Structural Rigidity Enables Amplified Spontaneous Emission in 2D Alkylammonium Tin Perovskites.

Two-dimensional tin perovskites are attracting increasing attention for coherent light emission, yet the impact of organic cations on their properties remains poorly understood. Here, we compare the Ruddlesden-Popper (RP) butylammonium tin iodide (BA2SnI4) and Dion-Jacobson (DJ) 1,4-diammoniobutane tin iodide (DABSnI4) perovskites to investigate the impact of the two structural types on their photophysical and optical gain properties. Combining X-ray diffraction and solid-state NMR spectroscopy, we reveal the different templating properties of the mono- and ditopic cations on the long-range structural order and local coordination environment, identifying an unreported phase transition for DABSnI4. The constrained molecular motions in the DJ perovskite provide an increased structural rigidity that also suppresses vibrational modes of the inorganic sublattice. The consequent lower exciton-phonon coupling and exciton binding energy, reduced defectivity, and modulation of the exciton recombination dynamics create favorable conditions to stabilize the population inversion and achieve amplified spontaneous emission (ASE) in DABSnI4, in net contrast with BA2SnI4 where ASE could not be obtained. This work highlights that Dion-Jacobson perovskites can create more rigid structural environments with positive feedback on the photophysical properties, providing a simple but effective design strategy for the synthesis of improved materials for optoelectronic applications.