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‐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 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 circularly polarized electroluminescence (CPEL) with external quantum efficiency (EQE) of 26.7%, which is superior to most of red‐emitting OLEDs through solution process.