Exciton Dynamics on the Efficiency Roll-Off of Exciplex-Based OLEDs and Low Efficiency Roll-off Phosphorescence OLEDs Based on Exciplex as Host

Abstract

Exciplexes with thermally activated delayed fluorescence (TADF) characteristics have been well applied to fabricate high performance organic light-emitting diodes (OLEDs). In this work, we proposed the exciton dynamics on the efficiency roll-off properties of OLEDs based on four different exciplexes as emitters, and demonstrated the effect of the relationship between the photoluminescence (PL) quantum efficiency and exciton decay rates on the electroluminescence (EL) performance of the exciplex-based OLEDs. Through simulation, the diffusion lengths of singlet and triplet excitons were calculated based on the annihilation rate constants. Moreover, high efficiency and low efficiency roll-off blue, green, yellow and red phosphorescence OLEDs (PHOLEDs) were fabricated by employing the optimized exciplexes as the host of four different color phosphors, fully elucidating the importance of matching the energy levels of exciplexes with the phosphor guests. This work is very helpful to better understanding the exciton dynamics on exciplexes and the fabrication of high efficiency and low efficiency roll-off PHOLEDs based on exciplexes as host.