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, A2SnI4 (with A = phenylethylammonium,
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.