Triplet Exciton Upconverting Blue Exciplex Host for Deep Blue Phosphors

Abstract A thermally activated delayed fluorescence (TADF)‐type exciplex host employing a novel electron‐transport type (n‐type) type host managing positive polarons and stabilizing excitons was developed to elongate the device lifetime of deep blue phosphorescent organic light‐emitting diodes (PhOLEDs). The bipolar n‐type host was designed to prevent hole leakage and secure hole stability while being stabilized under excitons by introducing a CN‐modified carbazole moiety as a weak donor. The TADF‐type exciplex host‐based blue PhOLEDs showed high (above 20 %) quantum efficiency with a deep blue color coordinate of (0.14, 0.16) and elongated device lifetime. The device operational lifetime of the blue PhOLEDs bearing the TADF‐type exciplex host was extended by more than twice compared to that of the exciplex‐free unipolar host. This work suggested a design concept of the n‐type host to develop the TADF‐type exciplex host for deep blue phosphors to reach a long lifespan in the deep blue PhOLEDs.