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

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-Ag₆Cu in 85 %-87 % yield by replacing one Ag(I) atom with Cu(I) in homometallic clusters R/S-Ag₇, achieving circularly polarized luminescence (CPL) with a quantum yield beyond 90 %. As a small energy gap (ca. 0.07 eV) between S₁ and T₁ states facilitates thermally activated delay fluorescence (TADF) through reverse intersystem crossing (RISC), the photoluminescence (PL) of R/S-Ag₇ and R/S-Ag₆Cu at ambient temperature originates mostly from TADF (85 % and 86 %) in place of phosphorescence (15 % and 14 %). Relative to those of R/S-Ag₇, copper(I) doping not only triples PL quantum yields of R/S-Ag₆Cu due to accelerating ISC (intersystem crossing) and RISC, but also doubles CPL asymmetry factors of R/S-Ag₆Cu 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.