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 MAPbI3 reduces defect concentration and enhances pore filling, while Eu enrichment in CsPbI3 reduces cation migration and enables device reusability. In this study, AVA-MAPbI3 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 PbI2 but is explained by a water-vacancy …