Ultra-stable 2D layered methylammonium cadmium trihalide perovskite photoelectrodes

For the first of time, we demonstrate that methylammonium cadmium halides show photoelectrochemical (PEC) response with excellent humidity and chemical resistance because the oxidation state of almost all cadmium compounds is +2. The photocurrent densities of two-dimensional (2D) layered (MA)₂CdCl₄ perovskites are about 0.30 mA cm^-2 under 100 mW cm^-2 irradiation. The interaction between these methylammonium cadmium halides and water vapor is studied by probing film morphology and characterizing single crystal structure. It is shown that H₂O is able to complex with the perovskite, forming a hydrate product with the molecular formula of MACd₃Cl₇·3H₂O upon humidity exposure. This causes a decrease in absorption and a recognizable change in the crystal structure of the material. When compared to methyl-ammonium lead iodide (MAPbI₃), the PEC stability of 2D layered (MA)₂CdCl₄ perovskites with BQ/BQ^- redox couples (where BQ is benzoquinone) in CH₂Cl₂ is enhanced from 50 hours to 600 hours, exhibiting an increase of 12 times.