As shown in FIG. 17 to FIG. 19 and Table 2, the light-emitting element 1 and the comparative light-emitting element 2 exhibited high current efficiency and high external quantum efficiency. In addition, a fall (roll-off) in the current efficiency and the external quantum efficiency of the light-emitting element 1 and the comparative light-emitting element 2 was small even on the high luminance side, which is excellent.
As shown in FIG. 20, the light-emitting element 1 and the comparative light-emitting element 2 emitted green light having electroluminescence spectra with peaks at wavelengths of 519 nm and 513 nm, respectively, and full widths at half maximum of 69 nm. The obtained electroluminescence spectrum reveals that light is emitted from Ir(ppy)3 as the guest material.
<Reliability of Light-Emitting Elements>
Next, driving tests at a constant current of 2 mA were performed on the light-emitting element 1 and the comparative light-emitting element 2. The results are shown in FIG. 21. As shown in FIG. 21, the luminance half-life of the light-emitting element 1 was approximately twice as long as that of the comparative light-emitting element 2. It is because 8Cz-4PCCzBfpm-02 of one embodiment of the present invention has high electrochemical stability by having a carbazole skeleton, which is one of condensed rings, in the 6-, 7-, 8-, or 9-position of a benzofuro[3,2-d]pyrimidine skeleton.
Example 4
