Photodegradation of 2D Ruddlesden‐Popper Perovskites: Consequences and Design Principles for Photoelectrochemical Applications

Abstract Halide perovskites (HaP), with their exceptional optoelectronic properties and high‐power conversion efficiencies in photovoltaic devices, hold promise for photoelectrochemical (PEC) applications in green fuel and chemical production. However, their stability in aqueous environments remains a challenge. This study investigates the stability and degradation mechanisms of the 2D Ruddlesden‐Popper phase phenylethyl ammonium lead iodide (PEA ⁽⁺⁾ ₂ PbI ₄ ) thin films in aqueous electrolytes under dark and illuminated conditions. While PEA ⁽⁺⁾ ₂ PbI ₄ thin films appear to be thermodynamically stable in an aqueous electrolyte with phenylethyl ammonium iodide (PEAI), illumination causes significant photodegradation generating a deprotonated and dehalogenated 2D intercalation product: phenylethylamine‐lead iodide, 2PEA ⁽⁰⁾ ‐PbI ₂ . The degradation of the 2D semiconductor leads to substantial reduction in the photovoltage, adversely impacting the material performance in photoelectrochemical (PEC) devices. To intercept photo‐excited charge carriers in the 2D semiconductor, the I ₃ ⁻ /I ⁻ redox is added, which reduced photodegradation. The findings underscore that while catalytic reactions at halide perovskite electrodes in aqueous electrolytes are feasible, reversible and irreversible photodegradation remains a critical limitation that must be addressed in the design of PEC devices employing metal halide semiconductor layers for direct electrochemical energy conversion.