Super-droplet-repellent carbon-based printable perovskite solar cells

Despite attractive cost-effectiveness, scalability, and superior stability, carbon-based printable perovskite solar cells (CPSCs) still face moisture-induced degradation that limits their lifespan and commercial potential. Here, we investigate the moisture-preventing mechanisms of thin nanostructured super-repellent coating (advancing contact angle $>$167$^{\circ}$ and contact angle hysteresis 7$^{\circ}$ integrated into CPSCs for different moisture forms (falling water droplets vs water vapor vs condensed water droplets). We show that unencapsulated super-repellent CPSCs have superior performance under continuous droplet impact for 12h (rain simulation experiments) compared to unencapsulated pristine (uncoated) CPSCs that degrade within seconds. Contrary to falling water droplets, where super-repellent coating serves as a shield, we found water vapor to physisorb through porous super-repellent coating (room temperature and relative humidity, RH 65\% and 85\%) that increased the CPSCs performance for 21\% during ~43 days similarly to pristine CPSCs. We further showed that, water condensation forms within or below the super-repellent coating (40$^{\circ}$ C and RH 85\%), followed by chemisorption and degradation of CPSCs. Because different forms of water have distinct effect on CPSC, we suggest that future standard tests for repellent CPSCs should include rain simulation and condensation tests. Our findings will thus inspire the development of super-repellent coatings for moisture prevention.