Solution-processed red CPL-OLEDs enabled by an exciplex-forming host and chiral helicene dopant

Abstract

A strategy for the fabrication of 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. 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, endowing OLED devices with electroluminescence centered at 506 nm and 503 nm, V_on of 4.8 V and 4.6 V, and EQE_max of 6.38% and 7.30%, respectively. The well-overlapped emission of the exciplex-forming blends and the absorption of the newly designed chiral helicene–perylene diimide emitter 3 facilitate an efficient Förster resonance energy transfer (FRET) process. Molecule 3 with excellent molecular rigidity exhibits red emission (630 nm) and strong CPL characteristics (|g_lum| ≈ 10⁻³) in solution. The incorporation of 3 as a dopant dispersed in the exciplex-forming co-host matrix affords red-emitting CPL-OLEDs with an EQE_max of 1.41% and |g_EL| of up to 1.1 × 10⁻³. These results demonstrate that the synergistic combination of TADF-enabling exciplex-based co-hosts and chiral helicene emitters to achieve CPL-OLEDs is a versatile approach for advanced chiral optoelectronic applications.