Exciplexes in OLEDs: Principles and promises

Blue Iridium (III) Phosphorescent OLEDs with High Brightness Over 10 000 cd m−2 and Ultralow Efficiency Roll‐Off

“…Many efforts have been employed to reduce the efficiency roll-off value through a variety of strategies. For examples, the employment of double emissive layers, [25,26] gradient doping, [27,28] or exciplex host [29][30][31] is studied for improving the injection process and leading to the reduction of the density of triplet excitons, eventually widening the recombination zone and suppressing STA and TTA processes during the operation of the OLEDs. [32,33] Recently, there has been growing reports to support that the use of fluorine atoms or −CF 3 group as the substituents on the cyclometalating ligands as phenylpyridine (C⊥N) and phenylimidazole (C⊥C) derivatives could also lead to an reduced efficiency roll-off values, as depicted in Scheme 1.…”

Exciplex-forming cohost systems with highly twisted hexaphenylbenzene-core donors for high-efficiency orange and red OLEDs

“…> 0.57 eV. 39 However, the −ΔG exciplex of the CzTT : CN-T2T blend was acquired at only 0.38 eV, implying a slower electron transfer process. In addition, the dual emission presented in the CzTT : CN-T2T blend reveals insufficient exciplex formation and therefore is excluded from OLED device application.…”

“…The characteristics of the OLED devices are consistent with the observed PLQYs of blend films with different D : A ratios, implying the EQEs of the exciplex-based OLED devices are governed by the PLQY of the EML. 39 Besides, according to the energy level diagram shown in Fig. S7, † the devices have smooth carrier injection barriers, rendering the charges to directly reach the EML and subsequently recombined at the D/A interface to give the emissive exciton.…”

Cationic Zinc(II) Complexes with Carbazole-Type Counter-Anions: Intracomplex Donor/Acceptor Pairs Affording Exciplexes with Thermally Activated Delayed Fluorescence

“…Because of the close contact between the donor and acceptor, charge transfer occurs from the donor to the acceptor on excited states, leading to the formation of intermolecular charge-transfer excited state (so-called exciplex) within the pair . The formed exciplex can have a very small energy gap (Δ E ST ) between the lowest-lying singlet (S 1 ) and triplet (T 1 ) states, due to the complete spatial separation of the highest occupied molecular orbital (HOMO) (residing on the donor) and the lowest unoccupied molecular orbital (LUMO) (residing on the acceptor). , The small Δ E ST can trigger fast reverse intersystem crossing (RISC) from the nonemissive T 1 to the emissive S 1 states, giving rise to thermally activated delayed fluorescence (TADF). ,− In recent years, donor/acceptor pairs affording exciplexes with a TADF feature have aroused huge research interest for their wide applications in optoelectronic devices, long persistent luminescence, and so on. − …”