This work reports on the ZnO thin films obtained by atomic layer deposition (ALD), at a deposition temperature down to 40 °C. The crystallinity of the material as a function of the film thickness and the deposition temperature was investigated. The photocatalytic performance was evaluated by the degradation of methylene blue (MB) dye in water under UV light irradiation. The effect of the film thickness and the deposition temperature on the photocatalysis was deeply elucidated. Once the optimized conditions (in terms of thickness and temperature) were found, the ALD process was transferred on a flexible polymeric substrate: polyethylene naphthalate (PEN). The photo-activity of the flexible materials was evidenced by the degradation of MB and phenols in water. The results demonstrate that low temperature growth by ALD can be fruitfully applied to synthesize flexible materials that can found applications in …