Doping Copper(I) in Ag₇ Cluster for Circularly Polarized OLEDs with External Quantum Efficiency of 26.7 %

Abstract Hetero‐metal doping or substitution to create alloy clusters is a highly appealing strategy for improving physicochemical characteristics as well as tailoring optical and electronic properties, although high‐yield synthesis of alloy clusters with precise positioning of doped metals is a daunting challenge. Herein, we manifest rational synthesis of chiral alloy cluster enantiomers R / S ‐Ag 6 Cu in 85 %–87 % yield by replacing one Ag(I) atom with Cu(I) in homometallic clusters R / S ‐Ag 7 , achieving circularly polarized luminescence (CPL) with a quantum yield beyond 90 %. As a small energy gap (ca. 0.07 eV) between S 1 and T 1 states facilitates thermally activated delay fluorescence (TADF) through reverse intersystem crossing (RISC), the photoluminescence (PL) of R / S ‐Ag 7 and R / S ‐Ag 6 Cu at ambient temperature originates mostly from TADF (85 % and 86 %) in place of phosphorescence (15 % and 14 %). Relative to those of R / S ‐Ag 7 , copper(I) doping not only triples PL quantum yields of R / S ‐Ag 6 Cu due to accelerating ISC (intersystem crossing) and RISC, but also doubles CPL asymmetry factors of R / S ‐Ag 6 Cu ascribed to rigidizing cluster structure through stronger Ag−Cu interaction apart from dramatically improving thermodynamic stability. Solution‐processable circularly polarized organic light‐emitting diodes (CP‐OLEDs) demonstrate high‐efficiency circularly polarized electroluminescence (CPEL) with external quantum efficiency (EQE) of 26.7 %, which is superior to most of red‐emitting OLEDs through solution process.