Precursor of SnX4 (X = Br and I): 907 mg of SnBr4 (2.0 mmol) is loaded in a 50-mL flask with 10 mL of 1-octadecene (ODE), 5 mL of oleic acid, and 5 mL of oleylamine. The mixture is then heated to 100 °C under reduced pressure for at least 1 h. The procedure is important to remove the water and oxygen from the precursor. The same procedure is followed to prepare the iodide precursor with SnI4 (1296 mg -2.0 mmol).