Photoelectrochemistry of Methylviologen Lead Iodide: Achieving Stability inside a Polar Solvent

Semiconductor photoelectrochemistry (PEC) is a promising technology for solar fuels and photovoltaics. However, the application of organic–inorganic halide perovskites (OIHPs) to PEC has been limited by their instability in polar solvents. Here, we report the use of methylviologen lead iodide (MVPb2I6) as an unprotected photoelectrode, which is stable inside an acetonitrile-based polar electrolyte. Moreover, the charge-transfer absorption inside MVPb2I6 reduces its band gap to 2.1 eV and thus makes it a suitable solar absorber. The stability of MVPb2I6 allows the use of cyclic voltammetry to determine its energetics. A stable anodic photocurrent was observed with only 28% decay after 15 h of operation under 1 sun illumination and 0.9 V (vs normal hydrogen electrode (NHE)) applied bias toward the oxidation of I–. The degradation mechanism due to the photoreduction of MVPb2I6 was also studied using scanning electron microscopy (SEM) and a rotating ring-disk electrode (RRDE). This work illustrates the potential and challenge of using viologen-based small-band-gap one-dimensional (1D) OIHPs to achieve stable PEC inside polar solvents without protection.