C2-, C3- spirobifluorene fused carbazole modified triazine as an electron transport type host of exciplex

Abstract In this work, we report a novel spirobifluorene carbazole (SBFCbz) donor developed by fusion of carbazole with 9,9'-spirobi[fluorene] (SBF) unit. The newly synthesized SBFCbz donor combined with a diphenyl triazine acceptor to offer an 5'-(4,6-diphenyl-1,3,5-triazin-2-yl)-5'H-spiro[fluorene-9,11'-indeno[1,2-b]carbazole] (SBFTrz) host which played a role of an n-type host. An exciplex host of SBFTrz: 9-([1,1'-biphenyl]-4-yl)-9'-phenyl-9H,9'H-3,3'-bicarbazole (BPBPCz) was developed by combining it with a p-type BPBPCz host. The developed exciplex host showed triplet energy of 2.59 eV, making it a suitable host for the green and red phosphorescent organic light-emitting diodes (PhOLEDs). The PhOLEDs fabricated using the exciplex host system offered excellent charge balance in the emitting layer, which resulted in above 20% external quantum efficiency (EQE) and resistance to the efficiency roll-off at high luminance. The green and red PhOLEDs developed showed the maximum EQE/EQE at 1,000 cd/m2 of 22.0/21.7% and 26.2/23.2%, respectively. Besides, the SBFTrz: BPBPCz exciplex host-based green and red devices showed three- and five-fold enhancement, respectively, in the operational lifetime compared to their corresponding SBFTrz single host devices. Thus, the above results confirmed the suitability of the SBFTrz: BPBPCz exciplex as a host to develop PhOLEDs with high efficiency, improved stability at high luminance, and a long operational lifetime.