Dual Excitonic Emission in Hybrid 2D Layered Tin Iodide Perovskites

Layered two-dimensional (2D) lead halide perovskites are already an important class of optoelectronic materials. Layered 2D tin-halide perovskites are also now emerging. Unlike lead analogs, tin-halide perovskites are environmentally benign. Furthermore, compared to three-dimensional (3D) tin-halide perovskites, 2D layered tin-halide perovskites show improved moisture stability. However, a better understanding of electronic and optical properties, along with novel material design approaches, are required to realize the potential layered tin-halide perovskites for optoelectronic applications. Here, we prepare a series of 2D layered tin-halide perovskite single crystals and find that all of the samples exhibit two excitonic emissions. Similar to the Ruddlesden-Popper phase, A(2)SnI(4) (with A = phenyl-ethylammonium, butylammonium, hexylammonium, and octylammonium monovalent cations) is prepared. Furthermore, A'SnI4 (similar to the Dion-Jacobson phase) (with A' = 4-(aminomethyl)piperidinium divalent cation) is prepared. All of the samples show two sharp photoluminescence (PL) peaks. Two absorption features are also observed corresponding to the two PL peaks. The time-resolved PL studies show that both emissions have a nearly similar and short (few nanoseconds) PL lifetimes. The two absorption features and short nanosecond PL lifetimes suggest that the two emissions are excitonic in nature. While dual excitonic emission is rather unusual for a typical semiconductor, recent studies showed such dual emissions from layered lead halide perovskites as well.