Preventing the degradation of metal perovskite solar cells (PSCs) by humid air poses a substantial challenge for their future deployment. We introduce here a two-dimensional (2D) A₂PbI₄ perovskite layer using pentafluorophenylethylammonium (FEA) as a fluoroarene cation inserted between the 3D light-harvesting perovskite film and the hole-transporting material (HTM). The perfluorinated benzene moiety confers an ultrahydrophobic character to the spacer layer, protecting the perovskite light-harvesting material from ambient moisture while mitigating ionic diffusion in the device. Unsealed 3D/2D PSCs retain 90% of their efficiency during photovoltaic operation for 1000 hours in humid air under simulated sunlight. Remarkably, the 2D layer also enhances interfacial hole extraction, suppressing nonradiative carrier recombination and enabling a power conversion efficiency (PCE) >22%, the highest reported for 3D/2D architectures. Our new approach provides water- and heat-resistant operationally stable PSCs with a record-level PCE.