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.