Hybrid Multibarrier Thin Film Encapsulation Structure for Enhanced Reliability of Flexible and Wearable OLED Devices

Thin-film encapsulation (TFE) is crucial for the reliability and performance of next-generation flexible, wearable, and stretchable organic light-emitting diode (OLED) devices. Although OLEDs offer advantages such as self-luminescence and flexibility, the absence of robust encapsulation layers poses significant challenges. They are particularly vulnerable to moisture, oxygen, and mechanical stress, leading to degradation, dark spots, and reduced lifespan in harsh environments. Therefore, developing reliable encapsulation systems to protect OLEDs from mechanical damage while maintaining moisture and oxygen barrier performance is essential.
Traditional encapsulation methods often rely on single-material inorganic layers, which frequently lack the mechanical robustness needed for flexible devices, exhibiting poor elongation limits below 1% due to the brittle nature of materials like Al2O3. Recent advancements have explored hybrid encapsulation systems that combine organic and inorganic layers to enhance flexibility and barrier performance. However, these multibarrier structures often suffer from mechanical limitations, such as cracking under strain, especially in dynamic applications.
In this study, we propose an innovative inorganic/organic multibarrier encapsulation system optimized to address reliability issues in flexible electronics. Our system integrates alternating inorganic materials, like Al2O3, with silane-based organic/inorganic hybrid polymer (silamer, S) layers to create a mechanically robust and environmentally stable barrier. Silamer is designed to provide excellent adhesion, flexibility, and chemical resistance, effectively shielding the brittle Al2O3 layer from moisture and mechanical stress. Using a novel tensile-testing-on-water (TOW) method, we evaluated the intrinsic mechanical properties of the freestanding multibarrier thin films, independent of substrate influence, ensuring a wrinkle-free testing environment.
The tensile tests show that the proposed multibarrier structure, particularly those with organic outer layers, exhibited superior elongation properties compared to conventional inorganic-only barriers. Symmetrical multibarrier structures incorporating silamer layers demonstrated elongation of up to 2.8%, far surpassing traditional inorganic layers, which typically fail below 1%. Stress-strain analyses revealed that the silamer layers dissipate strain energy, preventing crack propagation through the brittle inorganic layers.
In harsh conditions (85°C and 85% relative humidity), the encapsulation system maintained an elongation of 1.43% after 30 hours, highlighting its durability. The slight decrease in elongation and increase in modulus resulted from environmental hardening of the outer silamer layer, inducing compressive residual stress that enhanced mechanical robustness and delayed crack formation in the Al2O3 layer. Interfacial chemical bonding between the Al2O3 and silamer layers further improved durability against environmental degradation.
To assess commercial potential, we applied the hybrid structure to real-world applications, specifically foldable and wearable OLEDs. The optimized SASAS (silamer/Al2O3/silamer/Al2O3/silamer) structure demonstrated exceptional water resistance and mechanical robustness in a textile-based wearable OLED. The encapsulated OLED maintained 99.18% of its initial luminance after 250 hours, even after water exposure and bending strains of 1%. The SASAS structure also showed only a 10% reduction in elongation after 24 hours of water immersion, attributed to the silamer layer’s ability to shield the brittle Al2O3. This waterproof encapsulation barrier maintained structural integrity under repetitive bending and environmental stress, making it ideal for wearable electronics. These findings highlight the commercial viability of the SASAS encapsulation system for foldable smartphones, wearable displays, biomedical patches and other flexible devices.