High Triplet Energy Hosts for Blue Organic Light‐Emitting Diodes

Blue organic light-emitting diodes (OLEDs) have been a bottleneck for OLEDs lighting and flexible displays. Improving the operational lifetimes and simultaneously decreasing efficiency roll-off while maintaining high quantum efficiency is currently a challenge in the scientific community and industry. Optimizing the fabrication process of devices and developing stable and efficient luminescence and transporting materials and developing host materials with high triplet energy is an effective way to overcome this obstacle. On the one hand, the host material can disperse the blue emitters to reduce the possibility of exciton annihilation. On the other hand, it can adjust the carrier transport, exciton formation, and energy transfer in the device. In recent years, many efforts have been undertaken for the design, synthesis, and applications of the novel host. A systematic summary and comments on the recent advances of high triplet energy hosts for blue OLEDs are provided here, which specifically include bipolar transport hosts, single thermally activated delayed fluorescence (TADF) hosts, TADF assistant hosts, exciplex hosts, exciplex free type mixed hosts, and electroplex hosts. Moreover, future prospects for host for high performance blue OLEDs are also proposed.