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

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(+) 2PbI4) thin films in aqueous electrolytes under dark and illuminated conditions. While PEA(+) 2PbI4 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)-PbI2. 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 I3 -/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.