Mesoporous carbon-based (mC) hole-transporting layer-free architectures offer a cost-effective solution for the commercialization of perovskite solar cells (PSCs). Adding 5-aminovaleric acid (AVA) to MAPbI 3 reduces defect concentration and enhances pore filling, while Eu enrichment in CsPbI 3 reduces cation migration and enables device reusability. In this study, AVA-MAPbI 3 mC-PSCs were encapsulated at room temperature (RT) with a solvent- and water-free polyurethane (PU) resin. Under continuous ambient light, RT, and 40% relative humidity (RH), the PU encapsulant acts as a barrier to extend device durability and enable reusability. The formation of a bump in the J – V curve after ∼250 h, already reported at a low scan rate but here observed at 50 mV/s, strongly reduces the photovoltaic performances. We demonstrate that the bump is not linked to the formation of PbI 2 but is explained by a water-vacancy interaction that increases cation mobility and enhances screening effects near the electron-transport layer. The photovoltaic performances are fully restored by drying the devices under N 2 flow for ∼48 h. A further addition of a hydrophobic Kapton tape interlayer between the PU and device mitigates bump formation, boosts t 90 to ∼6000 h, and projects t 80 to ∼10,800 h. Differently from the Kapton tape used alone, PU provides effective sealing all around the devices, ensuring stability in 100% RH at 90 °C and even underwater. For indoor applications, Eu:CsPbI 3 mC-PSCs typically degrade from the γ- to δ-phase within ∼1 h in air, whereas PU-encapsulated devices achieve t 80 ∼250 h, extendable to 1250 h with an additional closure glass slide.