Flexible Near-White Alternating-Current Electroluminescent Devices Based on a Screen-Printable Transparent Dielectric Ink

Abstract

Flexible alternating-current electroluminescent (ACEL) devices are promising for patterned and mechanically compliant lighting, but integrating optical transparency, dielectric performance, and near-white emission within a simple printed structure remains challenging. Here, a screen-printable and UV-curable transparent dielectric ink based on polyurethane acrylate, 4-acryloylmorpholine, and propylene carbonate (PC) was developed for flexible ACEL devices containing a single phosphor-composite emissive layer. Among the investigated formulations, 30 wt % PC provided the best overall balance of printability, wettability, optical transmission, dielectric response, dielectric loss, and electroluminescent output, and this selection was further supported by quantitative multi-criteria analysis. The printed dielectric layer exhibited an ITO-PET-referenced transmittance above 90% over 400–700 nm and a relative permittivity of approximately 25 at 1 kHz. Dielectric-film specimens with an average thickness of 50.0 ± 1.6 μm showed a breakdown strength of 24.52 ± 0.40 MV m⁻¹. A single printed emissive layer containing ZnS:Cu and CaAlSiN₃:Eu²⁺ at a mass ratio of 3:1 exhibited near-white chromaticity. The optimized devices exhibited average CIE coordinates of (0.331 ± 0.002, 0.331 ± 0.002), a correlated color temperature of 5457 ± 71 K, a moderate color rendering index of 69 ± 1, and a luminance of 48.7 ± 1.0 cd m⁻² at 120 V and 500 Hz. Integrating-sphere measurements further yielded a luminous efficacy of 10.4 ± 0.3 lm W⁻¹ under the same driving conditions. After 1000 bending cycles at a radius of 5 mm, the devices retained approximately 77% of their initial luminance, showing that electroluminescent functionality was maintained under repeated bending.