Preparation and characterization of methylammonium tin iodide layers as photovoltaic absorbers

The preparation of absorber layers composed of methylammonium tin iodide (CH3NH3SnI3) in a two-step process was investigated. This material is designed as a less toxic alternative to CH3NH3PbI3 which is commonly used as active material in perovskite solar cells. Tin(II) iodide (SnI2) layers prepared by physical vapor deposition were converted to CH3NH3SnI3 by reaction with a spin-coated solution of methylammonium iodide (MAI). The perovskite particles formed in this process were over 200 nm in size and reached full surface coverage. A band gap of 1.23 eV was determined and the material, thus, absorbs over a broad part of the solar spectrum, broader even than CH3NH3PbI3. The chemical composition and solid state structure of the prepared films were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The films turned out to be remarkably stable, another key prerequisite for applications as absorber layers in perovskite solar cells.