Abstract: A light-emitting device with high emission efficiency, reliability, and color purity is to be provided. The light-emitting device includes a first electrode, a second electrode, and an organic compound layer. The organic compound layer is between the first electrode and the second electrode and includes a light-emitting layer. The light-emitting layer includes a first substance and a second substance. The second substance causes light emission from a doublet excited state. The doublet excited level of the second substance is lower than the singlet excited level of the first substance and is higher than the triplet excited level of the first substance. The second substance emits light.

Abstract: A highly efficient light-emitting device is provided. The light-emitting device includes a light-emitting layer between a first electrode and a second electrode. The light-emitting layer includes at least a light-emitting substance and a first substance, the half width of an emission spectrum of the light-emitting substance is 0.35 eV or less, the luminescence lifetime of delayed fluorescence caused by photoexcitation of the first substance is shorter at a first temperature than at a second temperature, the first temperature is lower than the second temperature, and the first temperature and the second temperature are each higher than or equal to 10 K and lower than or equal to 300 K.

Abstract: A light-emitting device with favorable carrier balance is provided. The light-emitting device includes a light-emitting layer between a first electrode and a second electrode. The light-emitting layer includes at least a first substance and a light-emitting substance, the first substance includes an organic compound having one or more of a carbazole ring, an aromatic amine skeleton, and a ?-electron deficient heteroaromatic ring, a luminescence lifetime of delayed fluorescence caused by photoexcitation of the light-emitting substance is shorter at a first temperature than at a second temperature, the first temperature is lower than the second temperature, and the first temperature and the second temperature are each higher than or equal to 10 K and lower than or equal to 300 K.

Abstract: A light-emitting device with high emission efficiency is provided. The light-emitting device includes an anode, a cathode, and an EL layer positioned between the anode and the cathode. The EL layer includes a light-emitting layer and an electron-transport layer; the light-emitting layer includes a light-emitting material; the electron-transport layer includes an organic compound having an electron-transport property and a metal complex of an alkali metal; the ordinary refractive index of the organic compound having an electron-transport property in a peak wavelength of light emitted from the light-emitting material is greater than or equal to 1.50 and less than or equal to 1.75; and the ordinary refractive index of the metal complex of an alkali metal in the peak wavelength of the light emitted from the light-emitting material is greater than or equal to 1.45 and less than or equal to 1.70.

Abstract: A multicolor light-emitting element that utilizes fluorescence and phosphorescence and is advantageous for practical application is provided. The light-emitting element has a stacked-layer structure of a first light-emitting layer containing a host material and a fluorescent substance and a second light-emitting layer containing two kinds of organic compounds and a substance that can convert triplet excitation energy into luminescence. Note that light emitted from the first light-emitting layer has an emission peak on the shorter wavelength side than light emitted from the second light-emitting layer.

Abstract: Provided is a light-emitting element with high external quantum efficiency, or a light-emitting element with a long lifetime. The light-emitting element includes, between a pair of electrodes, a light-emitting layer including a guest material and a host material, in which an emission spectrum of the host material overlaps with an absorption spectrum of the guest material, and phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material. By using the overlap between the emission spectrum of the host material and the absorption spectrum of the guest material, the energy smoothly transfers from the host material to the guest material, so that the energy transfer efficiency of the light-emitting element is high. Accordingly, a light-emitting element with high external quantum efficiency can be achieved.

Abstract: Emission efficiency of a light-emitting element is improved. The light-emitting element has a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a first light-emitting layer and a second light-emitting layer. The first light-emitting layer includes a fluorescent material and a host material. The second light-emitting layer includes a phosphorescent material, a first organic compound, and a second organic compound. An emission spectrum of the second light-emitting layer has a peak in a yellow wavelength region. The first organic compound and the second organic compound form an exciplex.

Abstract: A light-emitting device with high outcoupling efficiency is provided. In the light-emitting device including a light-emitting layer between a pair of electrodes, a low refractive index layer containing an organic compound and an inorganic compound is provided between the light-emitting layer and an anode or between the light-emitting layer and a cathode, and the low refractive index layer has a refractive index of less than or equal to 1.80 at a wavelength of light extracted from the light-emitting layer.

Abstract: A triarylamine derivative represented by a general formula (G1) given below is provided. Note that in the formula, Ar represents either a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenyl group; ? represents a substituted or unsubstituted naphthyl group; ? represents either hydrogen or a substituted or unsubstituted naphthyl group; n and m each independently represent 1 or 2; and R1 to R8 each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, or a phenyl group.

Abstract: A novel organic compound is to be provided. In other words, a novel organic compound effective in improving element characteristics is to be provided. The organic compound is represented by General Formula (G1) shown below. In General Formula (G1) above, at least one or two of A1 to A4 represent nitrogen, and the others represent carbon. At least one or two of A5 to A8 represent nitrogen, and the others represent carbon. In addition, B1 and B2 each independently represent hydrogen, an alkyl group having 1 to 6 carbon atoms, or a cyano group. In addition, Htuni1 and Htuni2 each independently represent a hole-transport skeleton.

Abstract: A novel organic compound is provided. A novel organic compound having a carrier-transport property is provided. A novel organic compound having a hole-transport property is provided. An organic compound having a low refractive index is provided. An organic compound having a low refractive index and a carrier-transport property is provided. An organic compound having a low refractive index and a hole-transport property is provided. An organic compound represented by the following general formula (G1) is provided.

Abstract: A reliable light-emitting element with low driving voltage is provided. The light-emitting element includes an electron-injection layer between a cathode and a light-emitting layer. The electron-injection layer is a mixed film of a transition metal and an organic compound having an unshared electron pair. An atom of the transition metal and the organic compound form SOMO.

Abstract: A novel light-emitting device that is highly convenient, useful, or reliable is provided. The light-emitting device includes a first electrode, a second electrode, and a first layer. The first layer is positioned between the first electrode and the second electrode. The first layer includes a light-emitting material, a first organic compound, and a first material. The light-emitting material has a function of emitting fluorescent light. The absorption spectrum of the light-emitting material has the longest-wavelength edge at a first wavelength. The first organic compound has a function of converting triplet excitation energy into light emission. The spectrum of the emitted light has the shortest-wavelength edge at a second wavelength. The second wavelength is positioned at a wavelength shorter than the first wavelength. The first organic compound includes a first substituent R1. The first substituent R1 is any of an alkyl group, a substituted or unsubstituted cycloalkyl group, and a trialkylsilyl group.

Abstract: A light-emitting element having high emission efficiency is provided. The light-emitting element includes a first organic compound, a second organic compound, and a third organic compound. The first organic compound has a function of converting triplet excitation energy into light emission. The second organic compound is preferably a TADF material. The third organic compound is a fluorescent compound. Light emitted from the light-emitting element is obtained from the third organic compound. Triplet excitation energy in a light-emitting layer is transferred to the third organic compound by reverse intersystem crossing caused by the second organic compound or through the first organic compound.

Abstract: A novel light-emitting device with a microcavity structure which can improve the emission efficiency compared to the conventional one is provided. In a light-emitting device with a microcavity structure that emits light in a near-infrared range, reflectance of one or both of a first electrode (reflective electrode) and a second electrode (semi-transmissive and semi-reflective electrode) with respect to light in a near-infrared range (e.g., light with a wavelength of 850 nm) is higher than the reflectance thereof with respect to light in a visible light range (greater than or equal to 400 nm and less than 750 nm).

Abstract: A light-emitting element with high emission efficiency and high reliability is provided. The light-emitting element includes a host material and a guest material in a light-emitting layer. The host material has a function of converting triplet excitation energy into light emission and the guest material emits fluorescence. The molecular structure of the guest material is a structure including a luminophore and protecting groups, and five or more protecting groups are included in one molecule of the guest material. The introduction of the protecting groups into the molecule inhibits energy transfer of triplet excitation energy by the Dexter mechanism from the host material to the guest material. As the protecting group, an alkyl group or a branched-chain alkyl group is used.

Abstract: A novel light-emitting device that is highly convenient, useful, or reliable is provided. The light-emitting device includes an anode over a cathode with an EL layer sandwiched therebetween. The EL layer includes at least a light-emitting layer and an oxidation-resistant layer over the light-emitting layer. The EL layer has a side surface. The light-emitting device includes a block layer in contact with a top surface and the side surface of the EL layer. The cathode is in contact with the side surface of the EL layer with the block layer therebetween. The block layer includes a heterocyclic compound. In the light-emitting device with the above structure, the oxidation-resistant layer may include any one or a plurality of oxides of metals belonging to Group 4 to Group 8 of the periodic table and an organic compound having an electron-withdrawing group.

Abstract: A light-emitting device with high emission efficiency and reliability is provided. The light-emitting device includes a fluorescent light-emitting layer and a phosphorescent light-emitting layer. A host material used in the fluorescent light-emitting layer has a function of converting triplet excitation energy into light emission and a guest material used in the fluorescent light-emitting layer emits fluorescence. The guest material has a molecular structure including a luminophore and a protecting group, and one molecule of the guest material includes five or more protecting groups. The introduction of the protecting groups into the molecule inhibits transfer of triplet excitation energy from the host material to the guest material by the Dexter mechanism. An alkyl group or a branched-chain alkyl group is used as the protecting group.

Abstract: A novel compound is provided. The novel compound is represented by General Formula (G1). In General Formula (G1), A represents a substituted or unsubstituted condensed aromatic ring having 10 to 30 carbon atoms or a substituted or unsubstituted condensed heteroaromatic ring having 10 to 30 carbon atoms, and R1 represents a substituted or unsubstituted aryl group having 6 to 25 carbon atoms. Each of Y1 and Y2 independently represents a cycloalkyl group having a bridge structure and having 7 to 10 carbon atoms.

Abstract: A contact includes a first metal member that includes a first tube section including a first cavity portion therein, and a plurality of first eaves portions extending from a side wall of the first tube section toward a center axis side of the first tube section, one of the plurality of first eaves portions being longer than the other first eaves portions and forming a first contact portion adapted to make contact with a first external part, a second metal member that includes a second tube section including a second cavity portion therein and being in electrical continuity with a second contact portion adapted to make contact with a second external part, and a spring extending from the first cavity portion to the second cavity portion and being accommodated in the cavity portions.