Solution-Processed Red CPL-OLEDs Enabled by Exciplex-forming Host and Chiral Helicene Dopant

Abstract

A strategy for efficient solution-processed red circularly polarized luminescent organic light-emitting diodes (CPL-OLEDs) has been proposed. Two mCP-derived carbazole materials, Cz2Cz and 2Cz2Cz, were synthesized and utilized as electron donors for exploring exciplex formation with an electron acceptor PO-T2T. The PO-T2T:Cz2Cz (3:7) and PO-T2T:2Cz2Cz (3:7) blends exhibit high photoluminescence quantum yields (PLQYs) of 26–27% and effective thermally activated delayed fluorescence (TADF) behavior, giving the OLED devices with the electroluminescence centered at 506 nm and 503 nm, V_on of 4.8 V and 4.6 V, EQE_max of 6.38% and 7.30%, respectively. The well-overlapped emission of the exciplex-forming blends and the absorption of a newly designed chiral helicene–perylene diimide emitter 3 facilitates efficient Förster resonance energy transfer (FRET) process. Molecule 3 with excellent molecular rigidity exhibits red emission (630 nm) and strong CPL characteristic (|g_lum| ≈ 10^-3) in solution. The incorporation of 3 as a dopant dispersed into the exciplex-forming co-host matrix affords devices with red-emitting CPL-OLEDs with EQE_max of 1.41% and |g_EL| up to 1.1 × 10^-3. These results demonstrate that the synergistic combination of TADF-enabling exciplex-based co-hosts and chiral helicene emitter to achieve CPL-OLEDs is a versatile approach for advanced chiral optoelectronic application.