Elucidating Degradation Pathways in Perovskite-Based Water Splitting Devices

Despite recent encapsulation strategies that suppress moisture-induced degradation and support high-performance operation, perovskite-based water splitting devices still exhibit limited operational stability. This instability originates from the slower consumption of photocarriers, compared with photovoltaic (PV) cells, which exacerbates charge accumulation at the catalyst/electrolyte interface. Herein, in situ and ex situ studies track how this intense charge buildup governs a distinct degradation pathway in water splitting anodes relative to encapsulated perovskite PV cells. Our observations show that the anodes undergo a charge-induced failure process: accelerated iodine migration triggers defect formation at the hole transport layer/perovskite interface located directly beneath the electrochemically active region. In contrast, encapsulated PV cells experience light-induced degradation within the illuminated area, where defects emerge only after extended operation and at the electron transport layer/perovskite interface. These results clarify that perovskite-based water splitting devices follow a distinct, electrochemically driven degradation mechanism, providing insights for designing more stable perovskite-based electrochemical systems.