Formamidinium tin triiodide (FASnI3) is a strong contender for sustainable harvesting of solar energy and further optoelectronic applications. So far, only a few studies have considered its fundamental structure–property relationships, given the challenge of ensuring a high material quality. In a concerted effort, we here study high-quality FASnI3 single crystals through a combination of X-ray crystallography, density-functional-theory-based electronic structure calculations, and photoluminescence spectroscopy from room temperature down to 4 K. The luminescence exhibits irregular trends upon cooling with a generally strong intensity increase, but a range of negative thermal quenching, leading to an intensity maximum around 185 K which is absent in low-quality samples. Differences in the photoluminescence peak position and density-functional-theory-calculated band-gap energies highlight the importance of dynamic processes to the observable properties of FASnI3. The presented data offer deeper insight into the temperature-dependent characteristics of this halide perovskite and present opportunities for future exploration of its optoelectronic properties.

The versatile potential of lead halide perovskites and two-dimensional materials is merged in the Ruddlesden− Popper perovskites having outstanding optical properties. Here, the coherent spin dynamics in Ruddlesden−Popper (PEA) 2 PbI 4 perovskites is investigated by picosecond pump−probe Kerr rotation in an external magnetic field. The Larmor spin precession of resident electrons with a spin dephasing time of 190 ps is identified. The longitudinal spin relaxation time in weak magnetic fields measured by the spin inertia method is as long as 25 μs. A significant anisotropy of the electron g-factor with the in-plane value of +2.45 and out-of-plane value of +2.05 is found. The exciton out-of-plane g-factor of +1.6 is measured by magnetoreflectivity. This work contributes to the understanding of the spindependent properties of two-dimensional perovskites and their spin dynamics.

No abstract