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

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, Al2O3/TiO2 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 Al2O3 and TiO2 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 Al2O3/TiO2 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 Al2O3‐ and TiO2‐encapsulated OLEDs (4 and 18 h). This work provides an analysis of the intrinsic mechanical properties of low‐temperature ALD Al2O3 and TiO2 thin films at 40 °C. A nanolaminate strategy is introduced to enhance the mechanical properties of single‐layered low‐temperature ALD thin films. The findings highlight the crucial role of nanolamination and offer insights for the development of future wearable OLEDs.