Controlled growth of MAPbBr₃ single crystal: understanding the growth morphologies of vicinal hillocks on (100) facet to form perfect cubes

Organic and inorganic hybrid perovskites have attracted significant attentions due to their impressive optoelectronic properties. MAPbBr₃, one of the most popular members in MAPbX₃ (MA = methyl ammonium and X = Cl, Br, I) family, is considered as new generation optoelectronic materials, especially in the field of solar cells. Compared to polycrystalline films, MAPbBr₃ single crystal is deemed more ideal for optoelectronic device because of fewer grain boundaries. To realize a controlled crystal growth, a thorough understanding of its growth mechanism, especially the role of surface structures played in growth kinetics, is of paramount importance. In this paper, hillocks on (100) facet of MAPbBr₃ crystal were observed using atomic force microscopy when grown from N-dimethylformamide (DMF) solution. The results revealed that the growth of (100) facet was controlled by 2D nucleation at low concentration, which derived plenty of elementary steps whose height was about 0.59 nm, equivalent to one unit cell. Then the growth transferred to step flow model along [011] direction. Step flow ceased when encountering holes on the terraces. The optical morphologies validated that cubic plates were prone to growing along [011] directions, which were in a layer-by-layer model. Moreover, the temperature reverse solubility of MAPbBr₃ in DMF solution was measured. In terms of the solubility and growth mechanism of MAPbBr₃, a series of MAPbBr₃ single crystals were successfully grown from thin cubic plates to thick and perfect cubes via temperature controlling rising method ultimately.