Formic acid: an accelerator and quality promoter for nonseeded growth of CH3NH3PbI3 single crystals

With the aid of formic acid, CH3NH3PbI3 single crystal of 9 mm in length was directly harvested within 3 days via a nonseeded solution temperature-lowering (STL) method. It showed a record-narrow full width at half maximum of 13 arcsec for the high-resolution X-ray rocking curve, a low trap-state density of 3.1 x 10(9) cm(-3), a high carrier mobility of 162 cm(2) V-1 s(-1) and high moisture stability. The addition of formic acid could suppress the oxidation of iodide ions in a conventional STL process, resulting in rapid growth of high-quality CH3NH3PbI3 single crystals.