A high-κ homogeneous ink for printable electroluminescent devices.

Flexible alternating-current electroluminescent (ACEL) devices combine light emission with mechanical flexibility, enabling applications in wearables, soft robotics, and human-machine interfaces. Previous attempts to lower the driving voltage using high-permittivity fillers (e.g., BaTiO₃, liquid metals, ionic liquids) improved dielectric properties, but the inclusion of these heterogeneous fillers often compromised transparency and pattern clarity. Here, we report a printable, transparent high-dielectric ink that addresses these issues. By incorporating small high-dielectric molecules into a polymer matrix and employing screen printing with one-step photopolymerization, we fabricated patterned ACEL devices of high quality. The ink exhibits a dielectric constant up to 25 and transparency up to 90%, enabling efficient emission at a low voltage of ~0.33 V µm⁻¹, among the lowest reported. Its excellent printability supports scalable, cost-effective patterning, and devices can be wirelessly powered by harvesting ambient electromagnetic energy for chip- and battery-free operation.