Polyurethane-Encapsulated\nMesoporous Carbon-Based\nPerovskite Solar Cells Resilient to Extreme Humidity and Mitigation\nof the Related Reversible <i>J</i>–<i>V</i> Bump

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