Deciphering Photophysical Carrier Dynamics in Lead-Free Perovskites: Influence of Lattice Dimensionality

The crystalline structure of semiconductor materials significantly alters their photophysical properties. In the case of halide perovskites, lattice dimensionality and crystalline structure change with cation and anion transmutation. In this study, we investigate the impact of lattice dimensionality on carrier dynamics in Cs3Bi2Br9 (2D) and Cs2AgBiBr6 (3D) perovskites. From steady-state absorption and photoluminescence spectra, we have observed that there is no such effect of the lattice dimensionality on these properties in nanocrystalline systems. Using femtosecond transient absorption spectroscopy, we observe that polaron formation and electron-acoustic phonon interaction in Cs3Bi2Br9 is stronger than Cs2AgBiBr6, which can be attributed to their low-dimensional lattice structure. However, the hot carrier relaxation is faster in the Cs2AgBiBr6 NCs. The study reveals that the introduction of Ag into the Cs3Bi2Br9 structure eliminates the strong localization of electron–hole pairs and alleviates the distortion of the BiBr6 octahedra. Our findings shed light on the fundamental behavior of halide perovskite materials, which can undergo lattice connectivity dimensionality changes and crystalline structure transformations with cation and anion variations.