Delayed fluorescence material and organic electroluminescence device

1. An organic electroluminescence device using in a light-emitting layer having a thickness of 20 nm or more an exciplex of an acceptor compound and a donor compound that satisfies the conditions represented by the following formulae (1) to (4):

T 1 A −S 1 >0.4 eV  (1)

T 1 D −S 1 ≧0.2 eV  (2)

|LUMO A |>2.0 eV  (3)

|HOMO D |≦5.3 eV  (4)

wherein T 1 A represents the excited triplet energy defined by the peak wavelength on the short wavelength side in the phosphorescence spectrum of the acceptor compound; T 1 D represents the excited triplet energy defined by the peak wavelength on the short wavelength side in the phosphorescence spectrum of the donor compound; S 1 represents the excited singlet energy of the exciplex defined by the peak wavelength of the exciplex light emission observed in the light-emitting layer; LUMO A represents the energy level of LUMO (lowest unoccupied molecular orbital) of the acceptor compound; and HOMO D represents the energy level of HOMO (highest occupied molecular orbital) of the donor compound.

2. The organic electroluminescence device according to claim 1 , which is so designed that the light-emitting layer is laminated between a layer containing the acceptor compound and a layer containing the donor compound.

3. The device of claim 1 wherein the light-emitting layer consists of the acceptor compound and the donor compound.

4. The organic electroluminescence device according to claim 1 , wherein the light-emitting layer exists when no voltage is applied to the device.

5. The organic electroluminescence device according to claim 1 , wherein the light-emitting layer has a thickness of from 20 nm to 80 nm.