Bio-material-based deformable out-coupling film with UV-blocking properties for stabilized organic light-emitting diodes

In multilayer organic light-emitting diodes (OLEDs), 70% of the generated light is lost due to differences in the refractive indices, resulting in total internal reflection. Therefore, external light-extraction films that can easily enhance efficiency are being researched. However, most of these films use petroleum-based polymers, raising waste disposal concerns. Additionally, ultraviolet (UV) light degrades organic materials. Hence, UV protection is essential for mitigating this damage. This study fabricated an eco-friendly external light-extraction film with UV-blocking capabilities using carboxymethyl cellulose (CMC) and sodium lignosulfonate (LS) extracted from plants. The phenolic groups in LS absorb UV light, while the sulfonate groups enhance its hydrophilicity, rendering it soluble in water. Therefore, a simple process was employed by casting a CMC-LS solution onto a microlens-array (MLA) template to fabricate a CMC-LS MLA film. The CMC-LS MLA film achieved 90% transmittance in the visible light range and exhibited excellent UV-blocking capabilities, simultaneously enhancing the lifespan of the OLED and improving the light-extraction efficiency by 30%.