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 π-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 (|glum|) values of about 6 × 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 (VT) of 2.6 V, four-fold maxmium-external quantum efficiency (EQEmax) 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 (gEL) values of −2.3 × 10−3 and +3.0 × 10−3. Meanwhile, this study also represents the first thermally activated sensitized fluorescent CP-OLEDs with markedly enhanced efficiencies and intense CPEL.