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A novel electroplex host with two triplet exciton up-converting channels for suppressed triplet exciton triggered degradation mechanisms was developed using an electron transport type host (n-type host) with thermally activated delayed fluorescence (TADF) characteristics to improve the device lifetime of deep blue phosphorescent organic light-emitting diodes (PhOLEDs). The TADF-natured n-type host with high triplet energy was derived from triazine with benzonitrile and carbazole units to induce the TADF characteristics. The TADF natured n-type host generated an electroplex with a hole transport type host and the electroplex-based PhOLEDs revealed an extended device lifetime by more than twice compared to the non-TADF natured n-type host based electroplex host. Transient photoluminescence and electroluminescence analyses revealed that two reverse intersystem crossing (RISC) mechanisms through the n-type TADF host and electroplex host could suppress triplet exciton related degradation and improved the device lifetime. Kinetic modeling of the electroplex supported the RISC mechanisms of the electroplex.

Benzonitirile modified host materials, 3-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-Trz), 3-(4-(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-2DBF-Trz) and 3-(4-(dibenzo[b,d]furan-4-yl)-6-phenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-4DBF-Trz), were synthesized for improved efficiency and lifetime in blue phosphorescent organic light-emitting diodes (PhOLEDs). Triazine and benzonitrile units were introduced commonly to the three host materials for electron transporting properties. The three hosts were applied to mixed host as electron transport type hosts with a hole transport type 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) for blue PhOLEDs. They formed exciplex with mCBP, and the exciplex of CNmSi-2DBF-Trz with mCBP showed high triplet energy above 2.9 eV. As a result, the blue PhOLEDs fabricated with the CNmSi-2DBF-Trz host achieved high EQE over 23% and 650 h lifetime up to 70% of initial luminance at 200 cd/m2 using the exciplex host system with mCBP.