Organic electroluminescence device
An organic EL device includes a pair of electrodes and an organic compound layer between pair of electrodes. The organic compound layer includes an emitting layer including a first material and a second material. The second material is a fluorescent material. Singlet energy EgS(H) of the first material and singlet energy EgS(D) of the second material satisfy a relationship of the following formula (1). The first material satisfies a relationship of the following formula (2) in terms of a difference ΔST(H) between the singlet energy EgS(H) and an energy gap Eg 77K (H) at 77K. EgS ( H )> EgS ( D ) (1) Δ ST ( H )= EgS ( H )− Eg 77K ( H )<0.3 (eV) (2)
1. An organic electroluminescence device comprising a pair of electrodes and an organic compound layer between the pair of electrodes, the organic compound layer comprising an emitting layer comprising a first material and a second material, wherein
the second material is a fluorescent material,
singlet energy EgS(H) of the first material and singlet energy EgS(D) of the second material satisfy a relationship of a formula (1) below, and
the first material satisfies a relationship of a formula (2) below in terms of a difference ΔST(H) between the singlet energy EgS(H) and an energy gap Eg 77K (H) at 77K
EgS ( H )> EgS ( D ) (1)
Δ ST ( H )= EgS ( H )− Eg 77K ( H )<0.3 (eV). (2)
2. The organic electroluminescence device according to claim 1 ,
wherein the organic electroluminescence device exhibits a ratio of the luminous intensity due to delayed fluorescence relative to the total luminous intensity larger than 37.5%.
3. The organic electroluminescence device according to claim 1 ,
wherein the organic electroluminescence device exhibits a residual intensity ratio larger than 36.0% after the elapse of 1 μs after voltage removal in a transitional EL measurement, wherein the residual intensity ratio is a ratio of the luminous intensity due to delayed fluorescence relative to the total luminous intensity after the elapse of 1 μs.
4. The organic electroluminescence device according to claim 1 , wherein a half bandwidth of a photoluminescence spectrum of the first material is 50 nm or more.
5. The organic electroluminescence device according to claim 1 , wherein a half bandwidth of a photoluminescence spectrum of the first material is 75 nm or more.
6. The organic electroluminescence device according to claim 1 , wherein
a difference ΔT between the energy gap Eg 77K (H) at 77K of the first material and an energy gap Eg 77K (D) at 77K of the second material satisfies a relationship of a formula (3) below
Δ T=Eg 77K ( H )− Eg 77K ( D )≧0.6 (eV). (3)