Persistent iodine contamination resulting from thermal evaporation of inorganic perovskites

Thermal evaporation is a promising technique for the fabrication of uniform perovskite films over large areas that forgo the use of hazardous solvents. However, evaporation equipment, particularly at the laboratory scale, is often shared between different materials systems and it is, thus, important to understand the potential impact that halide perovskite evaporation can have on other films and devices processed in the same chamber. Here, we observe that evaporation of perovskite precursors such as PbI2 and CsI results in significant iodine contamination that is not efficiently removed by conventional decontamination procedures such as solvent cleaning, chamber bakeout, and foil replacement. X-ray photoelectron spectra show that this iodine contamination can incorporate itself into organic and metal films grown in the same chamber, which degrades the performance of thermally evaporated organic photovoltaic cells by ∼90%. To remove the contamination and restore the performance of other optoelectronic devices grown in the same chamber, a total resurfacing/replacement of all interior evaporator surfaces was required.