High external quantum efficiency and low efficiency roll-off achieved simultaneously in nondoped pure-blue organic light-emitting diodes based on a hot-exciton fluorescent material

“Hot-exciton” fluorescent materials can efficiently convert triplet excitons into singlet excitons through a path from high-lying triplet excited states (Tn, n > 1) to singlet excited states (Sm, m ≥ 1). The fast reverse intersystem crossing (RISC) process of the hot-exciton channel promotes a high exciton utilization efficiency (EUE) and reduces the efficiency roll-off (ηroll-off) caused by the accumulation of low-lying triplet excitons (T1). Herein, a pure-blue-emitting molecule, PICNAnCz, exhibiting hot-exciton fluorescent emission is proposed. The optimized PICNAnCz-based nondoped organic light-emitting diode (OLED) device achieves a high external quantum efficiency of 9.05% corresponding to a large EUE of 87% and a low ηroll-off of 13%, achieving both high efficiency and a small ηroll-off. The maximum current efficiency and power efficiency of the nondoped device are 9.07 cd A−1 and 5.76 lm W−1, respectively. The nondoped device shows a novel blue electroluminescence (EL) emission with a peak wavelength of 448 nm and Commission Internationale de l’Eclairage coordinates of (0.16, 0.11). These results are among the best reported for hot-exciton blue-emitting materials for nondoped blue fluorescent OLEDs. The excellent EL performance is attributed to the nanosecond-scale RISC process from the high-lying triplet excited state (T2) to the lowest singlet excited state (S1).