Organic EL element, organic EL display panel, and organic EL element manufacturing method
An organic EL element including an anode, a cathode, and a light emitting layer between the anode and the cathode. The light emitting layer includes a fluorescent material and a host material. A difference between a lowest unoccupied molecular orbital (LUMO) level of the fluorescent material and a highest occupied molecular orbital (HOMO) level of the fluorescent material is less than or equal to a difference between a LUMO level and a HOMO level of the host material. The LUMO level of the fluorescent material is equal to or higher than the LUMO level of the host material. The HOMO level of the fluorescent material is equal to or higher than the HOMO level of the host material, and a difference in energy level between the HOMO level of the fluorescent material and the HOMO level of the host material is 0.3 eV or less.
1 . An organic electroluminescence (EL) element comprising:
an anode;
a cathode; and
a light emitting layer disposed between the anode and the cathode, wherein
the light emitting layer comprises a fluorescent material and a host material, the host material being an amine compound,
the difference between the lowest unoccupied molecular orbital (LUMO) level of the fluorescent material and the highest occupied molecular orbital (HOMO) level of the fluorescent material is less than or equal to the difference between the LUMO level and the HOMO level of the host material,
the emission intensity of the light-emitting layer at any time/after an application of current is cut off is I(t), and I(t) changes according to the R TTF , in which R TTF is the contribution of triplet-triplet fusion (TTF) to the emission efficiency,
the LUMO level of the fluorescent material is equal to or higher than the LUMO level of the host material,
the HOMO level of the fluorescent material is equal to or higher than the HOMO level of the host material, and the difference in energy level between the HOMO level of the fluorescent material and the HOMO level of the host material is 0.3 eV or less,
the R TTF is set to a value exceeding 20% by setting ΔHOMO to a value below 0.3 eV, ΔHOMO is the difference in energy level between the HOMO levels of the fluorescent material and the host material,
the hole mobility of the light emitting layer is higher than the electron mobility of the light emitting layer, and
a distance between the light emission center of the light emitting layer and a cathode-side surface of the light emitting layer is shorter than the distance between the light emission center and the anode-side surface of the light emitting layer, the relationship between the emission intensity I(t) at time t and the RTTF is based on the following equation
1
I
(
t
)
=
1
R
TTF
+
At
in which A is a constant.
2 . The organic EL element of claim 1 , further comprising an electron injection control layer and an intermediate layer between the light emitting layer and the cathode, wherein:
the hole mobility of the light emitting layer is higher than the electron mobility of the light emitting layer,
Eg(eicl) is set to a first threshold or more, Eg(eicl) is the energy gap when injecting electrons from the electron transport layer to the electron injection control layer,
Eg(eml) is set to a second threshold or less, Eg(eml) is the energy gap when injecting electrons from the electron injection control layer to the light emitting layer,
the first threshold is a threshold for accumulating holes near the interface between the light emitting layer and the electron injection control layer, and
the second threshold is a threshold for making the recombination region of electrons and holes in the light emitting layer near the interface between the light emitting layer and the electron injection control layer.
3 . The organic EL element of claim 1 , wherein
energy of singlet excitons of the host material is equal to or higher than the energy of singlet excitons of the fluorescent material,
a hole injection layer and a hole transport layer are provided between the anode and the light-emitting layer, and
ΔHOMO adjusts the trapping of holes injected from the hole transport layer to the light-emitting layer by the fluorescent material.
4 . The organic EL element of claim 1 , further comprising:
an electron injection control layer and an intermediate layer between the light emitting layer and the cathode, wherein
the electron injection control layer is in contact with both the light emitting layer and the intermediate layer,
the intermediate layer has at least one of a property of facilitating electron injection and a property of facilitating electron transport,
the electron injection control layer comprises a functional material,
the intermediate layer comprises a functional material, and
the LUMO level of the functional material contained in the electron injection control layer is 0.1 eV or more higher than the LUMO level of the functional material contained in the intermediate layer and is higher than the LUMO level of the host material.
5 . An organic electroluminescence (EL) panel comprising a plurality of the organic EL element of claim 1 disposed on a substrate.
6 . An organic electroluminescence (EL) element manufacturing method comprising:
forming a first electrode on a substrate;
forming a light emitting layer above the first electrode; and
forming a second electrode above the light emitting layer, wherein
in the forming of the light emitting layer, a fluorescent material and a host material are used as materials of the light emitting layer, the host material is an amine compound, and the fluorescent material and the host material are selected such that the difference between the lowest unoccupied molecular orbital (LUMO) level of the fluorescent material and the highest occupied molecular orbital (HOMO) level of the fluorescent material is less than or equal to the difference between the LUMO level and the HOMO level of the host material,
an emission intensity of the light-emitting layer at any time t after an application of current is cut off is I(t), and I(t) changes according to the R TTF , in which R TTF is the contribution of triplet-triplet fusion (TTF) to the emission efficiency,
the LUMO level of the fluorescent material is equal to or higher than the LUMO level of the host material,
the HOMO level of the fluorescent material is equal to or higher than the HOMO level of the host material,
the R TTF is set to a value exceeding 20% by setting ΔHOMO to a value below 0.3 eV, ΔHOMO is the difference in energy level between the HOMO levels of the fluorescent material and the host material,
the hole mobility of the light emitting layer is higher than the electron mobility of the light emitting layer, and
a distance between the light emission center of the light emitting layer and a cathode-side surface of the light emitting layer is shorter than the distance between the light emission center and the anode-side surface of the light emitting layer, the relationship between the emission intensity I(t) at time t and the RTTF is based on the following equation,
1
I
(
t
)
=
1
R
TTF
+
At
in which A is a constant.