More than 25,000 h device lifetime in blue phosphorescent organic light-emitting diodes via fast triplet up-conversion of n-type hosts with sub μs triplet exciton lifetime

A stable blue phosphorescent organic light-emitting diode exhibiting the device lifetime of 25,000h was realized by developing new n-type host material. The device lifetime was improved by fast triplet up-conversion in n-type host which has sub μs exciton lifetime. [Display omitted] •Thermally activated delayed fluorescence type host with less than microsecond exciton lifetime.•Device lifetime longer than 25,000 h in the blue phosphorescent organic light-emitting diodes.•High efficiency of over 20% and long device lifetime using a mixed host. Understanding and retardation of materials degradation phenomena in blue phosphorescent organic-light emitting diodes (PhOLEDs) are crucial to replace a fluorescent device with an efficient phosphorescent device in practical applications. Among the organic functional materials in the blue PhOLEDs, the host in the emitting layer is the most populated and fragile region in view of its density of states since singlet, triplet excitons, and polarons are continuously accumulated and consumed during operation. In this work, we presented novel n-type hosts which have thermally activated delayed fluorescence (TADF) features without loss of triplet energy even in the p-n mixed host structure. Both high triplet energy of mixed host and triplet up-conversion of a new n-type host within sub μs range allowed to demonstrate highly efficient and operationally stable blue PhOLEDs. Introducing 3,3-di(9H-carbazol-9-yl)biphenyl and 3-[bis(9H-carbazol-9-yl)-1,3,5-triazin-2-yl]-5-(triphenylsilyl)benzonitrile as a mixed host, blue PhOLEDs exhibited maximum external quantum efficiency of 20.9%, color coordinate of (0.16, 0.29), and device lifetime of 13,573 h at 100 cd m−2, which was 4.2 times longer than that of state of the art blue device. Furthermore, the optimized blue PhOLEDs demonstrated device lifetime longer than 25,000 h, which is one of the longest device lifetimes of blue PhOLEDs without any sensitization or outcoupling enhancement. This result indicated that triplet exciton recycling via TADF mechanism in the n-type host is one of the effective approaches to enhance the operational stability of blue PhOLEDs.