The Role of Fluorine-Substituted Positions on the Phase Transition in Organic-Inorganic Hybrid Perovskite Compounds.

Although research on organic-inorganic hybrid perovskites (OIHPs) has grown exponentially in the past two decades, the high phase transition temperature of OIHP materials is still one of the insurmountable difficulties. Herein, a series of ABX type OIHP materials [(2,-DFBA)PbCl] ( = 3, for ; = 4, for ; = 5, for ; = 6, for ) have been prepared by reactions of double-substituted difluorobenzylamine (difluorobenzylamine = DFBA) with lead chloride in concentrated HCl aqueous solution. It was found the OIHP compounds - proceed a switchable phase transition with phase transition temperatures () at 449 K (), 462 K () and 500 K (), higher than that of the parent compound [(BA)PbCl] (BA = benzylammonium) at 438 K, but compound exhibits no phase transition. A crystal structure analysis elucidated that the organic template ligands DFBA lead in the inorganic part in compounds - to a two-dimensional (2D) perovskite structure, while that in compound leads to a one-dimensional (1D) chain structure. The different double-substituted positions of fluorine atoms on benzylamine have important influences on the phase transition in compounds -.