Bicarbazole Derived High Triplet Energy P‐type Host for Blue Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes

ABSTRACT In this study, we developed new p‐type host materials based on a 9,9'‐diphenyl‐9 H ,9' H ‐3,3'‐bicarbazole (BPCz) core by introducing bulky blocking groups at the 2‐position of the BPCz core to control the intermolecular distance between host molecules. This structural modification induces steric hindrance, which suppresses intermolecular interactions and enables the material to maintain a high triplet energy. Two blocking groups, tetraphenylsilane and 9‐phenyl‐9 H ‐carbazole (phenylcarbazole), are introduced into the BPCz backbone structure. The bulky blocking groups enable a high triplet energy of 2.74 eV in a solid film for triplet exciton harvesting of blue emitters. The device using a host with an ortho ‐connected phenylcarbazole on the BPCz core exhibits excellent device performance in blue thermally activated delayed fluorescence organic light‐emitting diodes, achieving a low driving voltage of 5.0 V, a maximum external quantum efficiency of 28.6%, and minimized efficiency roll‐off. This work first demonstrates that the BPCz can be used as a core structure of a high triplet energy host for blue thermally activated delayed fluorescence organic light‐emitting diodes.