A novel strategy of hybrid halide perovskite single crystal growth based on a new type of “fugitive” solvent system is proposed. To demonstrate the universality of the developed approach, we have grown a set of high-quality single crystals of 3D hybrid perovskites APbX3 (A = MA+, FA+; X = Br–, I–) with pure and mixed compositions, layered 2D perovskites (BA)2(A) n – 1PbnI3n + 1 (n = 1–4), and iodobismuthates A3Bi2I9. The crystallization was governed by gradual chemical conversion of the initial mixed solvent to a nonsolvent and thus gave yields up to 90%. The growth proceeded within a few hours at moderate temperatures and required no heating/cooling or low-pressure evaporation steps, antisolvents, or any toxic solvents, which makes the whole process uniquely facile and eco-friendly. The high quality of the grown single crystals was confirmed by absorption and photoluminescence spectroscopy, revealing unexpectedly high charge carrier lifetime for 2D perovskites.

Solution methods remain the most popular means for the fabrication of hybrid halide perovskites. However, the solubility of hybrid perovskites has not yet been quantitively investigated. In this study, we present accurate solubility data for MAPbI3, FAPbI3, MAPbBr3 and FAPbBr3 in the two most widely used solvents, DMF and DMSO, and demonstrate huge differences in the solubility behavior depending on the solution compositions. By analyzing the donor numbers of the solvents and halide anions, we rationalize the differences in the solubility behavior of hybrid perovskites with various compositions, in order to take a step forward in the search for better processing conditions of hybrid perovskites for solar cells and optoelectronics.

A novel triiodide phase of the formamidinium cation, CH5N2 +·I3 −, crystallizes in the triclinic space group P\overline{1} at a temperature of 110 K. The structure consists of two independent isolated triiodide ions located on inversion centers. The centrosymmetric character of I3 − was additionally confirmed by the observed pronounced peaks of symmetrical oscillations of I3 − at 115–116 cm−1 in Raman scattering spectra. An additional structural feature is that each terminal iodine atom is connected with three neighboring planar formamidinium cations by N—H...I hydrogen bonding with the N—H...I bond length varying from 2.81 to 3.08 Å, forming a deformed two-dimensional framework of hydrogen bonds. A Mulliken population analysis showed that the calculated charges of hydrogen atoms correlate well with hydrogen-bond lengths. The crystal studied was refined as a three-component twin with domain ratios of 0.631 (1):0.211 (1):0.158 (1).

In this study, we thoroughly measured the joint solubility of MAI and PbI 2 components in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) solvents at different temperatures and analyzed the composition of solid phases in equilibrium with the saturated solutions to build phase diagrams for the two ternary systems of MAI−PbI 2 −DMSO and MAI− PbI 2 −DMF. A new solvate phase MAI•DMSO was discovered in the system MAI−PbI 2 −DMSO, and its crystal structure has been refined. Based on the obtained data, we compared and analyzed phase equilibria in these two systems. The diagrams give ground fundamental information on the ternary systems and explain how the solution composition influences the crystallization process and determines phase composition of the products and possible pathways of crystallization of hybrid perovskites.

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