Vacancy Passivation and ALD Alumina Encapsulation Strategies for Stable Multilayered All‐Inorganic Halide Perovskite Pc‐WLEDs

White light-emitting diodes (WLEDs) are extensively used in displays, architectural lighting, and flash devices. A combination of blue, green, and red components is required to achieve high-quality white emission. CsPbX₃ perovskite nanocrystals (PNCs) are particularly attractive for phosphor converted WLEDs (pc-WLEDs) owing to their high photoluminescence quantum yield (PLQY). However, their practical deployment is hindered by intrinsic instability and rapid anion exchange, which severely impact device performance and spectral purity. In this work, we demonstrate a combined strategy to suppress anion exchange in CsPbX₃ PNCs by incorporating PbSe islands to passivate halide vacancies and introducing an atomic layer deposited (ALD) -alumina layer to act as an ion diffusion barrier. This approach enables the fabrication of stable, multilayered pc-WLEDs that remain stable beyond 12 h of continuous illumination. Furthermore, we developed a micropatterned pc-WLED using a simple spray-coating method in both glass and flexible polyethylene terephthalate (PET) substrates. Thermal stability tests under repeated heating (60°C) and cooling (25°C) cycles revealed that both the green and red emissive layers remained stable even after 20 cycles. Additionally, the correlated color temperature (CCT) value of the pc-WLED could be tuned from 4595 to 5010 K by varying the driving current from 6 to 30 mA.