Single Crystallization of Cs 4 PbBr 6 Perovskite from Supersaturated Organic Solutions Optimized Through Solubility Studies.

We demonstrate the fabrication of millimeter-sized single crystals of 0D-Cs 4 PbBr 6 grown in a supersaturated solution consisting of organic solvents without HBr (aq). One of the precursors, CsBr, was dissolved in ethylene glycol (EG) mixed with dimethyl sulfoxide, which is a good solvent for the other precursor, PbBr 2 . At a solvent ratio of 20 vol % EG, the solubility of cesium bromide decreased and the title compound, Cs 4 PbBr 6 , was selectively formed, whereas, with an EG ratio of 80 vol %, 3D-CsPbBr 3 was formed. A phase diagram (solubility curve) of Cs 4 PbBr 6 in the mixed solvent containing 20 vol % EG was obtained by visually observing dissolution and crystal precipitation while changing the temperature. Because the solubility was proportional to the temperature, the solubility curve demonstrated an upper critical solution phenomenon. The solubility near the boiling point of the solution (150 °C) was approximately 0.14 M. A single crystal of Cs 4 PbBr 6 was formed by growing a seed crystal in a supersaturated solution on the low-temperature side of the solubility curve. X-ray analysis established the crystal structure; a fluorescence emission at 520 nm with a full width at half maximum of 20 nm confirms the composition of the single crystal to be Cs 4 PbBr 6 .