Thermally activated delayed fluorescence material-sensitized helicene enantiomer-based OLEDs: a new strategy for improving the efficiency of circularly polarized electroluminescence

A new strategy of thermally activated delayed fluorescence (TADF) material-sensitized circularly polarized luminescence (CPL) has been proposed for improving the efficiencies of fluorescent circularly polarized organic light-emitting diodes (OLEDs) (CP-OLEDs). Consequently, a pair of helicene enantiomers, (P)-HAI and (M)-HAI, were synthesized. The helicene enantiomers with the rigid helical pi-skeleton had highly thermal and enantiomeric stabilities, and they also showed excellent photophysical properties, especially, intense mirror-image CPL activities with large luminescence dissymmetry factor (vertical bar g(lum vertical bar)) values of about 6 x 10(-3). Notably, the CP-OLEDs with the helicene enantiomers as emitters and a TADF molecule as sensitizer not only displayed better performance of lower turn-on voltage (V-T) of 2.6 V, four-fold maxmium-external quantum efficiency (EQE(max)) of 5.3%, and lower efficiencies roll-off of 1.9% at 1000 cd m(-2), than those of the devices without TADF sensitizer, but also exhibited intense circularly polarized electroluminescence (CPEL) with the electroluminescence dissymmetry factor (g(EL)) values of -2.3 x 10(-3) and +3.0 x 10(-3). Meanwhile, this study also represents the first thermally activated sensitized fluorescent CP-OLEDs with markedly enhanced efficiencies and intense CPEL.