Introducing a stoichiometric excess of lead iodide (PbI2) in perovskite films has been demonstrated as an effective passivation strategy that can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, excess PbI2 is also known to accelerate the degradation of the perovskite layer. In this study, we show that this degradation primarily stems from the decomposition of PbI2 at the bottom of the perovskite film which is exposed to light. We further show that when using a two-step spin coating deposition procedure, the excess PbI2 results from the decomposition of the perovskite during the annealing process rather than the presence of non-reacted PbI2. Finally, we demonstrate that the spatial distribution of PbI2 within the perovskite films can be controlled in a way that mitigates the PbI2 induced perovskite decomposition. In this manner, we produced devices exhibiting initial power conversion efficiencies over 25%, maintaining 98.6% after 1000 h of maximum power point tracking under continuous illumination. These findings offer valuable insights into achieving high performance PSCs through judicious process control using a two-step spin-coating procedure. (c) 2025 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.