engineering and Computer Science, in partial fulfillment of the requirements for the degree of Masters of Science in Computer Science and Engineering at the Massachusetts Institute of Technology, February 2005, the disclosure of which is hereby incorporated herein by reference in its entirety.
[0302] Other materials, techniques, methods, applications, and information that may be useful with the present invention are described in: International Application No. PCT/US2007/008873, filed Apr. 9, 2007, of Coe-Sullivan et al., for "Composition Including Material, Methods Of Depositing Material, Articles Including Same And Systems For Depositing Material"; International Application No. PCT/US2007/003411, filed Feb. 8, 2007, of Beatty, et al., for "Device Including Semiconductor Nanocrystals And A Layer Including A Doped Organic Material And Methods"; International Application No. PCT/US2007/008721, filed Apr. 9, 2007, of Cox, et al., for "Methods Of Depositing Nanomaterial & Methods Of Making A Device"; International Application No. PCT/US2007/24320, filed Nov. 21, 2007, of Clough, et al., for "Nanocrystals Including A Group IIIa Element And A Group Va Element, Method, Composition, Device And Other Products"; International Application No. PCT/US2007/24305, filed Nov. 21, 2007, of Breen, et al., for "Blue Light Emitting Semiconductor Nanocrystal And Compositions And Devices Including Same"; International Application No. PCT/US2007/013152, filed Jun. 4, 2007, of Coe-Sullivan, et al., for "Light-Emitting Devices And Displays With Improved Performance"; International Application No. PCT/US2007/24310, filed Nov. 21, 2007, of Kazlas, et al., for "Light-Emitting Devices And Displays With Improved Performance"; International Application No. PCT/US2007/003677, filed Feb. 14, 2007, of Bulovic, et al., for "Solid State Lighting Devices Including Semiconductor Nanocrystals & Methods", U.S. Patent Application No. 61/016,227, filed 21 Dec. 2007, of Coe-Sullivan et al., for "Compositions, Optical Component, System Including an Optical Component, and Devices", U.S. Patent Application No. 60/949,306, filed 12 Jul. 2007, of Linton, et al., for "Compositions, Methods For Depositing Nanomaterial, Methods For Fabricating A Device, And Methods For Fabricating An Array Of Devices", U.S. Patent Application No. 60/992,598, filed 5 Dec. 2007, and International Application No. PCT/US2009/002123, of Zhou, et al. for "Light Emitting Device Including Quantum Dots", filed 3 Apr. 2009. The disclosures of each of the foregoing listed patent documents are hereby incorporated herein by reference in their entireties.
[0303] As used herein, the singular forms "a", "an" and "the" include plural unless the context clearly dictates otherwise. Thus, for example, reference to an emissive material includes reference to one or more of such materials.
[0304] As used herein, "top" and "bottom" are relative positional terms, based upon a location from a reference point. More particularly, "top" means furthest away from the substrate, while "bottom" means closest to the substrate. For example, for a light-emitting device including two electrodes, the bottom electrode is the electrode closest to the substrate, and is generally the first electrode fabricated; the top electrode is the electrode that is more remote from the substrate, on the top side of the light-emitting material. The bottom electrode has two surfaces, a bottom surface closest to the substrate, and a top surface further away from the substrate. Where, e.g., a first layer is described as disposed or deposited "over" a second layer, the first layer is disposed further away from substrate. There may be layers between the first and second layer, unless it is otherwise specified. For example, a cathode may be described as "disposed over" an anode, even though there are various organic and/or inorganic layers in between.
[0305] The entire contents of all patent publications and other publications cited in this disclosure are hereby incorporated herein by reference in their entirety. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.
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