Organic light-emitting diode containing co-hosts forming exciplex, and lighting device and display apparatus including same
Provided are an organic light-emitting diode (“OLED”) including a bottom electrode, a top electrode disposed opposite to the bottom electrode, and an organic layer that is interposed between the bottom electrode and the top electrode and includes a hole-transporting host and an electron-transporting host forming an exciplex and a phosphorescent dopant having a triplet energy which is lower than the triplet energy of the hole-transporting host, the triplet energy of the electron-transporting host, and the triplet energy of the exciplex, and a lighting device and a display apparatus including the OLED. Instead of a phosphorescent dopant, the fluorescent dopant having a singlet energy which is lower than the singlet energy of the exciplex may be also used.
1. An organic light-emitting diode (OLED) comprising:
an anode;
a cathode; and
an organic layer which is disposed between the anode and the cathode,
wherein the organic layer comprises a light emitting layer, a hole transport layer, and an electron transport layer;
wherein the light emitting layer comprises a mixed host comprising a hole-transporting host, and electron-transporting host, and a fluorescent dopant;
wherein the hole-transporting host and the electron-transporting host are mixed together in a single layer;
wherein the hole-transporting host and the electron-transporting host form an exciplex together; where the energy difference between a singlet energy and a triplet energy of the exciplex is less than 0.3 eV;
wherein λ max of photoluminescence of the exciplex is about 450 nm or less; and
wherein the fluorescent dopant has a singlet energy which is lower than the singlet energy of the exciplex.
2. The OLED of claim 1 , wherein the hole-transporting host and the electron-transporting host satisfy the following relational expressions 1 and 2:
(1) Lowest unoccupied molecular orbital (LUMO) energy of the hole-transporting host is greater than LUMO energy of the electron-transporting host by more than 0.2 eV and
(2) Highest occupied molecular orbital (HOMO) energy of the hole-transporting host is greater than HOMO energy of the electron-transporting host by more than 0.2 eV.
3. The OLED of claim 1 , wherein the hole transport layer comprises a hole-transporting material that is the same as the hole-transporting host, and the electron transport layer comprises an electron-transporting material that is the same as the electron-transporting host.
4. The OLED of claim 1 , wherein the hole-transporting host, the electron-transporting host, and the fluorescent dopant are mixed at a molar ratio in the range of 100:30 to 300:1 to 100.
5. The OLED of claim 1 , wherein the hole-transporting host and the electron-transporting host are mixed in a combination selected from TCTA:3TPYMB, TCTA: BmPyPB, and CBP:B3PYMPM.
6. A lighting device comprising the OLED according to claim 1 .
7. A display apparatus comprising the OLED according to claim 1 .