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An atmospheric‐pressure spatial atomic layer deposition system is used to rapidly deposit 60 nm zinc–aluminum oxide (Zn–AlOx) thin‐film‐encapsulation layers directly on perovskite solar cells at 130 °C without damaging the temperature‐sensitive perovskite and organic materials. Varying the Zn/Al ratio has a significant impact on the structural properties of the films and their moisture barrier performance. The Zn–AlOx films have higher refractive indexes, lower concentrations of OH─ groups, and lower water–vapor transmission rates (WVTR) than AlOx films without zinc. However, as the Zn/Al ratio increases beyond 0.21, excess Zn atoms segregate, leading to an increase in the number of available hydroxyl groups on the surface of the deposited film and a slight increase in the WVTR. The stability of the p–i–n formamidinium methylammonium lead iodide solar cells under standard ISOS‐D‐3 testing conditions (65 °C and 85% relative humidity) is significantly enhanced by the thin encapsulation layers. The layers with a Zn/Al ratio of 0.21 result in a seven‐fold increase the time required for the cells to degrade to 80% of their original efficiency. [ABSTRACT FROM AUTHOR]