4.2.2. Preparation of perovskite precursor solution
Methylammonium iodide (MAI) was prepared by mixing 25 mL of methylamine (33 wt% in ethanol, Sigma Aldrich, St. Louis, MO, USA) and 10 ml of hydroiodic acid (55–58%, Kanto Chemical, Tokyo, Japan) in a round-bottom flask, which was kept in an ice bath for 2 hours. The resulting product was then obtained using a rotary evaporator at 60°C for 1 hour. After evaporating, the precipitates were recrystallized several times using ethanol (99.9%, Daejung Chemicals, Siheung-si, Korea) and diethyl ether (99%, Daejung Chemicals, Siheung-si, Korea), followed by an overnight drying at 60°C in a vacuum oven. Finally, 45 wt% of MAI and lead (II) iodide with a 3:1 molar ratio were stirred in N,N-dimethylformamide (DMF, 99.8%, Sigma Aldrich, St. Louis, MO, USA) at 90 °C for 1 hour.