DIPz-TPTRZ Exciplex Films: Dual-Role Emitters and Hosts for Stable OLEDs with High-Efficiency and Reduced Efficiency Roll-Off

Exciplex, as one of the important categories of thermally activated delayed fluorescence (TADF), has long been hindered from widespread application due to the lack of stable exciplex-based organic light-emitting diodes (OLEDs). Here, we introduce stable donor molecules to improve exciplex-based OLED stability, utilizing components diindolo[3,2,1-<i>de</i>:3',2',1'-<i>kl</i>]phenazine (DIPz) derivatives, <i>N</i>⁵,<i>N</i>¹³-bis(4-(<i>tert</i>-butyl)phenyl)-2,10-dimesityl-<i>N</i>⁵,<i>N</i>¹³-diphenyldiindolo[3,2,1-<i>de</i>:3',2',1'-<i>kl</i>]phenazine-5,13-diamine (BDDPD) as the donor and triazine derivatives, 3-(9-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)dibenzo[<i>b</i>,<i>d</i>]furan-2-yl)-9-phenyl-9<i>H</i>-carbazole (DPTBF-PhCz), 2-(3'-(9,9'-spirobi[fluoren]-2-yl)-[1,1'-biphenyl]-3-yl)-4,6-diphenyl-1,3,5-triazine (Spiro-BDTA), 2,4-diphenyl-6-(3'-(triphenylen-2-yl)-[1,1'-biphenyl]-3-yl)-1,3,5-triazine (DTBTA), as the acceptors. These exciplexes exhibit high photoluminescence quantum yield (PLQY) and reverse intersystem crossing (RISC) rates. As a result, the exciplex-based OLEDs achieve a maximum external quantum efficiency (EQE) of 17.19% while also demonstrating a low efficiency roll-off. Even at a brightness of 1000 cd m^-2, the EQE can still maintain 16.36%. A stable exciplex-based OLED achieves an LT₅₀ of over 1000 h at 1000 cd m^-2, which is one of the best device lifetimes of exciplex-based OLEDs. These exciplexes can not only function as TADF emitters but also act as the host material to sensitize red fluorescent molecules. Red fluorescent OLEDs utilizing developed exciplexes as the host material achieve a high EQE of over 15%, with reduced efficiency roll-off. This research paves the way for a new strategy for the development of efficient and stable exciplex-based OLEDs.