Excellent Electroluminescent Property of Eu³⁺-Induced Polystyrene-co-poly(acrylic acid) Aggregates (EIPAs) in Polymeric Light-Emitting Diodes

Eu 3+ -induced polystyrene- co -poly(acrylic acid) aggregates (EIPAs) were synthesized using a self-assembly approach, and their structures and photophysical characteristics were examined to achieve effective monochromatic red emission in polymer light-emitting diodes (PLEDs). By adjusting the monomer ratio in RAFT polymerization, the size of Eu 3+ -induced block copolymer nanoaggregates can be regulated, thereby modulating the luminescence intensity. High-performance bilayer polymer light-emitting devices were fabricated using poly(9,9-dioctylfluorene) (PFO) and 2-( tert -butylphenyl)-5-biphenylyl-1,3,4-oxadiazole (PBD) as the host matrix, with EIPAs as the guest dopant. The devices exhibited narrow red emission at 615 nm with a full width at half-maximum (fwhm) of 15 nm across doping concentrations of 1, 3, 5, and 10 wt %. At a doping concentration of 3 wt %, the device achieved a maximum brightness of 1864.48 cd/m 2 at 193.82 mA/cm 2 and an external quantum efficiency of 3.20% at a current density of 3.5 mA/cm 2 . These results indicate that incorporating polystyrene- co -poly(acrylic acid) with Eu 3+ complexes enhances the excitation and emission intensity, as well as the structural stability of the emitting layer in PLEDs, thereby improving the device performance.