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Corrosion is a significant cause of degradation of silicon photovoltaic modules. In this study, the corrosion of multicrystalline passivated emitter and rear cells (PERC) was investigated using both experimental and numerical approaches to identify high-corrosion locations and their effect on cell parameters. Corrosion environments were simulated by immersing the device in acetic acid solution at various dwell times. The impact of the acetic acid concentration and relative humidity was examined. Thermodynamic and kinetic analyses of corrosion were performed using a Pourbaix diagram and finite element analysis, respectively. The results indicate that the device power reduces slowly in pure water but is faster in acidic environments at dwell times below 96 h. The power loss was over 60% in all environments at a dwell time of 144 h. In particular, a rapid power loss over 40% was observed at a high acetic acid concentration of 20 wt% after a dwell time of merely 48 h. The power loss in the water environment can essentially occur due to the formation of a surficial metal oxide layer, while in an acidic environment, it may be due to corrosion and/or metal electrode dissolution. The simulation and experimental results demonstrate that the rear aluminum around the silver contact suffers crucially from corrosion; thus, it is the main cause of device power losses. A polymer (EPDM) efficiently prevents water penetration into the electrode areas, thus minimizing power loss due to corrosion, and effectively solves the problem without impacting the production cost.