Organic Electroluminescent Devices
An electroluminescent device and luminescent technology, which is applied in the direction of organic semiconductor devices, electric solid devices, electrical components, etc., can solve the problem of low TTF ratio and achieve high efficiency
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no. 1 approach
[0055] The present invention utilizes the TTF phenomenon. The TTF phenomenon will be described below.
[0056] Holes and electrons respectively injected from the anode and the cathode recombine in the light emitting layer to generate excitons. As for the spin state, it is well known that singlet excitons account for 25% and triplet excitons account for 75%. In conventional known fluorescent devices, light is emitted when 25% of the singlet excitons are relaxed to the ground state. The remaining 75% of the triplet excitons return to the ground state without emitting light through the thermal inactivation process. Therefore, the theoretical limit value of the internal quantum efficiency of conventional fluorescent devices is considered to be 25%.
[0057] The behavior of triplet excitons generated in organic matter has been theoretically studied. According to S.M.Bachilo et al. (J.Phys.Chem.A, 104, 7711 (2000)), if higher-order excitons such as quintet excitons quickly retur...
no. 2 approach
[0493] The device of the invention may have a tandem device structure in which at least two organic layer units comprising a light-emitting layer are arranged. An intermediate layer (also referred to as an intermediate conductive layer, charge generation layer or CGL) is inserted between the two light emitting layers. Electron transport regions may be provided in individual cells. At least one light-emitting layer is a fluorescent light-emitting layer, and the unit comprising the light-emitting layer satisfies the above requirements. Specific examples of the stacking order are as follows. The light-emitting layer below may be a multilayer stack of light-emitting layers or one organic layer unit including a charge blocking layer as described in the third embodiment below.
[0494] Anode / fluorescence emitting layer / intermediate layer / fluorescence emitting layer / blocking layer / electron injection layer / cathode.
[0495] Anode / fluorescence emitting layer / blocking layer / electron ...
no. 3 approach
[0507] In the third embodiment, an anode, a plurality of light emitting layers, an electron transport region including a blocking layer adjacent to one of the light emitting layers and an electron injection layer adjacent to the blocking layer, and a cathode are provided in this order. The charge blocking layer is disposed between two light emitting layers of the plurality of light emitting layers. The light-emitting layer in contact with the charge blocking layer is a fluorescent light-emitting layer. The fluorescent emitting layer, as well as the blocking layer and the electron injection layer in the electron transport region all meet the above requirements.
[0508] As for the structure of a suitable organic EL device according to the third embodiment, structures disclosed in Japanese Patent No. 4134280, US Patent Publication US2007 / 0273270A1, and International Publication WO2008 / 023623A1 can be used. Specifically, an example of the structure is one in which an anode, a fi...
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