C1-Symmetrical [Ir(C^N1)(C^N2)(N^O)]-tris-heteroleptic Ir(iii)-complexes with one strong N^O-ancillary π-donor for efficient all-solution-processed near-infrared (NIR) polymer light-emitting diodes (PLEDs)

Abstract

Among reliable vacuum-deposited or solution-processed NIR-OLEDs/PLEDs doped with NIR-emitting iridium(III)-complexes, high-performance achievement of their all-solution-processed NIR-PLEDs remains a great challenge. In this study, owing to the forceful electronic perturbation achieved by incorporation of the strong π-donating N^O-ancillary ligand Hpbi, its NIR-emitting tris-heteroleptic [Ir(iqbt)(btp)(pbi)] (2) does not exhibit an augmented ³MLCT effect in comparison to the corresponding bis-heteroleptic [Ir(iqbt)₂(pbi)] (1) counterpart. Nonetheless, the transition dipole (TD) effect through k_r ∈ TD² dominates, rendering the k_r and the resulting Φ_PL (0.36; λ_em = 714 nm) of 2 larger than those of 1 (Φ_PL = 0.29; λ_em = 712 nm). Moreover, through electron injection/transport facilitated by the composite cathode Ba/Al instead of LiF/Al, better electroluminescent properties (η^Max_EQE = 3.53 (1) versus 4.24% (2) and negligible (<5%) efficiency roll-off) are realized for their all-solution-processed NIR-PLEDs. This result shows that: (i) both the ³MLCT and TD effects should be simultaneously taken into account in challenging the intrinsic low-efficiency of Ir(III)-complex-based NIR-emitters; (ii) in dependent on electron injection/transport facilitation with one specific composite cathode, high-performance and reliable all-solution-processed NIR-PLEDs especially based on [Ir(C^N¹)(C^N²)(L^X)]-tris-heteroleptic Ir(III)-complexes could desirably be approached.