High-Efficiency Organic Light-Emitting Diodes With D₁-A-D₂ Type Red Thermally Activated Delayed Fluorescence

At present, the development of novel high performance red thermally activated delayed fluorescence (TADF) materials still faces great challenges. In this work, the phenoxazin (PXZ) fragment was used as the strong electron donor with molecular rigidity (D₁), the triphenylamine (TPA) fragment was used as the strong electron donor with large steric hindrance (D₂), and the dibenzoa, cphenazine (BP) fragment composed of heterocyclic aromatic hydrocarbon was used as the strong electron acceptor (A). With the three fragments, a new high efficiency red TADF emitter with donor-receptor-donor (D₁-A-D₂) structure, 4, 4'-(3, 6-di (10H-phenoxazin-10-yl) dibenzoa, cphenazine-11, 12-diyl) bis (N, N-diphenylaniline) (2T-BP-2P), was designed. The photophysical, electrochemical and thermal properties of 2T-BP-2P were characterized by ultraviolet-visible (UV-Vis) absorption, photoluminescence (PL), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. At the same time, 2T-BP-2P was characterized and confirmed by nuclear magnetic resonance (NMR) and mass spectrometry (MS) technology. Results showed that 2T-BP-2P had a high photoluminescence quantum yield (Φ_PL) of 78.5% in the 15% mass fraction doped films with 4,4′-bis(N-carbazolyl)-1,1′-biphenyl(CBP) as a host material. The device based on 2T-BP-2P achieved red emission at 614.5 nm, maximum external quantum efficiency (EQE_max) of 12.2%, and the Commission International de l'Eclairage (CIE) coordinate of (0.59, 0.40). What’s more, the lowest turn-on voltage (V_on) was 2.9 eV, and the highest power efficiency (PE) and current efficiency (CE) of the device were 17.37 lm/W and 17.70 cd/A, respectively. The superior performance of this device is at the leading level among the known red-doped TADF-organic light-emitting diodes (OLEDs). A new strategy for the future development of high-performance red-emitting OLEDs is provided.