Direction and Temperature-Dependent Properties of an Antimony-Based Two-Dimensional Halide Double Perovskite

Two-dimensional (2D) organic-inorganic halide double perovskites have attracted wide attention due to their structural diversity and chemical tunability. Herein, we report a new 2D layered halide double perovskite material, (BrPA)₄AgSbBr₈ (BPAS), and its properties are compared with (BrPA)₄AgInBr₈ (BPAIn, PA─propylammonium) and previously reported noncentrosymmetric Cl_0.26Br_3.74PA₄AgSbBr₈ (CPAS, CPA─chloropropylammonium). BPAS and BPAIn crystallize in the P2/c monoclinic space group with 2D layers of inorganic octahedra formed by monovalent and trivalent cations separated by two layers of organic linkers. Unlike their 3D counterparts, Cs₂Ag(In/Sb)X₆ (X-halide), the octahedra are distorted, reducing their symmetry. This led to the broadening of the optical gap in the present materials and also affected the photoluminescence (PL) and conduction properties. The BPAS shows a slight indirect band gap but shows PL emission with contributions from band-to-band, free/bound excitonic, and self-trapped excitonic states. The STEs enabled broader emission in these two materials. The 2D nature of the material shows anisotropic conduction properties where the in-plane conduction is found to be different from out-of-plane conduction. The value of charge transfer resistance decreases from GΩ (at -73 °C) to kΩ (at 202 °C) due to the presence of thermally activated carrier mobility through a correlated barrier hopping mechanism.