Thin films of Ag nanowires (NWs) offer many advantages as transparent electrodes for flexible electronics, but their applications are hindered by issues including poor stability/durability of Ag NWs, high processing temperatures, heterogeneity of surfaces, and lack of gas-barrier function. This study reports novel mechanisms through which a conductive Hf:ZnO (HZO) film by atomic layer deposition (ALD) can be integrated with a sprayed Ag NWs film to address the issues of Ag NWs. Firstly, the ALD surface reactions can induce fusing of the Ag NWs into a connected network without the need for a thermal-sintering process. Secondly, the ALD process can in situ functionalize the Ag NWs to yield defect-free (in terms of blocking gas permation) coverage of the ALD HZO over the entire nanowire surfaces, which also enhances the ALD-induced fusing of Ag NWs. The composite HZO/Ag NWs films exhibit low sheet resistance (15 Ω sq), low water vapor transmission rate (WVTR) (5.1 × 10 g m day), high optical transmission (92%), excellent flexibility (12.5 mm bending radius), high stability/durability (against an extensive set of degradation modes and photolithographic patterning processes), and low processing temperature (90 °C); and can be used in perovskite solar cells to obtain high power conversion efficiency (14.46%).