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

Semiconductor photoelectrochemistry (PEC) is a promisingtechnologyfor solar fuels and photovoltaics. However, the application of organic-inorganichalide perovskites (OIHPs) to PEC has been limited by their instabilityin polar solvents. Here, we report the use of methylviologen leadiodide (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 solarabsorber. The stability of MVPb2I6 allows theuse of cyclic voltammetry to determine its energetics. A stable anodicphotocurrent was observed with only 28% decay after 15 h of operationunder 1 sun illumination and 0.9 V (vs normal hydrogen electrode (NHE))applied bias toward the oxidation of I-. The degradationmechanism due to the photoreduction of MVPb2I6 was also studied using scanning electron microscopy (SEM) and arotating ring-disk electrode (RRDE). This work illustrates the potentialand challenge of using viologen-based small-band-gap one-dimensional(1D) OIHPs to achieve stable PEC inside polar solvents without protection.

Automated summary

In this study, a stable unprotected photoelectrode, methylviologen lead iodide (MVPb2I6), was used in the semiconductor photoelectrochemistry (PEC) system of organic-inorganic halide perovskites (OIHPs) in polar solvents. The MVPb2I6 exhibits stability and suitable solar absorber band gap for PEC reactions in polar solution. The energetic properties of MVPb2I6 were determined by cyclic voltammetry, and the degradation mechanism due to photoreduction was studied using SEM and RRDE techniques.