Bimetallic Nanocluster-Based Light-Emitting Diodes With High External Quantum Efficiency and Saturated Red Emission

Self-emissive atomically precise metal nanoclusters (NCs) are emerging as promising emissive layer material for next-generation light-emitting diodes (LEDs), thanks to their solid-state luminescence, well-defined structures, photo/thermal stability, low toxicity, and unique excited-state properties. However, achieving high external quantum efficiency (EQE) in solid-state NCs remains a formidable challenge. In this study, a highly stable bimetallic gold-copper NC forming [Au₂Cu₆(Sadm)₆(DPPEO)₂] stabilized with 1-adamantanethiol (HSadm) and 1,2-bis(diphenylphosphino)ethane (DPPE) as the primary and secondary ligands, respectively is reported. Single-crystal X-ray diffraction and spectroscopic analyses suggest that the as-synthesized NC contains one phosphine bound to gold and the second phosphine has oxidized to phosphine oxide (P═O). The presence of such P═O moieties in the NC facilitated C─H···O interactions along with C─H···π and H···H interactions between ligands, promoting rapid crystallization. Due to the exceptional photo/thermal stability and enhanced solid-state photoluminescence quantum yield (PLQY), [Au₂Cu₆(Sadm)₆(DPPEO)₂] NC is utilized to fabricate the NC-based LED (NC-LED) via the solution-processed technique, without using any additional host materials. The fabricated NC-LED shows a maximum brightness of 1246 cd m^-2 and an EQE of 12.60% with a pure red emission ≈668 nm. This EQE value coupled with saturated pure red emission is the best among solution-processed and non-doped NC-LEDs, suggesting the enormous potential of the NCs for electro-optical devices.