We first describe the growth of cubic microcrystals in the presence of MLA. Small crystals prefer to be spherical to minimize surface energy, and lead bromide perovskite is no exceptio . When we quickly diluted a 1:1 dimethylformamide (DMF) solution of PbBr2 and MABr with an antisolvent, toluene, a mixture of µm-size elongated dodecahedrons and irregular cuboids formed (Fig. ) . When 0.5-4 molar equivalents of MLA per PbBr2 were added to the DMF solution, only cubic crystals formed (Fig. ). In the presence of lactic acid or succinic acid, which share a partial structure with MLA, crystal ripening and fusion took place (Fig. ). This highlights how critical the tridentate structure of MLA is since neither the diacid nor the a-hydroxy acid lead to the formation of such regular crystals. On the other hand, Oleic acid (OA), a common acidic additive in QD synthesis, afforded entirely fused crystals, sometimes with a hint of the outline of an elongated dodecahedron (Fig. ). Additional images can be found in the Supplementary Information (Figures S2 to S6