Ultrasound-Mediated Polymer Processing to Control Viscoelasticity for Inkjet-Printed Polymer LEDs

Inkjet printing offers a scalable and material-efficient route for fabricating high-resolution optoelectronic devices, yet the strong viscoelasticity of high-molecular-weight conjugated polymers remains a critical bottleneck for reliable jetting. Here, we introduce ultrasound-mediated polymer processing as a strategy to tune the viscoelasticity of a light-emitting polymeric material without external additives. Sonochemical treatment of Super Yellow selectively cleaved alkoxy side chains, as revealed by ¹H NMR and gel permeation chromatography, reducing molecular weight and entanglement density while preserving the π-conjugated backbone and its optical functionality. High-frequency rheological characterization using a piezo-axial vibrator confirmed that the treated inks exhibit markedly reduced elasticity and complex viscosity, enabling stable droplet formation under conditions that were previously unprintable. Leveraging this rheological control, we achieved precise pixel definition and uniform emissive layers in inkjet-printed OLEDs, which delivered a maximum external quantum efficiency of 4.55%, surpassing that of spin-coated references. This study establishes ultrasound-assisted rheological tuning as a generalizable approach to overcome viscoelastic constraints in polymer inks, opening new opportunities for high-resolution printed organic light-emitting diode displays and other solution-processed electronic devices.