Biocompatible Multilayered Encapsulation for Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) have tremendous potential in biotechnology, but their vulnerability to oxygen and moisture presents a significant challenge in encapsulation. In this study, we developed a multilayer thin-film encapsulation consisting of dual inorganic layers and Parylene-C, offering excellent protection and biocompatibility. This encapsulation enhances the suitability of OLEDs for flexible substrates and biological applications. The multilayer structure, composed of Al₂O₃/SiO_<i>x</i>N_<i>y</i>/Parylene-C, was fabricated entirely below 100 °C to ensure compatibility with temperature-sensitive OLEDs. The encapsulation also exhibited high transparency in the visible spectrum, making it ideal for top-emission OLEDs. We confirmed the stability of the OLED by immersing it in a biologically relevant environment, specifically 37 °C PBS solution, and demonstrated its excellent durability. Through direct cell growth experiments and MTT assay tests, the multilayer encapsulated OLEDs demonstrated high biocompatibility. To advance this work toward optogenetic applications, we fabricated flexible OLED-sensing electrode integrated devices on a polyimide substrate, incorporating 13 sensing electrodes and 12 OLEDs. The Al₂O₃/SiO_<i>x</i>N_<i>y</i>/Parylene-C encapsulation provided sufficient stability during the selective etching of the sensing electrode region while maintaining OLED protection. The device demonstrated stable operation after immersion in PBS at 37 °C and supported direct cell growth on its surface. Additionally, the OLED arrays remained well functional even when the polyimide substrate was bent. These results highlight the potential of our flexible OLED-sensing electrode integrated device as a promising platform for future optogenetic applications.