Highly Efficient TADF-OLEDs with Copper(I) Halide Complexes Containing Unsymmetrically Substituted Thiophenyl Triphosphine

Abstract

Highly efficient OLEDs fabricated with thermally activated delayed fluorescent Cu(I) complexes have attracted much attention. How to achieve high quantum efficiency and short decay lifetime remains a challenge. Here, two rigid triphosphine ligands containing two unsymmetrically substituted thiophenyl rings, and six mononuclear copper(I) halide complexes CuX(L1) and CuX(L2) [L1 = (2-PPh2-C4H2S)2(3-PPh), X = I (1), Br (2), Cl (3); L2 = (2-PPh2-5-SiMe3-C4HS)2(3-PPh), X = I (4), Br (5), Cl (6)], were successfully synthesized and characterized on their structures and photophysical properties. At room temperature, complexes 1–6 in powder exhibit intense yellow green to yellow delayed fluorescence (λem = 553–581 nm, τ = 3.8–9.4 μs, Φ = 0.19–0.29 for 1–3; λem = 565–589 nm, τ = 2.2–7.6 μs; Φ = 0.36–0.61 for 4–6). The introduction of two trimethylsilyl groups into two unsymmetrically substituted thiophenyl rings, significantly improves photoluminescence quantum yield (PLQY) and finely tunes the light-emitting color of the complexes. Among them, complex 4 displayed high PLQY of 0.61 and short decay lifetime of 2.2 µs. The radiative decay rate (kr) is 2.8 × 105 s−1, which is comparable with that of Ir(III) complexes. Vacuum deposited organic light-emitting devices that contained complex 4 exhibited yellow light with maximum external quantum efficiency (EQE) of 14.57% and current efficiency of 33.44 cd A−1.