Organic light-emitting diode containing co-hosts forming exciplex, and lighting device and display apparatus including same
An organic light-emitting diode (“OLED”) includes 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
a light emitting layer which is disposed between the anode and the cathode,
wherein the light emitting layer comprises,
a hole-transporting host and an electron-transporting host which form an exciplex together; wherein the hole-transporting host and the electron-transporting host are mixed together in a single layer; 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,
wherein λ max of photoluminescence of the exciplex is about 450 nm or less.
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 energy difference between a singlet energy and a triplet energy of the exciplex is less than 0.3 eV.
4. The OLED of claim 1 , further comprising a hole transport layer between the anode and the light emitting layer, and an electron transport layer between the light emitting layer and the cathode.
5. The OLED of claim 4 , 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.
6. The OLED of claim 1 , wherein the hole-transporting host, the electron-transporting host, and the phosphorescent dopant are mixed at a molar ratio in the range of 100:(30 to 300):(1 to 100).
7. 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.
8. A lighting device comprising the OLED according to claim 1 .
9. A display apparatus comprising the OLED according to claim 1 .