Nanolaminate‐Induced Mechanically and Environmentally Robust Al2O3/TiO2 Thin Film Encapsulation by Low‐Temperature Atomic Layer Deposition: Toward Flexible and Wearable OLEDs

Abstract The growing demand for low‐temperature thin‐film encapsulation (TFE) in advanced flexible and wearable organic light‐emitting diodes (OLEDs) has intensified to mitigate thermal issues, which deteriorate the device performance. Herein, Al 2 O 3 /TiO 2 nanolaminates (A/T NLs)are introduced and fabricated via thermal atomic layer deposition at an exceptionally low temperature of 40 °C, which exhibited enhanced mechanical and environmental robustness. Compared to the single‐layer Al 2 O 3 and TiO 2 thin films (0.06% and 0.31%), the A/T NLs with sublayer thickness under 15 nm exhibit dramatic improvement in elongation (0.46–0.53%), attributed to the effective decoupling of critical defects by the Al 2 O 3 /TiO 2 interfaces. Furthermore, the A/T NLs with 3 nm‐thick‐sublayer demonstrate highly improved water vapor transmission rates of 9.48 × 10 −5 g m −2 day −1 , making them promising candidates for TFE in wearable OLEDs. Notably, the optimized A/T NL‐encapsulated wearable phosphorescent OLEDs (phOLEDs) exhibit extended lifetimes (LT70), surpassing 200 h in the accelerated environmental conditions (40 °C/90% RH) which is 40 times longer lifetimes compared to the not encapsulated OLEDs. Additionally, the A/T NL‐encapsulated wearable phOLEDs displayed mechanical endurance, enduring 125 h even under the bending strain of 0.4% compared to the Al 2 O 3 ‐ and TiO 2 ‐encapsulated OLEDs (4 and 18 h).