Synergistical sensitization of ternary double exciplexes enables high-efficiency solution-processed pure red hyperfluorescent organic light-emitting diodes

Abstract

High-efficiency exciplex-sensitized hyperfluorescent organic light-emitting diodes (OLEDs) require sufficient triplet up-conversion of exciplex sensitizers and efficient energy transfer from exciplex sensitizers to traditional fluorescent dyes. However, incomplete singlet Förster energy transfer often impedes exciplex-sensitized hyperfluorescent OLEDs from concurrently achieving high color purity and high light-emitting efficiency. Here, we propose a synergistically sensitizing strategy of ternary double exciplexes to facilitate efficient Förster energy transfer between exciplex sensitizers and fluorescent dopants and achieve high-efficiency solution-processed red fluorescent OLEDs with high color purity. It is disclosed that in the ternary double exciplexes-sensitized fluorescent system, the high-energy exciplex TPDI:PO-T2T contributes to high up-conversion efficiency of triplet excitons to singlet excitons via reverse intersystem crossing, while the low-energy exciplex TPDI:tBuCzDBA enables more efficient Förster energy transfer of singlet excitons to the fluorescent dopant DBP, ultimately achieving efficient narrowband electroluminescence. By employing the ternary double exciplexes to synergistically sensitize fluorescent DBP, the prepared fluorescent OLEDs achieve a maximum external quantum efficiency of 14.0 %, not only surpassing single exciplex-sensitized fluorescent devices, but also representing the highest value reported for the exciplex-sensitized red fluorescent OLEDs with x chromatic coordinate greater than 0.60. Furthermore, the enhanced Förster energy transfer leads to a narrowband emission from fluorescent DBP with a color coordinate of (0.64, 0.36), approaching the standard red color coordinate of (0.67, 0.33).