Organic electroluminescent element

#The present invention relates to an organic electroluminescent element.

#Organic electroluminescent elements have attracted attention as a next-generation illumination light source because they enable planar light-emission and enable light emission of any color tone depending on the selection of light-emitting substances, and have been vigorously developed with the aim of practical use. In particular, research and development has been actively conducted especially with regard to technologies for improving color rendering properties, which is regarded as one of problems with inorganic LED lighting, and methods for improving color rendering properties by various design and technological developments of devices have been proposed. However, problems still remain in order to realize sufficient improvement in color rendering properties in comparison with conventional main lighting, that is, fluorescent lamps.

#In JP 2009-224274A (Patent Literature 1), a method is proposed for improving color rendering properties by stacking a blue-region light-emitting layer having the maximum emission wavelength in a wavelength region between 450 nm and 470 nm, a yellow-region light-emitting layer having a maximum emission wavelength in the wavelength region between 550 nm and 570 nm and a red-region light-emitting layer having the maximum emission wavelength in a wavelength region between 600 nm and 620 nm. High color rendering properties in which an average color rendering index (Ra) is 80 or more, can be realized by thus stacking three light-emitting layers whose emission wavelength regions have been appropriately selected, but Ra of a general fluorescent lamp is from 80 to 90, and problems still remain as a method for realizing sufficiently high color rendering properties in comparison with conventional light sources. Furthermore, a method for improving a special color rendering index R9 for red, which is a problem with inorganic LED lighting and is important to general lighting, is not referred to.

#FIG. 1 is a sectional view showing an overview of a layer structure of an organic electroluminescent element,

#FIG. 2 is a graph showing the relation between the maximum emission wavelength of a blue emission spectrum and an average color rendering index Ra of the organic electroluminescent element,

#FIG. 3A is a graph showing the relation between the half width of a second green emission spectrum and an average color rendering index Ra of the organic electroluminescent element,

#Hereinafter, embodiments of the present invention will be described.

#An example of the structure of an organic electroluminescent element according to the present invention is shown in FIG. 1. This organic electroluminescent element is formed by forming a transparent electrode 1 on a surface of a substrate 10, and stacking a first hole transporting layer 11, a blue light-emitting layer 2, a first green light-emitting layer 3, a first electron transporting layer 12, an intermediate layer 9, a second hole transporting layer 13, a red light-emitting layer 4, a second green light-emitting layer 5, a second electron transporting layer 14 and a reflecting electrode 6 on the transparent electrode 1 in this order. A light extracting layer 15 is further formed on an opposite surface of the substrate 10 to the transparent electrode 1. Hereinafter, embodiments will be described using this structure as an example, but this structure is merely an example, and the present invention is not limited to this structure within the intent of the present invention.

#It is preferable that the substrate 10 has optical transparency. The substrate 10 may be colorless and transparent or slightly colored. The substrate 10 may have a frosted glass appearance. Examples of materials for the substrate 10 include transparent glass such as soda-lime glass and alkali-free glass, and plastic such as polyester resin, polyolefin resin, polyamide resin, epoxy resin, and fluorine-based resin. The shape of the substrate 10 may be a film-like shape or a plate-like shape.