1. Field of the Invention
The present invention relates to a semiconductor device, a display device, a light-emitting device, a lighting device, or a fabrication method thereof. One embodiment of the present invention particularly relates to a method for fabricating a light-emitting element and to the light-emitting element.
2. Description of the Related Art
A light-emitting element having a structure in which a light-emitting layer including an organic compound that is a light-emitting substance is provided between a pair of electrodes has attracted attention as a next-generation flat panel display in terms of characteristics such as being thin and light in weight, high speed response, and direct current low voltage driving. A display device including this light-emitting element is superior in contrast and image quality, and has a wide viewing angle.
The above-described light-emitting element is broadly classified into an inorganic EL element using an inorganic compound and an organic EL element using an organic compound. For example, in fabrication of an organic EL element, an organic compound has a major effect on characteristics of the organic EL element. Many kinds of organic compounds having a variety of characteristics have been synthesized.
However, in the case where an organic compound containing an impurity such as a solvent used in its synthesis is employed in a light-emitting element, the impurity considerably affects the characteristics of the light-emitting element. In other words, the characteristics (e.g., drive voltage, emission efficiency, and lifetime) of the light-emitting element are influenced significantly by the purity of the organic compound used in fabrication of the light-emitting element.
A material with a reduced amount of impurity, which is subjected to purification by sublimation, is generally used as an organic compound for a light-emitting element. The purification by sublimation can remove a solvent remaining after synthesis or a small amount of impurity (see, for example, Patent Document 1). However, in some cases, even when organic compounds subjected to the sublimation purification are used in light-emitting elements, the characteristics of the light-emitting elements may vary.
Thus, in addition to development of a method for synthesizing a high-purity organic compound, development of a method for fabricating a light-emitting element containing a high-purity organic compound is eagerly anticipated to obtain a light-emitting element having excellent characteristics.