A-site cation engineering and halide tuning <i>via</i> precursor engineering to tune the optical properties of 2D perovskites

The optical properties of the metal halide perovskites (MHPs) have been modulated by replacing the typical A-site cations or, alternatively, by using different halides (I, Br or Cl) in the chemical composition. In this study, a combined strategy involving A-site cation engineering and halide tuning <i>via</i> precursor engineering has been employed to investigate its impact on the structural and optical properties of BA₂(MA_1-<i>x</i> )₂Pb₃X₁₀ (BA = butylammonium, MA = methylammonium, A = A-site cation, X = I, Br) two-dimensional (2D) perovskite. The substitution of guanidinium (Gua) and ethylammonium (EA) for methylammonium (MA), along with the use of Br instead of I as anions, was systematically analyzed. The obtained results demonstrate that these modifications significantly alter the dimensionality of the perovskite, favoring the formation of lower <i>n</i>-phases and resulting in blue-shifted absorption and photoluminescence due to quantum confinement. By adjusting the Gua/EA and I/Br content in the precursor solution, precise control of photoluminescence band position was achieved. The relevance of these findings was demonstrated as a proof-of-concept by fabricating light-emitting devices (LEDs), where the electroluminescence closely followed the compositional adjustments. Notably, Gua-based perovskites with Br anions exhibited enhanced LED performance due to optimal phase distribution. This research advances the understanding of structure-properties relationships and highlights the potential of composition engineering for innovative optical applications.