Since organic electroluminescent elements (which may hereinafter also be referred to as “elements” or “organic EL elements”) are capable of high-luminance light emitting using low voltage driving, they have been actively researched and developed. The organic electroluminescent elements have a pair of electrodes and an organic layer between the pair of electrodes, and utilize, for light emitting, energy of the exciton generated as a result of recombination of the electron injected from the cathode and the hole injected from the anode in the organic layer.
In recent years, by using phosphorescence emitting materials, organic electroluminescent elements are being enhanced in efficiency. For practical use, however, improvements are required in terms of durability and other properties.
On the contrary, an organic electroluminescent element is known using, as a host material of the light emitting layer, a compound having a structure obtained from triphenylamine by allowing the phenyl groups therein to be connected together to undergo ring fusion and thereby forming a carbazole ring.
Patent Document 1 describes an organic electroluminescent element in which a compound of a structure obtained by allowing two or three phenyl groups in triphenylamine to be connected together to undergo ring fusion is used as a host material of the light emitting layer, which is combined with a phosphorescence emitting material, and it can be seen from the examples in this document that the element is superior in driving voltage, luminous efficiency and durability.
Patent Document 2 describes a compound of a structure obtained by allowing two phenyl groups in triphenylamine to be connected to each other to undergo ring fusion. It is described in the document that, by using the compound as a host material of the light emitting layer, it is possible to provide an organic electroluminescent element with a good luminous efficiency and a low driving voltage.
Patent Document 3 describes an organic electroluminescent element in which a compound of a structure obtained by allowing two or three phenyl groups in triphenylamine to be connected together to undergo ring fusion is used as a host material of the light emitting layer, which is combined with a phosphorescence emitting material. It can be seen from the examples in this document that the element is superior in driving voltage, luminous efficiency and durability.
On the other hand, it is known that when driving an organic electroluminescent element, the driving is accompanied by increase in the driving voltage. The increase in the driving voltage associated with the driving is assumed to be caused by partial formation of a quencher, formation of a fine crystal, and the like, and actually has not been able to be avoided up to now. However, it is desirable to suppress the increase in the driving voltage as much as possible.