Studies are being made for increasing the light emission efficiency of an organic electroluminescent device (organic EL device). In particular, various studies have been made for enhancing the light emission efficiency by developing and combining organic layers having various functions constituting the organic electroluminescent device. Among the studies, there are studies relating to an organic electroluminescent device that utilizes energy transfer from the organic layer to the light emitting layer by providing an organic layer for forming excitons.
For example, Patent Document 1 describes an organic electroluminescent device having a light emitting region held between a pair of electrodes, in which the light emitting region has a fluorescent light emitting layer, a phosphorescent light emitting layer, and an exciton forming layer disposed between the fluorescent light emitting layer and the phosphorescent light emitting layer, and describes an example using CBP (4,4′-bis(carbazol-9-yl)biphenyl) as a material of the exciton forming layer. The organic electroluminescent device has an energy barrier interface of the carrier between the fluorescent light emitting layer and the exciton forming layer, and the carrier is accumulated in the barrier interface on the side of the exciton forming layer, thereby forming excitons. Among the excitons thus formed, singlet excitons undergo energy transfer to the fluorescent material of the fluorescent light emitting layer through the Foerster mechanism, and cause fluorescent light emission through excitation of the fluorescent singlet. On the other hand, triplet excitons enter the phosphorescent light emitting layer through energy transfer of the Dexter mechanism, and cause phosphorescent light emission through excitation of the phosphorescent triplet. The formation probability of the excitons formed through the recombination of the carrier is 25% for the singlet excitons and 75% for the triplet excitons, and it is stated that in the organic electroluminescent device, both the singlet excitons and the triplet excitons thus formed can be efficiently made to contribute to the light emission due to the aforementioned constitution.