Although Cl-doping is a common technique for achieving high photovoltaic (PV) performance, the Cl content is negligibly small and cannot easily be tuned. Therefore, we herein study the formation chemistry of Cl-doped perovskites by examining the chemical interactions between thermally evaporated MAI and PbCl sub(2) through X-ray photoemission spectroscopy (XPS). We show that PbCl sub(2) is not stable at the MAI/PbCl sub(2) contact surface. The Cl atom readily detaches from the PbCl sub(2), which subsequently initiates electron transition from Pb to MAI. Viathermal-evaporation, a perovskite with a high PbCl sub(2) content can be prepared and examined. We found that the presence of metallic Pb, associated with increased Cl content, can quench the photogenerated exciton in PV devices. By optimizing the ratio of MAI : PbCl sub(2), a perovskite solar cell with similar to 6% efficiency was obtained.