Engineering of interconnect position of bicarbazole for high external quantum efficiency in green and blue phosphorescent organic light-emitting diodes

Three bicarbazole based host materials with different interconnect positions between carbazole units, 3,3′-(9,9′-[3,3′-bicarbazole]-9,9′-diyl)dibenzonitrile (3CN33BCz), 3,3′-(9,9′-[3,4′-bicarbazole]-9,9′-diyl)dibenzonitrile (3CN34BCz), and 3,3′-(9,9′-[4,4′-bicarbazole]-9,9′-diyl)dibenzonitrile (3CN44BCz), were developed and their synthesis, material characterization, and device characterization were reported. Two carbazole units were connected via 3,3′-, 3,4′-, and 4,4′-positions to correlate the interconnect positions with photophysical properties and device performances. The linkage via 4,4′-position increased triplet energy and thermal stability of the host materials, while the linkage via 3,3′-position enhanced current density. All bicarbazole host materials showed good device performances and high quantum efficiency above 25% was attained using the biscarbazole derivatives for green and blue phosphorescent organic light-emitting diodes. In particular, the bicarbazole host materials with a linkage via 4-position showed high quantum efficiency above 30% in the green devices.