Two-dimensional copper (II) halide-based hybrid perovskite templated by 2-chloroethylammonium: Crystal structures, phase transitions, optical and electrical properties

Hybrid inorganic-organic perovskites attracted increasing attention because of variety of their applications in the fields of photovoltaics, photoelectronics and switchable dielectric devices. Diverse molecular functional materials can be assembled by modifying the length of the organic components and inorganic framework dimensionally and, thus, they might be promising candidates to obtain phase-transition materials. In this study, we present a new hybrid perovskite-like compound, (ClC2H4NH3)(2)CuBr4 (I), which follows the two-dimensional inorganic frameworks of the corner-sharing CuBr6 octahedra. Strikingly, compound (I) displays a dielectric phase transition at around 275 K, changing from the non-centrosymmetric space group of Pc (LT phase) to centrosyrnmetric P2(1)/a (HT phase) upon heating. The crystal structure analyses reveal that the unusual thermally activated conformation change of the 2-chloroethylammonium cations and distortions of CuBr64- network in the inorganic layers afford the driving force to the phase transition. Moreover, the Jahn-Teller distortion introduces elongation of coordination bonds in the inorganic planes, which confers higher flexibility to the structure. Compound (I) displays phase transitions at T-1 = 270 K and T-2 = 323 K, confirmed by DSC measurements. In addition, the UV/Vis optical spectrum indicates that (I) has an indirect band gap of 1.47 eV. This finding may extend the application of 2D layered lead-free hybrid perovskite-type materials to the field of photovoltaic as the photo absorber layer of solar cells.