Unravelling the Improved Electronic and Structural Properties of Methylammonium Lead Iodide Deposited from Acetonitrile

Perovskite-based photovoltaics are an emerging solar technology with lab scale device efficiencies of over 22 %, and significant steps are being made toward their commercialization. Conventionally high efficiency perovskite solar cells are formed from high boiling point, polar aprotic solvent solutions. Methylammonium lead iodide (CH 3 NH 3 PbI 3 ) films can be made from a range of solvents and blends; however, the role the solvent system plays in determining the properties of the resulting perovskite films is poorly understood. Acetonitrile (ACN), in the presence of methylamine (MA), is a viable nontoxic solvent for fabrication of CH 3 NH 3 PbI 3 photovoltaic devices with efficiencies >18 %. Herein we examine films prepared from ACN/MA and dimethylformamide (DMF) and scrutinize their physical and electronic properties using spectroscopy, scanning probe imaging, and ion scattering. Significant differences are observed in the chemistry and electronic structure of CH 3 NH 3 PbI 3 films made with each solvent, ACN/MA produces films with superior properties resulting in more efficient photovoltaic devices. Here we present a holistic and complete understanding of a high performance perovskite material from an electronic, physical, and structural perspective and establish a robust toolkit with which to understand and optimize photovoltaic perovskites.