Exciton dynamics of an aggregation-induced delayed fluorescence emitter in non-doped OLEDs and its application as host for high-efficiency red phosphorescent OLEDs

Abstract

Aggregation-induced delayed fluorescence (AIDF) materials have great potential in non-doped OLEDs due to their high photoluminescence (PL) quantum efficiency in film, high exciton utilization in the aggregated state and negligible efficiency roll-off at high luminance. However, their efficient mechanism in OLEDs is not yet well understood. Here, the exciton dynamics are used to investigate the electroluminescence (EL) mechanism of an AIDF emitter (4-(10H-phenoxazin-10-yl)phenyl)-(9-phenyl-9H-carbazol-3-yl)methanone (CP-BP-PXZ) in detail. It can be seen that the high efficiency and negligible efficiency roll-off in non-doped OLEDs based on CP-BP-PXZ as the emitter are ascribed to the effective reverse intersystem crossing (RISC) from high level triplet T₂ to singlet S₁ in the aggregated state. Furthermore, CP-BP-PXZ also exhibits excellent properties as a phosphor host due to its good AIDF properties. Thus, high-efficiency red phosphorescent OLEDs with low roll-off efficiency are successfully fabricated based on CP-BP-PXZ as the host. The maximum external quantum efficiency (EQE_max) reaches 23% and is maintained at 21% at a luminance of 1000 cd m⁻².